JP2012069801A - Quantum well optical detector and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantum well optical detector capable of obtaining sufficient sensitivity with improved optical absorption efficiency.SOLUTION: The quantum well optical detector includes a plurality of optical detection elements 3 each including multiple quantum well layers 5, 6 and contact layers 7-9 sandwiching the multiple quantum well layers. In each optical detection element, one surface is a plane parallel to the multiple quantum well layers. Also, the other surface on the opposite side to the one surface across the multiple quantum well layers and the contact layers is an inclined plane 20 inclined to the multiple quantum well layers. Further, a reflection film 10 is provided on the side face of the optical detection element on which incident light incident on the one surface and the inclined plane is refracted.

Description

  The present invention relates to a quantum well photodetector and a method for manufacturing the same.

2. Description of the Related Art In recent years, as a photodetector that detects light by a current that flows when incident light is absorbed, there is a quantum well photodetector that includes a photodetector including a multiple quantum well layer.
However, the quantum well photodetector does not absorb light incident perpendicularly to the multiple quantum well layer. In other words, the quantum well photodetector does not have sensitivity to light perpendicularly incident on the multiple quantum well layer.

  Therefore, conventionally, an optical coupling structure including a diffraction grating and a reflective electrode is provided on the opposite side of the light incident surface of the light detection element with the multiple quantum well layer interposed therebetween. Thereby, light incident perpendicularly to the multiple quantum well layer is reflected and deflected by the optical coupling structure and returned to the multiple quantum well layer so as to be absorbed.

JP 2000-183319 A

By the way, simply providing the optical coupling structure as described above cannot change the angle of light perpendicularly incident on the multiple quantum well layer, and therefore it is difficult to make the light incident on the multiple quantum well layer at an angle close to parallel. For this reason, the light absorption efficiency cannot be sufficiently increased, and sufficient sensitivity cannot be obtained.
Therefore, it is desired to improve the light absorption efficiency and obtain sufficient sensitivity in the quantum well photodetector.

  For this reason, the present quantum well type photodetector includes a plurality of photodetectors each including a multiple quantum well layer and a contact layer sandwiching the multiple quantum well layers, and each of the photodetectors has a multiple quantum well on one surface. It is a plane parallel to the layer, and the other surface on the opposite side across the multiple quantum well layer and the contact layer is inclined with respect to the multiple quantum well layer. It is a requirement that a reflective film is provided on the side surface on the side where incident light incident on one surface and the inclined surface is refracted.

  The method for manufacturing a quantum well photodetector includes a multiple quantum well layer and a contact layer sandwiching the multiple quantum well layer, and forms a plurality of photodetectors having a surface parallel to the multiple quantum well layer. And a step of forming an inclined surface inclined with respect to the multiple quantum well layer. The photodetecting element forming step includes a step of forming a reflective film on a parallel surface and an incident on the inclined surface of each photodetecting element. And a step of forming a reflection film on the side surface on the side where incident light to be refracted is included.

  Therefore, according to the present quantum well photodetector and the manufacturing method thereof, there is an advantage that the light absorption efficiency can be improved and sufficient sensitivity can be obtained.

It is a typical sectional view showing the composition of the quantum well type photodetector concerning a 1st embodiment. It is typical sectional drawing which shows the reflective path | route in the quantum well type photodetector concerning 1st Embodiment. (A), (B) is a schematic diagram for demonstrating the relationship between a refractive index, an incident angle, a refraction angle, and a reflection angle. (A) is typical sectional drawing which shows the structure for demonstrating the range of the preferable inclination | tilt angle in the photodetector which is contained in the quantum well type photodetector concerning 1st Embodiment, (B) is inclination It is a figure which shows the calculation result of each angle (theta) _{2- (} theta) ₅ at the time of changing angle (theta) ₁ . It is typical sectional drawing which shows the structural example and inclination path which made the inclination | tilt angle 25 degrees as a photon detection element contained in the quantum well type photodetector concerning 1st Embodiment. It is typical sectional drawing for demonstrating the reflection path | route when light injects into the short side surface side of the photon detection element contained in the quantum well type photodetector concerning 1st Embodiment. It is typical sectional drawing for demonstrating the reflective path | route when light injects into the long side surface side of the photon detection element contained in the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A)-(D) are typical sectional drawings for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A)-(F) are typical sectional drawings for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. (A)-(D) are typical sectional drawings for demonstrating the manufacturing method of the quantum well type photodetector concerning 1st Embodiment. It is typical sectional drawing which shows the other structural example of the photon detection element contained in the quantum well type photodetector concerning 1st Embodiment. It is typical sectional drawing which shows the reflection path | route when light injects into the structure of the photon detection element contained in the quantum well type photodetector concerning 2nd Embodiment, and one side surface side. It is typical sectional drawing which shows a reflective path | route when light injects into the other side surface side of the photon detection element contained in the quantum well type photodetector concerning 2nd Embodiment. It is a typical sectional view showing the composition of the quantum well type photodetector concerning a 3rd embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 3rd Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 3rd Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 3rd Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 3rd Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 3rd Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 3rd Embodiment. (A), (B) is typical sectional drawing for demonstrating the manufacturing method of the quantum well type photodetector concerning 3rd Embodiment.

Hereinafter, a quantum well photodetector according to an embodiment of the present invention and a method for manufacturing the same will be described with reference to the drawings.
[First Embodiment]
First, a quantum well photodetector and a manufacturing method thereof according to the first embodiment will be described with reference to FIGS.

In this embodiment, as a quantum well type photodetector that detects light by a current that flows when incident light is absorbed, a quantum well type infrared detector (QWIP; Quantum) that generates a photocurrent according to the amount of incident infrared rays Well Infrared Photodetector) will be described as an example.
As shown in FIG. 1, the quantum well infrared detector according to this embodiment includes an infrared detection element array 1 in which a plurality of infrared detection elements 3 are two-dimensionally arranged, and a plurality of infrared detection elements 3. And a signal processing circuit array 2 connected thereto.

  The infrared detection element 3 is also referred to as a quantum well infrared detection element, a light detection element, or a QWIP element. The infrared detector is also referred to as an infrared image sensor or an array sensor. The infrared detection element array 1 is also referred to as a sensor element array, an infrared focal plane array (IRFPA), or a QWIP focal plane array (QWIP-FPA). The signal processing circuit array 2 is also referred to as a signal processing circuit chip.

  Here, the infrared detection element array 1 is an infrared detection element array in which a plurality of infrared detection elements 3 are separated by a separation groove 4 and are two-dimensionally arranged. That is, the infrared detection element array 1 includes a plurality of infrared detection elements 3 and a separation groove 4 that separates the plurality of infrared detection elements 3. In the present embodiment, since the common contact layer connected to all of the plurality of infrared detection elements 3 is not provided, the plurality of infrared detection elements 3 are completely separated by the separation grooves 4.

Thus, since each infrared detection element 3 is separated by the separation groove 4, it is possible to prevent so-called crosstalk, in which reflected light reaches the adjacent infrared detection element 3.
In the present embodiment, the infrared detection element array 1 is formed of, for example, a GaAs-based semiconductor material. The plurality of infrared detection elements 3 constitute a plurality of pixels of the image sensor. For this reason, the infrared detection element 3 is also called a pixel. The separation groove 4 is also referred to as a pixel separation groove.

Here, each infrared detection element 3 includes multiple quantum well (MQW) layers 5 and 6. That is, each infrared detection element 3 includes MQW layers 5 and 6 and contact layers 7 to 9 sandwiching the MQW layers 5 and 6.
In this embodiment, each infrared detection element 3 is a two-wavelength QWIP element using two MQW layers 5 and 6 having sensitivity to different wavelength bands as infrared absorption layers (photosensitive layers).

  That is, each infrared detection element 3 includes a first MQW layer 5 that absorbs infrared light in one wavelength band, and a second MQW layer 6 that absorbs infrared light in another wavelength band. Each infrared detection element 3 includes a first contact layer 7 provided on one surface side with respect to the first MQW layer 5 and an intermediate contact layer provided between the first MQW layer 5 and the second MQW layer 6. 8 and a second contact layer provided on the other surface side with respect to the second MQW layer 6. That is, each infrared detecting element 3 has an element structure (semiconductor laminated structure) in which the first contact layer 7, the first MQW layer 5, the intermediate contact layer 8, the second MQW layer 6, and the second contact layer 9 are laminated from one surface side. Structure).

  In addition, one surface of the infrared detection element 3 is an element surface, and is an upper surface in FIG. Moreover, the other surface of the infrared detection element 3 is an element back surface, which is the lower surface in FIG. Here, the other surface of the infrared detection element 3 is a light incident surface. The first contact layer 7 is also referred to as an upper contact layer. The intermediate contact layer 8 is also referred to as a common contact layer. Further, the second contact layer 9 is also referred to as a lower contact layer.

