Khalid El-Awady

Spatially programmable temperature control and measurement for chemically amplified photoresist processing

Preliminary performance data is presented for a new thermal processing module. The system is directed towards conducting the temperature sensitive baking and chilling steps for chemically amplified photoresists. The module is comprised of 49 individual heating zones. The zones can be controlled independently with separate temperature sensing, actuation and feedback control mechanisms. A supervisory control strategy is applied to coordinate the individual zones. An in-situ chill plate is used to enable a temperature controlled cool-down phase without the need for substrate movement. Results are presented to demonstrate temperature control over the plate to within plus or minus 0.02 degrees Celsius. Wafer temperature is controlled to within plus or minus 0.05 degrees Celsius as measured at 5 sites. Photomask processing results are presented depicting steady-state control to within plus or minus 0.05 degrees Celsius as measured at 16 sites within one quadrant of the substrate. The advantages of the system are discussed including better temperature uniformity than conventional systems and the ability to conduct multiple experiments in a single run by biasing the setpoint across the substrate.

Integrated bake/chill for photoresist processing

A thermal cycling system for baking and chilling semiconductor wafers is presented for photoresist processing applications. The proposed unit differs from conventional systems as the bake and chill steps are conducted sequentially within the same module without substrate movement. The unit includes a circulating fluid that can be switched between hot and cold reservoirs and serves as the dominant means for heat transfer. A set of thermoelectric devices is used in conjunction with the hot/cold fluid to provide a distributed amount of heat to the wafer for uniformity and transient temperature control. Experimental results are provided to demonstrate temperature uniformity during both transient and steady-state operation.

Application of iterative feedback tuning to a thermal cycling module

Abstract The iterative feedback tuning (IFT) method is applied to proportional plus integral (PI) controller tuning for a thermal cycling module. We investigate the effects of setting the desired output equal to the reference, reducing the IFT method to one of finding the minimum integral square error (ISE) controller. It is shown that with proper time weighting of the control error the achieved performance can be modified, trading off, for example, rise time for overshoot.

Temperature cycling and control system for photosensitive materials processing

A temperature processing module and control system is presented for the thermal cycling of substrates such as semiconductor wafers and/or quartz photomasks. The module consists of a multizone etched foil heater adhered to the surface of a fluid heat exchanger. The heat exchanger is designed with aluminum foam that enables an angularly uniform temperature distribution on the heat exchanger surface as heat is transferred to it from the fluid. A temperature control algorithm is employed to manipulate the multizone surface heater to compensate for wafer temperature nonuniformities during the thermal cycle. The performance specifications for the thermal technology are: 30 s ramp-up time, 35 s ramp-down time, 3.5 °C peak nonuniformity during ramp up, 1 °C steady-state nonuniformity, and 3 °C peak nonuniformity during ramp down for a 200 mm wafer. The control results are achieved at the expense of significant energy expenditure. The total energy for the thermal cycle exceeded 10 kW compared to a theoretical mini...

A Primal-Dual Interior-Point Method for Iterative Feedback Tuning

Abstract Iterative Feedback Tuning (IFT) is a method to tune controllers using closed loop experimental data and estimation of gradients. In this paper is shown how IFT can be extended to the case when there are constraints on some of the performance measures. This is accomplished by solving the Karush-Kuhn-Tucker conditions for the optimization problem using a primal-dual interior-point method. It is shown that only a few extra experiments have to be performed as compared to traditional IFT.

Control of spatial and transient temperature trajectories for photoresist processing

Spatial and transient control of temperature trajectories by a new thermal cycling module is presented, with a focus on photoresist processing applications for semiconductor wafers and quartz reticles. In the proposed unit, the bake and chill steps are conducted sequentially within the same module without any substrate movement. The unit includes two heating sources. The first is a circulating fluid which can be switched between hot and cold reservoirs and serves as the dominant means for heat transfer. The second is a set of thermoelectric devices which are used to provide a distributed amount of heat to the substrate for uniformity and transient temperature control. Experimental data is provided to demonstrate temperature uniformity during both transient and steady state operation. The flexibility of the system to develop new processing temperature trajectories is presented.

Improvements in C/sub pk/ using real-time feedback control

The usual approach to bring the value of the process capability index, C/sub pk/, to an acceptable level is to design equipment and develop a process in which the process variable is robust to external disturbances. However, an alternative approach involves the use of in situ sensors and real-time feedback control. Currently this approach is not widely implemented in the semiconductor industry. In this paper we provide analytic justification to quantify the potential improvement in C/sub pk/ if a real-time feedback control scheme is used instead of the usual open-loop approach. We show that for the case of feedback control the level of C/sub pk/ is only limited by the accuracy and reproducibility of the sensor provided that the target values are indeed achievable by the processing equipment. This result also holds in the presence of disturbances and nonlinearities. C/sub pk/ values for open-loop and real-time feedback control strategies are compared for two experimental applications: single-wafer CVD nitride and polysilicon processes.