JPH0442835B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing an optical sensor widely used as a light receiving element, a solar cell, etc., and more specifically, a method for simultaneously forming a shallow junction and a BSF by infrared irradiation. The present invention relates to a method of manufacturing an optical sensor.

Here, BSF refers to an effect that can prevent recombination of fractional carriers on the backside by forming a potential gradient that pushes back the fractional carriers on the backside.

(Prior technology) A shallow junction between the anti-reflection film and the light-receiving surface of a Si solar cell is formed using a spin-on method using a mixture of TiO ₂ and P ₂ O ₅ .
Apply to the etched surface and heat in an electric furnace at 900℃ to 930℃.
The impurity P is diffused by heating for about 15 minutes.

Next, the Al film applied to the back side of the wafer by screen printing is heated in an electric furnace at 800°C to 825°C for about 2 minutes to form a p ⁺ layer, thereby imparting a BSF effect.

Finally, the electrodes on the light-receiving surface are made by screen printing silver paste on the A/R film (TiO ₂ film) and heating it at 600℃~
It is made by heating at 610 degrees Celsius, resulting in a solar cell with a maximum efficiency of 16%.

This method has the following problems.

It takes 15 minutes at 900°C to 930°C, which is a long time to form a shallow junction in the light-receiving layer.

Heat treatment at 800-825°C for 2 minutes is required to generate the BSF effect. The temperature and time are different and the process cannot be the same.

High temperature processing (900℃~930℃) time is as long as 15 minutes, which reduces the life of the board, increases reverse current,
It is expected that the open circuit voltage will decrease and the long wavelength response will decrease.

In order to solve the above problem by shortening the time to form a shallow junction in the light-receiving layer, one of the inventors of the present invention made a research in 1984.
“Low-cost Si solar cells using transient light irradiation technology” (paper number SSD84-
27) at the Institute of Electronics and Communication Engineers.

According to the method described in the paper, a shallow bonding layer can be formed by extremely short heat treatment. It is presumed that accelerated diffusion is occurring that cannot be explained solely by the thermal equilibrium state. This is thought to be due to distortion occurring due to the difference in thermal expansion coefficient between the semiconductor wafer and the impurity-containing insulating film. Since deterioration of the diffusion length of the substrate can be prevented by diffusion caused by short-time heat treatment, a high-quality bond can be formed in a short time, and the conventional manufacturing process for solar cells and the like can be significantly improved.

As a result of further investigation of the heat treatment, the present inventors obtained more data on the anomalous diffusion and found that it is possible to simultaneously form a semiconductor high-low bonding layer that provides a BSF effect on the back surface of a semiconductor wafer.

(Objective of the Invention) The object of the present invention is to provide a method for manufacturing an optical sensor that can simultaneously form shallow junctions and semiconductor high and low bonding layers that provide a BSF effect by extremely short heat treatment using infrared irradiation.

(Structure of the Invention) In order to achieve the above object, a method of manufacturing an optical sensor in which a shallow junction and a BSF are simultaneously formed by infrared irradiation according to the present invention includes: A method of manufacturing an optical sensor in which a junction is formed on a surface of a semiconductor wafer by diffusion. A metal film for high/low junction is formed on the back surface of the semiconductor wafer, an insulating film containing impurities that have a coefficient of thermal expansion different from that of the semiconductor and which tends to diffuse is formed on the surface of the semiconductor wafer, and the semiconductor wafer is exposed to an infrared ray source. The semiconductor wafer and the impurity-containing insulating film are placed in a furnace with a steep temperature gradient that causes distortion due to the difference in thermal expansion coefficient between the semiconductor wafer and the impurity-containing insulating film, and are heated for a very short time to form a shallow junction on the light receiving surface. It is configured to simultaneously form high and low junctions exhibiting a BSF effect on the back surface.

(Example) Hereinafter, the present invention will be described in more detail with reference to the drawings and the like.

FIG. 1 is a process diagram showing the manufacturing process of a first embodiment of the method for producing an optical sensor using infrared irradiation according to the present invention.

This process diagram shows the surface orientation (100) and resistivity of 10Ωcm.
Shown for a CZ silicon p-type wafer.

In a silicon wafer preparation step 10, the wafer is prepared. The thermal expansion coefficient of the wafer is 2.5×
10 ^-6 /℃.

In a backside treatment step 11, aluminum (Al) is deposited on the backside of the wafer by vacuum deposition.
In step 12 of forming an insulating film containing impurities, an insulating film containing impurities that are likely to diffuse into the surface of the wafer is formed.

A P-doped SiO ₂ film with a thickness of 2000 to 3000 Å was formed by the well-known spin-on method.

