JP2012124229A - Method of forming antireflection film using parallel flat plate type plasma cvd apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method with which it becomes possible to carry out termination processing of a dangling bond of a solar cell substrate in a solar cell production process with a high throughput.SOLUTION: In a termination process, plasma including a hydrogen ion is generated between a high-frequency electrode 6 and a substrate electrode 5 by supplying a first processing gas from a processing gas supply device 3 and applying high-frequency power at a first frequency from a high-frequency power source 2 to the high-frequency electrode 6, and a dangling bond of a solar cell substrate 8 is terminated by means of the hydrogen ion. Next, in a film formation process, plasma for forming an antireflection film on a surface of the solar cell substrate is generated between the high-frequency electrode and the substrate electrode by supplying a second processing gas from the processing gas supply device and applying high-frequency power at a second frequency, which is higher than the first frequency, from the high-frequency power source to the high-frequency electrode. The termination process and the film formation process are carried out in succession using a parallel flat plate type plasma CVD apparatus 1.

Description

  The present invention relates to a method for forming an antireflection film using a parallel plate type plasma CVD apparatus, and more particularly to a method for terminating dangling bonds at a substrate interface using a parallel plate type plasma CVD apparatus in the manufacture of solar cells. .

  In recent years, in the manufacture of solar cells and the like, there has been an increasing demand for reduction in manufacturing costs. For this reason, it is important to improve the throughput of an apparatus used for manufacturing a solar cell.

  In the manufacture of other semiconductor elements using a silicon-based material, dangling bonds exist on the surface of the silicon substrate. If an antireflection film or a passivation film is further formed without terminating the dangling bond after the formation of the transistor, the dangling bond traps carriers and causes a decrease in carrier mobility in the formed transistor. It is known that the performance of the element is degraded. In order to improve this, it is known to treat a silicon substrate with plasma containing hydrogen as a main component (see, for example, Patent Document 1).

  In particular, in a solar cell, when this dangling bond is combined with a polar molecule represented by water or an ionic molecule, not only the performance of the device becomes unstable, but also the efficiency and lifetime of the solar cell are greatly affected. In addition, the dangling bond termination process is required to be continuously performed in a manufacturing process that is as consistent as possible in order to improve throughput. In addition, a parallel plate type plasma CVD (PECVD) apparatus is most suitable for manufacturing a large area solar cell with high throughput, and since the electrode structure is simple, the cost as a manufacturing apparatus can be suppressed. The dangling bond termination process is also preferably performed in the manufacturing process using this PECVD apparatus.

In the manufacturing process of a solar cell substrate, termination of dangling bonds using hydrogen gas or hydrogen plasma is conventionally performed after an insulating film or a passivation film is formed on the substrate. This is because hydrogen plasma once dissociates in the process after terminating the dangling bonds by hydrogen plasma, so that an insulating film or a passivation film is generated and the substrate surface is stabilized before the termination process is performed. (See Patent Document 1).
Such processing is performed because these insulating films and passivation films are films other than SiN _x , and hydrogen gas or hydrogen plasma passes through these films, so that dangling bonds of the substrate can be terminated. This is because.

  In addition to this, there is known a method (see Patent Document 2) in which a hydrogen plasma treatment is performed from the back side of the substrate without a passivation film after the passivation film is formed on the semiconductor substrate. Speed improvement is difficult.

Since the SiN _x film is dense and does not transmit gas such as water vapor, when SiN _x is used for the antireflection film of the solar cell substrate, there is an advantageous characteristic that the pn junction is not affected from the outside. However, when a SiN _x film is used, hydrogen gas also does not pass through the SiN _x film. Therefore, in order to perform dangling bond termination treatment of the solar cell substrate with hydrogen gas, before forming the antireflection film, Must be done.

Termination treatment of dangling bonds by hydrogen plasma is performed by combining hydrogen ions in the hydrogen plasma with dangling bonds of the substrate. Since dangling bonds exist at the grain boundaries of the substrate, they exist not only on the substrate surface but also in the substrate. Therefore, in the processing of the substrate with hydrogen ions, it is necessary that the hydrogen ions penetrate into the substrate and terminate dangling bonds inside the substrate. For this purpose, it is important to accelerate hydrogen ions and implant ions into the substrate.
Although it is possible to use hydrogen ions by accelerating hydrogen ions as described in Patent Document 3 or using another additional acceleration method, the apparatus becomes complicated and expensive, and a large-area substrate is used. It is unsuitable for performing the above process uniformly, and it is necessary to use another acceleration method.
In the PECVD apparatus, a high frequency of 13.56 MHz is usually used for generating plasma. By generating plasma at a lower frequency, for example, 1 MHz or less instead of 13.56 MHz, ions in the plasma are sufficiently accelerated simultaneously with plasma generation, so that the accelerated ions are implanted into the substrate. It is known.
Patent Document 4 describes that although not a PECVD apparatus, plasma is generated by applying high-frequency power of 50 kHz to 500 kHz, and Si ions in the plasma are accelerated and implanted into the substrate. In this document, it is described that film formation of Si or the like is performed using the same apparatus. However, since a high frequency of 50 kHz to 500 kHz is used in all the steps, a large amount of high energy ion irradiation is performed. Therefore, although it is suitable for etching the substrate surface, the steps including the film formation are performed at a high throughput. Not suitable for doing.

