JPS62177916A - Removing method for impurity gas - Google Patents

Abstract

PURPOSE:To improve the purity of a gas by activating at least one of the principal constituent molecules of the gas or a specific impurity through optical irradiation, inducing an optical inducing chemical reaction and removing the specific impurity. CONSTITUTION:A gate valve 10 is opened, a pump 11 is operated and the inside of a silica tube 5 is evacuated, and a high-frequency power supply 7 is applied to a coil 6 to generate plasma. On the other hand, beams are irradiated from a mercury lamp 3 through a synthetic quartz window 9, raw material gas SiH4 is sprayed against Si 4 for capture irradiated by beams, and an Si substrate 1 for epitaxial growth is supplied with the Si 4. Oxygen in SiH4 is reacted with SiH4 and captured as SiO2 on the Si 4 for capture at that time, thus removing impurity oxygen. Accordingly, SiH4 gas, purity thereof is improved, can be fed onto the Si substrate 1 for epitaxial growth.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for removing impurities from gas.

(Prior Art and Problems to be Solved by the Invention) In thin film forming apparatuses, crystal growth apparatuses, etc., impurities contained in source gases are incorporated into films or crystals during film formation. Conventionally, methods to avoid this have been taken such as using a filter made of a desiccant agent or an agent for removing various impurities such as an oxygen scavenger at a position immediately before the reaction chamber in the gas introduction path.

In addition to using the above-mentioned filter, as a method to prevent impurity gases generated from the walls of the raw material gas introduction route from entering the raw material gas and being incorporated into the film or crystal, there is a method to prevent impurity gas generated from the walls of the raw material gas introduction route, etc. A method has been adopted in which impurity gases in the raw material gas introduction path are removed in advance by heating the reaction chamber to promote the generation of impurity gas from the wall surface and evacuating the path. However, it is extremely difficult to reduce the incorporation of impurities into the film or crystal to the order of PPb using only these methods. For example, in epitaxial growth of Si, when the growth is performed at a low temperature of 650°C or less, impurities, especially impurity oxygen, are significantly incorporated into the epitaxially grown film, and the concentration of impurity oxygen is 1018 to 1020 cm.
reach a certain degree. As mentioned above, one measure to reduce the intake of impurities is to use a filter made of an oxygen scavenger located just before the reaction chamber in the raw material gas supply path. Concentration is 5p
Although the oxygen scavenger itself becomes an impurity source, the concentration of impurities other than oxygen increases, and ultimately the impurity concentration cannot be reduced to ppbp-order.

The object of the present invention is to provide an impurity removal method that solves these conventional problems.

(Means for Solving the Problems) In order to solve the problems of the prior art described above, the present invention activates either or both of the main constituent molecules of the gas and the specific impurities contained in the gas. After irradiating the gas with light of the same wavelength, the gas was sent to a predetermined location where the gas described in (a) is to be used.

Furthermore, in the present invention, the gas is irradiated with light of a wavelength that activates either or both of the main constituent molecules of the gas or specific impurities contained in the gas, and the gas is irradiated with light of the wavelength. Alternatively, after bringing the gas being received into contact with a specific solid substance, the gas is sent to a predetermined location where the gas is to be used.

(Function) In the present invention, the main constituent molecules of the gas and specific impurity molecules contained in the gas undergo a light-induced chemical reaction at a specific wavelength, and the vaporization temperature is sufficiently higher than the temperature inside the thin film growth chamber or crystal growth chamber. It takes advantage of the fact that an in-phase compound can be formed whose vapor pressure is negligible with respect to the gas pressure (lppb or more F).

An in-phase compound that has a sufficiently high specific gravity compared to the main constituent molecules of the gas can follow the gas flow in a direction other than the direction of gravity, falls in the direction of gravity, and is separated from the gas flow\,c4),'). As a result, the impurity concentration in the gas stream is reduced and a highly purified gas is obtained.

