A new negative tone imaging with application of new developer to conventional ArF immersion resist materials is
proposed for narrow trench pattern formation, which is effective to the double trench process that is one of the
candidates of double patterning process for 32 nm node semiconductor devices. No swelling property was realized in
the developing step, in which the dissolution mechanism was discussed. Significantly better LWR and resolution on
narrow trench pattern were observed with this negative tone development compared to positive tone development.
These results suggest that this negative tone development process is one of the promising candidates for double trench
process. Feasibility of double development with negative and positive development process was evaluated as a
candidate for pitch frequency doubling process, and quite low k1 number of 0.23 was obtained.
The technology of 193nm immersion lithography has been progressing rapidly toward half-pitch 45 nm generation
device manufacturing. However, some intrinsic issues, the photoacid leaching and the watermark defect have remained
in the immersion process. Most of approaches to overcome them were the introduction of cover coating materials (top
coat) onto the resist film. Recently, we have established the non-top coat resist using novel two kinds of materials, a low
leaching PAG (PhotoAcid Generator) and a surface modifier. The hydrophobic photoacid generated from the low
leaching PAG decomposes by heating, and the acid migration changes to reduce the line-width roughness (LWR). The
surface modifier behaves as builded-topcoat by the distribution around resist surface and enhances the surface
hydrophobicity. Herein we propose the concept of novel PAG and surface modifier for immersion lithography.
The immersionspecific watermark defect is discussed in its formation mechanism and in the influence of materials and exposure process. The non-topcoat approach was the basis of the work, where the properties of resist surface itself played the key role. Water droplets left on the resist surface were considered to induce the watermark defect in two possible ways; (1) the droplet is carried over to PEB process and impact the resist properties under the heat, (2) the droplet already evaporates before the PEB leaving some residue on the surface. A notable reduction in the resist dissolution rate was observed in the former case, which could be due to either physical or chemical change in the resist materials triggered by the water, and thereby would result in an unavoidable patterning failure. Therefore it is essential not to leave any water droplets on the surface in preventing the watermark formation. A very much hydrophobic materials design was proven effective in achieving this. The watermark formation was correlated to the scanning speed of immersion showerhead and the defectivity was evaluated in this perspective. The receding contact angle of the resist surface was found to well correlate to the "allowable" scanning speed, and was concluded that the higher was the better. A resist material was newly designed by using a hydrophobic polymer on this basis and the resist demonstrated a promising results not only in the watermark defectivity but also in lithographic performance.
The interfacial mass transfer issues of resist components in ArF immersion lithography were investigated both for topcoat resist system and for non-topcoat resist system. PAGs and photoacids are known for the major components that leach out from the resist to water and topcoat has been simply expected to shut off this leaching. In this study, topcoat layer was acutally verified significantly to reduce the PAG leaching, but PAG (or photoacid) diffusion from the resist to topcoat was found as another issue. This resulted in T-top formation in the imaging due to the loss of photoacid nearby the resist surface caused by this diffusion. A material approach to reduce this interfacial diffusion was proposed through a thermodynamic consideration of the materials system. The free energy change for PAG-polymer solubilization is the key and the Solubility Parameter value was considered to represent a good measure of this free energy change. The experimental results well matched this analysis. On the other hand, a perfect suppression of the leaching without using topcoat would be more desirable if it is feasible. The influence of structural parameter of the resist component was investgiated. The hydrophobicity of PAG was found to well correlate inversely to the leaching amount of the PAG into water, and thereby a technical guideline was obtained in designing resist materials to make them resistant to the leaching. By optimizing each resist component on this bases, we actually demonstrated a resist that showed the PAG leaching level reduced down to 10-13[mol/cm2], which we believe far below to what we are today with conventional dry resists. A resist sample was thus developed targeting the non-topcoat approach and was examined for its imaging performance with a realistic immersion lithography tool without using any topcoat. The resist actually showed good imaging results fully with the benefits that we expected with the immersion exposure.
