Thermal behavior of residual strain in silicon-on-insulator bonded wafer and effects on electron mobility

Abstract

Residual lattice strain in a bonded SOI wafer and its influence on the electron mobility were investigated as a function of heat-treatment temperature ranging from 900 to 1050°C and duration from 6 to 30 h. The change in residual strain was measured by using the X-ray diffraction method. In as-received SOI wafers, tensile strain (tensile stress along the direction parallel to the surface) of the order of 10 −5–10 −4 was observed. For the specimens annealed at above 950°C, the strain varied abruptly from a tensile to a compressive one at an annealing time of 12–15 h, then approached a certain value with increasing annealing time. On the other hand, the remaining strain of the specimen annealed at 900°C exhibited the tensile region only, and did not achieve to the compressive one, even for long treatment. Significant variation in the electron Hall mobility was observed for both 1.5 and 5 μm thick SOI layers as the residual strain changes. Although samples with no strain showed identical mobility to the value in a bulk Si, the presence of the strain may anomalously affect the electron transportation.