JPH1065204A - Manufacture of semiconductor photodetector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an oblique super-lattice avalanche photodiode which is superior in interface characteristics to be enhanced in throughput. SOLUTION: Well layers 4 formed of second crystalline semiconductor thin film and barrier layers 5 formed of first crystalline semiconductor thin film are alternately laminated in a plurality of cycles for the formation of a semiconductor photodetector, wherein annealing is carried out using a laser beam which is so specified in wavelength as to be higher in transmissivity for the second crystalline semiconductor thin film 4 than for the amorphous semiconductor thin film 9, when the amorphous semiconductor thin films 9 are turned crystalline by annealing for the formation of the second crystalline semiconductor thin films 4 after the amorphous semiconductor thin films 9 and the barrier layers 5 formed of first crystalline semiconductor thin film are alternately laminated in a plurality of cycles.

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 Conventionally, CCDs have been widely used as elements for reading light in the visible light range, and thin-film type image sensors using semiconductor thin films have also been partly put into practical use. ing. In each of these light receiving elements, a photodiode is used for the light sensing unit, 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 in that it is necessary to irradiate the object to be read with strong light and to perform imaging in a state where 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 a sputtering method 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 a laser beam 10 using an excimer laser to be crystallized (FIG. 20).

Thus, as shown in FIG. 21, the amorphous silicon layer 9 becomes a polycrystalline silicon layer as the well layer 4.

Next, a silicon carbide (SiC) layer is deposited as a barrier layer 5 by a plasma CVD method, and an amorphous silicon layer 9 is formed thereon again by an LPCVD method by a plasma CVD method. As shown in FIG. 22, an excimer laser is used. To irradiate with a laser beam 10 for crystallization.

As a result, as shown in FIG. 23, the amorphous silicon layer 9 becomes a polycrystalline silicon layer (well layer 4).

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

Then, patterning is performed to form a multiplication layer having a super lattice structure in which a polycrystalline silicon layer and a silicon carbide layer are stacked in two cycles as shown in FIG.

In the avalanche photodiode thus formed, the photocarriers generated in the light absorption layer are amplified in the multiplication layer, and are taken out as current through the upper and lower electrodes, and the amplification action is performed. Will have.

[0011]

However, in this method, when forming a polycrystalline silicon / silicon carbide superlattice as a multiplication layer, the formation and crystallization of an amorphous silicon layer and the formation of a silicon carbide layer are performed. It has to be repeated alternately, and there is a problem that the throughput of the process is poor. In addition, the interface between the silicon carbide layer serving as the barrier layer 5 and the polycrystalline silicon layer serving as the well layer increases the defect levels at the interface due to adhesion of impurities when transported between the film forming apparatus and the annealing apparatus. As a result, the dark current of the avalanche photodiode increases, and the S / N ratio decreases. Further, a cleaning step is required to improve the adhesion of impurities, and there is a problem that the throughput is further deteriorated.

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

Therefore, the present invention provides a laminating step of alternately laminating a plurality of periodic layers of an amorphous semiconductor thin film and a barrier layer made of a first crystalline semiconductor thin film, and annealing the amorphous semiconductor thin film to crystallize it. An annealing step of forming a multiplication layer having a superlattice structure in which well layers and barrier layers are alternately stacked in a plurality of periods by forming a well layer made of the crystalline semiconductor thin film of Step 2; After the process, the first layer is connected to the multiplication layer.
And a step of forming a second electrode, wherein the annealing step includes a step of forming a laser having a wavelength higher in transmittance to the second crystalline semiconductor thin film than in the amorphous semiconductor thin film. And annealing.

According to a second aspect of the present invention, the thickness of the film is reduced toward the lower layer in accordance with the transmittance of the film laminated on the laser beam irradiation side, and the energy received from the laser is made substantially equal. It is characterized in that annealing is performed.

Further, in a third aspect of the present invention, when the amorphous semiconductor thin film is laser-annealed and crystallized to form a second crystalline semiconductor thin film, each layer is formed according to the transmittance of the film laminated on the laser beam irradiation side. The energy density of the laser beam is adjusted so that the energy of the laser for crystallization in the laser beam becomes substantially equal.

As a result of various experiments, the present inventors have found that the wavelength dependence of transmittance is different between an amorphous semiconductor thin film and a semiconductor thin film after crystallization, and the present inventors have focused on this. .

According to the above configuration, since each layer only needs to be crystallized sequentially after lamination, the workability is extremely good and the throughput is greatly improved. Also, the energy received by each layer for crystallization becomes equal, and crystallization can be performed uniformly.
Further, since the film is crystallized after being continuously stacked, the surface of the film is not contaminated when the film is transported between the devices, and an avalanche photodiode with few defect levels can be formed. Although the wavelength dependence of the transmittance slightly changes depending on the film thickness, the large tendency does not change. Therefore, this property is effective even when the film thickness is changed.

