JP2009272428A - Antireflective film coating method and antireflective film coating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high H<SB>2</SB>passivation effect in coating an antireflective film of a silicon nitride film. <P>SOLUTION: In coating the antireflective film of the silicon nitride film by a plasma, there are provided (a) a structure using a hollow cathode electrode as an electrode for forming the plasma, and (b) a structure in which an electric power to be supplied to the hollow cathode electrode is set to a low frequency of 100 KHz to 400 KHz. A high density plasma is formed by the hollow cathode electrode, and an efficiency of plasma dissociation caused by this high density plasma is enhanced, thereby enhancing a coating speed. By setting to the low frequency, an ion irradiation rate onto a semiconductor substrate of an H radical is raised, and the H<SB>2</SB>passivation effect of the semiconductor substrate is enhanced. Further, there are provided (c) a structure in which a distance between the semiconductor substrate and the hollow cathode electrode is proximity to each other, for example, ≤16 mm, and (d) a structure of increasing an applied electric power per electrode area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solar cell, a manufacturing method, and an antireflection film forming apparatus.

  2. Description of the Related Art A film forming apparatus that manufactures a thin film or the like by forming a film on a substrate is known. As such a film forming apparatus, there is a plasma CVD apparatus, which is used for manufacturing various semiconductors such as TFT arrays used for thin films for solar cells, photosensitive drums, liquid crystal displays, and the like.

A solar cell is generally composed of a semiconductor having a laminated structure of n-type silicon and p-type silicon. When light strikes the semiconductor, electricity is generated by a photoelectric effect. In solar cells, in order to efficiently absorb sunlight, the light receiving surface of the solar cell is usually covered with an antireflection film. Conventionally, as an antireflection film of this kind, a method of forming by PVD method and vapor deposition method, a method of applying and depositing by spin-on method, spray method, dip method, and then by heat treatment, as well as a method of forming hydrogen by plasma CVD method. There is known a technique for forming a silicon nitride film containing silicon on a light receiving surface of a solar cell (Patent Document 1). In the plasma CVD method, a semiconductor substrate is heated at, for example, 550 ° C. by parallel plate plasma CVD to form a silicon nitride film (SiN _x ) for an antireflection film.

  In addition, a passivation effect is known in which hydrogen in a silicon nitride film, which is an antireflection film of a solar cell, is diffused into the silicon substrate of the solar cell and the efficiency of the solar cell is increased (Patent Document 2).

  It is common to form a silicon nitride film by using a parallel plate plasma CVD apparatus to form an antireflection film, but when processing a large area substrate, an electrode corresponding to this large area is used. However, there is a problem that abnormal discharge is likely to occur, and since the electrode structure is complicated, it is difficult to obtain a frequency region suitable for high-density plasma.

In the silicon nitride films of Patent Document 1 and Patent Document 2, the concentration of hydrogen in silicon nitride is adjusted according to the film formation conditions during film formation by plasma CVD. For this reason, if an attempt is made to increase the content of hydrogen in silicon nitride in order to enhance the H ₂ passivation effect, the amount of reaction gas used during film formation increases and control of film formation conditions becomes difficult. There was a problem of causing a decline in sex.

In Patent Document 2, in order to increase of H ₂ passivation effect, to be taken as the deposition temperature and 350 ° C. or higher. For this reason, there is a problem that the amount of products adhering to the inside of the plasma CVD apparatus increases and the frequency of cleaning in the plasma CVD apparatus increases.

Further, it is known that a silicon nitride film (SiN _x ) having a high H ₂ passivation effect can be obtained by processing at a low frequency.

  In order to form a dense film, it is necessary to form a uniform temperature distribution by good thermal diffusion. Good thermal diffusion can be obtained by increasing the temperature, but when it is performed at a high temperature, as described above, the amount of products adhering to the inside of the plasma CVD apparatus increases and the frequency of maintenance increases. Will occur.

