KR20140019392A - Method and system for convergent polishing - Google Patents

Abstract

A polishing system for polishing an optical element includes a polishing pad having a predetermined radial size and a partition wall disposed on the polishing pad. The partition partially surrounds the optical element. The optical element contacts the polishing pad over a predetermined range of the radial size, and the pad wear rate of the polishing pad is substantially constant as a function of the radial size over the predetermined range of the radial size.

Description

Convergent Polishing Method and System {METHOD AND SYSTEM FOR CONVERGENT POLISHING}

Cross Reference of Related Application

This application is based on a claim of priority on US Provisional Patent Application No. 61 / 454,893, filed March 21, 2011, the disclosure of which is incorporated herein by reference in its entirety for any purpose. do.

Created by research or development with the support of the United States Federal Government

Claim of Right to Invention

The United States Government has signed an agreement between the United States Department of Energy and Lawrence Livermore National Security, LLC regarding the operation of the Lawrence Livermore National Laboratory. In accordance with AC52-07NA27344.

According to the present invention, techniques related to an optical system are provided. More specifically, embodiments of the present invention relate to deterministic polishing of an optical device that takes place within a short time, such as one iteration. By way of example only, the present invention has been applied to single iteration polishing of an optical element under a set of polishing parameters, independent of the initial form of the optical element. The methods and systems disclosed herein can be applied to the processing and manufacture of a wide range of optical materials, suitable for use in high power laser and amplifier systems.

Conventional optics manufacturing processes generally include 1) shaping, 2) grinding, 3) edge grinding / polishing, 4) full aperture intermediate polishing or lapping, and 5) Small tool polishing. Significant advances have been made in the manufacture of precision optics since the invention of the laser has rapidly increased the demand for materials of high light quality, including precise surface shapes. However, the manufacture of optical instruments in a manner that is commonly done today is a function or an art rather than a technology. In recent decades, the ability to remove material deterministically during the grinding process has developed significantly, thanks to advances in tool making and real-time diagnostics using Computer Numerical Controlled (CNC) grinding machines. Similarly, the emergence of small tool polishing (eg, computer controlled optical polishers (CCOS)) and magnetorheological finishing (MRF) has revolutionized the polishing industry. However, full aperture lap polishing, which is still the most widely used and generally the most economical method for polishing glass and silicon wafers, does not provide a deterministic process. While gradual improvements have been made, conventional polishing still requires highly skilled optical technicians using craftsmanship. This type of polishing generally requires a number of iterative cycles, including polishing, measurement, and parameter adjustment to converge to the desired surface shape (ie, flatness or suitability for a particular radius).

Accordingly, there is a need in the art for an improved method and system for polishing an optical device.

According to the present invention, techniques related to an optical system are provided. More specifically, embodiments of the present invention relate to deterministic polishing of an optical device that takes place in as little time as one iteration. By way of example only, the present invention has been applied to single iteration polishing of an optical element under a set of polishing parameters, independent of the initial form of the optical element. The methods and systems disclosed herein can be applied to the processing and manufacture of a wide range of optical materials, suitable for use in high power laser and amplifier systems.

According to another embodiment of the present invention, there is provided a method and system related to finishing without surface cracking. Scratch on the surface of expensive optical instruments used in high-peak-power laser systems are known to induce the onset of laser damage. Therefore, much effort has been made over the years to reduce the number and size of scratches formed during the manufacture of optical instruments. Scratches are caused, for example, by rogue particles or roughness under the load of the surface of the optical instrument during cleaning, polishing and handling. Conventional work to reduce log particles has involved the modification and modification of existing full aperture polishers. This method was sufficient to handle external log particles that induce scratches. Current mitigation strategies are generally limited to performing cleanup operations during polishing. However, this strategy is sensitive to the degree of cleaning work, the operator's function, and the complexity of the polisher. In addition, this strategy is difficult to implement with high efficiency. The second limitation in controlling log particles is limited understanding and control of the particle size distribution of the slurry during the polishing process. The state of the art today is an unoptimized, poorly understood filtration technique.

Embodiments of the present invention reduce the introduction of log particles during polishing by implementing one or more of the following steps: 1) Log particles are formed by hermetically sealing the polisher to prevent the slurry from drying. Forming an entire polishing system that ensures no entry into the wrap interface; 2) provide a 100% humidity environment to prevent dried slurry agglomeration that may act as log particles; 3) use chemically stable polishing slurry to minimize slurry particle agglomeration; 4) Use optimized filtration to continuously remove log particles generated in the polishing system.

According to one embodiment of the present invention, a polishing system for polishing an optical element is provided. The polishing system includes a polishing pad having a predetermined radial size and a partition wall disposed on the polishing pad and partially surrounding the optical element. The optical element contacts the polishing pad over a predetermined range of the radial size, and the pad wear rate of the polishing pad is substantially constant as a function of the radial size over the predetermined range of the radial size.

According to another embodiment of the present invention, a high humidity polishing system is provided. The high humidity polishing system includes a polishing unit including a polishing pad and a slurry supply system for providing a slurry to the polishing pad. The high humidity polishing system also includes an enclosure surrounding the polishing unit. The humidity in the enclosure is high enough to prevent the slurry from becoming too dry.

According to certain embodiments of the present invention, a slurry system for polishing an optical device is provided. The slurry system includes a solvent and an abrasive component contained in the solvent. The slurry system also includes a surfactant contained in the solvent.

According to another particular embodiment of the present invention, a method of mounting a workpiece on a substrate is provided. The method includes determining a height value between the heights and a value related to the pitch area. The method also includes calculating the relative area of the pitch, calculating the button radius, and calculating the number of pitch buttons. The method also includes connecting N pitch buttons to the workpiece and connecting the N pitch buttons to the substrate.

Embodiments of the present invention provide an apparatus and method for polishing flat, spherical, round, square surfaces of glass having various aspect ratios (diameter / thickness). The polishing system provided by embodiments of the present invention is convergent, initial surface independent, single iteration, and rogue-particle free ( Collectively, these four may be referred to as polishers, and provide one or more of the following characteristics:

1) the polishing parameters are fixed (ie not a variable) and are the same between / between the polishing operations regardless of the initial surface shape of the workpiece;

2) Polishing can be done in a single iteration from the foundation state since the shape of the workpiece will converge to the desired shape that matches the shape of the wrap;

3) polishing is performed in a log particle 'free' environment, with little or no scratching of the workpiece;

4) Polishing is performed using a highly controlled particle size distribution using chemical stabilization and / or engineering filtration systems.

Embodiments of the present invention rely on one or more of the following principles to achieve the desired polishing process:

1) All factors contributing to the removal of non-uniform spatial materials on the optics are necessarily removed except for optics-wrap mismatches (i.e., non-uniform physical separation between the optics and the wrap), which is why the optics surface shape is desired. Converge in form;

2) Log particles enter or enter the polishing system, or sources that cause log particles to be generated within the polishing system are being removed or actively removed, which results in little or no scratching of the workpiece.

As described in detail throughout the present application, the engineering features provided by embodiments of the present invention may include one or more of the following.

