![]() The global CD model was then used to investigate the impact of transient and steady-state temperature profiles on CD control. These results are consistent with the well-documented diffusion- controlled deprotection reaction taking place during the PEB process. An effective activation energy of 50 Kcal/mole was obtained for the Acetal resist whereas PROLITH simulations for an ESCAP type resist gave 69 Kcal/mole. A global CD model was created by fitting experimental data to a first order kinetics equation. Experimental studies on the Acetal resist resulted in very non-linear Critical Dimension (CD) sensitivities with CD variation largest for low Post Expose Bake (PEB) temperature and short PEB time. The effect of varying time and temperature profile at the PEB step on a 250 nm isolated line is studied for an Acetal and an ESCAP type Deep UV (DUV) resist. In summary, integrated metrology with closed loop control provides improved process control as well as enhanced throughput for oxide CMP. Lot charts showing thickness variations before and after the implementation of CLC have been recorded showing an improved distribution with CLC feedback leading to improvements in process capability by a factor of 1.5. A system as described was implemented on an IPEC 472 polisher at Motorola MOS6. Considering the results of the measurement of previously polished wafers, the polish time for the following wafer is adjusted to center the thickness distribution around the target. The utilized closed loop control algorithm (PID-type) can take the incoming distribution into account as well as first wafers effects and changes in layer type. In respect to optimizing the wafer to wafer variation within lot, the polish time can be adjusted for the subsequent wafer based on the previously polished wafers. This methodology reduces the set-up time significantly and allows a 100% control of the outgoing product with increased throughput versus using an off-line measurement system. An integrated measurement tool, that provides feedback immediately after the polish cycle, represents an intermediate solution. While these approaches allow a better control of the thickness remaining, they do not replace the off-line measurement because the correlation of the signal with the absolute thickness is difficult and no uniformity information is retrieved. Recently, systems have been introduced to endpoint on the polish platen itself using interference-based methods. This procedure causes a significant delay in feedback due to the off-line scrubbing process and wafer transfer. LAM RAINBOW 4520 MANUAL VERIFICATIONOxide chemical mechanical polishing process control has been limited in the past to off-line verification of layer thicknesses. ![]() Experimental results are performed for a commercial conventional bake plate and depict an order-of-magnitude improvement in the settling time and the integral-square temperature error between the optimal predictive controller and a feedback controller for a typical load disturbance. It is easy to design and implement for conventional thermal processing equipment. ![]() This procedure is based on an empirical model generated from data obtained during closed-loop operation. This results in a predictive controller that performs a pre-determined heating sequence prior to the arrival of the wafer as part of the resulting feedforward/feedback strategy to eliminate the load disturbance. The optimal control strategy is a model-based method using linear programming to minimize the worst-case deviation from a nominal temperature set-point during the load disturbance condition. An optimal control scheme is designed to improve repeatability by minimizing the loading effects induced by the common processing condition of placement of a semiconductor wafer/photomask at ambient temperature on a large thermal-mass bake plate at processing temperature. ![]()
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