In the formation of a silicon nitride film (SiN _x ) using plasma, in order to form a silicon nitride film having a high H ₂ passivation effect without increasing the temperature of the plasma CVD apparatus, the inventors of the present invention A film forming method using surface wave plasma has been proposed (Patent Document 3).

In addition, there has been proposed a plasma processing apparatus that forms high-density plasma with a hollow cathode electrode (Patent Documents 4 and 5).
JP 2000-299482 A JP 2003-273382 A JP 2005-340358 A JP 2004-353066 A JP 2005-72347 A

When a silicon nitride film (SiN _x ) for an antireflection film of a solar cell is formed by plasma treatment, a high temperature film formation of, for example, 450 ° C. or more is necessary. In the plasma treatment, when the film formation rate is increased at a low temperature film formation (for example, 400 ° C.) or lower, there is a problem that the H ₂ passivation effect is insufficient for a target film thickness of 800 mm.

  In order to solve such a problem, in Patent Document 3 described above, in manufacturing a solar cell in which an antireflection film of a silicon nitride film is formed on the light receiving surface side of a crystalline silicon substrate, the silicon nitride film is subjected to surface wave plasma treatment The processing temperature is lowered by heat-treating the formed silicon nitride film in an atmosphere containing hydrogen.

  According to this treatment, although the treatment temperature can be lowered, the silicon nitride film is heat-treated in an atmosphere containing hydrogen in addition to the film-forming process and film-forming means for forming the silicon nitride film by a high-density plasma CVD method. This requires a heat treatment process and heat treatment means to increase the number of processes and components.

Although Patent Documents 4 and 5 disclose a technique for forming a high-density plasma using a hollow cathode electrode and performing film formation by plasma processing, a silicon nitride film (SiN film) for an antireflection film of a solar cell is disclosed. There is no disclosure of H ₂ passivation treatment when forming _x ).

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above problems and obtain a high H ₂ passivation effect in the formation of an antireflection film of a silicon nitride film.

The present invention, in the formation of an antireflection film of a silicon nitride film by plasma,
(A) a configuration using a hollow cathode electrode as an electrode for forming plasma;
(B) A configuration in which the power supplied to the hollow cathode electrode is a low frequency of 100 KHz to 400 KHz,
Is provided.

  A high-density plasma is formed by the hollow cathode electrode, the efficiency of plasma separation by this high-density plasma is increased, and the deposition rate is improved.

By making the frequency low, the ion irradiation rate of the H radical to the semiconductor substrate is increased, and the H ₂ passivation effect of the semiconductor substrate is enhanced. The H ₂ passivation effect terminates dangling bonds existing in the Si semiconductor substrate with H ₂ and slows the recombination rate of carriers in the semiconductor substrate, thereby improving the conversion efficiency of the solar cell.

further,
(C) a configuration in which the distance between the semiconductor substrate and the hollow cathode electrode is close to, for example, 16 mm or less;
(D) The structure which increases the applied electric power per electrode area unit is provided.

By adding the configurations of (c) and (d), the H ₂ passivation necessary for H ₂ passivation is diffused in the substrate to promote grain boundary passivation using H ₂ and to improve the H ₂ passivation effect. be able to.

According to the present invention, a high H ₂ passivation effect can be obtained in the formation of the antireflection film of the silicon nitride film.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, a solar cell according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of a solar cell according to an embodiment of the present invention. The solar cell 100 includes a p-type silicon substrate layer 101, an n-type diffusion layer 102, a p ⁺ back side impurity diffusion layer 103, an antireflection film 104, a front surface electrode 105, a back surface electrode 106, and solder layers 107 and 108. The p-type silicon substrate layer 101 is formed of a silicon substrate manufactured by adding a small amount of a trivalent element such as boron. The p-type silicon substrate layer may be monocrystalline or polycrystalline. The n-type diffusion layer 102 is formed by diffusing phosphorus as an n-type dopant on the surface of the p-type silicon substrate, and a pn bond is formed by the p-type silicon substrate layer 101 and the n-type diffusion layer 102. The p ⁺ back side impurity diffusion layer 103 is formed by diffusing aluminum as a p-type dopant on the surface of the p-type silicon substrate. The antireflection film 104 is formed by depositing silicon nitride (SiN _x ) on the surface of the p-type silicon substrate layer 101. Here, silicon nitride (SiN _x ) is formed on the surface of the n-type diffusion layer 102 formed on the surface of the p-type silicon substrate layer 101. Further, Ag electrodes are used for the surface electrode 105 and the back electrode 106 for the surface of the n-type diffusion layer 102 and the p ⁺ back side impurity diffusion layer 103.

