In situ process could cause scientific revolution

11/01/1998

In situ process could cause scientific revolution

A mobile instrument being rolled around Bell Labs could change in situ particle detection during wafer processing from an art to a science and could have a major impact on semiconductor manufacturing. The experimental instrument can determine, in real time, the size and complete elemental makeup of particles from 0.9 ?m down to 1 nm in vacuum and atmospheric pressure wafer processing systems. It seems particularly well suited for detecting particles =0.2 ?m where they lose the ability to be detected via scattering light. This is the first such technology for real-time monitoring of particles in vacuum chambers and exceeds the chemical analysis ability of other techniques for atmospheric processing that reach their limits at ~0.5 ?m particles.

Development of the new instrument, dubbed Particle Blaster, is the brainchild of Bill Reents, a chemist at Bell Labs, the R&D arm of Lucent Technologies. Reents described his invention at the recent national meeting of the American Chemical Society held in Boston.

Reents` Particle Blaster attaches to a wafer processing tool and samples the process gas steam, which contains a sample of any particles present in the chamber. The tool is benign to the process and does not require any changes in pressure or other process conditions. Within the Particle Blaster, a pulsed, high intensity focused laser breaks particles into atoms, ionizes the atoms, and passes them to a mass spectrometer; the undisclosed energy, pulse width, and other laser characteristics are crucial to the instrument design (see figure). The laser fires at a steady rate, randomly striking particles that pass through its beam. The instrument`s output signals are proportional to the concentration of particles present in the sample.

The instrument`s output, virtually in real time, characterizes the size and chemistry of the original particles through their elemental volume and makeup. Reents explains, "From the ion signal we can determine the volume of the particle and convert that into equivalent particle diameter."

While this instrument is still classified as research, the roughly 2 ? 4 foot instrument is being "rolled around Bell Labs" for testing with various wafer processing tools to determine its utility. "In addition, we are talking to some `interested parties` about commercialization of this technology," says Reents.

Bell Labs` James W. Mitchell, director of the materials, reliability, and ecology research laboratory, says, "It`s crucial to develop tools that allow us to extend the limits of technology and advance the sensitivity limits of characterization tools." While Reents` Particle Blaster technology is important for analyzing semiconductor manufacturing process tool atmospheres, another possible application is performing trace analysis of particles in ultra-pure liquids, which are commonly used in both semiconductor and pharmaceutical manufacturing. - P.B.