Optimization of D0 Performance in LPCVD Nitride through Implementation of Ammonia Purge

This work focused on the improvement on defectivity and the prolongation of process cycle by the implementation of ammonia purging process that optimized the D0 performance in Low Pressure Chemical Vapor Deposition (LPCVD) Nitride process. This is important to achieve consistent semiconductor wafer productibility with stable D0 performance process. Nitride was processed in the vertical furnace by LPCVD method at the temperature of 700°C to 760°C. Nitride was processed continuously and film was deposited until a fixed target cumulative thickness limit in the furnace, with no conditioning along the whole process cycle until maximum target cumulative thickness achieved or before furnace perform for preventive maintenance. However, the accumulation of nitride deposition induced defective particles in the furnace when it approached the end of process cycle due to film stress accumulation. The stress increased gradually resulted in particles flaking caused process cycle need to be terminated which unable to continue deposition to maximum target cumulative thickness. The proposed method to improve D0 performance for process prolongation was carried out ammonia purge conditioning in between process cycle at the 57%, 86% and 100% interval of nitride cumulative thickness. The ammonia gas was introduced into the furnace tube at temperature higher than 760°C process temperature, which was relatively higher than the LPCVD nitride process temperature. Ammonia then reacted with defects or impurities to form a stable product and exhaust by purging, resulted in a more defect-free environment in the process tube. Ammonia purge conditioning was found to have a significant effect on particles expelled and furnace tube cleanliness controlled. The D0 performance morphology was obtained by defect monitoring throughout whole process cycle with use of metrology tool particles scanned. In summary, this work demonstrated that the high temperature ammonia purge significantly enhanced the D0 performance of LPCVD Nitride process. The result showed that the average defect counts were reduced effectively by 92% from previous high defectivity after ammonia purge conditioning. Process cycles cumulative thickness prolonged by 29% from initial maximum cumulative thickness target set. Preventive maintenance activity conducted frequency was reduced by 31%.