JPS6230338A - Vapor-phase oxide film forming method - Google Patents

Abstract

PURPOSE:To enhance the yield of an oxide film by removing moisture in gas contained in all the gases used in a vapor phase oxidizing method and especially gas having corrosiveness like HCl. CONSTITUTION:General gas and/or gas having corrosiveness is contacted with one side of a film of fluorine copolymer having cation exchange group, and dried purged gas is contacted with the other side or the other side is reduced under pressure to form an oxide film by using general dehumidified gas and/or gas having corrosiveness. The copolymer having the cation exchanger group is preferably that having cation exchange group like sulfonic acid group. The copolymer having sulfonic acid group is most excellent at the points of the easiness of manufacture, the degree of water content of the film and the thermal stability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxide film forming technology among thin film forming technologies.

[Conventional technology] One of the fields in which development competition is particularly intense in the current semiconductor industry.
This will be explained below in relation to the oxide film technology.

In the case of oxide film formation technology, the main causes of contamination are mobile ions supplied into the gas from the quartz tube wall, ports, gas piping, etc. during oxidation, and impurities remaining during substrate surface treatment. May enter the membrane. Furthermore, particulate matter may enter the oxide film and cause pinholes. Furthermore, as devices become smaller, junctions tend to become thinner, and it is quite conceivable that redistribution of impurities due to autodoping may have an adverse effect.

Against the background of the above situation, current silicon oxidation methods include not only 02, N20, N2, N2, and Ar, but also
As a halogen oxidation method, HCl, Gβ2, Br
2.) A mixed gas of 02 and lychlorethylene is used. This fixes the alkali ions present in the oxide film or at the interface, blocks impurities entering from the outside, and also suppresses oxidation-induced stacking faults. In this way, the halogen-added oxidation method is thought to have an impact on the production of stable devices with low interfacial charge density and on the improvement of yield.

Furthermore, there is a method called tube cleaning as one of the applications of the halogen oxidation method. When a quartz tube is heated in an oxidation furnace and HCρ gas is passed through the interior, a 5i02 film with excellent interfacial properties is formed in the subsequent oxidation process, making it particularly suitable for use with new furnaces and quartz tubes. This is a leaning method that is very effective.

When manufacturing semiconductor products, the oxide film is used as a selective diffusion mask,
In addition to being applied as surface passivation, gate insulating films for MOS devices, insulating films for capacitors, and ultra-thin oxide films for nonvolatile memories, it is also used to control impurity concentration in silicon substrates. These applications are due to the fact that oxide films are insulating films with excellent purity, but due to the variety of their applications, they are used many times (usually 4 to 6 times) when manufacturing one semiconductor product or intermediate product. ) must pass through an oxide film formation process. Moreover, since the properties of the oxide film have a very large effect on the performance of the product, there is a demand for the oxide film to be thinner, more purified, and of higher quality. Therefore, since the oxide film forming step is more susceptible to the influence of impurities than other steps, it is necessary to prevent impurities, especially moisture, from entering the gas used for forming the oxide film.

However, with the exception of some gases used in these oxidized hydrogen oxide formation techniques, purifiers for removing moisture have not been installed immediately before oxidation or before oxidation from the cylinder.

At present, an adsorption method using a molecular sieve is partially used for drying gas in the manufacturing process of these semiconductor wafers and semiconductor devices.

Molecular sieves are relatively easy to dry common gases, and are widely used as physical desiccant agents that do not cause problems such as deliquescence or swelling.

(However, drying to a moisture content of 1 ppm requires drying at low temperatures, which is difficult to do at room temperature.) However, in the commonly performed thermal regeneration, high temperatures of 200 to 400°C are required for a long time, and the thermal regeneration is repeated. The drawback is that it generates floating dust when used. In addition, acidic gas such as hydrogen chloride gas causes fragmentation of the molecular sieve, which causes floating dust.

Also, although this is completely unrelated to the dehumidification of semiconductor-related gases, methods that use polymer membranes as a general gas dehumidification method are:
JP-A-53-97248, JP-A-54-152f37
No. 9, but there is no mention of using these methods for dehumidifying semiconductor manufacturing gases.

