JP2000042902A - Polishing tool, and polishing work method using the tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing work method for simply and efficiently removing fine weaviness existing on a surface to be worked by using a polisher other than pitch, to obtain a highly precise smooth surface. SOLUTION: A polisher 11 composed of relatively soft material is supported by pitch 11 in a polishing tool 1. The polisher 11 of the polishing tool 1 is pressed onto the surface 3a to be worked of an optical element 3, while supplying abrasive liquid 7 including a free abrasive grain to the polisher 11. Relative movement is imparted between the surface 3a and the polisher 11 to make the surface 3a into a smooth surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing tool used for polishing a surface to be processed to a highly smooth surface and a polishing method using the same. In particular, the present invention relates to a polishing tool or the like suitable for polishing an optical element such as a lens or a reflection mirror or an ultra-precision mold for molding a lens.

[0002]

2. Description of the Related Art The prior art will be described by taking, as an example, a finish polishing process which is a final step in processing a lens used in a camera or a precision optical instrument. In this processing step, a viscoelastic body called a pitch (straight asphalt pitch) obtained by heating a petroleum pitch to remove volatile components and appropriately cure it is widely used as a polisher material.

FIG. 2 is a cross-sectional view schematically showing a conventional polishing tool using a pitch as a polisher. A pitch viscoelastic layer 23 is formed on a base metal 25 having a rotation shaft 27. Polishing work surface 21 which is the surface of pitch layer 23
a is formed into a shape in which the processing surface 31a of the workpiece 31 is inverted. Then, while supplying the polishing liquid 37 containing free abrasive grains from the nozzle 35 between the pitch and the surface to be processed,
A relative processing motion (rotation or swing) is given to the work surface 31a and the polishing work surface 21a. At this time, the loose abrasive selectively processes the fine projections of the processing surface 31a to form the processing surface 31a.
Is smoothed.

For example, in polishing a short wavelength optical glass lens such as a high-grade projection exposure lens relating to a fine pattern for a semiconductor device, which requires a special high quality and a high precision mirror surface among optical components, oxidation is required. A polishing plate (polishing tool) on which a pitch viscoelastic body (straight asphalt pitch) is attached as a polisher is used together with an abrasive in which cerium abrasive particles are dispersed in water.

[0005] As an excellent feature of pitch, first of all,
It is possible to remove minute undulations (ripples) that may cause a problem if they remain. Secondly, in the finish polishing step, no new minute waviness having a different wavelength is generated. With these two points, a high-precision smooth surface without undulation can be obtained. Here, the problematic undulation mainly refers to undulation generated in a pre-processing step such as grinding. This undulation causes scattering or absorption of light in a high-precision optical component, particularly an optical element for a short wavelength, and causes a decrease in optical performance.

Although there are still many unclear parts regarding the undulation removal mechanism, it is considered as follows. That is, the pitch viscoelastic body is soft in a microscopic region of the surface and is uniform over the entire polisher. Therefore, it follows macro asperities (shape errors) on the surface to be processed, and realizes a stable polisher contact area and a uniform pressure distribution state related thereto. This is the so-called "hit" condition. In the process in which the polishing work surface (polisher work surface) in a good condition is macroscopically smoothed as the work surface is smoothed, micro undulations are removed and the work surface is smoothed. It is thought to go.

The above description shows the characteristics of the shape viscoelastic body with respect to the shape following property (fitting property to the shape of the work surface). Another great advantage of the pitch for high precision smoothing is that it has excellent damping performance. The mechanical vibration and wobbles of the polisher due to the accuracy and environment of the polishing equipment emphasize the mechanical action during polishing, not only hinder the smoothing process but also generate new minute waviness. cause.

[0008] The damping performance of the pitch viscoelastic material effectively acts on the problem of mechanical vibration which can be considered as a factor that causes this minute waviness (micro shape error). That is, the pitch itself, which serves as a polisher, has an effect of absorbing mechanical vibration, for example, backlash generated at a mounting portion between the polishing apparatus and the polishing tool, and preventing transmission of the vibration to the polishing work surface. It can be inferred that this action suppresses the occurrence of new undulations. Due to the above characteristics, the pitch has been widely used as a polisher material for high-precision smoothing of optical glass.

