Extreme ultraviolet (EUV) lithography is considered to be the most effective strategy for realize 7 nm generation manufacturing and beyond. With recent rapid progress on the source power improvement, process and material explorations are more and more accelerated to achieve HVM requirements. Therefore, a key factor for the realization of EUV lithography is the choice of EUV resist material that is capable of resolving below 15-nm half pitch with high sensitivity. It has been thought that the main challenge of EUVL is satisfying Resolution (R) – LWR (L) – Sensitivity (S) requirements simultaneously. On the other hand, recent reports indicate defectivity caused by stochastic effect have to consider as well as RLS-tradeoff improvement.
For 7 nm node application, traditional chemically amplified resist (CAR) system is first candidate because of its well-studied property through KrF and ArF manufacturing process for many years, e.g. stability, metal contamination and post-litho process compatibility. However its low EUV absorption property enhancing photon-shot-noise (PSN) effect is one major disadvantage of conventional CAR system, especially for low dose resist process construction. In the past, several researches aiming high EUV absorption CAR system were reported, but material design and its lithographic performance still need detailed investigation.
The present study aims to clarify how we can overcome RLS-tradeoff and reduce defects. Accordingly, we investigated the PSN effect using progress dependency study and material design requirements to achieve high EUV absorption resists. Lithographic results of high EUV absorption resists based on the study were also described.
For semiconductor device manufacturing, line width roughness (LWR) and defect reduction is one of the most important items to obtain high yield. In this study we described the development of novel high absorption resists for use in extreme ultra violet (EUV) lithography system and its LWR and nano-bridge reduction capability. Herein decomposition rates of photo acid generator (PAG) and several high EUV absorption compounds were studied to clarify inefficient pass on acid generation mechanism. As a result, it is revealed that existence of decomposition pass on high EUV absorption compounds degenerates PAG decomposition efficiency. New high absorption materials were synthesized with taking into account its decomposition durability and its lithographic performance were investigated. 15-20% dose reduction keeping its LWR value and nano-bridge reduction were observed even at lower dose condition compared to non-high absorption platform.
Extreme ultraviolet (EUV) lithography is considered to be the most effective strategy for realize 7 nm generation manufacturing and beyond. A key factor for the realization of EUV lithography is the choice of EUV resist material that is capable of resolving below 15-nm half pitch with high sensitivity. Chemical Amplified Resist (CAR) using positive-tone development (PTD) is still one of the strongest candidates for EUV lithography. Recently, some researchers have reported concerns on the limitations in the performance of CAR materials. Consequently, there is a critical need for new chemistry and development of new resist materials. However, new resist materials still have lots of concerns for manufacturing, such like a non-CAR materials including metal resist. Therefore, CAR materials are still most important items for EUV lithography manufacturing.
We’ve been developing negative-tone imaging (organic solvent development) with EUV exposure (EUV-NTI) for a long time. EUV-NTI has advantages for line-width roughness (LWR) due to their low swelling and dissolving smoothly. New EUV-NTI performances will be shown and also process condition progress will be updated.
Also, the basic study will be reported, which is high absorption unit including materials for improving stochastic effect.
We report herein recent progress of CAR materials, both positive-tone and negative-tone for EUV lithography.
This study describes the use of a novel ultra-high sensitive ‘metal resist’ for use in extreme ultraviolet (EUV) lithography. Herein, the development of a metal resist has been studied for improving the sensitivity when using metal-containing non-chemically amplified resist materials; such materials are metal-containing organic–inorganic hybrid compounds and are referred to as EUVL Infrastructure Development Center, Inc. (EIDEC) standard metal EUV resist (ESMR). The novel metal resist’s ultra-high sensitivity has previously been investigated for use with electron beam (EB) lithography. The first demonstration of ESMR performance was presented in SPIE2015, where it was shown to achieve 17-nm lines with 1.5 mJ/cm<sup>2</sup>: equivalent in EUV lithography tool. The sensitivity of ESMR using EUV open-flame exposure was also observed to have the same high sensitivity as that when using EB lithography tool. Therefore, ESMR has been confirmed to have the potential of being used as an ultra-high sensitive EUV resist material. The metal-containing organic–inorganic hybrid compounds and the resist formulations were investigated by measuring their sensitivity and line-width roughness (LWR) improvement. Furthermore, new processing conditions, such as new development and rinse procedures, are an extremely effective way of improving lithographic performance. In addition, the optimal dry-etching selective conditions between the metal resist and spin-on carbon (SOC) were obtained. The etched SOC pattern was successfully constructed from a stacked film of metal resist and SOC.
