The continued miniaturization of integrated circuit features has been made possible through multilayer patterning processes where different etch steps transfer the patterned photoresist image through various hardmasks and ultimately to the underlying substrate. Spin-on carbons (SOCs) are a type of a solution-dispensable carbon hardmask that can offer excellent resistance to various etch gases for good pattern transfer fidelity, while simultaneously conferring desirable gap fill and planarization properties onto the underlying substrate. We recently reported on the development of a new SOC platform with excellent etch resistance, having a relative reactive ion etch (RIE) rate of 1.08 compared to amorphous carbon. However, one drawback we observed for this polymer was its relatively high absorbance between 400-700 nm which can complicate lithographic alignment. Here we report our work on reducing the absorbance of our SOC platform while maintaining its excellent etch resistance. We identify that the origin of high absorbance is from side reactions that occur during curing and discuss the various polymer modifications or additives that prevent these unwanted processes. We additionally look at any trade-offs that are observed between decreasing absorbance and etch resistance and optimize the SOC’s composition to minimize absorbance while having a minimal effect on its etch resistance.
As the critical dimension (CD) in semiconductor devices continues to shrink, the multilayer patterning process to transfer fine line patterns into an underlying substrate is becoming increasingly important. The trilayer processes consist of a photoresist film, a silicon-containing layer and a carbon rich underlayer. The distinctive difference in etch selectivity toward fluorine and oxygen based reactive ion etching (RIE) chemistry is critical to provide highly selective pattern transfer to the substrate. In response to the need for high etch resistant underlayers, we have developed carbon rich spin-on carbon (SOC) materials with good solubility in preferred casting solvents, high thermal stability and high dry etch resistance. To better understand structure-property relationships of high etch resistant SOC films, cured SOC films were analyzed by Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis), X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The design considerations for high etch resistance SOC underlayers, such as Ohnishi parameter, crosslinking and film density, will be discussed in this paper.
In the multilayer patterning process, underlayer material is often used to enable device size shrinkage for advanced integrated circuit manufacturing. This underlayer material, spin on carbon (SOC), with high etch resistance plays an important role in both gap fill and process of transferring high aspect ratio patterns. Good global planarization (PL) performance over various pattern topographies not only impacts on the following lithography process window but also boosts the overall device integration yield (Figure 1). As critical dimension (CD) size decreases in the advanced nodes such as 10 nm and beyond with multiple patterning steps, long range planarizing SOC material is needed to control the CD uniformity. During the single coat and single bake process, thermal flow ability of these carbon rich materials is one of the key property to achieve long range planarization performance. In addition, our strategy for designing long distance thermal flow polymers will be applied to both low/high thermal stability SOC materials. Herein, we report the development of a novel planarized SOC materials with good Fab drain line compatibility. As for material global planarization performance, the observation of flow ability can be monitored through the various cure conditions. Other key performance such as gap fill, etch rate toward various gases, solvent strip resistance and cured film thermal stability will be also highlighted in this paper.
The use of multilayer processes in advanced ArF patterning schemes continues to increase as device critical dimensions shrink. In a multilayer stack, underlayer materials play a critical role in terms of gap fill, planarization and etch resistance to enable high resolution and high aspect ratio patterning. The emerging quadlayer imaging process requires a unique spin on carbon (SOC) layer with high thermal stability to withstand subsequent deposition of an inorganic hard mask layer, commonly deposited via chemical vapor deposition (CVD). The thermal stability requirement associated with CVD compatibility largely limits the options of organic materials, which mostly decompose in the 300-450°C range. Thermal shrinkage and coefficient of thermal expansion (CTE) differences between layers are other key considerations in designing a high temperature stable, CVD compatible SOC material. Furthermore, the SOC polymer resin must be compatible with solvents and spin on products commonly used in the FAB. This paper highlights the development of a novel CVD compatible HT-SOC platform with excellent thermal stability (>500°C) and good FAB drain line compatibility. In addition, this polyaromatic SOC platform shows various improvements compared to traditional Novolacbased SOC, including reduced shrinkage, good gap fill, improved planarization, and low defectivity. Robust formulation design, high quality raw materials, and advanced metal removal technique synergistically enabled manufacturing of multigallon HT-SOC product with high quality. Application specific versions are available for more demanding planarization requirement and applications that require good adhesion to metal substrate. In addition, a newly developed method for quantitative measurement of long-range planarization was used to validate new material designs aimed at improving planarization.
