JPH0528912B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a method for manufacturing a photovoltaic device using an energy beam such as a laser beam.

(b) Prior art Figure 1 shows the basic structure of a photovoltaic device that is disclosed in U.S. Pat. No. 4,281,208 and has already been put into practical use. Substrate with optical properties, 2a, 2
b, 2c... are transparent electrode films deposited at regular intervals on the substrate 1, 3a, 3b, 3c... are amorphous semiconductor films such as amorphous silicon deposited on each transparent electrode film, 4a, 4b, 4c... are superimposed and deposited on each amorphous semiconductor film, and are adjacent to each transparent electrode film 2 on the right.
photoelectric conversion elements 5a, 5b, 5c... by each laminate of transparent electrode films 2a, 2b, 2c... or back electrode films 4a, 4b, 4c... is configured.

Each amorphous semiconductor film 3a, 3b, 3c... includes, for example, a PIN junction parallel to the film surface inside thereof, and therefore the transparent substrate 1 and the transparent electrode film 2a, 2b, 2c...
When light is incident sequentially through..., a photovoltaic force is generated. The photovoltaic force generated within each amorphous semiconductor film 3a, 3b, 3c... is the back electrode film 4a, 4b, 4c.
... are added in series by connection.

Photo-etching technology, which has excellent precision machinability, is usually used in photovoltaic devices having such a configuration. In the case of this technique, a step of depositing a transparent electrode film on the entire surface of the substrate 1, and each individual transparent electrode film 2a, 2b, 2c by photoresist and etching are performed.
Separation of..., that is, each transparent electrode film 2a, 2b, 2c
..., the step of depositing an amorphous semiconductor film on the entire surface of the substrate 1 including on each of these transparent electrode films, and the step of removing each individual amorphous semiconductor film 3a, by photoresist and etching. 3b, 3c..., that is, each amorphous semiconductor film 3a, 3b, 3c
. . . The steps of removing the adjacent spaced portions are sequentially performed.

However, although the photo-etching technique is excellent in terms of fine processing, it tends to cause defects in the amorphous semiconductor film due to pinholes or peeling at the periphery of the photoresist that defines the etching pattern.

The prior art disclosed in Japanese Unexamined Patent Publication No. 12568/1985 creates the above-mentioned adjacent spacing by burning out the film by laser beam irradiation, and does not use any photoresist, that is, a wet process, which is necessary for photolithography. This technique, which has excellent precision processing properties, is extremely effective in solving the above problems.

However, as mentioned above, although laser machining that does not use any wet process is extremely effective in terms of precision machining, it also has some problems, as shown in enlarged views of the main parts in Figures 2 a to c. There is. That is, an amorphous semiconductor film is formed continuously over the transparent electrode films 2a, 2b, which have already been divided and arranged for each photoelectric conversion element 5a, 5b, and the semiconductor film is applied to each photoelectric conversion element. When the semiconductor film located at adjacent intervals is removed by irradiation with the laser beam LB in order to divide the semiconductor film into two parts, as shown in FIG.
Since the periphery of the LB does not have enough energy to remove it, it is annealed and microcrystallized or crystallized, resulting in low resistance layers 6a and 6b.
It is not possible to accurately remove the semiconductor film in a predetermined pattern because of the formation of a molten semiconductor film or the residue 7 of the molten semiconductor film remaining at the interface of the removed portion as shown in FIG. 2b. The formation of the residue 7 and the low resistance layers 6a and 6b remaining at the interface of the removed portion is caused by the formation of the residual material 7 and the low resistance layers 6a and 6b on both sides of the adjacent gap portion to be removed because the energy density distribution in the laser beam LB is a normal distribution, that is, a Gaussian distribution. This is thought to occur as a result of a lower energy distribution at the periphery where the surface is irradiated than at the center. Furthermore, when the irradiated laser beam LB exhibits a Gaussian distribution in which the energy distribution is lower at the periphery than at the center as described above, the semiconductor film to be removed is the semiconductor film 3 for each photoelectric conversion element 5a, 5b...
It not only divides the photoelectric conversion elements 5a, 3b... but also exposes the transparent electrode film 2b to electrically connect these adjacent photoelectric conversion elements 5a, 5b... in series, and such exposed length increases the series resistance component. Therefore, a wide laser beam is required, resulting in an extremely high energy state at the center, causing thermal damage 8 as shown in Figure 2c. Put it away.

