Strain redistribution in free-standing bridge structure released from strained silicon-on-insulator

The strain evolution including relaxation and conversion during the fabrication of free-standing bridge structure, which is the building block for the gate-all-around transistor, has been investigated in strained silicon-on-insulator. Compared to the starting strained silicon-on-insulator substrate, the strain of the free-standing bridge structure transforms from the biaxial strain to the uniaxial strain after patterning and release due to its unique configuration, as suggested by UV-Raman spectroscopy. Furthermore, such uniaxial strain has strong correlation with the dimension of the suspended structure, and it is enhanced as the width of the free-standing bridge decreases and the size of the connected pad increases. For 0.5μm-wide free-standing bridge connected to the pad of 16 × 16 μm2, the maximum uniaxial tensile strain of 4.65% is obtained, which remarkably exceeds the levels that can be achieved by other techniques ever reported. The observed strain redistribution phenomenon is also analyzed by two-dimensional finite element modeling. The finite element modeling confirms the strain evolution in the suspended bridge structure after patterning and release, in agreement with the experimental observations.