P. J. C. King

Microcircuit imaging using an ion‐beam‐induced charge

Ionizing radiation such as photons, keV electrons, or MeV ions can generate electron‐hole pairs in semiconducting material. The high penetrating power of MeV light ions allows them to generate electron‐hole pairs from deep within intact microelectronic devices, so images can be formed of the device active areas with very little degradation of the spatial resolution of the focused MeV ion beam. Furthermore, the ion‐beam‐induced charge (IBIC) image contrast is not strongly affected by the energy loss through the overlying device layers. This article is the first to demonstrate the capability of a nuclear microprobe to generate IBIC images of the active regions of devices through the passivation and metallization layers. The effect of the carrier generation volume on IBIC resolution is assessed. The ability of IBIC to align the major crystal axes of semiconductor samples is shown, and the effect of ion‐induced damage on IBIC image contrast is considered.

Applications of scanning transmission ion microscopy

Abstract The use of scanning transmission ion microscopy (STIM) in conjunction with scanning PIXE (proton induced X-ray emission) and RBS (Rutherford backscattering spectrometry) represents a powerful combination of imaging and analytical techniques across a wide range of scientific disciplines. In the microelectronics field STIM is a valuable complement to PIXE and RBS for the characterisation of the layer distribution, composition and uniformity in complex microcircuits. A microcircuit with several metallisation layers has been studied using these three techniques. A defect in the metallisation structure has been imaged with STIM, and PIXE has been used to determine the nature of the defect. In the field of biological microanalysis, tissue is usually stained or otherwise chemically treated in order to identify pathological features prior to analysis. This inevitably leads to a reduction in the integrity of the sample, introducing problems both of contamination and the possible loss of elements of interest from the tissue. Results showing how STIM and PIXE can be used to analyse pathological features in unstained tissue from the brains of Alzheimers disease patients are given.

DISLOCATION IMAGING USING TRANSMISSION ION CHANNELING

Interface dislocations present in a Si0.85Ge0.15/Si sample have been imaged using the channeling scanning transmission ion microscopy (CSTIM) method with a 2 MeV proton beam 200 nm across. Groups of parallel dislocations gave dark bands of contrast down to ∼1.5 μm across, the contrast arising from dechanneling of the beam by the bent lattice planes. Tilting of the sample caused the band contrast to change and gave quantitative data concerning the local bending of the lattice planes. A low‐angle boundary model was developed to describe the effect of the groups of dislocations on the channeling contrast. Channeling and topography contrast were obtained from mesa structures present on the sample. Improvements in the sensitivity of the CSTIM method are discussed. The dislocations in the sample were initially characterized by transmission electron microscopy.

DISLOCATION IMAGING USING ION-BEAM-INDUCED CHARGE

The recently developed ion beam induced charge technique has been used to image bands of misfit dislocations in a 4 μm thick epitaxial layer of Si0.875Ge0.125 grown on a Si substrate. The smallest resolvable bandwidth is 0.8 μm under present conditions. The factors which presently limit this value, and methods for improving it are discussed.

Dislocation imaging with a scanning proton microprobe using channeling scanning transmission ion microscopy (CSTIM)

Abstract Scanning transmission ion microscopy (STIM) combined with channeling has previously been demonstrated to be able to map regions of relatively poor crystal quality due to beam induced damage [1,2]. This paper describes the implementation of the CSTIM technique on the Oxford scanning proton microprobe and its ability to image misfit dislocations at the interface of an epitaxial Si0.85Ge0.15 layer grown on a (001) silicon substrate. Proton energy loss maps are generated by detecting transmitted protons with the beam aligned with a major axis or plane of the crystal. The bending of the crystal lattice planes due to the presence of dislocations causes dechanneling of the beam, giving protons transmitted through these regions a greater energy loss than those transmitted through regions of good crystallinity. Groups of dislocations give rise to bands of contrast along the [110] and [110] directions. Changes in contrast on tilting the specimen are consistent with the dislocations being of the 60° type rather than edge type, in agreement with the TEM results obtained from this specimen. By imaging misfit dislocation “cross” patterns in a Si0.95Ge0.05 layer grown on a silicon substrate, it has been shown that the minimum number of dislocations in a group that can be imaged is approximately 5 with a beam size of about 0.3 μm.

Imaging of the strain field around precipitate particles using transmission ion channeling

This paper shows ion channeling images of the strain field produced by precipitate particles in a crystal matrix. Images have been produced by mapping the energy of 3 MeV protons transmitted through a thinned silicon crystal containing colonies of copper silicide particles, with the incident beam at or close to planar channeling directions of the lattice. Features of the precipitate contrast observed as a function of beam tilt angle away from channeling alignment are qualitatively explained using a model based on symmetrical plane rotation of the crystal lattice around the colonies.

Evidence from ion channeling images for the elastic relaxation of a Si0.85Ge0.15 layer grown on a patterned Si substrate

We demonstrate the ability of ion channeling analysis using a scanned, focused, 2 MeV proton beam from a nuclear microprobe to detect and quantify elastic relaxation in a Si1−xGex layer grown on a Si substrate. Channeling images of a sample consisting of a Si0.85Ge0.15 layer grown on a substrate patterned to produce 10 μm wide raised mesas were produced which revealed lattice plane bending of up to 0.25°, consistent with elastic relaxation of the epilayer. The channeling results are compared with those produced from electron backscattering diffraction.

MANIPULATION OF ION CHANNELING PATTERNS USING MAGNETIC QUADRUPOLE LENSES

This letter demonstrates that ion channeling patterns, produced by the passage of 3 MeV protons through a 0.5 μm thick [001] silicon crystal, can be transported and manipulated to produce enlarged or reduced area patterns using magnetic quadrupole lenses. The different effects on the ion channeling patterns obtained by using single quadrupole lenses and quadrupole multiplets are shown. The maximum attainable magnification under present conditions is investigated and a fundamental limitation to this process is identified as being the energy spread gained by the proton beam as it passes through the crystal.

APPLICATION OF TRANSMISSION ION CHANNELING TO THE IMAGING OF STACKING-FAULTS

Abstract The Nuclear Microprobe at the University of Oxford has been employed to produce images of crystal defects using transmission ion channeling. This paper describes the experimental set-up for the technique and shows how images of stacking faults near the surface of a 40 μm thick silicon crystal can be generated. The invisibility of faults for certain planar channeling directions produces information on the nature of these defects. For the faults that are visible, the choice of channeling direction affects the image contrast. It is estimated that faults at least 10 μm below the surface of the sample would be detectable for the analysing beam of 3 MeV protons.

Transmission ion channeling analysis of isolated 60° misfit dislocations

High-contrast transmission channeling images and linescans of isolated bunches and individual 60° misfit dislocations in thick partially relaxed Si1−xGex∕Si layers are presented. Changes in dislocation contrast with tilt angle are explained using a model of planar dechanneling by the two-edge components of 60° dislocations. By careful analysis of the tilting contrast, all of the four possible combinations of the two-edge components of the Burger’s vector of 60° dislocations may be distinguished.