PROCEEDINGS ARTICLE | April 5, 2007
Proc. SPIE. 6518, Metrology, Inspection, and Process Control for Microlithography XXI
KEYWORDS: Lithography, Etching, Diffusion, 3D modeling, Atomic force microscopy, Scanning electron microscopy, Photoresist materials, Line width roughness, Critical dimension metrology, Line edge roughness
The improvement of devices performances is due to many factors such as new architectures, new materials
and better lithography resolution. Resist chemical components play a key role in the final performance of a
specific resist. In addition to resist characteristics such as: resolution, etching selectivity, the final resist line
edge roughness (LER) and line width roughness (LWR) becomes a critical issue because it can degrade
resolution and linewidth accuracy and causes fluctuations of transistors performances1,2. LER and LWR are
currently calculated with top-down view SEM images. With chemically amplified resists, we can play on
photoacid generator size to partially control acid diffusion length during the post exposure bake.
In this paper we propose to compare two techniques, the CD-AFM and CD SEM in order to study the
impact of various acid diffusion lengths on LER and LWR. The results show that globally the two
techniques agree on most of the results and show the same trends. However, when the profiles vary the
linearity between the two techniques can vary drastically. In addition, as a complementary technique to the
CD-SEM technique, the CD-AFM gives additional information such as height (top loss), top rounding and
sidewall angle which allow us to understand more deeply the impact of PAG size. Therefore, these
additional information have a non negligible impact on near term new resist development and lithography
processes development. As an illustration of this work, we will present the latest resist development coming
from this understanding and leading to very low LER and LWR. Finally, we will propose strengths and
weakness of each technique.
