New Optical Metrology Method for Measuring Shape of a Lithography Photo Mask
Wooptix participates in the 39th Mask and Lithography Conference in Grenoble, presenting its latest results in Optical Metrology
Wooptix has recently presented a groundbreaking optical metrology method at the 39th Mask and Lithography Conference in Grenoble. This new technique promises to revolutionize the measurement and control of lithography photo masks, addressing critical challenges in semiconductor manufacturing and improving device yields.
The Abstract presented says: “On product overlay (OPO), with its continually shrinking budget, remains a constraint in increasing device yield1. The OPO performance consists of both scanner and process-related contributors. Both groups need to be addressed and optimized to minimize the overlay in order to keep up with Moore’s law”
The authors of this abstract are: Guillermo Castro Luis, Kiril Ivanov Kurteva, Miguel Jiménez, Juan M. Trujillo-Sevilla, Jose Manuel Ramos-Rodríguez, Jan O. Gaudestad
The Challenge of On Product Overlay (OPO)
On Product Overlay (OPO) refers to the alignment accuracy of different layers in semiconductor devices. As semiconductor components shrink and become more complex, achieving precise overlay becomes increasingly challenging. OPO performance is influenced by both scanner capabilities and process-related factors, such as wafer distortion caused by patterned stressed thin films and etching processes. Additionally, photo masks, which are used to transfer intricate circuit designs onto silicon wafers, can never be made perfectly identical, introducing further overlay errors.
Wafer distortions and mask flatness are significant contributors to OPO issues. Distortions up to the third order caused by process-induced factors can often be corrected with accurate shape measurements of the wafer. However, variations in mask flatness and thickness can introduce overlay errors that are more difficult to manage. This discrepancy between the need for improved overlay control and the capabilities of current metrology tools is particularly pronounced in multi-patterning applications, where multiple masks are used to create a single layer.
Introducing Wave Front Phase Imaging (WFPI)
Wooptix’s innovative metrology method, Wave Front Phase Imaging (WFPI), addresses these challenges by providing a highly accurate and detailed shape map of the entire optical photomask. This method is optimized for Deep Ultraviolet (DUV) lithography, which is crucial for the production of modern semiconductor devices.
The WFPI technique measures the wave front phase change of reflected light from both the front and backside of a quartz photomask. This approach allows for the generation of a shape map based on local slope measurements. The high-resolution capability of WFPI is particularly noteworthy, collecting 810,000 data points on an 86.4mm x 86.4mm area with a spatial resolution of 96µm.
Advantages of WFPI
High Precision: WFPI provides an unparalleled level of detail in measuring photomask flatness, enabling the identification and correction of minute distortions that could impact OPO.
Comprehensive Data Collection: By capturing data points across the entire surface of the photomask, WFPI ensures that all potential sources of overlay errors are accounted for.
Enhanced Overlay Control: The detailed shape maps generated by WFPI facilitate better overlay control, especially in complex multi-patterning processes, thus improving device yields and adhering to Moore’s Law.
Conclusion
The introduction of Wave Front Phase Imaging by Wooptix represents a significant advancement in the field of optical metrology. By addressing the critical issue of photomask flatness and providing high-resolution shape measurements, this new method stands to greatly enhance the precision and efficiency of semiconductor manufacturing. As the industry continues to push the boundaries of miniaturization and complexity, innovations like WFPI will be essential in maintaining the pace of technological progress.
About EMLC
The EMLC Conference annually brings together scientists, researchers, engineers and technicians from research institutes and companies from around the world to present their latest findings in mask and lithography techniques. It provides an overview of the current state of mask and lithography technologies and future strategy. Mask manufacturers and users have the opportunity to familiarize themselves with the latest developments and results.
