Method for separating multiple slices from a workpiece by a wire saw during a separation process - Patent Application 20070122997

Abstract

The present invention relates to a method for separating a plurality of slices from a workpiece (2) by means of a wire saw during a separation process, the wire saw comprising a wire grid consisting of a movable wire portion of a saw wire and a control mechanism, the wire grid being clamped in a plane between two wire guide rollers, each of the two wire guide rollers being mounted between a fixed bearing and a floating bearing, the method comprising the steps of: feeding the workpiece (2) through the wire grid by the control mechanism in a feed direction perpendicular to the workpiece axis and perpendicular to the plane of the wire grid; supplying a cutting means to the wire grid; supplying a temperature control medium to the workpiece; directing the temperature control liquid through the fixed bearings according to a temperature profile and / or a displacement profile; The present invention relates to a method comprising displacing a workpiece along a workpiece axis, directing a temperature-controlled liquid and / or displacing the workpiece along the workpiece axis, the temperature profile and the displacement profile being in opposition to the shape deviation, characterized by identifying camber curves of at least one slice from a workpiece start end (3) and at least one slice from a workpiece end end (4) of at least one preceding separation process using a wire saw, extracting a difference between the camber curves, setting a temperature and / or a volumetric speed of a cutting means during the separation process depending on the difference between the camber curves, and setting a temperature and / or a volumetric speed of a temperature-controlled liquid depending on the difference between the camber curves.

Description

[Technical Field]

[0001] The present invention provides a method for slicing multiple wafers from a workpiece with a wire saw during a slicing operation. [Background technology]

[0002] Conventional technology / issues This type of method is used, for example, in the production of semiconductor wafers, in particular wafers made of monocrystalline silicon, and is called the multi-wire slicing (MWS) method. One configuration of such a method provides that a workpiece, for example a cylindrical ingot of monocrystalline silicon, is fed through wire sections of a longitudinally moving saw wire, the wire sections being arranged parallel to one another to form a wire web in the presence of a suspension of cutting liquid, also called slurry, and hard material, which is cut into wafers in the process.

[0003] During this process, heat is generated at different locations on the wire saw and the workpiece, and the workpiece and wire web move relative to each other due to thermal expansion. This relative movement causes irregularities on the major surfaces of the sliced ​​wafers. Efforts have been made to mitigate this problem.

[0004] U.S. Patent Application Publication No. 20120178346 describes applying a cooling liquid to a workpiece and wiping the cooling liquid from the workpiece, which is disclosed to, among other things, reduce localized bowing of sliced ​​wafers.

[0005] US Patent Application Publication No. 20070178807 proposes adjusting the temperature and / or volumetric flow rate of the slurry supplied to the workpiece holder and the temperature and / or volumetric flow rate of the slurry supplied to the wire web depending on the cutting depth.

[0006] The method described in EP 3922386 A1 involves supplying a slurry to a wire web, wetting the workpiece with a cooling medium, and controlling the temperature of the fixed bearings of the wire guide rollers with the cooling liquid. The temperatures of the cooling medium and the cooling liquid are controlled according to respective temperature profiles that specify the temperatures of the cooling medium and the cooling liquid, respectively, as a function of the cutting depth, thereby reducing shape deviations from a planar target shape identified on a previously sliced ​​wafer. Instead of or in addition to controlling the temperature of the fixed bearings, displacement of the workpiece along the workpiece axis by an actuating element is proposed, and the profile of the displacement movement reduces shape deviations. The shape deviations of wafers produced in this manner are shown in the form of an average warpage curve and are relatively low. The method, its alternatives, and a combination of both are hereinafter referred to as methods for correcting average warpage.

[0007] During the slicing operation, the workpiece heats up and temporarily expands. The change in the distance between the wire and the nearest edge of the workpiece increases the shorter the distance between the wire and the nearest edge of the workpiece at the start of the slicing operation. If we define the workpiece start as the edge of the workpiece that is closest to the wire web at the point where the saw wire reaches the wire web, and the workpiece end as the edge of the workpiece that is closest to the wire web at the point where the saw wire leaves the wire web, it is clear that wafers that are closest to both the workpiece start and end will exhibit the greatest warpage due to thermal expansion of the workpiece. Furthermore, such wafers will have an inverse shape. Wafers sliced ​​near the workpiece start will have a concave shape, while wafers sliced ​​near the workpiece end will have a convex shape.

