Electron Beam Resists Research Articles

High-resolution, High-purity Calix[n]arene Electron Beam Resist.

Calixarene is a promising high-resolution negative electron-beam resist having a resolution of the order of 10nm because of its low molecular weight. We have made a purified calixarene resist containing metal contaminants whose concentrations are measured in parts per billion and which therefore do not degrade the performance of silicon devices. The purity of the calixarene itself was also improved and we obtained high-purity calix[6]arene and high-purity calix[7]arene, in both of which contain the main component is more than 95% of all the calixarene present. The resolution of both purified calixarene resists is almost same as that the nonpurified calixarene, but the sensitivity of calix[7]arene is higher than that of calix[6]arene because its molecular weight is higher.

High etch-resistant EB resists employing adamantyl protective groups and their application for 248-nm lithography.

We developed high-etch resistant resists for electron beam (EB) lithography. The incorporation of 2-alkyl-2-adamantyl groups as cleavable protective groups in a vinylphenol-methacrylate copolymer enabled us to enhance the dry-etch resistance and obtain excellent lithographic performance. In this paper, we investigate the reactivity of 2-methyl-(MAd) and 2-ethyladamantyl (EAd) group for an acidic condition as well as the heat-flow resistance of the resist. In addition, we applied vinylphenol-2-ethyl-2-adamantyl methacrylate (VP-EAdMA)-based resist to 248-nm exposures. We found that the reactivity of the EAd group was 2.5 times higher than that of the MAd group. We also found that the resist had a 140-nm resolution at 13.2mJ/cm2 without optimization of the process conditions. We think that these resists can be used for both EB and 248-nm exposure systems.

Dry-Developable Electron-Beam Resist. Synthesis and Resist Characteristic Evaluation of Amino-ended Poly(.ALPHA.-Methylstyrene).

Dry-Developable Electron-Beam Resist. Synthesis and Resist Characteristic Evaluation of Amino-ended Poly(.ALPHA.-Methylstyrene).

An analytical model of the diffusive scattering of low-energy electrons in electron-beam resists

An analytical model is developed for predicting the electron penetration profile created by the low-energy exposure of electron-beam sensitive resists. The model uses a multiple forward-scattering scheme adapted by the modified age diffusion approximation to the Boltzmann transport equation to produce a computationally efficient model. Model validation is performed using the literature and experimental results. The model is used to predict low-energy electron penetration profiles formed by a micro-mechanical prototyping device.

Effect of Chelating Agents on High Resolution Electron Beam Nanolithography of Spin-Coatable Al2O3 Gel Films

The effect of chelating agents on the electron beam exposure characteristics as well as environmental stability of the spin-coatable Al2O3 gel films is discussed. It was found that the Al2O3 gel films prepared by reacting aluminium tri-sec-butoxide, Al(OBus)3, with acetylacetone (AcAc), AcAc/Al2O3, gave better environmental stability and patterning characteristic than the gel films prepared by reacting the Al(OBus)3 with ethylacetoacetate (EAcAc), EAcAc/Al2O3. The latter suffered from a faster moisture attack in the laboratory atmosphere. Both EAcAc/Al2O3 and AcAc/Al2O3 films are ∼106 times more electron beam sensitive than sputtered AlOx films, thus bringing the formers' sensitivity very close to some of the organic electron beam resists. It was seen that the baking temperature up to 70°C has almost no effect on either the sensitivity or the contrast in both the films; but it has a significant effect on the developing characteristics. Electron beam nanolithography gave 20 nm linewidth with a rectangular cross-section in both EAcAc/Al2O3 and AcAc/Al2O3 films. It was observed that the etching characteristics of Al2O3 films in the electron cyclotron resonance (ECR) plasma are dependent upon the final baking temperature of the developed pattern. Preliminary plasma etching studies show that 15 nm lines on polysilicon can be etched.

Exposure mechanism of fullerene derivative electron beam resists

We report systematic studies of the response of C 60 derivatives to electron beam irradiation. Films of nine different methanofullerene C 60 monoadducts, produced by spin coating on Si surfaces, were irradiated with a 20 keV electron beam. All exhibited negative tone resist behaviour with a sensitivity much higher than that of C 60. In the case of derivatives with two polyether chains, the sensitivity was found to be linearly dependent upon the derivative mass, consistent with an increasing electron cross-section for larger derivatives. Features with widths of 20 nm were produced using these compounds, and the etch ratios of the compounds were found to be more than twice those of a standard novolac-based resist.

