JP2012256801A - Formation method of texture structure and manufacturing method of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a formation method of a texture structure capable of manufacturing a solar cell having high characteristics by reducing the curvature of a substrate, and to provide a manufacturing method of a solar cell.SOLUTION: The formation method of a texture structure includes a step for forming a silicon nitride film on the first surface, i.e. one surface, of a semiconductor substrate having a thickness of 300 μm or less, and a step for forming a texture structure by etching the second surface on the reverse side of the first surface of a semiconductor substrate. The content ratio of nitrogen atom to the silicon atom of the silicon nitride film is 1.3-2. A manufacturing method of solar cell is also provided.

Description

  The present invention relates to a texture structure forming method and a solar cell manufacturing method.

  In recent years, in particular, from the viewpoint of protecting the global environment, solar cells that convert solar energy into electrical energy have been rapidly expected as next-generation energy sources. There are various types of solar cells, such as those using compound semiconductors and those using organic materials, but currently, solar cells using silicon crystals are the mainstream.

  Currently, the most manufactured and sold solar cells have an n-electrode formed on the surface on which sunlight is incident (light-receiving surface), and a p-electrode on the surface opposite to the light-receiving surface (back surface). It is a double-sided electrode type solar cell having the formed structure. Further, development of a back electrode type solar battery cell in which an electrode is not formed on the light receiving surface of the solar battery cell and an n electrode and a p electrode are formed only on the back surface of the solar battery cell is also under development.

  Reflection of incident light on the light-receiving surface of the silicon substrate by forming minute pyramid-shaped irregularities called texture structures on the light-receiving surface of the silicon substrate in both the double-sided electrode type solar cell and the back-side electrode type solar cell. Technology to prevent this is important.

  For example, Patent Document 1 discloses that after a silicon oxide film is formed on one surface of a p-type silicon substrate by atmospheric pressure CVD, the surface of the p-type silicon substrate on which the silicon oxide film is not formed is made of an alkaline aqueous solution. A method for forming a textured structure by etching is disclosed.

  In Patent Document 2, a silicon oxide film is formed on each of the light receiving surface and the back surface of a silicon substrate by thermal oxidation, and the silicon oxide film on the light receiving surface of the silicon substrate is removed with an aqueous hydrogen fluoride solution. A method of forming a texture structure by etching a light receiving surface with an alkaline solution is disclosed.

JP 2010-93194 A JP 2009-147070 A

  However, in the method described in Patent Document 1, a thick silicon oxide film having a thickness of 750 nm has to be formed in order to function as a mask when forming a texture structure with an alkaline aqueous solution. When such a thick silicon oxide film is formed, the stress applied to the silicon substrate increases, which causes a problem that the silicon substrate is bent and it is difficult to manufacture a solar cell.

  In the method described in Patent Document 2, the thickness of the silicon oxide film itself can be reduced. However, when the silicon oxide film is formed, it is necessary to heat the silicon substrate at a high temperature of 900 ° C. to 1200 ° C. was there. Therefore, in the solar cell produced by forming the texture structure using the method described in Patent Document 2, there is a problem that the lifetime of minority carriers deteriorates and the characteristics of the solar cell deteriorate.

  In view of the above circumstances, an object of the present invention is to provide a texture structure forming method and a solar cell manufacturing method capable of manufacturing a solar cell having high characteristics while suppressing the curvature of the substrate.

  In the present invention, a step of forming a silicon nitride film on a first surface, which is one surface of a semiconductor substrate having a thickness of 300 μm or less, and a second surface opposite to the first surface of the semiconductor substrate are etched. A texture structure forming step, and the content ratio of nitrogen atoms to silicon atoms in the silicon nitride film is 1.3 or more and 2 or less.

  Here, the texture structure forming method of the present invention preferably further includes a step of removing the silicon nitride film using an aqueous hydrogen fluoride solution.

  In the texture structure forming method of the present invention, it is preferable that the silicon nitride film is formed to a thickness of 10 nm to 40 nm in the step of forming the silicon nitride film.

  In the texture structure forming method of the present invention, the silicon nitride film is preferably formed by plasma CVD or sputtering in the step of forming the silicon nitride film.

  In the texture structure forming method of the present invention, the plasma CVD method is performed by supplying a silane gas as a silicon source and supplying an ammonia gas as a nitrogen source. The silane gas and the ammonia gas are ammonia gas relative to the silane gas, respectively. The volume ratio is preferably 6 to 12 inclusive.

  In the texture structure forming method of the present invention, the sputtering method includes an atmosphere containing one or both of nitrogen gas and ammonia gas, or one or both of nitrogen gas and ammonia gas and a rare gas. It is preferably performed by sputtering the target in an atmosphere.

