JP2007321185A - Superprecision polishing method and superprecision polishing device by gas cluster ion beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superprecision polishing method and device using a gas cluster ion beam suitable in the case a workpiece has a curved surface. <P>SOLUTION: The method comprises: a first measurement step where, when the surface of the workpiece is polished by the irradiation of a gas cluster ion beam, an error from the objective surface shape of the surface shape in the workpiece is measured; a second measurement step where the surface of the second workpiece is irradiated with a gas cluster ion beam, and a working mark formed on the surface of the second workpiece is measured; a first calculation step where, on the basis of the working mark data obtained by performing the measurement with the second workpiece as the object, working mark data corresponding to the curvature of each surface position in the objective surface shape of the workpiece are generated; a second calculation step where, with the created working mark data as fundamental data, the irradiation dose distribution of the gas cluster ion beam for removing solid substance for the portion of the error is obtained; and a polishing step where the surface of the workpiece is irradiated with the above gas cluster ion beam in accordance with the above irradiation dose distribution, and the surface of the workpiece is polished. The polishing device is also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for smoothing the surface of a workpiece, and in particular, an ultraprecision polishing method for polishing a surface of an optical element such as a lens or a mold for molding the optical element, which requires shape accuracy, and The present invention relates to an ultra-precision polishing apparatus.

  As processing methods for optical elements such as rotationally symmetric spherical lenses and aspherical lenses, methods for processing optical elements directly by grinding or polishing, and processing methods for mass production molds that use press molds and so on.

  In general, when the optical element has poor shape accuracy, it causes aberrations in optical devices such as cameras, microscopes, and endoscopes in which the optical element is used, and the surface roughness of the optical element is rough. Flare is generated on the optical device, and in any case, the function of the optical device product is deteriorated.

  As a means for smoothing the surface roughness, the surface roughness of the processed optical element or molding die (collectively referred to as a workpiece) is irradiated with a gas cluster ion beam. Super-precision polishing technology is used to make it smooth.

  When the surface of the workpiece is irradiated with the gas cluster ion beam, the gas cluster ions are broken due to collision with the workpiece, and the cluster constituent atoms or molecules and the workpiece constituent atoms or molecules collide with each other. Activates the movement of horizontal atoms or molecules on the surface of objects. And the protrusion part on the surface of a workpiece will be mainly shaved by activation of this movement. When the ultra-precision polishing technique is used, such a principle acts to flatten the surface of the workpiece at the atomic size level (Patent Document 1).

As an example of using the technology using the gas cluster ion beam for ultra-precision polishing, the surface of the workpiece is irradiated with a gas cluster ion beam whose diameter is narrowed by an aperture. There is a method in which the irradiation time is controlled according to the position of the protrusion on the surface of the workpiece, and the surface of the workpiece is polished (Patent Document 2).
Patent No. 3451140 JP 2005-120393 A

As described above, a technique for smoothing the surface roughness of a workpiece by irradiating the surface of the workpiece with a gas cluster ion beam is known.
However, in the conventional ultra-precision polishing process, regardless of whether the surface shape of the workpiece is flat or curved, the projection is removed by always irradiating the surface with a gas cluster ion beam under the same control conditions. ing.

  In other words, when a workpiece having a curved surface is polished, the optimal gas cluster ion beam is used under the same control conditions when the surface is flat. Even if the surface of the workpiece after processing is smoothed, the overall shape is greatly collapsed and the shape accuracy is poor. This deterioration of the shape accuracy is a problem because it deteriorates the function of the optical device product in which the optical element is used.

  Therefore, the present invention provides a gas cluster ion beam that can be adapted not only when the surface of the workpiece is a flat surface but also when the surface is a curved surface or when the surface is a surface with a different curvature at each position. It is an object of the present invention to provide an ultraprecision polishing method and an ultraprecision polishing apparatus using a gas cluster ion beam.

In order to solve the above problems, the present invention is configured as follows.
One of the aspects of the ultraprecision polishing method of the present invention is that the target surface shape of the surface shape of the workpiece is polished on the premise that the surface of the workpiece is polished by irradiating the surface of the workpiece with a gas cluster ion beam. A first measuring step for measuring an error from the second, and measuring a processing mark (groove) formed on the surface of the second workpiece by irradiating the surface of the second workpiece with the gas cluster ion beam. Measurement step and first calculation step for generating machining trace data conforming to the curvature of each surface position in the target surface shape of the workpiece based on the machining trace data obtained by measuring the second workpiece On the surface of the workpiece, the gas cluster ion beam removes the solid material corresponding to the error (solid material constituting the workpiece) using the generated machining trace data as basic data. Find the irradiation dose at each position A calculation step, to perform a polishing step for polishing the workpiece surface the gas cluster ion beam is irradiated to the workpiece surface in accordance with the irradiation dose.

  Another aspect of the ultra-precision polishing method of the present invention is that the surface shape of the workpiece is polished on the premise that the workpiece surface is polished by irradiating the surface of the workpiece with a gas cluster ion beam. Measure and calculate an error from the preset target surface shape data of the surface shape data of the work piece obtained by the above measurement for each position on the surface of the work piece. Between the irradiation range of the workpiece surface by the gas cluster ion beam and the solid material removal depth (depth at which the surface solid material is removed by sputtering) when the surface of the gas cluster is irradiated with the gas cluster ion beam A reference profile is introduced to correct the reference profile for each position on the workpiece surface so that it follows the curvature of the position on the target surface shape. And a solid material removal depth within each irradiation range is changed for each position, and each position is corrected at a position where a plurality of correction profiles overlap. The workpiece is processed such that the errors are reduced in the polishing target range of the workpiece surface based on a predetermined relationship between the solid material removal depth and the irradiation dose amount by adding the solid material removal depth of the profile. The irradiation dose at each position on the surface of the object is determined, the irradiation dose at each position is converted into the scanning speed of the gas cluster ion beam, and the gas cluster ion beam is scanned onto the workpiece surface. The surface of the workpiece is polished by irradiation at a speed.

  In each of the above methods, a predetermined offset amount (minimum removal amount) is added to the error data for the entire range of the workpiece surface, and gas cluster ions are targeted for the entire range of the workpiece surface. A surface of the workpiece may be polished by scanning a beam.

  When the gas cluster ion beam irradiated to the workpiece and the gas cluster ion beam irradiated to the second workpiece are different, the relationship between the sputtering depth and the irradiation dose by each gas cluster ion beam. The reference profile may be corrected based on the above.

  One aspect of the ultra-precision polishing apparatus of the present invention is an irradiation means for irradiating a gas cluster ion beam at a predetermined power in a predetermined direction, and the gas cluster ion beam is incident vertically at an arbitrary position on the surface of the workpiece Each position on the surface of the workpiece is controlled so that the posture of the workpiece is controlled and the gas cluster ion beam is irradiated to each position on the surface of the workpiece with a predetermined irradiation dose. And a control means for controlling the scanning speed of the gas cluster ion beam.

