JPH1065205A - Fabrication of semiconductor light-receiving element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the steepness of the band gap between a polycrystalline silicon layer and a silicon carbide layer by crystallizing a first amorphous semiconductor film through annealing, forming a second amorphous semiconductor film and a barrier layer, and then crystallizing the second amorphous semiconductor through annealing. SOLUTION: A first amorphous silicon layer is formed on a substrate 1 and annealed using an excimer laser to form a polysilicon layer 4 having large grain size. Subsequently, a second amorphous silicon layer layer 9 thinner than the first amorphous silicon layer and a barrier layer 5, i.e., a silicon carbide layer, are formed and crystallized through annealing, by irradiating them with laser energy 10 at a lower energy density than that of the preceding process. The amorphous silicon layer layer 9 is crystallized in conjunction with the underlying polysilicon layer 4 to produce the polysilicon layer 4. Since the grain size is increased, total quantity of defective level for grain boundary in the layer can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor light receiving element, and particularly to a line image sensor for reading an image such as a copying machine and a facsimile, and a two-dimensional image sensor for inputting an image such as a video camera. More particularly, the present invention relates to a method for manufacturing a semiconductor light receiving element utilizing the avalanche effect of multiplying carriers generated by light by impact ionization.

[0002]

2. Description of the Related Art Heretofore, CCDs have been widely used as elements for reading light in the visible light region, and thin-film type image sensors using semiconductor thin films have been partly put into practical use. ing. In each of these light receiving elements, a photodiode is used for a light sensing portion, and in principle, one or less electrons are generated for one photon, and there is no amplification effect. Generally, an amplifier circuit is provided outside the light receiving element to thereby amplify electrons to improve sensitivity, but this method also amplifies noise components in the light receiving element at the same time. , There is a problem that the S / N ratio is lowered. Therefore, in order to obtain a clear image using these elements, there is a drawback that the image must be taken in a state where a strong light is applied to the object to be read and sufficient reflected light can be obtained.

In order to make up for this drawback, the present inventors have proposed a gradient superlattice having a sawtooth potential structure as a barrier layer in a polycrystalline silicon thin film / silicon carbide thin film superlattice formed by laser annealing. An avalanche photodiode (APD) having a lattice structure has been proposed.

This avalanche photodiode has a lower electrode 2 formed on a substrate 1 by sputtering as shown in FIGS.
a) After forming a thin film, n-type hydrogenated amorphous silicon (a
-Si: H) layer is formed. Next, an amorphous silicon (a-Si) layer 9 is formed by an LPCVD method, and is irradiated with laser energy 10 using an excimer laser to be crystallized (FIG. 16).

As a result, as shown in FIG. 17, the amorphous silicon layer 9 becomes a polycrystalline silicon layer as the well layer 4.

Thereafter, the barrier layer 5 is formed by a plasma CVD method.
A silicon carbide layer as a light absorbing layer, a hydrogenated amorphous silicon layer as a light absorbing layer 6, and a p-type hydrogenated amorphous silicon layer as an electron injection layer 7 are successively deposited, and further, as shown in FIG. An upper electrode 8 made of an indium tin oxide (ITO) layer is formed by a method.

By patterning, an avalanche photodiode having a superlattice structure in which a polycrystalline silicon layer and a silicon carbide layer are stacked as shown in FIG. 19 can be formed.

In the avalanche photodiode thus formed, the photocarriers generated in the light absorption layer are amplified by the multiplication layer and taken out as a current through the upper and lower electrodes, thereby providing an amplification function. It becomes what has.

[0009]

However, in this method, when forming a polycrystalline silicon / silicon carbide superlattice as a multiplication layer, formation of an amorphous silicon layer, crystallization thereof, and formation of a silicon carbide layer are performed. Like a film, crystallization must be performed during the film formation process.
Therefore, the interface between the silicon carbide layer serving as the barrier layer and the polycrystalline silicon layer serving as the well layer has a defect level at the interface due to the adhesion of impurities when transporting between the film forming apparatus and the annealing apparatus. As a result, the dark current of the avalanche photodiode is increased, and the multiplication factor and the S / N ratio are reduced. Further, a cleaning step is required to improve the adhesion of impurities, and there is a problem that the throughput is further deteriorated.

Therefore, a method has been proposed in which amorphous silicon and silicon carbide are successively deposited and then crystallization is performed by laser annealing. In this case, when the amorphous silicon is melted, the crystallization from the silicon carbide occurs. Diffusion of carbon occurs throughout the film, and the sharpness of the band gap at the interface between amorphous silicon and silicon carbide is lost, which has been a factor preventing improvement in the multiplication factor.