Versatile patterning process for semiconductorsbased on microcontact printing

A new patterning process based on the microcontact printing of self-assembled monolayers on gold is presented. The method is readily adapted to processes utilising standard optical or electron beam resists, and is fully compatible with industrial semiconductor fabrication technology. The process can also be applied to surfaces which exhibit extreme nonplanarity such as sharp edges of mesas or etch grooves.

A study of electron beam-induced conductivity in resists.

The charging of polymeric resist materials during electron beam irradiation leads to significant problems during imaging and lithography processes. Charging occurs because of charge deposition in the polymer and charge generation/trapping due to formation of electron-hole pairs in the dielectric. The presence of such charge also results in the phenomena of electron beam-induced conductivity (EBIC). Electron beam-induced conductivity data have been obtained for three commercial e-beam resists under a variety of dose rate and temperature conditions. From the observed values of induced conductivity under varying conditions significant information about the generation of electron-hole pair and the transport of charge in the resist can be obtained. Three electron beam resists, EBR900, ZEP7000, and PBS are examined by an external bias method. The difference in resist chemistry is considered to play the role in the initial state EBIC behaviors among three resists even though the way that it affects the behaviors is not clear. A comparison of the power consumption comparison is proposed as a measure to give a preliminary estimate of the carrier concentration and carrier drift velocity differences among the resists. A simple single trap model with constant activation energy is proposed and provides good agreement with experiment.

New High Resolution Liquid Crystal Electron Beam Resists

AbstractWe report the development of a new family of electron beam resists based on liquid crystalline polysubstituted derivatives of triphenylene. These new resists show excellent performance in terms of both high resolution and high durability to plasma etching. Films of the derivatives have been produced in a controlled manner via room temperature spin coating on hydrogen terminated silicon substrates. The dissolution behaviour of the derivatives in various organic solvents was altered by exposure to a 20 keV electron beam. The solubility of the derivative hexapentyloxytriphenylene, in polar solvents, was substantially increased by electron doses greater than ∼ 3 × 10-4 C/cm2 (positive tone behaviour). Doses greater than ∼ 2.5 × 10-3 C/cm2 led to negative tone behaviour in both polar and non-polar solvents. Other derivatives also demonstrated a reduction in their dissolution rate for doses between ∼ 1 × 10-3 and ∼ 7 × 10-3 C/cm2. The derivative sensitivity was found to be roughly proportional to the molecular mass. Negative tone patterns were found to have an etch durability ∼ 70 % greater than that of a conventional novolac based negative tone resist (SAL601). The performance of these new resists has been demonstrated by the definition of line and space patterns with a resolution of ∼ 14 nm, whilst structures with an aspect ratio of.∼ 50 to 1 were etched into the silicon substrate.

Design and synthesis of an optimum performance crosslinking resist based on poly (2,4-dimethylstyrene)

We have successfully synthesized and optimized a range of copolymers of 2,4-dimethylstyrene and 3/4-chloromethylstyrene (vinyl benzyl chloride, VBC) as high-performance single-stage-crosslinking electron-beam resists. The formulations were synthesized by a reproducible free-radical-initiated solution polymerization technique which has the merit of simplicity. While the product polymers are not monodisperse, and hence cannot achieve optimal lithographic contrast, they benefit from a structural feature which prevents chain scission during irradiation and hence increases the intrinsic sensitivity of the resist. Resists with sensitivities very close to target values of 5 and 12 μC cm-2 have been demonstrated, with negligible chain scission and lithographic contrast of 2.3. ©1999 Kluwer Academic Publishers

Synthesis of 2-Phenylallyl-ended Ply(.ALPHA.-Methylstyrene) and Application for Electron-Beam Resist.

Synthesis of 2-Phenylallyl-ended Ply(.ALPHA.-Methylstyrene) and Application for Electron-Beam Resist.