On the other hand, when polishing an optical component material other than the optical glass, for example, a ceramic material used for a mirror / reflection mirror for short wavelengths, it is common to not use the above-mentioned pitch. That is, in the case of processing a ceramic material, diamond powder is used for polishing abrasive grains, and abrasive grains for mechanochemical polishing for finish polishing (for example, abrasive grains of iron oxide and silicon carbide are used for a workpiece of silicon nitride). Abrasive grains other than cerium oxide are often used, such as chromium oxide abrasive grains for a workpiece and silicon oxide abrasive grains for a zirconium workpiece. And the polisher material also considers the hardness of the workpiece and the compatibility with the abrasive grains used,
Processing is performed using a polisher other than a relatively hard pitch, such as synthetic resin, acrylonitrile resin, or Teflon. This is because in mechanochemical polishing, processing heat may be generated, and the pitch may be softened and the shape may not be maintained.

[0010]

However, the above-mentioned prior art has the following disadvantages. (1) The polisher material other than the pitch lacks the shape following function and is inferior in fitting property. Polisher materials other than pitch, such as the aforementioned synthetic resin materials, do not have viscoelastic properties specific to pitch. For this reason, the function of smoothly fitting (fitting) a work surface having irregularities at first such as a pitch and smoothly changing in accordance with a change in the state of the work surface (R shape following function) is described above. Cannot be expected for polisher materials other than the pitch. If the polisher material other than the pitch lacks the shape-following function and is inferior in the fitting property, the "contact" (contact area) between the polished work surface and the work surface varies and becomes non-uniform.
Usually, since the polishing tool is pressurized with a constant load, the variation in the "hit" causes a pressure deviation, which is a factor for generating a new undulation.

(2) The polisher material other than the pitch is inferior in the damping ability characteristic. Further, since the synthetic resin material is inferior in the damping ability characteristic as compared with the pitch, it cannot absorb mechanical vibration, and mechanical vibration is transmitted to the polishing work surface. For this reason, the problem of not smoothing following the change in the state of the polished surface and the problem of transmitting vibration to the surface to be processed overlap, and in actual polishing, "chattering" often occurs, and a new undulation Is a factor that produces

To solve this problem, the thickness of the synthetic resin polisher is empirically reduced (about 0.5 mm to 2 mm), and a thin sheet-like felt having a thickness of several mm is disposed as a cushioning material thereunder. By using a layered structure, the "chamber phenomenon" was dealt with and polishing was performed. FIG. 3 is a cross-sectional view schematically showing a configuration of a conventional polishing tool having a felt buffer layer. The felt 57 is attached to the upper surface of the base metal 61 having the shaft 63 via the adhesive 59. A polisher material 53 is adhered thereon via an adhesive 55. Thus, the polishing tool 51 is configured.

However, the felt material has a slower elastic recovery after deformation and a smaller Young's modulus (softer) than the pitch. For these reasons, when a felt material is used, the followability of the R shape to the surface to be processed is poor, and the hit becomes uneven. Therefore, a new swell may occur,
There is a major defect that the shape accuracy of the work surface achieved by the pre-processing grinding process is rather deteriorated.

Furthermore, since the felt material is usually only commercially available in the form of a thin plate (sheet), when it is applied to a spherical metal base for processing a spherical optical component, uneven portions (wrinkles,
However, there is a problem that unevenness is generated, and a variation in expansion and contraction partially occurs in a spherical shape region, and it is difficult to obtain a good effect as a buffer material.

In addition, adhesives and double-sided tapes have been used for joining the base metal to the lower surface of the felt and the upper surface of the felt and the lower surface of the polisher. However, know-how for applying the adhesive evenly depends on the skill and requires time and effort. It costs. In addition, there was a problem that the double-sided tape was easily peeled off.

(3) More recently, in some glass materials, cerium oxide as abrasive grains and pitch as polisher remain as contaminants on the surface to be processed after polishing and become contaminated. Reduction of optical performance (eg transmittance)
It has been pointed out that deterioration occurs.

For the reasons described above, there is a demand for the establishment of a technique for smoothing and polishing optical elements by a polishing tool using a polisher material other than pitch. The present invention has been made in view of such a problem, and a fine undulation existing on a surface to be processed is easily and efficiently removed using a polisher other than a pitch to obtain a highly accurate smooth surface. An object of the present invention is to provide a polishing tool and a polishing method using the same.

[0018]

In order to solve the above problems, a polishing tool according to the present invention is characterized in that a polisher made of a relatively soft material is supported by a viscoelastic body such as a pitch.

