Single-grain growth in Si film by chevron-shaped cw laser beam scanning

Abstract

A single grain with a length of 450 µm and a width of 5–6 µm was grown in a 60 nm Si film on SiO2 by scanning a chevron-shaped cw laser beam, which was formed by passing a linear laser beam through a novel one-sided Dove prism. The crystal did not have any dominant orientations in both the growth and normal directions. The orientation rotated about the transverse direction at a rate of 0.47–0.51°/µm in the forward direction, which suggests that the lattice constant at the film surface was 0.049–0.053% larger than that at the film bottom.

Unseeded Crystal Growth of (100)-Oriented Grain-Boundary-Free Si Thin-Film by a Single Scan of the CW-Laser Lateral Crystallization of a-Si on Insulator

“…The geometry selection will not work effectively in very narrow and thin wires like the experiments of Yeh et al [29,36]. The nucleus with the {100} SD orientation is not always included in the nuclei randomly nucleated at the scan starting point in a limited space for nucleation if the crystallization stripe is narrow and thin.…”

“…So far, every laser crystallization method to produce grain-boundary-free films at a temperature less than 450 • C has failed to control crystal orientations of the crystallized region, and conversely, every method to obtain preferentially-oriented films has failed to eliminate grain boundaries from the crystallized region. The observation of the grain boundaries after the delineation by Secco etching of the crystallized film reveals that the grain boundaries can be eliminated from a defined area in the CW-laser crystallization, if isotherms are modulated by beam shaping [26][27][28][29], stripe cap patterning [30,31], Si island patterning [32][33][34], or substrate patterning [35]. The idea of these methods is to make the temperature of the controlled crystal growth region less than that of the peripheral regions, to suppress the disturbance to the growth region from the random nucleation at the peripheral.…”

“…Even if a grain boundary happened to be formed in a central crystallized region, the grain boundary is swept outward with scan travel. However, it is difficult to realize the surface orientation control in addition to the grain boundary elimination by these isotherm modulations [29,31,34]. Yeh et al reported a 1 mm-long grain-boundary-free Si stripe of 4 µm-width, having {100}-orientation in surface normal and {320}-orientation in scan direction, by crystallization with a chevron-shaped CW laser beam and a 300 nm-thick SiO 2 cap [36]; however, they also reported orientation rotation with the scan travel in other scans at the same crystallization conditions in the same paper [36].…”

Laser-Induced Crystallization of Copper Oxide Thin Films: A Comparison between Gaussian and Chevron Beam Profiles

“…Chevron-Beam Profile. The chevron-beam profile was established by having the output of a 405 nm wavelength multimode CW laser-diode pass through a one-sided dove prism that converted the line-beam profile into a chevron-beam profile 19 focused on the CuO layer. The initial structure in Figure 1a was mounted on a linearly moving stage that advanced at a speed (i.e., scan rate R scan ) in the range of 0.4−5 mm/s with respect to the fixed position of the laser with the laser power output P L varied in the range of 50−140 mW and thus provided the geometrical dimension of the chevron-beam profile; the areal laser power density was varied in the range of 1−1.5 × 10 6 W/cm 2 .…”

Tendency of crystal orientation rotation toward stable {001} <100> during lateral crystal growth of Si thin film sandwiched by SiO2

“…High-power ultraviolet (UV) or blue laser diode (LD) for CLC were proposed at around 2010, 22,25) in which we used line laser beam from a multimode UV-LD for CLC for the first time. 25) Then we proposed micro-chevron laser beam scanning (μCLBS) method 27) in which μCLB was produced using one-sided Dove prism and a multimode UV-LD, by which single crystal Si strip free of random grain boundary (RGB) was realized. Then we clarified that twinning in the strip was growth twin and was generally originated at Si/SiO 2 interface, so improvement of the interface quality is essential for reducing twin boundaries.…”