Method for producing wafer

Abstract

This method for producing a wafer comprises producing a wafer from a single-crystal ingot using a fixed abrasive grain wire saw, and comprises a slicing step for slicing the single-crystal ingot by relatively lowering a holding part for holding the single-crystal ingot with respect to a wire row composed of fixed abrasive grain wires while causing the wire row to travel, and an extraction step for extracting the single-crystal ingot after cutting from the wire row by relatively raising the holding part with respect to the wire row while causing the wire row to travel, the extraction step comprising relatively raising the holding part at a speed of 300 mm / min or more.

Description

Method for manufacturing a wafer

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

[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 due to 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 due to contact between the fixed abrasive wire saw and the wafer. If both sides of the wafer are damaged and the degree of damage is different between the front and back surfaces 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-out process are combined. 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 deteriorating productivity. Therefore, when manufacturing a wafer from a single crystal ingot using a fixed abrasive wire saw, studies have been conducted to suppress damage occurring on the wafer surface (see, for example, Patent Document 1).

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

[0006] International Publication No. 2018 / 203448

[0007] However, the configuration described in Patent Document 1 requires the use of a special joining member that is partly made 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.

[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.

[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, thereby promoting technological innovation and contributing to 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".

[0012] This is a schematic diagram showing the prerequisite technology, experimental examples conducted to derive the present invention, and the configuration of a fixed abrasive wire saw according to the embodiment. This is a schematic diagram showing the first to fifth measurement areas of the evaluation wafer according to the experimental example. This is a flowchart showing the method for manufacturing the wafer according to the embodiment.

[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 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 slicing section 2 has a total of three main rollers 21, two of which are located on the same horizontal plane and one located below and between these two. Fixed abrasive wires 22 are wound spirally around the three main rollers 21. By winding the fixed abrasive wires 22 around the main rollers 21 in this way, a wire row 22A is formed 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 the 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 and down. The fixed abrasive wire saw 1 may be configured so that both the slicing unit 2 and the holding unit 31 move up and down, or the slicing unit 2 may be configured so that only the slicing unit 2 moves up and down relative to the holding unit 31 which does not move up and down.

[0019] <Operation of the fixed abrasive wire saw> The fixed abrasive wire saw 1 is used in wafer manufacturing and performs a slicing process in which the ingot M is sliced ​​with the wire row 22A, and a drawing process in which the sliced ​​ingot M is drawn out from the wire row 22A.

[0020] In the slicing process, the fixed abrasive wire saw 1 rotates the main roller 21 to move the wire train 22A in the feed direction D1, and adjusts the vertical position of the tension roller 24 so that the tension of the wire train 22A is at a predetermined value, and supplies coolant C between the two upper main rollers 21A. The fixed abrasive wire saw 1 lowers the holding unit 31 while maintaining the direction of travel of the wire train 22A, travel speed and tension, and the supply state of the coolant C, and slices the ingot M by pressing it against the moving wire train 22A to produce multiple wafers. The fixed abrasive wire saw 1 gradually winds the fixed abrasive wire 22 on the right bobbin 25 while the wire train 22A alternately travels in the feed direction D1 and the return direction D2. As shown by the dashed line in Figure 1, the fixed abrasive wire saw 1 has its wire row 22A positioned above the upper end of the ingot M, and when it starts cutting the slicing table that constitutes the holding section 31, it stops lowering the holding section 31.

[0021] In the drawing process, the fixed abrasive wire saw 1 draws the ingot M from the wire saw 22A by running the wires 22A while maintaining the tension of the wires 22A and the supply amount of coolant C at predetermined levels, and by raising the holding part 31 at a predetermined drawing speed.

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

[0023] <Method for setting evaluation criteria> Multiple wafers were manufactured by performing a slicing process on an ingot M with a diameter of 200 mm 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. By 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] First to fifth measurement areas P1 to P5 were set on one surface of each evaluation wafer W. The first to fifth measurement areas P1 to P5 are linear areas 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 an imaginary line parallel to the vertical direction of the holding part 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 ends 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 areas P4 and P5 are located on a second imaginary line. The second imaginary line is an imaginary line that includes the center Wc and is perpendicular to the first imaginary line. The centers of the fourth and fifth measurement areas 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 areas P1 to P5 of each evaluation wafer W was measured. Using a contact-type surface roughness measuring instrument, the first measurement area P1 was measured along the length direction, and the difference between the maximum and minimum values ​​in the measurement results was calculated as the surface roughness Rmax. The surface roughness Rmax was also calculated for the second to fifth measurement areas P2 to P5. The surface roughness Rmax of the first to fifth measurement areas P1 to P5 of all evaluation wafers W was calculated, 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 value was 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 drawn out from the wire array 22A by performing a drawing process in which the holding unit 31 was raised at a drawing speed 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 unit 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 unit 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 unit 31 was raised at withdrawal speeds of 200 mm / min, 300 m / min, and 500 m / min, respectively. The withdrawal 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]

[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]

