JP2004306155A - Polishing surface plate and correcting carrier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technical means for optimizing the friction distance characteristic of a surface plate exerting influence upon the working accuracy of a work in the polishing surface plate used in lapping or polishing a hard brittle plate or highly hard materials and its correcting carrier. <P>SOLUTION: The surface of the polishing surface plate or the correcting carrier are taken as a set of two or more virtual rings centering around the center of rotation, a required area of every virtual ring is computed so that the relative friction distances in the respective positions in the radial direction of a work are made uniform, the surface of each virtual ring has a contact surface with the work having the required area, a groove or a recessed part is provided in the surface of the polishing surface plate or the correcting carrier, or the size and arranging mode of a polishing pellet stuck to the surface plate is determined. Accordingly, even in the case of a small diameter, the polishing surface plate and the correcting carrier having excellent polishing characteristic can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polishing platen used for a lapping device or a polishing device having a structure in which a work is rotated and pressed against a surface of a surface plate (including a surface plate having abrasive pellets adhered to the surface), and a repair carrier thereof. For example, the present invention relates to a polishing platen suitable for use in lapping or polishing of a hard material such as a hard brittle plate or sapphire represented by a semiconductor wafer and a carrier for repairing the same.
[0002]
[Prior art]
In the manufacturing process of a semiconductor wafer, a semiconductor ingot is cut, a crack layer of the cut wafer is removed by lapping, the thickness is adjusted to a predetermined thickness, processing distortion is removed by chemical polishing such as etching, and then a mirror surface is formed by polishing. Processing completes the wafer.
[0003]
At present, a 4-way lapping machine is mainly used as a processing apparatus for performing flat lapping, which is one of the semiconductor wafer manufacturing processes. The four-way lapping machine is a lapping machine to which the rotation of the work, the planetary movement (revolution) of the work around the platen axis, and the rotations of the upper and lower platens in opposite directions are added. In processing with a lapping machine, the amount of processing is proportional to the processing pressure and the relative friction distance between the workpiece and the lapping plate, as also given by the Preston equation. Therefore, if the processing pressure is constant, the better the friction distance at each position on the work surface is, the better the parallel plane can be obtained. In a four-way lapping machine, the larger the lapping base plate is used compared to the work, the more the friction distance can be obtained in which the friction distance characteristics are evenly distributed in the work radial direction, and a better parallel plane can be obtained. The diameter ratio between the work of a general lapping machine and the surface plate is about 1: 4.
[0004]
On the other hand, there is a problem that the size of the lapping machine increases with the increase in the diameter of the wafer. There is a problem that the flatness of the wafer in the lapping is reduced due to the deformation of the wafer and that the work of removing the surface plate becomes difficult.
[0005]
In order to avoid an increase in the size of the lapping machine, a sheet-fed lapping machine that grinds works one by one has been proposed. In the single-wafer lapping machine, the diameter of the platen for the work is made smaller than that of the 4-way lapping machine. However, when the diameter of the platen is reduced, the friction distance characteristic is reduced, which is the same problem as the 4-way lapping machine.
[0006]
The lapping efficiency in lapping largely depends on the friction distance between the lapping plate and the wafer. In other words, lapping naturally requires higher processing efficiency and higher flatness of the wafer. To achieve this, the friction distance on the wafer surface must be increased, and the variation in the friction distance on the entire wafer surface must be reduced. It is necessary.
[0007]
The four-way lapping machine and the single-wafer lapping machine are used to polish a work on the surface of the surface plate itself. As a method of polishing a high-hardness material such as ceramics and sapphire, a processing method generally called diamond smoothing is used. Is used. This method is a processing method in which a large number of short columnar diamond grindstones called pellets are attached to the surface of a disk, and the disk is rotated while the workpiece is pressed against the pellets to polish the work. In general, a plate having no grooves for a lapping machine is used as a disk on which pellets are stuck, and the pellets are stuck on the surface at regular intervals to form a polishing platen.
