JP2009028815A - Lapping slurry managing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lapping slurry managing method capable of extending a reuse period of lapping slurry. <P>SOLUTION: In this lapping slurry managing method, lapping slurry containing abrasive grains and a lapping liquid is supplied to a double face lapping machine, and used lapping slurry is circulated and reused while being filtered. The regeneration processing of the lapping slurry constituted of each of the following processes is performed for each work batch. A first process of takes out 10-30% of lapping slurry out of an entire content of the used lapping slurry, a second process supplements the lapping liquid equal to 10-20% of the entire content of the lapping slurry, a third process supplements abrasive grains equal to 20-40% of an initial injection amount, and a fourth process uniformly disperses the abrasive grains in the lapping liquid. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a double-sided lapping machine for lapping both surfaces of a wafer having high hardness such as a sapphire single crystal, and more particularly to a method for managing a lapping slurry supplied to the machine.

  Conventionally, a lapping machine has been used as an apparatus for polishing the surface of a wafer (see Non-Patent Document 1). Hereinafter, a double-sided wrapping machine will be described as an example. As shown in FIG. 1, the wafer W, which is a workpiece, is placed on the upper and lower polishing surface plates (usually, polishing cloths and the like are respectively attached to the opposing surfaces). 1) Abrasive grains (usually composed mainly of fine particles such as aluminum oxide and silicon carbide) 10 and lapping liquid (usually mineral oil, water, dispersant, etc.) The wrapping slurry containing the additive) is supplied between the polishing surface plates 1 and 2 and the wafer W, and the both surfaces of the wafer W are polished by sliding while applying pressure to both. Has been. In addition, as shown in FIG. 2, the lapping slurry used in the lapping machine is filtered to remove impurities such as chips that cause damage to the wafer surface, and the abrasive grains and lapping liquid from which impurities have been removed are slurried. The wrapping slurry is returned to the tank and circulated for reuse.

Note that the wrapping slurry that has been reused many times and exceeds the use limit is filtered by a filtration facility, and only the lap liquid is recovered and reused. Further, it has been common to dispose of solids made up of impurities such as abrasive grains and their crushed particles and chips as waste, or after being repeatedly used for a certain period of time.
Pages 27-31 of "Semiconductor Material Processing and Equipment" published by Metal Tokiwasha

  By the way, when both sides of a high-hardness wafer such as sapphire single crystal are lapping processed, the workpiece itself is a very hard substance, so compared with the case of processing a relatively soft material such as a compound semiconductor. Degradation of the material occurs rapidly, and the processing rate (polishing rate) decreases and the shape of the processed surface deteriorates rapidly due to the deterioration of the wrapping slurry.

  For this reason, the reuse period of the wrapping slurry is shortened, and it is necessary to frequently replace the wrapping slurry, the work man-hour is increased, the yield rate is deteriorated, and the productivity is extremely lowered. There was a problem that caused the production cost to increase.

  The present invention has been made paying attention to such problems, and the object of the present invention is to provide a management method of a wrapping slurry that can extend the reuse period of the wrapping slurry.

  In order to solve the above-mentioned problems, the present inventor observed the change in the particle size distribution and the shape of the abrasive grains in the wrapping slurry, and analyzed the relationship with the deterioration of the wrapping slurry related to reuse, and created a solution to the problem. Tried.

  And, as a result of the above observation, when double-sided lapping is performed on a wafer with high hardness such as a sapphire single crystal, the destruction and wear of abrasive grains proceed in a shorter time than when processing relatively soft materials, and the grain size of the abrasive grains It is confirmed that the distribution change (center value shift of particle size distribution, half-width expansion) and the shape change of the abrasive grains (the edges of the abrasive grains are rounded) are occurring rapidly, and these abrasive grains It has been found that the efficiency of the polishing process is extremely lowered due to the change in the particle size distribution and the shape change, resulting in a decrease in the processing rate and a deterioration in the shape of the processed surface.

  Therefore, after undergoing such a technical analysis, the present inventor conducted an earnest experiment to find a technique for preventing the deterioration of the wrapping slurry that is circulated and reused. It came to discover the management method of the wrapping slurry in which the change is minimized. The present invention has been completed by such technical discovery.

