Study on growth processes of particles in germane radio frequency discharges using laser light scattering and scanning electron microscopic methods

Growth processes of particles formed in germane (GeH₄) rf parallel plate discharges are studied using a laser light scattering and scanning electron microscopic methods. For GeH₄(5%)+He, 30 sccm, 80 Pa, and a relatively high power of 40 W(0.51 W/cm²), particles begin to be observed from a very early time of about 0.13 s after the discharge initiation around the plasma/sheath boundary near the powered electrode, where emission intensity of Ge atoms is high. This appearance time of particles is extremely early compared to that (about 0.5 s) in silane (SiH₄) rf discharges. The localized existence of particles suggests that short-lifetime radicals being generated at a high rate may contribute to the particle nucleation, while little information about reaction rates for GeH_x (x =0 - 3) radicals is available. After nucleation and subsequent initial growth of particles, they coagulate quickly with one another, which brings about a growth rate considerably high compared to that for SiH₄. Some Ge particles become submicron in size at an early time of 0.3 s and fall to the plasma/sheath boundary near the lower grounded electrode. For such a high coagulation rate (growth rate is about 800 nm/s), particles have irregular nonspherical shapes and most of them are agglomerates composed of chains, while they are almost spherical with a roughness of primary particle size (about 10 nm) for a low coagulation rate (growth rate is about 100 nm/s). Fast appearance of particles for GeH₄ discharges also brings about rapid decrease in discharge voltage and absolute value of self-bias voltage.