Silicone rubber molded body and production method for the same

A silicone rubber molded body (10) has an article contact surface (11). The article contact surface (11) has a coefficient of rolling resistance lowered by a fluorination treatment on the article contact surface (11).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase under 35. U.S.C. § 371 of International Application PCT/JP2019/022573, filed Jun. 6, 2019, which claims priority to Japanese Patent Application No. 2018-119422, filed Jun. 25, 2018. The disclosures of the above-described applications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a silicone rubber molded body and a method for producing the same.

BACKGROUND ART

The surface of silicone rubber generally has adhesiveness. For example, a chemical mechanical polishing apparatus (hereinafter, referred to as a “CMP apparatus”) adsorbs and retains a wafer by an elastic film, and presses the wafer against a polishing pad to polish the wafer. If this elastic film is a silicone rubber molded body, the following problem arises: the wafer adheres to and cannot be released from the elastic film due to the adhesiveness of the silicone rubber, and an attempt to forcedly peel the wafer may cause damage to the wafer. If a pad of an article grip in a robot arm is a silicone rubber molded body, the following problem arises: when a gripped article is tried to be placed at a desired location, the article adheres to and cannot be released from the pad due to the adhesiveness of the silicone rubber, and this may fail to place the article to the desired location. Further, if a case of a portable electronic device is a silicone rubber molded body, the following problem arises: gripping of the case causes unpleasant feeling to touch due to the adhesiveness of the silicon rubber.

In order to solve these problems, it has been proposed to reduce the adhesiveness by coating an article contact surface of the silicone rubber molded body (e.g., Patent Documents 1 to 4).

CITATION LIST

Patent Documents

SUMMARY OF THE INVENTION

The present invention is directed to a silicone rubber molded body having an article contact surface. The article contact surface has a coefficient of rolling resistance lowered by a fluorination treatment thereon.

The present invention is further directed to a method for producing the silicone rubber molded body of the present invention, the method including: performing a fluorination treatment of bringing an article contact surface of a silicone rubber-made, surface-untreated molded body into contact with a surface treating gas containing a fluorine gas with a partial pressure of 3.00 kPa or more.

DESCRIPTION OF EMBODIMENT

An embodiment will be described in detail below.

FIG.1illustrates an elastic film10(silicone rubber molded body) according to the embodiment, the elastic film10being for retaining a wafer in an CMP apparatus A. The elastic film10according to this embodiment is configured such that the elastic film10is attached to a CMP apparatus A so as to expose a wafer retaining surface11(article contact surface) to an outside, that the wafer retaining surface11adsorbs and retains a wafer S (article), and that the wafer S is polished by contacting with a polishing pad P at a uniform pressure.

The elastic film10according to the embodiment is a silicone rubber-made molded body made of a crosslinked silicone rubber. Examples of the silicone rubber include a (meth)acryloyloxy group-containing polysiloxane, vinyl polysiloxane, and a mercaptoalkyl group-containing polysiloxane. Suitably, as the silicone rubber, one of them is used, or two or more of them are used. The crosslinking of the silicone rubber may be achieved by any of using organic peroxide, performing condensation polymerization, and using a platinum catalyst.

The elastic film10according to the present embodiment has a wafer retaining surface11that has undergone a fluorination treatment. Specifically, the wafer retaining surface11has a Si—F bond introduced.

The wafer retaining surface11has a coefficient of rolling resistance lowered by a fluorination treatment thereon. Specifically, the silicone rubber having a wafer retaining surface11that has undergone a fluorination treatment, and that has a Si—F bond introduced has a coefficient of rolling resistance lower than the silicone rubber having a wafer retaining surface11before the fluorination treatment.

When the silicone rubber is coated to reduce its adhesiveness, a problem with the coating layer peeling off and creating foreign matters arises. The inventors of the present invention found that the coefficient of rolling resistance lowers when the surface of the silicone rubber undergoes a fluorination treatment, thereby allowing the adhesion of the silicone rubber to an article to be reduced. In the elastic film10according to the embodiment based on this finding, the wafer retaining surface11has a coefficient of rolling resistance lowered by a fluorination treatment thereon. This can reduce adhesion of the wafer S and avoid generation of foreign matters caused by peeling off of the coating layer as in the case of the coating treatment.

