JP2011233627A - Substrate processing method using parallel plate type plasma cvd device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of performing natural oxide film removal processing on a solar cell substrate with high throughput in a step of manufacturing a solar cell.SOLUTION: A method of forming an antireflection film on a surface of the solar cell substrate using the parallel plate type plasma CVD device comprises a removal step of generating plasma including nitrogen ions between a high frequency electrode and a substrate electrode by supplying first processing gas from a processing gas supply device and also applying high frequency electric power of first frequency from a high frequency power source to the high frequency electrode, and removing an oxide film on the solar cell substrate with the nitrogen ions; and a film formation step of generating plasma for forming the antireflection film on the surface of the solar cell substrate between the high frequency electrode and substrate electrode by supplying second processing gas from the processing gas supply device and also applying high frequency electric power of second frequency (>first frequency) from the high frequency power source to the high frequency electrode, and forming the antireflection film on the surface of the solar cell substrate with the plasma.

Description

  The present invention relates to a substrate processing method using a parallel plate type plasma CVD apparatus, and more particularly to a method for removing an oxide film at a substrate interface using a parallel plate type plasma CVD apparatus in the manufacture of a solar cell.

  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 a semiconductor element using a silicon-based material, since silicon is easily oxidized, a natural oxide film of about 1-5 nm is generally present on the surface of the silicon substrate. In particular, in a solar cell, if an antireflection film or a passivation film is further formed without removing the natural oxide film after the pn junction is formed, the mobility of the carrier is lowered, resulting in an open circuit voltage (VOC). It is known that the performance of the solar cell is reduced, for example, the In addition, if an oxide film remains, this becomes an obstacle, and a clean film such as an antireflection film or a passivation film using SiN _x or SiO ₂ is not formed. Therefore, the performance of these films may be deteriorated. It has become.

In recent years, apparatuses for removing oxide films by plasma etching have been commercialized, but these generate plasma using a fluorine-based gas mixture, mainly fluorine radicals in this plasma or activated fluorine-based ones. The surface oxide film is removed by gas (see, for example, Patent Document 1).
The oxide film removal method using fluorine radicals or activated fluorine-based gas can remove the natural oxide film on the substrate surface, but is not suitable for removing the oxide film at the particle interface inside the substrate.

  In particular, in a solar cell, processing is required to be performed continuously in as consistent a manufacturing process as possible in order to improve throughput. Moreover, the parallel plate type plasma CVD (PECVD) apparatus is suitable for manufacturing a large-area solar cell with high throughput, and the oxide film removal process is also performed in the manufacturing process using the PECVD apparatus. Is desirable.

In the manufacturing process of the solar cell substrate, an antireflection film using SiN _x or SiO ₂ is formed after removal of the natural oxide film. The reactive gas (processing gas) used for forming these films is It is a gas having a completely different composition from the fluorine-based gas. Therefore, when a fluorine-based gas is used, the fluorine-based gas is first sufficiently exhausted before forming the antireflection film, and then a reaction gas for film formation is introduced. In such a treatment process, an exhaust process is always included, so that it is difficult to increase the throughput required for the solar cell.

As another method for removing the oxide film, Patent Document 2 discloses that an ion source is used to generate nitrogen ions N ⁺ , which is accelerated as an N ⁺ beam and incident obliquely on the substrate surface. A method of nitriding the oxide film is disclosed. However, this is also not suitable for performing high-throughput uniform processing in the production of large-area substrate solar cells.

  Nitrogen ions can be generated by plasma, accelerated at a high frequency and injected into the substrate, and the oxide film on the substrate surface and the internal interface can be removed.

  In the PECVD apparatus, a high frequency of 13.56 MHz is normally used for plasma generation. Instead of this 13.56 MHz, plasma is generated at a lower frequency, for example, 1 MHz or less, so that plasma is generated simultaneously with plasma generation. Since ions therein are sufficiently accelerated, it is known that ions accelerated thereby are implanted into the substrate.

  Patent Document 3 describes that although not a PECVD apparatus, plasma is generated by applying a high frequency 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 2009-71334 A JP 2008-192919 A JP 2008-38217 A

  In the conventional large area solar cell manufacturing method using a parallel plate type plasma CVD (PECVD) apparatus, the oxide film removal treatment of the solar cell substrate cannot be performed at a high throughput in the solar cell manufacturing process. It was.