Silylated poly(4-hydroxystyrene)s as negative electron beam resists

Silylated poly(4-hydroxystyrene)s and radical polymerized 4-tert-butyldimethylsilyloxystyrene (TBDMSOSt) were examined as electron beam resists. Commercial poly(4-hydroxystyrene) (PHS) with Mw = 1.69 × 104 and Mw/Mn = 5.41 was silylated with 1-(trimethylsilyl)imidazole and tert-butylchlorodimethylsilane. Both silylation reactions proceeded quantitatively to afford trimethylsilylated PHS with Mw = 3.93 × 104 and Mw/Mn = 4.91, and tert-butyldimethylsilylated PHS with Mw = 4.08 × 104 and Mw/Mn = 3.81. These 2 silyl ether polymers acted as a negative working resist to electron beam (EB) exposure. Sensitivity and contrast of tert- butyldimethylsilylated PHS were not affected by prebake temperature around its Tg of 97°C, while those of PHS were dependent on prebake temperature around its Tg of 160°C. At a prebake temperature of 125°C, the sensitivity parameter and the contrast γ value were obtained as follows: 3.93 × 10−4 C cm−2 and 0.91 for PHS; 1.49 × 10−4 C cm−2 and 1.06 for trimethylsilylated PHS; 1.84 × 10−4 C cm−2 and 1.44 for tert-butyldimethylsilylated PHS. The silylation procedures obviously improved the sensitivity of PHS. TBDMSOSt was polymerized in bulk at 60°C with 2,2′-azobisisobutyronitrile (AIBN) as an initiator. The resultant poly(TBDMSOSt) possessed Mw = 3.01 × 105 and Mw/Mn = 1.92 and exhibited a sensitivity of 1.60 × 10−5 C cm−2 and a γ value of 1.47. More than 10 times enhancement of sensitivity was observed compared with tert-butyldimethylsilylated PHS. Such a high sensitivity is probably due to the high molecular weight of the bulk polymerized material. Poly(TBDMSOSt) resolved an isolated line of 0.20 μm width and 0.5 μm line and space patterns. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1151–1157, 1998

Silylated poly(4‐hydroxystyrene)s as negative electron beam resists

Silylated poly(4-hydroxystyrene)s and radical polymerized 4-tert-butyldimethylsilyloxystyrene (TBDMSOSt) were examined as electron beam resists. Commercial poly(4-hydroxystyrene) (PHS) with Mw = 1.69 × 104 and Mw/Mn = 5.41 was silylated with 1-(trimethylsilyl)imidazole and tert-butylchlorodimethylsilane. Both silylation reactions proceeded quantitatively to afford trimethylsilylated PHS with Mw = 3.93 × 104 and Mw/Mn = 4.91, and tert-butyldimethylsilylated PHS with Mw = 4.08 × 104 and Mw/Mn = 3.81. These 2 silyl ether polymers acted as a negative working resist to electron beam (EB) exposure. Sensitivity and contrast of tert- butyldimethylsilylated PHS were not affected by prebake temperature around its Tg of 97°C, while those of PHS were dependent on prebake temperature around its Tg of 160°C. At a prebake temperature of 125°C, the sensitivity parameter and the contrast γ value were obtained as follows: 3.93 × 10−4 C cm−2 and 0.91 for PHS; 1.49 × 10−4 C cm−2 and 1.06 for trimethylsilylated PHS; 1.84 × 10−4 C cm−2 and 1.44 for tert-butyldimethylsilylated PHS. The silylation procedures obviously improved the sensitivity of PHS. TBDMSOSt was polymerized in bulk at 60°C with 2,2′-azobisisobutyronitrile (AIBN) as an initiator. The resultant poly(TBDMSOSt) possessed Mw = 3.01 × 105 and Mw/Mn = 1.92 and exhibited a sensitivity of 1.60 × 10−5 C cm−2 and a γ value of 1.47. More than 10 times enhancement of sensitivity was observed compared with tert-butyldimethylsilylated PHS. Such a high sensitivity is probably due to the high molecular weight of the bulk polymerized material. Poly(TBDMSOSt) resolved an isolated line of 0.20 μm width and 0.5 μm line and space patterns. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1151–1157, 1998

Etching processes and characteristics for the fabrication of refractory x-ray masks

Refractory x-ray masks for a wide variety of pattern types were fabricated using tantalum silicon as the absorber material. Both positive (Shipley UVIII®) and negative (Shipley SNR200®) chemically amplified electron beam resists were exposed and the patterns transferred into a silicon oxynitride hardmask. The amorphous TaSi absorber was then etched using a Cl2/O2 reactive ion etch (RIE). From a mask manufacturing standpoint, the challenge is etching the wide variety of feature types that commonly occur in device processing. The overall etch process was characterized for the formation of both freestanding lines (using negative electron beam resist) and narrow trenches (using positive resist). RIE lag, feature shape dependence, and cross-mask uniformity in the etch bias were characterized for feature sizes down to 125 nm. The etch process has been implemented in a pilot line environment and is being used to produce product masks.

