JP2018006575A - Method of processing laminated wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated wafer processing method capable of preventing reduction in quality of a GaN layer.SOLUTION: The laminated wafer processing method according to one embodiment of the present invention includes: a laminated wafer generation step for generating a laminated wafer 6 by laminating a GaN layer 4 on an upper surface of a silicon substrate 2: and an annular crack formation step for forming an annular modified layer 16 in the inside of the silicon substrate 2 in the vicinity of an outer periphery by positioning a focus point FP on the inside of the silicon substrate 2 in the vicinity of the outer periphery and irradiating the laminated wafer with a laser beam LB of wavelength having transmissivity to the laminated wafer 6, and forming an annular crack 18 extended from the annular modified layer 16 up to an upper surface of the GaN layer 4 in the outer peripheral vicinity of the GaN layer 4.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for processing a laminated wafer in which a GaN (gallium nitride) layer is laminated on an upper surface of a silicon substrate.

  A wafer formed by dividing a plurality of devices such as ICs, LSIs, LEDs, and power devices on the surface by dividing lines, a dicing device having a cutting blade that can be rotated, and a laser processing device that performs processing by irradiating a laser beam Etc. to be divided into individual devices. Each of the divided devices is used for electric devices such as mobile phones, personal computers, and lighting devices.

  ICs and LSIs are generally formed by stacking multiple circuits on the top surface of a silicon substrate, while LEDs and power devices are formed by stacking multiple circuits on the top surface of a SiC (silicon carbide) substrate and GaN substrate. Is done. Further, since the productivity is low and the cost is high to produce a GaN substrate, a technique for growing and stacking a GaN layer on the upper surface of a silicon substrate has been proposed (see, for example, Patent Documents 1 and 2). ).

JP 2013-123052 A JP 2006-523033 A

  However, after laminating the GaN layer on the upper surface of the silicon substrate, there is a problem that cracks occur from the outer periphery of the GaN layer over time and gradually reach the inner side of the GaN layer, leading to deterioration of the quality of the GaN layer. is there.

  An object of the present invention made in view of the above-described fact is to provide a method for processing a laminated wafer that can prevent the quality of a GaN layer from being deteriorated.

  In order to solve the above problems, the present invention provides the following method for processing a laminated wafer. That is, a method for processing a laminated wafer in which a GaN layer is laminated on the upper surface of a silicon substrate, the laminated wafer generating step for producing a laminated wafer by laminating the GaN layer on the upper surface of the silicon substrate, and an inner portion in the vicinity of the outer periphery of the silicon substrate. An annular modified layer is formed inside the vicinity of the outer periphery of the silicon substrate by irradiating the laminated wafer with a laser beam having a wavelength that is transparent to the laminated wafer. And an annular crack forming step of forming an annular crack extending from the GaN layer to the upper surface of the GaN layer in the vicinity of the outer periphery of the GaN layer.

  Preferably, in the annular crack forming step, a laser beam is irradiated from the GaN layer side. In the annular crack forming step, it is preferable to irradiate a laser beam from the silicon substrate side.

  In the method for processing a laminated wafer provided by the present invention, a crack generated from the outer peripheral portion of the GaN layer can be blocked by an annular crack formed in the vicinity of the outer periphery of the GaN layer, and therefore, the crack reaches the inner portion of the GaN layer. It is possible to prevent deterioration of the quality of the GaN layer.

The perspective view (a) of a silicon substrate, the perspective view (b) of a laminated wafer, and the sectional view (c) of a laminated wafer. The perspective view (a) and sectional view (b) which show the state where the laser beam is irradiated from the GaN layer side and the annular crack formation process is carried out, and the cross section near the outer periphery of the laminated wafer in which the modified layer and the crack are formed FIG. The perspective view (a) and sectional view (b) which show the state where the laser beam is irradiated from the silicon substrate side and the annular crack formation process is carried out, and the cross section near the outer periphery of the laminated wafer in which the modified layer and the crack are formed FIG. Sectional drawing of the outer periphery vicinity of the laminated wafer by which the annular groove was formed in the GaN layer for reference.

  Hereinafter, an embodiment of a method for processing a laminated wafer according to the present invention will be described with reference to the drawings.

