JPH0787181B2 - Photo-excitation process equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical CVD apparatus and an excimer laser apparatus for forming a thin film on a substrate by a photochemical reaction from a reaction gas.

In this specification, the photo CVD apparatus and the excimer laser apparatus are collectively referred to as "photoexcitation process apparatus".

(Prior Art) A conventional photo-CVD apparatus has a reaction chamber (1) as shown in FIG.
It is mainly composed of a chamber (1a) for isolating the substrate from the surroundings, and a supporting table (3) is fixed to the upper part of the reaction chamber (1), and the substrate (5) is heated inside the supporting table (3). A heater (2) is attached for this purpose. A substrate holder (4) for mounting the substrate (5) is fixed to the lower part of the support base (3). In addition, a window (6) is provided below the chamber (1a) for introducing light (generally ultraviolet light) that causes a photochemical reaction required for film formation and advances the reaction. The window (6) is provided at a position where the light transmitted therethrough can irradiate the substrate (5). The material of the window (6) is generally made of a material such as quartz or magnesium fluoride that transmits ultraviolet rays.

A reaction gas, such as disilane (Si ₂ H ₆ ) gas, which causes a photochemical reaction to deposit a thin film of the reaction product on the substrate (5) is introduced into the reaction chamber (1), and the light source (7). When the substrate (5) is irradiated with light from the window through the window (6), disilane gas is decomposed and amorphous.
A thin film of silicon is deposited.

However, since the window (6) is also exposed to the reactive gas, the film is gradually deposited on the window (6) by irradiating the light, and the intensity of the light reaching the reaction chamber (1) is reduced by the film. Then, there was a problem that the film formation could not be continued at last.

In order to solve such a problem, conventionally, (a) window (6)
A method of preventing the deposition of a film on the window by applying oils and fats on the reaction gas side of (2) and a method of spraying (b) an inert gas on the window (6) have been proposed.

Further, the excimer laser device is attracting attention as the only high-power laser that oscillates in the ultraviolet region, and its application is expected in the electronic industry, polymer industry, chemical industry, energy industry and the like.

An apparatus that emits excimer laser light is called an excimer laser, and basically, as shown in FIG. 7, a reaction chamber (1) containing a laser gas and a chamber (1a for isolating the reaction chamber (1) from the surroundings. ) And a pair of discharge electrodes (13) as a kind of excitation means for exciting the laser gas, and a window (6) for transmitting the oscillated laser light to the outside of the housing, and this window may also be used. It consists of an optical resonator (14). One of the optical resonators (14) is a total reflection mirror and the other is a semi-transmission mirror.

In this case, the laser gas is a rare gas (R) such as xenon,
It consists of a mixture of krypton, argon and halogen (X) such as chlorine and fluorine, and gives a pulsed shock to this laser gas by electron beam irradiation, discharge, etc. to raise the rare gas (R) to the excited state (R ^* ). Then, it immediately combines with halogen (X) to form a molecule (RX ^* ) that exists only in the excited state. This molecule (RX ^* ) is an excimer (exci
mer) is called.

However, since the excimer is unstable and can not stand the state as it is, it immediately emits ultraviolet light, falls to the ground state, and again splits into a rare gas and a halogen. This is called a bound-free transition.

Therefore, an excimer laser device is one in which ultraviolet light based on bound-free transition is amplified in an optical resonator composed of a pair of mirrors and is extracted as laser light.

(Problems to be solved by the invention) However, in the photo-CVD, even if the former method (a) is used, the film is gradually deposited on the window (6), so that the window (6) is formed after film formation.
There is a problem in that it is not efficient because it is to clean and re-apply oils and fats. The latter (b) also does not completely suppress the deposition of the film. Furthermore, both will introduce a substance unrelated to the photochemical reaction into the reaction chamber,
There is a problem that the produced film is contaminated with impurities and the performance is significantly deteriorated.

Further, also in the excimer laser device that is often used as an ultraviolet light source, the reactive gas is adsorbed on the inner surface of the chamber of the window (6) to cause film deposition due to photoreaction, so that the transmittance of the window is reduced and the output of the laser is reduced. There was a problem that it lowered.

The present invention aims to solve these problems and prevent or suppress film deposition on the inner surface of the window (6) without introducing unnecessary substances into the reaction chamber (1).