[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 way as when setting the evaluation standard value. The first to fifth measurement areas P1 to P5 of each evaluation wafer W were measured with a contact-type surface roughness measuring instrument, and the average surface roughness A was calculated based on the measurement results. Similarly, the average surface roughness A was 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 row 22A travels in the return direction D2, and Table 2 shows the average surface roughness A for Experimental Examples 15 to 17 where the wire row 22A travels in 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 will be 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 without electroplated diamond abrasive grains to slice the ingot M while supplying a slurry containing abrasive grains. In this state of frictional resistance, 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 row 22A to lift up together with the holding part 31. Subsequently, when the tension of the wire row 22A exceeds a limit value, the wire row 22A is repelled and returns to its original position, damaging the slicing surface of the ingot M, i.e., the wafer surface. However, it was estimated that if the holding part 31 is raised at a high pulling speed, the pulling force of the holding part 31 becomes greater than the frictional resistance, suppressing the lifting of the wire row 22A, and as a result, reducing wafer damage.

[0038] In the above experimental examples, wafer damage was suppressed when the wire array 22A traveled at speeds of 5 m / min, 10 m / min, and 20 m / min, but 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 unit 31 was pulled out at speeds of 300 mm / min and 500 mm / min, but 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, but it is believed that damage would also be suppressed when manufacturing wafers with diameters other than 200 mm, for example, wafers with a diameter of 300 mm. The inventors have completed the present invention by finding that wafer damage can be suppressed with a simple configuration 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 traveling during the pulling process.

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

[0040] Next, the fixed abrasive wire saw 1 pulls out the sliced ingot M from the wire row 22A (pulling-out step: step S2). In the pulling-out step, the fixed abrasive wire saw 1 runs the wire row 22A and raises the holding portion 31 at a speed of 300 mm / min or more to pull out the ingot M from the wire row 22A. In the pulling-out step, the running direction of the wire row 22A may be one of the feeding direction D1 and the returning direction D2, or may be an alternating repetition of the feeding direction D1 and the returning direction D2.

[0041] In the pulling-out step, it is preferable that the pulling-out speed of the holding portion 31 is 1000 mm / min or less. With such a configuration, it is possible to suppress the wire breakage of the fixed abrasive wire 22 due to the unevenness of the sliced surface of the ingot M or the contact between the sliced surface and the inclusion between the sliced surface and the fixed abrasive wire 22. Examples of such inclusions that cause such wire breakage include, for example, lumps of Si generated by slicing or lumps of powder generated when the slicing table of the holding portion 31 is cut.

[0042] In the pulling-out step, it is preferable that the running speed of the wire row 22A is 5 m / min or more and 50 m / min or less. By setting the running speed of the wire row 22A to 50 m / min or less, it is possible to suppress the excessive increase in the number of diamond abrasive grains contacting the sliced surface per unit time and suppress the damage to the wafer.

[0043] In the pulling-out step, it is preferable that the tension of the wire row 22A is 10 N or more and 40 N or less. This is because when the tension is less than 10 N, the fixed abrasive wire 22 may greatly bend upward and break as the holding portion 31 rises, and when it exceeds 40 N, the fixed abrasive wire 22 may break beyond the breaking limit.

[0044] With a simple configuration that only raises the holding part 31 with respect to the wire row 22A at a speed of 300 mm / min or more while running the wire row 22A as in the above drawing-out process, a wafer with suppressed damage can be manufactured.

[0045] Next, a cleaning device (not shown) or an operator cleans the wafer by a well-known method (cleaning process: step S3).

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

[0047] Here, the warp evaluated in the warp evaluation process will be described. After the slicing process, the wafer may warp due to the slicing conditions. Examples of the slicing conditions that 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. Also, in the drawing-out process, if the drawing-out speed of the holding part 31 is less than 300 mm / min while running the wire row 22A without applying the conditions of the present embodiment, there is a risk of damage to both sides of the wafer. If both sides of the wafer are damaged, the wafer may warp depending on the degree of damage. When such warping occurs in the wafer, the warp evaluated in the warp evaluation process is a combined warp of the warp component caused by the slicing process and the warp component caused by the drawing-out process. However, in the present embodiment, since the drawing-out process is performed under the conditions of step S2, the occurrence of warp caused by the drawing-out process is suppressed. Therefore, the warp evaluated in the warp evaluation process is the warp caused only 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 slicing conditions is necessary (Step S5: YES), the operator, for example, changes the slicing conditions so as to suppress the occurrence of warping in the next slicing process (Step S6: Slicing Condition Change Process). In the Slicing Condition Change Process, for example, changes are made to the slicing conditions to reduce frictional heat, 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). Subsequently, post-processing is performed on the wafer after the lapping step.

[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 in 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 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 period from the end of the drawing process to the determination process of whether or not a change in the slicing conditions is necessary becomes longer, and productivity cannot be improved.

[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 period from the completion of the drawing process to the determination process of whether or not a change in the slicing conditions is necessary is shortened, and productivity can be improved.

[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 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 involves raising the holding part relative to the wire row at a speed of 300 mm / min or more.

2. A wafer manufacturing method according to claim 1, comprising: a warpage evaluation step for evaluating the warpage of the wafer after the drawing step; and a lapping step for polishing both sides of the wafer, wherein the warpage evaluation step is performed before the lapping step.

Images