Process-Machine Interaction (PMI) Modeling and Monitoring of Chemical Mechanical Planarization (CMP) Process Using Wireless Vibration Sensors
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We present a deterministic process-machine interaction (PMI) model that can associate different complex time-frequency patterns, including nonlinear dynamic behaviors that manifest in vibration signals measured during a chemical mechanical planarization (CMP) process for polishing blanket copper wafer surfaces to near-optical finish (Ra ~ 5nm) to specific process mechanisms. The model captures the effects of the nonuniform structural properties of the polishing pad, pad asperities, and machine kinematics on CMP dynamics using a deterministic 2 of freedom nonlinear differential equation. The model was validated using a Buehler (Automet 250) bench top CMP machine instrumented with a wireless (XBee IEEE 802.15.4 RF module) multi-sensor unit that includes a MEMS 3-axis accelerometer (Analog Devices ADXL 335). Extensive experiments suggest that the deterministic PMI model can capture such significant signal patterns as aperiodicity, broadband frequency spectra, and other prominent manifestations of process nonlinearity. Remarkably, the deterministic PMI model was able to explain not just the physical sources of various time-frequency patterns observed in the measured vibration signals, but also, their variations with process conditions. The features extracted from experimental vibration data, such as power spectral density over the 115-120 Hz band, and nonlinear recurrence measures were statistically significant estimators (R2 ~ 75%) of process parameter settings. The model together with sparse experimental data was able to estimate process drifts resulting from pad wear with high fidelity (R2 ~ 85%). The signal features identified using the PMI model can lead to effective real-time in-situ monitoring of wear and anomalies in the CMP process. Note to Practitioners - The semiconductor industry widely uses chemical mechanical planarization (CMP) process for realizing highly polished planar surfaces on inter-level dielectrics and metallic interconnects in the fabrication of integrated circuits. Accurate and timely detection of incipient process anomalies is critical for quality and yield assurance under emerging wafer density and performance specifications. While MEMS vibration sensors are considered a viable means for monitoring various real-world processes, the complexity of the vibration signal patterns from CMP process impedes their applicability for on-line quality monitoring. We have developed a deterministic processmachine interaction (PMI) model to delineate the physical sources underlying the various complex vibration signal patterns in CMP. Our experimental investigations suggest that the PMI model can capture the salient patterns of the measured vibration signals, and can therefore be effective for detecting process drifts, such as pad wear. 1988-2012 IEEE.
