JPH07227533A - Baking method of vacuum container - Google Patents

Abstract

PURPOSE:To provide a baking method enabling to make a vacuum container clean only by baking it for a short time at a low temp. of a specific deg.C. CONSTITUTION:In a vacuum heating degassing method of the vacuum container 2, a heating means 3 is provided on the vacuum container 2 and while the inside wall face 9 of the container is heated at 70-200 deg.C, high purity gaseous nitrogen 14 or other inert gas is allowed to flow into the container 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of baking a vacuum container used for processing and storing a substrate used in a semiconductor manufacturing process or the like.

[0002]

2. Description of the Related Art A vacuum space is indispensable for processing and storing wafers in the semiconductor manufacturing process and glass substrates in the liquid crystal display device manufacturing process, which are the most advanced technologies. A vacuum container is required to create a vacuum space that is indispensable for such state-of-the-art technology. To create a vacuum space using a vacuum container, the vacuum container can be connected to a vacuum pump and evacuated. However, in this state, water molecules attached to the wall of the vacuum container are separated from the wall of the vacuum container in a vacuum, and the degree of vacuum does not rise, or the separated molecules are stored (such as wafers and liquid crystals for manufacturing semiconductors). It is feared that the glass substrate for manufacturing the panel, etc.) is contaminated at the molecular level.

The vacuum container (chamber) has an exhaust port, and a vacuum pump is connected from the exhaust port through a communication pipe. These, as a whole, form one vacuum system. Initially, the inside of the vacuum container is at normal pressure (atmospheric pressure), but with the operation of the vacuum pump, the air inside the vacuum container is forcibly discharged to the vacuum pump through the exhaust port and the communication pipe, so the inside of the vacuum container gradually. The pressure is reduced. As the pressure inside the vacuum container is reduced, water molecules and the like attached to the inner wall surface of the vacuum container are released from the wall surface and flow out into the space inside the vacuum container. However, since the density of water molecules and the like in the vacuum container decreases, the cleaning at the molecular level advances accordingly.

When the inner wall surface of the vacuum container is heated and heated, the detachment of water molecules from the wall surface is further accelerated. When vacuum baking, the higher the baking temperature,
Further, it is natural that the longer the baking time is, the more effective the removal of the contaminant molecules attached to the inner wall surface of the vacuum container is.

[0005]

However, it is said that the Al alloy, which is a material often used for vacuum containers, has a low melting point and the upper limit of the baking temperature is 150 to 200 ° C.

Even if a material having a high melting point such as stainless steel is used for the vacuum container, the vacuum container and the exhaust port, the exhaust port and the communication pipe, and the like are made of rubber or Teflon at the connecting portions of the respective parts constituting the vacuum system. O-rings and other sealing materials are essential. Due to the properties of these sealing materials, the upper limit of the operating temperature is limited, and the upper limit temperature at which repeated baking is allowed in the long term is about 200 ° C. at most.

Further, in consideration of heat resistance, even if a stainless steel material is used as the material of the vacuum container and a metal sealing material is used for the seal portion, the carbon atom C in the stainless steel material is higher than that of the stainless steel at 350 ° C. or higher. There is a problem that the grain boundary segregates at the crystal grain boundaries and the strength of the stainless steel member decreases.

As described above, the conventional baking methods,
That is, a simple method of decompressing with a vacuum pump and heating of a vacuum container does not provide sufficient cleanliness because there is a limit to the heating temperature, and there is a limit to improving product quality and yield.

With regard to LSIs and liquid crystal display elements as products, not only improvement of product quality and yield but also cost reduction is an important factor. In mass production,
Since the cost reduction is closely related to the time required for these manufacturing processes, it is not economical to elevate the temperature of the vacuum system and to increase the baking time.

The present invention has been made in view of the problems of the prior art, and is for baking a vacuum container, which has a low vacuum baking temperature and can enhance the cleanliness of the vacuum container in a short baking time. The purpose is to provide a method.

[0011]

According to the method for baking a vacuum container of the present invention, in the vacuum heating degassing method for a vacuum container, the vacuum container is provided with a heating means, and the inner wall surface of the container is 70 to 20.
It is characterized in that high-purity nitrogen gas or other inert gas is caused to flow into the container while being heated to 0 ° C.

[0012]

In the vacuum container, a clean inert gas is fed from one inlet and the gas in the vacuum container is sucked out from the other outlet, so that a steady gas flow occurs. Since this gas flow is added as a force to separate contaminant molecules from the inner wall surface of the vacuum container and discharge them to the outside through the vacuum pump, it is considered that the inside of the vacuum container can be cleaned in a short time.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the structure of a baking apparatus used in the baking method of one embodiment of the present invention. In the structure of the baking apparatus 1, a pipe 4 for feeding a small amount of highly pure inert gas 14 is connected to the upper portion of the vacuum container 2. A communication pipe 7 for discharging the gas in the vacuum container from the vacuum pump 8 to the outside of the vacuum system is connected to the lower portion. A heater 3 is wound around the outer circumference of the vacuum container 2 so that the inner wall surface 9 of the vacuum container can be heated. A filter 5 is provided on the upper pipe 4 so that water and other particles contained in the inert gas 13 can be removed to achieve high purity.

