Real-time etch rate of thin transparent films is determined
within seconds by an in-situ two-color laser interferometer.
The use of two colors improves the accuracy of the calculated rates,
provides an absolute measure of film thickness for endpoint prediction,
and differentiates between etching and deposition.
The tool state parameters, rf power to the antenna and the wafer stage,
gas pressure and flow rates, are computer controlled and monitored.
Real-time etch rate characterization is obtained by monitoring the etch
dependence on varying tool state parameters.
The density of the etch radicals, chlorine and fluorine, is obtained with
xenon and argon actinometry using optical emission and mass spectra.
An etch rate model, based on the input power to the wafer stage and
the relative density of the etch radicals, is used to develop
a model-based real-time control algorithm.
This algorithm has been used to control the etch rate of unpatterned
polysilicon and SiO2.
It is established that nitridation of aluminum (Al) 6061-T4 by plasma source ion implantation (PSII) can dramatically enhance the pitting corrosion resistance of this alloy in marine environments (i.e., chlorine-ion-bearing aqueous solutions or humid atmospheres). Corrosion tests and microstructure analyses establish that the mechanism for successful passivation against chloride-induced pitting corrosion involves the formation of a multilayered microstructure, including the presence of a continuous layer of aluminum-nitride (AlN). Important process variables are the implantation voltage and the nitrogen dose (or total implantation time), as these two variables establish the implanted nitrogen concentration. Too high or too low an implanted nitrogen concentration will not yield the continuous AlN layer required for good corrosion resistance. PSII is attractive for this application as it provides for uniform, conformal implantation of irregularly shaped objects without masking, beam rastering, or object rotation.
Real-time etch-rate selectivity of thin transparent films is determined within seconds by an in situ two-colour laser interferometer. Two-point laser reflectrometry is used to determine the etch rates and etch selectivity of unpatterned polysilicon and SiO 2 films. The state of a magnetically confined inductively coupled plasma tool used in the experiments, including rf power to the antenna and the wafer stage, gas pressure and flow rates, is computer controlled and monitored. The dependence of the etch selectivity on tool state parameters is characterized in real time by varying the tool state and monitoring the etch rate of the films. The etch rate measurements have been combined with density characterization of the etch radicals in the discharge. The time-dependent density of atomic chlorine during the process is obtained by temporal optical-emission actinometry combined with in-line mass spectrometry from a pressure calibrated residual gas analyser. The etch selectivity of polysilicon to SiO 2 in a chlorine discharge, determined by a simultaneous etch of both films, differs from the etch-rate ratios of the films when they are etched separately. It is suggested that this difference is due to the presence of oxygen in the polysilicon etch process when the two films are etched simultaneously.
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