JP2010284743A - Method for cutting workpiece - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cutting a workpiece capable of simply and effectively preventing occurrence of warp in cutting a cylindrical workpiece by a wire saw. <P>SOLUTION: The method for cutting a workpiece into wafers by pressing the cylindrical workpiece against a row of wires formed by winding a wire spirally between a plurality of wire guides and running the wire while supplying slurry to a contact area between the workpiece and the wire includes steps of heating, before cutting, the workpiece to a temperature higher than that of the slurry to be supplied before cutting starts and lower than the highest temperature of the workpiece reached during the cutting of the workpiece, and then cutting the workpiece. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for cutting a workpiece into a wafer by a wire saw.

  A wire saw presses a workpiece against a wire array spirally wound between a plurality of wire guides, and supplies a slurry in which free abrasive grains are mixed with oil-based or water-soluble coolant to the contact portion between the workpiece and the wire. By doing so, it is an apparatus that simultaneously cuts a large number of wafers by the grinding action of loose abrasive grains. Specifically, during the reciprocating travel of the wire row, cutting is performed by scraping the workpiece at the bottom of the groove while pressing the free abrasive grains in the supplied abrasive liquid against the back of the wire groove (work cutting groove) with each wire. To do.

  In this way, the workpiece is cut into a wafer shape by free abrasive grains being rubbed against the inner part of the wire groove by the reciprocating wire. Due to the friction generated at this time, the cutting part generates heat, the workpiece is thermally expanded during cutting, and the wire guide is caused by frictional heat with the wire, frictional heat generated at the bearing part that supports the wire guide, etc. Due to thermal expansion, the relative position between the wire array spirally wound around the wire guide and the workpiece was changed during cutting.

The change in the relative position between the wire row and the workpiece due to the thermal expansion of these workpieces or the axial extension of the wire guide causes the cutting trajectory drawn on the workpiece by the wire to bend. There was a problem of being detected as Warp in shape measurement.
With respect to the problem that the temperature of the wafer fluctuates due to fluctuations in the frictional heat at the time of cutting described above, and the wafer surface is wavy, the length 2L where the wire and the wafer are simultaneously in contact with the number of wire rows A wire saw cutting method has been disclosed in which undulation is suppressed by absorbing heat from a slurry that supplies a heat quantity corresponding to the product of p to keep the temperature of the cutting portion of the wafer substantially constant (see Patent Document 1). ).

Japanese Patent Laid-Open No. 5-200734

However, in order to implement such a cutting method, an additional apparatus and complicated control are required, and the manufacturing cost is increased.
In addition, when the workpiece is a cylindrical ingot, the frictional heat generated is low because the wire length entering the workpiece is short at the start of cutting and the workpiece temperature is low, but the wire length entering the workpiece as the cutting progresses is low. It becomes longer, the generated frictional heat increases, and the workpiece expands. On the other hand, in the latter half of the cutting, the length of the wire entering the work is reduced, so that the frictional heat generated is lowered and the work temperature is also lowered, so that the work is contracted.

Due to the expansion and contraction of the workpiece, the change in the relative position between the wire row and the workpiece increases, the curvature of the cutting locus drawn on the workpiece also increases, and the Warp deteriorates.
As a feature of Warp due to such a workpiece temperature, the shape in the vicinity of both ends of the workpiece tends to be particularly deteriorated starting from the central portion in the longitudinal direction of the workpiece.

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a workpiece cutting method that can easily and effectively suppress the occurrence of Warp when cutting a cylindrical workpiece with a wire saw. And

  In order to achieve the above object, according to the present invention, a cylindrical workpiece is pressed against a wire row formed by winding a wire spirally between a plurality of wire guides, and the workpiece and the wire are In the workpiece cutting method of cutting the workpiece into a wafer shape by running the wire while supplying slurry to the contact portion, the workpiece is cut before the start of cutting the slurry to be supplied, at a temperature equal to or higher than the temperature. There is provided a method for cutting a workpiece, wherein the workpiece is cut after being heated to a temperature equal to or lower than a maximum temperature of the workpiece reached during the cutting of the workpiece.

  In this way, if the workpiece is cut after the workpiece is heated to a temperature not less than the temperature at the start of cutting of the supplied slurry and not more than the maximum temperature of the workpiece reached during the cutting of the workpiece before starting the cutting. In addition, while suppressing the sudden temperature change of the workpiece due to the contact between the slurry and the workpiece, the difference in workpiece temperature from the start of cutting to the end of cutting can be reduced to suppress the expansion and contraction amount of the workpiece, thus generating Warp. Can be easily and effectively suppressed.

