RTP Lamp Driver Circuit for Unity Power Factor Heating Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current rapid thermal process (RTP) chambers using SCR-based lamp driver circuits face inefficiencies due to low power factor, limited control accuracy, and inability to switch near zero voltage crossings, leading to suboptimal semiconductor wafer processing.
Innovation Solution
A rapid thermal process chamber employing a lamp driver circuit with MOSFET or bipolar transistors, where a first and second diode are connected in parallel with transistors, allowing for precise control of halogen lamps through pulsed AC power signals, enabling multiple switchings per half cycle and improved power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If SCR-based lamp driver circuits are used to control power to halogen lamps, then the circuit can be implemented with simple components, but the power factor becomes low (less than 50% at low power levels)
Solution Approach 1:
The patent changes the operating parameters of the lamp driver circuit by using transistors (Q1, Q2) with complementary symmetry configuration instead of SCR, enabling the circuit to operate at unity power factor through active power factor correction. The transistor switching timing is synchronized with the AC line voltage to ensure current and voltage are in phase, eliminating the power factor problem inherent in SCR-based designs.
Solution Approach 2:
The patent replaces the SCR (silicon controlled rectifier) component with a transistor-based complementary symmetry circuit. This substitution enables more precise control of the lamp power while maintaining unity power factor, as transistors can be switched on and off more rapidly and with better control characteristics than SCRs.
2Device complexity
If SCR-based lamp driver circuits are used, then the circuit structure is simple, but the switching control accuracy is limited (can only switch on and off two times per period)
Solution Approach 1:
The patent implements dynamic switching control using transistors Q1 and Q2 that can be switched on and off multiple times per AC cycle through pulse-width modulation (PWM). The duty cycle of the switching signals is dynamically adjusted based on the difference between actual and desired wafer temperature, enabling precise temperature control and rapid thermal processing.
Solution Approach 2:
The patent incorporates a feedback control loop where the actual wafer temperature (measured by sensor 20) is continuously compared with the desired temperature. The temperature controller (18) adjusts the duty cycle of the transistor switching signals based on this temperature difference, creating a closed-loop control system that achieves high temperature control accuracy.
3Device complexity
If SCR-based lamp driver circuits are used, then the circuit design is straightforward, but the minimum output voltage threshold prevents switching near zero voltage crossings
Solution Approach 1:
The patent inverts the conventional approach by using complementary symmetry transistor configuration where one transistor conducts during the positive half-cycle and the other during the negative half-cycle. This allows the circuit to switch at or near zero voltage crossings without the minimum voltage threshold problem of SCRs, as the transistors are switched based on synchronized PWM signals rather than requiring a minimum triggering voltage.
4Productivity
If faster switching is implemented to improve temperature control speed, then processing efficiency improves, but energy losses increase
Solution Approach 1:
The patent implements periodic switching action synchronized with the AC line frequency. The transistors Q1 and Q2 are switched on and off in synchronism with the AC voltage cycles, with the duty cycle modulated to control average power. This synchronized periodic switching achieves fast thermal response while minimizing energy losses by ensuring switching occurs at optimal points in the AC cycle.
Data Source
AI summary
A rapid thermal process chamber having a lamp driver circuit that includes two transistors and two diodes is described. The rapid thermal process chamber includes a plurality of halogen lamps, the lamp driver, a temperature sensor that measures wafer temperature, a temperature controller connected to the temperature sensor and to the lamp driver, the temperature controller providing control signals to the lamp driver that are functions of the wafer temperature and a desired temperature. The lamp driver includes two transistors that are controlled by the control signals so that the power factor of the power supplied to the plurality of halogen lamps is in the range of 0.9 to 1.