The negative tone development process enables the printing of dark field features on wafer using bright field masks
with a manufacturing capability for back-end-of-line processing. The performance of NTD photoresist has advanced
along two fronts: namely common process window for dense and semi-dense contacts and the resolution and line
width roughness of isolated trenches. Furthermore, the chemistry has evolved by the convergence of capability for
printing line/space and contact hole using a single photoresist formulation. The process performance of a series of
NTD photoresist is reported. Particular focus is placed on process latitude, CDU, thickness control, LWR and
resolution limit.
Herein, we investigate the dissolution behavior of 193-nm chemically amplified resist in different organic solvents at a
mechanistic level. We previously reported the effect of solvent developers on the negative tone development (NTD)
process in both dry and immersion lithography, and demonstrated various resist performance parameters such as
photospeed, critical dimension uniformity, and dissolution rate contrast are strongly affected by chemical nature of the
organic developer. We further pursued the investigation by examining the dependence of resist dissolution behavior on
their solubility properties using Hansen Solubility Parameter (HSP). The effects of monomer structure, and resist
composition, and the effects of different developer chemistry on dissolution behaviors were evaluated by using laser
interferometry and quartz crystal microbalance. We have found that dissolution behaviors of methacrylate based resists
are significantly different in different organic solvent developers such as OSDTM-1000 Developer* and n-butyl acetate
(nBA), affecting their resist performance. This study reveals that understanding the resist dissolution behavior helps to
design robust NTD materials for higher resolution imaging.
In this work, we investigate the Negative Tone Develop (NTD) process from a fundamental
materials/process interaction perspective. Several key differences exist between a negative tone develop
process and a traditional positive tone develop system. For example, the organic solvent dissolves the
unexposed material, while the deprotected resist remains intact. This causes key differences in key
patterning properties, such as pattern collapse, adhesion, remaining resist, and photoresist etch selectivity.
We have carried out fundamental studies to understand these new interactions between developer and
remaining resist with negative tone develop systems. We have characterized the dynamic dissolution
behavior of a model system with a quartz crystal microbalance with both positive and negative tone solvent
developers. We have also compared contrast curves, and a fundamental model of image collapse. In
addition, we present first results on Optical Proximity Correction (OPC) modeling results of current
Negative Tone Develop (NTD) resist/developer systems.
KEYWORDS: Line edge roughness, Atomic force microscopy, Line width roughness, Scanning electron microscopy, Critical dimension metrology, Diffusion, Photoresist materials, Lithography, 3D modeling, Etching
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.
Etch resistance and post etch roughness of ArF photoresists still remain some of the critical issues during process
integration for sub-100nm technology nodes. Compared to phenyl-containing KrF polymers, methacrylate
polymers commonly used for ArF lithography show weak bulk etch resistance in addition to a highly damaged
surface after standard etch processes. Counter to the photoresist, the etch rates of BARC are required to be very
fast to prevent degradation of the photoresist before the image has been transferred to the substrate.
There are a number of etch models in the literature which attempt to describe the correlation between polymer
structure and blanket etch rates. Ohnishi Parameter and Ring Parameter are the most common etch models
correlating atomic and structural trends in the resist polymer and etch rates. These etch models have been tested
in two ways: systematically changing the composition of a terpolymer and using polymers with different
functional groups. By comparing the etch rates of this large series of polymer structures it was found that these
etch models were not sufficient in describing the relationship between the atomic or structural trends in polymer
with etch rates. New etch models that describe the structure property relationship and etch rate trends have been
developed. These new models show a better correlation with the observed experimental results. Finally, new
polymers have been developed, for both ArF and BARC applications. These materials show a significant
improvement in term of etch properties.
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