  The control means corrects the first machining trace data to second machining trace data conforming to the curvature of each position on the target surface shape of the workpiece, and calculates the irradiation dose. The posture of the workpiece is controlled so that the cluster ion beam is vertically incident at an arbitrary position, and the gas cluster ion beam is irradiated at each position on the surface of the workpiece with the irradiation dose. It is preferable to comprise a movement control means for controlling the scanning speed of the gas cluster ion beam at each position on the surface of the workpiece.

The target surface shape of the workpiece may be a curved surface.
In the present invention, the solid material on the surface of the workpiece is removed by the gas cluster ion beam so that the target surface shape is obtained at each position on the surface of the workpiece. For this reason, the workpiece after the solid substance is removed has a smooth surface and a target surface shape. In particular, even when a workpiece whose target surface shape is a curved surface other than a plane is processed, machining trace data (in accordance with the curvature of each surface position in the target surface shape of the workpiece is calculated for the irradiation dose) ( (Or correction profile), the surface shape of the workpiece is finished to follow the curved surface shape, and the shape accuracy can be improved after the polishing process.

According to the present invention, the surface of a workpiece can be processed into a target surface shape as well as a smooth surface.
For this reason, in parts such as optical elements where slight deterioration in surface roughness and shape accuracy reduces the function of the optical device product, this polishing process can follow the target surface shape of the part, A component having a smooth surface and good shape accuracy can be obtained.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
In the present embodiment, in a precision polishing process for polishing a workpiece surface made of a solid material such as metal, alloy, glass, or ceramic, for example, an inert gas such as argon gas, oxygen gas, or nitrogen gas, or a compound In this method, the surface of the workpiece is polished by irradiating the surface of the workpiece with a gas cluster ion beam obtained by accelerating gas cluster ions composed of carbon dioxide gas.

  Conventionally, when the surface of a workpiece is irradiated with a gas cluster ion beam, the gas cluster ions are broken due to the collision with the workpiece, and the cluster constituent atoms or molecules collide with the workpiece constituent atoms or molecules. It is known to activate the movement of horizontal atoms or molecules on the workpiece surface. Under this activated movement, the protrusions on the workpiece surface are mainly scraped. The above-mentioned method of performing precise polishing of the workpiece surface by irradiating the gas cluster ion beam is performed based on such a principle, and by using such a method, the workpiece surface is obtained at the atomic size level. Ultra-precision polishing can be performed. A more detailed explanation of the above method is disclosed in, for example, Japanese Patent No. 3451140. For details, refer to the known literature.

  A feature of the present invention resides in a gas cluster ion beam irradiation control method for irradiating the workpiece surface when performing the ultra-precision polishing. In this method, the irradiation of the gas cluster ion beam to the workpiece surface is controlled at each position on the workpiece surface to be polished so that the workpiece has a target surface shape after polishing, Under this control, the solid material (material constituting the workpiece) on the surface of the workpiece is removed. Scanning on the workpiece surface with the gas cluster ion beam may be performed only on the region that does not match the target surface shape. However, because the beam cross section of the gas cluster ion beam has a region, it is usually processed. It is performed over the entire range of the object surface (all parts whose performance depends on the shape). That is, in this case, the gas cluster ion beam is also irradiated to the position on the workpiece surface that matches the target surface shape. For this reason, in this method, the solid material is removed so that the target surface shape becomes the target surface shape at each position on the workpiece surface, and in addition, the shape is maintained at the position that originally matches the target surface shape. However, the irradiation of the gas cluster ion beam on the surface of the workpiece is controlled so as to remove only the minimum necessary solid material.

  In addition, the irradiation control method of the gas cluster ion beam mentioned above is implemented by adjusting the irradiation position on the surface of a workpiece, and the irradiation amount to the position. The adjustment of the irradiation position and the irradiation amount can be realized by a configuration for controlling the irradiation direction and power of the gas cluster ion beam, a configuration for controlling the direction and moving speed of the workpiece, or a combination of these.

  By applying such a method to the polishing of a workpiece, the workpiece having an arbitrary surface shape can be obtained without deteriorating the surface shape accuracy of the entire workpiece (particularly, in each target surface shape). The surface can be smoothed at the atomic size level (following its shape to the curvature of the position). In addition, even if the shape of the workpiece surface is shifted from the target surface shape, the solid material is removed so that the target surface shape is obtained at each position on the workpiece surface. Can be further removed to make the workpiece shape the target surface shape.

FIG. 1 is a flow chart showing a series of steps for performing surface polishing by controlling irradiation of a workpiece with a gas cluster ion beam.
In the surface polishing flow of this example, first, an error of the surface shape of the workpiece from the target surface shape is measured (S1). In this step, the surface shape of the workpiece is measured, and the error of the workpiece shape with respect to the target surface shape is obtained from the measured data and the target processed shape data (the target surface shape).

  Next, the surface of a second workpiece (a workpiece made of the same material as the workpiece) different from the workpiece is irradiated with a gas cluster ion beam to measure the machining trace (S2). In this step, a gas cluster ion beam is continuously scanned along a predetermined path at each position on a second workpiece surface whose surface shape is known in advance, and a machining groove (referred to as a machining trace in this specification) is obtained. This processing mark is measured by forming a). In addition, you may introduce these processing trace data, when there exists ready-made data.

  Subsequently, machining trace data in accordance with the curvature of the target surface shape of the workpiece is generated based on the machining trace data obtained in step S2 (S3). When the target surface shape of the workpiece is different from the surface shape of the second workpiece (specifically, the surface shape of the region from which the machining mark data is collected), the gas cluster ion beam set under the same conditions is irradiated. The shape of each processing mark formed is different. For this reason, in this process, machining trace data that conforms to the curvature of the target surface shape of the workpiece is generated based on the machining trace data obtained from the second workpiece, and is optimal for each surface position of the workpiece. Get machining mark data. At this time, if the curvature of the target surface shape is different at each position on the surface of the workpiece, machining trace data conforming to the respective curvature is generated.

  Then, the irradiation dose amount at each position of the gas cluster ion beam for removing the solid material corresponding to the error is obtained using the processing trace data generated in step S3 as basic data (S4). The processing mark data generated in step 3 is irradiated with the beam diameter range centered on the position of the gas cluster ion beam on the optical axis and the solid material removal depth within this range (specifically, the beam diameter is irradiated with the beam diameter range). The relationship between the depth from the workpiece surface where the solid material on the workpiece surface is removed by the beam, so-called sputtering depth, is obtained. The solid substance removal depth has a predetermined relationship with the irradiation dose of the gas cluster ion beam irradiated to the range. From these relationships, the irradiation dose at each position on the workpiece surface necessary for removing the solid material up to the depth corresponding to the error is obtained.