Furthermore, the membranes disclosed in these documents cannot dehumidify to a highly dry state required for gases used in semiconductor-related applications.

[Problems to be solved by the invention] Various impurities adhere to the quartz tube walls, ports, susceptors, diffusion furnaces, piping, etc. of the CVN apparatus, and these impurities may enter during single crystal growth. Although it is known,
Poetry, which forms an oxide film, is also known to suffer from problems due to the intrusion of impurities. No matter how precisely the equipment is manufactured, this type of trouble cannot be avoided, and the current situation is that the product yield is always reduced due to alkali ions, deposits, etc. In particular, in gas phase oxidation such as halogen oxidation such as 02 dry meltification and hydrochloric acid oxidation, the yield of the product is affected depending on whether the drying of gases is strictly controlled. For example, even high-purity reprinted NCR gas may contain several tens of ppm of moisture.
In addition, there were few suitable tools for removing moisture during use. Furthermore, as the gas in the cylinder is consumed, the moisture in the cylinder increases rapidly and is mixed with the gas and fed into the reactor. The moisture contained in this gas has had a considerable effect on the yield of oxide films.

Therefore, water contained in all gases used in the gas phase oxidation method, especially HCI! Removing moisture from gases with R-contact properties is a technology that is widely expected to be developed in the semiconductor market.

[Means and effects for solving the problems] According to the present invention, when manufacturing semiconductor wafers, semiconductor devices, or intermediate products thereof, on one side of a fluorine-based copolymer membrane having a cation exchange group, Use a general gas and/or a corrosive gas that has been dehumidified by contacting a general gas and/or a gas with R-contact properties and contacting a dry purge gas on the other side, or reducing the pressure on the other side. Provided is a method for forming a vapor phase oxide film, which is characterized in that the oxide film is formed using a method of forming an oxide film.

The vapor phase oxide film forming method of the present invention is suitably used for dry oxide film formation such as dry O2 oxidation, oxygen partial pressure oxidation, halogen oxidation, and plasma oxidation.

The general gas that is the gas to be dried in the present invention is 02, N20
, N2, N2, Ar, etc., and corrosive gases refer to H(J!, C1h, Br2, etc.). However, although trichlorethylene is not corrosive, it is included in this @hare. do.

The gas to be dried in the method of the present invention is usually gas filled in a cylinder obtained on the market or gas supplied by a pipeline from on-site production equipment in a factory or from an adjacent area, and the water vapor concentration is It's not that expensive gas.

Gas filled in cylinders is usually around 10 ppm.
The amount is about 100 ppm+, but in some cases it is more than 1100 ppm.

Depending on the concentration of the target gas, the membrane area of the moisture separator can be changed or multi-staged to obtain the desired level of dehumidification.

The fluorine-based copolymer having a cation exchange group used in the present invention is preferably one having a cation exchange group such as a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group. It is best to use a fluorine-based copolymer having a sulfonic acid group in terms of ease of production, high water content of the membrane, and thermal stability.

There are various structures of fluorine-based copolymers having sulfonic acid groups, among which the repeating polymers represented by the general formula (I) (wherein = 0 or 1, n = an integer from 2 to 5) Fluorine-based copolymers containing units are preferred.

The above-mentioned fluorine-based copolymers include tetrafluoroethylene,
Fluorinated olefins such as trifluoroethylene, perfluorovinyl ether, vinylidene fluoride, vinyl fluoride and the general formula (II) 7F3 CFz=CF-(OGF2CF)-0-(CF2)n
s02F (II) (11=0 or 1, .=2~5
Preferably, those obtained by copolymerizing perfluorovinyl ether monomers (an integer of ) are preferred.

Further, the sulfonic acid group of the fluorine-based copolymer is preferably introduced in an amount that provides an ion exchange capacity of 0.5 to 2.5 mmol/g H-type dry resin in the copolymer. The ion exchange capacity of the fluorine-based copolymer is 0.5 to 2.
．． By setting the amount within the range of 5 milliequivalents/g of H-type dry resin, the water vapor permeation rate is not significantly reduced, and the melting point of the copolymer does not become too high, making it easy to manufacture thin polymer films. Moreover, the shape retention of the polymer thin film is also ensured without a decrease in physical strength. More preferably, the H-type dry resin has an ion exchange capacity of 0.8 to 1.8 milliequivalents/gram.

