JP4274893B2 - Ultraprecision polishing method and ultraprecision polishing apparatus - Google Patents

Description

  The present invention relates to an ultraprecision polishing method and an ultraprecision polishing apparatus used for polishing a surface of a workpiece such as a mold for forming an optical glass element.

  Optical glass elements such as lenses include rotationally symmetric spherical lenses and aspherical lenses. In order to mass-produce these, press molding using a mold is an effective processing means. In this case, if the shape accuracy of the lens press-molded by the mold is poor, aberration occurs in an optical device such as a camera in which the lens is incorporated, so that the function of the optical device is degraded. Further, when the surface roughness of the mold is rough, the surface roughness of the lens after molding becomes rough, and flare occurs in the optical device. As described above, in the lens press molding, the lens processing accuracy is important, but the lens processing accuracy is affected by the shape accuracy of the surface of the molding die transferred to the lens.

Japanese Patent Application Laid-Open No. Hei 8-120470 discloses a method of ultra-precise polishing of the surface of a workpiece such as a mold by irradiating the surface with a gas cluster ion beam. The gas cluster ion beam is broken by collision with the work piece by being irradiated on the work piece, and at that time, multi-body collision occurs with cluster constituent atoms or molecules and work piece constituent atoms or molecules, and the work piece. The movement in the horizontal direction with respect to the surface of the film becomes remarkable. Thereby, the convex part in the surface of a to-be-processed object is mainly shaved, and flat superprecision grinding | polishing by atomic size is attained.
JP-A-8-120470

  Since the radius of one atom constituting the gas cluster ion beam is several tens of meters, the cluster size is several nanometers to several tens of nanometers even if the cluster is composed of several hundred to several thousand atoms. . As shown in FIG. 7, when the pitch P of the projections T existing on the surface of the workpiece is in millimeters, when the conventional cluster ion beam having a large diameter is uniformly irradiated to the workpiece, As shown in FIG. 8, which is an enlargement of the portion A, the micro-projections are mainly shaved in a minimum area of about the cluster size or less, so that the surface roughness can be improved as shown in FIG. The protrusions T having the pitch P are still not removed, and the shape difference cannot be corrected with respect to the target shape. As a result, there is a problem that the shape accuracy cannot be improved.

  The present invention has been made in consideration of such conventional problems, and even with a gas cluster ion beam set to a spot diameter equal to or less than the pitch P of protrusions existing on the surface of the workpiece, It is an object of the present invention to provide an ultraprecision polishing method and an ultraprecision polishing apparatus capable of creating a shape by removing protrusions on a workpiece surface. The present invention also provides an ultraprecision polishing method and an ultraprecision polishing apparatus capable of improving surface roughness in a minimum area by utilizing the processing principle of a gas cluster ion beam in a shape creation process. The purpose is to do.

In order to achieve the above object, an ultra-precision polishing method according to the invention of claim 1 includes a step of measuring a protrusion height with respect to a surface position of a workpiece, the measured protrusion height, the surface position, and a protrusion determined in advance. Calculating the irradiation time of the gas cluster ion beam with respect to the surface position of the workpiece based on the irradiation dose amount of the gas cluster ion beam necessary to remove the gas, and the gas cluster based on the calculated irradiation time And a step of creating and polishing the shape of the surface of the workpiece by changing the irradiation time of the ion beam according to the surface position of the workpiece.

In the first aspect of the invention, the irradiation time of the gas cluster ion beam is calculated in advance, and the irradiation time of the gas cluster ion beam is changed depending on the surface position of the workpiece, so that polishing according to the surface state of the workpiece is performed. be able to. For this reason, highly accurate polishing can be performed.

The invention according to claim 2 is the ultraprecision polishing method according to claim 1 , wherein the gas cluster ion beam is irradiated so that the irradiation direction of the gas cluster ion beam and the surface of the workpiece are always perpendicular to each other. The irradiating means for rotating and the workpiece are relatively swung.