A trilayer stack of spin-on-carbon (SOC), silicon anti-reflective coating (SiARC) and photoresist (PR) is often used to enable high resolution implant layers for integrated circuit manufacturing. Damage to substrates from SiARC removal using dry etching or aqueous hydrogen fluoride has increased the demand for innovative SiARC materials for implant lithography process. Wet strippable SiARCs (WS-SiARCs) capable of stripping under mild conditions such as SC1 (ammonium hydroxide/hydrogen peroxide/water) while maintaining key performance metrics of standard SiARCs is highly desirable. Minimizing the formation of Si-O-Si linkages by introducing organic crosslink sites was effective to impart SC1 solubility particularly after O2 dry etching. Incorporation of acidic groups onto the crosslinking site further improved SC1 solubility. A new siloxane polymer architecture that has SC1 active functionality in the polymer backbone was developed to further enhance SC1 solubility. A new SiARC formulation based on the new siloxane polymer achieved equivalent lithographic performances to a classic SiARC and SC1 strip rate >240Å/min under a relatively low concentration SC1 condition such as ammonium hydroxide/hydrogen peroxide/water=1/1/40.
With the continuous demand for higher performance of computer chips and memories, device patterns and structures are becoming smaller and more complicated. Hard mask processes have been implemented in various steps in the devise manufacturing, and requirements for those materials are versatile. In this paper, novel organometal materials are presented as a new class of spin on solution in order to support the hard mask process. Type of metals, formulation scheme and processing conditions were carefully designed to meet the fundamental requirements as a spin on solution, and their characteristic properties were investigated in comparison to other conventional films such as spin on carbons (SOC), organic bottom anti-reflective coatings (oBARC) and inorganic films formed by chemical vapor deposition (CVD). Several advantages were identified with these SOMHM materials over other films which include 1) better thermal stability than SOC once fully cured, 2) reworkable with industry standard wet chemistry such as SC-1 where conventional Si-BARC is difficult to remove, 3) a wide range of optical constants to suppress reflection for photoresist imaging, 4) high etch resistance and 5) better gap filling property. Curing conditions showed a significant impact on the performance of SOMHM films, and X-ray photoelectron spectroscopy (XPS) was utilized to elucidate the trends. With SOMHM film as a BARC, photolithographic imaging was demonstrated under ArF immersion conditions with 40nm linewidth patterning.
EPICTM 2330 photoresist is an imaging material designed for conventional dry and immersion ArF exposure, its formulation is optimized for contact hole features. Although it performs well in both imaging modes, with good profile, it is not known whether the presence of water impacts the materials fundamental imaging characteristics. Acid generation efficiency, characteristic acid diffusion length and dissolution rates are determined for EPIC 2330 under dry and immersion imaging conditions. The results show, that within measurement errors, no difference is observed for these fundamental parameters whether water is present during exposure, or not.
We investigated the structure-property relationships of several polymer platforms containing hexafluoroisopropanol (HFIP) and tertiary alkyl ester functionalities in order to identify and develop fluorine-containing polymers suitable for 157nm lithography. We observed that the aqueous base solubility of homopolymers containing HFIP was highly dependent on the monomer structure, number of HFIP group per monomer unit, substituent on the alcohol and the polymer architecture. Copolymers of tert-butyl acrylate (TBA), tert-butyl 2-fluoroacrylate (TBFA) and tert-butyl 2-trifluoromethylacrylate (TBTFMA) with styrene hexafluoroisopropanol (STYHFIP) or norborene hexafluoro-isopropanol (NBHFIP) were also investigated to determine the effect of substitution at the acrylate α-position. Under the same ration of STYHFIP, the transparency of the co-polymers improved in the or der of CF3>F>H while the dry etch stability decreased in the order of CF3>F>H. When exposed to 157 nm radiation, photoresists of P(STYHFIP-TBA), P(STYHFIP-TBFA) and P(STYHFIP-TBTFMA) showed an increase in E0 ni the order of H<F<CF3, but the difference was marginal. The PEB sensitivity was nearly identical for all three co-polymers suggesting that the nature of the substituent at the α-position of the acrylate monomer did not have a significant impact on the deprotection chemistry. The photospeed of P(NBHFIP-TBTFMA) was much slower than that of P(STYHFIP-TBTFMA) due to a slower dissolution rate of NBHFIP than that of STYHFIP and to the influence of the polymer matrix on the deprotection reaction.