The suppression of outgassing from the EUV resist is one of the significant challenges, which has to be addressed for realizing EUV lithography (EUVL). The outgassing might be the main contributor involved in the contamination of the mirror optics in scanners. This may result in reflectivity losses. The pragmatic outgassing test that utilizes the witness sample (WS) was used as a general method to quantify the outgassing level for commercially available chemically amplified resists (CAR). There are two types of contaminations. The first type of contamination involves a cleanable contamination that mainly comprises hydrocarbons that can be removed by the hydrogen radical cleaning. Another type of contamination includes the noncleanable contamination that remains on the WS even after hydrogen radical cleaning. Several outgas qualification results were evaluated at the EIDEC [1, 2]. The data indicated that contaminations by the CAR mainly comprised the cleanable contaminations. The data also indicated that there were almost negligible noncleanable contaminations from the CAR. EUV resist communities accelerate the development of high sensitivity resists to compensate the low power of the EUV source. Nonchemically amplified resist (nonCAR) with a new platform is a candidate for high sensitivity resists. The nonCAR includes some types of metal elements with high absorbance for EUV light. There is very limited research on the outgassing characteristics of the nonCAR. In this study, we considered an EUV exposure process in the actual EUV scanner and EUV resists were exposed in a hydrogen environment. A potential risk could result from the reaction of the hydrogen radicals generated by the EUV light with the metal elements in the nonCAR and the metal hydride outgases from the resist. This would result in a noncleanable contamination on the EUV mirror . The knowledge with respect to outgassing from an organic metal complex is insufficient even in a vacuum condition. Hence, the study involved the preparation of certain types of organic metal complexes as model materials. Then, the outgassing evaluations for the materials were carried out as a fundamental studies in a vacuum condition. The results were reported in this study.
This study describes the recent progress of negative-tone imaging with EUV exposure (EUV-NTI) compared with positive-tone development (PTD). NTI uses organic solvent-based developer to provide low swelling and smooth-dissolving behavior. Therefore, EUV-NTI is expected to offer several advantages in terms of performance, especially for improving line-width roughness (LWR), which is expected to resolve the resolution, LWR, and sensitivity (RLS) tradeoff. Herein, novel chemical amplified resist materials for EUV-NTI are investigated to improve LWR and sensitivity. Results indicate that the EUV-NTI has better performance than PTD, with ‘single digit mJ/cm<sup>2</sup>,while maintaining the LWR performance. Furthermore, EUV-NTI processing such as the pre-applied bake (PAB) temperature, post-exposure bake (PEB) temperature, development procedure, and rinse procedure are very effective for improving the lithographic performance. In addition, the lithographic performance with NXE3100 scanner is also reported.
The suppression of extreme ultraviolet (EUV) photoresist-related outgassing is one of the challenges in high-volume manufacturing with EUV lithography (EUVL), because it contributes to the contamination of the EUV scanner mirror optics, resulting in reflectivity loss. Witness sample pragmatic outgas qualification has been developed into the general method for clarifying commercially available, chemically amplified resists. Preliminary results have suggested a linear correlation between contamination thickness in the electron-beam-based and the EUV-based evaluation systems. In fact, a positive relationship was observed between contamination thickness and exposure dose. However, recent experiments indicate that in some resists, this relationship is not linear. In the present study, a resist outgas model is proposed and tested to investigate the contamination thickness’ dependency on exposure dose. The model successfully explains the experimental outgas phenomenon. It is estimated that increasing exposure dose, in resists with low activation energies (Ea) in deprotection reactions, results in extreme increase in contamination thickness. Furthermore, the low-Ea resists have high contamination risk when exposure is extensive.
Manipulation of dissolution properties by changing organic solvent developer and rinse material provides a novel
technology to obtain fine pattern beyond the limitation of imaging system based on alkaline developer. QCM study
showed no swelling character in negative-tone imaging (NTI) process even for current developer of n-butyl acetate
(nBA). Actually, NTI process has shown advantages on resolution and line-width roughness (LWR) in loose pitch
around 30 ~ 45 nm hp as a consequence of its non-swelling character. On the other hand, bridge and collapse limited its
resolution below 20 nm hp, indicating that non-negligible amount of swelling still exists for tight pitch resolution. We
investigated effects of solubility parameter of organic solvents on resolution below 20 nm hp. A bridge was reduced with
a decrease in the solubility parameter dp from nBA. On the other hand, much lower dp caused film remaining due to its
extremely slow Rmax. Based on these results, we newly developed FN-DP301 containing organic solvent with smaller
dp than nBA. Although rinse solvent gave negligible effects on bridge, there is a clear improvement on pattern collapse
only in case of using new rinse solvent of FN-RP311.