[0008]
[Problems to be solved by the invention]
As one of means for solving the above-mentioned problem that the friction distance characteristic is reduced when the diameter of the lapping plate is reduced, a linear groove or a circumferential groove is provided on the outer peripheral side of the lapping plate to substantially reduce the outer peripheral portion of the lapping plate. It is considered effective to reduce the specific surface area (the area in contact with the work and contributing to the processing), thereby obtaining a uniform friction distance characteristic.
[0009]
Providing such a groove or recess for adjusting the area distribution on the surface of the surface plate is considered to be effective also in various types of lapping including a 4-way, 3-way lapping machine and the like. However, it is considered that any concave portion that does not contact the work may be used. Further, in the case of polishing, it is considered that an isolated recess may be used. On the other hand, as a problem when providing such a recess, what is to be provided and what area ratio is to be provided becomes a problem. If it is not provided in a rational manner, the friction distance characteristics may be deteriorated.
[0010]
This is also applicable to the above-described processing using the polishing platen to which the diamond pellets are attached, and the gap between the attached pellets becomes a recess formed on the polishing surface. In order to make the friction distance at the position uniform and to flatten the processed surface, it is important to determine the size of the pellets and the arrangement of the pellets.
[0011]
The present invention was made as a result of a test study for examining how to provide grooves or recesses for adjusting the area distribution for uniformly polishing the work on the surface of the surface plate. It is an object of the present invention to provide a technical means for optimizing a friction distance characteristic of a surface plate which affects accuracy.
[0012]
[Means for Solving the Problems]
In the present invention, the surface of the polishing platen or the correction carrier is regarded as an aggregate of a plurality of virtual rings centered on the rotation center, and each position in the radial direction of the work (in the case of the correction carrier, the polishing platen becomes the work). The required area of each virtual ring is calculated so that the relative friction distance is uniform, and the surface of each virtual ring is provided with a contact surface with the work having the required area. The above-mentioned problem is solved by providing grooves or recesses on the surface or determining the size and arrangement of the abrasive pellets to be attached to the surface plate.
[0013]
For the calculation of the required area for each virtual ring, various calculation methods or algorithms such as a neural network and a cellular automaton can be used. It is possible to improve it.
[0014]
According to the present invention, it is possible to provide a polishing platen for various types of lapping, polishing or smoothing, and a correction carrier for these platens, which have excellent polishing characteristics even with a small diameter.
[0015]
Therefore, the polishing surface plate according to the invention of claim 1 of the present application is a polishing surface plate for lapping or polishing, in which each surface ring is divided into a plurality of virtual rings centering on the rotation center of the surface surface, This is a polishing table provided with grooves or recesses for adjusting the area distribution at different area ratios so as to equalize the relative friction distance in the radial direction of the work due to relative movement with the table.
[0016]
Further, in the polishing platen in which a large number of diamond pellets or other polishing pellets are adhered to the platen surface, when the platen surface is divided into a plurality of virtual rings centered on the rotation center as described in claim 2, The pellets are adhered to each virtual ring at a different ratio of the area of the pellet surface to the surface of the surface plate for each virtual ring so as to equalize the relative friction distance in the radial direction of the work due to the relative movement with the surface plate. It is that.
[0017]
The invention according to claim 3 is characterized in that the area ratio in the polishing platen is determined using a genetic algorithm in which each virtual ring is an individual or an individual group.
[0018]
In the polishing platen according to the invention of claim 4 of the present application, the ratio of the area in contact with the work to the apparent surface area of the platen is in a region inside a circle having a radius of approximately 1/2 of the outer peripheral radius of the platen. A polishing surface plate in which grooves or recesses for area distribution adjustment are arranged so as to be constant and gradually decrease as the distance from the center of the surface plate increases in a region outside the circumference. .
