Hiromasa Ohmi

Low-Temperature Growth of Epitaxial Si Films by Atmospheric Pressure Plasma Chemical Vapor Deposition Using Porous Carbon Electrode

The low-temperature growth of epitaxial Si films by atmospheric pressure plasma chemical vapor deposition (AP-PCVD) was investigated. A 150 MHz very high frequency (VHF) power supply was used to generate an atmospheric pressure plasma of gas mixtures containing He, H2, and SiH4. Two types of electrode (i.e., cylindrical rotary and porous carbon electrodes) were used in plasma generation. When a cylindrical rotary electrode was used, polycrystalline Si growth was inevitable at the film edge on the upstream side. This is due to the variation in deposition rate along the gas flow direction, which is extremely high at the plasma/atmosphere interface on the upstream side. To solve this problem, we developed a novel porous carbon electrode where process gas molecules are directly supplied into the plasma region through a porous carbon plate a distance (0.8 mm) away from the substrate surface. Using such a porous carbon electrode, we successfully grew a defect-free epitaxial Si film on the entire surface of a 4 in. Si wafer at 600 °C. The average growth rate was 0.25–0.3 µm/min, which is as high as that obtained by thermal CVD at 900 °C. The epitaxial Si films grown at 600 °C were characterized by various methods, including transmission electron microscopy, atomic force microscopy, secondary ion mass spectrometry, and selective etching. The influence of adsorbed impurities in the porous carbon material on the quality of epitaxial Si films was also investigated.

Silicon film formation by chemical transport in atmospheric-pressure pure hydrogen plasma

To prepare polycrystalline silicon (poly-Si) films at low temperatures ( 93%) of Si solid source was realized in every c...

Atmospheric-pressure low-temperature plasma processes for thin film deposition

Nonthermal plasmas generated under atmospheric pressure (AP) have been receiving increased attention in direct plasma technology applications for thin film deposition. This is because the atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) is expected to realize low-cost and high-throughput processing with open air systems, which are of prime importance for various industrial applications. A large number of studies have been reported on the preparation of thin films using various types of AP plasma sources such as corona, dielectric barrier and AP glow discharges excited by pulsed or low-frequency power sources that can produce a nonequilibrium AP plasma. Most of the reported films using these common AP plasma sources have been related to polymers, oxides, and carbon materials. On the other hand, by virtue of the low ion energy due to the high collision frequency, AP-plasma process can have a nature of soft or gentle processing in addition to high-rate processing. Therefore, AP-PECVD...

Highly efficient oxidation of silicon at low temperatures using atmospheric pressure plasma

Silicon oxide (SiO2) layers were formed with initial oxidation rates in the range of 6.2–14.1nm∕min in the temperature range of 150–400°C by oxidizing Si(001) wafers. Such a high-rate and low-temperature oxidation was realized by using a stable glow He∕O2 plasma excited at atmospheric pressure by a 150MHz very high-frequency power. Increasing the temperature led to both the higher oxidation rate and the better quality of SiO2 and SiO2∕Si interface. The oxidation at 400°C showed an interface trap density of 6.2×1010eV−1cm−2, which is considerably lower than that in a radical oxidation process using low-pressure He∕O2 plasma at the same temperature.

High-rate growth of epitaxial silicon at low temperatures (530-690 °C) by atmospheric pressure plasma chemical vapor deposition

Abstract High-rate growth of epitaxial Si films at low temperatures by atmospheric pressure plasma chemical vapor deposition has been investigated. Si films are deposited on (001) Si wafers in gas mixtures containing He, H 2 and SiH 4 at substrate temperatures ranging from 530 to 690 °C. The films are characterized by reflection high-energy electron diffraction, atomic force microscopy and cross-sectional transmission electron microscopy. High quality Si films with excellent crystallinity and surface flatness similar to or better than those of commercial Si wafers are grown in the area where the deposition gap between the substrate and rotary electrode is small. Especially, in epitaxial Si film grown at 610 °C with an input plasma power of 2000 W, no lattice defects are observed by transmission electron microscopy. The maximum growth rate is approximately 6.6 μm/min at 690 °C with 1500 W and 1.2 μm/min at 610 °C with 2000 W, which is approximately 20–30 and 4–6 times faster than that obtained by thermal chemical vapor deposition at approximately 1100 °C, respectively.