  In the method for processing a laminated wafer according to the present invention, first, a laminated wafer generating step is performed. In the laminated wafer generating step, a GaN layer 4 is laminated on the upper surface of the silicon substrate 2 shown in FIG. For example, a silicon substrate 2 having a diameter of about 200 mm and a thickness of about 200 μm can be used. As shown in FIG. 1C, when the GaN layer 4 is laminated on the upper surface of the silicon substrate 2, the layer thickness T1 at the outer peripheral portion 4a of the GaN layer 4 is slightly thicker than the layer thickness T2 of the inner portion 4b of the GaN layer 4. Become. Specifically, when the layer thickness T2 of the circular inner portion 4b located on the radially inner side of the outer peripheral portion 4a is about 5 μm, the layer thickness T1 of the annular outer peripheral portion 4a is about 8 μm, and the inner portion The width W in the radial direction of the outer peripheral portion 4a where the layer thickness of the GaN layer 4 is thicker than the layer thickness T2 of 4b is about 0.5 to 1 mm.

  After performing the laminated wafer generating step, an annular modified layer is formed inside the silicon substrate 2 and an annular crack extending from the annular modified layer to the upper surface of the GaN layer 4 is formed near the outer periphery of the GaN layer 4. An annular crack forming step is performed. An annular crack formation process can be implemented, for example using the laser processing apparatus 8 which shows the one part in FIG. The laser processing apparatus 8 includes a chuck table 10 and a condenser 12. The chuck table 10 configured to adsorb a workpiece on the upper surface is rotated about a rotation axis Z extending in the vertical direction by a rotating means (not shown), and X is moved by an X-direction moving means. Advancing and retreating in the direction and advancing and retreating in the Y direction by the Y direction moving means (both not shown). The condenser 12 includes a condenser lens (none of which is shown) for condensing the pulse laser beam LB oscillated from the pulse laser beam oscillator of the laser processing apparatus 8 and irradiating the workpiece. Note that the X direction is a direction indicated by an arrow X in FIG. 2, and the Y direction is a direction indicated by an arrow Y in FIG. 2 and is a direction orthogonal to the X direction. The plane defined by the X direction and the Y direction is substantially horizontal.

This will be described with reference to FIG. In the annular crack forming step, first, a circular protective member 14 that can be formed from a synthetic resin sheet such as polyvinyl chloride (PVC) is attached to the surface on the silicon substrate 2 side. Next, the laminated wafer 6 is placed on the upper surface of the chuck table 10 with the surface on the GaN layer 4 side facing up and the center O of the laminated wafer 6 aligned with the rotation axis Z of the chuck table 10. Next, the surface on the silicon substrate 2 side (protective member 14 side) is attracted to the upper surface of the chuck table 10, and the laminated wafer 6 is fixed to the chuck table 10. Next, the chuck table 10 is moved by the X direction moving means and the Y direction moving means, and the vicinity of the outer periphery of the laminated wafer 6 is positioned immediately below the condenser 12. Next, the condensing point FP of the pulse laser beam LB is positioned in the vicinity of the outer periphery of the silicon substrate 2 (for example, a position on the inner side in the radial direction of about 2 to 5 mm from the outer periphery of the silicon substrate 2). That is, the radial position of the condensing point FP is positioned radially inward from the outer peripheral portion 4 a of the GaN layer 4. Next, a pulsed laser beam LB having a wavelength that is transmissive to the laminated wafer 6 is irradiated from the condenser 12 to the laminated wafer 6 while the chuck table 10 is rotated counterclockwise by a rotating means as viewed from above. To do. Thereby, the annular modified layer 16 can be formed in the vicinity of the outer periphery of the silicon substrate 2. When the modified layer 16 is formed inside the silicon substrate 2, as shown in FIG. 2C, the crack 18 propagates from the modified layer 16 upward and downward of the modified layer 16. The crack 18 extending toward the GaN layer 4 extends beyond the interface 20 between the silicon substrate 2 and the GaN layer 4 to the upper surface of the GaN layer 4. Therefore, when the annular modified layer 16 is formed in the vicinity of the outer periphery of the silicon substrate 2, an annular crack 18 extending from the annular modified layer 16 to the upper surface of the GaN layer 4 is formed in the vicinity of the outer periphery of the GaN layer 4. Is done. The vicinity of the outer periphery of the GaN layer 4 where the annular crack 18 is formed means an outer peripheral surplus region surrounding a device region where a plurality of devices are formed, and is radially inward from the outer peripheral portion 4 a of the GaN layer 4. Such an annular crack forming step can be performed, for example, under the following processing conditions.
Laser beam wavelength: 1064 nm
Repetition frequency: 50 kHz
Average output: 1W
Processing feed rate (circumferential speed at the focal point position): 100 mm / s

