THE EFFECT OF PATTERNS ON THERMAL-STRESS DURING RAPID THERMAL-PROCESSING OF SILICON-WAFERS

The presence of patterns can lead to temperature nonuniformity and und esirable levels of thermal stress in silicon wafers during rapid therm al processing (RTP), Plastic deformation of the wafer can lead to prod uction problems such as photolithography overlay errors and degraded d evice performance. In this work, the transient temperature fields in p atterned wafers are simulated using a detailed finite-element-based re actor transport model coupled with a thin film optics model for predic ting the effect of patterns on the wafer radiative properties. The tem perature distributions are then used to predict the stress fields in t he wafer and the onset of plastic deformation, Results show that patte rn-induced temperature nonuniformity can cause plastic deformation dur ing RTP, and that the problem is exacerbated by single-side heating, i ncreased processing temperature, and increased ramp rate, Pattern effe cts can be mitigated by stepping the die pattern out to the edge of th e wafer or by altering the thin film stack on the wafer periphery to m ake the radiative properties across the wafer more uniform.