It is also possible to use metal salts and ammonia salts as the salt type of the sulfonic acid group of the fluorine-based copolymer used in the present invention, but the 5O3H type has the highest water content, the highest water vapor permeation rate, and the highest heat resistance. It is also preferable since it has sufficient stability.

The shape of the fluorine-based copolymer may be either a flat membrane tube shape or a hollow fiber membrane shape, but a hollow fiber membrane is particularly preferred since it has a large membrane area per unit volume and a high throughput.

For example, moisture content 10 ppm or less, especially moisture content 5
In order to achieve a high degree of dryness of less than ppm, the airtightness of the apparatus is also important, and from this point of view, hollow fiber membranes are preferable.

The membrane of the fluorine-based copolymer having a cation exchange group used in the present invention is preferably a membrane of the fluorine-based copolymer containing the repeating unit represented by the above general formula (I), which has been pretreated with heat. . The heating pretreatment of this film is to form a fluorine-based copolymer obtained by copolymerizing a monomer represented by the general formula (TI) and a fluorinated olefin into a thin film, then hydrolyze it with an alkali and treat it with a strong acid. After converting the terminal group S02F into SO3H by doing so, the polymer is heat-treated.

The heat treatment can be carried out while purging with a dry gas, for example, nitrogen gas having a water content of 5 ppm or less, or under reduced pressure, if necessary.

The heat treatment temperature is suitably 60 to 250°C. If the temperature is too high, the ion exchange group may be removed, leading to a decrease in performance. The heat treatment temperature is particularly preferably 70 to 200°C.

The copolymer shrinks by several tens of percent through the heat treatment, and by using the heat treatment membrane, the gas can be reduced to a moisture content of 5 ppm+ or less, and furthermore, a moisture content of 1 at room temperature.
High-level dehumidification of ppm or less is possible. Therefore, it can be said that the membrane formed by heat-treating the above-mentioned copolymer has the ability to dehumidify to an extreme value that is unimaginable under the common knowledge of conventional membranes.

The copolymer shrinks by several tens of percent due to the heat treatment, and its water absorption rate also decreases.

The membrane obtained by heat treating a membrane of a fluorine-based copolymer containing repeating units represented by the above general formula CI) has a relationship between water absorption W and ion exchange capacity Q of the formula (III) 1.20Q -1, 984<RogW<1.20Q
-1,742 (III), and exhibits particularly excellent performance in high-level drying of gases.

A heat-treated membrane having the relationship expressed by formula (m) can achieve high dehumidification with a moisture content of 1 ppm or less at room temperature.

Therefore, if you set the conditions as necessary, the moisture content will be 10.
Of course, it is possible to dehumidify to any value such as ppm or less, 5 ppm or less. In actual use, 10
In some cases, it may be sufficient to have a content of less than 5 ppm, and in other cases, it may be less than 3 ppm or less than 1 ppm, and the present invention is applicable to any of these cases.

Among the above-mentioned heat-treated films, in the case of a flat film, whether or not it was made by heat treatment can be easily determined by measuring the water absorption rate.

However, if the membrane is in the form of a thin hollow fiber, it is difficult to measure the water absorption rate, so the determination can be made by measuring the temperature at which thermal contraction starts, as described below.

Attach a light weight to the hollow fiber membrane (enough weight to keep the fibers straight, but not enough to stretch them) and suspend them in an air tank. In this state, the temperature of the air tank is gradually increased, and changes in the length of the thread are measured using a reading telescope. An example of the measurement results is plotted in a graph with temperature on the horizontal axis and length on the vertical axis, as shown in Figure 5. L25 is the length of 25°C, LL
is the length at temperature t'0. In FIG. 5, the temperature indicated by the arrow, that is, the maximum temperature at which there is no dimensional change due to temperature increase, is defined as "the maximum temperature at which no thermal contraction occurs." Several hollow fibers with different heat treatment temperatures (1) were prepared, and their "maximum temperature (T) without thermal contraction" was measured, and the results were plotted on a graph as shown in Figure 6. That is, T=t, (1), and the heat treatment temperature (1) of the hollow fiber membrane can be determined by measuring the maximum temperature (T) at which no thermal contraction occurs.

