Semiconductors – essential components within microchips – are complex and high-value items which require regular quality control (QC) checks throughout the manufacturing process. As traditional QC methods begin to struggle to detect defects in the increasingly complex features of newer microchips, some manufacturers are employing Atomic Force Microscopy (AFM). This technique uses a physical probe to map semiconductor features by measuring the changing height of the probe as it runs over 3D features, calculating their height or depth. However, this technique is too slow to be used in routine quality control processes.
Infinitesima Limited, a venture capital funded startup, has developed the Metron 3D TM, an AFM tool that can measure 100 times faster than most AFMs on the market. Instead of relying on the slow control loop available with standard piezoelectric-based AFM devices, Metron 3D TM uses faster laser interferometry - in which a laser beam is reflected from the probe and laser interference is measured to determine its precise position.
Obtaining accurate laser interferometry measurements relies on multiple advanced components and carefully aligned setups. Infinitesima’s setup worked well, but required improvements in order to achieve the accuracy required for measuring the deep etched features found in the most advanced semiconductors, and to allow the company to sell to this valuable market segment. They approached NPL via the Measurement for Business programme (M4B) to help them achieve their goals.
Infinitesima had worked with NPL on previous projects, so the NPL team already had a relationship and an understanding of the device.
Building on this, NPL replicated the device design and performed measurements using standard artefacts to test for inconsistencies. Combining test data, modelling and decades of accumulated interferometry measurement expertise, NPL systematically worked through the various optical interferometry components and measurement processes used in the device, to understand how the accuracy of deep structure measurements could be improved.
“NPL took a really rigorous approach, looking at every aspect of the design.” says Patrick Hole, Senior Director of Development and Engineering at Infinitesima, “They ruled out some areas we thought might be an issue to improving deep measurement accuracy, instead confirming these were not causing an issue, and quickly honed in on the areas that were impacting the measurement result”.
NPL identified two technical points which could be improved: beam positioning and design inefficiencies within the interferometer block – and provided a report to Infinitesima outlining the issues. NPL tested and validated a new design for the interferometer block – an essential component of interferometry – which would improve accuracy.
As a result of the project, Infinitesima have improved their build process to better control for the beam positioning.
“The knowledge of our product design that we have gained from the project is now helping us make critical design improvements that will deliver the accuracy needed for our most advanced use cases,” says Patrick Hole.
The improvements will make the system viable for use in quality control for new FinFET transistors, which use complex 3D structures and deep channels to deliver more processing power in a smaller space. This is one of three key semiconductor markets that Infinitesima is targeting, which it estimates could be worth £100 million in sales.
The project also provided rigorous design and validation data, which can be requested by Infinitesima’s more exacting customers.
Whilst the product is still in customer trials, it could have huge potential in the semiconductor industry.
“Semiconductor manufacturing is incredibly high value and probably the most exacting of any modern industry,” says Patrick. “They can go through thousands of manufacturing steps to etch in nanoscale features, and tiny errors in any one of these can mean whole batches get thrown out at great expense. The semiconductor industry is dying for practical measurement tools that they can insert along the process to monitor and control processes. Scanning Electron Microscopy is no longer fit for purpose, and AFM has until now taken too long for in-line quality checks. Our new approach to AFM provides both speed and accuracy."
Thanks to NPL, we are now able to fully understand the physics behind our instrument, optimise the design to resolve errors that occurred when it was pushed to its limits, and gather validation data to assure customers. That’s good for us, and will be good for the global semiconductor industry, and the growing number of companies that rely on its cutting-edge chips
Patrick Hole, Senior Director of Development and Engineering - Infinitesima