Dislocation nucleation triggered by thermal stress during Ge/Si wafer bonding process at low annealing temperature

Abstract

We report nucleation of dislocations in Ge of Ge/Si bonded pairs annealed at low annealing temperatures (≤400 oC). Two types of dislocation networks are revealed near Ge/Si bonded interface for the first time, including sparsely distributed dislocations (type-I) and criss-crossingly arranged ones (type-II). A thin amorphous Si (a-Si) intermediate layer is introduced at the Ge/Si bonded interface to eradicate the influence of the lattice misfit between Si and Ge, and the thermal stress is proved to be the driving force for nucleation of both types of dislocation. Impact of annealing temperature on dislocation nucleation is identified. It is observed that type-I dislocations constitute the majority of dislocations in Ge wafer of bonded pairs annealed at annealing temperature range 275–350 ℃, and type-II ones start to prevail at annealing temperature range 350–400 °C. A kinetic model that accommodates the strain relaxation process and behavior of dislocation is constructed based on fundamental strain and dislocation theory. By fitting the experimental data, it is proposed that heterogeneous nucleation caused by “initial nucleation sites” correlated with surface fluctuation and pretreatment is dominant for dislocation nucleation at low annealing temperature range, and multiplication mechanism activated by secondary nucleation sites, such as Frank-Read sources, incurs the booming of dislocation density (DD) at elevated temperatures. This finding may cast light on the nature of crystallinity degradation of Ge wafers integrated on Si substrate by a hybrid wafer bonding technology.