Electron Beam Resists Research Articles

Characterization of Line Edge Roughness in Resist Patterns by Using Fourier Analysis and Auto-Correlation Function

We have evaluated periodicity of line edge roughness (LER) in electron beam (EB), KrF, and ArF resists. A set of 512 edge-point coordinates was obtained for a scanning electron microscope (SEM) image of one edge by using an in-house image-processing program. The edge-point fluctuations were given and analyzed by Fourier transform and auto-correlation function. Fourier analysis has shown that (1) the spatial frequency (f) distribution of LER can be described with the 1/f-rule and (2) an additional component appears at around 100 nm in the results from several kinds of ArF resists. The auto-correlation-function method gives histograms of the basic period of LER. The results from this method are consistent with those from Fourier analysis and show that several ArF resist samples have a specific period distribution at around 240 nm. Results from both of these methods show that not only the resist materials but also the lithographic tools and processes affect the period distribution.

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.

Measurement of resist response to heating

Resist heating is one of the major contributors to errors in high-throughput maskmaking using electron-beam lithography. Temperature affects the physical and chemical properties of resists. Response of resist sensitivity to the temperature was measured for a number of electron-beam resists. The following resists were characterized: PMMA, PBS, SPR-700, EBR-900, ZEP-7000, and chemically amplified resist UVII-HS. Two methods were used for such measurements: (a) using a heated stage, the temperature of which was controlled externally, (b) using a test pattern exposed at regular exposure conditions. Nonlinearity of sensitivity response was found for a number of resists. A resist heating quality parameter was introduced which allowed a practical comparison of resists in terms of heating. Resists were compared using this parameter.

Study on Radiation-Induced Reaction in Microscopic Region for Basic Understanding of Electron Beam Patterning in Lithographic Process (I) –Development of Subpicosecond Pulse Radiolysis and Relation between Space Resolution and Radiation-Induced Reactions of Onium Salt–

In the acid generation processes of chemically amplified electron beam and X-ray resists, the ionization of a base resin plays an important role. A proton is generated from the cation radical of the base resin. On the other hand, a counter anion is generated from an acid generator after the reaction of the acid generator with the electron generated by the ionization of the base resin. In the resist materials in which both the radical cation of base resin and the electron play important roles in forming a latent image, the initial separation distance between the cation radical and the electron and the subsequent reactions immediately after irradiation are important for the fabrication of nanoscale patterns. For the understanding of electron beam and X-ray patterning, we developed a subpicosecond pulse radiolysis system for conducting the absorption spectroscopy and investigated the reactions of onium salt. The onium salt efficiently reacts with an electron generated by ionization. The high efficiency of reaction of an onium salt with an electron is thought to block the migration of a thermalized electron in the resist matrix and prevent the degradation of the space resolution of resists caused by the migration of the thermalized electron.

Investigating Line-Edge Roughness in Calixarene Fine Patterns Using Fourier Analysis

The line-edge roughness (LER) of patterns of negative-tone electron-beam resists, methyl-acetoxy calix[n]arene (n=6–8), was investigated using Fourier analysis. LER measurements were carried out by determining the intensity peaks of the pattern edges in scanning electron micrographs. The Fourier analysis showed that the roughness of the resist materials produced large peaks in the 10 to 100 nm wavelength range. The total intensity of LER spectra clearly depended on the electron dose and the “n” number of the calixarene resists. The smallest LER was observed in the calix[7]arene films. In contrast, the calix[6]arene films had a relatively large intensity in their Fourier spectra. X-ray diffraction measurements (XRD) revealed crystallization in the calix[6]arene films and an amorphous phase in the calix[7]arene and calix[8]arene films.

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 .

Analysis of Pattern Collapse of Electron Beam Resist Ranging from 60 to 152 nm Width With Atomic Force Microscope Tip

Analysis of Pattern Collapse of Electron Beam Resist Ranging from 60 to 152 nm Width With Atomic Force Microscope Tip

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.