According to the second aspect of the present invention, since the irradiation means of the gas cluster ion beam and the workpiece are swung, the irradiation direction of the gas cluster ion beam is controlled to be perpendicular to the surface of the workpiece. Polishing according to the surface of a complicated workpiece such as a shape or a concave shape can be performed.

According to a third aspect of the present invention, there is provided an ultraprecision polishing apparatus comprising: a measuring means for measuring a projection height with respect to a surface position of a workpiece; an irradiation means for irradiating a surface of the workpiece with a glass cluster ion beam; In order to change the surface position of the workpiece irradiated with the ion beam, the moving means for relatively moving the irradiation means and the workpiece, the protrusion height measured by the measuring means, the surface position and Calculation means for calculating the irradiation time of the gas cluster ion beam with respect to the surface position of the workpiece based on the irradiation dose of the gas cluster ion beam necessary for removing the obtained protrusion, and the irradiation calculated by the calculation means It is equipped with a control means for changing the surface position of the workpiece irradiation time of said controlled movement means gas cluster ion beam on the basis of the time It is characterized in.

In the invention of claim 3 , since the calculating means calculates the irradiation time of the gas cluster ion beam, and the control means changes the irradiation time of the gas cluster ion beam according to the surface position of the workpiece, the surface state of the workpiece is set. A suitable polishing can be performed.

The invention of claim 4 is the ultra-precision polishing apparatus according to claim 3 , wherein the irradiation direction of the gas cluster ion beam irradiated from the irradiation means and the surface of the workpiece are always perpendicular. The apparatus further comprises swinging means for relatively swinging the means and the workpiece.

In the invention of claim 4 , since the swinging means swings the irradiation means of the gas cluster ion beam and the work piece so that they are perpendicular to each other, the convex shape, the concave shape and the like are complicated. Polishing according to the surface of the workpiece can be performed.

  According to the ultraprecision polishing method of the present invention, polishing is performed by controlling the irradiation time of the gas cluster ion beam in accordance with the surface position of the workpiece, so that the shape accuracy of the workpiece can be increased. At the same time, the surface roughness can be improved.

  According to the ultraprecision polishing apparatus of the present invention, the irradiation means of the gas cluster ion beam, the moving means for relatively moving the irradiation means and the workpiece, and the control means for controlling the irradiation time for irradiating the gas cluster beam Therefore, it is possible to control the irradiation of the gas cluster ion beam in accordance with the surface position of the workpiece, thereby improving the shape accuracy of the workpiece and improving the surface. Roughness can be improved.

  Hereinafter, the present invention will be specifically described with reference to embodiments shown in the drawings. In each embodiment, the same members are assigned the same reference numerals.

(Embodiment 1)
FIG. 1 shows a gas cluster ion beam processing apparatus used for ultraprecision polishing of the present invention.

  The gas cluster ion beam processing apparatus is constituted by three chambers of a source unit 1, a differential exhaust unit 2, and an ionization unit 3, and is connected to a control unit 100. In these chambers, it is necessary to remove impurity gas, water, oxygen, nitrogen, etc. as much as possible as preparation before ion beam irradiation. For this reason, the pressure is reduced to a desired vacuum level by a pump (not shown). ing.

Inside the source part 1, a nozzle part 4 and a skimmer 5 are arranged. The nozzle 4 is supplied with a high pressure gas of about 0.6 to 1.0 MPa from a gas cylinder (not shown). As this gas, for example, argon gas, oxygen gas, nitrogen gas, SF ₆ gas, helium gas, carbon dioxide gas, or a mixed gas of two or more kinds can be used. A gas cluster is generated by adiabatic expansion at the moment when the high-pressure gas is ejected from the nozzle 4 at supersonic speed, and then passes through the skimmer 5 to adjust the beam diameter of the gas cluster.