  In the present embodiment, each infrared detection element 3 has an n-type GaAs first contact layer 7, an AlGaAs / GaAs first MQW layer 5, an n-type GaAs intermediate contact layer 8, an AlGaAs / InGaAs second MQW layer 6 from one surface side. The n-type GaAs second contact layer 9 is laminated. That is, it has a two-layer structure in which two types of MQW layers 5 and 6 are sandwiched between n-type contact layers. The AlGaAs / GaAs first MQW layer 5 has a structure in which a number of quantum wells composed of an AlGaAs barrier layer and a GaAs well layer are repeated. Similarly, the AlGaAs / InGaAs second MQW layer 6 has a structure in which a large number of quantum wells composed of an AlGaAs barrier layer and an InGaAs well layer are repeated. Thus, each infrared detection element 3 is a QWIP element doped with an n-type impurity.

Each infrared detecting element 3 is provided with a reflective film 10 on one surface, and further, a reflective film 10 is provided on a side surface defined by the separation groove 4. Here, the reflective film 10 is, for example, a metal film.
Further, each infrared detection element 3 is provided with a first contact electrode 11 on one surface, that is, on the first contact layer 7. Each infrared detection element 3 is provided with a contact hole 12 extending from one surface side to the intermediate contact layer 8, and an intermediate contact electrode 13 is provided on the bottom surface of the contact hole 12. Further, each infrared detecting element 3 is provided with a contact hole 14 extending from one surface side to the second contact layer 9, and a second contact electrode 15 is provided on the bottom surface of the contact hole 14. The contact electrodes 11, 13, and 15 are also referred to as contact metals.

Further, a passivation film 16 is provided so as to cover the entire surface including the inside of the contact holes 12 and 14. Here, the passivation film 16 is an insulating film such as a silicon oxide film.
Further, three bumps 17 for electrically connecting to the signal processing circuit array 2 through the passivation film 16 are provided above one surface of each infrared detection element 3. Here, the bump 17 is a metal bump, for example, an In bump. The bump 17 is also referred to as a bump electrode. The three bumps 17 are connected to the above-described three contact electrodes 11, 13, and 15 via the wiring 18, respectively. Here, the wiring 18 is a metal wiring. In the region where the reflective film on one surface of each infrared detection element 3 is not provided, the contact electrode and the wiring function as a reflective film.

The signal processing circuit array 2 includes a signal processing circuit such as an input circuit for amplifying the electric signal output from each infrared detection element 3 and a readout circuit for reading the output of the input circuit to the outside. Note that the input circuit and the readout circuit may be collectively referred to as a readout circuit. In the present embodiment, the signal processing circuit array 2 is made of, for example, a Si-based semiconductor material.
The infrared detection element array 1 and the signal processing circuit array 2 are connected via bumps 17. Here, the signal processing circuit array 2 is connected to each of the three contact layers 7 to 9 of each infrared detection element 3 via wiring 18 and bumps 17. In this case, since the signal processing circuit array 2 is connected to one surface side of each infrared detection element 3, that is, the element surface side, each infrared detection element 3 is connected to the other surface side, that is, the element. Infrared rays are incident from the back side. Then, a photocurrent signal (output current) from the first MQW layer 5 or the second MQW layer 6 is signaled via the wiring 18 and the bump 17 connected to each of the three contact layers 7 to 9 of each infrared detection element 3. The data is individually read out to the signal processing circuits included in the processing circuit array 2. In this case, a bias voltage is applied to the first MQW layer 5 and the second MQW layer 6 through the intermediate contact layer 8 and the bumps 17 connected thereto. The photocurrent signal from the first MQW layer 5 can be read out through the first contact layer 7 and the bumps 17 connected thereto. In addition, the photocurrent signal from the second MQW layer 6 can be read out via the second contact layer 9 and the bumps 17 connected thereto.

A gap between the infrared detection element array 1 and the signal processing circuit array 2 is filled with a filler 19.
By the way, in a quantum well type infrared detector, it is not absorbed unless the electric field of incident light has a component in a direction perpendicular to the well layer, and does not contribute to generation of a photocurrent signal. Absent.

For this reason, in this embodiment, each infrared detection element 3 has one surface parallel to the MQW layers 5 and 6, and the MQW layers 5 and 6 and the contact layer 7 with respect to the one surface. The other surface on the opposite side across .about.9 is an inclined surface 20 inclined with respect to the MQW layers 5 and 6.
Specifically, each infrared detection element 3 includes a semiconductor layer 21 having an inclined surface 20 on the other surface side which is a light incident surface. Here, each infrared detection element 3 includes a GaAs layer 21 having an inclined surface 20 on the back surface side of the second contact layer 9. Note that the GaAs layer may contain impurities that are inevitably included. For this reason, the GaAs layer 21 is referred to as a semiconductor layer containing GaAs. The inclined surface 20 is formed by continuously increasing the thickness of the GaAs layer 21 from one element side surface toward the other element side surface. Thereby, the light incident from the direction perpendicular to the MQW layers 5 and 6 of each infrared detecting element 3 is refracted by the inclined surface 20 on the back surface of the element, and reflected by the element surface and the element side surface having the reflective film 10, It can be incident on the MQW layers 5 and 6 at an angle close to parallel. As a result, the light absorption efficiency can be improved.

  Here, the reflective film 10 is provided on all side surfaces of each infrared detection element 3, but in order to make the light refracted by the inclined surface 20 incident at an angle close to parallel to the MQW layers 5 and 6, at least The reflection film 10 may be provided on the side surface on the side where incident light incident on the inclined surface 20 is refracted. Further, by providing the reflective film 10 on the side surface opposite to the side surface on which incident light incident on the inclined surface 20 is refracted, light can be reciprocated in the element. Thereby, light absorption efficiency can be improved compared with the case where the reflecting film 10 is not provided on the opposite side surface.

Here, the semiconductor layer 21 having the inclined surface 20 is a GaAs layer, but the present invention is not limited to this. For example, the semiconductor layer having an inclined surface may be a semiconductor layer made of another semiconductor material having a refractive index of about 3.
In particular, the inclined surface 20 preferably has an inclination angle that satisfies the condition that the light reflected and returned from one surface is totally reflected. In this case, as shown in FIG. 2, the light incident from the direction perpendicular to the MQW layers 5 and 6 of each infrared detecting element 3 is refracted by the inclined surface 20 on the back surface of the element, reflected by the element surface, and inclined. It returns to the surface 20 and is totally reflected by the inclined surface 20. The light totally reflected by the inclined surface 20 in this manner is reflected by the side surface of the element and is incident on the MQW layers 5 and 6 at an angle close to parallel. Thereby, the light absorption efficiency can be improved. In FIG. 2, for convenience of explanation, one infrared detection element 3 is shown in a simplified manner such that two MQW layers are shown together and the intermediate contact layer 8 is omitted.

Specifically, when the semiconductor layer 21 having the inclined surface 20 is a GaAs layer, the inclined surface 20 preferably has an inclination angle of about 11 ° to about 33 °, as will be described later.
Here, as shown in FIGS. 3A and 3B, light is incident obliquely from a material having a high refractive index (refractive index n ₁ ) to a material having a low refractive index (refractive index n ₂ ). It is well known that light is refracted toward a material having a large refractive index. As the incident angle θ ₁ increases, the refraction angle θ ₂ also increases. When the angle reaches 90 °, the refracted light disappears and total reflection occurs.

The critical angle θ _c of total reflection when light is emitted from a material having a refractive index n _{1 to} a material having a refractive index n ₂ can be expressed by the following equation (1).

In particular, the critical angle θ _c of total reflection when light is emitted from the GaAs layer into the air is about 17.64 ° as expressed by the following equation (2) because the refractive index of GaAs is 3.3. Thus, it can be seen that even if it is incident at a considerably small angle, it is totally reflected. On the other hand, when light enters the GaAs layer 21 from the air, total reflection does not occur even if it has an angle.

  As described above, in the case of the infrared detecting element 3 including the GaAs layer 21 having the inclined surface 20, light incident from the direction perpendicular to the MQW layers 5 and 6 is refracted by the inclined surface 20 and the angle can be changed. , Reaches the element surface, is reflected by the element surface, and reaches the inclined surface 20 again (see FIG. 2). In this case, as will be described later, if the angle of the inclined surface 20, that is, the inclination angle is about 11 ° or more, the light returning to the inclined surface 20 is totally reflected. As will be described later, when the tilt angle is about 33 ° or less, the light totally reflected by the tilted surface 20 is reflected by the device side surface and is incident on the MQW layers 5 and 6 at an angle close to parallel. Thereby, the light absorption efficiency can be improved.

