It is getting more important to monitor all aspects of influencing parameters in critical etch steps and utilize them as tuning knobs for within-wafer uniformity improvement and wafer edge yield enhancement. Meanwhile, we took a dive in pursuing “measuring what matters” and challenged ourselves for more aspects of signals acquired in actual process conditions. Among these factors which are considered subtle previously, we identified Temperature, especially electrostatic chuck (ESC) Temperature measurement in real etch process conditions have direct correlation to in-line measurements. In this work, we used SensArray technique (EtchTemp-SE wafer) to measure ESC temperature profile on a 300mm wafer with plasma turning on to reproduce actual temperature pattern on wafers in real production process conditions. In field applications, we observed substantial correlation between ESC temperature and in-line optical metrology measurements and since temperature is a process factor that can be tuning through set-temperature modulations, we have identified process knobs with known impact on physical profile variations. Furthermore, ESC temperature profile on a 300mm wafer is configured as multiple zones upon radius and SensArray measurements mechanism could catch such zonal distribution as well, which enables detailed temperature modulations targeting edge ring only where most of chips can be harvested and critical zone for yield enhancement. Last but not least, compared with control reference (ESC Temperature in static plasma-off status), we also get additional factors to investigate in chamber-to-chamber matching study and make process tool fleet match on the basis really matters in production.
KLA-Tencor EtchTemp-SE wafer enables Plasma On wafer temperature monitoring of silicon etch process. This wafer is wireless and has 65 sensors with measurement range from 20 to 140°C. the wafer is designed to run in real production recipe plasma on condition with maximum RF power up to 7KW. The wafer surface is coated with Yttrium oxide film which allows Silicon Etch chemistry.
At Fab-8, we carried investigations in 14 nm FEOL critical etch process which has direct impact on yield, using SensorArray EtchTemp-SE wafer, we measured ESC temperature profile across multiple chambers, for both plasma on and plasma off, promising results achieved on chamber temperature signature identification, guideline for chamber to chamber matching improvement. Correlation between wafer mean temperature and determining criticality-process parameters of recess depth and CD is observed. Furthermore, detail zonal temperature/profile correlation is investigated to identify individual correlation in each chuck zone, and provided unique process knobs corresponding to each chunk. Meanwhile, passive ESC Chuck DOE was done to modulate wafer temperature at different zones, and Sensor Array wafer measurements verified temperature responding well with the ESC set point. Correlation R2 = 0.9979 for outer ring and R2 = 0.9981 for Mid Outer ring is observed, as shown in . Experiments planning to modulate edge zone ESC temperature to tune profile within-wafer uniformity and prove gain in edge yield enhancement and to improve edge yield is underway.
Fang Fang, Alok Vaid, Alina Vinslava, Richard Casselberry, Shailendra Mishra, Dhairya Dixit, Padraig Timoney, Dinh Chu, Candice Porter, Da Song, and Zhou Ren, "Correlation study of actual temperature profile and in-line metrology measurements for within-wafer uniformity improvement and wafer edge yield enhancement," Proc. SPIE 10585, Metrology, Inspection, and Process Control for Microlithography XXXII, 105851Q (Presented at SPIE Advanced Lithography: March 01, 2018; Published: 21 March 2018); https://doi.org/10.1117/12.2297213.
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