Photomask / Direct Write Lithography Documents

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A thermally assisted field emission electron beam exposure system

Electron beam lithography is widely used to fabricate densely packed devices such as high-frequency transistors, since optical lithography is unable to write the small patterns required for such devices. One major problem with micropattern writing with an electron beam exposure system, however, is slow writing speed; since the system has to write an extremely large number of patterns on low-sensitivity resist with a highly focused beam, exposure times are quite long. To speed up the writing process, we have attached a thermal field emission gun to our electron beam exposure system. This gun is designed to increase the electron source brightness and probe current density. In order to determine this new probe current density, we conducted an extensive evaluation on a complete lithography system which uses a thermal field emission gun. We have measured a current density of ~ 1000 A/cm2 at an accelerating voltage of 25 kV and conclude that this lithography system can be put to practical use in production areas requiring high throughput and submicron exposures.

Nanobeam process system: An ultrahigh vacuum electron beam lithography system with 3 nm probe size

We have constructed a "nanobeam process system" which is applicable to high resolution electron beam lithography using inorganic resists and is also compatible with electron beam induced surface reaction. It is a 50 kV electron beam lithography system with a gas introducible ultrahigh vacuum sample chamber using a double chamber stage system which isolates stage mechanisms from the sample chamber. The probe size measured with a knife edge method was 2.8 nm, where the probe current was 127 pA. The base pressure of the sample chamber was 3.5X10-7 Pa after baking. The pressure of the gun chamber did not vary at all and the pressure rise of the mechanism chamber was 3X10-6 Pa when the pressure of the sample chamber increased to 1X10-3 Pa during N2 gas introduction. Standard deviations of stitching and overlay accuracy were 14 and 18 nm, respectively. Line patterns with a width of about 5 nm and a pitch of 15 nm were delineated in SiO2 when used as a high resolution resist.

Electron Beam Writing and Direct Processing System for Nanolithography

This article describes the electron beam direct processing system developed for patterning beyond the resolution limit of conventional resists by using inorganic resists or electron beam induced surface reactions. A probe beam with the probe current of 120 pA was focused into 3nm with the newly developed optical column. An ultra high vacuum sample chamber, which can coexist with a precise stage driving mechanism and a LASER measuring system. The base pressure of the sample chamber after baking was 1x10-8 Torr and differential evacuation of the sample chamber and the mechanism chamber was demonstrated. The stabilities of the stage and the optical column were measured with a LASER measuring system and mark detection procedures. The standard deviations of stitching and overlay accuracy measured by an exposure of PMMA resists revealed that this FB system can delineate the lines with the ultimate resolution of PMMA resists.

NANO PMGI Resists: Positive Radiation Sensitive Resists for Lift-off, Planarization, and Multilayer Applications

The PMGI SF Series of resist is widely used in multilayer DUV flood exposure processes for lift-off applications, but is also suitable for single layer or multilayer e-beam and x-ray use. It is used in planarization schemes, thin film head metallization, T-gate processes, air-bridge construction, microelectromechanical device fabrication, and SAW manufacture. Both cap-on and cap-off processes are available. It is also finding uses as an SOG replacement and as an LCD alignment layer as it has reasonable dielectric properties.

Fabrication of 5-7 nm wide etched lines in silicon using 100 keV electron-beam lithography and polymethylmethacrylate resist

The present limit of around 10 nm for the width of lines fabricated by e-beam lithography using polymethylmethacrylate (PMMA) resist on silicon substrates has been overcome. 5–7 nm wide etched lines in bulk Si substrates have been produced. A 65 nm thick layer of PMMA was exposed with an 80 kV electron beam of diameter smaller than 5 nm. After exposure the resist was developed in 3:7 cellosolve:methanol with ultrasonic agitation. The pattern in resist was transferred to the Si substrate with reactive ion etching. Lines of width varying between 5 and 7 nm were recorded using an S-900 scanning electron microscope which has a resolution of 0.7 nm.

Nanometer-scale patterning of high-Tc superconductors for Josephson junction-based digital circuits

A straightforward method for nanometer-scale patterning of high-Tc superconductor thin films is discussed. The technique combines direct-write electron beam lithography with well-controlled aqueous etches and is applied to the fabrication of Josephson junction nanobridges in high-quality, epitaxial thin-film YBa2Cu3O7. We present the results of our studies of the dimensions, yield, uniformity, and mechanism of the junctions along with the performance of a representative digital circuit based on these junctions. Direct current junction parameter statistics measured at 77 K show critical currents of 27.5 µA ±13% for a sample set of 220 junctions. The Josephson behavior of the nanobridge is believed to arise from the aggregation of oxygen vacancies in the nanometer-scale bridge.

Nanofabrication of subwavelength, binary, high-efficiency diffractive optical elements in GaAs

A single-etch-step process for the fabrication of high-efficiency diffractive optical elements is presented. The technique uses subwavelength surface relief structures to create a material with an effective index of refraction determined by the fill factor of the binary pattern. Fabrication is performed using electron beam lithography and reactive-ion-beam etching on bulk GaAs, but the process is applicable to any material for which well-controlled etches exist. In this work, we designed and fabricated a blazed transmission grating for operation at 975 nm. The blazed grating exhibits a diffraction efficiency into the first order of 85% of the transmitted power,

Novel high-yield trilayer resist process for 0.1 µm T-gate fabrication

By utilizing a novel ZEP/PMGI/ZEP trilayer resist process, GaInAs/AlInAs T-gate modulation-doped field effect transistors on InP with 0.1 µm gate lengths have been demonstrated. The trilayer resist requires only a single exposure. An overhang structure for liftoff, with a 0.1 µm footprint, is created by a sequence of infinitely selective developments for each layer. Linewidths as narrow as 65 nm have been obtained.