  Then, the surface of the workpiece is polished by irradiating the surface of the workpiece with a gas cluster ion beam according to the irradiation dose at each position obtained in step S4 (S5). In this process, the workpiece surface is moved to the irradiation position of the gas cluster ion beam so that the gas cluster ion beam is irradiated to each position on the workpiece surface with the irradiation dose obtained in step S4. These positions are moved and controlled to adjust the irradiation position of the gas cluster ion beam on the surface of the workpiece and the irradiation amount to the position. By this series of irradiation control processes, the error is removed and the workpiece shape can be made the target surface shape.

  Note that the above is a description of the case where surface polishing is performed with a beam for a region that has an error from the target surface shape. In this case, a predetermined offset amount (minimum removal amount) may be included in the error from the target surface shape. When irradiating the entire workpiece, the gas cluster ion beam is also applied to the region that matches the target surface shape (that is, the error is zero), so that a minimum amount of solid material is removed even in this region. It becomes. Therefore, instead of the above error data, the minimum solid removal amount (minimum removal amount) is added to all regions (all regions with and without errors) irradiated with the gas cluster ion beam. In accordance with the irradiation dose amount (irradiation dose amount at each position on the workpiece surface) obtained based on this error data, the surface polishing is performed by controlling the irradiation of the gas cluster ion beam. In this case, the error is completely removed, the shape of each removal position matches the target surface shape, and the workpiece shape can be made the target surface shape with higher accuracy.

Needless to say, projections at the atomic size level on the surface of the workpiece irradiated with the gas cluster ion beam are smoothed.
As described above, by using the ultra-precision polishing method according to the present embodiment, in a workpiece having an arbitrary surface shape, the surface is smoothed at the atomic size level, and the surface shape of the entire workpiece is not destroyed. It becomes possible to approach the surface shape as much as possible.

Examples in which the ultraprecision polishing method according to the present embodiment is applied are shown below.
Example 1
FIG. 2 is an apparatus configuration diagram of the entire system for subjecting a workpiece to ultra-precision polishing with a gas cluster ion beam.

  The figure shows a gas cluster ion beam irradiation apparatus 1 as irradiation means, a moving mechanism 2 for changing the position and posture of a workpiece (workpiece, second workpiece, etc.), and calculation means for performing various calculation processes. 1 shows a computer (PC) 3, a movement control device 4 as movement control means for controlling the movement mechanism 2, and a measuring device 5 for measuring the shape and the like of a workpiece.

The moving mechanism 2, the PC 3, and the movement control device 4 constitute control means.
The gas cluster ion beam irradiation apparatus 1 generates a gas cluster ion beam (Beam) by three chambers (10-1, 11-1, 12-1) of a source unit 10, a differential exhaust unit 11, and an ionization unit 12. In this example, a gas cluster ion beam (Beam) is irradiated in a predetermined direction with a predetermined power.

  The chamber 11-1 of the differential exhaust unit 11 is decompressed to a desired vacuum level by a pump (not shown) before beam irradiation, and impurity gas, water, oxygen, nitrogen, etc. in the chamber 11-1 are possible. Excluded as much as possible.

A high pressure gas of about 0.6 to 1.0 MPa (for example, argon gas, nitrogen gas, oxygen gas, SF ₆ gas, helium gas, mixed gas of compound carbon dioxide or two or more gases) from a gas cylinder (not shown) Etc.) to the nozzle 100, and the gas is ejected from the nozzle 100 at supersonic speed. A gas cluster is generated by adiabatic expansion at the moment when the gas is ejected, and the beam diameter of the gas cluster is adjusted when the skimmer 101 passes.

  The beam passed through the skimmer 101 (which is still a neutral beam at this time) is decompressed to a desired vacuum degree by opening the shutter 110 in the irradiation direction, and the chamber 11- of the differential exhaust unit 11 is decompressed. 1 enters the ionization section 12, where it is ionized by collision with the thermal electrons of the tungsten filament 120. The ionized gas cluster ionization beam is accelerated by the acceleration electrode 12-2 of the ionization unit 12. Since the beam diameter at this time is about several millimeters to several tens of millimeters, the beam diameter is narrowed by setting the shape of the ground electrode 121 and the distance between the third electrode 122 and the ground electrode 121 to optimum conditions. Get a stable, focused beam. The desired beam diameter is obtained through the aperture 123 disposed at the end of the beam. The aperture 123 is a through hole obtained by, for example, making a hole in a plate material, and can be set to an accuracy in the range of several tens of micrometers to several tens of millimeters.

  The moving mechanism 2 is used to always set the incident angle of the beam irradiated to the surface of the workpiece 6 such as the workpiece 6-1 and the second workpiece 6-2 to 90 ° in an arbitrary region on the surface. And a mechanism for moving the position of the workpiece 6 and for changing the posture. In this example, the surface shape of the workpiece 6 has a rotational axis symmetrical shape, and the workpiece 6 is processed and polished while rotating about the rotation axis. The moving mechanism 2 is a rotating mechanism, It is composed of an X-axis moving mechanism, a Y-axis moving mechanism, and a swing mechanism. Although not specifically described in detail, these are arranged in the chamber 12-1 of the ionization section 12, and their control lines are drawn out from the inside of the chamber 12-1.

  The rotating mechanism includes a rotating stage 20 that can rotate about an axis and a rotating stage drive mechanism (not shown) that rotates the rotating stage 20 on an axis. The rotary stage 20 is arranged so that the mounting surface faces sideward (leftward in the state shown in the figure), and a central axis of the mounting surface, that is, a horizontal center, by a rotary stage driving mechanism (not shown). The shaft is configured to be rotatable about the shaft. The rotary stage drive mechanism can be configured, for example, by using a motor such as a stepping motor or a servo motor as a drive source and combining a plurality of gears so that the rotational power of the motor can be transmitted as the rotational power of the rotary stage 20. The workpiece 6 is mounted on the mounting surface with the center axes thereof aligned, and rotates about the center axis of the workpiece integrally with the rotational movement of the rotary stage.

  The X-axis moving mechanism is configured to move the X-axis stage 21 and the X-axis stage 21 from the front side to the back side (or the opposite direction), that is, in a direction perpendicular to the central axis and in a horizontal direction. The illustrated X axis stage drive mechanism is used. This X-axis stage drive mechanism can also be driven by a motor such as a stepping motor or servo motor. For example, the rotational power of this motor is converted into linear motion power using a ball screw or the like, and this power is converted into X power. It can be configured to transmit to the axis stage 21 and move the X-axis stage 21 from the front of the figure to the back (or the opposite direction).

