JPS631242B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing purified gas-phase silane by removing oxide impurities, particularly silicon oxide, contained in silane. This invention relates to silane mixed with 5 mol% or less of oxide, especially silicon oxide (hereinafter simply referred to as raw silane).
Raw silane (SiH ₄ ) to remove more oxides
By introducing into hydrogen fluoride (hereinafter referred to as HF) filled in a first container in a liquid state,
Oxides in the raw silane, particularly silicon oxide, are
It reacts with HF to purify water (H ₂ O) and silicon fluoride (denoted as SiF ₄ ) as reaction products. Furthermore, water is solidified in the first container and removed. As the next step, this silane is drawn out from this first container, kept at a temperature of -112 to -185°C, and liquefied in a second container, and further this liquefied silane is preferably -65 to -110°C. By vaporizing from a second container maintained at -75 to -100℃
A step of trapping SiF ₄ , HF and residual H ₂ O, or a second step in which silicon fluoride, water and hydrogen fluoride mixed therein are kept at -65 to -110°C, preferably -75 to -100°C. It is characterized by removing oxides from the raw silane and purifying it by trapping it in a container without liquefying it. In general, silane having extremely strong oxidizing power tends to easily contain silicon oxide as an impurity due to its oxidizing power. However, this silicon oxide is an ultrafine powder (particle size is 100Å).
) and is a solid. Because of this ultra-fine powder form, it is free in colloidal form in the silane container, and the reaction products reach the reaction container without passing through any filter to separate them from silane, which is a reactive gas for semiconductors. This results in the presence of silicon oxide as an impurity. Furthermore, since silicon oxide is conventionally a solid, it has been completely undetectable in chemical investigations of its purity as an impurity in silane, and it has been unclear to what extent it is present. That is, impurities in silane have been chemically measured and evaluated using methods such as mass spectrometry, atomic absorption, and gas chromatography. However, the amount of silicon oxide as an impurity was determined by the vapor phase method (PCVD [plasma chemical vapor deposition] method or LPCVD [low pressure gas phase] method) using this silane.
They were able to achieve this by forming a silicon film using a method (generally referred to as a general term for a method) and detecting and identifying the formed silicon film using a SIMS (Ion Micro Analyzer). When such identification was performed, it was found that the conventionally known silicon film contained oxygen at a concentration of 2×10 ¹⁹ to 1×10 ²¹ atoms/cc. In addition, since the silicon concentration was 2×10 ²² atoms/cc, it was found that oxygen was contained in a large amount of 0.1 to 5%. Furthermore, for SiO ₂ , SiO, and SiOH, the representative bonds are determined by their SIMS ionic strength (count/sec).
For example, SiO ₂ 1×10 ⁴ , SiOH2×10 ³ ,
It was also found that extremely large amounts of SiO3×10 ² and SiO ₂ were included. The purpose of the present invention is to remove such oxides, and furthermore, it is aimed at implementing this ultra-high purity silane at a factory (plant) level having a large-scale production of about 100 kg/month. In addition, the silicon semiconductor formed by the method of the present invention has an oxygen concentration of 1×10 ¹⁸ atoms/cc or less in the amorphous or semi-amorphous (semiconductor having a semi-amorphous structure) or insulating film. , preferably 5×
The aim is to reduce the amount to 10 ¹⁷ atoms/cc or less. The details of the reaction of the present invention will be explained below with reference to the drawings. Next, silane, especially monosilane (SiH ₄ MP−185
℃BP-112℃) is used as an example to show the reaction formula. SiH ₄ +O ₂ →SiO ₂ +2H ₂ …50 SiO ₂ +4HF→SiF ₄ ↑＋2H ₂ O↑ …51 SiF ₄ ↑＋2H ₂ O↑→SiF ₄ ↓＋2H ₂ O↓ …52 SiH ₄ →SiHx↓＋1/2（ 4-x) H ₂ ↑ ...53 (0≦x<4) Equation (50) represents the oxidation that is purified by the reaction between silane and oxygen, especially residual oxygen during silane production, or oxygen adsorbed on the inner wall of the introduction pipe. It is silicon. Silicon oxide includes SiOx such as SiO ₂ and SiO, and some hydroxyl groups may be mixed in to form SiOH bonds, but here, SiO ₂ is used to represent the reaction formula. When 0.1 to 5% of silicon oxide is present in a cylinder as a solid ultrafine powder in silane, no method has been known until now for removing the ultrafine silicon oxide. In the present invention, liquefaction is carried out in this first container.