Here, in the infrared detecting element 3 including the GaAs layer 21 having the inclined surface 20, in order to make light incident at an angle close to parallel to the MQW layers 5 and 6, the inclination angle is set to about 11 ° to about 33 °. The reason why this is preferable will be described.
Here, as shown in FIG. 4A, a case where light enters a GaAs element (refractive index n = 3.3) having an inclined surface with an inclination angle θ ₁ will be described as an example. It is assumed that a reflective film is provided on the surface and side surface opposite to the inclined surface as the incident surface.

First, it can be seen that the incident angle of the light incident on the inclined surface of the GaAs element is equal to the inclination angle θ ₁ of the inclined surface of the GaAs element and becomes θ ₁ .
Next, the refraction angle θ _{2 on} the inclined surface as the incident surface can be expressed by the following equation (3) from sin θ ₁ / sin θ ₂ = n.
θ ₂ = sin ⁻¹ (sin θ ₁ / n) (3)
Next, the incident angle θ ₃ to the surface opposite to the inclined surface can be expressed by the following equation (4).
θ ₃ = θ ₁ −θ ₂ (4)
Next, the incident angle θ ₄ of the light reflected on the surface opposite to the inclined surface and returned to the inclined surface can be expressed by the following equation (5).
θ ₄ = 90− (90−2θ ₁ + θ ₂ ) = 2θ ₁ −θ ₂ (5)
Next, an angle between the light reflected by the inclined surface and the horizontal direction, that is, an angle θ _{5 of} the light reflected by the inclined surface with respect to a direction perpendicular to the side surface of the GaAs element is θ ₁ + θ ₄ + θ ₅ = 90, It can be represented by the following formula (6).
θ ₅ = 90−3θ ₁ + θ ₂ (6)
When the angle of the inclined surface of the GaAs element, that is, the inclination angle θ ₁ is changed within a range of 10 ° to 40 °, for example, the angles θ _{2 to} θ ₄ are as shown in FIG. .

Here, as described above, the condition that the light reflected and reflected by the surface opposite to the inclined surface is totally reflected by the inclined surface is θ ₄ > 17.64 °. Therefore, in order to satisfy this condition, it is necessary that θ ₁ ≧ 11 ° as shown in FIG.
If θ ₅ <0, the light reflected by the inclined surface will be reflected from the side surface of the GaAs element and then go out of the GaAs element. Therefore, it is necessary that θ ₅ > 0. In order to satisfy this condition, it is necessary that θ ₅ ≦ 33 ° as shown in FIG.

Therefore, in the infrared detecting element 3 including the GaAs layer 21 having the inclined surface 20, in order to make light incident at an angle close to parallel to the MQW layers 5 and 6, the inclination angle of the inclined surface 20 is about 11 ° or more. It is preferable to set it to 33 ° or less (about 11 ° ≦ θ ₁ ≦ about 33 °).
In particular, by appropriately setting the tilt angle within this range, it becomes possible to make light incident at an angle that is substantially close to the direction parallel to the MQW layers 5 and 6.

Hereinafter, referring to FIG. 5 to FIG. 7, an infrared detecting element 3 including a GaAs layer 21 having an inclined surface 20 with an inclination angle of 25 ° and including one MQW layer 5X sandwiched between contact layers 7X and 9X is taken as an example. The reflection path and the light absorption efficiency will be described.
Here, for convenience of explanation, the infrared detection element 3 including one MQW layer 5X will be described, but the same applies to the infrared detection element 3 including two MQW layers 5 and 6 as in the present embodiment. It becomes a reflection path, and the same light absorption efficiency is obtained in each of the MQW layers 5 and 6.

  Here, as shown in FIG. 5, the width of the infrared detection element 3, that is, the pixel size is about 30 μm, the thickness of the MQW layer 5X is about 2 μm, and the thickness of the contact layers 7X and 9X above and below the MQW layer 5X. The thickness is about 1 μm. Further, a reflective film 10 is provided on the surface and side surface opposite to the inclined surface 20 as the incident surface. In FIG. 5, for convenience of explanation, one infrared detection element 3 is shown in a simplified manner.

In this case, incident light incident from a direction perpendicular to the MQW layer 5X is incident on the inclined surface 20 having an inclination angle of about 25 °, and thus the incident angle θ ₁ is about 25 °. And refraction angle (theta) ₂ can be calculated | required by following Formula (7).

ここでは、ｎ_１＝１（空気）、ｎ_２＝３．３（ＧａＡｓ）であるため、θ_２＝７．３６°である。
また、入射面としての傾斜面２０の反対側の素子表面での反射角θ_３は、θ_３＝θ_１−θ_２より、θ_３＝１７．６４°となる。

Here, since n ₁ = 1 (air) and n ₂ = 3.3 (GaAs), θ ₂ = 7.36 °.
Further, the reflection angle θ ₃ on the element surface opposite to the inclined surface 20 as the incident surface is θ ₃ = 17.64 ° from θ ₃ = θ ₁ −θ ₂ .

Further, the incident angle θ ₄ of the light reflected and returned from the element surface to the inclined surface 20 becomes θ ₄ = 42.64 ° from θ ₄ = 2θ ₁ −θ ₂ , and is totally reflected on the inclined surface 20. .
Further, the angle θ ₅ formed with the horizontal direction of the light totally reflected by the inclined surface 20 is θ ₅ = 22.36 ° from θ ₅ = 90−3θ ₁ + θ _{2, and} on the side surface of the element having the reflective film 10, Similarly, the light is reflected at an angle of 22.36 ° and travels toward the element surface. As a result, the light reflected from the side surface of the element enters the MQW layer 5X at an angle close to parallel. Thereafter, the light that has passed through the MQW layer 5X is again reflected at 67.64 ° on the element surface, and is incident again on the MQW layer 5X at an angle close to parallel. Thereby, the light absorption efficiency can be improved.

  By the way, in such an infrared detection element 3, for example, as shown in FIG. 6, when light is incident on a region far from the side surface of the element where the incident light incident on the inclined surface 20 is refracted, the MQW layer 5X is relatively Incident light can be incident at a shallow angle, that is, at an angle nearly parallel to the MQW layer 5X. Here, the region far from the element side surface is, for example, a region from the right side to the center in FIG. In FIG. 6, for convenience of explanation, one infrared detection element 3 is shown in a simplified manner, such as omitting the reflective film 10.

  In this case, the incident light enters the MQW layer 5X at a relatively deep angle, that is, at an angle close to vertical, and makes one round trip. Next, it enters the MQW layer 5X at a relatively shallow angle, that is, at an angle close to parallel to the MQW layer 5X, and makes one round trip. Thereafter, the light enters the MQW layer 5X at a relatively deep angle, that is, at an angle close to the vertical, and travels once and goes out of the element. For this reason, the light absorption efficiency is good.

  On the other hand, for example, as shown in FIG. 7, when light is incident on a region close to the side surface of the element on which incident light incident on the inclined surface 20 is refracted, the MQW layer 5X has a relatively shallow angle, that is, the MQW layer 5X. It is difficult to make it incident at an angle close to parallel to. In this case, incident light enters the MQW layer 5X at a relatively deep angle, that is, at an angle close to vertical, and exits the device after one round trip. For this reason, the light absorption efficiency is not good.

Thus, although the light absorption efficiency varies depending on the region where light enters, the infrared detection element 3 is added in the width direction of the infrared detection element 3, that is, from the right side to the left side in FIGS. The light absorption efficiency of 3 was calculated to be about 62.5%. This means that an efficiency improvement of about 30% is achieved as compared with the light absorption efficiency of about 48.8% when the diffraction grating is provided on the element surface side. Here, in calculating the light absorption efficiency, an absorption coefficient of 1.82 × 10 ³ cm ⁻¹ (for example, BF Levine, “Quantum-well infrared characteristics”, J. Appl. Phys, Vol. 74, No. 8 , R1-R81, 15 October 1993). Further, the reflectance on the element surface and the element side surface on which the reflective film 10 is provided was assumed to be 100%.

Next, the manufacturing method of this quantum well type | mold photodetector is demonstrated, referring FIGS. 8-19.
First, as shown in FIG. 8A, an InGaP first etching stopper layer 23, an undoped i-GaAs layer (semiconductor layer) 21, and an InGaP second etching stopper layer 24 are formed on a GaAs substrate (semiconductor substrate) 22. Grow. Thus, in the present embodiment, the lower InGaP first etching stopper layer 23 is formed between the GaAs substrate 22 and the i-GaAs layer 21. This is because the etching depth is accurately controlled so that the i-GaAs layer 21 is not removed when the GaAs substrate 22 is removed. The first etching stopper layer 23 is also referred to as a lower etching stopper layer.

