Kun-Chih Wang

Microstructures of low‐temperature‐deposited polycrystalline silicon with micrometer grains

The microstructures of low‐temperature polycrystalline silicon grown both on SiO2 and Corning 7059 glass substrate are presented. The silicon was deposited by the hydrogen dilution method using electron‐cyclotron‐resonance chemical‐vapor deposition at 250 °C without any thermal annealing. The hydrogen dilution ratios were varied from 90% to 99%. Transmission electron microscopy images, Raman shift spectra, and x‐ray‐diffraction (XRD) patterns of the films were obtained. The maximum grain size was about 1 μm and the crystalline fraction which was characterized from Raman shift spectra was near 100%. From the XRD patterns 〈111〉‐ and 〈110〉‐oriented crystalline silicon grains were clearly present in the polycrystalline silicon films.

Sulfurization of SiO2 surface for polycrystalline silicon growth on SiO2/Si structure at 250 °C

A study of sulfurizing SiO2 surfaces for the growth of Si/SiO2/Si structures was done in the present work. The silicon film was deposited at 250 °C by plasma enhanced chemical vapor deposition. All of the deposited Si films with or without sulfur treatment were of amorphous phases with a H2/(SiH4+H2) flow ratio less than 92%. For those films deposited at the H2/(SiH4+H2) flow ratio of 92%, a transition amorphous Si layer appeared between the SiO2 and polycrystalline silicon films in those samples without sulfur treatment. No transition amorphous Si layer was present in the sample deposited with sulfur treatment, and the largest grain size of polycrystalline silicon was estimated to be around 500 A. The polycrystalline phase was obtained in all the silicon films deposited on SiO2/Si substrate with a H2/(SiH4+H2) flow ratio larger than 92%. This technique would be applicable towards thin film transistor fabrication.

Very low temperature polycrystalline silicon films with very large grains deposited for thin film transistor applications

Abstract This paper presents the results of low temperature polycrystalline silicon growth on SiO 2 and glass substrates. The silicon films were deposited with the hydrogen dilution method by electron cyclotron resonance chemical vapor deposition at or below 250°C without any thermal annealing. Hydrogen passivation of the SiO 2 surface was applied to enhance the grain growth of poly-Si deposition. The polycrystallinity of the silicon films was established by transmission electron microscopy (TEM), Raman scattering, and X-ray diffraction. The maximum grain size was about 1 μm. The crystalline fraction of the polycrystalline silicon (poly-Si) films was near 100% as identified by Raman shift spectra. The preferred orientations of the poly-Si film were 〈110〉 and 〈111〉. Poly-Si films with a maximum grain size of 7000 A were formed at a substrate temperature as low as 100°C.

Electrical and structural properties of low temperature boron- and phosphorus-doped polycrystalline silicon thin films prepared by ECR-CVD

Abstract Boron-doped and phosphorus-doped polycrystalline silicon thin films were deposited on glass and SiO 2 substrates at a rather low temperature of 250°C by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using SiH 4 /Ar/H 2 /B 2 H 6 and SiH 4 /Ar/H 2 /PH 3 downstream plasma technique. The effects of in situ doping concentration and hydrogen dilution on the structural and electrical properties of heavily doped polycrystalline silicon thin films have been systematically investigated. The largest grain size of the heavily doped poly-Si films with ∼700 nm thickness (growth rate ∼20 nm/min) is approximately 500 nm, and the surface roughness is about 30 nm. With increasing the doping gas flow rate, the resistivity rapidly decreased and the minimum values of 0.025 Ω cm at [B 2 H 6 ]/[SiH 4 ] ∼9×10 −2 for p-type poly-Si films and 0.036 Ω cm at [PH 3 ]/[SiH 4 ] ∼7×10 −2 for n-type poly-Si films were achieved. The Hall mobility decrease as the carrier concentration increase can be explained by the impurity scattering increase with increasing the doping gas flow rate. X-ray diffraction, scanning electron microscopy and transmission electron microscopy indicated a change from to with slight decrease in the grain size. Furthermore, the grain shape of the deposited films was changed from elliptical to round. Similar to the undoped poly-Si thin films, larger hydrogen dilution ratio would increase the grain size, change the grain shape from round to elliptical. Otherwise, the Hall mobility simply decreased with increasing the hydrogen dilution ratio until 88% but it rapidly increased with further hydrogen dilution. On the other hand, the carrier concentration exhibited an entirely converse behavior with the hydrogen dilution ratio. The relationships between electrical properties and structure properties with regarding to the hydrogen dilution ratio and doping gas flow rate were attributed to the high surface coverage of atomic hydrogen species, doping precursors disturbance, solid solubility limitation and impurity scattering effect.

Microstructure evolution of hydrogenated silicon thin films at different hydrogen incorporation

This paper describes the microstructure evolution of hydrogenated silicon films containing various amounts of hydrogen. Microcrystalline silicon films were produced when the hydrogen content of the films was adjusted by using the diluted-hydrogen methods. Polycrystalline silicon films having grain sizes in the micrometer range were deposited at low temperature (250°C) by ECR-CVD with the hydrogen-dilution method. The microcrystalline and polycrystalline films were characterized by NMR, FTIR, Raman, X-ray and optical spectroscopy and electrical measurements. The results evaluate the possibility of even larger grain silicon films suitable for high performance solar cells which avoid the fundamental difficulties of amorphous Si:H solar cells.

Studies on low temperature silicon grain growth on SiO2 by electron cyclotron resonance chemical vapor deposition

Abstract Electron cyclotron resonance chemical vapor deposition has resulted in poly-Si films with grains of one micron dimension by using the hydrogen dilution method. The crystalline fraction of the poly-Si film is almost 100% as determined from analysis of Raman spectra. The poly-Si films have preferred 〈111〉 and 〈110〉 orientations according to their XRD spectra. The hydrogen content of the poly-Si films is less than 0.8%. A simple model of grain formation is proposed to explain grain growth in the electron cyclotron resonance chemical vapor deposition deposited poly-Si films.

Grain formation in polycrystalline silicon films deposition on SiO2 at very low temperatures

This paper describes the grain formation in very low temperature polycrystalline silicon (poly-Si) growth on SiO 2 . The silicon films were deposited by electron cyclotron resonance chemical vapor deposition with hydrogen dilution at 250°C and without any thermal annealing. The largest grain sizes observed in the poly-Si film is about 1 μm. The grains have a leaf-like shape as observed in plan-view transmission electron microscopy. The grain morphologies were determined by cross-sectional transmission electron microscopy and atomic force microscopy. Raman scattering spectrum was used to determine the crystalline fraction. X-ray diffraction patterns were used to study the film crystallinity. A simple model of grain formation is proposed.