  Hereinafter, the manufacturing method of the solar cell of this Embodiment is demonstrated, referring the flowchart of FIG.

  First, a surface treatment is performed to form a fine concavo-convex structure on the surface of the p-type silicon substrate 101. For this surface treatment, for example, a method of etching with an alkaline aqueous solution or a method of reactive ion etching can be used. By forming a fine relief structure on the surface of the silicon substrate, reflection of light on the surface of the silicon substrate can be suppressed (S1).

An n-type dopant is diffused from the surface of the p-type silicon substrate 101 to form an n-type diffusion layer 102. For example, phosphorus (P) is used as the n-type dopant. Examples of the method for diffusing phosphorus on the surface of the p-type silicon substrate include a vapor phase diffusion method using POCl ₃ , a coating diffusion method using P ₂ O _5, and an ion implantation method for directly diffusing P ions ( S2).

  Etching is performed to remove the n-type diffusion layer on one surface of the p-type silicon substrate 101 in which the n-type dopant is diffused (S3).

A p-type dopant is diffused from the surface of the etched p-type silicon substrate 21 to form a p ⁺ back side impurity diffusion layer 103. For example, aluminum (Al) is used as the p-type dopant. Al paste is applied to the surface of the etched p-type silicon substrate 101, and heat treatment is performed to diffuse aluminum into the surface of the p-type silicon substrate 101 (S4).

H ₂ gas (hydrogen gas) or NH ₃ gas (ammonia gas) is introduced into the surface of the n-type diffusion layer 102 and plasma treatment is performed using a low frequency of 250 KHz to perform H ₂ passivation. The low frequency can be in the range of 100 to 400 KHz (S5). Thereafter, an antireflection film 24 is formed on the semiconductor surface. A silicon nitride film (SiN _x ) is accumulated as an antireflection film (S6).

  The front electrode 105 and the back electrode 106 are patterned. The patterning is performed by screen printing an Ag paste made of Ag powder, a binder, and a frit. In order to increase the efficiency of the solar cell, the electrode is formed in a comb pattern (S7).

  The printed Ag paste is baked to form an electrode (S8). The solder layers 107 and 108 are formed by a solder dipping method (S9).

In the antireflection film forming apparatus, H2 passivation is performed on the semiconductor substrate surface of the solar cell completed in the manufacturing process up to S4 in the plasma processing process in S5, and silicon nitride (SiN _x ) is formed in the film forming process in S6. A film is formed to form the antireflection film 104.

Next, H ₂ passivation by plasma treatment and film formation of an antireflection film will be described. In addition, the solar cell completed by the manufacturing process of S2 is called the board | substrate before anti-reflective film formation here for convenience.

FIG. 3 shows a schematic configuration of the antireflection film forming apparatus 1 of the present invention. In FIG. 3, the antireflection film forming apparatus 1 can be composed of a vacuum heating chamber 10, a film forming chamber 20 including a plasma device, and an unload chamber 30. The vacuum heating chamber 10 heats the substrate carried into the chamber to a predetermined temperature in a vacuum state, and carries it out to the film forming chamber 20. The film formation chamber 20 has a plasma apparatus, and the surface of the substrate carried in from the vacuum heating chamber 10 is subjected to plasma treatment at a low frequency to perform H ₂ passivation, and a silicon nitride film is formed on the surface with high density plasma. . The substrate processed in the film formation chamber 20 is sent to the unload chamber 30 and then carried outside.

