Naokatsu Ikegami

Active-matrix nanocrystalline Si electron emitter array with a function of electronic aberration correction for massively parallel electron beam direct-write lithography: Electron emission and pattern transfer characteristics

A planar nanocrystalline silicon (nc-Si) electron emitter array compatible with an active-matrix large-scale integrated (LSI) driving circuit has been developed for massively parallel electron beam direct-write lithography. The electron-emitting part of the device consists of a 50-μm-pitch and 200 × 200 arrays of nc-Si dots fabricated on a Si substrate, and via-first-processed through-silicon-via (TSV) plugs of poly-Si connected with the dots from behind the substrate. Tapered emitter-array etching and electrochemical-oxidation with subsequent annealing and super-critical rinsing and drying processes significantly enhanced the electron emission current by improving and stabilizing uniformity and reducing the process temperature. When the emitter array was driven, electrons were effectively injected into the nc-Si layer through the TSV plugs and quasiballistically emitted through the gold surface electrode. The nc-Si emitter responded to the input signal within times of 0.1 μs or less. A 1:1 pattern transf...

Active-matrix nanocrystalline Si electron emitter array for massively parallel direct-write electron-beam system: first results of the performance evaluation

Abstract. We present a prototype electron emitter array integrated with an active-matrix driving large-scale integrated circuit (LSI) for a high-speed massively parallel direct-write electron-beam (e-beam) system. In addition, we describe the results of a performance evaluation of it as an electron source for massively parallel operations. The electron source is a nanocrystalline Si (nc-Si) ballistic surface electron emitter in which a 1∶1 projection of the e-beam can resolve patterns 30 nm wide. The electron-emitting part of the device consists of an array of nc-Si dots fabricated on an SOI or Si substrate and through silicon via (TSV) plugs connected to the dots from the back of the substrate. The device consists of an aligned joint of TSV plugs with driving pads on the active-matrix LSI. Electron emissions are driven by the LSI and are boosted to an appropriate level using a built-in voltage level shifter in accordance with a bitmap image preliminarily stored in the embedded memory. Electron emissions from a test array work as intended, showing the possibility of switching on and off the beamlets by changing the CMOS-compatible voltage.

Development of ballistic hot electron emitter and its applications to parallel processing: active-matrix massive direct-write lithography in vacuum and thin-film deposition in solutions

Abstract. Making the best use of the characteristic features in nanocrystalline Si (nc-Si) ballistic hot electron source, an alternative lithographic technology is presented based on two approaches: physical excitation in vacuum and chemical reduction in solutions. The nc-Si cold cathode is composed of a thin metal film, an nc-Si layer, an n+-Si substrate, and an ohmic back contact. Under a biased condition, energetic electrons are uniformly and directionally emitted through the thin surface electrodes. In vacuum, this emitter is available for active-matrix drive massive parallel lithography. Arrayed 100×100 emitters (each emitting area: 10×10  μm2) are fabricated on a silicon substrate by a conventional planar process, and then every emitter is bonded with the integrated driver using through-silicon-via interconnect technology. Another application is the use of this emitter as an active electrode supplying highly reducing electrons into solutions. A very small amount of metal-salt solutions is dripped onto the nc-Si emitter surface, and the emitter is driven without using any counter electrodes. After the emitter operation, thin metal and elemental semiconductors (Si and Ge) films are uniformly deposited on the emitting surface. Spectroscopic surface and compositional analyses indicate that there are no significant contaminations in deposited thin films.

Development of a MEMS electrostatic condenser lens array for nc-Si surface electron emitters of the Massive Parallel Electron Beam Direct-Write system

Developments of a Micro Electro-Mechanical System (MEMS) electrostatic Condenser Lens Array (CLA) for a Massively Parallel Electron Beam Direct Write (MPEBDW) lithography system are described. The CLA converges parallel electron beams for fine patterning. The structure of the CLA was designed on a basis of analysis by a finite element method (FEM) simulation. The lens was fabricated with precise machining and assembled with a nanocrystalline silicon (nc-Si) electron emitter array as an electron source of MPEBDW. The nc-Si electron emitter has the advantage that a vertical-emitted surface electron beam can be obtained without any extractor electrodes. FEM simulation of electron optics characteristics showed that the size of the electron beam emitted from the electron emitter was reduced to 15% by a radial direction, and the divergence angle is reduced to 1/18.

Development of MEMS pierce-type nanocrystalline Si electron-emitter array for massively parallel electron beam direct writing

This paper mainly reports the process development of a Pierce-type nanocrystalline Si (nc-Si) electron emitter array for massively parallel electron beam (EB) lithography based on active-matrix operation using a large-scaled integrated circuit (LSI). The emitter array consists of 100×100 hemispherical emitters formed by isotropic wet etching of Si. EB resist patterning was demonstrated by 1:1 projection exposure using a discrete emitter array at CMOS-compatible operation voltages. To independently control each emitter using the LSI, isolation trenches filled with benzocyclobutene (BCB) were fabricated in the Si substrate. In addition, the integration process of the emitter array, the LSI and an extraction electrode plate was developed based on Au-In and polymer bonding technologies.