  Furthermore, the present invention provides a step of forming a silicon nitride film on a first surface, which is one surface of a silicon substrate having a thickness of 300 μm or less, and a second surface opposite to the first surface of the silicon substrate. A step of forming a texture structure by etching, a step of removing the silicon nitride film using an aqueous hydrogen fluoride solution, a step of forming an impurity diffusion layer on the first surface of the silicon substrate, and an impurity diffusion layer on the impurity diffusion layer And a step of forming an electrode, wherein the content ratio of nitrogen atoms to silicon atoms in the silicon nitride film is 1.3 or more and 2 or less.

  Here, in the method for manufacturing a solar cell of the present invention, in the step of forming the silicon nitride film, the silicon nitride film is preferably formed to a thickness of 10 nm to 40 nm.

  In the method for manufacturing a solar cell of the present invention, in the step of forming the silicon nitride film, the silicon nitride film is preferably formed by a plasma CVD method or a sputtering method.

  In the method for manufacturing a solar cell of the present invention, the plasma CVD method is performed by supplying silane gas as a silicon source and supplying ammonia gas as a nitrogen source. The silane gas and the ammonia gas are ammonia gas relative to the silane gas, respectively. It is preferable that the volume ratio is 6 or more and 12 or less.

  In the method for producing a solar cell of the present invention, the sputtering method includes an atmosphere containing one or both of nitrogen gas and ammonia gas, or one or both of nitrogen gas and ammonia gas and a rare gas. It is preferably performed by sputtering a silicon target in an atmosphere.

  ADVANTAGE OF THE INVENTION According to this invention, the formation method of a texture structure and the manufacturing method of a solar cell which can suppress the curvature of a board | substrate and can manufacture a high characteristic solar cell can be provided.

It is typical sectional drawing illustrating the process of preparing the n-type silicon substrate of the manufacturing method of the back surface electrode type solar cell of this Embodiment. It is typical sectional drawing illustrating the process of forming the silicon nitride film of the manufacturing method of the back electrode type solar cell of this Embodiment. It is typical sectional drawing illustrating the process of forming a texture structure in the 2nd surface of the n-type silicon substrate of the manufacturing method of the back electrode type solar cell of this Embodiment. It is typical sectional drawing illustrating the process of removing the silicon nitride film of the manufacturing method of the back electrode type solar cell of this Embodiment. It is typical sectional drawing illustrating the process of forming the n-type impurity diffusion area | region and the p-type impurity diffusion area | region of the manufacturing method of the back surface electrode type solar cell of this Embodiment, respectively. It is typical sectional drawing illustrating the process of forming the passivation film of the manufacturing method of the back surface electrode type solar cell of this Embodiment. It is typical sectional drawing illustrating the process of forming the antireflection film of the manufacturing method of the back electrode type solar cell of this Embodiment. It is typical sectional drawing illustrating the process of forming a contact hole in the passivation film of the manufacturing method of the back electrode type solar cell of this Embodiment. It is typical sectional drawing illustrating the process of forming the electrode for n-types, and the electrode for p-types of the manufacturing method of the back surface electrode type solar cell of this Embodiment. It is a figure which shows the result of the elemental analysis by XPS of the samples 1 and 2 in an Example. It is an enlarged view of the peak corresponding to the 2p orbit of Si shown in FIG. FIG. 11 is an enlarged view of a peak corresponding to the N 1s orbit shown in FIG. 10. It is an enlarged view of the peak corresponding to 1s orbit of O shown in FIG. It is an enlarged view of the peak corresponding to the 1s orbit of C shown in FIG. It is an enlarged view of the peak corresponding to 1s orbit of F shown in FIG. It is the figure which divided the peak corresponding to 2p orbit of Si in the XPS analysis of sample 1 shown in Drawing 10 according to the valence of Si. It is the figure which divided the peak corresponding to 2p orbit of Si in the XPS analysis of sample 2 shown in Drawing 10 according to the valence of Si.

  Hereinafter, with reference to the schematic sectional views of FIGS. 1 to 9, a method for manufacturing the back electrode type solar cell of the present embodiment will be described. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts. In addition, other steps may be included before and after each step described later. Moreover, the order of each process mentioned later may be changed, and at least two processes of each process mentioned later may be performed simultaneously.

  First, as shown in FIG. 1, a step of preparing an n-type silicon substrate 1 as an example of a semiconductor substrate is performed. The n-type silicon substrate 1 has a first surface 1a and a second surface 1b opposite to the first surface 1a.

  The step of preparing the n-type silicon substrate 1 is performed by, for example, slicing an n-type single crystal silicon ingot grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method). This can be done by removing the slice damage. In the present embodiment, the case where n-type silicon substrate 1 which is an n-type semiconductor substrate is used as the semiconductor substrate will be described. However, a semiconductor substrate other than the n-type semiconductor substrate may be used, for example, a p-type silicon substrate. A p-type semiconductor substrate such as may be used. Further, the material of the semiconductor substrate is not limited to single crystal silicon, and other materials such as polycrystalline silicon may be used.

