JP2005223138A - Process for depositing silicon film and process for fabricating device using silicon film deposition process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for depositing a silicon film using liquid silicon material at a low cost while enhancing uniformity of the silicon film, and also to provide a process for fabricating a device using the silicon film deposition process. <P>SOLUTION: In the process for depositing the silicon film on the surface of a substrate using liquid silicon material, the surface of the substrate is coated with the liquid silicon material and then irradiated with microwave thus forming the silicon film on the surface of the substrate. The process for fabricating the device uses that silicon film deposition process. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a silicon film forming method applied to devices such as integrated circuits, thin film transistors, and photoelectric conversion devices, and a device manufacturing method using the silicon film forming method.

  Patterning of a silicon thin film (amorphous silicon film or polysilicon film) applied to an integrated circuit or a thin film transistor is performed by forming a silicon film on the entire surface of the substrate by a vacuum process such as a CVD (Chemical Vapor Deposition) method, and then performing photolithography. The process is generally performed by removing unnecessary portions. However, this method has problems such as requiring a large-scale device, poor use efficiency of the raw material, difficulty in handling because the raw material is gas, and generation of a large amount of waste.

  In contrast to such conventional methods, in recent years, a method has been proposed in which a liquid silicon material such as a liquid silane compound, a higher order silane compound, or a solution thereof is applied to a substrate, and a silicon film is formed by heating or UV irradiation. (For example, JP 2003-115532 A: Patent Document 1, JP 2003-124486 A: Patent Document 2, JP 2003-133306 A: Patent Document 3, JP 2003-171556 A: Patent. Reference 4). According to this method, since the raw material is a liquid, it is easy to handle and does not require a large-sized apparatus, so that a silicon film can be formed at low cost.

  Japanese Patent Laid-Open No. 2001-179167 discloses that a silicon film can be formed by directly patterning a solution silicon material by a technique such as ink-jet, thereby eliminating the man-hours and material waste caused by photolithography. Is disclosed (Patent Document 5).

  In the above prior art, as a method of forming a silicon film from a liquid silicon material by thermal decomposition, a method of annealing using heating by a hot plate or a furnace, UV light, laser irradiation or the like is disclosed. However, this method has a problem that the liquid silicon material is not uniformly decomposed by heat, light, or the like, and the uniformity of the obtained silicon film is not always sufficient.

Also, when annealing by laser irradiation, it takes a lot of time to process the substrate, and the equipment is large and expensive, which is disadvantageous in terms of time and cost, or when heating the substrate at high temperature There are also problems that it is necessary to use an expensive heat-resistant substrate and that the selection of materials and the heating process are limited.
JP 2003-115532 A JP 2003-124486 A JP 2003-133306 A JP 2003-171556 A JP 2001-179167 A

  Therefore, an object of the present invention is to provide a method for forming a silicon film at low cost by improving the uniformity of the silicon film in a method for forming a silicon film using a liquid silicon material.

  The present invention relates to a method for forming a silicon film on a surface of a substrate using a liquid silicon material, and after applying the liquid silicon material on the surface of the substrate, the surface of the substrate is irradiated with microwaves. Thus, a silicon film forming method is provided, in which a silicon film is formed on the surface of the substrate. By using microwaves when forming the silicon film, the temperature is uniformly applied within the film, and the thermal decomposition of the liquid silicon material proceeds uniformly, so that a silicon film with a stable film quality can be obtained. In addition, the irradiation time may be shorter than the conventional heating, and the equipment cost can be kept low, so that the time cost and the equipment cost can be kept down. Furthermore, since microwave heating is selective heating, damage due to overheating of the substrate and other layers of the device can be prevented beforehand by selecting a frequency that does not affect the substrate.

  In the present invention, the “liquid silicon material” refers to a material which is a liquid which is a substance containing at least a substance containing silicon in a molecule or a solution thereof.

  In an embodiment of the present invention, a silicon film made of amorphous silicon can be formed by irradiating the liquid material with microwaves and thermally decomposing the liquid silicon material with microwave energy.

