7.1
Surface Microstructure Evolution Upon Silicidation of Ni(Pt) and the Different Responses to Metal Etch
Surface Microstructure Evolution Upon Silicidation of Ni(Pt) and the Different Responses to Metal Etch
Tuesday, November 5, 2013: 1:05 PM
Meeting Room 230B (San Jose McEnery Convention Center)
Summary:
With 70 nm of Ni(5% of Pt) alloy deposited on Si <001>, an about 9 nm of polycrystalline NiSix forms on Si. After being annealed at below 400 ºC, the Ni(Pt) film was not entirely silicided and about 20 nm of residual Ni(Pt) was left un-reacted on Ni2Si. Subsequent metal stripping with aqua regia had removed the residual Ni(Pt) and etched the underlying Ni2Si, leaving a Si-oxide film on the wafer. With the annealing temperature raised to 550 ºC, the Ni(Pt) was entirely consumed, which allowed out-diffusion of both Si and Ni to the silicide surface. The out-diffusion resulted in a Ni-oxide layer on a stack of Si-oxide/NiSi. The stacking sequence stemmed from Si-oxide being thermodynamically more stable than the Ni-oxide. The Si-oxide layer, nonetheless, is not homogeneous but has instead embedded particles that contain Ni and Pt. The stack of Si-oxide/NiSi is more resistant to the etch of aqua regia, hence produced the desired etch selectivity of the metal stripping. The enhanced etch resistance is believed to result from the buffer provided by the Si-oxide, and the higher volume density of the Ni-Si bonds in the NiSi than those in the Ni2Si that formed at the reduced temperature.
With 70 nm of Ni(5% of Pt) alloy deposited on Si <001>, an about 9 nm of polycrystalline NiSix forms on Si. After being annealed at below 400 ºC, the Ni(Pt) film was not entirely silicided and about 20 nm of residual Ni(Pt) was left un-reacted on Ni2Si. Subsequent metal stripping with aqua regia had removed the residual Ni(Pt) and etched the underlying Ni2Si, leaving a Si-oxide film on the wafer. With the annealing temperature raised to 550 ºC, the Ni(Pt) was entirely consumed, which allowed out-diffusion of both Si and Ni to the silicide surface. The out-diffusion resulted in a Ni-oxide layer on a stack of Si-oxide/NiSi. The stacking sequence stemmed from Si-oxide being thermodynamically more stable than the Ni-oxide. The Si-oxide layer, nonetheless, is not homogeneous but has instead embedded particles that contain Ni and Pt. The stack of Si-oxide/NiSi is more resistant to the etch of aqua regia, hence produced the desired etch selectivity of the metal stripping. The enhanced etch resistance is believed to result from the buffer provided by the Si-oxide, and the higher volume density of the Ni-Si bonds in the NiSi than those in the Ni2Si that formed at the reduced temperature.