The minimum target specificatons of EUV resist material are the resolution < 30nm half pitch C/H, CDU < 3.0nm, and sensitivity < 20mJ. The major pending issue of EUV resist is how to simultaneously achieve high sensitivity, high resolution and low CD Uniformity (CDU). Thus, we have studied that which factors such as acid diffusion, solvents, polymer platform and film density etc are affecting to improve CDU, sensitivity and resolution. Especially, CDU and sensitivity are the main issues among above these performances. With the results of these experiments, we could determine polymer blend PAG as polymer platform for EUV resist material. We have also researched polymer to improve the sensitivity and CDU with variation of molecular weight, poly dispersity and monomer feed ratio. Additionally, we have studied the effects of resist solvents and film density. And we have measured the outgas of our EUV resist. In this paper, we will discuss the results of these studies obtained by EUV tools of SEMATECH.
It is well known EUV lithography is the most promising technology for next generation lithography. ITRS roadmap
predicts that EUV lithography will realize 22nm half pitch node and beyond. However, there are a lot of problems such
as light source power, exposure tools, mask blank defect and resist material for realizing of EUV lithography. Among
these problems, we try to develop the high performance resist material for EUV lithography in this paper. EUV resist
material are to achieve the Resoultion ≤ 22nm half pitch L/S, Line Width roughness ≤ 1.2nm, Sensitivity ≤ 10mJ.
The major development issue of EUV resist is how to simultaneously achieve high sensitivity, high resolution, low LWR.
Especially, LWR is the main issue among above RLS performances. So, we decided to choose the polymer bound PAG
as resin platform for EUV resist material. Thus, we have studied in various ways to know the relation between LWR
reduction and resin physical properties which represents substituted ratio of acid-cleavable unit, Mw, Pd. Additionally,
we studied the effects of steric hinderance of pending group with diversifying the size of pending group to make polymer
of high performance. We also attempt to know how is LWR affected by hydroxy group species. In this paper, we will
show and discuss the results of these studies obtained by tools of e-beam and EUV.
The main issue for developing EUV resist is to satisfy the ITRS target of sensitivity, line edge roughness(LER), and
resolution simultaneously. However, Resist researchers have difficulty in EUV resist development because they are
tradeoff relationships each other. Among them, LER is closely related to acid diffusion length of photo acid generator.
Researchers have tried to accomplish uniform distribution and diffusion minimization of PAG in photoresist film in order
to improve LER. They are mainly using two kinds of method for PAG introduction for uniform distribution and diffusion
minimization. One is use of sulfonium salts having ultra bulky anion or cation for the acid diffusion suppression, the
other is direct incorporation of the PAG into the polymer backbone. In that regard, we have pursued development of a
variety of 193nm and EUV CARs that contain photoacid generator(PAG) units covalently bonded directly to the resin
polymer backbone. When we consider polymer bound PAG, there can be anionic polymer bound PAG resist, cationic
polymer bound PAG resist and nonionic polymer bound resist. In this work, we will discuss diffusion length and line
edge roughness(LER) of these polymers. Acid diffusion length(Ld) and diffusion coefficient(D) were calculated by
according to the modified Fick,s equation. As a result of this measurements we knew that diffusion length of general
PAG use as ArF photoresist composition was ranged from thousands of nm to ten of nm and PAG diffusion length having
bulky anion and cation is was within a ten nm. In case of anionic polymer bound PAG, acid diffusion length showed
under 10nm.
