WAFER MANUFACTURING METHOD AND WAFER MANUFACTURING APPARATUS

Abstract

Wafer manufacturing method for producing a wafer (W) from a semiconductor ingot (50), comprising: a holding step for holding the semiconductor ingot (50) on a chuck table (22); a thermal stress wave generating step for applying a pulsed laser beam having a wavelength that can be absorbed by the semiconductor ingot (50) to an upper surface (52) of the semiconductor ingot (50) held on the chuck table (22) to generate a thermal stress wave and propagate the thermal stress wave in the semiconductor ingot (50); a fracture layer forming step of applying a pulsed laser beam having a wavelength that can be transmitted through the semiconductor ingot (50) to the upper surface (52) of the semiconductor ingot (50) in synchronization with a timing at which the thermal stress wave generated in the thermal stress wave generating step and propagated in the semiconductor ingot (50) at a speed of sound depending on the material of the semiconductor ingot (50) reaches a position corresponding to a thickness of a wafer (W) to be manufactured from the semiconductor ingot (50), thereby causing the pulsed laser beam, whose wavelength can be transmitted through the semiconductor ingot (50), to be absorbed in a region where a band gap is reduced by a tensile stress of the thermal stress wave, thereby forming a fracture layer (S) in the semiconductor ingot (50); and a detaching step for detaching the wafer (W) from the semiconductor ingot (50) along the fracture layer (S).

Description

BACKGROUND OF THE INVENTIONTechnical field

[0001] The present invention relates to a wafer manufacturing method for manufacturing a wafer from a semiconductor ingot and a wafer manufacturing apparatus for manufacturing a wafer from a semiconductor ingot. Description of the state of the art

[0002] Devices such as integrated circuits (ICs), large-scale integration (LSI) circuits, and light-emitting diodes (LEDs) are formed on a semiconductor wafer made of silicon, sapphire, or the like. A functional layer is deposited on one surface of the wafer and a plurality of regions are divided on the functional layer with a grid of planned division lines. A cutting device, a laser machining device, or the like then processes the semiconductor wafer along the planned division lines to divide the semiconductor wafer into individual device chips containing the respective devices used in various electronic devices such as mobile phones and personal computers.

[0003] Power devices, LEDs, or the like are formed on a wafer made of single-crystal SiC by coating a functional layer on one surface of the wafer and dividing multiple regions of the functional layer with a grid of planned dividing lines. Wafers on which devices are to be formed are generally formed by slicing a cylindrical semiconductor ingot with a band saw. The surfaces and back of the wafer, which are sliced ​​from the ingot, are polished to a mirror finish (see, for example, JP 2000-094221 A).

[0004] However, it is not economical to cut a semiconductor ingot into wafers with a band saw and polish the face and back sides of the wafer, because much of the semiconductor ingot, for example, 70 to 80% of it, would be wasted. In particular, SiC ingots are disadvantageous in that they have low productivity because they are very hard, difficult and time-consuming to saw with a band saw, and their unit costs are so high that wafers cannot be formed efficiently.The present applicant has proposed a technology in which a laser beam having a wavelength that can be transmitted through a single-crystal SiC is applied to a SiC ingot, while a focused laser spot is applied to the laser beam in the SiC ingot, thereby forming separation layers in planned fracture planes in the SiC ingot, and a wafer is cut from the SiC ingot along the planned fracture plane at which the separation layers are formed (see, for example, JP 2016 - 111 143 A).

[0005] Furthermore, published patent application JP 2012-109341 A discloses a method for separating a semiconductor material, in which a circumferential groove is first formed on an outer peripheral surface of an ingot using a scribing device. Next, a first and second laser beam are superimposed to be irradiated from an end surface onto the circumferential groove. Both laser beams are then moved in a spiral trajectory along a plane to be cut. The plane to be cut and an adjacent portion thereof are converted by the first laser beam into a modified region, onto which the second laser beam is irradiated. A crack generated in the circumferential groove propagates radially to separate a wafer. Another wafer manufacturing method is presented in published patent application DE 10 2016 205 589 A1. PRESENTATION OF THE INVENTION

[0006] To apply the laser beam to the SiC ingot while accurately positioning the focused spot of the laser beam inside the SiC ingot to form a separation layer in the SiC ingot and separate a wafer from the SiC ingot, it is necessary to accurately determine the height of a top surface of the SiC ingot. In addition, since the surface height of the SiC ingot varies each time a wafer is formed from the SiC ingot, it is necessary to detect the height of the top surface of the SiC ingot each time a wafer is produced from the SiC ingot, resulting in low productivity.