[0019]
Further, in the polishing platen according to the invention of claim 5, the ratio of the area of the polishing pellet to the area of the platen is constant in a region inside a circumference having a radius of about 1/2 of the outer peripheral radius of the surface plate, In a region outside the circumference, the polishing platen is provided with the pellets so that the pellets are gradually reduced as the distance from the center of the platen increases.
[0020]
The invention according to claims 6 and 7 relates to a repair carrier for a polishing platen, and the repair carrier according to the invention according to claim 6 has a plurality of dressing surfaces facing a polishing platen centered on the rotation center thereof. When forming an aggregate of virtual rings, the grooves for adjusting the area distribution at a different area ratio in each virtual ring so that the relative friction distance at each position in the radial direction of the polishing platen with respect to the dress surface becomes uniform. It is a polishing carrier of a polishing platen provided with a recess.
[0021]
The invention according to claim 7 is characterized in that the area ratio in the modified carrier is determined using a genetic algorithm in which each virtual ring is an individual or an individual group.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 2 shows, as an example of the friction distance characteristic of the single-wafer lapping machine, the radius of the platen Rlap = 200 mm, the radius of the work Rwork = 125 mm, the angular velocity of the platen ωlap = π / 3 rad / s, and the angular velocity of the work ωwork = π / shown in FIG. FIG. 9 is a diagram illustrating a calculation result of a friction distance at each radial position (horizontal axis) of the work when 4 rad / s and the amount of eccentricity between the surface plate and the work xn = 25 mm. In this example, a wafer is used as the workpiece, and the friction distance ratio on the right side of the vertical axis in FIG. 2 is a ratio using the friction distance at the center of the wafer (r = 0 mm) as a reference value. As shown in FIG. 2, at the center and edge of the wafer (r = 125 mm), there is about 4.5% deviation in the friction distance.
[0023]
Regarding the influence of the diameter ratio and the rotation speed ratio of the polishing surface plate and the work on the deviation of the friction distance, the rotation amount ratio of the surface plate and the work is closer to 1, and the larger the diameter ratio, the smaller the deviation amount. It has been confirmed by the study of the present inventor. However, as described above, increasing the diameter ratio means increasing the diameter of the platen, and increasing the size of the apparatus.
[0024]
It is presumed that by providing grooves on the surface of the polishing platen at appropriate positions, it is possible to reduce the deviation of the friction distance of the work and improve the polishing efficiency. That is, it is considered effective to determine and determine the position and size of the slurry supply groove or recess from the viewpoint of suppressing the deviation of the friction distance.
[0025]
Therefore, when providing grooves on the polishing platen, as a method of determining the position and size of the groove that optimizes the friction distance characteristic on the work surface, a plurality of virtual surfaces around the rotation center of the surface of the polishing platen are used. The required area of each virtual ring is calculated so that the relative friction distance between the surface of the work and the surface of the platen at each radial position of the workpiece is uniform, and the surface of each virtual ring becomes the required area. Determine the radial position and area of the groove or recess so as to provide a contact surface with the workpiece, and as a means of calculation, evolve the organism by repeating divergence, crossover, and mutation. By applying a genetic algorithm expressed mathematically (GA: Genetic Algorithm; hereinafter, abbreviated as "GA"), an attempt was made to uniform the friction distance characteristics on the work surface. One example is described below.
[0026]
GA is an algorithm that mathematically grasps the evolution of living organisms and searches for the optimal solution. As shown in FIG. 3, selection, crossover, and mutation are performed on the genome of one generation composed of N chromosomes. The generation change is repeated successively while performing. At this time, one chromosome is considered to be composed of M genes, and the fitness fkn is calculated from the value assigned to each chromosome.
[0027]
When this is applied to the optimization problem of the polishing table, the following numerical expression in the gene is defined. That is, when the numerical value of the gene is in the range of 0 to 1 and the polishing platen is apparently considered as a set of M virtual rings as shown in FIG. The ratio of the portion having no groove was defined as the gene value gkm. Assuming that the numerical value gkm of the gene in the m-th virtual ring is 0.70, it means that this ring is provided with a groove or a recess having an area ratio of 30%. In the case of the pellet-attached surface plate, it means that the pellets are attached to a region of 70% in the area ratio of the virtual ring.