This paper reports on the development of advanced bilayer resists for ArF and F2 lithography. Contamination of the optics with silicon has been identified as a major issue for the adoption of bilayer technology across all wavelengths. An investigation was carried out to fundamentally understand the effect of the polymer architecture on silicon outgassing. A laser outgassing system was developed and calibrated using model silicon compounds. Model polymers where prepared in which the silicon was incorporated in a number of different ways pendant to the polymer backbone and in the polymer backbone. It was observed that the placement of silicon into the polymer backbone as a poly(silsesquioxane), allows the incorporation of high silicon content for superior etch resistance, with no detectable outgassing of silicon during the exposure step. The design concepts used for these ultra thin silicon imaging systems has resulted in superior imaging capability, resolving sub 100nm dense patterns.
A survey of fluorine-containing aromatic polymers, with and without base soluble functionality, was conducted to determine their potential utility in 157 nm lithography. The focus was toward the design and evaluation of fluorine- containing polymers that closely paralleled the ESCAP matrix resins now successfully used in 248 nm photoresists. New 4- hydroxytetrafluorostyrene (HTFS) based homo-, co- and ter- polymers were prepared and evaluated for their potential utility at 157 nm resists. Significant advances were made toward reducing absorbance with fluorine substitution and monomer variation. The polymers form good films, have acceptable thermal stability and show good dry etch resistance with promising potential in thin film resist applications. The synthesis and pertinent characteristics of the new polymer systems as well as preliminary oxide etch results on representative polymers are discussed.
Fluorocarbon polymers and siloxane-based polymers have been identified as promising resist candidates for 157 nm material design because of their relatively high transparency at this wavelength. This paper reports our recent progress toward developing 157 nm resist materials based on the first of these two polymer systems. In addition to the 2-hydroxyhexafluoropropyl group, (alpha) -trifluoromethyl carboxylic acids have been identified as surprisingly transparent acidic functional groups. Polymers based on these groups have been prepared and preliminary imaging studies at 157 nm are described. 2-Trifluoromethyl-bicyclo[2,2,1] heptane-2-carboxylic acid methyl ester derived from methyl 2-(trifluoromethyl)acrylate was also prepared and gas-phase VUV measurements showed substantially improved transparency over norbornane. This appears to be a general characteristic of norbornane-bearing geminal electron-withdrawing substituents on the 2 carbon bridge. Unfortunately, neither the NiII nor PdII catalysts polymerize these transparent norbornene monomers by vinyl addition. However, several new approaches to incorporating these transparent monomers into functional polymers have been investigated. The first involved the synthesis of tricyclononene (TCN) monomers that move the bulky electron withdrawing groups further away from the site of addition. The hydrogenated geminally substituted TCN monomer still has far better transparency at 157 nm than norbornane. The second approach involved copolymerizing the norbornene monomers with carbon monoxide. The third approach involved free-radical polymerization of norbornene monomers with tetrafluoroethylene and/or other electron-deficient comonomers. All these approaches provided new materials with encouraging absorbance at 157 nm. The lithographic performance of some of these polymers is discussed.
Interest in developing materials with reduced environmental impact has led us to design resist formulations that can be cast from and developed with aqueous media. A water soluble chemically amplified positive tone photoresist based on thermal decarboxylation of a half ester of malonic acid has been designed. Two solubility switches are required for this application. Sequential volatilization of ammonia followed by decarboxylation of a malonic acid gives the first solubility switch and an acid catalyzed thermolysis of an acid labile protecting group gives the second. The thermal stability of the acid labile protecting group is critical in this design. Tert-butyl esters decompose during the decarboxylation process resulting in poor imaging contrast. Polymers bearing isobornyl esters are more thermally stable, and show excellent reaction selectivity between the decarboxylation and the thermolysis of the ester. Preliminary imaging of this system provided 1 micrometer resolution with 248 nm exposure and standard TMAH developer. The dry etch stability of the photoresist films is comparable to a conventional photoresist APEX-ER.
