JP3049323B2 - Manufacturing method of micro lens for infrared focusing - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method of manufacturing a microlens for infrared focusing and an infrared sensor with a microlens, for example, a non-contact thermometer capable of measuring body temperature in a non-contact state with a human body. The present invention relates to a microlens-equipped infrared sensor suitable for use in the present invention and a method of manufacturing an infrared focusing microlens used in this sensor.

[Related Art] For example, a thermometer used in a hospital or the like is preferably capable of quickly and accurately measuring a patient's body temperature and inexpensive.

However, even if the thermometer currently used is an electronic thermometer, a direct reading meter (which waits for the sensor to reach the same temperature as the substance to be measured and then measures) takes more than 5 minutes to measure the temperature. Even a so-called predictive thermometer that measures the temperature at the time of thermal equilibrium from the measured temperature and the elapsed time requires about one minute. Such a temperature measurement time is too long for infants and critically ill patients.

On the other hand, at present, the armpit or sublingual area is generally selected as the body temperature measurement part, but such a part does not indicate the exact body temperature of the whole body, and a more accurate temperature measurement result is obtained. In order to obtain it, it is necessary to measure the temperature at a temperature closer to the temperature of the brain, and such a temperature measuring part is a part in the auditory canal that is not easily affected by wind or the outside air, particularly close to the temperature of the brain It has been found that a site near the eardrum that reflects the temperature of the thalamus site is optimal.

Therefore, using a very small infrared sensor that can accurately detect the amount of infrared radiation emitted from the eardrum, the body temperature is measured in a very short time (for example, within 3 seconds) and with high accuracy (for example, 1/100 ° C). There has been a demand for the development of a so-called tympanic thermometer capable of doing so.

By the way, non-contact type thermometers need to detect a small amount of infrared radiation emitted from an object such as the human body that has almost no difference from the outside air temperature. If touched, accurate temperature measurement becomes impossible due to the effects of wind and thermal convection.

In order to reduce the influence of such disturbance, it is necessary to protect the infrared sensor element by putting it in a package.
Further, it is desirable that this package is provided with a minute lens for focusing infrared rays in order to efficiently guide infrared rays emitted from the temperature measuring object to the infrared sensor element.

Conventionally, in order to obtain a minute lens for focusing an infrared ray, an inorganic material that can transmit infrared rays, such as silicon, has been processed one by one and polished.

[Problems to be Solved by the Invention] However, in such a conventional method for manufacturing a lens, even if it is automated, a considerable time and effort is required for processing and polishing the lens, so that the lens becomes expensive, In addition, since there is a limit to the miniaturization of the lens, it is difficult to reduce the size of the infrared sensor, which is not suitable for the eardrum thermometer for measuring in the ear as described above.

In addition, it is difficult to align the infrared light focused by the lens with the light receiving portion of the infrared sensor element as the sensor element and the lens become minute, and if this alignment is not strictly performed, the characteristics of the infrared sensor may be deteriorated. Variations occur and yield decreases.

The present invention has been made in view of such a problem, a method for manufacturing a very minute infrared focusing lens without a need for any polishing step, a method capable of simultaneously producing a large amount, and a lens and an infrared element It is an object of the present invention to provide an infrared sensor with microlenses having uniform characteristics and accurately aligned.

Means for Solving the Problems In order to achieve the above-mentioned object, in the method for manufacturing a microlens for infrared focusing according to the present invention, a lens is manufactured by using a photolithography technique and an etching technique used in semiconductor manufacturing. It is characterized by doing. In manufacturing the lens, first, a lens substrate made of a material that can transmit infrared rays, such as silicon or germanium, is prepared, and an etching mask is formed on the lens substrate by using a photolithography technique. The mask pattern is circular for a convex lens and concentric for a Fresnel lens. When producing a convex lens, the etching mask is formed as a double film structure of a base film soluble in an etching solution used for etching a lens substrate and a photoresist film deposited on the base film. I do.

