Wafer manufacturing method

Abstract

To provide a wafer manufacturing method that can suppress scratches on the wafer with a simple configuration when manufacturing wafers from single-crystal ingots using a fixed abrasive wire saw. [Solution] A wafer manufacturing method is a wafer manufacturing method for manufacturing a wafer from a single crystal ingot using a fixed abrasive wire saw, comprising: a slicing step of slicing the single crystal ingot by lowering a holding part that holds the single crystal ingot relative to the wire row while running a wire row made of fixed abrasive wires; and a drawing step of pulling out the cut single crystal ingot from the wire row by raising the holding part relative to the wire row while running the wire row, wherein the drawing step raises the holding part relative to the wire row at a speed of 300 mm / min or more.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a wafer.

Background Art

[0002] Conventionally, when manufacturing a wafer from a single crystal ingot using a fixed abrasive wire saw, it has been regarded as a problem that the surface of the wafer is damaged by the contact between the fixed abrasive wire saw and the wafer.

[0003] The wafer after the slicing process may have warpage caused by the slicing conditions. Therefore, after the slicing process, a warpage evaluation process is performed, and if necessary, the slicing conditions are adjusted to suppress warpage.

[0004] On the other hand, there is a risk that the surface of the wafer may be damaged by the contact between the fixed abrasive wire saw and the wafer. When both sides of the wafer are damaged and the degree of damage is different between the front side and the back side of the wafer, warpage of the entire wafer due to the damage occurs. When such warpage occurs in the wafer, the warpage evaluated in the warpage evaluation process is the warpage in which the warpage component caused by the slicing process and the warpage component caused by the pulling process are synthesized. In order to evaluate only the warpage component caused by the slicing process in the warpage evaluation process and adjust the slicing conditions, a process of polishing both sides of the wafer to suppress warpage caused by the damage is required, which has contributed to the deterioration of productivity. Therefore, when manufacturing a wafer from a single crystal ingot using a fixed abrasive wire saw, studies have been conducted to suppress the damage generated on the wafer surface (for example, see Patent Document 1).

[0005] In the configuration described in Patent Document 1, the joining member attached to the workpiece is held by the workpiece holding means. After the slicing of the workpiece is completed and before the workpiece is pulled out from the wire row, the fixed abrasive wire is worn with a grindstone that forms part of the joining member to secure the clearance between the workpiece and the fixed abrasive wire, and then the workpiece is pulled out.

Prior Art Documents

[0006] [Patent Document 1] International Publication No. 2018 / 203448 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the configuration described in Patent Document 1 requires the use of a special joining member that is partly composed of a grinding wheel. Furthermore, there is a risk that the fixed abrasive wire may break when it is worn down by the grinding wheel.

[0008] The present invention aims to provide a wafer manufacturing method that can suppress scratches on the wafer with a simple configuration when manufacturing a wafer from a single crystal ingot using a fixed abrasive wire saw. [Means for solving the problem]

[0009] The wafer manufacturing method of the present invention is a wafer manufacturing method for manufacturing a wafer from a single crystal ingot using a fixed abrasive wire saw, comprising: a slicing step of slicing the single crystal ingot by lowering a holding part that holds the single crystal ingot relative to the wire row while running a wire row made of fixed abrasive wires; and a drawing step of pulling out the cut single crystal ingot from the wire row by raising the holding part relative to the wire row while running the wire row, wherein the drawing step raises the holding part relative to the wire row at a speed of 300 mm / min or more. [Effects of the Invention]

[0010] According to the present invention, when manufacturing wafers from single-crystal ingots using a fixed abrasive wire saw, a wafer manufacturing method can be provided that can suppress scratches on the wafer with a simple configuration.

