W.C. Nixon

Ultra high speed electron beam testing system

Abstract The requirements for high speed electron beam measurement of fast electrical transitions on devices and the limitations to temporal resolution achievable by electron beam test systems are examined in this paper. In the light of this, a novel beam pulsing strategy is presented which permits pulse widths of less than 15ps at sampling rates of up to 50GHz to be attained. Fundamental temporal resolution limitations due to the transit time effect are discussed and measurements of secondary electron energy dispersion are compared with computer models to substantiate this phenomenon in ultra high speed waveform measurements.

A Contactless 3-D Measuring Technique For IC Inspection

Digital filtering techniques have been combined with a scanning electron microscope to provide noise free, TV rate stereo images over the full magnification range of the SEM, giving a qualitative pseudo 3-D representation of the sample surface. In this paper, a development of this technique will be described which permits quantitative measurement of a surface in 3 dimensions. Image correlation techniques have been derived which, when coupled with the lens controls of the SEM in the form of a feedback loop, permit automatic profiling of small structures. The technique has potential applications to a range of integrated circuit inspection techniques including resist profiling and critical dimension measurements.

A dynamic real-time 3-D measurement technique for IC inspection

Abstract Stereoscopic imaging in the SEM enhances the ability to resolve topographical ambiguities encountered during IC process inspection. The limitations of previous implementations are examined and have been addressed during the development of a stereo system. Results are also presented for in situ height measurements within the instrument.

Ultrahigh Speed Electron Beam Pulsing Systems For Electron Beam Testing

Ultrahigh speed electron beam pulsing systems for electron beam testingJohn T. L. Thong, Simon C. J. Garth, William C. Nixon, Alec N. BroersDepartment of Engineering, Cambridge University, Trumpington Street, Cambridge CB2 1PZ, EnglandAbstractMeasurement of high speed waveforms within operating integrated circuits presents a major challenge to design engineers. Electron beam testing techniques are well suited to the task due to their essentially non-loading properties. A number of such systems are briefly reviewed and their properties and drawbacks outlined. In addition, a recently developed system is described which overcomes some of the difficulties encountered with previous implementations.IntroductionElectron beam testing techniques are rapidly becoming established as a standard diagnostic tool for failure analysis, characterization and debugging of pre-production integrated circuits. The principal reason behind the rapid increase in interest in the subject during the last 5 years is the capability of the technique to measure waveforms on minimum- dimension features within integrated circuits in an almost totally non-loading and non- invasive manner. This compares favourably with the more conventional technique of mechanical probing which is both damaging and significantly loading on small geometry device elements.An important area of application of electron beam testing techniques is that of measuring high speed signals within integrated circuits. The electron probe offers negligible capacitance to the device under test thus ensuring that the device operates identically irrespective of whether it is being measured or not. Additionally, the electron beam may be pulsed very rapidly allowing measurements with very high temporal resolution.VoltageElectron beam pulse or sampling gateOutput-I

An electron optical line source for microelectronic engineering

Abstract At present, most electron beam probe forming systems for microelectronic applications use emitting configurations of thermionic emitters in a triode gun of radial symmetry. Line sources open up the possibility of being able to form a cross-over that is comparable to a round source in one direction, but much longer in the other. A line source has been developed which produces a cross-over aspect ratio of 10:1. Patterns have been exposed and waveforms measured on a circuit. Line sources demonstrate clear advantages for microelectronic engineering applications which contain high aspect ratio circuit element geometries.

X-ray projection microscopy and transmission electron microscopy

Abstract Before joining Ellis Cossletts EM Group in October 1949, coming from Canada, I had chosen to work on the X-ray projection microscope. The new instrument was constructe, tested and improved and a Ph.D. degree awarded in June 1952. Many visitors came to see the instrument and the results. The universal comment was “How do you get such beautiful images from such a heap of junk?” The High Voltage Transmission Electron Microscope was a Cavendish project of the 1960s with K.C.A. Smith supervising. The High Resolution Electron Microscope of the 1970s was a joint Engineering and Physics Departments project with Cosslett as the Physics Principal Investigator, until his retirement in 1975, and Nixon as the Engineering Principal Investigator throughout.

The Behavior of Charged Particles in the Scanning Electron Microscope

Charging phenomena of small particles have been observed in the scanning electron microscope (SEM). Polystyrene particles, mounted on gold coated hologram grating substrates, are negatively charged by the primary beam in the SEM, and a significant distortion of the grating is seen. Computer generated images have been matched to the experimental images of gratings. Parameters related to the microscope, specimen and specimen-microscope geometry such as electron beam accelerating voltage, magnification, grating spacing, grating type, specimen tilt angles, charge location and magnitude are used to generate the calculated images. It has been found that gratings tilted at large angles to the optic axis of the microscope increase the effect of charge on electron trajectories and hence the accuracy to which charge can be measured. Typical charge values in the SEM are ~10-12C/particle. A second part of the investigation involves dynamic motion of small charged particles using television scanning rates in the SEM. Several effects were observed including uphill rolling motion towards the electron beam at low incident beam energy (10 kV), downhill motion at higher energy (20 kV), charge transfer, field lines between charged particles, and electrical contrast. It is possible to describe mathematically the motion of these particles.

Background to Electron Beam Testing Technology

Electron beam testing technology depends on the best possible design of a focused and scanned beam of electrons, with all the associated methods of voltage contrast detection—both static and dynamic—display and measurement of the results, and interpretation with fast computing of the essential features under investigation. All of these activities have been studied following the first demonstration of a useful scanning electron microscope by D. McMullan.(1) (Prior to this, a few microscopes had been built following the first by von Ardenne, (2) but none proved sufficiently promising for further investigation or development.) Work in the Cambridge University engineering department was started by C. W. Oatley in 1948 with McMullan as the first of many research students to work in scanning electron microscopy and related techniques. The McMullan publication in 1953 proved the principle and showed that the instrument could now be applied to a variety of specimen areas.