Quantitative Strain Measurement in Advanced Devices: A Comparison Between Convergent Beam Electron Diffraction and Nanobeam Diffraction
To enhance carrier mobility and drive current in metal-oxide–semiconductor field effect transistors, several approaches, mainly based on strain engineering have been used for several years [GHA 03, ANT 06, LEE 05, THO 06, PAY 08]. Among these, selective epitaxial growth of raised boron doped silicon–germanium in the transistor source and drain regions is proven to induce a longitudinal compressive stress in the Si channel [SMI 05, YEO 05]. A great challenge in the process development of advanced microelectronic devices is now to assess the in situ stress state in the channel region and to link the obtained results with electrical tests. With high resolution electron microscopy [HŸT 98, HUE 08] and more recently dark-field holography technique [HŸT 08], convergent beam electron diffraction (CBED) [ARM 03] and nanobeam diffraction (NBD) [USU 04] in a transmission electron microscope (TEM) have emerged as two of the best ways to measure strain at a nanometer scale. In this chapter, these two diffraction-based techniques are used to study the strain induced by the SiGe source and drain in sub-45 nm devices. Spatial resolution and sensitivity capabilities will be discussed. The main scope of this chapter is to compare first strain measurement provided by both techniques (CBED and NBD) and second, to correlate strain results ...