Investigation of silicon grain structure and electrical characteristics of TFTs fabricated using different crystallized silicon films by atmospheric pressure micro-thermal-plasma-jet irradiation

Abstract

Amorphous silicon (a-Si) films were crystallized using three grain growth modes induced by micro-thermal-plasma-jet (µ-TPJ) irradiation and applied to the channel regions of thin-film transistors (TFTs). Solid phase crystallization (SPC) formed microcrystalline grains and showed a lower crystallinity of 70%, whereas leading wave crystallization (LWC) and high-speed lateral crystallization (HSLC) formed significantly larger grains than the TFT channel region. The SPC-TFT showed a lower field-effect mobility (μFE) due to the small grain size and the existence of many grain boundaries, whereas LWC- and HSLC-TFT channels were formed by only single grains and showed a μFE higher than 300 cm2 V−1 s−1 in the n-channel. The defect density of HSLC was smaller than that of LWC; consequently, the HSLC-TFT performed better than the LWC-TFT. The maximum μFE values of n- and p-channel HSLC-TFTs were 418 and 224 cm2 V−1 s−1, respectively.

Grain Growth Control by Micro-Thermal-Plasma-Jet Irradiation to Very Narrow Amorphous Silicon Strips and Its Application to Thin Film Transistors

“…Dopant types of strips and low resistance regions are the same in order not to form PN junction. N-and p-type top gate TFTs were also fabricated by following the process steps as reported in [4]. The maximum temperature throughout the TFT fabrication process was 450°C.…”

“…We have proposed the application of atmospheric pressure discharge micro-thermal-plasma-jet (-TPJ) to high speed lateral crystallization (HSLC) of a-Si films [1][2][3]. HSLC is induced by moving the molten region at very high speed of 4000 mm/s to form a lateral temperature gradient, which results in the long growth of ~100 m [4]. In addition, we have attempted to control grain growth by µ-TPJ irradiation to a-Si pattern.…”

Void-Defect Location Control of Laser-Crystallized Silicon Thin Films with Hole-Pattern

“…However they have a low mobility, below 200 cm 2 V -1 s -1 with small silicon crystal grains of 0.5-1 μm [4]. Other laser-crystallization methods such as sequential lateral solidification (SLS), solid-phase crystallization (SPC), thermal plasma jet (TPJ), and flash lamp annealing (FLA) have been applied to grow large crystal grains, and high-performance LTPS-TFTs have been achieved [5][6][7]. However, the uniformity of TFT's performance has not been achieved by these methods since the non-uniform crystallinity of poly-Si thin films have been formed.…”

Effect of Grain Growth Control by Atmospheric Micro-Thermal- Plasma-Jet Crystallization of Amorphous Silicon Strips on TFT Characteristics

“…However, present LTPS technology, based excimer laser annealing (ELA) technique [5][6][7][8], must solve the cost and variability issues. We have proposed micro-thermal-plasmajet (µ-TPJ) technique for crystallization of amorphous silicon (a-Si) films [9][10][11][12][13][14]. Because of its simple structure and atmospheric pressure process, µ-TPJ enables low cost fabrication compared with ELA technique.…”

“…To solve these issues, we have controlled the lateral growth by ZMR using narrow a-Si strip patterns [15][16][17]. We have proposed new TFT pattern, which is composed of 1-µm-wide strips, and suppressed the variability of LTPS TFTs caused by random GBs [14][15][16][17]. This pattern enabled us to operate CMOS circuit with channel length (L) of 10 µm at a low supply voltage of 5V and a high frequency of 4MHz [17].…”