  A shutter 18 that opens and closes the gas cluster beam 10 is disposed in the differential exhaust unit 2. The gas cluster beam 10 exiting the source unit 1 is a neutral beam, but enters the ionization unit 3 via the differential pumping unit 2 and is ionized by the collision of thermoelectrons of the tungsten filament 6 in the ionization unit 3. Is done. Therefore, an irradiation means is comprised by the nozzle part 4 which produces | generates a gas cluster, and the tungsten filament which ionizes by collision of a thermoelectron.

  The gas cluster ion beam 10 is then accelerated by the acceleration electrode 7. At this time, since the diameter of the conventional gas cluster ion beam 10 is about several to several tens of millimeters, the gas cluster ion beam is changed by changing the shape of the ground electrode 8 and changing the distance between the third electrode 9 and the ground electrode 8. 10 is set to the optimum condition that can be stably and finely squeezed.

  Further, an aperture 11 is arranged on the downstream side of these. The aperture 11 makes the gas cluster ion beam 10 have a desired spot diameter. Since this aperture 11 has a simple structure in which holes are made in a plate material, the spot diameter can be arbitrarily set with high accuracy from several tens of μm to several tens of mm. On the downstream side of the aperture 11, a flat mold 12 as a workpiece is disposed so that the surface thereof is perpendicular to the incident direction of the gas cluster ion beam 10.

  The planar mold 12 is mounted on a rotary stage 13 as a rotating means that can rotate around a rotation axis that is square with the incident direction of the gas cluster ion beam 10. The rotary stage 13 is mounted on an X-axis stage 14 that can move in the front-rear direction (X-axis direction perpendicular to the rotation axis of the rotary stage 13 (see FIG. 5)) with respect to the paper surface.

  The rotary stage 13 and the X-axis stage 14 are equipped with a servo motor or a stepping motor (not shown) and can be controlled by a control unit 100 as a control means. The rotary stage 13 and the X axis stage 14 constitute moving means.

  A Y-axis stage 15 is attached to the side surface of the X-axis stage 14. The Y-axis stage 15 can be adjusted in position in the Y-axis direction perpendicular to the rotation axis of the rotary stage 13 and the X-axis of the X-axis stage 14, and the Y-axis stage 15 can be adjusted. Thus, the height position of the gas cluster ion beam 10 can be adjusted. The Y-axis stage 15 can be manually fine-tuned by a screw (not shown) or can be automatically fine-tuned by a servo motor or a stepping motor. The rotary stage 13, the X-axis stage 14 and the Y-axis stage 15 are mounted on a bracket 16 fixed on the base 17.

  The control unit 100 constitutes a control unit, and includes a calculation unit 102 as a calculation unit and a storage unit 103. A control program can be created for the control unit 100. Then, the rotation stage 13 and the X-axis stage 14 can be driven by the created control program. The interferometer 101 constitutes a measuring unit, measures the surface shape of the flat mold 12, and sends the data to the control unit 100.

  Next, preparations required before processing the flat mold 12 by the above apparatus will be described with reference to FIGS.

  First, using the interferometer 101, the height of the protrusion with respect to the position of the surface of the entire shape of the planar mold 12 to be processed is measured. FIG. 2 shows an example of the measured protrusion height, where the B portion is high and the C portion is low. The height of the B part is about 0.2 μm, the height of the C part is about 0.05 μm, and the difference between the B part and the C knowledge is about 0.15 μm. Therefore, the shape accuracy is PV (peak to valley) value: about 0.15 μm. By reducing the PV value, the shape accuracy can be improved.

  Then, a control program is created using the target shape stored in advance in the storage unit 103 and the point sequence data of the protrusion height and protrusion position obtained from the measurement result of the interferometer 101. Moreover, since the area of the horizontal cross section of the protrusion is found from the measurement result, the aperture 11 smaller than the area of the protrusion is selected and the spot diameter of the gas cluster ion beam 10 is set.