  The removal of the slice damage can be performed, for example, by etching the surface of the single crystal silicon after slicing with a mixed acid of hydrogen fluoride aqueous solution and nitric acid or an alkaline aqueous solution such as sodium hydroxide.

  In addition, the thickness T of the n-type silicon substrate 1 is 300 μm or less. However, the n-type silicon substrate 1 has a strength that can withstand application to a solar cell, and from the viewpoint of reducing the manufacturing cost by reducing the thickness, The thickness T is preferably 100 μm or more and 150 μm or less.

  Next, as shown in FIG. 2, a step of forming a silicon nitride film 2 on the first surface 1a of the n-type silicon substrate 1 is performed. Here, as the silicon nitride film 2, an amorphous silicon nitride film in which the content ratio of nitrogen atoms (N atoms) to silicon atoms (Si atoms) (the number of N atoms / the number of Si atoms) is 1.3 or more and 2 or less is used. It is formed.

  As a result of intensive studies by the present inventors, the silicon nitride film 2 in which the content ratio of N atoms to Si atoms (the number of N atoms / the number of Si atoms) is 1.3 or more and 2 or less is formed. This is because it has been found that the following points (i) to (iii) are advantageous.

  (I) Since the silicon nitride film 2 can be formed by a low temperature process such as a plasma CVD (Chemical Vapor Deposition) method or a sputtering method, the n-type silicon substrate 1 is formed at 900 ° C. to 1200 ° C. like a conventional thermal oxidation method. There is no need to heat at a high temperature such as ° C. Thereby, since the deterioration of the lifetime of the minority carrier in the n-type silicon substrate 1 can be suppressed, the characteristics of the solar cell can be improved as compared with the case where the conventional thermal oxidation method is used.

  (Ii) Even when the thickness t of the silicon nitride film 2 is 10 nm or more and 40 nm or less, preferably 20 nm or more and 30 nm or less, the silicon nitride film 2 can function as a mask for an alkaline aqueous solution used for forming a texture structure described later. Thereby, compared with the conventional case where the silicon oxide film is formed to a thickness of 750 nm, the curvature of the n-type silicon substrate 1 due to the thickness of the silicon nitride film 2 can be suppressed. A solar cell can be manufactured more easily than when a silicon oxide film is used.

  (Iii) By setting the content ratio of N atoms to Si atoms in the silicon nitride film 2 (the number of N atoms / the number of Si atoms) to be 1.3 or more and 2 or less, the etching rate for the hydrogen fluoride aqueous solution can be increased. . As a result, the silicon nitride film 2 can be removed with an aqueous hydrogen fluoride solution after the formation of the texture structure described later, and therefore there is no need to remove the silicon nitride film 2 using phosphoric acid.

When the silicon nitride film 2 is formed by plasma CVD, for example, a silane (SiH ₄ ) gas as a silicon source, ammonia (NH ₃ ) gas as a nitrogen source, and a carrier gas are contained in the plasma CVD apparatus. As a hydrogen (H ₂ ) gas.

Here, in order to set the content ratio of N atoms to Si atoms in the silicon nitride film 2 (the number of N atoms / the number of Si atoms) to be 1.3 or more and 2 or less, the supply amount ratio of NH ₃ gas to SiH ₄ gas [ (Volume ratio of NH ₃ gas) / (Volume ratio of SiH ₄ gas)] is preferably 6 or more and 12 or less. Further, it is preferable that the supply amount of H ₂ gas is approximately the same as the supply amount of SiH ₄ gas.

  Moreover, the pressure of the atmosphere in the plasma CVD apparatus when forming the silicon nitride film 2 can be set to, for example, 50 Pa to 70 Pa. Further, the power applied to the plasma CVD apparatus when forming the silicon nitride film 2 can be set to 0.5 kW to 1 kW, for example. Moreover, the temperature of the n-type silicon substrate 1 at the time of forming the silicon nitride film 2 can be set to 300 ° C. to 500 ° C., for example.

Further, when the silicon nitride film 2 is formed by the sputtering method, a silicon target is installed in the sputtering apparatus, and for example, nitrogen (N ₂ ) gas as a nitrogen source and a rare gas as a carrier gas are supplied. In the embodiment, argon (Ar) gas is supplied. Here, in order to set the content ratio of N atoms to Si atoms in the silicon nitride film 2 (N atom number / Si atom number) to 1.3 or more and 2 or less, supply amount of N ₂ gas and supply of Ar gas The ratio (volume ratio) to the amount is preferably N ₂ gas: Ar gas = 1 to 0.6: 0 to 0.4. Note that when the silicon nitride film 2 is formed by the sputtering method, the gas supplied into the sputtering apparatus is one or both of nitrogen gas and ammonia gas, or one of nitrogen gas and ammonia gas, or It is preferable to use a mixed gas of both and a rare gas.

