The Crystallographic Properties of Strained Silicon Measured by X-Ray Diffraction

Strained silicon represents a materials-based enhancement to further scaling of CMOS transistors. In epitaxial strained silicon substrates, strain is provided by a relaxed SiGe graded buffer layer that expands the in-plane lattice constant of silicon. Because this is accompanied by the introduction of crystalline defects, in the form of dislocations, mosaic structure, and lattice tilting, the deposition of strained silicon occurs on imperfect substrates. Therefore, there is a fundamental need to study the materials properties to ensure strained silicon substrates meet the rigorous criteria for CMOS processing. This paper focuses on the in-depth investigation of the crystallographic properties of epitaxial strained silicon and strained silicon on insulator (SSOI) substrates by X-ray diffraction (XRD). The results for both epitaxial strained silicon and bonded SSOI substrates are presented and contrasted, with particular emphasis on the effect of the layer transfer process used during the formation of SSOI substrates. Although the focus is on strained silicon, the X-ray diffraction techniques highlighted in this paper are readily extendable to other materials heterostructures, such as germanium on insulator, strained germanium, and III–V compound semiconductors on insulator, allowing characterization of many future microelectronic platforms.