JPH0789547B2 - Drying method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for drying an object whose surface is wet by a liquid, and in particular, an IC manufacturing substrate, an information recording substrate, in which surface contamination is a problem, After subjecting the liquid crystal display substrate to surface treatment using various liquid chemicals and washing with water,
The present invention relates to a drying method using vapor of an organic substance, which does not cause droplet traces (hereinafter referred to as "spots") and fine contaminants to adhere, and has a low risk of explosion and the like.

Conventional technology As a method that has been conventionally used for drying dried objects such as Si wafers after wet processing such as cleaning and wet etching, several Si wafers can be stored in a carrier (batch type),
Alternatively, a method of removing water droplets by rotating the Si wafer at 1000 to 3000 rpm while suction-holding one by one (single-wafer type) (hereinafter, referred to as spin drying method).

A method of blowing water or a gas such as N ₂ onto a Si wafer having water droplets to remove the water droplets (hereinafter referred to as blow drying method).

A method of immersing an object to be dried such as a Si wafer with water droplets in the liquid of an organic solvent and removing the droplets on the surface of the Si wafer by utilizing the difference in specific gravity between the organic solvent and water (hereinafter referred to as the solvent immersion method. ).

A method in which an organic solvent is heated by a heater to be vaporized, and a Si wafer having water droplets is put into the vapor to remove the water droplets (hereinafter referred to as vapor drying method).

Etc. are used.

Problems to be Solved by the Invention The above-mentioned drying method has the following problems in the conventional technique.

In the spin drying method, since it is necessary to rotate the Si wafer at a high speed, dust generated from the sliding part between the wall of the drying chamber and the rotating shaft, the rotary drive, etc. easily enters the drying chamber and contaminates the Si wafer. Cheap. Further, the water droplets scattered from the surface of the Si wafer collide with the inner wall of the drying chamber to be contaminated and float in the drying chamber in the form of mist, and there is a great risk of recontamination of the Si wafer.

In the blow drying method, there are no sliding parts in the drying chamber and Si
The risk of wafer contamination is low, but a large amount of clean gas is required, which increases running costs.

In the solvent dipping method, a large number of fine particles and impurities are contained in the organic solvent as compared with the air in the clean room. However, in the case of a liquid, it is difficult to pass the fine particles and it is difficult to obtain a clean solvent. If the Si wafer is immersed in such a solvent, the Si wafer will be contaminated.

The vapor drying method is an improvement over the drawbacks of 1. However, when gasifying (vaporizing) an organic solvent, a new problem arises in that the risk of fire and explosion becomes dramatically higher than when it is a liquid. . Further, since vaporization is performed by heating the solvent with a heater, a large amount of vapor of the solvent of the organic solvent is generated, which further increases the risk of fire and explosion, and also has a great adverse effect on the human body. To prevent these, commercially available steam dryers use a large distance between the liquid surface of the organic solvent and the top surface of the steam dryer to prevent steam from leaking out of the equipment, and use explosion-proof electrical parts for the steam dryer. In addition, a large area near the Si wafer input port needs to be exhausted, and the drying device is large and expensive.

In view of the above problems, the present invention does not contaminate the material to be dried such as Si wafers with fine particles and the like during drying, is easy and quick to dry, has a low risk of fire and explosion, and can be dried in large quantities and uniformly. The present invention provides a drying method capable of

Means for Solving the Problems In order to solve the above problems, the present invention provides a vapor of an organic substance inside a container equipped with a means for decompressing the interior,
After contacting the organic substance vapor and the material to be dried in the container,
A method of drying by applying a physical force to a liquid on the surface of an object to be dried under a pressure of atmospheric pressure or less, wherein the vapor of the organic substance is vaporized under a reduced pressure at which the organic substance does not boil at room temperature. The present invention provides a drying method characterized by using.