Impacts of noble gas dilution on Si film structure prepared by atmospheric-pressure plasma enhanced chemical transport

To control the structure of poly-Si films prepared by the atmospheric-pressure plasma enhanced chemical transport (APECT) method, we have investigated the effects of noble gas (He or Ar) dilution on film structure and plasma characteristics. The deposition rate in the noble gas dilution APECT method depends mainly on the hydrogen concentration in the process gas mixture. Diluting with noble gas changes the Si film morphology dramatically. When is decreased, the ring-like RHEED pattern becomes strongly spotty, indicating the epitaxial Si growth. It is found that the film structure can be modified by varying not only but also the noble gas element.

Microcrystalline Si films grown at low temperatures (90–220 °C) with high rates in atmospheric-pressure VHF plasma

This work deals with the structural properties of microcrystalline silicon (μc-Si:H) films grown at low temperatures (90–220 °C) with high rates in atmospheric-pressure He/H2/SiH4 plasma, which is excited by a 150 MHz very high frequency power using a porous carbon electrode. This plasma permits to enhance the chemical reactions both in gas phase and on the film-growing surface, while suppressing ion impingement upon the surface. Raman crystalline volume fractions of the μc-Si:H films are studied in detail as functions of film thickness and substrate temperature (Tsub). The results show that the μc-Si:H film deposited with 50 (SCCM) (SCCM denotes standard cubic centimeters per minute at STP) SiH4 has no amorphous transition layers at the film/substrate interface in spite of the high deposition rate of 6.4 nm/s, which is verified by the cross sectional observations with a transmission electron microscope. In addition, the Tsub dependence of Raman crystallinity of the μc-Si:H films indicates that a highly c...

Low-Temperature Crystallization of Amorphous Silicon by Atmospheric-Pressure Plasma Treatment in H2/He or H2/Ar Mixture

To crystallize amorphous silicon (a-Si) films at temperatures less than 600 °C, we propose an atmospheric pressure plasma (APP) treatment method using a H2/He or H2/Ar mixture. An atmospheric-pressure stable-glow plasma was generated using a 150 MHz very high frequency power supply. After APP treatment, the Si films were characterized by reflection high-energy electron diffraction analysis, Fourier-transform infrared spectroscopy and scanning electron microscopy. In addition, optical emission spectroscopy (OES) was employed to study the plasma. In the case of treatment with the H2/He plasma, the crystallization of the a-Si films started with in negligible incubation time at a substrate temperature as low as 200 °C, and the resulting Si crystallites showed anisotropic morphology. It was found that a-Si layers still existed under the crystallized layers. This result suggests that crystallization of a-Si by APP was predominated by chemical interactions between atomic hydrogen in the plasma and the treated surface. However, in the case of treatment with the H2/Ar plasma, Si crystallites of the treated film did not show anisotropic morphology, and film peeling was partly observed in the treated area. Additionally, from the OES, emission lines from atomic hydrogen were hardly observed in the H2/Ar plasma. This implies that physical interactions between Ar atoms and the film surface play a significant role in the crystallization of a-Si.

Purified Si film formation from metallurgical-grade Si by hydrogen plasma induced chemical transport

Purified Si film is prepared directly from metallurgical-grade Si (MG-Si) by using hydrogen plasma induced chemical transport at subatmospheric pressure. The purification mechanism is based on the different hydrogenation behaviors of the various impurity elements in MG-Si. The prepared Si films clearly had fewer typical metal impurities (Fe, Al, Ti, Cr, Mn, etc.) than those in the MG-Si. In particular, the Fe concentration was drastically reduced from 6900 mass ppm to less than 0.1 mass ppm by one time chemical transport. Furthermore, metal impurity concentrations were further reduced by repeating chemical transport deposition.

Significant enhancement of Si oxidation rate at low temperatures by atmospheric pressure Ar∕O2 plasma

Using stable atmospheric pressure plasma, the effect of inert gas (He, Ar, and Kr) mixed with O2 on the oxidation process of Si(001) wafers was investigated. Ar∕O2 plasma was shown capable of generating atomic oxygen most efficiently and significantly enhanced the oxidation rate in comparison with He∕O2 plasma, while Kr∕O2 plasma was not suitable for the low-temperature and high-rate oxidation of Si. As a result, by using Ar∕O2 plasma, oxide layers having equivalent quality to that by He∕O2 plasma could be formed with a drastically high initial oxidation rate of 28.0nm∕min.