HF (anhydrous hydrogen fluoride, purity 99.8% or more) (MP - 83℃
BP+19℃). Furthermore, after this, raw silane was introduced into this first container. Then, in this first container, as shown in equation (51), the silicon oxide present in the raw silane reacts with the liquefied HF, forming SiF (BP-65℃) and water (BP+100℃, MP0
°C). The container is generally maintained at a temperature below 0°C, the temperature being 0 to -83°C, preferably -5 to -40°C, e.g. -
It was 10℃. In this way, the water generated in the first container was transformed into a solid, and this water and silane were prevented from reacting again to form silicon oxide. On the other hand, since SiF ₄ and water produced by the reaction with HF are gases, they are discharged together with the silane into the second container. Furthermore, this raw silane mixed with SiF ₄ impurities is introduced into a second container, where it is once liquefied and then re-vaporized.
Or below -65 to -110℃ without liquefaction, preferably -
It was simply trapped in a second container at a temperature of 70 to -100°C. Then, the silicon fluoride in the silane becomes a liquid, and in addition, the impurity water that could not be removed in the first container becomes a solid and is trapped at the same time. Furthermore, hydrogen fluoride, etc., which have been slightly revaporized at the same time as the silane, can also become liquid or solid and be trapped in the second container. In order to prevent the trapped silicon fluoride from being mixed into the silane as a gas, the temperature of this second container is lower than the boiling point (BP) of silicon fluoride (-65°C) and the BP (BP) of the silane. A feature of the present invention is that the temperature is higher than -112°C. Equation (52) shows that impurities silicon fluoride and water are transformed from gas to liquid or solid. In order to prevent silicon fluoride from being mixed into the silane as a gas during the second purification, it is important that the temperature of the second container is lower than the boiling point (BP) of silicon fluoride - 65°C. Considering the partial pressure of each component near BP, it is preferable for the temperature of the vaporized silane to be in the range of -75 to -100°C, for example -90°C, for high purification. The thus purified silane gas was filled into a third container, a high-pressure container (cylinder), and sold externally. or directly LPCVD this purified silane
Or connected to the doping system of PCVD equipment. That is, the purified silane is mixed with, for example, solid silicon or hydrogen and converted into silicon in the reaction system using the PCVD method or the LPCVD method as shown in formula (52). That is, a non-single crystal semiconductor containing an amorphous or semi-amorphous semiconductor represented by formula (53) using purified silane,
Alternatively, a single crystal silicon semiconductor was formed. This reaction product is reacted with purified silane, ammonia, and hydrazine to form silicon nitride (Si ₃ N _4-x
0≦x<4). As described above, silicon or silicon nitride produced using the silane produced by the method of the present invention has an oxygen concentration as an impurity of 1×10 ²⁰ cm ^-3 when using a conventionally known silane cylinder. than
It was 1×10 ¹⁸ cm ^-3 or less, which is less than 1/100, and it was possible to obtain high purity silicon or silicon compounds. FIG. 1 is a block diagram for specifically showing the silane purification method of the present invention in more detail. Examples of the method of the present invention will be described below according to the drawings. In FIG. 1, the raw silane is supplied from 1,
It is purified through the first and second containers 2 and 3, and then the purified product is supplied and filled into a third container, for example, a cylinder. The conventional process of the refining plant apparatus shown in FIG. 1 (simply referred to as this apparatus) was carried out as follows. When filling the third container 4 with purified silane, connect the third container to the tank 40 of this device, close the valves 41, 13, 12, 24, 18, 38, and close the valves 15, 16, 23, 37, 17 was opened, and the purification system was evacuated using the vacuum pump 21 and turbo pump 22. At this time, the temperatures of the first, second, and third containers are all
Heaters 30, 31, and 32 were controlled by controllers 26, 27, and 28 to heat the mixture to 200 to 250°C, and deaeration was performed. The degree of vacuum was 1×10 ⁻⁵ torr or less, preferably 1×10 ⁻⁶ torr. After this, the valves 23, 15, 16, and 17 were closed. Hydrogen fluoride with a purity of 99.8% or more from 14 (hereinafter
(referred to as HF), the first container 2 is 18~-
The temperature was maintained at 90°C, preferably -3 to -30°C, for example -10°C. Then, the HF supplied by opening the valve 13 from 14 was liquefied and filled into the container 5 as 6. Furthermore, the valve 41 was opened and raw silane was supplied from 1. The steps of the trapping method (purifying impurities in gaseous silane by liquefying and vaporizing it) in the second container are shown below. After the inside of the second container was brought to a pressure higher than atmospheric pressure, for example, 0.2 Kg/cm ² , the valve 15 was opened little by little. The second container 3 was previously heated to -65 to -110°C, for example -90°C, using liquefied nitrogen using the controller 27.
