Chemistry Reference
In-Depth Information
shows the roughness measured on the silicon surfaces cleaned or etched in various
solutions.
The root mean square roughness is generally much smaller than that of the
valley-to-peak roughness, as one is a measure of the average and the other is the maxi-
mum. For example, the surface roughness is 0.2nm by the area average method but is
1-2 nm by the valley-to-peak method for the same sample.
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The size of the sampling
area is also important in roughness measurement. For example, for a KOH etched
silicon surface the valley-to-peak roughness measured over a distance of is
whereas it is only 25 nm over a distance of Thus, a surface that is macro-
scopically (over a large area) rough may be miscroscopically (over a small area)
smooth.
Surface roughness is an important factor in the performance and reliability of
devices having microscopic dimensions.
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It can essentially affect all aspects of silicon
technology.
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In order to guarantee the performance of electronic devices the
microstructures fabricated from silicon are required to be smooth, with roughness much
smaller than the dimensions of the structure components.
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For example, in order to
obtain high-quality extremely thin oxide film on the order of l0nm thick or less, it is
essential to realize atomic-order surface roughness.
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As the device dimension gets
smaller, the device will be composed of thinner oxides and shallower junctions and the
effect of surface roughness will become critical.
As an important parameter for surface quality, roughness is discussed in almost
every article on cleaning and etching. However, in most cases it is treated as a quality
control issue. As a result, the data on surface roughness reported in the literature for
silicon surfaces are obtained under diverse conditions and are generally not compara-
ble due to the fact that data are often reported without clear definition of the methods
of determination and the area of sampling.
7.7.
1 Microroughness
Microroughness, or surface unevenness, at the atomic scale is always present on
a real surface whether it is smooth or rough at the macroscopic scale. For a macro-
