Negative Electron Beam Resists Research Articles

Study and comparison of resist characteristics for different negative tone electron beam resists

In this work, four types of negative electron beam resists are investigated. Electron beam lithography (EBL) experiments were conducted using EBL system ZBA23 (Raith) with the variable-shaped electron beam cross-section at 40 keV electron energy. Important electron beam resist characteristics such as sensitivity, dissolution rate, aspect ratio and sidewall developed profiles in the chemically amplified resist (CAR) SU-8 2000, non-CARs ma-N 2410 and ARN-7520, and inorganic negative resist HSQ XR-1514 are studied and compared. This study was motivated by the selection of a suitable resist for practical use such as large area gratings fabrication for optoelectronics.

Functionalization dependence of the electron beam sensitivity for a conformationally immobile calix[6]arene resist

Calixarenes form a group of compounds that have been studied as high resolution negative electron beam resists. In this work, resists based on a conformationally immobile calix[6]arene molecule were synthesized and their sensitivities measured while the number of attached functional groups was systematically varied. This provided a direct test of the effect of the degree of functionalization on the electron beam resist sensitivity. The synthesis produced two basic molecular conformations: a cone conformer and a 1,2,3-alternate conformer. The number of attached allyl groups was deliberately varied from 0 to 8 allyls in steps of 2 allyls per synthesis. The resulting nine different resists were exposed and contrast curves were measured by atomic force microscopy. The least sensitive were the unfunctionalized calix[6]arenes with threshold doses of about 2 mC/cm2. The fully functionalized conformers had threshold doses around 0.1 mC/cm2. The sensitivities of both conformers were found to scale directly with th...

Characteristics of negative electron beam resists, ma-N2410 and ma-N2405

We have characterized the electron beam lithography (EBL) properties of the new negative tone resists, ma-N2410 and ma-N2405. These negative resists reacts under low electron dose values from 10 to 140μC/cm2, tested using 10, 20, 28keV electron beam. There was negligible loss of pattern height, which was attributed to the combined dose of the incident electron beam and the backscattered electrons. Experimental tests were performed under various EBL writing conditions of dose value, developing time, line-width and resist thickness. Our investigation showed that these new commercially available resists have high resolution and high contrast with non-chemical amplification, useful for micro-fabrication application.

Comparison of high resolution negative electron beam resists

Four high resolution negative electron beam resists are compared: TEBN-1 from Tokuyama Corp. Japan, ma-N 2401XP and mr-L 6000.1XP from microresist technology GmbH Germany, and SU-8 2000 series from MicroChem Corp., USA. Narrow linewidth high density patterns are defined by 100kV electron beam lithography, and the pattern is transferred into silicon by a highly anisotropic SF6∕O2∕CHF3 based reactive ion etch process with a selectivity between silicon and the investigated resists of approximately 2. 20nm half-pitch lines and 10nm lines with a pitch down to 60nm are written and transferred into silicon.

Synthesis, characterization, and investigation of a conformationally immobile calix[6]arene as a negative electron beam resist

Calixarenes of a variety of molecular weights and with several different functional attachments have been studied as high resolution, high contrast negative electron beam resists. In this article, results are presented for a new type of calixarene molecule to be used as an electron beam resist. The molecule differs from previous calixarene resists through the use of bridging groups to limit its conformational mobility and by having only a partial functionalization of the available phenol units with allyl groups to enhance the resist sensitivity. Both the sensitivity and contrast of the calixarene were measured. The measured contrast was found to be 4, while the sensitivity was 3.6mC∕cm2 which is comparable to other fully functionalized calix[6]arene resists. A closer comparison of this calixarene with similar calixarenes indicates that the measured sensitivity is better than would be expected for this partially functionalized molecule and that full functionalization might not be necessary to obtain a significant benefit from the functional groups.

Studies on sensitivity and etching resistance of calix[4]arene derivatives as negative tone electron beam resists

Several lower rim derivatives of calix[4]arene are compared as high resolution negative tone resists for electron beam lithography (EBL). The sensitivity of these derivatives is discussed in this paper. The suitability of calix[4]arene derivatives as top layers in bilayer resist systems is evaluated in studies on the etching resistance in an oxygen plasma. It is demonstrated that etching resistance can be improved by silylation of the resist molecules. The use of tetra(trimethylsilyloxy)calix[4]arene is compared to a common silylation step of an exposed tetraallylcalix[4]arene resist.