(Means for Solving Problems) A feature of the present invention is to provide cooling means for cooling the window,
During the photoexcitation process, the window is cooled to a temperature below the dew point of the water in the reaction chamber by the cooling means to condense the water on the window and cover the window with a layer of water. It is in.

(Function) Generally, the lower the substrate temperature, the more difficult it is to deposit a film on a substrate. Therefore, in the present invention, the window is cooled to make it difficult to deposit a film on the window.

Further, the reaction gas generally contains a very small amount of water as an impurity. Therefore, when the window is cooled below the dew point of water at the partial pressure of water in the reaction chamber according to the present invention, the water is deposited on the window to form a thin water layer. After that, when light is irradiated into the reaction chamber to start film formation, it becomes difficult for the film to be deposited on the water layer, and fogging of the window is significantly reduced.

Moreover, even if a film is deposited, it does not directly adhere to the window. Therefore, after the formation of the target film is completed, if the cooling is stopped and the heating is positively or left unheated to raise the temperature of the window, the inside of the reaction chamber is in a depressurized state and the condensed water evaporates. . When the water evaporates, the film deposited on top of the water layer peels away, eliminating the need to clean it. As a result, it becomes unnecessary to perform an action, which has been conventionally performed for cleaning the window, such as introducing an etching gas into the reaction chamber (plasma etching) or breaking the vacuum to wipe the window, which is extremely detrimental to the vacuum system.

It is desirable that the water layer deposited on the window surface due to the window surface being below the dew point has a constant and uniform thickness (for example, 10 to 1000Å). This film thickness is known, for example, by measuring the conductivity of the film nozzle or counting the interference fringes, and the temperature of the window surface is controlled to a constant value by using a temperature raising device such as a heater together with the cooling means. And it can be made uniform.

Example 1 One example of the present invention will be described below.

FIG. 1 is a diagram showing a schematic vertical cross section of the photoexcitation process apparatus of this embodiment.

A support base (3) is fixed to the upper part of the reaction chamber (1), and a heater (2) for heating the substrate (5) is attached inside the support base (3). On the other hand, a substrate holder (4) for mounting the substrate (5) is fixed to the lower surface of the support base (3).

A window (6) for transmitting light from a light source and irradiating a substrate (5) is attached to a part of the chamber (1a).
Several coolant passages (9) penetrate through the inside of the window (6) parallel to the surface, and circulation pipes are connected to both ends thereof.

Liquefied nitrogen, liquefied helium, or the like is used as the coolant, and these are cooled to a predetermined low temperature by a cooling device (not shown). The cooled coolant and the coolant circulation system constitute the cooling means of the present invention.

A light source chamber (8) is provided adjacent to the photoexcitation process apparatus of this embodiment, and a light source (7) is arranged inside the light source chamber.

The reaction chamber (1) and the light source chamber (8) are preliminarily high vacuum, for example, 1 × 10
^-5 to 1 × 10 ^-6 Torr. After introducing a reaction gas such as disilane 10 cc / min, ammonia 500 cc / min, and nitrogen 500 cc / min into the reaction chamber, the total gas pressure in the chamber is adjusted. 100 Torr. In this case, the chamber contains moisture with a partial pressure of 0.001 Torr. Further, an inert gas is introduced into the light source chamber (8) at the same pressure.

Then, a coolant (here, liquid nitrogen) is flown through the circulation pipe (9) to cool the window (6) to −75 ° C. (a dew point of partial pressure 0.001 Torr .; −75 ° C.) or lower. The coolant passes through the inside of the window (6) and cools only the window (6) without leaking into the airtight reaction chamber (1) and the light source chamber (8).

As a result, water begins to condense on the reaction chamber side surface of the window (6),
A very thin water film is formed.

Then, when the light source (7) is turned on and the substrate (5) is irradiated with light having a wavelength of 185 nm through the window, a silicon nitride film starts to be deposited on the substrate.

However, since the window (6) is extremely low temperature (-75 ° C. or lower), the film is hardly deposited on the inner surface of the window (6),
In addition, even if slightly deposited, the deposited film does not directly adhere because the water film is formed on the window (6).

Therefore, if the cooling is stopped and the temperature of the window is raised to the dew point or higher after the film formation, the water film evaporates and the deposited film peels off. Therefore, it is not necessary to clean the film again.