JP-A-5-243273 JP 2005-175028 A JP 2008-274334 A JP 2008-38217 A

  In a conventional large area solar cell manufacturing method using a parallel plate type plasma CVD (PECVD) apparatus, the dangling bond termination treatment of the solar cell substrate can be performed at a high throughput in the manufacturing process of the solar cell. Can not.

(1) The invention described in claim 1 is a method for forming an antireflection film on a solar cell substrate, wherein a processing gas supply device that supplies a processing gas, a high-frequency power source that outputs high-frequency power, Surface of solar cell substrate using parallel plate type plasma CVD apparatus provided with substrate electrode for placing solar cell substrate in vacuum vessel and high-frequency electrode arranged opposite to said substrate electrode in vacuum vessel In the method of forming an antireflection film on the substrate, a first processing gas is supplied from a processing gas supply device, a high frequency power of a first frequency is applied from a high frequency power source to a high frequency electrode, and the high frequency electrode and the substrate electrode are A plasma containing hydrogen ions is generated between them, a dangling bond of the solar cell substrate is terminated by the hydrogen ions, and a second processing gas is supplied from the processing gas supply device. A high frequency power having a second frequency higher than the first frequency is applied to the high frequency electrode from the frequency power source, and plasma for forming an antireflection film on the solar cell substrate surface is generated between the high frequency electrode and the substrate electrode. A method for forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus, wherein a film forming step of forming an antireflection film on the surface of the solar cell substrate by plasma is continuously performed. .
(2) The invention described in claim 2 is the method for forming an antireflection film for a solar cell substrate according to claim 1, wherein the termination step is a plasma containing hydrogen ions that terminate dangling bonds of the solar cell substrate. Including a first step of supplying a first processing gas for generating gas from a processing gas supply device, and a second step of generating high-frequency power of a first frequency from a high-frequency power source. Is completed, a third step of switching to supply a second processing gas for forming an antireflection film on the solar cell substrate from the processing gas supply device, and a higher frequency than the first frequency from the high frequency power source It is the film-forming method of the anti-reflective film of the solar cell substrate using the parallel plate type plasma CVD apparatus characterized by including the 4th process which generates the high frequency electric power of a 2nd frequency.
(3) The invention according to claim 3 is the method of forming a solar cell substrate antireflection film according to claim 1 or 2, wherein the first processing gas for generating plasma containing hydrogen ions is NH. ₃ is a method for forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus, which is one of ₃ and H ₂ .
(4) The invention described in claim 4 is the method for forming an antireflection film for a solar cell substrate according to any one of claims 1 to 3, wherein plasma containing hydrogen ions is generated in the termination step. In this case, the output of the high-frequency power source is set to the first frequency of 50 kHz to 800 kHz, and in the film forming process, when generating the plasma for forming the antireflection film on the surface of the solar cell substrate, A method for forming an antireflection film on a solar cell substrate using a parallel plate plasma CVD apparatus, wherein the output power is set to a second frequency of 13.56 MHz.
(5) The invention according to claim 5 is the method for forming an antireflection film for a solar cell substrate according to any one of claims 1 to 4, wherein the antireflection film is SiN _x , and the SiN _x A solar cell using a parallel plate plasma CVD apparatus, wherein the second processing gas for generating plasma for forming the antireflection film is a mixed gas of SiH ₄ , NH ₃ and N ₂ This is a method of forming an antireflection film on a substrate.
(6) The invention described in claim 6 is a parallel plate type plasma CVD apparatus, a processing gas supply apparatus for supplying a processing gas, a high-frequency power source for applying high-frequency power to a high-frequency electrode, and a vacuum vessel A substrate electrode on which the solar cell substrate is placed, a high-frequency electrode disposed opposite to the substrate electrode in a vacuum vessel, a processing gas supply device, and a control circuit for controlling the high-frequency power source provided, the control circuit, (a) for generating plasma containing hydrogen ions between the high-frequency electrode and the substrate electrode, thereby terminating dangling bonds of the solar cell substrate by the hydrogen ion, any of NH ₃ and H ₂ (B) a high-frequency power source is controlled so that low-frequency high-frequency power is applied to the high-frequency electrode. After terminating the ring bond, to generate a plasma for depositing the antireflection film of SiN _x on the solar cell substrate surface between the high-frequency electrode and the substrate electrode, forming an antireflection film on the solar cell substrate surface by the plasma In order to form a film, the processing gas supply device is controlled so as to supply a mixed gas of SiH ₄ , NH ₃ and N _2, and the high frequency power source is controlled so that high frequency power is applied to the high frequency electrode. This is a parallel plate type plasma CVD apparatus.
(7) The invention according to claim 7 is the parallel plate type plasma CVD apparatus according to claim 6, wherein the frequency of the high-frequency power when terminating the dangling bond is 50 kHz to 800 kHz, and the antireflection of SiN _x The parallel plate type plasma CVD apparatus is characterized in that the frequency of the high-frequency power when forming the film is 13.56 MHz.