That is, the invention according to claim 1
A method for managing a lapping slurry that supplies a certain amount of lapping slurry containing abrasive grains and lapping liquid to a double-sided lapping machine that lapping both sides of the wafer, and circulates and reuses the lapping slurry used. Assuming
When the unit of wafers that can be lapped at one time is defined as one batch,
The lapping slurry constituted by the following first to fourth steps is regenerated for each processing batch.
(1) First step of extracting 10-30% of the total volume of the lapping slurry from the used lapping slurry,
(2) a second step of replenishing the lapping liquid corresponding to 10 to 20% of the total volume of the wrapping slurry;
(3) a third step of replenishing abrasive grains corresponding to 20 to 40% of the initial charging amount;
(4) A fourth step of uniformly dispersing the abrasive grains in the lapping liquid.

Next, the invention according to claim 2
Based on the management method of the wrapping slurry according to the invention of claim 1,
The wafer is a sapphire single crystal wafer, and the abrasive grains are SiC abrasive grains,
The invention according to claim 3
Based on the management method of the wrapping slurry according to the invention of claim 1 or 2,
The particle size distribution measurement of the abrasive grains in the wrapping slurry before the regeneration treatment is performed, and when the half width exceeds 40 μm, all of the wrapping slurry is replaced.

According to the management method of the wrapping slurry according to the invention of claim 1,
(1) First step of extracting 10-30% of the total volume of the lapping slurry from the used lapping slurry,
(2) a second step of replenishing the lapping liquid corresponding to 10 to 20% of the total volume of the wrapping slurry;
(3) a third step of replenishing abrasive grains corresponding to 20 to 40% of the initial charging amount;
(4) a fourth step of uniformly dispersing the abrasive grains in the lapping liquid,
The regeneration process of the wrapping slurry constituted by each step is performed for each processing batch.

  Then, a part of the used lapping slurry is removed in the first step, fresh wrap liquid and abrasive grains are replenished in the second step and the third step, and abrasive grains are added to the lap solution in the fourth step. Is uniformly dispersed, it is difficult for the grain size distribution change and shape change of the abrasive grains in the wrapping slurry to occur, and the reuse period of the wrapping slurry can be extended.

  For this reason, it is not necessary to frequently replace the wrapping slurry, so that workability can be improved, and the yield rate can be improved by reducing the processing rate and the shape deterioration of the processed surface, thereby improving the productivity. .

  Embodiments of the present invention will be described in detail.

First, the lapping slurry management method according to the present invention supplies a fixed amount of lapping slurry containing abrasive grains and lapping liquid to a double-sided lapping machine that lapping both surfaces of a wafer, and filters the lapping slurry used. In the management method of the wrapping slurry that is circulated and reused,
When the unit of wafers that can be lapped at one time is defined as one batch,
The regeneration process of the wrapping slurry constituted by the following first to fourth steps is performed for each processing batch.
(1) First step of extracting 10-30% of the total volume of the lapping slurry from the used lapping slurry,
(2) a second step of replenishing the lapping liquid corresponding to 10 to 20% of the total volume of the wrapping slurry;
(3) a third step of replenishing abrasive grains corresponding to 20 to 40% of the initial charging amount;
(4) A fourth step of uniformly dispersing the abrasive grains in the lapping liquid.

  Hereinafter, the wrapping slurry management method according to the present invention will be described in more detail with reference to the drawings. As in the prior art, the wrapping slurry used in the wrapping machine is filtered to remove impurities such as chips. The abrasive grains and the lapping liquid from which impurities have been removed are returned to the slurry tank and circulated for reuse of the lapping slurry. Then, before the predetermined lapping process is completed and the next batch process is started, the regeneration process of the lapping slurry is performed.

  That is, as shown in FIG. 3, 10 to 30% of the used wrapping slurry is extracted from the slurry tank, and the particle size distribution of the abrasive grains in the wrapping slurry extracted by SEM (Scanning Electron Microscope). When the measurement is made and the half width of the particle size distribution does not exceed 40 μm, the lapping liquid corresponding to 10 to 20% of the total volume of the wrapping slurry and the abrasive grains corresponding to 20 to 40% of the initial charging amount Each of the above slurry tanks is replenished, and the abrasive grains are uniformly dispersed in the lapping liquid in the slurry tank, and then the next batch lapping is performed. As a result of the particle size distribution measurement, when the particle size distribution of the initially introduced abrasive grains changes and the half width exceeds 40 μm, all of the wrapping slurry is replaced with a new wrapping slurry for the following reason.