[0011] Furthermore, the present invention makes it possible to improve productivity when manufacturing wafers from single-crystal ingots using a fixed abrasive wire saw. This improvement in productivity enhances the manufacturing efficiency of semiconductor products, enabling the production of more high-quality products, and contributes to promoting technological innovation and the sustainable development of the industry. In other words, the present invention can contribute, for example, to Sustainable Development Goals (SDGs) "Goal 8: Decent Work and Economic Growth" and "Goal 9: Industry, Innovation and Infrastructure". [Brief explanation of the drawing]

[0012] [Figure 1] This diagram shows the prerequisite technology, experimental examples conducted to derive the present invention, and a schematic diagram illustrating the configuration of a fixed abrasive wire saw according to the embodiment. [Figure 2] This is a schematic diagram showing the first to fifth measurement areas of the evaluation wafer related to the above experimental example. [Figure 3] This is a flowchart showing the wafer manufacturing method according to the above embodiment. [Modes for carrying out the invention]

[0013] [Prerequisite technology] Before describing embodiments of the present invention, a fixed abrasive wire saw used in these embodiments will be described.

[0014] <Configuration of a fixed abrasive wire saw> The fixed abrasive wire saw 1 shown in Figure 1 comprises a slicing section 2 and a lifting section 3. The slice section 2 comprises a total of three main rollers 21, two of which are positioned on the same horizontal plane and one positioned below and between these two. Fixed abrasive wires 22 are spirally wound around the three main rollers 21. This winding of the fixed abrasive wires 22 around the main rollers 21 forms a wire row 22A between the two upper main rollers 21 (hereinafter sometimes referred to as "upper main rollers 21A"), in which multiple fixed abrasive wires 22 are arranged at a constant pitch along the rotation axis of the main rollers 21.

[0015] The fixed abrasive wire 22 comprises a steel wire and diamond abrasive grains electroplated onto the surface of the wire. The diamond abrasive grains preferably have a particle size of 6 μm or more and 12 μm or less, and more preferably an average particle size of 9 μm or less.

[0016] Both ends of the fixed abrasive wire 22 are fixed to two bobbins 25 that feed out and wind up the fixed abrasive wire 22 via multiple guide rollers 23 and tension rollers 24 (one of each shown in Figure 1). A traverser 26 is provided between each tension roller 24 and bobbin 25. The traverser 26 has the function of adjusting the feeding position and winding position of the fixed abrasive wire 22.

[0017] Above the upper main roller 21A, a pair of nozzles 27 are provided to supply coolant C at an intermediate position between the two upper main rollers 21A. An example of coolant C is a stock solution containing glycol and a surfactant, but without abrasive particles, which is diluted with pure water.

[0018] The lifting unit 3 moves a single crystal ingot M (hereinafter sometimes referred to as "ingot M") made of silicon, SiC, GaAs, sapphire, etc., between a pair of nozzles 27 relative to the wire row 22A. The lifting unit 3 includes a holding unit 31 that holds the ingot M, and a lifting drive unit 32 that moves the holding unit 31 up and down relative to the slicing unit 2 which does not move up or down. Note that the fixed abrasive wire saw 1 may be configured such that both the slicing section 2 and the holding section 31 move up and down, or the slicing section 2 may be configured to move up and down with respect to the holding section 31 that does not move up and down.

[0019] <Operation of the fixed abrasive wire saw> The fixed abrasive wire saw 1 is used in the production of wafers and performs a slicing process of slicing the ingot M with the wire row 22A and a pulling-out process of pulling out the sliced ingot M from the wire row 22A.

[0020] In the slicing process, the fixed abrasive wire saw 1 rotates the main roller 21 to run the wire row 22A in the feed direction D1, adjusts the vertical position of the tension roller 24 so that the tension of the wire row 22A becomes a predetermined value, and supplies the coolant C between the two upper main rollers 21A. The fixed abrasive wire saw 1 lowers the holding section 31 while maintaining the running direction, running speed, and tension of the wire row 22A and the supply state of the coolant C, and slices by pressing the ingot M against the running wire row 22A to produce a plurality of wafers. The fixed abrasive wire saw 1 gradually winds up the fixed abrasive wire 22 with the right bobbin 25 while alternately repeating the running of the wire row 22A in the feed direction D1 and the return direction D2. As shown by the two-dot chain line in FIG. 1, when the wire row 22A is positioned above the upper end of the ingot M and the cutting of the slicing table constituting the holding section 31 is started, the fixed abrasive wire saw 1 ends the lowering of the holding section 31.

