Effects Of Heavy Doping On The Mechanical Properties Of Czochralski Silicon Wafers

The mechanical properties of silicon often dictate fundamental limits on the fabrication and packaging of various devices including the most prominent integrated circuits.They also dominate the issues related to dislocation-free silicon crystal growth and epitaxial layer deposition,as well as the processing of silicon wafers.Therefore,a great deal of effort has been expended into the research of mechanical properties of silicon in the past decades.Nevertheless,the understanding of mechanical properties is not yet as in-depth as that of electronic and optical properties for silicon.Hence,enriching the knowledge of mechanical properties of silicon is still stringent.In this thesis,the influences of heavy phosphorus(P)-,arsenic(As)-,antimony(Sb)-and tin(Sn)-doping on the mechanical properties of Czochralski(Cz)silicon have been investigated by means of microindentation,nanoindentation,laser-acoustic echo,four-point bending method and so on.The significant results achieved in this thesis are listed as follows.The mechanical properties of heavily P-and As-doped Cz silicon have been comparatively investigated.Based on the statistical analysis on the Vickers hardness,it is found that the Vickers hardness of heavily P-doped CZ-Si is slightly higher than that of heavily As-doped CZ-Si.The nanoindentation and the laser-acoustic echo method reveal that heavily P-doped CZ-Si possesses a little bit lower Young's modulus than heavily As-doped counterpart.The load-depth curves of nanoindentation shows that the transition from the Si-?(diamond cubic)phase to the Si-?(?-Sn)phase is more significant in heavily As-doped Cz-Si than the heavily P-doped counterpart,which is confirmed by the Micro-Raman spectroscopy characterization.From the comparison on the occurring frequencies and the average lengths of the lateral crack,it is derived that heavily P-doped CZ-Si is of somewhat higher indentation fracture toughness,which is further confirmed by the quantitative derivation of indentation fracture toughness.This result is explained by the fact that the bonding energy of Si-P bond is higher than that of Si-As bond,which is derived from the density function theory calculations.The investigations on the motions of indentation-induced dislocations driven by the constant shear stress at low temperatures(600?)or the residual shear stress at high temperatures(900-1200?)indicate that heavily P-doped CZ-Si needs a higher critical shear stress for the dislocation motion than heavily As-doped counterpart.Moreover,the relation between the dislocation gliding velocity and the temperature reveals that heavily P-doped CZ-Si is of slightly lower activation energy for the dislocation motion.The mechanical properties have been comparatively investigated for heavily Sb-and Sn-doped Cz silicon wafers,where the concentrations of Sb and Sn are considerably close.The microindentation indicates that the Vickers hardness of differs hardly from that of heavily Sn-doped counterpart.The laser-acoustic echo method shows that the heavily Sb-and Sn-doped Cz silicon wafers have nearly the same Young's modulus.In addition,there is hardly difference between the fracture toughnesses of heavily Sb-and Sn-doped Cz silicon wafers,which are derived from the Young's modulus,hardness,and the radial crack length of micro-indentation.The investigation on the motions of indentation-induced dislocations driven by the constant shear stress indicates that the critical shear stress is higher for heavily Sb-doped Cz silicon than for heavily Sn-doped one at 500 ?,while,it becomes nearly the same for the two kind of silicon wafers at 500 ?.The situations of gliding of indentation-induced dislocations at 800-1200? driven by the residual shear stress indicate that there is hardly difference in the critical shear stress for dislocation motion between heavily Sb-and Sn-doped Cz silicon wafers.