  In the laminated wafer processing method of the present invention, as shown in FIG. 2 (c), the crack 22 generated from the outer peripheral portion 4 a of the GaN layer 4 can be blocked by the annular crack 18 formed in the vicinity of the outer periphery of the GaN layer 4. Therefore, the inner portion 4b of the GaN layer 4 is not cracked, and the deterioration of the quality of the GaN layer 4 can be prevented.

  In the explanation of the annular crack forming step, the example in which the pulse laser beam LB is irradiated from the GaN layer 4 side has been described. However, in the annular crack forming step, as shown in FIGS. The laser beam LB may be irradiated from the silicon substrate 2 side. Even when the pulse laser beam LB is irradiated from the silicon substrate 2 side, the annular modified layer 16 can be formed on the inner portion 4b in the vicinity of the outer periphery of the silicon substrate 2 as shown in FIG. An annular crack 18 extending from the modified layer 16 to the upper surface of the GaN layer 4 can be formed in the vicinity of the outer periphery of the GaN layer 4.

  In addition, a condensing point is positioned on the upper surface in the vicinity of the outer periphery of the GaN layer 4, and the GaN layer 4 is subjected to ablation by irradiating the GaN layer 4 with a laser beam having a wavelength that absorbs the laminated wafer 6. An annular groove 24 as shown in FIG. 4 extending from the upper surface of the GaN layer 4 to the interface 20 is formed in the vicinity of the outer periphery of the GaN layer 4, and the crack 22 generated from the outer peripheral portion 4 a of the GaN layer 4 is blocked by the annular groove 24. it can. However, when the annular groove 24 is formed in the GaN layer 4, there is a problem that debris generated when the ablation processing is performed on the GaN layer 4 adheres to the surface of the GaN layer 4 and the quality of the GaN layer 4 is deteriorated. . In this regard, in the method for processing a laminated wafer according to the present invention, in the annular crack forming step, a condensing point FP is positioned inside the vicinity of the outer periphery of the silicon substrate 2 and a pulse laser beam LB having a wavelength that is transparent to the laminated wafer 6. Is applied to the laminated wafer 6 to form an annular modified layer 16 in the vicinity of the outer periphery of the silicon substrate 2 and to form an annular crack 18 extending from the annular modified layer 16 to the upper surface of the GaN layer 4. 4 is formed in the vicinity of the outer periphery of 4 (that is, the inside of the laminated wafer 6 is processed), so that debris does not occur and the quality of the GaN layer 4 does not deteriorate.

2: Silicon substrate 4: GaN layer 6: Laminated wafer 16: Modified layer 18: Crack LB: Pulsed laser beam FP: Focusing point

Claims (3)

A method for processing a laminated wafer in which a GaN layer is laminated on an upper surface of a silicon substrate,
A laminated wafer generating step of forming a laminated wafer by laminating a GaN layer on the upper surface of the silicon substrate;
An annular modified layer is formed in the vicinity of the outer periphery of the silicon substrate by locating a focusing point in the vicinity of the outer periphery of the silicon substrate and irradiating the laminated wafer with a laser beam having a wavelength that is transparent to the stacked wafer. And an annular crack forming step of forming an annular crack from the annular modified layer to the upper surface of the GaN layer in the vicinity of the outer periphery of the GaN layer.   The method for processing a laminated wafer according to claim 1, wherein, in the annular crack forming step, a laser beam is irradiated from the GaN layer side.   3. The method for processing a laminated wafer according to claim 2, wherein in the annular crack forming step, a laser beam is irradiated from the silicon substrate side.