AVS 51st International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS1-MoA

Paper PS1-MoA1
Quantitative Plasma Beam Investigation of Polysilicon Sidewall Roughening

Monday, November 15, 2004, 2:00 pm, Room 213A

Session: Plasma Surface Interactions in Etching
Presenter: S.A. Rasgon, Massachusetts Institute of Technology
Authors: S.A. Rasgon, Massachusetts Institute of Technology
Y. Yin, Massachusetts Institute of Technology
H.H. Sawin, Massachusetts Institute of Technology
Correspondent: Click to Email
For the patterning of sub 100 nm features,a clear understanding of the origin and control of line edge roughness (LER) is extremely desirable, particularly at the gate level where variations in line width can adversely impact the electrical performance of the device. Plasma etching processes often roughen the feature sidewalls, leading to the formation of anisotropic striations. It is this post-etch sidewall roughness which will ultimately affect device performance. Our past research has focused on the observation of sidewall roughness via a novel AFM technique. The resulting images allow the extraction of quantitative information on sidewall roughness and spatial frequency as a function of depth, and vividly highlight the structure of the post-etch sidewall. While these images present a remarkable display of sidewall roughness encountered in common etching processes, a fundamental study of post-etch sidewall roughness remains elusive due to the inherent experimental difficulties encountered. Sidewall roughening during etching depends on the plasma chemistry, ion bombardment energy, and ion incident angle. A true fundamental study requires independent control of all three parameters, impossible to obtain in a conventional plasma etcher. To remedy these difficulties, an inductively-coupled plasma beam source was constructed that allows the exposure of a sample to a realistic ion and neutral flux, of any desired plasma chemistry, while allowing independent control of the ion bombardment energy and incident angle. By rotating the sample to a near-glancing angle, a sidewall can be simulated. This apparatus is used to conduct a fundamental study of sidewall roughness/striation during HBr etching of polysilicon. The resulting AFM images are analyzed for roughness magnitude/spatial frequency using a novel geostatistical technique, and are compared with real sidewalls. Finally, insight into the roughening mechanism is obtained through 3D modeling of the roughening process.