JP2013087043A - Substrate processing apparatus and method for the same, and thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate processing method capable of forming, with a low cost, an unevenness shape having a large optical confinement effect on the surface of a glass substrate constituting a thin film solar cell.SOLUTION: In the substrate processing method forming a texture structure on the surface of the glass substrate, when etching is carried out by supplying a mixed gas of HF gas and alcohol gas or water vapor to the surface of the glass substrate, the etching is carried out by timewise changing the ratio of flow rates of the HF gas, and the alcohol gas or the water vapor.

Description

  The present invention relates to a substrate processing apparatus and method, and a thin film solar cell.

  Since a thin film silicon (Si) solar cell can be formed at a relatively low temperature of about 100 ° C. to 200 ° C., substrates of various materials can be used as a substrate for forming the thin film Si solar cell. A commonly used glass substrate is a glass substrate. In this thin-film Si solar cell, improvement in conversion efficiency is an issue, and for that purpose, it is important to increase the light absorption amount of the thin-film Si layer that is a power generation layer formed on the glass substrate. Yes. Therefore, a so-called light confinement effect, which increases the optical path length of light in the light absorption layer, has been conventionally performed by forming a textured transparent conductive film having an uneven surface on the glass substrate. I have been.

  There are several methods for forming an uneven texture structure on the surface of a glass substrate, and one of them is a blast method. For example, after roughening by a water blasting method in which water mixed with alumina powder (maximum particle diameter of 19 μm) as a polishing agent is sprayed on a glass substrate, the substrate is treated in a hydrofluoric acid aqueous solution to form irregularities (for example, , And a method of forming irregularities with an average step of 3 μm by treating the surface of a glass substrate, which is a substrate for solar cells, by sandblasting using abrasive grains of # 200 count (for example, patents) Document 2) has been proposed. A transparent conductive film is formed on the surface of the glass substrate on which irregularities are formed by these methods.

JP 2000-223724 A Japanese Patent Laid-Open No. 7-122864

  However, the above-described method for forming a textured shape on the transparent conductive film on the glass substrate has a problem that a sufficient light confinement effect cannot be obtained because the size of the unevenness is several μm to several tens of μm. there were. Moreover, in the method of forming a transparent conductive film after forming irregularities on a glass substrate, damage to the glass substrate due to blasting remains, and further, wet etching treatment with a chemical solution is performed after blasting. Two processes are performed using two different manufacturing apparatuses, which is costly, but has a problem that high throughput cannot be obtained.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a substrate processing apparatus and method for forming a concavo-convex shape having a large light confinement effect at low cost on the surface of a glass substrate constituting a thin film solar cell. And Another object of the present invention is to obtain a thin film solar cell using such a substrate processing method.

  In order to achieve the above object, a substrate processing method according to the present invention is a substrate processing method for forming a texture structure on the surface of a glass substrate, wherein a mixed gas of HF gas and alcohol gas or water vapor is formed on the surface of the glass substrate. The etching is performed by changing the flow rate ratio of HF gas and alcohol gas or water vapor over time when etching is performed.

  According to this invention, it is possible to form a texture structure in which unevenness having a size of several μm to several tens of μm and unevenness having a size of 1 μm or less are mixed. The glass substrate can be formed with good controllability and low cost.

FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a substrate processing apparatus according to Embodiment 1 of the present invention. FIG. 2 is an SEM image showing the state of the surface of the glass substrate after etching with the flow rates of HF gas and CH ₃ OH gas being constant. FIG. 3 is a diagram showing the haze ratio of the glass substrate processed by the substrate processing method according to the first embodiment. FIG. 4 is a diagram schematically showing an etching mechanism using a mixed gas of HF and alcohol. FIG. 5 is a diagram schematically showing the etching mechanism of the glass substrate when an HF aqueous solution is used. FIG. 6 is a diagram schematically showing the etching mechanism of the glass substrate when HF gas is used. FIG. 7 is a time chart schematically showing the gas supply method according to the first embodiment. FIG. 8 is an SEM image showing the state of the surface of the glass substrate after the etching process while changing the CH ₃ OH / HF flow ratio with time. FIG. 9 is a SEM image showing the state of the surface of the glass substrate after the etching process with the CH ₃ OH / HF flow ratio kept constant at 1. FIG. 10 is a cross-sectional view schematically showing the structure of the thin-film solar cell according to the third embodiment.

