Real-time determination of plasma etch-rate selectivity

Abstract

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.

In situ selectivity monitor for dry etch of photomasks

“…Alternative in-situ film thickness monitoring technique, such as Laser reflectance interferometry (LRI) [2] does have the advantage of high signal to noise ratio, yet multiple colors is necessary for LRI to handle thin resist, which is hard to implement. In this study, we use optical emission from plasma as the light source.…”

“…δ m-1 is the phase thickness imposed by the bulk of the (m-1) th layer upon one traversal of light. Again, the refractive indexes in Equations (1), (2), and (4) take complex form (n -i k).…”

Progress and perspectives in dry processes for leading-edge manufacturing of devices: toward intelligent processes and virtual product development

“…8). [166][167][168][169] In 2003, Ref. 170 reported applications of process metrology based on optical critical dimension (CD) integrated metrology for gate etching.…”

“…Real-time etch rate of thin transparent films determined using an in situ two-color laser interferometer. 166) Fig. 9.…”