  The Y-axis movement mechanism includes a Y-axis stage 22 and a Y-axis stage drive mechanism (not shown) that moves the Y-axis stage 22 in the vertical direction (vertical direction) in the figure. This Y-axis moving mechanism is for adjusting the height of the position of the workpiece 6 relative to the beam irradiation position. As described above, in this example, beam irradiation is performed while rotating a workpiece having a rotational axis symmetry shape. A method of irradiating the workpiece during the polishing process will be described in detail later. In this example, the beam is scanned horizontally in the radial direction while rotating the shaft. Thus, the entire workpiece surface is processed and polished. For this reason, in the case of this example, the height of the workpiece 6 (particularly the workpiece) is such that the position where the beam hits and the height of the rotation axis of the workpiece coincide with each other before the machining and polishing treatment. There is no need to change the height during the processing and polishing. That is, it is only necessary to have a configuration that can finely adjust the height before the processing. In this example, the Y-axis stage moving mechanism has a simple configuration in which the height is adjusted by manually rotating a screw, for example, and the height of the beam irradiation position is adjusted by adjusting the height with the screw before the above processing and polishing process. And the height of the rotating shaft of the workpiece are matched.

  Of course, this Y-axis stage drive mechanism can also be driven by a motor such as a stepping motor or servo motor, and this rotational power is converted into linear motion power using, for example, a ball screw, and this power is converted. It may be configured to transmit to the Y-axis stage 22 and move the Y-axis stage 22 in the vertical direction in FIG.

  The swing mechanism swings the work piece so that the incident angle of the beam applied to the surface of the work piece 6 is always 90 ° in any region according to the surface shape (particularly the curved surface shape). It is a mechanism to make. In this example, since the beam is always scanned horizontally at a constant height without being displaced in the vertical direction on the surface of the workpiece, and the workpiece 6-1 has a rotationally symmetric shape, X A configuration in which the orientation of the mounting surface of the rotary stage is changed in a horizontal plane according to the position of the movement destination of the axis stage (that is, the orientation of the workpiece surface is changed by this) may be adopted. In this example, a second rotary stage 23 having a vertical axis in the figure as a rotation axis, a drive mechanism 24 for rotating the second rotary stage 23, and a second rotary stage 23 are provided upright. The bracket 25 that rotates together with the second stage constitutes the swing mechanism, and the stages 20, 21, and 22 are mounted on the bracket 25. The drive mechanism 24 includes a drive source such as a motor. Based on this drive source, the second rotary stage 23 and the bracket 25 are integrally rotated about the vertical axis center in FIG. The rotation axis is tilted in any direction within the horizontal plane of the figure.

  In this example, the rotary stage 20, the X-axis stage 21, and the Y-axis stage 22 are arranged in this order from the left to the right in the figure, and each stage 20, 21, 22 is all the stages located on the right side thereof. It is comprised so that it can move integrally with movement of. Each of these stages 20, 21, 22 is mounted on a bracket 25 configured on the second rotary stage 23.

  As described above, when the workpiece 6-1 is mounted on the mounting surface of the rotary stage 20, and the height is adjusted so that the height of the beam and the rotation axis of the workpiece 6-1 coincide with each other, After that, by controlling the X-axis moving mechanism and the swinging mechanism with a motor, it is possible to control the irradiation of the beam horizontally from the rotation axis of the work piece in the radial direction at a set speed. The incident angle on the object surface can always be kept at 90 ° during scanning. At this time, if the rotary stage 20 is further rotated at a predetermined angular velocity by controlling the rotation mechanism with a motor, the beam is irradiated perpendicularly to the surface while scanning the workpiece circularly or spirally. Will come to be.

  FIG. 3 shows a case in which the workpiece 6-1 has a curved surface shape that is rotationally symmetric, such as a convex lens, and a beam irradiated from a predetermined direction and an incident position on the workpiece surface by the beam. The angle relationship is shown from above the apparatus of FIG.

  FIG. 6A shows an arrangement in the case where a beam (Beam) is irradiated to the center (on the rotation axis) 60-1 of the workpiece surface 60. In this case, the workpiece 6-1 has a center 60 thereof. The position is controlled so that the beam is irradiated to -1, and the posture is controlled so that the rotation axis O coincides with the irradiation direction of the beam. By this control, the beam is vertically (90 °) incident on the center of the surface of the workpiece having a rotationally symmetric shape.

  FIG. 5B shows an arrangement in which a beam is irradiated to a position moved a predetermined distance from the center (on the rotation axis) 60-1 of the workpiece surface 60 in the radial direction (front side in FIG. 2) in the horizontal plane. In this case, the position of the work piece 6-1 is controlled such that the position is irradiated with the beam and the normal of the position matches the irradiation direction of the beam. The By this control, the position of the workpiece surface can be arranged in the beam irradiation range, and the surface can be arranged so that the beam can be incident perpendicularly (90 °). If the workpiece is rotated around the rotation axis O in this state, the machining trace as shown by the thick solid line 61-1 in the drawing (the machining trace on the concentric circle when viewed from the front side of the machining surface of the workpiece). ) Is formed.

  Then, for example, by moving the beam irradiation range horizontally in the radial direction from the center of the rotation axis while rotating the workpiece, the entire workpiece surface (one entire machining surface) is processed and polished. It becomes the object of processing.

FIG. 2 further shows the PC 3 and the movement control device 4.
The PC 3 is a computer in which a central processing unit (CPU), a memory such as a RAM and a ROM, and an input / output unit are connected by a bus. In the PC3, control information for controlling the position and orientation in accordance with the shape of the workpiece when performing surface polishing of the workpiece (referred to as movement control information in this specification) In other words, it can be called irradiation control information for controlling irradiation of the beam), and a polishing program incorporating the movement control information is registered in the movement control device 4 from the input / output unit. This movement control device 4 controls each part (especially each motor of the said moving mechanism 2) according to the procedure designated by the said grinding | polishing program, and movement control information.

The figure further shows a measuring device 5 for measuring the shape and the like of the workpiece 6.
This measuring device 5 is used to measure the surface shape of the workpiece 6-1 that will eventually become a product and the machining trace of the second workpiece 6-2 that has been irradiated with the beam for collecting sample data. Device.

  For example, a stylus type surface shape measuring instrument is used as the measuring device 5, and in this case, the surface of the workpiece (including the second workpiece) is directly traced by the detection needle, and the surface shape is slightly undulated. The change is detected as finely as possible, and data on the amount of change in height from the reference plane is collected for each position on the surface. Various data obtained here are collected before processing and polishing of the workpiece 6-1 and transferred to the PC 3 via a communication port, a portable recording medium, etc. Used for derivation.

FIG. 4 is a flowchart of the ultraprecision polishing process.
5 to 14 are explanatory diagrams of a preferable method for deriving the movement control information.
In this example, the workpiece 6-1 to be processed and polished will be described as a 10 mm diameter convex lens. Then, it is assumed that a shape error from the target surface shape (the ideal shape of the convex lens) in the convex lens occurs symmetrically with the rotational axis.

