Yasuhiro Torii

Low‐temperature film growth of Si by reactive ion beam deposition

A new low‐temperature film formation technique is proposed. It uses ionized species produced by an electron cyclotron resonance‐type microwave ion source with reactive gases and controlled in the low ion energy region, less than about 500 eV. Good quality homoepitaxial films on Si(111) are obtained at 600 °C and 100–500 eV ion energy by using SiH4 as a material gas. By increasing the ion energy to 250‐300 eV, homoepitaxial growth at 400 °C can be achieved. Polycrystalline Si films on the same type of substrates can also be obtained at 200 °C.

A high-current density and long lifetime ECR source for oxygen implanters

A high‐current ECR source has been developed for oxygen implanters for use in fabricating separation by implanted oxygen (SIMOX) substrates. The new source has the following features: (1) high‐current density (150 mA/cm2) and large extracted current (more than 200 mA), (2) stable and long lifetime operation (more than 200 h), (3) high O+ ratio (more than 80%), and (4) low‐divergence beam. The improved performance is obtained by incorporating the following: (1) Localized high‐density plasma generation at the center of the plasma chamber. (2) A newly developed multilayer window to satisfy two requirements: efficient coupling of the microwave with high‐density plasma and high resistance to high‐speed backstream electrons. (3) Optimized combination of plasma chamber length and axial magnetic field distribution. (4) Sophisticated compact magnetic circuit that yields the optimum magnetic field for obtaining high‐density plasma. An industrial‐version ECR source was developed for production use on EATON NV‐200 im...

Low‐temperature homoepitaxial film growth of Si by reactive ion beam deposition

Homoepitaxial film growth maintaining primary surface structures of Si substrates was investigated by using the reactive ion beam deposition method proposed recently. This method uses ionized species of reactive SiH4 gas controlled in the low‐energy region of less than 500 eV. At 100–150 eV, homoepitaxial film growth on Si(111) and Si(100) maintaining their primary 7×7 and two‐domain 2×1 surface structures, respectively, can be achieved at the low temperatures of 650 and 600 °C, respectively. In addition, oxygen impurities on substrate surfaces, due to imperfect substrate cleaning and recontamination caused by residual gases in a growth chamber before film growth, were successfully reduced at 600 °C by irradiating the 100‐eV controlled ionized species onto them.

Low‐temperature polycrystalline Si film growth on amorphous insulators by reactive ion beam deposition

Polycrystalline Si (polysilicon) film growth on amorphous insulators, such as borosilicate glass, fused quartz, silicon oxide films, and silicon nitride films, was investigated by using the reactive ion beam deposition (RIBD) method proposed recently. The RIBD method is based on the use of reactive ionized species produced from SiH4 electron‐cyclotron‐resonance plasma and controlled in the low‐energy region of less than 500 eV. Polysilicon films can be grown at the low temperature of 250 °C. In the growth temperature range between 550 and 700 °C, polysilicon films with the strong Si(220)‐preferred orientation parallel to the substrate surface can be obtained. X‐ray diffraction intensity corresponding to Si(220) lattice planes was clearly dependent on ion energy, which presented a maximal level at 70–130 eV.

Thin heteroepitaxial Si‐on‐sapphire films grown at 600 °C by reactive ion beam deposition

Thin low‐temperature heteroepitaxial film growth of Si on sapphire (SOS) was investigated by using the reactive ion beam deposition method proposed recently. This method uses low‐energy controlled ionized species produced from reactive SiH4 gas plasma. By accommodating the ion energy to two film growth stages, i.e., an initial heteroepitaxial growth stage followed by a homoepitaxial growth stage, thin SOS films about 200 nm in thickness with no superficial microtwins can be grown at the low temperature of 600 °C. The energy level is adjusted to 300 eV in the initial heteroepitaxial film growth stage (about 50 nm in thickness), and then to 100 eV until the total film thickness is about 200 nm.

Advanced high‐current ECR ion sources for implanters

We have already introduced a high‐current ECR ion source producing a 200‐mA beam of oxygen ions with an 80% O+ fraction. Two more advanced ECR sources with a high‐current density of more than 100 mA/cm2 have been newly developed. One source provides high‐current density without the accompanying damage to the microwave transmitting window found with the earlier source. This damage, which occurs when high‐speed backstream electrons attack the window, limits source lifetime. By adopting a multiple microwave inlet configuration for the introduction of microwaves into the plasma chamber, the ECR condition can be satisfied and high‐density plasma can be generated without an attack by backstream electrons. The other is a very compact source producing a high‐current beam at a very low‐power consumption. This is achieved by reducing the inner diameter of the plasma chamber to 5 cm φ, which is smaller than the cutoff dimensions for propagation of the 2.45 GHz microwave. A high‐plasma density of 1 × 1013 cm−3 has be...

High current ECR source for oxygen implantation: Life tests and comparison to duopigatron performance

An ECR source has been built for production use on Eaton’s NV200 oxygen implanter. It can be retrofitted in place of the duopigatron normally used on that machine. This article reports results of 200 continuous hours of operation of the source, producing 95 mA of O+ ions, on a special test stand which emulates the injector of the NV200. Currents up to 200 mA at 45 kV were briefly obtained on this stand, the upper limit being set by thermal capacity of the beam dump. The ECR source was installed on an NV200 and used to implant wafers at 200 keV. Its performance is compared to that of the duopigatron source under similar conditions.

Reservoir‐type liquid metal ion source of Al

A liquid metal ion source of Al with a boride reservoir was developed. In this reservoir a shorter boride emitter was designed to overcome the brittleness of boride materials and some problems in supplying the Al material. This source makes possible a long continuous operation time and enhanced reliability. The fundamental performance characteristics did not change after 250 h of operation. A stable Al ion beam emission was obtained for more than 500 h and its current fluctuation was less than ±1%/3 h for a 20–30‐μA source ion current. The energy spread was less than 9 eV (FWHM) for a 30‐μA/sr angular current intensity.

A Thin-Film Transistor Using a Reactive-Ion-Beam-Deposited Polycrystalline Silicon Film

A thin-film transistor (TFT) has been fabricated at a maximum temperature of 600degC using a reactive ion-beam-deposited polycrystalline silicon (polysilicon) film. To improve TFT characteristics, the deposition conditions of polysilicon film have been investigated. It is found that polysilicon film crystallinity can be improved by controlling the energy of ionized species. X-ray diffraction spectra and reflective high-energy electron diffraction (RHEED) patterns indicate that (110)-preferred orientation dominates in the film. The deviation of the (110) textured axis becomes very small as ion energy increases. The field effect mobility of TFTs increases as ion energy increases.

An Aluminum Liquid Metal Ion Source with Prolonged Lifetime Using a Sintered Boride Emitter

A field-emission liquid Al ion source with a sintered boride emitter, such as TiB2, BN-TiB2 composite, has been built to prolong the utilization term of an aluminum ion beam emission. In this approach, a stable Al ion beam emission was successfully obtained for more than 100 hours without any recognizable degradation. Emission current fluctuation was less than ±1% over 1 hour for 10 µA source ion current without any feedback stabilization. Moreover, 20–30 µA/sr angular intensity at 5–10 µA source ion current, 17° emission half-angle at 10 µA source current, and a large source ion current of more than 1.5 mA were also observed.