The wafer retaining surface11that has undergone a fluorination treatment has a coefficient of rolling resistance of suitably 0.040 or less, more suitably 0.030 or less, yet more suitably 0.020 or less. A reduction rate represented by a percentage of the difference between the coefficients of rolling resistance before and after the fluorination treatment, to the coefficient of rolling resistance before the fluorination treatment is suitably 20% or more, more suitably 40% or more, yet more suitably 60% or more. The coefficient of rolling resistance herein is calculated as follows. First, a measurement surface of a test piece is cleaned with methanol and is then left in an atmosphere at a temperature of 20° C. and a humidity of 40% for 24 hours or more. Thereafter, a SUS304-made rolling probe having a smooth outer circumferential surface with a diameter of 30 mm is pressed against the measurement surface in the same atmosphere so as to apply a load of 1000 g while rolling the probe at a moving speed of 2000 mm/min. A rolling resistance during the steady state at this time is divided by the load to obtain a coefficient of rolling resistance.

Suitably, the wafer retaining surface11has a coefficient of static friction raised by the fluorination treatment thereon. Specifically, the silicone rubber having a wafer retaining surface11that has undergone a fluorination treatment and that has a Si—F bond introduced has a coefficient of static friction higher than the silicone rubber having a wafer retaining surface11before the fluorination treatment. In this manner, the wafer retaining surface11has a coefficient of static friction raised by the fluorination treatment thereon, thereby obtaining a high grip performance for the wafer S and allowing a reduction in spinning out of control of the wafer S when polished.

The wafer retaining surface11that has undergone a fluorination treatment has a coefficient of static friction of suitably 0.75 or more, more suitably 1.00 or more, yet more suitably 1.25 or more, and suitably 2.00 or less. An increase rate represented by a percentage of the difference between the coefficients of static friction before and after the fluorination treatment, to the coefficient of static friction before the fluorination treatment is suitably 60% or more, more suitably 100% or more, yet more suitably 150% or more. The coefficient of static friction herein is calculated as follows. First, a measurement surface of a test piece is cleaned with methanol and is then left in an atmosphere at a temperature of 20° C. and a humidity of 40% for 24 hours or more. Thereafter, a hemispherical tip with a diameter of 10 mm of a SUS304-made probe is pressed against the measurement surface in the same atmosphere so as to apply a load of 100 g while sliding the hemispherical tip at a moving speed of 75 mm/min. A peak value of a frictional resistance immediately after the start of moving the hemispherical tip is divided by the load to obtain a coefficient of static friction.

The contact angle (wettability) of the wafer retaining surface11is suitably 100° or more, more suitably 110° or more, for reducing adhesion of slurry used in polishing. This contact angle (wettability) is measured based on a half-angle (θ/2) method when a measurement surface is cleaned with methanol and is then left in an atmosphere at a temperature of 20° C. and a humidity of 40% for 24 hours or more, and thereafter, droplets of distilled water are applied on the measurement surface in the same atmosphere.

An increase in hardness of the wafer retaining surface11before and after the fluorination treatment is suitably A10 or less, more suitably A8 or less for avoiding a decrease in pressure dispersibility. The hardness is measured with a type A durometer. This hardness is measured in accordance with JIS K 6253-3:2012.

Now, a method for producing an elastic film10according to the embodiment will be described.

In the method for producing the elastic film10according to the embodiment, first, a silicone rubber-made, surface-untreated elastic film (surface-untreated molded body) was produced, and a wafer retaining surface thereof then underwent a fluorination treatment of bringing the wafer retaining surface into contact with a surface treating gas containing a fluorine gas with a partial pressure of 3.00 kPa or more.

The surface-untreated elastic film can be produced from an uncrosslinked silicone rubber material by, for example, press molding or injection molding. The surface-untreated elastic film can undergo a fluorination treatment typically by placing the surface-untreated elastic film in a chamber, hermetically sealing the chamber, then filling the chamber with a surface treating gas to expose the surface-untreated elastic film to the surface treating gas.