  First, the surface shape error from the target surface shape is measured in the convex lens before processing and polishing processing (S1-1). In this step, the surface shape of the convex lens before processing and polishing is actually measured by the measuring device 5. Next, by comparing the surface shape data obtained by the actual measurement and the data of the target surface shape for each position on the convex lens surface, the error of the surface shape of the convex lens with respect to the target surface shape is determined. Calculation is performed for each of the above positions (S1-2). The reference point at that time (that is, the position where error = 0) is the error when the error does not take a negative value in the entire measurement range (that is, when the measured shape does not fall below the target shape). Set the position to take the minimum value. The error data thus obtained (data indicating the relationship between position and error) is sent to the memory of the PC 3 and held there.

FIG. 5 is a graph showing the error data obtained in step S1-2.
In this example, since the target surface shape is a rotationally symmetrical shape and the convex lens in which the surface shape error appears symmetrically about the rotational axis, the target changes from the center (rotating axis) to an arbitrary radial direction. The error from the surface shape is shown in the same graph. In the figure, the horizontal axis indicates the position (mm) on the convex lens surface and the vertical axis indicates the error amount (μm), and the change in error on one diameter is displayed in a graph. Hereinafter, the error amount is referred to as a PV (Peak to Valley) value.

  In the figure, a target surface shape at each position on the diameter is indicated by a one-dot chain line 500, and an error from the target surface shape is indicated by a solid line 510. Since the target surface shape is a reference shape, the target surface shape is indicated by a straight line 500 with a slope of 0 in this graph.

  As shown in the figure, the convex lens of this example has the maximum error amount (0.15μm) on the rotation axis (Top part), and the position away from the rotation axis by less than 5mm in the radial direction (Bottom part) And having an error amount (0 μm). This Bottom portion is a location that coincides with the target surface shape 50, and in the subsequent processing and polishing processing, processing and polishing of at least the region excluding this region is required. Further, the error change 510 is expressed symmetrically about the rotation axis so as to confirm that the change in error in each radial direction around the rotation axis (0 mm) is the same. In this example, the error data is composed of data indicating the relationship between the radial position from the rotation axis center and the error.

  In the process following step S1-2 in FIG. 4, gas is applied to the surface of a second workpiece different from the workpiece (in this example, a workpiece having a planar shape made of the same material as the convex lens). The irradiation range of the gas cluster ion beam on the surface of the second workpiece when the cluster ion beam is irradiated, and the resulting solid material removal depth (the gas cluster ions reach the interior by removing the solid material on the surface by sputtering) A reference profile indicating a relationship with the depth (which is also referred to as a sputtering depth in this specification) is introduced (S2-1).

  The reference profile may be prepared in advance, or, for example, the second workpiece (the second workpiece in FIG. 2) with the surface facing the left side of the mounting surface of the rotary stage 20 in FIG. Place the workpiece 6-2) and measure the beam machining trace directly formed on the surface of the second workpiece by irradiating the surface (in this example, the planar surface) with a gas cluster ion beam. You may get it.

  In this example, when processing and polishing the convex lens using the configuration of FIG. 2, predetermined setting conditions (unit irradiation dose, gas type, gas pressure, gas flow rate, acceleration voltage, rotation speed of the workpiece) ) To irradiate the convex lens with the gas cluster ion beam. In this case, while the convex lens rotates for a certain time, the beam continues to irradiate a position at a certain distance from the rotation axis or a predetermined distance from the position in the radial direction. A machining groove is formed as the machining trace on a concentric circle or a spiral trajectory (continuous path) having a radius at the center and the distance. Therefore, when using the second workpiece to obtain the reference profile, the second workpiece surface (planar surface) is set to the same setting conditions and locus as described above (this locus is used for processing and polishing the convex lens). In this case, the beam is scanned with a circle centered on the rotation axis regardless of whether the beam is irradiated concentrically or spirally. Generate a reference profile from In this case, since the second workpiece has a planar shape, the swinging operation is not performed so that the beam is always irradiated perpendicularly to the surface of the second workpiece.

  In this example, in order to generate the reference profile, data is collected from the processing traces of the beam irradiated to the planar shape. However, the data is acquired from the processing traces of the beam irradiated to the spherical surface or aspherical surface instead of the planar shape. May be collected.

FIG. 6 is an overview image diagram of a processing mark formed by irradiating a beam onto the surface (surface of a planar shape) of the second workpiece that rotates on the axis under the above-described setting conditions.
In this example, three second workpieces 6-2 having a planar surface are prepared, and the beam scanning positions (radial positions from the center) are shifted from each other, and beams are formed at a plurality of positions. To scan. Each figure (a), (b), and (c) is irradiated with a continuous beam while the second workpiece is rotated once or more (two rotations, three rotations,...) Based on the above setting conditions. The outline image of the processing trace on each second workpiece formed in this way is shown separately.

  As is apparent from each figure, on each second workpiece surface 60-2, a plurality of circular grooves 61-2 centering on the rotation axis passing through the position r0 (in this example, 3). Specifically, in the first second workpiece shown in FIG. (A), circular grooves 61-2 are formed at radial positions = r0, r3, and r6, as shown in FIG. (B). A circular groove 61-2 is formed in the radial position = r1, r4, and r7 in the second second workpiece, and the radial position in the third second workpiece shown in FIG. = Circular grooves 61-2 are formed at r2, r5, and r8. Since the beam has a certain spread, the solid substance having a predetermined radius from the optical axis is removed. For this reason, the processing mark is constituted by a groove having a predetermined width with the trajectory scanned by the optical axis as the center line. Due to the influence of this width, the number of workpiece trace samples that can be collected with only one second workpiece is limited. Therefore, in this example, three second workpieces are used, and the machining traces at each radial position are used. Collect data.

Each processing mark is measured by the measuring device 5 and stored in the memory of the PC as a reference profile shown below.
FIG. 7 is a graph display of the profile of the machining trace.

  In the figure, for the radial direction of the second workpiece, the horizontal axis is the radial position (mm) on the surface, and the vertical axis is the solid material removal depth (μm). Data of all formed traces (in this example, cross-sectional shape data of a plane perpendicular to the rotation direction) 700 is shown in an overlapping manner. In order to clarify the correspondence relationship with the machining marks shown in FIG. 6, the same reference numerals indicating the radial positions as in FIG. 6 are attached to the graph.

  Since the gas cluster ion beam has a predetermined area spread at the irradiation position, when irradiated near the rotation axis, the irradiation range of the beam extends to the range of the symmetrical position including the axis, and the solid substance is formed during one rotation. It will be removed redundantly. For this reason, although it is clearly shown by displaying the graph in the same figure, the removal depth is deeper in the vicinity of the center (near the radial position r0 = 0) than in the other radial positions.

  In this example, the number of points of the reference profile is set to be small so that the graph can be read easily, and will be described below with a small number of points. However, the higher the number of points of this reference profile, the higher the accuracy of machining. This is desirable because it can be performed. Specifically, it is preferable to generate at intervals smaller than 1/5 of the diameter of the reference profile.