  Further, the pressure of the atmosphere in the sputtering apparatus when forming the silicon nitride film 2 can be set to 0.5 Pa to 10 Pa, for example. The power applied to the sputtering apparatus when forming the silicon nitride film 2 can be set to 5 kW to 15 kW, for example. Moreover, the temperature of the n-type silicon substrate 1 at the time of forming the silicon nitride film 2 can be set to 25 ° C. to 500 ° C., for example.

  Next, as shown in FIG. 3, a step of forming the texture structure 3 on the second surface 1b of the n-type silicon substrate 1 is performed. The step of forming the texture structure 3 includes, for example, an n-type silicon substrate 1 using an etching solution obtained by heating a solution obtained by adding isopropyl alcohol to an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide to 70 ° C. or more and 80 ° C. or less. This can be done by etching the second surface 1b.

  Here, in the present embodiment, as described above, the silicon nitride film 2 in which the content ratio of N atoms to Si atoms (the number of N atoms / the number of Si atoms) is 1.3 or more and 2 or less is the texture structure 3. Since it is used as a mask at the time of formation, even when the thickness t of the silicon nitride film 2 is a thin film of 10 nm to 40 nm, preferably 20 nm to 30 nm, it can function as a mask for an alkaline aqueous solution. Therefore, since the curvature of the n-type silicon substrate 1 can be suppressed as in the conventional case, the solar cell can be easily manufactured as compared with the case of using the conventional silicon oxide film by the atmospheric pressure CVD method.

  Next, as shown in FIG. 4, a step of removing the silicon nitride film 2 using a liquid containing an aqueous hydrogen fluoride solution is performed. The step of removing the silicon nitride film 2 can be performed, for example, by immersing the silicon nitride film 2 in an aqueous hydrogen fluoride solution and etching the silicon nitride film 2.

  Here, in this embodiment, the silicon nitride film 2 in which the content ratio of N atoms to Si atoms (the number of N atoms / the number of Si atoms) is 1.3 or more and 2 or less is used as a mask when forming the texture structure 3. Since it uses, the etching rate with respect to hydrogen fluoride aqueous solution can be made higher than before.

  Usually, phosphoric acid is used to remove the silicon nitride film, but in this embodiment, since the silicon nitride film 2 can be removed by using an aqueous hydrogen fluoride solution, the silicon nitride film is made using phosphoric acid. There is no need to remove 2. This is advantageous in that the following problems (a) and (b) do not occur when the silicon nitride film is removed using phosphoric acid.

  (A) In the manufacturing process of a crystalline solar cell using crystalline silicon as a semiconductor substrate, processing using phosphoric acid is not usually performed. Therefore, when a treatment using phosphoric acid is performed, a new chemical solution is added, resulting in a complicated factory system and an increase in manufacturing cost. In particular, when it is necessary to immerse hundreds of thousands of semiconductor substrates per day, the amount of the chemical solution used becomes enormous, resulting in a further increase in manufacturing cost.

  (B) When removing the silicon nitride film 2 using phosphoric acid, it must be treated at a high temperature (at least 100 ° C. and usually about 140 ° C. to 180 ° C.). There is a danger that the chemicals evaporate.

  Next, as shown in FIG. 5, a step of forming n-type impurity diffusion region 5 and p-type impurity diffusion region 6 on first surface 1a of n-type silicon substrate 1 is performed. The n-type impurity diffusion region 5 is formed by a method such as vapor phase diffusion using a gas containing an n-type impurity such as phosphorus or coating diffusion in which a solution containing an n-type impurity such as phosphorus is applied and then heated. be able to. The p-type impurity diffusion region 6 is formed by, for example, a vapor phase diffusion using a gas containing a p-type impurity such as boron, or a coating diffusion in which a solution containing a p-type impurity such as boron is applied and then heated. Can be formed.

  The n-type impurity diffusion region 5 and the p-type impurity diffusion region 6 are each formed in a strip shape extending to the front surface side and / or the back surface side of FIG. Are alternately arranged at predetermined intervals on the first surface 1a of the n-type silicon substrate 1.

  N-type impurity diffusion region 5 is not particularly limited as long as it includes an n-type impurity and exhibits n-type conductivity. The p-type impurity diffusion region 6 is not particularly limited as long as it includes a p-type impurity and exhibits p-type conductivity.

  Next, as shown in FIG. 6, a step of forming a passivation film 4 on the first surface 1 a of the n-type silicon substrate 1 is performed. Here, the step of forming the passivation film 4 can be performed by forming a silicon oxide film, a silicon nitride film, or a stacked body of a silicon oxide film and a silicon nitride film, for example, by a plasma CVD method.

  Next, as shown in FIG. 7, a step of forming an antireflection film 7 on the texture structure 3 of the n-type silicon substrate 1 is performed. Here, the step of forming the antireflection film 7 can be performed by forming a silicon nitride film or the like, for example, by plasma CVD.