  A substrate processing apparatus and method, and a thin film solar cell according to embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments. Moreover, the cross-sectional views of the thin-film solar cell used in the following embodiments are schematic, and the relationship between the thickness and width of the layer, the ratio of the thickness of each layer, and the like may differ from the actual ones.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a substrate processing apparatus according to Embodiment 1 of the present invention. The substrate processing apparatus 10 is disposed in a vacuum chamber 11 that is a processing chamber 15 so as to face a substrate stage 12 on which a substrate such as a glass substrate 51 to be processed is placed, and a substrate placement surface of the substrate stage 12. The gas discharge part 13 to be provided. In this example, the substrate stage 12 is provided in the lower part in the vacuum chamber 11, and the gas discharge unit 13 is provided in the upper part in the vacuum chamber 11. On the surface of the gas discharge unit 13 on the substrate stage 12 side, a shower plate 14 that supplies gas in a shower shape toward the glass substrate 51 is provided. Moreover, the substrate stage 12 has a cooling mechanism such as a heating mechanism or a water cooling type so that the temperature of the glass substrate 51 to be held can be adjusted to a predetermined temperature.

  Further, an exhaust port 17 is provided in the lower part of the vacuum chamber 11, and a pressure adjusting unit 16 such as a gate valve for adjusting the pressure in the processing chamber 15 is provided on a pipe connecting the processing chamber 15 and the exhaust port 17. And a vacuum pump (not shown) is connected to the exhaust port 17. By the pressure adjusting unit 16 and the vacuum pump, the pressure in the processing chamber 15 can be adjusted to a desired pressure.

A processing gas supply mechanism 20 that supplies a processing gas into the processing chamber 15 is connected to the gas discharge unit 13. The processing gas supply mechanism 20 includes a first gas supply pipe 21 that supplies a first gas, and a second gas supply pipe 24 that supplies a second gas. In the first gas supply pipe 21, a mass flow controller 22 that adjusts the flow rate of the first gas flowing through the first gas supply pipe 21, and the flow-adjusted first gas are continuously supplied to the gas discharge unit 13. Alternatively, a pulse valve 23 that can be supplied intermittently is provided. In the second gas supply pipe 24, a mass flow controller 25 for adjusting the flow rate of the second gas flowing through the second gas supply pipe 24 and the second gas whose flow rate has been adjusted are continuously supplied to the gas discharge unit 13. Alternatively, a pulse valve 26 that can be supplied intermittently is provided. Here, as the first gas, HF gas for etching the glass substrate 51 can be used, and as the second gas, methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH), isopropyl alcohol, or the like can be used. Alcohol gas or water vapor (H ₂ O) can be used. The mass flow controllers 22 and 25 and the pulse valves 23 and 26 are controlled by a control device (not shown) by a method described later.

  The first gas from the first gas supply pipe 21 and the second gas from the second gas supply pipe 24 are each adjusted in flow rate and merged and mixed before entering the gas discharge section 13 to discharge the gas. A mixed gas (vapor) is supplied to the section 13. Then, the gas is discharged from the shower plate 14 of the gas discharge unit 13 onto the glass substrate 51 on the substrate stage 12. A method of etching by supplying gas intermittently with the pulse valves 23 and 26 will be described later.

  Next, the substrate processing method in the substrate processing apparatus 10 will be described separately for (1) etching with a constant gas flow rate and (2) etching with changing the gas flow rate ratio.

(1) Etching with a constant gas flow rate A glass substrate 51 containing an alkali component of 28% is placed on the substrate stage 12 of the substrate processing apparatus 10 having the configuration shown in FIG. Here, the temperature of the glass substrate 51 correlates with the etching rate of SiO _{2 in} the glass, and a sufficient etching rate cannot be obtained at 80 ° C. or higher. Therefore, the temperature of the substrate stage 12 is set to a predetermined temperature (less than 80 ° C.). For example, 40 ° C.). Then, the inside of the processing chamber 15 is exhausted by a vacuum pump (not shown) until a predetermined degree of vacuum is reached.

