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The characterization of silicon (Si) wafers by optical methods using infrared (IR) radiation is often impeded by interference effects caused by multiple reflections on the Si air interfaces.
English (United States)
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Suppression of IR Interference Effects in Silicon Wafers by Doping
The characterization of silicon (Si) wafers by optical methods using infrared
(IR) radiation is often impeded by interference effects caused by multiple
reflections on the Si air interfaces.
To suppress interference in full or in part, it is proposed to induce a suitably
chosen profile into one side (front or back) of the wafer (Fig. 1).
Particularly effective suppression of interference in the 10 to 12 micron range
is obtained by implanting As at an energy of 50 keV and a dose of 2E15 As/cm
followed by baking at 1100 degrees C for 2.5 hours in an N2 atmosphere. (Prior
to baking, an 0(2) flush has to be applied for 3 minutes.)
The resulting doping profile is represented in Fig. 1B. Fig. 2 shows the
decrease in interference effects of the transmitted light at two different doses for
a wafer with two polished surfaces. A noticeable constriction of interference
amplitudes exists in both curves, the center of which depends on the doping level
and the doping profile.
Similar curves of reduced interference amplitudes are obtained for wafers
with one unpolished surface.
The reduction or suppression of interference amplitudes may also be of
interest for optical components in infrared devices, for example, windows for
high-power IR lasers.
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