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

[0018]

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

FIG. 1 is a diagram illustrating the principle of the present invention.

That is, in the method of the present invention, an amorphous silicon thin film and a silicon carbide thin film are alternately laminated,
An amorphous silicon thin film is annealed and crystallized to form a polycrystalline silicon thin film. FIG. 1 shows the results of measuring the wavelength dependence of the transmittance of silicon carbide, amorphous silicon, and polycrystalline silicon. As is clear from this figure, for example, for light having a wavelength of about 620 nm, amorphous silicon shows a transmittance of 10% or less, but polycrystalline silicon obtained by crystallization shows a high transmittance of about 80%. I understand. Further, the silicon carbide thin film interposed therebetween has a transmittance of about 100%. Therefore, first, when the uppermost amorphous silicon thin film is crystallized in the first annealing step to form polycrystalline silicon, a high transmittance is exhibited, so that the lower amorphous silicon thin film is further transmitted through the lower silicon carbide thin film. Crystallizes. In this manner, crystallization proceeds satisfactorily one layer at a time.

Next, a method of manufacturing a superlattice type avalanche photodiode as a first embodiment of the present invention will be described with reference to the drawings.

First, as shown in FIG. 2, a tantalum (T) is formed as a lower electrode 2 on a glass substrate 1 by a sputtering method.
a) After a thin film is formed to have a thickness of about 500 nm, n-type hydrogenated amorphous silicon (a) having a thickness of about 50 nm is formed as a hole injection blocking layer 3 by a plasma CVD method.
-Si: H) layer is formed. Then, amorphous silicon (a-S) having a thickness of about 100 nm is formed by LPCVD.
i) A layer 9 is formed, a silicon carbide (SiC) layer (barrier layer 5) having a thickness of about 50 nm is alternately laminated for two periods, and a laser beam 1 is emitted using a pulse dye laser having an oscillation wavelength of 620 nm.
Irradiate with 0 and crystallize (FIG. 2).

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. 3, the amorphous silicon layer 9 forms the polycrystalline silicon layer 4 as a well layer having extremely high crystallinity.

Next, in this state, an oscillation wavelength of 620 n
A laser beam 10 is irradiated using a pulse dye laser of m to crystallize (FIG. 4). Here, the silicon carbide layer 5 as the uppermost barrier layer 5 and the crystallized polycrystalline silicon layer 4 under the silicon carbide layer 5 exhibit a high transmittance to this light. Reach,
Here as well, it is similarly well absorbed and amorphous silicon melts and recrystallizes.

Thus, as shown in FIG. 5, the amorphous silicon layer 9 becomes the polycrystalline silicon layer 4.

Thereafter, a 1 μm-thick hydrogenated amorphous silicon layer is formed as the 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. 6, 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 in which a polycrystalline silicon layer and a silicon carbide layer are stacked in two cycles is formed.

In the avalanche photodiode thus formed, when forming a polycrystalline silicon / silicon carbide superlattice as a multiplication layer, an amorphous silicon layer and a silicon carbide layer are alternately stacked. Since the layers are sequentially crystallized, no impurities are mixed into the interface between the well layer and the barrier layer, and the throughput is reduced by 30% compared with the conventional case.
% Improved.

As a result of irradiating the avalanche photodiode with light and measuring the characteristics, it can be seen that the dark current is greatly reduced as shown in FIG. This is considered to be due to the following reasons. According to this method, the well layer is made of polycrystalline silicon having no impurities and good crystallinity. Therefore, when a reverse bias is applied to the avalanche photodiode, since the barrier layer has a high resistance with respect to the well layer, almost no electric field is applied to the well layer, 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.

In this example, crystallization was performed without changing the irradiation energy in the two laser annealing steps. However, in the second laser annealing step, the amorphous silicon layer was formed in the first laser annealing step in consideration of the transmittance. The irradiation energy may be slightly increased so that the same energy as described above can be absorbed.

Next, a second embodiment of the present invention will be described. FIG. 9 to FIG. 14 are views showing the manufacturing process of this avalanche photodiode. In the first embodiment,
The thickness of the two amorphous silicon layers 9 is set to be substantially the same, but here, the upper amorphous silicon layer is 100 nm, and the lower amorphous silicon layer is 8 nm.
0 nm and the lower layer side are formed thin so that the crystallization energies per unit volume are equalized.

