OPC models describe the entire patterning process, including photomask, optics, resist, and etch as a set of separately characterized modules. It is difficult, however, to definitively calibrate the optics model since the aerial image is not easily measurable. It is therefore common to calibrate relevant optical parameters using a constant threshold applied to the aerial image in order to best fit the experimentally measured photoresist CDs. With the optical model thus fixed, a subsequent tuning of resist model parameters is enabled. Alternatively, both optical and resist parameters can be tuned in a single lumped calibration to the measurement data. The parameters associated with the calibration of the photomask, optical, resist and etch processes can be sorted into three classes. There are parameters that are directly measurable or known as designed-in values, such as wavelength, numerical aperture (NA), illumination source profile, and film stack optical constants. A second class of parameters is associated with physical phenomena, where direct measurement is not done, but rather the model contains mathematical proxies for the parameters. A final class of calibration options includes software options for altering the approximations used in the model, such as number of optical kernels, optical diameter, and the functional form of the resist or etch model. The degree to which the model can faithfully decouple photomask from optical exposure from resist processing is related not only to the details of the resist model, but also to the nature of the approximations "upstream" in the representation of the mask and optical system. This paper will systematically explore the impact of all components in the photomask and optical models, and will provide a pathway to sub-nanometer accuracy required for 20 nm technology.

Date Published: 29 June 2012
PDF: 12 pages
Proc. SPIE 8441, Photomask and Next-Generation Lithography Mask Technology XIX, 84410H (29 June 2012);

Published in SPIE Proceedings Vol. 8441:
Photomask and Next-Generation Lithography Mask Technology XIX
Kokoro Kato, Editor(s)