The gas to be dried may be supplied to either side of the fluorocopolymer thin film. The purpose of dehumidification is achieved by separating the membrane and flowing a dry purge gas with a low moisture content on the moisture permeation side, or by reducing the pressure with a vacuum pump, etc., to create a partial pressure difference that is the driving force for membrane permeation.

The membrane used in the present invention is preferably a thin membrane with a thickness of several to several hundred liters. As for the film thickness, the thinner it is, the higher the permeability of the water vapor and the better the performance, which is preferable, but the moldability and
Limited by pressure resistance.

In the case of hollow fiber membranes, the inner diameter is 400 to 5, depending on the diameter of the hollow fiber.
For those with a thickness of 40 to 60, the thickness is preferably 40 to 60.

Dry purge gas with a low moisture content is a gas that is supplied to remove moisture contained in the gas to be dried through a membrane, and is an inert gas that does not react as much as possible even when the temperature rises. preferable. Reduced pressure means a pressure lower than atmospheric pressure, although it depends on the pressure of the raw material gas to be supplied.

In the present invention, an oxide film is formed using the dehumidified gas using the above-mentioned specific film having excellent dehumidifying ability. The oxide film is formed by introducing the highly dehumidified general gas and/or the corrosive gas into the oxidizer.

[Effect of the invention] The effects of the present invention are summarized as follows.

(1) If moisture enters during the oxide film formation process in the manufacture of semiconductor wafers, semiconductor devices, or their intermediate products, it will cause stacking faults, and on the other hand, this defective area will become a place for oxygen molecules to deposit, and impurities will also adhere to this area. However, by removing moisture, one of the causes of stacking faults can be removed. Therefore, a high-quality oxide film can be stably formed, and the product yield can be improved.

(2) HCl2, CR2, Br2. N20,
When a gas such as F2 is supplied from a cylinder, the quality of the gas in the cylinder is affected as it is used, and the moisture that was initially contained in the gas increases rapidly. and has an adverse effect on oxide film formation.

However, in the present invention, the moisture content of all gases including the above gases supplied is kept constant and extremely small, and the oxide film is formed using gases whose quality is stable, resulting in high purity and high quality. oxide film can be formed, and the yield of the product can be improved.

(3) Similarly to (2) above, 02, F2, N2, Ar gas, etc. are supplied via pipelines from on-site production equipment within the factory or from adjacent areas, and are further transported via piping within the factory to the reactor location. However, during this time, valves and the like are installed at the joints and branching parts of the pipes, but moisture may also infiltrate through these parts. Therefore, in the end, the present invention dehumidifies these gases just before the reactor to reduce the moisture content of the gases used, and forms an oxide film using stable gases of constant quality. It is possible to form a high-purity, high-quality oxide film without being adversely affected by poor connection of valves, etc.

(4) If halogen gas contains moisture, this moisture may contain impurities, or moisture may remain in gaps between equipment in the reactor, causing unexpected reactions with other gases. However, according to the present invention, since the oxide film is formed using a gas from which moisture is removed, unexpected reactions that have an adverse effect can be suppressed, and a high-quality oxide film can be formed.

(5) The dehumidifying ability of the membrane used in the present invention is higher than that of molecular sieves, and since no dust is generated, dehumidification is possible at room temperature, and cooling means and dust removal means required when molecular sieves are used are not required. This becomes unnecessary, and the entire apparatus used in the oxide film forming process can be simplified.

(6) By removing moisture from the corrosive gas, corrosion of the piping through which the corrosive gas passes is prevented; 1. Generation of fine heavy metals, dust, etc. is prevented. At the same time, preventing corrosion of piping, gas flow regulators, etc. will extend the life of these accessories and contribute to significant cost reductions.

[Examples] The present invention will be explained in more detail below using production examples, reference examples, and examples, but the present invention is not limited to the examples.

The moisture content of the gases in the Production Examples, Reference Examples, Examples, and Comparative Examples was measured using a dew point meter or a moisture meter, or depending on the gas, the Karl Fischer method.

