ThinLayerAnalysis
Cross sectioning - Cross
sectional imaging using either optical or electron microscopy is a
standard and well developed technique for the analysis of metals and
hard materials. A small section of the specimen is cut free
(using a hacksaw or diamond saw) and mounted in a sample holder at the
required angle. Progressively finer grit sizes are used to
produce a mirror finish on the cut surface which is then observed using
optical or electron microscopy. Features can be enhanced by
etching or staining the surface to expose metallic grain structure or
semiconductor dopant.
The rotary wheel polisher has been a standard tool in laboratories for
many years. However, when changing grit size there is
always the possibility of transfering coarse grit particles from one
wheel to the next, leading to scratches. Similarly, the
large area of an 8 or 12 inch wheel increases the chance of the wheel
being contaminated by particles from the environment.
Thin Layer Analysis
uses the Minimet 1000 polishing
machine from Buehler. This has self contained polishing bowls for
standard cross sectional polishing thereby reducing contamination.
We have also developed a number of specialised mounts for the
machine that permit accurate bevelling and the production of thin
sections for TEM (transmission electron microscopy) and petrology.
A sample mount has also been designed specifically for backside
chemical analysis (by methods such as SIMS or XPS) where the
substrate material is abrasively removed permitting depth profile to be
achieved from the rear of the sample. This requires angular
control to nanometre precision.
A major advantage of the minimet system is the microprocessor
control of polishing load, speed and duration, that permits highly
reproducible results and removes much of the 'black art' that was once
associated with specimen preparation. The picture below shows
cross sectional polishing of a silicon chip in progress.
The polishing media is diamond paste on a prepared glass plate.
This system substantially reduces rounding at the edge of the
specimen - vital for semiconductors where the region of interest lies
in the few microns nearest to the edge.
forward to bevelling >