Kyung Min Ahn

Improvement in Thermal Stability of Nickel Silicides Using NiNx Films

A nickel nitride (NiN x ) film is proposed as a Ni source for silicidation to improve the thermal stability of a nickel silicide (NiSi) layer. The stability of the film was investigated for temperatures above 700°C. The nitrogen content in the NiN x film could be controlled by varying the N 2 flow ratio during deposition. When the NiN x film was annealed, the formation temperature of the NiSi layer was higher than that of layers formed from the pure Ni film due to the retardation of Ni diffusion into the Si substrate by an amorphous Si-N layer at the nickel nitride/Si interface. After an additional annealing above 700°C, the sheet resistances (R s ) of the NiSi layers formed from the NiN x film remained low, while the R s of those formed from the pure Ni film increased sharply. Apparently, the suppression of the agglomeration of the NiSi layer by the utilization of the NiN x film can improve its thermal stability.

Fabrication of a high-performance poly-Si thin-film transistor using a poly-Si film prepared by silicide-enhanced rapid thermal annealing process

AbstractA 50-nm thick polycrystalline Si film was fabricated by the crystallization of anamorphous Si film using silicide-enhanced rapid thermal annealing (SERTA). The amorphous Si film was deposited on a 5-nm thick polycrystalline Si seed layer containing nickel silicide precipitates in grain boundary areas. With the help of the silicide precipitates, the RTA temperature decreased from 730 to 680°C and the grain size of the crystallized polycrystalline Si film increased to 1.4 — 2.2 μm. Few defects were found within the grains and the Ni concentration in the polycrystalline film decreased to 1 × 1018 cm−3 due to the very-thin seed layer that contained nickel silicide precipitates. As a result, the field-effect hole mobility in the p-channel poly-Si thin film transistors (TFTs), fabricated employing the polycrystalline Si film, was as high as 169 cm2/V∙s at a drain voltage of VD = −0.1 V; the subthreshold swing was as small as 0.24 V/decade. The minimum leakage current at VD= 5V was 1.5 × 10−10 A with very good diode characteristics.

Silicon Epitaxial Growth on Poly-Si Film by HWCVD for Low-Temperature Poly-Si TFTs

A two-step process consisting of the preparation of poly-Si seed film by vapor-induced crystallization and the growth of an epitaxial Si layer on the poly-Si seed film via hot-wire chemical vapor deposition (HWCVD) is introduced to obtain a high-quality poly-Si film at a temperature below 500°C. The epitaxial Si by HWCVD was successfully grown on the poly-Si seed film at 450°C, and the crystallinity of the poly-Si seed film was maintained up to the surface of the epitaxial Si. With the two-step process, it was observed that the grain size was enlarged twofold compared to that of the poly-Si seed film. It was also found that the grain-boundary defect density was reduced. Moreover, the concentration of Ni and Al, which were introduced for the crystallization of a-Si, was lower at the surface.

Low-Temperature Growth of N-doped SiO2 Layer Using Inductively-Coupled Plasma Oxidation and Its Effect on the Characteristics of Thin Film Transistors

Silicon dioxide as gate dielectrics was grown at 400 C on a polycrystalline Si substrate by inductively coupled plasma oxidation using a mixture of O and N O to improve the performance of polycrystalline Si thin film transistors. In conventional high-temperature N O annealing, nitrogen can be supplied to the Si/SiO interface because a NO molecule can diffuse through the oxide. However, it was found that nitrogen cannot be supplied to the Si/SiO interface by plasma oxidation as the N O molecule is broken in the plasma and because a dense Si-N bond is formed at the SiO surface, preventing further diffusion of nitrogen into the oxide. Nitrogen was added to the Si/SiO interface by the plasma oxidation of mixtures of O /N O gas, leading to an enhancement of the field effect mobility of polycrystalline Si TFTs due to the reduction in the number of trap densities at the interface and at the Si grain boundaries due to nitrogen passivation.