Airborne chemical contaminants (AMCs) in the lithography cell are responsible for yield-impacting issues such as scanner haze and wafer defects. Detecting and monitoring these chemicals in real-time is critical in IC fabs. Many technologies have been deployed to monitor AMCs, but many of them are not production-worthy solutions that meet the stringent sensitivity and throughput requirements driving Moore's law. Here, we demonstrate a fully integrated AMC monitoring system, Picarro SAM (Sample. Analyze. Monitor.), that detects a variety of chemicals in real-time from multiple locations in a lithography cell. Multiple scanners, track tools, and reticle stockers are monitored 24X7 for excursions of critical inorganic AMCs such as hydrochloric acid, hydrofluoric acid, ammonia, and sulfur dioxide, as well as volatile organic compounds such as acetic acid, PGMEA, NMP, siloxanes, etc. that impact the performance of the lithography process. The SAM system integrates sensors based on Cavity Ring-Down Spectroscopy (CRDS) with a high-performance sampling system. While CRDS is an established technology to detect critical inorganic AMCs, here we demonstrate the ability to measure several critical VOCs using a new technique called broadband CRDS. SAM monitors contaminants in various parts of the scanner and track with multiple sampling tubes extending to a hundred feet or more to accommodate remote areas of the process tool. The SAM system is a fast, easy-to-use, production-ready analytical tool to monitor trace VOC and inorganic contaminants in the parts per trillion to low ppb range within seconds that helps engineers take corrective actions much faster than ever before.
There is widespread recognition in the industry that as the design rule decreases, the number of airborne molecular compounds that can drive defect formation is increasing at an exponential rate [citation: IRDS 2020]. The vast majority of these new critically important AMCs are volatile organic compounds. These VOCs are difficult to measure in the gas phase at the parts-per-billion and parts-per-trillion levels that are needed for the tight process control requirements of advanced design rules. In this paper, we report on a novel AMC chemical metrology solution for measuring critical VOCs that are relevant to the photolithography cell. The heart of the system is a real-time laserbased analyzer based on a new analytical technique called Broad Band Cavity Ring Down Spectroscopy (BB-CRDS). The VOC monitoring system has several features which make it ideally suited to AMC measurements in the production environment: ultra-trace measurements at ppb levels without the need for calibration, 24/7 operation without user intervention, and negligible consumables. The analyzer was integrated into a state-of-the-art multiplexer to monitor ten VOC species in the photolithography cell in a modern semiconductor fab. We report on multiple observations made, including transient solvent leak events, multifunction chemical filter performance, and baseline characterization of AMCs inside track tools.
It has long been understood1 that in photolithographic mini-environments, acetic acid reacts with residual ammonia to form salts that cause haze formation on the scanner optics. It also induces cosmetic defects (satellite defect) on the surface of the photoresist. The acetic acid is generated in multi-function chemical filters, where PGMEA (a photoresist solvent) undergoes hydrolysis in the acidified media used to remove bases, producing PGME and acetic acid. Acetic acid is difficult to measure in the gas phase at parts-per-billion levels, requiring either costly and cumbersome mass spectrometers that are unsuitable for deployment in a production environment, or ion chromatography, a labor-intensive, off-line technique commonly performed off-site by a third-party analytical services lab. In this manuscript, we report on a novel AMC monitoring solution for measuring acetic acid, PGMEA, PGME, NH3, and other VOCs (volatile organic compounds). The heart of the system is a real-time laser-based analyzer based on a new analytical technique called Broad Band Cavity Ring Down Spectroscopy (BB-CRDS). The VOC monitoring system has several features which make it well-suited to AMC measurements in the production environment: ultra-trace measurements of a variety of VOC species; 24/7 operation without user intervention; little to no consumables; unparalleled accuracy without the need for calibration. The AMC system also consists of a high performance 8-port multiplexer, monitoring the photolithography bay at STMicroelectronics - Rousset fab. Here we report on acetic acid and PGMEA levels observed in several track tool and scanner minienvironments, over a period of several months.
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