A methodology was developed in order to characterize the deprotection mechanisms implied in 193nm chemically
amplified (CA) resists. This method is based on resist outgassing measurements as a function of exposure dose and bake
temperature using Thermal Desorption-Gas Chromatography - Mass Spectrometry / Flame Ionization Detector (TDGCMS/
FID) technique. This approach allows both quantitative and qualitative studies of the outgassing behaviour and
was validated from a 193nm model resist representative of CA formulations. In so doing, the identification of outgassed
by-products respectively coming from the PAG, from the polymer as well as from the solvent is made possible. In
parallel, quantitative results as a function of exposure dose and temperature allowed us to monitor the deprotection
process and the solvent evaporation. The quantitative results obtained by this technique were in good agreement with
Thermo-Gravimetric Analysis (TGA) results. Such a methodology can be used not only to characterise 193nm resist
outgassing during exposure, but also be extended to monitor resist behaviour during implant, thermal treatment, e-beam
Chemically Amplified resists are complex systems. If the main mechanisms implied have already been described, the
challenge to even better control and model these formulations remains important as performance requirements become
more and more stringent and critical dimensions get smaller and smaller. This paper tries to assess and deconvolute some
of the main potential mechanisms involved during the process of a 193 nm chemically amplified resist, before correlating
them with the final lithographic results obtained.
A formulation was selected in order to offer a large range of film physical properties, thus allowing the resist film to switch from non-annealing to annealing conditions. The use of thermal analysis as the main characterization technique allowed correlation between the variations in physico-chemical properties and process conditions. This investigation also included a study of the behavior of some additives during bake steps. In so doing, it became possible to correlate the variations of the resist properties under different bake conditions to the changes in its final lithographic performance, i.e. contrast, sensitivity and line edge roughness.
Experimental results on etched silicon wafers show that after two consecutive spin-coat processes the upper
material surface achieves near planar flatness. This was observed for three separate dual layer BARC systems and the
case of photoresist over a single layer BARC. The wafer topography step height (60 nm) and the thicknesses of the
organic films (20 nm - 100 nm) were typical for state-of-the-art IC manufacturing lithography processes.
A lithographic proximity effect driven by wafer topography pitch was experimentally observed for a single
layer BARC system. The response was reproduced with good quantitative accuracy using rigorous wafer plane EMF
simulations incorporating ideal etched wafer topography, a planarizing resist film and a simple spin-coat approximation
of the BARC coverage, as observed by x-section SEM. In contrast, simulations assuming the limiting cases of a
perfectly conformal BARC and a perfectly planarizing BARC failed to predict any meaningful proximity effect.
Since they have been introduced to substitute poly(hydroxystyrene) based 248nm photoresists (PR), 193nm photoresists
based on acrylate chemistry have raised issues regarding their dry etch resistance. These resists undergo severe
degradations during typical dry etch processes involved in gate patterning, resulting in strong film loss, resist chemical
modifications, critical surface roughening and also linewidth roughness (LWR). Other studies have shown that applying
plasma treatments to 193nm photoresist patterns prior to the other plasma etching processes is a way to minimize PR
degradation. Among these plasma treatments, the HBr plasma cure is known to reinforce the 193nm photoresist etch
resistance and to reduce the resist LWR.
In this study, we propose to go further in the understanding of cure plasma treatments impact on a 193nm model resist
polymer (from Rohm & Haas Electronic Materials) using real time in-situ ellipsometry experiments correlated to several
characterization techniques such as in-situ X-Ray Photoelectrons Spectroscopy (XPS), Fourier Transformed Infrared
Spectroscopy (FTIR) and Dynamic Mechanical Analysis (DMA).
The impact of Ar and HBr cure plasma treatments on 193nm PR is investigated and compared. Both treatments lead to
surface and also bulk modifications of the resist films. XPS analyses show that the 10 first nanometers of the resist film
are graphitized after only 20s plasma treatment, resulting in a higher carbon content and therefore indicating a better
etch resistance following the Ohnishi parameter. Besides this superficial modification, FTIR show that the resist film
can be completely modified after HBr cure plasma treatment with the removal of lactone and leaving groups present in
the polymer. The same kinds of modifications are observed with Ar cure plasma treatment but only the first 80nm of the
resist film are chemically modified. A significant decrease of the glass transition temperature is also observed with both
treatments and is related to lactone and leaving group units that remain in the film
Finally, we show that the resist etch resistance is indeed improved if the resist is previously cured. However, in the case
of Ar plasma treatment, the etch resistance is only improved while etching the first 80nm chemically modified resist.
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.
The weaker etch resistance of 193 nm resists<sup>1</sup> is raising questions concerning their usability for the coming nodes as a single layer resist. We have found that 193 nm positive tone resists, that have been designed<sup>2</sup> incorporating etch resistant groups like adamantyl or isobornyl<sup>3-7</sup>, exhibit chemical modifications concerning these grafted functions while undergoing an oxide etch step. Previously performed experiments have pointed out that the photoacid generator (PAG) that is still contained in the unexposed regions of the sacrificial layer might be a reason for the modifications in the chemical buildup of this resists. Therefore, this work has focused on evaluating the impact of reactive ion oxide etching<sup>8-10</sup> on 193nm materials, for positive and negative tone chemically amplified resists. We used Thermo Gravimetric Analysis (TGA), Fourier Transformed Infra Red Spectroscopy (FTIR) and Atomic Force Microscopy (AFM) in order to check model formulations based on PHS, methacrylate or cyclic olefin polymers with various protecting groups having different activation energies and formulated with or without PAG and in order to understand the impact of the photoactive compound in the resist degradation behavior during plasma etch.