HF gas is used as the first gas, the flow rate is set to 100 sccm by the mass flow controller 22, CH ₃ OH is used as the second gas, and the flow rate is set to 200 sccm by the mass flow controller 25. In this example, the pulse valves 23 and 26 are continuously operated so that they are always open, and the flow rate ratio of CH ₃ OH / HF is kept constant so as to be 2.

Further, the distance between the shower plate 14 that ejects the mixed gas of HF and CH ₃ OH and the substrate stage 12 is appropriately set in consideration of the size of the glass substrate and the uniformity of the etching rate. The pressure in the processing chamber 15 during the etching is set to 10 to 10,000 Pa depending on the etching rate, the surface unevenness size, and the like. Here, the pressure is set to 2,000 Pa by the pressure adjusting unit 16. In addition, when the pressure in the processing chamber 15 is less than 10 Pa or greater than 10,000 Pa, the etching rate is low, and it may take more time than necessary. It is desirable to set the range. Etching is performed for 20 minutes under the above conditions.

As a result, it is recognized that the surface of the glass substrate 51 is etched. The etched glass substrate 51 is subjected to surface observation with an SEM (Scanning Electron Microscope), and the haze ratio is measured. FIG. 2 is an SEM image showing the state of the surface of the glass substrate after etching with the flow rates of HF gas and CH ₃ OH gas being constant, and FIG. 3 is processed by the substrate processing method according to the first embodiment. It is a figure which shows the haze rate of a glass substrate. In FIG. 3, the horizontal axis indicates the wavelength (Wavelength, nm), and the vertical axis indicates the haze ratio (Haze,%). Moreover, the curve (A) in the figure shows the haze ratio of the glass substrate etched by setting the flow rates of the HF gas and the CH ₃ OH gas to be constant over time, and the curve (B) shows the HF gas shown later. The haze ratio of the glass substrate etched by changing the flow rate ratio of the CH ₃ OH gas with time is shown.

  As shown in FIG. 2, irregularities of several μm to several tens of μm are formed on the surface of the glass substrate 51. Moreover, as shown by the curve (A) in FIG. 3, a high haze ratio is obtained in the short wavelength to long wavelength region. In particular, at a wavelength of 500 nm, a haze ratio of 63% is obtained. Thus, it can be seen that a good light confinement effect can be obtained by the unevenness formed on the surface of the glass substrate 51.

Here, the etching mechanism of the glass substrate by the mixed gas of HF and alcohol will be described. FIG. 4 is a diagram schematically showing an etching mechanism using a mixed gas of HF and alcohol. As described above, the glass substrate 51 used in the solar cell panel is so-called soda glass in which silicon dioxide (SiO ₂ ) is a main component and 10 to 30% of Na ₂ O, CaO, MgO or the like serving as an alkali component is added. Manufactured as. Therefore, in the glass substrate 51, the alkali component particles are dispersed and mixed in the main component SiO ₂ shown in FIG.

When HF gas is ejected (discharged) onto the surface of the glass substrate 51, etching progresses from the surface of the glass substrate 51 by the reaction between HF and SiO ₂ . The reason why HF etches glass is that HF reacts with SiO ₂ , which is the main component of glass, as shown in the following formulas (1) and (2).
SiO ₂ + 6HF → H ₂ SiF ₆ + 2H ₂ O (1)
H ₂ SiF ₆ → SiF ₄ ↑ + 2HF (2)

Then, the following equation (3) is derived from these equations (1) and (2).
SiO ₂ + 4HF → SiF ₄ ↑ + 2H ₂ O (3)

Specifically, as shown in FIG. 4A, the HF gas exists in a chain-like hexamer structure and reacts with SiO ₂ . As a result, H ₂ SiF ₆ and H ₂ O are formed as shown in equation (1). Further, as shown in the equation (2), H ₂ SiF ₆ is decomposed into SiF ₄ and HF. As a result, SiF ₄ and H ₂ O are generated and volatilized by reacting SiO ₂ and HF gas as shown in equation (3). Thus, the surface of the glass substrate 51 that has been exposed to the HF gas is etched.

On the other hand, as shown in FIG. 4B, Na, Ca, Mg present in the glass substrate 51 reacts with fluorine to form a non-volatile and non-volatile fluoride in water, and the above (1) ) - (3) functions as a mask during etching of the SiO ₂ of the formula. As a result, the portion where the HF gas does not come into contact with SiO ₂ is not etched, and only the portion where the HF gas comes into contact with SiO ₂ is etched. As a result, irregularities are formed on the surface of the glass substrate 51.

