JPWO2015060047A1 - Precision polishing apparatus and method - Google Patents

Abstract

It is an object of the present invention to provide a precision polishing apparatus capable of accurately and efficiently polishing a workpiece having a curved surface. An aperture comprising: an irradiation source SB that irradiates the gas cluster ion beam B2, a stage 41a that fixes the workpiece WA, and an aperture 42 that is directly fixed to the stage 41a and covers a part of the workpiece WA. 42 is arranged such that the edge 42g on the irradiation source SB side of the opening inner side surface 42e of the aperture 42 is separated from the surface 90s of the workpiece WA by a predetermined distance, and the gas cluster ion beam B2 is a gas cluster ion beam. Irradiation is performed so that the traveling direction of B2 is such that the inclination angle of the gas cluster ion beam B2 with respect to an axis perpendicular to the reference plane ST including the edge 42g of the aperture 42 is greater than 0 °.

Description

  The present invention relates to a precision polishing apparatus for precisely polishing a mold or an optical element and a precision polishing method using the precision polishing apparatus.

  As optical elements such as lenses, rotationally symmetric spherical lenses and aspherical lenses exist, and in order to mass-produce them, press molding using a molding die, injection molding or the like is an effective processing means. When the transfer surface of the molding die is rough, the surface roughness of the lens after molding also increases, and flare occurs in the optical device. In addition, when the shape accuracy of the lens molded by the molding die 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.

  There is a polishing method using a gas cluster ion beam (GCIB), which is a kind of charged particle beam, for improving the surface roughness and correcting the shape error of the optical element and its mold (see Patent Documents 1 and 2). In order to realize these techniques, it is necessary to make the beam hit only a desired range in the workpiece.

  In the polishing method disclosed in Patent Document 1, fine irregularities of the cutting trace are smoothed by irradiating GCIB during mold processing, and the surface roughness is improved. Here, in Patent Document 1, when the GCIB irradiation angle is 0 ° (vertical irradiation), the surface roughness is improved, while on the other hand, the irradiation angle is increased by tilting the beam (irradiation limit incident angle). It is disclosed that the surface roughness is worse than before irradiation when exceeding. In the polishing method of this patent document 1, since the entire area cannot be vertically irradiated with respect to a workpiece having a curvature such as an optical element or its mold, the surface roughness may be affected. This Patent Document 1 shows a method of polishing a convex mold. However, when a beam is irradiated perpendicularly to the top surface near the center of the mold, the irradiation angle becomes the irradiation limit incident angle in the periphery. Exceed. Therefore, irradiation is performed while changing the angle of the beam with respect to the workpiece so that the irradiation angle does not always exceed the irradiation limit incident angle according to the irradiation position. At this time, it is necessary to reduce the beam diameter by an internal aperture which is arranged on the irradiation source side and limits the irradiation range. For example, when irradiating near the center of the object to be processed at an angle close to the vertical, The beam is prevented from hitting the peripheral side, and when the peripheral side of the workpiece is irradiated at an angle close to vertical, the beam is prevented from hitting the vicinity of the center of the workpiece. In Patent Document 1, the internal aperture is a flat plate having an opening having the same shape as the desired irradiation range.

The polishing method of Patent Document 2 discloses that the GCIB irradiation dose (total amount of injected material) and the processing depth are linear. Since the irradiation dose is proportional to the irradiation time as in the following formula, a very small processing depth of nano-order can be controlled by the irradiation time.
Irradiation time = (irradiation dose x irradiation area x elementary charge) / (detection ion current)
In Patent Document 2, the shape of the workpiece is measured, the required removal amount at each position is calculated from the shape error, and the removal amount is converted into the irradiation time. Thereafter, irradiation is performed for the irradiation time calculated by GCIB through an internal aperture that is arranged on the irradiation source side and has an opening corresponding to only a desired processing position. By repeating such a process while replacing the internal aperture as necessary, the shape error is corrected and the shape of the workpiece can be created. In the polishing method of Patent Document 2, as in Patent Document 1, the internal aperture is a flat plate having an opening having the same shape as the desired irradiation range.

  In order to irradiate only a desired position on the workpiece, it is necessary to arrange both positions with high precision so that the desired irradiation position of the workpiece comes ahead of the beam traveling direction of the opening of the internal aperture. is there. However, since the GCIB cannot directly observe the beam, the Faraday cup detector is usually used to calculate the coordinates of the center of the beam at the stage, and the workpiece is processed from the relative position of the Faraday cup and the workpiece. It is necessary to calculate the coordinates of the desired irradiation position on the object. However, the Faraday cup has low sensitivity to beam center deviation, and the accuracy of calculating the beam center coordinates is poor. Since the measurement error of the relative position between the center of the Faraday cup and the workpiece is added to this calculation error, a deviation is likely to occur between the target irradiation position and the actual irradiation position. In particular, in the case of a workpiece having a small surface such as a microlens or a microlens array, there is a problem that the effect of this deviation becomes significant and a desired irradiation effect cannot be obtained.

  In the polishing methods of Patent Documents 1 and 2, the shape of the irradiation spot is determined by the shape of the opening of the internal aperture. When the workpiece is polished as in Patent Document 1, the workpiece can be efficiently polished by using a large irradiation spot or a small irradiation spot. However, when such a method is employed, irradiation must be performed while exchanging an internal aperture having a large opening and an internal aperture having a small opening. Moreover, when performing shape correction processing like patent document 2, since the place where machining depth is insufficient differs for every workpiece, an internal aperture must be replaced | exchanged according to replacement | exchange of a workpiece. At this time, since the internal aperture is in the apparatus, there is a problem that the exchange workability is poor.