The present invention has been made in view of the above circumstances, and has as its object to provide a tilted superlattice type avalanche photodiode having good interface characteristics.

[0012]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for manufacturing a semiconductor light receiving element in which a well layer made of a crystalline semiconductor thin film and a barrier layer made of a crystalline semiconductor thin film are sequentially laminated. Forming an amorphous semiconductor thin film, crystallizing the first amorphous semiconductor thin film by annealing, and forming a first crystalline semiconductor thin film;
Forming a second amorphous semiconductor thin film made of the same material as the first amorphous semiconductor thin film and thinner than the first amorphous semiconductor thin film, and forming a barrier layer made of the crystalline semiconductor thin film thereon And a step of providing the second amorphous semiconductor thin film with energy sufficient to recrystallize the first crystalline semiconductor thin film as a seed to crystallize to form a second crystalline semiconductor thin film. Features.

Preferably, the first and second amorphous semiconductor thin films are made of amorphous silicon, the first and second crystalline semiconductor thin films are made of polycrystalline silicon, and the barrier layer is made of silicon carbide. I do.

Preferably, the second amorphous semiconductor thin film and the barrier layer are continuously formed without breaking vacuum.

The step of annealing the second amorphous semiconductor thin film is an annealing step using laser light.

That is, according to the method of the present invention, sufficient energy is applied in advance to crystallize the first amorphous semiconductor thin film and the first amorphous semiconductor thin film is crystallized to obtain a polycrystalline semiconductor thin film having a sufficiently large grain size. After forming the amorphous semiconductor thin film and further forming the barrier layer, by applying energy enough to fuse the second amorphous semiconductor thin film with the already crystallized polycrystalline semiconductor thin film,
A second crystalline semiconductor thin film is formed while maintaining the crystallinity of the polycrystalline semiconductor thin film. Therefore, only the thin second amorphous semiconductor thin film is melted in the annealing step after the formation of the barrier layer, and therefore carbon diffuses from silicon carbide only up to the thickness of the second amorphous semiconductor thin film. The sharpness of the band gap can be greatly improved as compared with the case where carbon diffuses throughout the entire crystalline semiconductor thin film as in the related art.

Further, since the second amorphous semiconductor thin film and the barrier layer are formed continuously without breaking vacuum, the surface of the film is not contaminated and the avalanche photodiode having few defect levels is formed. Can be formed. In addition, if the film is formed in the same chamber, it is possible to form a better thin film without being contaminated during transportation between the apparatuses.

In the case of crystallizing amorphous silicon, only the surface layer can be selectively crystallized by appropriately selecting the wavelength using laser light.

It is desirable that the thickness ratio between the first and second amorphous semiconductor thin films is 2 to 10: 1, and the energy is 500 mJ / cm ² or less.

Here, the first and second crystalline semiconductor thin films usually indicate polycrystals, but may be single crystals.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIGS. 1 to 4 are views for explaining the principle of the method for manufacturing a semiconductor light receiving element according to the present invention. That is, in the method of the present invention, a sufficient energy is applied to the crystallization of the first amorphous semiconductor thin film to crystallize it, and a polycrystalline semiconductor thin film having a sufficiently large grain size is obtained. After forming and further forming a barrier layer,
Forming the second crystalline semiconductor thin film while maintaining the crystallinity of the polycrystalline semiconductor thin film by applying energy enough to fuse the second amorphous semiconductor thin film with the already crystallized polycrystalline semiconductor thin film. Thereby, a photoelectric conversion layer having an inclined superlattice structure of an amorphous silicon thin film and a silicon carbide thin film is formed.

First, as shown in FIG. 1, a first amorphous silicon (a-Si) layer 9 is formed on a substrate 1 and crystallized by irradiating a laser energy 10 using an excimer laser.

Thus, as shown in FIG. 2, a polycrystalline silicon layer 4 having a large grain size is formed.

Thereafter, as shown in FIG. 3, a thin second amorphous silicon thin film 9 and a silicon carbide layer 5 are formed, and a laser energy 10 having an energy density lower than that of the above-described process is irradiated on the thin second amorphous silicon thin film 9 and the silicon carbide layer 5 using an excimer laser. And crystallize.

