JPH05121389A - Solvent cleaning device - Google Patents

Abstract

PURPOSE:To prevent generation of a stain due to absorption of moisture to an Al base or a dew-condensation at the time of degreasing and cleaning the base with a solvent having a low boiling point and high latent heat of vaporization, such as CH2Cl2, etc. CONSTITUTION:Dry gas is blown to the top of a free board 10. As the gas, dry air or vapor of CH2Cl2 is employed, and an absolute humidity is decreased to 0.0O9kg/kg or less. In the case of the vapor of the CH2Cl2, an atmosphere on the board 10 is heated, and an evaporating speed decreasing effect of the CH2Cl2 can be also utilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al or glass substrate for a photosensitive drum, an Al substrate for a magnetic disk, an Al substrate for a polygon mirror of a laser beam printer, or an IC.
The present invention relates to a solvent cleaning device for cleaning wafers and the like.
The present invention particularly relates to prevention of characteristic deterioration due to moisture adsorption or dew condensation on a substrate or wafer after cleaning.

[0002]

2. Description of the Related Art An Al substrate or a glass substrate of a photosensitive drum, or the above-mentioned magnetic disk substrate, IC wafer or the like is washed with a solvent after processing to degrease and remove processing chips. Conventionally used solvents are freon solvents such as C2F3Cl3 and halon solvents such as CH3CCl3. Since these solvents have high boiling points and low latent heat of vaporization,
Adhesion of water does not pose a problem after the object to be cleaned has been lifted from the surface of the solvent (freeboard). But C2F3C
l3 is a substance for which the destruction of the ozone layer is a particular problem.
H3CCl3 is also a substance that should not be used because ozone depletion becomes a problem. Therefore, it is necessary to replace these solvents with other solvents.

CH2Cl2 is attracting attention as an alternative to these solvents. For example CH2Cl2 and CH3CC
Comparing the ozone depletion potential with that of L3, it was 0.03 for CH2Cl2 and 0.13 for CH3CCl3.
Has an ozone depletion potential less than 1/4 that of CH3CCl3.

However, the inventor has found that CH2Cl2 has a low boiling point and a large latent heat of vaporization, so that water is adsorbed or condensed on the substrate after washing, which adversely affects the subsequent steps. For example, in the case of an Al or glass substrate of the photosensitive drum, a spot is generated on the surface due to adsorption of moisture or dew condensation, and this spot causes a film formation defect of the photosensitive layer and causes an image defect. Such stains are generated when the substrate is pulled up after cleaning, and are caused by adsorption of water vapor or dew condensation on the freeboard of the cleaning tank. The stain problem is particularly serious in the case of a metal substrate, for example, an Al substrate of a photosensitive drum,
This is because the thermal conductivity of Al is high and the specific heat is small, so that the cooling of the solvent after it is pulled up from the freeboard in the drying step is remarkable.

CH3CCl3 does not cause stains, and CH2C
It is generated at 12 because it has a low boiling point and high latent heat of vaporization. The boiling point of CH2Cl2 is 39.75 ° C and the latent heat of vaporization is 7.
8.7 cal / g, CH3CCl3 has a boiling point of 74.0
C., latent heat of vaporization is 56.7 cal / g. CH2Cl2
When the object to be cleaned is washed and pulled up therein, the evaporation rate of the solvent is high because of the low boiling point, and the latent heat of evaporation is large, so the amount of heat taken from the object to be cleaned is large. For this reason, the Al substrate or the like of the object to be cleaned is rapidly cooled, and water adsorption or dew condensation occurs.

As a device for heating an object to be cleaned when it is pulled up from the freeboard, as shown in FIG. 3, the solvent 4 in the cleaning tank 2 is boiled by a heater 6 to form a layer of solvent vapor on the freeboard. Things are known. However, according to the experiments conducted by the inventor, this device was not sufficient to prevent the occurrence of stains on the Al substrate of the photosensitive drum. This is because CH2Cl2 has a low boiling point and high latent heat of vaporization, so in order to form a solvent vapor layer sufficient to prevent the generation of stains, the CH2Cl2 solvent 4 in the cleaning tank 2 must be vigorously boiled and the original degreasing cleaning is performed. This is because the device becomes unsuitable. For example, when the solvent 4 is vigorously boiled, the Al base 8 rolls and the base 8 is wrapped with bubbles. Also CH
Since 2Cl2 has a low boiling point, the vapor temperature is low and the effect of heating the atmosphere above the freeboard is small.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent water from adsorbing or condensing on an object to be cleaned when it is pulled up from a freeboard when cleaning with a solvent having a low boiling point and a high latent heat of vaporization.