1) respond to uneven pad wear rates using specially designed bulkhead (s) for round or square workpieces;

2) use specially designed bulkheads to cope with viscoelastically induced non-uniform stress distribution and non-uniform material removal;

3) specially designed bulkheads are used to ensure a uniform distribution of the slurry on the workpiece;

4) glass-based square partitions provide stability to uniform pad wear;

5) CVO diamond based square partitions are used for conditioning pads to ensure a constant removal rate for polishing time;

6) use wheel drive workpieces to prevent moment forces from contributing to non-uniform stress distributions and non-uniform material removal;

7) use low-z pivot point mounting to minimize moment forces on the workpiece and bulkhead;

8) use kinematics to cause a uniform time-averaged velocity on the workpiece to prevent non-uniform material removal due to kinematics (movement of the workpiece and the lap);

9) Polishing slurries chemically stable (e.g., anions (e.g., at a suitable pH) and cerium oxide (Hastilite PO slurry) concentrations to minimize particle agglomeration (source of log particles) Micro-90) or cationic surfactants and chelators;

10) Using a hermetically sealed polishing chamber at 100% humidity, a) prevents drying of a polishing slurry known to generate log particles causing scratches, and b) external log particles in the surroundings entering the polishing system. Prevents;

11) use rigid button bonding technology (also known as pitch button bonding (PBB)) to prevent deformation of the workpiece in high aspect ratio (thin) workpieces / optical instruments;

12) use flexible button bonding technology (also known as foam button bonding (FBB)) to counter the effect of residual stresses on the foundation surface on non-uniform removal and workpiece curvature;

13) use pre-etching (eg, HF or buffered-oxide etching) techniques on the underlying workpiece to remove residual stresses that can cause non-uniform removal and workpiece curvature;

14) use a pre-etch (eg, HF or buffered-oxide etch) technique on the base workpiece to remove potential log particles on the base surface that may contribute to scratching;

15) using a fluorinated coating on the interior and parts of the polisher housing to provide low slurry particle adhesion to facilitate slurry cleaning and minimize the generation of log particles between polishing iterations;

16) use a polisher design that minimizes corners or gaps where slurry particles collect to minimize the generation of log particles; And / or

17) Use an active slurry filtration system that efficiently removes log particles and controls the particle size distribution of the slurry.

The present invention provides a number of advantages over the prior art. For example, embodiments of the present invention provide a method and system suitable for polishing an optical instrument in a predetermined form in a single iteration. Embodiments of the present invention are described in more detail in the following detailed description and the accompanying drawings, together with their advantages and features.

1 is a chart showing parameters affecting polishing non-uniformity, according to one embodiment of the invention.
2A is a simplified graph showing peak-to-valley height as a function of polishing time for different polishing configurations, according to one embodiment of the invention.
2B-2G illustrate different polishing configurations in accordance with one embodiment of the present invention.
FIG. 2H is a simplified graph showing the height between floors as a function of polishing time for one polishing configuration, according to one embodiment of the invention.
3A-3D are simplified graphs showing polishing convergence for various initial forms, according to one embodiment of the invention.
4A-4E are surface contours showing the height between floors at various polishing times, according to one embodiment of the invention.
5A is a simplified perspective view of a polishing septum, in accordance with an embodiment of the present invention.
5B is a simplified cross-sectional view of a polishing partition, according to one embodiment of the invention.
6 is a simplified graph showing pad wear rate as a function of radial distance, according to one embodiment of the invention.
FIG. 7 is a simplified graph showing partition widths as a function of radial distance, in accordance with an embodiment of the present invention. FIG.
8A-8C are simplified graphs showing partition load as a function of radial distance, in accordance with an embodiment of the present invention.
FIG. 9A is a simplified conceptual diagram illustrating scratching by rogue particles. FIG.
9B is an image showing scratching by log particles.
10 is a simplified perspective view of a high humidity polishing system according to one embodiment of the present invention.
11 is a simplified plan view of a portion of a high humidity polishing system according to another embodiment of the present invention.
FIG. 12 is a graph showing the normalized interface height as a function of time for polishing solutions in a range of dilution, according to one embodiment of the invention.
FIG. 13 is a graph showing normalized interface height for polishing solutions under the influence of agitation, in accordance with an embodiment of the present invention.
FIG. 14 is a graph showing the normalized interface height for polishing solutions as a function of time, according to one embodiment of the invention.
FIG. 15 is a simplified graph showing the relative interface height as a function of time for stabilized and unstabilized polishing solutions, according to one embodiment of the invention.
Figure 16 shows the polishing solution volume for stabilized and unstabilized polishing solutions, as a function of particle size, according to one embodiment of the invention.
17 is a simplified flowchart illustrating a method of polishing a set of optical elements, according to one embodiment of the invention.
18A-18C are images showing surface curvature before grinding, after grinding, and after chemical etching, according to one embodiment of the invention.
FIG. 19 is a simplified conceptual diagram illustrating a method of performing pitch button combining according to an embodiment of the present invention.
20 is a graph showing the change in the measured value in the surface shape of fused silica and phosphate glass in various PBB shapes according to one embodiment of the present invention.
21 is a graph measuring the thermal expansion of the pitch according to an embodiment of the present invention.
FIG. 22A is a graph showing the height between workpieces as a function of undercooling of pitch for a single button or three buttons according to one embodiment of the present invention. FIG.
22B is a graph showing the height between workpieces as a function of pitch button radius in accordance with one embodiment of the present invention.
FIG. 22C is a graph showing normalized height between workpieces as a function of pitch button offset in accordance with one embodiment of the present invention. FIG.
FIG. 22D is a graph showing the height between workpieces as a function of relative total pitch button area, according to one embodiment of the invention. FIG.
23 is a simplified conceptual diagram illustrating pitch button coupling parameters according to an embodiment of the present invention.
24A and 24B illustrate an optimized pitch button coupling pattern for an optical element, according to one embodiment of the invention.
25A is a graph illustrating the height between workpieces as a function of the spacing between buttons, according to one embodiment of the invention.
25B is a graph showing the height between workpieces as a function of area fraction, in accordance with an embodiment of the present invention.
FIG. 26 is a simplified flowchart illustrating a method of determining a pitch button combining parameter according to an embodiment of the present invention.

1 is a chart showing parameters affecting polishing non-uniformity, according to one embodiment of the invention. Embodiments of the present invention provide techniques and systems that mitigate polishing non-uniformity. Control of some of the parameters described in FIG. 1 is described in detail in US patent application Ser. No. 12 / 695,986, filed Jan. 28, 2010, the disclosure of which is incorporated herein by reference in its entirety. As described in more detail throughout this application, embodiments of the present invention provide a mirror septum to reduce the elastic wrap response (4.2) and the viscoelastic effect (4.5) and to provide a constant wrap wear (4.6.1). ) Is used. The form of optics is used to allow the polishing process to converge (4.6.4).

As shown in FIG. 1, various parameters except one variable have been reduced or eliminated, and this one variable is used to converge to the desired shape for the optical element in the full aperture polishing system. This is drastically different from previous techniques in which various parameters are simultaneously changed in real time by the optical engineer in an attempt to make the desired shape. The inventors of the present invention have understood and reduced or eliminated the parameters affecting the material removal described in FIG. 1, leaving only one variable, the mismatch between the optics and the lap. Using a wrap having the shape that the optical device would eventually take, the optical device is polished in a converging manner to match the shape of the wrap.