Next, an embodiment of the baking method of the present invention will be described. First, a small amount of high-purity N2 gas 14 in a vacuum container 2
It is made to flow in from the inlet 11 of. At this time, the inner wall surface 9 of the vacuum container is preferably heated to 70 ° C. or higher and 200 ° C. or lower by the heater 3. On the other hand, the vacuum pump 8 is operated to discharge the gas in the vacuum container as the exhaust gas 15 from the outlet 12 at the lower part of the vacuum container through the communication pipe 7. That is, vacuum baking is performed while flowing an inert gas.

The effect appears when the baking temperature is 70 ° C. or higher, but more preferably 100 ° C. or higher. The higher the baking temperature, the better, but from the experimental results, it can be expected to be sufficiently effective at about 120 ° C. Further, if the temperature is 200 ° C. or higher, a problem may occur with the sealing material or the like of the vacuum connection part.

As a method of applying heat to the vacuum container, a ribbon heater may be wound around the outer surface of the vacuum container or may be heated from the outside by an infrared lamp. Alternatively, a method of spraying a heating element on a vacuum container to form a heater may be used.

At this time, the flow rate of the high-purity N 2 gas or other high-purity inert gas flowing in the vacuum container is 100
If the vacuum container of about L is evacuated using a vacuum pump of about 300 L / s, 100 SCCM (Standa
A small gas flow rate less than rd Cube Centimeter Per Minute) is sufficient. The gas flow in the vacuum container is more effective in the viscous flow region where the number of molecules per unit volume is larger than that in the molecular flow region where the number of molecules per unit volume interferes and the adhesive force acts. Of course, a high-purity inert gas such as argon may be used in place of the high-purity N2 gas which flows in the vacuum container.

Next, an experiment was conducted to confirm the effect of the method for baking a vacuum container according to the present invention, which will be described.

The vacuum container has a volume of 27 L, a turbo molecular pump having an evacuation capacity of 300 L / s is used as the vacuum pump, and the baking adopts a heating system in which a ribbon heater is wound around the vacuum container.

In order to know the baking effect, after the wafer is vacuum-stored in a vacuum container under different baking conditions for a long time, the wafer is taken out and measured by a contact angle method, and the inside of the vacuum container is contaminated during storage. Estimated degree.

The contact angle method is widely known as a method for detecting contamination at the molecular level. That is, this is a measurement method in which pure water is dropped on the wafer surface and the contact angle formed by the degree of rising of the water surface and the water droplet is measured. When an organic film or the like is formed on the silicon surface, the contact angle of water drops dropped on the surface is large, and the contact angle is small if there is no contamination.

If the baking of the vacuum container is insufficient, a large amount of desorbed gas is released from the inner wall surface of the vacuum container. Since this gas adheres to the surface of the wafer being vacuum-stored while adsorbing various impurities in the vacuum container, residual impurities and organic films are present on the surface after the wafer is taken out. The contact angle increases with the degree of contamination at the molecular level.

The initial value of the contact angle of the test sample wafer was 1.5 °. After this, the wafer was stored for 16 hours in a vacuum container that had been baked for a certain period of time. After storage, the contact angle of the wafer was measured. However, the degree of vacuum during storage is 1.0.times.10@-6 Torr.

Table 1 shows the baking conditions and contact angles of the vacuum container.

[Table 1]

The graph of FIG. 2 is a graph of the results of Table 1. The following is clear from the experimental results. (1) Without baking, the contact angle increased to more than 7 times the initial value, resulting in large contamination. (2) With N2 gas (20 SCCM), although the baking temperature is low (120 ° C.), the cleanliness of the stored wafers is maintained only by baking for a short time. (3) On the contrary, without N2 gas (0 SCCM), the cleanliness is not improved so much even though the temperature is increased and baking is performed for a long time.

As described above, by flowing N2 gas during baking, the baking temperature can be lowered and the baking can be completed in a short time.

Although the gas inlet and the gas outlet are installed on the opposite sides of the vacuum container in FIG. 1, the position of the gas inlet may be any position. However, it is desirable to install the vacuum container at a position where the gas flows uniformly. The gas inlet is not limited to one, and two or more gas inlets may be installed. As described above, various modifications can be made without departing from the spirit of the present invention.

[0029]

As described above, according to the present invention, the vacuum container can be cleaned at a relatively low temperature and in a short time only by flowing a small amount of an inert gas into the vacuum container during baking. Therefore, L
With regard to the manufacture of SI and liquid crystal display elements, not only the effect on quality and yield, but also the effect of shortening the required baking time and reducing the cost of the product can be expected.

[Brief description of drawings]

FIG. 1 is a sectional view of a baking apparatus having an inert gas inflow means according to an embodiment of the present invention.

FIG. 2 is a graph showing the effect of cleaning by vacuum baking of the present invention and the prior art.

[Explanation of symbols]

 2 vacuum container 3 heater 4 pipe 5 filter 7 communication pipe 8 vacuum pump 9 inner wall of vacuum container 10 space inside vacuum container 11 gas inlet 12 gas exhaust port 14 high purity N2 gas 15 exhaust gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Yoshioka 4-2-1 Motofujisawa, Fujisawa-shi, Kanagawa Stock company EBARA Research Institute

Claims (1)

[Claims] 1. A vacuum heating and degassing method for a vacuum container, wherein the vacuum container is provided with a heating means, and the inner wall surface of the container is 70-70.
A method for baking a vacuum container, characterized in that high-purity nitrogen gas or another inert gas is caused to flow into the container while being heated to 200 ° C.