At this time, since the transmittance of the uppermost silicon carbide layer 5 is about 100%, this light satisfactorily reaches the thin amorphous silicon layer 9, acts on crystallization, and acts as an underlying polycrystalline silicon layer 4. The second amorphous silicon layer 9 is crystallized continuously with this as a nucleus while inheriting the crystallinity of the polycrystalline silicon layer, as shown in FIG. The crystalline silicon layer 4 is formed.

When the recrystallization is performed by the excimer laser as described above, polycrystalline silicon composed of columnar crystals having a grain size substantially equal to the film thickness is formed. As the grain size increases, the volume occupied by the crystal grain boundaries in the film becomes relatively low, and as a result, the total amount of defect levels existing in the grain boundaries in the film is reduced.

With the polycrystalline silicon layer crystallized so as to have a sufficiently large grain size as a nucleus, the upper thin amorphous silicon layer is crystallized, and finally the polycrystalline silicon having a large grain size is obtained. Is formed.

Further, in the annealing step after the formation of the barrier layer, the thin amorphous silicon is melted. Therefore, carbon diffuses from silicon carbide only up to the thickness of the second amorphous silicon thin film. The sharpness of the band gap can be greatly improved as compared with the case where carbon is diffused over the entire crystalline semiconductor thin film as in the related art.

Further, since the second amorphous silicon thin film and the barrier layer are continuously formed, the surface of the film is not contaminated when transported between apparatuses, and the photoelectric conversion with few defect levels is performed. A layer can be formed.

Furthermore, polycrystalline silicon having a larger grain size can be obtained by using furnace annealing. However, furnace annealing requires a longer time as it is performed at a lower temperature, which greatly affects throughput.

Next, the manufacturing process of the avalanche photodiode according to the first embodiment of the present invention will be described. First, FIG.
As shown in FIG. 5, a 500 nm tantalum (Ta) thin film is formed as a lower electrode 2 on a glass substrate 1 by a sputtering method.
After forming to a film thickness of about m, plasma CVD
The hole injection blocking layer 3 is formed by the
A hydrogenated amorphous silicon (a-Si: H) layer is formed. Next, a first amorphous silicon (a-Si) layer 9 having a thickness of about 100 nm is formed by LPCVD, and is irradiated with a laser beam 10 of about 300 mJ / cm ² using a XeF excimer laser having an oscillation wavelength of 351 nm to crystallize. I do.

As a result, the first amorphous silicon layer 9 is melted and recrystallized to form a first polycrystalline silicon layer.
Then, a second amorphous silicon layer 9 having a thickness of 20 nm is formed on this upper layer by LPCVD, and then silicon carbide (S) having a thickness of about 50 nm is formed by plasma CVD.
iC) A layer 5 is formed and similarly irradiated with a laser energy 10 of about 100 mJ / cm ² using a XeF excimer laser as shown in FIG.

As a result, the transmittance of the uppermost silicon carbide layer 5 is about 100%, so that this light reaches the amorphous silicon layer 9 satisfactorily. Most of the irradiation energy acts on the crystallization of this layer, and as shown in FIG. 8, the amorphous silicon layer 9 forms columnar polycrystal with high crystallinity using the lower polycrystalline silicon layer 4 as a nucleus. A polycrystalline silicon layer 4 having a thickness of about 120 nm is formed as a well layer.
This polycrystalline silicon layer had a particle size of 100 nm.

Thereafter, a 1 μm-thick hydrogenated amorphous silicon layer is formed as a light absorbing layer 6 by a plasma CVD method.
A p-type hydrogenated amorphous silicon layer as an electron injection blocking layer 7 is continuously deposited, and as shown in FIG. 8, an indium tin oxide (I
An upper electrode 8 made of a (TO) layer and having a thickness of 60 nm is formed.

Then, patterning is performed as shown in FIG.
An avalanche photodiode having a superlattice structure composed of a polycrystalline silicon layer and a silicon carbide layer is formed.

When the avalanche photodiode thus formed was examined for defect levels at the polycrystalline silicon / silicon carbide interface, it was found that the defect level was significantly improved as compared with the prior art. It was also confirmed that carbon diffusion occurred only in a thin region in the upper layer of the polycrystalline silicon layer.

The results of irradiating the avalanche photodiode with light and measuring the characteristics are shown in FIGS. FIG. 10 shows the relationship between the applied voltage and the multiplication factor.
1 indicates the relationship between the applied voltage and the dark current. In each case, the solid line shows the measurement result of the avalanche photodiode formed by the method of the present invention, and the dotted line shows the measurement result of the avalanche photodiode formed by the conventional method. From these results, it is understood that the dark current is reduced and the S / N ratio is greatly improved according to the method of the present invention.

