Hugo K. Seitz

Energy and time-resolved photoemission in a promising new approach for contactless integrated-circuit testing

Abstract A novel approach to contactless measurement of voltages on internal nodes of integrated circuits is presented. The method is based on time-resolved photoemission exploiting the single-photon process with short laser pulses in the ultra-violet. The method allows spatial resolution in the submicron range given by the diffraction limit for UV photons, a time resolution of a few picoseconds given by the width of the laser pulses and the electron transit-time effect, and a voltage resolution of a few microvolts within a signal integration time of one second.

Photoemission sampling technique for high-speed integrated-circuit testing

After a short review of the basic principles of time-resolved photoemission and its capabilities as a method for contactless electrical testing of integrated circuits, this paper reports on the progress made toward meeting the requirements for integrated-circuit (IC) testing and diagnostic equipment. The goals of IC testing are to provide high time and voltage resolutions with short testing time, and simultaneously high spatial resolution independent of the circuit technology (Si, GaAs). Here, the emphasis is on the time and voltage resolutions and short testing time. In the photoemission process, these parameters are independent of the spatial resolution in the regime of interest. The investigation is carried out with a pulsed-laser system generating picosecond pulses in the UV range. The measurements presented were performed on photoconductive switches. This allows testing the time resolution of the method by ultra-fast signals, and generating the electric transients to be sampled by the same laser source as the sampling pulse, guaranteeing almost jitter-free operation. The results clearly demonstrate that photoemission sampling is capable of contactless diagnostics and testing of very high-speed circuits with a high-voltage resolution and short testing time.

High-Speed Integrated Circuit Testing by Time-Resolved Photoemission

The growing complexity of integrated circuits (IC) and the rapid development in VHSICs require contactless testing methods for logic state analysis and waveform measurements on internal nodes of VLSI chips. Considering the fast evolution of VLSI/VHSIC technologies, a contactless testing method has simultaneously to provide challenging features like high-voltage resolution (mV), high spatial resolution (sub-micrometer), and high time resolution (ps) in a short testing time. In addition to these requirements, it is desired that the method should be applicable to all technologies, e.g., Si as well as GaAs-based ones.

Photoemission sampling measurements of a dispersing voltage pulse traveling on a transmission line

The newly developed method of photoemission sampling, based on the single‐photon process, has been applied to measure the dispersion of a picosecond voltage pulse traveling on a transmission line. The dispersion of the propagating pulse is clearly revealed in the spectra which show signal rise times of about 17 ps at 2 mm away from the pulse generating switch, and change into rise times of about 30 ps at 1.5 mm further away. The time resolution of the measurements is better than 7 ps. Therefore, photoemission sampling with picosecond laser pulses permits the measurement of changes in signal waveforms at arbitrary points of a transmission line and for arbitrary substrate materials with sufficient time resolution.

Contactless high-speed waveform measurements on GaAs integrated circuits with the photoemission sampling technique

After giving brief background information on photoemission testing with emphasis on measurement time, the authors describe progress made in detector design and viewing capability. The usefulness of equipment, using the photoemission sampling technique has been demonstrated through measurements delay and rise times of integrated GaAs MESFET circuits. The switching time of these circuits is around 200 ps, therefore presenting no challenge to the time resolution of the system, which had been substantiated by earlier measurements of electrical pulses with 8-ps rise time. The ability to activate devices within a chip by a pulsed visible light beam is also demonstrated.<<ETX>>

Contactless, high-speed waveform measurements on gallium arsenide ICs

A setup for photoemission testing, which compares favorably with results from electron-beam testing, particularly in terms of measurement time, is presented. The photoemission sampling system described has a unique detector design and a viewer for the added convenience of the equipment operator. performance results when this technique is used to measure delay and rise times on integrated gallium arsenide MESFET circuits are reported. The switching time of these circuits is around 200 ps. The system measures electrical pulses with an 8-ps rise time, so these GaAs circuits can be tested by the system. An interesting feature for special testing is the systems ability to activate devices within a chip by a pulsed visible light beam.<<ETX>>

Voltage detector and sub‐micrometer focusing unit for photoemission probing

A voltage detector and its connected focusing system for voltage measurements on integrated circuits by laser induced photoemission are presented. The capabilities of the system are analyzed theoretically and verified experimentally. Application to metal lines of submicrometer width and spacing is possible, combined with picosecond time resolution and a voltage sensitivity far exceeding that of electron beam probing. An excellent insensitivity to static crosstalk perturbations is demonstrated. Voltage contrast measurements and measurements of photoemission spectra have also been performed with this system.

Progress in photoemission sampling

The basic principles, fundamental limits, and recent results of the novel photoemission probing method are reviewed. The possible range of applications as a contactless diagnostic method for integrated circuits in the real-time and sampling modes of photoemission probing is discussed on the basis of theoretical and experimental studies. In photoemission sampling, electron emission is induced in a sample by an incident light beam (in most cases a laser beam), and the photoemitted electrons are then accelerated towards a reference or retarding field electrode. If the reference electrode is at the same potential as the point of electron emission on the VLSI circuit, all photoemitted electrons can pass the reference electrode and are guided towards an electron detector.<<ETX>>