In particular, the formation of the low resistance layers 6a and 6b of the semiconductor film is performed by irradiating the semiconductor film 3 with the laser beam LB.
Even if it is possible to physically separate a, 3b..., the photoelectric conversion element 5b... is coupled to the transparent electrode film 2b... and the back electrode film 4b... of the same photoelectric conversion element 5b via the low resistance layer 6b. It causes a short circuit.

(c) Problems to be Solved by the Invention The present invention solves the formation of a low resistance layer at the interface of the removed portion of the semiconductor film, which causes short circuit accidents as described above, and also solves the problem of forming a low resistance layer at the interface of the removed portion of the semiconductor film, which causes the short circuit accident as described above. This is an attempt to solve the problem of residual heat and thermal damage to the underlying layer.

(d) Means for Solving the Problems In order to solve the above problems, the present invention provides a method for manufacturing a photovoltaic device in which a plurality of photoelectric conversion elements are electrically connected in series on an insulating surface of a substrate. Then, an energy beam having a substantially uniform energy distribution over the irradiation area is irradiated onto the amorphous semiconductor film disposed continuously over the plurality of substrate-side electrode films constituting the plurality of photoelectric conversion elements. By doing so, the semiconductor film in the irradiation area is removed without forming a residue, the semiconductor film is divided into a plurality of photoelectric conversion elements, and during the removal, the semiconductor film under the irradiation area is removed. It is characterized by suppressing thermal damage to the film and substantially not forming a low-resistance layer on the semiconductor film at the peripheral portion of the irradiation area.

(e) Effect As described above, by irradiating a predetermined location of the semiconductor film disposed on the substrate-side electrode film with an energy beam whose energy distribution is substantially uniform over the irradiation region, the semiconductor film in the irradiation region is While only the film portion is removed without substantially forming a low resistance layer,
Thermal damage to the underlying substrate-side electrode film can be reduced.

(f) Examples FIGS. 3 to 8 show examples of the method of the present invention in the order of steps.

In the process shown in Figure 3, the thickness is 1 mm to 3 mm, the area is 10 cm x
Substrate 10 of transparent glass, etc., approximately 10cm to 1m x 1m
Tin oxide (SnO ₂ ) with a thickness of 2000 Å to 5000 Å on the entire top surface
A transparent electrode film 11 consisting of the following is deposited.

In the process shown in FIG. 4, the adjacent spacing portions 11' are removed by laser beam irradiation, and individual transparent electrode films 11a, 11b, 11c, . . . are formed separately. It is appropriate for the laser used to have a wavelength that is hardly absorbed by the substrate 10, and for the above-mentioned glass, a pulse oscillation type laser with a wavelength of 0.35 μm to 2.5 μm is preferable. Such a preferred embodiment has a wavelength of approximately
1.06μm energy density 13J/cm ² , pulse frequency 3K
Hz Nd:YAG laser, adjacent interval part 11'
The interval L ₁ is set to about 100 μm.

In the process shown in FIG. 5, each transparent electrode film 11a, 11
An amorphous semiconductor film 12 such as amorphous silicon (a-Si) with a thickness of 5000 Å to 7000 Å that effectively contributes to photoelectric conversion is spread over the entire surface of the substrate 10 including the surfaces of
is deposited. Such a semiconductor film 12 includes a PIN junction parallel to the film surface within it, and therefore, more specifically, P-type amorphous silicon carbide is first deposited, and then I-type and N-type amorphous silicon carbide is deposited. The high quality silicone is deposited in successive layers.

In the process shown in FIG. 6, the adjacent spacing portions 12' are removed by laser beam irradiation, and individual amorphous semiconductor films 12a, 12b, 12c, . . . are formed separately. A feature of this process is that the energy distribution of the laser beam used has a substantially uniform distribution over the irradiation area. Figure 9 shows the temperature distribution on the irradiated surface when the irradiated area is irradiated with a circular laser beam with a substantially uniform energy distribution and the irradiated area has a radius of 40 μm, and the temperature distribution at the center of the circular laser beam. The diagram is drawn in the radial direction starting from the point. As is clear from FIG. 9, the temperature distribution of a laser beam with a substantially uniform energy distribution results in a substantially constant high temperature distribution corresponding to the energy distribution over the irradiation area, and a slight temperature distribution at the interface of the irradiation area. Although a temperature gradient due to heat conduction of the irradiated medium is observed, the temperature drops sharply to the room temperature of the non-irradiated area, and the overall distribution is approximately rectangular.