[0008] When shape deviations are reduced by controlling the temperature of the stationary bearings and / or by displacing the workpiece, and plots of the warpage curves of edge-sliced ​​wafers are superimposed, a cluster of curves is obtained that resembles the outline of a wrapped candy. Due to the inverse nature described above, the variation in the warpage curves is greatest at the entry cut, the cut center, and the exit cut. Summary of the Invention [Problem to be solved by the invention]

[0009] The aim of the present invention is to reduce this variability. [Means for solving the problem]

[0010] The object of the present invention is to provide a method for slicing a plurality of wafers from a workpiece by means of a wire saw during a slicing operation, the wire saw comprising a wire web of a movable wire part of a saw wire and an actuator, the wire web being tensioned in a plane between two wire guide rollers, each of the two wire guide rollers being supported between a fixed bearing and a floating bearing, the method comprising: feeding the workpiece through the wire web along a feed direction perpendicular to the workpiece axis and perpendicular to the plane of the wire web by an actuator; supplying a cutting agent to the wire web; supplying a temperature control medium to the workpiece; directing a temperature-controlled liquid through the fixed bearing according to a temperature profile and / or displacing the workpiece along the workpiece axis according to a displacement profile, wherein the temperature profile and the displacement profile reduce shape deviations; and Including, determining a warpage curve of at least one wafer from the beginning of the workpiece and at least one wafer from the end of the workpiece from at least one previous slicing operation using a wire saw; Extracting the difference between the warpage curves; adjusting the temperature and / or volume flow rate of the cutting agent during the slicing operation according to the difference between the warpage curves; and adjusting the temperature and / or volume flow rate of the temperature control medium according to the difference between the warpage curves. This is achieved by a method characterized by:

[0011] To control the temperature of the workpiece during the slicing operation, the method uses wire saw-specific data because they are provided by wafers produced using the same wire saw. The wire saw includes two or more wire guide rollers. Each warpage curve in the cutting direction along the diameter of the wafer in one or more slicing operations using the wire saw preceding the slicing operation is identified. At least two wafers are selected, which originate from a workpiece start end and a workpiece end end. The warpage curves of the one or more wafers from the workpiece start end and the one or more wafers from the workpiece end end are averaged to form common warpage curves representing the wafers from the workpiece start end and the wafers from the workpiece end end, respectively. A difference between the warpage curves of the one or more wafers from the workpiece end end and the one or more wafers from the workpiece start end in at least one preceding slicing operation is then formed. When the difference between the warpage curves is based on the warpage curves derived from wafers from the beginning and end of the workpiece in multiple preceding slicing operations, the warpage curves of the wafers from the beginning and end of the workpiece are averaged to form the respective warpage curves before forming the difference. The temperature and / or volume flow rate of the cutting agent and the temperature control medium during the slicing operation are adjusted based on the difference between the warpage curves. In other words, the temperature and / or volume flow rate of the cutting agent and the temperature control medium are determined according to the difference between the warpage curves, and the temperature control performance can be divided differently between the cutting agent and the temperature control medium. Preferably, the temperature control performance of the temperature control medium is overweighted at the beginning of the slicing operation and overweighted at the end of the slicing operation because the side of the workpiece that can be wetted by the temperature control medium decreases as the cutting (cutting) depth increases.

[0012] If the difference between the camber curves at the determined cutting depth is positive, more heat is supplied to the workpiece relative to the heat supply when the difference is zero. If the difference between the camber curves at the determined cutting depth is negative, more heat is extracted from the workpiece relative to the heat supply when the difference is zero. It is possible to respond to a negative difference between the camber curves with a decrease in the temperature of the cutting agent, an increase in the volumetric flow rate of the cutting agent, a decrease in the temperature of the temperature control medium, or an increase in the volumetric flow rate of the temperature control medium. Correspondingly, it is possible to respond to a positive difference between the camber curves with an increase in the temperature of the cutting agent, a decrease in the volumetric flow rate of the cutting agent, an increase in the temperature of the temperature control medium, or a decrease in the volumetric flow rate of the temperature control medium. A combination of one or more of these response possibilities can be selected. In particular, it is preferable to omit the response by the temperature control medium and adjust the supply of the temperature control medium after reaching a cutting depth of 85% or less.

[0013] Of course, it is also possible to extract the difference between the camber curves from one or more wafers from the beginning of the workpiece and one or more wafers from the end of the workpiece. In that case, the difference will have an opposite sign and will be responded to in a correspondingly opposite way. For example, a positive difference will result in less heat being supplied to the workpiece relative to a heat supply when the difference is zero. Correspondingly, a positive difference between the camber curves will be responded to by one or more of the following means: a decrease in the temperature of the cutting agent, an increase in the volumetric flow rate of the cutting agent, a decrease in the temperature of the temperature control medium, and an increase in the volumetric flow rate of the temperature control medium.

