JPH04105314A - Manufacture of amorphous silicon - Google Patents

Abstract

PURPOSE:To form amorphous Si excellent in film quality by a practical photo assisted CVD method instead of a plasma CVD method, by supplying gas of hydrogen compound of Si in a space on a substrate surface, decomposing the hydrogen compound by projecting electromagnetic waves containing specified wavelength light, and depositing generated simple substance Si or low- hydrogenated on the substrate. CONSTITUTION:Gas of hydrogen compound of silicon is supplied in a space on a substrate 3; electromagnetic waves containing light whose wavelength is suitable to excite 2P electrons of silicon atoms is projected, thereby decomposing the hydrogen compound; generated single substance silicon or low- hydrogenated silicon is deposited on the substrate 3. For example, the substrate 3 on a substrate mounting stand 2 in a reaction chamber 1 is cooled at 95K by making liquid nitrogen flow in a cooling pipe 4. Material gas obtained by diluting SiH4 to be concentration of 5% with He is fed into a reaction chamber via a leak valve 8 and a solenoid valve 9. Gas in the reaction chamber is discharged by an exhauster constituted of a turbo pump 10 and a rotary pump 11, and the inside pressure is kept at 0.1-1Torr. SOR light 12 is projected from above the substrate 3.

Description

[Detailed description of the invention] [Summary] The present invention relates to the formation of an amorphous silicon layer used in solar cells, thin film transistors, electrophotographic photosensitive materials, etc. plasma CVD
The purpose of the present invention is to provide a photo-excited CVD method that is an alternative to the conventional method, and the photo-excited CVD method of the present invention involves supplying a silicon hydrogen compound gas to a space above a substrate surface and including light having a wavelength that excites 2P electrons of silicon atoms. S
It is constructed by irradiating OR light to decompose the hydrogen compound and depositing the resulting single silicon or low hydrogenation silicon on the substrate.

Furthermore, in one invention of the present application, in order to increase the probability of reaction on the substrate surface, the above-mentioned photo-excited CVD is performed while cooling the substrate to a temperature below 125°C.

[Industrial application field]

The present invention is concerned with the formation of amorphous silicon (silicon is hereinafter referred to as Si), and in particular, the amorphous silicon has good electronic properties because the bonds that do not participate in bonding between Si are bonded to hydrogen. Involved in the formation of 1isi.

In recent years, hydrogen-containing amorphous Si has been increasingly used as a material for solar cells, thin film transistors, and electrophotographic photoreceptors. Since amorphous Sl does not have a lattice arrangement, bonds are generated that do not participate in bonding between Si. If this vacant bond is bonded to hydrogen (H), the amorphous Si
has good electronic properties, and the properties of the electronic device or material made of such amorphous S1 are also excellent.

(Problem to be solved by the prior art and the invention) Amorphous S1 containing hydrogen is silane (S i H=) or disilane (S
It is usually formed by chemical vapor deposition (CVD) using izHb) gas as a raw material.

In the simplest process of this CVD method, Si is liberated by thermal decomposition of the raw material gas and deposited on the substrate. A plasma CVD method is generally used in which a source gas is decomposed in discharge plasma by applying an electric field.

In this process, charged particles generated in the plasma are accelerated by the applied electric field and collide with the substrate surface, and the damage caused thereby deteriorates the film quality of the grown layer. In this specification, sit refers to the chemical and physical properties of the amorphous 1isi layer that affect the characteristics of elements and photosensitive materials formed using it.

Since this problem is caused by the application of an electric field during CVD, it is sufficient to promote the decomposition of the source gas in a manner that does not cause a situation in which charged particles are accelerated. Photoexcitation C is a CVD method that satisfies such conditions.
The VD method is known, but the light from a mercury lamp or laser contains only a small amount of light with a wavelength that can excite and decompose silane or disilane, and furthermore, since the irradiation target is a gas, the absorption efficiency of the excitation light is low. It is difficult to obtain sufficient processing speed.

An object of the present invention is to provide a practical photo-excited CVD treatment method to replace the plasma CVD method, and thereby to provide a method for forming amorphous Si with good film quality.

(Means for Solving the Problems) In order to achieve the above object, in the photo-excited CVD method, which is one invention of the present invention, a gas of a hydrogen compound of Si is supplied to the space above the substrate surface, and
The hydrogen compound is decomposed by irradiating electromagnetic waves containing light with a wavelength that excites the 2P electrons of one atom, and the resulting simple substance S
1 or low hydrogenation Si is deposited on the substrate.

Further, in another invention of the present application, in order to increase the reaction probability on the substrate surface, the above-mentioned photo-excited CVD is performed while cooling the substrate to 125°C or less.

Furthermore, in these embodiments of the invention of the present application, S
Synchrotron radiation light (SOR light) is used as a light source to excite the 2P electrons of the i atom.

[Function] In order to efficiently decompose molecules such as silane and monosilane, it is necessary to supply enough energy to excite the inner shell electrons of the Si atom at the center of the molecule. 2P of Sl
Absorption by electrons is at a position of approximately +00 eV, and such short wavelength light cannot be obtained with conventional light sources such as mercury lamps, but SOR light contains light in the above energy range with sufficient intensity for practical use. Therefore, if this is used, it becomes possible to efficiently decompose Plan and Jinran and deposit amorphous Si by photo-excited CVD method.

In addition, if the raw material gas is at a low pressure of I Torr or lower, sufficient absorption of excitation light will not occur, resulting in amorphous S
The deposition rate of i is also low, but when the substrate is cooled as in the present invention, the raw material gas aggregates on the substrate surface, and the excitation light is efficiently absorbed in that area, so that the surface reaction on the substrate increases. Activated, the deposition rate of amorphous Si is increased.