is held in Then, the raw silane is guided into the liquefied HF in the first container through the nozzle, and is passed upward as fine bubbles from below. During this step, the oxide present in the silane bubbles reacts with HF, and formula (51) is fulfilled. Furthermore, this silane passes through the valve 15 and reaches the second container. At this time, part of the HF, the reaction product
Since SiF ₄ and H ₂ O are mixed at the same time, they are trapped in the second container. In this second container,
As shown in equation (52), HF becomes a solid at -90°C and is trapped in the second container. In order to increase the productivity and the filling pressure in the third container, raw silane was further pressurized and laminated so that the pressure inside the pipe of this apparatus was 10 to 30 Kg/cm ² , for example, 20 Kg/cm ² . Even by using such a pressurizing step, the equation (51) in the first container and the equation (52) in the second container were sufficiently satisfied. The silane thus purified passed through the second container, passed through the needle valve 42 for flow rate control, and by opening the valve 17, could be filled into the third container. It was effective to attach a flow meter to the valve 42 and monitor the flow rate. In the method described above, in which the impurities are reacted with the raw silane in the first container, and the impurities are trapped in the second container at -65 to -110°C, for example, -90°C, this apparatus is operated under pressure. Since it can be placed at a low temperature, it is highly productive in large quantities, and is effective as a low-cost plant for mass production. However, at the start of purification, there is a risk that sufficient impurities will not be trapped in the second container and will be drawn out at the same time as the purified silane, so it is necessary to precisely control the flow rate and pressure using a microcomputer. It was hot. Next, a case will be described in which impurities are trapped by liquefying and revaporizing the silane itself. That is, in addition to the steps described above, after the step of formula (51), silane is placed in a second container maintained at -112 to -185°C, for example, -150°C, with valves 17 and 18 closed and valve 15 opened. It was supplied as The silane and its impurities thus become liquefied silane in the second container, in addition to the impurities SiF ₄ , H ₂ O,
The HF solidifies and is captured in the second container. Next, the second container was maintained at a temperature of -65 to -110°C, for example -90°C, by the controller 27. Then, the liquefied silane begins to vaporize, and the needle valve 42
Then, the valve 17 was opened and the third container 4 was supplied and filled. During this filling process, the third container 4 was heated to -150°C and liquefied and filled, and when it reached room temperature, it was 10 to 30 kg/cm ²
For example, the pressure was set to 20 kg/cm ² . In this way, impurities are preliminarily reduced to -150 in the second container.
