JPH0526324B2 - - Google Patents

Description

[Detailed description of the invention]

In the present invention, when filling a high-pressure container with a reactive gas having a purity of 98% or higher, typically silane or germane, in addition to evacuating the high-pressure container, the container is heated to 100°C or higher. The present invention relates to a method of filling a high-pressure container with a reactive gas after removing adsorbed gas inside the container. The present invention deals with the heavy metals remaining in the reactive gas, water,
Oxygen or carbon remaining in the reactive gas after purification by removing oxide impurities, especially ultrafine silicon oxide particles, especially oxygen concentration, is reduced to 3×10 ¹⁷ cm ^-3 or less, preferably 1×10 ¹⁵ to 3×10 The purpose is to make it possible to achieve ¹⁶ cm ^-3 . Conventionally, reactive gases for semiconductors have been filled in iron cylinders, and semiconductor device manufacturers and research laboratories have simply used them as plasma vapor deposition equipment (PCVD equipment) and low pressure vapor deposition equipment (LP CVD equipment). It was also used in epitaxial growth equipment. However, although silane, which is typically a reactive gas for semiconductors, is produced chemically when producing raw materials, its purity is limited.
It has 6N to 7N, and the impurity is 1PPM or less. This is clear from the fact that the oxygen concentration in FZ single crystal silicon using raw material silane is 1 to 9×10 ¹⁶ cm ⁻³ or less. However, when such raw materials are transferred to transfer tanks and further subdivided into 3.4, 10 or 47 common steel high-pressure cylinders, the control is insufficient, resulting in contamination of hydrocarbons in the oil component and air leakage. As much as 0.1 to 0.01% of oxygen impurities were mixed in. For this reason, the inventor has filed a patent application for ``Semi-Amorphous Semiconductor'' (55-26388 S55.3.3 application) or ``Semiconductor device for photovoltaic power generation'' having PN junction using beautiful crystal (49-71738 S49). .6.22 application)
When attempting to fabricate a hydrogenated non-single crystal containing an amorphous semiconductor using the PCVD method, the oxygen or carbon is mixed into the silicon semiconductor as a silicon oxide insulator or silicon carbide insulator, and the semiconductor As a result, its characteristics have deteriorated. In particular, when this mixed oxygen mixes into a hydrogenated non-single crystal semiconductor, if it forms 5 to 50 oxygen clusters, it acts as a recombination center, and if it has dangling bonds, the semiconductor N
This caused the semiconductor to act as a donor center, deteriorating its properties as a semiconductor in all aspects. In addition, such oxygen is
In the production of non-single-crystalline semiconductors using the glow discharge method that utilizes a high-frequency discharge of 13.56 MHz, it is necessary to use materials that inhibit the quantum-theoretical ordering in the short range of 5 to 200 Å and impede microcrystallinity. It was decided that something was true. It has been found that purification of silane, which is the starting characteristic of the present invention, is extremely important when attempting to remove these and create a silicon thin film as an original semiconductor by the PCVD method. The present invention deals with such semiconductors, especially at low temperatures (typically room temperature to 400°C) where the deterioration effect due to the addition of oxygen is significant.
The present invention relates to a purification method for producing high-purity silane for forming semiconductor films at a temperature of 200 to 300°C. The details will be explained below with reference to the drawings. FIG. 1 is a block diagram showing a purification method using a reactive gas for semiconductors, particularly silane, according to the present invention. In the case where germane is used instead of silane, or diborane or phosphine diluted with hydrogen or the like is prepared, it can be prepared in the same manner as described below. In the drawing, silane cylinder 1, liquefaction vaporization cylinder 1
a container 2, a second container 3, a third final container 4, a container 5 for removing residual moisture in the purge hydrogen 14, a degassing heater 9 for heating the containers 6, 7, and 8 containing liquid nitrogen; 10, 36, and temperature controllers 11, 12, 37. The block diagram in FIG. 1 is for two-stage purification, and the same applies to single-stage or multi-stage purification. In the drawings, the cleaning of the first, second, and third containers and the piping system connected thereto is omitted. Table 1 shows the process based on the block diagram of FIG. Cleaning of purification equipment (Table 1) 1. All valves (hereinafter abbreviated as V) are closed. Installing the silan cylinder. 2 Heat the heaters 9, 10, and 36 to 200 to 350°C using the controllers 11, 12, and 37. 3 Open V38 from N13 and exhaust 18 from mixer 17 using flow meter 39. 4 Oil-free exhaust system 16 on, V28, V
44, V25, V24, V21, V46 open, vacuum containers 4, 3, 2, and 5. Approximately 1 to 5 hours. 5 At V29, hydrogen is purified in container 5 (77°K) and then introduced to remove impurities such as water in container 4.
Approximately 1 to 3 hours. 6 Close V25, fill containers 2 and 3 with hydrogen, and after the pressure reaches 1 atmosphere or more, open V22 and remove the adsorbed substances in containers 2 and 3 by heating. Approximately 1 to 5 hours. 7 V22 closed, V46 closed, V25 open, container 2,
Vacuum 3 and 4. 8 The heaters 9, 10, 36 are connected to the controller 11,
Off at 12.37. Furthermore, in this way, the adsorbed substances in the widths of the containers 2, 3, and 4 in the apparatus 40 constituting the purification section were removed. In particular, containers that are made of stainless steel and have a sufficiently flat mirror finish on the inside are pressure sensitive.
It was designed to withstand up to 150 kg/cm ² to prevent residual fine powder from sticking to the recesses on the inner wall and making it impossible to remove. Furthermore, in order to remove adsorbed oxygen and water in the containers 2, 3, and 4, when the inside of the container heated from the outside to 200 to 350 DEG C. was evacuated, the vacuum device 16 was designed to prevent hydrocarbons, especially oil vapor, from flowing back. That is, in the present invention, we discovered the fact that conventionally, the inside of a cylinder was simply evacuated to 10 ^-3 torr using a rotary pump, which resulted in hydrocarbons of the order of 0.1% being mixed in. ,
In order to remove such impurities, a continuous exhaust turbo pump is used to evacuate to 9×10 ^-5 to ^{10 -8} torr, and the oil component is back-diffused to 9×10 torr. ^-6 torr or less, preferably 10 ^-7 to ^{10 -9} torr. Thus, containers 2, 3, and 4 contain water, carbon dioxide,
Hydrocarbon residue 0.01PPM preferably 0.1~
I vacuumed it enough until it reached 10PPB. Container 2 was then cooled to -150°C, and silane, a reactive gas for semiconductors, was transferred from cylinder 1. Furthermore, the liquid was vaporized and purified once again from this container 2 and transferred from container 4 to the second stage container. At this time, the vaporization temperature is -100 to -90℃, and the temperature is 5 to 50℃.