[0007] It is therefore an object of the present invention to provide a wafer manufacturing method and a wafer manufacturing apparatus capable of forming wafers of a desired thickness from an ingot without having to detect the height of an upper surface of the ingot each time a wafer is manufactured from the ingot.

[0008] In accordance with one aspect of the present invention, there is provided a wafer manufacturing method for manufacturing a wafer from a semiconductor ingot, including: a holding step of holding the semiconductor ingot on a chuck table; a thermal stress wave forming step of applying a pulsed laser beam having a wavelength that can be absorbed by the semiconductor ingot to an upper surface of the semiconductor ingot held on the chuck table to form a thermal stress wave and propagate the thermal stress wave in the semiconductor ingot;a fracture layer forming step of applying a pulsed laser beam having a wavelength that can be transmitted through the semiconductor ingot to the upper surface of the semiconductor ingot in synchronization with a timing at which the thermal stress wave generated in the thermal stress wave forming step and traveling in the semiconductor ingot at a speed of sound depending on the material of the semiconductor ingot reaches a position corresponding to a thickness of a wafer to be formed from the semiconductor ingot, thereby causing the pulsed laser beam having a wavelength that can be transmitted through the semiconductor ingot to be absorbed in a region where a band gap is reduced by a tensile stress of the thermal stress wave, thereby forming a fracture layer in the semiconductor ingot;and a detaching step of detaching the wafer from the semiconductor ingot along the fracture layer;

[0009] Preferably, the wafer manufacturing method further includes, after the peeling step, a planarizing step of planarizing a surface of the semiconductor ingot from which the laser has been peeled.

[0010] In accordance with another aspect of the present invention, there is provided a wafer manufacturing apparatus for manufacturing a wafer from a semiconductor ingot, including: a chuck table for holding the semiconductor ingot thereon; thermal stress wave generating means for applying a pulsed laser beam having a wavelength that can be absorbed by the semiconductor ingot to an upper surface of the semiconductor ingot held on the chuck table to generate a thermal stress wave and propagate the thermal stress wave in the semiconductor ingot;and a fracture layer forming means for applying a pulsed laser beam having a wavelength that can be transmitted through the semiconductor ingot to the upper surface of the semiconductor ingot in synchronization with a timing at which the thermal stress wave generated by the thermal stress generating means and propagating in the semiconductor ingot at a speed of sound depending on the material of the semiconductor ingot reaches a position corresponding to a thickness of the wafer to be manufactured from the semiconductor ingot, thereby causing the pulsed laser beam having a wavelength that can be transmitted through the semiconductor ingot to be absorbed in a region where a band gap is reduced by a tensile stress of the thermal stress wave, thereby forming a fracture layer in the semiconductor ingot.

[0011] Preferably, the wafer manufacturing apparatus further includes a detaching means for detaching the wafer from the semiconductor ingot along the fracture layer formed by the fracture layer forming means.

[0012] The wafer manufacturing method according to the present invention allows the thickness of the wafer to be manufactured to be controlled only by the period at which the thermal stress wave propagates at the speed of sound depending on the material of the semiconductor ingot, without detecting the height of the top surface of the semiconductor ingot, which increases productivity.

[0013] Furthermore, the wafer manufacturing apparatus according to the present invention, as well as the wafer manufacturing method, allows the thickness of the wafer being manufactured to be controlled only by the time during which the thermal stress wave propagates at the speed of sound depending on the material of the semiconductor ingot, without detecting the height of the top surface of the semiconductor ingot, resulting in increased productivity.

[0014] The above and other objects, features and advantages of the present invention and the mode for carrying them out will become more apparent and the invention itself will be best understood by studying the following description and the appended claims with reference to the attached drawings which show a preferred embodiment of the invention. SHORT DESCRIPTION OF THE CHARACTERS Fig. 1 is a perspective view of a wafer manufacturing apparatus according to an embodiment of the present invention; Fig. Fig. 2A is a schematic view, partly in block form, of an optical system of a laser beam application unit of the wafer manufacturing apparatus shown in Fig. 1 is shown; Fig. 2B is an enlarged partial view of an ingot at the time when a thermal stress wave generation step and a fracture layer formation step are performed; Fig. 3 is a perspective view illustrating a detachment step; and Fig. 4 is a perspective view showing a step toward planar design. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] A wafer manufacturing method according to a preferred embodiment of the present invention and a wafer manufacturing apparatus according to the present embodiment suitable for carrying out the wafer manufacturing method will be described in detail below with reference to the accompanying drawings.