Lithographic performances of NTI process using nBA and FN-DP301 together with the other organic solvents were
described in this paper under exposures with an E-beam and a EUV light. It is emphasized that 14 nm hp resolution was
obtained only using FN-DP301 as a developer and FN-RP311 as a rinse under E-beam exposure. NTI showed 43% faster
photospeed in comparison with PTI at 16 nm hp, indicating that NTI is applicable to obtain high throughput with
maintaining resolution. In addition, sub-20 nm trench was obtained using NTI without bridge under EUV exposure, all of
which are attributed to the low swelling character of NTI process. Similarly, NTI was able to print 20 nm dots using
NXE:3100 with only a little peeling. Conversely CH patterning was significantly worse with NTI compared to PTI, that
is, only 36 nm contacts with 60 nm pitch was resolved under EUV exposure.
This paper reports on an all-out effort to reduce the intersite gap of the resist outgassing contamination growth in the results obtained under the round-robin scheme. All test sites collaborated to determine the causes of such gaps. First, it was determined that wafer temperature during exposure could impact the amount of contamination growth. We discovered a huge intersite gap of wafer temperatures among the sites by using a wafer-shaped remote thermometer with wireless transmitting capability. Second, whether the contamination-limited regime was attained during testing could have been another primary root cause for such a difference. We found that for one of the model resists whose protecting unit had lower activation energy and molecular weight the contamination-limited regime was insufficient at one test site. Third, the ratio of the exposed area to pumping speed is necessary to equalize contamination growth. We validated the effect of matching the ratio of exposure area to pumping speed on reducing the intersite gap. This study and the protocols put in place should reduce the intersite gap dramatically.
Polymers with a different Tg and activation energy were prepared to clarify influences of acid diffusion on resolution at 15 nm half-pitch (hp) and 14 nm hp using a EUV micro-field exposure tool (MET) at LBNL. Resolution on such a narrow pattern was limited by collapse and pinching. Clear relationship between pinching numbers and polymer Tg indicates that acid diffusion is one of major contributors on the pinching. In addition, polymers with a low thermal activation energy (Ea) on deprotection were effective for reducing pinching. This is probably originated from its high chemically amplification character even in low post-exposure bake (PEB) temperature to obtain both large chemical contrast and short acid diffusion. On the other hand, a good correlation between a cleanable outgassing amount and Ea indicates trade-off relationship between outgassing and resolution. Advantages of n-butyl acetate (nBA) developer have been investigated in viewpoint of dissolution uniformity. Surface roughness of a non-patterned resist film at half-exposed area, which was well correlated with LWR, was measured by AFM as indicator of uniformity in development process. To avoid any differences in resist chemistry other than development process, cross linking negative tone resist was applied for this study. The surface roughness obtained by nBA, which is conventional negative-tone imaging (NTI)
developer, was 32 % lower than that obtained by 2.38 % TMAH solution. NTI resist system with a nBA developer and optimized resist reduced LWR from 4.8 nm to 3.0 nm in comparison with conventional positive tone resist with a 2.38 % TMAH developer. In addition, advantage on semi-dense trench patterning was well defined. New EUV sensitizer with 1.15 times higher EUV absorption resulted in 1.15 times higher acid yield by EUV exposure. Lithography performance of the new EUV sensitizer has been investigated by MET at SEMATECH Albany. Sensitivity was indeed improved from 20 mJ/cm<sup>2</sup> to 17 mJ/cm<sup>2</sup> according to the acid yield increase, but resolution was significantly degraded.
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.
Lithographic properties of a variety of acetal-derivatized styrene based polymers are reported. The structural modifications in the polymers involve varying the size of the pendent acetal moiety. the lithographic performances of the resists containing structurally modified acetals were found to be superior to the conventional acetals. In the cases where the acidolysis products of the modified acetals are non-volatile alcohols, the post-exposure volatilization, film shrinkage and plasma etch resistance were found to be significantly improved.