Production example with tetrafluoroethylene? F3 CF2 = CFOGF2CF-0 (C:F2)3-9O
By copolymerizing 2F, the ion exchange capacity is 0.94 meq/
A Gram H type dry resin was obtained. The resulting resin was molded at a temperature of 2.
After making a film of 500 JLm at 50 °C and hydrolyzing this film with an alkaline alcohol solution,
Ion exchange was performed with an aqueous hydrochloric acid solution to convert the end of the side chain into a sulfonic acid type (H type), and the product was air-dried. The obtained film was subjected to dry-wet treatment in a vacuum, and then the equilibrium water absorption rate was determined at 25°C (Fig. 1).

As shown in FIG. 1, when the dry heat treatment temperature was about 70° C. or higher, the water absorption rate decreased significantly. The water absorption rate remained almost constant even at higher temperatures.

Similarly, as shown in Table A, polymer films with ion exchange capacities of 0.8 to 1.1 meq/g were prepared by changing the type of nanatsuma, and those having the water absorption rates shown in Table A were produced. From the results in Table A, the relationship between the ion exchange capacity and water absorption rate of the membrane of the present invention is shown in the shaded area in FIG.

Reference example Tetrafluoroethylene and (1”F3 CF2 = CFOGh 0F-0(CF2)2-502
By copolymerizing F, the ion exchange capacity is 0.9 milliequivalent/
A Gram H type dry resin was obtained. The obtained resin was melt-spun using a molding machine equipped with a spinneret for producing hollow fibers, and the inner diameter was 500 gm.
, a hollow fiber membrane with a membrane thickness of 60 lm was obtained.

This hollow fiber was hydrolyzed with an alkaline alcohol solution, and then ion-exchanged with an aqueous hydrochloric acid solution to convert the end of the side chain into a sulfonic acid type (H type) and air-dried.

Bundle 400 pieces of the obtained thread to a length of 40 cm,
It was fixed to a SUS separator with epoxy resin at both ends to create a water separator as shown in Figure 3. N2 gas adjusted to a moisture content of 1 ppm (dew point -76°C) or less was pressurized to 5 kg/cm2G in the moisture separator, and 0.5 i'/win was applied.
It was flowed inside the hollow fiber at a flow rate of (flow rate is converted to atmospheric pressure. The same applies hereinafter).

N2 gas, which was also adjusted to have a moisture content of 1 ppm (dew point -76°C) or less, was flowed to the outside at a flow rate of 0.75j)/win.

This was placed in a constant temperature bath at 70°C and heated for 3 hours, then the water separator was returned to room temperature and the water content was 31 ppm (
dew point -52℃), pressure adjusted to 5 kg/cm2G
2 gas (sample gas) was flowed inside the hollow fiber at a rate of 0.5j'/win, and N2 gas adjusted to a moisture content of ippm (dew point -76°C) or less was flowed at 0.75β/m on the outside of the hollow fiber.
I ran it in. When the dew point of the sample gas outlet of the moisture separator was measured, the moisture content was lppm (dew point -78°C).
It was below. Continuous operation was continued, and even after 24 hours, the moisture content at the sample gas outlet remained below Klppm (dew point -76°C).

On the other hand, when the dew point at the outlet of the moisture separator was measured for the purge gas outside the hollow fibers after 24 hours, the moisture content was 4.
It was 6 ppm (dew point -86°C). Thereafter, after approximately 1000 hours of continuous operation under the same conditions, the moisture content at the outlet of the sample gas remained below ippm (dew point -76°C), and the moisture content of the sampling gas decreased in the moisture separator and the moisture content of the purge gas. The ratio of water content increased in the separator was 1.2:1, which was approximately within measurement error.

As shown in Table A, results similar to those of the reference example were obtained with other films of the present invention.

Comparative Reference Example When the sample gas and purge gas were measured under the same conditions as in Example 2 using the same equipment as in the reference example without any heating pretreatment, the moisture content of the sample gas was 10.4 hours after 44 hours. E
ippm (dew point -80°C) was not reached.