[0016] Fig. Fig. 1 perspectively illustrates the wafer manufacturing apparatus, indicated at 2, according to the present embodiment. The wafer manufacturing apparatus 2 includes a base 3, a holding unit 4 for holding a workpiece, a moving mechanism 5 for moving the holding unit 4, a laser beam application unit 6 for applying a laser beam to the workpiece held by the holding unit 4, the laser beam application unit 6 including thermal stress wave generating means and fracture layer forming means, which will be described later, an image pickup unit 12, a display unit 14, a peeling unit 16, and a control unit, which is not shown.

[0017] The holding unit 4 includes a rectangular X-axis movable plate 18 fixed to a front position of the base 3 and movable along a pair of guide rails 3a extending in the X-axis direction, a rectangular Y-axis movable plate 20 fixed to the X-axis movable plate 18 and movable along a pair of guide rails 18a extending in the Y-axis direction, and a hollow cylindrical chuck table 22 rotatably mounted on an upper surface of the Y-axis movable plate 20. The X-axis directions are indicated by an arrow X in Fig. 1 and the Y-axis directions are indicated by an arrow Y in Fig. 1 and extend perpendicular to the X-axis directions. An XY plane is defined by X and Y axes along the X-axis and Y-axis directions, respectively, and is essentially horizontal.

[0018] The movement mechanism 5 includes an X-axis movement mechanism 24 for moving the X-axis movable plate 18 back and forth in the X-axis direction and a Y-axis movement mechanism 26 for moving the Y-axis movable plate 20 back and forth in the Y-axis direction. The X-axis movement mechanism 24 includes a ball screw 28 extending in the X-axis direction above the base 3 and an electric motor 30 connected to one end of the ball screw 28. The ball screw 28 is screwed by a nut (not shown) fixed to a lower surface of the X-axis movable plate 18.The X-axis moving mechanism 24 is operated to convert a rotary motion of the electric motor 30 into a linear motion with the ball screw 28 and transmit the linear motion to the X-axis movable plate 18, thereby moving the X-axis movable plate 18 back and forth in the X-axis directions along the guide rails 3a of the base 3.

[0019] The Y-axis moving mechanism 26 includes a ball screw 32 extending in the Y-axis direction across the X-axis movable plate 18, and an electric motor 34 coupled to one end of the ball screw 32. The ball screw 32 is screwed by a nut (not shown) that is fixed to a lower surface of the Y-axis movable plate 20. The Y-axis moving mechanism 26 is operated to convert a rotary motion of the electric motor 34 into a linear motion with the ball screw 32 and transmit the linear motion to the Y-axis movable plate 20, thereby moving the Y-axis movable plate 20 back and forth in the Y-axis direction along the guide rails 18a on the X-axis movable plate 18.The moving mechanism 5 includes a rotating mechanism, not shown, having an electric motor housed in the chuck table 22 for rotating the chuck table 22 about its central axis with respect to the Y-axis movable plate 20.

[0020] The wafer manufacturing apparatus 2 includes a frame 36 erected at a rear portion of the base 3 spaced from the front portion of the base 3. The frame 36 includes a vertical wall 36a extending upward from an upper surface of the base 3 and a horizontal support 36b extending substantially horizontally from an upper end portion of the vertical wall 36a in an overhanging relationship with the moving mechanism 5. The horizontal support 36b houses an optical system of the laser beam application unit 6, which includes the thermal stress wave generating means and the fracture layer forming means described later. The laser beam application unit 6 also includes a beam condenser 69 disposed on a lower surface of a distal end of the horizontal support 36b of the frame 36.