  The film forming chamber 20 includes an antireflection film forming apparatus in which a plasma CVD apparatus is provided inside the chamber 2, and the inside of the chamber 2 is evacuated by evacuation by a vacuum exhaust apparatus.

  The plasma CVD apparatus forms a silicon nitride film on the substrate surface before the formation of the antireflection film. Note that by providing the transfer device, the substrate before forming the antireflection film is carried into the plasma CVD apparatus in the chamber, and the substrate on which the silicon nitride film is formed by the plasma CVD apparatus is carried out of the chamber.

  Hereinafter, the configuration of the film forming chamber of the antireflection film forming apparatus will be described with reference to the schematic diagram shown in FIG.

  In FIG. 4, the antireflection film forming apparatus 1 includes two electrodes (3, 4) in a chamber 2, a vacuum exhaust pipe 2c for evacuating the chamber 2, and a process gas and a material gas in the chamber 2. And an introduction port 2b to be introduced.

The chamber 2 is reflected on the surface of the semiconductor substrate 6 by performing an H ₂ passivation process performed by irradiating the semiconductor substrate 6 with ions and a film forming process for generating a SiN _x film by plasma generated in the internal space. This is an airtight container for preventing film formation, and is provided with a vacuum exhaust pipe 2c for evacuating the inside, and is evacuated by a vacuum pump (not shown). Further, a sample stage (not shown) for holding the semiconductor substrate 6 and a heater (not shown) for heating the semiconductor substrate may be provided in the chamber 2. Moreover, it is good also as a structure which cools and a structure which applies an electric field as needed.

The chamber 2 includes an upper lid portion 2a that seals the inside of the chamber 2. The upper lid 2a is provided with a gas introduction port 2b for introducing process gas, H ₂ passivation gas, and material gas into the chamber 2.

For example, a process gas such as Ar gas, H ₂ gas (hydrogen gas), or NH ₃ gas (ammonia gas) is connected to the gas inlet 2b through a regulating valve (not shown) from a mass flow controller (not shown). The material gas such as H ₂ passivation gas, SiH ₄ gas, Si ₂ H ₆ gas or the like is introduced.

In the chamber 2, two electrodes of a hollow cathode electrode 3 and a substrate electrode 4 are arranged to face each other, and a semiconductor substrate is formed by high-density plasma formed in a space 2 d sandwiched between the hollow cathode electrode 3 and the substrate electrode 4. 6 is subjected to H ₂ passivation treatment and SiN _x film formation treatment.

  The hollow cathode electrode 3 has a plurality of electrode holes 3a, and communicates between a space 2e and a space 2d formed with the hollow cathode electrode 3 interposed therebetween. On the other hand, the substrate electrode 4 is an electrode that supports the semiconductor substrate 6, and is disposed in the hollow cathode electrode 3 so as to face the surface on the wide diameter side of the electrode hole 3 a. The substrate electrode 4 may be disposed on a sample stage (not shown), and a heater (not shown) may be provided inside the sample stage.

  A high frequency power source 5 is connected between the hollow cathode electrode 3 and the substrate electrode 4, and low frequency power is supplied between the hollow cathode electrode 3 and the substrate electrode 4.

  In addition, the distance between the hollow cathode electrode 3 and the substrate electrode 4 is set so close that the distance between the hollow cathode electrode 3 and the semiconductor substrate 6 placed on the substrate electrode 4 is, for example, 16 mm or less.

Plasma is generated by supplying high-frequency power between the hollow cathode electrode 3 and the substrate electrode 4, and H ₂ gas (hydrogen gas) or NH ₃ gas (ammonia gas) is introduced from the gas inlet ₂ b. A gas is introduced between the hollow cathode electrode 3 and the substrate electrode 4 through the electrode hole 3a, and H ₂ is generated by the separation of the plasma radicals. This H ₂ promotes grain boundary passivation and performs H ₂ passivation treatment.