[0021] [[ID=十四]]In the pulling-out process, the fixed abrasive wire saw 1 runs the wire row 22A while maintaining the tension of the wire row 22A and the supply amount of the coolant C at predetermined amounts, and pulls out the ingot M from the wire row 22A by raising the holding section 31 at a predetermined pulling-out speed.

[0022] [Background leading to the present invention] Next, the background leading to the present invention will be described. The inventors conducted an experiment using a fixed abrasive wire saw 1 to investigate the relationship between the travel speed of the fixed abrasive wire 22, the withdrawal speed of the holding part 31, and the state of damage to the wafer.

[0023] <How to set evaluation criteria> Multiple wafers were manufactured by slicing a 200mm diameter ingot M using a fixed abrasive wire saw 1 while supplying coolant C at a supply rate of 120 L / min. After the slicing process, the wire strands 22A were cut without performing a drawing process, and the cut wire strands 22A were pulled horizontally from the slicing table. In this method, the wire strands 22A could be pulled out without damaging the wafer.

[0024] From among multiple wafers, five evaluation wafers W located at equal intervals from each other along the length of the ingot M were selected as the evaluation wafers W shown in Figure 2. The five evaluation wafers W include a wafer located in the center along the length of the ingot M and wafers located a predetermined number of wafers inward from both ends along the length.

[0025] On one surface of each evaluation wafer W, the first to fifth measurement areas P1 to P5 were set. The first to fifth measurement areas P1 to P5 are linear regions parallel to the vertical direction of the ingot M (holding part 31). The length of the first to fifth measurement areas P1 to P5 is 40 mm. The first to third measurement areas P1 to P3 are located on a first imaginary line. The first imaginary line includes the center Wc of the evaluation wafer W and is parallel to the vertical direction of the holding section 31. The first measurement area P1 is located between the second measurement area P2 and the third measurement area P3, and is centered on the center Wc. The edges of the second and third measurement areas P2 and P3 are located 10 mm inward from the outer edge of the evaluation wafer W. The centers of the fourth and fifth measurement regions P4 and P5 lie on the second imaginary line. The second imaginary line includes the center Wc and is perpendicular to the first imaginary line. The centers of the fourth and fifth measurement regions P4 and P5 are located 10 mm inward from the point where the second imaginary line overlaps with the outer edge of the evaluation wafer W.

[0026] The surface roughness of the first to fifth measurement regions P1 to P5 was measured on each evaluation wafer W. Using a contact-type surface roughness measuring instrument, the first measurement area P1 was measured along its length, and the difference between the maximum and minimum values ​​in the measurement results was calculated as the surface roughness Rmax. Surface roughness Rmax was also calculated for the second to fifth measurement areas P2 to P5. Surface roughness Rmax for the first to fifth measurement areas P1 to P5 was calculated for all evaluation wafers W, and the average value A (hereinafter sometimes referred to as "average surface roughness A") and standard deviation σ of these surface roughness Rmax values ​​were calculated. The average surface roughness A was 10.3 μm, and the standard deviation σ was 1.1 μm. The average surface roughness A and standard deviation σ calculated in this way correspond to the surface roughness of wafers that were not scratched by the fixed abrasive wire 22. Based on these results, the evaluation criterion value E was set to 11.4 μm (= A + σ).

[0027] <Experimental Method> Seventeen ingots M with a diameter of 200 mm were prepared, and slicing and drawing processes were performed under the conditions of Experimental Examples 1 to 17 shown in Tables 1 and 2 below.

[0028] (Experimental Example 1) Multiple wafers were manufactured by slicing ingot M under the same slicing conditions as when the evaluation criteria were set. After the slicing process, while supplying coolant C at the same supply rate of 120 L / min as in the slicing process, the ingot M was withdrawn from the wire array 22A by performing a withdrawal process in which the holding unit 31 was raised at a withdrawal rate of 50 mm / min without moving the wire array 22A, as shown in Table 1. (Experimental Example 2) The slicing and drawing processes were performed under the same conditions as in Experimental Example 1, except that the holding section 31 was raised at a drawing speed of 500 mm / min.