JP 2009-108368 A JP 2006-241550 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a precision polishing apparatus that can accurately and efficiently polish a workpiece having a curved surface.

  Another object of the present invention is to provide a precision polishing method using the above-described precision polishing apparatus.

  In order to solve the above-described problems, a precision polishing apparatus according to the present invention includes an irradiation source that irradiates a charged particle beam, a stage that fixes a workpiece, and a workpiece that is directly or indirectly fixed to the stage. An aperture that covers a part of the aperture, and the aperture is arranged such that the edge of the inner surface of the opening of the aperture on the irradiation source side is spaced apart from the surface of the workpiece, and the charged particle beam Irradiation is performed such that the traveling angle of the charged particle beam with respect to an axis perpendicular to the reference plane defined by the edge of the aperture is greater than 0 °. Here, the reference plane is, for example, a plane that entirely includes the edge of the aperture.

  According to the precision polishing apparatus, since the aperture and the workpiece can be handled integrally, the positional relationship between the two can be accurately matched. Further, since they are relatively close to each other, the influence of the deviation from the desired desired position on the irradiation position is small. Further, even if the irradiation position or irradiation center of the beam at the aperture position is slightly deviated from the center of the aperture, the processing position is not affected. Further, by adjusting the tilt angle of the beam, an irradiation spot whose size can be adjusted without exchanging the aperture can be formed. Further, since the aperture is fixed to the stage directly or indirectly, the aperture is substantially fixed to the workpiece, and the aperture can be replaced simultaneously with the replacement of the workpiece. From the above, even a workpiece having a curved surface can be polished with high accuracy and efficiency.

  In order to solve the above problems, a precision polishing method according to the present invention includes a step of fixing a workpiece to the stage, and an aperture directly or indirectly fixed to the stage so as to cover a part of the workpiece. And the step of irradiating a charged particle beam using an irradiation source, and the aperture is arranged such that the edge on the irradiation source side of the inner surface of the opening of the aperture is spaced from the surface of the workpiece, The charged particle beam is irradiated so that the inclination angle of the charged particle beam with respect to an axis perpendicular to the reference plane defined by the edge of the aperture is greater than 0 °.

  According to the precision polishing method, the positional relationship between the aperture and the workpiece can be accurately matched. Further, by adjusting the tilt angle of the beam, an irradiation spot whose size can be adjusted without exchanging the aperture can be formed. Further, since the aperture is fixed to the stage directly or indirectly, the aperture is substantially fixed to the workpiece, and the aperture can be replaced simultaneously with the replacement of the workpiece. From the above, even a workpiece having a curved surface can be polished with high accuracy and efficiency.

1 is a conceptual cross-sectional view illustrating a precision polishing apparatus according to a first embodiment. FIG. 2A is a diagram illustrating an irradiation state when the tilt angle of the charged particle beam is relatively large, and FIG. 2B is a diagram illustrating an irradiation state when the tilt angle of the charged particle beam is relatively small. 3A and 3B are diagrams for explaining the relationship between the tilt angle of the charged particle beam and the surface angle of the workpiece of the workpiece. 4A and 4B are diagrams illustrating the dimensional relationship between the aperture and the workpiece. FIG. 5A is a diagram for explaining a state in which the aperture and the workpiece are fixed to the stage, and FIG. 5B is a diagram for explaining a state in which the stage of FIG. 5A is tilted. It is a partial expanded sectional view explaining an aperture etc. among precision polishing equipment concerning a 2nd embodiment. It is a partial expanded sectional view explaining an aperture etc. among precision polishing equipment concerning a 3rd embodiment. FIG. 8A is a partially enlarged cross-sectional view for explaining an aperture and the like in the precision polishing apparatus according to the fourth embodiment, and FIGS. 8B and 8C are modifications of the apparatus of FIG. 8A.

[First Embodiment]
The precision polishing apparatus of the first embodiment and the precision polishing method using the same will be described below with reference to the drawings.

  As shown in FIG. 1, the precision polishing apparatus 100 of the present embodiment includes an apparatus main body 10, a support device driving unit 70, and a control device 80.

  The apparatus main body 10 of the precision polishing apparatus 100 is an apparatus that performs polishing by using a vacuum technique, and includes a source chamber 11, an ion chamber 12, and a process chamber 13. Each chamber 11, 12, 13 is accompanied by exhaust devices 4a, 4b, 4c including a vacuum pump. Each chamber 11, 12, 13 is maintained at a vacuum degree suitable for each chamber.

The source chamber 11 is a part that injects gas into vacuum, and in addition to the exhaust device 4a, a gas source 21 is attached, and a nozzle 22 and a skimmer 23 are provided. The gas supplied from the gas source 21 is, for example, argon gas, oxygen gas, nitrogen gas, SF ₆ gas, helium gas, carbon dioxide gas of a compound, etc., and two or more kinds of gases can be mixed. . The nozzle 22 is supplied with a high pressure gas of about 0.1 to 1.0 MPa from the gas source 21 and injects the high pressure gas into a vacuum at supersonic speed. As a result, the high-pressure gas is adiabatically expanded and gas clusters are generated. The skimmer 23 that partitions the source chamber 11 and the ion chamber 12 has an opening, and selectively passes through a gas cluster on the center side of the high-pressure gas ejected from the nozzle 22 to form a beam. That is, the gas cluster beam B <b> 1 is emitted from the source chamber 11.

