Osamu Sugiura

High-mobility poly-Si thin-film transistors fabricated by a novel excimer laser crystallization method

High-mobility poly-Si thin-film transistors (TFTs) were fabricated by a novel excimer laser crystallization method based on dual-beam irradiation. The new method can reduce the solidification velocity of the top Si layer by heating the bottom Si layer of the Si/SiO/sub 2//Si/glass substrate structure by means of laser irradiation not only from the front side but also from the back side. The grain size of poly-Si film was enlarged up to 2 mu m. The field-effect mobilities of the TFT exceeded 380 cm/sup 2//V-s for electrons and 100 cm/sup 2//V-s for holes. >

Atomic layer epitaxy of Si using atomic H

Abstract Atomic H is proposed for the reducer gas in the atomic layer epitaxy (ALE) of Si. Its high reactivity makes it possible to remove surface-terminating adsorbates, which cause the self-limitation of unwanted successive deposition of Si compounds, at low temperature. The ALE growth was attempted by the alternating exposure of the Si(111) substrate to SiH 2 Cl 2 and H. Ideal monolayer growth was obtained and the growth rate was independent of the gas volumes and the substrate temperature. The lower ALE limit of the substrate temperature was 540 °C, about 250 °C lower than the case of H 2 as the reducer gas.

Drastic enlargement of grain size of excimer-laser-crystallized polysilicon films

Polysilicon thin films with extremely large grains (grain size more than 50 µm, i.e., three orders of magnitude more than the typical value) have been formed using an excimer-laser crystallization method for the first time. This drastic enlargement was achieved by the reduction of the solidification rate of molten silicon by the small heat capacitance effect of the thin silicon-dioxide membrane used as a substrate. Crystallinity and film properties have been evaluated from Raman spectroscopy, resistivity, Hall effect and transistor characteristics. The Hall mobility of electrons was as high as 610 cm2/Vs.

On-Chip Bottom-Gate Polysilicon and Amorphous Silicon Thin-Film Transistors Using Excimer Laser Annealing

High-performance bottom-gate thin-film transistors (TFTs) with both polysilicon (poly-Si) and amorphous silicon (a-Si) have been fabricated, for the first time, using chemical-vapor-deposited a-Si film as a starting semiconductor material. The feature of this technology is that both TFTs can be produced in the same process and at the same time on a single substrate except for the local laser crystallization step of the a-Si. The field-effect mobilities were 60 cm2/V s for the poly-Si TFT and 1.3 cm2/V s for the a-Si TFT, respectively. Their on-off current ratios were more than 106.

A Novel Atomic Layer Epitaxy Method of Silicon

A new atomic layer epitaxy (ALE) method of silicon has been investigated. Substrate temperature Ts is increased to more than a critical temperature, and decreased to less than another critical temperature alternatively, and trisilane gas is injected as source molecules only in a short interval within the low-Ts phase. This method separates an adsorption phase of silicon hydrides with one-monolayer thickness from a desorption phase of hydrogen, resulting in the monolayer growth per cycle. ALE growth conditions were estimated from gas-source MBE characteristics, and ALE growth (with 0.8 monolayer/cycle) was demonstrated. The grown layer had good surface morphology and crystallinity.

Lateral growth of poly-Si film by excimer laser and its thin film transistor application

Thin Si film on a SiO2 membrane has been recrystallized by single-shot excimer laser. Since there is no substrate acting as a heat sink to the latent heat in the molten Si film, the heat flow can be reduced immensely and also controlled well to form a temperature gradient along the membrane, resulting in the lateral growth of large grains, more than 70 µ m in length and a few µ m in width. Two thin film transistors (TFTs) with the channels parallel and perpendicular to the grain boundary, were fabricated using the laterally grown poly-Si film. The parallel TFT showed the maximum field-effect mobilities of more than 600 cm2/Vs for electrons and about 300 cm2/Vs for holes.

High-Mobility Bottom-Gate Thin-Film Transistors with Laser-Crystallized and Hydrogen-Radical-Annealed Polysilicon Films

High-performance bottom-gate thin-film transistors (TFTs) have been realized with excimer-laser-crystallized polysilicon films, for the first time. TFT characteristics were greatly dependent on the silicon film thickness as well as the pulsed-laser energy density. It was found also that posthydrogenation based on hydrogen-radical annealing improves the TFT characteristics drastically. The field-effect mobilities exceeded 220 cm2/Vs for electrons and 140 cm2/Vs for holes, respectively.

High-performance poly-Si thin-film transistors with excimer-laser annealed silicon-nitride gate

We report, for the first time, that ArF excimer laser annealing can improve silicon-nitride film properties. It is shown that the 15-nm-thick top region of the laser preannealed film had a lower hydrogen content and a much lower etching rate than the as-deposited film. The laser preannealed film is very useful as the gate insulator of high-performance bottom-gate thin-film transistors fabricated with the laser-recrystallized poly-Si film. The field-effect mobility of electrons was as high as 200 cm 2 /V-s, while the mobility was as low as 40 cm 2 /V-s without preannealing the silicon-nitride film

Chemical vapor deposition of amorphous silicon using tetrasilane

Hydrogenated amorphous-silicon films have been deposited by the plasma-free chemical-vapor-deposition method using tetrasilane (Si4H10) at temperatures as low as 350°C. The film deposited at 350°C and 9 Torr had hydrogen content as high as 15 at.%, optical bandgap of 1.78 eV, logarithmic ratio of photoconductivity (at a light intensity of 100 mW/cm2 under AM1 conditions) to dark conductivity of 3.2, activation energy of 0.78 eV and the Urbach tail slope as small as 56 meV. Thin-film transistors have been fabricated using the film deposited at 350°C. The electron mobility was 0.6 cm2/V s under as-deposited conditions.

Cryogenic InSb detector for radiation measurements

The energy spectra of 241Am alpha particles were measured by a detector employing the compound semiconductor InSb at an operating temperature below 4.2 K. The fabrication method and current–voltage curves are shown. Though the energy resolution of the detector is not discussed in this article, this is the first report on an InSb radiation detector.