[0014] Due to the proposed method of supplying the cutting agent and the temperature control medium, the shape of the wafer in the slicing operation, expressed as a warpage curve, varies to a much smaller extent than would occur without this measure.

[0015] The cutting agent is a slurry, i.e., a suspension of hard material particles in a liquid, and the temperature control medium can be this slurry, a slurry of a different composition, or a liquid that does not contain hard material particles.

[0016] The conduction of the temperature-control liquid through the fixed bearing and / or the displacement of the workpiece along the workpiece axis influences the appearance of the wafer in the slicing operation, which is expressed as an average warpage curve after averaging the warpage curves of the wafer. The temperature of the temperature-control liquid as a function of the cutting depth follows a temperature profile, which reduces or cancels shape deviations, and the thermal expansion or contraction of the fixed bearing causes axial displacement of the floating bearing. Correspondingly, the displacement of the workpiece as a function of the cutting depth follows a displacement profile, which specifies the direction and magnitude of the displacement, thereby reducing shape deviations. Preferably, the temperature profile and / or the displacement profile reduces shape deviations indicated by the average warpage curve of the wafer sliced ​​during at least one preceding slicing operation, or shape deviations as defined in EP 3922386 A1. The conduction of the temperature-control liquid through the fixed bearing according to the temperature profile specification and the displacement of the workpiece along the workpiece axis according to the displacement profile specification can be performed simultaneously. However, it is also possible to omit one or the other.

[0017] Additionally, it is preferable to minimize the mutual influence of the cutting agent and the temperature control medium by wiping and draining the temperature control medium from the workpiece before it can fall onto the wire web, which may be done, for example, as described in U.S. Patent Application Publication No. 20120178346.

[0018] The expression "wafer bow" refers to the sum of the values ​​of the maximum upward and downward distances between a reference plane and the central plane of a relaxed wafer, the reference plane being the plane that best fits the central plane. Bow measurement is described in the standard SEMI MF1390. The bow curve (linear shape scan) corresponds to a one-dimensional profile obtained when the difference between the central curve of the diametric central plane and the reference straight line of the reference plane is observed, preferably in the cutting direction, or at most a few degrees from it, if the influence of the orientation notch is avoided. The influence of gravity on the bow curve can be taken into account by vertical positioning of the wafer when measuring the bow or by a correction when calculating the difference. In the bow curve difference formation according to the present invention, the bow curve may be filtered or subjected to another mathematical operation, provided that the resulting changes cancel each other out.

[0019] The present invention will now be described with reference to the drawings. [Brief explanation of the drawings]

[0020] [Figure 1] 1 shows a schematic representation of a saw wire cutting profile of a wire web through a workpiece, said profile typically being produced due to temporary thermal expansion of the workpiece despite application of methods to compensate for the average bow. [Figure 2] The top shows an overview of typical warpage curves of wafers from the start of the workpiece and wafers from the end of the workpiece, the middle shows the average warpage curves of wafers from the start of the workpiece and wafers from the end of the workpiece, and the bottom shows the difference between the average warpage curve from the start of the workpiece and the average warpage curve from the end of the workpiece. [Figure 3] The left half shows the volumetric flow rate (top) and temperature (bottom) profiles of the cutting agent as a function of cutting depth, and the right half shows the volumetric flow rate (top) and temperature (bottom) profiles of the temperature control medium as a function of cutting depth. [Figure 4]The top shows the variation of the warpage curves of a wafer from the beginning of a workpiece and a wafer from the end of a workpiece, the wafer being sliced ​​from a workpiece without using the present invention; the bottom shows the variation of the warpage curves of a wafer from the beginning of a workpiece and a wafer from the end of a workpiece, the wafer being sliced ​​from a workpiece that has been cut into wafers by the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS IN ACCORDANCE WITH THE INVENTION 1 shows a schematic diagram of a cutting profile of a wire portion 1 of a wire web, said profile being typically produced due to temporary thermal expansion of a workpiece 2. When the resulting wafer is rotated 90° clockwise, the wafer from the workpiece start end 3 has a concave shape and the wafer from the workpiece end 4 has a convex shape.

[0022] Figure 2 (top) shows typical warpage curves WP of wafers from the beginning and end of a workpiece. The warpage curves were confirmed using a MX7012-type capacitance motion measurement device manufactured by E+H Metrology GmbH, Germany. The variations in the warpage curves are particularly noticeable at the beginning, middle, and end of the slicing operation. Figure 2 (center) shows two warpage curves obtained by averaging, representing wafers from the beginning and end of a workpiece, and Figure 2 (bottom) shows the difference ΔWP between these warpage curves.

