Progress in deep-UV resists using CARL technology

Three positive working Si-CARL resists for bilayer applications with oxygen-RIE pattern transfer were investigated, and their lithographic performance at deep-UV exposure was compared. With all three we obtained good focus latitudes for 0.35 μm lines and spaces ranging from 1.6 to 2.2 μm exposed with an 0.37 NA KrF-excimer laser stepper. The zero bias exposure dose required for resist R1, of the diazodiketone type, is relatively high (70 mJ/cm²), but R1 has the advantage of not suffering from linewidth fluctuations caused by post-exposure delay time effects. Processing for resists R2 and R3, which are based on acid catalyzed deprotection of t-BOC-imide and t-butylester, respectively, had to be optimized to avoid bridging of isolated spaces after Chemical Amplification of Resist Lines (CARL). This bridging is caused indirectly by evaporation of triflate acid during PEB. Resist R2 needs only 8.5 mJ/cm² for exposure but has a poor linewidth increase after CARL, which seems to be the reason for eroded 0.25 μm patterns after oxygen-RIE. Resist R3 shows the steepest resist slopes and the best overall performance. The ultimate resolution for resists R1 and R3 is 0.25 μm, which, according to the Rayleigh equation for resolution, corresponds to a k-factor of 0.37.     

A new contrast enhanced lithography (cel) process using “chinese rosin” as a binder

A new contrast enhanced lithography (CEL) process using Chinese rosin as a binder is described. This binder is soluble in both non-polar organic solvent and aqueous alkaline solution. Good coatability with organic solvent, no formation of mixing layer, and direct development without removing the CEL layer are the major advantages of this process. Among the three different kinds of photobleachable dyes, DZ-2 (diazonium salt) has the best optical property and the resist profile is improved on g-line reduction projection printing at the smallest dose. Moreover, this DZ-2—Chinese rosin system is also effective at 365 nm, and the resist profile and the focus margin are improved on i-line reduction projection printing by using this system.     

Direct patterning using metallo-organics and its application to mask repair

Au patterns are formed by photographical patterning of polymeric Au mercaptoterpenes (Au resinate), followed by bakeout of the Au resinate patterns to remove carbonaceous materials. Since commercially available Au resinate is not sensitive to 436 nm (g-line) light and cannot be photographically patterned, we mixed azide (photocrosslinker) with Au resinate to give photosensitivity to the g-line. The mixture of Au resinate and azide was spun on an Si substrate, and then exposed with 436 nm (g-line) light by a standard contact printing technique. Upon exposure, Au resinate was crosslinked by the reaction with azide, and became insoluble. Au resinate patterns were generated by development with monochlorobenzene. On baking out the Au resinate patterns to remove carbonaceous materials, we obtained 2 μm line and space Au patterns. The conductivity of the Au patterns obtained was 1/4 that of bulk Au. For a mask repair application, we mixed Cr resinate with a mixture of Au resinate and azide to improve the adhesion of the resulting metal patterns onto the quartz plate. The transmittance and the adhesion were found to depend on the bakeout condition and the mixing ratios of the Cr resinate. Bakeout in vacuum with 0.1 torr oxygen gave far better adhesion and opaqueness than bakeout in air, because of residual carbon in the resultant metal. Mask repair was carried out at the optimized condition by using a spot exposure system. The clear defect was repaired with the transmittance < 1% and good adhesion.     

248nm光致抗蚀剂成膜树脂研究进展

光致抗蚀剂(photoresist)是制造超大规模集成电路的关键性材料之一,随着集成电路集成度的不断增加,光致抗蚀剂由g线(436nm)胶、i线(365nm)胶,逐渐发展到深紫外(DUV)(248nmKrF与193 nm ArF)胶。成膜树脂作为光致抗蚀剂的主要成分之一,决定了抗蚀剂的主要性能,因此研究成膜树脂具有重要的意义。本文综述了248 nm KrF光致抗蚀剂成膜树脂的研究进展,重点介绍了聚对羟基苯乙烯及其衍生物,并简要介绍了其合成方法及成像机理。     