Example 1 (i) A moisture separator similar to the reference example with a moisture content of 1 pp
Nitrogen gas pressurized to a pressure of 5 kg/cm 2 G (measured with a moisture meter) was flowed inside the hollow fiber for 0.5 R/min. Dry nitrogen gas (purge gas) with a water content of 1 ppm or less was flowed to the outside at 0.75 n/min at atmospheric pressure.

This was placed in a constant temperature bath at 70°C, and after preheating treatment for 3 hours,
Return to room temperature and reduce the moisture content of the inside of the hollow fiber to 3 lppm.
Hydrogen chloride gas (sample gas) adjusted to 5 kg/cm2 G and pressurized to 0.5 I! The moisture content of the sample gas at the outlet of the moisture separator was measured and found to be 3 ppIll. Continuous operation 24 times as is
Even after the time, the outlet water content of the sample gas remained at the 3pP layer.

On the other hand, regarding the purge gas outside the hollow fiber, the moisture content at the outlet of the moisture separator was measured after 24 hours, and it was found to be 5 p
After about 1200 hours under the same conditions as above, the moisture content at the outlet of the sample gas remained at 3 ppm.

Next, using hydrogen chloride gas with a moisture content of 3 ppm after treatment with a moisture separator, an oxidation device as shown in Figure 4 was used to form an oxide film to produce an intermediate product of a semiconductor device, but no dehumidification occurred. A yield improvement of 4% was achieved compared to the case using gas.

(ii) Almost the same results as above were obtained with a hollow fiber membrane made of a polytetrafluoroethylene copolymer (ion exchange capacity 0.94 meq/H type dry resin) having another repeating unit.

Example 2 (i) Using the same moisture separator as in Example 1, the pressure of the sample gas was set to the same conditions, and the moisture content after treatment with the moisture separator was measured using the reduced pressure method in the same manner as in Example 1. The results shown in Table 1 below were obtained.

Table 1 Next, hydrogen chloride gas with a moisture content of 3 ppm after treatment with a moisture separator was used to form an oxide film using an oxidation device as shown in Figure 4, and an intermediate product of a semiconductor device was manufactured. A yield improvement of 4% was achieved compared to the case using a gas that did not contain the above-mentioned conditions.

(ii) Almost the same results as above were obtained with a hollow fiber membrane made of a polytetrafluoroethylene copolymer (ion exchange capacity 0.94 meq/H type dry resin) having another repeating unit.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the dry heat treatment temperature and the equilibrium water absorption rate of the polymer semipermeable membrane obtained in the production example, and Figure 2 is the ion exchange capacity produced by dry heat treatment at 70°C or higher in the production example. 0.
Figure 3 is a graph showing the relationship between polymer water absorption (W) and ion exchange capacity (Q) of polymer semipermeable membranes of No. 8 to 1.1. Conceptual diagram,
Figure 4 is a conceptual diagram showing the position where a water separator is used in an oxidizer, and Figure 5 is a graph to determine the maximum temperature without thermal contraction of a hollow fiber membrane, where the horizontal axis is temperature and the vertical axis is is the length of the hollow fiber membrane at t°C (Lt) and the temperature 25
It is the ratio of the length L25) at ℃. FIG. 6 is a graph showing the relationship between the degree of heat treatment (1) of the hollow fiber membrane and the maximum temperature at which no heat shrinkage occurs, and the heat treatment temperature can be determined from this graph. 1...Hollow fiber membrane, 2...Sample gas inlet, 3...
・Sample gas outlet, 4... Purge gas inlet (closed when depressurizing), 5... Purge gas outlet (pressure reducing port when depressurizing), 6... Cell, 7... Partition plate, 8...・Moisture separator, 9
...Oxidizer, 10...Various cylinders, 11...Cock (valve).

Claims (1)

[Claims] When manufacturing semiconductor wafers, semiconductor devices, or intermediate products thereof, one side of a fluorine-based copolymer membrane having cation exchange groups is brought into contact with a general gas and/or a corrosive gas, and the other side is brought into contact with a general gas and/or a corrosive gas. A method for forming an oxide film in a vapor phase, characterized in that an oxide film is formed using a general gas and/or a corrosive gas that has been dehumidified by contacting with a dry purge gas or by reducing the pressure on the other side.