In this H ₂ passivation treatment, the ion irradiation rate is improved by supplying low frequency power of 100 KHz to 400 KHz between the hollow cathode electrode 3 and the substrate electrode 4. Furthermore, by increasing the distance between the hollow cathode electrode 3 and the substrate electrode 4 and increasing the applied power per unit electrode area, the ion irradiation rate can be further improved.

Of the film forming gas introduced into the chamber 2, the process gas is a gas that is a raw material for reactive active species such as N ₂ gas, O ₂ gas, H ₂ gas, NO ₂ gas, NO gas, and NH ₃ gas. In addition, there are rare gases such as Ar gas, He gas, Ne gas, Kr gas, and Xe gas. In addition, the material gas in the film forming gas is a gas containing Si element which is a component of a silicon thin film or a silicon compound thin film such as SiH ₄ gas or Si ₂ H ₆ gas.

  The exhaust port 2c provided in the chamber 21 can maintain the interior of the chamber 2 at a predetermined pressure by exhausting the gas introduced into the chamber 2 through the gas introduction port 2b at a predetermined flow rate.

In the formation of the antireflection film, the present invention generates low-energy and high-density plasma by supplying low-frequency power to the hollow cathode electrode 3, and gas is generated in the low-energy region of the high-density plasma. H ₂ gas (hydrogen gas) or NH ₃ gas (ammonia gas) is introduced through the introduction port 2b and the electrode hole 3a to generate radicals, and H ₂ passivation is performed by this plasma treatment.

  Thereafter, Ar gas is introduced into the high-density plasma between the hollow cathode electrode 3 and the semiconductor substrate 6 through the gas inlet 2b and the electrode hole 3a to generate radicals, and by introducing the material gas, low damage is caused. Perform high-speed film formation.

FIG. 5 illustrates details of the H ₂ passivation process using the H ₂ gas or NH ₃ gas of S5 and the film forming process of forming a silicon nitride (SiN _x ) film of S6 in the flowchart of FIG. It is a flowchart for.

In the H ₂ passivation treatment step, first, the chamber 2 is evacuated (S5a), H ₂ gas or NH ₃ gas (ammonia gas) is introduced from the gas inlet 2b (S5b), and low frequency high frequency power is supplied. Is supplied between the hollow cathode electrode 3 and the substrate electrode 4 to generate radicals, and this plasma treatment promotes grain boundary passivation to promote H ₂ passivation.

The conditions of the plasma treatment with NH ₃ gas (ammonia gas) are, for example, 20 sccm for NH ₃ gas (ammonia gas), 80 sccm for N ₂ gas, 700 kw for power, and 0 for the pressure in the chamber. .5 Torr, the distance between the hollow cathode electrode 3 and the substrate electrode 4 can be 16 mm.

Next, after the H2 passivation treatment, the gas introduced from the gas inlet 2b is switched from NH ₃ gas (ammonia gas) to process gas (Ar gas) (S6a), and a material gas (for example, SiH ₄ gas) is introduced. (S6b), an antireflection film is formed on the surface of the semiconductor substrate subjected to H ₂ passivation (S6c).

The film formation conditions of the antireflection film for forming the antireflection film having a refractive index of 2.20 are, for example, that the film formation temperature is 450 ° C., the amount of SiH ₄ gas is 18 sccm, and the amount of NH ₃ gas is 20 sccm. .

  Here, the electrode size is 240 mm in diameter. In the present invention, in order to form high-density plasma, the applied power per electrode unit area is increased. In the above condition example, the applied power per unit electrode area can be expressed as 700 kw / Φ240 mm.

As a phenomenon in which the effect of H ₂ passivation is enhanced by performing the plasma treatment before the formation of the antireflection film, for example, the substrate surface temperature is raised by performing the plasma treatment, and thermal diffusion of hydrogen contained in silicon nitride is caused. It can be promoted.

  In the present embodiment, the following operational effects are achieved.