[0029] (Experimental Example 3) The slicing and drawing processes were performed under the same conditions as in Experimental Example 1, except that the wire train 22A was moved in the return direction D2 at a travel speed of 5 m / min while the holding section 31 was raised at a withdrawal speed of 50 mm / min. The travel speed of 5 m / min was the lower limit setting speed of the fixed abrasive wire saw 1 used in the experiment. (Experimental Examples 4-6) The slicing and drawing processes were performed under the same conditions as in Experimental Example 3, except that the holding section 31 was increased at drawing speeds of 200 mm / min, 300 m / min, and 500 m / min, respectively. The drawing speed of 500 mm / min was the upper limit setting speed of the fixed abrasive wire saw 1 used in the experiment.

[0030] (Experimental Examples 7-10) The slicing and drawing processes were performed under the same conditions as in Experimental Examples 3-6, except that the wire train 22A was moved in the return direction D2 at a travel speed of 10 m / min. (Experimental Examples 11-14) The slicing and drawing processes were performed under the same conditions as in Experimental Examples 3-6, except that the wire train 22A was moved in the return direction D2 at a travel speed of 20 m / min.

[0031] [Table 1]

[0032] (Experimental Examples 15-17) As shown in Table 2, the slicing and drawing processes were performed under the same conditions as in Experimental Examples 4, 5, and 7, except that the wire array 22A was moved in the feeding direction D1.

[0033] [Table 2]

[0034] <Experimental Results> As shown in Table 1, in Experimental Example 1, during the drawing process, the diamond abrasive grains caught on the slice surface of the ingot M, causing the fixed abrasive wire 22 to lift and break. On the other hand, in Experimental Examples 2 to 17, wafers could be manufactured without the fixed abrasive wire 22 breaking. From the multiple wafers manufactured in Experimental Example 2, five evaluation wafers W were taken, in the same manner as when setting the evaluation criteria. The first to fifth measurement areas P1 to P5 of each evaluation wafer W were measured using a contact-type surface roughness measuring instrument, and the average surface roughness A was calculated based on the measurement results. The average surface roughness A was similarly calculated for the wafers manufactured in Experimental Examples 3 to 17. Table 1 shows the average surface roughness A for Experimental Examples 2 to 14 where the wire train 22A travels in the return direction D2, and Table 2 shows the average surface roughness A for Experimental Examples 15 to 17 where the feed direction D1.

[0035] As shown in the thick border in Table 1, it was confirmed that when the wire train 22A is traveling in the return direction D2, the average surface roughness A is below the evaluation standard value if the pull-out speed is 300 mm / min or higher. As shown in the thick border in Table 2, it was confirmed that, similar to the case of the return direction D2, when the wire train 22A is traveling in the feed direction D1, the average surface roughness A is below the evaluation standard value if the pull-out speed is 300 mm / min or higher.

[0036] <Summary> As shown in Tables 1 and 2, if the wire array 22A travels at a speed of 5 m / min or more and 20 m / min or less, and the holding part 31 is pulled out at a speed of 300 mm / min or more and 500 mm / min or less, the average surface roughness A is below the evaluation standard value, regardless of the direction in which the wire array 22A travels, confirming that the wafer is not scratched. The inventors speculated on the reason for this as follows.

[0037] Compared to a free-grain wire saw, the fixed-grain wire saw 1 exhibits greater frictional resistance between the slicing surface of the ingot M and the wire row 22A. A free-grain wire saw is a wire saw that uses a wire row composed of wires that do not have diamond abrasive particles electroplated onto them, and slices the ingot M while supplying a slurry containing abrasive particles. In this state where frictional resistance is present, if the holding part 31 is raised at a low pulling speed, the frictional resistance is greater than the pulling force of the holding part 31, causing the wire array 22A to lift up together with the holding part 31. Subsequently, when the tension of the wire array 22A exceeds a limit value, the wire array 22A is repelled and returns to its original position, and in the process, the slice surface of the ingot M, that is, the surface of the wafer, is damaged. However, it was estimated that if the holding portion 31 is raised at a high pulling speed, the pulling force of the holding portion 31 becomes greater than the frictional resistance force, suppressing the lifting of the wire array 22A, and as a result, wafer damage is suppressed.