This is considered to be due to the following reasons. In this method, no impurities are mixed into the interface between the well layer and the barrier layer, and polycrystalline silicon having good crystallinity is formed. Therefore, when a reverse bias is applied to the avalanche photodiode, since the barrier layer has a high resistance to the well layer, the well layer is hardly electrolyzed, and unnecessary electron / hole pairs are generated. And the generation of dark current can be suppressed, and the polycrystalline silicon has a high mobility, so that high sensitivity is obtained.

Next, a second embodiment of the present invention will be described. Here, the steps up to the step of forming the first amorphous silicon layer and annealing to form the first polycrystalline silicon layer 4 are performed using the same method as in the first embodiment.
Thereafter, the upper electrode 8 is removed from the second amorphous silicon layer 9.
, And thereafter, laser light is irradiated from the substrate surface side.

First, in the same manner as in the first embodiment, as shown in FIG. 12, a light-transmissive ITO thin film was formed on a glass substrate 1 by sputtering as a lower electrode 2 for 100 nm.
After forming to a film thickness of about m, plasma CVD
The hole injection blocking layer 3 is formed by the
A hydrogenated amorphous silicon (a-Si: H) layer is formed. Next, a first amorphous silicon (a-Si) layer 9 having a thickness of about 100 nm is formed by LPCVD, and is crystallized by irradiating a laser beam 10 of about 300 mJ / cm ² using a XeF excimer laser having an oscillation wavelength of 351 nm. .

As a result, the first amorphous silicon layer 9 is melted and recrystallized to form a first polycrystalline silicon layer.
Then, a second amorphous silicon layer 9 having a thickness of 20 nm is formed on this upper layer by LPCVD, and then silicon carbide (S) having a thickness of about 50 nm is formed by plasma CVD.
iC) forming a layer 5 and further forming a light absorbing layer 6 having a thickness of 1 μm
m hydrogenated amorphous silicon layer, electron injection blocking layer 7
A p-type hydrogenated amorphous silicon layer having a thickness of about 50 nm is continuously deposited, and a 60 nm-thick upper electrode 8 made of an indium tin oxide (ITO) layer is formed thereon by a sputtering method. Here, all layers other than the indium tin oxide layer can be formed in a continuous process. Then, the laser beam 10 of 100 mJ / cm ² is irradiated from the glass substrate side using a pulsed dye laser having an oscillation wavelength of 620 nm to recrystallize the second amorphous silicon layer (FIG. 13).

Thus, the ITO as the lower electrode 2
The layer, the n-type hydrogenated amorphous silicon layer as the hole injection blocking layer 3 and the silicon carbide layer 5 have a transmittance of about 100%, and the crystallized first polycrystalline silicon layer 4
Has a transmittance of about 80%, this light reaches the amorphous silicon layer 9 well, and this layer has a very low transmittance, is well absorbed by this layer, and most of the irradiation energy is crystallized in this layer. As shown in FIG. 14, the second amorphous silicon layer 9 is melt-recrystallized to form the polycrystalline silicon layer 4 as a well layer having extremely high crystallinity.

Thereafter, patterning is performed to form an avalanche photodiode having a super lattice structure in which a polycrystalline silicon layer and a silicon carbide layer are laminated as shown in FIG.

The avalanche photodiode thus formed also has a significantly reduced dark current, similarly to the avalanche photodiode formed by the method of the first embodiment.

In the above embodiment, a glass substrate is used as the substrate. However, other insulating materials such as ceramic, quartz and polyimide may be used, and a conductive material such as a metal plate may be used for the avalanche photodiode. It can be used depending on the application. However, when irradiating laser light from the substrate side, it is necessary to select a material that transmits laser light. As the lower electrode, in addition to tantalum, metal materials such as molybdenum, titanium, and tungsten, tantalum silicide, molybdenum silicide, titanium silicide,
Metal silicide such as tungsten silicide may be used. In addition, the hole injection blocking layer is not limited to n-type hydrogenated amorphous silicon, but may be crystalline silicon,
Polycrystalline silicon may be used. Selenium, germanium, and the like are also applicable. The electron injection blocking layer is not limited to p-type hydrogenated amorphous silicon, but may be crystalline silicon, polycrystalline silicon, or the like. The barrier layer is not limited to silicon carbide, but may be silicon nitride or the like. The light absorbing layer is not limited to hydrogenated amorphous silicon, and selenium, germanium, and the like can be used. The upper electrode is not limited to indium tin oxide, but can be changed as appropriate, such as tin oxide.

