Expansion method

Abstract

To provide an extension method capable of performing a heat contraction of a sheet after an expansion.SOLUTION: A extension method comprises: an expansion step 1001 of expanding a sheet between an outer periphery of a wafer of a wafer unit and an inner periphery of an annular frame; and a heating step 1002 of contracting slackness of the sheet generated by the expansion step 1001 by heating a region of the sheet of the outer periphery of the wafer and the inner periphery of the annular frame with a heating unit for heating the sheet after the execution of the expansion step 1001. The region of the sheet contains: a first region; and a second region that is hardly constructed by a heating than the first region. On the sheet, a heat spot of which a temperature is higher than that of the sheet of the circumference by a heat radiated to the sheet from the heating unit. In the heating step 1002, the heat unit is moved so that the heat spot is positioned to a whole region of at least the second region.SELECTED DRAWING: Figure 9

Description

【Technical Field】 【0001】 The present invention relates to an expansion method for expanding a sheet of a wafer unit. 【Background Art】 【0002】 In order to eliminate the slack of the sheet generated by expansion, the sheet is heated and shrunk. Conventionally, the sheet has been heated by rotating and moving a heater facing the heated area of the sheet along the heated area (see, for example, Patent Document 1). 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2012-156400 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 On the other hand, the sheet has MD (Machine direction) and TD (Transverse direction), and both ends in the TD direction are difficult to shrink even when the sheet is heated. 【0005】 If the sheet is not sufficiently shrunk, a sufficient interval is not formed between the chips formed by dividing the wafer, and there is a risk that adjacent chips may contact and be damaged during handling. 【0006】 An object of the present invention is to provide an expansion method capable of heating and shrinking an expanded sheet. 【Means for Solving the Problems】 【0007】 To solve the above-mentioned problems and achieve the objective, the present invention provides an expansion method for expanding a sheet of a wafer unit comprising a wafer, a sheet to which the wafer is attached, and an annular frame to which the outer edge of the sheet is attached and which has an opening for housing the wafer, the method comprising: an expansion step of expanding the sheet between the outer periphery of the wafer of the wafer unit and the inner periphery of the annular frame; and after performing the expansion step, Heat radiated from the heating element The heating step includes heating the heated area of ​​the sheet between the outer edge of the wafer and the inner circumference of the annular frame with a heating unit to heat the sheet, thereby shrinking the slack in the sheet generated in the expansion step, wherein the heated area of ​​the sheet includes a first area and a second area which is less susceptible to shrinkage by heating than the first area, and the heating unit the heating part The heat radiated onto the sheet creates a hot spot on the sheet that is hotter than the surrounding sheet, and in the heating step, the heating unit is moved so that the hot spot is located over at least the entire area of ​​the second region. In addition, the heating portion is positioned over at least the entire radial area of ​​the second region while the heating unit is moving. It is characterized by the following: 【0008】 In the expansion method described above, in the heating step, the heat spot moves in a circular motion along the outer circumference of the wafer in the heated region, and In at least the second region, the heating unit is moved back and forth in the radial direction of the wafer, The heating unit may be moved so that the heat spot moves back and forth in the radial direction of the wafer. 【0009】 In the expansion method described above, the heating step is performed such that the heat spot moves concentrically on the area to be heated. By changing the radial position of the heating element on the wafer The entire heated area of ​​the sheet may be heated by moving the heating unit. [Effects of the Invention] 【0010】 This invention has the effect of allowing the expanded sheet to be heat-shrunk. [Brief explanation of the drawing] 【0011】 [Figure 1]Figure 1 is a perspective view showing an example configuration of a wafer unit comprising a sheet to be expanded according to Embodiment 1 of the expansion method. [Figure 2] Figure 2 is a plan view of the wafer unit shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram showing the molecular chains of the sheet in part III in Figure 2. [Figure 4] Figure 4 schematically shows the molecular chains of the sheet in section IV in Figure 2. [Figure 5] Figure 5 is a perspective view showing an example configuration of an expansion device that implements the expansion method according to Embodiment 1. [Figure 6] Figure 6 is a schematic cross-sectional view showing an example of the configuration of the divided unit of the expansion device shown in Figure 5. [Figure 7] Figure 7 is a schematic cross-sectional view showing an example of the configuration of the heating unit of the expansion device shown in Figure 5. [Figure 8] Figure 8 is a schematic side view showing the positional relationship between the heating section of the heating unit shown in Figure 7 and the wafer unit. [Figure 9] Figure 9 is a flowchart showing the flow of the extension method according to Embodiment 1. [Figure 10] Figure 10 is a schematic cross-sectional view showing the extension steps of the extension method shown in Figure 9. [Figure 11] Figure 11 is a cross-sectional view of the heating step of the expansion method shown in Figure 9, in which the frame fixing unit of the heating unit fixes the frame of the wafer unit. [Figure 12] Figure 12 is a cross-sectional view of the sheet after it has been expanded during the heating step of the expansion method shown in Figure 9. [Figure 13] Figure 13 is a cross-sectional view of the heating step of the expansion method shown in Figure 9, in which the wafer unit is held by suction on the holding table of the heating unit, and the push-up member and the holding table are lowered. [Figure 14] Figure 14 is a cross-sectional view showing the heating process of the expansion method shown in Figure 9, where the slack in the sheet region is being heated. [Figure 15]FIG. 15 is a plan view schematically showing a movement locus of a heating unit that heats the slack of a sheet region in the heating step of the expansion method shown in FIG. 9. [Figure 16] FIG. 16 is a plan view schematically showing a movement locus of a heat spot in the XVI portion in FIG. 15. [Figure 17] FIG. 17 is a plan view schematically showing a movement locus of a heat spot in the XVII portion in FIG. 15. [Figure 18] FIG. 18 is a plan view schematically showing a movement locus of a heat spot in the second region of the comparative example. [Figure 19] FIG. 19 is a plan view schematically showing a movement locus of a heating unit that heats the slack of a sheet region in the heating step of the expansion method according to Embodiment 2. [Figure 20] FIG. 20 is a plan view schematically showing a movement locus of a heating unit that heats the re-inner circumference of a sheet region in the heating step of the expansion method according to Embodiment 3. [Figure 21] FIG. 21 is a plan view schematically showing a movement locus of a heating unit that heats the radial center of a sheet region in the heating step of the expansion method according to Embodiment 3. [Figure 22] FIG. 22 is a plan view schematically showing a movement locus of a heating unit that heats the re-outer circumference of a sheet region in the heating step of the expansion method according to Embodiment 3. 