At this time, a treatment temperature during the fluorination treatment is suitably 0° C. or more to 100° C. or less, more suitably 10° C. or more to 50° C. or less, for lowering the coefficient of rolling resistance of the wafer retaining surface11and reducing the treatment time to enhance productivity. The treatment pressure (total pressure) is suitably 3 kPa or more to 200 kPa or less, more suitably 3 kPa or more to 110 kPa or less, for the same purposes. The partial pressure of the fluorine gas is 3.00 kPa or more, and is suitably 3.00 kPa or more to 20.0 kPa or less, more suitably 3.00 kPa or more to 10.0 kPa or less, for the same purposes. The treatment time is suitably 1 minute or more to 60 minutes or less, more suitably 1 minute or more to 10 minutes or less, for reducing the treatment time to enhance productivity.

The surface treating gas may have a content of the fluorine gas of 100 vol %, i.e., may consist of a fluorine gas alone. Alternatively, the surface treating gas may contain one or more kinds of other gas in addition to the fluorine gas. Examples of the other gas than the fluorine gas include an inactive gas such as a nitrogen gas and argon. In this case, the surface treating gas suitably contains a nitrogen gas for versatility. Further, the surface treating gas suitably contains no oxygen gas, for raising the coefficient of static friction and lowering the coefficient of rolling resistance of the wafer retaining surface11. The content of the fluorine gas in the surface treating gas is suitably 10 vol % or more, more suitably 20 vol % or more, yet more suitably 30 vol % or more, for raising the coefficient of static friction and lowering the coefficient of rolling resistance of the wafer retaining surface11.

The embodiment shows, as a non-limiting example of the silicone rubber molded body, the elastic film10for retaining a wafer in a CMP apparatus, but the silicone rubber molded body may be any of other substances. For example, when the silicone rubber molded body used in the embodiment forms a pad of an article grip in the robot arm, adhesion of the article can be reduced without generating foreign matters, thereby allowing the gripped article to be released at a desired position. In addition, when the silicone rubber molded body has a coefficient of static friction raised by the fluorination treatment, a high grip performance to the article can be obtained. Further, when the silicone rubber molded body used in the embodiment forms a case (casing or a protective case) of a portable electronic device such as a mobile phone and a tablet device, adhesion of the article can be reduced without generating foreign matters, thereby allowing unpleasant feeling to touch at the time of grabbing the case of the silicone rubber molded body into which the portable electronic device has been put to be reduced. In addition, when the silicone rubber molded body has a coefficient of static friction raised by the fluorination treatment, the case of the silicone rubber molded body into which the portable electronic device has been put can be grabbed tightly, thereby allowing the chance of slipping to be reduced.

EXAMPLES

Rubber sheets of Examples 1 and 2 and Comparative Examples 1 to 4 were produced.

A silicone rubber sheet having a length of 100 mm, a width of 50 mm, and a thickness of 2 mm was produced by press molding, and a surface of the silicone rubber sheet then underwent a fluorination treatment, thereby producing a rubber sheet of Example 1. The fluorination treatment was performed at a treatment temperature of 25° C. and a treatment pressure (total pressure) of 22.0 kPa for a treatment time of 10 minutes. As a surface treating gas, a mixed gas of 30 vol % fluorine gas and 70 vol % nitrogen gas was used. Accordingly, the partial pressure of the fluorine gas was 6.60 kPa.

A rubber sheet of Example 2 was produced in the same manner as in Example 1 except that 100 vol % fluorine gas was used alone as the surface treating gas, and that the treatment pressure (total pressure), i.e., the partial pressure of the fluorine gas was 6.67 kPa.

Comparative Example 1

A rubber sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that the fluorination treatment was not performed.

Comparative Example 2

A rubber sheet of Comparative Example 2 was produced in the same manner as in Example 1 except that the surface of the silicone rubber sheet was provided with a parylene coating layer as a substitute for undergoing the fluorination treatment.

Comparative Example 3

A rubber sheet of Comparative Example 3 was produced in the same manner as in example 1 except that the surface of the silicone rubber sheet was provided with a DLC coating layer as a substitute for undergoing the fluorination treatment.

Comparative Example 4

A rubber sheet of Comparative Example 4 was produced in the same manner as in Example 1 except that the surface of the silicone rubber sheet was provided with a fluororesin coating layer as a substitute for undergoing the fluorination treatment.

