We observe the magnetic-field-induced bifurcation of quantum levels into surface states and bulklike Landau states. The disruption of the electric field quantization by a magnetic field is most dramatic for electrons bound in two dimensions perpendicular to the magnetic field. The interplay between competing spatial and magnetic quantization mechanisms results in a pronounced and complex level splitting. The observed splitting of zero-dimensional energy levels depends critically on the size of the quantum dots, and can be explained with a calculated single-particle energy spectrum.PACS numbers: 73.20.Dx, 73.40.Kp, 73.50.Jt For more than half a century confined electron systems in a magnetic field have been investigated theoretically in terms of their influence on the Landau diamagnetism of free electrons. 1 " 3 Investigations of surface states in confined electron systems have been revived more recently in order to explain the quantized Hall effect. 4,5 Their skipping orbit nature is also demonstrated by transport measurements with ballistic point contacts. 6,7 The influence of edge states on the properties of the electron system is expected to increase with decreasing system size and even more dramatically with decreasing dimensionality. In an electron system that is free to move in only one dimension perpendicular to the magnetic field each electric subband transforms into a hybrid band when the magnetic length /# = (ft/e/?) 1/2 becomes comparable to the width of the electron system. With increasing magnetic field the energy separation between adjacent hybrid bands approaches the cyclotron energy and the density of states at the bottom of each hybrid band increases, so that the bands become Landau-level-like at high magnetic fields. There is a continuous transition and a one-to-one correspondence between the electric subband structure at zero-magnetic field and Landau-level-like hybrid bands at high-magnetic field. 8 " 10 In contrast a far more complex behavior is predicted for zero-dimensional (OD) systems. 1 " 3 At zero magnetic field the discrete energy levels are each occupied by two electrons except for degeneracies that depend on the symmetry of the confinement. With increasing magnetic field this degeneracy is lifted and hybrid levels originating from the same zero-field energy level join different Landau levels at high magnetic field. In general, there is no one-to-one correspondence between energy levels at zero magnetic field and Landau levels at high magnetic fields.The splitting of OD energy levels at low magnetic field is similar to the normal Zeeman splitting of electronic states in atoms. However, in atomic physics the magnetic field is usually a weak perturbation of the Coulomb confinement. To observe Landau-level-like behavior of atomic electrons either the magnetic field must be several orders of magnitude larger than those experimentally realizable today 11 or the atoms must be highly excited. 12 Because of the low effective mass and the high dielectric constant the hydrogenic states of s...

Physical phenomena underlying failure due to electromigration and stress-induced voiding in fine AI and AI-alloy thin-film conducting lines are examined in the context of accelerated testing methods and structures. Aspects examined include effects due to line isolation (the absence of reservoirs at conductor ends), solute and precipitate phenomena, conductor critical (Blech) length, microstructure, film deposition conditions, and thermal processing subsequent to film deposition. Emphasis is on the isolated, submicron-wide, AI(Cu)-based thin-film interconnection lines of IBM VLSI logic and memory chips. "Copyright 1995 by International Business Machines Corporation. Copying in printed form for private use is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract, but no other portions, of this paper may be copied or distributed royalty free without further permission by computer-based and other information-service systems. Permission to republish any other portion of this paper must be obtained from the Editor.

The Aharonov-Bohm (AB) interference patterns in ring-shaped conductors are usually dominated by random features. The amplitude of the oscillations is random from sample to sample and from point to point on the magnetic field axis owing to random scattering of the electron trajectories by impurities within the wires. We report experiments on new devices made with wet etching and global gates, which have shown major progress towards removing the random features. In loops that exhibit ballistic conductance plateaux and cyclotron orbit trapping at 4.2K, the random pattern of AB oscillations (observed for T < 0.1K) can be replaced by much more ordered one -especially if only a few transverse modes are populated in the ring. The amplitude and shape of the oscillation envelope function change systematically as subbands are populated in the wires forming the loops. Mechanisms governing the AB effect in the ballistic regime are discussed. Correlation has been found between the G(V g , B = 0) staircase and the "beating period" of the envelope functions. Quantum oscillations in G(V g , B = 0) are consistent with direct interference of paths of unequal length. Both the correlations and the quantum oscillations in gate voltage are signatures of ballistic transport.

A heavy ion implanted pocket 0.10 μm ntype metal-oxide-semiconductor field effect transistor with hybrid lithography (electronbeam/deep ultraviolet) and specific gate passivation process ZEP-520 and KRS resist systems have been evaluated as candidates for use in low voltage electron beam lithography. ZEP-520 is a conventional chain scission resist which has a positive tone for over two orders of magnitude in exposure dose. KRS is a chemically amplified resist which can be easily tone reversed with a sensitivity ϳ8 C/cm 2 at 1 keV. Both resist systems are shown to have sensitivities ϳ1 C/cm 2 for positive tone area exposures to 1 keV electrons. A decrease in contrast in 50 nm thick resist layers is seen when exposure voltage is lowered from 2 to 1 keV, indicating nonuniform energy deposition over the resist thickness. High resolution single pass lines have been transferred into both Si and SiO 2 substrates at both low and high voltages in each resist system without using multilayer resist masks. The ZEP-520 and KRS resists are shown to have resolutions of 50 and 60 nm, respectively, at 1 kV, within a factor of 2 of their high voltage resolutions under identical development conditions. A cusp shaped etch profile in Si allows high aspect ratio 20 nm wide trenches to be fabricated using these resists on bulk Si. Low voltage exposures have been used to pattern gratings with periods as small as 75 and 100 nm in ZEP-520 and KRS, respectively. Low voltage exposures on SiO 2 show no indications of pattern distortion due to charging or proximity effects.

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