Reciprocal space mapping for semiconductor substrates and device heterostructures

We produced wafer maps of triple-axis X-ray diffraction omega scans (omega or omega-map) to determine the location of high and low crystalline perfection in both the substrate and the 15-20 nm channel region in device-quality GaAs and InP-based pseudomorphic high electron mobility transistors. The triple-axis maps are more sensitive to different types of crystallographic defects than are double-axis measurements. A map showing full width at half-maximum variations provides information on variations in crystallographic tilt; a map showing full width at five thousandths maximum shows polishing damage variations across the wafer. Monitoring the detector position determines lattice parameter variations across the wafer as well, although we did not observe significant lattice parameter variations in a given wafer. The crystallographic perfection of the channel layer replicates that of the underlying substrate and electrical measurements taken at the different regions show that the lower crystalline quality conforms with reduced electrical performance. Omega maps are also used to assess the influence of different growth parameters and post-growth annealing treatments on substrate crystallographic perfection. The non-destructive nature of this technique makes it ideal for studying structure/performance relationships in semiconductor heterostructures.