That is, the surface of the glass substrate 51 has a concavo-convex shape due to volatilized SiO ₂ and a mask made of fluoride of Na, Ca, Mg, and a texture structure having a concavo-convex of several μm to several tens μm as etching progresses. Is formed.

In the etching of the glass substrate 51, HF gas, that is, anhydrous hydrogen fluoride alone, has low reactivity with SiO _{2 of the} glass substrate 51, so H ₂ O or alcohol is added. As a result, HF is ion-dissociated to generate fluoride ions F ⁻ , and the F ⁻ ions act on the silicon oxide film and the SiO ₂ etching reaction proceeds.

  It is known that an uneven texture can be formed on the surface of the glass substrate 51 even when an HF aqueous solution is used. Therefore, a difference in texture formation on the glass substrate 51 between the case where the HF aqueous solution is used and the case where the HF gas according to Embodiment 1 is used will be described. FIG. 5 is a diagram schematically showing a glass substrate etching mechanism when an HF aqueous solution is used, and FIG. 6 is a diagram schematically showing a glass substrate etching mechanism when HF gas is used. is there.

When an HF aqueous solution is used, etching is performed by the action of F ⁻ ions on SiO ₂ as in the case of HF gas. At the same time, Na, Ca, Mg, which are alkali components in the glass substrate 51, are also fluorine. Reacts to form water-insoluble and non-volatile fluorides. However, in the etching using an HF aqueous solution, as shown in FIG. 5A, the alkali component fluoride is lifted off by the flow of the etching solution. Therefore, isotropic etching is dominant without remaining in the glass substrate 51. As a result, after the etching process and the water washing process, as shown in FIG. 5B, the texture size of the unevenness becomes 10 μm or more.

On the other hand, when HF gas is used, as shown in FIG. 6A, the alkali component fluoride generated during the etching remains in the glass substrate 51 without being lifted off. . Since the alkali component fluoride is non-volatile, it serves as a mask for etching as described above, and etching of SiO ₂ proceeds. Thereafter, when a water washing treatment is performed, as shown in FIG. 6B, the fluoride of the alkali component is removed, and irregularities with a small period can be formed as compared with the case of using the HF aqueous solution.

  In other words, in the texture forming method of the first embodiment, the reaction between the glass and the HF gas is an accumulation of reactions in a microscopic region at the molecular level, so it is possible to control from fine pitch irregularities to large pitch irregularities. It becomes. In particular, the fine pitch unevenness results in processing of an area that is impossible by conventional blasting and wet etching.

  The above-described method for forming irregularities on the surface of a glass substrate with a mixed gas of HF and alcohol has been found by the present inventors. By using this method, a simple method can be used in the production of a solar cell panel. A texture structure having a large light confinement effect can be formed.

(2) Etching while changing the gas flow rate ratio Even in the case of etching with the gas flow rate fixed in (1) above, it is possible to form a texture structure with a large light confinement effect in the manufacture of solar cell panels. However, a method of forming irregularities on the surface of the glass substrate that can further improve the light confinement effect by the texture structure as compared with the method (1) will be described.

  Here, as in the case of (1), the glass substrate 51 containing 28% of the alkali component is placed on the substrate stage 12 of the substrate processing apparatus 10 having the configuration shown in FIG. Then, the temperature of the substrate stage 12 is set to a predetermined temperature lower than 80 ° C. (for example, 40 ° C.), and the inside of the processing chamber 15 is exhausted until a predetermined degree of vacuum is reached.

Thereafter, the first gas (HF gas) and the second gas (CH ₃ OH) are supplied from the first gas supply pipe 21 and the second gas supply pipe 24. Here, in the case of (1) In contrast, the gas is supplied in a pulsed manner. FIG. 7 is a time chart schematically showing the gas supply method according to the first embodiment. In this figure, the horizontal axis indicates time.

The upper part shows the opening / closing operation (ON / OFF timing) of the pulse valves 23 and 26. In this example, the pulse valve 23 provided in the first gas (HF gas) supply pipe 21 is intermittently pulsed, and the pulse valve 26 provided in the second gas (CH ₃ OH) supply pipe 24 is steadily operated. Operate continuously.