【BEST MODE FOR CARRYING OUT THE INVENTION】 【0012】 A mode (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the content described in the following embodiments. In addition, the constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Also, various omissions, substitutions, or changes in the configuration can be made without departing from the gist of the present invention. 【0013】 〔Embodiment 1〕 The expansion method according to Embodiment 1 of the present invention will be described with reference to the drawings. Figure 1 is a perspective view showing an example configuration of a wafer unit having a sheet to be expanded according to the expansion method according to Embodiment 1. Figure 2 is a plan view of the wafer unit shown in Figure 1. Figure 3 is a schematic diagram showing the molecular chains of the sheet in part III in Figure 2. Figure 4 is a schematic diagram showing the molecular chains of the sheet in part IV in Figure 2. 【0014】 (Wafer unit) The expansion method according to Embodiment 1 is a device for expanding the sheet 202 of the wafer unit 200 shown in Figure 1. As shown in Figure 1, the wafer unit 200 comprises a wafer 201, a sheet 202 to which the wafer 201 is attached, and an annular frame 204 to which the outer edge of the sheet 202 is attached and which has an opening 203 for accommodating the wafer 201. 【0015】 In Embodiment 1, the wafer 201 is a disc-shaped semiconductor wafer or optical device wafer, etc., with a substrate made of silicon, sapphire, gallium arsenide, or SiC (silicon carbide). As shown in Figure 1, the wafer 201 has devices 207 formed in each region partitioned by a plurality of intersecting division lines 206 on its surface 205. 【0016】 Device 207 is, for example, an integrated circuit such as an IC (Integrated Circuit) or LSI (Large Scale Integration), an image sensor such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), a MEMS (Micro Electro Mechanical Systems), or memory (semiconductor memory device). 【0017】 The wafer 201 is irradiated with a laser beam of a wavelength that is transparent to the substrate from the back surface 208 side of the front surface 205 along the division line 206, forming a modified layer 209 (shown as a dotted line in Figure 1), which is the starting point for division, inside the substrate along the division line 206. The wafer 201 is divided into individual chips 210 starting from the modified layer 209. Each chip 210 comprises a portion of the substrate divided along the division line 206 and a device 207 formed on the surface of the substrate. 【0018】 The modified layer 209 refers to a region whose density, refractive index, mechanical strength, and other physical properties differ from those of the surrounding area. Examples include melted regions, cracked regions, dielectric breakdown regions, refractive index change regions, and regions where these regions are mixed. The mechanical strength of the modified layer 209 is lower than the mechanical strength of other parts of the substrate. 【0019】 The sheet 202 is made of a stretchable resin and has thermal shrinkage properties, shrinking when heated. The sheet 202 is formed in a disc shape with a diameter larger than the diameter of the wafer 201. In Embodiment 1, it comprises a base layer made of a synthetic resin that is stretchable and thermally shrinkable, and an adhesive layer made of a synthetic resin that is laminated on the base layer and adheres to the wafer 201. The sheet 202 has an annular frame 204 attached to its outer edge and the back surface 211 of the wafer 201 attached to its central part. In this invention, the sheet 202 may consist only of a base layer made of polyolefin, which is a thermoplastic resin, and may not have an adhesive layer. 【0020】 The sheet 202 is stretchable and, for example, is formed by stretching a heated synthetic resin along a first direction 212 while simultaneously stretching it in a second direction 213 perpendicular to the first direction 212. In Embodiment 1, the first direction 212 is the so-called flow direction (MD: Machine Direction), and the second direction 213 is the so-called perpendicular direction (TD: Transverse Direction). In Embodiment 1, the sheet 202 includes molecular chains 214 stretched in the first direction 212, as shown in Figures 3 and 4. 【0021】 In Embodiment 1, since the sheet 202 contains molecular chains 214 extended in the first direction 212, when heated, it shrinks less in the second direction 213 than in the first direction 212. That is, the amount of shrinkage in the second direction 213 of the sheet 202 when heated is less than the amount of shrinkage in the first direction 212. Thus, the sheet 202 includes a first region 216 located at both ends of the first direction 212 and a second region 217 located at both ends of the second direction 213, which shrinks less when heated than the first region 216, in the region 215 (shown in Figures 1 and 2, corresponding to the heated region) between the inner circumference of the annular frame 204 and the outer circumference of the wafer 201. 【0022】 Although Figure 2 shows the boundary between the first region 216 and the second region 217, in reality, the sheet 202 does not have a boundary separating the first region 216 and the second region 217. Also, in the example shown in Figure 2, the first region 216 and the second region 217 are alternately arranged at 90-degree intervals centered on the center of the sheet 202, but in the present invention, the arrangement of the first region 216 and the second region 217 is not limited to that shown in Figure 2, and it is desirable that the arrangement be appropriately determined depending on the type of sheet 202 and the size of the chip 210, as long as the first region 216 is located at both ends of the first direction 212 and the second region 217 is located at both ends of the second direction 213. 【0023】 The annular frame 204 is formed in an annular shape with an inner diameter larger than the diameter of the wafer 201, and the outer circumference of the sheet 202 is attached to it. 【0024】 The wafer unit 200 with the above configuration is made up of a sheet 202 to which the back surface 208 of the wafer 201 is attached, and an annular frame 204 is attached to the outer edge of the sheet 202, and so on. 【0025】 (Expansion device) An expansion device 1 for implementing the expansion method according to Embodiment 1 will be described. Figure 5 is a perspective view showing an example configuration of an expansion device for implementing the expansion method according to Embodiment 1. Figure 6 is a schematic cross-sectional view showing an example configuration of the divided unit of the expansion device shown in Figure 5. Figure 7 is a schematic cross-sectional view showing an example configuration of the heating unit of the expansion device shown in Figure 5. Figure 8 is a schematic side view showing the positional relationship between the heating section and the wafer unit of the heating unit shown in Figure 7. 