NETSL: Nanoscale Electro-Thermal Sciences Lab

Overview | Properties Measurement | Temperature Measurements | Transometer | Self-Adaptive Code

Thermal Properties Measurements (TTR)

Thermal Properties Measurements of Thin-Films

· Thermal properties measurements, both in-plane and through-plane

· 7 ns pulse width of the heating laser allows measuring the thermal conductivity of semiconductor and dielectric materials

· Probing spot diameter smaller than 0.7 mm

· Computer controlled probing
for up to 8-inch samples

· Sample base maintained at
fixed temperature (0°-200°C) during measurements

· High responsivity enables differentiation between the thermal conductivity of Si samples with different doping levels

The Transient Thermo-Reflectance system at the SMU Submicron Electro-Thermal Sciences Laboratory (SETSL) is designed to measure the thermal properties of thin-film materials used in high-performance integrated circuits. The heating source is provided by an Nd:YAG pulsed laser whose wavelength is 532 nm and maximum pulse energy is 0.5 mJ. The adjustable heating spot of the YAG was characterized by CCD imaging and fast photodiode detection, and was found to have good spatial uniformity and a Gaussian temporal distribution. The probing light source is an Ar-Ion CW laser with a linearly polarized, single-mode irradiation beam at a wavelength of 488 nm. The beam is delivered to the microscope assembly via a polarization preserving, fiber optic cable with TEM₀₀ mode. The probing beam reflects from the heated surface back along its optical path to the sensitive area of a pre-amplified silicon PIN photodiode (rise time ≤ 1 ns) through a fiber optic cable. The photodiode signal, representing the variations in the surface reflectivity, is acquired with an 8-bit resolution by a digital oscilloscope at a rate of 2 Giga-Samples per second.

Probing and heating spot

The integrated CCD camera and microscope system is mounted on a precision probing station, making it possible to view the sample and to position the laser beams on its surface with a resolution of 1 µm. The microscope has a motorized, 40X continuous zoom capability. Five microscope objective lenses (5X – 100X) are available, providing a maximum magnification of 4000X. The system has been designed so that the heating and probing beams may be located concentrically (for through-plane property measurements) or eccentrically (for in-plane measurements). The sample under test is placed on a thermal chuck, capable of maintaining the bottom of the sample at an isothermal condition, in the range of 0–200°C with increments of 0.1°C. All components are computer interfaced for control and data acquisition. The results in the figure to the right demonstrate the ability of the system to provide the thermal conductivity of Si samples with different boron doping levels of the surface layer. The high responsivity of the system allows measuring thermal conductivity of Si with an uncertainty of ± 5.

Effect of doping level on the thermal conductivity of Silicon
(Silicon samples courtesy of Isonics, Inc.)

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