Paper AS-ThP10
Nanoindentation Study of Silicon-on-Insulator (SOI) and Strained (sSOI) Multilayers Composite Films

Thursday, October 18, 2007, 5:30 pm, Room 4C

Silicon-on-Insulator (SOI) technology provides an engineered composite substrate where the active top Si device layer is decoupled from the mechanical support wafer by an interspersed electrically insulating and mechanically compliant silicon oxide layer. The main application of SOI technology is found in microelectronics, where SOI offers CMOS performance enhancement with the use of an embedded oxide layer to isolate transistors from the substrate, which results in lower parasitic capacitance and reduced junction leakage and a host of other benefits. For further performance gain lattice strain can be incorporated into SOI films in order to enhance carrier mobility for MOSFETs. Bi-axially tensile strained sSOI films were obtained with a fabrication sequence of epitaxially growing 150 Å to 600 Å strained Si films on a relaxed 20% Ge containing Si_1-xGe_x buffer layer on a donor wafer. During epitaxy the Si lattice stretches to match the larger Si_1-xGe_x lattice. The larger lattice constant of Ge produces a 4.1% lattice mismatch with the Si crystal. The higher the Ge alloy concentration, the higher the embedded strain becomes. Following successful bonding of both wafers, the donor wafer was split off with the Smart Cut^TM exfoliation technique. The surface was then finished with an etching process to completely remove all traces of the Si_1-xGe_x film, resulting in a Ge-free bi-axially strained Si film on amorphous SiO₂ insulator. In this work we use nanoindentation to investigate the hardness and modulus of standard relaxed SOI and bi-axially tensile strained sSOI with Si films ranging in thickness from 10 to 60 nm and extreme strained xsSOI multilayer samples. The elastic response of the silicon-oxide-silicon substrate multilayer system to indentation can be modeled using elasticity theory, which reveals excellent agreement with the experimental results. The nanoindentation experiments detect a 5% difference in composite modulus with indent depths between 30 and 40 nm deep for 60 nm-thick tensile strained sSOI films compared to SOI films. These strained films are grown epitaxially on a Si_0.80Ge_0.20 buffer layer followed by wafer bonding and film exfoliation by the Smart Cut^TM technology. The sSOI and xsSOI thin films exhibit mean tensile stress levels of 1.3 GPa and 2.5 GPa respectively using a Si_0.60Ge_0.40 buffer layer.