Gen Tochitani

Optical emission diagnostics of H2+CH4 50‐Hz–13.56‐MHz plasmas for chemical vapor deposition

The emission spectra of H2+CH4 plasmas excited at 50 Hz–13.56 MHz were measured. The emission intensity ratios of Hα/H*2 (3Σg →3Σu) from H2+CH4 plasma at 50 Hz and 13.56 MHz were about 0.7 and 0.05, respectively. The electron temperature was obtained from the two‐line radiance ratio method using the Balmer lines (Hα and Hβ), and rapidly decreased with an increase above 200 kHz. The electron temperature for H2+CH4 plasma is 16 000 K at 1 kHz and 8200 K at 13.56 MHz. The plasma‐maintaining voltages for H2 and H2+CH4 mixtures were also measured. The maintaining voltages were constant below 200 kHz, and rapidly decreased between 200 kHz and 13.56 MHz. The position dependence of emission intensity was also measured for Hα, Hβ, and H*2 at 50 Hz and 13.56 MHz. The results are interpreted in terms of the electron distribution in the plasma.

Annealing behavior of HF-treated GaAs capped with SiO2 films prepared by 50-Hz plasma-assisted chemical vapor deposition

Thermal stability of the SiO2/GaAs interface structures prepared by 50-Hz plasma-assisted chemical vapor deposition (PCVD) and the electrical activation of Si implanted into GaAs with SiO2 cap were investigated. X-ray photoelectron spectroscopy (XPS) analysis showed that the 50-Hz PCVD method at 200°C allowed the presence of an As-enriched layer, intentionally inserted by HF treatment before SiO2 deposition, at the SiO2/GaAs interface. After rapid thermal annealing (RTA) at 950°C for 20 s, in fact, the As-enriched layer still remained and it was effective in suppressing interfacial reactions which caused various shortcomings. In addition, carrier concentration profiles in excellent agreement with Lindhard-Scharff-Schiott (LSS) curves were reproducibly obtained by RTA in Si-implanted GaAs capped with both the As-enriched layer and the SiO2 film, demonstrating that this process is applicable to post-annealing of ion-implanted GaAs.

Properties of hydrogenated amorphous silicon films prepared by low‐frequency (50 Hz) plasma‐enhanced chemical‐vapor deposition

Deposition of hydrogenated amorphous silicon (a‐Si:H) films is performed by low‐frequency (50 Hz) plasma‐enhanced chemical‐vapor deposition (PECVD). The results show that the undoped a‐Si:H films deposited at a substrate temperature of 200 °C are high‐quality films comparable to those deposited by conventional rf PECVD at a substrate temperature of 300 °C. The photoconductivity and dark conductivity of the films are 4 × 10−4 S/cm and 5 × 10−9 S/cm respectively. The activation energy is 0.78 eV and the optical gap is 1.8 eV. Furthermore, it is possible to control the dark conductivity and activation energy by doping with substitutional impurities of boron and phosphorus. These properties are very similar to those of the a‐Si:H films deposited by conventional rf PECVD in the optimum substrate temperature range from 250 to 300 °C. These results show that the 50 Hz PECVD can deposit high‐quality a‐Si:H films.Deposition of hydrogenated amorphous silicon (a‐Si:H) films is performed by low‐frequency (50 Hz) plasma‐enhanced chemical‐vapor deposition (PECVD). The results show that the undoped a‐Si:H films deposited at a substrate temperature of 200 °C are high‐quality films comparable to those deposited by conventional rf PECVD at a substrate temperature of 300 °C. The photoconductivity and dark conductivity of the films are 4 × 10−4 S/cm and 5 × 10−9 S/cm respectively. The activation energy is 0.78 eV and the optical gap is 1.8 eV. Furthermore, it is possible to control the dark conductivity and activation energy by doping with substitutional impurities of boron and phosphorus. These properties are very similar to those of the a‐Si:H films deposited by conventional rf PECVD in the optimum substrate temperature range from 250 to 300 °C. These results show that the 50 Hz PECVD can deposit high‐quality a‐Si:H films.

Hydrogenated amorphous carbon films deposited by low-frequency plasma chemical vapor deposition at room temperature

Hydrogenated amorphous carbon (a‐C:H) films were prepared at room temperature by low‐frequency (50‐Hz) plasma chemical vapor deposition using CH4 and H2 . The a‐C:H films were transparent, highly resistive, and very uniform. Infrared absorption measurements, as well as Raman spectroscopy, indicated that the C bonding in the a‐C:H films was predominantly sp3 . Moreover, the optical band gap of the a‐C:H films was measured.

Potential Oscillations in an Electronegative Plasma Driven by an Asymmetry RF Discharge

Potential oscillations of electronegative plasmas have been experimentally studied in a strongly asymmetric rf (13.56 MHz) discharge. Oscillation amplitudes in the plasma were found to increase suddenly from 10 to 60 V with increasing concentration of SF6 gas in He gas, while gradually from 10 to 40 V in CF4 mixed plasma. The electron energy distribution functions (EEDFs) measurement predicted an electron beam travelling from the plasma towards the rf electrode because of the potential double layer in the sheath picked up by an emissive probe. A clear difference in potential formation and EEDFs profiles in comparison to those in electropositive plasmas has been detected. A more marked gas concentration dependence was obtained in a SF6 gas than in a CF4 one due to the more active production of negative ions in a SF6 plasma.

Measurements of Ion Energy Distribution Functions in an Radio Frequency Plasma Excited with an m = 0 Mode Helical Antenna and Thin Film Preparation

Ion energy distribution functions were measured using an electrostatic analyier in an Ar radio frequency plasma excited with a helical antenna in a magnetic field, where a plasma density jump occurred. The functions showed a two peak and a single peak profile before and after the density jump had occurred, respectively. The electron temperature and the plasma potential decreased after the density jump. The formation of CN films was also studied by sputtering a cylindrical graphite target in an Ar + N 2 mixture.