Process Design & Integration of Salicide and Source/Drain process Modules for Improved Device Performance

Abstract

To enable swift integration of process modules into manufacturable process flows; three components – individual process modules, their interactions and their variability-must be understood well. At dimensions ≤ 0.25 μm, this understanding is especially critical, and also quite challenging. We present here an approach to address this challenge by joint process design, using two key modules-salicide and source/drain-as an example. Together, these modules impact the silicide-to-diffusion contact resistance, (R_c), and the gate sheet resistance (R_s); which, in turn, significantly affect transistor series resistance and circuit delays respectively. We have built a model to help provide insight into the underlying physical mechanisms, and to help provide a quantitative framework for optimizing performance and variability. R_c, depends critically on the doping concentration immediately adjacent to the silicide, and this concentration is determined by the combined effect of silicide processing and the two-dimensional source/drain dopant profile. R_s depends on the thickness and phase of the silicide film formed, which, in turn, depend on the salicide process variables as well as the source/drain doping concentration, because both affect the silicide growth kinetics. Process conditions favoring R_s. and R_c are opposite to each other: thicker silicide films and higher thermal budgets help in the phase-transformation to the low-resistivity C54 phase and improve R_s but they increase dopant redistribution and worsen R_c. Optimal process design can improve the transistor drive current (I_d) by ≈5%, and circuit performance, as measured by the figure-of-merit (FOM) by ≈ 4%. This improvement is significant, and an added benefit of this approach is that other transistor characteristics such as effective channel length, off-current, substrate current, etc. remain unchanged. In summary, we have demonstrated that by joint process design and integration of the salicide and source/drain modules, insight can be gained into the underlying physical mechanisms, and device and circuit performance can be improved significantly.