  The ion chamber 12 is a part that turns the gas cluster beam B1 into a gas cluster ion beam B2 for polishing. The ion chamber 12 includes an ionization unit 31, an acceleration unit 32, a lens unit 33, and an internal aperture 34. The ionization part 31 has a filament, and makes the gas cluster beam B1 a charged particle beam by causing the thermoelectrons from the filament to collide with the gas cluster beam B1. The acceleration unit 32 accelerates the charged particle beam obtained from the gas cluster beam B1 to a desired energy. The lens unit 33 uses the charged particle beam that has passed through the acceleration unit 32 as a beam that travels substantially parallel along the irradiation axis AX. As a result, a gas cluster ion beam B2 that is collimated and has a relatively large diameter is emitted from the internal aperture 34 of the ion chamber 12. The internal aperture 34 also has a shutter function, and can turn on / off the gas cluster ion beam B2 at a desired timing. Particles constituting the gas cluster ion beam B2 are broken by collision with the workpiece WA by irradiating the workpiece WA, which will be described later, and at that time, the cluster constituent atoms or molecules and the workpiece constituent atoms or molecules And the movement in the horizontal direction becomes significant with respect to the surface of the workpiece WA. Thereby, the protrusions on the surface of the workpiece WA are mainly shaved, and flat ultra-precision polishing at the atomic size becomes possible.

  The gas source 21, the nozzle 22, the skimmer 23, the ionization unit 31, the acceleration unit 32, the lens unit 33, and the internal aperture 34 described above serve as the irradiation source SB of the gas cluster ion beam B2 that is a charged particle beam. By using the gas cluster ion beam B2, ultraprecision polishing and nano-order shape creation are possible.

  The process chamber 13 is a portion for causing a cluster ion to collide with the workpiece WA and performing a precision polishing process on the order of submicron or nanometer, and includes a support device 41 and an aperture 42. The support device 41 has a stage 41a, supports the workpiece WA on the stage 41a, and adjusts the posture of the workpiece WA with respect to the gas cluster ion beam B2 to a desired state. The aperture 42 is fixed to the stage 41a of the support device 41 together with the workpiece WA, and partially shields the gas cluster ion beam B2 that irradiates the workpiece WA. That is, the aperture 42 functions as a mask. Only the gas cluster ion beam B2 that has passed through the opening 42a of the aperture 42 is incident on the workpiece WA. The stage 41a is rotatable at a desired rotation speed around the rotation axis RX inclined by the support device 41. Note that the support device 41 can freely adjust the direction of the rotation axis RX of the stage 41a. For example, the rotation axis RX can be inclined at a desired angle within a plane including the irradiation axis AX. It is also possible to move 41a in the process chamber 13 three-dimensionally. That is, the support device 41 can freely control the three-dimensional position and posture of the workpiece WA via the stage 41a, and the aperture 42 fixed relative to the workpiece WA also includes the workpiece 42. Displaces with WA.

  The support device driving unit 70 drives the support device 41 in the process chamber 13 to adjust the position and posture of the stage 41a, and moves the workpiece WA and the aperture 42 around the rotation axis RX together with the stage 41a. Rotate.

  The control device 80 comprehensively controls the operation of the device body 10. That is, the control device 80 controls the irradiation state of the workpiece WA and the aperture 42 by the gas cluster ion beam B2 by appropriately operating the support device driving unit 70. In addition, the control device 80 directly or indirectly monitors and controls operation states of the gas source 21, the ionization unit 31, the acceleration unit 32, the lens unit 33, the exhaust devices 4a, 4b, and 4c.

  Hereinafter, the shape and arrangement relationship of the apertures 42 on the stage 41a will be described in detail with reference to FIG. 2A and the like.

  As shown in FIG. 2A, the aperture 42 has a cylindrical portion 42c that covers the surface 90s of the workpiece WA. A cylindrical and thick opening 42a is formed in the cylindrical portion 42c. The upper end of the cylindrical portion 42c of the aperture 42 is a flat ring-shaped end surface 42d, and the periphery of the opening 42a is a cylindrical opening inner side surface 42e. At the boundary between the end face 42d and the opening inner side face 42e, a circular edged edge 42g is formed. Although details will be described later, in the aperture 42, the edge 42g on the irradiation source SB side of the opening inner side surface 42e is separated from the surface of the workpiece WA (specifically, the surface portion 91b) by a predetermined distance. Has been placed. A plane defined by the edge 42g and the end face 42d (specifically, a plane including the upper edge 42g and extending along the end face 42d) is a reference plane ST extending perpendicular to the rotation axis RX of the stage 41a. That is, the edge 42g and the end surface 42d are also arranged to be perpendicular to the rotation axis RX of the stage 41a. Here, the central axis CX of the edge 42g or the opening inner side surface 42e can be made to coincide with the rotation axis RX of the stage 41a by pre-adjustment. Of the workpiece WA, the surface (specifically, the surface portion 91b) on the inner surface 42e side of the opening and the aperture 42 are entirely in contact with each other. Thereby, the unintended intrusion of the gas cluster ion beam B2 or the charged particle beam is prevented by the lower edge 42h of the opening inner side surface 42e, and as a result, the outer diameter of the irradiation range of the beam becomes constant.

