JP2005154849A - Method of depositing silicon thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of depositing a silicon thin film required for depositing a silicon thin film used for a liquid crystal display or the like at a lower temperature. <P>SOLUTION: In the method of depositing a silicon thin film, at the time of depositing a silicon thin film on a substrate by a CVD (chemical vapor deposition) method, a silicon-containing raw material compound having a structure in the general formula (1) is used; wherein, R<SB>1</SB>to R<SB>4</SB>are a 1 to 4C alkyl group or a hydrogen atom; and R<SB>5</SB>to R<SB>8</SB>are a 1 to 4C alkyl group. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming a silicon thin film by forming a silicon thin film on a substrate by a chemical vapor deposition method (hereinafter referred to as a CVD method). More specifically, for example, a silicon thin film such as amorphous silicon or polysilicon (hereinafter, these thin films are collectively referred to as a silicon thin film) is manufactured by a CVD method on a glass substrate or the like that is used when manufacturing a liquid crystal display or the like. The present invention relates to a method for forming a silicon thin film using a specific silicon-containing compound as a raw material.

Conventionally, most active matrix type liquid crystal displays are of the type using amorphous silicon for TFTs (thin film transistors). When manufacturing this amorphous silicon TFT liquid crystal display, a CVD method using a Si—H compound such as SiH ₄ (hereinafter referred to as monosilane) or Si ₂ H ₆ (hereinafter referred to as disilane) as a raw material, A step of forming amorphous silicon on a glass substrate; With the recent increase in the area of displays, problems such as thermal expansion of glass substrates are becoming prominent, and a technique for forming amorphous silicon at a lower temperature is required in the film forming process (Non-patent Document). See 1st etc.).

  On the other hand, for the purpose of high definition, low power consumption, chip-on-glass, etc., polysilicon (also referred to as polycrystalline silicon) is formed on a glass substrate, and a liquid crystal display using this as a TFT is known. In the case of forming polysilicon on a glass substrate, a method has been reported in which amorphous silicon is first deposited on a substrate and then crystallized using excimer laser annealing (hereinafter referred to as laser annealing) (patent) Reference 1). As described above, the reason why the laser annealing is used without directly forming the polysilicon on the glass substrate is usually due to the heat resistance problem of the glass substrate used in the liquid crystal display. On the other hand, as a method of forming polysilicon on a substrate without laser annealing, it is usually necessary to set the substrate temperature to 600 ° C. to 900 ° C. or higher, and an expensive quartz glass substrate must be used as the substrate. There is no current situation, and it costs money. In the method having a laser annealing step or the like, inexpensive glass such as non-alkali glass can be used for the glass substrate. However, as the number of manufacturing steps increases, there are problems such as higher manufacturing costs compared to the type using amorphous silicon for TFT, and there are also problems such as difficulty in responding to the increase in display area. Yes.

  Therefore, in order to form a high-performance, large-area liquid crystal display at low cost, a polycrystal is formed on a glass substrate for liquid crystal displays such as non-alkali glass at a temperature lower than the heat resistant temperature of the glass substrate without using laser annealing. A technique for directly forming a silicon thin film is required.

  Furthermore, with the development of the information industry in the future, for the purpose of improving weight reduction, impact resistance, flexibility, etc. for electronic paper, etc., this resin is used as a substrate with a melting point lower than that of a glass substrate. A technique for forming a silicon thin film on a film has been studied. Therefore, it is expected that a process for forming a silicon thin film at a lower temperature will be required.

  Under such circumstances, studies focusing on “improving the film forming apparatus and process” have been conducted as the development of a low temperature silicon thin film forming technique. However, Si-H-based materials such as silane and disilane are still used as silicon-containing CVD materials, and low-temperature film formation has been sufficiently achieved due to restrictions associated with the chemical characteristics of the Si-H-based materials. Absent.

Regarding the examination of the method for forming a silicon thin film in consideration of the change of the silicon-containing CVD raw material, for example, Patent Document 2 discloses that a compound represented by H _x Si (NR ₂ ) _4-x is used as a raw material. It is. According to this document, it is described that various silicon films and the like are formed on a substrate by a CVD method, and it is safe and easy to control a film formation reaction. There is almost no description about the silicon thin film, and it was actually impossible to form the silicon thin film from the contents described in the literature.