  In this case, since it takes time to generate all the reference profiles by processing, a reference profile positioned between the two reference profiles from two adjacent reference profiles obtained by actually processing. May be obtained by calculation.

Specifically, as shown in FIG. 8, two adjacent reference profiles having a distance x in the radial direction from the center of the rotation axis at positions i = j and x = i, x = j are expressed as a function P _{x. When i =} x ( _j ) and P _{x = j} (x), the reference profile P _{x = k} (x) at x = k where i <k <j is obtained from the following equation.

P _{x = k} (x) = {(j−k) · P _{x = i} (x + k−i) + (k−i) · P _{x = j} (x + k−j)} / (j−i)
The reference profile 700 obtained in this way is stored in the memory of the PC3.

  Then, as a process following step S2-1 in FIG. 4, the PC3 performs a correction process from the reference profile 700 to a profile according to the curvature of each position in the following procedure (S3-1), and further, step S1-1. Using the error data 510 obtained in the above, the irradiation dose calculation processing at each position is performed based on the correction profile (S4-1 to S4-3).

  In this procedure, first, for each profile (hereinafter referred to as a partial reference profile) of the reference profile 700 obtained in step S2-1, the correspondence between each position within the irradiation range and the removal depth at those positions is determined. Ask.

FIG. 9 is a diagram showing one of the profiles (partial reference profile M) extracted from the reference profile 700 of FIG.
In the figure, the partial reference profile M (having a width of 1 mm in this example) is placed outside the position where the solid material removal depth is the deepest (that is, the position corresponding to the optical axis of the beam) A. The relationship between the subdivided position and the removal depth at each position is shown.

  In this example, a line segment centered on position A (this line segment indicates the irradiation range) is equally divided as position F2 to position F1, and a straight line is vertically formed from each position (F2 to A1 to F1). The straight line segment (E2-E2 ′ to E1-E1 ′) divided by the partial profile curve 700-1 corresponding to the partial reference profile M is set as the removal amount at that position.

  In other words, the removal amount at each subdivided position is removal amount 0 at the F2 position, removal amount E2-E2 'at the E2 position, ... maximum removal amount AA' at the A position, ... removal at the E1 position. The removal amount 0 can be indicated at the positions E1-E1 ′ and F1.

  In this way, by performing the same procedure for the other partial reference profiles, it is possible to obtain correspondence data of each position within the irradiation range and the removal depth at those positions for each partial reference profile.

  Since the above is the partial reference profile when the surface shape is a planar shape, the partial reference profile when the surface shape to be actually processed and polished is a curved surface shape is obtained by calculation.

  FIG. 10 is a diagram for explaining a method of adapting the partial reference profile M when the surface shape is a planar shape to the convex lens of this example. In the figure, the partial reference profile M shown in FIG. 9 is indicated by a broken line.

  A solid line 900-1 in the figure represents the surface shape (that is, the convex shape) of the convex lens to be polished in this example as a function curve. The function curve 900-1 can be represented by a function of a circle, for example, so as to show one curvature within the range (F2 to A1 to F1) in FIG.

This function curve 900-1 is placed on the partial reference profile of FIG. 9 so as to be in contact with the reference line (removal depth value = 0) at point A which is the passing position of the optical axis.
When a beam is irradiated from the upper side of the figure, the beam is incident on each position on the function curve 900-1 representing the convex shape of the convex lens surface from the upper side to the lower side. Then, the incident beam removes the solid substance in the depth direction (downward in the figure) starting from the position on the superimposed function curve 900-1 instead of the horizontal line in the figure. It will be.

  Therefore, starting from the point (f2,..., A1, f1) on the function curve 900-1, each removal amount in the planar shape obtained in the explanation of FIG. Added in the negative direction (downward in the figure), and connected points (f2 ', ..., a', ... f1 ') at each position (F2-A-F1) A new curve is defined as a profile (correction profile) 910 corresponding to the surface shape of the convex lens. In this example, the removal amount is 0 at the f2 position, the removal amount E2-E2 ′ at the e2 position, the maximum removal amount AA ′ at the a position, the removal amount E1-E1 ′ at the e1 position, and the removal at the f1 position. Calculate as quantity 0.

The correction profile 910 thus obtained is substantially closer to the profile of the machining trace obtained in the convex shape than the partial reference profile obtained from the planar machining trace.
Each correction profile at each position on the surface of the convex lens is acquired by the method as described above, and the reference profile shown in FIG. 7 is corrected according to those correction profiles. In this case, since the width of the partial reference profile and the newly generated correction profile are the same, the correction profile 910 is translated so that f2 matches F2 (and f1 matches F1). The partial reference profile is replaced with a newly generated correction profile.

FIG. 11 is a profile corresponding to a convex shape obtained by performing the above processing.
As can be seen from the figure, each correction profile configured in this profile 1000 is indicated by a curve having a gentler curve than the partial reference profile, and the dose amount at each position is obtained based on this profile.

  Now, as described above, the convex lens to be processed and polished has an error as shown in FIG. In subsequent processing and polishing processes, the error amount of solid material must be removed.

  FIG. 12 is a diagram in which the error graph of FIG. 5 is inverted up and down around the horizontal axis of the figure. The area that needs to be removed in the figure is a hatched area surrounded by the horizontal axis and the curve 1100. Ideally, it is only necessary to remove the solid material that falls in the shaded area, but in this example, all the positions in the radial direction of the convex lens are included in the irradiation range of the beam, that is, the beam is not irradiated at all. There is no place, and the minimum amount of solid material is removed even at the two Bottom points in FIG. 12 (the amount of solid material removed is 0 at this position).

Therefore, an actual removal curve is generated based on the ideal removal curve 1100.
FIG. 13 is a distribution (actual removal curve) of the generated solid substance removal amount including the minimum necessary solid substance removal amount (minimum removal amount).

  This distribution is generated by sliding (offset) the entire curve 1100 shown in FIG. 12 downward by the minimum removal amount (offset amount) L. At this time, the region where the solid material needs to be removed is a hatched region surrounded by the horizontal axis and the removal curve 1200, and the solid material with the minimum removal amount L is the target of removal even at the two Bottom points.

  The minimum removal amount L can be a solid material removal amount (the depth) that is surely removed by the maximum rotation speed possible in the apparatus configuration and the maximum scanning speed of the beam scanned in the radial direction. .

Here, processing is performed to match the profile 1000 (FIG. 11) obtained above with the removal distribution (processing amount distribution) 1200 (FIG. 13).
In this process, the function curve is deformed by multiplying the entire function curve of each correction profile configured in the profile 1000 by an individual coefficient, and the function curve after deformation of each correction profile is changed at each position on the radius. The coefficient is determined so that the added curve matches or substantially matches the curve of the removal distribution 1200.

FIGS. 14 and 15 are diagrams for explaining the process of fitting.
FIG. 14 is a diagram for explaining the deformation process of the function curve of one correction profile configured in the profile 1000, and FIG. 15 is a comparison diagram of the function curve of each correction profile and the removal distribution curve 1200. .

