Fabrication and Analysis of Poly-Si Thin Film Transistor and Si Nanowire Field Effect Transistor
Date Issued
2006
Date
2006
Author(s)
Meng, Chao-Yu
DOI
en-US
Abstract
The fabrication and analysis of poly-Si thin film transistor (TFTs) and Si nanowires (SiNWs) field effect transistor were studied in this thesis. The poly-Si with regular and large grain was fabricated by employing metallic pads as the heat sinks and with underlying silicon oxynitride (SiON) as the heat absorption layer. The TFTs fabricated by this method achieves a field effect mobility of 246 cm2/V-sec and an on/off current ratio exceeding 5×105. Besides, the degradation behavior of body-contact (BC) polysilicon thin film transistors under DC and AC stress were investigated and compared with conventional ones. It was found that the reliability of body-contact poly-Si TFTs is better than the conventional TFTs under both DC and AC stress conditions. After 1000s AC stress, the degradation of BC poly-Si TFTs become an order of magnitude less than the conventional ones. Therefore, a model was proposed to explain the degradation improvement of body-contact poly-Si TFTs.
The fabrication of SiNWs has been demonstrated using excimer laser annealed gold nanoparticles as the catalyst and vapor-liquid-solid (VLS) growth. Scanning electron microscopes images of the excimer laser annealed Au nanoparticles from 2.5, 5, and 10 nm Au film showed that the nanoparticles had mean diameters of 12, 13, and, 15nm, respectively. The results show that the diameter controlled uniform silicon nanowires can be obtained utilizing controlled thickness of Au film combined with suitable laser power density.
The un-doped and boron-doped SiNWs grown via VLS mechanism were studied. The diameters of un-doped and boron-doped SiNWs varied from 18.5 to 75.3 nm and 26.6 to 66.1 nm, respectively. The critical growth temperature of boron-doped SiNWs is 10 ℃ lower than that of un-doped ones and the diameters of the boron-doped SiNWs is always larger than that of the un-doped ones under different growth
temperatures. This is because that the introduction of diborane enhanced the dissociation of SiH4 which determines the growth process of SiNW.
Un-doped, N-type, and P-type doped SiNWs were grown at 460oC and 25 torr. The intensity ratio of anti-Stokes/Stokes (IAS/IS) peaks is used as an index of the sample temperature. Different SiNWs exhibit different Raman frequency shifts because their compressive stresses due to heating differ. The slopes of the IAS/IS peak ratio versus the Raman frequency for boron-doped, un-doped, phosphorous-doped SiNWs and bulk Si are -0.078, -0.036, -0.035 and -0.02 per cm-1, respectively. The different slopes reveal the different heating-induced compressive stresses in the SiNWs with different dopants and bulk Si.
The electric-field-directed growth of SiNWs was performed utilizing Au film with different thicknesses. It is found that the 1 and 0.5 nm Au film are more suitable for the electric-field-directed growth of SiNWs due to the formation of separated Au clusters during the thermal evaporation. Besides, the electric field in the range 0.5~2.5 V/μm are suitable for the direction controlled growth of SiNWs.
For further improvement of the position and direction controlled growth of SiNWs, the 20 nm Au nanoparticles were used as the catalyst to control the diameter of SiNWs. In the self-aligned structure, parts of the SiNWs across the gap become huger and the possible DC plasma enhance coating model is proposed to explain the phenomenon. It is also found that the position controlled structure with one sided Au catalyst is better and more suitable for the position and direction controlled SiNWs growth. Finally, the position and direction controlled SiNWs FETs were successfully fabricated by electric field directed growth. It demonstrates the feasibility to fabricate the SiNWs array and electrical devices with low cost.
Subjects
低溫多晶矽薄膜電晶體
矽奈米線場效電晶體
Poly-Si Thin Film Transistor
Si Nanowire Field Effect Transistor
Type
thesis
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