2A is a simplified graph showing peak-to-valley height as a function of polishing time for different polishing configurations, according to one embodiment of the invention. As shown in FIG. 2A, a graph showing the elevation height of the optical element as a function of polishing time is shown for various polishing configurations. As shown, since the parameters described in FIG. 1 have been solved by the inventors of the present invention, the optical element can be polished with little change in the height between the elevations as a function of the polishing time. As shown by the "reduced pad wear" curve (# 5), the inventors of the present invention deform the shape of the pad when polishing, and as a result, the deformation of this shape changes the pressure distribution on the optical element being polished. I found out. Accordingly, embodiments of the present invention use barrier ribs to contact the wrap and essentially cause reverse wear (ie, spatial) that the optical element generates, thereby balancing pad wear so that pad wear is spatially uniform. Thus, embodiments of the present invention reduce the viscoelastic effect as shown in curve # 6 and allow the elevation between the elevations as a function of time to be substantially flat.

2B-2G illustrate different polishing configurations in accordance with one embodiment of the present invention. The parameters shown in FIGS. 2B-2G correspond to the curve numbers in FIG. 2A.

The inventors of the present invention show that, while FIG. 2A shows a stable elevation between plots # 6 (reduced viscoelasticity 77), the elevation between elevations can be increased to a higher level at times longer than 100 hours, It was found that liver height can increase as a function of time. FIG. 2H is a simplified graph showing the height between floors as a function of polishing time for one polishing configuration, according to one embodiment of the invention. As shown in FIG. 2H, the convergence point moves within a period between 0 and 150 hours. Without limiting embodiments of the present invention, the inventors of the present invention believe that one mechanism that potentially causes the movement of the convergence point is that the balance between pad wear caused by the optical element and pad wear caused by the partition wall is broken and I believe that the result is an increase in height.

Embodiments of the present invention adjust the convergence point by removing the optical element being polished and operating the polishing system with only the partition wall. By operating the system with only the bulkhead, the convergence point is adjusted so that the height between the bottoms and lowers returns to a value lower than a predetermined level. The shift of the convergence point occurs over a longer period than the period associated with the polishing operation for one optical element. As an example, the polishing time for a particular optical element may be 10 hours, and a number of optical elements (eg, 15 optical elements) may have a ˜150 hour period shown in FIG. 2H before the elevation height increases above 2.5 μm. Polished within. Thus, the adjustment of the convergence point is provided over a long time period as compared to the time period generally used for polishing one optical element. Embodiments of the present invention are not limited to this long term adjustment of convergence points, but the following examples are presented in relation to the periods associated with polishing processes for multiple optical elements.

Referring to FIG. 2H, the convergence point moves from about 0.5 μm to about 2.5 μm during the first 150 hours of polishing. In order to reduce the value of the convergence point, embodiments of the present invention eliminate the optical element to operate the polishing system using only the partition wall for a period of time to reduce the height between the heights to a predetermined level. As shown in FIG. 2H, the operation of a polishing system using only 0.6 psi bulkheads over a period of ˜200 hours to ˜400 hours reduces the point of convergence as indicated by the low-rise height falling to 0.48 mm. As shown, the rate of decrease in height between elevations is relatively low (eg, ˜1.7 μm / 212 hours = 7.3 nm / hour), but is controllable and substantially linear. In the period after ˜400 hours, both the partition wall and the optical element are used, and as a result, the convergence point changes again during the period of ˜400 hours to ˜500 hours. As can be seen by the last few data points, polishing using only bulkheads after ~ 500 hours reduces the convergence point as expected. In this way, embodiments use a process of polishing only partitions (eg, 0.6 psi partitions) without using optical elements as a method of precisely adjusting the convergence point. Those skilled in the art (hereinafter, also referred to as those skilled in the art) will recognize many variations, modifications, and alternatives.

Additional discussion of converging pad polishing can be found in Tayyab Suratwala, Rusty Steele, Michael Feit, Richard Desjardin and Dan Mason's "Convergent Pad Polishing of Amorphous Silica" (International Journal of Applied Glass Science, Special Issue) : Part 1, The Flow and Fracture of Advanced Glasses Part 2, General Glass Science, Volume 3, Issue 1, pages 14-28, March 2012), the contents of which are incorporated herein by reference in their entirety for any purpose. Incorporated by reference.

17 is a simplified flowchart illustrating a method of polishing a set of optical elements, according to one embodiment of the invention. The method 1700 includes polishing (1710) a first subset of optical elements using a polishing process that is characterized by a septum and an elevation height less than a predetermined first value. The method also includes determining whether the elevation height is greater than or equal to the predetermined first value (1712). When the elevation height reaches the predetermined first value, the last optical element of the first subset of optical elements is removed and the polishing system is operated (1714) without optical elements for a period of time. After the period, it is determined whether the inter-floor height has been reduced to a value smaller than the second predetermined value (1716). In some embodiments, the second predetermined value is less than the first predetermined value. In another embodiment, the second predetermined value is equal to the first predetermined value.

In some embodiments, the operation of the polishing system while adjusting the convergence point may be performed by removing the partition without an optical element, one of the optical elements (discussed in connection with another embodiment later), or a partition or other device other than the optical element. I use it. Therefore, forms other than the partition wall adjusting the convergence point are included in the scope of the present invention.

When the elevation height reaches the predetermined second value, the second subset of the optical elements is polished using a polishing process characterized by the elevation height less than the partition and the predetermined first value (1718). ).

In another embodiment, wherein the height between elevations is increased in the negative direction as a function of time, a process for removing the partition and polishing one or the dummy optical elements of the optical elements in the set of optical elements without using the partition. By modifying 1714, the method shown in FIG. 17 can be modified. In this way, the elevation height increasing in the negative direction can be adjusted using this complementary correction method.

3A is a simplified graph showing polishing convergence for various initial forms, according to one embodiment of the invention. In FIG. 3A, the optical element is a low aspect ratio round workpiece. As shown in FIG. 3A, the peak-to-valley variation in the workpiece (ie, optical element) is originally about 7 μm (ie, about 14 waves) for Experiment 79. ) To about −1 μm (ie, about 2 waves). For Experiment 80, the original inter-floor deviation is about −7 μm and is reduced to about −1.5 μm. In this way, embodiments of the present invention provide a polishing technique that enables optical polishing to converge with uniform smoothness regardless of the original deviation of the optical element. Although the current convergence zone shown in FIG. 3 is characterized by a low-to-low deviation that is less than about 0.5 μm wide and negative, the present invention is not limited to this specific deviation but also shows other zones with narrower deviations around zero. It belongs to the scope of the present invention.

Using the present invention, shape convergence is induced by a mismatch between the shape of the wrap and the optics, which allows for an initial surface-independent polishing process by single iteration. During polishing, the optics converge to the same shape as the wrap due to the optics-wrap mismatch normalization of the pressure. In this way, embodiments of the present invention allow the polishing process to converge into a zone having a predetermined inter-floor height, and the inter-floor height is maintained within the zone for an extended period of time.