  The workpiece WA fixed on the stage 41a is, for example, a mold member for lens molding, and has a transfer portion 90a on the center side and a non-transfer portion 90b on the peripheral side. The surface portion 91a of the transfer portion 90a has an optical transfer surface OS. In the present embodiment, the surface portion 91a is a workpiece and has a curved surface. Specifically, the surface portion 91a is an axisymmetric aspherical surface having a circular outline in plan view, and has a concave shape in which the surface angle increases toward the periphery (for example, a maximum of 50 °). The surface portion 91b of the non-transfer portion 90b has a flat surface corresponding to a parting surface at the time of mold matching. Here, the optical axis OX (symmetry axis) of the surface portion 91a or the optical transfer surface OS is matched with the rotation axis RX of the stage 41a by a pre-adjustment. That is, the optical axis OX of the workpiece WA coincides with the rotation axis RX of the stage 41a and the center axis CX of the aperture 42. Therefore, when the stage 41a is driven to rotate, the workpiece WA rotates around the optical axis OX, and the edge 42g of the aperture 42 or the opening inner side surface 42e also rotates around the optical axis OX. At this time, the gas cluster ion beam B2 irradiates the surface portion 91a so that the traveling direction of the beam is inclined with respect to the reference plane ST including the edge 42g of the aperture 42. Thereby, an upper shade of the cylindrical portion 42c is formed on the surface 90s of the workpiece WA. As a result, out of the surface 90s of the workpiece WA, the outer region A1 corresponding to the outer edge portion of the surface portion 91a or the optical transfer surface OS and the peripheral region included in the outer surface portion 91b is a gas cluster ion beam B2. The inner region A0 is not irradiated with the gas cluster ion beam B2. As a result, only the outer region A1 can be selectively irradiated with the gas cluster ion beam B2, and only the outer region A1 can be selectively precisely polished in the order of submicron or nanometer.

  FIG. 2B shows an example in which the tilt angle θ of the gas cluster ion beam B2 is decreased by adjusting the tilt angle of the stage 41a. As described above, when the tilt angle θ of the irradiation axis AX of the gas cluster ion beam B2 is decreased, the area of the object to be precisely polished in the workpiece WA is increased, and the precision polishing process is performed on the wider eccentric area A2. can do. In this case, the gas cluster ion beam B2 is continuously irradiated in the inner area A21 of the workpiece WA, and the gas cluster ion beam B2 is intermittently irradiated in the outer area A22 of the workpiece WA. . That is, the precision polishing by the gas cluster ion beam B2 is performed mainly on the inner area A21 of the workpiece WA, but is performed on the entire optical transfer surface OS.

  As described above, the outer region A1 (see FIG. 2A) of the optical transfer surface OS of the workpiece WA can be selectively polished only by adjusting the inclination angle θ of the gas cluster ion beam B2 by the stage 41a. And the lateral width of the outer region A1 can be adjusted.

  Further, by adjusting the inclination angle θ of the gas cluster ion beam B2 by the stage 41a, it is possible to polish the outer region A22 while deeply polishing the inner region A21 in the optical transfer surface OS of the workpiece WA (see FIG. 2B), and the inner region A21 diameter and outer region A22 width can be adjusted.

  Note that the outer region A22 shown in FIG. 2B may or may not coincide with the outer region A1 shown in FIG. 2A. Further, the inclination angle θ of the gas cluster ion beam B2 can be changed during the irradiation of the gas cluster ion beam B2. Alternatively, when the gas cluster ion beam B2 is irradiated in a plurality of stages, the inclination angle θ of the gas cluster ion beam B2 can be switched at each stage.

Hereinafter, the dimensional relationship between the aperture 42 and the workpiece WA will be described.
As shown in FIGS. 3A and 3B, between a focused position K of the surface portion 91a (object to be processed) corresponding to the optical transfer surface OS of the workpiece WA and the optical axis OX that is the center of the surface portion 91a. The distance is r, the inclination angle formed by the traveling direction of the gas cluster ion beam B2 and the axis perpendicular to the reference plane ST (for example, the optical axis OX) is θ, and the distance of the surface portion 91a from the optical axis OX is When the surface angle at r is β, the incident angle i of the beam BC at the position K of the gas cluster ion beam B2 or the beam BC becomes an absolute value | β (r) −θ | . When the gas cluster ion beam B2 is irradiated frontward along the optical axis OX, that is, when the gas cluster ion beam B2 is incident perpendicularly to the reference plane ST, the incident angle i = surface angle β.
With reference to front irradiation along the optical axis OX of the beam BC, for example, as shown in FIG. 3A, the surface angle β around the surface portion 91a, that is, the incident angle i at the position of the maximum surface angle βmax deteriorates the surface roughness. When it becomes larger than the incident angle (irradiation limit incident angle α) to start, for example, as shown in FIG. 3B, the beam BC is inclined so that the tilt angle θ of the tilted beam BC is larger than βmax−α. When BC is irradiated, it is possible to prevent deterioration of the polishing roughness around the surface portion 91a. At this time, in the region near the optical axis OX in the surface portion 91a, since the surface angle β is small (βmin), the incident angle i ′ near the center exceeds the irradiation limit incident angle α. May get worse. For example, when α = 30 °, βmax = 60 °, βmin = 0 °, and θ = 50 °, the incident angle i to the peripheral transfer surface portion is | 60−50 | = 10 °. That is, since the tilt angle θ of the beam BC is smaller than the irradiation limit incident angle α, the surface roughness does not deteriorate. However, the inclination angle θ of the beam BC in the vicinity of the optical axis OX is | 0−50 | = 50 °, and the incident angle i ′ near the center exceeds the irradiation limit incident angle α. . If the beam BC that deteriorates the surface roughness is designed to be shielded by the aperture 42, it is possible to prevent the surface roughness from being deteriorated.

With reference to FIGS. 4A and 4B, the shape of the aperture 42 and the angle of the beam BC will be considered. The radius of the opening inner side surface 42e of the aperture 42 is R, and the distance between the position K of the surface portion 91a and the upper end surface (specifically, the surface portion 91b) of the workpiece WA is s (r). Here, a workpiece that crosses a line or a surface in which a light beam hitting a position K at a distance r from the optical axis OX of the surface portion 91a passes through the edge 42g of the opening 42a of the aperture 42 in a direction perpendicular to the reference surface ST. The height Z from the surface portion 91b of the WA is expressed by the following equation: Z = (R + r) / tan θ−s (r)
Can be expressed as Note that s (r) is a function of the distance r between the position K of the surface portion 91a of the workpiece WA and the center of the surface portion 91a. Further, the inclination angle θ of the gas cluster ion beam B2 with respect to the axis perpendicular to the reference plane ST is larger than 0 °.