  Furthermore, a step of forming polysilicon by irradiating the amorphous silicon with microwaves can be included.

  By adding a dopant to the liquid silicon material, the silicon film can be a silicon film including a doped silicon film.

  A step of removing the solvent in the liquid silicon material after applying the liquid silicon material on the surface of the substrate may be included. If the removal of the solvent contained in the liquid silicon material is incomplete, the remaining solvent may cause deterioration of the characteristics of the silicon film, but if microwaves are irradiated, the microwaves directly act on the solvent molecules, As a result of changing to thermal energy by the molecular friction, the solvent molecules themselves are heated and evaporated, so that the solvent inside the film can be more easily removed than the conventional heating method.

The microwave irradiation is preferably performed in a reduced-pressure atmosphere, particularly at 10 ^{−7 to} 10 Torr. Irradiation with microwaves in a reduced-pressure atmosphere makes it easier to remove the solvent, and a silicon film with better performance with fewer impurities such as a solvent can be formed.

  The microwave irradiation is preferably performed while heating the substrate. Appropriate heating facilitates removal of the solvent for the liquid silicon material containing the solvent, and can further reduce the time for forming the silicon film. Specifically, it is appropriately set according to the heat resistant temperature of the substrate.

  The frequency of the microwave is appropriately adjusted according to the irradiation time of the microwave and other conditions, but is preferably 0.3 to 30 GHz from the viewpoint of improving the effect.

  The liquid silicon material contains a silane compound and / or a higher order silane.

  The present invention also provides a device manufacturing method using the silicon film forming method described above. If a device is manufactured by the above-described silicon film formation method, the quality of the silicon film is stable, and thus a device with good and stable quality can be obtained.

  According to the present invention, by using microwaves for forming the silicon film, the temperature is uniformly applied in the film as compared with heating by a hot plate, an IR lamp, or the like. It is possible to obtain a high-performance silicon film having a low defect density and a very good in-plane film thickness uniformity. In addition, compared to the case where laser irradiation or annealing at a high temperature is performed, the equipment cost is not required, and the treatment can be performed safely and in a short time. Furthermore, since microwave irradiation is selective heating, damage to the substrate can be prevented by selecting a frequency that does not affect the substrate, and improvement in the performance of the resulting device can be expected.

  Next, a method for forming a silicon film will be described in detail. As described above, the present invention provides a method for forming a silicon film on a surface of a substrate using a liquid silicon material, and after applying the liquid silicon material on the surface of the substrate, A silicon film is formed on the surface of the substrate by irradiation with microwaves.

  A microwave irradiation device can be used as the means for irradiating the microwave. As a microwave irradiation apparatus, it is preferable that what can irradiate a microwave in the range of 0.3-30 GHz. For example, as a commercially available microwave irradiation device, a 28 GHz millimeter wave heating device (FMW-3-28) manufactured by Fuji Radio Industry Co., Ltd., a batch type microwave heating device or a conveyor type microwave heating device manufactured by Shimada Rika Industry Co., Ltd. The microwave oven etc. which are used for can be used.

  The frequency of the microwave is preferably in the range of 0.3 to 30 GHz, and more preferably 1 to 5 GHz. The film can be formed with this frequency set to a constant value, but the frequency setting can be changed before the silicon film is formed.

  In the case where a material containing a solvent is used as the liquid silicon material, after the liquid silicon material is applied onto the surface of the substrate, the substrate is irradiated with microwaves, for example, to remove the solvent in the liquid silicon material Can be included.

  A step of forming an amorphous silicon film from the silicon material from which the solvent is removed, a step of forming a polysilicon film from the amorphous silicon film, a step of removing the solvent, a step of forming the amorphous silicon film, The microwave frequency can be set for each step of forming the polysilicon film, and the silicon film can be formed efficiently.

  The microwave irradiation time is preferably 1 second to 60 minutes, more preferably 30 seconds to 10 minutes.

