Rhett B. Jucha

Open-loop predictive control of plasma etching of tungsten using an in-situ film thickness sensor

Automated control schemes would greatly improve the reproducibility of plasma-assisted etching processes. In this paper we report on the application of an in situ metal film thickness sensor to control a plasma tungsten etch process. The process consists of an anisotropic step to control line profile and remove as much tungsten as possible, followed by an isotropic step which etches through to the underlying layer. In typical operations, a pilot wafer is measured off-line to determine the initial tungsten thickness. An etch time for the first step is then calculated before processing the entire lot. Single wafer lots require the elimination of a pilot wafer. Recently, we integrated a metal film thickness sensor (based on the technology of eddy currents) into a single-wafer plasma tungsten etch module. Our control strategy uses the sensor in a feedforward manner. A measurement of the tungsten film thickness is made in situ prior to processing. Process control software adjusts the etch time for the wafer based on the measured thickness and the predicted etch rate for the equipment settings. The etch rate is calculated from an empirical model obtained using response- surface methodology. A three-fold decrease in wafer-to-wafer variability in final thickness after the etch step was realized compared to that for the deposited thickness.

Interferometric monitoring and control of silicon incorporation in the diffusion-enhanced silylated resist process

The diffusion enhanced silylated resist or DESIRER process is a well known surface imaging lithographic technique consisting of three steps: exposure, silylation, and dry develop. The success of this method for patterning submicron features depends critically on controlling silicon incorporation in the resist. In this report interferometric data obtained during the resist silylation step and subsequent dry develop etch have been used to correlate silylation parameters and exposure dose with the depth of silicon incorporation. Contrast and linewidth variation as a function of silylation depth have been derived. A kinetics model in conjunction with image intensity simulations has been used to understand the effects of process parameters on pattern quality. The potential of using the interferometric data for process monitoring is also discussed.