Recent progress in electron-beam resists for advanced mask-making

Resists for advanced mask-making with high-voltage electron-beam writing tools have undergone dramatic changes over the last three decades. From PMMA and the other early chain-scission resists for micron dimensions to the aqueous-base-developable, dry-etchable chemically amplified systems being developed today, careful tuning of the chemistry and processing conditions of these resist systems has allowed the patterning of photomasks of increasing complexity containing increasingly finer features. Most recently, our research efforts have been focused on a low-activation-energy chemically amplified resist based on ketal-protected poly(hydroxystyrene). These ketal resist systems, or KRSs, have undergone a series of optimization and evaluation cycles in order to fine-tune their performance for advanced mask-fabrication applications using the 75-kV IBM EL4+ vector scan e-beam exposure system. The experiments have led to an optimized formulation, KRS-XE, that exhibits superior lithographic performance and has a high level of processing robustness. In addition, we describe advanced formulations of KRS-XE incorporating organometallic species, which have shown superior dry-etch resistance to novolak-based resists in the Cr etch process while maintaining excellent lithographic performance. Finally, current challenges facing the implementation of a chemically amplified resist in the photomask manufacturing process are outlined, along with current approaches being pursued to extend the capabilities of KRS technology.

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 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.

System for measurement of the development parameters of electron beam resists

AbstractThe accuracy of profile simulation calculations depends heavily on the accuracy of the parameters used. In particular, the development parameters, which represent the development characteristics (profile and sensitivity) of the resist, have a significant effect on profile simulation accuracy. However, as yet there have been almost no studies into methods used to calculate the development parameters for electron beam lithography, nor have there been comparisons of simulation results using these development parameters with observed resist profiles. In light of this, the authors have developed a system for the measurement of development parameters for use in simulations of electron beam lithography, and have undertaken study into the methods used to calculate such development parameters. In addition, the authors have also attempted to compare simulation results with observed resist profiles. Specifically, a diazanaphthoquinone–novolac resin positive‐type electron beam resist and a chemically amplified positive‐type electron beam resist were used, to which the Fujino development rate equation and the Mack development rate equation were applied. Trial calculations of the development parameters were performed, and the parameters thus obtained were input into a ProBEAM/3D electron beam lithography simulator. The electron beam resist profiles were simulated and compared with SEM images of actual resist samples. From the results it was found that both the Fujino and Mack development rate equations accurately reproduce resist behavior for the novolac positive‐type electron beam resist, whereas the Mack development rate equation was more accurate than the Fujino equation for the chemically amplified positive‐type electron beam resist. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(4): 16–25, 2001

Fabrication of SIS junctions for space borne submillimeter wave mixers using negative resist e-beam lithography

We report on the development of a new process for the fabrication of Nb/Al-AlO/sub x//Nb tunnel junctions for channel 1 (480-640 GHz) Superconductor-Insulator-Superconductor (SIS) mixers of HIFI, the Heterodyne Instrument for FIRST (Far InfraRed & Submillimeter Telescope). The process is derived from a standard self-aligned lift-off process but uses negative resist electron beam lithography (EBL) for junction definition. The junction area is tightly controlled down to below 1 /spl mu/m/sup 2/ without the complexity of processes using positive electron beam resists. We describe process parameters and experimental results: DC-tests and Fourier Transform Spectrometer (FTS) measurements.

Organic-Inorganic Hybrid Type Electron Beam Resist.

Organic-Inorganic Hybrid Type Electron Beam Resist.

Polysubstituted derivatives of triphenylene as high resolution electron beam resists for nanolithography

We have explored the application of polysubstituted derivatives of triphenylene as high resolution, high etch durability electron beam resists. Room temperature spin coating was used to produce films of the derivatives on silicon substrates. Exposure to a 20 keV electron beam was found to alter the dissolution rate of these derivatives in various organic solvents. Doses of between ∼3×10−4 and ∼2.5×10−3 C/cm2 substantially increased the solubility of the derivative hexapentyloxytriphenylene in polar solvents (positive tone behavior). Doses greater than ∼2.5×10−3 C/cm2 led to a decrease in solubility in both polar and nonpolar solvents (negative tone behavior). Other derivatives also demonstrated a reduction in their dissolution rate for doses between ∼1.5×10−3 and ∼6.5×10−3 C/cm2. The etch durabilities of the positive and negative tone patterns were found to be, respectively, ∼25% less and ∼70% greater than that of a conventional novolac based negative tone resist. Line and space patterns were defined in one of the resists with a resolution of ∼14 nm and structures with an aspect ratio of ∼50–1 were etched into silicon.