  In addition, the amorphous silicon film can be formed from the liquid silicon material by appropriately adjusting the frequency and energy of the microwave, the irradiation time, the pressure in the chamber at the time of the microwave irradiation, the temperature, and the like. You can also. That is, by irradiating a substrate coated with a liquid silicon material with microwaves, the solvent is first desorbed, and then a film mainly composed of amorphous silicon is formed by thermal decomposition of the liquid silicon material, and then the silicon film is crystallized. (Polysilicon film formation) occurs. Since these steps occur continuously or simultaneously depending on the above irradiation conditions, an amorphous silicon film can be formed from a liquid silicon material or a polysilicon film can be formed by appropriately adjusting these irradiation conditions.

  Here, as the liquid silicon material, it is preferable to use a silane compound or a higher order silane. Further, a doped silicon film can be formed by using a silane compound, higher order silane, or a solution obtained by adding a dopant to the solution.

  Here, the “dopant” is included in the liquid silicon material, and can form an n-type or p-type doped silicon film by the above-described activation by microwave irradiation. Examples thereof include compounds containing group elements or Group 5B elements of the periodic table, specifically boron, yellow phosphorus, decaborane, and substances as disclosed in JP 2000-31066 A.

Examples of the silane compound include a general formula Si _n X _m (wherein n is 3 or more and m is an independent integer of 4 or more, and X is a substituent such as a hydrogen atom and / or a halogen atom). The silane compound etc. which are represented by this is mentioned.

  The liquid silicon material may be a composition containing a higher order silane obtained by photopolymerization by irradiating the silane compound with ultraviolet rays (hereinafter referred to as “UV”), or a solution of the silane compound. In addition, a composition containing a higher order silane obtained by photopolymerization by irradiation with UV can also be used.

This higher order silane is formed by irradiating UV to a solution of a photopolymerizable silane compound and photopolymerizing the silane compound, and its molecular weight is a silane used in a conventional silicon production method. Compared to a compound (for example, Si ₆ H ₁₄ has a molecular weight of 182), it is too large to be compared (having a molecular weight of up to about 1800). Higher-order silanes with such a huge molecular weight have a boiling point higher than the decomposition point, and can form a film before it evaporates. Formation can be performed. In addition, when such higher order silane is actually heated, it decomposes before reaching the boiling point, so a boiling point higher than the decomposition point cannot be determined experimentally. However, here, it means the temperature dependence of the vapor pressure and the boiling point at normal pressure as a theoretical value obtained by theoretical calculation.

  In addition, if a liquid silicon material containing such higher order silane is used, the boiling point of this higher order silane is higher than the decomposition point, so that it is rapidly heated at a high temperature before evaporating as in the prior art. There is no need. That is, it is possible to perform a process in which the heating rate is moderated or heating is performed at a relatively low temperature while reducing the pressure. This not only controls the bonding speed between silicon when forming a silicon film, but also maintains the temperature higher than the boiling point of the solvent but not so high as to form a silicon film. This means that it is possible to reduce the solvent that causes the deterioration of film characteristics more efficiently than the conventional method.

  As described above, the higher order silane formed by photopolymerization preferably has a boiling point higher than its decomposition point. Higher order silanes having a boiling point higher than the decomposition point are selected from the following preferable silane compounds as silane compounds as precursors, or UV having a preferable wavelength described below as irradiation UV, irradiation time, irradiation method, It can be easily obtained by selecting irradiation energy, a solvent to be used, and a purification method after UV irradiation.

  Further, the molecular weight distribution of this higher order silane can be controlled by the UV irradiation time, irradiation amount, and irradiation method. Furthermore, this higher order silane can be taken out of the higher order silane compound having an arbitrary molecular weight by separating and purifying using GPC which is a general polymer purification method after UV irradiation of the silane compound. . Further, purification can be performed by utilizing the difference in solubility between higher order silane compounds having different molecular weights. Further, purification by fractional distillation can be performed by utilizing the difference in boiling points between higher-order silane compounds having different molecular weights under normal pressure or reduced pressure. In this way, by controlling the molecular weight of the higher order silane in the liquid material, it is possible to obtain a high-quality silicon layer in which the characteristic variation is further suppressed.