For the rubber sheets of Examples 1 and 2 and Comparative Examples 1 to 4, their surfaces were cleaned with methanol; the rubber sheets were then left in an atmosphere at a temperature of 20° C. and a humidity of 40% for 24 hours; and thereafter, a SUS304-made rolling probe having a smooth outer circumferential surface with a diameter of 30 mm was pressed against the cleaned surfaces in the same atmosphere so as to apply the load of 1000 g while rolling the probe at a moving speed of 2000 mm/min. Then, each coefficient of rolling resistance was calculated by dividing a rolling resistance during the steady state by the load. The rolling resistance was measured with Heidon Type 14, which is a surface property tester manufactured by SHINTO Scientific Co., Ltd.

<Coefficient of Static Friction>

For the rubber sheets of Examples 1 and 2 and Comparative Examples 1 to 4, their surfaces were cleaned with methanol; the rubber sheets were then left in an atmosphere at a temperature of 20° C. and a humidity of 40% for 24 hours; and thereafter, a hemispherical tip with a diameter of 10 mm of a SUS304-made probe was pressed against the cleaned surfaces in the same atmosphere so as to apply the load of 100 g while sliding the hemispherical tip at a moving speed of 75 mm/min. Then, each coefficient of static friction was calculated by dividing a peak value of a frictional resistance immediately after the start of the movement by the load. The frictional resistance was measured with Heidon Type 14, which is a surface property tester manufactured by SHINTO Scientific Co., Ltd.

For the rubber sheets of Examples 1 and 2 and Comparative Examples 1 to 4, their surfaces were cleaned with methanol; the rubber sheets were then left in an atmosphere at a temperature of 20° C. and a humidity of 40% for 24 hours; and thereafter, droplets of distilled water were applied on the cleaned surfaces in the same atmosphere, to measure a contact angle based on a half-angle (θ/2) method.

The hardness of each of the rubber sheets of Examples 1 and 2 before and after the fluorination treatment was measured with a type A durometer in accordance with JIS K 6253-3:2012, and the difference, i.e., the increase in the hardness was then calculated.

The rubber sheets of Examples 1 to 2 and Comparative Examples 1 to 4 were stretched by 50%, and the stretching was then released. Thereafter, the surfaces of the rubber sheets were observed with a SEM to check the presence or absence of cracks. If no crack was observed, it was evaluated as A. If any crack was observed, it was evaluated as B.

The rubber sheets of Examples 1 to 2 and Comparative Examples 1 to 4 underwent a cross-cut test in accordance with JIS K 5600-5-6:1999, and the surfaces of the rubber sheets were then visually observed to check the presence or absence of peeling. If no peeling was observed, it was evaluated as A. If any peeling was observed, it was evaluated as B.

The test results are shown in Table 1.

Comparison of Examples 1 and 2 in which the surfaces underwent a fluorination treatment under strict conditions with Comparative Example 1 in which no surface underwent a fluorination treatment based on Table 1 shows that each of Examples 1 and 2 has a lowered coefficient of rolling resistance. This expects the reduction in adhesion to the article. Further, each of Examples 1 and 2 has a raised coefficient of static friction. This expects a high grip performance to the article. Further, it can be seen that water repellency is imparted to Examples 1 and 2. This can expect the reduction in adhesion of slurry used at the time of polishing when Examples 1 and 2 are applied as elastic films for retaining a wafer in a CMP apparatus. It is also demonstrated that the surface modification by the fluorination treatment in Examples 1 and 2 avoids cracking of the surface in the 50% tensile test and avoids generation of foreign matters caused by peeling of the surface layer in the cross-cut test.

The coefficient of rolling resistance of each of Comparative Examples 2 to 4 each having a surface provided with a coating layer was low. However, in Comparative Examples 2 to 4, cracking of the coating layer on each surface was observed in the 50% tensile test, and generation of foreign matters caused by peeling of the coating layer on each surface was observed in the cross-cut test.

INDUSTRIAL APPLICABILITY

The present invention is useful in the technical fields of a silicone rubber molded body and a method for producing the same.

DESCRIPTION OF REFERENCE CHARACTERS