(Embodiment 2) In a second embodiment shown in FIG. 3, the circulation pipe (10) is arranged on the surface without providing the coolant passage (9) inside the window (6). In this way, it is not necessary to hollow out the inside of the window (6) for the coolant passage (9), but instead, for the part exposed to the light of the light source, the circulation pipe (10) should be made of a material with good transmittance. Otherwise, it is necessary to obey the light shielding by the circulation pipe (10).

(Example 3) The side of the window (6) not facing the inside of the reaction chamber, for example, the light source side in the photoexcitation process apparatus and the outer side (hereinafter referred to as the outside of the window) in the excimer laser are exposed to the atmosphere and If both sides are cooled, frost may form on the atmosphere side, which may hinder the transmission of light.

To avoid this, as shown in FIG. 6, the window (6)
The outside of the light source side of is heated by a heater. A high vacuum is applied to the outside of the window (6) (preferably multiple windows are used and a high vacuum is applied between them). The outside of the window is covered with a high-purity dry gas (preferably at the same pressure as the reaction chamber and a high-purity He , H ₂ ) may be combined with any of the above.

Example 4 The window (6) of the excimer laser device shown in FIG. 7 was replaced with the window used in Example 3. As a result, the window (6) did not fog even after long-term use.

EFFECTS OF THE INVENTION As described above, cooling a window in accordance with the present invention eliminates or reduces film deposition on the window during the photoexcitation process.

Generally, when a film is formed on a substrate, the film deposition becomes more difficult as the substrate temperature is lower. Therefore, cooling the window according to the present invention makes it possible to reduce the film deposition on the window.

When the window is cooled by the cooling means below the dew point of the moisture (moisture in the reaction chamber) so that the moisture in the reaction chamber is condensed in the window during the photoexcitation process, water is condensed on the window. However, since the window is covered with the water layer, it becomes difficult to deposit the film, and even if the deposited film adheres slightly, the water layer is interposed between the window and the film, so that the deposited film is directly attached. Does not adhere to windows. Therefore, after the film formation, the temperature of the window is naturally increased by stopping the cooling of the window, or when the temperature of the window is actively heated to raise the temperature of the window to room temperature or higher, water evaporates. Along with this, the film deposited on the window peels off as the water evaporates.

Therefore, the film can be re-formed without breaking the vacuum, the clarity of the reaction chamber can be maintained, and a continuous process on the same substrate is possible. When water as impurities contained in the reaction gas is condensed on the window, the purity of the reaction gas is increased, and as a result, the purity of the deposited film is also improved.

Further, according to the present invention, it is not necessary to introduce a substance unnecessary for the photochemical reaction into the reaction chamber in order to prevent the film from being deposited on the window, so that the reaction gas is not contaminated.

In addition, even in an ultraviolet light source such as an excimer laser device,
Since the window can be regenerated without adversely affecting the laser gas in the reaction chamber, the life of the light source can be extended.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an optical excitation process device according to a first embodiment of the present invention. FIG. 2 is a schematic plan view of a window. FIG. 3 is a schematic vertical sectional view of an optical excitation process device according to a second embodiment of the present invention. FIG. 4 is a schematic plan view of the window. FIG. 5 is a schematic vertical sectional view of a conventional photo-CVD apparatus. FIG. 6 is a schematic vertical sectional view of an optical excitation process device according to a third embodiment of the present invention. FIG. 7 is a schematic vertical sectional view of an excimer laser according to the fourth embodiment of the present invention. (Description of symbols of main parts) 1 ... Reaction chamber 1a ... Chamber 2, 11 ... Heater 3 ... Support stand 4 ... Substrate holder 5 ... Substrate 6 ... Window 7 ... Light source 8 ... Light source chamber 9 ... Coolant passage (a member that constitutes an example of cooling means) 10 ... Coolant circulation pipe (a member that constitutes an example of cooling means) 12 ... Glass 13 ... Discharge electrode 14 ... Optical resonator 15 ... … Membrane forming gas inlet 16 …… Membrane forming gas outlet 17 …… High vacuum

Claims (1)

[Claims] 1. A photo-excitation process apparatus comprising a reaction chamber and a window, wherein cooling means for cooling the window is provided, and the window is cooled by the cooling means during the photo-excitation process to remove moisture in the reaction chamber. The photoexcitation process apparatus, wherein the water is condensed on the window by cooling to below the dew point, and the window is covered with a layer of water.