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Scanning Acoustic Resonance Spectroscopy Disclosure Number: IPCOM000103659D
Original Publication Date: 1993-Jan-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 4 page(s) / 151K

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Bayer, T: AUTHOR [+1]


This article describes a new method for surface scanning a memory chip by a microprobe.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 47% of the total text.

Scanning Acoustic Resonance Spectroscopy

       This article describes a new method for surface scanning
a memory chip by a microprobe.

      Surfaces may be imaged and characterized by nearfield
microscopy (such as tunnel or force microscopy) in a variety of ways.
For special reasons (stability of sensor), very deep and narrow
structures are normally either not detected or detected only to a
very limited extent.

      This article proposes to enhance the measuring facilities of
nearfield microscopy, thus allowing the characterization in
particular of deep structures.  For this purpose, a microprobe
consisting of a miniature beam and a (suitably shaped) tip is used as
a local detector to excite and detect acoustic waves, attenuation and
resonance phenomena which indicate the depth and, in some cases, the
shape of a structure.  The new measuring principle may be implemented
in existing means with a minimum amount of changes.

      Very fine and deep structures (or trenches) are important in
increasingly miniaturized memory chips and for micromechanical
applications, such as the production of test heads and laser
ablation.  Depth/width ratios exceeding 10 or even 20 have been
realized both in deep trench capacitors and during the production of
test heads.  Currently, such trenches can only be characterized by
replica techniques leading to the destruction of the chip.  The new
raster force microscopy method for mechanically scanning surface
structures is not suitable for a depth/ width ratio of 10 because of
the unduly high lateral yield of the special tip or probe, that would
occur in this case.

      The proposed method comprises a microprobe which raster scans
the surface of a memory chip and which, similar to a raster force
microscope, consists of a miniature cantilever and, for example, of a
cylindrical (submicron) stem (tip) (Fig. 1).

      The typical diameter of the stem is several 0.1 - 10 mm and its
length several mm.  A trench is characterized by exciting an
ultrasonic acoustic wave of the gas column in the trench and by this
wave interacting with the stem of the microprobe.  This may be done
in various ways.
     1.   Local excitation and detection by the measuring head
          The cantilever of the measuring head is excited by a
piezoelectric generator.  The amplitude is optically measured.  If
the excitation and the resonance frequencies of the trench match,
characteristic peaks in the excitation spectrum are obtained.
          The mean resonance frequency no of a gas column is derived
from the depth d of the trench and the speed of sound C in the
gas medium.
          Example: d = 10 mm, c = 340 m (air)

                            (Image Omitted)

          The harmonics are
          Fig. 2 shows measured resonance spectra of a sensor...