Hiroshi Kanoh

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.

Hot-Wall Chemical-Vapor-Deposition of Amorphous-Silicon and Its Application to Thin-Film Transistors

Hot-wall chemical vapor deposition of amorphous-silicon has been investigated, aiming at a batch process for thin-film transistors (TFTs). High-performance TFTs (mobility=1.7 cm2/Vs, threshold voltage =9 V and subthreshold voltage swing =0.8 V/decade) have been successfully fabricated. Similar good TFT characteristics were obtained over a wide range of a-Si deposition conditions.

Amorphous-silicon/silicon-nitride thin-film transistors fabricated by plasma-free (chemical vapor deposition) method

The application of chemical-vapor-deposited (CVD) amorphous-silicon and silicon-nitride films to active layers of thin-film transistors on a glass substrate is discussed. The maximum process temperature was 485 degrees C. The maximum field-effect mobility and the typical on-off current ratio were more than 0.9 cm/sup 2//V-s and 10/sup 6/, respectively. Advantages of applying the fully plasma-free CVD method in the amorphous-silicon thin-film transistor process are discussed.<<ETX>>

Optimization of Chemical Vapor Deposition Conditions of Amorphous-Silicon Films for Thin-Film Transistor Application

The optimum condition has been investigated for chemical vapor deposition (CVD) of amorphous-silicon (a-Si) films to form high-performance a-Si thin-film transistors (TFTs) by a fully plasma-free process. It was found that hydrogen annealings improve the TFT characteristics a great deal and that there is an optimum deposition temperature and gas flow rate. The maximum field-effect mobility of electrons and on/off current-ratio were more than 0.8 cm2V-1s-1 and 106, respectively.

Low-Temperature Chemical Vapor Deposition of Silicon Nitride Using A New Source Gas (Hydrogen Azide)

Silicon nitride films were deposited at temperatures as low as 350°C by chemical vapor deposition using a new source gas, hydrogen azide (HN3). Silicon nitride film deposited at 425°C was nitrogen-rich and showed hydrogen content of about 28 atomic%. The breakdown field strength was as high as 8.7 MV/cm and the resistivity was as high as 1015 Ωcm. Amorphous silicon thin-film transistors equipped with this film as the gate dielectric showed good transistor characteristics.

Hydrogen-radical annealing of chemical vapor-deposited amorphous silicon films

This letter describes that photogenerated hydrogen-radical annealing (HRA) is very effective for improving the electric properties of chemical-vapor-deposited amorphous silicon films. The ratio of photoconductivity to dark conductivity (at a light intensity of 100 mW/cm2) changed from 100 to 6×104 upon annealing in a hydrogen-radical-rich ambient at 280°C. Thin-film transistor (TFT) characteristics were also improved by HRA.

Low-Temperature Chemical-Vapor-Deposition of Silicon-Nitride from Tetra-Silane and Hydrogen Azide

Silicon nitride films have been successfully deposited at a temperature as low as 300°C by chemical-vapor-deposition using tctra-silane (Si 4 H 10 ) and hydrogen azidc (HN 3 ). Atomic ratio (N/Si) of the film deposited at 400°C was 1.47, i.e., the film was N-rich. Total hydrogen content was about 25atomic%. The breakdown-field strength was 6.5MV/cm at leakage-current density of 1μA/cm 2 , and the low-field resistivity was more than 10 15 Ωcm. Similar electrical characteristics were obtained from films deposited at a temperature range between 300°C and 500°C. Amorphous silicon thin-film transistors equipped with this film as the gate dielectric showed good transfer characteristics.

Chemical Vapour Deposition of Amorphous Silicon with Silanes for Thin Film Transistors —The Influence of the Amorphous Silicon Deposition Temperature—

Amorphous silicon films have been prepared by low pressure chemical vapour deposition of monosilane, disilane and trisilane. The deposition temperatures ranged from 385°C to 555°C. The hydrogen content in the films was approximately 3 atomic percent and the optical band-gap was 1.6~1.7 eV. Simple inverted staggered thin-film transistors were made with thermal silicon dioxide as the gate insulator. After annealing in a hydrogen radical rich ambient the field-effect mobilities for electrons were as high as 2.0 cm2/Vs and almost independent of temperature from 385°C to 500°C. At higher temperatures the mobility decreased rapidly and was less than 0.1 cm2/Vs at 555°C. These results appeared to be independent of the source gas.

Characterization of chemical-vapor-deposited amorphous-silicon films

We have studied post-hydrogenation characteristics and photo-absorption characteristics of amorphous-silicon films thermally deposited from disilane at 500°C. There is a critical post-hydrogenation temperature of about 400°C, below which both the density of hydrogen (deuterium) atoms on the surface and the activation energy of their diffusion constants are constant. Post-hydrogenation drastically enhances the decrease of the photo-absorption coefficient for photon energies less than the optical bandgap. The optimum density of hydrogen atoms introduced by post-hydrogenation was between 3 at% and 3.5 at%. The Urbach tail slope E0 was 42 meV, i.e., about 8 meV lower than the typical value of the film deposited by plasma enhanced chemical vapor deposition (PECVD) method.

Amorphous-Silicon Thin-Film Transistors Using Chemical Vapor Deposition of Disilane

Amorphous silicon layers have been deposited by low pressure chemical vapour deposition at 450°C using disilane as the only source gas. Simple inverted staggered thin-film transistors were made with thermal silicon dioxide as the gate insulator. Field-effect mobilities for electrons and holes were 1.4 cm2/V s and 0.1 cm2/V s, respectively. In order to obtain these high mobilities the transistor structures were carefully annealed in a hydrogen-radical rich ambient.