|
The incorporation of B in SiGe has been attracted attention during recent years for source/drain (S/D) application in CMOS structures. The focus has been on formation of elevated or recessed S/D junctions. In the later application, a high Ge amount is required to induce uniaxial strain in the channel region. The induced strain in the channel region results in an enhancement of the hole mobility. In this design, incorporation of high B concentration is a crucial point for reducing S/D parasitic resistances. The presence of B in SiGe has also been reported to increase the thermal stability of the Ni salicide.
In these SiGe layers the small size of boron atoms compensates the compressive strain of SiGe layers. Thus, in order to have a high strain amount in S/D regions we need to apply a high Ge content.
One of the most important problems in implementation of recessed S/D SiGe junctions is pattern dependency of selective epitaxy growth of SiGe layers which leads to different layer profiles (layer thickness, Ge and B content) depending on opening sizes. Previous studies have shown that the pattern dependency becomes stronger for layers with higher Ge content. Thus having a fully-controlled selectively grown SiGe layer with high Ge and B concentration together with a high strain amount in the recessed junction is not an easy task and needs to be more investigated.
In this study the incorporation of high amount of boron (1×1020-1×1021 cm-3) in selective epitaxial growth of Si1-xGex (x=0.15 to 0.315) layers for recessed or elevated S/D junctions in CMOS has been studied. The effect of high boron doping on growth rate, Ge content and appearance of defect in the epi-layers was investigated. Furthermore, integration issues were oriented towards having high layer quality whereas still high amount of boron is implemented and the selectivity of the epitaxy is preserved.
The substitutional B concentration and Ge amount of the grown layers in the oxide openings were measured directly by high resolution x-ray diffraction (HRXRD). In our investigations, atomic force microscopy (AFM) was used to measure surface roughness, layer thickness and recess depth of the junctions.
|