The effect of chuck temperature adjustment on critical dimension uniformity was studied for the shallow trench isolation etch process by introducing a temperature gradient in a multi-temperature-zone electrostatic chuck. It is shown that the initial radial critical dimension non-uniformity can be improved by a gradual temperature adjustment of the electrostatic chuck and results in the target specification values of uniformity, 3σ ≤ 1.5 nm, for a critical dimension of about 35 nm. Both temperature and RF sensor wafers were used to analyze the impact of an electrostatic chuck temperature gradient on process uniformity by utilizing their unique in situ spatial and temporal mapping capabilities. Thus, the across-wafer thermal sensitivity of the critical dimension was estimated for dense structures: a temperature change of 1 °C leads to a critical dimension change of ∼0.7 nm. The RF sensor wafer was also shown to have a clear response of RF current uniformity to the electrostatic chuck temperature gradient that suggests there could be other phenomena affecting critical dimension uniformity besides temperature itself. The pure temperature contribution to critical dimension change was found to be less than 0.3 nm/°C for the temperature range studied. Finally, a possible mechanism of critical dimension tuning is discussed and an assessment of each separate etch step’s sensitivity to the electrostatic chuck temperature gradient is performed.
A system for monitoring the transient and steady state temperature profiles during the deep UV (DUV) post exposure bake (PEB) is described. The system, called Accura°C, consists of a sensor wafer, a wireless electronics unit and software on a laptop computer. To monitor temperature platinum resistance temperature detectors (RTDs) are embedded into silicon wafers. A flexible high temperature printed circuit (PC) ribbon cable connects the wireless electronics unit to the wafer. The system robot moves both the sensor wafer and electronics unit through the system. Communication between the electronics unit and a laptop computer is accomplished by a Bluetooth RF link. The RF link enables the laptop computer to analyze the temperature measurements in real time. The rechargeable batteries in the electronics unit allow detailed examination of all process chambers. Further the long operating time and real time data stream provide for bake chamber optimization such as tuning. The sensor integration into the wafer provides accurate, artifact free measurements of the rapid temperature changes during PEB ramps.
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