In this case, in order to make the etched cross section of the lens substrate into a lens shape, the base film of the etching mask is etched simultaneously with the lens substrate along with the etching of the lens substrate, and the etching speed V _{2 of the} base film is set to the lens. to have a relationship of V _2> V ₁ with respect to the etching rate V ₁ of the substrate. When the lens substrate is made of silicon,
Silicon nitride (SiN _x ) is suitable as a material for the base film of the etching mask, and the etching rate V ₂ is controlled by the formation method and film formation conditions.

In addition, in order to form a convex lens on the lens substrate by etching, the thickness of the underlying film is reduced, so that the flow of the etchant under the photoresist film is suppressed toward the center of the etching pattern. Is made to decrease as the apparent etching rate becomes closer to the center of the lens. By etching the lens substrate under such conditions, a desired lens can be formed on the lens substrate.

If such considerations are not made and only the base film having an etching rate higher than the etching rate of the lens substrate is used, the etching of the lens substrate proceeds linearly, and the desired convex lens-shaped cross-sectional shape is obtained. Can not get.

The lens substrate provided with the microlenses formed in this way is bonded to a lens substrate made of silicon or the like having a microinfrared sensor element similarly formed using photolithography technology and etching technology on the upper surface. You. In this case, it is preferable to provide a concave portion for hermetically receiving the infrared sensor element provided on the sensor substrate on the joint surface on the lens substrate side. After the lens substrate and the sensor substrate are aligned using an alignment device, they are bonded using, for example, an anodic bonding method.

[Operation] According to the method of manufacturing a microlens for infrared focusing according to the present invention, since a lens portion is formed on a lens substrate using a photolithography technique and an etching technique, a large number of lenses are formed on one lens substrate. A minute lens portion can be manufactured at the same time, and a minute lens can be obtained at low cost.

In addition, when mounting an infrared focusing lens on an infrared sensor substrate, it is difficult to align the lens and the sensor as the sensor and the lens become smaller, so that it is difficult to obtain an infrared sensor with a minute lens having uniform characteristics in the past. However, when a large number of microlenses are produced on a single lens substrate by the method of the present invention, the lens portion on the lens substrate is similarly adapted using photolithography technology and etching technology. For the sensor substrate with many infrared sensor elements manufactured at the
Since accurate alignment can be performed by the alignment device, if the bonded body is cut into a predetermined size after bonding both substrates, an infrared sensor chip having a large amount of uniform characteristics can be obtained at the same time.

Furthermore, by performing the alignment and bonding work between the lens substrate and the sensor substrate in a vacuum, an infrared sensor whose light receiving portion is accommodated in a vacuum can be obtained, thereby improving the sensitivity of the infrared sensor and improving the temperature measurement accuracy. Can be improved.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 and FIG. 2 are a plan view and a longitudinal sectional view showing a part of a lens substrate on which a large number of microlenses are formed by the manufacturing method of the present invention. On the flat back surface 1b of the lens substrate 1 provided with a lens portion 20 having a convex lens-shaped cross section on the upper surface side, a concave portion 21 for accommodating an infrared sensor element 10 of a sensor substrate 11, which will be described later, joined to the back surface 1b. Are formed.

The lens portion 20 has, for example, a diameter D of 1.44 mm and a height H of
Since it is extremely small, about 0.6 mm, the lens section 2
In manufacturing 0, a calculation method of a thin lens is approximately used.

In general, the focal length f of a lens having a spherical surface on one side is represented by f when the radius of curvature of the spherical surface is r and the refractive index of the lens is n.
= R / (n-1). When the lens material is silicon, since n = 3.4, it is necessary to use a lens having a radius of curvature r = 0.72 mm in order to set the focal length f = 0.3 mm. The focal position of the infrared light focused by the lens unit 20 is
It can be changed by the depth of the recess 21 together with the radius of curvature r. In the case of a lens having a radius of curvature r = 0.72 mm, the concave portion 21
By making the depth of about 0.1 mm, it is possible to focus on a position at a distance of about 0.6 mm from the lens upper surface.