When θ is determined such that the irradiation limit incident angle α is | βmax−θ | <α with respect to the maximum surface angle βmax around the known surface portion 91a, the surface is changed while r is changed from the periphery toward the center. When the angle β and the like are calculated, the absolute value | β (r) −θ | = α of the difference is obtained at a certain predetermined position (that is, the critical position K0). That is, the absolute value of the difference between the maximum surface angle of the surface portion 91a of the workpiece WA and the inclination angle θ of the gas cluster ion beam B2 is equal to the incident angle (irradiation limit incident angle α) at which the surface roughness starts to deteriorate. Become. When the distance from the center (optical axis OX) at this time is r0, the radius R and height H of the aperture 42 are expressed by the following equation (R + r0) / tan θ−s (r0) <H
If it is designed to satisfy the above condition, a light beam having an incident angle exceeding the irradiation limit incident angle α (light beam having an incident angle i ′ shown in FIG. 3B) may be shielded by the aperture 42 and hit the central region within the radius r0 of the workpiece WA. And the surface roughness does not deteriorate.

  In the present embodiment, the gas cluster ion beam B2 is irradiated with two or more different inclination angles θ with respect to the reference plane ST. Specifically, when the angle formed by the line segment L1 connecting the optical axis OX of the surface portion 91a of the workpiece WA and the edge 42g at the upper end of the opening inner side surface 42e and the optical axis OX of the surface portion 91a is γ. In addition, the charged particle beam is irradiated to the opening inner side surface 42e at a relatively small inclination angle satisfying θ <γ and a relatively large inclination angle satisfying θ> γ. When the beam is irradiated at an inclination angle of θ <γ, the beam always hits the vicinity of the center of the object to be processed, whereas the periphery repeats irradiation and shielding by the aperture during rotation. The dose is reduced. On the other hand, when the beam is irradiated at an inclination angle of θ> γ, even if the peripheral surface roughness is deteriorated by the previous irradiation, the periphery is precisely polished by this irradiation. At this time, since the beam does not hit the vicinity of the center, the vicinity of the center remains precisely polished by the previous irradiation. As described above, the entire surface portion 91a to be processed is precisely polished. Further, in this irradiation, since the beam hits only the periphery, the peripheral dose is increased as compared with the vicinity of the center.

  The gas cluster ion beam B2 can adjust the irradiation dose according to the shape error based on the shape of the workpiece WA measured in advance. If the dose amount of each irradiation is adjusted so that the total dose amount of irradiation is uniform over the entire region, the shape of the workpiece WA can be prevented from changing before and after the irradiation. Specifically, for example, when the outer region A22 shown in FIG. 2B and the outer region A1 shown in FIG. 2A are substantially coincident or slightly overlapped, if the dose is balanced so as to substantially coincide between the inner side and the outer side, The entire area of the surface portion 91a to be processed is precisely polished over the entire surface without greatly changing the shape. When the processing depth near the optical axis OX of the surface portion 91a of the workpiece WA is insufficient, by increasing the dose amount of θ <γ instead of a constant dose amount, the dose amount near the center can be increased compared to the periphery. It becomes more and can selectively deepen the vicinity of the center. In addition, when the processing depth around the surface portion 91a is insufficient, increasing the dose amount of θ> γ instead of a constant dose amount increases the peripheral dose amount near the center, and selects the periphery. Can be deep.

Hereinafter, a precision machining method for the workpiece WA will be described.
First, the gas cluster ion beam B2 irradiates substantially the entire aperture 42 that covers the workpiece WA fixed on the stage 41a. Since the gas cluster ion beam B2 cannot directly observe the beam, for example, the Faraday cup (not shown) is used to calculate the coordinates of the center of the beam (irradiation center) on the stage 41a. Therefore, the irradiation axis AX of the gas cluster ion beam B2 is aligned so as to pass through the opening 42a of the aperture 42.

  Next, a portion where the processing depth is insufficient is calculated by measuring the shape of the surface portion 91a (particularly the optical transfer surface OS) of the workpiece WA. A necessary processing amount is converted into a dose amount based on the relationship between the dose amount and the processing amount prepared in advance. The combination of the tilt angle θ and the irradiation time of the tilt angle θ is calculated so that the dose amount in the portion where the processing depth is insufficient is relatively larger than the other portions by the required processing amount. At this time, the first irradiation condition and the second irradiation condition are set from the smaller inclination angle θ. That is, it is assumed that among the optical transfer surface OS of the workpiece WA, the center side around the optical axis OX is polished first, and the peripheral side of the optical transfer surface OS is polished later. Thereby, it can prevent that the inclination angle and incident angle of gas cluster ion beam B2 become large, and the roughness of grinding | polishing generate | occur | produces.