【0026】 The expansion device 1 shown in Figure 5 is a device that expands the sheet 202 of the wafer unit 200 and divides the wafer 201, on which a modified layer 209 has been formed as a dividing starting point, into individual chips 210 along the dividing line 206. As shown in Figure 5, the expansion device 1 comprises a cassette elevator 3 provided on the device body 2, a dividing unit 10, a heating unit 30, a cleaning unit 40, a transport unit 50, and a control unit 100 which is a control means. 【0027】 The cassette elevator 3 is positioned at one end of the main body 2 in the Y-axis direction parallel to the horizontal direction, and a cassette 4 containing multiple wafer units 200 is detachably mounted on it. The cassette 4 accommodates multiple wafer units 200 at intervals in the Z-axis direction parallel to the vertical direction. The cassette 4 is mounted on the cassette elevator 3 with an opening 5 that allows wafer units 200 to be inserted and removed facing the center of the main body 2 in the Y-axis direction. The cassette elevator 3 raises and lowers the cassette 4 in the Z-axis direction. 【0028】 The expansion device 1 also includes a pair of first guide rails 6 and a pair of second guide rails 7 on which wafer units 200 to be inserted into and removed from the cassette 4 are temporarily placed. The pair of first guide rails 6 are parallel to the Y-axis direction and are spaced apart from each other in the X-axis direction, which is parallel to the horizontal direction and perpendicular to the Y-axis direction. The pair of first guide rails 6 are positioned in the center of the device body 2 in the Y-axis direction so as to be aligned with both ends in the X-axis direction of the opening 5 of the cassette 4, which is placed on the cassette elevator 3, in the Y-axis direction. The pair of first guide rails 6 are provided to be movable in the X-axis direction by a drive mechanism (not shown), and move closer to and away from each other by the drive mechanism. When the pair of first guide rails 6 are placed on the wafer units 200 to be inserted into and removed from the cassette 4 and move closer to each other by the drive mechanism, they position the wafer units 200 in the X-axis direction. 【0029】 The pair of second guide rails 7 are used to temporarily place wafer units 200 and the like that have been transported from the first guide rail 6 by the transport unit 50. The pair of second guide rails 7 are parallel to the Y-axis direction, parallel to the horizontal direction, and spaced apart from each other in the X-axis direction. The pair of second guide rails 7 are located in the center of the apparatus body 2 in the Y-axis direction and next to the first guide rail 6 in the X-axis direction. The pair of second guide rails 7 are provided to be movable in the X-axis direction by a drive mechanism (not shown), and move closer to or further apart from each other by the drive mechanism. When wafer units 200 and the like that have been transported from the first guide rail 6 are placed on the pair of second guide rails 7 and move closer to each other by the drive mechanism, the wafer units 200 are positioned in the X-axis direction. 【0030】 The transport unit 50 includes a first transport unit 51 that transports the wafer unit 200 between the cassette 4 and the first guide rail 6, a second transport unit 52 that transports the wafer unit 200 between the first guide rail 6 and the second guide rail 7, between the second guide rail 7 and the heating unit 30, between the heating unit 30 and the cleaning unit 40, and between the cleaning unit 40 and the first guide rail 6, and a third transport unit 53 that transports the wafer unit 200 between the second guide rail 7 and the splitting unit 10. 【0031】 The split unit 10 is positioned next to one side of the pair of second guide rails 7 in the Y-axis direction. As shown in Figure 6, the split unit 10 comprises a frame fixing unit 11 and a pressing unit 12. The frame fixing unit 11, the pressing unit 12, and the device body 2 are housed in a cooling chamber 14 (shown in Figure 1) whose interior is cooled, which is positioned next to one side of the pair of second guide rails 7 in the Y-axis direction. 【0032】 The frame fixing unit 11 fixes the annular frame 204 of the wafer unit 200 and comprises a frame mounting plate 15 and a frame retaining plate 16. The frame mounting plate 15 has a circular opening 151 in its planar shape and is formed as a plate with a flat upper surface 152 that is parallel to the horizontal direction. The inner diameter of the opening 151 of the frame mounting plate 15 is slightly smaller than the inner diameter of the annular frame 204 and larger than the diameter of the wafer 201. The annular frame 204 of the wafer unit 200 is placed on the upper surface 152 of the frame mounting plate 15 with the wafer 201 positioned on the opening 151. 【0033】 In Embodiment 1, the frame mounting plate 15 is raised in the Z-axis direction by the cylinder 17 from a position where its upper surface 152 is on the same plane as the lower surface of the annular frame 204 of the wafer unit 200, which is positioned in the X-axis direction by the second guide rail 7. That is, the frame mounting plate 15 is attached to the tip of the extendable rod 171 of the cylinder 17, and is provided to be able to move up and down in the Z-axis direction by extending and retracting the rod 171 of the cylinder 17. 【0034】 The frame retaining plate 16 is fixed above the frame mounting plate 15. The frame retaining plate 16 is formed in a plate shape with approximately the same dimensions as the frame mounting plate 15, and has a circular opening 161 in the center that is the same dimensions as the opening 151. The opening 161 of the frame retaining plate 16 is positioned coaxially with the opening 151 of the frame mounting plate 15. 【0035】 The frame fixing unit 11 receives the wafer unit 200 by the third transport unit 53 as the rod 171 retracts and the wafer unit 200 is transported to the upper surface 152 of the frame mounting plate 15 located below it. After the annular frame 204 of the wafer unit 200 is placed on the upper surface 152 of the frame mounting plate 15, the rod 171 of the cylinder 17 extends and the frame mounting plate 15 rises. The frame fixing unit 11 then fixes the wafer unit 200 by sandwiching the annular frame 204 of the wafer unit 200 between the frame retaining plate 16 and the raised frame mounting plate 15. 【0036】 The pressing unit 12 presses the area 215 between the inner circumference of the annular frame 204 and the outer circumference of the wafer 201 of the wafer unit 200, which includes an annular frame 204 fixed by the frame fixing unit 11. The pressing unit 12 comprises an expansion drum 121 and a plurality of rollers 122. 【0037】 In Embodiment 1, the expansion drum 121 is formed in a cylindrical shape with a closed bottom, and its diameter is smaller than the inner diameter of the annular frame 204 that is placed on the upper surface 152 of the frame mounting plate 15, and its inner diameter is larger than the diameter of the wafer 201 that is attached to the sheet 202. The expansion drum 121 is arranged coaxially with the openings 151 and 161 of the frame fixing unit 11. 