In other words, in the current silicon thin film forming technology, when manufacturing a liquid crystal display such as a TFT, a technology for forming a silicon thin film on a glass substrate at a low temperature has been able to cope with the recent increase in area of the display. There is no technology for directly forming a polysilicon thin film at a lower temperature than the heat resistance temperature of the glass substrate without using excimer laser annealing in the polysilicon thin film, and for electronic paper, etc. There are various problems such as a technique for forming a silicon thin film on a resin film having a melting point lower than that of a glass substrate has not been established, and there is a need to solve these problems.
Japanese Patent Laid-Open No. 10-12548 JP-A-5-251354 Liquid crystal 131p-142p vol. 4 No. 2 2000

  An object of the present invention is to provide a film forming method for forming a silicon thin film used for a liquid crystal display or the like at a lower temperature.

  The inventors of the present invention have intensively studied a method for forming a silicon thin film for the purpose of forming a silicon thin film by a CVD method at a lower temperature. As a result, since the Si-H bond is difficult to dissociate in a compound having a Si-H bond, it is considered that there is a limit to lowering the temperature of the silicon thin film, and the Si-N bond is dissociated compared to the Si-H bond. By using a silicon-containing compound having a structure represented by the following general formula (1) having no Si—H in the molecule and having only Si—N as a source gas, And found that a silicon thin film can be formed, and the present invention was completed.

That is, the present invention uses a silicon-containing compound having a structure represented by the following general formula (1) as a source gas when a silicon thin film is formed on a substrate by a CVD method. This is a film forming method.

(In the formula, R _{1 to} R ₄ represent an alkyl group having 1 to ₄ carbon atoms or a hydrogen atom, and R _{5 to} R ₈ represent an alkyl group having 1 to 4 carbon atoms.)

  According to the present invention, by using the silicon-containing compound as a source gas, a silicon thin film can be formed at a low temperature by a CVD method.

Hereinafter, the method for producing a silicon thin film of the present invention will be described in detail.
The method for producing a silicon thin film of the present invention is characterized in that a silicon-containing compound having a structure represented by the general formula (1) is used as a source gas when a silicon thin film is formed on a substrate by a CVD method. And

First, the silicon-containing compound having the structure of the general formula (1) used in the present invention will be described. Here, R _{1 to} R ₄ in the general formula (1) are an alkyl group having 1 to ₄ carbon atoms or a hydrogen atom, and R _{5 to} R ₈ are alkyl groups having 1 to 4 carbon atoms. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, and a butyl group. Preferably, they are a methyl group and an ethyl group. These substituents R _{1 to} R ₈ are independent of each other and may be the same or not the same, and may be selected appropriately in consideration of the ease of synthesis of the compound and the stability of the compound. Can do. However, even in the silicon-containing raw material compound group, if two groups bonded to the same nitrogen atom are both H, the group bonded to Si becomes an NH ₂ group, which may cause instability because a condensation reaction occurs. Get higher. Further, when the number of carbon atoms is larger than 4, the structure may become unstable.

Examples of specific compounds represented by the general formula (1) include Si {N (CH ₃ ) ₂ } ₄ , Si {N (C ₂ H ₅ ) ₂ } ₄ , Si {NH (n—C ₄ H). ₉ )} ₄ etc. are mentioned. Si {N (CH ₃ ) ₂ } ₄ is preferable in consideration of ease of synthesis of the compound.

  The silicon-containing compound is preferably selected from those having a vapor pressure under specific conditions for its use. For example, those having a vapor pressure of 0.1 to 760 Torr at at least one point in the temperature range of −200 ° C. to 300 ° C. are preferable. Considering the purpose of use, those having a high vapor pressure at a lower temperature are preferred.

  Further, considering the purpose of use of the silicon-containing compound, these gases are preferably gaseous or liquid at room temperature. When it is solid at room temperature, the melting point is preferably 200 ° C. or lower, more preferably 100 ° C. or lower. If the melting point becomes high, supply as the CVD raw material may become difficult.

  The method for forming a silicon thin film of the present invention forms a silicon thin film on a substrate using a CVD apparatus. The CVD apparatus is preferably composed mainly of a CVD raw material supply / vaporization apparatus and a CVD reaction film forming apparatus (hereinafter referred to as a CVD chamber) that decomposes the vaporized raw material and deposits it as a silicon thin film on the substrate.

  As an example of the film forming method, a silicon-containing compound having a structure represented by the general formula (1) is filled as a raw material for CVD into a raw material supply / vaporization device of a CVD apparatus. When the raw material is a gas, the raw material is filled in a cylinder and supplied from the cylinder. In the case where the raw material is liquid, a method of bubbling and supplying the raw material filled in the container with a carrier gas, a method of directly heating the container to vaporize it, and the like are used. The type of apparatus is appropriately selected according to the properties of the raw material. Usually, the gasified raw material is supplied together with a carrier gas. As the carrier gas, a rare gas such as He or Ar is preferable.

