JPH0381296B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses tetrafluoride as a raw material gas for the purpose of introducing fluorine and hydrogen into a silicon thin film in the process of manufacturing a semiconductor element by forming a silicon thin film on an arbitrary substrate in a plasma atmosphere. The present invention relates to a film forming method using a fluorosilane-silane (SiF ₄ -SiH ₄ ) mixed gas. Normally, in the manufacturing process of amorphous silicon films containing fluorine and hydrogen, a tetrafluorosilane-hydrogen (SiF ₄ -H ₂ ) mixed gas is used as a raw material, and SiF ₄ is decomposed in a plasma atmosphere and deposited on any substrate. (See Nature 276 , 482 (1978)). The disadvantage of the film formation method using SiF ₄ −H ₂ mixed gas is that the film formation conditions are very strict and the film formation requires a large amount of power (about 1.0 W/cm ² in cathode side plasma discharge power density).
(above) and high gas pressure (approximately 1 torr), which resulted in nonuniformity in the plasma state, deposited film thickness, and its properties. Furthermore, trace amounts of impurities such as oxygen, sulfur, phosphorus, and boron contained in the source gas or attached or adsorbed in the vacuum equipment used for film formation are selectively removed from the silicon film. The photoelectric properties of the film and its reproducibility deteriorate. This is particularly problematic when manufacturing junction devices such as P-N, P-I-N and Schottky barrier types. For example, phosphine is added to the SiF ₄ −H ₂ mixed gas.
When an N-type film is prepared by mixing PH ₃ and immediately doping, the inside of the vacuum equipment is contaminated with phosphorus element, and then it is mixed with SiF ₄ -H ₂ gas without PH ₃ .
Even if an attempt is made to create a type film, phosphorous elements are observed in the film over a long period of time, making it extremely difficult to create an amorphous type I film with high resistance. moreover,
Even if an attempt is made to grow a P-type semiconductor film layer on an N-type semiconductor film layer using this SiF ₄ -H ₂ gas to produce a P-N junction film, the phosphorus atoms in the initial N layer will be removed from the P layer. During the film formation, it is incorporated into the P layer, making it extremely difficult to form a predetermined P layer. The same holds true when growing an I layer on an N layer; phosphorus atoms in the N layer are incorporated into the I layer being formed, making it difficult to form a desired I layer. These are SiF ₄ −H ₂
This is due to the fact that the film forming conditions when using gas are extremely strict and limited as described above, and the incorporation of impurities into the thin film cannot be fully controlled. The present invention aims to eliminate such drawbacks, and uses a tetrafluorosilane-silane (SiF ₄ -SiH ₄ ) mixed gas instead of the SiF ₄ -H ₂ mixed gas to achieve a low gas pressure (about 0.01 torr). By maintaining stable discharge at a low power density (about 0.06W/ ^cm2 ) and introducing fluorine and hydrogen during film formation,
The present invention provides a method for efficiently manufacturing a silicon thin film containing fluorine and hydrogen. In particular, in the production of silicon thin films by the method of the present invention,
It is characterized by a very wide range of gas pressure (0.01 torr or more), power density (0.06 W/cm ² or more), and film formation conditions. For this reason, silicon thin films with no residual impurity effects can be created at relatively low power densities (for example, around 0.06 W/cm ² ), and silicon thin films with high electrical conductivity can be created at high power densities (for example, around 1.0 W/cm ² ). It has the advantage of being able to be generated. The SiF ₄ − SiH ₄ mixed gas used is helium,
It can be diluted with a noble gas such as neon, argon, or hydrogen. Silicon is also produced by mixing it into the above-mentioned mixed gas as a dopant for a gas consisting of a group element of the periodic table such as boron or aluminum or a compound thereof, or a group element such as phosphorus or arsenic or a compound thereof. The thin film can be doped. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an apparatus and its operation for carrying out the method of manufacturing a silicon thin film containing fluorine and hydrogen according to the present invention will be described below with reference to the drawings. In Figure 1, the entire equipment system including the mixing vessel 1 is operated using an oil rotary pump 2 and an oil diffusion pump 3.