One of the advantages provided by the present invention is that the convergence polishing process ends at a constant high and low deviation and stays at this convergence value for an extended period of time. Unlike conventional polishing techniques in which polishing must be terminated at the correct time to prevent excessive polishing, the convergent polishing technique of the present invention terminates itself after one iteration and is based on the shape of the wrap, independent of the original surface of the optical element. To provide the desired form.

FIG. 3B is a simplified graph showing polishing convergence for a low aspect ratio rounded optical element, according to one embodiment of the invention. The polishing pad used for the polishing process shown in FIG. 3B (i.e., the IC1000 ^™ polishing pad available from Dow Chemical Company, Midland, Michigan) is a suba commercially available from the polishing process shown in FIG. 3A (ie, Dow Chemical Company). ^TM 550 polishing pads). 3C is a simplified graph illustrating polishing convergence for a rectangular optical element according to one embodiment of the present invention. FIG. 3D is a simplified graph showing polishing convergence for a round, high aspect ratio optical element, according to one embodiment of the invention.

As shown in FIGS. 3A-3D, the inter-floor height as a function of polishing time for workpieces with different initial surface shapes, and for four different configurations, converges to a predetermined zone. As an example, in FIG. 3C a low aspect ratio rectangular workpiece was polished using an IC1000 ^™ polishing pad, and in FIG. 3D a high aspect ratio round (grinded or polished) workpiece was polished using an IC1000 ^™ polishing pad. . In the polishing run shown in these figures, the workpieces characterized by the non-uniform initial surface shape converged equally and all the workpieces converged to a substantially flat final form, demonstrating convergent full aperture polishing.

4A-4E are surface contours showing the height between floors at various polishing times, according to one embodiment of the invention. The original surface with the height-to-high height deviation (PV) of 6.5 μm is shown in FIG. 4A. The surface after 1 hour polishing is shown in FIG. 4B, and PV = 4.64 μm. Polishing time thereafter is shown in FIGS. 4C-4E: 2 hour polishing PV = 3.59 μm (FIG. 4C); 6 hour polishing PV = -1.04 μm (FIG. 4D); And 24 hour polishing PV = -0.95 μm (FIG. 4E). As shown in Figures 4D and 4E, the converging polishing process ends at a fixed PV after a predetermined period of time.

5A is a simplified perspective view of a polishing partition, according to one embodiment of the invention. The partition wall 500 in the embodiment shown in FIG. 5A includes a curved portion 510 shaped to receive a rounded optical element. In another embodiment, the partition wall, which may be a victim that responds to spatially nonuniform pad wear caused by the optical element being polished and also causes pad wear, includes square optics, rectangular optics, and the like. It is adapted to accommodate optical elements, which may also be called workpieces, of other forms. Bulkhead 500 is a stack of materials such as that shown in FIG. 5B, such as a structural layer 520 formed of a 25 mm stainless steel or other material with sufficient rigidity and density, such as 3 mm rubber or other compliant material. A flexible layer 522 formed of a lamella, and a polishing layer 524 formed of, for example, 1.1 mm fused silica or other material similar to an optical element being polished. Depending on the mass of the desired partition, the materials used in the various layers can be modified to provide functions of strength / mass, flexibility, and polishing similarity. As an example, the structural layer may be formed from aluminum or other dense material, including laminated materials, preferably to provide a low aspect ratio for the partition wall. The partition shown in FIG. 5A is suitable for polishing a circular optical element, but other forms, including square and rectangular optical elements, are also within the scope of the present invention.

The partition can provide a flat shape thanks to the flexible layer allowing homogenization of the pressure such that the pressure applied to the pad is uniform across the partition. Materials other than rubber, such as soft polymers, foams, silicones, or combinations thereof, may also be used. The flexible layer can be bonded to the structural layer using epoxy or other adhesive as needed. Use of the same material as the optics polished to the polishing layer is useful in providing the same pad wear rate, but other materials may be used to suit particular applications. It will be apparent to those skilled in the art that the use of optics and other materials to be polished will change the shape of the partition. In the partition design shown in FIG. 5, the pressure on the lap generated by the partition (ie, the load) is matched to the pressure from the optics. In other designs, different types of partitions are produced by specifying different pressures between the partitions and the optics.

6 is a simplified graph showing pad wear rate as a function of radial distance, according to one embodiment of the invention. Referring to Figure 6, wear due to the workpiece (i.e. wear rate of the polishing pad) is indicated by the area crosshatched to the right as a function of the distance from the center of the polisher. This area under the curve indicates how much pad wears out when the optical element is placed on the wrapping pad. In the graph shown, an optical element (also called an optical instrument) is placed 25 mm from the center of the polisher having a diameter of 100 mm. Where the optics are not in contact with the pad (eg 0-25 mm), there is no pad wear, so the pad wear rate is zero in this region. Similar zero pad wear is seen at distances greater than 125 mm. Given the wear rates shown, over time, reversing this curve results in the form of grooves that wear out during polishing.

Polishing pad wear (indicated by compensatory wear by area crosshatched to the left) is provided so that the overall pad wear rate is a constant C as a function of distance. As will be apparent to those skilled in the art, the difference between the constant value and the wear caused by the workpiece will provide a guide for the design of the partition wall resulting in a wear rate as shown.

The pad wear rate can be expressed as a combination of pad wear due to the workpiece (ie, optical element) and pad wear due to the septum:

here,

r = distance from the center of the pad,

s = displacement from the pad center of the optical element,

K _L = Preston Coefficient (the same value if the polishing surface of the optical element and partition is the same material),

μ = friction coefficient,

σ = load (pressure), which may be the same for both the optical element and the bulkhead,

circumferential width of the optical element at f _o (r) = r,

circumferential width of the bulkhead at f _s (r) = r,

The relative velocity between the optical element and the pad at V _ro = r (same as R _o s if R _O = R _L ),

Relative velocity between bulkhead and pad at V _rs = r (same as R _L r if R _O = R _L ),

R _O = rotational speed of the optical element,

R _L = rotational speed of the wrap (ie pad).

)을 위한 격벽의 형태는 상기 격벽의 폭을 다음과 같이 계산함으로써 결정된다:Constant pad wear rate (

The shape of the bulkhead for) is determined by calculating the width of the bulkhead as:

이다.In the circular optical element,

to be.

The partition provided by embodiments of the present invention, as shown in FIG. 5A, provides advantages not available using conventional polishing techniques. The shape of the septum is designed using the Preston equations described in connection with FIGS. 6 and 7 to provide uniform pad wear rates as a function of position throughout the optics. In some embodiments, the uniformity of pad wear is characterized by a pad wear rate value that differs by less than 5% at the pad portion in contact with the optical element. In another embodiment, the pad wear rate value is less than 2%, less than 1.5%, less than 1%, less than 0.75%, less than 0.5%, less than 0.4%, less than 0.3%, less than 0.2%, 0.1 The difference is less than%, less than 0.05%, less than 0.025%, or less than 0.01%. For example, the first pad wear rate as a function of position is associated with wear due to the optical element, and the second pad wear rate as a function of position is associated with the septum (see FIG. 6). The sum of these pad wear rates provides a substantially uniform ratio in the portions of the pad in contact with the optical element. As will be apparent to one skilled in the art, in certain embodiments, the uniformity of pad wear rate extends to portions of the pad that are not in contact with the optical element (e.g., radial distances less than 25 mm and greater than 125 mm in FIG. 6). Such uniformity may be reduced within these areas. Those skilled in the art will recognize many variations, modifications, and alternatives.