【0038】 The rollers 122 are formed in a cylindrical shape and are supported at the upper end of the expansion drum 121 so as to be rotatable around an axis (hereinafter referred to as the rotation axis). The rollers 122 are arranged at equal intervals in the circumferential direction. The rollers 122 are arranged at equal intervals at the upper end of the expansion drum 121, with a diameter smaller than the inner diameter of the annular frame 204 placed on the upper surface 152 of the frame mounting plate 15 and an inner diameter larger than the diameter of the wafer 201 attached to the sheet 202. In a plan view, they are arranged in an annular shape surrounding the wafer 201. 【0039】 The roller 122 has its axis of rotation parallel to the tangent to the expansion drum 121 in a plan view. The roller 122 is rotatably supported at the upper end of the expansion drum 121 around an axis of rotation parallel to the tangent to the expansion drum 121 in a plan view, and is therefore arranged in a direction that allows radial rotation of the wafer 201. 【0040】 The expansion drum 121 is attached to the cylinder 18 and moves up and down in the Z-axis direction by the cylinder 18. That is, the expansion drum 121 is attached to the end of the extendable rod 181 of the cylinder 18 and is provided to move up and down in the Z-axis direction as the rod 181 of the cylinder 18 extends and retracts. 【0041】 In Embodiment 1, the expansion drum 121 moves up and down in the Z-axis direction by the cylinder 18 between a position where the upper end of the roller 122 is located below the upper surface 152 of the frame mounting plate 15 of the frame fixing unit 11 that secures the annular frame 204, and a position where the upper end of the roller 122 is located above the upper surface 152 of the frame mounting plate 15 of the frame fixing unit 11 that secures the annular frame 204. 【0042】 As the cylinder 18 rises, the upper end of the roller 122 is positioned above the upper surface 152 of the frame mounting plate 15 of the frame fixing unit 11 that secures the annular frame 204. Therefore, the roller 122 presses against the region 215 between the inner circumference of the annular frame 204 and the outer circumference of the wafer 201 of the sheet 202 of the wafer unit 200, which is fixed by the frame fixing unit 11. 【0043】 The splitting unit 10 fixes the annular frame 204 of the wafer unit 200 with the frame fixing unit 11, and raises the expansion drum 121 from a position where the upper end of the roller 122 is below the upper surface 152 of the frame mounting plate 15 of the frame fixing unit 11 that fixes the annular frame 204, thereby pressing the region 215 between the inner circumference of the annular frame 204 and the outer circumference of the wafer 201 of the sheet 202 of the wafer unit 200 and expanding the sheet 202 in the planar direction. After expanding the sheet 202, the splitting unit 10 lowers the expansion drum 121, thereby creating slack in the region 215 between the inner circumference of the annular frame 204 and the outer circumference of the wafer 201 of the sheet 202 of the wafer unit 200. 【0044】 The heating unit 30 is positioned next to the other side of the pair of second guide rails 7 in the Y-axis direction. As shown in Figure 7, the heating unit 30 comprises a holding table 32, a frame fixing unit 31, a seat extension unit 36, and a heating unit 37. 【0045】 The holding table 32 has a holding surface 321 that suction-holds the wafer 201 of the wafer unit 200 via the sheet 202. The holding table 32 is disc-shaped with a diameter smaller than the inner diameter of the annular frame 204, and comprises a disc-shaped frame 322 made of a metal such as stainless steel, and a disc-shaped suction part 323 made of a porous material such as porous ceramic and surrounded by the frame 322. 【0046】 The upper surfaces of the frame 322 and the suction part 323 are arranged on the same plane, forming a holding surface 321 that attracts and holds the wafer 201. The suction part 323 has approximately the same diameter as the wafer 201. The suction part 323 is connected to a suction source 325, such as an ejector, via a suction passage 324 formed in the frame 322, etc. The suction passage 324 is provided with an on / off valve 326. 【0047】 The back surface 208 side of the wafer 201 is placed on the holding surface 321 of the holding table 32 via the sheet 202 of the wafer unit 200 that has been transported by the second transport unit 52. The holding table 32 is held in place by suction, with the back surface 208 side of the wafer 201 being attracted to the holding surface 321 by the suction part 323 of the holding surface 321, when the on / off valve 326 opens or the suction source 325 opens. 【0048】 The frame fixing unit 31 fixes the annular frame 204 of the wafer unit 200. The frame fixing unit 31 comprises a frame mounting plate 33 and a frame retaining plate 34. The frame mounting plate 33 has a circular opening 331 in its planar shape, and its upper surface 332 is formed as a flat plate parallel to the horizontal direction. The inner diameter of the opening 331 of the frame mounting plate 33 is slightly smaller than the inner diameter of the annular frame 204 and larger than the diameter of the wafer 201. The frame mounting plate 33 has a holding table 32 placed inside the opening 331, and the opening 331 is positioned coaxially with the holding table 32. As shown in Figure 5, the frame mounting plate 33 is provided with centering guides 333 at the four corners of its upper surface 332, which are movable horizontally and adjust the position of the annular frame 204 by moving horizontally, thereby positioning the wafer 201 in a position coaxial with the suction portion 323 of the holding surface 321 of the holding table 32. 【0049】 Furthermore, the frame mounting plate 33 is provided so as to be able to move up and down in the Z-axis direction by the cylinder 35. That is, the frame mounting plate 33 is attached to the end of the extendable rod 351 of the cylinder 35, and is provided so as to be able to move up and down in the Z-axis direction by the extension and retraction of the rod 351 of the cylinder 35. 【0050】 The frame retaining plate 34 is formed in a plate shape with approximately the same dimensions as the frame mounting plate 33, and has a circular opening 341 in the center that is the same dimensions as the opening 331. The frame retaining plate 34 is attached to the tip of the piston rod of a cylinder (not shown), and is movable between a position above the frame mounting plate 33 and a position retracted from above the frame mounting plate 33 as the piston rod extends and retracts along the Y-axis. As shown in Figure 5, the frame retaining plate 34 has elongated holes 342 at its four corners into which the centering guide 333 can enter. 【0051】 The frame fixing unit 31 is positioned with the frame retaining plate 34 retracted from above the frame mounting plate 33, and with the centering guides 333 separated from each other, the annular frame 204 of the wafer unit 200, which has been transported by the second transport unit 52, is placed on the upper surface 332 of the frame mounting plate 33. The frame fixing unit 31 brings the centering guides 333 closer together to position the wafer 201 of the wafer unit 200. The frame fixing unit 31 positions the frame retaining plate 34 above the frame mounting plate 33, and the frame mounting plate 33 is raised by the cylinder 35, so that the annular frame 204 of the wafer unit 200 is sandwiched and fixed between the frame mounting plate 33 and the frame retaining plate 34. 