Recombination Lifetime Variations and Defect Introduction by Rapid Thermal Processing

摘要

Extended defects generated during RTP processing at the quartz wafer support and contact fingers of the wafer transfer robot have been examined by minority carrier recombination lifetime, τ_r, and X-Ray Topography. Silicon CZ wafers of 8"dia have been mapped laterally, and the defects imaged as a function of depth. Various RTP chamber cleaning and annealing experiments were carried out to control the reduced lifetime/pin defect formation process. A τ_r reduction of up to two orders of magnitude can occur at the contact points. The low lifetime has been profiled in-depth by Laser Microwave Photoconductance Decay following sequential sample thinning to yield 3D lifetime maps. HF-passivation was used to lower the impact of surface recombination. A two exponential model was used to separate the surface and bulk components of lifetime, which were resolved by the Nelder-Mead non-linear fitting method. The range of lifetime degradation at the RTP induced defects varies with the level of contamination which occurs during pin/wafer contact. Fortunately, the extended defects, i.e. slip dislocations, are confined to the wafer backside, where they getter the contaminants.