(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, Antireflection 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 substrate electrode in vacuum vessel In the method of forming a film, a first processing gas is supplied from a processing gas supply device, a high frequency power of a first frequency is applied to a high frequency electrode from a high frequency power source, and nitrogen is interposed between the high frequency electrode and the substrate electrode. A removal process of generating plasma containing ions and removing the oxide film of the solar cell substrate by the nitrogen ions, supplying a second processing gas from the processing gas supply device, and supplying a high-frequency power from a high-frequency power source A high frequency power of a second frequency (> first frequency) is applied to the substrate to generate a plasma for forming an antireflection film on the surface of the solar cell substrate between the high frequency electrode and the substrate electrode. The method for forming an antireflection film on a solar cell substrate using a parallel plate plasma CVD apparatus is characterized in that a film forming step for forming an antireflection film is continuously performed.
(2) The invention described in claim 2 is the solar cell substrate antireflection film forming method according to claim 1, wherein the removing step generates plasma containing nitrogen ions for removing the oxide film of the solar cell substrate. A first step of supplying a first processing gas for processing 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, and the film-forming step ends the removal step Then, 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 second frequency higher than the first frequency from the high frequency power source A method for forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus, comprising a fourth step of generating a high-frequency power.
(3) The invention described in claim 3 is the method for forming an antireflection film on a solar cell substrate according to claim 1 or 2, wherein the first processing gas for generating plasma containing nitrogen ions is N _2. An antireflection film forming method for a solar cell substrate using a parallel plate type plasma CVD apparatus.
(4) The invention according to 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 in the removing step, plasma containing nitrogen ions is generated. In this case, the output power of the high-frequency power source is set to the first frequency of 50 kHz to 800 kHz, and when the plasma for forming the antireflection film on the solar cell substrate surface is generated in the film-forming process, An antireflection film forming method for a solar cell substrate using a parallel plate type plasma CVD apparatus, characterized in that 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 for forming an antireflection film on a substrate.
(6) The invention described in claim 6 is a processing gas supply device that supplies a processing gas, a high-frequency power source that applies high-frequency power to a high-frequency electrode, and a substrate on which a solar cell substrate is placed in a vacuum vessel. And a control circuit for controlling the processing gas supply device and the high-frequency power source, the control circuit comprising: (a) the high-frequency electrode and the substrate In order to generate a plasma containing nitrogen ions between the electrodes and remove the oxide film of the solar cell substrate by the nitrogen ions, the processing gas supply device is controlled to supply N _2, and a low frequency high frequency controls high-frequency power source so as to apply power to the high frequency electrode, (b) after removal of the oxide film, the antireflection film of SiN _x on the solar cell substrate surface between the high-frequency electrode and the substrate electrode The deposition plasma is generated, the plasma for forming the antireflection film on the solar cell substrate surface by, controlling the process gas supply system to supply a mixed gas of SiH ₄ and NH ₃ and N ₂ In addition, the parallel plate type plasma CVD apparatus is characterized in that the high frequency power source is controlled so that high frequency high frequency power is applied to the high frequency electrode.
(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 removing the oxide film is 50 kHz to 800 kHz, and the antireflection film 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 natural oxide film removal treatment on the surface of the solar cell substrate and the internal particle interface can be performed in a continuous process before the production of the antireflection film by using a parallel plate type plasma CVD apparatus. Good solar cells can be manufactured with high throughput.