【0052】 The seat extension unit 36 ​​extends the seat 202 by relatively moving the holding table 32 and the frame fixing unit 31 to positions that are separated from each other along an axis that is in the vertical direction. As shown in Figure 7, the seat extension unit 36 ​​comprises a push-up member 361, a push-up member lifting unit 362, and a holding table lifting unit 363. 【0053】 The push-up member 361 is formed in a cylindrical shape, with a diameter smaller than the inner diameter of the annular frame 204 that rests on the upper surface 332 of the frame mounting plate 33, and an inner diameter larger than the diameters of the wafer 201 and the holding table 32 that are attached to the sheet 202. The push-up member 361 is positioned coaxially with the holding table 32, with the holding table 32 positioned inside it. A roller 364 is rotatably attached to the upper end of the push-up member 361. 【0054】 The lifting member lifting unit 362 moves the lifting member 361 up and down in the Z-axis direction, between a position where the roller 364 is located below the upper surface 332 of the lowered frame mounting plate 33 and a position where it is located above the upper surface 332 of the raised frame mounting plate 33. 【0055】 The holding table lifting unit 363 raises and lowers the holding table 32 in the Z-axis direction, between a position where the holding surface 321 is below the upper surface 332 of the lowered frame mounting plate 33 and a position where it is above the upper surface 332 of the raised frame mounting plate 33. 【0056】 The heating unit 37 heats and shrinks the slack in the region 215 between the annular frame 204 of the sheet 202, which is formed when the sheet 202 is expanded by the dividing unit 10, and the wafer 201. The heating unit 37 comprises a disc-shaped disc portion 371 that is movable in the Z-axis direction and rotates around an axis parallel to the Z-axis direction, and a plurality of heating portions 372. 【0057】 The heating units 372 are arranged at equal intervals in the circumferential direction above the region 215 of the sheet 202 of the wafer unit 200, which includes an annular frame 204 fixed to the disc portion 371 by a frame fixing unit 31, and are positioned on a circle corresponding to the region 215 of the sheet 202. The heating units 372 are positioned facing the region 215 of the sheet 202 of the wafer unit 200 held by the holding table 32 of the disc portion 371 and the frame fixing unit 31 in the Z-axis direction. In Embodiment 1, four heating units 372 are provided at equal intervals in the circumferential direction, but the present invention is not limited to four. 【0058】 The heating unit 372 is of a type that heats a region 215 of the sheet 202 by irradiating infrared rays 373 downwards. For example, it is an infrared ceramic heater that heats up when a voltage is applied and emits infrared rays 373. The heating unit 372 rotates over the aforementioned region 215 of the sheet 202 by the rotation of its disc portion 371 around an axis coaxial with the axis of the holding table 32. The heating unit 372 is also mounted on the disc portion 371 so as to be movable in the radial direction of the sheet 202 of the wafer unit 200 held by the frame fixing unit 31 by a drive unit (not shown). 【0059】 The heating unit 37 has a disc portion 371 that descends, and the heating portion 372 faces vertically the region 215 of the sheet 202 of the wafer unit 200 held by the holding table 32 and the frame fixing unit 31. The disc portion 371 rotates around its axis and swirls over the aforementioned region 215 of the sheet 202, thereby heating and contracting the slack in the region 215 of the sheet 202. 【0060】 Furthermore, as shown in Figure 8, the heating portion 372 of the heating unit 37 radiates infrared rays 373 toward the sheet 202, forming a heat spot 374 on the region 215 of the sheet 202 that is hotter than the surrounding sheet 202. In this way, the infrared rays 373 radiated from the heating portion 372 of the heating unit 37 toward the sheet 202 form a heat spot 374 on the region 215 of the sheet 202 that is hotter than the surrounding sheet 202. In Embodiment 1, the heat spot 374 is formed in the region 215 of the sheet 202 at a position opposite the radial center of the sheet 202 in the Z-axis direction (directly below the center of the heating portion 372). 【0061】 The cleaning unit 40 cleans mainly the wafer 201 of the wafer unit 200, which has its sheet 202 expanded by the splitting unit 10 and its slack heated and contracted by the heating unit 30. The cleaning unit 40 includes a spinner table 41 positioned below a pair of first guide rails 6 and which holds the wafer 201 of the wafer unit 200 by suction via the sheet 202, and a cleaning water supply nozzle (not shown) that supplies cleaning water to the surface 205 of the wafer 201 held by the spinner table 41 by suction. 【0062】 When the pair of first guide rails 6 separate, the cleaning unit 40 has the slack heated by the heating unit 30 via the second transport unit 52, and the contracted wafer unit 200 is placed on the spinner table 41. The cleaning unit 40 cleans the wafer 201 by supplying cleaning water from the cleaning water supply nozzle to the surface 205 of the wafer 201 while rotating the spinner table 41 around an axis parallel to the Z-axis direction. 【0063】 The control unit 100 controls the aforementioned components of the expansion device 1 to cause the expansion device 1 to perform the expansion operation of the sheet 202 onto the wafer unit 200. The control unit 100 is a computer having an arithmetic processing unit with a microprocessor such as a CPU (central processing unit), a storage device with memory such as ROM (read-only memory) or RAM (random access memory), and an input / output interface device. The arithmetic processing unit of the control unit 100 performs arithmetic processing according to the computer program stored in the storage device and outputs control signals for controlling the expansion device 1 to the aforementioned components of the expansion device 1 via the input / output interface device. 【0064】 The control unit 100 is connected to a display unit (not shown) which consists of a liquid crystal display device that displays the status of machining operations and images, and an input unit (not shown) which is used by the operator to register machining content information. The input unit consists of at least one of the following: a touch panel provided on the display unit and an external input device such as a keyboard. 【0065】 Next, the extension method according to Embodiment 1 will be described. Figure 9 is a flowchart showing the flow of the extension method according to Embodiment 1. 【0066】 The expansion method according to Embodiment 1 is a method of expanding the sheet 202 of the wafer unit 200, rupturing the wafer 201 starting from the modified layer 209, and dividing the wafer 201 into individual chips 210. As shown in Figure 9, the expansion method comprises an expansion step 1001, a heating step 1002, and a cleaning step 1003. 【0067】 (Extension step) Figure 10 is a schematic cross-sectional view showing the expansion step of the expansion method shown in Figure 9. Expansion step 1001 is a step in which the sheet 202 between the outer circumference of the wafer 201 of the wafer unit 200 and the inner circumference of the annular frame 204 is expanded to divide the wafer 201 into individual chips 210 starting from the modified layer 209. 