  Next, on the InGaP second etching stopper layer 24, the n-GaAs second contact layer 9, the AlGaAs / InGaAs second MQW layer 6, the n-GaAs intermediate contact layer 8, the AlGaAs / GaAs first MQW layer 5, the n-GaAs second contact layer. One contact layer 7 is grown. Thus, in the present embodiment, the upper InGaP second etching stopper layer 24 is formed immediately below the n-GaAs second contact layer 9. This is because the etching depth is accurately controlled so that the i-GaAs layer 21 is not removed when the isolation trench 4 is formed. The second etching stopper layer 24 is also referred to as an upper etching stopper layer.

In this way, a semiconductor laminated structure (wafer structure) constituting each infrared detecting element 3 is formed.
Next, as shown in FIGS. 8B and 9A, two contact holes 12 and 14 are formed in each region where each infrared detection element 3 (each pixel) is formed.
That is, first, as shown in FIG. 8B, two contact holes 12, 14X extending from the surface of the n-GaAs first contact layer 7 to the n-GaAs intermediate contact layer 8 are formed by, for example, dry etching. Thereby, contact holes 12 extending from one surface side to the intermediate contact layer 8 are formed.

  Next, as shown in FIG. 9A, the n-GaAs intermediate contact layer 8, the AlGaAs / InGaAs second MQW layer 6, and the n-GaAs second contact layer 9 formed below the one contact hole 14X. A part of is removed by, for example, dry etching. Thereby, a contact hole 14 extending from one surface side to the second contact layer 9 is formed.

Next, as shown in FIG. 9B, a passivation film 16 is formed so as to cover the entire surface including the inside of the contact holes 12 and 14 by, for example, a plasma CVD (Chemical Vapor Deposition) method.
Next, as shown in FIG. 10A, after removing the passivation film 16 in the region where the three contact electrodes 11, 13, 15 of each infrared detecting element 3 are provided by, for example, dry etching, three contacts are formed by, for example, vapor deposition. Electrodes 11, 13, and 15 are formed.

That is, after removing a part of the passivation film 16 formed on the surface of the n-GaAs first contact layer 7 by, for example, dry etching, the first contact electrode 11 is formed by, for example, vapor deposition. As a result, the first contact electrode 11 is formed on the n-GaAs first contact layer 7.
Further, after removing a part of the passivation film 16 formed on the bottom surface of the contact hole 12, that is, on the n-GaAs intermediate contact layer 8, by, for example, dry etching, the intermediate contact electrode 13 is formed by, for example, vapor deposition. Thereby, the intermediate contact electrode 13 is formed on the bottom surface of the contact hole 12, that is, on the n-GaAs intermediate contact layer 8.

  Further, a part of the passivation film 16 formed on the bottom surface of the contact hole 14, that is, on the n-GaAs second contact layer 9, is removed by, for example, dry etching, and then the second contact electrode 15 is formed by, for example, vapor deposition. . As a result, the second contact electrode 15 is formed on the bottom surface of the contact hole 14, that is, on the n-GaAs second contact layer 9.

In this way, contact electrodes 11, 13, and 15 are formed on the surfaces of the three contact layers 7 to 9, respectively.
Next, as shown in FIG. 10B, after the passivation film 16 in the region where the reflection film 10 is provided on one surface of each infrared detection element 3 is removed by, for example, dry etching, the reflection film 10 is formed by, for example, sputtering. Form. That is, the reflective film 10 is formed on the surface of the n-GaAs first contact layer 7, that is, on the surface parallel to the MQW layers 5 and 6.

Next, as shown in FIG. 11A, a passivation film 16 is formed again so as to cover the entire surface.
Next, as shown in FIG. 11B, a wiring 18 is formed extending from the upper part of each of the three contact electrodes 11, 13, 15 to a region where the bump 17 on the surface is provided.
That is, after the passivation film 16 formed on each of the three contact electrodes 11, 13, 15 is removed by, for example, dry etching, for example, a wiring metal is sputtered, and unnecessary portions are removed by, for example, ion milling. 18 is formed. Note that the portion of the wiring 18 formed in the area where the bumps 17 are provided on the surface has a shape that can also function as a base layer of the bumps 17.

Next, as shown in FIG. 12A, separation grooves 4 for separating the infrared detection elements 3 are formed by dry etching, for example. That is, the separation groove 4 is formed so that a plurality of infrared detection elements 3 are formed. Here, the separation groove 4 reaching the i-GaAs layer 21 from the surface side is formed.
Next, as shown in FIG. 12B, after forming the passivation film 16 again so as to cover the entire surface, the inner wall surface of the separation groove 4, that is, each infrared detection element, for example, by sputtering and ion milling. The reflective film 10 is formed on the side surface 3. That is, the reflective film 10 is formed on the side surface of each infrared detection element 3 defined by the separation groove 4.

  Here, the reflection film 10 is formed on all side surfaces of each infrared detection element 3, but in order to make the light refracted by the inclined surface 20 incident on the MQW layers 5 and 6 at an angle close to parallel, at least the inclined film 20 is inclined. The reflective film 10 may be formed on the side surface on the side where incident light incident on the surface 20 is refracted. In addition, by forming the reflective film 10 on the side surface opposite to the side surface on which incident light incident on the inclined surface 20 is refracted, the light can be reciprocated in the element. Thereby, light absorption efficiency can be improved compared with the case where the reflecting film 10 is not provided on the opposite side surface.

In this manner, the MQW layers 5 and 6 and the contact layers 7 to 9 sandwiching the MQW layers 5 and 6 are provided above the i-GaAs layer 21, and the surface is parallel to the MQW layers 5 and 6. A plurality of infrared detecting elements 3 having the above are formed. The above-described process is referred to as an infrared detection element formation process (light detection element formation process).
Next, as shown in FIG. 13A, the passivation film 16 in the region where the bumps 17 of the infrared detection elements 3 are provided is removed by, for example, dry etching. Thereafter, bumps 17 are formed on the surfaces of the wirings 18 connected to the three contact electrodes 11, 13, 15 by, for example, vapor deposition or plating. In this way, bumps 17 are formed on each infrared detection element 3.

  Next, as shown in FIG. 13B, after dicing (cutting) into a chip size to form an infrared detection element array 1 in which a plurality of infrared detection elements 3 are two-dimensionally arranged, The signal processing circuit array 2 is bonded by flip chip bonding (FCB). In this way, each infrared detection element 3 is bonded to the signal processing circuit array 2 via the bumps 17.

Next, as shown in FIG. 14A, a filler (filler) 19 is filled in the gap between the infrared detection element array 1 and the signal processing circuit array 2. Here, in order to match the thermal expansion coefficient with the material constituting the infrared detecting element 3, the filler 19 is made of epoxy resin turbid with fine silica particles. In the following, four pixels are illustrated.
Next, an inclined surface 20 inclined with respect to the MQW layers 5 and 6 is formed on the other surface of each infrared detection element 3 included in the infrared detection element array 1. This process is called an inclined surface forming process.

That is, first, as shown in FIG. 14B, the GaAs substrate 22 is removed by, for example, wet etching. Since the etching for removing the GaAs substrate 22 stops at the InGaP first etching stopper layer 23, the InGaP first etching stopper layer 23 is removed with, for example, HCl.
Next, as shown in FIG. 15A, a resist 25 is patterned on the surface of the i-GaAs layer 21. Here, the resist 25 is patterned by changing the thickness.

Thus, when patterning the resist 25 by changing the thickness, for example, the following three methods are conceivable as a method for applying the resist 25.
First, as a first method, a method of applying the resist 25 by spray coating capable of nozzle position control is conceivable. That is, as shown in FIGS. 17A to 17D, a resist pattern with a changed thickness can be formed by changing the range in which the resist 25 is applied and applying the resist 25 thinly multiple times.

Next, as a second method, as shown in FIGS. 18 (A) to 18 (F), first, after a thick resist 25 is applied, masks 26 and 27 having different sizes are used for exposure and exposure. A method of developing is conceivable.
That is, first, as shown in FIG. 18A, a thick resist 25 is applied by, eg, spin coating.

Next, as shown in FIGS. 18B and 18C, a region 26 having the largest thickness is covered using a mask 26 having a narrow width, and after exposure, development is performed. Here, as an exposure condition, the exposure amount is considerably reduced so that the extreme surface of the resist 25 is developed.
Next, as shown in FIGS. 18D and 18E, a mask 27 having a slightly wider width is used to cover a region where the thickness is to be increased, and after exposure, development is performed. Do. The exposure conditions are the same as the previous time.