  Here, if the amount of the used wrapping slurry withdrawn is less than 10% of the total capacity, the amount of withdrawn is too small to secure a replenishment amount of new abrasive grains and lapping liquid. The correction effect cannot be obtained for the range expansion. Furthermore, when the extraction amount is less than 10% of the total capacity, it is not possible to sufficiently obtain the effect of removing the worn particles that cause the half-width expansion in the particle size distribution. On the other hand, when the amount of used wrapping slurry withdrawn exceeds 30% of the total capacity, the amount of withdrawn is large, so it is necessary to increase the replenishment amount of new abrasive grains and lapping liquid, and the cost performance decreases. Further, the effect of further improving the processing rate and the surface quality accompanying the increase in the replenishment amount cannot be expected. In general, the lapping slurry requires that the abrasive grains and the lapping liquid are uniformly dispersed. If the slurry is not uniformly dispersed, the processing rate is lowered and the surface quality is adversely affected. For this reason, if the used lapping slurry is extracted in a large amount exceeding 30%, it is difficult to uniformly disperse the abrasive grains and the lapping liquid. Therefore, it is necessary that the used wrapping slurry is withdrawn in an amount of 10 to 30% of the total volume.

  Filtering of used wrapping slurry affects the life of the wrapping slurry, and at the same time, removes wafer debris generated during polishing and chips from the polishing surface plate to suppress the generation of scratches on the wafer surface and improve yield. There is an effect to make.

  Next, replenishment of new abrasive grains and lapping liquid is performed in order to correct the particle size distribution of the used lapping slurry, which has changed with reuse, to the initial appropriate value. And the particle size distribution which changed by throwing in a large amount of new abrasive grains and lapping liquid can be sufficiently corrected. However, the balance with the cost is also important with respect to the input amount, and a sufficient correction effect and sufficient cost performance cannot be obtained even if the amount is replenished in a larger amount than the above range. That is, when the replenishing amount of the abrasive grains is less than 20% of the initial charging amount, the center value shift of the particle size distribution cannot be corrected appropriately, and the effect on the processing rate and the surface quality is hardly obtained. On the other hand, when the replenishment amount of abrasive grains exceeds 40% of the initial input amount, the effect of correction accompanying the input increases, but sufficient cost performance cannot be obtained. Therefore, it is necessary to replenish abrasive grains corresponding to 20 to 40% of the initial charging amount, and for the same reason, it is necessary to replenish lapping liquid corresponding to 10 to 20% of the total volume of the wrapping slurry.

  In addition, the wrapping slurry inevitably deteriorates due to the fine particles of the sapphire single crystal wafer and other chips and abrasive grains as the reuse period becomes longer, and adversely affects the surface quality such as deterioration of flatness. And when the half-value width of the particle size distribution in the wrapping slurry exceeds 40 μm, the initial state (the shape of the abrasive grains, the particle size distribution, etc.) even if the regeneration treatment of the wrapping slurry composed of the first step to the fourth step is performed. It will be difficult to return to For this reason, the particle size distribution of the extracted wrapping slurry is measured, and when the half width of the particle size distribution exceeds 40 μm, it is necessary to replace all of the wrapping slurry with a new wrapping slurry.

  Hereinafter, the present invention will be described specifically by way of examples.

  A lapping slurry in which the SiC abrasive grains were uniformly dispersed was prepared by adding 17 liters of lapping liquid and 9 kg of SiC abrasive grains to the slurry tank shown in FIG.

  Further, during the lapping process, the lapping slurry is recirculated and reused while the SiC abrasive grains are uniformly dispersed in the slurry tank by the stirring blades and filtered by the filter. At this time, the amount of slurry supplied to the wrapping machine was 5 liters / min.

  Under this condition, double-sided lapping of the sapphire single crystal wafer was performed. The lapping time for one batch was 90 minutes. Further, the processing rate (polishing rate) at this time was 0.7 μm / min, the thickness variation (TTV) in the wafer surface was 2 μm, and the surface roughness (Ra) was 0.89 μm. It was.

  After finishing the lapping of the first batch, 4 liters of slurry was extracted from the used wrapping slurry in the slurry tank and replenished with 2 liters of lapping solution and 3 kg of SiC abrasives to regenerate the wrapping slurry. .

  Then, a double-sided lapping process for 90 minutes was performed on the second batch of sapphire single crystal wafer under the same conditions as the first batch.

  The processing rate (polishing rate) of the second batch is 0.7 μm / min, the thickness variation (TTV) in the wafer surface is 3 μm, and the surface roughness (Ra) is 0.84 μm. Compared to the first batch It was stable.

  After finishing the second batch of lapping, the lapping slurry regeneration process was repeated for each processing batch, and repeated lapping was performed for a total of 10 batches (900 minutes).