As a method for forming the amorphous semiconductor layer and the crystalline semiconductor layer, LPCVD and plasma CVD are used.
It goes without saying that other methods such as ECRCVD, optical CVD, sputtering, and vapor deposition may be used without being limited to the method.

In the above embodiment, an excimer laser, a dye laser, or the like is used as a laser in the annealing step. However, a krypton laser, a ruby laser, an Ar laser, a CW dye laser, a Q switch laser, or the like may be used. Also, lamp annealing and thermal annealing can be applied.

Further, in the above-described embodiment, the avalanche photodiode detects light from the element side with respect to the substrate, but may be configured to detect light from the substrate side. As the multiplication layer, the well layer and the barrier layer may have a multilayer structure instead of one period. Also, the electrodes are sandwiched between the upper and lower portions, but may be replaced.

[0050]

As described above, according to the present invention, the defect level at the interface between the polycrystalline silicon layer and the silicon carbide layer can be reduced, and the steepness of the band gap difference can be maintained. It is possible to obtain a high-quality avalanche photodiode with low dark current.

[Brief description of the drawings]

FIG. 1 illustrates the principle of the method of the present invention.

FIG. 2 is a diagram illustrating the principle of the method of the present invention.

FIG. 3 is a diagram illustrating the principle of the method of the present invention.

FIG. 4 is a diagram illustrating the principle of the method of the present invention.

FIG. 5 is a manufacturing process diagram of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 6 is a manufacturing process diagram of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 7 is a manufacturing process diagram of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 8 is a manufacturing process diagram of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 9 is a manufacturing process diagram of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 10 is a diagram showing the relationship between the applied voltage and the multiplication factor of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 11 is a diagram illustrating a relationship between an applied voltage and a dark current of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 12 is a manufacturing process diagram of the avalanche photodiode according to the second embodiment of the present invention.

FIG. 13 is a manufacturing process diagram of the avalanche photodiode according to the second embodiment of the present invention.

FIG. 14 is a manufacturing process diagram of the avalanche photodiode according to the second embodiment of the present invention.

FIG. 15 is a manufacturing process diagram of the avalanche photodiode according to the second embodiment of the present invention.

FIG. 16 is a manufacturing process diagram of a conventional avalanche photodiode.

FIG. 17 is a manufacturing process diagram of a conventional avalanche photodiode.

FIG. 18 is a manufacturing process diagram of a conventional avalanche photodiode.

FIG. 19 is a manufacturing process diagram of a conventional avalanche photodiode.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 glass substrate 2 lower electrode 3 hole injection blocking layer 4 well layer 5 barrier layer 6 light absorbing layer 7 electron injection blocking layer 8 upper electrode 9 amorphous silicon layer 10 laser light

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinya Kyozuka 430 Sakai Nakai-cho, Ashigara-gun, Kanagawa Green Tech Nakai Inside Fuji Xerox Co., Ltd.

Claims (4)

[Claims] 1. A method for manufacturing a semiconductor light receiving element comprising a multiplication layer formed by laminating a well layer made of a crystalline semiconductor thin film and a barrier layer made of a crystalline semiconductor thin film between a pair of electrodes, The step of forming the multiplication layer forms a first amorphous semiconductor thin film having a sufficient thickness,
Crystallizing the first amorphous semiconductor thin film by annealing to form a first crystalline semiconductor thin film; and a second thin film made of the same material as the first amorphous semiconductor thin film and thinner than the first amorphous semiconductor thin film. A step of forming an amorphous semiconductor thin film, and a step of forming a barrier layer made of the crystalline semiconductor thin film thereon.
Applying a degree of energy to the second amorphous semiconductor thin film for recrystallization with the first crystalline semiconductor thin film as a nucleus to form a second crystalline semiconductor thin film. A method for manufacturing a semiconductor light receiving element. 2. The semiconductor device according to claim 1, wherein said first and second amorphous semiconductor thin films are amorphous silicon, said first and second crystalline semiconductor thin films are polycrystalline silicon, and said barrier layer is silicon carbide. Item 2. A method for manufacturing a semiconductor light receiving element according to Item 1. 3. The method according to claim 1, wherein the second amorphous semiconductor thin film and the barrier layer are continuously formed without breaking vacuum. 4. The method according to claim 1, wherein the step of annealing the second amorphous semiconductor thin film is an annealing step using a laser beam.