Session: 14-01: Measurement Techniques and Thermophysical Properties in Micro/Nanoscale

Paper Number: 132942

132942 - Anisotropic Thermal Resistance Characterization Using 3-Omega Joule Heating Thermometry and Scanning Thermal Microscopy 

Abstract: 

In next generation chip stacks thermal conduction occurs through the Back End Of the Line (BEOL) layers and bonding layers between multiple chips. To accurately predict temperature profiles and design appropriate cooling solutions, thermal design of next generation chip stacks needs accurate thermal properties for the BEOL layers, underfill, and interlayer interfaces. 

Current state of the art (SoA) for measuring BEOL thermal resistance for chips employs test vehicles (TV) with customized microfabricated heaters and thermistors located within the BEOL stack. Moreover, SoA determines the thermal resistance only in the direction of layer thickness. However, the BEOL film stacks are anisotropic and their effective thermal conductivity changes with location.

At Rensselaer Polytechnic Institute (RPI) in the Nanoscale Thermophysics and Energy Conversion lab we developed and employed several techniques for thin film and interface thermal resistance characterization. For effective thermal conductivity measurements of individual and multilayer films on substrate we successfully employed 3w based techniques, which can determine both in-plane and cross-plane effective thermal conductivity of layers when micro-heaters with dissimilar widths are used in the experiment and the data reduction employs our anisotropic multilayer thermal transport model.  All the samples tested previously with the 3w have been however spatially homogeneous in plane, meaning in the plane direction of the sample the composition of the layers did not change.

On another hand at RPI we developed and employed a non-contact heated-probe Scanning Thermal Microscopy measurement technique that can accurately measure film thermal conductivity with microscale in-plane spatial resolution and we successfully tested it on samples where either the in-plane thermal transport was dominant (high thermal conductivity films on low thermal conductivity substrate) or cross-plane thermal transport was dominant (low thermal conductivity films on high thermal conductivity substrate). In addition to being able to determine the spatial distribution of sample thermal resistance, the SThM technique does not require sample preparation. However, all the samples tested so far have been in-plane homogeneus.

In this paper we will report the anisotropic properties of several homogeneous BEOL films and film structures measured using the 3w method. In addition we will explore how the non-contact SThM technique can be adapted for anisotropic thermal measurements using a similar idea to anisotropic 3w measurements: use 2 heat sources with largely different sizes. We will explore this idea using analytical and 3D modeling for SThM probes with different probe dimensions. Probes where the temperature sensing element is a metallic wire acting as both a heater and thermistor will be selected for this study.

Presenting Author: Theodorian Borca-Tasciuc Rensselaer Polytechnic Institute

Presenting Author Biography: Dr. Theodorian (Theo) Borca-Tasciuc has a B.S. in Physics from Bucharest University and a Ph.D. in Mechanical Engineering from UCLA. He started his academic career in 2001 at Rensselaer Polytechnic Institute and since 2013 he is a full professor. He is the director of the Nanoscale Thermophysics and Energy Conversion Laboratory (NanoTEC) on the Rensselaer campus. His research interests include fundamental and multiscale investigations of thermal transport and energy conversion particularly in solid-state and development of innovative materials, devices, and systems with applications ranging from sustainable buildings to medical devices.

Authors:

Nazia Islam Rensselaer Polytechnic Institute
Theodorian Borca-Tasciuc Rensselaer Polytechnic Institute