In-situ control and monitoring of wet and dry etching of patterned semiconductors using real time spectroscopic ellipsometry.

摘要

Real time spectroscopic ellipsometry (RTSE) was used to control the etch depth into a semiconductor substrate. Lateral interference due to patterning is the mechanism by which this optical technique can determine etch depth into bulk material. Scalar analysis permitted fast data fitting and real time control. Si substrates were patterned with photoresist into line or square patterns with periods of 10, 20, or 40 μm, and reactive ion etched using a CF₄/O₂ plasma. RTSE data were collected and simultaneously analyzed for etch depth. When the fitted etch depth reached a target value (500 nm) the etch was stopped. SEM and ex-situ spectroscopic ellipsometry (SE) analysis of the etched Si, with the photoresist removed, both agreed well with the RTSE results. It was also demonstrated that the Si etch rate as a function of experimental variable can be rapidly determined using RTSE without interrupting the etching. Bulk GaAs wafers patterned with the same patterns were etched in a citric acid solution while RTSE data were simultaneously analyzed for etch depth. Final etch depth measured by SEM was always within 5% of the target depth (1μm or 1.6 μm) and ex-situ SE analysis of the etched GaAs agreed well with the RTSE results. Endpoint detection was achieved during etching of patterned GaAs/AlGaAs heterostructures using RTSE. To the best of our knowledge, this is the first instance of real time fitting of optical reflection data for control during etching of patterned substrates, and the first application to monitor etching into bulk material.; RTSE measurements were made during the oxidation of bulk GaAs in deionized water (DI H₂O) and in hydrogen peroxide (H₂O₂). Despite limitations on the RTSE analysis due to UV absorption by the ambient liquids and bubble formation in H₂O₂, it was demonstrated that in DI H₂O the initial oxide layer growth was nearly linear in time while in H₂O₂ it tended to saturate. In both cases the grown oxides were porous.