A time-of-flight voltage contrast detector for measurements on VLSI circuits

Abstract

The authors present developments in the design of a new type of voltage contrast detector. Voltage contrast measurements are made by recording transit times of secondary electrons as they are emitted from a specimen and collected above the final lens of an SEM. The study shows that such a voltage contrast detector can be designed to combine a high spatial resolution with a large field of view: voltage measurements using sub- mu m probe sizes can be maintained over a 6 mm by 6 mm square region. The detector is also predicted to have data-acquisition times that are at least a factor of 30 times shorter than those of conventional retarding field-type detectors. The detector is expected to sample waveforms in its normal multi-stroboscopic mode of operation at frequencies up to 20 MHz.

Quantitative voltage contrast method for electron irradiated insulators in SEM

“…The principle of the method is not fundamentally different from that proposed in most existing quantitative voltage contrast systems [9][10][11][12][13]. The energy distribution of SEs is fixed relatively to V S .…”

“…The knowledge of the spatial variation of V S is therefore very much required. For moderately charged surfaces (V S is of a few volts to hundreds of volts), numerous quantitative voltage contrast systems have been developed [9][10][11][12][13] and are widely used for failure analyses of integrated circuits, where the surface potential reaches only a few volts. An overview of these methods can be found, e.g., in [14,15].…”

Voltage and Dopant Concentration Measurements of Semiconductors using a Band-Pass Toroidal Energy Analyzer Inside a Scanning Electron Microscope

“…More reliable quantitative information about dopant concentration changes can be obtained by the use of an electron energy analyzer, which relies on detecting shifts in the scattered SE energy spectrum. It is well known that multichannel or band-pass analyzers, which acquire the SE energy spectrum directly, have an order of magnitude better signal-to-noise characteristics than retarding field analyzers (Dubbeldam & Kruit, 1987;Khursheed & Dinnis, 1990). However, the electron energy analyzer arrangement used by them is a relatively poor analyzer design from a signal-to-noise perspective (Khursheed, 2011).…”

“…The output signal from this type of analyzer represents the integrated form of the SE spectrum. It is well known that multichannel or band-pass analyzers, which acquire the SE energy spectrum directly, have an order of magnitude better signal-to-noise characteristics than retarding field analyzers (Dubbeldam & Kruit, 1987; Khursheed & Dinnis, 1990). In the context of p – n junction dopant mapping, retarding field analyzers have typically recorded output signal shifts in the “tenths of an eV” range.…”

Scanning electron microscope design for quantitative multicontrast

“…For the electron beam testing of integrated circuits, the time-of-flight spectrometer is predicted to have a signal-tonoise improvement of over 30 with respect to existing conventional retarding-field spectrometers (Khursheed and Dinnis 1990). It also has the advantage of being intrinsically open-loop in its method of operation, obtaining voltage measurements directly from a simple algorithm applied to the output signal.…”