Thereafter, by repeating the same procedure, a resist pattern with a different thickness can be formed as shown in FIG.
Next, as a third method, as shown in FIGS. 19A to 19D, after applying a resist 25 and performing exposure and development using a mask 28 to form a resist pattern, A method of baking can be considered. That is, by baking the resist pattern and providing an angle around the resist pattern, it is possible to form a resist pattern with a different thickness.

  Next, as shown in FIG. 15B, the i-GaAs layer 21 is processed by dry etching, for example, using a resist pattern patterned by changing the thickness of the resist 25 to form the i-GaAs layer 21. The inclined surface 20 is formed. Thereby, the i-GaAs layer 21 having the inclined surface 20 is formed. It should be noted that the dry etching conditions are such that the selectivity between the resist and GaAs is not so large.

As described above, in order to form the inclined surface 20 in the i-GaAs layer 21, the GaAs substrate 22 used in manufacturing each infrared detection element 3 is removed. The infrared detection element 3 does not include the GaAs substrate 22.
After the resist is removed by dry etching as described above, the resist 29 is patterned again so that an opening is formed above the separation groove 4 as shown in FIG.

  Then, as shown in FIG. 16B, the i-GaAs layer 21, the InGaP second etching stopper layer 24 and the passivation film 16 above the separation groove 4 are removed by dry etching, for example, and connected to the separation groove 4. A groove 30 is formed. Since the groove 30 connected to the separation groove 4 also separates the infrared detection elements 3, the whole of the separation groove 4 and the groove 30 connected to the separation groove 4 can be regarded as a separation groove.

Thereafter, the reflective film 10 is formed inside the groove 30 connected to the separation groove 4, that is, on the side surface of each infrared detection element 3 by, for example, sputtering and ion milling.
In this manner, the quantum well type photodetector according to the present embodiment is completed.
Therefore, according to the quantum well photodetector and the manufacturing method thereof according to the present embodiment, there is an advantage that the light absorption efficiency can be improved and sufficient sensitivity can be obtained.

In the above-described embodiment, the angle of the inclined surface 20 is constant, but the present invention is not limited to this.
For example, as shown in FIG. 20, the inclination angle may be changed in the middle of the inclined surface 20. That is, in each infrared detection element 3, the inclination angle of the inclined surface 20 may be changed within the element width.

Even in the infrared detection element 3 including the semiconductor layer 21 having the inclined surface 20 as in the above-described embodiment, when light is incident on a region near the element side surface on which incident light incident on the inclined surface 20 is refracted. It is difficult to improve the light absorption efficiency by making the light incident on the MQW layers 5 and 6 at an angle close to parallel (see FIG. 7). For this reason, as shown in FIG. 20, even if the inclination angle of the inclined surface 20 is reduced in the region close to the side surface of the element on the side where the incident light incident on the inclined surface 20 is refracted, it is equivalent to the case of the above embodiment. An effect is obtained. That is, the inclined surface 20 may include a first inclined surface 20A having a first inclination angle and a second inclined surface 20B having a second inclination angle different from the first inclination angle. In this case, the first tilt angle may be set to a tilt angle that satisfies the condition that the light reflected and returned from one surface is totally reflected. With such a structure, the depth of the separation groove 4 can be reduced, and the processing becomes easy.
[Second Embodiment]
Next, a quantum well photodetector and a method for manufacturing the same according to a second embodiment will be described with reference to FIGS.

The quantum well type photodetector according to the present embodiment is different in the configuration of the inclined surface 20 from the above-described first embodiment.
In other words, in the present embodiment, as shown in FIG. 21, each infrared detection element 3 has a mountain-shaped inclined surface 20Z formed by combining different inclined surfaces 20X, 20Y as the inclined surface 20 on the other surface side. A plurality of semiconductor layers 21 are provided. That is, each infrared detection element 3 has a plurality of first inclined surfaces 20X having one inclination direction, an inclination angle having the same magnitude as the first inclination surface 20X, and different from the one inclination direction. The semiconductor layer 21 having a plurality of second inclined surfaces 20 </ b> Y having a plurality of inclination directions. And the 1st inclined surface 20X and the 2nd inclined surface 20Y are provided alternately. In FIG. 21, for convenience of explanation, one infrared detection element 3 is shown in a simplified manner such that two MQW layers 5 and 6 are shown together and the intermediate contact layer 8 is omitted.

  Here, one mountain-shaped inclined surface 20Z is constituted by one first inclined surface 20X and one second inclined surface 20Y, and a plurality of mountain-shaped inclined surfaces 20Z having the same shape are periodically provided. A semiconductor layer 21 having a mold inclined surface 20Z is formed. Therefore, the length of one mountain-shaped inclined surface 20Z, that is, the length obtained by adding the length of one first inclined surface 20X and the length of one second inclined surface 20Y is called the length of one cycle. . Here, the inclination angle is an angle of the inclined surfaces 20X and 20Y with respect to a plane parallel to the MQW layers 5 and 6. Further, the inclination direction is a direction in which the inclined surfaces 20X and 20Y extend.

In particular, light incident on one first inclined surface 20X is reflected on one surface and returned to the other first inclined surface 20X, and light incident on one second inclined surface 20Y is reflected on one surface. Then, it is preferable to set the inclination angle, the length of the inclined surfaces 20X and 20Y, and the thickness of the light detecting element 3 so as to return to the other second inclined surface 20Y.
Also in this case, each of the infrared detection elements 3 has one surface parallel to the MQW layers 5 and 6, and the MQW layers 5 and 6 and the contact layers 7 to 9 are sandwiched between the one surface. Thus, the other surface on the opposite side is an inclined surface 20 inclined with respect to the MQW layers 5 and 6.

  Specifically, each infrared detection element 3 includes a GaAs layer 21 having a plurality of angled inclined surfaces 20 </ b> Z on the back surface side of the second contact layer 9. As a result, light incident from the direction perpendicular to the MQW layers 5 and 6 of each infrared detection element 3 is refracted by the inclined surface 20 on the back surface of the element and reflected by the element surface or the side surface of the element. , 6 can be incident at an angle close to parallel. As a result, the light absorption efficiency can be improved.

  In particular, it is preferable that the first inclined surface 20X and the second inclined surface 20Y have an inclination angle that satisfies the condition that the light reflected and returned from one surface is totally reflected. In this case, light incident from a direction perpendicular to the MQW layers 5 and 6 of each infrared detection element 3 is refracted by the inclined surface 20 on the back surface of the element, reflected by the element surface, and returns to the inclined surface 20. Totally reflected by the inclined surface 20. The light totally reflected by the inclined surface 20 in this manner is reflected by the side surface of the element and is incident on the MQW layers 5 and 6 at an angle close to parallel. Thereby, the light absorption efficiency can be improved.

Specifically, when the semiconductor layer 21 having the plurality of mountain-shaped inclined surfaces 20Z is a GaAs layer, the first inclined surface 20X and the second inclined surface 20Y are about 11 ° or more and about 33 ° or less, as will be described later. It is preferable to have an inclination angle of
Hereinafter, with reference to FIG. 21 and FIG. 22, a GaAs layer 21 having a plurality of mountain-shaped inclined surfaces 20Z composed of a first inclined surface 20X having an inclination angle of 24 ° and a second inclined surface 20Y having an inclination angle of 24 ° is provided. The infrared detection element 3 having one MQW layer 5X sandwiched between the contact layers 7 and 9 will be described as an example to describe the reflection path and the light absorption efficiency.

Here, for convenience of explanation, the infrared detection element 3 including one MQW layer 5X will be described, but the same applies to the infrared detection element 3 including two MQW layers 5 and 6 as in the present embodiment. It becomes a reflection path, and the same light absorption efficiency is obtained in each of the MQW layers 5 and 6.
Here, as shown in FIG. 21, the first inclined surface 20X and the second inclined surface 20Y each have a length of about 5 μm and an inclination angle of about 24 °. Further, the width of the infrared detection element 3, that is, the pixel size is set to about 30 μm, the thickness of the MQW layer 5X is set to about 2 μm, and the thickness of the contact layers 7 and 9 above and below the MQW layer 5X is set to about 1 μm. The thickness D of the infrared detection element 3 is about 16.4 μm. Thereby, the light incident from one first inclined surface 20X is refracted and reflected, and the other first inclined surface 20X (here, the first inclined surface 20X adjacent to the first inclined surface 20X; the next period) The first inclined surface 20X). In FIG. 21, for convenience of explanation, one infrared detection element 3 is shown in a simplified manner.

