JPH1176959A - Finish cleaning - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent particles from being stuck to a ferroelectric material by immersing an object to be cleaned in any one liquid of pure water and a nonaqueous solvent, and thereafter, pulling up the object from the liquid while subjecting the object to ion irradiation or blowing ion wind on the object. SOLUTION: In this cleaning method, pure water or any nonaqueous solvent contains no ionic component and, therefore, has no electrical conductivity, and accordingly, static electricity is generated in such a liquid by the action of liquid streams within a cleaning device. Since an object to be cleaned 2 is in an electrically insulated state from the cleaning device, static electricity is generated by the friction between the object 2 and a liquid 8 in a cleaning vessel 1, that accompanies the movement of the liquid 8 and the object 2 in the cleaning vessel 1, such as fluctuation of the level of the liquid 8 and the pulling-up of the object 2. In this state as it is, when the object is pulled up, the object 2 is electrified so as to have surface charge and the particles surrounding the object 2 are attracted to the object 2 by the action of static electricity. On the other hand, in this method, since the pulling-up of the object 2 is performed in an ion wind atmosphere, the surface charge on the object 2 can be released by the ions, and accordingly, sticking of particles to the object 2 due to static electricity can be prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning optical parts and semiconductor parts made of ferroelectric materials, and more particularly to a method for cleaning and cleaning these parts.

[0002]

2. Description of the Related Art Precision cleaning of parts and products in the precision field occupies an important position as well as processing. For cleaning in these precision fields, halogen-based solvents such as chlorofluorocarbons and trichloroethane, which are highly safe to the human body, have good workability, and are capable of high-purity regeneration, have been used. Due to the problem of ozone depletion, its use has been banned and its use reduced worldwide.

[0003] For this reason, cleaning methods have been developed in place of halogenated solvents. In this case, with the rapid progress in manufacturing technology, there has been a demand for a great improvement in the quality desired for cleaning by ultraprecision such as improvement of processing accuracy, practical use of difficult-to-machine parts, and improvement of required accuracy. JP-A-5-3451
No. 74 and JP-A-5-68951 describe a conventional cleaning method for performing such cleaning.

In the cleaning method disclosed in Japanese Patent Application Laid-Open No. 5-345174, after the object to be cleaned is subjected to ultrasonic treatment when rinsing the object to be cleaned in a rinsing tank, the object to be cleaned is tilted when the object to be cleaned is lifted from the rinsing tank. The liquid is drained by holding it.

In the cleaning method disclosed in Japanese Patent Application Laid-Open No. Hei 5-68951, a plurality of pure water tanks are provided in a drying step after the cleaning.
The temperature of the final pure water tank is set at 70 to 85 ° C., and the surface of the object to be cleaned is dried when the object to be cleaned is pulled up from the final pure water tank. Because pure water does not contain an ionic component, it does not produce a dry residue and is suitable for precision cleaning.

[0006]

By the way, with the recent refinement of industry, needs for cleaning special materials such as crystal materials and ferroelectric materials have been increasing. The ferroelectric material is charged by causing a temperature change or a surface change due to its pyroelectricity and piezoelectricity. On the other hand, pure water or an organic solvent used for finishing the cleaning is a small conductive substance. When the ferroelectric material is washed using pure water or a solvent, static electricity is generated due to friction between the ferroelectric material and pure water, and particles in the air adhere. In addition, heat generation during drying and heat radiation during evaporation also have a problem that a surface charge is caused by a change in temperature, which adversely affects cleaning quality.

[0007] It is an object of the present invention to provide a method capable of preventing particles from adhering to a ferroelectric material and finishing the ferroelectric material with high precision when cleaning and finishing such a ferroelectric material.

[0008]

According to a first aspect of the present invention, there is provided a cleaning method for cleaning a cleaning object made of a ferroelectric material with pure water or a non-aqueous solvent. After being immersed in any one of the liquids, the object to be cleaned is pulled up while being irradiated with ions.

In this method, the surface of the object to be cleaned is released by irradiating ions to the object to be cleaned made of a ferroelectric material, and the adhesion of particles due to static electricity is suppressed.