It should be noted that the use of bulkheads as described herein, in addition to improving spatial pad wear uniformity, can result in other mutual benefits due to linearly changing phenomena for speed and pressure. . Some examples of such phenomena include pad compression and viscoelasticity, pad glazing, effects of friction induced heat, slurry distribution, and the like.

Using embodiments of the invention, the pad wear as a function of position is substantially uniform as a function of position, for example less than a few waves for the optical element. In one embodiment, the pad wear uniformity is within one wave over the radial distance in contact with the optical element, but the uniformity may be characterized by more uniform pad wear, for example less than one wave.

FIG. 7 is a simplified graph showing partition widths as a function of radial distance, in accordance with an embodiment of the present invention. FIG. In FIG. 7 the partition width (i.e. the circumferential width) is the maximum thickness set by the circumference of the lap at a particular radial distance (the circumference that can be covered by the partition at a small radial distance is that much) and the viscoelastic effect and strength It is bounded by the minimum thickness set by the rigid punch effect. The viscoelastic effect is more important for soft pads, while the strength punch effect is more important for hard pads.

In Fig. 7, the shape of the partition wall is defined with respect to the circular optical apparatus, but other types of optical elements are also within the scope of the present invention. Using the equations disclosed herein, the load on the partition wall can be different from the load of the optical instrument, for example, can be a non-uniform load. The function f _o (s) can be calculated for a given shape, for example circular or rectangular optics, and can be put into this formula to define the shape of the partition. The functions f _o (r) and f _s (r), referred to herein as circumferential widths, are defined as the portion around the lap at radius r covered by the optics or partition, respectively.

Since the radial velocity tends to approach zero as the radial distance decreases, the constant values shown in FIG. 6 may not be obtained in parts of the partition wall near the polisher center (small radial distance on the wrap). However, since the optics are at a finite distance from the center (eg, 25 mm in the illustrated embodiment), this design constraint is satisfied by the partition design disclosed herein. Since the optics do not overlap radial distances less than 25 mm, design flexibility is provided for constant pad wear rates at radial distances that do not overlap with the optics.

8A-8C are simplified graphs showing partition load as a function of radial distance, in accordance with an embodiment of the present invention. Embodiments of the present invention may utilize a partition with uniform load distribution (FIG. 8A), a differential distribution partition (FIG. 8B), or a continuously distributed partition (FIG. 8C). 8A-8C show that the load σ (r) may be a function of position, as discussed in relation to the pad wear rate.

FIG. 9A is a simplified conceptual diagram illustrating scratching by rogue particles. FIG. In some optical device polishing applications, such as, for example, high energy laser and amplifier systems, stringent requirements may be added to scratch density. Without limiting embodiments of the present invention, the inventors have found that some scratches have a larger particle size distribution than the average particle size of particles larger than other particles present in the polishing slurry, such as other particles in the slurry. It is believed that it occurs during polishing by log particles, which are particles having or have external particles. As shown in FIG. 9A, log particles create a higher load on the optics and cause a scratch or a series of scratches. Despite attempts to filter out log particles, scratches of the optics are still observed. 9B is an image showing scratching by log particles.

Without limiting embodiments of the present invention, the inventors believe that an additional source for producing log particles is drying of the slurry. For example, during polishing of a compound comprising cerium oxide, the slurry not only dries up but chemically reacts with itself to produce a hard mass that is dried from a soft mass. The agglomerates can produce scratches as shown in FIG. 9B.

Embodiments of the present invention prevent the drying of the slurry by enclosing the polishing system, which not only prevents foreign particles from entering, but also provides a high humidity environment to prevent the slurry from drying out. A rinsing system may be used to clean the optics to prevent slurry from remaining on the optics when the optics are removed from the system. In this way, after the slurry is removed from the cleaning process without drying, the cleaned optics can be dried. To further aid in cleaning the slurry from the system, the system parts can be coated with a fluorinated polymer to reduce adhesion between the slurry and the various system parts.

10 is a simplified perspective view of a high humidity polishing system according to one embodiment of the present invention. The high humidity polishing system 1000 includes a polishing surface 1010, which may be a polishing pad, and an optical instrument 1012 partially surrounded by a partition 1014. Removable cover 1020 may be positioned to contact enclosure 1022 to form a controlled environment surrounding the polishing surface. Input and output ports (not shown) for polishing slurries and input ports 1030 and output ports 1032 for wet gases (eg, water vapor) are provided as part of the system.

In the embodiment shown in FIG. 10, the humidity inside the polishing system is higher than the ambient humidity, eg, at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 98%. At least 99%, or 100%. In some embodiments, the humidity is provided at a high level that prevents the slurry in the system from being too dry. Drying does not occur well within this environment, thereby preventing scratching associated with the formation of a hard mass.

FIG. 11 is a simplified plan view of a portion of the high humidity polishing system shown in FIG. 10 and in some respects another high humidity polishing system. As shown in FIG. 11, an optical instrument 1105 is disposed on the wrap 1110 and spatially controlled using a guide wheel. In the embodiment shown in FIG. 11, different partition designs are used and mirror partition 1120 is provided to create uniform pad wear. A 100% humidity supply port 1030 may be provided near wrap 1110 to provide a desired controlled, high humidity environment in a similar manner as a sealed chamber (eg, a closed chamber 1107). Embodiments of the present invention are not limited to the design shown in FIG. 11, which is provided by way of example only.

FIG. 12 is a graph showing the normalized interface height as a function of time for polishing solutions in a range of dilution, according to one embodiment of the invention. The normalized interface height as a function of time provides insight into the settling properties of the slurry, which separates the slurry from the slurry as it sinks to the bottom of the vessel (eg, graduated cylinder). Because the interface between them decreases in height. Hastilite PO mixed with DI water in a 1: 4 ratio is the fastest settling, and the normalized interface height drops to 30% in about 25 minutes. The 1: 1 dilution of Hastilite PO and DI water increases the settling time by one digit and reaches 30% normalized interface height after about 300 minutes. Undiluted Hastilite PO provides the longest settling time and drops by 60% at 300 minutes. Thus, dilution of the slurry, such as hastilite PO, affects the settling time.

FIG. 13 is a graph showing normalized interface height for polishing solutions under the influence of agitation, in accordance with an embodiment of the present invention. As shown in FIG. 13, for slurry diluted in DI water or tap water, agitation makes a negligible difference in the settling time.