Simulation analysis of a miniaturized electron optics of the massively parallel electron-beam direct-write (MPEBDW) for multi-column system

In this study, a simulation analysis of a miniaturized electron optics for the Multi-Column Massively Parallel Electron Beam Writing system is demonstrated. Analytical evaluation of space charge effect with prototype Massively Parallel Electron Beam Writing (MPEBW) system showed 2.86 nm blur in radius occurs on each beam with a convergence half angle of 3 mrad. The angle of each beam was increased to 10 mrad to reduce the space charge effect, the coulomb blur amount can be kept to less than 1 nm in radius. However, there was limitation to increasing the angle due to a spherical aberration. Since the beam current density from the electron emitter array in the prototype MPEBW system was 100 μA/cm2 and the total beam current was 1μA with 100×100 array of 10μm square emitter, the influence of coulomb blur was small. By contrast, considerably increasing the number of beams and the beam current are planned in near future in MPEBW. The coulomb blur and other aberrations will not be controlled by merely adjusting the beam convergence angle. In order to increase total beam current, miniaturized electron optics have been designed for Multi-beam+Multi-column system. Reduction lens in the designed miniaturized electron optics with crossover free to reduce the influence of coulomb repulsion with narrow convergence half angle. Unlike conventional methods, the electron beams as principal rays do not intersect at one point, so even if the beam becomes extremely narrow, the coulomb repulsion effect does not increase at the crossover area. The reduction of the entire size of parallel beams in the designed electron optics was confirmed by simulation software. The simulation results showed that least confusion disk of 6.5 nm size was obtained at the beam convergence half angles of 3 mrad corresponding to the incident beam of ±0.1 mrad divergence angle. It showed that the miniaturized electron optics was suitable for 10 nm order EB writing. The crossover free electron optics of the miniaturized electron optics is possible due to dispersing the intersection points of the principal rays by a combination of a concentric electron optics and a tapered lens electrode of the reduction lens.

Fabrication of through silicon via with highly phosphorus-doped polycrystalline Si plugs for driving an active-matrix nanocrystalline Si electron emitter array

Present advanced-process for the fabrication of through silicon via (TSV) with highly phosphorus-doped n++-polycrystalline Si plugs for driving an active-matrix nanocrystalline Si (nc-Si) electron emitter array was described. The resistance per one TSV was measured to be 150 Ω, and voltage drop at the TSV plug in a normal driving operation was sufficiently small to apply the diode current to the nc-Si layer. Electrons could be effectively injected into the nc-Si layer from the back-side n++-poly-Si through the TSV plugs, and were quasi-ballistically emitted through the surface Ti/Au electrode.

Development of ballistic hot electron emitter and its applications to parallel processing: active-matrix massive direct-write lithography in vacuum and thin films deposition in solutions

Making the best use of the characteristic features in nanocrystalline Si (nc-Si) ballistic hot electron source, the alternative lithographic technology is presented based on the two approaches: physical excitation in vacuum and chemical reduction in solutions. The nc-Si cold cathode is a kind of metal-insulator-semiconductor (MIS) diode, composed of a thin metal film, an nc-Si layer, an n+-Si substrate, and an ohmic back contact. Under a biased condition, energetic electrons are uniformly and directionally emitted through the thin surface electrodes. In vacuum, this emitter is available for active-matrix drive massive parallel lithography. Arrayed 100×100 emitters (each size: 10×10 μm2, pitch: 100 μm) are fabricated on silicon substrate by conventional planar process, and then every emitter is bonded with integrated complementary metal-oxide-semiconductor (CMOS) driver using through-silicon-via (TSV) interconnect technology. Electron multi-beams emitted from selected devices are focused by a micro-electro-mechanical system (MEMS) condenser lens array and introduced into an accelerating system with a demagnification factor of 100. The electron accelerating voltage is 5 kV. The designed size of each beam landing on the target is 10×10 nm2 in square. Here we discuss the fabrication process of the emitter array with TSV holes, implementation of integrated ctive-matrix driver circuit, the bonding of these components, the construction of electron optics, and the overall operation in the exposure system including the correction of possible aberrations. The experimental results of this mask-less parallel pattern transfer are shown in terms of simple 1:1 projection and parallel lithography under an active-matrix drive scheme. Another application is the use of this emitter as an active electrode supplying highly reducing electrons into solutions. A very small amount of metal-salt solutions is dripped onto the nc-Si emitter surface, and the emitter is driven without using any counter electrodes. After the emitter operation, thin metal (Cu, Ni, Co, and so on) and elemental semiconductors (Si and Ge) films are uniformly deposited on the emitting surface. Spectroscopic surface and compositional analyses indicate that there are no significant contaminations in deposited thin films. The implication is that ballistic hot electrons injected into solutions with appropriate kinetic energies induce preferential reduction of positive ions in solutions with no by-products followed by atom migration, nuclei formation, and the subsequent thin film growth. The availability of this technique for depositing thin SiGe films is also demonstrated by using a mixture solution. When patterned fine emission windows are formed on the emitter surface, metal and semiconductor wires array are directly deposited in parallel.