The metal containing resist is one of the strong candidates for high lithographic performance Extreme Ultraviolet (EUV) resists. EIDEC has prepared the infrastructure for outgas testing in hydrogen environment for metal containing resists at High Power EUV irradiation tool (HPEUV). We have experimentally obtained the preliminary results of the non-cleanable metal contamination on witness sample using model material by HPEUV . The metal contamination was observed at only the condition of hydrogen environment. It suggested the generation of volatile metal hydrides by hydrogen radicals. Additionally, the metal contamination on a witness sample covered with Ru was not removed by hydrogen radical cleaning. The strong interaction between the metal hydride and Ru was confirmed by the absorption simulation . Recently, ASML announced a resist outgassing barrier technology using Dynamic Gas Lock (DGL) membrane located between projection optics and wafer stage [3, 4]. DGL membrane blocks the diffusion of all kinds of resist outgassing to the projection optics and prevents the reflectivity loss of EUV mirrors. The investigation of DGL membrane for high volume manufacturing is just going on. It extends the limitation of material design for EUV resists. However, the DGL membrane has an impact for the productivity of EUV scanners due to the transmission loss of EUV light and the necessity of periodic maintenance. The well understanding and control of the outgassing characteristics of metal containing resists may help to improve the productivity of EUV scanner. We consider the outgas evaluation for the resists still useful. For the improvement of resist outgas testing in hydrogen, there are some issues such as the contamination limited regime, the optimization of exposure dose to obtain the measurable contamination film thickness and the detection of minimum amount of metal related outgas species generated. We are considering a new platform of outgas testing for metal containing resists based on the electron-beam irradiation system as one of the solutions for these issues. The concept is presented in this paper.
The metal containing resist is one of the candidates for high sensitivity resists. EIDEC has prepared the infrastructure for outgas testing in hydrogen environment for metal containing resists at High Power EUV irradiation tool (HPEUV). We have experimentally obtained the preliminary results of the non-cleanable metal contamination on witness sample using model material by HPEUV . The metal contamination was observed at only the condition of hydrogen environment. It suggested the generation of volatile metal hydrides by hydrogen radicals. Additionally, the metal contamination on a witness sample covered with Ru was not removed by hydrogen radical cleaning. The strong interaction between the metal hydride and Ru was confirmed by the absorption simulation.
Recently, ASML announced a resist outgassing barrier technology using Dynamic Gas Lock (DGL) membrane located between projection optics and wafer stage , . DGL membrane blocks the diffusion of all kinds of resist outgassing to the projection optics and prevents the reflectivity loss of EUV mirrors. The investigation of DGL membrane for high volume manufacturing is just going on. It extends the limitation of material design for EUV resists. However, the DGL membrane has an impact for the productivity of EUV scanners due to the transmission loss of EUV light and the necessity of periodic maintenance. The well understanding and control of the outgassing characteristics of metal containing resists may help to improve the productivity of EUV scanner. We consider the outgas evaluation for the resists still useful.
For the improvement of resist outgas testing by HPEUV, there are some issues such as the contamination limited regime, the optimization of exposure dose to obtain the measurable contamination film thickness and the detection of minimum amount of metal related outgas species generated. The investigation and improvement for these issues are ongoing. The updates will be presented in the conference.
This work was supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO).
 Eishi Shiobara, Shinji Mikami, Satoshi Tanaka, International Symposium on EUV Lithography, Hiroshima, Japan, P-RE-01, (2016).
 Mark van de Kerkhof, Hans Jasper, Leon Levasier, Rudy Peeters, Roderik van Es, Jan-Willem Bosker, Alexander Zdravkov, Egbert Lenderink, Fabrizio Evangelista, Par Broman, Bartosz Bilski, Thorsten Last, Proc. of SPIE Vol. 10143, 101430D (2017).
 Oktay Yildirim, Elizabeth Buitrago, Rik Hoefnagels, Marieke Meeuwissen, Sander Wuister, Gijsbert Rispens, Anton van Oosten, Paul Derks, Jo Finders, Michaela Vockenhuber, Yasin Ekinci, Proc. of SPIE Vol. 10143, 101430Q (2017).
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.