Transparency of the resist film at exposure wavelength affects lithographic performances, such as sensitivity, profile and resolution. Not only binder polymer, but also photo acid generator (PAG) itself has a significant impact on transparency of the formulated resist. Triphenylsulfonium salt (TPS) or Diphenyliodonium salt (DPI) have been widely used as PAGs in DUV chemically amplified (CA) resists, however, aromatic groups there have strong absorption at 193nm and thereby these PAGs have to suffer from low transparency. In this paper, we will report a novel class of transparent enone sulfonium salt PAGs(ENS-PAG), which we believe useful for 193nm resist. The ENS-PAGs do not have any aromatic groups but have an α,β-unsaturated ketone structure for the absorbing moiety in the backbone. These PAGs showed excellent transparency, thermal stability, and demonstrated an advantage in the line edge roughness (LER).
Resist materials for 157nm lithography is believed to be one of the key technology for producing patterns below 70nm. Many different types of fluorine-containing polymer platforms have been energetically pursued by a number of researchers, and some of them appear to be promising in giving a high transparency that has been the essential challenge in realizing this technology. While such highly transparent polymers are the premise in achieving a good imaging, how to get sufficient etch resistance of the polymers can be of another challenge. Actually it is often reported that the etch resistance and the transparency are in trade-off relationship in many cases as a function of fluorine atom content in the polymers. Therefore how to design an etch-resistant polymer while maintaining the good transparency is still a big challenge in developing a practically usable 157nm polymer platform. One of the polymer platforms that the authors believe useful for 157nm is the polymers having hexafluoroisopropanolstyrene (HFIPS) monomer unite in their backbones. The HFIPS unit is attractive because the styrene group provides good etch resistance and hexafluoroisopropanol group (HFIP) provides an acidic molecule while implementing a transparency into the molecule. The lithographic potential of the HFIPS-based polymer system was demonstrated with the fact that a prototype resist from this system was able to print a 75nm line and space 1:1 pairs with an attenuated PSM under 0.60NA stepper exposure. A relatively thin resist thickness, 100nm, was applied due to the limited transparency of the polymer. The patterned exhibited very smooth line edge and a clear pattern definition although a slight T-topping was observed. The results imply that we should be able to achieve a similar lithographic performance with a thicker film (150~200nm), if we can further increase the transparency of the HFIPS-based polymer. The authors are pursuing the approach further aiming at this direction and are getting several new polymers that are more transparent. The paper will present some of the results from later work with such an attempt. The paper will also discuss etch resistance of the HFIPS-based polymer. The etch rates measured for the HFIPS-based polymers were only around 10% faster than standard 248nm resist, which we believe fairly good among various fluorine-containing polymers so far proposed. This was convincing that this polymer system could provide a competitive platform in the practical use. It is generally thought that the etch rate of resist films are mainly affected by their polymer compositions or structures but there are few reported on the influence of the other components in resist formulation. The authors found that the concentration of PAG and quencher influenced both etch rate and resist surface roughness after the etch in this materials system, which implied there are some more room for further etch resistance improvement.
Physical and lithographic properties of functionalized acetal- based polymers, newly designed bulky acetals, were investigated for the use of KrF DUV resist. The key structural design was to incorporate some functional groups into the acetal moieties in the polymers through an ether or ester linkage. The polymers were synthesized by reacting poly p- hydroxy styrene (PHS) with variety of functionalized vinyl ethers that were prepared with substitution reaction of chloroethyl vinyl ether. By selecting large moieties in size for the functional group, the polymers showed good lithographic performance even with a low level of the acetal blocking. This was advantageous for minimizing the defects that could generally be formed in image development and also for improving dry etch resistance of the resist. The ester- linked polymers showed a high dissolution discrimination which could be accounted for with dissolution inhibition induced by a molecular interaction of the ester group with photo acid generator (PAG) in the resist composition. A new class of acetal polymers having additional another acid-decomposable group in the functional group is also proposed for achieving a further improvement in lithographic property.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.