  As a result, even in the lapping process of the 10th batch, the processing rate (polishing rate) is 0.8 μm / min, the thickness variation (TTV) in the wafer surface is 5 μm, and the surface roughness (Ra) is 0.84 μm. Compared to the lapping process of the first batch, the processing rate and the surface roughness were hardly changed and were very stable.

  However, the thickness variation (TTV) in the wafer surface tended to increase, and the half-value width of the particle size distribution exceeded 40 μm at the 10th batch as shown in the graph of FIG. Therefore, the full width at half maximum is 40 μm and the entire slurry is exchanged.

  The wrapping process and the wrapping slurry regeneration process were repeated 3 cycles, and the stability was confirmed. As shown in Table 1 below, the same results were obtained.

  In Table 1, “Rate” indicates the processing rate (polishing rate), “Parallel” indicates the thickness variation (TTV) in the wafer surface, and “Roughness (Ra)” indicates the surface roughness (Ra). .

［比較例１］
粒度分布の半値幅が１０バッチ目で４０μｍを超えないようにするため、実施例１におけるラッピングスラリーの再生処理条件を変更して、実施例１と同様のラッピング加工とラッピングスラリーの再生処理を行った。

[Comparative Example 1]
In order to prevent the half-value width of the particle size distribution from exceeding 40 μm at the 10th batch, the lapping slurry regeneration processing conditions in Example 1 were changed, and lapping processing and lapping slurry regeneration processing similar to Example 1 were performed. It was.

  That is, the amount of slurry extracted from the used wrapping slurry is set to be larger than 4 liters, and the replenishment amount of the lapping liquid and SiC abrasive grains is also set to be larger than that of the first embodiment (that is, the replenishing amount of the lapping liquid is lapping) The amount of slurry exceeding 20% of the total volume and the amount of SiC abrasive replenishment set to an amount exceeding 40% of the initial charged amount were respectively set), and lapping processing similar to Example 1 and lapping slurry regeneration processing were performed. .

  The half width of the particle size distribution did not exceed 40 μm at the 10th batch (900 minutes). However, when the reuse time of the wrapping slurry exceeded 1000 hours, the above half width had exceeded 40 μm.

  As a result, it was possible to slightly extend the reuse time of the wrapping slurry from Example 1 by increasing the replenishment amount of the lapping liquid and the abrasive grains, but a further effect commensurate with the increased amount could not be expected.

  That is, it was confirmed that even if the lapping liquid and the abrasive grains were replenished in an excessive amount, it was not possible to obtain a sufficient correction effect and a sufficient cost performance corresponding to a large amount of replenishment.

  According to the management method of the wrapping slurry according to the present invention, it is not necessary to frequently replace the wrapping slurry, so that the workability can be improved, and the reduction of the processing rate and the deterioration of the shape of the processing surface are prevented, and the yield rate is reduced. Improvements can be made and productivity can be improved.

  Therefore, it has industrial applicability applied to polishing methods for sapphire single crystal wafers and the like.

The schematic block diagram of a double-sided wrapping machine. Explanatory drawing which shows the management method of the conventional wrapping slurry. Explanatory drawing which shows the management method of the wrapping slurry of this invention. The graph which shows the relationship between the frequency | count of repeated use of a lapping slurry, and the change of the half value width in the particle size distribution of the abrasive grain in used slurry.

Explanation of symbols

1 Upper polishing surface plate 2 Lower polishing surface plate 10 Abrasive grain W Wafer

Claims (3)

In a lapping slurry management method, a fixed amount of lapping slurry containing abrasive grains and lapping liquid is supplied to a double-sided lapping machine that lapping both sides of the wafer, and the lapping slurry used is circulated and reused while filtering. ,
When the unit of wafers that can be lapped at one time is defined as one batch,
A method for managing a wrapping slurry, wherein a regeneration process of the wrapping slurry constituted by the following first to fourth steps is performed for each processing batch.
(1) First step of extracting 10-30% of the total volume of the lapping slurry from the used lapping slurry,
(2) a second step of replenishing the lapping liquid corresponding to 10 to 20% of the total volume of the wrapping slurry;
(3) a third step of replenishing abrasive grains corresponding to 20 to 40% of the initial charging amount;
(4) A fourth step of uniformly dispersing the abrasive grains in the lapping liquid.   The wrapping slurry management method according to claim 1, wherein the wafer is a sapphire single crystal wafer, and the abrasive grains are SiC abrasive grains.   The lapping slurry according to claim 1 or 2, wherein the particle size distribution measurement of the abrasive grains in the wrapping slurry before the regeneration treatment is performed, and when the half width exceeds 40 µm, all of the wrapping slurry is replaced. How to manage slurry.

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