[0021] The image pickup unit 12 is arranged on the lower surface of the distal end of the horizontal support 36b at a position spaced apart from the beam condenser 69 in the X-axis direction. The image pickup unit 12 includes a conventional image pickup device, i.e., a charge-coupled device (CCD), for capturing an image of the workpiece with a visible light beam, an infrared ray applying means for applying infrared ray to the workpiece, an optical system for receiving the infrared ray applied by the infrared ray applying means, and an image pickup device, i.e., an infrared CCD, for outputting an electrical signal representing the infrared ray captured by the optical system.The display unit 14, which is fixed to an upper surface of the horizontal support 36b of the frame 36, displays the image captured by the image pickup unit 12.

[0022] The detaching unit 16 includes a housing 16a shaped as a rectangular parallelepiped extending upward from terminal ends of the guide rails 3a on the base 3, and an arm 16b extending in one of the X-axis directions from a proximal end, which is vertically movably supported in the housing 16a. The housing 16a houses a raising and lowering means (not shown) for raising and lowering, i.e., vertically moving, the arm 16b. An electric motor 16c is arranged at a distal end of the arm 16b. The detaching unit 16 also includes a disk-shaped suction member 16d coupled to a lower surface of the electric motor 16c and rotatable about a vertical axis. The suction member 16d has a plurality of suction ports (not shown) formed in its lower surface. A suction means, not shown, is connected to the suction element 16d through a fluid channel.The suction member 16d houses an ultrasonic vibration applying means, not shown, for applying ultrasonic vibration to the lower surface of the suction member 16d.

[0023] The control unit is configured as a computer and includes a central processing unit (CPU) for performing arithmetic calculation operations according to a control program, a read-only memory (ROM) for storing the control programs, etc., and a random access memory (RAM) for storing the results of the arithmetic calculation operations. The control unit is electrically connected to the moving mechanism 5, the laser beam application unit 6, the image pickup unit 12, the display unit 14, and the peeling unit 16 and controls their operation.

[0024] According to the present embodiment, the workpiece to be processed by the wafer manufacturing apparatus 2 is a cylindrical silicon (Si) ingot, hereinafter referred to simply as “ingot” 50, which is Fig. 1. The ingot 50 has a circular upper surface 52 and a circular lower surface 54 positioned axially opposite the upper surface 52.

[0025] The optical system of the laser beam application unit 6 housed in the horizontal support 36b of the wafer manufacturing apparatus 2 will be described in detail below with reference to Fig. 2A. As described in Fig. 2A, the optical system of the laser beam application unit 6 includes a first laser beam generator 6A for forming a first pulsed laser beam PL1 having a wavelength that can be absorbed by the ingot 50, a second laser beam generator 6B for forming a second pulsed laser beam PL2 having a wavelength that can be transmitted through the ingot 50, and a laser beam application unit 6C for applying the first pulsed laser beam PL1 generated by the first laser beam generator 6A and the second pulsed laser beam PL2 generated by the second laser beam generator 6B to the upper surface 52 of the ingot 50 held by the holding unit 4.

[0026] The first laser beam generator 6A includes a first laser beam generator means 61 for forming and emitting the first pulsed laser beam PL1, and a reflection mirror 62 for changing an optical path of the first pulsed laser beam PL1 emitted from the first laser beam generator means 61. The first laser beam generator means 61 includes a first laser oscillator 611 for emitting the first pulsed laser beam PL1, which has a wavelength of 355 nm, for example, and a first attenuator 612 for adjusting an output power of the first pulsed laser beam PL1 emitted from the first laser beam generator means 61 to a desired level and emitting the adjusted first pulsed laser beam PL1 to the reflection mirror 62.

[0027] The second laser beam generator 6B includes a second laser beam generator 63 for forming and emitting the second pulsed laser beam PL2, and a delaying means 64 for delaying the second pulsed laser beam PL2 emitted from the second laser beam generator 63 by a desired time. The second laser beam generator 63 includes a second laser oscillator 631 for emitting the second pulsed laser beam PL2 having a wavelength of, for example, 1064 nm, and a second attenuator 632 for adjusting the output power of the second pulsed laser beam PL2 emitted from the second laser oscillator 631 to a desired level and emitting the adjusted second pulsed laser beam PL2.The second laser oscillator 631 operates at the same repetition frequency as the first laser oscillator 611 and emits the second pulsed laser beam PL2 synchronously with the first pulsed laser beam PL1. The delay means 64 for delaying the second pulsed laser beam PL2 emitted from the second laser oscillator 631 can be implemented, for example, by an optical fiber (not shown) having a length corresponding to the time by which the second pulsed laser beam PL2 is to be delayed, so that the second pulsed laser beam PL2 delayed by this time can be output from the delay means 64.