新型氧酰基肟酯类光引发剂的制备与性能

制备了3种新型氧酰基肟酯类光引发剂。并用TLC、DSC和UV等手段对其溶解稳定性、热稳定性及紫外吸收特性进行了表征,发现其溶解稳定性良好,可溶于常见的有机溶剂,有着非常好的热稳定性,并且在g线(436nm)、i线(365nm)和深紫外处(DUV,248nm)都有很好的紫外吸收;还利用实时红外(RT-IR)红外实验及感光性能测试实验对此类光引发剂的光固化性能进行了测试。结果表明,与常见的自由基引发剂ITX、TPO、261等相比,其更适合用于405nm紫激光自由基光聚合成像体系及其他化学增幅光致抗蚀试剂体系中。     

Tetrahydropyranyl- and furanyl-protected polyhydroxystyrene in chemical amplification systems

Tetrahydropyranyl- (THP) and furanyl- (THF) protected polyhydroxystyrene (PHS) polymers have been investigated for their potential use in conjunction with onium salt acid precursors to yield high-sensitivity resist systems. The synthesized polymers have high transmittance at 248 nm (the wavelength used in next-generation excimer laser, KrF exposure tools). At 248 nm the transmittance for a 1-μm thick film is ～ 80% (Abs = 0.097 μm^?1). The acid sensitivity of the acetal functionality at room temperature is high, requiring careful handling of all materials to prevent any premature deprotection of the hydroxy group. The highest lithographic sensitivities obtained so far with a system consisting of poly(p-tetrahydropyranyl-oxy-styrene) base resin and 1 mol % of bis (p-tert-butyl phenyl) iodinium triflate (TBIT) was ～ 2 mJ / cm². High-resolution line and space patterns (0.35 μm) were obtained with a system comprising PHS-p-THP and an acid precursor, using an excimer laser step and repeat exposure at 248 nm.     

A sub-0.5 μm bilevel lithographic process using the deep-UV electron-beam resist p(si-cms)

Optimization of the deep-UV and electron-beam lithographic properties of a copolymer of trimethylsilylmethyl methacrylate (SI) and chloromethylstyrene (CMS), P(SI-CMS), within a weight average molecular weight range of 1.4 to 4.1 × 10⁵ and 90 to 93 mole percent SI composition has been achieved. The solubility behavior of P(SI-CMS) resist was examined using the Hansen 3-dimensional solubility parameter model and dissolution rate measurements. Swelling of the resist has been minimized through the identification of a single component developer (2-propanol) and rinse (water) system. For the material containing 90 mole percent SI (14.9 weight percent Si) and M?_ω = 1.4 × 10⁵, the sensitivity to 248 nm radiation is 65 mJ/cm² and to electron-beam exposure is 3.4 μC/cm² at 20 kV. This material Is applicable to bilevel lithographic processes, and the O₂ reactive ion etching (RIE) rate is 16 times slower than standard hard-baked photoresist. Using a He/O₂(60/40) RIE pattern transfer process, 0.4 μm line/space patterns have been resolved in a 1.3 μm bilayer structure for deep-UV exposures, and 0.25 μm imaging has been demonstrated in a 0.7 μm thick planarizing layer using electron beam irradiation. The loss in linewidth associated with the 0.25 μm process is ～0.04 μm.     

Epoxy resins for deep UV lithography

A negative resist based upon photo-acid initiated cationic polymerization of an epoxy resin (1, 2) was reported in the early eighties with the advent of onium salts (3–5). An efficient acid generating onium salt, triphenylsulfonium hexafluoroantimonate (6), absorbs light in the deep UV producing acid upon direct photolysis in this region of the spectrum. The resin component of such a negative resist system must be optically transparent over the exposure wavelengths to obtain vertical image profiles. Another difficulty often encountered with crosslinking negative resists is swelling of the crosslinked matrix during development with organic solvents. This swelling manifests itself in distorted images and/or complete adhesion loss, especially when submicron features are involved. Our goal has been to address these problems and develop an organic developable deep UV resist capable of providing submicron images. Optically transparent commercial resins, styrene-allyl alcohol copolymers, have been converted to glycidyl ethers, thereby providing cationically polymerizable functionalities. Careful choice of the resin was made to obtain reactive ion etch resistance, thermal stability, good adhesion, and coating properties. The synthetic procedure and characterization of the epoxy resin will be presented. The effect of the molecular weight distribution upon swelling during development and general solubility properties also will be discussed. Resist formulations exhibited sensitivities of 19 to 30 mJ/cm² on a Perkin Elmer 500 in the deep UV (UV2) mode. The electron beam sensitivity is 3 to 5 μC/cm² at 20 KeV. Submicron images have been generated in both optical and electron beam lithography.     

