How a new microscopy method peers inside the heart of tomorrow鈥檚 chips
Dipankar Mukherjee defended his PhD thesis at the Department of Mechanical Engineering on October 28th.
As computer chips shrink and their architectures become three-dimensional, traditional tools struggle to see what鈥檚 happening deep inside. In his PhD research Dipankar Mukherjee shows that Subsurface Scanning Probe Microscopy (SSPM) can do what no other method can: look through opaque layers and reveal buried structures鈥攚ithout cutting or damaging the chip. This technique could revolutionize how next-generation semiconductors are made, helping manufacturers build faster, more efficient, and more sustainable electronics.
Modern chips are no longer flat. New transistor designs鈥攍ike Gate-All-Around (GAA) and Complementary Field Effect Transistors (CFET)鈥攕tack layers of materials in three dimensions to pack more power into less space. But this also makes them incredibly hard to inspect.
Many key features lie buried under multiple opaque layers, invisible to light-based or electron-beam tools. Without precise measurement of these hidden structures, manufacturers risk defects, lower yields, and soaring production costs. Accurate subsurface metrology has become one of the biggest roadblocks to the future of microelectronics.
A new eye beneath the surface
That鈥檚 where Subsurface Scanning Probe Microscopy (SSPM) comes in.
Unlike conventional techniques, SSPM uses a tiny vibrating tip to sense mechanical properties deep beneath the surface, creating non-destructive, three-dimensional nanoscale images. Dipankar Mukherjee shows that SSPM can detect features smaller than 10 nanometers, even when they鈥檙e hidden under about 100 nanometers of solid material鈥攁 level of detail previously thought impossible.
In simple terms, it鈥檚 like using touch instead of sight to feel the structure of a chip鈥攚ithout ever opening it.
Sharper, faster, and smarter
By experimenting with different modes of SSPM, the researcher found ways to boost both precision and reliability. In single-frequency mode, SSPM detects subtle differences in stiffness and geometry beneath the surface, which makes it ideal for identifying small variations in etch depth. When operated in mixed-frequency, or 鈥渢hree-tonal,鈥� mode, the technique becomes even more sensitive, generating higher-order harmonics that reveal depth and structure with remarkable clarity.
This approach achieved around 20-nanometer lateral resolution and clearly distinguished sub-10-nanometer etch differences, outperforming many existing metrology tools. Even better, SSPM measurements are faster and cheaper than the destructive cross-sectional electron microscopy traditionally used in chip manufacturing.
From the lab to the factory floor
Beyond the lab, SSPM鈥檚 potential is huge. It can replace slow and costly inspection steps, enable real-time process control, and improve chip yield and performance in advanced transistors.
By making manufacturing more efficient and reducing waste, SSPM also supports sustainability鈥攗sing less material and energy while minimizing costly errors.
In short, it helps manufacturers see what they couldn鈥檛 before, making each chip both smarter and cleaner to produce.
Powering a sustainable and inclusive tech future
By improving production efficiency and lowering inspection costs, SSPM helps make cutting-edge technology more affordable and accessible. It strengthens the global semiconductor supply chain, supports economic growth, and advances sustainability goals鈥攁ll while pushing the boundaries of what chips can do.
As we continue to demand faster, greener, and more powerful devices, SSPM could become a key technology that keeps Moore鈥檚 Law alive鈥攈elping the world see deeper, build better, and think smaller.
Title of PhD thesis: . Supervisors: Prof. Henk Nijmeijer and Dr. Simon Eugster.