  Higher order silanes have higher boiling points and lower solubility in solvents as the molecular weight increases. For this reason, depending on the UV irradiation conditions, higher-order silane after photopolymerization may not be completely dissolved in the solvent and may be precipitated. In that case, insoluble components are removed by filtration using a microfilter, etc. Secondary silanes can be purified.

  The UV irradiation time is preferably from 0.1 seconds to 120 minutes, particularly preferably from 1 to 30 minutes, in order to obtain a high-order silane having a desired molecular weight distribution.

  Moreover, about the said liquid material containing the silane compound which is a precursor of such higher order silane, the viscosity and surface tension are adjusted with the said adjustment method regarding the molecular weight distribution of the higher order silane to form, and a solvent. Can be easily controlled. This is because when a silicon layer is formed from a liquid material, the greatest merit is that a patterning method using an ink jet method can be adopted. The fact that the tension can be easily controlled by the solvent serves as a very advantageous point.

The silane compound to be a precursor of the high-order silane is not particularly limited as long as having a photopolymerizable that can be polymerized by irradiation with UV, for example, in the above-mentioned general formula Si _n X _m (wherein, n represents 3 And m represents an independent integer of 4 or more, and X represents a substituent such as a hydrogen atom and / or a halogen atom).

As such a silane compound, a cyclic silane compound represented by the general formula Si _n X _2n (wherein n represents an integer of 3 or more and X represents a hydrogen atom and / or a halogen atom), In addition to a silane compound having two or more cyclic structures represented by the general formula Si _n X _2n-2 (wherein n represents an integer of 4 or more and X represents a hydrogen atom and / or a halogen atom), All of the silane compounds to which the polymerization process by microwave irradiation according to the present invention can be applied, such as silicon hydride having at least one cyclic structure in the molecule and a halogen substitution product thereof.

Specifically, examples having one cyclic structure include cyclotrisilane, cyclotetrasilane, cyclopentasilane, cyclohexasilane, cycloheptasilane, and the like, and those having two cyclic structures include 1 1, 1'-bicyclobutasilane, 1, 1'-bicyclopentasilane, 1, 1'-bicyclohexasilane, 1, 1'-bicycloheptasilane, 1, 1'-cyclobutasilylcyclopentasilane, 1, 1 '-Cyclobutasilylcyclohexasilane, 1,1'-cyclobutasilylcycloheptasilane, 1,1'-cyclopentasilylcyclohexasilane, 1,1'-cyclopentasilylcycloheptasilane, 1,1'- Cyclohexasilylcycloheptasilane, spiro [2.2] pentasilane, spiro [3.3] heptatasilane, spiro [4.4] nona Examples include silane, spiro [4.5] decasilane, spiro [4.6] undecasilane, spiro [5.5] undecasilane, spiro [5.6] undecasilane, spiro [6.6] tridecasilane, and the like. Examples thereof include silicon compounds in which the hydrogen atoms of the skeleton are partially substituted with SiH ₃ groups or halogen atoms. These may be used in combination of two or more.

Among these compounds, a silane compound having a cyclic structure in at least one position in the molecule is extremely high in reactivity with UV, and it is preferable to use this as a raw material because it can be efficiently polymerized by UV. Among these, Si _n X _2n such as cyclotetrasilane, cyclopentasilane, cyclohexasilane, cycloheptasilane (wherein n represents an integer of 3 or more, X is a hydrogen atom and / or a fluorine atom, a chlorine atom, A silane compound represented by a halogen atom such as a bromine atom or an iodine atom is particularly preferable because it has an advantage of being easily synthesized and purified in addition to the above reasons.