The mixture is evacuated to a degree of vacuum of 10 ^-6 torr, and then gases are introduced into the mixing container 1 at a required ratio from the SiF ₄ cylinder 4 and the SiH ₄ cylinder 5, and if necessary, the doping gas cylinder 6 or 7, and mixed. The mixed gas is introduced into the vacuum vessel 9 through the flow meter 8 at a constant flow rate. The required pressure is maintained by operating the main valve 10 and monitoring the degree of vacuum in the vacuum container 9 with the vacuum gauge 11. A high frequency voltage is applied between the electrodes (13 and 13') by a high frequency oscillator 12 to cause glow discharge. The substrate 15 is placed on a base heated by the heater 14 and heated to a required temperature by the heater, and a silicon thin film containing fluorine and hydrogen is formed on the substrate 15. FIG. 2 shows the fluorine and hydrogen content (curves 16 and 17) in silicon thin films produced according to the invention as a function of the gas mixture composition. The contents of fluorine and hydrogen in silicon thin films were measured using EPMA method, XPS method, and infrared absorption spectroscopy. FIG. 2 proves that it is possible to introduce fluorine into a silicon thin film by the method of the present invention. FIG. 3 shows, as an example, SiF ₄ :SiH ₄ =1:
σdark (electrical conductivity in the dark) and △ of a silicon thin film formed when using a mixed gas of 1, using a glass plate as a substrate, and changing the substrate temperature Ts.
σphoto (difference between electrical conductivity when irradiated with light of intensity 300 μW/cm ² and wavelength 6328 Å and electrical conductivity in the dark)
(curves 18 and 19). FIG. 3 proves that the silicon thin film produced by the method of the present invention has extremely good photoelectric properties, indicating that this film is excellent as a material for photoelectric conversion elements and image elements. Figure 4 shows an experimental example in which the produced silicon thin film was doped with phosphorus.
Curve 20 in the figure shows, as an example, SiF ₄ :SiH ₄ =1:
The concentration of PF 5 in the mixed gas and the amount of PF ₅ produced when using the mixed gas of 1 and further mixing phosphorus pentafluoride PF ₅ as a dopant to form a film under the conditions of a substrate temperature of 300°C and a power density of 0.06 W/cm ² are as follows. The relationship between σdark and silico thin film is shown. Furthermore, in order to obtain a silicon thin film with high electrical conductivity, a mixed gas of SiF ₄ :SH ₄ =1:1 was diluted 27 times with hydrogen, that is, SiF ₄ :SiH ₄ :H ₂ =
Using a 1:1:54 mixed gas, as a dopant
4000ppm of PF ₅ to SiF ₄ + SiH ₄ (volume basis)
The σdark values of the silicon thin film when mixed and deposited under the conditions of a substrate temperature of 300℃ and a power density of 1.0W/cm ² and 1.6W/cm ² are respectively 21 and 2 in Figure 4.
Indicated by 2. These values indicate that silicon thin films with extremely high electrical conductivity can be produced by diluting the raw material gas with hydrogen or rare gases such as He, Ne, Ar, etc. and applying high power while suppressing the film formation rate. It shows what is possible. Therefore, when applied as a photoelectric conversion element, this film has advantages such as good ohmic characteristics with electrodes and lowering the series resistance of the element, making it extremely effective for use in photoelectric conversion elements. FIG. 5 shows an experimental example of the residual effect due to impurity contamination after the doping operation, and the broken line 23 in the figure shows the result of the doping operation using a mixed gas of SiF ₄ :SiH ₄ =1:1 as an example. This is the result of attempting to form a post-I type film. The film forming conditions were: substrate temperature 300℃,
1 immediately after the doping operation at a power density of 0.06W/ ^cm2 .