Design and synthesis of new photoresist materials for ArF lithography

A new class of photoresist matrix polymers based on vinyl ether–maleic anhydride (VEMA) alternating copolymers was developed for ArF single‐layer lithography. These polymers were synthesized by copolymerization of alkyl vinyl ether and maleic anhydride alternating copolymers with acrylate derivatives containing bulky alicyclic acid‐labile protecting groups. The resulting polymers showed good control of polymerization and high transmittance. Also, these resists exhibited good adhesion to the substrate, high dry‐etching resistance against CF₄ mixture gas (1.02 times the etching rate of deep UV resist), and high selectivity to silicon oxide etching. Using an ArF excimer laser exposure system with 0.6 NA, 120‐nm L/S patterns were resolved under conventional illumination. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 165–170, 2004     

Evaluation of optics and resists for 3000 Å wavelength photolithography with a Perkin-Elmer printer

A Model 111 Perkin-Elmer projection printer, with a 3100 Å exposure capability was evaluated for far-UV printing. The improvement found in resolution at 3100 Å compared to 4000 Å was roughly proportional to the mean exposure wavelengths in the near and far-UV as verified by electrical probe yield data of printed meander patterns. The processing latitude of various photoresists of the diazide type was found in the 1.0 μm and 2.5 μm line width range by electrically measuring the line widths of meanders etched into metal films using the appropriate resist mask. Exposures were varied continuously on individual wafers so that the resist linewidth change vs exposure could be determined using a minimum number of wafers. It was found that resists such as AZ-2400 which pass much of the exposing radiation have better latitude than those that absorb most of the exposing radiation (HPR-204, MPR). Some new, unconventional resists studied have even greater latitude than the diazide resists. Design compensations which have to be made for proximity and related effects at fine dimension are in the 0.1 μm to 0.2 μm range. Depth-of-focus for the printer studied seems to be adequate for careful work at 1.0 μm using 3100 A exposure. The overlay printing capability, which includes mask quality, operator error, and printer optics and stability, is within 0.25 μm from level-to-level.     

A Miniature Device for Shock Initiation of Hexanitrostilbene by High‐Speed Flyer

A miniature device for shock initiation of the hexanitrostilbene (HNS) through micro‐charge detonation‐driven flyer was fabricated. This device consisted of the substrate, micro‐charge, flyer, and barrel. Four types of flyer (titanium of 28 μm, aluminum of 22 μm, copper of 22 μm and polyimide (PI) of 55 μm in thickness) were studied and the effect of micro‐charge thickness, diameter, and barrel length were investigated by measuring the average flyer velocities using polyvinylidene fluoride (PVDF) films. The results show that the titanium flyer is more proper for such initiation device compared to aluminum, copper, and polyimide flyer. The average velocity of the flyer increased with the thickness of micro‐charge and the increment was larger when the thickness increases from 0.3 mm to 0.4 mm than when the thickness increases from 0.4 mm to 0.6 mm. The flyer velocity significantly increased with the increase in the diameter of micro‐charge until a plateau appeared at 0.8 mm. The flyer velocity increased first and then decreased sharply with the increase in barrel length. The average velocity for a 28 μm thick titanium flyer was measured to be as high as 2468 m s⁻¹ when the thickness, micro‐charge diameter and the length of barrel were 0.6 mm, 0.8 mm and 659 μm, respectively. The HNS‐IV explosive with density 1.57 g cm⁻³ was initiated by this miniature device.     

Evaluation of poly(allyl methacrylate)-co-(hydroxyethyl methacrylate) as negative electron-beam resist

Poly(allyl methacrylate)-co-(hydroxyethyl methacrylate) has been evaluated as a high-sensitivity, high-resolution, high temperature-resistant negative electron resist. The effects of molecular weight and polydispersity of the copolymer on its lithographic performance as an E-beam resist were studied. The sensitivity of the copolymer is nearly constant in the weight-average-molecular-weight range of 50,000 to 75,000, and it gradually decreases with a decrease in molecular weight. As expected for a negative resist, the resist contrast increases as the polydispersity is decreased. The sensitivity curve shape of the polymer was independent of the prebake temperature, which varied from 70 to 110°C, and of the various developers used. The exposed coating requires vacuum curing for image optimization. Resolution of 0.5 μm line/space pairs was obtained from a 0.6 μm thick resist by exposing the resist to 10 keV electrons with either a raster-scan-type or vector-scan-type electron-beam exposure machine. After postbaking at 170°C, the resist had good resistance to both chemical etching and dry etching. The plasma-etch resistance was about twice that of PMMA.     

