Low temperature polycrystalline silicon with single orientation on glass by blue laser annealing

We report high performance p-type poly-Si thin-film transistors (TFTs) achieved by lateral grain growth of amorphous silicon (a-Si) by using a continuous-wave blue diode laser of wavelength 445 nm. The blue laser beam is efficiently absorbed into the a-Si film, such that full melting and lateral crystallization is achieved in all thicknesses investigated, 50–200 nm. TFTs fabricated with 75-, 100-, and 125-nm-thick poly-Si films laterally grown by the blue laser annealing exhibited field-effect mobility of 108 ± 7, 104 ± 9, and 134 ± 12 cm2/ $\textrm {V}\cdot \textrm {s}$ , and subthreshold swing of 210±51, 191±16, and 193±53 mV/decade, respectively, and high ON/OFF current ratio of $\sim 10^{8}$ .

Lateral Grain Growth of Amorphous Silicon Films With Wide Thickness Range by Blue Laser Annealing and Application to High Performance Poly-Si TFTs

The structure of amorphous Ge (a-Ge) films prepared by sputter-deposition and the effects of aging at ambient temperature and pressure were studied by pair-distribution-function (PDF) analysis from electron scattering and molecular dynamics simulations. The PDFs of the as-deposited and aged samples for 3–13 months showed that the major peaks for Ge-Ge bonds decrease in intensity and broaden with aging for up to 7 months. In the PDFs of a-Ge of molecular dynamics simulation obtained by quenching liquid at different rates, the major peak intensities of a slowly cooled model are higher than those of a rapidly cooled model. Analyses on short- and medium-range configurations show that the slowly cooled model includes a certain amount of medium-range ordered (MRO) clusters, while the rapidly cooled model includes liquid-like configurations rather than MRO clusters. The similarity between experimental and computational PDFs implies that as-deposited films are similar in structure to the slowly cooled model, whereas the fully aged films are similar to the rapidly cooled model. It is assumed that as they undergo room-temperature aging, the MRO clusters disintegrate and transform into liquid-like regions in the same matrix. This transition in local configurations is discussed in terms of instability and the non-equilibrium of nanoclusters produced by a vapor-deposition process.

Structural transition in sputter-deposited amorphous germanium films by aging at ambient temperature

Phase transformation of amorphous-silicon during millisecond annealing using micro-thermal-plasma-jet irradiation was directly observed using a high-speed camera with microsecond time resolution. An oval-shaped molten-silicon region adjacent to the solid phase crystallization region was clearly observed, followed by lateral large grain growth perpendicular to a liquid-solid interface. Furthermore, leading wave crystallization (LWC), which showed intermittent explosive crystallization, was discovered in front of the moving molten region. The growth mechanism of LWC has been investigated on the basis of numerical simulation implementing explosive movement of a thin liquid layer driven by released latent heat diffusion in a lateral direction.

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Direct observation of grain growth from molten silicon formed by micro-thermal-plasma-jet irradiation.

Sequential lateral crystallization of amorphous silicon on glass by blue laser annealing for high mobility thin-film transistors

Semiconductor blue-multi-laser-diode annealing (BLDA) for amorphous Si film was performed to obtain a film containing uniform polycrystalline silicon (poly-Si) grains as a low temperature poly-Si (LTPS) process used for thin-film transistor (TFT). By adopting continuous wave (CW) mode at the 445 nm wavelength of the BLDA system, the light beam is efficiently absorbed into the thin amorphous silicon film of 50 nm thickness and can be crystallized stably. By adjusting simply the laser power below 6 W with controlled beam shape, the isotropic Si grains from uniform micro-grains to arbitral grain size of polycrystalline phase can be obtained with reproducible by fixing the scan speed at 500 mm/s. As a result of analysis using electron microscopy and atomic force microscopy (AFM), uniform distributed micro-poly-Si grains of smooth surface were observed at a power condition below 5 W and the preferred crystal orientation of (111) face was confirmed. As arbitral grain size can be obtained stably and reproducibly merely by controlling the laser power, BLDA is promising as a next-generation LTPS process for AM OLED panel including a system on glass (SoG).