  Next, the gas cluster ion beam 10 in a state where the irradiation position does not move is matched with the center position of the planar mold 12 having a planar shape. At this time, in the height direction of the gas cluster ion beam 10, the Y-axis stage 15 is moved manually or automatically by a servo motor or a stepping motor. On the other hand, in the horizontal direction, the X-axis stage 14 is moved by driving a servo motor or a stepping motor (not shown).

Further, the irradiation dose necessary for removing the protrusions is previously grasped as experimental data. FIG. 3 shows an example of this experimental data. This figure shows a beam processing trace when a flat mold is fixed, a hole diameter of the aperture 11 is about 3000 μm, and a gas cluster ion beam 10 having an irradiation dose of 3 × 10 ¹⁶ (ions / cm) is irradiated to one point. It is. This measurement can be calculated by a measuring instrument (form chrysurf) that scans in a state where the probe is in contact and measures the shape and surface roughness. In FIG. 3, the horizontal axis represents the measurement position of the beam machining trace, and the vertical axis represents the sputtering depth at the measurement position. This experiment also shows the case where the irradiation dose is 9 × 10 ¹⁶ (ions / cm ² ), and FIG. 4 is a graph plotting the result. From this result, it can be confirmed that the sputtering depth is proportional to the irradiation dose. The gas cluster ion beam is also characterized by the ability to transport a large number of atoms at low speed, which reduces the energy possessed by the cluster and allows a small amount of sputtering without damaging the surface. Control becomes possible.

In the processing method according to this embodiment, the following relational expressions hold.
Irradiation time = (irradiation dose amount × irradiation area × elementary electron amount e) / (detection ion current amount) (1)

  Therefore, when removing the protrusion height, the sputtering depth at the surface position of the planar mold 12 is set, and the irradiation dose at that time is calculated based on the graph of FIG. This is possible by determining the irradiation time according to (1).

  The actual processing method for polishing will be described. The X-axis stage 14 is moved so that the gas cluster ion beam 10 can be irradiated to the vicinity of the outer periphery of the planar mold 12. Thereafter, the shutter 18 is opened and the gas cluster ion beam 10 is irradiated. In order to create the shape of the flat mold 12, the rotary stage 13 is rotated, and the X-axis stage 14 is moved to irradiate the gas cluster ion beam 10. At this time, as described above, the height and position of the protrusions are known in advance, and when the gas cluster ion beam 10 is irradiated, the gas cluster ion beam 10 is irradiated in an amount necessary for removing the protrusions.

  FIG. 5 shows an irradiation method of the gas cluster ion beam 10. First, irradiation is performed while rotating the rotary stage 13 to the outer peripheral portion of the flat mold 12, and when the projection position is reached, the rotation time is low, or the rotation is stopped so that the dwell time of irradiation is controlled by the control unit 100. Then, the protrusion is removed so as to have a desired shape.

  After one round of irradiation is completed, the X-axis stage 14 is moved in the X-axis direction so that the gas cluster ion beam 10 can be irradiated in the center direction. In FIG. 5, the movement amount at this time is indicated by a movement pitch 19. Then, as described above, the rotary stage 13 is rotated while being controlled. By repeating the above cycle, the shape of the entire surface of the flat mold 12 is created.

  In this embodiment, it is possible to improve the surface roughness in the minimum area by utilizing the processing principle of the gas cluster ion beam 10 in the process of creating the shape. That is, the cluster is a state in which atoms or molecules are loosely bonded, and when the cluster collides perpendicularly with the planar forming die 12 that is the workpiece, the particles of the workpiece 12 are scattered and repelled by the cluster. Are scattered in the horizontal direction and deposited. As a result, a lateral sputtering effect that makes it possible to improve the surface roughness is utilized.

  According to such an embodiment, the protrusions are selectively removed by the processing process of the gas cluster ion beam 10 based on the height and position data of the protrusions of the planar mold 12 measured in advance. For this reason, the shape accuracy of the flat mold 10 can be improved. Further, by using the processing principle of gas cluster ion beam processing, it is possible to improve the surface roughness in a minimum area.

