Effects of Antimony- and Tin-Doping on the Mechanical Propertiesof Czochralski Silicon: Revealing the Role of Electrical Activity of Antimony

Abstract

The mechanical properties of Czochralski (Cz) silicon wafers dictate fundamental limits on the fabrication of diverse electronic devices. Certain impurities with sufficiently high concentrations may affect the mechanical properties of Cz silicon. The underlying mechanisms for such influences have been being explored in the past decades. In this work, the effects of antimony (Sb)- and tin (Sn)-doping at 1018 cm−3 level on the mechanical properties of Czochralski (Cz) silicon have been comparatively investigated. Since Sb and Sn have quite close tetrahedral covalent radii in silicon, the lattice strains resulted from Sb- and Sn-doping and their consequent effects on the mechanical properties of silicon are approximately identical. In silicon, Sb is an electrically active impurity while Sn is a neutral one. Therefore, the present work can essentially reveal the role of electrical activity of Sb playing in the mechanical properties of Cz silicon. It is found that Sb-doped Cz (Sb-Cz) silicon possesses a slightly higher hardness than Sn-doped Cz (Sn-Cz) silicon. Moreover, the dislocation gliding at 500 or 600 °C in Sb-Cz silicon requires a much larger critical resolved shear stress than that in Sn-Cz silicon. At such two temperatures, Sb-Cz silicon remains to be n-type in electrical conduction. The aforementioned two results are believed to be ascribed to the resistance of dislocation motion by the Coulomb interaction between the positively charged Sb ions and the dislocations that are deep-level acceptors thus being negatively charged in Sb-Cz silicon. As the temperature is increased to 700 °C and above, the dislocation gliding in Sb-Cz silicon is not substantially different from that in Sn-Cz silicon. At such elevated temperatures, Sb-Cz silicon becomes intrinsic in electrical conduction like Sn-Cz silicon. In this context, there is no Coulomb interaction between Sb ions and dislocations anymore to impede the dislocation gliding in Sb-Cz silicon. In addition, it is found that the indentation fracture toughness of Sb-Cz is almost the same as that of Sn-Cz silicon. Actually, the fracture of silicon is essentially a cleavage process, to which the electrical activity of Sb is irrelevant.