A study of particle generation in sputtering and reactive ion etching of silicon and silicon dioxide

Abstract

Particle formation in an Ar sputtering plasma and a reactive ion etching plasma of CCl2F2/Ar was investigated using silicon and silicon dioxide substrates.

In both the supttering and the reactive ion etching, the smallest particles detected on the wafers were 100 - 200 nm in size, and nearly spherical particles ranging down to 70 nm were collected on grids downstream between the wafer and the exhaust even before the onset of laser light scattering. In the sputtering, most particles were spherical and must have been formed in the plasma, and the density of the particles in the clouds was estimated to be approximately 10^7 cm^-3. Electron microscopy revealed the structure as well as the size distribution of the particles. The size distribution was essentially monodisperse for very small particles, but became wider and spatially varied as the average particle size increased with time.

The kinetics of particle growth was studied as a function of rf power, chamber pressure, and flow rate, using laser light scattering. Threshold values of the rf power, the pressure, and the flow rate were necessary for the particles to appear. The pressure and the flow rate determined the spatial position and the extent of development of particle clouds above the wafer. The spatial dependence of the particle clouds on the pressure and the flow rate could be used to control the formation of the particles in the plasma and the deposition of the particles on the wafer. In both the sputtering and the reactive ion etching, onset and development of the particle clouds were faster for Si substrates than for SiO2 substrates. Also, the onset and development of the formation of the particle couds in the supttering plasma were faster than in the reactive ion etching plasma.

Si atoms produced from the substrates were responsible for nucleation and growth of the particles in both the sputtering and the reactive ion etching plasmas, as evidenced by onset rate results, etch rate results, energy dispersive X-ray analysis of the particles, and by the results from optical emission spectroscopy.