In addition to the effect of dilution, the inventors of the present invention have found that addition of additives to prevent agglomeration in the slurry can achieve stabilization and increased settling time of the slurry. FIG. 14 is a graph showing the normalized interface height for polishing solutions as a function of time, according to one embodiment of the invention. The slurry shown in FIG. 14 is Hastilite PO, and other slurries are included within the scope of the present invention. Referring to FIG. 14, Hastilite PO (square) diluted in Baume 9 has the fastest settling time and drops to 10% of the original normalized interface height after a period of about 30 minutes. The pure formulation of Hastilite PO (cross) provides increased settling time in a manner similar to the dilution effect shown in FIG. 12. The addition of additives to prevent flocculation provides the greatest settling time, as shown by Hastilite PO (Diamond) diluted in Baume 9 with 1% volume of surfactant μ-90. As shown in FIG. 14, the addition of surfactant increases the settling time and provides a normalized interface height that is almost 90% of the original height at 8000 minutes.

In addition to μ-90, exemplary anionic surfactants include alkyl sulfates (eg, sodium dodecyl sulfate or ammonium lauryl sulfate, etc.); Alkyl sulfonate (eg, Dodecyl benzene sulfonic acid, Sulphonic 100, or Calimulse EM-99, etc.); Alkyl ether phosphates (eg, Triton H66 or Triton QS44, etc.); Alkyl carboxylates (eg, sodium stearate, etc.) or other suitable anionic surfactants. It should be noted that the surfactants that can be used as additives in the polishing slurry may include sodium, ammonium, or potassium salts in which counterions are not activated. The inventors of the present invention have found that stabilization of the slurry with a surfactant (at a suitable pH in some embodiments) provides improved polishing results.

Embodiments of the invention are not limited to the use of anionic surfactants, but may also include the use of cationic surfactants. Exemplary cationic surfactants include Trimethylalkylammonium chlorides (eg, cetyltrimethylammonium bromide (CTAB) or distearyl dimethyl ammonium chloride, etc.); Benzalkonium chlorides; Alkylpyridinium chlorides (eg, cetylpyridinium chloride); Or other suitable cationic surfactants. The surfactant may include chloride or bromide salts in which counter ions are not activated.

In some embodiments, the surfactant is effective to separate polishing by-products from the optical device being polished. The presence of these by-products can reduce the stabilization of the polishing slurry. In some embodiments, the surfactant is effective to prevent agglomeration of by-products, thus increasing the long term stabilization of the polishing slurry. Examples of byproducts from glass polished during polishing are cations (eg, K +, Na +, Ca2 +, Mg2 +, etc.).

In some embodiments, the water used to prepare the slurry may contain various concentrations of metallic cations. In addition, cations such as Na +, B3 +, Fe2 +, Ca2 +, Mg2 + and Al3 + are introduced into the slurry as a byproduct of the polishing process. The presence of these ions has the potential to reduce the efficacy of the stabilizer by disrupting the electrostatic interaction between the slurry particles and the stabilizer molecules.

Chelation agents (e.g., glycine, citric acid or ethylenediaminetetraacetic acid (EDTA), etc.) form the desired complex with cations, sequester them in solution and Prevents interaction with slurry particles. Thus, adding chelating agents to the slurry can enhance the initial stabilizing effect and extend its stability as polishing byproducts accumulate. In this way, embodiments of the present invention utilize chelating agents to improve slurry stabilization.

FIG. 15 is a simplified graph showing the relative interface height as a function of time for stabilized and unstabilized polishing solutions, according to one embodiment of the invention. As shown in FIG. 15, stabilization of the slurry, for example by the addition of an anionic surfactant additive, significantly increases the settling time.

Figure 16 shows the polishing solution volume for stabilized and unstabilized polishing solutions, as a function of particle size, according to one embodiment of the invention. Adding an additive to the slurry results in a reduction in particle size in the slurry, in addition to an increase in settling time and stabilization of the slurry. Referring to FIG. 15, the particle size distribution for the stabilized slurry is characterized in that the size of the plurality of particles is smaller than 1 μm and has a peak of distribution at about 0.25 μm. For unstabilized slurries, the peak of the distribution is centered about 1 μm and one half or many of the particles are characterized by a larger particle size distribution. The stabilized slurry improves polishing results, because smaller particle size distributions provide smaller slurry particles during the polishing process. The inventors of the present invention have demonstrated that the addition of additives provides a slurry characterized by a satisfactory material removal rate and improved micro roughness.

According to the inventors of the present invention, in some optical instrument finishing operations of polishing a thin optical element after grinding, stress may be introduced by the grinding operation, and bending may occur in the optical element according to the grinding-induced stress. Figured out. To reduce this stress, the optical element is chemically etched to remove the surface layers, and as a result can reduce the stress present in the optical element. As an example, the optical device may be exposed to an acid or other suitable etchant after grinding to remove a predetermined surface area of the optical device (eg, immersed in a vessel containing acid). .

In one embodiment, the optical element with the first bend curvature is ground. After grinding, the optical element has a second bending curvature greater than the first bending curvature. In some embodiments, the increase in bending curvature results from the stress introduced into the workpiece during the grinding process. The optical element is chemically etched to remove the predetermined portion. After chemical etching, the optical element has a third bending curvature that is less than the second bending curvature. In some embodiments, the third bending curvature is less than or equal to the first bending curvature and returns the optical element to the curvature of the optical element before the start of the finishing process. In this way, in some embodiments, the chemical etching process reduces the stress introduced during grinding.

18A to 18C are images showing surface curvatures before grinding, after grinding, and after chemical etching, according to an embodiment of the present invention. As shown in FIG. 18A, the surface curvature before grinding is characterized by a low to low value of 1.29 μm. Due to the introduction of stress by the grinding process, the surface curvature after grinding is characterized by a low to medium value of 3.65 μm as shown in FIG. 18B. Embodiments of the present invention utilize chemical etching of the ground surface to remove residual stresses present after the grinding process to return its shape to approximately its original form, as shown in FIG. The curvature is characterized by a high to low value of 1.16 μm. In this way, embodiments of the present invention provide methods and systems in which chemical etching is a mitigation technique useful for removing or reducing residual stresses that contribute to optics / wrap mismatch.

The inventors of the present invention have found that in some polishing applications, pitch button bonding techniques can be used to improve the quality of the finished optical element. Table 1 provides a summary of the pitch button coupling (PBB) process (also known as the pitch button blocking process) and the change in height between the process parameters and the elevation between the workpieces (also called optical elements) before and after blocking (ΔPV). Shows a measurement of the change in surface shape as shown in FIG. As described herein, the PBB includes a mounting technique that uses small pitch islands between the workpiece and the mount, which mount is cooled from the softening temperature of the pitch. At room temperature, the workpiece-pitch button-mount system is hard (ie, high in hardness) and the workpiece generally maintains the initial surface shape. After polishing using the PBB technique, the workpiece converges in the form of a lap, since the work-wrap mismatch due to the effect of the form of the workpiece on the pressure distribution without bending the workpiece predominates, This cause does not limit the embodiments of the present invention.

P = Phosphate Glass; FS = fused silica; NA = not applicable; Code agreement (negative convex, positive concave)

The inventors of the present invention have found that an optical element (eg, fused silica or phosphate glass optics) can be bonded to a substrate (eg, stainless steel blank) using a pitch button. The shape of the pitch button prevents deformation of the workpiece due to the difference in coefficient of thermal expansion between the workpiece and the substrate, as described in more detail below. In some embodiments, isothermal cooling is used to eliminate or reduce deformation of the workpiece.