At this time, the temperature of the slurry supplied during the cutting of the workpiece can be made constant.
Thus, if the temperature of the slurry supplied during the cutting of the workpiece is kept constant, the cutting method can be easily implemented, and the temperature of the workpiece can be controlled without performing complicated slurry temperature control during cutting. The height difference can be reduced to suppress the expansion and contraction of the workpiece, and the effect of improving Warp can be achieved.

  In the present invention, a cylindrical workpiece is pressed against a wire row formed by winding a wire spirally between a plurality of wire guides, and slurry is supplied to a contact portion between the workpiece and the wire. In the workpiece cutting method for cutting the workpiece into a wafer shape by running the workpiece, the workpiece reaches the highest temperature during cutting of the workpiece at a temperature higher than the temperature at which cutting of the supplied slurry is started before the cutting is started. Since the workpiece is cut after being heated to a temperature below the temperature, the rapid temperature change of the workpiece due to the contact between the slurry and the workpiece is suppressed, and the difference in temperature of the workpiece from the start of cutting to the end of cutting is reduced. Therefore, the amount of expansion and contraction of the workpiece can be suppressed, and the generation of Warp can be easily and effectively suppressed.

It is the schematic which shows an example of the wire saw which can be used with the cutting method of the workpiece | work of this invention. It is the schematic which shows an example of the workpiece | work feed mechanism of the wire saw which can be used for the cutting method of the workpiece | work of this invention. It is explanatory drawing explaining the measuring method of the temperature of a workpiece | work. It is a figure which shows the temperature change of the workpiece | work in Example 1, Example 2, the comparative example 1, and the comparative example 2. FIG. It is a figure which shows Warp shape of the workpiece feed direction cross section in Example 1. FIG. It is a figure which shows the Warp shape of the workpiece | work feed direction cross section in Example 2. FIG. It is a figure which shows the Warp shape of the workpiece | work feed direction cross section in the comparative example 1. It is a figure which shows Warp shape of the workpiece | work feed direction cross section in the comparative example 2.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
Warp generated when a cylindrical workpiece is cut with a wire saw affects not only the quality after cutting but also the quality of the final product. For this reason, with the miniaturization of design rules, improvement in the quality of the cut shape in cutting a workpiece with a wire saw has become an issue.
There are various generation factors for such warp. Among them, there is a warp due to the temperature change of the workpiece. Specifically, the workpiece is caused by contact with the slurry supplied during cutting or generation of frictional heat. This is caused by the expansion and contraction of the workpiece due to the increase in temperature of the workpiece and the decrease in the temperature of the workpiece due to the decrease in the frictional heat generated because the length of the wire entering the workpiece in the latter half of the cutting is reduced.

  As a feature of Warp due to the workpiece temperature, the shape in the vicinity of both ends of the workpiece tends to be particularly deteriorated starting from the central portion in the longitudinal direction of the workpiece.

  Therefore, the present inventors have made extensive studies to solve such problems. As a result, the maximum temperature of the workpiece being cut does not depend on the temperature of the workpiece at the start of cutting, and if the temperature of the slurry supplied during cutting of the workpiece is constant, the temperature of the workpiece at the time of cutting It was found that the temperature was almost constant at the temperature to which frictional heat was applied. Then, the workpiece is heated to a temperature within the range of the slurry temperature at the start of cutting and the maximum temperature of the workpiece reached during the cutting of the workpiece before starting cutting, so that the sudden temperature of the workpiece due to the temperature difference between the workpiece and the slurry is increased. It is possible to reduce the difference in temperature of the workpiece during cutting without causing a change, and as a result, it is conceived that warp can be greatly improved by suppressing the amount of expansion and contraction of the workpiece, thereby completing the present invention. It was.

FIG. 1 is a schematic view showing an example of a wire saw that can be used in the workpiece cutting method of the present invention. FIG. 2 is a schematic view showing an example of the workpiece feeding mechanism of the wire saw.
As shown in FIG. 1, the wire saw 1 mainly includes a wire 2 for cutting the workpiece W, a wire guide 3 for winding the wire 2, a wire tension applying mechanism 4 for applying tension to the wire 2, 4 ′, a workpiece feeding mechanism 5 for feeding a workpiece W to be cut relatively downward, a slurry supply mechanism 6 for supplying slurry at the time of cutting, and the like.

  The wire 2 is unwound from one wire reel 7 and passes through a traverser 8 through a wire tension applying mechanism 4 including a powder clutch (constant torque motor 9), a dancer roller (dead weight) (not shown), etc. In. A wire row is formed by winding the wire 2 around the wire guide 3. The wire 2 is wound around the wire reel 7 'through the other wire tension applying mechanism 4'.

