Full factorial and Taguchi orthogonal arrays were used to characterize the silicon nitride low pressure chemical vapor deposition (LPCVD) process for film uniformity and particle density. Thickness and refractive index were measured using standard ellipsometric techniques. Particles were measured on patterned wafers using a Tencor Surfscan 7000 particle counter with pattern recognition capability. Both design methodologies produced identical results, with particles most dependent on total gas volume, and uniformity of the deposited film dependent on NH3:DCS (ammonia:dichlorosilane) gas ratio. Particle counts were minimized at both 4:1 and 6:1 NH3:DCS ratios and by reducing the total gas volume 10 percent, while uniformity continually improved as a 6:1 ratio was approached. It was learned that it is possible to choose an NH3:DCS gas ratio of 6:1 that simultaneously optimizes particles and film uniformity.
The use of statistical process control (SPC) methods to improve process capability as measured by process capability (Cp) were employed to measure an overall increase in Cp from 1.1 to 1.5 for film uniformity. Implementation of the new process resulted in a 2.5-fold reduction in particle counts.