Characterization of the boron doping process using boron nitride solid source diffusion

by Castro, Susana Patricia.

CASTRO, SUSANA PATRICIA. Characterization of the Boron Doping Process Using Boron Nitride Solid Source Diffusion The purpose of this research has been to develop an optimum process for the boron doping of implants and polysilicon gates of metal-oxide-semiconductor (MOS) devices. An experimental design was constructed to determine the effects of diffusion temperature, time, and ambient on characteristics of the doping process. A temperature range of 800 to 1000 degrees Celsius was studied with a diffusion time between 10 and 60 minutes. Two diffusion ambients were used for doping processes, a pure nitrogen ambient and a nitrogen-oxygen gaseous mixture. Device wafers were fabricated, and the testing of MOS capacitors and van der Pauw test structures was performed to determine the effect of diffusion conditions on flatband voltage and poly gate doping. Materials characterization techniques were used on monitor wafers for each diffusion process to determine the wafer structure formed for each process and evaluate the effectiveness of the deglaze etch. The processes that resulted in the best device characteristics without suffering from significant poly depletion effects and flatband voltage shifts were wafers doped at 800 degrees Celsius in a pure nitrogen atmosphere for 20 minutes and 45 minutes. The presence of oxygen in the atmosphere caused the depletion of boron from the Si wafer surface. The formation of the Si-B phase only occurred on devices processed at 1000 degrees Celsius. The deglaze process used in this experiment did not fully remove this layer, and thus all devices doped at this temperature were seriously degraded.