Semiconductor Wafer Temperature Control Using Feedforward and Temporary Setpoints
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Solution Overview
Problem
Existing temperature control methods for semiconductor wafers face performance degradation due to saturation of temperature adjusters, limiting their ability to respond quickly to setpoints and maintain uniformity among control loops.
Innovation Solution
A temperature control system with a master loop and slave loops, utilizing a manipulated variable calculator to calculate and convert variables, incorporating a setpoint setting section, deviation calculators, and a feedforward variable addition to reduce interference and enable fast temperature adjustment by initially using a temporary setpoint followed by feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If temperature adjusters are controlled using conventional master-slave or gradient temperature control methods, then temperature uniformity can be maintained, but control performance degrades when temperature adjusters saturate
Solution Approach 1:
The patent applies preliminary action by introducing a feedforward variable that is added to the manipulated variable before the temperature adjusters are saturated. This feedforward component anticipates the saturation issue and adjusts the control signal in advance, preventing the degradation of control performance that would otherwise occur when the temperature adjusters reach their saturation limits. The feedforward variable is calculated based on the deviation between the actual temperature and the setpoint, allowing the system to proactively compensate for potential saturation effects.
2Device complexity
If conventional control methods are used, then system complexity is reduced, but response speed to setpoint changes is limited due to saturation
Solution Approach 1:
The feedforward variable is introduced as a preliminary action that enhances the response speed without significantly increasing system complexity. By calculating and adding this feedforward component based on temperature deviation, the system can respond more quickly to setpoint changes while maintaining a relatively simple control architecture. The feedforward mechanism provides an additional control pathway that operates in parallel with the conventional feedback loops.
3Speed
If temperature adjusters operate at maximum capacity to respond quickly to setpoints, then response speed improves, but interference among loops increases
Solution Approach 1:
The patent converts the harmful effect of loop interference into a benefit by using the feedforward variable to coordinate the operation of multiple temperature adjusters. Instead of allowing interference to occur when adjusters operate at maximum capacity, the feedforward mechanism distributes the control effort in a way that reduces mutual interference while maintaining fast response. The feedforward calculation considers the interactions between loops and adjusts individual adjuster outputs to minimize harmful interference effects.
Data Source
AI summary
A temperature controller that performs a temperature control on a plurality of temperature adjusters including a reference temperature adjuster to adjust a temperature of a semiconductor wafer includes a setpoint setting section that: sets a temperature detected by a master temperature detector as a control setpoint for a reference one of the temperature adjusters of a master loop, until a temporary setpoint below an actual control setpoint preset as a desired temperature of the semiconductor wafer is reached; and sets the actual control setpoint as the control setpoint for the master loop after the temporary setpoint is reached.