In this step, the film was formed in exactly the same manner as in the first embodiment except that the thickness of the amorphous silicon layer was changed. The same elements have the same reference characters allotted, and description thereof will not be repeated.

The avalanche photodiode thus formed was slightly better than that shown in FIG. Here, the transmittance of polycrystalline silicon is approximately 80%.
Since the thickness of the lower layer is 80% of that of the upper layer, the energy per unit volume received by each film is almost equal, and a well layer having almost the same crystallinity can be formed. It is considered that the problem that the film quality of the polycrystalline silicon was almost equal in this manner and the problem that one of the well layers had many defects and the S / N ratio was lowered was reduced. Further, the throughput of the process was improved by about 40% as compared with the case where the conventional method was used.

Next, a third embodiment of the present invention will be described. Here, the method is characterized in that the upper electrode 8 is sequentially laminated using the same method as in the first and second embodiments, and then laser light is irradiated from the substrate surface side.

First, as shown in FIG. 15, a light-transmitting indium tin oxide (ITO) thin film is formed as a lower electrode 12 on the glass substrate 1 by sputtering so as to have a thickness of about 100 nm. By law,
An n-type microcrystal silicon layer (μc-Si) layer having a thickness of about 50 nm is formed as the hole injection blocking layer 13. Then, an amorphous silicon (a-Si) layer 9 having a thickness of about 100 nm is formed by LPCVD,
Silicon carbide (SiC) layer 5 of about 0 nm, film thickness 80 n
an amorphous silicon (a-Si) layer 9 having a thickness of about m and a silicon carbide (SiC) layer 5 having a thickness of about 50 nm,
Further, a hydrogenated amorphous silicon layer having a thickness of 1 μm is formed as the light absorption layer 6, and a 50 nm film is formed as the electron injection blocking layer 7.
An approximately p-type hydrogenated amorphous silicon layer 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 substrate is irradiated with laser light 10 from the back side of the substrate using a pulsed dye laser having an oscillation wavelength of 620 nm to crystallize (FIG. 15).

As a result, since the transmittance of the silicon carbide layer 5 is about 100%, this light reaches the amorphous silicon layer 9 satisfactorily, and since this layer has an extremely low transmittance, it is well absorbed by this layer. Most of the irradiation energy affects the crystallization of this layer, and as shown in FIG. 16, the amorphous silicon layer 9 forms the polycrystalline silicon layer 4 as a well layer having extremely high crystallinity.

Next, in this state, an oscillation wavelength of 620 n
The substrate is irradiated with a laser beam 10 using a pulse dye laser of m for crystallization (FIG. 17). Here, the silicon carbide layer as the lowermost barrier layer 5 and the crystallized polycrystalline silicon layer 4 above the silicon carbide layer 5 exhibit a high transmittance to this light. At which point it is similarly well absorbed and melting and recrystallization of the amorphous silicon occurs.

As a result, as shown in FIG. 18, the upper amorphous silicon layer 9 becomes the polycrystalline silicon layer 4.

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 stacked in two cycles as shown in FIG.

The avalanche photodiode thus formed was slightly better than that shown in FIG. Here, the transmittance of polycrystalline silicon is approximately 80%.
Since the thickness of the upper layer is 80% of that of the lower layer, the energy per unit volume received by each film is almost equal, and a well layer having almost the same crystallinity can be formed. It is considered that the problem that the film quality of the polycrystalline silicon was almost equal in this manner and the problem that one of the well layers had many defects and the S / N ratio was lowered was reduced. Further, the throughput of the process was improved by about 40% as compared with the case where the conventional method was used. The characteristics were measured by irradiating the avalanche photodiode with light, and it was found that the dark current was significantly reduced.

In the above embodiment, a glass substrate was used as the substrate. However, other insulating materials such as ceramic, quartz and polyimide may be used. In addition, 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, a metal material such as molybdenum, titanium, or tungsten, or a metal silicide such as tantalum silicide, molybdenum silicide, titanium silicide, or tungsten silicide may be used in addition to tantalum or ITO. Further, the hole injection blocking layer is not limited to n-type hydrogenated amorphous silicon, but may be crystalline silicon, polycrystalline silicon, or the like. 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 of 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, a pulse dye laser having a wavelength of 620 nm was used as a laser. However, the difference in transmittance between amorphous silicon and polycrystalline silicon, such as a krypton laser, a CW dye laser, a Q switch laser, and a ruby laser, was used. What is necessary is just to be able to obtain a laser beam having a certain wavelength. It is also possible to shape and condense the beam using an optical system before use. Furthermore, in the above-described embodiment, the light is detected from the element side with respect to the substrate, but the light may be detected from the substrate side. As the multiplication layer, two well layers and two barrier layers are used.
A multilayer structure may be used instead of the period. As for the electrodes, the multiplication layer was sandwiched between the upper electrode and the lower electrode.
Without being limited to this, it can be changed as appropriate.