The coefficient of thermal expansion of the insulating film containing the impurities is
It is 0.5×10 ^-6 /℃.

In the irradiation heating step 13, the wafer on which the aluminum vapor-deposited surface and the impurity-containing insulating film were formed was placed in a halogen lamp furnace, and transient heating was performed in an inert gas (N ₂ ).

FIG. 2 is a temperature program diagram showing an example of transient heating.

Temperature was monitored using a chromel-alumel thermocouple in contact with the wafer.

Check the wafer temperature before lighting the halogen lamp.
Keep it at 100℃.

Figure 2 shows an example in which the temperature inside the furnace is increased to 900°C at a rate of 50°C/sec. The wafer heat-treated in this manner is processed into chips of 1×1 cm ² in a well-known electrode forming step 15 and an element cutting step 16.

After turning on the halogen lamp, set the temperature (second
The set temperature is maintained for a short time after reaching 900℃ (in the figure). In this specification, the time from when the set temperature reaches 98% until the halogen lamp is turned off is tentatively defined as the diffusion time. .

Various samples were obtained by appropriately selecting diffusion times in the range of 1 to 20 seconds at set times of 800, 850, 900, and 950°C.

Hall measurement 4: By repeating anodic oxidation and Hall measurement on these samples, the distribution of the diffused carrier concentration in the depth direction was measured.

FIG. 3 shows a graph of the carrier concentration and mobility obtained in the above measurements.

When the set temperature is 900°C and 950°C, an abnormally large amount of diffusion occurs in the first second, and a larger amount of diffusion is observed between 1 and 5 seconds.

This is detailed in the above article.

At a set temperature of 900°C, the inventors of the present invention
Other temperature increase rates other than 50℃/sec: 10℃/sec, 20℃/sec
sec, 30° C./sec was selected, and the heat treatment was performed with a diffusion time of 5 seconds.

Figure 4 shows the measurement results of carrier concentration.

It can be understood from this measurement result that a larger diffusion depth can be obtained with a larger temperature increase rate.

Next, a solar cell (n ⁺ /pp ⁺ type) in which a BSF effect layer was formed by the method of the present invention, and a solar cell (n ⁺ /pp + type) which was subjected to the same heat treatment but without forming a BSF effect layer.
Compare the characteristics of each type (p type).

ρ=10Ωcm, thickness to form BSF effect layer
3000 Å of Al is deposited on the back surface of a 500 μm p-type Si wafer, and an insulating layer containing impurities is formed on the surface using the above method.

Other samples form an insulating layer containing impurities on the surface of the same wafer.

Both wafers were set at a temperature of 900°C and a diffusion time of 10 seconds.
Heat treatment was performed at a temperature increase rate of 50°C/sec.

FIG. 5 shows a comparison of the spectral characteristics of each of the solar cells.

Solar cells with a BSF effect layer have higher sensitivity on the long wavelength side than solar cells without a BSF effect layer.

FIG. 6 shows a comparison of the IV characteristics of each of the solar cells.

Compared to solar cells without a BSF effect layer, solar cells with a BSF effect layer have an efficiency of 9.01% to 10.88%, an increase of approximately 20%. The above data is based on the case where no anti-reflection film is applied to the surface, but it is known that adding an anti-reflection film can increase efficiency by 30 to 40%.

Therefore, assuming that the efficiency can be increased by 35% by forming an antireflection film, if the antireflection film is formed on a solar cell according to the method of the present invention, a solar cell with an efficiency of about 14.7% will be obtained.

It is also possible to manufacture an optical sensor using a group V compound wafer in the same process as in the first embodiment described above.

A second embodiment using a gallium-arsenic-phosphorus (GaAsP) wafer will be described.

Similar to the above embodiment, the wafer is subjected to a wafer preparation step 10, a backside treatment step 11, an impurity-containing insulating film forming step 12, and then an irradiation heating step 13 on which the aluminum vapor-deposited surface and an impurity-containing insulating film are formed. Perform diffusion at 800℃ for 2 seconds.

Next, through steps 15 and 16, gallium, arsenic,
An optical sensor using a phosphor wafer was obtained.

FIG. 7 shows a comparison of the voltage-current characteristics of the optical sensor obtained in the above process and one formed on the same substrate using the conventional diffusion method (800° C., 60 minutes).

FIG. 8 is a graph comparing the spectral sensitivity characteristics of the optical sensor according to the second embodiment and one formed using the conventional diffusion method (800° C., 60 minutes).

It can be seen that the second example exhibits excellent voltage-current characteristics and has sufficient sensitivity even on the short wavelength side.