[0028] The laser beam introduction unit 6C includes a dichroic mirror 65 for reflecting the first pulsed laser beam PL1 reflected by the reflection mirror 62 of the first laser beam generator 6A and transmitting the second pulsed laser beam PL2 from the second laser beam generator 6B, a reflection mirror 66 for changing an optical path of the pulsed laser beam emitted from the dichroic mirror 65, an index scanner 67 configured as a galvanometer scanner, for example, for moving the pulsed laser beams reflected by the reflection mirror 66 in the Y-axis directions across the chuck table 22, a raster scanner 68 configured as a resonant scanner, for example, for scanning the pulsed laser beams reflected by the reflection mirror 66 in the X-axis directions across the chuck table 22, and a Beam condenser 69,which includes an fθ lens 691 for concentrating the pulsed laser beams emitted by the raster scanner 68 onto the upper surface 52 of the ingot 50 held on the chuck table 22 at a position defined by X and Y coordinates thereon. The first pulsed laser beam PL1 and the second pulsed laser beam PL2, which are guided to the dichroic mirror 65, are applied to the same area of ​​the chuck table 22.

[0029] The first laser beam generator 6A and the laser beam introduction unit 6C together form the thermal stress wave generating means designated H1 in Fig. 2A, according to the present invention. The thermal stress generating means H1 serves as a means for applying the first pulsed laser beam PL1, whose wavelength can be absorbed by the ingot 50, to the upper surface 52 of the ingot 50 held by the holding unit 4, forming a thermal stress wave, and propagating the thermal stress wave into the ingot 50.

[0030] The second laser beam generator 6B and the laser beam introduction unit 6C together form a fracture layer forming means which is filled with H2 in Fig. 2A, according to the present invention. The fracture layer forming means H2 serves as a means for applying the second pulsed laser beam PL2, whose wavelength can be transmitted through the ingot 50, to the upper surface 52 of the ingot 50 in synchronization with a predetermined time, during which the thermal stress wave generated on the upper surface 52 of the ingot 50 by the thermal stress wave generating means H1 and propagated in the ingot 50 at a speed of sound depending on the material of the ingot 50 reaches a depth position reached from the upper surface 52 of the ingot 50 and corresponding to a thickness of a wafer W (see Fig. 3) to be made from the ingot 50, for example, a depth of 1 mm from the top surface 52 of the ingot 50, which causes the second pulsed laser beam PL2 to be absorbed in a region where the band gap is reduced by a tensile stress of the thermal stress wave, thereby forming a fracture layer in the ingot 50.

[0031] The wafer manufacturing method according to the present embodiment for forming the wafer W from the ingot 50 on the wafer manufacturing apparatus 2 described above will be described in detail below with reference to Fig. 1, Fig. 2A and Fig. 2B.

[0032] To form the wafer W having a desired thickness of 1 mm from the ingot 50, the ingot 50 is first held on the chuck table 22 of the holding unit 4 (holding step). Specifically, the ingot 50 is secured to the chuck table 22 by an adhesive, such as an epoxy adhesive, disposed between an upper surface of the chuck table 22 and the lower surface 54 of the ingot 50.

[0033] Then, to perform the thermal stress wave forming step and a fracture layer forming step, the moving mechanism 5 is actuated to move the chuck table 22 to a position immediately below the image pickup unit 12. The image pickup unit 12 captures an image of the ingot 50 and detects a position, that is, a machining start position on the upper surface 52 of the ingot 50 where the ingot 50 is initially machined (alignment step). Then, the control unit (not shown) controls the moving mechanism 5 to position the machining start position on the upper surface 52 of the ingot 50 below the beam condenser 69.

[0034] Thereafter, the thermal stress wave generating means H1 is energized to form the first pulsed laser beam PL1 whose wavelength of 355 nm can be absorbed by the material (Si) of the ingot 50 and to apply the first pulsed laser beam PL1 to the upper surface 52 of the ingot 50 at a predetermined position thereon by the laser beam applying unit 6C (thermal stress wave generating step).