  Next, as shown in FIG. 5A, the workpiece WA and the aperture 42 are fixed to the stage 41a. The workpiece WA and the aperture 42 are fixed to each other using a jig 46 attached to the stage 41a. The aperture 42 has a main body portion 48a that contributes to shielding, and a base portion 48b that supports the main body portion 48a. The base portion 48b is fixed to the jig 46 by using a fastener 46s, so that the workpiece WA is formed. It is supported so as to be sandwiched between the main body portion 48 a of the aperture 42 and the jig 46. At this time, the side surface 91 s of the workpiece WA and the inner surface 48 s of the base portion 48 b of the aperture 42 are pressed by pushing the workpiece WA from the side by one or more biasing members 48 e provided on the base portion 48 b of the aperture 42. Are brought into close contact with each other to achieve alignment in the lateral direction (direction perpendicular to the rotation axis RX) of the workpiece WA with respect to the aperture 42. The jig 46 to which the workpiece WA or the like is fixed is fixed to the rotation drive unit 47 of the stage 41a. When the jig 46 is fixed to the rotation drive unit 47 of the stage 41a, the optical axis OX of the surface portion 91a of the workpiece WA coincides with the central axis CX of the opening inner side surface 42e of the aperture 42. Thereby, the workpiece WA and the aperture 42 can be handled integrally.

  Next, as shown in FIG. 5B, the support device 41 is driven by the support device drive unit 70 (see FIG. 1) to adjust the inclination angle θ of the rotation drive unit 47 that supports the workpiece WA and the aperture 42. At the same time, the workpiece WA moves so as to be in a predetermined position. At this time, the support device 41 rotates the rotation drive unit 47 around the tilt axis TX passing through the center of the opening 42 a of the aperture 42. Thereby, the position of the opening 42a of the aperture 42 can be kept substantially constant regardless of the inclination angle θ of the workpiece WA or the aperture 42. As described above, the stage 41a can be tilted so that the tilt angle θ of the gas cluster ion beam B2 becomes a desired angle.

  Next, as shown in FIG. 2B, the first irradiation is performed on the workpiece WA. Specifically, the gas cluster is rotated while rotating the workpiece WA around the rotation axis RX through the stage 41a under the above-described first irradiation condition (relatively small tilt angle, specifically, θ <γ). Ion beam B2 is irradiated. In the first irradiation, the inclination angle θ near the center of the surface portion 91a of the workpiece WA is set so as to realize an incident angle that does not exceed the irradiation limit incident angle α (for example, 30 °). The neighborhood is super-precision polished. On the other hand, since the inclination angle exceeds the irradiation limit incident angle α around the surface portion 91a, the surface roughness can be deteriorated. Further, since the dose amount near the center is larger than the periphery, the machining amount near the center is increased by the increased amount.

  Next, as shown in FIG. 2A, a second irradiation is performed on the workpiece WA. Specifically, the gas cluster is rotated while rotating the workpiece WA around the rotation axis RX via the stage 41a under the above-mentioned second irradiation condition (relatively large tilt angle, specifically θ> γ). Ion beam B2 is irradiated. Here, in the first irradiation and the second irradiation, since the range of the irradiation spot can be changed only by adjusting the inclination angle θ of the aperture 42, it is not necessary to replace the aperture 42. In the second irradiation, since the inclination angle θ around the surface portion 91a of the workpiece WA is set so as to realize an incident angle that does not exceed the irradiation limit incident angle α, the periphery is processed with ultra-precision. On the other hand, when this inclination angle θ is assumed, the incident angle can exceed the irradiation limit incident angle α in the vicinity of the center of the surface portion 91a. However, since it is designed so that all the ray paths whose inclination angle θ exceeds the irradiation limit incident angle α are shielded by the aperture 42, the beam does not hit the center in the second irradiation. Therefore, in the vicinity of the center, the state of ultra-precision polishing by the first irradiation is maintained. In other words, since the beam hits only the periphery of the surface portion 91a, the periphery is selectively processed by the dose amount. As described above, the ultraprecision polishing is completed in the entire surface portion 91a of the workpiece WA. Since each dose amount is calculated so that the total processing amount in the first and second irradiations corrects the shape error measured above, the shape error existing before the irradiation can be corrected.

  According to the precision polishing apparatus described above, the aperture 42 and the workpiece WA can be handled integrally, so that the positional relationship between the two can be accurately adjusted. Moreover, since both are in a relatively close position, the influence from the deviation from the desired position on the irradiation position is small. Further, even if the irradiation position or irradiation center of the beam at the position of the aperture 42 is slightly deviated from the center of the opening 42a, the processing position is not affected. Further, by adjusting the beam inclination angle θ, it is possible to form an irradiation spot whose size can be increased or decreased without replacing the aperture 42. For example, when the tilt angle θ of the beam is reduced, a wide range can be irradiated at once, and when the tilt angle θ is increased, only a narrow range can be irradiated. Thus, since a large spot and a small spot can be used properly, the beam can be irradiated efficiently. Further, since the aperture 42 is fixed to the stage 41a, the aperture 42 is substantially fixed to the workpiece WA, and the aperture 42 can be replaced simultaneously with the replacement of the workpiece WA. From the above, it is possible to polish the workpiece WA having a curved surface with high accuracy and efficiency. In particular, in the above example, the inclination angle θ of the gas cluster ion beam B2 can be appropriately adjusted according to the curved surface of the surface portion 91a of the workpiece WA.

  In the prior art, since the aperture for adjusting the diameter of the irradiation spot is provided in the apparatus, the aperture and the workpiece WA cannot be handled integrally or measured. In addition, since the distance between the aperture and the workpiece WA is large, if the two are slightly deviated from the desired position, the irradiation position is greatly affected. Further, since the irradiation spot is determined by the shape of the aperture opening, the size of the spot cannot be changed without exchanging the aperture. In addition, when the aperture is exchanged according to the shape of the workpiece WA, the workability of the exchange is deteriorated because the aperture is in the apparatus.

[Second Embodiment]
Hereinafter, a precision polishing apparatus and the like according to the second embodiment will be described. The precision polishing apparatus and the like of the second embodiment is a modification of the precision polishing apparatus and the like of the first embodiment, and matters that are not particularly described are the same as those of the first embodiment.

