JP2000044256A - Production of optical element and optical element forming die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To assure the optical finishing surface of quartz glass by thermoforing as the quartz glass is increasingly used as the optical element of a semiconductor exposure device in recent, while there is the possibility that the state of a shrinkage fit and infeasibility in taking out of the optical element are resulted and lead to the failure of a mold since the thermal shrinkage rate of the mold exceeds that of the glass when the quartz glass or the like having the extremely small coefft. of thermal expansion is used as a blank. SOLUTION: This process for producing the optical element consists in arranging the optical material 1 of low thermal expansion between upper and lower dies 2, 3, arranging the upper and lower dies and the optical material into the mold 4 divided to a plurality, softening the optical material 1 by heating, transferring the finish surface by pressurizing the optical material 1 with the mold 4 and the upper and lower dies 2, 3 and releasing the pressurization of the mold 4 and the upper and lower dies at the time of lowering the temp. of the optical material 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a low thermal expansion optical element represented by quartz glass.
More specifically, the present invention relates to a mold structure used for press molding and a method for manufacturing an optical element using the same.

[0002]

2. Description of the Related Art Recently, high-precision lenses (especially aspherical lenses) have been developed.
And specially shaped optical elements (prisms, fly-eye lenses, etc.)
As a method of manufacturing the method, a method of manufacturing by press molding without requiring a polishing step has been used. As a result, complicated steps conventionally performed in the manufacture of optical elements are omitted, and a large number of articles having the same shape can be manufactured at low cost.

An example of a conventional optical element molding method will be described below. FIG. 6 is a cross-sectional view showing a state in which a rectangular parallelepiped glass material is formed into a fly-eye shape using an optical element forming die. 101 is a trunk mold, 102 is an upper mold, 1
03 is a lower mold, 104 is an optical element, and 105 is a press head. The upper dies 102
And placed in the body mold 101 sandwiched by the lower mold 103 and set in a vacuum chamber equipped with a heating mechanism. After a desired degree of vacuum is obtained, the glass material is heated to a temperature at which the glass material can be deformed and pressed by the press head 105.
The optical element 104 is gradually cooled to a temperature at which it can be taken out. After introducing the atmosphere, the upper mold 10 is moved from the body mold 101 to the upper mold 10.
2. The lower mold 103 is removed and the final optical element 104 is removed.
Is obtained. The glass material used for such molding generally has a larger coefficient of thermal expansion than the molding die.
Therefore, the optical element naturally separates from the barrel mold due to the difference in heat shrinkage during cooling. The advantage of molding using such a barrel mold is that
If the accuracy of the molds 102 and 103 and the body mold 101 is ensured, the misalignment of the upper and lower molding surfaces can be easily avoided.

[0004]

However, in the above-mentioned prior art, when quartz glass or the like having an extremely small coefficient of thermal expansion is used as a material, the heat shrinkage of the body mold exceeds that of glass, so As a result, not only the optical element cannot be taken out, but also the body mold may be damaged. In recent years, quartz glass has been used as an optical element in a semiconductor exposure apparatus, and it has been desired to secure an optically finished surface of quartz glass by heat molding.

[0005] The present invention has been made in view of the above problems, and it is possible to form a good finished surface without causing problems such as fouling and breakage of a barrel mold by heat molding of a low thermal expansion material. It is an object of the present invention to provide a method for manufacturing an optical element and a mold for an optical element.

[0006]

A first means for solving the above-mentioned problem is that a low thermal expansion optical material is arranged in the middle of an upper and lower mold, and the upper and lower molds and the optical material are divided into a plurality of cylinders. Placed in a mold, softened by heating the optical material, transferring the finished surface by pressing the optical material with the barrel mold and upper and lower molds, when lowering the temperature of the optical material, the barrel mold and A method of manufacturing an optical element, wherein the pressure of the upper and lower molds is removed (claim 1).

[0007] In this means, the body mold is divided into a plurality of parts, and in the cooling process after the completion of the molding, the pressurization by the body mold is released. An optical element having a good finished surface can be manufactured because defects such as generation of cracks and burrs do not occur. A second means for solving the above-mentioned problem is the first means, wherein a position at which the body mold presses the optical material is determined by side surfaces of the upper and lower molds (claim). Item 2).

[0008] In this case, since the barrel mold divided at the time of pressurization is fixed to a position where it comes into contact with the side surfaces of the upper and lower molds, the upper and lower molds serve as a reference for the barrel mold, and the outer periphery of the formed element is straightened. Both the angle and the degree of parallelism can be secured, and a highly accurate optical element can be manufactured. A third means for solving the above problem is the first or second means, wherein the optical material is quartz glass (Claim 3).

The present invention provides particularly good results when using quartz glass materials. A fourth means for solving the above problem is the first, second or third means, wherein the optical element is a fly-eye lens having a plurality of optical function surfaces, and the upper and lower molds are the optical function surfaces. The method according to claim 4, wherein a plurality of finishing surfaces for finishing the surface are formed.

The present invention provides good results, especially when manufacturing fly-eye lenses. A fifth means for solving the above problem is the first, second, third or fourth means,
The method according to claim 5, wherein the body mold is divided into two to four.

By doing so, it is possible to satisfactorily pressurize and depressurize the optical material. A sixth means for solving the above-mentioned problem is an optical element molding die having a trunk die and a molding die arranged in the trunk die for press-molding a molding surface of an optical material, wherein the trunk die is An optical element molding die which is divided.

