The role of photoresist has become more important for down scaling of electric devises. One of the key factors which identify the photoresist is a diffusion of acid through the lithography process. The ‘top coat method’ was proposed for measuring the distance of diffusion of acid which was generated from PAG and calculating the diffusion coefficient1-3. In this method, top coat material containing PAG (2nd layer) is coated on a PAG-free resist (1st layer), then the exposure and PEB processes are performed. The generated acid in 2nd layer during the exposure diffuses into 1st layer when the PEB is performed. After that, we can obtain the acid diffusion length based on the quantity of film removed by the development. In this work, we applied TOF-SIMS measurement with gas cluster ion beam (GCIB) etching to the samples that were prepared for top coat method. This measurement has revealed the distribution of diffusing PAG and residual protecting groups of the resin in the resist (1st layer). The diffusion length of the acid which is obtained by the top coat method has corresponded to the depth profile of the acid and the deprotection rate which is acquired by TOFSIMS with GCIB. We can estimate the marginal deprotection rate which is needed for the development by the result of these two methods. It has also been clear that the distributions of acid shifted into the resist according to the PEB temperature.
In order to understand the mechanism of the pattern wiggling distortion and to find control knobs for improving wiggle performance of spin-on carbon hard mask materials, we have developed analysis method of underlayer (UL) films by utilizing XPS depth profiling using Gas Cluster Ion Beam(GCIB-XPS). Differences of distributions of elemental compositions from the surface to the bottom of the processed or un-processed films have been visualized by GCIB-XPS analysis. Besides, these achievements allow us to identify fluoro substitution of oxygen during etching process as the control knob for the pattern wiggling distortion.
In order to understand the mechanism of line width roughness (LWR) generation and to find control knobs for improving resist patterning properties, we developed precise direct analysis method of resist patterns. This method comprise three important processes: 1. Selective sampling of resist pattern surface and pattern core, 2. Analysis and preparative isolation of collected resist ingredient by μGPC, 3. Structural analysis by Py-GC/MS. μGPC and Py-GC/MS analysis provid resist ingredient distribution information inside resist pattern, which includes original polymer, reacted polymer, and photo acid generator (PAG) through the ArF patterning process. This novel analytical method can provide remarkably helpful information about identifying proper control knobs for lithographic performance of ArF resist and for next generation lithography (NGL), especially extreme ultra violet lithography (EUVL) materials, where exposure tool time is very limited.
In order to understand the mechanism of line width roughness (LWR) generation and to find control knobs for improving photoresist design, we established PAG activity analysis methods by utilizing Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and Transmission Electron Microscopy (TEM). TOF-SIMS depth profiling using Gas Cluster Ion Beam (GCIB) allowed the ability to clearly identify photoresist ingredient distribution in the photoresist films from the surface to the bottom of the resist films. TEM provided distribution information of photoresist ingredients in nanometer scale. As a result, PAG function and polymer reaction mechanism can be monitored by these methods. The TOFSIMS outputs during coating, exposure, and post-exposure bake (PEB) steps provide indications of distribution change of PAGs, quenching reaction derivatives, and remaining protecting group, which correspond to acid generation distribution, acid diffusion, and diffusion of deprotection reaction in photoresist film respectively during each consecutive lithographic patterning step. The difference in activity of PAGs can also be observed. These novel analytical methods can provide remarkably helpful information about identifying proper control knobs for lithographic performance of photoresist and for next generation lithography (NGL), especially extreme ultra violet lithography (EUVL) materials, where exposure tool time is very limited.
A non-topcoat (non-TC) resist is a photoresist that contains a hydrophobic additive, which segregates to the surface and
forms a layer to minimize surface free energy. The improvement of surface hydrophobicity and the suppression of resist
component leaching were confirmed by using this segregation layer. Compared to conventional topcoat process, it is
speculated that the use of non-TC resist will reduce the cost of lithographic materials, improve throughput, and will be
compatible for the scanning speed improvement of immersion scanners. One issue for the non-TC resist is the possibility
of increased defect generation compared to processes using topcoats. It is assumed that the high resist surface
hydrophobicity and the developer insolubility of the hydrophobic additive are main factors causing the increase in defect.
Therefore, it is important to work out solutions for reducing these defects to realize the non-TC resists. A process of
selectively removing the hydrophobic additive between exposure and development process for the purpose of defective
reduction of non-TC resist was investigated. Specifically, wet processing was performed to the wafer after exposure
using an organic solvent to dissolve the hydrophobic additive. As a result, defect count was reduced to less than 1/1000
with the effective removal of the segregation layer without affecting pattern size. These results prove the effectiveness of
the proposed process named 'selective segregation removal (SSR)' treatment in reducing defects for non-TC resists.
A dynamic receding contact angle (RCA) is a well-known guideline to estimate the degree of watermark (WM)
defects, which shapes circle and bridges inside of the defect and reduces with enlarging the RCA of topcoat (TC).
However, our recent investigation revealed the occurrence of the circular shape defects in spite of using the TC with a
large RCA, bringing about a change of line and space pattern pitch. In this paper, we clarify the origin of these defects
and propose a new key factor of the dynamic surface properties of immersion-specific defects. It was found that the
pitch-change defect is caused by the lens effect of the air bubbles embedded between advancing water meniscus and the
TC. To well understand generation of the bubble defects, we defined the "effective" hysteresis (EH) as the hysteresis of
dynamic contact angle taken the effects of water-absorption into account. An analysis with the EH indicates that the
bubble defect arises from not only to the large ACA but also small amount of water uptake and the amount of
water-absorption could be substituted by the dissolution rate of TC. It was demonstrated that the EH proposed is a new
key factor for estimating the number of bubble defects. The EH is very useful for analyzing the bubble defects in
immersion lithography. The characteristics of the bubble defect are also discussed with a focus on the structure of the
polymer attached to water.