【0068】 In expansion step 1001, the back surface 208 of the wafer 201 is attached to the sheet 202, and the annular frame 204 is attached to the outer edge of the sheet 202 to constitute the wafer unit 200. In Embodiment 1, in expansion step 1001, an operator or the like places the wafer unit 200 into the cassette 4, and the expansion device 1 places the cassette 4 containing the multiple wafer units 200 on the cassette elevator 3. 【0069】 Furthermore, in Embodiment 1, in expansion step 1001, the control unit 100 receives processing content information via the input unit and stores it in the storage device. In Embodiment 1, in expansion step 1001, when the control unit 100 receives a processing start instruction from the operator, the expansion device 1 lowers the expansion drum 121 of the division unit 10, takes out one wafer unit 200 from the cassette 4 with the first transport unit 51, temporarily places the wafer unit 200 on a pair of first guide rails 6, and then brings the pair of first guide rails 6 closer together to position the wafer unit 200 in the X-axis direction. 【0070】 In expansion step 1001, the expansion device 1 uses a second transport unit 52 to transport the wafer unit 200 from the first guide rail 6 onto the second guide rail 7, bringing the pair of second guide rails 7 closer together to position the wafer unit 200 in the X-axis direction. In frame fixing step 302, the expansion device 1 uses a third transport unit 53 to transport the wafer unit 200 from the pair of second guide rails 7 onto the upper surface 152 of the lowered frame mounting plate 15 of the splitting unit 10. 【0071】 In expansion step 1001, the expansion device 1 raises the frame mounting plate 15 of the splitting unit 10 to sandwich the annular frame 204 between the frame retaining plate 16 and the frame mounting plate 15, thereby fixing the wafer unit 200. In expansion step 1001, the expansion device 1 lowers the retaining drum 131 of the splitting unit 10, bringing the lower end of the upper roller 132 into contact with the area 215 of the sheet 202 of the wafer unit 200, which includes the annular frame 204 fixed by the frame fixing unit 11. 【0072】 In expansion step 1001, the expansion device 1 raises the expansion drum 121, as shown in Figure 10. As a result, the roller 122 provided at the upper end of the expansion drum 121 comes into contact with the region 215 of the sheet 202, and the roller 122 presses the region 215 from below upward, causing the sheet 202 to expand in the planar direction. In expansion step 1001, as a result of the expansion of the sheet 202, tensile forces act radially on the sheet 202. 【0073】 When a tensile force is applied radially to the sheet 202 attached to the back surface 208 of the wafer 201 in this manner, the wafer 201 is divided into individual chips 210 along the planned division line 206, with the modified layer 209 forming along the planned division line 206, using the modified layer 209 as a starting point. In addition, the wafer 201 widens, and gaps are formed between the chips 210. 【0074】 In expansion step 1001, the expansion device 1 lowers the expansion drum 121 of the splitting unit 10. As a result, the wafer unit 200 forms slack in the area 215 of the sheet 202 because the sheet 202 has been expanded. 【0075】 (Heating step) Figure 11 is a cross-sectional view of the heating unit's frame fixing unit fixing the wafer unit's frame during the heating step of the expansion method shown in Figure 9. Figure 12 is a cross-sectional view of the sheet expanded during the heating step of the expansion method shown in Figure 9. Figure 13 is a cross-sectional view of the heating unit's holding table holding the wafer unit by suction during the heating step of the expansion method shown in Figure 9, with the push-up member and holding table lowered. Figure 14 is a cross-sectional view of the sheet heating the slack in the sheet region during the heating step of the expansion method shown in Figure 9. Figure 15 is a schematic plan view showing the movement trajectory of the heating unit heating the slack in the sheet region during the heating step of the expansion method shown in Figure 9. Figure 16 is a schematic plan view showing the movement trajectory of the heat spot in area XVI in Figure 15. Figure 17 is a schematic plan view showing the movement trajectory of the heat spot in area XVII in Figure 15. Figure 18 is a schematic plan view showing the movement trajectory of the heat spot in the second region of the comparative example. 【0076】 The heating step 1002 is a step in which, after performing the expansion step 1001, the heating unit 372 heats the sheet region 215 between the outside of the wafer 201 and the inside of the annular frame 204 to shrink the slack in the sheet region 215 of the sheet 202 that was created in the expansion step 1001. In the heating step 1002, the expansion device 1 lowers the frame mounting plate 15 of the frame fixing unit 11 of the dividing unit 10 and the third transport unit 53 transports the wafer unit 200 on the frame mounting plate 33 onto a pair of second guide rails 7. 【0077】 In the heating step 1002, the expansion device 1 lowers the push-up member 361 and the holding table 32 of the heating unit 30, and positions the frame retaining plate 34 of the frame fixing unit 31 in the retracted position, and the second transport unit 52 transports the wafer unit 200 on the second guide rail 7 onto the upper surface 332 of the frame mounting plate 33. 【0078】 In heating step 1002, the expansion device 1 brings the centering guides 333 of the frame fixing unit 31 closer together to position the wafer 201 of the wafer unit 200. In heating step 1002, the expansion device 1 raises the frame mounting plate 33 and fixes the wafer unit 200 by sandwiching the annular frame 204 between the frame mounting plate 33 and the frame retaining plate 34, as shown in Figure 11. 【0079】 In heating step 1002, the expansion device 1 raises the push-up member 361 and the holding table 32 of the heating unit 30 to stretch the expanded sheet 202 area 215, as shown in Figure 12, and create a gap between the chips 210. In heating step 1002, the expansion device 1 opens the on / off valve 326 and uses the suction source 325 to draw in the suction part 323, holding the back surface 208 side of the wafer 201 to the holding surface 321 via the sheet 202, thereby maintaining the gap between the chips 210. 【0080】 In heating step 1002, as shown in Figure 13, the expansion device 1 lowers the push-up member 361 to below the upper surface 332 of the frame mounting plate 33, and lowers the holding table 32 until the holding surface 321 is on the same plane as the upper surface 332 of the frame mounting plate 33. This causes slack in the area 215 of the sheet 202. 【0081】 In heating step 1002, the expansion device 1 lowers the heating unit 37 of the heating unit 30, bringing the heating section 372 facing the region 215 of the sheet 202. In Embodiment 1, in heating step 1002, the expansion device 1 drives all the heating sections 372 of the heating unit 37 of the heating unit 30, causing the heating section 372 to rotate above the region 215 a predetermined number of times at a predetermined rotational speed while emitting infrared rays from all the heating sections 372. In this way, in heating step 1002, the expansion device 1 heats and shrinks the slack in the region 215 around its entire circumference. 