As described above, by appropriately selecting the combination of the laser energy and the film thickness, superlattices having different film qualities can be obtained.

[0045]

As described above, according to the present invention, it is possible to obtain a high-quality avalanche photodiode with improved throughput and reduced dark current.

[Brief description of the drawings]

FIG. 1 is a diagram showing the dependence of wavelength on transmittance (a diagram illustrating the principle of the present invention).

FIG. 2 is a manufacturing process diagram of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 3 is a manufacturing process diagram of the avalanche photodiode according to the first embodiment of the present invention.

FIG. 4 is a manufacturing process diagram of the avalanche photodiode according to the first embodiment 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 diagram showing a relationship between an applied voltage and a dark current 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 second embodiment of the present invention.

FIG. 10 is a manufacturing process diagram of the avalanche photodiode according to the second embodiment of the present invention.

FIG. 11 is a manufacturing process diagram of an avalanche photodiode according to a second 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 third embodiment of the present invention.

FIG. 16 is a manufacturing process diagram of the avalanche photodiode according to the third embodiment of the present invention.

FIG. 17 is a manufacturing process diagram of the avalanche photodiode according to the third embodiment of the present invention.

FIG. 18 is a manufacturing process diagram of the avalanche photodiode according to the third embodiment of the present invention.

FIG. 19 is a manufacturing process diagram of the avalanche photodiode according to the third embodiment of the present invention.

FIG. 20 is a manufacturing process diagram of a conventional avalanche photodiode.

FIG. 21 is a manufacturing process diagram of a conventional avalanche photodiode.

FIG. 22 is a manufacturing process diagram of a conventional avalanche photodiode.

FIG. 23 is a manufacturing process diagram of a conventional avalanche photodiode.

FIG. 24 is a manufacturing process diagram of a conventional avalanche photodiode.

FIG. 25 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 absorption layer 7 electron injection blocking layer 8 upper electrode 9 amorphous silicon layer 10 laser beam 12 lower electrode 13 hole injection blocking layer

 ──────────────────────────────────────────────────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 (3)

[Claims] 1. A laminating step of alternately laminating a plurality of cycles of an amorphous semiconductor thin film and a barrier layer made of a first crystalline semiconductor thin film, and a well layer made of an amorphous semiconductor thin film which is annealed and crystallized to form a second crystalline semiconductor thin film By forming
An annealing step of forming a multiplication layer having a superlattice structure in which well layers and barrier layers are alternately stacked in a plurality of cycles; and a first and a second layer connected to the multiplication layer before the lamination step or after the annealing step. Forming a second electrode, the annealing step, wherein the transmittance of the second crystalline semiconductor thin film is higher than the transmittance of the amorphous semiconductor thin film,
A method for manufacturing a semiconductor light receiving element, wherein the step of annealing is performed using a laser having a high wavelength. 2. A laminating step of alternately laminating a plurality of cycles of an amorphous semiconductor thin film and a barrier layer made of a first crystalline semiconductor thin film, and a well layer made of an amorphous semiconductor thin film which is annealed and crystallized and made of a second crystalline semiconductor thin film By forming
An annealing step of forming a multiplication layer having a superlattice structure in which well layers and barrier layers are alternately stacked in a plurality of cycles; and a first and a second layer connected to the multiplication layer before the lamination step or after the annealing step. Forming a second electrode, the manufacturing process of the semiconductor light receiving element, the laminating step, depending on the transmittance of the film formed on the laser light irradiation side, the film thickness is reduced toward the lower layer, A method for manufacturing a semiconductor light receiving element, comprising a step of forming a film so that energy received from a laser is substantially equal. 3. A laminating step of alternately laminating a plurality of periods of an amorphous semiconductor thin film and a barrier layer made of a first crystalline semiconductor thin film, and a well layer made of an amorphous semiconductor thin film which is annealed and crystallized and made of a second crystalline semiconductor thin film. By forming
An annealing step of forming a multiplication layer having a superlattice structure in which well layers and barrier layers are alternately stacked in a plurality of cycles; and a first and a second layer connected to the multiplication layer before the lamination step or after the annealing step. Forming a second electrode, wherein the annealing step includes the steps of: crystallizing the amorphous semiconductor layer in each cycle according to the transmittance of a film formed on the laser beam irradiation side; Characterized in that the energy density of the laser beam is adjusted so that the laser energy for the laser beam becomes substantially equal.