On the other hand, Fig. 10 shows a radius with a conventional Gaussian distribution.
The temperature distribution on the irradiated surface when a 50 μm laser beam is used is plotted in the radial direction starting from the center, similar to FIG. 9. The temperature reached at the center is shown in Figures 9 and 10.
Both figures are the same, for example, by irradiating with such a laser beam, an amorphous semiconductor with a thickness of 5000 Å that is a workpiece can be removed, and thermal damage to the underlying transparent electrode films 11a, 11b, and 11c can be avoided. The possible absolute temperature is set to approximately 1400K.

FIG. 11 shows the temperature distribution in the depth (thickness) direction when the energy distribution is approximately uniform and the temperature distribution on the irradiated surface, that is, the surface of the amorphous semiconductor film 12, exhibits the approximately rectangular distribution shown in FIG. This is a simulation of the temperature distribution using isotherms every 100K. The sample to be simulated has a structure in which a transparent electrode film 11 made of SnO ₂ with a thickness of 2000 Å and a semiconductor film 12 of amorphous silicon with a thickness of 5000 Å are laminated on a glass substrate 10. As a result of such simulation, when a temperature of about 1400 K is applied to the surface of the semiconductor film 12, the isothermal distribution width in the thickness direction, which is the depth direction of the semiconductor film 12, is wide, and the temperature is increased at the interface with the SnO ₂ transparent electrode film 11. Even if the temperature is about 1200 K or higher, the semiconductor film 12 can be removed. On the other hand, the isothermal distribution width in the radial direction, that is, in the surface direction, is extremely narrow because the interfacial temperature gradient at the irradiated surface falls steeply.

Incidentally, the temperature at which the amorphous silicon semiconductor film 12 can be removed varies somewhat depending on the method and conditions for forming the semiconductor film 12, but is generally about 1200 K or higher as mentioned above. The temperature to be converted is between about 1000 K and the removal temperature of about 1200 K. Therefore, the above 11th
In the simulation shown in the figure, the semiconductor film 12 in the temperature range of 1200K or higher is removed, and the temperature range of 1000K to 1200K is
Assuming that the semiconductor film in the temperature range of is converted into a low resistance layer, the semiconductor film 12 is approximately
A region of 38 μm is removed and a substantially negligible low resistance layer is formed at the removed interface.

On the other hand, when using a conventional laser beam with a Gaussian distribution, the temperature distribution on the irradiated surface is
As shown in Figure 0, it exhibits a Gaussian distribution equivalent to the energy distribution, and when this temperature distribution in the depth direction is simulated using isotherms every 100K when using a Uthian beam, it becomes as shown in Figure 12. . That is, although the temperature distribution in the depth direction at the center of the irradiation area is equal to the uniform distribution shown in Fig. 11, the width of the isothermal distribution in the radial direction is 1200K because the temperature gradient at the irradiation surface is gentle. ~
In the annealing temperature range of 1000K, the surface area is approximately 8μm, and the interface area with the SnO ₂ transparent electrode film is approximately 8μm.
It has a width of 11μm. Therefore, in conventional processing using a Gaussian laser beam, even if a semiconductor film in a temperature range of 1200K or higher is removed, the semiconductor film will be removed approximately 8 μm or more in the radial direction from the removed interface.
A wide range of 11 μm was converted into a low resistance layer. Furthermore, in conventional processing, the width of semiconductor film removal is less than 10 μm in radius, which is narrower than about 38 μm in the processing shown in FIG. As a result, in order to electrically connect adjacent photoelectric conversion elements in series through the exposed portion of the transparent electrode film exposed by the removal of the semiconductor film, if the removal width of the semiconductor film is increased, (a) A method of increasing the intensity of the laser beam and bringing the center into a high temperature state to widen the isothermal distribution width above 1200K; (b) A method of increasing the number of scans of the laser beam instead of increasing the intensity of the laser beam. There are two possible methods.

However, in both of these methods, the formation of a low resistance layer is inevitable, and in method (a), the center of the laser beam is in an extremely high energy state, causing thermal damage to the underlying transparent electrode film. give or
In method (b), the number of scans increases, resulting in a decrease in work efficiency. On the other hand, in this embodiment, which uses a laser beam with a substantially uniform energy distribution over the irradiation area, there is no substantial formation of a low-resistance layer, no thermal damage to the underlying film, and The processing range can be expanded.