3 (A) to 3 (L) show a manufacturing process of an infrared sensor with a micro convex lens according to the present invention. First, as shown in FIG. 3 (A), a smooth and flat front surface 1a and a back surface are shown.
A lens substrate 1 made of a silicon wafer having 1b is prepared.

Next, as shown in FIG. 3 (B), the surface of the lens substrate 1
A surface protective film 2 is applied and formed on 1a, and a photoresist film 3 is applied and formed on the back surface 1b. The pattern of the concave portion 21 for accommodating the infrared sensor element is formed on the photoresist film 3. It is formed using a normal photolithography technique.

Next, using the photoresist film 3 as a mask, the back surface 1b of the lens substrate 1 is etched to form a concave portion 21 on the back surface 1b as shown in FIG. 3 (C). As shown, the surface protection film 2 and the photoresist film 3 are removed from the surfaces 1a and 1b, respectively. Subsequently, as shown in FIG. 3 (E), a silicon nitride film 5 as a base film is formed on the surface 1a of the lens substrate 1 by using a plasma CVD method.
Is formed to a thickness of 0.2 μm.

An etchant used for etching the lens substrate 1 together with the base film 5 is preferably of a composition such that the surface of the etched lens substrate 1 forms a smooth surface. When the lens substrate 1 is made of silicon, a typical isotropic etching solution having a composition of nitric acid: hydrofluoric acid: acetic acid = 7: 2: 1 or 7: 1.2: 1.8 may be used.
These etchants etch silicon at a rate of about 30-70 μm / min. When the underlying film is silicon nitride as an etching mask, the etching rate of the silicon nitride film formed by the plasma CVD method with the above-mentioned etching solution is about 150 to 250 μm / min.
When annealing treatment is performed at 30 ° C. for 30 minutes, the etching rate is 60 to 90 μm / min, which is a suitable etching rate for etching the lens substrate 1 into a convex lens shape.

For the silicon nitride film 5 as the underlayer, 82
After annealing at a temperature of 0 ° C. for about 30 minutes, a photoresist film 6 is applied on the surface of the silicon nitride film 5 and a surface protective film 7 is applied on the back surface 1 b of the lens substrate 1. . Then, for the photoresist film 6,
Using a photolithography technique, a circular lens pattern is formed as shown in FIG. Subsequently, using the photoresist film 6 as a mask, the silicon nitride film 5 is etched to form a circular pattern corresponding to the circular pattern of the photoresist film 6 on the silicon nitride film 5 as shown in FIG. Then, an etching master 8 composed of a double film of the silicon nitride film 5 as the base film and the photoresist film 6 deposited thereon is formed.

Next, using this etching master 8, nitric acid: hydrofluoric acid:
The lens substrate 1 is etched with an etchant having a composition of acetic acid = 7: 2: 1. As the lens substrate 1 is etched, the silicon nitride film 5 having an etching rate higher than the etching rate of the lens substrate 1
Is etched from the periphery to the center as shown in FIG. 3 (H).
Is etched so that a convex lens-shaped protrusion 20 'grows below the silicon nitride film 5, and when the etching on the lens substrate 1 is almost completed, the state shown in FIG. Finally, as shown in FIG. 3 (J), a lens portion 20 having a substantially ideal convex lens shape was formed on the lens substrate 1 made of silicon. And
When the surface protective film 7 is removed from the back surface 1b of the lens substrate 1 (the photoresist film 6 is lifted off with the etching of the silicon nitride film 5), the lens portion 20 and the concave portion 21 as shown in FIG. The lens substrate 1 on which was formed was obtained.