[0023] The temperature of the cutting agent and the temperature and / or volumetric flow rate of the temperature control medium delivered to the wire web and the workpiece during the slicing operation are based on the difference in such warpage curves and thus depend on data ascertained after at least one prior slicing operation.

[0024] If the difference is zero, the temperature or volumetric flow rate provided to the process is adjusted, respectively; if the difference is positive, a corresponding higher temperature or lower volumetric flow rate is adjusted; and if the difference is negative, a corresponding lower temperature or higher flow rate is adjusted.

[0025] Figure 3 shows, as an example, the profiles of the volumetric flow rate V (top) and temperature T (bottom) of the cutting agent SML (left half) and the temperature control medium TPM (right half) as a function of the cutting depth D. A silicon semiconductor wafer was sliced ​​from a single crystal. The profile is based on the difference between the warpage curves shown in Figure 2 (bottom). The difference is greater than zero at the beginning and end of the cutting profile and less than zero at the intermediate cutting depth. The temperature and volumetric flow rate profiles according to Figure 3 are consistent with this. Therefore, the volumetric flow rate of the cutting agent is adjusted to be relatively high, and the temperature of the cutting agent is adjusted to be relatively low during the intermediate cutting depth. The same is true for the volumetric flow rate and temperature of the temperature control medium. The temperature control performance of the cutting agent and the temperature control medium has different weights during the cutting profile. Towards the end of the cutting profile, the temperature control performance is entirely on the side of the cutting agent, because at that point the temperature control medium is no longer supplied to the workpiece.

[0026] 4 shows the difference between the method according to the invention (bottom) and a method that does not adjust the temperature and / or volumetric flow rate of the cutting agent and temperature control medium according to the difference in the camber curves (top) in relation to the simultaneous display of the camber curves from the beginning and end of the workpiece. When applying the method according to the invention, the variations in the camber curves are significantly less pronounced, especially at the beginning, middle and end of the cutting profile. [Explanation of symbols]

[0027] List of references used 1 Wire section 2 workpieces 3 Workpiece start 4 Workpiece End D cutting depth WP warpage curve ΔWP warpage curve difference V volumetric flow rate T temperature SML Cutting Agent TPM Temperature Control Medium

Claims

1. 1. A method for slicing a plurality of wafers from a workpiece with a wire saw during a slicing operation, the wire saw comprising a wire web of a movable wire portion of a saw wire and an actuator, the wire web being tensioned in a plane between two wire guide rollers, each of the two wire guide rollers being supported between a fixed bearing and a floating bearing, the method comprising: feeding the workpiece through the wire web along a feed direction perpendicular to a workpiece axis and perpendicular to the plane of the wire web with the actuator; applying a cutting agent to the wire web; providing a temperature control medium to the workpiece; directing a temperature controlled liquid through the fixed bearing according to a temperature profile and / or displacing the workpiece along the workpiece axis according to a displacement profile, wherein the temperature profile and the displacement profile reduce shape deviation; determining a warpage curve of at least one wafer from the beginning of the workpiece and at least one wafer from the end of the workpiece from at least one previous slicing operation using the wire saw; Extracting the difference between the warpage curves; adjusting the temperature and / or volume flow rate of the cutting agent during the slicing operation in response to the difference between the camber curves; adjusting the temperature and / or the volumetric flow rate of the temperature control medium in response to the difference between the warp curves.

2. 10. The method of claim 1, characterized by an overweighting of the temperature control performance of the temperature control medium at the beginning of the slicing operation and an overweighting of the temperature control performance of the cutting agent at the end of the slicing operation.

3. The method of claim 1 characterized by wiping the temperature control medium from the workpiece.

4. The method according to any one of claims 1 to 3, characterized in that an average warpage curve of wafers sliced ​​during said at least one previous slicing operation exhibits said shape deviation.

5. 5. The method according to claim 1, wherein the supply of the temperature control medium to the workpiece is adjusted after a cutting depth of 85% or more has been reached.

6. The method according to any one of claims 1 to 5, characterized in that the difference between the warpage curves is based on warpage curves derived from wafers from the workpiece start end and the workpiece end end in a plurality of previous slicing operations, and the warpage curves of the wafers from the workpiece start end and the wafers from the workpiece end end are respectively averaged to form respective warpage curves before forming the difference.

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