  According to the present invention, the dangling bond termination treatment of the solar cell substrate can be performed in a continuous process before the production of the antireflection film by using a parallel plate type plasma CVD apparatus. Can be manufactured.

It is a vertical sectional view explaining the outline of one embodiment of a parallel plate type plasma CVD apparatus used in the present invention. FIG. 2 is a horizontal sectional view of the parallel plate type plasma CVD apparatus of FIG. 1, and is a schematic view of the upper side (high-frequency electrode side) taken along line A2-A2 of FIG. FIG. 2 is a horizontal sectional view of the parallel plate type plasma CVD apparatus of FIG. 1, and is a schematic view of the lower side (substrate electrode side) taken along line A 4 -A 4 of FIG.

An embodiment of parallel plate type plasma CVD used in the present invention will be described with reference to FIGS.
The plasma CVD apparatus according to an embodiment of the present invention is a parallel plate type plasma CVD. As shown in FIGS. 1 and 2, a vacuum vessel (reaction chamber) 1, a high-frequency power source 2, and a processing gas supply unit 3 are used. And a vacuum pump 4. The high-frequency power source 2, the processing gas supply unit 3, and the vacuum pump 4 have a common configuration common to well-known plasma CVD apparatuses, and a description thereof is omitted here, and an internal configuration of the vacuum vessel 1 is described below. To do.

  Inside the vacuum vessel 1, a cart (substrate electrode) 5 and a high-frequency electrode 6 are provided so as to face the cart. High frequency power is supplied to the high frequency electrode 6 from the high frequency power source 2 through the wiring 7. The high frequency electrode 6 is provided with a gas discharge hole 6a communicating with the processing gas supply unit 3, the high frequency electrode 6 is provided with an electrode plate 6b, and the electrode plate 6b is provided with a plurality of pores 6c. The processing gas is discharged into the reaction chamber 1 from the plurality of pores 6c. Plasma is generated between the electrode plate 6 b of the high-frequency electrode 6 and the substrate electrode 5.

  In this apparatus, gases having different compositions are supplied in the case of dangling bond processing of the solar cell substrate and in the subsequent film formation processing of the antireflection film, and plasma suitable for these processing is generated. Further, the high frequency power source 2 switches the frequency and output of the high frequency power to be applied to the high frequency electrode 6 in accordance with the generation of plasma in each processing.

  A plurality of solar cell substrates 8 (hereinafter referred to as solar cell substrates 8) to be subjected to plasma treatment are carried into the reaction chamber 1 from a carry-in window (not shown) of the reaction chamber 1 while being mounted on the cart 5. . The cart 5 is grounded in the reaction chamber 1 and becomes a substrate electrode of a parallel plate type plasma apparatus. A plurality of heaters 9 for heating the substrate together with the cart are installed below the cart 5.

  A ground shield 10 is provided around the high-frequency electrode 6 so as to surround the high-frequency electrode 6 (see FIGS. 1, 2, and 3). The earth shield 10 functions to prevent the electric field between the high-frequency electrode 6 and the substrate electrode 5 from leaking outside from these electrodes, and to prevent the density of plasma generated between the high-frequency electrode 6 and the substrate electrode 5 from decreasing. Therefore, high-density plasma is generated in the space between the high-frequency electrode 6 and the substrate electrode 5 inside the earth shield 10, and this region becomes a processing region where plasma processing is performed. A plurality of solar cell substrates 8 to be plasma processed are processed in this region.