According to a second aspect of the present invention, after the lifting according to the first aspect, the object to be cleaned is dried by blowing air at a temperature of 25 to 40 ° C. or supplying ionic air.

[0011] These blowings prevent particles from being deposited due to pyroelectricity of the ferroelectric material.

According to a third aspect of the present invention, the non-aqueous solvent according to the first aspect has a 95% distillation temperature within 5 ° C. from the initial boiling point,
And at least one selected from the group consisting of saturated hydrocarbons having 8 to 12 carbon atoms and a distilling temperature of 99% within 10 ° C. from the initial boiling point or hexamethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane. Features.

By using these liquids, stains due to the cleaning agent are prevented, and the cleaning quality is improved.

[0014]

FIG. 1 shows the structure of a cleaning apparatus used in the present invention. A cleaning tank 1 and a preliminary tank 4 are connected by a pipe. Circulating between 1 and the preliminary tank 4. The circulation of the liquid 8 prevents the dirt mixed in from the previous process from staying. The object to be cleaned 2 is made of a ferroelectric material,
It is introduced into the cleaning tank 1 while being placed on the transfer arm 7. A nozzle 6 to which an ion wind is supplied from the ionizer 5 is disposed above the cleaning tank 1, and the ion wind supplied to the nozzle 6 is blown out from a blowing hole 6 a to near the liquid surface of the cleaning tank 1.

In this apparatus, the object to be cleaned 2 is introduced into the cleaning tank 1, and the cleaning liquid from the previous step is replaced and rinsed by the liquid in the cleaning tank 1. At this time, the ion wind is supplied from the ionizer 5 to the nozzle 6, and the ion wind is blown from the blowing hole 6 a of the nozzle 6. Then, after performing replacement or rinsing for a predetermined time in the cleaning tank 1, the transfer arm 7 is pulled up. The object 2 to be cleaned is
Rises in the liquid 8 and floats on the liquid surface.

When the object to be cleaned 2 is pulled up, the object to be cleaned 2 is charged by static electricity generated by rubbing against the liquid 8 in the cleaning tank 1. On the other hand, when the ion wind blows out from the nozzle 6, the liquid surface of the liquid 8 has an ion wind atmosphere. The surface charge of the object to be cleaned 2 is released by passing through the ionic atmosphere. Therefore, particles do not adhere to the article 1 to be cleaned. In addition, since the ionizer 5 performs molecular decomposition by electric discharge and generates ions by the molecular decomposition, no particles are generated. Therefore, the generated ions can perform only a pure potential change.

The liquid 8 used in the present invention is pure water or a non-aqueous solvent. Among them, as the non-aqueous solvent,
Saturated hydrocarbons or siloxanes are used. Since pure water or non-aqueous solvents do not contain ionic components, they do not have conductivity, and static electricity is generated in these liquids by a liquid flow in the apparatus. In this case, stainless steel (SUS), which is a conductive material, is generally used for the cleaning device, and charges are released in a portion that comes into contact with the SUS. However, since the object to be cleaned 2 is insulated from these cleaning devices, static electricity is generated by friction between the object to be cleaned 1 and the liquid 8 due to the movement of the cleaning tank 1 such as swinging and lifting.

When the object to be cleaned 2 is pulled up from the liquid 8 in this state, the object to be cleaned 2 becomes charged with surface charges, and the surrounding particles are attracted by static electricity. These particles become a major obstacle to the subsequent process and cause a reduction in yield. As described above, the present invention provides
Is lifted into the ion wind atmosphere, so that the surface charges can be released by the ions. Therefore, adhesion of particles due to static electricity can be prevented.

After the lifting, drying is performed by natural drying or by using a drying device.
At the time of such drying, drying can be performed by blowing air from the ionizer 5. Excessive heating during drying promotes an increase in surface charge, so it is necessary to limit heating to a minimum necessary. Therefore, the drying temperature range is 2
5 to 40 ° C is good. In an environment where the drying temperature exceeds 40 ° C., the surface charge increases and causes particles in the air to adhere.

