AVS 58th Annual International Symposium and Exhibition
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoM

Paper PS-MoM2
Effect of Si Damage on Shallow Source-Drain (SSD) Recess Structures

Monday, October 31, 2011, 8:40 am, Room 201

Session: Advanced FEOL / Gate Etching I
Presenter: Joydeep Guha, Lam Research Corporation
Authors: J. Guha, Lam Research Corporation
S. Sriraman, Lam Research Corporation
Correspondent: Click to Email
Continued scaling in the semiconductor industry provides new challenges for critical Front-end-of the-line (FEOL) process etch applications in front-end logic devices. One such application that is utilized in the PMOS transistor is the Strained Source Drain recess (SSD) structure that embeds an epitaxial strained SiGe thin film that significantly improves hole mobility in the channel region. Scale down of critical dimensions (CD) in current and future CMOS devices puts ever increasing emphasis in reducing post-etch Si surface damage in a source-drain (SD) recess structures. For a typical SSD application, the roughness of Si surface obtained after SD etch governs both the epitaxial growth of SiGe as well as the roughness of the SiGe layer, and ultimately determines the device performance. This paper will discuss the factors that contribute to the Si surface roughness arising from a representative SD process etch step and its impact on the subsequent SiGe epitaxy and device performance. Typically, the SD etch sequence may consist of an anisotropic etch (halogen/oxygen based chemistry) followed by an isotropic etch (halogen/halogen based chemistry). Surface roughness of the etched silicon is quantified and spatially resolved through atomic force microscopy and surface haze measurements, and contributions of the anisotropic and isotropic etch steps to surface roughness are inferred. The effects of halogen ratio and relative halogen atom reactivity in the isotropic etch chemistry on surface roughness and the vertical-to-lateral (V/L) etch ratio in the SSD recess feature will be discussed and a surface reaction model proposed to characterize roughness evolution.