Electron beam lithographic evaluation and chain scissioning yields of itaconate resists

Copolymers of itaconic acid with methyl methacrylate, P(ItA–MMA), have been synthesized as promising positive working electron beam resists.^1,2 However, attempts to obtain greater electron beam sensitivity by increasing the itaconic acid content and initial molecular weight of these copolymers have been hindered by difficulties in synthesizing itaconic acid copolymers with an ItA content greater than 50 mol% or with a molecular weight above 250,000. The usefulness of the MMA–ItA copolymers is also limited by their susceptibility to anhydride formation which makes this resist very sensitive to prebake conditions and aging times. To overcome these limitations and to develop resist materials with improved sensitivity, alkyl ester derivatives of itaconic acid have been synthesized, both as homopolymers and as copolymers with methyl methacrylate. The electron-beam chain scissioning yields, G(s), of these derivatives have been determined, and the most promising of these copolymers and homopolymers have been evaluated for lithographic performance. The G(s) values of the alkyl itaconate copolymers depend greatly on the structure of the alkyl group. The mono-alkyl itaconate copolymers exhibit G(s) values 2–3 times greater than the corresponding dialkyl itaconate copolymers. In particular, copolymers of monomethyl itaconate (MeI) with methyl methacrylate are found to be promising resist materials with high sensitivities and compatability with processing conditions. A trend in sensitivity is observed for a series of MMA–MeI copolymers ranging from 20 to 85 mol % MeI, with a maximum sensitivity observed for the 57 and 73% MeI compositions. These copolymers exhibit improved sensitivity over that of the itaconic acid copolymers. Anhydride is formed less readily from the MeI copolymers than from the ItA copolymers, improving the stability of the resist for process conditions. Areas exposed in P(MMA–73 mol % MeI) at 4 μC/cm² (20 kV) were developed with less than 10% thinning of unexposed resist and with a contrast (γ) of 2. Vertical walls were observed for 1 μm wide lines using P(MMA μ73% MeI) at a dose of about 6 μC/cm².     

A negative resist,LMR (low molecular weight resist), for deep UV lithography

A negative deep UV resist, LMR, has been developed. LMR is a diazonaphthoquinonesulfonate of cresol novolac resin and possesses a high sensitivity of 15 mJ/cm² and a high resolution up to 0.2 μm by contact printing. An important feature of LMR is the production of negative images with overhung profiles. Such profiles are attributed to LMR possessing a large absorbance in the deep UV region (12 μm^?1 at 250 nm), which is of great advantage to the lift-off process in the fabrication of GaAs-FET, surface acoustic wave (SAW) devices, and so on. Furthermore, because of the good thermal stability of LMR, it can liftoff hard metals such as Ni and Mo. In order to elucidate the phenomenon that deep UV irradiation retards the dissolution rate of LMR, a mechanistic study has been carried out. In both LMR and its analog lacking diazoquinone moiety, their molecular weights Increase upon deep UV irradiation, which suggests that crosslinking occurs in the base resin. This is supported by 13C NMR analyses of photochemical reaction products and by detection of radical species produced from the base resin. The photochemical reaction of the base resin is important to understand the overall lithographic performance of LMR.     

Synthesis and characterization of water-soluble diazonium salts as contrast-enhancement materials

Water soluble aromatic diazonium double salts, p-diazodiphenylamine chloride zinc chloride (DZS-1) and p-diazoanisol chloride zinc chloride (DZS-2), have been evaluated as photobleachable dyes for contrast enhancement lithography. After testing the bleaching characteristics, aqueous solutions of DZS-1 and poly(vinyl alcohol) were used as a contrast enhancement material. Thermal stability, resist contrast, exposure parameters and other bleaching characteristics of the photobleachable membranes were investigated. A. commercial i-line photoresist was used to evaluate the contrast ratio of the DZS-1/PVA CEL layer. The contrast ratio obtained in this investigation is 1.67.     