The function curve 1300 of the correction profile shown in FIG. 14 shows the correction profile extracted at the radial position r = i (0 ≦ i ≦ 5) in the profile of FIG.
Now, when the function curve of the correction profile 1300 having the center at the radial position r = i is denoted by Fi (r), the profile G on the radius (in the range of 0 mm to 5 mm) obtained by superimposing the correction profiles. r) can be expressed as G (r) = ΣFi (r).

  Then, with the removal distribution curve 1200 as E (r), the value of E (i) −G (i) is verified. If this value is positive (that is, when the function curve of the correction profile is located above the removal distribution), Fi (r) is multiplied by a value of 1 + e (e is a positive value) to obtain a new Fi (r). And Conversely, if the value of E (i) -G (i) is negative (that is, if the function curve of the correction profile is located below the removal distribution), Fi (r) has 1 + e (e has its absolute value) Multiply by a negative value not exceeding 1 to obtain a new Fi (r). Here, e is a value determined according to the magnitude of the absolute value of E (i) -G (i), and takes a larger value in advance as the absolute value of E (i) -G (i) increases. Set as follows. The function curve 1301 in FIG. 14 is a new function curve obtained by multiplying 1 + e (e is a positive value) when the value of E (i) −G (i) for the function curve 1300 is positive. It is an example. In the example in the figure, e = 0.3, the removal depth indicated by the function curve 1300 is multiplied by 1.3 at each point, and a function curve 1301 having a removal depth 1.3 times deeper than the function curve 1300 is newly obtained. Yes.

  Thus, the determination of a new Fi (r) by multiplying by 1 + e starts from the machining start position (radial position = 0 in this example), and the direction in which the center position of the adjacent correction profile exists (radial direction in this example). ) Are shifted one by one, and when reaching the machining end position, the process returns to the machining start position and the determination process is performed in the same manner. Such a series of determination processes is repeated until the values of Σ (E (i) −G (i)) and (0 ≦ i ≦ 5) are equal to or less than a predetermined value. Note that this value is desirably set to a small value (for example, approximately 0). Thus, each coefficient (1 + e) i finally obtained is set as a coefficient to be given to each correction profile Fi (r).

Through the above processing, the shape of the curve obtained by adding the correction profiles in FIG. 15 approximates (fits) to the shape indicated by the removal distribution curve 120 in FIG.
By the way, it is known that a predetermined relationship can be shown between the irradiation condition of the beam and the removal amount of the solid substance by the beam. More specifically, the irradiation dose at the position irradiated with the beam and the sputtering depth at that position (the solid material removal depth at the center of the irradiation range) are the sputtering depth as the irradiation dose is increased. For example, a relationship as disclosed in Japanese Patent Application Laid-Open No. 2005-120393 can be obtained. In this example, it is assumed that the relationship between the irradiation dose and the sputtering depth is proportional to Japanese Patent Application Laid-Open No. 2005-120393. As a result, the reference irradiation dose (in this example, the irradiation dose at the irradiation position of the beam irradiated to the second workpiece for generating the reference profile) is multiplied by the calculated coefficient (1 + e) i. Thus, the irradiation dose necessary for removing the solid substance corresponding to the removal distribution curve 120 in FIG. 15 can be obtained for each radial position.

  When the irradiation dose is obtained as described above, following step S4-3 in FIG. 4, the surface of the workpiece is polished by irradiating the surface of the convex lens with the gas cluster ion beam according to the irradiation dose (S5). -1 to S5-4). Specifically, for example, the irradiation dose is set to the radius on the surface of the convex lens according to the irradiation dose at each position obtained in step S4-1. The movement mechanism 2 in FIG. 2 is controlled by the movement control device 4 by converting it into a scanning speed.

  The movement control information necessary for the control of the movement mechanism 2 is as follows, for example, when the surface of the convex lens is scanned in a spiral shape in the radial direction from the center of the rotation axis at the time of processing (or polishing). Can be sought.

First, the following relationship is established between the irradiation time of the gas cluster ion beam and the irradiation dose.
Irradiation time = (irradiation dose amount × irradiation area × elementary electric amount) / detection ion current amount (1)
The irradiation area is a processing mark area, the amount of electric element is a constant, and the detected ion current amount is a constant value determined by processing conditions. That is, if the irradiation dose is determined, the corresponding irradiation time can be uniquely determined by the equation (1). In the case of this example, since processing is performed in a spiral shape while rotating, the irradiation area is rotated by one or more integer rotations starting from each point of the correction profile (the radial position of the center of each correction profile) and then adjacent to the adjacent area. This is the area of the machining groove on the spiral trajectory that reaches the point (the radial position of the center of the adjacent correction profile). Therefore, during the irradiation time, the center of the beam moves from a point with a correction profile (radius position at the center of the correction profile) to an adjacent point (radius position at the center of the next correction profile) while the convex lens rotates the integer number of times. It will be time to complete.

Further, the following relational expression can be applied as an expression showing the relation between the irradiation time and the beam scanning speed in the radial direction.
Scanning speed = distance between centers of adjacent correction profiles / irradiation time (2)
FIG. 16 shows the relationship between machining marks at two points, that is, a point of a certain correction profile and a point of a correction profile adjacent in the radial direction.

  The figure shows a cross-sectional view of the above two points on a certain radial direction. From this figure, as the distance between the two points becomes shorter, not only the machining shape at the position of the two points but also the two points. It can be seen that the machining shape in between can be brought close to the desired shape.

  Therefore, when processing (or polishing) in a spiral shape as in this example, it is possible to more accurately perform processing corresponding to the obtained irradiation dose amount at each position by increasing the number of correction profiles. And can be processed seamlessly.

  Although the above points have already been described, it is preferable to generate them at intervals smaller than 1/5 of the diameter of the reference profile, and it is even better to generate them at intervals as small as possible. This is because by increasing the number of points, the locus of the beam becomes closer to a perfect circle, and machining in a concentric circle located at an equal distance in the radial direction from the central axis can be made uniform on the axis.

  By applying equation (2) under such a relationship, conversion to the scanning speed from each position to the next position, which is more accurately associated with the irradiation dose amount for each position of the above-mentioned points, is performed. Can do. In the case of this configuration example, the X-axis stage 21 for moving the irradiation position on the surface of the convex lens of the beam irradiated with the predetermined power in the predetermined direction from each radial position on the surface to the next radial position at each scanning speed. (And rotation stage 20) movement control information information set (in this example, the movement control information of rotation stage 20 is predetermined rotation speed information). This information set is given to a motor control parameter for driving the X-axis stage 21 (and the rotary stage 20) in a program at the time of processing and polishing.

