Browse Prior Art Database

Measurement of Trench Depth During Etching Process

IP.com Disclosure Number: IPCOM000102584D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Batchelder, JS: AUTHOR [+2]

Abstract

The use of high aspect ratio trenches is a common and critical geometry in integrated circuits for use as isolation wells or vertical capacitors. Typical trench geometries are 1 mm by 6 mm for CMOS technology (DRAM) capacitors and 3 mm by 3 mm for bipolar isolation. Trends in device geometries are likely to make aspect ratios even greater, as trench widths shrink. Because of the high aspect ratio and widths similar to optical wavelengths, the measurements of trench depth is quite often relied on for this information. This obviously does not allow measurement of the trench depth during the etching process. Concept

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Measurement of Trench Depth During Etching Process

       The use of high aspect ratio trenches is a common and
critical geometry in integrated circuits for use as isolation wells
or vertical capacitors.  Typical trench geometries are 1 mm by 6 mm
for CMOS technology (DRAM) capacitors and 3 mm by 3 mm for bipolar
isolation.  Trends in device geometries are likely to make aspect
ratios even greater, as trench widths shrink.  Because of the high
aspect ratio and widths similar to optical wavelengths, the
measurements of trench depth is quite often relied on for this
information.  This obviously does not allow measurement of the trench
depth during the etching process. Concept

      Although the trench appears to be an intractable optical
problem when viewed from outside the substrate (the front), when
viewed from the inside (the back), it appears as a tall post of
refractive index 1.0, in a media of higher index (e.g., silicon 3.5).
Since the light no longer need travel down a long optically narrow
path, optical techniques may once again be considered.  In addition,
the backside of the wafer is normally accessible in an RIE reactor
(the front is not), and is usually polished to within reasonable
optical standards. Instrument

      One possible configuration for this instrument is a
differential interferometer based on Nomarski microscopy, employing a
wavelength to which the substrate is transparent.  For silicon, this
would require g greater than about 1.1 mm.  With 1.3 mm (conveniently
available from diode pumped YAG lasers) being nearly ideal in terms
of minim...