Next, an alignment device is used to align the lens substrate 1 with a sensor substrate 11 made of a silicon wafer having a large number of infrared sensor elements 10 at positions corresponding to the lens portions 20 on the lens substrate 1 on the flat surface 11a. When the vacuum device reaches a degree of vacuum of about 1 × 10 ⁻⁵ torr, the manipulator of the alignment device is operated to align the lens substrate 1 with the sensor substrate 11. . When this alignment is completed, both substrates 1 and 11 are
The substrates 1 and 11 are joined together using an anodic bonding method as shown in FIG. 3 (L).

The anodic bonding method is a technique for bonding glass and silicon, etc., in which the smooth surfaces of glass and silicon are overlapped, and a negative voltage of about 500 V is applied to the glass side while being heated to 300 to 400 ° C. Then, alkali ions in the glass move to form a space charge layer near the interface. For this reason, a large electrostatic attraction is generated between glass and silicon, and a chemical bond is formed at the interface.

In this embodiment, a silicon substrate on which a low-melting-point glass film is adhered and another silicon substrate are overlapped, a positive voltage is applied to the silicon substrate on which the glass film is not adhered, and bonding is performed at room temperature. While adopting the joining method,
This anodic bonding is performed in a vacuum.

The joined body of the lens substrate 1 and the sensor substrate 11 joined by the anodic bonding method as described above is cut at a position of a line L shown in FIG.
Infrared chip 25 with individual microlenses as shown
Could be obtained.

[Effects of the Invention] As is clear from the above description, according to the method for manufacturing a microlens for infrared focusing according to the present invention, a large number of microlenses are simultaneously formed on a lens substrate by using photolithography technology and etching technology. Since it can be manufactured, the price of the microlens can be significantly reduced. In addition, by using an alignment device to align the sensor substrate on which a large number of sensor elements are formed in correspondence with the positions of the lenses on the lens substrate, infrared rays can be accurately incident on the light receiving portions of the individual infrared sensors. And an infrared sensor chip having uniform characteristics can be obtained. In addition, by aligning the lens substrate and the sensor substrate and joining the two substrates in a vacuum, the infrared light receiving section can be housed in a vacuum chamber, and a more sensitive and accurate infrared sensor can be obtained. It will be understood that the infrared sensor with microlenses according to the present invention is suitable for use in the eardrum thermometer described above.

[Brief description of the drawings]

FIG. 1 is a plan view showing a part of a lens substrate on which a lens portion is formed by a method of manufacturing a microlens of the present invention, FIG. 2 is a longitudinal sectional view taken along line II-III in FIG. 1, and FIG. (A)
(L) to (L) are schematic cross-sectional views showing sequential steps in a method of manufacturing a microlens, and FIG. 4 is a longitudinal cross-sectional view of an infrared sensor with microlenses according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Lens substrate, 5 ... Silicon nitride film 8 ... Etching mask 10 ... Infrared sensor element 11 ... Sensor substrate, 20 ... Lens part 21 ... Recess

Continuation of the front page (56) References JP-A-63-265842 (JP, A) JP-A-61-240201 (JP, A) JP-A-62-261025 (JP, A) JP-A-64-47923 (JP) , A) JP-A-61-23926 (JP, A) JP-A-62-291257 (JP, A) JP-A-60-119155 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB Name) G02B 3/00

Claims (4)

(57) [Claims] A mask film having a predetermined pattern is formed on a substrate, and the substrate is etched using the mask film as an etching mask. In this case, an etching solution used for etching the substrate is used as the mask film. A base film made of a material that is soluble in and has an etching rate higher than the etching rate of the substrate, and a double film made of a photoresist film deposited on the base film, And when simultaneously etching the base film with the etching solution,
The thickness of the base film is selected and a lens portion is formed on the substrate so that the etching solution is prevented from flowing to the lower part of the photoresist film toward the center of the predetermined pattern. A method for manufacturing a microlens for infrared focusing. 2. The method according to claim 1, wherein the pattern of the mask film is circular. 3. The method according to claim 1, wherein the pattern of the mask film is a concentric circle. 4. The method according to claim 1, wherein silicon is used as said substrate material and silicon nitride is used as said base film material.