The middle stage shows the time change of the gas flow rate in that case, and the flow rate of the HF gas as the first gas greatly changes with time by on / off supply. That is, when the pulse valve 23 is turned on, the amount of HF gas supplied from the first gas supply pipe 21 to the gas discharge unit 13 increases rapidly, and when the pulse valve 23 is turned off, the gas discharge The amount of HF gas supplied to the section 13 decreases. The pattern of increasing / decreasing the supply amount of HF gas is repeated by switching on / off the pulse valve 23 in a predetermined cycle. On the other hand, the flow rate of the CH ₃ OH gas as the second gas is constant regardless of time.

The lower part shows the time change of the flow rate ratio of the second gas to the first gas, that is, the CH ₃ OH / HF flow rate ratio. The CH ₃ OH / HF flow rate ratio varies greatly with time because the first gas changes greatly with time and the second gas remains constant regardless of time. Therefore, the CH ₃ OH / HF flow rate ratio of the mixed gas supplied from the gas discharge unit 13 through the shower plate 14 into the processing chamber 15 has a large change with time.

In this example, the first gas is supplied in a pulsed manner and the second gas is supplied in a steady manner. However, the first gas is supplied in a steady manner and the second gas is supplied in a pulsed manner. However, similarly, the CH ₃ OH / HF flow rate ratio can be greatly changed over time.

In this manner, the glass substrate 51 is etched while changing the CH ₃ OH / HF flow rate ratio with time. As in the case of (1) above, the specific processing conditions are such that HF gas is used for the first gas, the average gas flow rate of HF is set to 100 sccm, and CH ₃ OH is used for the second gas. The average flow rate of CH ₃ OH is set to 200 sccm. The first gas pulse valve 23 is operated with an on-time of 2 seconds and an off-time of 4 seconds to supply HF gas in a pulsed manner, and the second gas pulse valve 26 is constantly operated as an open operation. To supply. As a result, the HF gas and the CH ₃ OH gas are transferred from the shower plate 14 of the gas discharge section 13 into the processing chamber 15 while the CH ₃ OH / HF flow rate ratio greatly changes to about 0.5 to 5.0 over time. Discharged. The pressure in the processing chamber 15 fluctuates with time due to pulsed gas supply. Here, the pressure adjusting unit 16 is fixed at a predetermined position to set an average gas pressure. Other processing methods are the same as those in the case of (1). Further, such on / off switching operation of the pulse valves 23 and 26 is performed by a control unit (not shown). Etching is performed for 20 minutes under the above conditions.

As a result, it is recognized that the surface of the glass substrate 51 is etched. About this etched glass substrate 51, a surface state is observed with SEM, and also a haze rate is measured. FIG. 8 is an SEM image showing the state of the surface of the glass substrate after the etching process while changing the CH ₃ OH / HF flow ratio with time.

  As shown in FIG. 8, the surface of the glass substrate 51 is formed with large unevenness of several μm to several tens of μm and small unevenness of 1 μm or less mixed together. Further, as shown by the curve (B) in FIG. 3, a higher haze ratio is obtained from the short wavelength to the long wavelength as compared with the case of the curve (A). In particular, at a wavelength of 500 nm, a haze ratio of 77% is obtained. Thus, it can be seen that the concavity and convexity formed on the surface of the glass substrate 51 can provide a better light confinement effect than in the case of (1).

Here, when the surface of the glass substrate 51 is etched while temporally changing the flow rate ratio of the HF gas and the CH ₃ OH gas, the reason why a texture structure having a high light confinement effect with a high haze ratio is formed, The following evaluation is further performed.

The flow rates of the first gas (HF) and the second gas (CH ₃ OH) are constantly supplied, the HF flow rate of the first gas is 100 sccm, and the CH ₃ OH flow rate of the second gas is 100 sccm. To do. That is, the glass substrate 51 is etched for 20 minutes with a CH ₃ OH / HF flow rate ratio of 1, and the surface state is observed by SEM.