In particular, the thickness D of the infrared detecting element 3 is adjusted to enter one end portion of one first inclined surface 20X, that is, the thinnest portion of the semiconductor layer 21 (symbol A in FIG. 21). The light thus reached reaches one end of the other first inclined surface 20X, that is, the thinnest portion (reference numeral B in FIG. 21) of the semiconductor layer 21.
Here, the second inclined surface 20Y has the same length and the same angle as the first inclined surface 20X. For this reason, similarly, the light incident from one second inclined surface 20Y is refracted and reflected to another second inclined surface 20Y (here, the second inclined surface 20Y adjacent to the one second inclined surface 20Y; The second inclined surface 20Y) of the next cycle is reached. In addition, light incident on one end portion of one second inclined surface 20Y, that is, the thinnest portion of the semiconductor layer 21, becomes one end portion of the other second inclined surface 20Y, that is, the semiconductor layer. 21 will reach the thinnest part.

Specifically, the thickness D of the infrared detecting element 3 is set such that the inclination angle is θ ₁ , the length of the inclined surface is x _0, and the refraction angle when light is incident on the inclined surface 20 is θ ₂ . It can be obtained by equation (8).

この式（８）より、ここでは、上述のように、赤外線検知素子３の厚さＤを約１６．４μｍとしている。
この場合、図２１に示すように、ＭＱＷ層５Ｘに対して垂直な方向から入射する入射光は、第１傾斜面２０Ｘに対して入射角約２４°で入射し、屈折角７．０８°で屈折する。このようにして入射・屈折した光は、入射面としての傾斜面２０の反対側の素子表面で反射される。そして、戻ってきた光は、傾斜面２０（ここでは２０Ｘ）で全反射され、反射膜１０を有する素子側面で反射されて、素子表面方向へ向かう。この結果、ＭＱＷ層５Ｘに平行に近い角度で入射することになる。その後、ＭＱＷ層５Ｘを通過した光は、再度、素子表面で反射され、再び、ＭＱＷ層５Ｘに平行に近い角度で入射することになる。これにより、光吸収効率を向上させることができる。

From this equation (8), here, the thickness D of the infrared detection element 3 is set to about 16.4 μm as described above.
In this case, as shown in FIG. 21, incident light incident from a direction perpendicular to the MQW layer 5X is incident on the first inclined surface 20X at an incident angle of about 24 ° and has a refraction angle of 7.08 °. Refract. The light incident and refracted in this way is reflected by the element surface opposite to the inclined surface 20 as the incident surface. The returned light is totally reflected by the inclined surface 20 (here, 20X), reflected by the side surface of the element having the reflective film 10, and directed toward the element surface. As a result, the light enters the MQW layer 5X at an angle close to parallel. Thereafter, the light that has passed through the MQW layer 5X is again reflected on the element surface, and is incident again at an angle close to parallel to the MQW layer 5X. Thereby, the light absorption efficiency can be improved.

  By the way, in such an infrared detecting element 3, when light is incident on the other end of the first inclined surface 20X, that is, a region near the thickest part of the semiconductor layer 21, the reflected light is reflected by the other first. It will come off the 1 inclined surface 20X, and will come out of an element. Strictly speaking, a part of the light is reflected and remains in the element. Here, the region near the other end of the first inclined surface 20X is a region near the apex of the mountain-shaped inclined surface 20Z. Here, it is a region exceeding about 70% of the height of the mountain-shaped inclined surface 20Z. The same applies to the light incident on the second inclined surface 20Y.

  On the other hand, as shown in FIG. 22, even if light is incident on a region near one element side surface, the reflection path is somewhat complicated if it is incident on a region near one end of the first inclined surface 20X. However, as in the case where the light is incident on a region far from the side surface of one element, the light can be incident on the MQW layer 5X at an angle close to parallel. In this case, incident light incident from a direction perpendicular to the MQW layer 5X is incident on the first inclined surface 20X, refracted, and then reflected by the element surface opposite to the inclined surface 20 as the incident surface. . Then, the returned light is reflected by one element side surface having the reflective film 10, totally reflected by the second inclined surface 20 </ b> Y, then reflected by the other element side surface having the reflective film 10, and toward the element surface direction. Head. As a result, the light enters the MQW layer 5X at an angle close to parallel. Thereafter, the light that has passed through the MQW layer 5X is again reflected on the element surface, and is incident again at an angle close to parallel to the MQW layer 5X. Thereby, the light absorption efficiency can be improved. Here, the region close to one end of the first inclined surface 20X is a region close to the valley of the mountain-shaped inclined surface 20Z. Here, it is an area within about 30% of the height of the mountain-shaped inclined surface 20Z. The same applies to the light incident on the second inclined surface 20Z.

  As in the case of the first embodiment described above, the light of the infrared detection element 3 is added in the width direction of the infrared detection element 3, that is, by adding the light absorption efficiency from the right side to the left side in FIGS. When the absorption efficiency was calculated, it was about 69.5%. This means that an efficiency improvement of about 42% is achieved as compared with the light absorption efficiency of about 48.8% when the diffraction grating is provided on the element surface side.

Other details are the same as in the case of the first embodiment described above, and a description thereof will be omitted here.
Therefore, according to the quantum well photodetector and the manufacturing method thereof according to the present embodiment, the light absorption efficiency can be improved and sufficient sensitivity can be obtained as in the case of the first embodiment described above. There is an advantage of becoming.

In the above-described embodiment, the plurality of mountain-shaped inclined surfaces 20Z are provided. However, the present invention is not limited to this. For example, one mountain-shaped inclined surface may be provided.
[Third Embodiment]
Next, a quantum well photodetector according to a third embodiment and a method for manufacturing the same will be described with reference to FIGS.

The quantum well photodetector according to this embodiment is different from that of the first embodiment described above, as shown in FIG. 23, each infrared detection element 3 has one sensitivity with respect to one wavelength band. The difference is that it is a one-wavelength QWIP element using the MQW layer 5X as an infrared absorption layer.
For this reason, in this embodiment, each infrared detecting element 3 includes an MQW layer 5X that absorbs infrared rays in one wavelength band. Each infrared detecting element 3 includes a first contact layer 7X provided on one surface (element surface) side with respect to the MQW layer 5X, and the other surface (element back surface; light incident surface) with respect to the MQW layer 5X. ) Side and provided with a second contact layer 9X common to the plurality of infrared detection elements 3. That is, each infrared detecting element 3 has an element structure (semiconductor laminated structure) in which the first contact layer 7X, the MQW layer 5X, and the second contact layer 9X are laminated from one surface side. The first contact layer 7X is also referred to as an upper contact layer. The second contact layer 9X is also referred to as a lower contact layer or a common contact layer.

  Specifically, each infrared detection element 3 has a structure in which an n-type GaAs first contact layer 7X, an AlGaAs / GaAs MQW layer 5X, and an n-type GaAs second contact layer 9X are stacked from one surface side. . That is, it has a single layer structure in which one MQW layer 5X is sandwiched between the n-type contact layers 7X and 9X. The AlGaAs / GaAs MQW layer 5X has a structure in which a large number of quantum wells composed of an AlGaAs barrier layer and a GaAs well layer are repeated. Thus, each infrared detection element 3 is a QWIP element doped with an n-type impurity.

  Further, each infrared detection element 3 is provided with a first contact electrode 11 on one surface, that is, on the first contact layer 7X. The second contact layer 9 </ b> X is not separated by the separation groove 4, and is a common contact layer connected to all the infrared detection elements 3. Here, the second contact layer 9X extends to the outer periphery of the chip. Although not shown, a contact hole extending from one surface side to the second contact layer 9X is provided on the outer periphery of the chip, and the second contact electrode is formed on the second contact layer 9X on the bottom surface of the contact hole. Is provided. Note that the second contact electrode is also referred to as a common contact electrode or a common electrode.

In addition, one bump 17 (metal bump electrode; here, In bump) for electrically connecting to the signal processing circuit array 2 via the passivation film 16 is provided above one surface of each infrared detection element 3. Is provided. The bumps 17 are connected to the first contact electrode 11.
Further, although not shown, a bump (metal bump electrode; In bump here) is electrically connected to the signal processing circuit array 2 via the passivation film 16 above one surface of the outer periphery of the chip. Is provided. The bump is connected to the second contact electrode. The bumps provided on the outer periphery of the chip are also called common electrodes.