In the above temperature range of 25 to 40 ° C., drying tends to be difficult. For this reason, in the present invention, the liquid 8 in the cleaning tank 1 that is easily dried even at a low temperature is used. As the liquid 8, a liquid having a high vapor pressure and a low latent heat of evaporation is preferable, and it is preferable to use a saturated hydrocarbon and siloxane as a non-aqueous solvent.

The latent heat of evaporation contributes to energy efficiency during drying. The change of phase from liquid to gas requires heat of vaporization as energy. This heat of vaporization depends on the latent heat of vaporization of the substance. If the latent heat of vaporization is large, large energy is required during vaporization. Therefore, at the time of vaporization, heat is removed from the object 2 to be cleaned, and the surface of the object 2 is cooled. At this time, a temperature difference from the surrounding environment occurs, and moisture in the air condenses, thereby deteriorating the cleaning quality. Since the saturated hydrocarbon and siloxane used in the present invention have a small latent heat of evaporation, the temperature of the article to be cleaned 2 is small, the dew condensation is suppressed, and a clean cleaning surface can be obtained.

The drying temperature is desirably (normal temperature) + (minimum energy required for drying), and a temperature in the range of 25 to 40 ° C. is a temperature range in which both drying property and washing quality can be satisfied. The saturated hydrocarbon and siloxane used in the present invention need to have a low viscosity and a low surface tension, and by using such a saturated hydrocarbon and siloxane, the amount of liquid adhering to an object to be cleaned can be reduced. .

The saturated hydrocarbon satisfying the above requirements has a 95% distillation temperature within 5 ° C. from the initial boiling point and 99%.
Saturated hydrocarbons having 8 to 12 carbon atoms having a% distillation temperature within 10 ° C from the initial boiling point are good. As the saturated hydrocarbon, isooctane, isononane, n-nonane,
One of n-decane and isodecane can be selected. As the siloxane, one of hexamethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane can be selected.

In order to reduce the amount of liquid adhering to the object to be cleaned 2, a method of changing the pulling speed from the liquid 8 can be used in addition to the various physical properties of the liquid 8. When the object to be cleaned is pulled up from the liquid 8, the liquid 8 remains on the surface of the object to be cleaned 2 due to the action of the cohesive force or surface tension, and the remaining liquid drops from the object to be cleaned by gravity. .
At this time, if the speed of lifting the object to be cleaned is lower than the falling speed of the liquid, the cleaning liquid on the surface of the object to be cleaned remains uniformly thin, which is not preferable. On the other hand, if the liquid is pulled up at a speed higher than the falling speed of the liquid, dripping of the liquid on the surface of the object to be cleaned occurs significantly, which affects the cleaning quality. In the case where the above-mentioned saturated hydrocarbon or siloxane is used, the pulling speed is desirably 70 mm / S based on the results of experiments by the inventors.

In the present invention as described above, the amount of liquid remaining on the object to be cleaned can be uniformly reduced by adjusting the properties of the saturated hydrocarbon and the siloxane and the pulling rate, and the amount of liquid remaining can be suppressed. . Further, since the object to be cleaned is lifted in an ion wind atmosphere at the time of lifting, particles can be prevented from adhering and a clean surface can be secured. Also, since the heat change during drying can be reduced,
Particle adhesion due to pyroelectricity can be prevented.

The adhesion of particles is not limited to air only. If there are many particles in the liquid, particles in the liquid remaining on the surface at the time of final lifting remain on the surface of the object to be cleaned, which may cause poor quality. Become. As a result of measurement by the inventors, the liquid circulated through a 0.1 μm mesh filter has 50 particles of 0.2 μm or more /
It was less than 100 ml.

[0027]

【Example】

Example 1 A 0.5-mm-thick 3-inch square piece crystal made of barium titanate (BaTiO ₃ ) was mirror-polished on one side to obtain an object to be cleaned, and was washed in the steps shown in Table 1. In Table 1, "US" indicates ultrasonic vibration. The cleaning liquid “SE-10” is a trade name of a cleaning agent manufactured by Olympus Optical Industries, Ltd. The final lifting was performed with pure water, and two types, one using an ionizer at the time of lifting and one not using it, were performed as experiments. The atmosphere at the time of this experiment was class 10.0 with particles of 0.5 μm.
00 level.

