Tham khảo tài liệu 'micro electronic and mechanical systems 2009 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 306 Micro Electronic and Mechanical Systems Pd SiC contact at 700 0C initializes dissociation of SiC surface in the presence of Pd atoms. The released Si atoms interact with palladium to form palladium silicide while the dissolved carbon atoms start to accumulate at the interface. The XPS spectra have established the presence of the two palladium silicides Pd3Si and Pd2Si together with carbon in graphite state distributed in the whole contact film. As a result the SiC interface is shifted into the SiC bulk since a part of the original interface is consumed to supply Si for the Pd3Si formation. After annealing of the Au Pd Ti Pd contact a new contact composition has been obtained. The contact layer consists of Au in a metal state unreacted Pd palladium rich silicide Pd3Si and TiC while the interface layer is composed of a less Pd-rich silicide Pd2Si . As in the Pd SiC contact a part of the original interface is consumed due to the partial dissociation of SiC to Si and C. Again the free Si atoms interact with Pd to form Pd2Si in the interface near region and Pd3Si in the more remote contact layer while the dissolved C atoms react with Ti and TiC is formed. Due to the presence of Ti in the contact composition the carbon resulting from SiC dissociation during annealing is completely consumed. It should be noted that in contrast to the Pd SiC contact no carbon in graphite state has been observed in the annealed Au Pd Ti Pd contact. The absence of free C in the annealed contact causes improvement of the contact stability during the long-term treatments and at high operating temperatures. The presence of Au and Pd in metal state contributes to the good contact conductivity. 100 I----- -----1---- ----1--- ----1---- ----1---- ----1 100 Sputtering time min Sputtering time min Fig. 11. XPS depth profiles of Pd-based contacts a Pd SiC annealed at 700 0C and b Au Pd Ti Pd SiC annealed at 900 0C. Thermal stability of n- and p-type ohmic contacts to SiC. By contrast with the
