Flash-Lamp-Induced Crystal Growth of Silicon on Amorphous Substrates Using Artificial Surface-Relief Structures

Abstract

Crystallization of amorphous silicon films deposited over surface‐relief structures etched into SiO2 layers is achieved by large area processing with incoherent light pulses of 10 ms duration. The structures are either gratings with a constant top width of 3 μm and bottoms with a width between 3 and 20 μm or otherwise shaped artificial surface‐relief micropatterns. The crystalline films are found to consist of very large crystallites, which are either separated from each other by grain boundaries or twinned to one another.

Formation of regularly arranged large grain silicon islands by using embedded micro mirrors in the flash crystallization of amorphous silicon

“…Due to the poor wetting of the liquid silicon on the underlying SiO 2 , the melt collapses and forms droplets. 10,15,30,31 During cooling, the droplets solidify at their current position. In this connection, it is noticeable that all droplets are located within the regions defined by the former a-Si islands.…”

“…Consequently, the melt collapses and shows a tendency to agglomerate somewhere else. 10,15,30,31 However, since it is surrounded by silicon which is only partially molten or still solid, the liquid finds proper adherence there and hence drifts towards these areas. Surprisingly, the melt does not accumulate considerably at the edges, but instead the liquid slops on the material of the interspace regions and cover these regions completely.…”

“…Examples are the application of patterned absorbing layers on top or below the a-Si, 12 the use of a local thinner oxide below the a-Si to produce a heat sink, 31 an a-Si film with a locally increased thickness, 31 the structuring of the a-Si itself, 12,32 or a combination of these approaches. The largest silicon grains obtained so far by FLA in a controlled manner were reported by Scharff et al 15,16 They used artificial surface relief structures covered 15 or filled 16 with a-Si to produce silicon islands that are embedded in the surrounding oxide and consist of grains with a size of several tens of micrometers. In the field of crystallization by ELA, the so-called l-Czochralski process 31 is one of the most advanced techniques to produce large silicon grains in a controlled manner.…”

“…Since there is no method to deposit a high quality silicon film directly without exceeding this thermal budget, a film of amorphous silicon (a-Si) has to be deposited at first and crystallized thereafter. Common annealing techniques for that purpose are flash-lamp annealing (FLA) [7][8][9][10][11][12][13][14][15][16] and excimerlaser annealing (ELA). [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] In these processes, a sample is exposed to a light flash with durations typically in the ms and the ns range for FLA and ELA, respectively.…”