Calibrating Surface Defect Inspection Systems

Semiconductor devices continue to grow in performance and complexity without an increased cost or power consumption. This is largely due to the ability of the semiconductor manufacturing industry to continually shrink device features, allowing more components (primarily transistors) to be integrated into smaller packages. For five decades, CPU technology followed Moore's law, which stated that the number of components per integrated circuit would double every year.

As devices decrease in size, smaller particles can damage or "kill" the components. These "killer defects" must be detected during the manufacturing process and their sources mitigated to reach and maintain high manufacturing yields. Surface inspection systems are used to search for defects on wafer and photomask surfaces as a crucial part of the advanced process control (APC) applied to semiconductor integrated circuit fabrication.

There are different types of defects, including:

Defects from a process – which happen when the process is not working as intended. It causes issues such as missing materials or rounded transistor edges instead of straight edges.

Particle defects – which happen when a particle works its way into a sensitive part of a component, such as the trench of a transistor.

• If the particle connects the sides of the trench, it will cause a short.
• If the particle prevents material from being deposited, it will create a void. A void prevents conduction from happening and ruins the component.

There are many different sources for defects, ranging from materials, to processes, to equipment, to the processing substrate (wafer) itself. In order to pinpoint which source is responsible for the defect, the wafer is inspected at each stage of the manufacturing process. Different inspection stages require different metrology tools.

The first stage of inspection is on bare wafers. Latter stages involve inspection of wafers with a uniform film. Bare wafers and films are called unpatterned surfaces, and they are examined for particles that could become killer defects. These stages of inspection are meant to:

1. Check the different tools involved in the process to make sure they are not generating defects.
2. Detect contamination excursions, when a lot of defects are generated by a certain process for an unknown reason.

Photomasks (reticles) used in photolithography for printing patterns in thin films must also be inspected for defects embedded in the photomask patterns ("hard defects") and particles that land on the photomask surface ("soft defects"). Sufficiently large hard or soft defects will result in defects in the pattern printed on each die of the wafer ("printable defects"). Unpatterned photomask (reticle) inspection systems inspect mask surfaces for printable defects.

Unpatterned wafer and unpatterned reticle inspection systems must be properly calibrated and qualified to reliably detect killer defects and printable defects. Wafer and photomask contamination standards deposited with particles of known material and accurately controlled particle size and count are essential for effective equipment calibration. MSP is happy to provide these contamination standards and the equipment used to produce these standards to help semiconductor manufacturers and equipment suppliers at any stage of the surface defect detection process.

Semiconductor Clients

We have a wide range of semiconductor clients, and each type of client uses our semiconductor metrology products and services in a different way.

Integrated Device Manufacturers (IDM)

What do they need it for? IDMs manufacture the devices using advanced process control to maximize manufacturing yield and product reliability. 

How do they use it? IDMs need to calibrate their inspection and defect review systems, and want to reduce the amount of variability between tools. The end goal is to understand how their inspection systems perform, as installed and with continuous use, so the systems can find "killer defects" before they result in significant product loss during the manufacturing process. (“Killer defects” refers to a defect large enough to render the device useless, and can be as small as 10nm.) MSP provides highly-automated particle deposition systems, which produce custom wafer contamination standards for inspection system calibration, qualification, and performance monitoring. Knowing the strengths and limitations of the inspection systems allows IDMs to ultimately improve their yield of viable microchips.

Process Tool OEMs

What do they need it for? Process Tool OEMs manufacture the equipment used for creating the microchips (equipment that helps to complete some of the hundreds of process steps) and need both contamination standards and inspection/defect review systems. The contamination standards support the metrology required for developing their process tools/equipment and supporting the process control used by their customers. The inspection/defect review systems help them develop their equipment and processes.

How do they use it? Process Tool OEMs use inspection and defect review systems to analyze the output of the tools they develop (for example, film quality) and to try to identify sources of contaminant particles generated by their equipment and processes. They use high-quality custom wafer and reticle contamination standards, developed by MSP, to calibrate and monitor the performance of their inspection systems. They also use MSP Particle Deposition Systems to develop their own contamination standards and inspection tool recipes tailored to the process control needs of each customer. 

Inspection Tool OEMs

What do they need it for? Inspection Tool OEMs manufacture wafer and reticle inspection systems/tools, and need to verify that their inspection systems can detect defects with enough sensitivity and reliability.

How do they use it? Inspection Tool OEMs need to characterize the performance of their systems – each system needs to detect down to a specific particle size on a specific substrate with a specific film or surface finish. To verify inspection system performance and to calibrate the equipment, test wafers or reticles deposited with particles of proper size, shape, and composition are needed. MSP supplies deposited wafers and reticles (photomasks) for Inspection Tool OEMs to test and calibrate their equipment. We also provide conformance standards that are shipped with the equipment when it is sold to the end user so they can check/validate the tool’s performance periodically.