Studies of co-implanted helium and hydrogen with an intermediate annealing step for thermal splitting of bonded silicon to oxide-coated wafers

摘要

Layer transfer by thermal or mechanical splitting of implanted silicon wafers can often require processing at elevated temperatures before bonding and annealing. The possibility has been investigated here of making two implants, the first defining a damage plane for splitting, the second being made after high-temperature processing. Helium and hydrogen implanted wafers were annealed at various temperatures, T-a, this being followed by a second implantation of either gas. Thermal splitting of bonded wafer pairs was studied for both implants to the same projected range, R-p, and with hydrogen implanted to R-p = 25% less than helium. In the former case, complete thermal splitting occurred for T-a less than or equal to 550 degreesC; for T-a > 550 degreesC, wafers failed to split or delaminated at the bond interface. When hydrogen was implanted to a shallower depth complete thermal splitting occurred for T-a less than or equal to 500 degreesC. The split occurred at the hydrogen R-p for T-a < 400 degreesC and at the helium R-p for T-a = or > 400 degreesC. Above T-a = 500 degreesC a decreasing percentage of the total silicon area was transferred. At 400 degreesC measurements suggested that splitting occurred at both helium and hydrogen R-p planes and it is believed that helium platelet formation at this temperature is an important factor. For T-a < 400 degreesC, helium, a proportion of which may have diffused towards the peak of the hydrogen distribution, is believed to react and produce splitting there during bond-annealing. For T-a > 400 degreesC, sufficient hydrogen is thought to diffuse during bond-annealing towards the peak of the helium distribution and react there to produce the weakest splitting plane. For T-a > 500 degreesC, loss of helium, annealing out of strain and break-up of platelets into bubble-cavities reduces the probability of thermal splitting. When hydrogen was implanted first, complete thermal splitting occurred for T-a less than or equal to 300 degreesC but was inconsistent at 400 degreesC and above. (C) 2004 Elsevier Ltd. All rights reserved.