[0008]

According to the present invention, in a solvent cleaning apparatus having a cooler for recovering solvent vapor provided above a cleaning tank containing a solvent for cleaning an object to be cleaned, the liquid level of the solvent in the cleaning tank is And for blowing a dry gas between the cooler and
It is characterized in that a dry gas blowing means is provided.

As the solvent having a low boiling point and a high latent heat of vaporization used here, in addition to CH2Cl2, CH3COCH3 (boiling point 5
6.5 ° C., latent heat of vaporization 125 cal / g), etc. As the dry gas, vapor of the solvent itself, dry air, dry nitrogen or the like is used. Among these, the vapor of the solvent itself, which is easily recovered, and the inexpensive dry air are preferable. The absolute humidity of the atmosphere brought into the drying space of the object to be cleaned above the freeboard is preferably 0.009 kg / kg or less,
It is more preferably 0.008 kg / kg or less, and most preferably 0.007 kg / kg or less. 0.009 kg
The absolute humidity of / kg is a condition under which the Al substrate of the photosensitive drum is not stained when the CH2Cl2 solvent in the cleaning tank is kept at the boiling point.

Here, the atmosphere brought into the dry space is an average of the ambient air entering from the upper part of the cleaning tank and the dry gas blown in at the mixing ratio. The concept of the atmosphere to bring into the dry space, from the atmosphere of the dry space,
The cleaning tank is obtained by removing the evaporated solvent vapor. When the vapor of the solvent itself is blown as the dry gas, the blown solvent vapor is considered to be included in the atmosphere brought into the drying space. This concept is how much dry gas is blown to the air containing water vapor coming from the surroundings,
It means how much absolute humidity the ambient air is dried with. It should be noted that in this specification, as an absolute humidity, the absolute humidity in which only two of the ambient air and the blown dry gas are taken into consideration may be used as the absolute humidity, excluding the solvent vapor evaporated from the cleaning tank. This absolute humidity appears larger than the actual absolute humidity in the dry space when the evaporation of the solvent vapor is intense. However, when the solvent is used at a low temperature of about 20 ° C. as in normal cleaning, the vapor pressure of the solvent vapor is low, and the absolute humidity considering only the ambient air and the dry gas blown in and the actual absolute humidity are The difference between is small.

[0011]

According to the present invention, the dry gas is blown into the drying space of the object to be cleaned on the freeboard to reduce the absolute humidity, thereby preventing adsorption of water and dew condensation. When the vapor of the solvent itself is used as the dry gas, the concentration of the solvent vapor in the atmosphere is increased to reduce the evaporation rate of the solvent from the object to be cleaned, and the atmosphere from the solvent vapor is heated to heat the object to be cleaned. It also has the effect of preventing cooling.

[0012]

EXAMPLE FIG. 1 shows an example using the blowing of solvent vapor. In the figure, 2 is a cleaning tank, 4 is a solvent with a low boiling point and high latent heat of vaporization such as CH2Cl2, 6 is a heater, and 8 is an Al substrate of the photosensitive drum of the object to be cleaned. Here, A of the photosensitive drum
l Degreasing cleaning after precision mirror surface processing of a substrate is shown as an example, but degreasing cleaning of a glass photosensitive drum, an Al substrate of a magnetic disk,
The same applies to cleaning the Al substrate of the polygon mirror of the laser beam printer. The present invention can also be used for cleaning IC wafers. Of these, particularly important is the case where a metal substrate, which has a high thermal conductivity and a small heat capacity, has a high cooling rate, and in which dew condensation and moisture adsorption during pulling up from the freeboard become particularly serious, as the object to be cleaned,
In the case of electronic parts, it is mainly an Al substrate.

10 is the liquid surface (freeboard) of the solvent 4,
Reference numeral 12 is a solvent vapor layer on the freeboard 10, and 14 is a cooling coil for cooling and collecting the solvent vapor, which is an example of a cooler. 16 is a heat exchanger, 18 is a solvent recovery pipe, 20 is a water separator for separating water from the recovered solvent, 22 is a solvent vapor generator, 24 is its heater, and 26 is a solvent vapor blowing pipe. A blowing port 28 is provided at a height between the freeboard 10 and the cooling coil 14. Reference numeral 30 is an ultrasonic transducer for cleaning. 32 and 34 are heaters 6 and 2
A power source 4 and a drive circuit 36 for the ultrasonic transducer 30.

