Motion Of Indentation Dislocations In Czochralski Silicon

Czochralksi (Cz) silicon is the base material for intergrated circuits (ICs). Its mechanical strength is one of the important subject matters to receive research attention. With the increasingly stringent requirements on the accuracy of lithography in IC fabrication, the mechanical strength of Cz silicon wafers are even more important. To a large extent, the gliding of dislocations driven by stress reflects the mechanical strength of silicon wafers. In the past decade, the confocal micro-Raman microscopy has been very mature. Crystalline silicon has a characteristic Raman peak and its wavenumber is quite sensitive to the lattice stress. Therefore, the confocal Raman microscopy can be used to quantitatively characterize stress and its distribution on the silicon wafer, which is advantageous for the investigation on the correlation between the dislocation gliding and residual stress on the silicon wafer. In this thesis, the effect of residual stress around the Vicker indentation on the dislocation gliding has been investigated by means of confocal micro-Raman microscopy. The primary results achieved in this thesis are listed in the following.1. The effect of boron-doping on the gliding of dislocations initiated from the Vicker indentations in Cz silicon wafers has been investigate. Here, the stresses around the indentations are measured by confocal micro-Raman microscopy. It is found that the increasing boron-doping level significantly decreases the stress around the indentations. After the 900 ℃/2h anneal, the dislocations in the silicon wafer with a resistivity of ～1mΩ.cm hardly glide, while those in the silicon wafer with a resistivity of～10mΩ·cm glide significantly. It is believed that the high concentration of boron atoms exert remarkable pinning effect on dislocations thus suppressing the dislocation gliding.2. The relationship between the residual stresses and the dislocation glidings of lightly and heavily boron-doped Cz silicon wafers has been investigate.The ressons of stress-relief during the anneal process also has been discussed. It is found that two reasons contribute to the stress-relief around the indentation during the process of anneal at 900 ℃:in the first several minutes, residual stresses released sharply because of the relief of the elastic deformationjafter that,the dislocation glidings have been the major reason:the residual stresses decreased with the dislocations gliding,and they did not change when the dislocations did not glide.3. The stress-relief around the indentation due to the anneal at 300 or 500 ℃ has been characterized by using micro-Raman microscopy. Then the effect of such relief-stress on the gliding of indentation dislocations at 700-900 ℃ has been investigated.lt is found that the indentation dislocation gliding velocity is significantly decreased due to the stress-relief and, moreover, such decrease in gliding velocity is more remarkable at lower subsequent annealing temperature. Despite the prior stress-relief, as long as the annealing time at 700-900 ℃ is sufficiently extended, the indentation dislocations can glide to the maximum distance which is the same as that occurs in the case without the prior stress-relief, In view of the above results, it is believed that the maximum gliding distance of indentation dislocations at a given temperature is independent on the values of residual stresses around the indentation provided that the residual stresses are larger than the critical stress for driving the dislocation gliding. Nevertheless, the time for achieving the maximum gliding distance should be remarkably extended as the residual stresses around the indentation are relieved.