  The infrared detection element array 1 and the signal processing circuit array 2 are connected via bumps 17. Here, the signal processing circuit array 2 is connected to each of the two contact layers 7X and 9X of each infrared detection element 3 via bumps 17. In this case, since the signal processing circuit array 2 is connected to one surface side of each infrared detection element 3, that is, the element surface side, each infrared detection element 3 is connected to the other surface side, that is, the element. Light enters from the back side. Then, the photocurrent signal (output current) from the MQW layer 5X is included in the signal processing circuit array 2 via the bumps 17 connected to the two contact layers 7X and 9X of each infrared detection element 3. It is read out individually in the circuit. In this case, a bias voltage is applied to the MQW layer 5X through the second contact layer 9X common to the plurality of infrared detection elements 3 and the bumps connected thereto. Then, the photocurrent signal from the MQW layer 5X can be read out through the first contact layer 7X and the bumps 17 connected thereto.

Next, the manufacturing method of this quantum well type | mold photodetector is demonstrated, referring FIGS. 24-30.
First, as shown in FIG. 24A, an InGaP first etching stopper layer 23 and an undoped i-GaAs layer (semiconductor layer) 21 are grown on a GaAs substrate (semiconductor substrate) 22. Thus, in the present embodiment, the lower InGaP first etching stopper layer 23 is formed between the GaAs substrate 22 and the i-GaAs layer 21. This is because the etching depth is accurately controlled so that the i-GaAs layer 21 is not removed when the GaAs substrate 22 is removed. The first etching stopper layer 23 is also referred to as a lower etching stopper layer.

  Next, on the i-GaAs layer 21, an InGaP second etching stopper layer 24, an n-GaAs second contact layer 9X, an InGaP third etching stopper layer 31, an AlGaAs / GaAs MQW layer 5X, and an n-GaAs first contact layer 7X. Grow. Thus, in the present embodiment, the intermediate InGaP second etching stopper layer 24 is formed immediately below the n-GaAs second contact layer 9X. This is because the etching depth is accurately controlled so that the n-GaAs second contact layer 9X is not removed when the trench 30X is formed as described later. The second etching stopper layer 24 is also referred to as an intermediate etching stopper layer. Further, the upper InGaP third etching stopper layer 31 is formed immediately below the AlGaAs / GaAs MQW layer 5X. This is because the etching depth is accurately controlled so that the second contact layer 9X is not cut when the isolation groove 4 is formed. Note that the third etching stopper layer 31 is also referred to as an upper etching stopper layer.

In this way, a semiconductor laminated structure (wafer structure) constituting each infrared detecting element 3 is formed.
Next, as shown in FIG. 24B, a passivation film 16 (insulating film; for example, a silicon oxide film) is formed so as to cover the entire surface by, eg, plasma CVD.
Next, as shown in FIG. 25A, after the passivation film 16 in the region where the contact electrode 11 of each infrared detecting element 3 is provided is removed by, for example, dry etching, the contact electrode 11 is formed by, for example, vapor deposition.

That is, after removing a part of the passivation film 16 formed on the surface of the n-GaAs first contact layer 7X by, for example, dry etching, the contact electrode 11 is formed by, for example, vapor deposition. Thereby, the contact electrode 11 is formed on the n-GaAs first contact layer 7X.
Next, as shown in FIG. 25B, after the passivation film 16 in the region where the reflective film 10 is provided on one surface of each infrared detection element 3 is removed by, for example, dry etching, the reflective film (metal) is formed by, for example, sputtering. Film) 10 is formed. That is, the reflective film 10 is formed on the surface of the n-GaAs first contact layer 7X, that is, on the surface parallel to the MQW layer 5X.

  Next, as shown in FIG. 26A, separation grooves 4 for separating the infrared detection elements 3 (each pixel) are formed by dry etching, for example. That is, the separation groove 4 is formed so that a plurality of infrared detection elements 3 are formed. Here, the InGaP third etching stopper layer 31 is formed immediately below the AlGaAs / GaAs MQW layer 5X, and the etching stops at the InGaP third etching stopper layer 31. Therefore, after that, the InGaP third etching stopper layer 31 is removed by, for example, HCl. Further, a part of the n-GaAs second contact layer 9X is removed, and the separation groove 4 reaching the n-GaAs second contact layer 9X from the surface side is formed.

Next, as shown in FIG. 26B, after forming the passivation film 16 again so as to cover the entire surface, the inner wall surface of the separation groove 4, that is, each infrared detection element, for example, by sputtering and ion milling. The reflective film 10 is formed on the side surface 3. That is, the reflective film 10 is formed on the side surface of each infrared detection element 3 defined by the separation groove 4.
In this way, a plurality of infrared detection elements 3 including the MQW layer 5X and the contact layers 7X and 9X sandwiching the MQW layer 5X above the i-GaAs layer 21 and having surfaces parallel to the MQW layer 5X. Form. The above-described process is referred to as an infrared detection element formation process (light detection element formation process).

  Next, as shown in FIG. 27A, the passivation film 16 in the region where the bumps 17 of the respective infrared detection elements 3 are provided, that is, the passivation film 16 above the contact electrode 11 is removed by, for example, dry etching to form contact holes. 40 is formed. Thereafter, bumps 17 (here, In bump electrodes) are formed on the surface of the contact electrode 11 by, for example, vapor deposition or plating. In this way, bumps 17 are formed on each infrared detection element 3.

  Next, as shown in FIG. 27B, after dicing (cutting) into a chip size to form an infrared detection element array 1 in which a plurality of infrared detection elements 3 are two-dimensionally arranged, The signal processing circuit array 2 is bonded by flip chip bonding (FCB). In this way, each infrared detection element 3 is bonded to the signal processing circuit chip 2 via the bumps 17.

Next, as shown in FIG. 28A, a filler (filler) 19 is filled in the gap between the infrared detection element array 1 and the signal processing circuit array 2. Hereafter, three pixels are illustrated.
Next, an inclined surface 20 inclined with respect to the MQW layer 5X is formed on the other surface of each infrared detecting element 3 included in the infrared detecting element array 1. This process is called an inclined surface forming process.

That is, first, as shown in FIG. 28B, the GaAs substrate 22 is removed by, for example, wet etching. Since the etching for removing the GaAs substrate 22 stops at the InGaP first etching stopper layer 23, the InGaP first etching stopper layer 23 is then removed with, for example, HCl.
Next, as shown in FIG. 29A, a resist 25 (photoresist) is patterned on the surface of the i-GaAs layer 21. Here, the resist 25 is patterned by changing the thickness.

Next, as shown in FIG. 29B, the i-GaAs layer 21 is processed by dry etching, for example, using a resist pattern patterned by changing the thickness of the resist 25 to form the i-GaAs layer 21. The inclined surface 20 is formed. Thereby, the i-GaAs layer 21 having the inclined surface 20 is formed.
As described above, in order to form the inclined surface 20 in the i-GaAs layer 21, the GaAs substrate 22 used in manufacturing each infrared detection element 3 is removed. The infrared detection element 3 does not include the GaAs substrate 22.

Next, as shown in FIG. 30A, after the resist is stripped, the resist 29 is patterned again so that an opening is formed above the separation groove 4.
Then, as shown in FIG. 30B, the i-GaAs layer 21 above the separation groove 4 is removed by dry etching, for example, to form a groove 30X. Here, the InGaP second etching stopper layer 24 is formed immediately below the i-GaAs layer 21, and the etching stops at the InGaP second etching stopper layer 24. Thereby, the groove 30 </ b> X extending from the surface side to the InGaP second etching stopper layer 24 is formed. In addition, since this groove | channel 30X isolate | separates each infrared rays detection element 3, it can also be regarded as a separation groove.

Thereafter, the reflective film 10 is formed inside the groove 30 </ b> X, that is, on the side surface of each infrared detection element 3 by, for example, sputtering and ion milling.
In this manner, the quantum well type photodetector according to the present embodiment is completed.
Other details are the same as in the case of the first embodiment described above, and a description thereof will be omitted here.

Therefore, according to the quantum well photodetector and the manufacturing method thereof according to the present embodiment, the light absorption efficiency can be improved and sufficient sensitivity can be obtained as in the case of the first embodiment described above. There is an advantage of becoming.
In addition, although the above-described embodiment has been described as a modified example of the above-described first embodiment, the present invention is not limited to this, and can be configured as a modified example of the above-described second embodiment.
[Others]
Note that the present invention is not limited to the configurations described in the above-described embodiments and modifications, and various modifications can be made without departing from the spirit of the present invention.

For example, in each of the above-described embodiments and modifications, the semiconductor layer 21 having the inclined surface 20 is provided on the other surface side, that is, on the back surface side of the second contact layers 9 and 9X. is not.
For example, the inclined surface may be formed in the second contact layer (here, n-type GaAs layer) provided on the other surface side without providing the semiconductor layer having the inclined surface. That is, each light detection element may be provided with a contact layer having an inclined surface. In this case, when manufacturing the quantum well type photodetector, it is not necessary to form a semiconductor layer for forming the inclined surface in the photodetector element forming step. In the inclined surface forming step, the semiconductor substrate may be removed and an inclined surface may be formed on the second contact layer formed on the semiconductor substrate side. Note that the n-type GaAs layer as the second contact layer may contain impurities that are inevitably included. For this reason, the n-type GaAs layer is referred to as a semiconductor layer (contact layer) containing GaAs.