As shown in FIG _. 15, the laser beam having a substantially uniform energy distribution over the irradiation area as described above is placed in the optical path of the normal laser beam LB ₁ A having a Gaussian energy distribution.
An iris 21 having a square or round hole 20 having an aperture diameter of about 25% of the incident diameter starting from the center of the
The laser beam LB ₂ passing through the round hole 20 of the iris 21 is guided to the condenser lens 22, and the laser beam LB ₃ is condensed by the condenser lens 22.
It can be obtained by irradiating the surface of the workpiece under the following conditions. That is, the distance from the iris 21 to the center of the condensing lens 22 is a, and the distance from the condensing lens 22 is
Let b be the distance from the center of the surface to the surface to be processed, and f be the focal length of the condenser lens 22. When 1/a+1/b=1/f is satisfied, the laser beam LB ₃ irradiated onto the surface to be processed is The energy distribution is approximately uniform.

In the process shown in FIG. 7, as described above, a laser beam having a substantially uniform energy distribution over the irradiation area is irradiated onto the adjacent spaced parts of the amorphous semiconductor film 12, so that the amorphous semiconductor film 12 is individually separated. Separated amorphous semiconductor films 12a, 12b, 12c... and transparent electrode film 11
a, 11b, 11c... The entire surface of the substrate 10, including the exposed portions, has a single-layer aluminum structure with a thickness of about 2000 Å or more, or a two-layer structure in which titanium or titanium-silver is laminated on the aluminum, or even such a two-layer structure. A back electrode film 13 having a double stacked layer structure is deposited.

In the final step shown in FIG. 8, the back electrode film 13 is attached to the amorphous semiconductor film 12 shown in FIG.
As in the separation step, the irradiation area is divided into individual back electrode films 13a, 13b, 13c, . . . by irradiation with a laser beam having a substantially uniform energy distribution. As a result, each individually divided transparent electrode film 1
1a, 11b, 11c..., amorphous semiconductor film 12
a, 12b, 12c... and back electrode films 13a, 1
Photoelectric conversion element 1 consisting of a laminate of 3b, 13c...
4a, 14b, 14c, . . . are electrically connected in series on the substrate 10.

FIG. 13 shows a laser beam starting from the center of the irradiation surface when irradiating the irradiation area with a laser beam having a substantially uniform energy distribution and a circular irradiation area as shown in FIG. The temperature distribution in the depth (thickness) direction when dividing the back electrode film 13 using a laser beam whose temperature distribution in the radial direction exhibits a substantially rectangular distribution is simulated using isotherms at intervals of 200K. It is. The sample targeted for simulation was a film with a thickness of 2000 Å on the glass substrate 10 used in the previous simulation.
A back electrode film 13 having a single layer aluminum structure and having a thickness of 5000 Å was further superimposed on the laminate of the SnO ₂ transparent electrode film 11 and the amorphous semiconductor film 12 having a thickness of 5000 Å.
As a result of this simulation, the melting point of aluminum is about 930K in terms of insulation temperature, and the back electrode film portion of the aluminum single-layer structure with a radius of about 38 μm from the center of the temperature distribution above 930K is removed. On the other hand, according to this simulation, a temperature distribution of 1000 K or more slightly exists on the side of the amorphous silicon semiconductor film 12 that is in contact with the back electrode film portion.
Although the temperature distribution above 1000K means that the amorphous silicon semiconductor film 12 in such a region is microcrystallized or crystallized and converted into a low resistance layer, the formation of the low resistance layer is extremely shallow from the surface. Since it remains in the area, it is of virtually negligible magnitude.

FIG. 14 shows an attempt to obtain approximately the same removal width of the back electrode film 13 as in the laser processing shown in FIG. 13 using a conventional laser beam with a Gaussian distribution.
This is a temperature distribution simulation in the depth direction using isotherms every 200K. As a result of such simulation, although the removal width of the back electrode film 13 is approximately the same as that of the laser processing shown in FIG. 13, the temperature gradient is gentle and the temperature distribution near the melting point of the back electrode film 13 is wide. melting of the electrode film forming material may occur at the removed interface, and not only the region of the amorphous silicon semiconductor film 12 with a temperature of 1200K or more is removed, but also the region of 1200K to 1000K at the removed interface with a low resistance It can be seen that it has been converted to a layer.