FIG. 9 is a SEM image showing the state of the surface of the glass substrate after the etching process with the CH ₃ OH / HF flow ratio kept constant at 1. As shown in FIG. 9, small irregularities of 1 μm or less were formed on the surface of the etched glass substrate 51, and the etching amount of the glass substrate 51 was small. On the other hand, as shown in FIG. 2, when etching is performed with the CH ₃ OH / HF flow rate ratio kept constant at 2, unevenness of several μm to several tens of μm is formed as described above.

Thus, when the CH ₃ OH / HF flow rate ratio is as small as about 1, small irregularities (1 μm or less) are formed, and when the CH ₃ OH / HF flow rate ratio is as large as 2 or more (for example, about 5). It is considered that relatively large unevenness (several μm to several tens μm) is formed. Therefore, when the CH ₃ OH / HF flow rate ratio is greatly changed with time, it is considered that etching progresses while the size of the unevenness changes in the thickness direction of the glass substrate 51.

That is, when the flow rate ratio of the HF gas and the CH ₃ OH gas is changed with time, the shape of the unevenness is changed by changing the etching selection ratio between the alkali component in the glass substrate 51 and SiO ₂ with time. It is done. The size of the unevenness and the ratio of the size of the unevenness can be controlled to a desired texture structure according to the pulse condition when the first gas or the second gas is intermittently supplied.

The etching rate of the glass by HF gas and CH ₃ OH gas is adapted to vary the flow rate ratio of HF gas and CH ₃ OH gas also depends on the gas pressure in the vacuum chamber 11. Therefore, in the method of Embodiment 1 in which the flow ratio of both gases is changed with time, the unevenness may be small even when the flow ratio is large, and the unevenness may be large even when the flow ratio is small. However, even in such a case, the texture shape can be controlled by etching the glass substrate 51 while changing the flow rate ratio with time.

  In the first embodiment, etching is performed by discharging a mixed gas in which the flow rate ratio of the HF gas and the alcohol gas is temporally changed to the glass substrate 51. It is possible to form a texture structure in which large unevenness of ten and several μm and small unevenness of 1 μm or less are mixed with good controllability. Similarly, the etching may be performed by changing the flow rate ratio of HF gas and water vapor with time. As a result, a glass substrate having a greater light confinement effect than conventional can be formed. In addition, as compared with the conventional method of forming irregularities by performing wet etching treatment with a chemical solution after blasting, there is only one apparatus used to form irregularities (only one process is required to form irregularities). ), And has an effect of realizing low cost and high throughput.

Embodiment 2. FIG.
In Embodiment 1, after carrying a glass substrate in a vacuum chamber, after evacuating until the inside of a vacuum chamber became a predetermined vacuum degree, etching gas was introduce | transduced and it etched. In the second embodiment, an etching method capable of forming a texture with higher accuracy than in the first embodiment will be described.

  First, a glass substrate 51 containing 28% of an alkali component is placed on the substrate stage 12 of the substrate processing apparatus 10 having the configuration shown in FIG. Then, the temperature of the substrate stage 12 is set to a predetermined temperature lower than 80 ° C. (for example, 40 ° C.), and the inside of the processing chamber 15 is exhausted until a predetermined degree of vacuum is reached.

When the inside of the processing chamber 15 reaches a predetermined degree of vacuum, the pressure adjusting unit 16 is adjusted, and only 200 sccm of the second gas CH ₃ OH is constantly supplied to raise the pressure in the processing chamber 15 to 1, A predetermined pressure in the range of 000 to 10,000 Pa (for example, 2,000 Pa) is set. In this state, since only the CH ₃ OH gas is contained in the processing chamber 15, the surface of the glass substrate 51 is not etched.

When the inside of the processing chamber 15 reaches a predetermined pressure, in addition to the second gas, HF of the first gas is supplied in a pulse manner with an average flow rate of 100 sccm as in the case of (2) of the first embodiment. The inside of the processing chamber 15 is a mixed gas of CH ₃ OH gas and HF gas. At this time, a mixed gas of CH ₃ OH gas and HF gas in which the CH ₃ OH / HF flow rate ratio greatly changes with time is supplied from the shower plate 14 of the gas discharge unit 13. Then, etching of SiO ₂ with HF is started from a high pressure state of 2,000 Pa. SiO ₂ in the glass substrate 51 is etched by the reaction with HF as described above, but the etching rate has a correlation with the gas pressure, and is relatively high etching at a pressure of about 1,000 to 10,000 Pa. Since the speed is obtained, the etching is performed at a relatively high etching speed from the time when the supply of the HF gas is started.