Action In the present invention, the Si wafer is brought into contact with the vapor of an organic substance in order to remove water droplets from the surface of the Si wafer and dry the same.
Organic solvents are suitable as those that easily generate vapor in organic matter, as a means for generating organic solvent vapor, put the organic solvent inside a container equipped with a means for decompressing (hereinafter referred to as a decompression container), When the pressure inside the decompression container is reduced after sealing the decompression container, vaporization of the organic solvent is promoted and the decompression container is filled. The vapor thus created is a vapor in which only organic solvent molecules are vaporized and is a clean vapor containing no fine particles in the organic solvent, and the Si wafer is not contaminated by the vapor of the organic solvent. Further, as long as the inside of the decompression container is in a decompressed state, the organic substance vapor produced by the method of the present invention does not leak into the atmosphere through the gap between the decompression container and the tube to cause a fire or adversely affect the human body.

However, if the pressure is lowered too much, the organic solvent will boil, and the organic solvent will be scattered as fine particles containing mist and will be contaminated on the Si wafer. It should be more than pressure.

The effect of the vapor of the organic solvent on the drying of the Si wafer is that when the vapor of the organic solvent comes into contact with the Si wafer, an organic film is formed on the surface of the Si wafer and the Si wafer becomes hydrophobic and the contact angle with water droplets increases. This makes it easier to remove water drops.

When the Si wafer is standing vertically in this state, gravity acts on the water droplets and the water droplets drop on the surface of the Si wafer to remove the water droplets from the Si wafer, or by blowing air or N ₂ gas onto the Si wafer, Water drops can be easily removed by applying mechanical force to the water drops by a method such as rotating at a low speed at which dust of 200 to 500 rpm is unlikely to occur.

Such an organic film formed on the surface of the Si wafer (hereinafter referred to as an organic film) includes a hydrophilic water droplet and a Si wafer surface which may be either hydrophilic or hydrophobic depending on the processing state. In order to form an organic film, an organic substance having a hydrophilic group and a hydrophobic group in the molecule is suitable. These substances are
Depending on the surface properties of the Si wafer, the adsorption and orientation directions change and become hydrophobic.

Such substances include methanol, ethanol, n-
There are alcohols such as propanol, isopropanol and glycol, ketones such as acetone, carboxylic acids such as acetic acid, esters such as methyl acetate and ethyl acetate, amines such as ethylamine, sulfonic acid and surfactants. In the present invention, it is possible to use a single substance or a mixture of any of these substances, but methanol, ethanol, ethylamine, acetic acid, methyl acetate, ethyl acetate, which has a small adsorbing ability to the Si wafer and can be easily replaced with the treatment liquid, Acetone, isopropanol, n-propanol, n-butanol, etc. are suitable.

Furthermore, isopropanol, n, which has a certain solubility and is easily adsorbed on the surface of water droplets, is not completely dissolved in water.
-Butanol and n-propanol are more suitable.

On the other hand, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, tert-butyl alcohol and other alcohols such as ethyl acetate, propyl acetate, butyl acetate, isopropyl acetate, butyl acetate, butyl acetate, isobutyl acetate, propyl formate. , Isopropyl formate, methyl butyrate, etc., ethers such as isopropyl ether ethyl ether, methyl propyl ether, etc., methyl ethyl ketone etc. form a minimum azeotropic mixture of water and two or three components, and decompress at constant temperature to obtain only water. It has the effect of drying faster than in the case. The lower the pressure at this time, the shorter the drying time, but usually 50 Torr
It is preferably 20 Torr or less.

These organic solvents may be used alone or in combination in which a plurality of solvents are mixed and used to form a minimum azeotropic mixture.

These effects of the organic solvent work effectively to dry the Si wafer quickly and prevent dust from adhering.

As a means for reducing the pressure inside the pressure reducing container, the degree of vacuum required to vaporize the organic solvent without boiling is 200 to 20 Tor.
Since it is r, any means such as a rotary pump, an oil diffusion pump, and a mechanical booster pump, which are usually used as a vacuum pump, can be used as long as it has the ability to reduce the pressure of the pressure reducing container to about 20 Torr. Also,
If the organic solvent is discharged from the pressure reducing container together with the exhaust air for a long period of time and is trapped and mixed in the oil of the vacuum pump, the exhaust capability of the vacuum pump is deteriorated. Therefore, it is desirable to have a device for removing the organic solvent in the middle of the exhaust pipe.