After transferring for a long period of time, the container 4 was filled with the silane purified by the liquefaction-vaporization purification. The liquefaction-vaporization process of this silane is shown in Table 2 below. Liquefaction and vaporization purification of silane gas (Table 2) 1 Confirm with compound gauges 30, 31, and 32 that containers 2, 3, and 4 are evacuated. 2 Exhaust system on, V28, V44, V25, V2
4, 24, V23 open, V26, V27, V4
6. Check that V22 is closed. 3 Fill the deurea 6 of container 2 with liquid nitrogen. −150±
The temperature was 10℃. 4. Open the silane cylinder 1, open the V21, and while supplying liquid nitrogen so as not to overflow while watching the flow meter 41, liquefy the silane in the cylinder in the container 2. During the liquefaction work, the pressure gauge 30 shows 0.5 to 5 atm. do. 5 After transferring the silane from silane cylinder 1, close V21 and close cylinder 1. 6 V24 was closed, the deurer 7 was filled with liquid nitrogen, and the container 3 was set at -150±10°C. 7 Open V24, transfer the liquefied silane in container 2 to container 3 over time, and perform liquefaction and vaporization purification. (5～
50 hours) The flow meter 42 is set at 10 to 500 c.c./min, typically 100 c.c./min. The pressure of the compound gauge is 0.5 to 34 atm, and the temperature of the container 2 is controlled to be -90 to -100°C by a controller. 8 After completing the transfer, close V23, V27, V46, V
Confirm that 44 is closed. 9 V24, V25 open, duer 7 -50 to -70
℃ and phase transfer the liquefied silane to vessel 4, taking the same precautions as in item 7. 10 After filling container 4 (compatible with end cylinder) to 12 to 5 atmospheres, complete purification by closing V25. In this purification process, the silane oxide in the cylinder 1 has become a fine powder of silicon oxide, so
Mere purification through liquefaction and vaporization is not sufficient. Therefore, in order to remove such fine powder, two stages of sintered stainless steel filters 34 and 35 are provided in each container 2 and 3.
This was soaked in liquefied silane, and the fine powder was adsorbed onto the filter to remove it. By hiding the purified silane, the oxygen concentration can be reduced.
It is now possible to reduce the carbon content to 0.01 PPM (10 ¹⁴ - 10 ¹⁵ cm ^-3 ), which is equivalent to the detection limit of SIMS or activation analyzers, and in addition, it has become possible to reduce the carbon content to 1 PPM or less. Traditionally, silane is simply used as a starting material.
Although it is only contaminated with oxygen components at a concentration of 10 ¹⁶ to 10 ¹⁷ cm ^-3 , when refilling this silane, the container becomes like the so-called ``inner wall of the human intestine'' with many irregularities. Because of this, the removal of impurities is not sufficient. Furthermore, since vacuuming prior to filling was performed simply by a rotary pump, containers such as those of the present invention were heated to 10 ^-5 torr.
It is an extremely significant advance that the residual oxygen and carbon components in the container were reduced to 0.1 PPM or less by doing the following: In addition, by adding physical refining to the silane that had previously only been chemically refined, we were able to further reduce the oxygen concentration to 1/100 of that, 0.01 PPM. Finally, the evacuation of the silane remaining in the containers 2 and 3 containing impurities after being purified by the purification method of the present invention shown in FIG. 1 will be briefly described below. Exhaust of residual silane gas impurities (Table 3) 1. Confirm that all valves are closed. 2 Open N13 and V38 and exhaust 18 from flow meter 39 via mixer 17. 3 Fill containers 2 and 3 with H14 with V29, V46, V24, and V23 open. 4 Open V22, gradually flow into the mixer 17 from about 5c.c./min using the flowmeter 49 (H+SiH)/N>
Set it to 100. 1 to 3 hours. 5. Wait until the difference in flow rate between flowmeters 49 and 45 disappears. 6 Heat heaters 9 and 10 to 100 to 150℃ and supply hydrogen.
0.5 to 2/minute Evacuation of impurities in the flow containers 2 and 3 for 1 to 5 hours. 7 V22, V23, V24, V46, V29
Closed, compound gauges 30 and 31 are maintained at 0.5 to 3.0 atmospheres in hydrogen. The above-mentioned method for purifying a reactive gas and using the method made it possible to fill a high-pressure container with an ultra-high purity reactive gas for semiconductors. Using this high-purity silane gas, the plasma CVD method using the glow discharge method was used to generate a 0.1 torr, 250
A non-single crystal silicon semiconductor was formed under the following conditions: °C, RF power (13.56 MHz), 10 W, and 100% silane. In the drawing, curve 53 is produced using a conventionally known silane cylinder;
4 is a case in which the residual content inside the container with the stainless steel inner surface finish of the present invention is sufficiently removed to 9×10 ^-5 torr, preferably 10 ^-5 torr or less, without carrying out the liquid refining of the present invention at once. . That is, the inner wall of the container was mirror-finished and the container was made of stainless steel and was made of high pressure and heat resistant material. In addition, when filling with silane, the container is heated to 100° C. or higher, preferably 250 to 300° C., to sufficiently exhaust the adsorbate. In this way, by devising the container itself as in the present invention and paying sufficient attention to the filling method, it was possible to reduce the amount of mixed oxygen, etc. to 1/100 to 1/1000. In the drawing, it is presumed that 55 has almost no residual silane, so the silicon oxide remaining in the container has leaked out. Furthermore, by carrying out two stages of liquefaction and vaporization purification according to the present invention, it was possible to further reduce these to 1/10 to 1/1000. In particular, even if all the gas remaining in the container is used, the silicon oxide component will not increase in it.
It was found that the number of measurement points of 7 did not increase as much as the number of measurement points of 55. Furthermore, when silane is used as a reactive gas for semiconductors in the method of the present invention, the container shown in FIG.
483gr, residual amount 10g, residual pressure 0.5Kg/ ^cm2 , and furthermore, this silane is designed so that the internal volume in the container is 1.5, and the residual gas and impurities are 10g in container 2 and 10g in container 3. 4 is a 10-cylinder cylinder, and the silane is filled into this container 4 by cooling it to -150±10°C in the same way as containers 2 and 3, and then passing the silane to the usage system 15 at the atmospheric concentration as shown in the figure through the valve 27.
I opened it and used it. For this reason, the working pressure of container 4 is
15 to 17 Kg/cm ² , and can be used in the same manner as conventionally used silane cylinders. Instead of silane, the reactive gas for the semiconductor may be germane or helium, diborane diluted with hydrogen, phoscine, or arsine. Their chemical properties are shown in Table 4 below.

