Laser-Imaging Patterned Wafer Inspection System
KLA-Tencor Corp.'s ILM-2230 patterned wafer inspection system is the first system to combine oblique angle darkfield illumination with KLA-Tencor's small-pixel, high data rate image processing. This combination of technologies provides superior capture rate for a wide range of yield-critical defect types on 0.25 micron and smaller devices, at high throughput and with a low nuisance defect rate. The system is optimized for advanced interconnect process-inspection applications, such as chemical mechanical planarization (CMP).
Patterned wafer inspection systems are a critical component in a fab's yield learning strategy, providing in-line detection of pattern defects and contaminants, which drive down yields. High throughput and sensitivity allow these tools to detect such process issues and to identify critical base line defects that must be corrected to improve yields.
CMP is a critical process in the development and production of sub-quarter micron devices, enabling both increased levels of interconnect and tighter packing densities. The CMP process, however, also introduces many new yield-limiting defect types and noise sources, including: color from oxide thickness variation; underlying and top surface pattern variations; and grain noise from metal and polysilicon. The ILM-2230 suppresses these noise sources to provide a high capture rate on the new classes of defects encountered in the CMP process, while delivering throughput of up to 20 wafers per hour at the sensitivities required for sub-quarter micron devices.
The ILM-2230 incorporates several features that combine to deliver critical levels of sensitivity and noise suppression. The digital image processing system uses a new proprietary, low noise, high-speed sensor specifically designed for darkfield illumination. The sensor helps provide the exceptional sensitivity needed to detect the yield-critical defect types, such as microscratches, pattern deformations, residual metal tungsten and microbridging, typically found in CMP inspection applications. The ILM-2230 employs two proprietary advanced optical filtering techniques, which facilitate collection of the non-repetitive defect signal and block noise from horizontal and vertical lines. In addition, KLA-Tencor's segmented auto threshold (SAT) technology, a proprietary image processing technique, further enhances defect detection sensitivity on wafers with the grainy metal and color variations encountered in CMP and metal etch processes.
By reflecting light off the wafer at an angle instead of directly, oblique angle darkfield illumination increases surface selectivity and suppresses noise resulting from the wafer's granular surface features.
Another feature, circular (C) polarization suppresses color and grain noise from underlying layers and minimizes capture of previous layer defects, a capability particularly critical for oxide CMP inspection applications.
KLA-Tencor's new patterned wafer inspection system leverages the company's IMPACT/Online automatic defect classification (ADC) software to rapidly identify both process excursions and key yield-limiting defect types, accelerating the yield-learning curve. In addition, the ILM-2230 is built on the 2100 Series platform, leveraging its proven technology and high reliability and benefiting from a common recipe set up and user interface.
KLA-Tencor Corporation, 160 Rio Robles, San Jose, CA 95134. Tel: 408-875-4200.