CS Metrology Award
With rising demand for LED chips for a wide range of applications, including general lighting, backlighting and displays, the use of patterned sapphire substrates (PSS) has climbed in recent years due to the significant increase in light extraction efficiency these wafers afford. Process control challenges for LED manufacturers using PSS wafers such as diffuse surface reflectivity and cone shapes with high slopes require optically efficient metrology with high light throughput.
The Zeta Optical Profiler was designed to solve these challenges. The Zeta Optical Profiler is a fully automated optical profiler for bump height, roughness, etch depth, film thickness and wafer bow applications. Proprietary ZDot™ technology is used for automated macro defect inspection of patterned sapphire substrate (PSS) wafers to find missing PSS structures, bridging, tear out and contamination. Process-critical metrology measurements of the cones, domes and pillars as well as the height, pitch and the diameter of PSS bumps can also be made.
Once defects are detected, the system automatically scans the defects of interest and provides highresolution images. Multiple broadband white light high-brightness LED light sources enable simultaneous acquisition of surface metrology data and substrate color information. ZDot optical profiling technology overcomes the disadvantages of white light interferometry with a high light throughput optical design that is impervious to vibration and sample tilt "“ key benefits in working with PSS wafers.
Before the introduction of the Zeta Optical Profiler, PSS size and height measurements were performed using either scanning electron microscope (SEM) or atomic force microscope (AFM) metrology"”both slow, inefficient and costly approaches. The Zeta Optical Profiler offers a unique, non-contact, non-destructive, high throughput and low-cost approach. The ZDot optics and unique algorithms provide a complete set of inspection and metrology solutions for both dryetch and wet-etch PSS. The 100μm² inspection area is much larger than the 10μm² or smaller area that an AFM or SEM can inspect, allowing users to collect statistical information from hundreds of bumps in one quick scan "“ typically in less than 30 seconds. By comparison, AFM or SEM can take several minutes to scan one site.
Additionally, the Zeta Optical Profiler can identify process variations down to 20 nm changes in height, a critical parameter for PSS wafer quality. Since its introduction, the Zeta Optical Profiler has become the tool of record for PSS manufacturers around the world. The low-cost of ownership"”due to the absence of consumables such as AFM probe tips"”greatly reduces long-term costs for customers, and its speed and non-contact features enable PSS manufacturers to monitor their processes with many more data points and real-time feedback, significantly improving quality control.
Editors comment
“Patterned sapphire is now a key ingredient in the majority of LEDs. It is important to have a tool that can quickly measure all the key properties of these wafers.â€
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