Laser diagnostic studies of particulate contamination generated by etching plasmas

Abstract

Using laser light scattering as an in-situ probe of particulate contamination, it has been shown that certain silicon etching plasmas can produce significant amounts of particulate contamination. In addition, using spatially resolved measurements, it has been shown that most particles are suspended at the sheath boundaries, a finding attributed to electrostatic charging. Further evidence for this unexpected result has been provided by simultaneous space and time measurements of laser light scattering with measurement of plasma negative ions. The parametric conditions favorable for particle formation and growth have been identified. Generation of particles is seen to be strongly affected by the choice of process feedgas, flow rate, pressure, and the presence and exposed area of the etch substrate. Comparison of light scattering measurements with negative ion laser-induced fluorescence measurements suggests the involvement of plasma negative ions in the formation of particulates. A mechanism for nucleation and growth, involving clustering of plasma negative ions and etch products, has been identified.