Characterization of excimer-laser-annealed polycrystalline silicon films grown by ultrahigh-vacuum chemical vapor deposition

Abstract

Polycrystalline silicon (poly-Si) films grown by ultrahigh-vacuum chemical vapor deposition (UHVCVD) system and then annealed by excimer laser at room temperature have been investigated for the applications in polycrystalline silicon thin-film transistors (poly-Si TFTs). The results showed that the grain size of the laser-annealed poly-Si film decreased with laser energy density when a lower laser energy density below 157.7 mJ/cm2 was used. At about the threshold laser energy density (∼134.5 mJ/cm2), the finest grain structure could be obtained due to the partial melting in the top layer of the film. When the energy density of the excimer laser was larger than the threshold energy density, the large grain growth was initiated. The largest grain structure could be obtained at ∼184 mJ/cm2, while its surface roughness was better than that of the nonannealed UHVCVD poly-Si films. The surface roughening was suggested to arise from the specific melt-regrowth process but not the rapid release of hydrogen or capillary wave mechanism derived from laser-annealed amorphous silicon. By use of the laser-annealed UHVCVD poly-Si films as the active layer, the fabricated poly-Si TFT exhibited a field-effect mobility of 138 cm2/V s, a subthreshold swing of 0.8 V/dec, a threshold voltage of 3.5 V, and an on/off current ratio of ∼106.

Characterization of local electrical properties of polycrystalline silicon thin films and hydrogen termination effect by conductive atomic force microscopy

“…In the poly-Si films crystallized by conventional ELA, a prominent ridge was formed at a grain boundary owing to the stress concentration. 13 Thus, it is expected that crystal strain is easily caused near grain boundaries. Therefore, we concluded that hydrogen termination does not randomly progress, and there are regions that cannot be easily inactivated near grain boundaries.…”

Effects of oxygen in Ni films on Ni-induced lateral crystallization of amorphous silicon films at various temperatures

“…Among these three processes, ELA of a-Si films appears to be very promising due to its lower thermal budget, shorter processing time, and ability to produce poly-Si films with better quality. 4 However, the equipment cost is high. As for the SPC method, it is a well-established poly-Si formation technique with several advantages over ELA, including smoother surfaces, better uniformity, and the use of the batch process in furnace annealing.…”

Excimer Laser Annealing Effects of Silicon-Rich Silicon Nitride Films Prepared by Using Catalytic Chemical Vapor Deposition

“…However, this method was not compatible for display device process because it usually need a high temperature (>700 ℃) [3][4]. Excimer laser annealing (ELA) is promising method for a low temperature fabrication process upon illumination of laser pulses, amorphous silicon film was melted and re-crystallized as the poly crystalline silicon film [5][6]. Thus, Si QDs could be nucleated and crystallized in silicon-rich silicon nitride (SRSN) film by using ELA.…”