Browse Prior Art Database

Method and System Design for Measuring Fine Line Electromigration Under High Frequency Bidirectional Current Stressing Conditions

IP.com Disclosure Number: IPCOM000115276D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 130K

Publishing Venue

IBM

Related People

Blusnavage, VA: AUTHOR [+8]

Abstract

Under large current densities, aluminum metal and its alloys experience a driving force to migrate in the direction of current flow. This phenomenon, known as electromigration, is well known in the microelectronics industry and leads to device failures. For bipolar circuitry, which operates under constant current conditions, screening of metallurgies for electromigration resistance is straightforward because testing can be performed under dc conditions. For CMOS logic devices, which do not operate under constant current conditions, testing under realistic operating conditions at high frequencies requires a novel tester design. The design and method taught by this invention allow typical electromigration test sites of varying electrical characteristics to be used for high frequency pulsed bidirectional current testing.

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Method and System Design for Measuring Fine Line Electromigration
Under High Frequency Bidirectional Current Stressing Conditions

      Under large current densities, aluminum metal and its alloys
experience a driving force to migrate in the direction of current
flow.  This phenomenon, known as electromigration, is well known in
the microelectronics industry and leads to device failures.  For
bipolar circuitry, which operates under constant current conditions,
screening of metallurgies for electromigration resistance is
straightforward because testing can be performed under dc conditions.
For CMOS logic devices, which do not operate under constant current
conditions, testing under realistic operating conditions at high
frequencies requires a novel tester design.  The design and method
taught by this invention allow typical electromigration test sites of
varying electrical characteristics to be used for high frequency
pulsed bidirectional current testing.

      At microwave frequencies, the power which can be successfully
delivered to a sample and the ability to measure it is highly
dependent on the capability of supplying matched impedance
connections from the excitation source to the sample, and
successfully tuning out reactive components from the sample itself.
The design of the system described here and shown schematically in
Fig. 1 provides that capability by using coaxial cables with a
characteristic impedance of 50 &Omega..  Providing a controlled
impedance connection through the oven door is achieved by using a
"ceramic" P.C.  board with a 50 &Omega.  impedance microstrip line
which terminates at the sample itself.  The tuning of the sample to
eliminate the inductive component of its impedance is accomplished by
connecting a small trimmer capacitor in series.

      The uniqueness of the design lies in the approach to sensing
the power being supplied to the sample.  A typical system might
monitor the power by measuring the current across a sense resistor in
series with the sample after all reactances have been tuned out by a
matching network.  In this invention, power to the sample is
monitored by a directional coupler which permits both the forward and
reflected power to be measured through a power meter.  The difference
of the two values is the power delivered to the sample.  By using
such an approach, the matching network can be greatly simplified and,
in fact, can be reduced to a single trimmer capacitor connected in
series with the sample.  As a result of the series capacitor, the DC
resistance of the sample cannot be monitored as would typically be
done by switching out the AC signal temporarily.  The present system
relies on changes in the reflected power due to changes in the real
part of the sample impedance to provide sample monitoring.  The
simplicity of this scheme, which consists of using a directional
coupler to both monitor sample power and impedance changes in the
sample, is the true novelty...