  When the first gas and the second gas are simultaneously supplied into the processing chamber 15 as in the first embodiment, only a low etching rate is required until the processing chamber 15 reaches a predetermined pressure from a high vacuum state. Since it cannot be obtained, it is difficult to form a desired uneven shape.

On the other hand, in the second embodiment, the second gas is supplied into the processing chamber 15 in a high vacuum state, and after reaching a predetermined pressure of about 1,000 to 10,000 Pa, the HF gas is intermittently supplied. Then, a mixed gas of CH ₃ OH and HF is supplied onto the glass substrate 51 under the condition that the CH ₃ OH / HF flow rate ratio greatly changes with time. As a result, etching is started at a relatively high rate from the time when the HF gas is supplied into the processing chamber 15, and the controllability of the concavo-convex shape and structure is improved, and a highly accurate texture with a large light confinement effect is formed with a high yield. It has the effect that it can be done.

Embodiment 3 FIG.
FIG. 10 is a cross-sectional view schematically showing the structure of the thin-film solar cell according to the third embodiment. This thin-film solar cell 50 has an undercoat layer 52 and a first electrode layer 53 made of a transparent conductive film on the glass substrate 51 having the texture structure formed in the first or second embodiment on the surface, A photoelectric conversion layer 54 made of a semiconductor layer having a pin junction made of a p-type semiconductor film, an i-type semiconductor film that is a power generation layer, and an n-type semiconductor film, and a second electrode layer 55 made of a transparent conductive film 551 and a metal electrode film 552. And have a laminated structure.

Here, the undercoat layer 52 has a function of preventing the diffusion of alkali components from the glass substrate 51, and for example, a SiO ₂ film or the like can be used. As the first electrode layer 53, a transparent conductive oxide film such as ZnO, SnO ₂ , or ITO, or a film obtained by adding a metal such as Al to these transparent conductive oxide films to improve conductivity can be used. . As the photoelectric conversion layer 54, a p-type hydrogenated microcrystalline silicon (μc-Si: H) layer, an i-type hydrogenated microcrystalline silicon (μc-Si: H) layer, and an n-type hydrogenated microcrystalline silicon (μc). A layer in which -Si: H) layers are sequentially stacked can be used. As the transparent conductive film 551 of the second electrode layer 55, a transparent conductive oxide film such as ZnO, SnO ₂ or ITO, or a film obtained by adding a metal such as Al to these transparent conductive oxide films can be used. As the metal electrode film 552, Ag or the like can be used. Although not shown here, the stacked structure is formed for each cell, and a solar cell module can be obtained by connecting the cells in series or in parallel.

  Next, a manufacturing method of the thin film solar cell having such a structure will be described. In actual manufacturing, a solar cell module is manufactured by being separated into a plurality of cells by a laser scribing method or the like, but is omitted here and only the film structure is shown.

First, the glass substrate 51 that has undergone predetermined cleaning is etched using the method described in the first embodiment or the second embodiment to form the texture structure 51 a on the surface of the glass substrate 51. Then, if necessary, a SiO ₂ film is formed as an undercoat layer 52 by sputtering on the glass substrate 51 on which the texture structure 51a is formed. Thereafter, a ZnO film is formed as a first electrode layer 53 on the undercoat layer 52 by a film forming method such as a sputtering method or a CVD (Chemical Vapor Deposition) method.

Next, a silicon thin film that becomes the photoelectric conversion layer 54 is formed on the first electrode layer 53 by a plasma CVD method. Here, as the photoelectric conversion layer 54, a p-type μc-Si: H layer, an i-type μc-Si: H layer, and an n-type μc-Si: H layer are sequentially stacked from the first electrode layer 53 side. Thereafter, SnO ₂ as the transparent conductive film 551 is formed on the photoelectric conversion layer 54 by a film forming method such as sputtering, and an Ag film as the metal electrode film 552 is further formed on the transparent conductive film 551 by sputtering. The second electrode layer 55 is formed by a film formation method. As a result, a thin film solar cell is formed.

  The structure of the thin-film solar cell 50 is merely an example, and the photoelectric conversion layer 54 may have a tandem structure in which a plurality of semiconductor layers having different band gaps are stacked. Moreover, the material of each above-mentioned layer is an illustration, and is not limited to this.

