The Development of Semi-insulating Silicon Substrates for Microwave Devices

Abstract

The concept of fully encapsulated, semi-insulating silicon (SI-Si) Cz-SOI substrates for silicon microwave devices is presented. Results show that, using gold as a compensating impurity, a silicon resistivity of 180 kΩcm can be achieved. Sufficiently high resistivity substrates for microwave applications are obtained by depositing gold on silicon and annealing for one hour at 1000C. Silicon oxide and silicon nitride are considered as diffusion barriers for use in the new technology. At 1000C the diffusivity of gold in PECVD silicon nitride is found to be ~ 3.7x10-13cm2s-1, whilst for silicon oxide it is less than 6x10-14cm2s-1. These results imply that silicon nitride would be ineffective as a diffusion barrier in the SI-Si technology but that a silicon oxide BOX 600nm thick might allow devices to be processed with a thermal budget of up to 15 hours at 1000C without impurity contamination.