One of the most important factors in ArF resist development is a resin platform, which dominates a lot of parts of resist characteristics. It has been much changed in order to improve their physical properties such as resolution, pattern profile, etch resistance and line edge roughness. Through the low etch resistance in ArF initial (meth)acryl type copolymer and low transmittance in COMA type copolymer most researchers were interested in developing of (meth)acryl type copolymer again for ArF photoresist. On the other hand, we have studied various polymer platforms suitable ArF photoresist except for meth(acryl) type copolymer. As a result of this study we had developed ROMA type polymers and cycloolefin-(meth)acryl type copolymers. Among the polymers cycloolefin-(meth)acryl type copolymer has many attractions such as etch roughness, resist reflow which needs low glass transition temperature and solvent solubility. In this study, we intend to find out cycloolefin-(meth)acryl copolymer characteristics compared with (meth)acryl copolymer. And, we have tried to find out any differences between acrylate type copolymer and cycloolefin-(meth)acrylate type copolymer with various evaluation results. As a result of this study we are going to talk about the reason that the resist using acrylate type copolymer and cycloolefin-(meth)acryl type copolymer show good pattern profile while acrylate type copolymer show poor pattern profile. We also intend to explain the role of cycloolefin as a function of molecular weight variation and substitution ratio variation of cycloolefin in cycloolefin-(meth)acrylate resin.One of the most important factors in ArF resist development is a resin platform, which dominates a lot of parts of resist characteristics. It has been much changed in order to improve their physical properties such as resolution, pattern profile, etch resistance and line edge roughness. Through the low etch resistance in ArF initial (meth)acryl type copolymer and low transmittance in COMA type copolymer most researchers were interested in developing of (meth)acryl type copolymer again for ArF photoresist. On the other hand, we have studied various polymer platforms suitable ArF photoresist except for meth(acryl) type copolymer. As a result of this study we had developed ROMA type polymers and cycloolefin-(meth)acryl type copolymers. Among the polymers cycloolefin-(meth)acryl type copolymer has many attractions such as etch roughness, resist reflow which needs low glass transition temperature and solvent solubility. In this study, we intend to find out cycloolefin-(meth)acryl copolymer characteristics compared with (meth)acryl copolymer. And, we have tried to find out any differences between acrylate type copolymer and cycloolefin-(meth)acrylate type copolymer with various evaluation results. As a result of this study we are going to talk about the reason that the resist using acrylate type copolymer and cycloolefin-(meth)acryl type copolymer show good pattern profile while acrylate type copolymer show poor pattern profile. We also intend to explain the role of cycloolefin as a function of molecular weight variation and substitution ratio variation of cycloolefin in cycloolefin-(meth)acrylate resin.
A recent new class of resists referred to as polymer-bound PAG resists, which have slightly increased PAG loading and reduced photo acid diffusion relative to tranditional blended CAR systems have shown promise in improving resolution, faster photospeed, higher stablility and LER. we have developed two kinds of PAG, which are cationic and anionic polymerizable PAGs. One is that the polymer backbone is directly connected with cationic part in PAG and the other is that the polymer backbone is directly connected with anionic part in PAG. In this study we described the synthetic process of polymerizable PAGs and the polymerization process to make PAG-bound polymers and then, the lithography properties of resists composed of PAG-bound polymer were reffed to.
As the minimum feature size of electronic devices continues to shrink, the industry is moving from wavelength of 248-nm KrF excimer laser sources to shorter wavelength of 193-nrn ArF excimer laser and ArF immersion to achieve required higher resolution. As minimum feature sizes are reduced, the ability to minimize defects is getting more important, because they have a close connection with yield. With the replacement of laser source, 248-nm with 193-nm, the platform of polymer was also converted from phenolic polymer into acrylic polymer. With this platform changes unexpected various defect problems had been occurred. Although KrF process causes not much of defect, ArF process causes more serious defect problems. One of those major defect source is solidification of polymer in track nozzle. The solidified polymer at track nozzle needs to be removed periodically, unless it causes significant throughput loss in mass production. The amount of this type of defect relies on physical properties of polymer platform such as hydrophilicity, solubility or structural rigidity. The hydrophilic phenol based KrF polymer shows minor defects, contrarily hydrophobic acryl based ArF polymer causes serious defects. The solidification of acrylate type polymer was caused by poor solubility. In order to improve solubility, olefinic moieties such as norbornylene, norbornyl devertives and opened maleic anhydride monomers were adopted in acrylate polymer. Those inserted olefins and opened maleic anhydride in acrylic polymer changed overall structure such as rigid helix structure into flexible structure. With the increase of solubility, particle defect was dramatically reduced. Conclusively, insertion of cycloolefin and opened maleic anhydride moiety releases rigid acrylic structure and it improves solubility. As solubility improves, crystallization at nozzle has been decreased and the particle defect is reduced. Moreover this flexible structure allows the resist reflow at the moderate temperature which is one of the resolution enhancement techniques.