  At the time of processing and polishing of the convex lens, the convex lens is mounted on the rotary stage 20 in FIG. 2 with the processing target surface facing the beam irradiation direction, and the program is executed by the movement control device, and the X-axis stage and the rotary stage. The processing and polishing of the convex lens surface is performed under appropriate control. In the case of this example, the convex lens rotates at an appropriate rotational speed at each position of the beam, and further moves in the X-axis direction at an appropriate speed (the scanning speed or a speed corresponding thereto), so that the center of the surface is obtained. The solid substance is continuously removed in the radial direction. In this process, a swinging operation is appropriately performed so that the beam is perpendicularly incident on the surface according to the beam irradiation position on the surface.

  By this series of irradiation control processes, the above error is removed, and the curvature of the removal position (including the position where the solid material with the minimum removal amount is removed although no error occurs) takes the curvature of the target surface shape, and is a convex lens. Can be a target surface shape.

In the above description, an example in which a certain gas type is used as the reference gas as the gas cluster ion beam has been described.
However, even when processing and polishing are performed using another gas species different from the reference gas, the above-described method can be applied as it is simply by correcting the reference profile.

FIG. 17 is a diagram showing the relationship between the irradiation doses of the reference gas and other gas species and the sputtering depth.
As described above, it has been described that the reference gas can apply a proportional relationship between the irradiation dose and the sputtering depth.

The same can be said for other gas types, and the gas type A and gas type B shown in the figure can also be shown in a proportional relationship.
Therefore, the reference profile obtained from the second workpiece is deformed according to the proportional coefficient shown in the figure, that is, the ratio of the proportional coefficient of the other gas when the proportional coefficient of the reference gas is set to 1 is the reference profile shown in FIG. Is multiplied at each position (in this case, the downward direction in FIG. 9 is positive) to obtain a new reference profile.

Then, the above-described procedures are similarly performed based on this new reference profile.
As described above, when the ultra-precision polishing method according to this example is used, in a convex lens having a curved surface shape, the surface is smoothed at the atomic size level, and the target surface shape is limited without breaking the surface shape of the entire convex lens. It becomes possible to get closer.

It is a flowchart of the superprecision grinding | polishing method of this invention. It is an apparatus block diagram for performing ultraprecision polishing treatment. It is the figure which showed the relationship between the position on the surface of a workpiece, and the incident angle of a beam. It is a flowchart of the superprecision grinding | polishing processing method in an Example. It is a graph display figure of error data. It is a general-view image figure of the processing trace formed in the 2nd workpiece surface. FIG. 7 is a graph showing the profile of the machining mark in FIG. 6. It is explanatory drawing of the process which calculates | requires the reference | standard profile between two reference | standard profiles. FIG. 6 is a diagram showing a partial reference profile M. It is explanatory drawing of the method of adapting the partial reference profile M to a convex lens shape. It is a profile corresponding to a convex shape. FIG. 6 is an upside down view of the error graph of FIG. 5. It is distribution of the amount of solid substance removal. It is explanatory drawing of the deformation | transformation process of a correction profile. It is a comparison figure of the function curve and removal distribution curve 1200 of each correction profile. It is a related figure of the process trace which adjoins. It is a related figure of irradiation dose amount of various gas, and sputtering depth.

Explanation of symbols

1 Gas cluster ion beam irradiation device 2 Movement mechanism 3 Computer (PC)
4 Movement control device 5 Measuring device

Claims (7)

An ultra-precise polishing method for irradiating a workpiece surface with a gas cluster ion beam to polish the workpiece surface,
A first measurement step for measuring an error of the surface shape of the workpiece from the target surface shape;
A second measurement step of measuring a processing mark formed on the surface of the second workpiece by irradiating the surface of the second workpiece with the gas cluster ion beam;
A first calculation step for generating machining trace data in accordance with the curvature of each surface position in the target surface shape of the workpiece based on the machining trace data obtained by measuring the second workpiece;
A second calculation step of obtaining an irradiation dose amount at each position on the workpiece surface for removing the solid material corresponding to the error by the gas cluster ion beam based on the generated machining trace data; ,
A polishing step of polishing the surface of the workpiece by irradiating the surface of the workpiece with the gas cluster ion beam according to the irradiation dose;
An ultraprecision polishing method comprising: An ultra-precise polishing method for irradiating a workpiece surface with a gas cluster ion beam to polish the workpiece surface,
Measure the surface shape of the workpiece,
An error from the preset target surface shape data of the surface shape data of the workpiece obtained by the measurement is calculated for each position on the surface of the workpiece,
Introducing a reference profile indicating the relationship between the irradiation range on the workpiece surface by the gas cluster ion beam and the solid material removal depth when the gas cluster ion beam is irradiated on the surface of the second workpiece,
For each position on the workpiece surface, generate a correction profile by correcting the reference profile so as to follow the curvature of the position in the target surface shape,
With the correction profile for each position as an object, the solid substance removal depth within each irradiation range is changed for each position, and the solid material removal of each correction profile at the position is performed at a position where a plurality of correction profiles overlap. Add depth,
Based on a predetermined relationship between the solid material removal depth and the irradiation dose amount, the irradiation dose amount at each position on the workpiece surface such that the error is reduced in the polishing target range of the workpiece surface. Decide
The irradiation dose at each position is converted into a scanning speed of the gas cluster ion beam,
Polishing the surface of the workpiece by irradiating the surface of the workpiece with the gas cluster ion beam at the scanning speed;
An ultra-precision polishing method characterized by that. Adding a predetermined offset to the error data for the entire range of the workpiece surface;
The surface of the workpiece is polished by scanning a gas cluster ion beam over the entire range of the workpiece surface.
The ultra-precision polishing method according to claim 1 or 2, wherein When the gas cluster ion beam irradiated to the workpiece and the gas cluster ion beam irradiated to the second workpiece are different,
Correcting the reference profile based on the relationship between the sputtering depth and irradiation dose by each gas cluster ion beam,
The ultra-precision polishing method according to claim 2. Irradiating means for irradiating a gas cluster ion beam at a predetermined power in a predetermined direction;
The posture of the workpiece is controlled so that the gas cluster ion beam is perpendicularly incident at an arbitrary position on the surface of the workpiece, and the position on the surface of the workpiece is set at a predetermined irradiation dose. Control means for controlling the scanning speed of the gas cluster ion beam at each position on the surface of the workpiece so that the gas cluster ion beam is irradiated;
An ultra-precision polishing apparatus characterized by comprising: The control means includes
Calculating means for correcting the first processing trace data to second processing trace data following the curvature of each position on the target surface shape of the workpiece and calculating the irradiation dose;
The posture of the workpiece is controlled so that the gas cluster ion beam is vertically incident at an arbitrary position, and each position on the surface of the workpiece is irradiated with the gas cluster ion beam at the irradiation dose. Movement control means for controlling the scanning speed of the gas cluster ion beam at each position on the surface of the workpiece;
The ultra-precision polishing apparatus according to claim 5, wherein The target surface shape of the workpiece is a curved surface,
The ultra-precision polishing apparatus according to claim 6.

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