  The high-frequency power source 2, the processing gas supply unit 3, and the vacuum pump 4 are controlled by an external control device (not shown) to evacuate the vacuum vessel 1, supply the processing gas, and high-frequency power. May be applied. In particular, as will be described later, in the present invention, the processing gas is switched and the high-frequency power is switched at high frequency. Therefore, by performing these controls using this control device, the antireflection film for the solar cell substrate according to the present invention is used. Can be formed at a higher throughput.

  Here, the operation of the parallel plate type plasma CVD apparatus according to one embodiment of the present invention, the dangling bond termination treatment of the solar cell substrate 8 and the antireflection film forming method on the solar cell substrate 8 will be described.

The solar cell substrate 8 placed on the cart 5 as described above is carried into the reaction chamber 1, and the reaction chamber 1 is evacuated by the vacuum pump 4. The loaded solar cell substrate 8 is heated by the heater together with the cart 5 so that the substrate surface is adjusted to about 450 ° C. A dangling bond termination processing gas (H ₂ or NH ₃ ) of the solar cell substrate 8 is supplied from the processing gas supply unit 3 and is released into the reaction chamber 1 from the pores 6 c of the high-frequency electrode 6.

  At this time, a high frequency power of 50 kHz to 800 kHz having a frequency lower than 13.56 MHz normally used in a PECVD apparatus is applied to the high frequency electrode from the high frequency power source 2. As a result, plasma containing hydrogen ions (hydrogen plasma) is formed from the processing gas. At high frequency of this frequency, the generated ions in the plasma are also accelerated and decelerated following this frequency, so that the hydrogen ions near the solar cell substrate 8 are accelerated and injected into the substrate, and are also bonded to dangling bonds inside the substrate. And terminate them.

When the dangling bond process is completed, the high frequency power application is stopped.
Next, a film forming gas (SiH ₄ , NH ₃ , N ₂ ) for forming an antireflection film is supplied from the processing gas supply unit 3 and is released into the reaction chamber 1 from the pores 6 c of the high frequency electrode. The H ₂ or NH ₃ gas introduced into the reaction chamber 1 for dangling bond termination treatment is the same component as the film forming gas for forming the antireflection film, and the generation of plasma using the film forming gas is performed. In this case, the deposition gas is introduced into the reactor 1 after completion of the dangling bond termination process.

Next, high frequency power of 13.56 MHz is applied to the high frequency electrode 6 from the external high frequency power source 2, and reactive plasma is generated between the electrode plate 6 b and the cart 5 from the released film forming gas. The This plasma contains reactive neutral particles such as various ions and radicals, and these adhere to the solar cell substrate 8 and react to react with SiN _{x as} an antireflection film on the solar cell substrate. Film formation is performed.
When the film forming process is completed, the solar cell substrate 8 is removed from the reaction chamber 1 after the heat is removed, and then the cart 5 is unloaded from the reaction chamber 1 and the next processed solar cell substrate 8 reacts with the cart 5. It is carried into the chamber 1.

As described above, according to the present invention, the dangling bond process of the solar cell substrate 8 by hydrogen plasma in one apparatus, and subsequently the deposition process of the antireflection film of SiN _{x on} the solar cell substrate 8 is performed. Is done. According to the present invention, after the dangling bond treatment, it is not necessary to take the solar cell substrate out of the reaction chamber in order to form the antireflection film with another apparatus, so that the processing throughput of the solar cell substrate can be improved. Moreover, it becomes possible to protect the solar cell substrate surface without changing by forming an antireflection film immediately after the dangling treatment.

In the above-described embodiment of the present invention, only the dangling bond treatment of the solar cell substrate 8 has been described. It is possible to do with throughput. In addition, even if the plasma containing hydrogen ions used to terminate dangling bonds is a processing gas other than NH ₃ or H ₂ , hydrogen ions are not generated in the generated plasma unless it affects the characteristics of the solar cell. Anything included can be used.

Further, as an embodiment of the present invention has been described in example of forming an antireflection film made of SiN _x on the surface of the solar cell substrate 8, the present invention is not limited to the deposition of the SiN _x film, the process gas Is also effective when performing other types of film forming processes such as SiO ₂ and ITO. Therefore, it is not limited to the formation of an antireflection film for solar cells, but also for the formation of passivation films for solar cells and various semiconductor devices, the formation of sealing films for EL panels, and the formation of transparent electrode films for liquid crystals. It is valid.