  As shown in FIG. 6, a gap 42k is provided between the aperture 42 and at least a part of the surface 90s of the workpiece WA on the opening inner side surface 42e side. Since the lower side of the opening 42a, that is, the gap 42k does not shield the gas cluster ion beam B2, the outer side of the surface portion 91b of the workpiece WA that is farther from the surface portion 91a as the inclination angle θ of the gas cluster ion beam B2 increases. Polishing is performed up to the region. That is, the outer diameter of the irradiation range of the gas cluster ion beam B2 depends on the inclination angle θ of the gas cluster ion beam B2. The inclination angle θ of the gas cluster ion beam B2 on the outer surface portion 91b of the workpiece WA is larger than the irradiation limit incident angle α. However, the surface portion 91b does not directly affect the transfer of the optical surface of the molded product, and the surface accuracy as high as the surface portion 91a is not required.

  According to the polishing apparatus or the like of the present embodiment, the workpiece 42, the aperture 42, or the like is set in the precision polishing apparatus 100 by providing the gap 42k between the workpiece WA and the aperture 42. Even if foreign matter such as dust adheres to the surface of the WA, it is possible to prevent the foreign matter from entering the gap 42k and collecting the foreign matter on the surface portion 91a that is the workpiece of the workpiece WA.

[Third Embodiment]
Hereinafter, a precision polishing apparatus and the like according to the third embodiment will be described. Note that the precision polishing apparatus and the like of the third embodiment are modifications of the precision polishing apparatus and the like of the first embodiment, and items that are not particularly described are the same as those of the first embodiment.

  As shown in FIG. 7, the aperture 42 is directly fixed to the workpiece WA. The workpiece WA and the aperture 42 are aligned by abutting the side surface 91p of the workpiece WA and the side surface 42p of the aperture 42 against the flat surface 81p of the block 81. The block 81 is fixed to the stage 41a. That is, the aperture 42 is indirectly fixed to the stage 41a.

  According to the polishing apparatus or the like of the present embodiment, the aperture 42 can be fixed to the workpiece WA in a state where the workpiece WA and the aperture 42 are aligned. Thereby, both positional relationship can be match | combined accurately.

  In the present embodiment, the aperture 42 may have a gap 42k between the workpiece WA and the aperture 42 as in the second embodiment.

[Fourth Embodiment]
Hereinafter, a precision polishing apparatus and the like according to the fourth embodiment will be described. Note that the precision polishing apparatus and the like of the fourth embodiment are modifications of the precision polishing apparatus and the like of the first embodiment, and items not specifically described are the same as those of the first embodiment.

  As shown in FIG. 8A, the edge 42g of the opening inner surface 42e on the irradiation source SB side of the aperture 42 protrudes radially inward. The opening inner side surface 42e other than the edge 42g is recessed outward in the radial direction. The aperture 42 is formed, for example, by providing a thin plate member 42m having a hole corresponding to the edge 42g on the upper end surface of the cylindrical portion 42c. If a plurality of plate members 42m having holes of different sizes are prepared, the irradiation range of the gas cluster ion beam B2 can be adjusted together with the condition of the inclination angle θ by simply replacing the plate members 42m. . Also in the present embodiment, as in the second embodiment, as the inclination angle θ of the gas cluster ion beam B2 increases, polishing is performed to an outer region farther from the surface portion 91a in the surface portion 91b of the workpiece WA. . The edge 42g of the aperture 42 may be projected by inclining the opening inner side surface 42e in a reverse taper shape without using the plate-like member 42m.

  In the present embodiment, as shown in FIG. 8B, an annular hole may be formed in the plate-like member 42 m of the aperture 42. In the aperture 42, the outer edge 42g and the inner edge 42n are connected via a plurality of thin members although not shown. In this case, even the portion of the surface portion 91b of the workpiece WA that is away from the surface portion 91a can be subjected to ultraprecision polishing.

  Further, in the present embodiment, as shown in FIG. 8C, the center of the edge 42 g of the aperture 42 may be shifted from the center of the aperture 42. In this case, an irradiation spot having a relatively small diameter can be formed, and the entire surface portion 91a can be subjected to ultraprecision polishing.

  Although the precision polishing apparatus and the like according to the present embodiment have been described above, the precision polishing apparatus and the like according to the present invention are not limited to the above. For example, in the above-described embodiment, the shape and size of the transfer portion 90a of the workpiece WA can be appropriately changed according to the application and function. For example, the transfer unit 90a is not limited to a concave shape, and may have a convex shape. In addition, the shape of the opening 42a of the aperture 42 can be appropriately changed according to the shape of the transfer portion 90a. Note that the openings 42a of the aperture 42 do not have to be all arranged on the reference plane ST, a part of the edge 42g is arranged on the reference plane ST, and the rest are at different positions with respect to the direction of the rotation axis RX. It may be arranged.

  In the above embodiment, the workpiece WA is not limited to a molding die, and may be an optical element such as a lens.

  In the above embodiment, the charged particle beam is not limited to the gas cluster ion beam, but may be an ion beam (IB) or a focused ion beam (FIB).

  In the above embodiment, the stage 41a is rotated, but it is not necessary to rotate it. For example, when the transfer portion 90a of the workpiece WA has an elongated transfer surface extending along a line segment, the tilt angle θ need only be changed without rotating the stage 41a. Alternatively, the charged particle beam may be rotated without rotating the workpiece WA, for example, by providing a drive mechanism on the beam side.

  In the above embodiment, the inclination angle θ of the gas cluster ion beam B2 is not limited to being changed in two steps, and may be changed in three or more steps. For example, when correcting the shape error of the workpiece WA, the inclination angle θ of the gas cluster ion beam B2 may be one step.

