AVS 49th International Symposium
    Applied Surface Science Wednesday Sessions
       Session AS-WeM

Paper AS-WeM2
Measurement of Semi-Isolated Poly-Silicon Gate Structure with Optical Critical Dimension Technique

Wednesday, November 6, 2002, 8:40 am, Room C-106

Session: Optical Methods and High-k Dielectrics Characterization
Presenter: D. Shivaprasad, Nanometrics, Inc.
Authors: D. Shivaprasad, Nanometrics, Inc.
J. Hu, Nanometrics, Inc.
M. Tabet, Nanometrics, Inc.
R. Hoobler, Nanometrics, Inc.
W. Liu, Applied Materials
H. Sasano, Applied Materials
C. Bencher, Applied Materials
D. Mui, Applied Materials
Correspondent: Click to Email
The ITRS predicts the production of sub-100 nm transistor gates by 2004 pushing further the limit of the size and speed posed by 180 nm gates which are currently in use. With decreases in gate length, it has become extremely critical to measure these dimensions accurately using non-destructive techniques. Optical Critical Dimension (OCD) measurements are emerging as one of the most promising CD measurement techniques for sub-0.1 micron device fabrication. Compared to CD-SEM and X-SEM, OCD measurements are non-destructive, relatively high throughput, sensitive to sidewall profiles, and sensitive to sub-100nm linewidths. In the OCD technique, a broadband polarized light beam is focused onto the grating surface, and the spectrum of the 0th order reflection is measured. The spectrum contains a signature of the grating profile that is analyzed in real time using Rigorous Coupled Wave Analysis (RCWA). The real time curve fitting algorithms, which do not require library generation, make the analysis simple and easy to extend to a variety of grating structures. Since the OCD technique is based on specular diffraction, a primary requirement for the OCD measurement target is to have periodical grating structures with a line to space ratio typically 1:5. In this paper, we report using the OCD technique to measure poly-silicon gate grating with line to space ratio as large as 1:20. Poly-silicon gate grating structures with critical dimensions of 30—40 nm were measured with line to space ratios of 1:10 and 1:20. In both cases, the measurement showed excellent sensitivity to linewidth variations and detailed profile changes, without deterioration of repeatability. Data from an un-cleaned wafer with the hard mask still remaining will also be presented. This study has significantly extended the measurement range of the OCD technique and its application to isolated line measurements.