Using SSTR to Spatially Isolate Defect Layers on Thin Films

SSTR can measure the thermal conductivity of thin films to isolate the conductivity effects of defect layers from high quality crystalline regimes.

The Challenge

Thin film thermal conductivity is notoriously lower than that of bulk material due to interface and defect effects that impact phonon scattering. These defects can be spatially heterogeneous or deep under the surface.

The Solution

SSTR offers a unique ability to control the depth to which thermal conductivity is measured, a capability we can leverage to measure the thermal conductivity of thin AlN films while specifically isolating the thermal conductivity in the high-quality region near the top of the film from that of the lower quality nucleation layer near the AlN/substrate interface.

We show that the high-quality top portion of the film has bulk like thermal conductivity (both in plane and cross plane), but once the measurement volume samples the defect nucleation region, the thermal conductivity drops since the crystal quality in this region is poor. This unique ability to spatially isolate various regions of a sample and measure the thermal conductivity is enabled by SSTR’s ability to dynamically change spot size (and thus control the depth of probe).

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Nanoscale to bulk

Thermal conductivity of nanoscale thin films

SSTR is ideal for your thin film thermal conductivity testing needs.
In addition to measurements of bulk wafers and substrates (source 1, source 2), SSTR has the unprecedented spatial resolution to measure the thermal conductivity of thin films.
For example, SSTR can measure the thermal conductivity of single nanometer thick ALD grown thin films or micron thick AlN films (source).

SSTR measurements on ALD grown ultrathin film amorphous gate dielectrics (compared to TDTR) (source).

SSTR measurements of AlN crystalline thin films.2 SSTR data (temperature rise vs. power) on right for AlN film and silicon wafer control.

Validated results

SSTR-F measures the thermal conductivity of Corning Pyroceram 9606 and Corning high purity fused silica (HPFS) 7980 to within 5% of their published values.
Additional validation was provided by measuring samples from the same piece of material using the Transient Plane Source technique.
Pyroceram is no longer available from NIST but was measured on similar material to the material that was validated as a Certified Reference Material.
Corning HPFS was procured from a distributor of HPFS 7980 wafers.

	Literature Value	TPS Measurement	SSTR-F Measurement
Pyroceram 9606	4.07 +/- .26	3.95	3.95 +/- 0.2
HPFS 7980	1.38	1.39	1.39 +/- 0.09

Unparalleled reliability

Thermal conductivity measurements: Accuracy +/- 10%, Repeatability +/- 0.5%, Reproducibility +/- 1%
Accurate thermal conductivity measurements of materials in agreement with literature values
With exceptional instrumentation reliability and repeatability, SSTR-F offers unprecedented measurement stability on a daily basis for any user, exemplified by the SSTR-F data shown below. Spread in randomly sampled spots are sample related, not measurement driven.

Source

20 SSTR-F measurements at same spot

20 SSTR-F measurements at random spots

Turnkey testing

Our patented fiber-optic design enables turnkey, automated testing of thermal conductivity.
High-throughput SSTR-F testing of multiple samples facilitates, for example, screening the thermal conductivity of different thin films processed under different conditions
Defects, stresses, compositional differences, and changes in density and microstructure that occur up during film growth result in changes in thermal conductivity, easily and rapidly identified vis SSTR-F

SSTR-F data on 4 different 200 nm dielectric films on silicon with thermal conductivity ranging from ~0.35 W/m/K up to 1.8 W/m/K. SSTR-F allows for easy, rapid and automated identification of different temperature rises based on the thermal conductivity of the different films.