Because it completely solidifies at ℃, there is no risk of these impurities vaporizing and getting mixed into the purified silane, and it has the great advantage of being able to produce ultra-high purity silane. But on the other hand, the second container is -
It has the disadvantage that it is relatively expensive because it requires cooling to 150°C and then lowering this temperature to -90°C, and uses liquid nitrogen as a coolant. In FIG. 1, the removal of the third container is as follows. That is, after closing the lid of the third container and closing valve 17, valve 37 was opened to evacuate the silane between 17, 37, and 40. I also removed that joint. In the third container, joints 40, 39, etc. can be similarly filled with a plurality of silane cylinders, thereby improving productivity. We also describe the recovery of impurities after the reaction in this device. That is, after the reaction, the first container is heated to room temperature for 12
Hydrofluoric acid could be obtained from 11 by opening the pulp. Further, by opening the valve 23, liquefied silicon fluoride can be obtained from the second container into the fourth container 9. This fourth container was able to separate SiF ₄ from HF and water, and it was possible to obtain high purity SiF from 25. As described above, in this device, hydrofluoric acid, which can be used as waste, can be obtained from the first container, and SiF ₄ can be obtained from the second container, and there is no risk of discarding the chemical products. As a result, it was extremely cost effective and improved profits. Using the purified silane shown in FIG.
In order to evaluate the physical properties of the silane gas, it was connected to a CVD device, such as a PCVD (plasma vapor deposition) device, and a silicon film was formed on a glass substrate using this device. The semiconductor reactive gas made of silane reaches the reaction system via the doping system. This reaction system has 100
~400℃, preferably 150-300℃, typically 210℃
A surface to be formed was maintained at a temperature of 0.degree. C., the pressure in the reaction zone was 0.01 to 2 torr, e.g. 0.1 torr, and the silane flow rate was 1 to 100 c.c./min, e.g. 20 c.c./min. Furthermore, electrical energy was applied from a high-frequency oscillator (13.56 MHz) to a pair of capacitively coupled electrodes, causing a plasma glow discharge and a PCVD reaction. The substrate position was in the positive column region of the glow discharge, and a silicon film was formed by plasma discharge on the surface to be formed, for example, a glass substrate, based on equation (53). The growth rate was 1-10 Å/sec, for example 3 Å/sec. In the manner described above, a silicon film could be formed on the surface to be formed. When the film quality of this silicon film was examined, it was found that the oxygen concentration was less than 1×10 ¹⁸ atoms/cc (discharge output less than 10 W) as measured by SIMS. This discharge output is 10 W or less in the device of the present invention, and its characteristics change greatly especially when the electrode area and the distance between the electrodes change. In this 10W, the formed film contains microcrystals (microcrystals with a grain size of 50 Å or more) in a volume of about 50%. That is, 10 W or less is an indicator that the formed film is in a mixed state with amorphous amorphous, semi-amorphous, or low-grade microcrystals. Furthermore, if the discharge output is 2W, then 2×
10 ¹⁷ atoms/cc and further decreased to 1/5 of that, and when connected to a conventionally known silane doping system and examining the film, it was 3 × 10 ¹⁹ atoms/cc, which was reduced to about 1/100 of this value. It turned out that it was. In addition, the one made at 20W, which creates a polycrystalline structure in a conventional cylinder, is 1×
It contained 10 ²¹ atoms/cc, about 5%. This result shows that, using the conventional method, an absorption peak exists at a wave number of 1065 cm ^-1 using a Fourier infrared spectrometer, and the absorption peak was detected to have a concentration of about 5%. However, in the silicon semiconductor film using silane produced by the method of the present invention, the presence of oxygen could not be confirmed even with a Fourier infrared spectrometer. Table 2 below shows the results of impurities in a silicon film produced by the PCVD method using the silane obtained by the method of the present invention. Furthermore, Table 1 shows the results obtained using the same equipment in the conventional PCVD method using silane.

【table】

[Table] As a result of examining the crystal structure of the silicon film as shown in Tables 1 and 2 using the X-ray diffraction method, it was found that in the conventional method, it had microcrystalline properties at 10W and 20W;
5W has a mixed crystal semi-amorphous structure, and 2W
The so-called amorphous structure was observed. Furthermore, in the method of the present invention, a so-called semi-amorphous silicon semiconductor having crystallinity with lattice distortion was observed at 2W. In addition, 5W, 10W,
Microcrystallinity was observed at 20W. From this, by reducing the oxygen content to 5×10 ¹⁷ or less, it was possible to virtually eliminate the so-called amorphous silicon and create a semiconductor with some crystallinity or crystallinity even at 210°C. This crystallinity progressed further by increasing the substrate temperature to 250°C and 300°C. The temperature at which this reaction product is produced is also not 210℃,
This was also possible at temperatures of 150 to 300°C. However, at high temperatures of 650 to 700℃, plasma
Instead of using the CVD method, the LPCVD method (low-pressure gas phase reaction method), which simply adds heat, was used, and no electrical energy was required. The electrical characteristics of this were investigated. In other words, a 0.5μ silicon semiconductor layer is deposited at 2W on a glass substrate using this PCVD method.