The operation of the embodiment will be described. The Al substrate 8 is dipped in the solvent 4 kept at a boiling point or a temperature lower than the boiling point, washed with ultrasonic waves from the ultrasonic oscillator 30, and degreased of oil and the like adhering during mirror finishing. In the embodiment, a solvent cleaning device is used for degreasing cleaning after mirror finishing, but it may be used for cleaning in other steps. Freeboard 1 after cleaning substrate 8
When the solvent vapor layer 12 is pulled up from 0, the solvent attached to the substrate 8 is evaporated. Since CH2Cl2 has a low boiling point (boiling point of about 40 ° C.), the evaporation rate is high. Also CH2Cl2
Has a high latent heat of vaporization (78.7 cal / g), so a large amount of heat is lost by vaporization. Therefore, when the solvent 4 having a low boiling point and high latent heat of vaporization such as CH2Cl2 is used, the substrate 8 is rapidly cooled. When the substrate 8 is made of a metal such as Al, the thermal conductivity is high and the heat capacity is small, so that the effect of cooling by evaporation of the solvent becomes more remarkable.

In order to prevent dew condensation and water adsorption on the substrate 8, a heated solvent vapor is blown from the outlet 28,
The absolute humidity in the solvent vapor layer 12 is reduced. Absolute humidity in the mixture of the blown solvent vapor and the mixed ambient air is
It is preferably 0.009 kg / kg or less, more preferably 0.008 kg / kg or less, and further preferably 0.007.
Kg / kg or less. Next, the solvent vapor concentration in the vapor layer 12 is increased by blowing in the solvent vapor, and the substrate 8
Reduce the evaporation rate of the solvent from. The temperature of the solvent vapor is set to about the boiling point (40 ° C.) to raise the ambient temperature of the solvent vapor layer 12 and prevent the substrate 8 from being cooled. A heater may be provided near the outlet 28 to heat the solvent vapor to a temperature equal to or higher than the boiling point and blow the solvent vapor. The blowing of the solvent vapor has three effects of lowering the absolute humidity, lowering the evaporation rate, and warming the atmosphere, thereby preventing moisture (condensation or adsorption) from adhering to the substrate 8.

The solvent vapor in the vapor layer 12 is cooled by the cooling coil 14.
The solvent is recovered from the solvent recovery pipe 18, and the water is separated and regenerated by the water separator 20. As a result, the injected solvent vapor is not lost.

FIG. 2 shows an embodiment in which dry air is blown in instead of the solvent vapor. This embodiment is the same as the embodiment of FIG. 1 unless otherwise specified. In the figure, reference numeral 40 denotes a dry air source such as a compressor, and a dry air cylinder, a dry nitrogen cylinder, a dry CO2 cylinder or the like may be used. In this embodiment, the compressor 40 compresses ambient air to dehumidify it, and blows dry air through the blow-in port 28.
Then, the absolute humidity in the air-fuel mixture of the ambient air entering the vapor layer 12 and the blown dry air is reduced to 0.009 kg / kg or less to prevent adsorption of water or dew condensation on the substrate 8 during pulling. When a compressor is used, the heat of compression heats the dry air to several tens of degrees, and the vapor layer 1
It is possible to further prevent the adsorption of moisture on the substrate 8 and the dew condensation by raising the ambient temperature of 2. Of course, in other cases as well, dry air is heated and supplied from the outlet 28,
The temperature of the vapor layer 12 may be raised.

A test example will be described with reference to the embodiments shown in FIGS. CH2Cl2 solvent 4 is added to the washing tank 2 of 30 Litter,
An Al substrate 8 for a photosensitive drum having a diameter of 108 mm, a length of 358 mm and a wall thickness of 5 mm was dipped and ultrasonically cleaned for 2 minutes. C
The liquid temperature of the H2Cl2 solvent 4 was adjusted by the heater 6. After ultrasonic cleaning, the substrate 8 was pulled up at a speed of 8 mm / sec, and it was observed whether or not stains were generated on the surface of the substrate 8. The ambient air had a temperature of 20 ° C. and a relative humidity of 57%.

In the embodiment shown in FIG. 1, at the height between the freeboard 10 and the cooling coil 14, CH2Cl2 vapor blowing ports (diameter 1/2 inch) are provided at four positions. The solvent vapor was generated by adding 15 Litter of CH2Cl2 solvent to the vapor generator 22 and boiling it by applying 750 W of electric power with the heater 24. Table 1 shows the relationship between the liquid temperature in the cleaning tank 2 and the occurrence of stains, together with the same comparative example except that no solvent vapor was added.

[0020]

[Table 1] Table 1 Liquid temperature and presence / absence of spots CH2Cl2 liquid temperature (° C) in the cleaning tank and evaluation 25 28 32 36 Boiling point Example (solvent vapor supply) ○ ○ ○ ○ ○ Comparative example (solvent vapor supply) No) × × × × Δ * Evaluation is that no stain is generated on the substrate 8: ○ Stain is generated in an area of 1/4 or less of the surface area of the substrate 8: Δ In area of 1/4 or more of the surface area of the substrate 8 Staining: Indicated by a three-level evaluation of ×.