Items to be cleaned made of barium titanate include:
Dirt and dust are attached as dirt. Cleaning liquid SE
In the cleaning of the first tank using -10, in addition to the removal of the dirt by the surfactant, the surface cleaning effect by the alkali builder is obtained, and the cleaning effect is obtained. In order to replace the SE-10, the second and third tanks were rinsed with pure water, and the final fourth tank was pulled up.

In the lifting using an ionizer, an ion wind is blown onto the liquid surface, and the object to be cleaned is placed in an ion wind atmosphere. The ionic wind neutralizes static electricity generated by the rubbing of the interface between pure water and barium titanate. In the lifting without using the ionizer, particles floating in the cleaning device adhered due to static electricity generated at the time of lifting from pure water, resulting in a difference in cleaning quality.

After the above steps, the surface observation was evaluated by a metallographic microscope. As a result, when the ionizer was used, the amount of foreign matter remaining on the surface was small. Therefore, it was confirmed that the surface of barium titanate can be cleaned with high quality by blowing ion wind when pulling up from pure water.

[0031]

[Table 1]

Example 2 Lithium niobate (LiNb)
Table 2 shows the cleaning process of this example, in which a wafer having a diameter of 3 inches made of O ₃ ) was used as an object to be cleaned. Cleaning agent "E
E-1120 "is a cleaning agent manufactured by Olympus Optical Co., Ltd. Washing was performed using a tank configuration of pure water, IPA (manufactured by Tokuyama Soda Co., Ltd.), and hexamethyldisiloxane (manufactured by Shin-Etsu Chemical Co., Ltd.). In addition, at the time of final pulling up from hexamethyldisiloxane in the seventh tank, comparison was made between those using an ionizer and those not using it.

A 3-inch wafer made of lithium niobate has a residue of abrasives in addition to dust and dust. First
In the bath, the wafer was cleaned with a cleaning agent EE-1120. The cleaning agent EE-1120 is cleaned by dissolving dirt with a surfactant, dispersing foreign substances, and etching with an alkali component. In order to rinse the cleaning agent EE-1120, the subsequent second to fourth tanks were subjected to pure water cleaning. In the fifth tank, pure water was replaced with IPA in order to perform final finishing with hexamethyldisiloxane which is a non-aqueous solvent. In the sixth tank, IPA was replaced with hexamethyldisiloxane, and the object to be cleaned was introduced into the final seventh tank.

The final lifting from the hexamethyldisiloxane in the seventh tank was performed in the vicinity of the liquid surface under an atmosphere using ion wind. Hexamethyldisiloxane is a low-molecular silicone oil and has high insulating properties. Therefore, when the object to be cleaned is pulled up, static electricity is generated due to friction between the liquid surface and the wafer surface. This static electricity is a factor that causes surrounding particles to adhere when being lifted from the seventh tank. However, in an ionic wind atmosphere, the charge is neutralized, and the adhesion of particles can be suppressed.

The cleaning was evaluated after depositing the SiO ₂ thin film on the wafer. If there is a foreign substance remaining, the thin film may be peeled off. The peeling of the thin film was inspected with a metallographic microscope. As a result, a clear difference was observed in the peeling of the thin film depending on whether or not the ion wind was blown, and the one using the ionizer was excellent. Therefore, it was confirmed that the use of an ionizer enables high quality finishing without particle adhesion even in finish drying using a non-aqueous solvent having a high insulating property such as hexamethyldisiloxane. .

[0036]

[Table 2]

Example 3 4 composed of lithium titanate
An object to be cleaned was an inch wafer and a 3-inch wafer made of lithium niobate. In this example, the difference in cleaning accuracy based on the difference in drying temperature was examined.

Lithium titanate wafers and lithium niobate wafers which had been washed in advance according to the structure of Example 2 were washed with a saturated hydrocarbon solvent, trade name "Kyowasol C-900" (manufactured by Kyowa Hakko Co., Ltd.). ), And pulled up and dried at a speed of 60 mm / s in an ionic wind atmosphere. The drying temperature was 30 ° C and 70 ° C.