According to the polishing method of the present invention, there is provided a polishing tool in which a polisher made of a relatively soft material is supported by a viscoelastic body such as a pitch, and a polishing liquid containing free abrasive grains is contained in the polisher of the polishing tool. Is applied to the surface of the optical element to be processed, and a relative motion is applied between the surface to be processed and the polisher to remove minute undulations present on the surface to be processed and to smooth the surface to be processed of the optical element. It is characterized by the following.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a polishing tool according to one embodiment of the present invention and how an optical element is processed using the polishing tool. The polishing tool 1 of this example includes a base 15, a pitch viscoelastic layer 13 and a polisher 1
1 is composed of three layers. The base metal 15 in this example is a disk made of cast iron or the like, whose central portion is slightly raised. Mount 1
In the center of the lower surface of 5, an integral shaft 17 protrudes downward.

The pitch viscoelastic layer 13 is laminated on the base metal 15. The pitch viscoelastic layer 13 newly adds a shape following function and a function of attenuating disturbance to the surface to be processed.

On the pitch viscoelastic layer 13, a polisher 11 made of a synthetic resin sheet is adhered. In this example, the thickness of the polisher 11 is 0.5 mm. The polishing work surface 1a, which is the surface of the pitch layer 13, is
Is formed into an inverted shape of the surface 3a to be processed. And
While supplying the polishing liquid 7 containing loose abrasive particles from the nozzle 5 between the pitch and the processing surface, a relative processing motion (rotation or swing) is applied to the processing surface 3a and the polishing work surface 1a. At this time, the free abrasive grains selectively process fine projections on the surface 3a to be processed, thereby smoothing the surface 3a to be processed.

Next, a method of adjusting the polishing tool of this embodiment will be described. The arrangement and attachment of the pitch viscoelastic body layer 13 are performed in the same manner as in a normal pitch polisher manufacturing method. The upper surface of the pitch viscoelastic body layer 13 is formed into an R shape using (not shown). Next, the pitch viscoelastic body layer 13 and the base metal 15 are heated again to a temperature lower than the softening temperature, and the polisher 11 is arranged and attached.

According to this method, since the pitch has tackiness in a heated state, the pitch itself functions as an adhesive, and it is not particularly necessary to separately prepare an adhesive. According to the method of this embodiment, the labor and skill required for bonding the polisher material, the know-how, the quality of the polishing performance due to the unevenness of the adhesive, and the like are eliminated, and the production of the polishing tool is facilitated.

In this embodiment, a synthetic resin material which is formed into a sheet shape and which is commercially available is used. However, after the resin before curing is applied on the pitch, an R shape is formed using a molding die. It is also possible to cure while polishing to obtain a polishing tool. According to this method, there is an advantage that the thickness of the polisher can be adjusted and a complicated shape can be handled.

Using the polishing tool of the present embodiment and diamond abrasive grains (average particle size: 1 μm), spherical machining of ceramic material (silicon carbide) was performed in an Oscar-type polishing apparatus. It was confirmed that a surface could be obtained. In addition, in consideration of the shape following function, the pitch viscoelastic body layer 13 used a soft-eyed pitch having a penetration of 20 degrees.

[0027]

As is apparent from the above description, according to the present invention, fine undulations existing on the surface to be processed can be easily and efficiently removed using a polisher other than the pitch.
A polishing tool for obtaining a high-precision smooth surface and a polishing method using the same can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a polishing tool according to one embodiment of the present invention and a state of processing an optical element using the polishing tool.

FIG. 2 is a cross-sectional view schematically showing a conventional polishing tool using a pitch as a polisher.

FIG. 3 is a cross-sectional view schematically showing a configuration of a conventional polishing tool having a felt buffer layer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Polishing tool 1a Polishing work surface 3 Workpiece 3a Workpiece surface 5 Nozzle 7 Polishing liquid 11 Polisher 13 Pitch viscoelastic layer 15 Base metal 17 axis

Claims (2)

[Claims] 1. A polishing tool wherein a polisher made of a relatively soft material is supported by a viscoelastic body such as a pitch. 2. A polishing tool in which a polisher made of a relatively flexible material is supported by a viscoelastic body such as a pitch, and an optical element is supplied while supplying a polishing liquid containing free abrasive grains to the polisher of the polishing tool. The surface of the optical element is smoothed by applying relative motion between the surface to be processed and the polisher to remove minute undulations present on the surface to be processed. Polishing method.