EIDEC has built a high-power EUV irradiation tool equipped with a laser-produced plasma source to investigate the effect of EUV power and pulsed irradiation on the resist outgassing and durability of the mask and pellicle elements. In this paper, we discuss the feasibility study on the impact of high-power EUV irradiation on key elements through the application of a high-power EUV irradiation tool. The equipment comprises a laser-produced plasma source similar to those used in presently available EUV scanners and relay mirrors which facilitates the EUV irradiation on the sample plane. The equipped laser-produced plasma source has lower power at the intermediate focus than those expected in future high-volume manufacturing EUV scanners. However, with fewer relay mirrors compared to these EUV scanners, sufficient EUV power density is emulated on the sample plane i.e. EUV power equivalent to what is expected in future high volume manufacturing EUV scanners can be obtained. The basic design configuration and performance of the laser-produced plasma source and the entire system are discussed. Tests for investigating the effect of EUV power density on the outgassing and durability of mask blanks have commenced, and the preliminary results are presented in this paper.
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.
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.
The suppression of outgassing from extreme ultraviolet (EUV) resist needs to be addressed for realizing EUV lithography (EUVL) because outgassing is likely the main contributor to the contamination of mirror optics in EUV scanners, which results in reflectivity loss. Resist outgassing causes two types of contamination: cleanable contamination, involving hydrocarbon contaminants, and noncleanable contamination, involving noncarbon components. The relation of cleanable contamination between EUV- and electron beam (EB)-based evaluations is linear. However, the relation of noncleanable contamination is not clear. In this study, we investigated the contribution of EUV resist components to noncleanable contamination using different photoacid generator components. The cleanability of noncleanable elements (sulfur, iodine, chlorine, and bromine) in contamination films was measured and compared for the EUV- and EB-based outgas testers. The result suggested that the chlorine and bromine contaminants were completely removed after cleaning. On the other hand, sulfur and iodine remained even after cleaning. This suggested that the careful use of iodine in resist materials is necessary due to its high photoabsorption and low cleanability. In addition, the cleaning rate and noncleanability of contaminants in the EUV-based test were larger than in the EB-based test. This suggests that the contamination film in the EUV-based test is more porous than that in the EB-based test.
The carbon contamination growth (CG) on the witness samples by resist outgassing during exposure were evaluated for
the model EUV resist samples having different protecting groups for chemical amplification. Four kinds of different
protecting groups were chosen to compare the effects of difference in activation energy for de-protection, the molecular
size and polarity of de-protected unit on CG. The residual gas analysis (RGA) measurements were also performed for all
samples. Those results were compared between EUV irradiation and e-beam irradiation. On the contrary to the original
expectation, it was found that the dependence of the activation energy on CG was small. From the results of RGA, it was
confirmed that the size of the protecting group does not also simply correlate with the outgassing amount or CG. In the
sample with relatively bigger protecting group we found larger outgassing amount than that with smaller protecting
group. The smallest outgassing amount and CG were given by the sample which has the polar de-protecting unit. It is
indicating that if there is the interaction between the outgassing molecules and the resist film components, the escaping
of the molecules from the resist film out to the vacuum is restricted, resulting in the small outgassing and small CG. All
of those features were same in EUV and e-beam irradiation.
For extreme ultraviolet (EUV) lithography, some critical issues concerning possible tool optics contamination due to
resist outgassing remain to be resolved [1-4]. Before resists can be used on the ASML NXE:3100 and ASML NXE:3300
EUV scanners, they need to be tested in dedicated equipment and qualify according to the ASML NXE outgassing
guidelines. In view of these guidelines, EIDEC has been working on an infrastructure set-up to enable resist outgassing testing. However, further investigations are still necessary to realize the application of the proposed outgassing evaluation method. Moreover, given the significant number of resists to be tested, fundamental studies to established concepts that reduce the number of resist outgassing tests are necessary. The application of these concepts focused on resist outgassing characterization based on resist composition and processes is presented. Moreover, a suggestion on how this fundamental information can be applied to reduce the total number of resist outgassing tests required for various EUV resists is discussed.
EUV lithography is the most promising future technology for manufacturing devices at and below 16-nm half-pitch node. However, line width roughness (LWR) and pattern collapse are major concerns in device manufacture. In this study, the ability of surfactant rinses to reduce LWR and suppress pattern collapse was investigated. Certain surfactant rinses achieved both. We analyzed the critical dimension (CD) variation of resist patterns during surfactant rinse by highspeed atomic force microscopy (HS-AFM). No significant swelling was observed during the rinse process. We also evaluated a smoothing process subsequent to rinsing; namely, the highly controllable post-bake process. Surfactant rinse followed by post-bake process further reduced LWR.
