ASTM F1261M-96(2003)

Standard Test Method for Determining the Average Electrical Width of a Straight, Thin-Film Metal Line [Metric] (Withdrawn 2009)

SCOPE
1.1 This test method is designed for determining the average electrical width of a narrow thin-film metallization line.
1.2 This test method is intended for measuring thin metallization lines such as are used in microelectronic circuits where the width of the lines may range from micrometres to tenths of micrometres.
1.3 The test structure used in this test method may be measured while still part of a wafer, or part therefrom, or as part of a test chip bonded to a package and electrically accessible by means of package terminals.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
WITHDRAWN RATIONALE
This test method is designed for determining the average electrical width of a narrow thin-film metallization line.
Formerly under the jurisdiction of Committee F01 on Electronics and Subcommittee F01.11 on Nuclear and Space Radiation Effects, this practice was withdrawn in May 2009 with no replacement because the committee is not aware of the need to maintain the standard. Reference to the standard will remain available, but at this time, the committee does not wish to actively maintain the standard.

General Information

• Status: Withdrawn
• Publication Date: 09-Jun-1996
• Withdrawal Date: 30-Apr-2009
• Technical Committee: F01 - Electronics
• Drafting Committee: F01.11 - Nuclear and Space Radiation Effects

Relations

• Replaces: ASTM F1261M-96 - Standard Test Method for Determining the Average Electrical Width of a Straight, Thin-Film Metal Line [Metric]
• Effective Date: 10-Jun-1996