  Next, as shown in FIG. 8, a step of forming contact holes 9 and 10 in the passivation film 4 formed on the first surface 1a of the n-type silicon substrate 1 is performed. Here, the contact hole 9 is formed so that the n-type impurity diffusion region 5 is exposed, and the contact hole 10 is formed so that the p-type impurity diffusion region 6 is exposed.

  Note that the contact hole 9 and the contact hole 10 are each formed by, for example, forming a resist pattern on the passivation film 4 with an opening in a portion corresponding to the formation position of the contact hole 9 and the contact hole 10 by using a photolithography technique. The method of removing the passivation film 4 from the opening of the pattern by etching or the like, or etching the passivation film 4 by applying an etching paste to the portion of the passivation film 4 corresponding to the location where the contact hole 9 and the contact hole 10 are formed and then heating. Then, it can be formed by a removal method or the like.

  Next, as shown in FIG. 9, a process of forming an n-type electrode 11 on the n-type impurity diffusion region 5 and forming a p-type electrode 12 on the p-type impurity diffusion region 6 is performed. Here, the n-type electrode 11 is formed in contact with the n-type impurity diffusion region 5 through the contact hole 9, and the p-type electrode 12 is in contact with the p-type impurity diffusion region 6 through the contact hole 10. It is formed.

Thus, the back electrode type solar battery cell according to the present embodiment is completed.
As described above, the resistance of the silicon oxide film formed by the thermal oxidation method to the alkaline aqueous solution is higher than the resistance of the silicon oxide film formed by the atmospheric pressure CVD method to the alkaline aqueous solution. Therefore, when a silicon oxide film formed by a thermal oxidation method is used as a mask when forming the texture structure, the thickness of the mask can be reduced.

  For example, in order to have a mask performance equivalent to the thickness of 750 nm of the silicon oxide film formed by the atmospheric pressure CVD method, the thickness of the silicon oxide film formed by the thermal oxidation method may be about 100 nm. However, the following problems occur.

  That is, when the silicon substrate is exposed to a high temperature during the formation of the silicon oxide film by the thermal oxidation method, the lifetime of minority carriers deteriorates and the power generation efficiency of the solar cell decreases. The reason why the lifetime of minority carriers is shortened is considered to be that, for example, impurities such as metals existing on the surface of the silicon substrate diffuse into the silicon substrate to become recombination centers of minority carriers.

  Such a phenomenon is particularly noticeable in a single crystal silicon substrate manufactured by the CZ method, and the occurrence of the phenomenon is higher in a single crystal silicon substrate manufactured by the FZ method than in a single crystal silicon substrate manufactured by the CZ method. It can be suppressed. Therefore, the recombination centers generated due to oxygen contained in the silicon substrate during the heat treatment are considered to affect the lifetime of minority carriers.

  In the present invention, a silicon nitride film can be formed by a plasma CVD method or a sputtering method, which is a lower temperature process than a thermal oxidation method. Therefore, deterioration of the minority carrier lifetime in the semiconductor substrate is suppressed, and high characteristics are achieved. It becomes possible to manufacture a solar cell having

  It should be noted that the concept of the back electrode type solar cell in the present invention includes only the structure in which both the n type electrode and the p type electrode are formed only on one surface side (back side) of the semiconductor substrate described above. Rather than so-called back contact solar cells (light-receiving surface side of solar cells) such as MWT (Metal Wrap Through) cells (solar cells having a configuration in which a part of an electrode is arranged in a through hole provided in a semiconductor substrate) All of the solar cells having a structure in which a current is taken out from the back side opposite to the front side.

  Moreover, in the above, although the case where the back electrode type solar cell was manufactured was explained, the present invention can be applied to other solar cells such as a double-sided electrode type solar cell other than the back electrode type solar cell. Needless to say.

(Production of silicon nitride film)
In the sputtering apparatus, a silicon target and an n-type single crystal silicon substrate having a thickness of 150 μm were placed at a predetermined distance so as to face each other. Then, by sputtering the silicon target while supplying N ₂ gas as a nitrogen source into the sputtering apparatus under the following film forming conditions, amorphous nitridation with a thickness of 26 nm is formed on the surface of the n-type single crystal silicon substrate. A silicon film was formed by a sputtering method. Thereafter, the surface of the silicon nitride film was immersed in a hydrogen fluoride aqueous solution having a hydrogen fluoride concentration of 1% by mass to remove the natural oxide film, thereby producing a silicon nitride film of Sample 1.

<Film formation conditions>
Pressure of atmosphere in sputtering apparatus: 0.9 Pa
Temperature of n-type single crystal silicon substrate: 25 ° C.
Supply amount ratio (volume ratio) of N ₂ gas and Ar gas: N ₂ gas: Ar gas = 1: 0
Power applied to the sputtering device: 12 kW
Similarly to the above, an amorphous silicon nitride film having a thickness of 26 nm is formed on the surface of an n-type single crystal silicon substrate having a thickness of 150 μm, and the silicon nitride film is heat-treated at 200 ° C. for 5 minutes in a nitrogen atmosphere. Then, the silicon nitride film of Sample 2 was fabricated by immersing the surface of the silicon nitride film in a hydrogen fluoride aqueous solution having a hydrogen fluoride concentration of 1 mass% to remove the natural oxide film.