(Modifications) Various modifications can be made to the embodiments described in detail above within the scope of the present invention.

In each of the embodiments described above, if an insulating film forming step not containing impurities is provided next to the step 12 of forming an insulating film containing impurities, it is possible to prevent impurities from dissipating into the gas phase.

In each of the above embodiments, the inert gas in the furnace in the irradiation and heating step 13 may be replaced with air or hydrogen.

In addition, although an example of a gallium-arsenic-phosphorus (GaAsP) wafer is shown as a second embodiment, other -V
A similar process can be applied to group compounds (GaAs) (GaP), etc.

(Effects of the Invention) As explained above, according to the manufacturing method of the present invention, a thin bond on the front surface and a BSF effect layer on the back surface can be simultaneously formed by one short heat treatment, and moreover, it is possible to simultaneously form a thin bond on the front surface and a BSF effect layer on the back surface. Solar cells with higher efficiency than solar cells can be obtained.

Furthermore, since the manufacturing process is simple and takes only a short time, the manufacturing process for solar cells and the like can be significantly streamlined.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing an embodiment of the manufacturing process of an optical sensor using infrared irradiation according to the present invention. Second
The figure is a graph showing an example of controlling the temperature inside the furnace. Third
The figure is a graph showing the carrier concentration and hole mobility obtained in the above measurements. FIG. 4 is a graph comparing the depth of diffusion by changing the heating rate.
FIG. 5 is a graph showing the spectral characteristics of the solar cell manufactured by the method according to the present invention, and FIG. 6 is a graph showing the I-V properties of the solar cell manufactured by the method according to the present invention, both of which were subjected to the same heat treatment. A comparison is shown with the characteristics of a solar cell manufactured by applying the BSF effect layer without forming a BSF effect layer. FIG. 7 shows a method according to the present invention, in which an optical sensor manufactured using a gallium-arsenic-phosphorus (GaAsP) wafer and an optical sensor manufactured by applying a conventional diffusion method to the same wafer are connected at different voltages. It is a graph showing a comparison of current characteristics. FIG. 8 shows a method according to the present invention, in which an optical sensor manufactured using a gallium-arsenic-phosphorus (GaAsP) wafer and an optical sensor manufactured by applying a conventional diffusion method to the same wafer are separated into spectral spectra. This is a graph showing a comparison of sensitivity characteristics. 10...Silicon wafer preparation process, 11...
Al vapor deposition process, 12... Insulating film formation process containing impurities, 13... Irradiation heating process, 14... Hole measurement, 15... Electrode creation process, 16... Element cutting process.

Claims (1)

[Claims] 1. In a method for manufacturing an optical sensor that forms a junction on the surface by diffusion, a metal film for high/low junction is formed on the back surface of a semiconductor wafer, and the surface of the semiconductor wafer is exposed to heat different from that of the semiconductor. forming an insulating film containing an impurity that has an expansion coefficient and is likely to diffuse; placing the semiconductor wafer in a furnace with an infrared source; Shallow bonding by infrared irradiation characterized by a structure that simultaneously forms a shallow bond on the light-receiving surface that is heated with a sharp temperature gradient that causes strain and is heated for an extremely short time, and a high/low bond that exhibits a BSF effect on the back surface. A method for manufacturing an optical sensor that simultaneously forms BSF and BSF. 2. A method of manufacturing an optical sensor in which a shallow junction and a BSF are simultaneously formed by infrared irradiation according to claim 1, wherein the semiconductor wafer is a silicon wafer. 3. The method of manufacturing an optical sensor in which a shallow junction and a BSF are simultaneously formed by infrared irradiation according to claim 2, wherein the silicon wafer is a CZ silicon p-type wafer with a plane orientation (100) and a specific resistance of 10 Ωcm. 4. A method for manufacturing an optical sensor in which a shallow junction and a BSF are simultaneously formed by infrared irradiation according to claim 2, wherein the impurity-containing insulating film is a P-doped SiO ₂ film formed by a spin-on method. 5 The thickness of the insulating film containing the impurity is 2000~
A method for manufacturing an optical sensor, in which a shallow junction and a BSF are simultaneously formed by infrared irradiation according to claim 4, which has a thickness of 3000 Å. 6. A method for manufacturing an optical sensor in which a shallow junction and a BSF are simultaneously formed by infrared irradiation according to claim 1, wherein the metal film for the high/low junction is aluminum. 7. A method of manufacturing an optical sensor in which a shallow junction and a BSF are simultaneously formed by infrared irradiation according to claim 1, wherein the semiconductor wafer is a -V group compound.