In the above embodiment, when the workpiece WA has a plurality of surface portions 91a (objects to be processed), a plurality of openings 42a corresponding to the respective surface portions 91a may be provided in the aperture 42.
In the above description, the workpiece WA is, for example, a transfer mold for a lens. However, the lens here includes a lens array obtained by integrally molding a plurality of lenses. When such a mold part for molding a lens array is precisely polished, an aperture 42 provided with a plurality of openings 42a corresponding to the transfer part of each lens element constituting the lens array is formed on the workpiece WA. Can be fixed.

  In the above embodiment, the apparatus main body 10 may not include the lens unit 33, the internal aperture 34, and the like.

  In the first embodiment, the edge 42g of the aperture 42 and the outer edge of the surface portion 91a of the workpiece WA are circular and concentric, but the edge 42g and the outer edge of the surface portion 91a are circular. Not limited to various shapes. Also in this case, the region where the surface portion 91a can be properly polished can be defined by the shape of the edge 42g.

Claims (16)

An irradiation source for irradiating a charged particle beam;
A stage for fixing the workpiece;
An aperture fixed directly or indirectly to the stage and covering a part of the workpiece;
With
The aperture is arranged such that an edge of the aperture inner surface of the aperture on the irradiation source side is spaced from the surface of the workpiece.
The charged particle beam is irradiated so that a traveling direction of the charged particle beam is greater than 0 ° with respect to an axis perpendicular to a reference plane defined by the edge of the aperture. A precision polishing device that is characterized.   The precision polishing apparatus according to claim 1, wherein the charged particle beam is a gas cluster ion beam.   The precision polishing apparatus according to claim 1, wherein the workpiece has a curved surface.   4. The gap according to claim 1, wherein a gap is provided between at least a part of the surface of the workpiece on the inner side surface side of the opening and the aperture. 5. Precision polishing equipment.   The precision polishing apparatus according to any one of claims 1 to 3, wherein the surface of the workpiece on the inner side surface side of the opening and the aperture are in contact with each other. An inclination angle, which is an angle formed between the traveling direction of the charged particle beam and an axis perpendicular to the reference plane, is θ, and the absolute value of the difference between the maximum surface angle of the workpiece and the inclination angle θ of the workpiece is The distance between the predetermined position where the surface roughness starts to deteriorate and the center of the workpiece is r0, and the distance between the predetermined position of the workpiece and the surface of the workpiece is r0. S (r0), where R is the radius of the inner surface of the opening of the aperture, and H is the height of the aperture, the following conditional expression (R + r0) / tan θ−s (r0) <H
Satisfied,
6. The charged particle beam is irradiated in a state in which the workpiece is rotated relative to the charged particle beam with a central axis of the workpiece as a rotation axis. The precision polishing apparatus as described in any one of Claims.   The precision polishing apparatus according to claim 6, wherein the charged particle beam is irradiated at two or more different inclination angles with respect to the reference plane.   The precision polishing apparatus according to claim 7, wherein the charged particle beam adjusts an irradiation dose according to a shape error based on a shape of the workpiece measured in advance. A support device having the stage; and a support device driving unit that drives the support device.
The support device driving unit drives the support device to adjust the position and posture of the stage so that the traveling direction of the charged particle beam is inclined with respect to the reference plane defined by the edge of the aperture. The precision polishing apparatus according to any one of claims 1 to 8, wherein the charged particle beam is irradiated to the surface. Fixing the work piece on the stage;
Fixing the aperture directly or indirectly to the stage so as to cover a part of the workpiece;
Irradiating a charged particle beam with an irradiation source;
With
The aperture is arranged such that an edge of the aperture inner surface of the aperture on the irradiation source side is spaced from the surface of the workpiece.
The charged particle beam is irradiated such that a traveling direction of the charged particle beam is greater than an angle of inclination of the charged particle beam with respect to an axis perpendicular to a reference plane defined by the edge of the aperture. Precision polishing method.   The precision polishing method according to claim 10, wherein the charged particle beam is a gas cluster ion beam.   The precision polishing method according to claim 10, wherein the workpiece has a curved surface. An inclination angle, which is an angle formed between the traveling direction of the charged particle beam and an axis perpendicular to the reference plane, is θ, and the absolute value of the difference between the maximum surface angle of the workpiece and the inclination angle θ of the workpiece is The distance between the predetermined position where the surface roughness starts to deteriorate and the center of the workpiece is r0, and the distance between the predetermined position of the workpiece and the surface of the workpiece is r0. S (r0), where R is the radius of the inner surface of the opening of the aperture, and H is the height of the aperture, the following conditional expression (R + r0) / tan θ−s (r0) <H
Satisfied,
The charged particle beam is irradiated in a state where the workpiece is rotated relative to the charged particle beam with a center axis of the workpiece as a rotation axis. The precision polishing method as described in any one of Claims.   The precision polishing method according to claim 13, wherein the charged particle beam is irradiated at two or more different inclination angles with respect to the reference plane.   An angle between the traveling direction of the charged particle beam and an axis perpendicular to the reference plane is θ, a line segment connecting the center of the object to be processed and the edge of the inner surface of the opening, and the center axis of the object to be processed Wherein the charged particle beam is irradiated with an inclination angle satisfying θ <γ and an inclination angle satisfying θ> γ with respect to the inner surface of the opening. Item 15. The precision polishing method according to Item 14. Further measuring the shape of the workpiece in advance and calculating a shape error;
The precision polishing according to any one of claims 14 and 15, wherein the charged particle beam adjusts an irradiation dose according to a shape error based on a shape of the workpiece measured in advance. Method.

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