Electron Beam Writing

This article reviews the progress made in the sub-10 nm electron beam patterning of metal oxides over the last thirty years. The patterning of inorganic resists began with metal halides, they were soon taken over by metal oxides due to their excellent environmental stability. However, these inorganic materials, both halides and oxides, suffered from the requirement of very steep dose, thus rendering them useless for practical applications. This gave way to highly electron beam-sensitive stabilized metal alkoxides and metal naphthenates, with sensitively close to conventional electron beam resists such as poly(methylmethacrylate) (PMMA) and calixarene. Furthermore, they show excellent line edge roughness characteristics at sub-10 nm scale, which is currently unmatched by any other electron beam resist. Recent applications of these resists such as an etch mask and their suitability as gate oxides will be highlighted.

The electron beam exposure characteristics of sputtered AlO x and spin-coatable Al 2 O 3 resists are compared and contrasted. When exposed to an electron beam, sputtered AlO x 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 Al 2 O 3 resist was prepared by reacting aluminum tri-sec-butoxide, Al͑OBu s ) 3 , with acetylacetone ͑AcAc͒ in isopropyl alcohol. These are negative tone resists and they are Ͼ10 6 times more sensitive to an electron beam than the sputtered AlO x , 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.

We report on e-beam lithographic (EBL) and reactive ion etching (RIE) experiments with the positive chemically amplified resist (CAR) CAMP6 used for the fabrication of silicon structures ranging in size from the nanometer scale up to the micron scale in relatively thick resist film. Direct-write EBL at 30 keV was used to study the pre-and post-exposure processing on the resulting resist-relief structures. We measured the basic resist characteristics and also the influence of proximity effects. The resolved single-layer resist-relief structures at optimised process conditions have shown high aspect ratios with nearly vertical side-walls and T-top profiles in 0.6-1.7 Ixm thick films up to nanometer lateral dimensions. The paper will discuss the deep pattern transfer results into the underlying 2.6 Ixm thick SiO 2 and/or directly into the Si-substrate by using RIE. We achieved excellent vertical side-walls free of passivation. The building of facets was observed to be on an acceptable scale. Keywords: Chemically amplified resist (CAR); E-beam lithography (EBL); Reactive ion etching (RIE); T-top profiles; Deep pattern transfer; Vertical side-walls free of passivation * Corresponding author. Elsevier Science B.V. SSDI: 0167-9317(95)00103-4 Peter Hudek was born in Bratislava, Czechoslovakia. He received the Dipl-Ing. degree in 1977 and the Dr.-Ing. degree in 1987 from the Electrotechnical Faculty of the Technical University Bratislava. In 1977 he joined the Institute of Technical Cybernetics of the Slovak Academy of Sciences in Bratislava. He has worked in the field of developing e-beam lithography systems for multilayer direct electron-beam writing. Since 1982 he is in charge of developing experimental and theoretical models of sub micro-and nanometer processes for special devices. Currently he is a project leader at the Institute of Computer Systems and his research interests include non conventional lithographic and plasma processing techniques for microlithographic master-masks fabrication. I.W. Rangelow was born in Lom, Bulgaria. He received the Dipl.-Ing degree in 1977 and the Dr. Sci.(Eng.) degree in 1981 from the Electron Technology Faculty of the Technical University Wroclaw, Poland in field of ion beam etching, microlithography, and ion beam sources.

The electron-beam response of new chemically amplified positive multi-component ARCH-resist family (ARCH and ARCH2) and the suitability of pattern transfer through single layer has been evaluated. The electron-beam lithographic parameters for thicker layers (1-2~tm) of these resists and the optimization possibilities of the exposure and etching conditions were investigated as well. Under fixed resist-handling processes, both resists exhibit high sensitivity (< 101aC/cm0 and an enormous high contrast. The study includes the effects of resist-process variations on the global 3-D resist-relief structure. Vertical side-walls of the resist profile is a necessary condition for a successful deep-, and a good CD-controlled anizotropical pattern transfer with high aspect ratio of structures into the substrate.

209-212 209 Elsevier Improved Resist Contrast with Novolac based E-beam Resists using Modified Development Procedures. R. Jonckheere, N. Samarakone, L. Van den hove, and I. Daraktchiev* IMEC, Kapeldreef 75, B-3030, Leuven, Belgium *Olin Hunt NV, Europark-Noord 17-18, B-2700, St Niklaas, Belgium Improvements in the contrast of e-beam exposed resists have been reported via the use of multiple interrupted development techniques. Additional baking is claimed to effect greater improvements in optical lithography. This so called intermediate development bake or (IDB) process, has recently been further simplified through adoption of a warm water treatment for the baking step. In the w_arm water IDB process, the need to spin dry wafers is eliminated, thereby improving development throughput. We report on the application of all of these treatments to resists exposed using e-beam. Contrast curves obtained with multiple ww IDB processes at different temperatures and times are presented and compared with those obtained utilizing conventional development with varying PEB conditions. The effect on sizing both the top and base of the resist image as a function of exposure is also examined. Olin Hunt HEBR 214 has been at the focus of our work, although we additionally report on HEBR 242 and HPR 204, as well as Aspect System 912.