After plasma processing is performed on the surface of the semiconductor substrate before the formation of the antireflection film with plasma of H ₂ gas (hydrogen) or NH ₃ gas (ammonia gas) using a plasma apparatus, an antireflection film of silicon nitride is formed on the surface of the semiconductor substrate. by forming, it can be enhanced with H ₂ passivation effect.

  Since the reaction gas is completely dissociated by the surface wave excitation plasma apparatus, the amount of products adhering to the inside of the surface wave excitation plasma apparatus is small. For this reason, the cleaning frequency of the surface wave excitation plasma apparatus is reduced.

In the film formation process, productivity can be improved by depositing a silicon nitride (SiN _x ) film at high speed by using high-density plasma.

  The film formation method of the antireflection film of the solar cell of the above embodiment can be modified as follows.

When forming a silicon nitride film with a plasma apparatus, SiH ₄ , NH ₃ , N ₂ gas may be used instead of SiH ₄ , NH ₃ , Ar gas.

  When performing heat treatment in the heating chamber, a hot plate or a sheath heater may be used instead of the lamp heater.

  The present invention is not limited to the thin film for solar cells, and can be applied to the deposition of a thin film on a substrate having similar deposition requirements.

It is sectional drawing of the solar cell by embodiment of this invention. It is a flowchart for demonstrating the manufacturing method of the solar cell of this Embodiment. It is a figure which shows schematic structure of the anti-reflective film forming apparatus of this invention. It is the schematic for demonstrating the structure of the antireflection film film-forming apparatus of this invention. It is a flowchart for explaining details of H ₂ passivated and the deposition process of the anti-reflection film of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Antireflection film-forming apparatus, 2 ... Chamber, 2a ... Upper cover part, 2b ... Gas introduction port, 2c ... Exhaust port, 2d, 2e ... Space, 3 ... Hollow cathode electrode, 3a ... Electrode hole, 4 ... Substrate electrode DESCRIPTION OF SYMBOLS 5 ... High frequency power supply, 6 ... Semiconductor substrate, 10 ... Vacuum heating chamber, 20 ... Deposition chamber, 30 ... Unload chamber, 100 ... Solar cell, 101 ... P-type silicon substrate, 102 ... N-type diffusion layer, 103 ... p ⁺ back side impurity diffusion layer, 104 ... antireflection film, 105 ... front electrode, 106 ... back electrode, 107, 108 ... solder layer, 110 ... substrate.

Claims (4)

In a film forming method for forming an antireflection film of a silicon nitride (SiN _x ) film on the surface of a solar cell,
Supply low frequency power from 100 KHz to 400 KHz to the hollow cathode electrode,
High-density plasma is generated by the hollow cathode electrode to increase the plasma separation efficiency of the process gas and improve the deposition rate,
Increasing the incidence efficiency of hydrogen ions on the semiconductor substrate by the low frequency to improve the H ₂ passivation effect,
A method for forming an antireflection film for a solar cell, comprising forming a silicon nitride (SiN _x ) film on a semiconductor substrate.   The incident efficiency of hydrogen ions to the semiconductor substrate is increased by bringing the semiconductor substrate close to a hollow cathode electrode to 16 mm or less and increasing the applied power per unit electrode area. A method for forming an antireflection film for a solar cell. In a film forming apparatus for forming an antireflection film of a silicon nitride (SiN _x ) film on a semiconductor surface of a solar cell,
A hollow cathode electrode and a substrate electrode;
A high frequency power source for supplying low frequency power between the hollow cathode electrode and the substrate electrode;
An antireflection film forming apparatus comprising: a gas source for introducing a plasma gas and a process gas between the hollow cathode electrode and the substrate electrode. The distance between the hollow cathode electrode and the substrate electrode is 16 mm or less,
The anti-reflection film forming apparatus according to claim 3, wherein the high-frequency power source supplies low-frequency power of 100 KHz to 400 KHz to the hollow cathode electrode.