Oregon Graduate Center

Jonathan H Orloff

Lynwood W Swanson

Joseph Puretz

Richard A Elliott

Richard K DeFreez

A method of forming one or more optical surfaces of the designer's choice in a body of material. The method includes the steps of exposing in a work zone a selected face in a body of selected material, directing a focused ion beam in a predetermined manner into the work zone to impinge the selected face, and by such directing and impinging, removing material from the body to create the desired optical surface(s). Preferably, beam direction is accomplished under the control of a suitably programmed computer.

Focused ion beam micromachining of optical surfaces in materials

A three element asymmetric lens system having a very low chromatic aberration coefficient is used in conjunction with a TFE electron source having an angular intensity of approximately 10.sup.-3 amperes per steradian to achieve precise focusing of the resulting electron beam despite the large energy spread thereof for beam, accelerating ratios in the range from 0.2 to 6.0. In one embodiment, an FI ion source is used in conjunction with the same type of lens system to initially visualize the surface of the integrated circuit. The ion beam then is rapidly focused on and scanned across a small area of passivation over an underlying metal conductor to sputter a hole through the passivation layer to the metal. A secondary electron collecting apparatus detects a large increase in the secondary electron emission when the ion beam reaches the metal. The electron beam then is scanned across the surface of the integrated circuit. The resulting secondary electrons are collected, amplified and input to the intensity control of a CRT, resulting in a display in which the brightness of the location of the milled hole accurately represents the voltage of the metal conductor.

Electron and ion beam apparatus and passivation milling

A liquid metal field ionization source is used in conjunction with a three element asymmetric lens system to provide an ion gun having greater magnitude beam currents focused on a smaller spot size than has been previously possible for intermediate energy beams. An ultra-clean emitter surface is achieved by means of an argon sputtering and/or plasma etching process applied to the emitter surface before liquid metal is applied to the emitter surface to ensure uniform and sufficient flow of liquid metal to the apex of the emitter. The three element asymmetric lens system has a very low chromatic aberration coefficient, enabling precise focusing of beams with large energy spreads. For beam accelerating ratios in the range from 0.2 to 6, the ion gun produces very high current densities in beams focused on very small spot areas, despite the relatively large energy spread of beams produced by liquid metal ionization sources. The energy spread of the ion beam is minimized by operating the emitter at a voltage close to the onset voltage and at a temperature close to the melting point of the liquid metal.

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Portland, OR, United States of America

Jonathan H Orloff