(Elemental analysis)
The silicon nitride films of Sample 1 and Sample 2 produced as described above were subjected to elemental analysis by XPS (X-ray Photoelectron Spectroscopy) under the following measurement conditions. The results are shown in FIGS. 10 to 17, the horizontal axis represents the binding energy (eV), and the vertical axis in FIGS. 10 to 17 represents the strength (au). Moreover, in FIGS. 10-15, the analysis result of the sample 1 is shown by the continuous line, and the analysis result of the sample 2 is shown by the broken line.

<Measurement conditions>
Excitation X-ray: Al mono
Detection area: 100 μmφ
Extraction angle: 45 °
Detection depth: about 4-5 nm
11 is an enlarged view of a peak corresponding to the Si 2p orbit shown in FIG. 10, and FIG. 12 is an enlarged view of a peak corresponding to the N 1s orbit shown in FIG. 13 is an enlarged view of a peak corresponding to the O 1s orbit shown in FIG. 10, and FIG. 14 is an enlarged view of a peak corresponding to the 1s orbit of C shown in FIG. Further, FIG. 15 is an enlarged view of a peak corresponding to the 1s orbit of F shown in FIG.

  16 is a diagram in which peaks corresponding to 2p orbitals of Si in the XPS analysis of sample 1 shown in FIG. 10 are divided for each valence of Si, and FIG. 17 is an XPS analysis of sample 2 shown in FIG. It is the figure which divided the peak corresponding to 2p orbit of Si in every valence of Si. 16 and 17, Si1 to Si5 indicate that the following bonds and compounds are included, respectively.

<Si1-Si5>
Si1: Si-Si
Si2: valence small SiN _x, SiO _x or the like _{Si3: Si 3 N 4, SiO} x or the like Si4: SiON or the like Si5: _to, SiO ₂ Table 1, the elements of the sample 1 and Sample 2 calculated from FIGS. 10 to 15 The analysis results are shown.

  As shown in Table 1, sample 1 contains 37.2 atomic% Si and 53.1 atomic% N, and the ratio of the number of N atoms to the number of Si atoms (the number of N atoms / the number of Si atoms). Was confirmed to be 1.43.

  Further, as shown in Table 1, sample 2 contains 37.3 atomic% Si and 52.7 atomic% N, and the ratio of the number of N atoms to the number of Si atoms (N atoms / Si atoms) Number) was confirmed to be 1.41.

  Table 2 shows the area ratio (%) of each peak of Si1 to Si5 of Sample 1 and Sample 2 calculated from FIG. 16 and FIG.

  As shown in Table 2, in both Sample 1 and Sample 2, the peak corresponding to the Si 2p orbit was almost occupied by the Si3 and Si4 peaks indicating the presence of silicon nitride. Therefore, it was confirmed that Sample 1 and Sample 2 were each formed from silicon nitride.

(Alkali resistance)
About the sample 1 produced as mentioned above and the sample 2, the tolerance with respect to alkaline aqueous solution was evaluated, respectively.

  Specifically, a potassium hydroxide aqueous solution (liquid temperature 90 ° C.) having a potassium hydroxide concentration of 5% by mass was prepared, and Sample 1 and Sample 2 were each immersed in the potassium hydroxide aqueous solution for 900 seconds.

  As a result, both sample 1 and sample 2 were etched only to a thickness of 5 nm in 900 seconds, and it was confirmed that the etching rate with respect to the aqueous potassium hydroxide solution was about 0.006 nm / second.

  On the other hand, as a comparison, the resistance to an alkaline aqueous solution was also evaluated in the same manner as described above for a silicon oxide film formed by atmospheric pressure CVD, which was used as a mask when forming a conventional texture structure.

  As a result, the silicon oxide film formed by atmospheric pressure CVD, which was used as a mask for forming the conventional texture structure, was etched to a thickness of 5.56 nm in 1 second. It was confirmed that it was about 5.56 nm / second.

  Therefore, it was confirmed that Sample 1 and Sample 2 have resistance to an alkaline aqueous solution as compared with a conventional silicon oxide film formed by atmospheric pressure CVD, and are excellent as a mask when forming a texture structure.

  In consideration of the etching time during the formation of the texture structure, when Sample 1 and Sample 2 are used as masks during the formation of the texture structure, the thickness of Sample 1 and Sample 2 is preferably 10 nm or more and 40 nm or less, preferably It was confirmed that a thin film having a thickness of 20 nm to 30 nm is sufficient.