As the solvent used for the liquid material in the present invention, in the case of a silane composition, the silane compound is dissolved, while in the case of a higher order silane composition, the higher order silane formed by photopolymerization of the silane compound. As long as it dissolves and does not react with the silane compound or higher silane, there is no particular limitation. As this solvent, those having a vapor pressure of 1 × 10 ⁻³ to 2 × 10 ² Torr at room temperature are usually used. This is because when the vapor pressure is higher than 2 × 10 ² Torr, the solvent evaporates first when forming a coating film by coating, and it becomes difficult to form a good coating film. On the other hand, in the case where the vapor pressure is lower than 1 × 10 ⁻³ Torr, drying is slow when a coating film is similarly formed by coating, and the solvent tends to remain in the coating film of higher order silane. This is because it is difficult to obtain a high-quality silicon film even after irradiation.

  As the solvent, it is preferable to use a solvent having a boiling point at normal pressure of room temperature or higher and lower than 250 ° C. to 300 ° C. which is the decomposition point of the silane compound or higher silane. By using a solvent lower than the decomposition point of the silane compound or higher silane, it is possible to selectively remove only the solvent without decomposing the silane compound or higher silane by heating after coating. This is because it is possible to prevent the solvent from remaining and to obtain a higher quality film.

  The solvent is preferably a solvent that absorbs microwaves when irradiated with microwaves. Specifically, it is preferable to select a solvent having high absorption when the microwave frequency is in the range of 0.3 to 30 GHz.

  The solvent used for the liquid material is, for example, a solvent in a solution of a silane compound in the case of containing a silane compound, and a solution in a solution of a silane compound as a precursor before UV irradiation in the case of a solution containing a higher order silane. It is a solvent and means a solvent in a higher silane solution after UV irradiation. Specific examples thereof include hydrocarbon solvents such as n-hexane, n-heptane, n-octane, n-decane, dicyclopentane, benzene, toluene, xylene, durene, indene, tetrahydronaphthalene, decahydronaphthalene and squalane. In addition, dipropyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, tetrahydrofuran, tetrahydropyran, 1,2-dimethoxyethane, bis (2- Methoxyethyl) ether, ether solvents such as p-dioxane, propylene carbonate, γ-butyrolactone, N- Chill-2-pyrrolidone, dimethylformamide, acetonitrile, polar solvent such as dimethyl sulfoxide.

  When the liquid silicon material used in the film forming method of the present invention uses a solution containing a silane compound or a higher order silane as a solute, the solvent includes those exemplified above. The solute concentration is usually about 1 to 80% by weight, preferably about 5 to 30% by weight, and can be prepared according to the desired silicon film thickness. If it exceeds 80% by weight, higher-order silane tends to precipitate, and it becomes difficult to obtain a uniform coating film.

  Further, the viscosity of the liquid silicon material can usually be adjusted in the range of 1 to 100 mPa · s, but the viscosity can be appropriately selected according to the coating apparatus and the target coating film thickness. When the viscosity is less than 1 mPa · s, coating becomes difficult, and when it exceeds 100 mPa · s, it is difficult to obtain a uniform coating film.

  Note that a small amount of a surface tension adjusting material such as a fluorine-based material, a silicone-based material, or a nonionic-based material can be added to the liquid silicon material as necessary as long as the target function is not impaired. This nonionic surface tension modifier improves the wettability of the solution to the application target, improves the leveling of the applied film, and helps prevent the occurrence of coating crushing and the occurrence of distorted skin. It is.

  The substrate used in the present invention is a base material for applying the liquid material containing the silane compound onto the surface of the substrate and then performing microwave irradiation, and can be used in the present invention. As for, it is not restrict | limited to the kind etc., A various material can be selected. Therefore, a flexible substrate (film) such as film-like polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) can be suitably used. Of course, non-flexible substrates such as silicon and glass which have been conventionally used as general substrates can also be used.

  In addition, from the viewpoint of promoting the thermal decomposition of the liquid silicon material, and from the viewpoint of promoting the removal of the solvent when a liquid silicon material containing a solvent is used, the microwave irradiation does not damage the substrate due to the micro absorption. It is preferable to select a substrate of such a material, a wavelength of micro group, and energy.