【0082】 In Embodiment 1, during the heating step 1002, the expansion device 1 moves the heating unit 372, or heat spot 374, located directly above the second region 217, in the radial direction of the wafer 201 as indicated by arrow 218 in Figure 15, and also moves the heating unit 372, or heat spot 374, located directly above the first region 216, along the outer circumference of the wafer 201 at the radial center of region 215. Thus, in Embodiment 1, during the heating step 1002, the expansion device 1 moves the heat spot 374 in a circular motion along the outer circumference of the wafer 201 on the first region 216, and moves the heating unit 372 of the heating unit 37 so that the heat spot 374 reciprocates between a dead point on the outer circumference and a dead point on the inner circumference in the radial direction of the wafer 201 on the second region 217. Thus, in the heating step 1002, as shown in Figure 16, the expansion device 1 moves the heat spot 374 in the first region 216 so as to intersect with multiple molecular chains 214, and as shown in Figure 17, in the second region 217, the heat spot 374 moves radially so as to intersect with multiple molecular chains 214 and pass over multiple molecular chains 214. 【0083】 Thus, in Embodiment 1, during the heating step 1002, the expansion device 1 moves the heating unit 372 of the heating unit 37 so that the heat spot 374 reciprocates in the radial direction of the wafer 201 in the second region 217, thereby moving the heating unit 372 of the heating unit 37 so that the heat spot 374 is positioned over at least the entire area of ​​the second region 217. In this invention, moving the heating unit 372 of the heating unit 37 so that the heat spot 374 is positioned over the entire area of ​​the second region 217 means, in Embodiment 1, moving the heat spot 374 while moving it radially so as to intersect with the plurality of molecular chains 214 in the second region 217, and passing over the plurality of molecular chains 214. 【0084】 (Washing step) The cleaning step 1003 is a step in which the wafer 201 is cleaned in the cleaning unit 40 after the heating step 1002 has been performed. In the cleaning step 1003, the expansion device 1 stops the rotation and heating of the heating section 372 of the heating unit 37 of the heating unit 30, lowers the frame mounting plate 33 of the frame fixing unit 31 of the heating unit 30, and stops the suction holding of the holding table 32, etc. In the cleaning step 1003, the expansion device 1 transports the wafer unit 200 to the cleaning unit 40 in the second transport unit 52. In the cleaning step 1003, the expansion device 1 cleans the wafer unit 200 in the cleaning unit 40. 【0085】 In the cleaning step 1003, the expansion device 1 transports the wafer units 200 from the cleaning unit 40 to the cassette 4 using the second transport unit 52 and the first transport unit 51, and houses them in the cassette 4. The expansion device 1 sequentially expands the sheets 202 of the wafer units 200 in the cassette 4 to divide the wafers 201 into individual chips 210. Once the sheets 202 of all the wafer units 200 in the cassette 4 have been expanded and the wafers 201 have been divided into individual chips 210, the processing operation is completed. 【0086】 When the sheet 202 is heated by the heating unit 372, the infrared rays 373 emitted from the heating unit 372 locally heat the area directly below the radial center of the heating unit 372, forming a heat spot 374 that is hotter than the surrounding sheet 202. 【0087】 However, the expansion method according to Embodiment 1 moves the heating element 372, or heat spot 374, radially on the second region 217, allowing it to pass over more molecular chains 214, compared to the comparative example shown in Figure 18, which moves the heating element 372, or heat spot 374, circumferentially on the second region 217 and along the molecular chains 214 through which the heat spot 374 passes. For this reason, the expansion method according to Embodiment 1 heats the second region 217, which is less prone to shrinkage, so that the heat spot 374 is positioned over the entire region 215. In particular, it can suppress localized heating of the sheet 202 in the second region 217. As a result, the expansion method according to Embodiment 1 has the effect of allowing the expanded sheet 202 to be heat-shrunk. 【0088】 [Embodiment 2] The expansion method according to Embodiment 2 of the present invention will be described with reference to the drawings. Figure 19 is a schematic plan view showing the movement trajectory of the heating unit that heats the slack in the sheet area during the heating step of the expansion method according to Embodiment 2. Note that in Figure 19, the same reference numerals are used for the same parts as in Embodiment 1, and their description is omitted. 【0089】 The expansion method according to Embodiment 2 is the same as Embodiment 1, except that the heating step 1002 is different from that of Embodiment 1. In the expansion method according to Embodiment 2, in the heating step 1002, the expansion device 1 moves the heating section 372, i.e., the heat spot 374, located directly above the first region 216 and the second region 217, in the radial direction of the wafer 201 as shown by the arrow 218 in Figure 19. Thus, in Embodiment 2, in the heating step 1002, the expansion device 1 moves the heating section 372 of the heating unit 37 so that the heat spot 374 reciprocates between a dead point on the outer circumference and a dead point on the inner circumference in the radial direction of the wafer 201. 【0090】 Thus, in Embodiment 2, during the heating step 1002, the expansion device 1 moves the heating section 372 of the heating unit 37 so that the heat spot 374 reciprocates in the radial direction of the wafer 201 in the first region 216 and the second region 217, thereby moving the heating section 372 of the heating unit 37 so that the heat spot 374 is positioned over at least the entire area of ​​the second region 217. In this invention, moving the heating section 372 of the heating unit 37 so that the heat spot 374 is positioned over the entire area of ​​the second region 217 means, in Embodiment 2, moving the heat spot 374 radially so as to intersect with the plurality of molecular chains 214 in the second region 217, and passing over the plurality of molecular chains 214. 【0091】 The expansion method according to Embodiment 2 has the effect of allowing the expanded sheet 202 to be heat-shrunk, as it heats the second region 217 so that the heating portion 372, i.e., the heat spot 374, moves radially on the second region 217 and passes over multiple molecular chains 214, so that the heat spot 374 is positioned over the entire area of ​​region 215 in the second region 217 which is less prone to shrinking. 【0092】 [Embodiment 3] The expansion method according to Embodiment 3 of the present invention will be described with reference to the drawings. Figure 20 is a schematic plan view showing the movement trajectory of the heating unit that heats the innermost circumference of the sheet area in the heating step of the expansion method according to Embodiment 3. Figure 21 is a schematic plan view showing the movement trajectory of the heating unit that heats the radial center of the sheet area in the heating step of the expansion method according to Embodiment 3. Figure 22 is a schematic plan view showing the movement trajectory of the heating unit that heats the outermost circumference of the sheet area in the heating step of the expansion method according to Embodiment 3. Note that Figures 20, 21, and 22 use the same reference numerals as Embodiment 1 for the same parts and their descriptions are omitted. 