  Next, the raw material vaporized by the supply / vaporization apparatus is supplied into the CVD chamber. The pressure in the chamber is appropriately selected according to the raw material, the type of other equipment, the vapor deposition method, and the like. Usually, the plasma CVD is performed at 0.01 to 50 torr and the thermal CVD is performed at 0.01 to 760 torr. . The raw material gas feed amount is appropriately selected according to the shape of the apparatus, the type of raw material, the film thickness, and the like, but is generally selected within 0.01 L / min to 10 L / min (standard state conversion). A substrate is installed in the CVD chamber, and a silicon thin film can be formed on the substrate by decomposing the CVD raw material in the chamber.

  In the CVD chamber, the silicon-containing CVD raw material is decomposed. This decomposition method is a method in which the temperature of the substrate is raised and deposited by thermal decomposition (thermal CVD method), a high-frequency electric field is applied in the reaction vessel, He, Plasma is generated in a rare gas such as Ar, the source gas is decomposed in the generated plasma and deposited on the substrate (plasma CVD method), and the source gas is chemically reacted and decomposed using a hot wire such as tungsten as a catalyst. Any of existing methods such as a method of depositing on a substrate (also referred to as a catalytic CVD method or a CAT-CVD method) can be employed, and is not particularly limited.

  In order to promote the decomposition of the source gas, it is preferable to coexist hydrogen in the chamber. The amount of hydrogen addition is usually in the range of 0.01 L / min to 1000 L / min (standard state conversion) in consideration of the type of raw material gas, supply amount, decomposition method, and film quality of the obtained silicon film. Hydrogen gas may be used for the carrier gas described above.

  Examples of the substrate to be formed include glass for liquid crystal display such as alkali-free glass, and resin films such as polyimide and polyethylene terephthalate, but are not particularly limited.

  The film forming method of the present invention can be applied not only to substrates for liquid crystal displays but also to Si wafers for LSIs. In this case, it is possible to contribute to lowering the temperature of the silicon thin film forming process performed at the time of manufacturing the semiconductor integrated circuit. In the present invention, the thin film generally indicates a film having a thickness of 1 μm or less, and the thickness can be controlled by manufacturing conditions depending on the application.

  The substrate temperature during film formation can usually be formed at 400 ° C. or lower. It is appropriately determined in consideration of the properties of the substrate (heat resistance, coefficient of thermal expansion, etc.), required characteristics of the silicon thin film to be formed, the decomposition method of CVD, etc., and is not particularly limited. For example, when a silicon thin film is formed on a glass substrate for liquid crystal by a thermal CVD method or a plasma CVD method, it is preferably 300 ° C. or less, preferably when a silicon thin film is formed on a resin film by a plasma CVD method. It becomes 100 degrees C or less.

  The silicon thin film to be formed is appropriately selected depending on the required performance for film characteristics, the film forming method, etc., such as an amorphous silicon thin film and a polysilicon thin film.

Using Si {N (CH ₃ ) ₂ } ₄ [melting point: 16 ° C., vapor pressure: 1 Torr (12 ° C.)] as a raw material for the silicon thin film, the following operation was performed to form a silicon thin film.
Film formation was carried out using a quartz tube in the chamber, supplying a source gas of 0.1 L / min and hydrogen of 1.5 L / min, and a substrate temperature of 300 ° C. (implemented by a thermal CVD method). An alkali-free glass piece (10 mm × 30 mm × 0.7 mm (thickness)) was used for the substrate. As a result, deposition of a silicon thin film on the substrate was confirmed to be 30 nm.
When this thin film was analyzed by a wide scan method by X photoelectron spectroscopy (ESCA), silicon was confirmed, but carbon and nitrogen were not confirmed. Further, when analyzed by infrared spectroscopy (IR), no Si—H peak was confirmed.

Comparative Example 1
An attempt was made to form a silicon thin film by the same method as in Example 1 except that monosilane was used instead of Si {N (CH ₃ ) ₂ } ₄ as the silicon-containing CVD raw material for the silicon thin film.
As a result, no silicon thin film was deposited on the glass substrate.

  It can be used for forming a silicon thin film on a glass substrate for a liquid crystal display, or for forming a silicon thin film on a resin film having low heat resistance such as for electronic paper. Further, it can be used for lowering the temperature of the silicon thin film forming process that is performed when the semiconductor integrated circuit is manufactured.

Claims (1)

A method for forming a silicon thin film, wherein a silicon-containing compound having a structure represented by the following general formula (1) is used as a raw material gas when forming a silicon thin film on a substrate by a CVD method.

(In the formula, R _{1 to} R ₄ represent an alkyl group having 1 to ₄ carbon atoms or a hydrogen atom, and R _{5 to} R ₈ represent an alkyl group having 1 to 4 carbon atoms.)