In-phase compounds whose specific gravity is not sufficiently high compared to the main constituent molecules of the gas may exist as suspended substances in the gas, making it difficult to separate them in the direction of gravity. The use of certain solid substances to separate them from the gas stream. In this case, the gas stream is brought into contact with a specific solid substance, and a photo-induced chemical reaction occurs between the main constituent molecules of the gas and the impurity molecules contained in the gas at the contact surface, or a same-phase compound is formed in advance. By contacting this particular solid material with a gas stream that is irradiated with light and contains in-phase compounds produced by a photo-induced chemical reaction,
Certain in-phase compounds can be separated from a gas stream by being trapped within, including at the surface of, certain solid materials by physical adsorption.

In addition, if the impurity molecules in the gas do not react with the main constituent molecules, or if they do not generate the same phase compound even if they react, the gas stream is brought into contact with this solid substance, By irradiating the contact surface with light having a wavelength that activates the impurity molecules, a photo-induced chemical reaction between the solid substance and the impurity molecules is caused. As a result, an in-phase compound of the solid substance and impurity molecules is formed inside the solid substance including its surface, so that the impurity molecules are separated from the gas. Note that if the lifetime of the impurity molecules in the activated state is sufficiently long, it is not necessarily necessary to cause a reaction at the contact surface, and the gas flow containing the impurity molecules activated by prior light irradiation is It is also possible to induce a reaction between the impurity molecules and the solid substance by bringing them into contact with a substance.

(Embodiments of the Invention) Hereinafter, embodiments in which the present invention is applied to epitaxial growth of silicon by plasma CVD will be described in detail with reference to the drawings.

The figure is a schematic diagram of an apparatus to which the present invention is applied to a silicon epitaxial growth apparatus by plasma CVD. In addition to a normal plasma CVD epitaxial apparatus, the apparatus used in the present invention can remove 02 contained as an impurity in the raw material gas SiH4 or inert gas N2, or 02 that adheres to piping and mixes with the raw material gas. It is characterized by the provision of a mercury lamp (1849 people) as a light source for activation.

Furthermore, when SiH4 is used as the raw material gas, it is used as a substance that captures 5i02 generated by reacting with SiH4 molecules due to this activation, and when an inert gas is used, it is used as a substance that reacts with activated 02. Another feature is that Si is used.

The implementation procedure of the present invention is to first open the gate pulp 10,
The quartz tube 5 is evacuated to about 10-5 Pa by operating the turbo molecular pump 11, and then plasma is generated by applying high frequency power from the high frequency power source 7 to both ends of the coil 6 wound around the quartz tube 5. After that, the Si substrate 1 for epitaxial growth is heated to 650° C. or higher by the heater 2 for heating the substrate after blowing the source gas SiH4 through the synthetic quartz window 9 onto the Si4 capture material that has been irradiated with light from the mercury lamp 3. Epitaxial growth of Si was carried out by supplying .

The temperature of Si4 for capture was adjusted by a capture portion temperature controller 8 to a temperature range of 200° C. to 300° C. that would allow sufficient adhesion of 5i02.

Oxygen in SiH4 is reacted with SiH4 to capture Si4
On the top, SiH4 captured as 5i02 and highly purified with reduced impurity oxygen is deposited on a Si substrate 1 for epitaxial growth.
By supplying Si to the top, it was possible to obtain a Si pitaxially grown film with an oxygen concentration at the interface of 1016 cm-3, which is more than two orders of magnitude lower than that of the conventional method.

In this example, SiH4 and oxygen are reacted on the capture Si4, but the reaction does not necessarily need to occur on the capture material. In advance, a large number of holes smaller than the size of the 5i02 particles were made in Si to the extent that the gas flow containing 5i02 generated by light irradiation was not obstructed.
5 by installing it in a position that blocks the gas flow.
i02 particles can be separated from the gas stream Note that although Si is used to capture l,t'5i02 in this example, it is not necessary to use an in-phase material for capture. If part of the SiH4 gas supply piping is a quartz tube and the raw material gas is irradiated with Hg lamp light through this quartz tube, most of the generated 5i02 will accumulate at the bottom of the tube and S
Separated from iH4. However, when using this method, a part of 5i02 may not be completely separated and may float in SiH4, so in order to promote the separation of 5i02 from SiH4, the gas is moved in the opposite direction of gravity. It is necessary to take measures such as introducing

Note that the present invention is not necessarily applied only to the epitaxial growth of Si. If TMA is used as the raw material gas, a metallic aluminum thin film with less oxygen contamination can be formed by capturing impurity oxygen as aluminum oxide.