Therefore, the back electrode films 13a, 13b, 13c, . . . , which are divided in the final step of FIG.
a, 14b, 14c... are reliably connected in series.

In the final step shown in FIG. 8, the back electrode films 13a, 13b, 13c, . . .
2a, 12b, 12c... are removed by irradiation with a laser beam with a substantially uniform energy distribution, the surface portion of the amorphous semiconductor film exposed in such removed portions has some of the above-mentioned Although a low-resistivity layer is formed, this low-resistance layer is practically non-existent when the photovoltaic device is used in sunlight or under normal illuminance (400 Lux or higher) even in indoor light. do not have. However, under low illuminance of less than about 200 Lux, negative effects such as leakage due to the above-mentioned low resistance layer may occur. In such a case, the low-resistance layer may be etched away by reactive ion etching (plasma etching) using, for example, CF ₄ using the back electrode films 13a, 13b, 13c, . . . as an etching-resistant mask; As shown in the figure, in the step of removing the back electrode film 13, the underlying amorphous semiconductor film 12 may be removed simultaneously without selectively removing only the back electrode film.

Furthermore, even in the final step shown in FIG. 8 in the above embodiment, the energy distribution of the laser beam used was approximately uniform over the irradiation area as in the step shown in FIG. Laser beams with the same Gaussian distribution may also be used. However, in this case, the photoelectric conversion element 14 adjacent to the lower amorphous semiconductor film portion
A, 14b, 14c, etc. are formed with a low resistance layer that may cause a short circuit, so the divided back electrode films 13a, 13b, 13c,... are etched using _CF4 as an anti-etching mask to form a low resistance layer. Since etching must be applied and removed, a slight lack of workability is inevitable.

(G) Effects of the Invention As is clear from the above description, the manufacturing method of the present invention irradiates a predetermined location of a semiconductor film disposed on a substrate-side electrode film with an energy beam whose energy distribution is substantially uniform over the irradiation area. Therefore, only the semiconductor film portion in the irradiated area can be removed without substantially forming a low resistance layer, and short-circuit accidents between adjacent photoelectric conversion elements or one photoelectric conversion element can be prevented. At the same time, it is possible to avoid the residual residue at the removed interface and the occurrence of thermal damage to the underlying layer.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the basic structure of a photovoltaic device, Figs. 2 a to c are enlarged sectional views of main parts to explain the drawbacks of the conventional method, and Figs. 3 to 8 are sectional views showing the method of the present invention. 9 is a temperature distribution characteristic diagram illustrating the energy distribution of the laser beam used in the method of the present invention; FIG. 10 is a temperature distribution characteristic diagram illustrating the energy distribution of the conventional method; FIGS. Fig. 12 is an isothermal distribution characteristic diagram when an amorphous silicon semiconductor film is irradiated with a laser beam having the energy distribution shown in Figs. 9 and 10, respectively, and Figs. Figure 10 is an isothermal distribution characteristic diagram when an aluminum back electrode film is irradiated with a laser beam having the energy distribution shown in Figure 10. Figure 15 is a schematic diagram showing the principle of the laser beam creation method used in the method of the present invention, Figure 16. FIG. 2 is a cross-sectional view showing another embodiment of the final step of the method of the present invention. 10...Substrate, 11, 11a, 11b, 11c...
Transparent electrode film, 12, 12a, 12b, 12c...Amorphous semiconductor film, 13, 13a, 13b, 13c...
Back electrode film, 14a, 14b, 14c...photoelectric conversion element, 21...iris, 22...condensing lens.

Claims (1)

[Claims] 1. A method for manufacturing a photovoltaic device in which a plurality of photoelectric conversion elements are electrically connected in series on an insulating surface of a substrate, the method comprising continuously forming a photovoltaic device on a plurality of substrate-side electrode films constituting the plurality of photoelectric conversion elements. By irradiating the amorphous semiconductor film disposed across the straddling region with an energy beam whose energy distribution is substantially uniform over the irradiation region, the semiconductor film in the irradiation region is removed without forming any residue. The semiconductor film is divided into a plurality of photoelectric conversion elements, and during the removal, thermal damage to the electrode film under the irradiation area is suppressed, and the semiconductor film at the periphery of the irradiation area is substantially removed. A method for manufacturing a photovoltaic device, characterized in that a low resistance layer is not formed.