[0035] Application conditions for a laser beam in the thermal stress wave generation step are exemplified below. An average output power of the first pulsed laser beam PL1 is adjusted by the first damper 612 of the thermal stress wave generation means H1 to such a level that, although the first pulsed laser beam PL1 is absorbed by the ingot 50, it does not cause ablation on the upper surface 52 of the ingot 50. Wavelength: 355 nm Repetition frequency: 50 kHz average output power: 1 W Pulse duration: 100 ps or less.

[0036] When the first pulsed laser beam PL1 is applied to the upper surface 52 of the ingot 50 in the thermal stress wave generation step, the upper surface 52 of the ingot 50 is thermally excited, and a thermal stress wave generated by the thermal excitation of the upper surface 52 of the ingot 50 is propagated in the ingot 50 as represented by N1 → N2 → N3 in Fig. 2B. The thermal stress wave is progressively propagated in the ingot 50, as indicated by N1 → N2 → N3, at a speed of sound (9620 m / s) depending on the material (Si) of the ingot 50. The thermal stress wave propagated in a semiconductor such as silicon is a tensile stress wave of short pulses, and the band gap is narrower than normal at a position where a tensile stress is applied. In other words, a region where the band gap is reduced progressively propagates in the ingot 50 from the upper surface 52 to the lower surface 54. The fracture layer formation step is performed together with the thermal stress wave generation step as follows.

[0037] To perform the fracture layer forming step, the fracture layer forming means H2 is energized to synchronously emit the second pulsed laser beam PL2, whose wavelength is 1064 nm and can be transmitted through the material (Si) of the ingot 50, from the second laser oscillator 631 at the same repetition frequency of 50 kHz as the first laser oscillator 611. Then, the output power of the second pulsed laser beam PL2 is adjusted to a predetermined level by the second attenuator 632, and the second pulsed laser beam PL2 is delayed by a predetermined time from the first pulsed laser beam PL1 by the delay means 64.The predetermined time by which the pulsed laser beam PL2 is delayed by the delay means 64 refers to a time during which the thermal stress wave generated on the upper surface 52 of the ingot 50 in the thermal stress wave generation step and propagating in the ingot 50 at a speed of sound (9620 m / s) reaches a depth position 1 mm apart from the upper surface 52 of the ingot 50 and corresponds to the thickness of the wafer W to be formed from the wafer 50. According to this embodiment, the predetermined time is 103.9 ns. The second pulsed laser beam PL2 is applied by the laser beam application unit 6C to the portion of the upper surface 52 of the ingot 50 to which the first pulsed laser beam PL1 was applied.

[0038] The application conditions for a laser beam in the formation step for a fracture layer are given as an example below. Wavelength: 1064 nm Repetition frequency: 50 kHz average output power: 10 W Pulse duration: 10 ns

[0039] When the thermal stress wave generation step and the fracture layer formation step are performed, the second pulsed laser beam PL2 applied by the fracture layer formation means H2 is delayed by a predetermined time of 103.9 ns from the first pulsed laser beam PL1 by the delay means 64. As shown in Fig. 2B, the first pulsed laser beam PL1 is applied to the upper surface 52 of the ingot 50, so that the thermal stress wave is formed, which is propagated progressively at the speed of sound depending on the material of the ingot 50, as indicated by N1 → N2 → N3, and a region where the band gap is reduced is formed at a depth position P 1 mm from the upper surface 52 corresponding to the thickness of the wafer W. The second pulsed laser beam PL2, which is also applied to the ingot 50, is absorbed in the thus-formed region, thereby applying destructive stresses in the ingot 50 and locally breaking the ingot.

[0040] As described above, the wafer manufacturing apparatus 2 according to the present embodiment includes the raster scanner 68 and the index scanner 67 as shown in Fig. 2A. The raster scanner 68 and the index scanner 67 are actuated to apply the first pulsed laser beam PL1 and the second pulsed laser beam PL2 through the fθ lens 691 onto the upper surface 52 of the ingot 50 in a predetermined range defined by X and Y coordinates, thereby forming a fracture layer S in the ingot 50 spaced 1 mm deep from the upper surface 52 of the ingot 50.The moving mechanism 5 is operated to move the chuck table 22 in the X-axis directions and the Y-axis directions to positions not irradiated by the pulsed laser beam PL1 and the second pulsed laser beam PL2, progressively in the range where the first pulsed laser beam PL1 and the second pulsed laser beam PL2 are to be applied from the condenser, thereby performing a thermal stress wave generation step and the fracture layer formation step over the entire upper surface 52 of the ingot 50 to form the fracture layer S entirely over the ingot 50 at a depth of 1 mm from the upper surface 52.