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:F 1261M–96 (Reapproved 2003)
Standard Test Method for
Determining the Average Electrical Width of a Straight, Thin-
Film Metal Line (Metric)
This standard is issued under the fixed designation F 1261M; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.3 test structure—a passive metallization structure, with
terminals to permit electrical access, that is fabricated on a
1.1 Thistestmethodisdesignedfordeterminingtheaverage
semiconductor wafer by procedures used to manufacture mi-
electrical width of a narrow thin-film metallization line.
croelectronic integrated circuits.
1.2 This test method is intended for measuring thin metal-
lization lines such as are used in microelectronic circuits where
4. Summary of Test Method
the width of the lines may range from micrometres to tenths of
4.1 This test method uses a cross-bridge test structure that
micrometres.
has two components: One is a cross, consisting of two
1.3 The test structure used in this test method may be
perpendicularly intersecting metallization lines, which is used
measured while still part of a wafer, or part therefrom, or as
to determine the sheet resistance by a van der Pauw method in
part of a test chip bonded to a package and electrically
which a forcing current, I , through two adjacent arms to the
accessible by means of package terminals.
cross, develops a voltage that is measured using the remaining
1.4 This standard does not purport to address all of the
two arms. The other component is a bridge element that
safety concerns, if any, associated with its use. It is the
includes the line whose width is to be determined.Two voltage
responsibility of the user of this standard to establish appro-
taps contact this line at a known distance from each other. By
priate safety and health practices and determine the applica-
forcing a known current, I , through the line and measuring the
bility of regulatory limitations prior to use.
voltage difference beween the voltage taps, the mean width of
2. Referenced Documents the line can be calculated.
2.1 ASTM Standards:
5. Significance and Use
E 178 Practice for Dealing With Outlying Observations
5.1 The width of a conductor line is important to ensure
F 1260M Test Method for Estimating Electromigration Me-
predictable timing performance of the electrical interconnect
dian Time-To-Failure and Sigma of Integrated Circuit
system, to assure control of critical device parameters, and to
Metallizations [Metric]
control various processes involved in microcircuit manufac-
3. Terminology ture.
5.2 Thewidthofaconductorline,withitsthickness,defines
3.1 Definitions of Terms Specific to This Standard:
the cross-sectional area and therefrom the current density for a
3.1.1 electrical linewidth—the width of the line as calcu-
given current. Knowledge about the current density is impor-
lated by the product of the sheet resistance of the metal film
tant in procedures for estimating reliability against degradation
and the line length, divided by the line resistance.
due to electromigration and in the conduct of electromigration
3.1.2 metallization—the thin-film metallic conductor used
stress tests to obtain sample estimates of the median-time-to-
as electrical interconnects in a microelectronic integrated
failure and sigma (see Test Method F 1260).
circuit.
6. Interferences
6.1 If the four cross-resistance values (in 8.1.8) differ by
This test method is under the jurisdiction of ASTM Committee F01 on
more than approximately 5 %, when “wafer-level” measure-
Electronics and is the direct responsibility of Subcommittee F01.11 on Nuclear and
ments are made with contact probes at room temperature, then
Space Radiation Effects.
poor electrical contact may be the cause. Poor contacts will
Current edition approved June 10, 2003. Published June 2003. Originally
approved in 1989. Last previous edition approved in 1996 as F 1261M – 96.
leadtoanerroneousvalueforthecrossresistanceaswellasfor
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the linewidth. When measurements are made at elevated
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
temperatures,thedifferencesinthefourcross-resistancevalues
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. will be larger. Good electrical contact will then be indicated
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F 1261M–96 (2003)
when the relative values of the cross resistances remain 7.3.1 The cross-bridge test structure shall conform to the
approximately the same with subsequent placements of the following specifications: L >2W ; L >2W ; L > 150 µm and
e b t b b
contact probes on the same or similar structures. 20W ; and L $ 2W .
b c c
6.2 Measurements should be conducted in a time that is 7.3.2 The test structure shall also be designed so that width
shortincomparisontoanytemperaturechangesthatmayoccur of the voltage-tap lines to the bridge structure shall be
in the metallization. If measurements are made in an environ- minimized but shall be no smaller than 1.2 times the minimum
ment where the temperature of the metallization changes by dT resolvable linewidth.
between the time that the resistance of the cross and the
NOTE 2—The width of the voltage-tap line should be kept as small as
resistance of the bridge line are measured, then an error of
practicable to minimize the error due to the shunting effect of the
TCR(T)dT % in the calculation of the linewidth will result due
finite-width voltage taps. The specification for the minimum allowed
to the thermal coefficient of resistance, TCR(T), of the metal-
design width is included to avoid the possibility of having the voltage-tap
line as the weakest link in the patterning process.
lization.
6.3 If the bridge line has been so over etched that its cross
7.3.3 So that the resistance of the cross can be measured
section becomes triangular and its peak is less than the
without heating the metallization by more than 0.1°C, due to
thickness of the metal in the cross, then the test method will
joule heating, the width of the cross shall satisfy the following
provide a width that is too small.
condition:
p t·t
7. Apparatus i
W $ V ~cm!,
c Πi
ln2 r·K·dT
i
7.1 Constant Current Supply, capable of forcing through the
cross bridge test structure a current that is constant and has a
where:
current-displayresolutionofatleast1 %oftheforcingcurrents t and t = design thickness of the metallization and of the
i
required.
underlying electrical insulator, respectively,
7.2 Voltmeter, capable of measuring the voltage developed (cm),
in the cross-bridge test structure and that has a display r = estimated resistivity of the metallization,
(V·cm),
resolution of at least 1 % of the voltage measured.
K = estimated thermal conductivity of the insulator,
i
NOTE 1—Sensitive measurement equipment is needed to determine the
(w/cm°C),
resistance of the cross. The typical resistance of the cross is only 12 to 18
V = 100 times the display resolution of the voltmeter
mV for a 0.5-µm-thick, aluminum-alloy metallization and the forcing
used in the procedure, (V), and
current must be limited to avoid measurement errors due to joule-heating.
dT = 0.1°C.
7.3 Cross-Bridge Test Structure, whose essential features
In calculating the value for W (cm), use either the value for
c
are illustrated in Fig. 1. In the bridge element of the structure,
K that has been determined for the electrical insulator or 0.10,
i
they are: the width of the test line, W ; the width of voltage-tap
b
0.010, and 0.0015 W/cm°C for K when the insulator is silicon
i
lines, W; the center-to-center distance between the voltage-tap
t
nitride, silicon dioxide, and a polyimide, respectively.
lines, L ; the length of the voltage-tap lines, L; and the length
b t
NOTE 3—In most cases, the specifications for W will be satisfied by a
of the test-line extensions beyond the tap lines, L . In the cross
c
e
width of 30 µm.
element, they are: the width of the cross lines, W ; and the
c
lengths (not necessarily all equal) of the straight sections of
7.3.4 If it is the intent for the cross-bridge structure to be
these lines from their intersection as represented by L . The
used to measure, indirectly, the widths of lines elsewhere on
c
contact pads are labeled for use in the procedure.
the chip, the bridge line must duplicate the environment of
those lines. Hence, the bridge line must be parallel to these
lines and have the same local design features that can a
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