Next, an example in which the impurity 02 contained in the inert gas N2 is reduced will be described as an example in which the method of removing impurities as a compound with a specific in-phase substance among the methods according to the present invention is applied. Oxygen in N2 has an adverse effect on the material to be nitrided or on the film when used in a nitriding process or as a carrier gas for other raw material gases. In this example, impurity 02 contained in N2 was reduced by activating impurity 02 in N2 sprayed onto capture Si4 by irradiation with mercury lamp 3 (1849 people) and reacting with capture Si4. .

In this embodiment, the impurity oxygen is activated on the capture Si4 using the mercury lamp 3, but it is not necessarily necessary to activate it on the capture Si4. It is also possible to reduce the impurity oxygen in N2 by activating the impurity oxygen by light irradiation in advance and then spraying N2 containing this onto the capture Si4 to cause the Si to react with the impurity oxygen. However, in this case, the time required for the gas flow to travel the distance from the irradiation position of the mercury lamp 3 to the capture Si 4 must be shorter than the lifetime of the activated oxygen in its excited state.

Furthermore, it goes without saying that the present invention can be applied not only to CVD but also to a wide range of other gas phase process techniques.

Further, in this embodiment, an example was described in which only one type of impurity gas is removed, but multiple types of impurity gases can be removed by irradiating light with wavelengths corresponding to each type within the scope of the present invention. Needless to say, impurity gas can be effectively removed.

In addition, although the examples describe only the case of activating impurity molecules in the gas, in the present invention, by activating the main constituent molecules of the gas, a compound with the impurity molecules in the gas is generated and the impurity molecules are activated. It is also possible to remove it. Furthermore, in the present invention, it is also possible to remove the impurity molecules by activating the impurity trapping substance to generate a compound with the impurity molecules.

(Effects of the Invention) As explained above, according to the present invention, either or both of the main constituent molecules of the gas or the specific impurities contained in this gas are activated by light irradiation of a specific wavelength, and the impurities and the main constituent molecules are activated. By inducing a photo-induced chemical reaction with molecules and separating and removing specific impurities from the gas phase as in-phase compounds, the gas can be purified to a degree that was not possible with conventional impurity gas removal methods. I can do it. Further, according to the present invention, specific impurities contained in the gas are activated by light irradiation with a specific wavelength to induce a photo-induced chemical reaction with the specific substance, and the specific impurities are separated from the gas phase as an in-phase compound with the specific substance. By removing impurity gases, it is possible to improve the purity of the gas to a degree that has not been possible with conventional impurity gas removal methods.

[Brief explanation of drawings]

The figure is a schematic diagram showing an embodiment to which the present invention is applied. 1... Si substrate for epitaxial growth 2... Heater for heating the substrate 3... Mercury lamp 4... Si for capturing 5... Quartz tube 6... Coil 7... High frequency power source 8... Capture section temperature regulator 9...Synthetic quartz window 10...Gate valve

Claims (2)

[Claims] (1) After irradiating the gas with light of a wavelength that activates either or both of the main constituent molecules of the gas or specific impurities contained in the gas, the gas is placed at a predetermined location where the gas will be used. An impurity gas removal method characterized by sending in. (2) The gas is irradiated with light of a wavelength that activates either or both of the main constituent molecules of the gas or specific impurities contained in the gas, and the gas is irradiated with or receives light of the wavelength. A method for removing impurity gas, comprising: bringing the gas into contact with a specific solid substance, and then sending the gas to a predetermined location where the gas is to be used.