[0028]
At this time, it is necessary to first confirm the lap efficiency of each apparent ring in the surface plate. For example, when M = 4, the polishing platen is considered to be composed of four virtual rings, but under the same conditions as in FIG. 2, the lap of the first ring # 1 to the fourth ring # 4 The result of calculating the efficiency is shown in FIG. In addition, the line described as the sum is the sum total of the rings # 1 to # 4. If the gene of ring # 1 is 0.70, the wrap efficiency of ring # 1 is 70% as indicated by the dotted line in FIG.
[0029]
With such a method, various conditions in the GA were determined as follows regarding the groove arrangement on the surface of the surface plate, which is one of the optimization problems of the shape of the lap surface plate.
a) The conditions for the basic single-wafer lap method were the same as the conditions when the results of FIG. 2 were obtained, which showed a relatively large friction distance and a small deviation of the friction distance.
b) The degree of decomposition of the gene value was set to 0.01.
c) The fitness of each chromosome was defined as the fitness of the friction distance.
d) In selection, half of the chromosomes (N / 2) having high fitness were selected from the N chromosomes, and the other half were selected according to the roulette rule method.
e) In the crossover, the crossover probability was set to Pc, and the crossover positions were determined by generating random numbers, assuming each crossover combination was independent.
f) Mutation was randomly generated from N × M genes in one genome, with the mutation probability as Pm. At this time, the ratio of the non-grooved portion as a numerical value in the mutated gene was determined by random number generation.
[0030]
FIG. 6 shows an example of a result calculated by the above-described setting for the groove arrangement problem of the polishing platen by the GA. FIG. 6 shows the minimum deviation of the friction distance as the fitness of each of the N chromosomes in each generation. It shows how the value changes with the generation change by GA.
[0031]
FIG. 7 shows the friction distance characteristics at the 5000th generation, which is the last generation in the above calculation. As described above, the calculation conditions are as described above, the platen radius Rlap = 200 mm, the work radius Rwork = 125 mm, the platen angular velocity ωlap = π / 3 rad / s, the work angular velocity ωwork = π / 4 rad / s, and the eccentricity of the platen and the work. The quantity xn = 25 mm, the number of chromosomes N = 20, the number of genes on each chromosome M = 24, the crossover probability Pc = 0.25, and the mutation probability Pm = 0.01. As described above, by performing the calculation by GA up to about 5000 generations, the deviation is about 0.5% compared to the case where no groove is provided (the deviation of 4.5% shown in FIG. 2). Thus, the deviation can be significantly reduced.
[0032]
FIG. 8 illustrates the gene values of the chromosomes at the 5000th generation, and this is the set value of the work contact area ratio on the surface of the lap plate of the above-described embodiment using GA. That is, for example, in the range of R9 <R <R10 as the tenth ring, it is preferable to provide a groove of about 7%. In the case of a pellet sticking surface plate, it is sufficient to stick the pellet so that the area ratio of the pellet is about 93%.
[0033]
In the results of the GA up to this point, the calculation is performed assuming that grooves or recesses are provided in all virtual rings as shown in FIG. However, even if grooves are actually provided on the lapping plate, it is considered that increasing the number thereof is not so preferable in manufacturing the lapping plate. Therefore, in the central part of the lap surface plate, that is, in the region where the ring number is small in the lap surface plate, the gene was set to 1 and no groove was formed, thereby verifying the effect of the improvement at that time. FIG. 9 shows the result. It should be noted that the results shown in the figure represent the average value of the fitness at the 5000th generation obtained by performing the GA calculation of the 5000th generation 50 times and performing each trial calculation. Also in this case, the total number of rings M is set to 24. For example, in the case of 5 on the horizontal axis, it means that all the rings 1 to 5 have no groove.
