ASTM F390-98
(Test Method)Standard Test Method for Sheet Resistance of Thin Metallic Films With a Collinear Four-Probe Array
Standard Test Method for Sheet Resistance of Thin Metallic Films With a Collinear Four-Probe Array
SCOPE
1.1 This test method covers the measurement of the sheet resistance of metallic thin films with a collinear four-probe array. It is intended for use with rectangular metallic films between 0.01 and 100 [mu]m thick, formed by deposition of a material or by a thinning process and supported by an insulating substrate, in the sheet resistance range from 10 to 10 [omega]/[open-box] (see 3.1.3).
1.2 This test method is suitable for referee measurement purposes as well as for routine acceptance measurements.
1.3 The values stated in Si units are to be regarded as the standard. The values given in parentheses are for information only.
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.
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Designation: F 390 – 98
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Sheet Resistance of Thin Metallic Films With a Collinear
1
Four-Probe Array
This standard is issued under the fixed designation F 390; 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 film, the quotient of the resistance, measured along the length
of the film, divided by the length, l, to width, w, ratio. The ratio
1.1 This test method covers the measurement of the sheet
l/w is the number of squares.
resistance of metallic thin films with a collinear four-probe
array. It is intended for use with rectangular metallic films
4. Summary of Test Method
between 0.01 and 100 μm thick, formed by deposition of a
4.1 A collinear four-probe array is used to determine the
material or by a thinning process and supported by an
−2
sheet resistance by passing a measured direct current through
insulating substrate, in the sheet resistance range from 10 to
4 the specimen between the outer probes and measuring the
10 V/h (see 3.1.3).
resulting potential difference between the inner probes. The
1.2 This test method is suitable for referee measurement
sheet resistance is calculated from the measured current and
purposes as well as for routine acceptance measurements.
potential values using correction factors associated with the
1.3 The values stated in Si units are to be regarded as the
geometry of the specimen and the probe spacing.
standard. The values given in parentheses are for information
4.2 This test method includes procedures for checking both
only.
the probe assembly and the electrical measuring apparatus.
1.4 This standard does not purport to address the safety
4.2.1 The spacings between the four probe tips are deter-
concerns, if any, associated with its use. It is the responsibility
mined from measurements of indentations made by the tips in
of whoever uses this standard to consult and establish appro-
a suitable surface. This test also is used to determine the
priate safety and health practices and determine the applica-
condition of the tips.
bility of regulatory limitations prior to use.
4.2.2 The accuracy of the electrical measuring equipment is
2. Referenced Documents tested by means of an analog circuit containing a known
standard resistor together with other resistors which simulate
2.1 ASTM Standards:
2
the resistance at the contacts between the probe tips and the
E 1 Specification for ASTM Thermometers
film surface.
F 388 Method for Measurement of Oxide Thickness on
Silicon Wafers and Metallization Thickness by Multiple-
5. Apparatus
3
Beam Interference (Tolansky Method)
5.1 Probe Assembly:
3. Terminology 5.1.1 Probes—The probe shaft and tip shall be constructed
of tungsten carbide, Monel, hardened tool steel, or hard copper
3.1 Definitions:
and have a conical tip with included angle of 45 to 90°.
3.1.1 thin film—a film having a thickness much smaller than
Alternatively, the tip may be formed from a platinum-
any lateral dimension, formed by deposition of a material or by
palladium alloy and resistance welded to the shaft. The tip shall
a thinning process.
have a nominal initial radius of 25 to 50 μm. In all cases all of
3.1.2 thin metallic film—a thin film composed of a material
−8
the four paths from the electrical measurement equipment
or materials with resistivity in the range from 10 to
−3
inputs to the film surface must be identical.
10 V·cm.
5.1.2 Probe Force—The probes shall be uniformly loaded
3.1.3 sheet resistance, R [V/h]—in a thin film, the ratio of
s
to exert a force sufficient to deform the metal film but
the potential gradient parallel to the current to the product of
insufficient to puncture the film. A rough guide for loading is a
the current density and the film thickness; in a rectangular thin
load of 20 g/Mohs (unit of hardness) of the film material on
each probe.
1
This test method is under the jurisdiction of ASTM Committee F-1 on
5.1.3 Probe Characteristics—The probes shall be mounted
Electronics and is the direct responsibility of Subcommittee F01.17 on Sputtered
in an insulating fixture such as a sapphire bearing in a methyl
Thin Films.
Current edition approved May 10, 1998. Published October 1998. Originally
methacrylate or hardened polystyrene block in an equally
published as F 390 – 73 T. Last previous edition F 390 – 97.
spaced linear array. The electrical insulation between adjacent
2
Annual Book of ASTM Standards, Vol 14.03.
5
3 probe points shall be at least 10 times gre
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