In the experiments to evaluate outgassing of EUV resists, it was found that the amount of PAG anion and/or Fluorine observed on the witness sample (WS) was different for the variety of WS location and direction in the testing chamber. The XPS measurements showed there were about 10 times of Fluorine atoms on the WS which were put to face the exposing position of the resist on the wafer compared to that were put to turn the back on the wafer. As the Fluorine is the component of photo-acid-generator (PAG) of resists used in the experiments, it is thought that the PAG anion and/or its decomposed species have high sticking coefficient to the WS. The simulation was performed to understand the directivity of outgassing from the exposing point, using the Direct Simulation Monte Carlo (DSMC) method. The results indicated that the sticking coefficient of PAG anion is about 0.8, suggesting that the position and direction of WS in the chamber relative to the wafer strongly affects the amounts of deposition of the species having big sticking coefficients.
For high volume manufacturing (HVM) utilizing extreme ultraviolet (EUV) lithography, practical resist outgassing
qualification system is required. Witness sample (WS) testing systems using electron beam (EB) or low power EUV
light have been proposed as candidates, however some issues remain on how these alternative light sources, in
comparison to high power EUV, will affect resist chemical reactions and ultimately resist outgassing. In this paper, we
have investigated resist induced optics contamination by utilizing two types of WS test systems of high power EUV light
and EB sources. A correlation between these light sources is discussed, especially focusing on the resulting chemical
phenomena depending on resist material properties.
The spacer patterning process is one of the strongest double patterning technology candidates for fabricating 2xnm node
semiconductor devices by ultra-low-k1 lithography. However, a severe problem exists with this process, it has an
excessive number of steps, including resist patterning, core film etching, spacer film deposition, spacer film etchback,
core film removal, and hard mask patterning steps. We devised a simpler process in which a resist pattern is directly used
as the core film pattern and the spacer film is a low-temperature-deposited oxide film that can be fabricated around the
resist pattern without damaging the resist material. Thus, this new process, which we call "resist-core" spacer patterning,
has significantly fewer patterning steps. When we used the new process to fabricate 2xnm node semiconductor devices
with an ArF immersion scanner, two key issues arose. The first issue regarding the controllability of the resist pattern
profile, which can directly affect the spacer film pattern profile, was addressed by applying various resist patterning
conditions such as resist materials, illumination conditions, and bottom anti-reflecting materials. The second issue,
regarding the resist slimming method was addressed by evaluating two alternative techniques, wet slimming and dry
This paper reports the extracted risk issues on practical EUV resist processes and discusses verifications of them. The
risk issues were extracted with emphasis on critical dimension, defectivity and productivity for mass production EUV
resist processes. The authors verified these risk factors by utilizing available empirical knowledge. The authors found
that the micro loading effect of by-product in the resist development process was a key factor for CD uniformity. Also
discovered, was that high surface energy differences on the patterned wafers were a key factor for defectivity. As a result,
application of scan-dynamic development and dynamic scan rinse to EUV processes on a mass production level will
contribute greatly to CD and defect control as well as productivity.
The lithography process on topographic substrate is one of the most critical issues for device manufacturing.
Topographic substrate-induced focus variation occurs between top position and bottom position in a layer. That is,
common depth of focus is reduced. This focus variation is sure to ruin the focus budget in low k1 lithography.
From the focus budget of CMOS device, substrate topography is required to be less than 30nm for hp 45-nm
generation devices and less than 15nm for hp 32-nm generation devices.
In this paper, the authors evaluate a novel concept for hp45-nm generation dual damascene layer for global surface
planarization. The novel concept is thin planarization layer with bottom anti-reflecting (BAR) function. This
planarization layer with optical performance is materialized by UV crosslink materials and process. This concept is
expected to lead to a simpler planarization process. Thin planarization layer with BAR function clear BARC layer and
simplifies the etching process.
Our study showed that the planarization performance of UV crosslink layer with 100nm thickness was 20nm
thickness bias between the field area and dense via hole area. This thickness bias achieved the requirement of hp
45nm generation. Furthermore, fine resist pattern was resolved on the planarization layer by the optimization of acid
components and additive.