  Further, for example, an inclined surface may be formed on a semiconductor substrate (here, a GaAs substrate) provided on the other surface side without providing a semiconductor layer having an inclined surface. That is, each infrared detection element may include a semiconductor substrate having an inclined surface. In this case, when manufacturing the quantum well type photodetector, it is not necessary to form a semiconductor layer for forming the inclined surface in the photodetector element forming step. In the inclined surface forming step, the inclined surface may be formed on the semiconductor substrate without removing the semiconductor substrate. Note that the GaAs substrate may contain impurities that are inevitably included. For this reason, the GaAs substrate is referred to as a semiconductor substrate containing GaAs.

In addition, for example, the laminated structure of the infrared detection elements, the number of bumps, the number of contact holes, the wiring, and the like are not limited to the structures of the above-described embodiments and modifications. For example, in the two-wavelength QWIP, one infrared detection element may be provided with one bump and one contact hole.
Hereinafter, additional notes will be disclosed regarding the above-described embodiments and modifications.

(Appendix 1)
Comprising a plurality of photodetectors comprising a multiple quantum well layer and a contact layer sandwiching the multiple quantum well layer;
Each of the photodetecting elements has one surface parallel to the multiple quantum well layer, and the other surface on the opposite side of the one surface across the multiple quantum well layer and the contact layer. The surface of the quantum well is an inclined surface inclined with respect to the multiple quantum well layer, and a reflective film is provided on the one surface and a side surface on which incident light incident on the inclined surface is refracted. Well type photodetector.

(Appendix 2)
2. The quantum well photodetector according to claim 1, further comprising a reflective film on a side surface opposite to the side surface.
(Appendix 3)
3. The quantum well photodetector according to appendix 1 or 2, wherein the inclined surface has an inclination angle that satisfies a condition that the light reflected and returned from the one surface is totally reflected.

(Appendix 4)
The supplementary note 1 or 2, wherein the slope includes a first slope having a first slope and a second slope having a second slope different from the first slope. Quantum well type photodetector.
(Appendix 5)
The quantum well photodetector according to appendix 4, wherein the first tilt angle is a tilt angle that satisfies a condition that the light reflected and returned from the one surface is totally reflected.

(Appendix 6)
As the inclined surface, a plurality of first inclined surfaces having one inclination direction and another inclination direction having an inclination angle of the same size as the first inclined surface and different from the one inclination direction are used. The quantum well according to any one of appendices 1 to 3, further comprising a plurality of second inclined surfaces, wherein the first inclined surfaces and the second inclined surfaces are alternately provided. Type light detector.

(Appendix 7)
Light incident on one first inclined surface among the plurality of first inclined surfaces is reflected by the one surface and returns to the other first inclined surface, and in the plurality of second inclined surfaces The angle of inclination, the length of the first inclined surface, and the length of the second inclined surface so that light incident on one second inclined surface is reflected by the one surface and returns to the other second inclined surface. The quantum well photodetector according to appendix 6, wherein the thickness of the photodetector and the thickness of the photodetector are set.

(Appendix 8)
Each said photodetector element is equipped with the semiconductor layer which has the said inclined surface, or the semiconductor substrate which has the said inclined surface, The quantum well type photodetector of any one of Additional remarks 1-7 characterized by the above-mentioned.
(Appendix 9)
One of the said contact layers has the said inclined surface, The quantum well type | mold photodetector of any one of Additional remarks 1-7 characterized by the above-mentioned.

(Appendix 10)
The quantum well photodetector according to any one of appendices 1 to 9, wherein the inclined surface has an inclination angle of 11 ° to 33 °.
(Appendix 11)
As the multiple quantum well layer, a first multiple quantum well layer that absorbs light in one wavelength band, and a second multiple quantum well layer that absorbs light in another wavelength band,
As the contact layer, a first contact layer provided on the one surface side with respect to the first multiple quantum well layer, and provided between the first multiple quantum well layer and the second multiple quantum well layer The supplementary intermediate contact layer and the second contact layer provided on the other surface side with respect to the second multiple quantum well layer are provided. Quantum well type photodetector.

(Appendix 12)
As the multiple quantum well layer, comprising a multiple quantum well layer that absorbs light of one wavelength band,
As the contact layer, a first contact layer provided on the one surface side with respect to the multiple quantum well layer, and a plurality of light detections provided on the other surface side with respect to the multiple quantum well layer The quantum well photodetector according to any one of appendices 1 to 10, further comprising a second contact layer common to the element.

(Appendix 13)
The quantum well photodetector according to any one of appendices 1 to 12, further comprising a signal processing circuit connected to each of the plurality of photodetectors.
(Appendix 14)
A step of forming a plurality of photodetecting elements each having a multiple quantum well layer and a contact layer sandwiching the multiple quantum well layer, and having a surface parallel to the multiple quantum well layer;
Forming an inclined surface inclined with respect to the multiple quantum well layer,
The photodetecting element forming step includes a step of forming a reflective film on the parallel surfaces, and a step of forming a reflective film on a side surface on the side where incident light incident on the inclined surface of each photodetecting element is refracted. A manufacturing method of a quantum well type photodetector characterized by including.

DESCRIPTION OF SYMBOLS 1 Infrared sensing element array 2 Signal processing circuit array 3 Infrared sensing element 4 Separation groove 5 AlGaAs / GaAs 1st MQW layer (1st MQW layer)
5X MQW layer (AlGaAs / GaAs MQW layer)
6 AlGaAs / InGaAs second MQW layer (second MQW layer)
7 n-GaAs first contact layer (first contact layer)
7X contact layer (n-GaAs first contact layer)
8 n-GaAs intermediate contact layer (intermediate contact layer)
9 n-GaAs second contact layer (second contact layer)
9X contact layer (n-GaAs second contact layer)
DESCRIPTION OF SYMBOLS 10 Reflective film 11 1st contact electrode 12 Contact hole 13 Intermediate contact electrode 14, 14X Contact hole 15 2nd contact electrode 16 Passivation film 17 Bump 18 Wiring 19 Filler 20 Inclined surface 20A 1st inclined surface 20B 2nd inclined surface 20X 2nd 1 inclined surface 20Y second inclined surface 20Z mountain-shaped inclined surface 21 i-GaAs layer (GaAs layer; semiconductor layer)
22 GaAs substrate (semiconductor substrate)
23 InGaP first etching stopper layer 24 InGaP second etching stopper layer 25, 29 Resist 26, 27, 28 Mask 30, 30X Groove 31 InGaP third etching stopper layer 40 Contact hole

Claims (6)

Comprising a plurality of photodetectors comprising a multiple quantum well layer and a contact layer sandwiching the multiple quantum well layer;
Each of the photodetecting elements has one surface parallel to the multiple quantum well layer, and the other surface on the opposite side of the one surface across the multiple quantum well layer and the contact layer. The surface of the quantum well is an inclined surface inclined with respect to the multiple quantum well layer, and a reflective film is provided on the one surface and a side surface on which incident light incident on the inclined surface is refracted. Well type photodetector.   The quantum well photodetector according to claim 1, further comprising a reflective film on a side surface opposite to the side surface.   3. The quantum well photodetector according to claim 1, wherein the inclined surface has an inclination angle that satisfies a condition that the light reflected and returned from the one surface is totally reflected. 4.   The said inclined surface is provided with the 1st inclined surface which has a 1st inclination angle, and the 2nd inclined surface which has a 2nd inclination angle different from the said 1st inclination angle, The Claim 1 or 2 characterized by the above-mentioned. Quantum well type photodetector.   As the inclined surface, a plurality of first inclined surfaces having one inclination direction and another inclination direction having an inclination angle of the same size as the first inclined surface and different from the one inclination direction are used. 4. The quantum according to claim 1, comprising a plurality of second inclined surfaces, wherein the first inclined surfaces and the second inclined surfaces are alternately provided. 5. Well type photodetector. A step of forming a plurality of photodetecting elements each having a multiple quantum well layer and a contact layer sandwiching the multiple quantum well layer, and having a surface parallel to the multiple quantum well layer;
Forming an inclined surface inclined with respect to the multiple quantum well layer,
The photodetecting element forming step includes a step of forming a reflective film on the parallel surfaces, and a step of forming a reflective film on a side surface on the side where incident light incident on the inclined surface of each photodetecting element is refracted. A manufacturing method of a quantum well type photodetector characterized by including.

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