Residual lattice strain in thin silicon-on-insulator bonded wafers: Effects on electrical properties and Raman shifts

The effects of the residual strain in thin bonded silicon-on-insulator (SOI ) wafers on the Hall mobilities and the Raman shifts were investigated as a function of the annealing temperature and duration. For samples with an n- type Si layer of 5 mum thickness and a p-type layer of 2.2 mum thickness, m obilities identical to the theoretical values calculated from the piezoresi stive effect were found. However, a sample with an n-type SOI layer of 1.5 mum thickness showed anomalous variation in the electron mobility. While sa mples with little strain had mobilities close to the corresponding value of the bulk Si, the presence of residual strain brought about a significant d ecrease to one tenth of the corresponding value of the bulk Si with increas ing residual strain. The observed drop in the mobility in the sample N1.5 c annot be explained by the piezoresistive effect only. A Raman microprobe wa s used to examine the change in the residual strain of SOI layers. A single Raman peak observed for the SOI specimens was nearly identical to that of bulk Si in intensity and half width. However, a shift associated with the r esidual strain was observed. From a combination of the observed Raman shift s and the precisely evaluated built-in strain in the SOI layers, the result s were compared with relationships that are commonly used for quantitative determination of the existing built-in strain and associated stress from th e results of Raman characterization. (C) 2001 American Institute of Physics .