Abstract
We investigated the crystallinities of poly silicon (poly Si) annealed via green laser annealing (GLA) with a 532-nm pulsed laser and blue laser annealing (BLA) with 450-nm continuous-wave lasers. Three-dimensional heat transfer simulations were performed to obtain the temperature distributions in an amorphous silicon (a-Si) thin film, and GLA and BLA experiments were conducted based on the thermal simulation results. The crystallinity of annealed poly Si samples was analyzed using Raman spectroscopy and spectroscopic ellipsometry. To evaluate the degree of crystallization for the annealed samples quantitatively, the measured spectra of laser-annealed poly Si were fitted to those of crystalline Si and a-Si, and the crystal volume fraction (fc) of the annealed poly Si sample was determined. Both the Raman spectroscopy and ellipsometry showed consistent results on fc. The fc values were found to reach >85% for optimum laser power of GLA and BLA, showing good crystallinity of the laser-annealed poly Si thin films comparable to thermal furnace annealing.
Highlights
Laser annealing has been widely adopted as a low-temperature polycrystalline silicon (LTPS) process to crystalize amorphous silicon (a-Si) materials into polycrystalline silicon grains
Various laser annealing technologies have been developed for LTPS processes as alternatives to excimer laser annealing (ELA): green laser annealing (GLA) [12,13,14,15], near-ultraviolet laser annealing (NULA) [16,17,18,19], and blue laser annealing (BLA) [20,21,22]
The analysis results of this study showed that BLA could be better laser annealing process than GLA for the annealing of a 100-nm-thick a-Si layer, which is attributed to the CW laser operation in BLA
Summary
Laser annealing has been widely adopted as a low-temperature polycrystalline silicon (LTPS) process to crystalize amorphous silicon (a-Si) materials into polycrystalline silicon (poly Si) grains. Si films with high mobility can be achieved by the LTPS process, leading to the realization of low-power thin-film transistor (TFT) panels in liquid crystal or organic light-emitting diode displays [1,2]. In the laser annealing process for a large-area TFT panel, excimer laser annealing (ELA) using ArF (197 nm), KrF (308 nm), or XeCl (308 nm) lasers have been widely employed owing to their high laser power and large absorption coefficient for a-Si [8,9,10,11]. In BLA, high-power continuous-wave (CW) blue laser diodes emitted around
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