Property of nickel silicides with 10 nm-thick Ni/amorphous silicon layers using low temperature process

60 nm- and 20 nm-thick hydrogenated amorphous silicon (a-Si:H) layers were deposited on 200 nm SiO₂/Si substrates using ICP-CVD (inductively coupled plasma chemical vapor deposition). A 10 nm-Ni layer was then deposited by e-beam evaporation. Finally, 10 nm-Ni/60 nm a-Si:H/200 nm-SiO₂/Si and 10 nm-Ni/20 nm a-Si:H/200 nm-SiO₂/Si structures were prepared. The samples were annealed by rapid thermal annealing for 40 seconds at 200∼500°C to produce NiSi_x. The resulting changes in sheet resistance, microstructure, phase, chemical composition and surface roughness were examined. The nickel silicide on a 60 nm a-Si:H substrate showed a low sheet resistance at T (temperatures) >450°C. The nickel silicide on the 20 nm a-Si:H substrate showed a low sheet resistance at T > 300°C. HRXRD analysis revealed a phase transformation of the nickel silicide on a 60 nm a-Si:H substrate (δ-Ni₂Si → ζ-Ni₂Si→ (NiSi + ζ-Ni₂Si)) at annealing temperatures of 300°C → 400→C → 500°C. The nickel silicide on the 20 nm a-Si:H substrate had a composition of δ-Ni₂Si with no secondary phases. Through FE-SEM and TEM analysis, the nickel silicide layer on the 60 nm a-Si:H substrate showed a 60 nm-thick silicide layer with a columnar shape, which contained both residual a-Si:H and Ni₂Si layers, regardless of annealing temperatures. The nickel silicide on the 20 nm a-Si:H substrate had a uniform thickness of 40 nm with a columnar shape and no residual silicon. SPM analysis shows that the surface roughness was > 1.8 nm regardless of the a-Si:H-thickness. It was confirmed that the low temperature silicide process using a 20 nm a-Si:H substrate is more suitable for thin film transistor (TFT) active layer applications.