19A-19F are simplified conceptual diagrams illustrating a method of performing pitch button combining, in accordance with an embodiment of the present invention. As shown in Fig. 19A, an adhesive / protective layer is applied to the surface S2 of the workpiece and reflected wavefront which increases the adhesion between the glass-pitch interface and prevents contamination of the glass surface due to pitch contact, residual slurry contact, etc. wavefront) is measured through surface S1. In some embodiments the adhesive / protective layer is a tape and the tape is optional in accordance with an embodiment. As shown in Fig. 19B, the pitch button is disposed on the surface of the tape (or the surface S2 of the workpiece). The placement of the pitch button is done taking into account several variables including the pitch type, the radius of the pitch button r _p , the thickness of the pitch button t _p , the spacing s between the pitch buttons, and the like. Pitch buttons are annealed (eg in an oven) using, for example, a heating element, as shown in FIG. 19C. The temperature of the annealing process, which may be a function of time, is such that the temperature raised to near the temperature of the pitch (denoted in Tg) at which the entire system (eg, glass, block, and pitch) begins to experience significant stress relaxation. If possible, the system is then selected to isothermally cool as much as possible to prevent or reduce the effects of residual stresses that deform the shape of the workpiece.

19D illustrates attaching the annealed pitch button and workpiece to a preheated substrate (eg, aluminum or stainless steel block) having sufficient strength and mechanical properties for use during the polishing process. A shim of a predetermined thickness (eg, 1.25 mm) may be used while mounting the workpiece on the substrate. The mounted structure is placed in the center of the substrate and, for example, cooled using air cooling and the shims are removed as shown in FIG. 19E. In order to characterize the optical properties of the workpiece after mounting, the reflected wavefront can be measured through surface S1 as shown in FIG. 19F.

It is a graph which shows the change of the measured value in the surface shape of fused silica and phosphate glass in various PBB shapes by one Example of this invention. 20 shows the change in the surface shape of the fused silica (FS) and phosphate glass (PG) optical elements for three conditions. The workpieces used for the measurements shown in FIG. 20 were 100 mm in diameter and 2.2 mmd thick. For bonding with the solid layer of the pitch, the relative surface height FS varies from about 7.5 μm in the circumferential portion to about 3.7 μm in the center portion and from about 10.1 μm to about 4.2 μm for the PG.

The mounting of workpieces using PBB technology significantly reduced the variation in relative surface heights; first, the unoptimized PBB technology produced deviations of convex curvature (FS) and concave curvature (PS) of about 1/2 micron. . By optimizing the PBB process as disclosed herein, the variation in relative surface height is substantially reduced to zero as shown in FIG. 20.

21 is a graph measuring the thermal expansion of the pitch according to an embodiment of the present invention. Referring to FIG. 21, two pitches measured using thermo-mechanical analysis (blocking pitch-1 black (BP1) available from Universal Photonics and Sycad black gold light available from Cycad Products) Thermal expansion of the polishing pitch) is shown. As the temperature increases, the magnitude of the pitch increases and the measured coefficient of thermal expansion is ³⁷ × 10 ⁻⁶ ° C ⁻¹ for BP1 and 43 × 10 ⁻⁶ ° C ⁻¹ for ccad.

22A is a graph showing the height between workpieces as a function of undercooling of pitch for a single button or three buttons according to one embodiment of the present invention. In FIGS. 22B-D, fused silica workpieces (d _w = 100 mm diameter, t _w = 2.2 mm, E _p = 73 GPa, α = 5.4 × 10 ⁻⁷ ° C ⁻¹ ) were used. Workpiece PV height after PBB is shown as a function of the supercooling temperature of the pitch for a single button (r = 25mm) and 3 buttons (s = 50mm; r = 10mm). The use of multiple pitch buttons significantly reduced the workpiece PV height.

22B is a graph showing the height between workpieces as a function of pitch button radius in accordance with one embodiment of the present invention. The pitch button radius affects the workpiece PV height, as can be seen in FIG. 22B, which shows the PV height for various pitch modulus, thickness and coefficient of thermal expansion (ΔT = 54 ° C.) for a single button case. Crazy

FIG. 22C is a graph showing normalized height between workpieces as a function of pitch button offset in accordance with one embodiment of the present invention. FIG. In FIG. 22C, the PV height after PBB is normalized by dividing the PV height by the relative total button area in microns and is expressed as a function of the separation distance (d _m ) between buttons, measured in millimeters for 3 and 9 buttons. In the case of three buttons, the size of the pitch buttons varies from 10 mm to 20 mm in radius. Pitch button parameters were ΔT = 54 ° C, t = 1mm, E _p = 0.22GPa, α = 54 × 10 ⁻⁶ ° C ⁻¹ . The curve in FIG. 22 shows an empirical curve that approximates the calculated data.

FIG. 22D is a graph showing the height between workpieces as a function of relative total pitch button area, according to one embodiment of the invention. FIG. Fig. 22D shows the case of 3 buttons and 9 buttons after PBB, where the spacing between the buttons is maintained at a value larger than 20 mm. The curve in FIG. 22D shows an empirical curve that approximates the calculated data.

23 is a simplified conceptual diagram illustrating pitch button coupling parameters according to an embodiment of the present invention. PBB parameters include the modulus (E _p and E _w ), the coefficients of thermal expansion (α _p and α _w ), and the thicknesses t _p and t _w of the pitch button and the workpiece, respectively. The PBB parameters also include the radius r _p of the pitch button, the radius r _{w of the} workpiece, the distance s between the center and the center between the pitch buttons, and the spacing d _m between the pitch buttons. The total number of pitch buttons is indicated by N. Pitch buttons may have uniform dimensions or various dimensions to suit a particular application. In this way, material and geometrical parameters are used in the methods and systems disclosed herein.

24A and 24B illustrate an optimized pitch button coupling pattern for an optical element, according to one embodiment of the invention. In FIG. 24A, an optimized PBB pattern is shown for a 100 mm diameter fused silica workpiece (ie, samples S18-S20). In FIG. 24B, the optimized PBB pattern is shown for a 100 mm diameter phosphate glass workpiece (samples P1-P2).

25A is a graph illustrating the height between workpieces as a function of the spacing between buttons, according to one embodiment of the invention. FIG. 25A shows the change in surface shape of fused silica workpieces (ie FS optical elements 100 mm diameter × 2.2 mm thick) in various PBB configurations using pitch materials as a function of button spacing d _m . 25B is a graph showing the height between workpieces as a function of area fraction, according to one embodiment of the invention. Changes in the surface shape of fused silica and phosphate glass workpieces (ie, workpieces 100 mm diameter × 2.2 mm thick) are shown as a function of area ratio for various PBB shapes (N = 11 and d _m > 20 mm). Figure 25b denote points in the measured data lines is α _p = 2.4x10 ^-6 ℃ ^- are approximated curve using the ^1.

