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Rapid Mechanical Properties of
Multi-layer Film Stacks
Application Note
Jennifer Hay,
Agilent Technologies
Abstract Agilent's most recent leap in technology,
In this work, we measure the mechanical Express Test, improves our ability to
properties of 50nm films with remarkable characterize thin films by dramatically
precision and accuracy. The precision increasing the number of independent
is due to Express Test, which performs measurements which can be made in a
indentations at a rate of one per second, given time period. Why is it important to
thereby allowing many indentations to make more measurements on thin films?
be included in the final determination It is important, because nanoindentation
of modulus and hardness. The accuracy measurements of Young's modulus and
is due, in part, to an analytic model hardness tend to grow more scattered
which yields the substrate-independent as the indentation depth decreases,
moduli of thin films. In order to apply the primarily due to surface roughness,
thin-film model to a stack of multiple but more scatter can be overcome with
films, the film modulus of each new more measurements. Express Test
layer is determined and then used as is Agilent's proprietary technology
the "substrate" modulus for the next for rapid indentation. Express Test
layer. This process could be repeated performs indentations in less than five
ad infinitum. The thin-film model reveals seconds, thus dramatically increasing
a large difference in Young's modulus the number of statistically independent
between two 50nm films. measurements which can be made in a
given time period.
Introduction For all its advantages, Express Test is
The primary motivation behind nanoindentation at its simplest. The
nanoindentation has always been the indenter approaches the test surface
desire to measure the mechanical until contact is detected, loads to
properties of small volumes of material, achieve the target force or displacement,
especially in the form of thin films. In withdraws the indenter from the
the present application, we see how two sample, and then moves the sample into
recent developments in nanoindentation position for the next indentation. The
work together to allow the quantitative contact stiffness is calculated using
characterization of films as thin as 50nm. the upper 50% of the unloading curve
(i.e. forces which are greater than 50%
of the peak force, and corresponding properties of the supporting substrate. Experimental Method
displacements, acquired during However, Agilent's proprietary thin- Samples
unloading). All downstream calculations film model fully accounts for substrate The samples identified in Table 1
such as contact depth, contact area, influence, regardless of whether the were tested. Basically, the substrate
hardness and Young's modulus are film is stiffer or more compliant than was tested alone (sample 1) and then
calculated according to established the substrate. The details of this model subsequent layers were tested as they
norms, and Young's moduli measured by are provided elsewhere, and are not were deposited.
Express Test agree with values measured reiterated here [4, 5].
by other means for a wide variety of Equipment and Procedure
materials. Express Test derives its speed In the present application, we show All samples were tested with an Agilent
not from novel procedures or analyses, how these two advances, Express G200 NanoIndenter, configured with
but from a comprehensive understanding Test and thin-film modeling, combine the Express Test option. All tests were
of instrument dynamics, combined with to dramatically improve thin-film performed using a DCM II head fitted
strategic advances in data acquisition characterization. Figure 1 shows a with a Berkovich indenter. Sample
and storage [1]. schematic of the unique material tested positioning was accomplished with the
in this work. The substrate is a sintered NanoVision option. This combination of
Like other indentation methods, composite of alumina (Al2O 3) and hardware (the DCM II and NanoVision
Express Test returns a triplet of force, titanium carbide (TiC), the microstructure stage) allowed Express Test to perform
displacement, and stiffness for each of which is shown in Figure 2. Upon this one indentation every second.
indentation, but this information is only substrate is a layer of sputter-deposited
as good as the model which relates these Al2O 3 having a thickness of 2600nm. The Preliminary testing was done on
fundamental measurements to useful topmost layer of this structure is 50nm sample 2 in order to know the depth
mechanical properties, such as Young's of either silica (SiO 2) or alumina (Al2O 3). profile of properties for this material.
modulus and hardness. The most basic, The properties of each layer are not only This preliminary test was accomplished
and oft-cited, model for interpreting important in their own right, but also with the method "Express Test, Varied
fundamental indentation measurements must be known in order to accurately Force" which automatically performs
is due to Ian Sneddon, but Sneddon's calculate the properties of subsequent an array of 20 x 20 indentations over
model presumes that the test material layers via the thin-film model. Thus, an appropriate range of forces within a
is large and uniform throughout [2, 3]. in this work, we provide a practical 100