[0034]
As shown in FIG. 9, assuming that no groove is provided near the center of the surface plate, it is better to provide no groove until 0 <R <Rlap / 2 for the surface plate of radius Rlap. I understand. In addition, although not shown in the figure, it was also found that conversely, forming all the grooves in the center portion (for example, making holes so as not to contact the work) adversely affects the deviation of the friction distance.
[0035]
FIG. 10 and FIG. 11 show friction distance characteristics obtained when the optimization calculation by GA is performed under the same conditions as above without providing grooves or recesses in the first to eleventh rings, Also, the values of genes on the chromosome at the last 5000th generation are shown. Here, 11/24 is a value at which the graph of FIG. 9 shows the minimum value. In this way, as shown in FIG. 11, no groove or recess for adjusting the wear distance characteristic is provided from the center of the surface plate to approximately 1/2 of the outer radius, and the area of the surface that comes into contact with the workpiece on the outer peripheral side is not provided. By using a surface plate distributed in a direction in which the ratio decreases as the radius increases, a much better lapping process can be performed in which the deviation of the friction distance is about 0.1% as shown in FIG. .
[0036]
FIG. 12 is a plan view showing an example of the groove arrangement of the lap surface plate obtained from the above test results. The grooves a and b shown by grid lines at equal intervals in the vertical and horizontal directions are grooves for supplying slurry. Since the grooves a and b are provided uniformly on the surface of the surface plate, the wear distance characteristics are not changed. In other words, the area where only the lattice-shaped grooves a and b are provided is an area where no grooves or recesses for equalizing the friction distance are provided. On the other hand, the circular groove c and the radial straight groove d provided outside the circumference having a radius of 11/24 of the outer radius of the platen shown in the figure are used for adjusting the area distribution for equalizing the friction distance. It is a groove.
[0037]
This area distribution adjusting groove is such that, in each of the virtual rings obtained by dividing the surface of the surface plate into 24 equal parts, the area ratio of the surface actually in contact with the work to the area of the part excluding the slurry supply grooves a and b is: They are arranged so as to have the ratio shown in FIG. Specifically, from the results of FIG. 12, the area of the first to eleventh virtual rings is not provided with the area distribution adjusting groove, and the area of the twelfth virtual ring is excluding the slurry supply groove. Similarly, so that the ratio of the surface contacting the workpiece with respect to is 0.996%.
0.994% in the 13th area,
0.989% in the 14th area,
0.984% in the fifteenth area,
0.981% in the 16th area,
0.974% in the 17th area,
0.966% in the 18th area,
0.962% in the 19th area,
0.955% in the 20th area,
0.949% in the 21st area,
0.943% in the 22nd area,
0.935% in the 23rd area,
0.929% in the outermost 24th area,
The circular groove c and the straight groove d are arranged such that
[0038]
The above is intended to equalize the relative friction distance by forming a groove or a recess on the surface of the surface plate. In the case of a pellet-attached surface plate, for example, the diameter of the pellet to be attached is assumed to be a ring width. The surface of the platen is divided by a ring, the polishing area of each virtual ring required to obtain the optimal friction distance characteristics is obtained using a calculation method such as GA, and the pellet is attached so that the obtained area is obtained. Thus, an optimal polishing platen can be obtained.
[0039]
Note that, in the above embodiment, an example of a single-wafer lapping plate in which the platen and the work make a rotational movement has been described, but a 4-way lapping plate in which the work revolves, as well as a platen diameter smaller than the work diameter. Also, in the case of motion such as superimposing oscillating motion on rotation or revolution, the surface of the surface plate is formed with a plurality of virtual rings so that the relative friction distance in the radial direction of the workpiece to be processed is uniform. By calculating the required area ratio for each virtual ring when divided using GA or another algorithm, by providing a groove or a recess on the surface of the surface plate so that each virtual ring has such an area ratio, It is possible to carry out optimization design of the polishing table and the repair carrier.
