Browse Prior Art Database

Detection of Interfacial Failure using Picosecond Ultrasonics

IP.com Disclosure Number: IPCOM000104209D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 125K

Publishing Venue

IBM

Related People

Oehrlein, GS: AUTHOR [+3]

Abstract

Disclosed is a technique in which laser-generated ultrasound pulses and echoes are used to detect failure in the physical structure of interfaces (e.g., contacts and interconnections)

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 42% of the total text.

Detection of Interfacial Failure using Picosecond Ultrasonics

      Disclosed is a technique in which laser-generated ultrasound
pulses and echoes are used to detect failure in the physical
structure of interfaces (e.g., contacts and interconnections)

      The detection of physical failure in contacts, interconnects,
and other complex microstructures is important but difficult.
Delamination and cracking are two such cases where failure can lead
to major reliability and yield problems.  Although electrical testing
can identify at least some of the yield problems directly (not
usually the reliability problems), it is common that electrical test
only follows well past the point in the process where fabrication of
the structure was flawed; thus significant penalties in turn-around
time and debugging are incurred simply because no detection scheme
was available to discern incipient or extensive delamination,
cracking, etc. when it occurred.

      This invention provides a method to detecting interfacial
failures such as delamination, cracking, or miscellaneous missing
interlayers.  It uses picosecond laser techniques in a pump-probe
arrangement to accomplish noncontact, nondestructive characterization
of the mechanical/acoustic properties of a buried interface, where
major alteration of those properties is expected when either partial
or full delamination has occurred.  Relevant experimental results are
given for a prototype of an interfacial delamination, namely the
presence of an ultrathin fluorocarbon interlayer representing much
weaker interfacial bonding as would be expected for incipient or
complete delamination.

      Recently a new approach to physical analysis has been pioneered
which exploits picosecond laser-induced ultrasonic pulses [1,2].  By
causing light absorption from a laser in ps time scales, an
ultrasonic stress wave is generated which can propagate through thin
films or in principle also along wires or other microstructures.
This stress wave undergoes attenuation and scattering in materials,
and it notably also exhibits reflection at interfaces.  When a
reflected wave reaches an exposed surface, it causes a detectable
change in optical reflectivity, seen as a transient.  The depth of
interfaces which cause a reflected pulse can be determined with
relatively high accuracy because of the high time resolution of the
laser pump/probe combination - i.e., ~  1 ps laser pulses and
sound velocities ~  50 A/ps.  This experimental technique
provides at least two vehicles for detecting interfacial bonding
properties, and particularly failure modes like delamination:

1.  The lineshape of the probe laser's reflectivity transient depicts
    aspects of the mechani- cal/acoustic properties of the buried
    interface.

2.  Furthermore, the modest local heating of the pump laser pulse
    leads to cooling rates - seen by the probe pulse in the transient
    reflectivity response - which depend on the...