Suppression of misfit dislocations in heavily boron-doped silicon layer for micro-machining

Abstract

It has been found that the misfit dislocations in heavily boron-doped silicon layers which are useful materials in micro-machining are originated from the wafer edge, where the boron-doped layers were formed by thermal diffusion. And, a heavily boron-doped silicon region which is free of misfit dislocation has been obtained by surrounding the region with an undoped region which prevents the propagation of the misfit dislocations from the wafer edge. The surrounding undoped region using chemical vapor deposited oxide can suppress effectively the misfit dislocations, while many misfit dislocations are usually generated in the heavily boron-doped regions surrounded by the undoped regions using the thermal oxide and low-pressured chemical vapor deposited nitride due to the oxidation-induced stacking faults and half-loop dislocations, respectively. In the case of chemical vapor deposited oxide, well aligning of the surrounding undoped region to [110] direction as well as large width of the region is very critical for the suppression of the misfit dislocations because misfit dislocations can penetrate with climb motion through a tilted undoped region to [110] direction due to the tensile stress in the region induced from the boron-doped regions, while the induced tensile stress in the well aligned undoped region is relaxed by the $60^\circ$ dislocations in the region. Using the heavily boron-doped silicon layer without misfit dislocations, heavily boron-doped silicon membranes which are free of misfit dislocation have been fabricated. The surface roughness of the dislocation-free membrane at the etch-stopped surface have been measured as small as 20 \AA peak-to-peak, while that of the conventional membrane which contains many misfit dislocations as 500 \AA peak-to-peak. Using blister test, the fracture strength and residual tensile stress of the dislocation-free membrane have been extracted as high as $1.39 \times 10^{10} dyne/cm^2$ and $2.7 \times 10^9 dyne/cm^2$, w...