[0041] Then, a detaching step is performed to detach the wafer W from the ingot 50 at the fracture layer S. The detaching step is described in detail below with reference to Fig. 1 and Fig. 3 described.

[0042] To perform the detaching step, first, the moving mechanism 5 is operated to move the chuck table 22 to a position below the suction member 16d of the detaching unit 16. Then, the raising and lowering means (not shown) housed in the casing 16a is operated to lower the arm 16b to bring the lower surface of the suction member 16d into close contact with the upper surface 52 of the ingot 50.Next, the suction means (not shown) coupled to the suction element 16d is actuated to draw the upper surface 52 of the ingot 50 to the lower surface of the suction element 16d under suction, and then the ultrasonic vibration applying means (not shown) housed in the suction element 16d is actuated to apply ultrasonic vibrations to the lower surface of the suction element 16d, while simultaneously energizing the electric motor 16c to rotate the suction element 16d. Now, the ingot 50 is fractured along the fracture layer S, thereby detaching the portion of the ingot 50 above the fracture layer S while the wafer W has a desired thickness of 1 mm. The detaching step is thus completed.After the detachment step is performed, the thermal stress wave generation step, the fracture layer formation step, and the detachment step are successively performed on the ingot 50 to successively form wafer W from the ingot 50.

[0043] According to the present embodiment described above, the fracture layer S in the ingot can be formed at a position corresponding to the 1 mm thickness of the wafer W to be formed from the ingot 50 simply by applying the first pulsed laser beam PL1, whose wavelength can be absorbed by the ingot 50, to the upper surface 52 to generate and propagate the thermal stress wave in the ingot 50, and applying the second pulsed laser beam PL2 delayed by a time of 103.9 ns while the thermal stress wave reaches the depth position corresponding to the 1 mm thickness of the wafer W to be formed. Consequently, the thickness of the wafer W can be controlled without detecting the height of the upper surface 52 of the ingot 50, thus increasing productivity.

[0044] When the peeling step is performed as described above, the surface of the ingot 50 from which the wafer W has been peeled, that is, a new upper surface 52 of the ingot 50, is a rough surface because surface asperities remain due to the fracture layer S. Therefore, for forming wafers W repeatedly from the ingot 50, it is preferable to perform a planarizing step for planarizing the new upper surface 52 of the ingot 50 from which the wafer W has been peeled.

[0045] To carry out the step of planarizing the upper surface 52 of the ingot 50, the ingot 50 having the upper surface 52 from which the wafer W has been detached may be brought to a separate grinding device, where the upper surface 52 is ground and planarized. Alternatively, the wafer manufacturing apparatus 2 may additionally include a grinding unit that grinds and planarizes the upper surface 52 of the ingot 50. According to the present embodiment, the wafer manufacturing apparatus 2 includes a grinding unit 7 partially disposed in Fig. 4, which is attached to the base 3 for performing a planarizing step to grind the upper surface 52 of the ingot 50 to make it planar.

[0046] As in Fig. 4, the grinding unit 7 includes a servomotor (not shown), a vertical spindle 7a rotatable about its central axis by the servomotor, a wheel mount 7b disposed at a lower end of the spindle 7a, a grinding wheel 7c fixed to a lower surface of the wheel mount 7b, and a plurality of grinding stones 7d arranged in an annular array on a lower surface of the grinding wheel 7c. The grinding unit 7 has its vertical position precisely controlled in grinding feed directions, i.e., vertical directions, by a raising and lowering means (not shown) coupled thereto.

[0047] To carry out the planar shaping step, the clamping table 22 with the ingot 50 held thereon is positioned below the grinding unit 7, as shown in Fig.4. Then, the chuck table 22 is rotated about its central axis at a rotational speed of 300 rpm, for example, by the rotating mechanism housed therein, and the grinding wheel 7c is rotated about its central axis at a rotational speed of 6000 rpm, for example, by the servo motor. The elevating and lowering means is operated to lower the grinding unit 7 to bring the grinding stones 7d into contact with the upper surface 52 of the ingot 50 from which the wafer W has been peeled. After the grinding stones 7d are held in contact with the upper surface 52 of the ingot 50, the elevating and lowering means further lowers the grinding unit 7 at a predetermined grinding feed speed of 0.1 μm / s, for example, thereby grinding and flattening the upper surface 52 of the ingot 50.

