Improved Ge Doped Cap Layer for Embedded SiGe Epitaxial Growth in 28 nm CMOS Technology

For the purpose of modulating the channel mobility of the transistor, the Ge content in SiGe has been continuously increased, which induces the nickel silicide changes from low resistivity phase to high resistivity phase. The method of epitaxial silicon cap layer on SiGe is adopted to reduce the contact resistance. Due to the graphics effect, the silicon germanium layer is prone to form the crystal surface <;111> with the lowest growth rate, resulting in exposed silicon germanium because of uneven growth of the silicon cap layer. This paper reported the introduction of germanium in traditional silicon cap layer by optimizing epitaxial growth parameters, realize the low concentration of germanium silicon cap layer. High concentration of germanium silicon stressor capped with low concentration of germanium silicon form uniform nickel silicide follow-up, reduce the contact resistance of the device, which is conducive to 28 nm process product yield improvement.