  In the above description, the plasma for forming the antireflection film is normally 13.56 MHz. However, this plasma may be generated at a frequency other than this frequency. It should be noted that various ions including hydrogen ions cannot follow this frequency at frequencies in this region, and only electrons follow this frequency to efficiently ionize the processing gas to generate high-concentration plasma. The

1. Vacuum container (reaction chamber)
2. High frequency power source 3. Treatment gas supply 4 Vacuum pump
5. Cart (substrate electrode)
6. High frequency electrode
6a ... Gas discharge hole 6b ... Electrode plate 6c ... Pore 7 ... Wiring 8 ... Solar cell substrate 9 ... Heater 10 ... Earth shield 11 ... Upper protection plate 12 ... Lower protection plate

Claims (7)

A processing gas supply device for supplying a processing gas;
A high frequency power source that outputs high frequency power; and
A substrate electrode for placing a solar cell substrate in a vacuum vessel;
In the method of forming an antireflection film on the surface of a solar cell substrate using a parallel plate type plasma CVD apparatus provided with a high-frequency electrode disposed opposite to the substrate electrode in the vacuum vessel,
A first processing gas is supplied from the processing gas supply device, a high frequency power of a first frequency is applied from the high frequency power source to the high frequency electrode, and hydrogen ions are included between the high frequency electrode and the substrate electrode. A termination step of generating plasma and terminating dangling bonds of the solar cell substrate by the hydrogen ions;
Supplying a second processing gas from the processing gas supply device and applying a high-frequency power having a second frequency higher than the first frequency from the high-frequency power source to the high-frequency electrode; and the high-frequency electrode, the substrate electrode, A plasma for forming an antireflection film on the surface of the solar cell substrate is generated during the period, and a film forming step for forming the antireflection film on the surface of the solar cell substrate by the plasma is continuously performed. A method of forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus. In the film-forming method of the anti-reflective film of the solar cell substrate of Claim 1,
The termination step includes a first step of supplying a first processing gas for generating plasma containing hydrogen ions that terminate dangling bonds of the solar cell substrate from the processing gas supply device, and the high-frequency power source. A second step of generating high frequency power of the first frequency from
The film forming step is a third step of switching to supply a second processing gas for forming the antireflection film on the solar cell substrate from the processing gas supply device after the termination step is completed. And a fourth step of generating a high-frequency power having a second frequency higher than the first frequency from the high-frequency power source, and forming an antireflection film for a solar cell substrate using a parallel plate type plasma CVD apparatus Membrane method. In the film-forming method of the anti-reflective film of the solar cell substrate of Claim 1 or 2,
The first processing gas for generating the plasma containing hydrogen ions is either NH ₃ or H _2. The antireflection film for the solar cell substrate using the parallel plate type plasma CVD apparatus The film forming method. In the film-forming method of the antireflection film of the solar cell substrate according to any one of claims 1 to 3,
In the termination step, when generating the plasma containing the hydrogen ions, the output of the high-frequency power source is set to a first frequency of 50 kHz to 800 kHz,
In the film formation step, when generating plasma for forming an antireflection film on the surface of the solar cell substrate, the output power of the power supply unit is set to a second frequency of 13.56 MHz. A method of forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus. In the film-forming method of the antireflection film of the solar cell substrate according to any one of claims 1 to 4,
The antireflection film is SiN _x , and the second processing gas for generating plasma for forming the SiN _x antireflection film is a mixed gas of SiH ₄ , NH _3, and N _2. A method for forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus. A processing gas supply device for supplying a processing gas;
A high frequency power source for applying high frequency power to the high frequency electrode;
A substrate electrode for placing the solar cell substrate in a vacuum vessel;
A high frequency electrode disposed opposite to the substrate electrode in the vacuum vessel;
A control circuit for controlling the processing gas supply device and the high-frequency power source,
The control circuit includes:
(A) To generate plasma containing hydrogen ions between the high-frequency electrode and the substrate electrode, and to terminate dangling bonds of the solar cell substrate by the hydrogen ions, supply either NH ₃ or H ₂ Controlling the processing gas supply device to control the high-frequency power source so as to apply low-frequency high-frequency power to the high-frequency electrode,
(B) After terminating the dangling bond, plasma is generated between the high-frequency electrode and the substrate electrode to form a SiN _x antireflection film on the surface of the solar cell substrate. In order to form the antireflection film on the surface, the processing gas supply device is controlled so as to supply a mixed gas of SiH ₄ , NH ₃ and N _2, and high frequency high frequency power is applied to the high frequency electrode. A parallel plate type plasma CVD apparatus, wherein the high-frequency power source is controlled to be applied. In the parallel plate type plasma CVD apparatus according to claim 6,
The frequency of the high-frequency power when terminating the dangling bond is 50 kHz to 800 kHz, and the frequency of the high-frequency power when forming the SiN _x antireflection film is 13.56 MHz. A flat plate type plasma CVD apparatus.

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