Live Monitoring of Conductivity in Heated Thin Metal Films

Thin films in semiconductor and microelectronic structures

Our increasingly interconnected world is driven by advances in semiconductor and microelectronic devices. As semiconductor structures continue to decrease in size and increase in complexity, reliability and precision are needed down to the atomic scale. These cutting-edge structures contain very thin metal films that are 50-100 nm thick and, consequently, even tiny imperfections can have substantial consequences for device performance.

Grain growth and dewetting

Two critical processes that occur when a thin film is heated are grain growth and dewetting, which directly impact the microstructure of the film. Grains are the individual particles (or crystallites) that compose a solid metal. In the case of semiconductor thin films, increased grain size has generally been correlated with increased conductivity.

Time-lapse video showing grain growth in a thin gold film, recorded on a Phenom Pharos Desktop SEM.

Dewetting describes the transition of the thin film into more energetically favorable droplets of metal on the surface of the material. As these droplets effectively reduce the surface area covered by the film, dewetting will decrease conductivity.

Thin metal film on a MEMS-based heater, imaged before and after dewetting. The oval irregularities in the film are thin windows in the heater chip – these are only needed for transmission electron microscopy analysis.

Monitoring thin film conductivity with desktop SEM

Accurately determining how, and at what temperatures, these transitions occur requires live monitoring. Our application scientists, in collaboration with researchers at Delft University of Technology (TU Delft) have developed a new modified sample stage for the Thermo Scientific Phenom Pharos Desktop Scanning Electron Microscope (SEM) that includes a MEMS-based heating device. The heating of the (gold) metal film, combined with the high-quality imaging of the Pharos field emission gun (FEG) enabled them to observe both grain growth up to 500 K and the subsequent dewetting at higher temperatures. The resistance of the thin film was found to decrease exponentially with grain size and conversely increased as the dewetted area grew larger.

Photos of the modified sample stage with MEMS-based heating device developed at Delft University of Technology.

 These real-time observations can enable semiconductor developers to fine tune the physical characteristics and conductivity of their thin metal films, guiding the next generation of microelectronic and semiconductor structures.

Time-lapse video showing dewetting of a thin gold film, recorded on a Phenom Pharos Desktop SEM.

To learn more about this research, read the full proceedings from the Microscopy & Microanalysis 2020 conference, visit the Phenom Pharos product page for instrument specifications and details, or visit our Semiconductor Analysis page to see more of our tools and workflows for the semiconductor industry.

Alexander Bouman is a Product Marketing Manager for desktop SEM at Thermo Fisher Scientific. This blog was written in collaboration with Alex Ilitchev, Science Writer at Thermo Fisher Scientific. Research was performed by students and staff at Delft University of Technology (TU Delft).