Line width roughness (LWR) reduction is a critical issue for low k1 ArF immersion lithography. Various approaches
such as materials, exposure technology and the track process have been performed for LWR reduction during
It was reported that the post-development bake process had good performance for LWR reduction (1). However, the
post-development bake process induced large CD change owing to the degradation of large isolated resist pattern.
Therefore post-development process with small iso-dense bias is required in low k1 ArF immersion lithography.
The resist smoothing process is one of the candidates for LWR reduction with small iso-dense bias. This method
whereby the resist pattern surface is partially melted in organic-solvent atmosphere was shown to have a significant
LWR reduction effect on resist patterns. This paper reports on the application of the resist smoothing process to the
ArF immersion resist pattern after development. It was found that the resist smoothing process was effective to reduce
LWR for ArF immersion resist. As a result of LWR trace from after development to after the hard mask etching process,
the effect of LWR reduction with the resist smoothing process continued after the hard mask etching process.
Furthermore CD change of large isolated patterns with the smoothing process was smaller than in the case of post-development
bake process. We confirmed that the resist smoothing process is an effective method for decreasing LWR
in ArF immersion lithography.
We constructed CD budget for spacer patterning technology which is one of the strongest candidates in double
patterning technologies for below 3x nm half pitch generations. In the CD budgeting, three patterning portions of grid
patterns should be considered, namely, "line", "paired space" and "adjoined space", because they have individual
process error sources that affect CD variations. Analysis of the patterning process flow revealed that the amount of CD
variations for positive type spacer patterning technology was in the order of "adjoined space" > "paired space" > "line".
Also, the experimental verifications in CD variations substantiated the constructed CD budget. From the viewpoint of
design for manufacturability (DfM), these process features should be taken into account in the device engineering.
Therefore, for the successful implementation of spacer patterning technology into high-end devices, we propose a cross-
functional development scheme encompassing device technologies and process technologies using the constructed CD
In immersion lithography, it is necessary that the surface of wafer has high hydrohybicity in order to prevent the residue of immersion fluid, i.e. pure water, that cause watermark defect. Usage of a cover material film over the resist film is effective to consistent with high hydrohybicity of the surface and high performance of resist film. But it was problem that much pattern deformation defects was observed with the use of an alkali-soluble type cover material film and an immersion exposure tool. As a result of the examination, it was identified that the fraction of film which caused the pattern deformation in the area of several micrometers were the fraction of the cover material. And the fractions of cover coat material were oriented in the coating defects of the cover material film and in the film peeling after scan of the immersion nozzle at the wafer bevel. The coating defects were improved with the chemical of the cover material. An adhesion process was effective to prevent the film peeling of cover material.
Recently, gate length variation such as Line Width Roughness (LWR) is severe problem in MPU. The LWR of resist pattern is mainly due to resist material and optical contrast. However it is hard to improve these factors. Many techniques have reported to decrease LWR, but there were no reports which process was more effective for improvement on LWR. Some methods were considered to improve resist roughness. This paper discusses about LWR of ArF resist in gate layer of 65 nm node device. We tied post bake process after development to smooth resist pattern surface by its surface tension. Recess process of resist roughness by using a pattern shrink film was also investigated. LWR’s were 36% and 26% decreased by post baking process and recess process, respectively. Post bake temperature was near resist melting point. From the consideration of thermal flow process, distance of smoothing force by surface tension is considered about several hundreds nm. Pattern shrink film is using acid catalysis reaction, so its distance of smoothing by acid diffusion is considered about one hundred nm. It is considered that effect of post development process is caused by distance of smoothing force. Moreover influence of those processes for lithographic performance will be evaluated.
We investigated dependence of ArF resist on Exposed Area Ratio (EAR). Because it can be one of the CD variation factor and it is difficult to correct by OPC. Acrylate polymer based resist showed dependence on EAR. At low EAR, resist showed T-top profile and its CD became large. It could be considered that the profile change was caused by acid evaporation and re-sticking. Resist profile simulation indicated that CD variation appeared at only low EAR. To decreasing the effect of acid evaporation and re-sticking, we tried to increase the amount of acid evaporation by increasing PAB temperature. CD variation by EAR was decreased with increasing PAB temperature.