It can be seen that an I-type film is formed from the sample film of the second time. A broken line 24 in the figure shows the result of a film formation test of an I-type film after a doping operation using a mixed gas of SiF ₄ :H ₂ =9:1. The residual effects of impurities appear for a long time after the doping operation. As described above, according to the method of the present invention, it is possible to form a good type I film without any residual effects of impurities. To manufacture a P-I-N junction semiconductor device,
Using a SiF ₄ -SiH ₄ mixed gas and an appropriate dopant as the raw material gas, the P and N layers were formed by diluting the raw material gas and applying high power while suppressing the film formation rate, as in the experimental example shown in Figure 4. The intermediate I layer can be formed by applying a small amount of power. Additionally, various additional embodiments of the invention are tabulated. In the tests (examples) listed in this table,
In addition to changing the mixing ratio of the SiF ₄ -SiH ₄ mixed gas, the mixing ratio of these with the diluting gas, and the mixing ratio of the doping gas, the gas flow rate (SCCM), the cathode side power density (W/cm ² ), the substrate temperature ( ℃), deposition pressure (Torr), and film thickness (μm), deposition rate (Å/sec), σdark, and △σphoto.
was measured. In these examples, No. 1 to No.
No. 7 simply changed the mixing ratio of SiF ₄ /SiH ₄ mixed gas, Nos. 8 to 11 had various ratios of doping gas PF ₅ added to the 1:1 SiF ₄ /SiH ₄ mixed gas, and No.
Nos. 12 and 13 are SiF ₄ /SiH ₄ 1:1 mixed gas diluted with hydrogen and doping gas PF ₅ is added, and Nos. 14 to 16 are simply SiF ₄ /SiH ₄ 1:1 mixed gas. belongs to. Of these, No. 12 and No.
13, high power of 1.0 W/cm ² and 1.6 W/cm ² was input, and the dark electrical conductivity σdark of the thin film produced in this case was 3.81×10 ^-3 and 8.73×, respectively.
It has been shown to be as high as 10 ^-3 (Ω ^-1 cm ^-1 ). Thus, it can be seen that a thin film with high electrical conductivity can be obtained by diluting with a diluent gas, mixing a dopant, and applying high power. In other examples, lower powers of 0.06 to 0.14 W/cm ² are applied, and it will be appreciated that in this case the electrical conductivity of the thin film produced is generally low. As explained above, according to the method of the present invention,
We can provide thin films suitable as photoelectric conversion elements and image element materials with excellent photoelectric properties, thin films suitable as photoelectric conversion elements with high electrical conductivity and good ohmic characteristics with electrodes, and I-type films with no residual effects. The effects of the present invention are extremely large, such as the ability to form a film, thereby making it possible to efficiently manufacture a P-I-N junction semiconductor device. 【table】

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an apparatus system for forming a silicon thin film containing fluorine and hydrogen on an arbitrary substrate in a plasma atmosphere according to the present invention, and FIGS. 3 is a graph showing various properties of a silicon thin film produced by the method. 1: Mixing container, 2: Oil rotary pump, 3: Oil diffusion pump, 4 to 7: Gas cylinder, 8: Flow meter,
9: Vacuum vessel, 10: Main valve, 12: High frequency oscillator, 13, 13': Electrode, 14: Heater,
15: Substrate.

Claims (1)

[Claims] 1. A mixed gas in which tetrafluorosilane (SiF ₄ ) and silane (SiH ₄ ) are mixed in a ratio of tetrafluorosilane (SiF ₄ ):silane (SiH ₄ )=9:1 to 1:1. A method for producing a silicon thin film containing fluorine and hydrogen on a substrate in a plasma atmosphere, the method using as a raw material and changing the film characteristics by changing the plasma discharge power input during film formation. . 2. Claims for doping by mixing an element in a group of the periodic table such as boron or aluminum or a compound thereof, or an element in a group such as phosphorus or arsenic, or a gas consisting of a compound thereof as a dopant into the mixed gas. The method described in paragraph 1. 3 Tetrafluorosilane-silane mixed gas prepared by mixing tetrafluorosilane (SiF ₄ ) and silane (SiH ₄ ) in a ratio of tetrafluorosilane (SiF ₄ ):silane (SiH ₄ )=9:1 to 1:1. With rare gases such as helium, neon, argon, etc. or hydrogen,
Mixed gas: rare gas = diluted at a ratio of 1:1/49 to 1:27 and used as a raw material Claim 1
or the method described in paragraph 2.