[0048] After the upper surface 52 of the ingot 50 is planarized, the thermal stress wave generation step, the fracture layer formation step, the peeling step, and the planarization step are performed again in the manner described above. The wafer manufacturing process according to the above order is repeated to efficiently form a plurality of wafers W from the ingot 50. According to the above-described embodiment, the planarization step is performed using the grinding unit 7. However, the present invention is not limited to such details. The planarization step may be performed by a polishing agent with a polishing wheel.

[0049] The present invention is not limited to the above-described embodiment. In the above embodiment, the thermal stress wave generating means H1 and the fracture layer forming means H2 share the laser beam application unit 6C to apply the first pulsed laser beam PL1 and the second pulsed laser beam PL2 from one direction. However, it is not necessarily necessary to apply the first pulsed laser beam PL1 and the second pulsed laser beam PL2 from one direction; rather, the thermal stress wave generating means H1 and the fracture layer forming means H2 may each have different laser beam application units for applying the first pulsed laser beam PL1 and the second pulsed laser beam PL2 at different angles, respectively, to the ingot 50.

[0050] The present invention is not limited to the details of the preferred embodiment described above. The scope of the invention is defined by the appended claims, and all changes and modifications that fall within the equivalent scope of the claims are therefore encompassed by the invention.

Claims

[1] A wafer manufacturing method for manufacturing a wafer (W) from a semiconductor ingot (50), comprising: a holding step for holding the semiconductor ingot (50) on a chuck table (22); a thermal stress wave generating step for applying a pulsed laser beam having a wavelength that can be absorbed by the semiconductor ingot (50) to an upper surface (52) of the semiconductor ingot (50) held on the chuck table (22) to generate a thermal stress wave and propagate the thermal stress wave in the semiconductor ingot (50); a fracture layer forming step of applying a pulsed laser beam having a wavelength that can be transmitted through the semiconductor ingot (50) to the upper surface (52) of the semiconductor ingot (50) in synchronization with a timing at which the thermal stress wave generated in the thermal stress wave generating step and propagated in the semiconductor ingot (50) at a speed of sound depending on the material of the semiconductor ingot (50) reaches a position corresponding to a thickness of a wafer (W) to be manufactured from the semiconductor ingot (50), thereby causing the pulsed laser beam, whose wavelength can be transmitted through the semiconductor ingot (50), to be absorbed in a region where a band gap is reduced by a tensile stress of the thermal stress wave, thereby forming a fracture layer (S) in the semiconductor ingot (50); and a detaching step for detaching the wafer (W) from the semiconductor ingot (50) along the fracture layer (S). [2] The wafer manufacturing method according to claim 1, further comprising: after the detaching step, a step of planarizing a surface (52) of the semiconductor ingot (50) from which the wafer was detached. [3] A wafer manufacturing apparatus for manufacturing a wafer (W) from a semiconductor ingot (50), comprising: a clamping table (22) for holding the semiconductor ingot (50) thereon; a thermal stress wave generator means for applying a pulsed laser beam having a wavelength that can be absorbed by the semiconductor ingot (50) to an upper surface (52) of the semiconductor ingot (50) held on the chuck table (22) to generate a thermal stress wave and propagate the thermal stress wave in the semiconductor ingot (50); and a fracture layer forming means configured to apply a pulsed laser beam having a wavelength capable of being transmitted through the semiconductor ingot (50) to the upper surface (52) of the semiconductor ingot (50) in synchronization with a timing at which the thermal stress wave generated by the thermal stress wave generating means and propagated in the semiconductor ingot (50) at a speed of sound depending on the material of the semiconductor ingot (50) reaches a position corresponding to a thickness of a wafer to be manufactured from the semiconductor ingot (50), thereby causing the pulsed laser beam having a wavelength capable of being transmitted through the semiconductor ingot (50) to be absorbed in a region where a band gap is reduced by a tensile stress of the thermal stress wave, thereby forming a fracture layer (S) in the semiconductor ingot (50). [4] The wafer manufacturing apparatus according to claim 3, further comprising: a detaching means for detaching the wafer (W) from the semiconductor ingot (50) along the fracture layer (S) formed by the fracture layer forming means.

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