The basic requirements for polymer design rule in photoresist are as following. The performances of the photoresist relate to transmittance, adhesion on BARC material, dry etch resistance and process margin as a function of the exposure tool. However, it is very difficult for us to find the polymer that has good performance for 193 nm ArF photoresist, because it has many limitations as target feature size of photoresist become smaller. One of the most important properties in it is adhesion. Researchers usually introduce functional group, as an adhesion promoter, such as carboxylic acid group, hydroxyl group and lactone group at the side chain of the polymer. Carboxylic acid group represents the highest adhesive property, but it has poor dark erosion because of affinity with developer, 2.38 wt% TMAH solution. Lactone group has a limit for introduction as a functional group because it can cause low dry etch resistance and pattern slope. On the other hand, in case of primary alcohol, the hydroxyl group occurs cross-link with carbonyl unit of a neighboring unit. We have recently synthesized cycloolefin copolymer, which has a secondary hindered alcohol in its side chain. And they showed good performances in adhesion, resolution, PED stability, processing window, dry etch resistance, and good pattern profile in both L/S and C/H pattern profile. In this paper we will discuss the properties and the evaluation results.
There are numerous methods being explored by lithographers to achieve the patterning of sub-90nm contact hole features. Regarding optical impact on contact imaging, various optical extension techniques such as assist features, focus drilling, phase shift masks, and off-axis illumination are being employed to improve the aerial image. One possible option for improving of the process window in contact hole patterning is resist reflow. We have already reported the resist using a ring opened polymer of maleic anhydride unit(ROMA) during the past two years in this conference. It has several good properties such as UV transmittance, PED stability, solubility and storage stability. The resist using ROMA polymer as a matrix resin showed a good lithographic performance at C/H pattern and one of the best characteristics in a ROMA polymer is the property of thermal shrinkage. It has a specific glass transition temperature(Tg) each polymers, so they made a applying of resist reflow technique to print sub-90nm C/H possible. Recently, we have researched about advanced ROMA polymer(ROMA II), which is composed of cycloolefine derivatives with existing ROMA type polymer(ROMA I), for dry etch resistance increasing, high resolution, and good thermal shrinkage property. In this paper, we will present the structure, thermal shrinkage properties, Tg control, material properties for ROMA II polymer and will show characteristics, the lithographic performance for iso and dense C/H applications of the resist using ROMA II polymer. In addition, we will discuss resist reflow data gained at C/H profile of sub-90nm sizes, which has good process window.
We have already reported the resist using a ring opened polymer of maleic anhydride unit (ROMA). The synthesis of the ROMA polymer is as follows: 1)copolymerization of cycloolefin derivatives and maleic anhydride 2)ring opening reaction of maleic anhydride unit. 3)substitution reaction of pendant group. The ROMA Polymer has several good properties such as UV transmittance, pattern profile, PED stability and storage stability. Especially, we have been known that the resist using a ROMA polymer has a good character for application of Resist Flow Process(RFP), recently. The ROMA polymer has shown various Tg value ranging from 100°C to 170°C in accordance with substituents and substituted degree. The resist made by ROMA polymer as a matrix resin showed a good lithographic performance at direct C/H pattern. We also got a good C/H pattern profile by resist flow process at sub-100nm hole size. In this study we will discuss about it and illustrate about various Tg value of ROMA polymers and data gotten by means of resist flow process.