Since the body mold is divided as described above, the force escapes during heat shrinkage, so that troubles such as flicking and damage to the body mold do not occur, and a good finished surface can be formed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. Square 30 as shown in FIG.
The upper and lower dies 2 and 5 each made of a quartz glass material 1 having a thickness of 20 mm and a thickness of 20 mm, each of which is divided into 25 pieces of 6 mm × 6 mm and each of which has a plurality of finished surfaces polished concavely to R8 mm. 3 and placed in the barrel 4. FIG. 2A is a sectional view of the body mold 4 as viewed from above. As shown in FIG.
And 4b. In the present embodiment, the body type of the dividing method shown in FIG.
A barrel mold of any of the dividing methods (b) to (d) may be used. The quartz glass material 1, the upper mold 2, the lower mold 3, and the divided body mold 4 are set as a work 5 in the apparatus shown in FIG. When disposing, the air cylinders 21 and 24 are first extended and positioned from the horizontal direction, and the work 5 is adjusted to the positioning position of the air cylinders 21 and 24. Subsequently, the opposing cylinders 22 and 23 are extended and fixed while pressing the body mold. The pressing force is 1 kgf / cm ² .

The valve 16 is opened and the chamber 18 is roughly evacuated by the oil rotary pump 12. After roughing, the valve 16 is closed, the valves 14 and 15 are opened, and the oil diffusion pump 1
The book is drawn at 3. Degree of vacuum of vacuum gauge 19 is 5 × ^10-5 T
When the temperature falls below orr, heating is started by the ceramic heater 8 according to the heating schedule shown in FIG. Temperature 50
In 1 minute, raise to 1450 ° C. and hold at 1450 ° C. for 10 minutes. Five minutes after the start of holding, the pressurizing cylinder 10 is operated to pressurize. The pressure is 50 kgf / cm ² . If the vertical pressing force is increased to 50 kgf / cm ² , the horizontal positioning pressing force becomes insufficient and a positional deviation occurs. Therefore, the horizontal positioning pressing force is increased in conjunction with the vertical pressing force. The pressing force in the horizontal direction is controlled so as to be always 1 kgf / cm ² higher than the pressure in the vertical direction. Therefore, the pressing force in the horizontal direction is 51 kgf / cm ² during molding. Five minutes after the start of the pressurization, the heating by the heater 8 is completed, and the temperature is lowered. Five minutes after the start of the temperature drop, the pressure in the vertical direction is released. At the time of pressure removal at the end of pressurization, the pressing force in the horizontal direction is also released in conjunction with the pressure in the vertical direction, similarly to the end of pressurization. The pressing force in the horizontal direction at the end of molding is 1
Set to 0 instead of kgf / cm ² . At the end of pressurization, the temperature is 1100 ° C. or less. Then, it is left to cool and the temperature is lowered to room temperature.

When the temperature reaches room temperature, the horizontal cylinder is lowered so that the work can be taken out, the valve 15 is closed, the leak valve 17 is opened, and the atmosphere is introduced. After the work 5 is introduced into the atmosphere, the upper mold 2, the lower mold 3, and the body mold are removed, and a fly-eye lens having a desired shape from the quartz flat plate shape 1 is completed as shown in FIG. The accuracy of each element of the completed quartz fly-eye lens is the surface roughness Rmax10n
m or less, and the dispersion of spherical Newton rings was ± 5 or less. In addition, the variation in the length of each element is ±
5 μm or less. The fabricated quartz fly-eye lens was incorporated into an actual optical system, and the performance was evaluated. As a result, the optical performance was greatly improved compared to the conventional product.

[0016]

As described above, according to the present invention, even if an optical element using a low thermal expansion material is manufactured by heat molding,
It is possible to manufacture an optical element having a good finished surface without causing problems such as flicking and breakage of a trunk mold.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a manufacturing method according to the present invention.

FIG. 2 is a sectional view showing a split barrel type according to the present invention.

FIG. 3 is a schematic view showing an optical element manufactured according to the present invention.

FIG. 4 is a schematic structural diagram showing an apparatus used for the present invention.

FIG. 5 is a heating schedule diagram of an embodiment.

FIG. 6 is a torso view for explaining a conventional technique.

[Explanation of Signs of Main Parts]

 1 ··· Quartz glass material 2 ··· Upper mold 3 ··· Lower mold 4 ··· Body mold 5 ··· Work 6 ··· Placement table 7 ··· Press shaft 8 ··· Ceramic heater 9 · · · heat insulating plate 10 · · · vertical pressurized cylinder 11 · · · body 12 · · · oil rotary pump 13 · · · oil diffusion pump 14 · · · valve 15 · · · Valve 16 ... Valve 17 ... Leak valve 18 ... Chamber 19 ... Vacuum gauge 21 ... Horizontal cylinder 22 ... Horizontal cylinder 23 ... Horizontal cylinder 24 ... Horizontal direction cylinder

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kazuo Kitazawa 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation

Claims (6)

[Claims] 1. An optical material having a low thermal expansion is disposed in the middle of an upper and lower mold, the upper and lower molds and the optical material are arranged in a plurality of divided barrel molds, and the optical material is softened by heating. A method of manufacturing an optical element, comprising transferring a finished surface by pressing an optical material with the body mold and the upper and lower molds, and removing the pressure of the body mold and the upper and lower molds when lowering the temperature of the optical material. . 2. The method according to claim 1, wherein a position at which the barrel mold presses the optical material is determined by a side surface of the upper and lower molds. 3. The method according to claim 1, wherein the optical material is quartz glass. 4. The optical element is a fly-eye lens having a plurality of optical functional surfaces, and the upper and lower molds are formed with a plurality of finishing surfaces for finishing the optical functional surfaces. 4. The method according to 1, 2, or 3. 5. The method according to claim 1, wherein the body mold is divided into two to four. 6. An optical element molding die having a body die and a molding die disposed in the body die for press-molding a molding surface of an optical material, wherein the body die is divided. Optical element mold.