Invited Paper AS-WeM5
A High Brightness Plasma Source for Next Generation FIB, SIMS and Surface Engineering

Wednesday, October 20, 2010, 9:20 am, Room Cochiti

Milling speeds with a gallium focused ion beam (FIB) are often much too slow for many sample preparation and surface engineering applications. For example, cross-sectioning stacked-die semiconductor devices, prototyping micro-mechanical structures and delayering IC’s for circuit mapping are growing applications that require a milling rate that far exceeds that provided by the gallium FIB.

Furthermore, secondary ion mass spectrometry (SIMS) imaging has been limited to a lateral resolution of 200nm when using an oxygen focused ion beam for high sensitivity surface analysis. Many applications in material science could benefit from an ability to image trace level surface chemistry with <20nm resolution. Example applications include, sub-cellular imaging of trace metals in the brain for neurodegenerative disease studies, analysis of trace element segregation in metal alloys and studying isotope distributions in meteorites and interplanetary dust particles.

In the more general area of direct-write surface engineering, precision milling and deposition with nanometer precision is limited to volumes of <10⁴um³ when using gallium FIB systems. Also, engineered devices must generally be tolerant of high gallium concentrations being implanted in the near-surface region. These are major restrictions when fabricating devices that require nanometer precision across dimensions of several hundred micrometers. Additionally, inherent gallium implantation can render structures bio-incompatible and compromise the electrical properties of many materials.

Here, we review a plasma ion source technology (Hyperion^TM) that can provide a focused ion beam capable of milling silicon at a rate of >5000um³/s with <4um milling resolution and <20nm imaging resolution with 30keV xenon ions. The same ion source is also readily operated as a high brightness source of oxygen, hydrogen and any inert ions.

By transferring energy to plasma electrons via a RF induction field, it is possible to create a plasma state without a cathodic electrode. This approach can create high plasma densities (>1x10¹³ ion cm^-3), with very low mean thermal ion energies (<0.05eV), providing the conditions for an energy normalized beam brightness that now exceeds 1x10⁴ Am^-2sr^-1V^-1. This high brightness can be attained with long lifetimes (>>2000 hours), stable beam current (<±0.5% drift per 30 minutes) and an axial energy spread for the extracted beam of 5-6eV and for an array of ion species.

This paper presents FIB and SIMS data from this new ion source. The operating principles of the ion source, the properties of the beam(s) being created and the projected future for this technology are also described.