Effect of Substrate Bias on Deposition Behavior of Charged Silicon Nanoparticles in ICP-CVD Process

Abstract

The effect of a substrate bias on the deposition behavior of crystalline silicon nanoparticles during inductively coupled plasma chemical vapor deposition (ICP-CVD) was approached by nonclassical crystallization, in which the building block is a nanoparticle rather than an individual atom or molecule. This study consists of two major parts. One is the effect of the substrate bias on the deposition behavior of crystalline silicon nanoparticles during the thin-film deposition condition in the ICP-CVD process. The other is the effect of the substrate bias on the deposition behavior of crystalline silicon nanoparticles during the nanoparticle synthesis condition in the ICP-CVD process In the first part, the coexistence of positively and negatively charged nanoparticles in the plasma and their role in Si film deposition are confirmed by applying a bias voltage on the substrate, which is so small as not to vary the plasma potential. The sizes of positively and negatively charged nanoparticles captured on the TEM grid membrane were respectively 2.7 ~ 5.5 nm and 6 ~ 13 nm. The film deposited by positively charged nanoparticles has a typical columnar structure. In contrast, the film deposited by negatively charged nanoparticles has the structure like a powder compact with the deposition rate about three times higher than that deposited by positively charged nanoparticles. All the films have crystallinity although the substrate is at room temperature, which is attributed to the deposition of crystalline nanoparticles formed in the plasma. The film deposited by negatively charged nanoparticles has the highest crystalline fraction of 0.84. In the second part, the effect of the substrate bias on the size and amount of crystalline silicon nanoparticles deposited on the substrate with inserting grounded grids are investigated in an inductively coupled plasma chemical vapor deposition (ICP-CVD) process. By inserting grounded grids above the substrate, the lower region of the grounded grids was separated from the plasma. Thereby, the film formation in the ICP-CVD process could be avoided on the substrate and as a result crystalline Si nanoparticles formed in the plasma could be deposited on the substrate. Moreover the size and the amount of nanoparticles could be controlled by applying the direct current (DC) bias on the substrate. When the 1 mm square mesh grid was used, the nanoparticle flux was increased as the negative substrate bias was increased from 0 V to - 50 V. On the other hand, when positive biases were applied to the substrate, Si nanoparticles were not deposited at all. When the 2 mm square mesh grid was used, sizes of nanoparticles were increased as the substrate bias was increased from -50 V to 50 V.