[Example] FIG. 1 is a diagram schematically showing the configuration of an optical CVD apparatus used in the present invention. Hereinafter, embodiments of the amorphous Si deposition method of the present invention will be described with reference to the drawings.

There is a substrate mounting table 2 inside the reaction chamber 1, and a substrate 3 on the table is placed inside the reaction chamber 1.
is cooled to 95 K by flowing liquid nitrogen through the cooling pipe 4. In addition to simple cooling, when maintaining the substrate temperature at a specific value, heating power controlled by the temperature control device 5 is applied to the heater 6. The substrate temperature is measured by a thermocouple 7. Further, in this embodiment, the substrate is an S1 wafer on which a 40 nm thermal oxide film is attached.

Silane (S i H4) with helium (He)
% of the raw material gas is sent into the reaction chamber through a leak valve 8 and a solenoid valve 9.

The gas in the reaction chamber is evacuated by an exhaust system consisting of a turbo pump 10 and a rotary pump 11, and the internal pressure is maintained at 0.1 to I Torr. At this time, 5iHa
The partial pressure of is 5 X 10-' to 5 X 10-''
It becomes.

The SOR light 12 is irradiated from above the substrate. Although not shown in the figure, above the reaction chamber partitioned by the gate valve 13, there is an optical path space that is successively maintained at a high vacuum by differential pumping, and the space is filled with light emitted from the electron storage ring of the synchrotron. The generated SOR light reaches the reaction chamber via this optical path and irradiates the substrate. In this example, SO
The effective short wavelength of R light is 123 eV, and the 2p wavelength of Si
It has enough energy to excite the '1 child.

Furthermore, 14 in the figure is a baratron gauge, and 15 is a cold cathode gauge.

Figure 2 shows the results obtained by changing only the substrate temperature among the above processing conditions.
FIG. 3 is a diagram showing the relationship between the thickness of the Si layer when amorphous tSi is deposited over time, that is, the deposition rate per hour, and the substrate temperature. As is clear from this figure, the deposition rate increases linearly when the substrate temperature is below about 125°C, and the effect of substrate cooling becomes significant, but the tendency for the deposition rate to increase appears from about 125°C onwards.

Further, in a low temperature range, the deposition rate hardly changes even if the pressure of the source gas changes.

FIG. 3 is a graph showing the results of an Auger analysis conducted to confirm that the deposits according to the above examples were Si. In other words, the intensity of Auger signals corresponding to Si and O was measured while the substrate on which amorphous TSI was deposited was ground by argon sputtering from the surface, and the time on the horizontal axis corresponds to the depth from the surface. The part where the Auger signal intensity of O is high is the region of the thermal oxide film formed on the surface of the Si wafer. In the areas on both sides of this, that is, the area between the deposited layer and the S1 wafer, the signals indicating Si appear with equal intensity, so the deposited layer is Si.
It is determined that

〔Effect of the invention〕

As explained above, in the deposition formation of amorphous Si in the present invention, amorphous Si is deposited by photoexcitation CD using SOR light, and the amorphous Si is deposited by cooling the substrate. The speed has been significantly improved.

Since amorphous Si with excellent film quality can be obtained by the method of the present invention, solar cells, thin film transistors, and electrophotographic photosensitive materials using the amorphous Si also have excellent properties.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the optical CVD apparatus used in the present invention, FIG. 2 is a diagram showing the relationship between substrate temperature and deposition rate, and FIG. 3 is a diagram showing the results of Auger analysis of Si and O. 1 is a reaction chamber, 2 is a substrate mounting table, 3 is a substrate, 4 is a cooling pipe, 5 is a temperature control device, 6 is a heater 7 is a thermocouple, 8 is a leak valve, 9 is a solenoid valve, 10 is a turbo pump, 11 is a rotary pump, 12 is an SOR light, and 13 is a gate valve. Substrate temperature (K) Figure 2 shows the relationship between substrate temperature and deposition rate Figure 1 shows the optical CVD apparatus used in the present invention Sputtering time (minutes) Figure 3 shows the results of Auger analysis of Si and O

Claims (5)

[Claims] (1) A silicon hydrogen compound gas is supplied into the space above the substrate surface, and the hydrogen compound is decomposed by irradiation with electromagnetic waves containing light with a wavelength that excites the 2P electrons of silicon atoms, resulting in the generation of simple silicon Alternatively, a method for producing amorphous silicon, comprising depositing low hydrogenation silicon on the substrate. (2) In the method for manufacturing amorphous silicon according to claim 1,
A method for producing amorphous silicon, characterized in that the electromagnetic wave to be irradiated is synchrotron radiation light. (3) The method for manufacturing amorphous silicon according to claim 1 or 2, characterized in that the process is performed by cooling the substrate to 125K or less and irradiating the electromagnetic wave onto the surface of the substrate. (4) A solar cell, a thin film transistor, or an electrophotographic photosensitive material, characterized in that the solar cell, thin film transistor, or electrophotographic photosensitive material is partially or entirely constructed of amorphous silicon formed by the method according to any one of claims 1 to 3. (5) A reaction chamber, a source gas supply device that supplies a raw material gas, which is a hydrogen compound of silicon, to the reaction chamber at a constant rate, and an exhaust that discharges the gas from the reaction chamber while keeping the pressure inside the reaction chamber constant. An optical path for SOR light that couples the electron storage ring of the synchrotron with the reaction chamber, an optical path space for the SOR light that is set by continuously changing the degree of vacuum by differential pumping, and an optical path space for the SOR light that connects the electron storage ring of the synchrotron and the reaction chamber; 1. An apparatus for manufacturing amorphous silicon, comprising: a substrate mounting table, which is provided on a substrate mounting table, and is capable of cooling a substrate mounted thereon by circulating a cooling liquid.