Lithium titanate and lithium niobate have pyroelectricity. Pyroelectricity is a property of causing a potential change due to a temperature change. On the other hand, the trade name “Kyowasol C-900” is a saturated hydrocarbon solvent containing 99% or more of isononane, and has low conductivity. Therefore, when the wafer is pulled up from the liquid of “Kyowasol C-900”, static electricity is generated due to friction between the liquid surface and the interface of the wafer, but this potential change is neutralized by the ionic wind atmosphere.

When lifting the wafer from the solvent "Kyowasol C-900", the lifting speed is lower than the speed at which the liquid falls. As a result, a uniform film of Kyowasol C-900 is formed on the surface of the wafer, and then naturally dried. In the subsequent drying step, since both lithium titanate and lithium niobate have pyroelectricity, the potential of the wafer changes with the temperature change during drying. For this reason,
Particles adhere to the periphery when the cleaning device goes out of the cleaning device after the drying process.

After the drying step, a polarizing film made of TiO ₂ was vapor-deposited on the wafer, and the vapor-deposited surface was evaluated using a metal microscope. As a result of the study by the inventor, it has been found that the irregularities on the deposition surface depend on the particles on the wafer surface. Observation of the deposition surface of the wafer after the drying process at temperatures of 30 ° C. and 70 ° C. revealed that the wafer dried at 70 ° C. had more irregularities than the wafer surface dried at 30 ° C., and lithium titanate and niobium were observed. It was found that this was consistent with the pyroelectricity of lithium oxide. From these facts, it has been clarified that the drying of the object to be cleaned made of a ferroelectric material is most preferably performed at a temperature close to room temperature of about 30 ° C.

From the above description, the following technical ideas are derived from the present invention. (1) In the final finishing of cleaning the object to be cleaned made of a ferroelectric material, the object to be cleaned is immersed in one liquid of pure water or a non-aqueous solvent and then irradiated with ions to the object to be cleaned. A cleaning finish method, wherein the object to be cleaned is pulled up at a pulling speed of 70 mm / sec or less.

According to this method, since the liquid does not remain on the surface of the object to be cleaned and the liquid does not sag on the surface of the object to be cleaned, high-quality finishing can be achieved.

[0044]

As described above, according to the first aspect of the present invention, since the object to be cleaned is lifted while being irradiated with ions, the surface charge of the object to be cleaned can be released, and the adhesion of particles due to static electricity can be suppressed. Can be. For this reason, high quality can be achieved.

According to the second aspect of the present invention, the adhesion of particles due to the pyroelectricity of the ferroelectric material can be prevented by blowing air or supplying ionic wind at a temperature of 25 to 40 ° C.

According to the third aspect of the present invention, the saturated carbon having 8 to 12 carbon atoms has a 95% distillation temperature within 5 ° C. from the initial boiling point and a 99% distillation temperature within 10 ° C. from the initial boiling point. By using at least one selected from hydrocarbons, hexamethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane, it is possible to prevent stain residue caused by the cleaning agent and improve the cleaning quality.

[Brief description of the drawings]

FIG. 1 is a sectional view of a cleaning apparatus used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cleaning tank 2 Object to be washed 3 Circulation pump 4 Preparatory tank 5 Ionizer 6 Nozzle 7 Transfer arm 8 Liquid

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // G02B 1/10 G02B 1/10 Z

Claims (3)

[Claims] In a final step of cleaning an object to be cleaned made of a ferroelectric material, the object to be cleaned is immersed in one of pure water and a non-aqueous solvent and then irradiated with ions. A cleaning finishing method characterized by lifting while raising. 2. After the lifting according to claim 1, 25-4.
A cleaning and finishing method characterized by drying an object to be cleaned by blowing air or supplying ionic air at a temperature of 0 ° C. 3. The non-aqueous solvent according to claim 1, wherein the 95% distillation temperature is within 5 ° C. from the initial boiling point and the 99% distillation temperature is within 10 ° C. from the initial boiling point. 12. A cleaning and finishing method, wherein the method is a saturated hydrocarbon or at least one selected from hexamethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane.