Lamp Driver Circuit Switching for High-Power-Factor Wafer Heating
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Solution Overview
Problem
Rapid thermal process chambers using SCR-based lamp driver circuits face inefficiencies due to low power factor, especially at low power levels, limited control accuracy, and inability to switch near zero voltage crossings, which hinder precise temperature control and energy efficiency in 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-transistor pair is connected in parallel to halogen lamps, allowing for precise control signals to be generated by a temperature controller to turn the switches on and off multiple times per AC half cycle, improving power factor to approximately 1 and enabling faster and more accurate temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If SCR-based lamp driver circuits are used, then the circuit can control power to lamps, 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 transistor-based switching instead of SCR-based phase angle control. This allows the circuit to operate in a mode that maintains high power factor (close to 1.0) across all power levels, particularly improving performance at low power levels where SCR circuits suffer from power factor degradation.
Solution Approach 2:
The patent replaces the SCR (silicon controlled rectifier) based mechanical/electronic switching system with a transistor-based electronic switching system. This substitution enables more precise control of the lamp driver circuit operation, allowing for high power factor maintenance through proper switching timing and control signal generation.
2Ease of operation
If SCR-based lamp driver circuits are used, then the circuit can control lamp power, but the minimal output current has a threshold due to minimum voltage requirement for turning on
Solution Approach 1:
The patent changes the control parameters by implementing a transistor-based switching system that can operate with very low minimum output currents. The control circuit generates switching signals that allow the transistors to turn on and off at appropriate points in the AC cycle, enabling precise control down to minimal power levels without the voltage threshold limitations of SCR circuits.
Solution Approach 2:
The patent implements dynamic control of the lamp driver circuit through programmable control signals that can adjust switching timing and duration. This dynamic control allows the system to adapt to different power levels and processing requirements, providing both wide control range and high precision temperature control through real-time adjustments of the switching parameters.
3Productivity
If SCR-based lamp driver circuits are used, then the circuit can switch lamps on and off, but only two times per period due to SCR nature
Solution Approach 1:
The patent implements dynamic switching control using transistors that can be turned on and off multiple times per AC period based on control signals. This allows the lamp driver circuit to provide rapid temperature adjustments by switching the lamps on and off frequently, enabling faster response to temperature control requirements compared to the fixed two-times-per-period limitation of SCR circuits.
Solution Approach 2:
The patent uses periodic control signals to switch the transistors on and off multiple times within each AC period. This periodic switching action enables fine-grained control of the average power delivered to the lamps, allowing for rapid temperature modulation and improved processing speed through multiple switching cycles per fundamental AC period.
4Ease of operation
If SCR-based lamp driver circuits are used, then the circuit can control lamp power, but it cannot be turned on near voltage zero crossings
Solution Approach 1:
The patent implements dynamic switching control that can operate at any point in the AC voltage cycle, including near zero crossings. The transistor-based system responds to control signals that determine switching timing, allowing the circuit to be turned on at optimal moments for temperature control precision without the minimum voltage threshold constraints that prevent SCR circuits from operating near zero crossings.
Data Source
AI summary
A thermal process chamber having a lamp driver circuit that includes two transistors and two diodes is described. The 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.