Multi-adduct derivatives of C60 for electron beam nano-resists

Abstract Methanofullerenes, C 60 derivatives, work as negative type electron beam resists, which have 10-nm scale resolution and high dry-etch durability. Their sensitivity (∼10 −3 C/cm 2 ) is one order of magnitude better than that of C 60 . We studied side-chain dependence of the sensitivities of methanofullerene resists, and found that the methano bridge and >CO near the C 60 cage in the side chains play important roles in the sensitivity enhancement. We have improved the sensitivity further by synthesizing multi-adduct methanofullerene (four to six side chains), which has about two orders of magnitude higher sensitivity (3.8×10 −4 C/cm 2 ) than that of C 60 .

Amorphous molecular materials: development of novel negative electron-beam molecular resists

Novel molecular resist materials, 1,3,5-tris[2-(4-vinylphenylcarbonyloxy)phenyl]benzene ( o-VCTPB), 1,3,5-tris[3-(4-vinylphenylcarbonyloxy)phenyl]benzene ( m-VCTPB), and 1,3,5-tris[4-(4-vinylphenylcarbonyloxy)phenyl]benzene ( p-VCTPB), were designed and synthesized. They function as negative electron-beam resists, becoming insoluble in developer upon electron-beam exposure. The sensitivity of o-, m-, and p-VCTPB upon exposure to a 20-keV electron beam were 15, 46, and 30 μC cm −2, respectively. These materials permitted the fabrication of line patterns of 100–200 nm upon exposure to a 50-keV electron beam. It is shown that molecular resists are promising candidates for use in the future electron-beam lithography.

Nanoscale patterning of self-assembled monolayers by e-beam lithography

The resolution of e-beam lithography in standard resists is limited by the size of the molecules in the resist. High resolution e-beam resists therefore should not only show a specific sensitivity to electrons but also be thin and composed of small subunits. Self-assembled monolayers (SAMs) fulfil these criteria because they are homogeneous, highly ordered films of amphiphilic molecules with a typical thickness of 1–2 nm and an intermolecular spacing of 1–0.5 nm. We demonstrate that gold nanostructures can be fabricated using aliphatic and aromatic thiol self-assembled monolayers as positive and negative electron beam resists.

Electron beam lithography in passivated gold nanoclusters

We have employed thin films of passivated gold nanoclusters, deposited from solution onto a range of surfaces (graphite, silicon, thermally grown silicon dioxide and sputtered silicon dioxide), as a negative tone electron beam resists. The best resolution achieved to date is 26 nm. Response curves obtained for monolayer films on the SiO 2 surfaces indicate that the sensitivity depends on the substrate, attributed to backscattering of the primary beam (and secondary electron generation), as confirmed by Monte Carlo simulations.

Nanoscale patterning of self-assembled monolayers with electrons

We show the fabrication of gold nanostructures using self-assembled monolayers of aliphatic and aromatic thiols as positive and negative electron beam resists. We applied a simple and versatile proximity printing technique using focused ion beam structured stencil masks and low energy (300 eV) electrons. We also used conventional e-beam lithography with a beam energy of 2.5 keV and doses from 3500 to 80 000 μC/cm2. Gold patterns were generated by wet etching in KCN/KOH and characterized by atomic force microscopy and scanning electron microscopy. The width of the finest lines is ∼20 nm; their edge definition is limited by the isotropic etching process in the polycrystalline gold.

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

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.

Nanolithography Using Fullerene Films as an Electron Beam Resist.

Nanometer scale patterns have been fabricated using evaporated films of C60 and its derivative, C60(CH2)2(C10H6), as negative type electron beam (e-be am) resists. E-beam irradiation reduces the dissolution rate of the films in organic solvents such as monochlorobenzene. In addition, the rate of thermal sublimation in vacuum is also reduced by the exposure. These molecules have quite similar resist properties. They exhibits good resolution and high dry-etch durability. The performance of the resists was demonstrated by defining about 20nm dot patterns in the resist films and fabricating Si nanopillars, about 20nm in diameter and 100nm high, by subsequent plasma etching. The results of optical measurements suggest that the exposure mechanism of C60 resist may be due to destruction of the molecules by e-beam irradiation.

Polydiacetylene mono- and multilayer Langmuir-Blodgett films as electron beam resists: scanning electron microscope and Raman images

Multilayer Langmuir-Blodgett (LB) films of the diacetylene 10, 12-pentacosadyinoic acid (12-8 DA) have been successfully used as negative electron beam resists. Electron beam sensitivity and pattern quality have been optimized using Raman microscopy. Micrometre-sized aluminum features have been patterned using both wet etch and lift-off techniques. Submicrometre pattern features have been written onto the LB layers.