https://iopscience.iop.org/article/10.1143/JJAP.49.03CA10/pdf

Advanced Micro-Polycrystalline Silicon Films Formed by Blue-Multi-Laser-Diode Annealing

Si thin film coated on a flexible polyimide (PI) substrate was successfully crystallized by blue multi-laser diode annealing (BLDA) in the CW mode. The precursor Si film of 50 nm thickness was stably deposited at room temperature using a radio-frequency (RF) sputtering machine. Subsequently, a blue (445 nm) laser beam of 1.1 W was irradiated onto the Si film at a scan speed of 500 mm/s. After irradiation, neither damage to the substrate nor degradation of the Si film surface was observed, and the Si surface was kept smooth within 4.2 nm (RMS). By Raman peak shift at 520 cm-1 and transmission electron microscope (TEM) observation, the crystalline fraction of 100% was estimated in spite of the presence of micro-grains of ~50 nm in diameter. The BLDA allows the realization of ultra-low temperature polycrystalline silicon (poly-Si) and is suitable for the next-generation system on panel (SoP).

http://iopscience.iop.org/article/10.1143/JJAP.51.03CA02/pdf

Crystallization of Si Thin Film on Flexible Plastic Substrate by Blue Multi-Laser Diode Annealing

Semiconductor blue-multi-laser-diode annealing (BLDA) for amorphous silicon film prepared by radio frequency (RF) sputtering was performed to investigate the controllability of the crystallization behavior by changing the scanning velocity of BLDA ranging from 300 to 500 mm/s at a constant power of 3.4 W. From the evaluation results of polycrystallized Si films, crystallization occurred in solid phase under high temperature heating, and rather small grains of dendrite-like structure with distinctly preferred crystal orientation of (111) face was observed at the higher scanning velocity of 500 mm/s. On the other hand, crystallization occurred in liquid phase and randomly oriented rather larger grains with the size of 100–200 nm were observed for the scanning velocity at 300 mm/s. It was verified successfully that high crystallinity poly-Si films of arbitrary grain structure could be obtained by controlling the scanning velocity of BLDA.

https://iopscience.iop.org/article/10.1143/JJAP.50.021402/pdf

Crystallization Behavior of Sputtered Amorphous Silicon Films by Blue-Multi-Laser-Diode Annealing

Blue-Multi-Laser-Diode Annealing (BLDA) was performed in the continuous wave (CW) mode on Si films as thick as 0.5 μm and 1 μm deposited by rf sputtering. As a result of controlling the laser power from 4.0 to 4.8 W, a whole Si layer of 0.5 μm in thickness was completely crystallized and consisted of a columnar structure of fine grains beneath a partially melted Si surface owing to the high temperature gradient along the depth in the Si layer. After additional hydrogenation in a furnace ambient, the ratio of the photo/dark current under AM1.5 illumination distinctly improved to 6 times higher than that of as-deposited condition. The BLDA is expected to be applied to thin-film solar cells and/or to thin film transistor (TFT) photo-sensor systems on panels as a new low-temperature poly-silicon (LTPS) fabrication technique.

Crystallization of silicon films of submicron thickness by blue-multi-laser-diode annealing

In this paper, we have successfully crystallized the amorphous silicon thin films on flexible thin glass of 100 μm by adopting blue-multi-diode-laser annealing. The crystallized films on flexible thin glass showed high crystallinity and good electrical properties as well as on the conventional thick glass with the thickness of 0.7 mm.

Jean de Dieu Mugiraneza

Papers

Advanced Micro-Polycrystalline Silicon Films Formed by Blue-Multi-Laser-Diode Annealing

Crystallization of Si Thin Film on Flexible Plastic Substrate by Blue Multi-Laser Diode Annealing

Crystallization Behavior of Sputtered Amorphous Silicon Films by Blue-Multi-Laser-Diode Annealing

Crystallization of silicon films of submicron thickness by blue-multi-laser-diode annealing

P‐140L: Late‐News Poster: Crystallization of Amorphous Silicon Films on Flexible Glass by Blue‐Multi‐Diode‐Laser Annealing as a New LTPS