Joo Hyeon Park, Dong-Chul Seo, Chang-Min Kim, Young Lim, Seong Jo, Jong-Bum Lee, Hyeon Joo, Hyun Jeon, Seong-Ju Kim, Jae Chang Jung, Ki-Soo Shin, Keun-Kyu Kong, Tatsuya Yamada
We have investigated new photoresist materials based on modified cycloolefin-maleic anhydride resin for 193nm lithography. Compared to COMA resin, the new resin offers several good properties such as UV transmittance, taper in pattern profile, PED stability and storage stability. The resist using the new resin showed good lithographic performances on ArF exposure tool. So, we obtained good hole patterns below 90nm with condition of exposure: PAS 5500/900 full field scanner, resist thickness: 320nm, development: 2.38% TMAH, for 40sec., Illumination: 0.61NA, conventional SOB: 110 degree(s)C/90sec, PEB:130 degree(s)C/90sec, on BARC. In this paper we will report on the properties of new polymer and will show the contact hole pattern that demonstrate progress in these areas.
Polyacrylate derivative was first developed as raw material for ArF resist and it was selected the first candidate in spite of some defects. Cycloolefin-maleic anhydride polymer[COMA] and other polymers were therefore given opportunity. The resist based on COMA shows a good dry-etch resistance compared with that based on acrylate polymer. However, the pattern profile of the resist formulated by using COMA has some defects such as taper and low resolution because of transmittance issue of the polymer. In order to solve the issue, we have developed a new polymer [It was named ROMA Resin]. The new polymer has good physical properties such as UV transmittance, stability during storage and moderate glass transition temperature. We also found that the pattern profile of the resist formulated by using the polymer shows good results in terms of pattern profile, CD SEM slimming and PED stability.
Photoresist using maleic anhydride/cycloolefin copolymer is a leading candidate for the 193 nm photolithography. Until recently, the efforts to improve 193 nm photoresist have been focused on resolution and dry-etch resistance. Therefore, we have synthesized some kinds of matrix resins and additives containing alicyclic group and acid labile group. The matrix resin is alternating copolymer obtained by free radical polymerization of maleic anhydride and cycloolefinic derivatives. And, the additives have a low molecular weight containing alicyclic group and acid labile group. The additives not only serve as dissolution inhibitors but also improve the pattern profile and dry-etch resistance. In this paper, we will describe the approaches to the resist materials, which are involved in our photoacid generator concept.
In order to develop a new series of chemically amplified photoresists for 193-nm lithography, norbornene substituted with a steroid derivative was copolymerized with maleic anhydride by free radical polymerization. The resulting polymers have excellent transmittance at 193 nm and possess good thermal stability up to 260 degrees C. The resist formulated with the polymers showed better dry-etching resistance than the conventional poly(hydroxystyrene) resist for Cl2/O2 plasma. With the standard developer, the resists from 0.15-0.20 micrometers patterns at doses of 5-18 mJ/cm2 using an ArF excimer laser stepper.
New matrix resins containing maleic anhydride and cycloolefin units for ArF excimer laser resist have been developed. Several series of these matrix resins having good dry-etching durability were prepared by free radical polymerization using AlBN as free radical initiator. All of the resists using the matrix resins revealed good coating uniformity and adhesion to silicon wafer, and were readily soluble in a variety of resist solvents such as MMP, EEP, PGMEA and EL. In preliminary 193 nm testing a resist formulated with the matrix resins sulfonium triflate as photoacid generator afforded positive images with 0.14 micrometers L/S resolution. In this paper, we will discuss the polymerization results and lithographic properties for 193 nm exposure tool.
Fully and partially pendant acetal group substituted polyvinylphenols were synthesized by the methods of free radical polymerization and chemical modification on polyvinylphenol, respectively. The glass transition temperature (Tg) of the partially acetal-substituted polyvinylphenols is in the range of 135 degrees to approximately 148 degrees Celsius, which is enough to overcome the thermal treatments for resist processing. The partially acetal- substituted polyvinylphenols are promising materials for chemically amplified negative tone deep UV photoresist.
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