It was created using the output of Furthermore, silicon nitride was added as a barrier layer to prevent oxidation on the top surface using the same reaction apparatus shown in Figure 1.
Laminated to a thickness of . Thereafter, a portion of this silicon nitride was removed, and an ohmic contact electrode was provided in this portion as a parallel electrode, and the electrical conductivity characteristics were investigated. Then, the semiconductor film using conventional raw silane is
The dark electrical conductivity is on the order of 10 ^-7 (Ωcm) ^-1 (1 to 9
×10 ^-7 (Ωcm) ^-1 ) value. On the other hand, when silane was used for purification according to the present invention, the dark conductivity was reduced to about 1/100, with a value of 1 to 30×10 ^-9 (Ωcm) ^-1 . When AM1 (100 mW/cm ² ) was irradiated in the area 60, it had 1×10 ⁻⁴ (Ωcm) ⁻¹ in the conventional method using raw silane. On the other hand, in the method using the purified silane of the present invention, the photoconductivity was on the order of 2×10 ^-3 (Ωcm) ^-1 , which was about one order of magnitude higher than that of the conventional example. From the above, in the conventional method, there was only a difference of 10 ³ to 10 ⁴ between dark conductivity and photo conductivity. However, it has been found that by using the purified silane of the present invention, it is possible to achieve a semiconductor that has a difference of as much as 10 ⁵ to 10 ⁶ and is sensitive to light. As is clear from the above explanation, by using a method in which oxygen, mainly silicon oxide, which is an impurity in the silane of the present invention, is denatured, and further removed by this denatured impurity, We were able to produce ultra-high purity silane. As a result, the oxygen concentration of a semiconductor film, particularly a silicon film, using this purified silane could be reduced to about 1/100, and the electrical characteristics could be further improved. This improvement in electrical properties promotes improved industrial properties and reliability in semiconductor electronics, and is used in semiconductor devices such as photoelectric conversion devices, optical sensors, electrostatic copying machines, insulated gate field-effect semiconductors, and their integrated devices. It was extremely effective. In the present invention, the cylinder was used as the third container as shown in FIG. However, it is possible to manufacture a silicon semiconductor, silicon nitride, or silicon compound film by directly connecting the doping system of a PCVD device or LPCVD device and integrating the reaction system for manufacturing a semiconductor device with the method of the present invention without using this cylinder. is valid. Furthermore, the present invention primarily refers to monosilane. However, the method of the present invention, which allows impurities to react once and then uses the difference in BP to remove and purify impurities that could not be removed conventionally, also produces reaction products (water, hydrogen fluoride, etc.) for other semiconductor gases. etc.) and the product to be purified (silane, etc.) is 20°C or more.

[Brief explanation of the drawing]

FIG. 1 shows a purification system using the method of the present invention.

Claims (1)

[Claims] 1. Silane gas is introduced into a first container filled with a hydrogen fluoride liquid and mixed, thereby converting silicon oxide impurities contained in the silane into water and silicon fluoride. The silane extracted from the first container is liquefied by maintaining it at a temperature of -112 to -185°C in a second container, and the liquefied silane is further vaporized at -65 to -110°C. The step of trapping the water, silicon fluoride and hydrogen fluoride, or introducing the silane extracted from the first container into a second container maintained at a temperature of -65 to -110° C. It is characterized by comprising a step of purifying silane by trapping water, silicon fluoride, and hydrogen fluoride, and a step of thereafter supplying the purified silane to a third storage container or a reaction system. Silane purification method. 2. The silane purification method according to claim 1, characterized in that water as a reaction product is solidified in the first container by maintaining liquefied hydrogen fluoride at a temperature of 0 to -83°C.