Copolymer approach to charge-dissipating electron-beam resists

During electron-beam lithographic exposure on insulating substrates, pattern distortions and displacements are observed due to charging of the surface. To alleviate these displacements, conducting polymers have been investigated in the past decade as negative-tone resists and as unimageable top or bottom layers in a multilayer stack. Our approach uses a graft copolymer: an acrylic backbone for the imaging performance of the resist and a conducting polymer grafted onto the backbone for the charge-dissipating performance. By using this system, the respective properties of the two components can be individually optimized for such properties as speed, etch resistance, solubility, and conductivity. This system also permits positive-tone single-layer imaging, which has not been achievable previously. High-resolution features (<0.10 μm), minimal pattern distortions, and no change in the clearing dose, were observed for graft copolymers containing <1% of the charge-dissipating component that were processed identically to commercially available PMMA resist.

Polycyanoacrylate electron beam resists deposited by the Langmuir–Schaefer technique

New co-polymers based on cyanoacrylates were used for the deposition of negative electron beam resists. Sensitivity and contrast were measured and patterns in chromium films were obtained using a wet etching process. One type of resist was found suitable for use in dry etching processes, but was not sensitive enough. On the contrary, the films of co-polymers of two other types based on heptylcyanoacrylate exhibited high values of sensitivity and contrast. The remarkable feature of studied co-polymers is the ability to form extremely uniform defectless films when deposited by the Langmuir–Schaefer (LS) technique onto heated substrates. This opens the way to deposit in few minutes films composed of 20–30 monolayers, which possess high protective properties, onto the substrates of large areas usually used in microelectronics. Such an approach enables one to decrease dust accumulation and to suppress formation of defects of other types. The films of various thicknesses were thus deposited onto glass plates of 126×126 mm size with chromium coatings and the quality of deposition was examined. Properties of films of these co-polymers and ordinary polycyanoacrylates were compared with each other.

Electron beam induced fragmentation of fullerene derivatives

Spin coating has been used to produce films of various chemical derivatives of C60 on the hydrogen terminated silicon (100) surface. Irradiation of these films using a 20 keV electron beam has been found to reduce substantially their dissolution rate in organic solvents such as monochlorobenzene and chloroform. Raman and FTIR spectroscopy have shown that the reduced solubility of the derivative films is due to fragmentation of the molecules. The electron dose threshold of the derivative films for fragmentation is between 10−3 and 10−2 C/cm2, suggesting that these derivatives could be used as electron beam resists.

A Fullerene derivative as an electron beam resist for nanolithography

We have explored the application of chemical derivatives of C60 as high-resolution electron beam resists. Facile spin coating was used to produce ∼100-nm-thick films of a C60 tris adduct (three functional groups) on Si surfaces. We find that these films function as high-resolution negative resists for electron beam lithography using monochlorobenzene as a developer. The film has a sensitivity of ∼1 mC/cm2 for 20 keV electrons, an order of magnitude higher than that of C60 itself, and the dry-etch durability is much better than that of conventional novolac based electron beam resists. Features with widths of 20 nm were produced.

Plasma Grafit Polymerized Styrene as an Electron-beam Resist

AbstractPlasma graft polymerized styrene was formed by a reactor with a parallel plate electrode system on a pulsed plasma polymerized styrene film in a monomer vapor, where the pulsed plasma polymerization was performed by a low frequency 100%pulse modulation of 13.56 MHz power source in styrene vapor. The pulse duration was varied in the range of 0.01∼1 sec and ON time/duty cycle ratio was 1/10 and 1/20. The processes were monitored by a quartz crystal microbalance. The initial stage of plasma polymerization and grafting are discussed in this paper. Also sub 100 nm lines and spaces pattern on the resist delineated by an electron-beam pattering machine was developed by hexane.

化学増幅ポジ型３成分系電子線レジストの設計と開発

化学増幅ポジ型３成分系電子線レジストの設計と開発