By the way, since the organic solvent vapor generated by the above means does not generate much at atmospheric pressure and is generated only when the inside of the decompression container is in a decompressed state, a large amount of organic solvent vapor as in the case of heater heating in the conventional vapor drying method is used. The risk of fire explosion, which can quickly generate the required amount of organic solvent vapor when and when needed, is extremely reduced. Further, since the generated organic solvent vapor stays only in the decompression container and the exhaust tube, the risk of fire explosion is further reduced.

Example A first example will be described below with reference to the drawings.

The figure shows a cross section of a drying device equipped with a rotary pump 12 as means for reducing the pressure inside the decompression container 11 in the first embodiment of the present invention. In the figure, 11 is a decompression container, 12 is a rotary vacuum pump as decompression means, and 13 is Si.
Wafer, 14 is isopropyl alcohol (hereinafter referred to as IPA) as an organic substance, 15 is an IPA container, 16 is a Si wafer supporting jig (hereinafter referred to as hanger), 17 is a valve, and 18 and 19 are vent valves. , 20 is a filter, and 21 is a vacuum gauge.

Hereinafter, the specific content of this example will be described.

Pyrogenic method on 13 inch Si wafer with 5 inch diameter
A SiO ₂ film was formed with a thickness of 3000Å. After applying a photoresist (thickness 1.2 μm) on the SiO ₂ film, exposure and phenomenon were performed to form a pattern. CHF ₃ and C ₂ F ₆
Of the SiO ₂ film by applying RF with a mixed gas of
After dry etching to a depth of 00Å, the photoresist on the Si wafer 13 was sufficiently removed by an O ₂ plasma resist asher. The Si wafer 13 thus obtained is immersed in a cleaning solution (NH ₄ OH: H ₂ O ₂ : H ₂ O = 1: 1: 5,60 ° C; hereinafter referred to as RCA cleaning solution) in a quartz bath for 10 minutes. Then, in another quartz tank, supply ultrapure water (specific resistance value 18 MΩ · cm) from the bottom of the tank, and quickly immerse it in the overflowing washing tank from the top of the tank to quickly wash the washing water with a specific resistance value of 17 MΩ. -Washed with water until it became cm or more.
At this time, the surface of the Si wafer 13 was hydrophilic and the entire surface was wet with water.

The pattern formed on the Si wafer 13 is a test pattern, and is a square with a side of 0.2 μm from 1.0 μm to 3.0 μm.

On the other hand, isopropanol (500 ml, 20 ° C.) 14 was put in a glass container 15 and placed in a vacuum container (internal volume 10) 11 shown in the figure, and valves 17, 18 and 19 were closed. Next, the Si wafer 13 that had been washed with water was placed upright on the hanger 16.
The contact area between the Si wafer 13 and the hanger 16 is designed to be as small as possible in order to prevent water accumulation at the contact points.

After that, the decompression container 11 is sealed and the rotary vacuum pump 12 is operated to reduce the pressure in the decompression container 11 to 60 Torr in about 10 seconds, and the pressure is reduced to 40 Torr to further reduce the pressure and prevent boiling of isopropanol 14. Open the valve 19 a little to filter the air (minimum particle size removal 0.002μ
While maintaining this state for 5 minutes while introducing it into the decompression container through m) 20, the Si wafer 13 was brought into contact with isopropanol vapor. Then, after closing the valve 17 and fully opening the valve 19 to return the internal pressure of the decompression container 11 to the atmospheric pressure, a door (not shown) was opened and the Si wafer 13 was taken out. Observing the surface of the Si wafer 13 at this time, the Si wafer that was initially wet with water
After decompressing the decompression container 11 with the rotary vacuum pump 12, the surface of the Si wafer 13 suddenly becomes hydrophobic and the water film drops downward after a few seconds, and when the Si wafer 13 is taken out, it is completely dried. Was there.

In addition, an SiO ₂ film and a pattern were not formed on the Si wafer, and a Si wafer having only a natural oxide film on the surface was used to perform RC
After the step of cleaning with the cleaning solution A, the Si wafer that had been cleaned, washed with water and dried in the same manner as the above step was attached to the surface of the Si wafer 13 using a laser surface inspection device (WM-2 manufactured by Tokyo Optical Machine Co., Ltd.). The number of fine particles (diameter 0.3 μm or more) present was measured. The results are shown in Table 1.

The second embodiment of the present invention will be described below.