[Table] That is, when using these reactive gases, in order to achieve a concentration of 100%, the same procedure as described above can be used for silane. If diluted with hydrogen, after filling the required system with a reactive gas for semiconductors, fill the hydrogen under pressure from 14 through the cold trap 5 and through the valve 46 to dilute it to 50 to 5000 PPM. It's fine. Further, if the dilution gas is hydrogen or helium, it may be introduced from 14 in the same manner. As is clear from the above description, the present invention eliminates impurities mixed in when the reactive gas for semiconductors is subdivided into cylinders in order to reduce the amount of oxygen and carbon mixed in to 1 PPM or less, preferably 1 to 100 ppb. In addition, during this subdivision, the amount of mixed oxide gas is reduced to less than 1/1000 of the conventional method by using a liquefaction, vaporization purification and adsorption method of the reactive gas, and the purified reaction For the first time, it has become possible to control purification using gas using plasma CVD.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the reactive gas purification method of the present invention. , and FIG. 2 compares the residual oxygen concentration in silicon investigated using the silane obtained by the method of the present invention with that of the conventional method.

Claims (1)

[Claims] 1. A step of heating a heat-resistant and corrosion-resistant sealed high-pressure container for filling with a reactive gas to 100°C or more from the outside and evacuating it using an oil-free vacuum evacuation device; A reactive gas filling method characterized in that, after the step, the reactive gas is filled into the high pressure container. 2. The reactive gas filling method according to claim 1, wherein the oil-free evacuation device is a turbo molecular pump. 3. A step of heating a heat-resistant and corrosion-resistant sealed high-pressure container for filling a reactive gas to 100°C or more from the outside and evacuating it using an oil-free evacuation device, and after this step, the reaction A method for filling a reactive gas, comprising filling the high-pressure container with a reactive gas through a filter. 4. The reactive gas filling method according to claim 3, wherein the oil-free evacuation device is a turbo molecular pump.