Real-Time Monitoring and Control of Plasma Etching

Abstract

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.

Optical Diagnostics for Thin Film Processing

“…Reflection interferometry has been used to monitor the growth and etching of C-doped GaAs on GaAs caused by the slightly different refractive index of the doped layer (194) and plasma (195) and wet (196) etching of Si. Dual wavelength interferometry has also been used to control plasma etching of transparent materials, such as SiO 2 (197). The densities of etch radicals C and F were also obtained with Xe and Ar OES actinometry and used as inputs to an etch rate model for model-based real-time control.…”

Role of plasma-aided manufacturing in semiconductor fabrication

“…2) Real Time: Sarfaty et al [53] have solved this problem by developing a technique that measures etch rate from approximately 0.1 of a fringe. They were able to measure real time etch rates of unpatterned SiO and Si films.…”

Real-time virtual metrology and control for plasma etch

“…Real-time control of plasma etch rate has been reported by a number of researchers, but typically requires the use of bulky, expensive, or invasive measurement techniques. For example, Sarfaty et al [17] implement real-time control of etch rate using a proportionalintegral-derivative (PID) controller, model-based feed-forward action for large changes in etch rate set point, and laser reflectance interferometry (LRI) to measure the etch rate. Stokes and May [18,19] describe control of etch rate using indirect adaptive control and data from LRI Laser interferometry (LI), residual gas analysis (RGA), and optical emission spectroscopy (OES) for process feedback.…”