It can be seen from the table that the case where the liquid temperature is the boiling point corresponds to the conventional example of FIG. 3, and the conventional example of FIG. 3 is not sufficient to prevent the generation of stains unless the boiling is extremely violent. .. Further, in the examples, it is understood that the stain does not occur at an arbitrary liquid temperature, and the stain can be completely prevented.

Table 2 shows the test results for the embodiment of FIG. In this test example, 16 ° C. dry air (dew point 11.5
0 ° C or less) from 0 to 6 m ³ /
Dry air and vapor layer 1 blown in at a flow rate of time
Absolute humidity was changed in the range of 0.0065 kg / kg to 0.014 kg / kg with respect to the total amount of ambient air entering from the upper part of No. 2, and the presence or absence of stains was observed. Other test conditions are the same as for steam. The liquid temperature of the cleaning tank 2 was set to the boiling point. The results are shown in Table 2. By using dry air in which the absolute humidity of the ambient air is blown to 0.009 kg / kg or less, it is possible to prevent the generation of stains in the boiling point CH2Cl2 solvent 4, and by setting it to 0.008 kg / kg or less, the temperature of 28 ° C Staining with CH2Cl2 solvent 4 can be prevented, and by adjusting the amount to 0.007 kg / kg or less, 20.
Staining with CH2Cl2 solvent 4 at 5 ° C can be prevented. 0.0
09 kg / kg or less means 21 ° C when converted into temperature and humidity
58% or less, 0.008 kg / kg or less is 1
9 ° C. corresponds to 58%, and 0.007 kg / kg or less corresponds to 18 ° C. 55%.

[0023]

[Table 2] Table 2 Liquid Temperature and Presence of Stain Absolute Humidity (Kg / Kg) Evaluation Corresponding Temperature and Humidity Conditions Example 0.0065 ○ 16 ° C 58% 0.0070 ○ 18 ° C 55% 0.0080 ○ 19 ° C 58 % 0.0085 ○ 20 ° C. 58% 0.0090 ○ 21 ° C. 58% Comparative example 0.0095 × 22 ° C. 57% 0.014 × 24 ° C. 74% * Evaluation shows no stain on the substrate 8: ○ substrate 8: Staining occurs: It is shown by a two-level evaluation of x. * Absolute humidity indicates the absolute humidity of the ambient air / dry air mixture, considering the dry gas blown in and the ambient air drawn in from the surroundings, excluding solvent vapor. * Corresponding temperature / humidity conditions are expressed by converting the absolute humidity of the mixture of blown dry air and ambient air into temperature / humidity conditions. For example, the display of 20 ° C. 58% is obtained by excluding the solvent vapor from the gas in the vapor layer 12 and obtaining the absolute humidity only for the air that has entered from the surroundings and the dry air that has been blown in and converted this to a typical temperature and humidity. Is.

[0024]

As described above, according to the present invention, a dry gas such as dry air or the solvent vapor itself is blown into the solvent vapor in the upper portion of the cleaning tank to reduce the absolute humidity, so that the portion to be cleaned is cleaned. Prevents adsorption of water and condensation. This makes it possible to use a solvent having a low boiling point and a high latent heat of vaporization such as CH2Cl2 and prevent the influence on the ozone layer. Although the type of the object to be cleaned is arbitrary, it is particularly effective for cleaning the photosensitive drum substrate in which precise film formation is required in the post-process, and the generation of stains leads to film formation defects. Even the cleaning of the base of the photosensitive drum is particularly effective for cleaning the Al base having a high thermal conductivity and a small heat capacity.

[Brief description of drawings]

FIG. 1 is a diagram showing a solvent cleaning apparatus of an embodiment using blowing of a solvent vapor.

FIG. 2 is a diagram showing a solvent cleaning apparatus of an embodiment using a blowing of dry air.

FIG. 3 is a diagram showing a conventional solvent cleaning apparatus in which a solvent in a cleaning tank is vigorously boiled to heat an object to be cleaned.

[Explanation of symbols]

 2 Cleaning Tank 4 Solvent 6 Heater 8 Photosensitive Drum Al Substrate 10 Freeboard 12 Vapor Layer 14 Cooling Coil 20 Moisture Separator 22 Steam Generator 26 Solvent Vapor Pipe 28 Inlet 40 Dry Air Source

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H01L 21/304 341 V 8831-4M

Claims (1)

[Claims] 1. A solvent cleaning apparatus having a cooler for recovering solvent vapor provided above a cleaning tank containing a solvent for cleaning an object to be cleaned, wherein the liquid level of the solvent in the cleaning tank and the cooler. A solvent cleaning device, characterized in that a dry gas blowing means for blowing a dry gas is provided between the cleaning device and the cleaning device.