In 45nm-node CMOS, the k1 value is around 0.35. In the low-k1 lithography, the robust design for lens aberration and process fluctuation such as mask CD error is required for manufacturing. The technologies of robust design for 45nm-node CMOS are proposed. The alternating phase shift mask has been applied to obtain high accurate CD controllability for gate level. Since the sensitivity to lens aberration is high, design rule is restricted. Immersion lithography with hyper NA over 1.0 is necessary for contact hole level to get large DOF margin. Since the mask enhanced error factor is large, high accurate CD uniformity on mask is necessary. Using hyper NA immersion tool, high density SRAM whose area is 0.25um2 can be clearly resolved.
We investigated resist profile dependence on Exposed Area Ratio (EAR). Using high activation type chemically amplified positive resist, profile changed from T-top to rounded profile with increasing EAR. We thought that this profile change was caused by acid evaporation and re- sticking. To estimate the effect of re-sticking acid, we performed resist sandwich tests. We measured resist thickness loss after PEB and observed resist profile change caused by re-sticking acid. The results thereby obtained suggest the model we propose. To reduce acid evaporation and re-sticking, we tried to use an overcoat layer. The overcoat layer was found to reduce acid evaporation and be useful for reducing resist profile dependence on EAR.
Application of polysilanes for a deep UV (DUV) bottom anti- reflective coating (BARC), in order to resolve the problem posed by the insufficient anti-reflection with thin conventional organic BARC applied on transparent dielectric film, is described. The newly developed polysilane anti- reflective coating has the real part of refractive index, n equals 2.00, and the imaginary part, k equals 0.23 at 248 nm. The polysilane coating is immiscible with a chemically amplified photoresist, and is not removable during normal wet development of photoresist. Etching rate of the polysilane is 2 times faster than that of DUV resist during BARC etching, and lower than that of DUV resist during dielectric film etching. The polysilane layer is easily removed by ashing using O2 gas process. Using thick polysilane coating, it can realize both the suppression of the interface reflection between the resist and BARC and good critical dimension control on dielectric film.
Recently, resist edge roughness with reducing pattern size has become a serious problem. We investigated the roughness of chemically amplified, positive-tone resists, experimentally. To reduce the roughness, we added a quencher with strong basicity to the resist, and observed sub quarter micron nested lines. As a result, the roughness was improved with increasing the quencher concentration, especially in 0.15 micrometers nested line patterns. Adding quencher was not too much effective for the larger size patterns. The acid concentration in resist was increased by adding quencher, because the nominal dose became large by that. It was also indicated experimentally that generated acid concentration at pattern edge was nearly equal to that of quencher at nominal dose. The nominal dose was determined by quencher concentration. We defined effective acid concentration as remaining acid concentration after quenching. This effective acid concentration increased with increasing quencher concentration too. The roughness seemed to be generated when effective acid concentration profile was lowered. It is indicated that the resist edge roughness with reducing pattern size can be expected from its effective acid concentration profile.
Reducing resist thickness easily and simultaneously decreases the k1 factor and increases the k2 factor in conventional Rayleigh equations, without changing the wavelength of the illumination light and NA of the optics. In this work, we investigated the effect of reduced resist thickness on process latitude and optical proximity effect (OPE) at the sub-quarter micron level. The experiment exposures were performed by a 0.6 NA KrF excimer step and scan system with an in-house chemically amplified positive resist in the thickness range of 0.6 micrometers to 0.25 micrometers . The results showed remarkable improvements in process latitude of both 0.175 micrometers L&S and 0.225 micrometers contact hole, as well as OPE such as a CD variation between different pitches and a feature deformation at isolation by reducing resist thickness.
Lithographic characteristics of dual-trench type alternating phase-shifting mask (PSM), whose shifters are made of perpendicular trenches with different depth alternately, are evaluated numerically and experimentally. The structure of dual-trench type PSM could reduce the difference of adjacent peak intensities created by topography on the mask. Exposure characteristics of the mask varied with depth of deep and shallow trenches, and depth of both trenches should be controlled so as to have the optimum value. Mainly, the difference in depth of deep and shallow trenches caused varying "effective phase" and depth of shallow trench caused varying "effective transmission". The depth of focus using the mask was sensitive to the effective phase difference controlled by adjusting etched depth difference between both trenches, and insensitive to depth of shallow portion. From analysis of mask process margin, respecting acceptable error of depth of both trenches, it was found that the effective transmission error caused reduction of acceptable depth error.