Thj Bisschops

Measurement of electron densities by a microwave cavity method in 13.56-MHz RF plasmas of Ar, CF4, C2F6, and CHF3

Electron densit ies have been determined /or RF plasmas that were generated within a microwave resonant cavity by measuring the difference of the resonance frequencies with and without plasma. Since that method only yields a value of the electron density weighted ouer the microwave electric field distribution, to obtain real values an assumption on the spatial distribution of the electron density had to he made. Spatial profiles were taken of the emission of a 4s–5p Ar line at 419.8 not (with a small Ar admixture). The electron densities have been determined as a function of pressure and RF power in Ar, CF4, C2 F6 and CHF, plasmas. The results indicate that the electron density for the last three gases decreases as a function of pressure above 50 m Torr. Typical values for the electron density for the investigated parameter range are 1–6 · 103 cm−3. Furthermore, the electron density is the lowest in gases with a high attachment cross .section.

In situ ellipsometry during plasma etching of SiO2 films on Si

The etching of SiO2 films on a Si substrate in an rf plasma in CF4 has been studied with i n s i t uellipsometry. The etch rate was measured as a function of flow, rf power and pressure. An accurate analysis of the experimental data using numerical simulations based on multilayermodels has yielded information both on the refractive index of the etched SiO2 film and on the existence of a top layer. It could be established that a layer is present on top of the SiO2 during etching, which is probably caused by roughening of the SiO2 layer. Furthermore at high pressures (>8 Pa) it was demonstrated that after the complete removal of the SiO2 film a polymer layer starts growing on the Si substrate.

Plasma surface modification and plasma chemistry

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Spatially resolved high resolution interferometry

The construction of a cheap but very stable and accurate Michelson interferometer is described. To avoid (expensive) lock-in techniques a DC feedback loop has been implemented. A major advantage of this system is that the signal is proportional to the optical path length change itself, and not to the sine thereof. The frequency stabilization of the He-Ne laser used-necessary to attain the desired high resolution-is outlined. the Abel inversion procedure, used in a cylindrically symmetrical situation to convert lateral measurements into radial profiles, is discussed. A length-equivalent accuracy of about 0.1 nm has been accomplished. The system has been used to measure the radial profile of the refractive index of RF plasmas in CF4 and Ar.