Etching characteristics of thin films of tungsten, amorphous silicon carbide, and SAL-603 resist submitted to a surface-wave driven SF6 magnetoplasma near electron cyclotron resonance conditions

Abstract

The etching of thin films of tungsten, amorphous silicon carbide (a-SiC:H), and SAL-603 resist has been investigated in a magnetoplasma sustained by microwaves under conditions close to the electron cyclotron resonance. This was done in a newly developed large diameter (280 mm i.d.) reactor operating in a uniform static magnetic field and supplied with the plasma from a surface-wave-sustained discharge. A pure SF6 discharge was used. The etch rate of W, a-SiC:H, and SAL-603 resist materials was systematically determined as functions of operating parameters such as the SF6 pressure in the 0.1–5 mTorr range, the absorbed microwave power, and the distance of the substrate to the surface-wave launching gap. It is shown, in particular, that the etching selectivity of W with respect to a-SiC:H and SAL-603 resist is strongly influenced by the SF6 pressure. Optimal etching selectivities as high as 10 and 25 were obtained for W relative to a-SiC:H and SAL-603 resist, respectively, when the SF6 gas pressure is close to 4 mTorr. At this pressure, a high etch rate of about 1700 Å/min for W was recorded. This SF6 magnetoplasma was characterized using two classical diagnostics: electrostatic probe and optical emission spectroscopy (actinometry method). The electron temperature, the sheath potential, the ion current density, and the fluorine atom concentration in the reactor were determined in this way as functions of the above-mentioned operating parameters. Analyzing the variations of both the plasma characteristics and the etch rates of these three materials as functions of the operating parameters, it was found that (i) the etch rate of W is linearly correlated to the concentration of neutral fluorine atoms whereas (ii) the etch rates of a-SiC:H and SAL-603 resist are linearly correlated to the ion current density of the SF6 plasma. It was also shown that, in contrast to W, the etching of a-SiC:H and SAL-603 resist is strongly influenced by the biasing voltage applied to the substrate.