Relationship between electron sensitivity and chemical structures of polymers as electron beam resist. VII: Electron sensitivity of vinyl polymers containing pendant 1,3‐dioxolan groups

AbstractVinyl polymers containing pendant acetal groups were synthesized using (2,2‐dimethyl‐l,3‐dioxolan‐4‐yl)methyl acrylate (DMA) and (2,2‐dimethyl‐l,3‐dioxo‐lan‐4‐yl)methyl methacrylate (DMM), and were evaluated as negative electron beam (EB) resists. It was found that the EB sensitivity of polymers containing acetal groups in the side chain was higher than that of polymers containing acetal groups in the main chain. A high sensitivity of 3.6 × 10−8 C/cm2 was observed. Copolymers of DMA or DMM with styrene were also synthesized in order to improve the durability for dry etching process. It was found that the copolymers had an excellent dry etching durability and were adaptable to EB lithography.

Relationship between electron sensitivity and chemical structures of polymers as electron beam resists. VI: Electron sensitivity of various acetalized poly(vinyl alcohol)s

AbstractAcetalized poly(vinyl alcohol)s which were synthesized from poly(vinyl alcohol) (PVA) and aldehyde or ketone were evaluated as electron beam (EB) resists, in order to investigate the relationship between EB sensitivity and chemical structures of the polymers. It was found that the acetalized PVAs were easily crosslinked by EB exposure. The main mechanism of crosslinking may be radical reaction at acetal group. The sensitivity of the acetalized PVA depended on the structure of the acetal group. Acetalized PVAs synthesized from benzaldehyde, in which the electron attracting group was substituted on the benzene ring and from linear aliphatic aldehyde having a long alkyl chain, had high sensitivity. A high sensitivity of 7.2 × 10−7 C/cm2 was attained when the acetalized PVA synthesized from p‐chloro‐benzaldehyde was used. Acetalized PVAs synthesized from PVA and aldehyde having a cyclic structure had an excellent dry etching durability and were suitable as negative EB resists.

Reactive plasticizers in negative electron beam resists

Negative electron resists generally exhibit excellent sensitivity, but suffer from swelling during development which results in poor resolution. A new approach to this problem is presented, in which reactive monomers are blended with host polymers to provide sensitive negative resists with improved resolution. Polychloromethylstyrene (PCMS) and VMCH (a terpolymer containing 86% vinyl chloride, 13% vinyl acetate, and 1% maleic acid) were both found to be compatible with two reactive monomers, trimethylolpropanetrimethacrylate and dipentaerythritolpentaacrylate (DPEPA). Addition of 20 wt. % of either monomer to PCMS or VMCH resulted in approximately tenfold increases in sensitivity. Sensitivity increases dramatically with increasing monomer content, with a 1:1 blend of VMCH and DPEPA exhibiting a sensitivity of ∼0.15 μC/cm2. This represents a more than 100-fold increase in sensitivity over that of VMCH alone. These blends exhibit resolution of 0.5 μm. Blends of the reactive monomers with fractionated base polymers possessing low molecular weight and low polydispersities are promising. Low molecular weight PCMS and VMCH exhibit good contrast and resolution, but suffer from poor sensitivity. Addition of reactive monomers to these base polymers increases their sensitivity, while maintaining contrast and resolution that is superior to the high molecular weight unfractionated polymer alone. These blends exhibit less swelling than the host polymers.

Barium fluoride and strontium fluoride negative electron beam resists

The suitability of strontium and barium fluoride as electron beam resist materials has been studied. Their sensitivity to high energy electron beams was measured, and the exposure mechanisms were described using scanning transmission electron microscopy. The effect of crystallite size and film composition on the exposure and development conditions of these inorganic resist systems were investigated. Finally, these resists were directly used as etch masks on gallium arsenide, and their performance was evaluated. Both barium and strontium fluoride were found to be sensitive negative resists, requiring exposure doses of 25–100 μC/cm2. The resolution of pure strontium and barium fluoride is limited by the grain size of the original fluoride deposits. The resolution and development conditions were improved by deposition of a mixture of barium and strontium fluoride (of approximately 50 at. % BaF2 in SrF2), which yielded line resolutions of better than 100 nm. All of these fluorides are extremely resistant to reactive ion etching with halogen containing gases and can be used as etch masks to pattern GaAs.