Finding materials that offer the all of the characteristics required of photoresist matrix resin polymers while trying to maintain a high level of transparency at 157 nm is a daunting challenge. To simplify this task, we have broken the design of these polymers down into subunits, each of which is responsible for a required function in the final material. In addition, we have begun collecting gas-phase VUV spectra of these potential subunits to measure their individual absorbance contributions. Progress on developing materials for each of these subunits are presented along with plans for future studies.
The acid-catalyzed interconversion of cyclic anhydride and di-acid or ester-acid groups within polymers rich in vicinal dicarboxyls, such as are found in many copolymers of maleic anhydride, is the basis for a new kind of resist chemistry that is not susceptible to many of the problems found in existing chemically-amplified resists that are based on acid-cleavable carbonate, ester, ether or acetal groups. With sufficient vicinal dicarboxyls, or other hydrophilic contribution, the hydrated forms of these relatively UV- transparent polymers dissolve in relatively polar solvents, and even (in the extreme) in neutral water, in which the dehydrated (i.e. anhydride) forms are insoluble. Combining with water-dispersible diphenyliodonium initiator gives chemically-amplified resists that can thus be spin-coated, then (according to sequence of heat, humidity and UV radiation) developed into an image of either positive or negative tone, and eventually stripped from substrate--each step using only plain neutral water as the processing liquid. Plasma etch resistance was evaluated for both hydrated and dehydrated forms of several of these polymers, including some with polycyclic comonomers: in general, a larger number of cycles in the structure improved the etch resistance, even (surprisingly so) when such were oxygen- containing rings of the cyclic anhydride functionalities. Such reactive films would also lend themselves well to incorporation of a variety of organic and inorganic species for `functional patterning', and oxygen plasma development.
The interest in imaging materials with improved environmental characteristics has led us to consider imaging formulations coated from and developed in aqueous media, thus avoiding the need for both organic solvents and basic aqueous developer solutions. We have previously reported on the design of several negative-tone resists operating via radiation-induced crosslinking, and while the performance of these negative-tone systems met our basic goals, the resolution that could be achieved was limited due to swelling occurring during development. We now report on various other designs based on polyoxazoline, poly(vinyl alcohol), and methacrylate resins that circumvent this problem with approaches towards both negative- and positive- tone systems.
This paper presents the progress we have made toward the development of fully water processable, negative and positive tone I-line resist systems. The negative tone system is based on styrene copolymers bearing pendant ammonium sulfonate groups and vicinal diol functionalities. The salt provides the means of rendering the polymer water soluble. The diol undergoes an acid catalyzed pinacol rearrangement that results in a polarity switch within the exposed polymer film, i.e. a solubility differential. The styrene backbone was chosen to provide dry etch resistance. Positive tone imaging requires two solubility switches. The two solubility switches are based on the reaction between acidic hydroxyl groups in a matrix polymer and vinyl ethers that are introduced as a pendant group of the polymer or as a monomeric cross-linker, i.e. a bisvinyl ether. During the post application bake, the vinyl ether reacts with an acidic hydroxyl group in a thermally activated switch, forming a crosslinked, water insoluble network through acetal linkages. These acid labile crosslink sites are then cleaved by a photochemical switch through the generation of acid, thereby rendering the exposed areas water developable.
We report the study of a novel class of resists designed to be coated from and developed in pure water, avoiding both the need for the traditional organic solvents and the developers containing organic bases in aqueous solution. We have previously reported on the design of several negative tone resists that operate on the basis of radiation-induced crosslinking. The performance of these negative tone systems meets our fundamental objective of coating from and development in pure water, but their design involving the crosslinking of a matrix polymer limits the resolution that may be achieved because of the swelling that occurs during development. We have now explored novel designs involving positive tone water developable resists that may help alleviate this limitation. For example, water-soluble polymers containing pendant oxazoline units may be insolubilized in situ through their heat-activated reaction with additives containing carboxylic acid groups. Exposure to UV radiation is then used to cleave these solubility modifiers hence restoring solubility to the exposed areas. Analogous materials that involve the addition of divinyl ethers to poly(acrylic acid), followed by photogenerated acid cleavage of the crosslinks have been used generate water-developed positive tone images.