We report on e-beam lithographic (EBL) and reactive ion etching (RIE) experiments with the positive chemically amplified resist (CAR) CAMP6 used for the fabrication of silicon structures ranging in size from the nanometer scale up to the micron scale in relatively thick resist film. Direct-write EBL at 30 keV was used to study the pre-and post-exposure processing on the resulting resist-relief structures. We measured the basic resist characteristics and also the influence of proximity effects. The resolved single-layer resist-relief structures at optimised process conditions have shown high aspect ratios with nearly vertical side-walls and T-top profiles in 0.6-1.7 Ixm thick films up to nanometer lateral dimensions. The paper will discuss the deep pattern transfer results into the underlying 2.6 Ixm thick SiO 2 and/or directly into the Si-substrate by using RIE. We achieved excellent vertical side-walls free of passivation. The building of facets was observed to be on an acceptable scale. Keywords: Chemically amplified resist (CAR); E-beam lithography (EBL); Reactive ion etching (RIE); T-top profiles; Deep pattern transfer; Vertical side-walls free of passivation * Corresponding author. Elsevier Science B.V. SSDI: 0167-9317(95)00103-4 Peter Hudek was born in Bratislava, Czechoslovakia. He received the Dipl-Ing. degree in 1977 and the Dr.-Ing. degree in 1987 from the Electrotechnical Faculty of the Technical University Bratislava. In 1977 he joined the Institute of Technical Cybernetics of the Slovak Academy of Sciences in Bratislava. He has worked in the field of developing e-beam lithography systems for multilayer direct electron-beam writing. Since 1982 he is in charge of developing experimental and theoretical models of sub micro-and nanometer processes for special devices. Currently he is a project leader at the Institute of Computer Systems and his research interests include non conventional lithographic and plasma processing techniques for microlithographic master-masks fabrication. I.W. Rangelow was born in Lom, Bulgaria. He received the Dipl.-Ing degree in 1977 and the Dr. Sci.(Eng.) degree in 1981 from the Electron Technology Faculty of the Technical University Wroclaw, Poland in field of ion beam etching, microlithography, and ion beam sources.

A silicon on insulator field effect transistor for cryogenic operation has been fabricated using a sol-gel derived TiO 2 electron beam resist as a high-k gate dielectric and characterized over a range of temperatures. The TiO 2 dielectric layer allows too large a gate leakage current for good device operation at room temperature, but the leakage current is strongly suppressed at cryogenic temperatures and good transistor characteristics were observed. The temperature dependence of the gate leakage current suggests that Frenkel-Poole and trap-assisted tunneling dominates the conduction in the dielectric layer. The drain current shows peaks at certain frequencies under continuous wave microwave irradiation, which may be caused by the resonance of electrons trapped in defects at the TiO 2 / SiO 2 interface. These resonances offer the possibility to manipulate single electrons for nonclassical information processing.

We describe a direct write technique using an electron beam to pattern ZrO 2 on a sub-10 nm scale that bypasses the conventional method of sputtering and lift-off. This technique utilizes spin-coatable ZrO 2 resist prepared by chemically reacting zirconium n-butoxide with benzoyl acetone in ethanol. The patterned resist has a sensitivity and contrast of ∼40 mC cm −2 and 3, respectively. Baking the resist at 85 • C increases the sensitivity to ∼9 mC cm −2 . The electron-beam-exposed regions become insoluble in acetone, thus yielding negative patterns. This property was exploited to write high-resolution patterns as small as 9 nm wide. Such negative patterns can be written with a pitch as close as 30 nm.

Focused electron beam induced etching (FEBIE) with chlorine as etching agent has been used to geometrically shape and to electrically modify semiconductor nanodevices. Selected sections of monocrystalline nanowires were modified directly without the requirement for a photomask or a resist layer. FEBIE as a subtractive nanofabrication technology allows to locally etch active semiconductor devices made of Si or Ge. In this work, chlorine is used as the etchant gas to thin germanium channel structures fabricated by standard photolithography. For effective material removal a sufficiently high electron influence is essential to avoid the pitfalls of this method. Topography and conductivity of FEBIE-modified structures prior and after the etching process was studied by AFM and by electrical I–V characteristics. The presented work demonstrates the potential of Cl-based FEBIE for device prototyping and electrical trimming of future Ge-based nanodevices.

Electron beam-sensitive spin-coatable Al 2 O 3 resists were prepared by chemically modifying aluminium tri-sec-butoxide with various β-ketoesters (R-acetoacetates, R = methyl, ethyl, isopropyl, isobutyl, isoamyl, heptyl, benzyl and 2-[methacryloyloxy] ethyl) in isopropyl alcohol. The reaction product was a chelated complex. With increasing molecular weight of R, there was an increase in electron beam sensitivity of spin-coatable Al 2 O 3 resists. This appears to be due to decreased stability of the chelated complex formed by higher molecular weight R-acetoacetates. Fourier transform infrared (FTIR) spectroscopy studies indicate that exposure to an electron beam results in the breakdown of chelate rings, making the exposed area insoluble during development. Electron beam nanolithography produced 8 nm wide lines. These are the smallest oxide lines written using a sol-gel-based resist.

The electron beam exposure characteristics of sputtered AlO x and spin-coatable Al 2 O 3 resists are compared and contrasted. When exposed to an electron beam, sputtered AlO x 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 Al 2 O 3 resist was prepared by reacting aluminum tri-sec-butoxide, Al͑OBu s) 3 , with acetylacetone ͑AcAc͒ in isopropyl alcohol. These are negative tone resists and they are Ͼ10 6 times more sensitive to an electron beam than the sputtered AlO x , 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.

The transient behavior of a trapped electron in the TiO 2 sol-gel based gate dielectric layer of a silicon-on-insulator metal-oxide-semiconductor field effect transistor is investigated. Defects in this dielectric layer give rise to microwave resonances that are electrically detected via the channel current. The lifetime of the excited state is inferred from the quality factor of the resonance. A single shot measurement, carried out on the same resonance, is used to characterize the transient behavior and to directly measure the lifetime of the excited state. Possible applications of transient measurements on high-k dielectric layers are discussed.