Metal Induced Lateral Crystallization of Amorphous Silicon Through a Silicon Nitride Cap Layer

Abstract

We studied a new method of Ni-induced crystallization of amorphous silicon ͑a-Si͒ through a silicon-nitride (SiN x ) cap layer. A 0.5 nm of Ni layer was deposited on the SiN x /a-Si layers and then this was annealed in a rapid thermal annealing system. The Ni diffused through the cap layer and formed the NiSi 2 nuclei. Then, disk-shaped grains were grown from these nuclei. The grain size is between 20 and 90 m, and the surface roughness of the poly-Si is 0.76 nm, which is smoother than that ͑0.96 nm͒ of the poly-Si without a cap layer.Polycrystalline silicon ͑poly-Si͒ on glass is a promising material for large-area electronics such as active-matrix liquid crystal displays, active-matrix organic light emitting diodes, and solar cells.To improve the quality of the poly-Si on insulator, several approaches have been conducted on the crystallization of amorphous silicon ͑a-Si͒ including a capping layer on it. For example, in zonemelting recrystallization of Si with a strip heater, an encapsulation layer is necessary and appears to play three major roles: to achieve a smooth surface, to prevent agglomeration, and to induce preferred orientation ͑100͒ texture. 1 To control the lateral growth of excimer laser crystallization poly-Si through lateral thermal gradients, three different patterned capping layers have been used: antireflective (SiO 2 ), heat-sink ͑silicon nitride͒, and reflective ͑metal͒ capping layers. 2 On the other hand, Ni-induced crystallization using various Ni solutions 3,4 and an ultrathin Ni layer of ϳ10 13 cm Ϫ2 has been studied. 5,6 Recently, high quality poly-Si on insulator by metal-induced lateral crystallization ͑MILC͒ has been demonstrated. 6,7 However, the metal layer for the conventional metal induced crystallization ͑MIC͒, and/or MILC poly-Si, was deposited at least on a portion of the surface on the a-Si. In this case, the metal-contacted region on the a-Si for metal-induced crystallization is contaminated by metal impurities.To reduce metal contamination and to have uniform grain size with clean and smooth surface, we have studied Ni-induced crystallization of a-Si using a thin Ni layer on a SiN x /a-Si:H, where the capping layer (SiN x ) is a filter for metal diffusion.We deposited an a-Si:H layer first on glass and then SiN x by plasma-enhanced chemical vapor deposition ͑PECVD͒. The thicknesses of a-Si:H and SiN x are 100 and 150 nm, respectively. The 0.5 nm thick Ni layer was deposited using radio frequency sputtering with a very low power density and patterned to have a square of 360 ϫ 360 m. Figure 1 shows a schematic illustration of a Ni/SiN x /a-Si structure for Ni-induced crystallization. The samples were heated by using a rapid thermal annealing ͑RTA͒ system in N 2 ambient. The temperatures during the heating, cooling, and keeping the sample were controlled. The first step is to dehydrogenate the a-Si:H and SiN x at 430°C for 1 h. The hydrogen atoms in the a-Si:H and SiN x are effused out and the film is changed to a hydrogen-free amorphous silicon. The second step is a pulsed hea...

Ni behaviors in polycrystalline silicon with disk-shaped grains

“…Disk-shaped grains are observed in polycrystalline silicon (poly-Si) made by using a SiN x cap layer, which plays the role of a filter against contamination during Ni silicide-mediated crystallization (SMC) of amorphous silicon (a-Si) [1,2]. Ni diffuses through the SiN x cap layer and then reaches the a-Si to form NiSi 2 crystallites, which act as nucleation sites for crystallization.…”

“…The grain size and crystallinity of poly-Si depend on the Ni area density [1,3]. Therefore, it is important to investigate Ni behaviors in a-Si and poly-Si thin films.…”

Production-Scale Electrodeposited Silicon Solar Cells: Issues to be Solved for Continous Manufacture

“…The web is deposited with Cu followed by Ni/Pd as the bottom metallization. Both amorphous and crystalline forms of silicon can be deposited whose combination can provide increased efficiencies by conversion of amorphous silicon to crystalline using a number of different processes (1,2,3,4,5).…”

Dynamic characteristics of MICC polycrystalline thin film transistors

“…In this paper, we have investigated the stability of the ring oscillator made of p-channel LTPS poly-Si TFT. The poly-Si was made using metal-induced crystallization of a-Si through a cap layer (MICC) [3,4].…”