Increased Lateral Crystallization Width during Nickel Induced Lateral Crystallization of Amorphous Silicon Using Fluorine Implantation

Abstract

This paper reports a study of the effect of fluorine implantation on the nickel-induced lateral crystallization of amorphous silicon. To distinguish the effects of the fluorine and the implantation damage, the fluorine implant is either made directly into the ␣-Si or into the buffer oxide below the ␣-Si. For a 20 h anneal at 500°C, both types of fluorine implant give a 65% increase in the lateral crystallization width, a five times reduction in the density of nickel silicide precipitates, and an improved grain texture. In contrast, for 20 h anneals at 550 and 600°C, both types of fluorine implant give 29% and 85% reductions in the lateral crystallization width, respectively. The identical results obtained for fluorine implantation into the ␣-Si and the buffer oxide indicates that the effects observed are due to chemical effects of the fluorine rather than implantation damage in the ␣-Si. The increased crystallization width at 500°C is explained by the suppression of random crystallization at the bottom ␣-Si/SiO 2 interface. The reduced crystallization widths at 550 and 600°C are attributed to the diffusion and activation of fluorine and the formation of Si-F bonds making the ␣-Si more resistant to silicide-mediated phase transformation.The crystallization of amorphous silicon ͑␣-Si͒ has been intensively investigated for application in active-matrix flat-panel displays and three-dimensional ͑3D͒ electronics. 1-17 Solid phase crystallization was originally used to produce polysilicon from amorphous silicon, and can be typically achieved using a 20 h anneal at a temperature around 600°C. 1,2 The disadvantages of solid phase crystallization ͑SPC͒ are a small grain size, typically 0.5-1 m, and a lack of control over grain boundary locations. 1 As a result, thin-film transistors realized ͑TFT͒ on SPC films exhibit degraded performance. 3 To improve the performance of TFTs fabricated on SPC films, fluorination of the film after or before amorphous silicon crystallization has been used in the past. 4-9 For fluorination applied after amorphous silicon crystallization, the fluorine had demonstrable passivation effects on grain boundaries and gave improved device performance. 4-7 For fluorination applied prior to amorphous silicon crystallization, improved TFT electrical characteristics were shown to come from both grain size enhancement and fluorine passivation. 8,9 It was shown that fluorine ͑F͒ implantation with a dose greater that 2 ϫ 10 15 /cm 2 and a projected range at the bottom ␣-Si/SiO 2 interface, resulted in a significant increase in grain size 9 and a strong ͑111͒ preferred orientation 8 in the SPC film. This improvement in grain size was attributed to the retardation of the random crystallization owing to the higher degree of amorphization at the bottom ␣-Si/SiO 2 interface as a result of the fluorine implant. 8 Similar results were also reported in fluorine implanted silicongermanium ͑SiGe͒ films. 10 More recently, several techniques have been studied for the fabrication of large grain polycrystalline silicon ...

Effect of an Oxide Cap Layer and Fluorine Implantation on the Metal-Induced Lateral Crystallization of Amorphous Silicon

“…The samples without an oxide cap are seen to give larger values of To further investigate the effect of the oxide cap layer, fluorine implanted samples are also studied as fluorine implant has been found to suppress random crystallization in amorphous silicon. 2,16 Fig. 5 shows optical Nomarski micrographs of fluorine implanted samples without (Fig.…”

“…6. Our earlier research 2,16 showed that fluorine enhances the crystallization length in amorphous silicon sheets and nanowires due to the suppression of random grain nucleation at the interface between the amorphous silicon and the underlying silicon dioxide layer. This mechanism also explains the results in Fig.…”

Effect of Fluorine on the Lateral Crystallization of Amorphous Silicon Nanowires

“…Earlier research 18 has shown that fluorine enhances the crystallization length in amorphous silicon sheets due to the suppression of random grain nucleation at the interface between the amorphous silicon and the underlying silicon dioxide buffer layer. To investigate whether this mechanism contributes to the improved reproducibility of the lateral crystallization seen in this work, Raman spectroscopy has been performed in regions of the nanowires outside of the laterally crystallized regions, as indicated by the crosses in Fig.…”

“…This mechanism also gave reduced metal contamination in the crystallized film. 18 Other benefits of fluorine have been reported in thin film devices, such as the passivation of grain boundary traps 19 and the improvement of the uniformity of device electrical characteristics. To date, no work has been reported on the effect of fluorine in Si nanowires.…”

“…[7][8][9] For low-cost applications such as displays, the use of low cost glass substrates requires polysilicon films to be produced at temperatures significantly lower than the typical deposition temperature of 625 • C. 10 Several techniques have been investigated including solid-phase crystallization (SPC), 11 excimer laser crystallization (ELC) [12][13][14] and metal-induced lateral crystallization (MILC). 15 MILC is particularly attractive for low cost applications and the typical anneal temperature for MILC is 500 • C to 550 • C. 16,17 Fluorine implantation into amorphous silicon has been shown to significantly increase the lateral crystallization length during MILC 18 and hence enables polysilicon films to be produced at lower temperatures. This behavior was explained by the action of fluorine in suppressing random crystallization in the amorphous silicon film.…”