industry metrology
Uncovering imperfections in SiC
The miniscule scratches and pits found on the surface of SiC substrates spawn yield-killing defects in the epiwafers. It is not possible to pick- up these minor imperfections and track their consequences with conventional light- scattering inspection tools, but this can be done with our detection systems employing confocal optics and differential interferometry, argues Yuji Asakawa from Lasertec Corporation.
T
o reduce carbon dioxide emissions and meet the rapidly growing energy demand in emerging economies, engineers are installing more eco-friendly energy sources and trying to increase the efficiency of many different products. These efforts can be aided by the introduction of a range of new technologies that increase the efficiency of electronic devices.
Today, the vast majority of electronic devices are made from silicon. This material is relatively cheap to process, but it cannot deliver device efficiencies as high as equivalents built from wide bandgap semiconductors. These alternatives promise to enhance electric power conversion efficiency in a wide range of applications, including electric vehicles, inverters for solar systems and air- conditioning.
A handful of companies have already brought diodes and transistors made from wide bandgap materials to market, but in general, this industry is still in the development stage. For sales to rise, the quality of these products must improve and their production costs fall, so that they can be seen as genuine competitors to the silicon incumbents.
Introducing inspection tools that set a new benchmark for scrutinizing substrates and epiwafers will help to make better products and drive up device yields. At Lasertec Corporation, an inspection tool manufacturer with headquarters in Yokohama, Japan, we have launched a range of tools that do just this: the SICA61 series, which is designed to inspect SiC material and is discussed in the remainder of this article; and TROIS, an instrument for scrutinizing other wide bandgap materials, which is described in the box “Inspecting and reviewing wide bandgap semiconductors”, which can be found on page 34.
Left: Lasertec’s SICA series is capable of identifying scratches with a depth of less than 1 nm in SiC substrates
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www.compoundsemiconductor.net October 2012
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