Silicon carbide wafers with relaxed positive bow and related methods
Silicon carbide (SiC) wafers and related methods are disclosed that include intentional or imposed wafer shapes that are configured to reduce manufacturing problems associated with deformation, bowing, or sagging of such wafers due to gravitational forces or from preexisting crystal stress. Intentional or imposed wafer shapes may comprise SiC wafers with a relaxed positive bow from silicon faces thereof. In this manner, effects associated with deformation, bowing, or sagging for SiC wafers, and in particular for large area SiC wafers, may be reduced. Related methods for providing SiC wafers with relaxed positive bow are disclosed that provide reduced kerf losses of bulk crystalline material. Such methods may include laser-assisted separation of SiC wafers from bulk crystalline material.
1. A crystalline material processing method comprising:
providing a bulk crystalline material comprising silicon carbide (SiC);
forming a subsurface laser damage pattern within the bulk crystalline material by variably adjusting at least one of a laser power and a laser focal point to form a nonlinear profile of the subsurface laser damage pattern from a perimeter of the bulk crystalline material to a center of the bulk crystalline material; and
separating a SiC wafer from the bulk crystalline material along the subsurface laser damage pattern.
2. The crystalline material processing method of claim 1 , wherein the nonlinear profile forms a curved shape from the perimeter of the bulk crystalline material to the center of the bulk crystalline material.
3. The crystalline material processing method of claim 1 , wherein the laser power is variably adjusted such that the laser power is different along the perimeter of the bulk crystalline material than at the center of the bulk crystalline material.
4. The crystalline material processing method of claim 3 , wherein the laser power is greater at the center of the bulk crystalline material than along the perimeter of the bulk crystalline material.
5. The crystalline material processing method of claim 1 , wherein the laser power is variably adjusted in a range including 2 watts (W) to 6 W.
6. The crystalline material processing method of claim 1 , wherein the laser focal point is variably adjusted such that a height position of the laser focal point is different along the perimeter of the bulk crystalline material than at the center of the bulk crystalline material.
7. The crystalline material processing method of claim 6 , wherein the height position of the laser focal point is configured deeper into the bulk crystalline material at the center of the bulk crystalline material than along the perimeter of the bulk crystalline material.
8. The crystalline material processing method of claim 1 , wherein forming the subsurface laser damage pattern within the bulk crystalline material comprises variably adjusting the laser power and the laser focal point to form the nonlinear profile of the subsurface laser damage pattern.
9. The crystalline material processing method of claim 1 , wherein the bulk crystalline material comprises a radial doping profile that is variable from the perimeter of the bulk crystalline material to the center of the bulk crystalline material.
10. The crystalline material processing method of claim 9 , wherein the radial doping profile comprises a lower doping region near the perimeter of the bulk crystalline material and a higher doping region that is closer to the center of the bulk crystalline material than the perimeter of the bulk crystalline material.
11. The crystalline material processing method of claim 10 , wherein the higher doping region is positioned at the center of the bulk crystalline material.
12. The crystalline material processing method of claim 10 , wherein the higher doping region is positioned offset from the center of the bulk crystalline material.
13. The crystalline material processing method of claim 1 , wherein the subsurface laser damage pattern comprises a plurality of subsurface laser damage lines formed at different depths within the bulk crystalline material.
14. The crystalline material processing method of claim 13 , wherein the plurality of subsurface laser damage lines are formed at different depths in a range including 2 microns (μm) and 5 μm.
15. The crystalline material processing method of claim 13 , wherein the plurality of subsurface laser damage lines are formed non-perpendicular to a [11 2 0] crystal direction of SiC.
16. The crystalline material processing method of claim 1 , wherein the SiC comprises 4-H SiC.
17. The crystalline material processing method of claim 1 , wherein the SiC comprises off-axis 4-H SiC in a range including 0.5 degrees to 10 degrees from a c-axis of the SiC.
18. The crystalline material processing method of claim 1 , wherein the SiC comprises on-axis 4-H SiC.
19. The crystalline material processing method of claim 1 , wherein the SiC wafer forms a relaxed positive bow from a silicon face of the SiC wafer.
20. The crystalline material processing method of claim 19 , wherein the relaxed positive bow is in a range from greater than 0 microns (μm) to 15 μm.
21. The crystalline material processing method of claim 19 , wherein the relaxed positive bow is in a range including 30 microns (μm) to 50 μm.
22. The crystalline material processing method of claim 19 , wherein the relaxed positive bow is in a range including 8 microns (μm) to 16 μm.
23. The crystalline material processing method of claim 1 , wherein the SiC wafer comprises a diameter to thickness ratio of at least 250.
24. The crystalline material processing method of claim 1 , wherein the SiC wafer comprises a diameter to thickness ratio of at least 300.
25. The crystalline material processing method of claim 1 , wherein the SiC wafer comprises a diameter to thickness ratio of at least 400.
26. The crystalline material processing method of claim 1 , wherein the SiC wafer comprises a diameter to thickness ratio in a range including 250 to 1020.
27. The crystalline material processing method of claim 1 , wherein a kerf loss associated with forming the SiC wafer from the bulk crystalline material is less than 250 microns (μm).
28. The crystalline material processing method of claim 27 , wherein the kerf loss is in a range including 100 μm to 250 μm.
29. The crystalline material processing method of claim 27 , wherein the kerf loss is less than 175 μm.
30. The crystalline material processing method of claim 1 , wherein the SiC wafer forms a relaxed positive bow from a silicon face of the SiC wafer, and a carbon face of the SiC wafer comprises a shape that corresponds to the relaxed positive bow from the silicon face.
31. The crystalline material processing method of claim 1 , wherein the SiC wafer comprises a diameter that is in a range from 150 millimeters (mm) to 205 mm.