New Phase Modulators for Next-Generation Low-Temperature Crystallization Method of Si Films

Abstract

A conventional phase modulator having only “holes” (or “bumps”) on a quartz plate has been found to have insufficient depth-of-focus (DOF) characteristics. This poor DOF can be attributed to the phase advancement (or retardation) of the zeroth-order diffracted light wave. This phase effect has been applied to developing two types of modulator: one with a sufficiently large DOF, and the other, a single-plate phase modulator capable of producing a two-dimensional light intensity profile suitable for growing arrays of large grains. It was confirmed experimentally that this single-plate modulator could grow arrays of large grains 5 µm in pitch.

Ultrahigh-Performance Polycrystalline Silicon Thin-Film Transistors on Excimer-Laser-Processed Pseudo-Single-Crystal Films

“…Figure 1 shows a scanning electron microscope (SEM) image of the PSX Si film and a schematic of the TFT layout. Using the desirable effects of a laser light intensity profile generated by a carefully designed phase modulator, 16) each large grain started to grow two-dimensionally from a single nucleus generated near a predetermined position on the sample surface. As a result, roughly 5-mm-long and 5mm-wide PSXs were grown in a periodic array.…”

Pseudo-Single-Nucleus Lateral Crystallization of Si Thin Films

“…However, in this case, only a dull conelike form can be realized. Because it is necessary for us to make a conelike form of the light intensity that is very sharp, we use a bipolar phase modulator (BPM) 7) pattern in place of the metal dot pattern.…”

Novel Optical Method for Widening Process Window of Phase-Modulated Excimer Laser Crystallization

“…Generally speaking, the intensity, I b , at the bottom of the dip should be designed to be about half the maximum light intensity tolerated by the sample, because lateral grain growth has been found experimentally to start at this intensity position. Accordingly, should be about 60 , 10) with the duty ratio of 0.5, but must be adjusted depending on the details of the phase modulator specifications and the crystallization conditions. In the following discussion, we use ¼ 90 , but the conclusions are not restricted to this condition.…”

“…After laser light pulse irradiation, a nucleus will be born in a limited sample area corresponding to the dip position and will grow laterally in the surrounding supercooled melt not only along the intensity slope but also perpendicular to this direction, resulting in a large grain at a predetermined position. The optimally designed PM pattern 9,10) can generate such profiles, and its design methodology has been established, particularly for a bipolar PM (BPM) made of a crystal quartz plate having a stripe pattern of bump and hole areas on its surface. In this method, however, there remains the serious shortcoming that the sample surface must be located accurately at the focal position of the projection optics, because defocus, i.e., displacement of the sample surface from the focal position, causes undesirable deformation in the intensity profile and deteriorates the crystallized film morphology.…”