[0038] In the above experimental examples, wafer damage was suppressed when the wire train 22A traveled at speeds of 5 m / min, 10 m / min, and 20 m / min. However, it is believed that damage would also be suppressed when traveling at speeds exceeding 20 m / min. In the above experimental examples, wafer damage was suppressed when the holding section 31 was pulled out at speeds of 300 mm / min and 500 mm / min. However, it is believed that damage would also be suppressed when pulled out at speeds exceeding 500 mm / min. In the above experimental examples, damage was suppressed when manufacturing wafers with a diameter of 200 mm. However, it is believed that damage would also be suppressed when manufacturing wafers with diameters other than 200 mm, such as 300 mm wafers. The inventors of the present invention have discovered that, in the drawing process, a simple configuration is used in which the holding unit 31 is raised relative to the wire array 22A at a speed of 300 mm / min or more while the wire array 22A is running, thereby suppressing damage to the wafer, and have completed the present invention.

[0039] [Embodiment] <Wafer manufacturing method> A method for manufacturing wafers according to an embodiment of the present invention will be described. As shown in Figure 3, in the wafer manufacturing method, the fixed abrasive wire saw 1 slices the ingot M (slicing process: step S1).

[0040] Next, the fixed abrasive wire saw 1 pulls the sliced ​​ingot M from the wire row 22A (pulling process: step S2). In the drawing process, the fixed abrasive wire saw 1 moves along the wire train 22A and raises the holding section 31 at a speed of 300 mm / min or more to draw the ingot M from the wire train 22A. In the drawing process, the direction of travel of the wire train 22A may be either the feed direction D1 or the return direction D2, or it may be an alternating cycle of the feed direction D1 and the return direction D2.

[0041] In the drawing process, the drawing speed of the holding section 31 is preferably 1000 mm / min or less. With this configuration, it is possible to suppress the breakage of the fixed abrasive wire 22 due to irregularities on the slice surface of the ingot M or contact with inclusions between the slice surface and the fixed abrasive wire 22. Examples of inclusions that cause such breakage include lumps of Si generated by slicing, or lumps of powder generated when the slicing table of the holding section 31 is cut.

[0042] In the drawing process, the travel speed of the wire array 22A is preferably 5 m / min or more and 50 m / min or less. By setting the travel speed of the wire array 22A to 50 m / min or less, it is possible to suppress the number of diamond abrasive grains that come into contact with the slice surface per unit time from becoming too large, thereby suppressing scratches on the wafer.

[0043] In the drawing process, the tension of the wire row 22A is preferably between 10N and 40N. If the tension is less than 10N, the fixed abrasive wire 22 may bend significantly upward as the holding portion 31 rises, potentially causing it to break. If the tension exceeds 40N, the fixed abrasive wire 22 may break because it exceeds the breaking limit.

[0044] As described above in the drawing process, a simple configuration is used in which the holding unit 31 is raised relative to the wire array 22A at a speed of 300 mm / min or more while the wire array 22A is being moved, enabling the manufacture of wafers with reduced damage.

[0045] Next, a cleaning apparatus or operator (not shown) cleans the wafer in a well-known manner (cleaning process: step S3).

[0046] Next, a warpage evaluation device (not shown) evaluates the warpage of the cleaned wafer (warpage evaluation step: step S4). In the warpage evaluation process, a flatness measuring instrument (ADE9600, manufactured by ADE Corporation) can be used as the warpage evaluation device. Using such a flatness measuring instrument, the thickness of the wafer is measured using a pair of capacitance sensors installed on the top and bottom, and the Warp value obtained based on the thickness measurement result is evaluated as warpage.