The role of the latent image in a new dual image,aqueous developable,thermally stable photoresist

A new dual image, aqueous developable photoresist can be processed to yield either positive or negative images that are crosslinked and thermally stable to temperatures >300°C. Positive images have similar resolution and processing parameters to conventional positive novolak resists. Negative resists from this system have a number of new and interesting properties that surpass the capabilities of their positive counterparts. In addition to producing highly resolved submicron images, thick coatings of resist can be used to form images with high aspect ratios. By adjusting the exposure of the resist, images with inward sloping wall profiles can be realized. As a result of the images being crosslinked and Insoluble in the resist coating solution, images can be recoated and new images formed over the top of existing patterns to form structures. A hypothetical mechanism that suggests that resist defects caused by dust on the mask or photoresist surface can be reduced In negative mode processing is also presented.     

Highly sensitive self-developing soft X-ray resists of silicon-containing aldehyde copolymers and sensitive novolac-based composite resists containing aldehyde copolymer

Copolymers of aliphatic aldehydes containing a trimethylsilyl group were prepared at ?78°C in toluene using diethylaluminum diphenylamide as an initiator. The copolymer depolymerized into monomeric aldehydes on exposure to soft X-rays. When the copolymer was used as a soft X-ray resist, almost complete development was accomplished by exposure alone. No development step was required. The soft X-ray sensitivity of poly(3-trimethylsilylpropanal-co-propanal) was 50 mJ/cm² at the film thickness of 1.0 μm. A composite resist system consisting of a novolac resin and an aldehyde copolymer containing trimethylsilyl groups has also been developed and used as an alkaline-developable positive electron-beam and soft X-ray resist.     

Study on organosilicon positive resist. III. Organosilicon positive excimer laser resist (OSPR-2016)

A new alkali-developable organosilicon positive excimer laser (KrF) resist (OSPR-2016) has been developed for a bilayer resist system. OSPR-2016 is composed of poly(p-hydroxybenzylsilsesquioxane) and methyl cholate-tris (α-diazoacetoacetate). The ratio is 72.5 : 27.5 w/w. A sample of 0.5-μ thick OSPR-2016 resolved 0.35 μ L&S patterns when exposed to a dose of 320 mJ/cm² from an excimer laser projection printer (NA = 0.37).     

Synthesis and lithographic evaluation of poly[(methacrylic acid tert-butyl cholate ester)-co-(γ-butyrolactone-2-yl methacrylate)]

Poly[(methacrylic acid tert-butyl cholate ester)-co-(γ-butyrolactone-2-yl methacrylate)] was synthesized and evaluated as a new 193-nm chemically amplified photoresist. This polymer showed good thermal stability up to 240 °C and had a good transmittance at 193 nm. This material showed good resistance to CF₄-reactive ion etching. The resist patterns of 0.15 μm feature size were obtained at a dose of 11 mJ cm⁻² using an argon fluoride excimer laser stepper.     

Effect of particle size on flame retardancy and mechanical properties of hydroxyethyl diphosphate modified aluminum hydroxide intrinsic polyethylene terephthalate

Organic–inorganic hybrid flame retardant was obtained by modifying aluminum hydroxide with different particle size with 1-hydroxyethylidene-1,1-diphosphonic acid. The structure of the organic–inorganic hybrid flame retardant is characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, while ¹H-NMR spectroscopy only characterizes specific samples. The thermal stability and flame retardancy of the samples were analyzed by thermogravimetric analysis, limiting oxygen index (LOI), vertical combustion of UL-94 and cone calorimeter. The results show that the modified 10 μm aluminum hydroxide has a better effect than the 25 μm aluminum hydroxide and 100 nm aluminum hydroxide. Compared with pure polyethylene terephthalate (PET), the LOI value of the best sample is increased by 24.4%, and UL-94 V reaches V-0 level. Heat release rate, total heat release rate, and carbon monoxide production rate decreased by 45.8%, 33.2%, and 41.5%, respectively, compared to pure PET. The results showed that the aluminum hydroxide with a particle size of 10 μm exhibited the best flame retardant effect, which could be attributed to the decomposition of organic phosphoric acid and the dehydration of aluminum hydroxide, yielding a higher amount of residual carbon.