Yoshiyuki Takeishi

Effects of Crystallographic Orientation on Mobility, Surface State Density, and Noise in p-Type Inversion Layers on Oxidized Silicon Surfaces

Experimental results are reported concerning the anisotropy of surface state density, Nss, 1/f-type equivalent noise voltaze, VN, and field effect mobilitv, µFE, in p-channel MOS transistors with various crystallographic orientations in and zones. The amounts of VN and Nss are strongly correlated to each other, and both appear to be smallest around (811)-oriented surfaces. µFE under strong electric field normal to the surface shows no apparent correlation to Nss, but is markedly dependent on the direction of current flow on each surface except (111) and (100): µFE is maximum in the direction parallel to [01] on (011) plane and µFE⊥[01] is higher than µFE//[01] on the planes between (111) and (100). The mobility anisotropy is interpreted in terms of the effective mass anisotropy caused by quantized hole motion, considering that the energy band structure at high energy remarkably differs from the one at lower energy.

Electrical Properties of Metal-GaAs Schottky Barrier Contacts

Experimental studies are reported concerning surface states and current transport properties of the Schottky barrier diodes prepared by evaporation of various metals under high vacuum on chemically etched n-type GaAs (111) surfaces. Surface state density, determined from a relation of the barrier height and vacuum work function of metals, amounts to 7×1013 cm-2 eV-1 and the effective thickness of interfacial layer is estimated to be 3~8 A from an analysis of various diode characteristics. Density distribution of the surface states in the lower half of the band gap is derived. Dependences of current-voltage characteristics on donor concentration in the range 2×1015 to 5×1017 cm-3 and on temperature, 4.2 to 400°K, are accounted for in terms of thermionic-field emission and field emission theories. Effects of deep-lying donors on reverse characteristics and others are discussed. Changes in barrier properties by heat treatment at temperatures up to 400°C are presented.

A LOW‐ENERGY ELECTRON DIFFRACTION STUDY OF THE EPITAXIAL SILICON LAYERS ON A Ge(111) SURFACE

Silicon atoms were evaporated onto cleaned and annealed Ge(111) surfaces at a rate of 2 × 1014 atoms/cm2 min up to 40 min. Analyses of LEED patterns have revealed, on the substrate at 870°K, truncated tetrahedra consisting of reconstructed {311} and (111) planes, which have a 3 × 1 and a 7 × 7 superstructure, respectively. The 3 × 1 superstructure was observed on cleaned and annealed Si(311) surfaces in an independent experiment.

An Electron Beam Exposure System (VL-R1)

The system design and performance of a newly developed electron beam exposure system are reported. The basic operation is of a raster scan over a narrow field with a continuously moving stage. The system is capable of practical making of master masks and reticles including composite patterns. A pattern size as large as 105×105 dots is managed by a data compaction method and by a continuous data flow method from a magnetic disk to a DMA. LSI patterns of 2 µm geometry are delineated at a speed of 2 cm2/min. The electron charge density as high as 15 µC/cm2 at 20 kV was achieved.

Invited) Electron Beam Lithography in Practical Use for Integrated Circuits

Current requisites for practical electron beam lithographic technology that is expected for making photomasks are reviewed and discussed. Corresponding capability of a new raster-scan type electron beam exposure system is outlined. Some experimental results of exposing PMMA resists with the high electron beam current density (up to 700A/cm2) are reported. Examples of a large reticle pattern of 66×88 mm delineated by a 1 µm beam and of a model VLSI pattern of 1 µm geometry are presented.