Control of higher-silane generation by dilution gases in SiH₄ plasmas

Abstract

Higher-silane related reactive species (HSRS) is considered as a key factor in increasing the degree of photo-induced degradation, which is a serious problem for hydrogenated amorphous silicon (a-Si:H) film. Dilution gases (H2, He, Ar) are used to control the generation of HSRS. A global model for SiH4-containing discharge is developed to investigate the concentration of HSRS. The model calculations are compared with the available measurements, presenting a reasonable agreement. Increasing pressure contributes to more power loss via volumetric processes, which brings about the decline in the electron density and temperature with the same absorbed power. The average electronegativity rises with the silane content or pressure log-linearly, but decreases with the power log-linearly. As the main precursor of the anion formation, S i H 3 − is the starting point for the formation of large silyl anions ( S i n H 2 n + 1 − ). The HSRS density rises first and then falls with the increase of the absorbed power, which can be explained by the decomposition of SiH4. The dilution of H2 promotes the generation of H atomics, enhancing the production of SiH2 with abstraction reaction (H + SiH3 ⇒ H2 + SiH2). However, due to the declined content of SiH4, the insertion reaction (SiH2 + SiH4 ⇒ Si2H6) is inhibited. A higher Ar fraction results in more total ionization and a larger ion density. Due to the high threshold energies of He for both excitation and ionization, the dilution of He does not contribute much to the variation of the neutral radical density.

Computational Fluid Dynamics Analysis of Particle Deposition Induced by a Showerhead Electrode in a Capacitively Coupled Plasma Reactor

“…As stated above, a dirty gas line can be an important source of contamination because the impurities can be delivered to the gas distribution assembly and accumulate inside this assembly. In addition, source gases such as SiH 4 and TEOS can contaminate the interior walls of the gas distribution assembly at higher gas pressure [25,26]. This section presents our analysis of the transportation of particles from the gas distribution assembly to the heater surface.…”

Superior Phosphorous Doping in Nanocrystalline Silicon Thin Films and Their Application as Emitter Layers in Silicon Heterojunction Solar Cells

“…Furthermore, a high H 2 -dilution in the plasma is commonly used for attaining crystallinity in the doped matrix at a low temperature, which inevitably reduces the growth rate. − To retain the growth rate, sometimes SiH 4 has been diluted by the noble gases e.g., Ar, He, etc., and the crystallinity is sustained using their excited states in the plasma. − However, when used in higher dilutions, the larger atomic dimension of the noble gases compared to H imparts additional structural disorders in the Si network. , Accordingly, a combination of H 2 and noble gas is frequently used. − The novelty in the present work lies in developing the P-doped nc-Si thin films of significant crystallinity at a low substrate temperature (∼250 °C) and without supplementary H 2 -dilution of the precursor gas in an inductively coupled plasma (ICP) CVD system. The characteristic high atomic-H density in the low-pressure ICP plasma of SiH 4 induces the electrically active phosphorous donor ions at the c-Si lattice sites to incur higher doping efficiency .…”

Effect of dilution gas on the distribution characteristics of capacitively coupled plasma by comparing SiH4/He and SiH4/Ar

“…Furthermore, important discharge characteristics such as the surface flux of ions and radicals measured at the electrode surface could be optimized as a result of changing the dilution gas. Since the control of the plasma density distribution is of great importance to achieve process optimization, the dilution gas in CCP discharges has been studied extensively to determine its effect on the process [13][14][15][16][17][18][19][20].…”

“…In addition, a different dilution gas would enable the properties of the deposited thin films to be improved. Zhang and Zhang found higher-silane related reactive species (HSRS) to be an important factor for increasing the photo-induced degradation of hydrogenated amorphous silicon (a-Si:H) films [20]. They controlled the generation of HSRS with the use of dilution gases such as H 2 , He, and Ar.…”