[0040]
【The invention's effect】
As described above, by determining the groove shape of the lap surface plate using the genetic algorithm (GA), it is possible to significantly improve the friction distance characteristics of the lapping process. Further, in a region radially inward from a substantially middle of the outer peripheral radius of the lap surface plate, there is no groove or a groove required for slurry supply, and a groove or a recess for area distribution adjustment is provided in a portion outside the groove. By providing such that the area ratio gradually increases, an optimum friction distance characteristic can be obtained. As a result, in a lapping machine, in particular, in a single-wafer lapping machine, there is an effect that a lapping machine capable of performing high-precision machining with a small-diameter platen can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic plan view showing a platen for single-wafer lapping and a work. FIG. 2 A change in friction distance in a work radial direction when a platen having no grooves or recesses for area distribution adjustment is used. FIG. 3 is an explanatory diagram of an operation using a genetic algorithm. FIG. 4 is an explanatory diagram showing an example of applying a genetic algorithm to the operation of a polishing surface plate. FIG. 6 shows a calculation result of a friction distance of each ring with respect to a work when divided into rings. FIG. 6 shows a convergence state of an adaptive function by a genetic algorithm. FIG. 7 shows a first example optimized by the present invention. FIG. 8 is a diagram showing a friction distance characteristic of a polishing table. FIG. 8 is a diagram showing an area distribution in a radial direction of the polishing table having the friction distance characteristic of FIG. 7. FIG. FIG. 10 shows a change in the friction distance characteristic when no recess is provided. FIG. 11 is a view showing a friction distance characteristic of the polishing table of the second example optimized by the method. FIG. 11 is a view showing an area distribution in a radial direction of the polishing table having the friction distance characteristic of FIG. 10. FIG. Schematic plan view showing an example of a polishing platen provided with grooves and grooves for requesting an area distribution value

Claims (7)

On a polishing surface plate for lapping or polishing, when the surface of the surface plate is divided into multiple virtual rings centered on the center of rotation, the relative friction distance in the workpiece radial direction due to relative motion with the surface plate is uniform on each virtual ring. Polishing surface plate provided with grooves or recesses for adjusting the area distribution at different area ratios. In the polishing platen where a large number of abrasive pellets are adhered to the surface plate surface, when the surface plate surface is divided into a plurality of virtual rings centered on the rotation center, each virtual ring has a work radial direction due to relative motion with the surface plate. A polishing platen on which the pellets are adhered with different ratios of the area ratio of the pellet surface to the platen surface of each virtual ring so as to make the relative friction distance uniform. 3. The polishing table according to claim 1, wherein the area ratio is determined using a genetic algorithm in which each virtual ring is an individual or an individual group. The ratio of the area in contact with the work to the apparent surface area of the surface plate is constant in a region inside the circumference having a radius of approximately 1/2 of the outer radius of the surface plate, and constant in the region outside the circumference. A polishing platen in which grooves or recesses for adjusting area distribution are arranged so as to gradually decrease as the distance from the center of the plate increases. The ratio of the area of the polishing pellet to the area of the surface plate is constant in a region inside a circumference having a radius of approximately 1/2 of the outer circumference of the surface plate, and in a region outside the circumference, A polishing platen on which the pellets are arranged so as to gradually decrease as the distance from the center increases. When the dress surface facing the polishing platen is an aggregate of a plurality of virtual rings centered on the rotation center, the relative friction distance at each position in the radial direction of the polishing platen with respect to the dress surface becomes uniform. As described above, the correction carrier of the polishing platen, in which grooves or recesses for adjusting the area distribution are provided at different area ratios in each virtual ring. 7. The modified carrier according to claim 6, wherein the area ratio is determined using a genetic algorithm in which each virtual ring is an individual or an individual group.

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