SOI formation from amorphous silicon by metal-induced-lateral-crystallization (MILC) and subsequent high temperature annealing

Abstract

In current SOI technology, the formation of circuit elements requires the use of some special starting material like SIMOX, BESOI or Unibond wafers, which usually cannot be made in-house. As such, it leads to a divergence between SOI technology and bulk technology, and there are debates on justification on the initial material cost. TFTs formed in polysilicon have similar structures to SOI, and have been used as the load element in SRAM. Comparing TFT and SOI transistors, the TFT is easier to fabricate in term of starting material and compatibility with bulk processes. However, its performance is usually very poor for high performance circuits. The TFT structure consists of a large number of small size crystallized silicon grains. It is desirable to have a very large grain size so that a single transistor can lie entirely on a single grain. In this case, the TFT becomes an SOI MOSFET. Metal-induced-lateral-crystallization (MILC) has been used to enlarge the polysilicon TFT grain size. However, due to the limitation in low temperature formation, the grain size is still not desirable. With the use of high temperature annealing at a temperature above 900/spl deg/C after MILC, we found that much larger crystals of the order of 10 /spl mu/m can be formed. For the advanced technology which comes with device scaling, it is possible to individually recrystallize the active region of each transistor, giving TFTs (as formed) with SOI MOSFET performance.