【0093】 The expansion method according to Embodiment 3 is the same as Embodiment 1, except that the heating step 1002 is different from that of Embodiment 1. In the expansion method according to Embodiment 3, in the heating step 1002, the expansion device 1 heats the entire area 215 of the sheet 202 by moving the heating unit 37 so that the heat spots 374 move concentrically on the area 215. In the expansion method according to Embodiment 3, in the heating step 1002, as shown in Figure 20, the expansion device 1 positions all the heating parts 372, i.e., the heat spots 374, on the innermost radial circumference of the area 215, and moves the heat spots 374 in a circular motion along the outer circumference of the wafer 201 a predetermined number of times on the first area 216 and the second area 217. 【0094】 Subsequently, in the heating step 1002 of the expansion method according to Embodiment 3, the expansion device 1 positions all heating units 372, i.e., heat spots 374, on the radial center of the region 215, as shown in Figure 21, and moves the heat spots 374 in a circular motion along the outer circumference of the wafer 201 a predetermined number of times on the first region 216 and the second region 217. In the heating step 1002 of the expansion method according to Embodiment 3, the expansion device 1 positions all heating units 372, i.e., heat spots 374, on the radial outermost circumference of the region 215, as shown in Figure 22, and moves the heat spots 374 in a circular motion along the outer circumference of the wafer 201 a predetermined number of times on the first region 216 and the second region 217. 【0095】 Thus, in the expansion method according to Embodiment 3, in the heating step 1002, the expansion device 1 sequentially positions the radial position of the heating unit 372, i.e., the heat spot 374, at a plurality of positions, and moves the heating unit 372, i.e., the heat spot 374, positioned at each position in a circular manner along the outer circumference of the wafer 201, thereby moving the heating unit 372, i.e., the heat spot 374, along a plurality of molecular chains 214 on the second region 217. In Embodiment 3, in the heating step 1002, the expansion device 1 sequentially positions the radial position of the heating unit 372, i.e., the heat spot 374, at three positions, and moves the heating unit 372, i.e., the heat spot 374, in a circular manner along the outer circumference of the wafer 201. However, in the present invention, it may be positioned sequentially at two positions, or at four or more positions. 【0096】 Thus, in Embodiment 3, during the heating step 1002, the expansion device 1 sequentially positions the heating section 372, i.e., the heat spot 374, at multiple radial positions, and moves the heating section 372, i.e., the heat spot 374, positioned at each position in a circular motion along the outer circumference of the wafer 201, thereby moving the heating section 372 of the heating unit 37 so that the heat spot 374 is positioned over at least the entire area of ​​the second region 217. In this invention, moving the heating section 372 of the heating unit 37 so that the heat spot 374 is positioned over the entire area of ​​the second region 217 means, in Embodiment 3, moving the heat spot 374 along multiple molecular chains 214 of the second region 217. 【0097】 The expansion method according to Embodiment 3 involves sequentially positioning the radial position of the heating element 372, i.e., the heat spot 374, at multiple positions, and moving the heating element 372, i.e., the heat spot 374, positioned at each position in a circular motion along the outer circumference of the wafer 201. In order to heat the wafer so that the heat spot 374 is positioned over the entire area of ​​region 215 in at least the less shrinkable second region 217, the expanded sheet 202 can be heated and shrunk. 【0098】 It should be noted that the present invention is not limited to the embodiments described above. That is, it can be implemented with various modifications without departing from the core principles of the present invention. In Embodiment 1, a modified layer 209 was formed as the dividing point, but the present invention is not limited to this, and a laser-processed groove or a cutting groove may be formed as the dividing point. 【0099】 Furthermore, in Embodiment 1, even if the wafer 201 of the wafer unit 200 is divided into individual chips 210 along the division line 206 by division grooves formed on the division line 206, the expansion method of the present invention may expand the sheet 202 to widen the spacing between the chips 210. In addition, in the present invention, the wafer unit 200 may be equipped with a die attach film (hereinafter referred to as DAF) attached to the back surface 211 of the wafer 201. The DAF is an adhesive film for die bonding to fix the individually divided chips 210 to other chips or substrates, etc. [Explanation of Symbols] 【0100】 37 Heating Unit 200 wafer units 201 wafer 202 seats 203 Aperture 204 Ring Frame 215 area (heated area) 216 First area 217 Second area 373 Infrared (heat) 374 Heat Spots 1001 Extension Step 1002 Heating step

Claims

[Claim 1] A method for expanding a wafer unit comprising a wafer, a sheet to which the wafer is attached, and an annular frame to which the outer edge of the sheet is attached and which has an opening for housing the wafer, wherein the sheet is expanded, An expansion step of expanding the sheet between the outer circumference of the wafer of the wafer unit and the inner circumference of the annular frame, After performing the expansion step, a heating step is provided in which the heated area of ​​the sheet between the outer edge of the wafer and the inner circumference of the annular frame is heated by a heating unit that heats the sheet with heat radiated from a heating section, thereby shrinking the slack in the sheet generated in the expansion step. The heated area of ​​the sheet includes a first area and a second area that is less susceptible to shrinkage by heating than the first area. The heat radiated from the heating element of the heating unit onto the sheet creates a hot spot on the sheet that is hotter than the surrounding sheet. An expansion method comprising: moving the heating unit in the heating step so that the heat spot is positioned over at least the entire area of ​​the second region, and positioning the heating portion over at least the entire radial area of ​​the second region during the movement of the heating unit. [Claim 2] The expansion method according to claim 1, wherein in the heating step, the heat spot moves in a circular manner along the outer circumference of the wafer in the heated region, and in at least the second region, the heating unit is moved back and forth in the radial direction of the wafer to move the heat spot back and forth in the radial direction of the wafer. [Claim 3] The expansion method according to claim 1, wherein in the heating step, the heating unit is moved by changing the radial position of the heating part of the wafer so that the heat spot moves concentrically on the heated area, thereby heating the entire heated area of ​​the sheet.

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