(Embodiment 2)
FIG. 6 shows a second embodiment of the present invention. In this embodiment, the convex spherical molding die 20 is processed as a workpiece.

  A swing stage 21 as a swing means is provided on the rotary stage 13 so that the gas cluster ion beam 10 can be irradiated perpendicularly to the surface of the spherical mold 20, and the spherical mold 20 is held via the swing stage 21. The swing stage 21 has a control function that can be controlled in accordance with the surface shape of the spherical mold 20.

  In this embodiment, the tilt of the swing stage 21 is controlled so that the gas cluster ion beam 10 can always be irradiated vertically with respect to the surface shape of the spherical mold 20. Then, while performing the tilt control, as in the first embodiment, the rotary stage 13 is rotated and the X-axis stage 14 is moved, while the gas cluster ion beam 10 is irradiated onto the spherical mold 20 and selectively projected. To create a shape.

  In such an embodiment, in addition to the effects of the first embodiment, by providing the swing stage 21, it is possible to improve the shape accuracy and surface roughness of the convex spherical molding die 20. Has an effect. Further, in this embodiment, it is possible to process not only the convex shape but also the concave shape, and not only the spherical mold but also the aspherical mold.

It is sectional drawing of the gas cluster ion beam processing apparatus used for this invention. It is sectional drawing which shows an example of the surface shape of the to-be-processed object measured with the interferometer. It is a graph which shows the beam processing trace by the irradiated gas cluster ion beam. It is a graph which shows irradiation dose amount. It is a front view explaining an example of gas cluster ion beam irradiation with respect to a to-be-processed object. It is a side view which shows the process of Embodiment 2 of this invention. It is a graph which shows the surface state of a to-be-processed object. It is a graph which shows the surface state of the workpiece processed by irradiating with a gas cluster ion beam. It is a graph which shows the partial expansion of the processed workpiece.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Source part 2 Actuation exhaust part 3 Ionization part 10 Gas cluster ion beam 12 Flat shaping | molding die

Claims (4)

Measuring the protrusion height relative to the surface position of the workpiece ;
Calculate the irradiation time of the gas cluster ion beam for the surface position of the workpiece based on the measured protrusion height, its surface position, and the irradiation dose of the gas cluster ion beam necessary to remove the protrusions obtained in advance. And the process of
Based on the calculated irradiation time, changing the irradiation time of the gas cluster ion beam according to the surface position of the workpiece, and creating and polishing the shape of the surface of the workpiece;
An ultraprecision polishing method comprising: The irradiation means for irradiating the gas cluster ion beam and the workpiece are relatively swung so that the irradiation direction of the gas cluster ion beam and the surface of the workpiece are always perpendicular to each other. The ultraprecision polishing method according to claim 1 . Measuring means for measuring the height of the protrusion relative to the surface position of the workpiece;
Irradiation means for irradiating the surface of the workpiece with a glass cluster ion beam;
Moving means for relatively moving the irradiation means and the workpiece to change the surface position of the workpiece irradiated with the gas cluster ion beam;
Irradiation of the gas cluster ion beam to the surface position of the workpiece based on the projection height measured by the measurement means, the surface position thereof, and the irradiation dose of the gas cluster ion beam necessary for removing the projections obtained in advance. A calculation means for calculating time;
Control means for controlling the moving means based on the irradiation time calculated by the calculation means to change the irradiation time of the gas cluster ion beam according to the surface position of the workpiece;
An ultra-precise polishing apparatus comprising: Further provided is a swinging means for relatively swinging the irradiation means and the workpiece so that the irradiation direction of the gas cluster ion beam irradiated from the irradiation means is always perpendicular to the surface of the workpiece. The ultraprecision polishing apparatus according to claim 3 .

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