In the drying device shown in the drawing used in the first embodiment, a vacuum container
11 Isopropanol 14 contained in a glass container 15 was placed inside, depressurized in the same manner as in the first embodiment, and held at 40 Torr to vaporize isopropanol 14 without boiling,
After filling the decompression container 11, the valve 17 was closed to return the internal pressure of the decompression container 11 to the atmospheric pressure.

A patterned Si wafer 13 formed in the same manner as in the first embodiment was placed horizontally in the decompression container 11 for 1 minute and brought into contact with vapor of isopropanol.

After taking out the Si wafer 13 from the decompression container 11, the Si wafer was stored in a fluororesin Si wafer carrier and put in a spin dryer (manufactured by Fuji Advance Co., Ltd.) and dried for 1 minute at 300 rpm. It was dry.

In order to measure the number of dust adhering to the Si wafer by this drying method, after the RCA cleaning, the water washing, the standing in the decompression container 11 and the spin drying in the same manner as above using the Si wafer without the pattern formed. The number of dusts was measured with a laser surface inspection device.

The results are also shown in Table 1.

On the other hand, the Si wafer after being brought into contact with the vapor of isopropanol is taken out from the decompression container 11, and N ₂ gas is blown onto the front surface of the Si wafer while adsorbing and holding the back surface with vacuum tweezers (N ₂ gas amount 200 / min). And the water drops splattered easily and dried. The number of dusts attached to the Si wafer by this drying method was measured in the same manner as above using a Si wafer having no pattern, and the results are also shown in Table 1.

Hereinafter, an experiment for comparison is shown below.

As a first comparative example, in the first embodiment, a decompression container
When the Si wafer 13 was dried in exactly the same manner as in the first embodiment, except that isopropanol 14 was not put in 11, the water film on the surface remained even if the Si wafer 13 was left under reduced pressure for 10 minutes or more. It does not disappear completely and the drying speed is very slow.

As a second comparative example, in the second embodiment, a decompression container
Water droplets remained on the surface of the Si wafer and were not dried even when isopropanol 14 was not put in 11 and the others were rotated for 1 minute at 300 rpm as in the second embodiment.

As a third comparative example, according to the method described in the second example, a Si wafer having no pattern formed thereon is washed with an RCA cleaning solution, rinsed with water, and then spin dried at 1200 rpm for 5 minutes using a spin dryer. Moreover, the number of dusts on the surface of the Si wafer was measured by a laser surface inspection device. The results are also shown in Table 1.

Effects of the Invention According to the invention as described above, by vaporizing the organic matter only under reduced pressure, the organic matter vapor does not leak outside from the gap of the decompression container or the pipe, and can be vaporized in a necessary amount when needed. Therefore, it is extremely unlikely to have a fire / explosion or adversely affect the human body. In addition, there is no need for a violently moving device or mechanism in the vicinity of the dry part, and there is little risk of contaminating the material to be dried. Furthermore, by contacting the material to be dried with organic vapor, the surface of the material to be dried becomes hydrophobic, and a small external force acts on the water droplets to facilitate draining and facilitate drying.
Impurities in water are also removed from the surface of the material to be dried, and there are effects such as not remaining as stains or dust.

[Brief description of drawings]

The figure is a cross-sectional view of an apparatus capable of reducing pressure in the first embodiment. 11 ... Decompression container, 12 ... Rotary vacuum pump as decompression means, 13 ... Si wafer, 14 ... Isopropanol as organic matter, 15 ... Isopropanol container, 16 ... Si
Wafer support jig, 17 …… valve, 18, 19 …… vent valve, 20 …… filter, 21 …… vacuum gauge.

Claims (2)

[Claims] 1. An organic substance vapor is present inside a container equipped with a means for reducing the pressure inside the container, and the organic substance vapor is brought into contact with the substance to be dried in the container, and then the pressure is lower than atmospheric pressure. In the method of drying by applying a physical force to the liquid on the surface of the object to be dried, as the vapor of the organic substance, the organic substance vaporized under reduced pressure that does not boil at room temperature is used. And the drying method. 2. The drying method according to claim 1, wherein the organic substance contains at least one organic solvent having a hydrophilic group and a hydrophobic group in the molecule and soluble in water.