(Etching property for hydrogen fluoride aqueous solution)
About the sample 1 and the sample 2 which were produced as mentioned above, the etching property with respect to hydrogen fluoride aqueous solution was also evaluated, respectively.

  Specifically, a hydrogen fluoride aqueous solution having a hydrogen fluoride concentration of 2.5% by mass was prepared, and Sample 1 and Sample 2 each having a thickness of 26 nm were immersed in the hydrogen fluoride aqueous solution for 200 seconds.

  As a result, for both Sample 1 and Sample 2, all of the thickness of 26 nm was etched in 200 seconds, so that the etching rate for Sample 1 and Sample 2 with respect to the aqueous hydrogen fluoride solution was 0.13 nm / second. It was confirmed.

  On the other hand, as for the silicon nitride film used for the conventional passivation film, the 26 nm silicon nitride film could not be completely removed by etching with the hydrogen fluoride aqueous solution for 20 minutes or more. It was confirmed that the etching rate with respect to was less than 0.0217 nm / second.

  Therefore, it was confirmed that the etching rates of Sample 1 and Sample 2 with respect to the aqueous hydrogen fluoride solution can be significantly higher than the etching rates of the silicon nitride film used for the conventional passivation film with respect to the aqueous hydrogen fluoride solution.

As the silicon nitride film used in a conventional passivation film, and SiH ₄ gas supplied into the plasma CVD apparatus, and NH ₃ gas supply amount ratio of N ₂ gas (volume ratio), SiH ₄ gas : NH ₃ gas: N ₂ gas = 1: 3: 3 was used. Here, SiH ₄ gas is a silicon source, NH ₃ gas is a nitrogen source of silicon nitride, and N ₂ gas is mainly used as a carrier gas.

(Evaluation of other examples)
Except for changing the film forming conditions of the silicon nitride film by the sputtering method as described below, in the same manner as Sample 1, amorphous silicon nitride having a thickness of 26 nm on the surface of an n-type single crystal silicon substrate having a thickness of 150 μm. A membrane (Sample 3) was formed. Thereafter, the silicon nitride film of Sample 3 was evaluated in the same manner as described above for elemental analysis, alkali resistance, and etchability with respect to an aqueous hydrogen fluoride solution. As a result, it was confirmed that the same results as those of the sample 1 and sample 2 were obtained for the silicon nitride film of Sample 3.

<Film formation conditions>
Pressure of atmosphere in sputtering apparatus: 1Pa
Temperature of n-type single crystal silicon substrate: 25 ° C.
Supply amount ratio (volume ratio) of N ₂ gas and Ar gas: N ₂ gas: Ar gas = 0.85: 0.15
Power applied to the sputtering device: 11 kW
In addition, an n-type single crystal silicon substrate having a thickness of 150 μm is installed in the plasma CVD apparatus, and an amorphous silicon nitride film having a thickness of 26 nm (on the surface of the n-type single crystal silicon substrate ( Sample 4) was formed by plasma CVD. Then, the silicon nitride film of Sample 4 was evaluated in the same manner as described above for elemental analysis, alkali resistance, and etchability with respect to an aqueous hydrogen fluoride solution. As a result, it was confirmed that the same results as those of the sample 1 and sample 2 were obtained for the silicon nitride film of sample 4.

<Film formation conditions>
Pressure of atmosphere in plasma CVD apparatus: 66Pa
n-type single crystal silicon substrate temperature: 450 ° C.
Supply amount ratio (volume ratio) of SiH ₄ gas, NH ₃ gas, and N ₂ gas: SiH ₄ gas: NH ₃ gas: N ₂ gas = 1: 11: 10
Power applied to plasma CVD apparatus: 500W
Further, in addition to the above, an amorphous silicon nitride film having a thickness of 26 nm with different content ratios of N atoms to Si atoms (number of N atoms / number of Si atoms) on the surface of an n-type single crystal silicon substrate having a thickness of 150 μm. A plurality of were prepared by plasma CVD or sputtering. Each of these silicon nitride films was evaluated for elemental analysis, alkali resistance, and etching properties with respect to an aqueous hydrogen fluoride solution in the same manner as described above.

  As a result, for the silicon nitride film in which the content ratio of N atoms to Si atoms (the number of N atoms / the number of Si atoms) is in the range of 1.3 or more and 2 or less, the same results as in Samples 1 to 4 above are obtained. Although it was confirmed that the silicon nitride film outside the range where the content ratio of N atoms to Si atoms (N atom number / Si atom number) is not less than 1.3 and not more than 2, it is the same as Samples 1 to 4 above. It was confirmed that the results were not obtained.

A silicon nitride film having a content ratio of N atoms to Si atoms (the number of N atoms / the number of Si atoms) of 1.3 or more and 2 or less includes SiH ₄ gas, NH ₃ gas, and H ₂ gas in the plasma CVD apparatus. It was also confirmed that the film can be stably formed when the ratio (volume ratio) of the NH ₃ gas supply amount to the SiH ₄ gas supply amount is 6 or more and 12 or less.

