Flash Lamp Annealing Circuit for Tail Current Suppression
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Solution Overview
Problem
Existing flash lamp annealing technologies face challenges in achieving short emission times for high-intensity light due to the limitations of insulated gate bipolar transistors (IGBTs), which result in tail currents and reduced cooling rates, and increased stress on the flash lamps, leading to shortened lifespan.
Innovation Solution
Incorporating a gate commutated turn-off thyristor (GCT) in series or parallel with the flash lamp to control the current flow, allowing for precise management of the emission time and reducing tail currents, thereby extending the flash lamp's lifespan and improving cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high-intensity flash of light is emitted for a short time period to achieve low heat history annealing, then the heating speed and cooling rate are improved, but the required current exceeds the rated current of conventional IGBTs, making the system inoperable
Solution Approach 1:
The patent changes the switching element parameter from IGBT to GCT thyristor, which has a higher current rating (6000A vs 4000A requirement). This parameter change enables the system to deliver the required high current for short-duration high-intensity flash emission without exceeding component ratings, thereby achieving both fast heating and reliable operation
2Reliability
If the emission time is extended to allow conventional IGBTs to handle the current, then the circuit element reliability is improved, but the cooling rate decreases and heat history increases
Solution Approach 1:
By changing the switching element from IGBT to GCT thyristor with higher current capacity, the patent enables shorter emission times (0.1ms or less) while maintaining component reliability. The GCT's higher rated current (6000A) allows the system to deliver sufficient current even during brief emission pulses, thus achieving both reliability and fast cooling requirements
3Loss of time
If the rated current of circuit elements is increased to accommodate large current for short emission time, then the emission time can be reduced, but the device complexity and cost increase
Solution Approach 1:
The patent uses a GCT thyristor that can be replaced if needed, accepting the higher initial cost and complexity as a trade-off for achieving the required performance. The system design acknowledges that specialized components like GCTs are more complex but necessary for enabling short-duration high-current operation without compromising reliability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The GCT thyristor enables efficient suppression of tail currents, allowing for rapid heating and cooling of semiconductor wafers with reduced heat history, while also reducing the stress on the flash lamps, thus enhancing the overall performance and longevity of the heat treatment apparatus.
Implementation Method 1
The light produced by the xenon flash lamps has wavelengths shorter than those of conventional halogen lamps, and almost coincides in fundamental absorption band with semiconductor wafers made of silicon. Thus, when the xenon flash lamp emits a flash of light to the semiconductor wafer, it can rapidly increase the temperature of the semiconductor wafer with less transmitted light.
Implementation Method 2
Incorporating a gate commutated turn-off thyristor (GCT) in series or parallel with the flash lamp to control the current flow, allowing for precise management of the emission time and reducing tail currents
Data Source
AI summary
A flash lamp emits a flash of light to a front surface of a semiconductor wafer held in a chamber to heat the semiconductor wafer. A GCT thyristor is connected in parallel with the flash lamp. After a lapse of a predetermined time period since a current starts to flow through the flash lamp, the GCT thyristor enters an ON state. This allows a discharge current to flow through the GCT thyristor with a smaller impedance, and prevents any current from flowing through the flash lamp. Consequently, a tail current flowing through the flash lamp can be suppressed. Furthermore, reduction in a voltage charged into a capacitor can prevent the life of the flash lamp from being shortened.