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Photoelectron Microscope for High Speed Integrated Circuit Testing and Ultrafast Electron Spectroscopy

IP.com Disclosure Number: IPCOM000035762D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 4 page(s) / 86K

Publishing Venue

IBM

Related People

Chiu, G: AUTHOR [+3]

Abstract

This article describes the use of a high current pulsed electron beam (E-beam) source with high repetition rate, 1 picosecond time resolution and 100 angstroms (a) spatial resolution to generate short electron pulses via photoemission.

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Photoelectron Microscope for High Speed Integrated Circuit Testing and Ultrafast Electron Spectroscopy

This article describes the use of a high current pulsed electron beam (E- beam) source with high repetition rate, 1 picosecond time resolution and 100 angstroms (a) spatial resolution to generate short electron pulses via photoemission.

The use of electron beams for testing devices is a well established technique that takes advantage of the superior spatial resolution, depth of field, and steering capability offered by electron optics as compared to other techniques. An instrument is disclosed herein which, through the use of a photoelectron source, offers these capabilities and, in addition, greatly enhances temporal resolution and pulsed currents intensities as compared to existing guns used in high- speed non-contact testing of devices (see Fig. 1). In addition such a source has important applications in time resolved electron spectroscopy techniques for surface studies such as Auger Electron Spectroscopy.

The key feature of the gun is the use of ultrafast laser pulses to generate short electron pulses via photoemission. Recent advances in laser technology have provided intense ultrashort laser pulses at photon energies above the work functions of simple metals. A continuous wave (CW) mode-locked neodynium yttrium aluminum garnet (Nd-YAG) laser is used together with a fiber-grating pair optical compressor and a potassium trihydrogen phosphate (KTP) crystal frequency

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doubler to produce 2 ps pulses at 532 nm and an average power of 400 mW. These pulses are further doubled in potassium dihydrogen phosphate (KDP) to produce 1 picosecond pulses at 266 nm and at an average power of 3 mW (the use of urea as a doubling crystal will give better conversion efficiency). The photocathode used is a thin roughened film of gold deposited on quartz operated in transmission mode and mounted in the top of the scanning electron microscope (SEM) column (Fig. 1). The efficiency of the photocathode is 0.5 10- 3 electrons to photons which results in an average photocurrent of 100 nA equivalent to 10,000 electrons per pulse, an order of magnitude greater than the number of electrons per pulse available from conventional blanked sources. The average current is less than in conventional sources, but is sufficient to see high resolution real time 2D images, which is a necessary precursor to integrated circuit (IC) testing where the electron beam is positioned on the circuit point of interest. Using an extraction mesh close to the cathode with fields of 1kV/mm these electrons are accelerated with minimum temporal dispersion, and the electron pulses travelling down the microscope column are about 1 ps in duration. Typical operating conditions are shown in the diagram. Because the work function of gold is very close (few 10's of meV) to the photon energy (4.66 eV), the energy spread of these electrons is also less than in the thermionic cas...