Investigation of Multiple Heat Source Effects in Lock-In Thermography Applications in Semiconductor Packages

Three-dimensional (3-D) packages have become a technology integrator for multiple functional devices into one component as a cost-effective way to enable Moore’s law for continuous scale-down. There are new challenges arising from the 3-D packages for fault isolation because of continued miniaturization and added complexity in the
$z$
-direction of advanced IC devices, which require the development of more capable fault isolation tools and techniques for better accuracy, resolution, and sensitivity. Lock-in thermography is a powerful noncontact and nondestructive investigating technique that has recently become widely adopted in the semiconductor industry because of its sensitivity and quick time to data. As more components are integrated into 3-D packages, there are more active devices and routing becomes very complex. It is very common that multiple defects or heat sources can exist at the same time in a single package. These multiple heat sources interact with each other and affect defect depth accuracy to a very large extent. This paper presents a fundamental analysis to understand the interaction between multiple defects and its effect on the accuracy of defect depth estimation. Furthermore, this paper also presents real test cases to further the understanding and confidence in the proposed correlations. The learnings and techniques discussed in this paper can lead to industry-wide tool and technical developments, and benefit the failure analysis and 3-D package development community.