Growth of particles in cluster-size range in low pressure and low power SiH4 rf discharges

Abstract

Growth processes of particles in a cluster-size range below a few nm in size in low pressure and low power SiH4 rf discharges are studied using the new method, in which the threshold photoemission method is coupled with the microwave interferometry, for measurements of their size and density. The density of particles is above 1010 cm−3 and much exceeds that of positive ions, the result of which shows that most of them are neutral. The particles grow mainly around the plasma/sheath boundary near the powered electrode and their size growth rate is 3.4–4.4 nm/s, being much higher than a film growth rate of 0.064–0.12 nm/s. These features strongly indicate that their growth is due to deposition of polymerized species, originated from short lifetime SiH2 radicals, on them, while coagulation between particles becomes appreciable after a time when their density reaches about 1011 cm−3. Moreover, the pulse modulation of rf discharge is found to be effective in reducing the density of cluster-size particles. The reduction can be explained by a model taking account of diffusion of the polymerized species through the radical production region, where the particles nucleate and grow.

Nanoparticles in SiH4-Ar plasma: Modelling and comparison with experimental data

“…Thus, in the context of our "one-step model" of cluster formation, [26][27][28] the first step in cluster production (i.e., the formation of dimers-radicals) is exclusively controlled by SiH 2 . This determines the significant role of the SiH 2 radical in the chain of events leading to the formation of clusters and nanoparticles, which is confirmed by experimental data 8,9,11,12 and has also been reported in Ref. 20.…”

“…12, with the experimental values obtained in this work for RF discharge in pure silane. For this, we made a small change in Eq.…”

“…(1), taking into account the geometry of the discharge in Ref. 12. We assumed that 30% of the discharge power was transformed into gas heat.…”

“…To this end, one such task is the investigation of Si nanoparticles, which are often studied using plasma chemical reactors at low pressure (10 to 100 Pa), and radio frequency (RF) discharge in pure silane or gas mixtures such as Ar-SiH 4 and He-SiH 4 (see, for example, the book 1 ). Detailed experimental investigations of Si particle growth have been performed, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] while theoretical studies of Si nanoparticle growth have also been carried out, developing both complex [19][20][21][22] and relatively simple [23][24][25][26][27][28] models. However, direct comparisons of experimental and theoretical results have not been shown in most cases.…”

“…(R3)), 30,32 which provides better agreement with the measured low SiH 2 concentrations in silane-Ar discharges. 8,9,12 For the case of dissociation by Ar * , the measured values of branching ratios are not known and, for SiH 2 , we also used a low value ( % 0.1) (see Eq. (R15)).…”