FIG. 26 is a simplified flowchart illustrating a method of determining a pitch button combining parameter according to an embodiment of the present invention. The method includes a step 2610 of determining a height-to-high (PV) height value and a step 2612 of a value related to a pitch area. In one embodiment, the PV height value is the minimum allowable PV height (eg, 0.05 μm) measured as magnitude or the minimum allowable PV height (eg, λ / 10) measured as the wavelength of light transmitted by the optical element. Can be. The value related to the pitch area (also called the area constant) can be the PV height deviation (eg C = 1.0 μm) associated with the solid layer of approximately pitch. In some embodiments, the area constant C may be determined by measuring the PV height associated with the solid pitch layer and may include processing conditions (ΔT = 54 ° C.), thermal expansion coefficients (eg, α _p = 54 × 10 ⁻⁷ ° C. ⁻¹ ), modulus ( For example, it may be valid for a given material system based on E _p = 0.22 GPa), pitch thickness (t _p = 1.0 mm), and the like. In general, the values of area constants are sized as follows:

Is the change in coefficient of thermal expansion between the pitch and the workpiece material, ΔT is the temperature decrease from T _g to room temperature, and t _p is the pitch thickness. As will be apparent to those skilled in the art, for example, since phosphate glass has a higher coefficient of thermal expansion than fused silica, a change in pitch or workpiece can result in a change in C. It should be noted that fused silica deforms convexly, while phosphate glass deforms concavely. In some embodiments, it may be useful to maximize area coverage to increase the interface strength between the workpiece and the substrate.

The method also includes the step (2614) for calculating a pitch of the relative area (A _r), and the relative surface area is calculated as follows:

As an example, for PV _s = 0.05 μm and C = 1.0 μm, A _r = 0.05.

The method further comprises calculating 2616 a button radius r _p , wherein the button radius is calculated as follows:

In the above example, r _p = 3.4 mm for d _m = 23.1 mm.

In addition, the method includes calculating 2618 the number N of pitch buttons that are constantly spaced apart from each other. N pitch buttons are placed in the workpiece in accordance with the parameters calculated using the method to connect the pitch buttons to the workpiece (2620). As shown in FIG. 19B, the pitch buttons may be disposed on an adhesive and / or protective material such as a tape or other suitable material connected to the workpiece. The workpiece is then mounted 2622 by connecting the N pitch buttons to the substrate in an optical plane comprising a substrate, such as stainless steel, aluminum, or a combination thereof.

The specific steps shown in FIG. 26 provide a specific method of determining pitch button coupling parameters according to an embodiment of the present invention. In other embodiments, other sequences of steps may be executed. For example, another embodiment of the present invention may execute always steps in a different order. In addition, each of the steps shown in FIG. 26 may include a number of substeps that may be executed in various orders to suit individual steps. In addition, additional steps may be added or removed depending on the particular embodiment. Those skilled in the art will recognize many variations, modifications, and alternatives.

The examples and embodiments disclosed herein are merely for purposes of illustration and one of ordinary skill in the art would be able to derive various modifications or variations, and such various modifications or variations are the spirit of the present application. And scope, and it is to be understood that the appended claims are to be included.

Claims (32)

In a polishing system for polishing an optical element,
A polishing pad having a predetermined radial size; And
A partition on the polishing pad, the partition partially enclosing an optical element,
The optical element contacts the polishing pad over a predetermined range of the radial size, and the pad wear rate of the polishing pad is substantially constant as a function of the radial size over the predetermined range of the radial size,
Polishing system.
The method of claim 1,
And the optical element comprises a circular lens.
The method of claim 1,
Wherein,
Structural layers;
A compliance layer; And
A polishing system comprising a polishing layer.
The method of claim 3,
The structural layer has a higher density than the flexible layer or the polishing layer,
Polishing system.
The method of claim 3,
The optical element comprises an optical material and the polishing layer comprises the optical material,
Polishing system.
6. The method of claim 5,
And the optical material comprises fused silica.
The method of claim 1,
The polishing pad can accommodate a slurry comprising an abrasive component and an additive contained in a solvent,
Polishing system.
The method of claim 7, wherein
And the additive comprises a surfactant.
9. The method of claim 8,
And the surfactant comprises an anionic surfactant.
9. The method of claim 8,
And the surfactant comprises a cationic surfactant.
The method of claim 1,
A chamber surrounding the polishing pad,
And the chamber has a humidity above ambient humidity.
12. The method of claim 11,
And the humidity is substantially 100%.
The method of claim 1,
And the optical element is characterized by a height between elevations that is stabilized to a fixed value after a predetermined polishing time.
In the high humidity polishing system,
A polishing unit comprising a polishing pad;
A slurry supply system for providing a slurry to the polishing pad; And
An enclosure surrounding the polishing unit,
The humidity in the enclosure is high enough to prevent the slurry from becoming too dry.
High humidity polishing system.
15. The method of claim 14,
And the humidity is higher than the ambient humidity.
16. The method of claim 15,
Wherein the humidity is substantially 100%.
15. The method of claim 14,
And the slurry comprises a solvent, an abrasive component contained in the solvent, and an additive contained in the solvent.
15. The method of claim 14,
The polishing unit further includes a partition wall disposed in proximity to the polishing pad, the partition wall partially surrounds an optical element in contact with the polishing pad over a predetermined range of a radial size of the polishing pad, Pad wear rate is substantially constant as a function of radial size over the predetermined range of radial magnitude,
High humidity polishing system.
19. The method of claim 18,
And the slurry comprises a solvent, an abrasive component contained in the solvent, and a surfactant contained in the solvent.
A slurry system for polishing an optical element,
solvent;
Polishing components contained in the solvent; And
Surfactant in the Solvent
Slurry system comprising a.
21. The method of claim 20,
The solvent system comprises a solvent.
21. The method of claim 20,
And the polishing component comprises at least one of cerium oxide and Hastilite PO.
21. The method of claim 20,
Wherein said surfactant comprises an anionic surfactant.
24. The method of claim 23,
The anionic surfactant comprises at least one of μ-90 and ammonium lauryl sulfate.
21. The method of claim 20,
Wherein said surfactant comprises a cationic surfactant.
21. The method of claim 20,
Slurry system further comprising a chelator.
In the method of mounting the workpiece on the substrate,
Determining a height height value;
Determining a value related to the pitch area;
Calculating the relative area of the pitch;
Calculating a button radius;
Calculating the number of pitch buttons;
Coupling N pitch buttons to the workpiece; And
Connecting the N pitch buttons to the substrate
Workpiece mounting method comprising a.
28. The method of claim 27,
Wherein the inter-floor height value is based on a measurement of the inter-floor height associated with a solid pitch layer.
28. The method of claim 27,
And the relative area of the pitch is equal to the height between heights divided by the value related to the pitch area.
28. The method of claim 27,
And the spacing between the N pitch buttons is substantially uniform.
28. The method of claim 27,
Coupling the N pitch buttons to the workpiece comprises disposing N pitch buttons on a tape layer coupled to the workpiece.
28. The method of claim 27,
The workpiece comprises an optical element, the substrate comprising an optical plane,
How to mount the workpiece.

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