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 unit 2 through the wiring 7. The high-frequency electrode 6 is provided with a gas discharge hole 6a for discharging a processing gas, 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, and a plurality of fine electrodes. A processing gas is discharged into the reaction chamber 1 from the hole 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 process for removing the oxide film from the solar cell substrate and the subsequent film forming process for the antireflection film, and plasma suitable for these processes is generated. Further, the high frequency power source 2 switches the frequency and output of the high frequency 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 the substrate electrode 5 of the 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 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 natural oxide film removal 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 solar cell substrate 8 is heated by the heater 9 together with the cart 5 and adjusted so that the substrate surface becomes about 450 ° C. A gas (N ₂ ) for removing the oxide film of the solar cell substrate 8 is supplied from the processing gas supply unit 3 and discharged 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 nitrogen ions (nitrogen plasma) is formed from the processing gas. At the high frequency of this frequency, the generated ions in the plasma are also accelerated and decelerated following this frequency, so that the nitrogen ions near the solar cell substrate 8 are accelerated and implanted into the substrate, and the oxide film at the particle interface inside the substrate. Reacts with oxygen in it to remove oxygen. As a result, the oxide film is removed.

When the oxide film removal 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 6. . Note that the N ₂ gas introduced into the reaction chamber 1 for the oxide film removal treatment is the same as one of the components of the film forming gas for forming the antireflection film, and the plasma is generated using the film forming gas. Since this is not an obstacle, the deposition gas is introduced into the reactor 1 following the completion of the oxide film removal process.

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. 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 carried out from the reaction chamber 1 together with the cart 5, and the solar cell substrate 8 to be processed next is carried into the reaction chamber 1 together with the cart 5.

As described above, according to the present invention, the oxide film removal process of the solar cell substrate 8 by nitrogen plasma in one apparatus, and the film formation process of the antireflection film of SiN _{x on} the solar cell substrate 8 subsequently. Is done. According to the present invention, 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 after the oxide film removal process, so that the processing throughput of the solar cell substrate can be improved. Further, by forming an antireflection film immediately after the oxide film removal treatment, it is possible to protect the surface of the solar cell substrate without changing.

In the above-described embodiment of the present invention, only the processing of the oxide film of the solar cell substrate 8 has been described. It can be performed with high throughput. Further, even if the plasma containing nitrogen ions used for removing the oxide film is a processing gas other than N ₂ , the generated plasma contains nitrogen ions as long as it does not affect the characteristics of the solar cell. Anything 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 nitrogen ions cannot follow this frequency at frequencies in this region, and only the 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

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 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 nitrogen ions are included between the high frequency electrode and the substrate electrode. Removing step of generating plasma and removing the oxide film of the solar cell substrate by the nitrogen ions;
A second processing gas is supplied from the processing gas supply device, a high frequency power of a second frequency (> first frequency) is applied from the high frequency power source to the high frequency electrode, and the high frequency electrode and the substrate electrode In the meantime, a plasma for forming an antireflection film on the surface of the solar cell substrate is generated, 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 for forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus. In the solar cell substrate antireflection film-forming method according to claim 1,
The removing step includes a first step of supplying a first processing gas for generating a plasma containing nitrogen ions for removing an oxide film on the solar cell substrate from the processing gas supply device, and the high frequency power source. Including a second step of generating high-frequency power of a first frequency,
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 removal step is completed. And a fourth step of generating high-frequency power having a second frequency higher than the first frequency from the high-frequency power source, and forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus Method. In the solar cell substrate antireflection film-forming method according to claim 1 or 2,
A method for forming an antireflection film on a solar cell substrate using a parallel plate plasma CVD apparatus, wherein the first processing gas for generating plasma containing nitrogen ions is N ₂ . In the solar cell substrate antireflection film-forming method according to any one of claims 1 to 3,
In the removing step, when generating the plasma containing nitrogen ions, the output power 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 high frequency power source is set to a second frequency of 13.56 MHz. A method for forming an antireflection film on a solar cell substrate using a parallel plate type plasma CVD apparatus. In the solar cell substrate antireflection film-forming method 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 antireflection film of SiN _x 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) The processing gas is supplied so as to supply N ₂ in order to generate a plasma containing nitrogen ions between the high-frequency electrode and the substrate electrode, and to remove the oxide film of the solar cell substrate by the nitrogen ions. Controlling the supply device, and controlling the high-frequency power source to apply low-frequency high-frequency power to the high-frequency electrode,
(B) After removing the oxide film, a plasma is formed 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, 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 characterized by controlling the high-frequency power source. In the parallel plate type plasma CVD apparatus according to claim 6,
The frequency of the high-frequency power when removing the oxide film 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. Type plasma CVD equipment.

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