David Pirkle

Control of Plasma Damage to Gate Oxide during High Density Plasma Chemical Vapor Deposition

Gate oxide damage resulting from high density plasma chemical vapor deposition of silicon oxide was investigated using damage sensitive antenna structures with area ratios up to 200,000 :1. Significant damage was detected from an unoptimized oxide deposition process. A 2 4-1 fractional factorial experimental design was used to screen the effect of four parameters : radio frequency power, microwave power, electrostatic chuck potential, and magnetic field. RF power and electrostatic chuck potential made no contribution to oxide degradation. The main factor was microwave power, and further experiments with microwave power ranging from 1500 to 2500 W showed that gate charging damage increased with microwave power, with the extent and distribution of damage depending on the magnetic field shape.

Near-infrared diode laser hydrogen fluoride monitor for dielectric etch

A hydrogen fluoride (HF) monitor, using a tunable diode laser, is designed and used to detect the etch endpoints for dielectric film etching in a commercial plasma reactor. The reactor plasma contains HF, a reaction product of feedstock gas CF4 and the hydrogen-containing films (photoresist, SiOCH) on the substrate. A near-infrared diode laser is used to scan the P(3) transition in the first overtone of HF near 1.31μm to monitor changes in the level of HF concentration in the plasma. Using 200ms averaging and a signal modulation technique, we estimate a minimum detectable HF absorbance of 6×10−5 in the etch plasma, corresponding to an HF partial pressure of 0.03mTorr. The sensor could indicate, in situ, the SiOCH over tetraethoxysilane oxide (TEOS) trench endpoint, which was not readily discerned by optical emission. These measurements demonstrate the feasibility of a real-time diode laser-based sensor for etch endpoint monitoring and a potential for process control.