  The wire guide 3 is a roller in which polyurethane resin is press-fitted around a steel cylinder and grooves are cut on the surface thereof at a constant pitch. A wire tension applying mechanism 4 is applied to the wire 2 wound around the wire guide 3. Thus, the wire 2 can be moved in the reciprocating direction by the driving motor 10 while applying an appropriate tension.

  As shown in FIG. 2, the workpiece feeding mechanism 5 includes a workpiece holding unit 11, an LM guide 12, and a workpiece feeding main body 13 for pushing down while holding the workpiece W. The work W is bonded to the contact plate 14, and the contact plate 14 is held by the work plate 15. Then, the work W is held by the work holding unit 11 through the contact plate 14 and the work plate 15. The work W held in this way can be sent out at a feed speed programmed in advance by driving the work holding unit 11 along the LM guide 12 by computer control.

  The workpiece W held by the workpiece holding portion 11 of the workpiece feeding mechanism 5 is thus sent to the wire 2 which is positioned below the workpiece feeding mechanism 5 and reciprocates in the axial direction when cutting. The wire 2 is cut and fed downward until the wire 2 reaches the contact plate 14.

  Further, a nozzle 17 is disposed above the wire 2, and when cutting the workpiece W, the slurry can be supplied from the slurry supply mechanism 6 to the contact portion between the workpiece W and the wire 2 through the nozzle 17. It is like that. The slurry supply mechanism 6 is connected to a nozzle 17 from a slurry tank 18 via a slurry chiller 16, and the supplied slurry can be supplied from the nozzle 17 with a supply temperature controlled by the slurry chiller 16.

The workpiece cutting method of the present invention when the wire saw shown in FIG. 1 configured as described above is used will be described below.
First, as shown in FIG. 2, the workpiece W to be cut is held by the workpiece feeding mechanism 5. Further, tension is applied to the wire 2 to reciprocate in the axial direction.

  And before starting the cutting | disconnection of the workpiece | work W, the workpiece | work W is heated. Here, the workpiece W may be heated before the start of cutting, and is not limited to the order of holding the workpiece W, traveling the wire 2, and the like. For example, after heating the workpiece W The workpiece W may be held. Moreover, the method of heating the workpiece | work W is not specifically limited, For example, it can heat using a thermostat, a hotplate, a warm air type heater, a lamp type heater, etc.

At this time, the temperature at which the workpiece W is heated before the start of cutting is set to be equal to or higher than the temperature at the start of cutting the slurry to be supplied and equal to or lower than the maximum temperature of the workpiece W reached during the cutting of the workpiece W. The maximum temperature of the workpiece W can be obtained in advance, for example, by experiments.
As described above, when the temperature of the workpiece W to be heated before the start of cutting is set to be equal to or higher than the temperature at the start of cutting of the slurry to be supplied, it is possible to suppress a sudden increase in the temperature of the workpiece due to the contact between the workpiece and the slurry. Moreover, if this temperature is set to be equal to or lower than the maximum temperature of the workpiece W reached during the cutting of the workpiece W, it is possible to suppress a rapid decrease in the temperature of the workpiece due to contact between the workpiece and the slurry, and an increase in time for heating. In addition, the economical efficiency and workability of electric power for heating are not deteriorated.

  Moreover, the temperature of the workpiece | work W can be measured by providing a thermocouple in the both end surfaces of the longitudinal direction of the workpiece | work W, for example, as shown in FIG. And the average value of the temperature measured with both these thermocouples can be made into the temperature of the workpiece | work W. FIG.

Next, the workpiece W held by the workpiece feeding mechanism 5 is relatively lowered, and the workpiece W is pressed against a wire row formed by winding the wire 2 in a spiral shape between the plurality of wire guides 3. Further, the slurry is supplied to the contact portion between the workpiece W and the wire 2 by the slurry supply mechanism 6. The temperature of the slurry to be supplied can be controlled to a desired temperature by the slurry chiller 16, and can be set to, for example, 15 ° C. to 30 ° C., but is not particularly limited thereto.
Here, the kind of slurry to be used is not particularly limited, and the same type as that of the conventional one can be used. For example, GC (silicon carbide) abrasive grains dispersed in a liquid can be used.

  With the slurry supplied to the contact portion between the workpiece W and the wire 2 while the wire 2 is traveling in this way, the workpiece W is cut and fed into the wire row to cut the workpiece W into a wafer shape. Then, the workpiece W is cut and fed until the wire 2 reaches the contact plate 14, and the cutting of the workpiece W is completed. Thereafter, the cut workpiece W can be pulled out from the wire row by reversing the feeding direction of the workpiece W.