[0047] Here, we will explain the warpage that is evaluated in the warpage evaluation process. Wafers after the slicing process may warp due to slicing conditions. Examples of slicing conditions that can cause such warping include frictional heat generated by friction with the fixed abrasive wire 22, deterioration of the quality of the materials constituting the fixed abrasive wire saw 1, such as the fixed abrasive wire 22, and the temperature and humidity around the fixed abrasive wire saw 1. Furthermore, if, during the drawing process, the conditions of this embodiment are not applied and the drawing speed of the holding unit 31 is set to less than 300 mm / min while the wire array 22A is running, there is a risk of scratches on both sides of the wafer. If scratches occur on both sides of the wafer, warping may occur in the wafer depending on the extent of the scratches. If such warping occurs in the wafer, the warping evaluated in the warping evaluation process will be a composite of the warping component caused by the slicing process and the warping component caused by the drawing process. However, in this embodiment, since the drawing process is performed under the conditions of step S2, the occurrence of warping caused by the drawing process is suppressed. Therefore, the warp evaluated in the warp evaluation process will be limited to warp caused solely by the slicing process.

[0048] Next, a computer or operator (not shown) determines, based on the warpage evaluation results, whether or not it is necessary to change the slicing conditions in the slicing process (step S5).

[0049] If the computer or operator determines that the measured Warp value exceeds a threshold, meaning that the warping caused solely by the slicing process is greater than the threshold level and that a change in the slicing conditions is necessary (Step S5: YES), the operator, for example, changes the slicing conditions to suppress the occurrence of warping in the next slicing process (Step S6: Slicing Condition Change Process). In the slicing condition modification process, for example, the slicing conditions are modified to reduce frictional heat, the materials constituting the fixed abrasive wire saw 1 are replaced or maintained, and the temperature and humidity around the fixed abrasive wire saw 1 are adjusted.

[0050] After the slicing condition change step, a lapping apparatus (not shown) polishes both sides of the wafer, whose warpage has been evaluated by a well-known method (Step S7: Lapping step). Afterward, post-processing is performed on the wafer following the wrapping process.

[0051] On the other hand, if the computer or operator determines that the measurement result of the Warp value is below the threshold, meaning that the warping caused solely by the slicing process is below the threshold level and that there is no need to change the slicing conditions (Step S5: NO), the lapping device performs the lapping process (Step S7).

[0052] If the conditions of step S2 are not used in the drawing process, the warpage evaluated in the warpage evaluation process will be a composite of the warpage component caused by the slicing process and the warpage component caused by the drawing process, as described above. Therefore, it becomes difficult to properly evaluate the warpage caused solely by the slicing process, and it becomes impossible to properly determine whether or not a change in the slicing conditions is necessary based on the warpage evaluated in the warpage evaluation process. In this case, if a lapping process is performed to remove any scratches on the wafer caused by the drawing process before the warpage evaluation process, thereby removing the warpage component caused by the drawing process, then the warpage caused solely by the slicing process can be properly evaluated. However, the time between the completion of the drawing process and the determination of whether or not the slicing conditions need to be changed becomes longer, preventing improvements in productivity.

[0053] On the other hand, in this embodiment, since the conditions of step S2 are used in the drawing process, warping caused solely by the slicing process can be appropriately evaluated without performing the lapping process before the warping evaluation process. Therefore, the time between the completion of the drawing process and the determination of whether or not a change in slicing conditions is necessary is shortened, thereby improving productivity. [Explanation of Symbols]

[0054] 1...Fixed abrasive wire saw, 22...Fixed abrasive wire, 22A...Wire row, 31...Holding part, M...Single crystal ingot.

Claims

1. A wafer manufacturing method for producing wafers from single crystal ingots using a fixed abrasive wire saw, A slicing step is performed in which a single crystal ingot is sliced ​​by moving a wire row consisting of fixed abrasive wires and lowering a holding part that holds the single crystal ingot relative to the wire row, The system includes a drawing step in which the single crystal ingot after cutting is pulled out from the wire row by raising the holding part relative to the wire row while the wire row is being moved, The drawing process is a wafer manufacturing method comprising raising the holding portion relatively at a speed of 300 mm / min or more.

2. In the wafer manufacturing method described in claim 1, A warpage evaluation step for evaluating the warpage of the wafer after the drawing step, The process includes a lapping step for polishing both sides of the wafer, The aforementioned warpage evaluation step is a wafer manufacturing method performed before the aforementioned lapping step.

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