Advanced Four-Mask Process Bottom-Gate Poly-Si TFT via Self-Aligned NiSi2 Seed-Induced Lateral Crystallization

We report on a method to fabricate high-performance bottom-gate poly-Si (BGPS) thin-film transistors (TFTs) with a four-mask process via self-aligned (SA) NiSi
₂
seed-induced lateral crystallization (SILC). Previously, the BGPS TFT crystallized by SILC was reported to have high electrical performance with a simple process. However, this approach still requires an additional mask for lateral crystallization, making the process more complicated and expensive. In this letter, by using the SA-SILC method, only a few NiSi
₂
seeds reach the intrinsic Si surface through the side edges of the etch stopper and then crystallize the channel. This SA-SILC enables low metal contamination by a few seeds in the channel, shorter annealing time due to reduced length for SILC, and a simple four-mask process. The SA-SILC BGPS TFTs exhibited a steep subthreshold slope of 0.16 Vdecade
^-1
, a high field-effect mobility of 230 cm
²
V
^-1
s
^-1
, and kink-free output characteristics.