  According to the third embodiment, since the thin-film solar cell 50 is formed using the glass substrate 51 having the irregularities formed on the surface by the substrate processing method of the first or second embodiment, in the photoelectric conversion layer 54 The optical path length is increased, and the light incident from the glass substrate 51 side can be efficiently used for power generation by the photoelectric conversion layer 54.

  In the above-described embodiment, parameters such as the gas flow rate and pressure have been described with specific numerical values, but are not limited to these values. Moreover, the ratio of the alkali component in the glass substrate 51 is an example, and is not limited to this.

DESCRIPTION OF SYMBOLS 10 Substrate processing apparatus 11 Vacuum chamber 12 Substrate stage 13 Gas discharge part 14 Shower plate 15 Processing chamber 16 Pressure adjustment part 17 Exhaust port 20 Process gas supply mechanism 21 1st gas supply piping 22, 25 Mass flow controller 23, 26 Pulse valve 24 Second gas supply pipe 50 Thin film solar cell 51 Glass substrate 51a Texture structure 52 Undercoat layer 53 First electrode layer 54 Photoelectric conversion layer 55 Second electrode layer 551 Transparent conductive film 552 Metal electrode film

Claims (11)

In a substrate processing method for forming a texture structure on the surface of a glass substrate,
Etching is performed by supplying a mixed gas of HF gas and alcohol gas or water vapor to the surface of the glass substrate while changing the flow rate ratio of HF gas and alcohol gas or water vapor over time. A substrate processing method.   The substrate processing method according to claim 1, wherein the flow rate of the alcohol gas or the water vapor is constant, and the flow rate of the HF gas is changed with time.   The substrate processing method according to claim 1, wherein the flow rate of the HF gas is constant and the flow rate of the alcohol gas or the water vapor is changed with time.   The substrate processing method according to any one of claims 1 to 3, wherein a pressure of an area on which the glass substrate is placed during the etching is 10 to 10,000 Pa.   The alcohol gas or the water vapor is supplied in a certain amount so that the pressure of the region where the glass substrate is placed during the etching is 1,000 to 10,000 Pa, and the glass substrate is placed. After the pressure in the region reaches 1,000 to 10,000 Pa, the flow rate of the HF gas is changed with time while supplying the alcohol gas or the water vapor in a constant amount, and the glass substrate is placed. The substrate processing method according to claim 1, wherein the mixed gas is supplied to a region to be processed. A vacuum chamber;
Substrate holding means for placing a glass substrate in the vacuum chamber;
Gas discharge means for discharging gas onto the glass substrate mounting surface of the substrate holding means in the vacuum chamber;
First gas supply means for supplying HF gas to the gas discharge means;
Second gas supply means for supplying alcohol gas or water vapor to the gas discharge means;
Exhaust means for exhausting the gas in the vacuum chamber;
A first gas valve for switching on / off of HF gas supplied from the first gas supply means to the gas discharge means;
A second gas valve for switching on / off alcohol gas or water vapor supplied from the second gas supply means to the gas discharge means;
Control means for switching on and off the first gas valve and the second gas valve so that the flow rate ratio between the HF gas and the alcohol gas or the water vapor changes with time;
A substrate processing apparatus comprising:   The substrate processing apparatus according to claim 6, wherein the control unit performs control so that the first gas valve is intermittently turned on and the second gas valve is kept on.   The substrate processing apparatus according to claim 6, wherein the control unit controls the second gas valve to be intermittently turned on while keeping the first gas valve turned on.   The control means evacuates the vacuum chamber by the exhaust means, and then turns on the second gas valve. When the pressure in the vacuum chamber reaches 1,000 to 10,000 Pa, the second gas valve is turned on. The substrate processing apparatus according to claim 6, wherein the first gas valve is intermittently turned on as it is.   The substrate processing apparatus according to claim 6, wherein the glass substrate is soda glass containing an alkali component.   A first electrode layer made of a transparent conductive material and a pin junction are formed on the surface of the glass substrate processed by the substrate processing method according to claim 1, on which the texture structure is formed. A thin-film solar battery comprising a cell in which a photoelectric conversion layer including one or more semiconductor layers and a second electrode layer including a metal film are stacked.