  As a method for applying the liquid silicon material to the substrate, it is preferable to use a general droplet applying apparatus such as an ink jet apparatus, a dispenser, or a micro dispenser. Since the silane compound and the higher order silane are denatured by reacting with water and oxygen, the series of steps is preferably in a state where water and oxygen are not present. Therefore, the atmosphere during the series of steps is preferably performed in an inert gas such as nitrogen, helium, or argon. Furthermore, what mixed reducing gas, such as hydrogen, as needed is preferable. Further, it is desirable to use a solvent or additive from which water or oxygen has been removed.

  In the device manufacturing method according to the present invention, the above-described silicon film forming method is used. Since the device manufactured by the above-described silicon film formation method has a stable silicon film quality, it can exhibit a good quality and stable function.

  For example, it is suitable for the manufacture of devices such as integrated circuits, thin film transistors (TFTs), photoelectric conversion devices such as solar cells.

FIG. 1 shows an example of a manufacturing process of a device in which a silicon film is formed by irradiation with microwaves. First, an ITO electrode was formed by sputtering on one entire surface of a PET film as a substrate (see FIG. 1 (1)). Next, a solution (solution A) obtained by irradiating a 20 wt% toluene solution of hexasilane with UV lamp light having a wavelength of 436 nm for 5 minutes was prepared. After 0.1% by weight of decaborane was added to this solution A and filtered through a filter, it was applied onto the ITO electrode by an inkjet method. This substrate is placed in a chamber (not shown) of a microwave heating apparatus depressurized to 10 ⁻⁴ Torr, and irradiated with 500 W and 2.45 GHz microwave for 10 minutes while heating the substrate at 100 ° C. Thus, the solvent was removed, and a p-type doped polysilicon film (p ⁺ -Si) was formed (see FIG. 1 (2)).

Next, by applying the above-described solution A on the polysilicon film (p ⁺ -Si) by an inkjet method and irradiating microwaves under the same conditions as when forming a p-type doped polysilicon film A non-doped polysilicon film (i-Si) was formed (see FIG. 1 (3)).

Next, 0.1% by weight of phosphorus chloride is added to the solution A, filtered through a filter, and then applied onto a non-doped polysilicon film (i-Si) by an ink jet method. By irradiating waves, an n-type doped polysilicon film (n ⁺ -Si) was formed (see FIG. 1 (4)).

Furthermore, an ITO electrode is formed by sputtering on an n-type doped polysilicon film (n ⁺ -Si) (see FIG. 1 (5)), and then a protective film is formed, thereby forming a flexible film. A solar cell substrate was prepared. As a result of measuring the photovoltaic power of a solar cell made from this substrate and determining its energy conversion efficiency, it was possible to obtain a sufficient energy conversion efficiency of 9%.

It is a figure explaining an example of the manufacturing process of the device which formed the silicon film by irradiating a microwave.

Claims (11)

In a method of forming a silicon film on the surface of a substrate using a liquid silicon material,
After the liquid silicon material is applied on the surface of the substrate, a silicon film is formed on the surface of the substrate by irradiating microwaves on the surface of the substrate. Method.   The silicon film forming method according to claim 1, wherein the silicon film is made of amorphous silicon.   3. The method of forming a silicon film according to claim 2, further comprising the step of converting the amorphous silicon into polysilicon.   The method of forming a silicon film according to claim 1, wherein the silicon film is made of polysilicon. The liquid silicon material is doped with a dopant,
The method of forming a silicon film according to claim 1, wherein the silicon film is a doped silicon film.   6. The silicon film according to claim 1, further comprising: removing a solvent in the liquid silicon material after applying the material containing a solvent as the liquid silicon material on the surface of the substrate. Film forming method.   The method for forming a silicon film according to claim 1, wherein the microwave irradiation is performed in a reduced pressure atmosphere.   The method for forming a silicon film according to claim 1, wherein the microwave irradiation is performed while heating the substrate.   The method for forming a silicon film according to claim 1, wherein a frequency of the microwave is 0.3 to 30 GHz.   The method for forming a silicon film according to claim 1, wherein the liquid silicon material includes a silane compound and / or a higher order silane.   The manufacturing method of the device which uses the film-forming method of the silicon film of any one of Claims 1-10.

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