Mechanical strength of Czochralski silicon crystal: Effects of co-doping germanium and nitrogen

Abstract

Czochralski (CZ) silicon is a base material for manufacturing integrated circuits (ICs). The mechanical strength of CZ silicon determines the processing limitations and often dominates the issues related to packaging and failure of ICs. With the ever-smaller feature size of ICs, the scaling of device dimensions may indirectly lead to increase the stress in silicon substrate, thus increasing the probability of generating dislocations. Consequently, improving the mechanical strength of CZ silicon is of significance for increasing the manufacturing yield of ICs. In this work, we propose a strategy of co-doping germanium (Ge) impurity and nitrogen (N) impurity into CZ silicon to achieve better mechanical strength. In order to explore the feasibility of such a strategy, we comparatively investigate the room-temperature hardness and dislocation gliding behaviors in the temperature range of 600–1200 ℃ in the conventional CZ silicon, Ge-doped CZ silicon, N-doped CZ silicon, as well as N and Ge co-doped CZ silicon. The significant experimental results are described as follows. 1) Ge-doping, N-doping or co-doping of Ge and N hardly influences the hardness and therefore the dislocation gliding behavior at room temperature. 2) The suppressing effect of N-doping on the dislocation gliding is remarkable at 600–1000 ℃ and becomes weakened at the temperatures higher than 1100 ℃, while Ge-doping hardly affects the dislocation gliding at 600–900 ℃ but exhibits a strong suppressing effect on the dislocation gliding at 1000–1200 ℃. 3) Co-doping Ge and N impurities into CZ silicon can take the complementary advantages of both Ge- and N-doping to suppress the dislocation gliding at 600–1200 ℃. It is believed that N-doping can result in the formation of N-O complex-related pinning agents within the dislocation cores to suppress the dislocation gliding at 600–1000 ℃. For Ge-doping, it is supposed that Ge-O complexes acting as the pinning agents can form near the front of a single dislocation when the temperature is as high as 1000 ℃ and above. In a word, it is verified in this work that co-doping Ge and N into CZ silicon can further improve the mechanical strength at the processing temperatures of ICs fabrication.