Chipmaker use our products to address chip printing as well as inspection through data feedback loops that allow them to increase accuracy and yield.
Types of metrology and inspection
There are two ways to examine the quality of the printed features on a chip: diffraction-based optical measurement and e-beam inspection.
Diffraction examines how light reflects from the wafer, while e-beam observes how electrons scatter when they come into contact with the wafer.
ASML uses both: YieldStar systems use diffraction-based measuring to measure the quality of patterns on the wafer, and HMI e-beam inspection systems help locate and analyze individual chip defects. Combined with the information from the sensors inside our lithography machines, YieldStar and HMI systems provide a host of data that chipmakers use to optimize their manufacturing process.
Diffraction-based optical metrology
ASML's YieldStar systems do just what their name suggests: They help our customers to increase their yield, or the proportion of chips on the wafer that perform properly. YieldStar allows manufacturers to track key production parameters such as overlay (the accuracy with which two layers of a chip are aligned). YieldStar systems are usually integrated into the production line so that they can measure quickly and accurately, looping the data back to the lithography system for real-time corrections to the manufacturing process.
How it works
Diffraction-based metrology is based on the simple fact that an object’s shape determines how light reflects from it. For example, shine a beam of light onto a repeating pattern of lines on a wafer, and you can easily predict what the resulting pattern of scattered light should look like. If you collect the scattered light using a high-resolution digital camera, you can quickly determine how well the prediction matches reality and thus how well the pattern of lines has been printed.
Fast, accurate wafer metrology
In wafer metrology, key manufacturing parameters such as overlay (the accuracy with which two layers of a chip are aligned) and focus (how sharp the image is) are monitored by measuring how well a particular repeating pattern (the ‘metrology target’) is printed on the wafer. These measurements are made at marked locations across the wafer.
Integrated into the production line
Prior to YieldStar, wafers were taken out of the production line to be measured manually. By integrating our solution into the production line (or ‘track’), chipmakers can now use YieldStar to gather their metrology data quickly and accurately, offering better control over their production processes. Metrology data is analyzed in control software and fed back to the lithography system in real-time, which enables customers to tune the manufacturing process further for optimal yield.
From repeating patterns to real structures
Our latest developments in diffraction-based metrology feature new optics technology to generate even more accurate data faster, measuring thousands of data points for each batch of wafers. YieldStar matches the productivity of our lithography systems for wafer-to-wafer control on the most advanced chip nodes. Additionally, YieldStar is being used for after-etch metrology to inspect actual device structures with more accuracy and higher measuring speed than our competitors’ scanning electron microscope (SEM) solutions.
For today’s advanced microchips, defects as small as a couple of nanometers can be enough to render the entire chip useless. With its 1-nanometer resolution, e-beam inspection offers just the right kind of eyes to spot those tiny misprints.
ASML is at the forefront of developments in e-beam metrology and inspection. E-beam boasts a higher resolution than YieldStar, but it measures more slowly, which means that it’s typically used after the pattern has been etched into the wafer.
How it works
‘E’ is for ‘electron’
E-beam technology has been around for decades. The basic concept is that a metal wire is heated until it gives off electrons, which are accelerated and formed into a beam by electric and magnetic fields. Unlike visible and ultraviolet light (but just like extreme ultraviolet light) electron beams have to travel in a vacuum so they are not deflected or absorbed before reaching the target.
In metrology and inspection in the semiconductor industry, the e-beam scans across the wafer. The electrons strike the surface and penetrate a small distance into the material, generating new 'secondary electrons' before being scattered. Just as with diffraction-based measurements, measuring the scattering of secondary electrons allows us to build up a very high-resolution picture of the surface. The more focused the beam, the smaller the details that can be measured.
Speeding up e-beam imaging
The tricky thing with e-beam measurements is that they’re quite slow. As a result, they have only typically been used in the early R&D phase of chip manufacturing, where time is less of an issue.
ASML is leading the way in speeding up e-beam measurements so that manufacturers can enjoy their benefits in volume production. One way we do that is by developing solutions that focus e-beam measurements on specific hotspots where defects are more likely or more critical.
Our most recent e-beam system, the HMI eScan 1000, combines high-resolution e-beam measurements with state-of-the-art computational modeling, machine learning algorithms and data from the lithography system.
The HMI eScan 1000 uses multiple e-beams to inspect a greater surface area of the wafer faster. First shipped to customers in May, 2020, the eScan 1000 is a 3x3 multibeam system that can increase throughput by around a factor of nine. But we don't intend to stop there – we plan to increase the number of beams and beam resolution for future generations to align with chipmakers’ product roadmap requirements.
In-line wafer and reticle inspection
By speeding up the process and narrowing down the search to specific areas, e-beam can be used directly in the production line for wafer inspection while maintaining productivity levels.
Each of our lithography machines is fitted with hundreds of sensors – some 1,500 in our latest EUV systems. These monitor everything that happens inside the system: from mapping the wafer’s surface and temperature to verifying the reticle’s positioning and checking for local heating in the lens. A single lithography system can generate up 31 terabytes of data per week from these sensors – that’s three times more than the Hubble Space Telescope gathers in a year.
Fast feedback loops
Data is only useful if you can act on it. That’s why our lithography systems have thousands of actuators that can minutely adjust key elements in the wafer and reticle stages, the lens system and the illuminator. These allow the system settings to be precisely tailored as required.
The link between data and actuator within the lithography system is automatic. Beyond that, we have developed powerful software tools that can analyze data from optical metrology and e-beam inspection to identify variations in the manufacturing process. Armed with that knowledge, we calculate the best settings for our lithography systems to ensure the manufacturing process yields optimal results.
Pattern fidelity control (PFC) is a new paradigm in chip manufacturing, aiming to deliver the full benefits of our holistic lithography approach. By drawing and analyzing the most precise data from a wider range of sources throughout the entire chip development and manufacturing process, it gives chipmakers unprecedented insight into the patterns they are actually printing on wafers. Power algorithms then translate that insight into actions that can be implemented in the lithography system to prevent pattern defects and enable high yields even when producing the most complex chips.
Delivering the data
The vision for PFC is to draw relevant data from wherever possible in the microchip development and production processes. To do that, we work together with other semiconductor equipment makers in the fab to bring the most benefit to chipmakers. We of course use typical data sources such as YieldStar metrology systems, e-beam inspection tools and the wafer mapping within our lithography systems. But we also leverage the information from our computational lithography solutions as well as non-ASML equipment in the production line. Finally, we are developing a range of pattern fidelity metrology options that harness the high resolution of e-beam measurements in ways that can be integrated into the production line.
Working with domain experts in particular competence fields such as overlay performance or illumination configuration, the vast amounts of data are first manually pre-processed to remove spurious relationships (where the domain experts see a correlation but know there is no causal relationship). That data is then analyzed with advanced computer models and machine learning algorithms to uncover interactions between the many factors that contribute to defects, affecting the performance of the finished microchip. We finally calculate suitable corrections to be applied in the lithography. This will deliver the advanced control that manufacturers need for sub 10 nm features.
More about ASML technology
EUV lithography systems
Providing highest resolution in high-volume manufacturing, ASML’s extreme ultraviolet lithography machines are pushing Moore’s Law forward.
DUV lithography systems
ASML's deep ultraviolet (DUV) lithography systems dive deep into the UV spectrum to print the tiny features that form the basis of the microchip.
Metrology & inspection systems
Delivering speed and accuracy, our metrology and inspection portfolio covers every step manufacturing processes, from R&D to mass production.