Silicon Hot-wire Chemical Vapor Deposition Research Articles

Effect of Bias Applied to Hot Wires on Generation of Positive and Negative Charges during Silicon Hot-Wire Chemical Vapor Deposition

Hot-wire chemical vapor deposition of silicon films has been studied focusing on the generation of electric charge during the process. The currents measured 1.5 cm below the input and output positions, with respect to the DC power supply, of the hot wires at 2000 °C were +4 and −544 nA/cm2, respectively, and those 4.5 cm below the input and output positions were +3 and −64 nA/cm2, respectively. These data imply that both positive and negative charges are generated presumably by surface ionization of gas molecules on the hot wires, but an appreciable fraction of negative charges was attracted to the electric field around the hot wires, which have the input and output potentials of +18 and 0 V, respectively, provided by the DC power supply. The additional biases of +25 and −25 V applied to the hot wires produced +2.38 and −4.86 × 104 nA/cm2, respectively, 1.5 cm below the input position of the hot wires. The absolute value of the current measured under the negative bias is much larger than that under the po...

Effect of electric bias on the deposition behavior of silicon on flexible polyethylene terephthalate (PET) during hot-wire chemical vapor deposition

The deposition behavior of silicon films during hot-wire chemical vapor deposition (HWCVD) was studied based on the concept of the two-step growth: the generation of charged silicon nanoparticles in the gas phase and their incorporation into films. If the charged crystalline silicon nanoparticles generated in the gas phase during HWCVD are made to be incorporated into films, microcrystalline silicon films can be obtained at such a low temperature as to be deposited on a flexible substrate of polyethylene terephthalate (PET). Besides, the deposition would be affected by the electric bias applied to the substrate. This possibility was studied in this paper. Electric biases of +150, 0, and −150 V were applied to the substrates of stainless steel and PET maintained at ∼90 °C during silicon HWCVD under 0.6 Torr at a filament temperature of 1700 °C. The growth rate on stainless steel at biases of +150 and −150 V was higher than that of the zero bias, whereas the growth rate on PET was higher at a bias of −150 V and lower at a bias of +150 V than that of the zero bias.

Gas phase nucleation of crystalline silicon and their role in low-temperature deposition of microcrystalline films during hot-wire chemical vapor deposition

Although deposition of crystalline silicon films at low temperature below 400 °C has been intensively studied using hot wire or plasma, the mechanism has not been clearly understood. As a mechanism of low-temperature deposition of crystalline silicon, we suggest that crystalline silicon nanoparticles are generated in the high-temperature region of hot wire with their subsequent incorporation into a film during hot-wire chemical vapor deposition (HWCVD). Here, the generation of such crystalline silicon nanoparticles in the gas phase was studied during silicon HWCVD.

Elementary processes in silicon hot wire CVD

The reaction kinetics for the silicon hot-wire chemical vapor deposition (HWCVD) method has been investigated. A time of flight mass spectroscopy (TOF-MS) with a VUV (Vacuum Ultra Violet) single photon ionization technique was used to detect the gas phase chemical species. Si 2H 6 and Si 3H 8 were identified as the main gas phase species during the HWCVD film growth processes in the present work. Raman spectra of the deposited films were also recorded to monitor the film properties. Microcrystalline or amorphous films were obtained depending on the experimental conditions, but the mass spectral pattern were almost the same in both microcrystalline and amorphous film growth conditions. A chemical kinetic mechanism for the Si-film growth was discussed on the basis of these observations.

Chemical kinetics for film growth in silicon HWCVD

Resonance enhanced multiphoton ionization spectroscopy coupled with molecular beam technique has been used to measure H and Si atoms produced by the hot-wire induced decomposition of silane. The catalytic decomposition of silane on the hot filament exhibited different temperature distributions between H and Si atoms. A chemical kinetic model starting with Si+SiH 4 and H+SiH 4 reactions was proposed to explain the chemical kinetic phenomena occurring in the silicon hot-wire chemical vapor deposition (HWCVD). The modeling results suggest that temperature sensitivity of film growth properties is primarily due to the gas composition near the surface.

Gas phase and surface kinetic processes in polycrystalline silicon hot-wire chemical vapor deposition

Experiments and numerical simulations have been conducted to determine critical parameters for growth of polycrystalline silicon via hot-wire chemical vapor deposition. Reactor-scale simulations performed using the Direct Simulation Monte Carlo (DSMC) method have revealed a number of important phenomena such as a sharp drop of 1700 K in the gas temperature from the wire to substrate. The gas-phase reaction of silicon atoms produced on the wire with ambient silane molecules has been studied using ab initio quantum chemical calculations. Results reveal that collisional stabilization of the adduct (H3SiSiH) is unlikely under typical growth pressures, but an energetically favorable, low-pressure pathway has been found that leads to the formation of Si2H2 and H2. Threshold ionization mass spectrometry measurements of radicals have revealed that at the pressure characteristic of growth (2-200 mTorr of 1% SiH4 in He), the radical SiH2 is predominant. Finally, film growth studies reveal that hot-wire-produced atomic hydrogen may preferentially etch amorphous silicon and suppress the formation of small nuclei.