  Here, the magnitude of the tension applied to the wire 2, the traveling speed of the wire 2, and the like can be set as appropriate. For example, the traveling speed of the wire can be set to 400 to 800 m / min. Moreover, the wire reversal cycle at the time of reciprocating the wire 2 at the time of workpiece | work cutting | disconnection can be about 60 s, for example. However, these conditions are not limited to this.

  In this way, the workpiece W is heated to a temperature within the range of the temperature at the start of cutting of the slurry to be supplied and the maximum temperature of the workpiece W reached during the cutting of the workpiece W before the cutting starts, and then the workpiece W is cut. Thus, when the slurry and the workpiece are in contact with each other, it is possible to suppress a sudden change in the temperature of the workpiece due to the temperature difference between the two, and the maximum temperature of the workpiece W reached during cutting is the maximum temperature of the workpiece W at the start of cutting. Since it does not depend on the temperature, the difference in temperature of the workpiece W from the start of cutting to the end of cutting can be reduced, and the amount of expansion and contraction of the workpiece W can be suppressed. As a result, the change in the relative position between the wire row and the workpiece W that has occurred due to the expansion and contraction of the workpiece W is suppressed, and the generation of Warp can be suppressed. In addition, with such a method, complicated temperature control of the workpiece and no additional device are required, and the conventional device can be used simply as it is, and the manufacturing cost increases. Can be suppressed.

  Here, in the example of the workpiece feeding mechanism 5 as shown in FIG. 2, the workpiece W is pushed down and cut and fed. However, in the present invention, if workpiece feeding is performed by relatively pushing it down. good. That is, instead of sending the workpiece W downward, the workpiece W may be sent out by pushing the wire row upward.

At this time, the temperature of the slurry supplied during the cutting of the workpiece can be made constant.
As described above, by the inventors of the present application, the maximum temperature of the workpiece being cut does not depend on the temperature of the workpiece at the start of cutting, and if the temperature of the slurry supplied during cutting of the workpiece is constant It has been discovered that the frictional heat at the time of cutting is added to the temperature of this slurry, and it becomes almost constant. By making the temperature of the slurry constant, the maximum temperature of the workpiece that can be reached during cutting of the workpiece can be easily achieved. Can be sought. The temperature of the workpiece W to be heated before the start of cutting can be easily set according to the maximum temperature obtained, and Warp can be easily suppressed without performing complicated slurry temperature control during cutting. A cutting method that can be performed.

  However, the workpiece cutting method of the present application does not exclude the control of changing the temperature of the slurry being cut. That is, in addition to heating before the start of cutting, by controlling to change the temperature of the slurry being cut, the temperature difference of the workpiece W being cut can be reduced more accurately. You can also.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

Example 1
Using a wire saw as shown in FIG. 1, a cylindrical silicon ingot having a diameter of 300 mm and a length of 200 mm was cut into a wafer under the cutting conditions shown in Table 1. Here, the temperature of the workpiece W to be heated before the start of cutting was set to 24.2 ° C., and the temperature of the slurry was controlled to be constant during cutting at 24 ° C. Then, the temperature of the workpiece from the start of cutting to the completion of cutting was measured, and the warp of the cut wafer was evaluated. As shown in FIG. 3, the temperature of the workpiece was measured with thermocouples provided on both end faces of the workpiece, and an average value of the measured temperatures was adopted.

  The result of the measured temperature is shown in FIG. As shown in FIG. 4, the maximum temperature of the workpiece during cutting is 38.6 ° C., and the difference in the temperature of the workpiece from the start of cutting to the end of cutting is reduced compared to Comparative Examples 1 and 2 described later. I understood that. Moreover, the average value of Warp of the whole wafer after cutting was 5.9 μm, which was improved by 17% from Comparative Example 1 described later.

FIG. 5 shows a Warp shape of a cross section in the feed direction of the workpiece. As described above, Warp due to the temperature of the workpiece appears prominently at both ends of the workpiece. Therefore, in FIG. 5, a part of one end of the workpiece is extracted. Specifically, from the Warp measurement data, 1 on the new wire supply side of the wire is extracted. The data of 11 wafers extracted every 5 wafers from the first wafer is shown. As shown in FIG. 5, it can be seen that, compared with the results of Comparative Examples 1 and 2 to be described later, the curvature in the vicinity of the end of the workpiece is suppressed, and a good Warp shape is obtained.
As described above, the workpiece cutting method of the present application can reduce the difference in the temperature of the workpiece from the start of cutting to the end of cutting, thereby suppressing the expansion and contraction amount of the workpiece, and easily and effectively generating Warp. It was confirmed that it could be suppressed.

