PROCEEDINGS ARTICLE | May 21, 1996
Proc. SPIE. 2725, Metrology, Inspection, and Process Control for Microlithography X
KEYWORDS: Oxides, Ellipsometry, Diffraction, Metrology, Scanning electron microscopy, Scatterometry, Photoresist processing, Semiconducting wafers, Scatter measurement, Diffraction gratings
Scatterometry, the characterization of periodic structures via diffracted light analysis, is shown to be a versatile metrology technique applicable to several processes involved in microlithography. Unlike contemporary inspection technologies, such as scanning force microscopy (SFM) and scanning electron microscopy (SEM), scatterometry is rapid, non- destructive, inexpensive and has the potential for use in-situ. Furthermore, the flexibility of the technique allows it to be used for a number of different process measurements. In the production of a sub-micron microelectronic device, a typical series of process steps could involve the deposition of a poly-Si layer on oxide, followed by the application of an anti- reflection coating (ARC) and resist layer. Thus in total there are four parameters which will ultimately affect the overall quality of subsequent processing: the linewidth of the resist, the resist height, and the thicknesses of the ARC and poly-Si. We have demonstrated that the scatterometer measurement technique is robust to changes in the thickness of underlying films. Indeed, there is sufficient information in one signature to determine four parameters at once, even when the linewidth dimensions are as small as 0.16 micrometer and the poly-Si thickness is on the order of 2500 angstrom. Results from determining these dimensions on several wafers show excellent agreement between the scatterometry measurements and measurements made with other metrology instruments (top down and cross-section SEM, and ellipsometer). For example, the average bias between nine scatterometry and cross-section SEM measurements on nominal 0.35 micrometer lines is minus 1.7 nm; for 0.25 micrometer lines, the average difference is minus 7.3 nm. In addition, results from measuring the sidewall angle (a fifth parameter) from these same scatter signatures indicate that the resist profiles at optimum focus and exposure are near-vertical. Finally, the dynamic repeatability of this technique is shown to be excellent for all of the parameters measured (linewidth, resist height, ARC thickness and poly thickness). For example, the 3(sigma) repeatability of measurements on a 207 nm linewidth is 0.75 nm and the 3 sigma repeatability for measurements on a 311 nm linewidth is 1.08 nm.