Influence of developer and development conditions on the behavior of high molecular weight electron beam resists

The nature of the developer and development conditions of high molecular weight electron beam resists is known to influence sensitivity, contrast, line edge roughness, and ultimate resolution. These resist characteristics are explained using a dissolution model based on reptation theory and predictions are compared with experimental results on high molecular weight poly(methylmethacrylate) developed in a range of solvent mixtures and conditions, including ultrasonically assisted development.

Comparative study of sputtered and spin-coatable aluminum oxide electron beam resists

The electron beam exposure characteristics of sputtered AlOx and spin-coatable Al2O3 resists are compared and contrasted. When exposed to an electron beam, sputtered AlOx resists on a silicon substrate undergo an intense mass loss. However, electron energy loss spectroscopy shows that even after a prolonged exposure some aluminum and oxygen remains on the silicon surface. Spin-coatable Al2O3 resist was prepared by reacting aluminum tri-sec-butoxide, Al(OBus)3, with acetylacetone (AcAc) in isopropyl alcohol. These are negative tone resists and they are >106 times more sensitive to an electron beam than the sputtered AlOx, bringing its sensitivity very close to high resolution organic resists such as calixarene. The exposure properties of spin-coatable and sputtered aluminum oxide resists are discussed together with their sensitivity, damage mechanisms, line edge roughness, and etching characteristics. A brief note on the change of methodology of resist design is added when inorganic resists are to be used in high resolution electron beam nanolithography.

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.

The thermal chemistry of model organosulfur compounds on gallium arsenide (110)

Organothiols and related organosulfur compounds hold promise for use as self-assembled ultra-thin electron beam resists, II–VI material growth precursors, and monolayer passivation layers. We report the results of temperature-programmed reaction and desorption (TPR/D) studies of the surface chemistry of three model organosulfur compounds, CH 3SH, (CH 3S) 2 and (CH 3) 2S, on the (110) face of gallium arsenide. Our measurements indicate that each of these species interacts strongly with the GaAs(110) surface. The first monolayer of CH 3SH desorbs at ∼300 K, with a desorption wave peak temperature (extrapolated to the zero coverage limit) corresponding to a desorption activation energy of 0.81 eV. This value is high compared to ∼110 K for the second layer, suggesting a chemical interaction between the thiol and the surface, despite the fact that the monolayer feature in the TPR/D spectra exhibits first-order kinetics, and the molecule is observed to desorb intact. The behavior of (CH 3S) 2 is markedly different; the disulfide decomposes upon adsorption (or during the TPR/D temperature ramp) and desorbs predominantly as (CH 3) 2S at ∼500 K, perhaps as the result of a concerted associative/dissociative desorption process that leaves sulfur at the surface. This result is also evidence that adsorbed CH 3SH and (CH 3) 2S do not assume equivalent surface-bound forms and supports the idea that the hydrogen atom of the thiol remains in close association with the adsorbed parent molecule, while the disulfide undergoes dissociative adsorption. Finally, our results indicate that (CH 3) 2S, like CH 3SH, molecularly adsorbs/desorbs. The desorption activation energy, extrapolated to zero coverage, is 0.79 eV, consistent with a strong adsorbate–substrate interaction. The similarity of this value to that for CH 3SH suggests that a specific sulfur–surface interaction dominates the desorption kinetics at low coverage. In the monolayer regime, with increasing exposure, the monolayer desorption feature in the TPR/D spectra broadens and exhibits strong asymmetry, and ultimately develops a lower temperature feature, indicating complex kinetics consistent with coverage-dependent phase behavior. Finally, by comparison of the measured desorption energies of the organosulfur compounds with those of the alkyl halides, for which the adsorption on GaAs(110) has been extensively investigated, an estimation of the chemical and physical contributions to the molecule–surface interaction is obtained. Our analysis suggests that both types of interactions play important roles in the adsorption energetics.

Nanolithography by Electron Beam Resist-trimming Technique

AbstractWe have investigated a resist-trimming process for SAL601 chemically amplified negative electron beam resist. Ultra-fine SAL601 resist patterns with a width of 16nm were obtained by an isotropic trimming process in oxygen plasma. This pattern resolution in SAL601 could not be obtained through direct electron beam lithography alone. Using the trimmed electron beam resists, we have successfully fabricated ultra-fine poly-silicon patterns of less than 20nm width. We applied this nanolithography technique to fabricating an ultra-small metal-oxide-semiconductor field-effect-transistor (MOSFET) and revealed that this trimming process is a useful method for nanometer-scale silicon device fabrication.