(Example 2)
A silicon ingot was cut into a wafer under the same conditions as in Example 1 except that the temperature of the workpiece W heated before the start of cutting was 28 ° C., and evaluated in the same manner as in Example 1.
The result of the measured temperature is shown in FIG. As shown in FIG. 4, the maximum temperature of the workpiece during cutting is 38.9 ° C., and compared with Comparative Examples 1 and 2 and Example 1 described later, there is a difference in the temperature of the workpiece from the start of cutting to the end of cutting. It turned out that it was reduced. Moreover, the average value of Warp of the whole wafer after cutting was 5.2 μm, which was a better value than that of Example 1, which was 27% improved from Comparative Example 1 described later.

  FIG. 6 shows a Warp shape in the same manner as in the first embodiment. As shown in FIG. 6, it can be seen that the curvature in the vicinity of the end portion of the workpiece is further suppressed as compared with the result of Example 1, and a good Warp shape is obtained.

(Comparative Example 1)
The silicon ingot was cut under the same conditions as in Example 1 except that the cutting was started without heating the workpiece W before the cutting was started, and evaluation was made in the same manner as in Example 1.
The result of the measured temperature is shown in FIG. As shown in FIG. 4, the workpiece W before the start of cutting is 20.4 ° C., and the maximum temperature of the workpiece during cutting is 39.2 ° C., which is almost the same as in Example 1, from the start of cutting to the end of cutting. It was found that the difference in temperature of the workpiece was larger than that in Example 1 and Example 2. Moreover, it turned out that the average value of Warp of the whole wafer after cutting is 7.1 μm, which is worse than that of Example 1 and Example 2.

  FIG. 7 shows the Warp shape in the same manner as in the first embodiment. As shown in FIG. 7, it can be seen that the vicinity of the end portion of the workpiece is strongly curved, causing the Warp to deteriorate.

(Comparative Example 2)
The silicon ingot is cut under the same conditions as in Example 1 except that the workpiece W is heated to 39.7 ° C., which is higher than the maximum temperature of the workpiece being cut, before cutting is started, and cutting is started. Evaluation was performed in the same manner as in Example 1. At this time, the maximum temperature of the workpiece during cutting was 39.2 ° C., which was almost the same as in Example 1. The expected maximum temperature of the workpiece during cutting was obtained in advance by experiments.
The result of the measured temperature is shown in FIG. As shown in FIG. 4, it can be seen that the temperature of the workpiece W rapidly decreases due to contact with the slurry after the start of cutting, and the workpiece temperature is rapidly reversed in the vicinity of the cutting position of 50 mm. Moreover, it turned out that the average value of Warp of the whole wafer after a cutting | disconnection is 9.6 micrometers, compared with Example 1 and Example 2 significantly.

FIG. 8 shows a Warp shape in the same manner as in the first embodiment. As shown in FIG. 8, it can be seen that the influence of the rapid decrease in the workpiece temperature as shown in FIG. 4 appears in the cut surface shape of the wafer, causing the Warp to deteriorate.
Thus, in order to improve Warp, the temperature at which the workpiece W is heated before the start of cutting needs to be equal to or higher than the temperature at the start of cutting of the slurry to be supplied and lower than the maximum temperature of the workpiece reached during the cutting of the workpiece. is there.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same function and effect. It is included in the technical scope.

1 ... Wire saw, 2 ... Wire, 3 ... Wire guide,
4, 4 '... wire tension applying mechanism, 5 ... work feeding mechanism, 6 ... slurry supply mechanism,
7, 7 '... wire reel, 8 ... traverser, 9 ... constant torque motor,
DESCRIPTION OF SYMBOLS 10 ... Motor for drive, 11 ... Work holding part, 12 ... LM guide,
13 ... work feed main body, 14 ... pad, 15 ... work plate,
16 ... Slurry chiller, 17 ... Nozzle, 18 ... Slurry tank.

Claims (2)

A cylindrical workpiece is pressed against a wire row formed by winding a wire spirally between a plurality of wire guides, and the wire is caused to travel while supplying slurry to a contact portion between the workpiece and the wire. In the workpiece cutting method for cutting the workpiece into a wafer,
Before the cutting starts, the workpiece is heated to a temperature not lower than the temperature at the start of cutting of the supplied slurry and not higher than the maximum temperature of the workpiece reached during the cutting of the workpiece, and then the workpiece is cut. How to cut the workpiece.   The work cutting method according to claim 1, wherein the temperature of the slurry supplied during the cutting of the work is made constant.

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