  Further, regarding an n-type single crystal silicon substrate having a thickness of 150 μm on which a silicon nitride film in which the content ratio of N atoms to Si atoms (the number of N atoms / the number of Si atoms) is in the range of 1.3 to 2 is formed. In comparison with an n-type single crystal silicon substrate having a thickness of 150 μm on which a silicon nitride film having a content ratio of N atoms to Si atoms (number of N atoms / number of Si atoms) outside the range of 1.3 to 2 is formed, It was also confirmed that the bending of the n-type single crystal silicon substrate was suppressed.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention may be suitably used for a texture structure forming method and a solar cell manufacturing method.

  1 n-type silicon substrate, 1a first surface, 1b second surface, 2 silicon nitride film, 3 texture structure, 4 passivation film, 5 n-type impurity diffusion region, 6 p-type impurity diffusion region, 7 antireflection film, 9, 10 Contact hole, 11 n-type electrode, 12 p-type electrode.

In the present invention, a step of forming a silicon nitride film on a first surface, which is one surface of a semiconductor substrate having a thickness of 300 μm or less, and a second surface opposite to the first surface of the semiconductor substrate are etched. A texture structure forming step, and the content ratio of nitrogen atoms to silicon atoms in the silicon nitride film is 1.41 or more and 2 or less.

Furthermore, the present invention provides a step of forming a silicon nitride film on a first surface, which is one surface of a silicon substrate having a thickness of 300 μm or less, and a second surface opposite to the first surface of the silicon substrate. A step of forming a texture structure by etching, a step of removing the silicon nitride film using an aqueous hydrogen fluoride solution, a step of forming an impurity diffusion layer on the first surface of the silicon substrate, and an impurity diffusion layer on the impurity diffusion layer And a step of forming an electrode, wherein the content ratio of nitrogen atoms to silicon atoms in the silicon nitride film is 1.41 or more and 2 or less.

Claims (11)

Forming a silicon nitride film on a first surface which is one surface of a semiconductor substrate having a thickness of 300 μm or less;
Forming a texture structure by etching a second surface of the semiconductor substrate opposite to the first surface;
The method for forming a texture structure, wherein a content ratio of nitrogen atoms to silicon atoms in the silicon nitride film is 1.3 or more and 2 or less.   The method for forming a texture structure according to claim 1, further comprising a step of removing the silicon nitride film using an aqueous hydrogen fluoride solution.   3. The method for forming a texture structure according to claim 1, wherein in the step of forming the silicon nitride film, the silicon nitride film is formed to a thickness of 10 nm to 40 nm.   The method for forming a texture structure according to claim 1, wherein in the step of forming the silicon nitride film, the silicon nitride film is formed by a plasma CVD method or a sputtering method. The plasma CVD method is performed by supplying silane gas as a silicon source and supplying ammonia gas as a nitrogen source,
The texture structure forming method according to claim 4, wherein the silane gas and the ammonia gas are respectively supplied such that a volume ratio of the ammonia gas to the silane gas is 6 or more and 12 or less.   The sputtering method is performed by sputtering the target in an atmosphere containing one or both of nitrogen gas and ammonia gas, or in an atmosphere containing one or both of nitrogen gas and ammonia gas and a rare gas. The method for forming a texture structure according to claim 4. Forming a silicon nitride film on a first surface which is one surface of a silicon substrate having a thickness of 300 μm or less;
Forming a textured structure by etching a second surface of the silicon substrate opposite to the first surface;
Removing the silicon nitride film using an aqueous hydrogen fluoride solution;
Forming an impurity diffusion layer on the first surface of the silicon substrate;
Forming an electrode on the impurity diffusion layer,
The method for manufacturing a solar cell, wherein a content ratio of nitrogen atoms to silicon atoms in the silicon nitride film is 1.3 or more and 2 or less.   The method for manufacturing a solar cell according to claim 7, wherein in the step of forming the silicon nitride film, the silicon nitride film is formed to a thickness of 10 nm to 40 nm.   The method for manufacturing a solar cell according to claim 7 or 8, wherein in the step of forming the silicon nitride film, the silicon nitride film is formed by a plasma CVD method or a sputtering method. The plasma CVD method is performed by supplying silane gas as a silicon source and supplying ammonia gas as a nitrogen source,
10. The method for manufacturing a solar cell according to claim 9, wherein the silane gas and the ammonia gas are supplied such that a volume ratio of the ammonia gas to the silane gas is 6 or more and 12 or less.   The sputtering method is performed by sputtering a silicon target in an atmosphere containing one or both of nitrogen gas and ammonia gas, or in an atmosphere containing one or both of nitrogen gas and ammonia gas and a rare gas. The method for manufacturing a solar cell according to claim 9.

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