Variable Frequency Microwave Annealing for Semiconductor Thermal Control
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Solution Overview
Problem
Current annealing processes for semiconductor devices face challenges in achieving consistent process uniformity and repeatability, particularly in ultra-shallow junctions and nickel silicide formation, due to high thermal budgets and uncontrollable temperature spikes, which can lead to warpage and stress in the device structure.
Innovation Solution
The use of Variable Frequency Microwave (VFM) heating with dual non-contacting thermal measurement devices, one sensitive to emissivity changes and the other not, allows for real-time monitoring and control of the annealing process, reducing thermal stress and warpage by using emissivity changes as a proxy for process progress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If furnace annealing is used to process semiconductor wafers, then large batches of wafers can be heated to activate dopants and change film properties, but the processing time becomes extremely long (several hours up to a day)
Solution Approach 1:
The patent replaces conventional furnace heating with microwave energy heating. The microwave energy couples directly with the semiconductor material to provide rapid volumetric heating, eliminating the slow thermal diffusion process inherent in furnace annealing. This substitution of heating mechanism reduces processing time from hours to minutes while maintaining batch processing capability.
Solution Approach 2:
The patent employs periodic pulsed microwave heating cycles with specific duty cycles and pulse widths. This periodic action allows for rapid thermal cycles that achieve the required dopant activation and film property changes in minutes, compared to continuous slow heating in furnaces. The pulsed nature also prevents excessive thermal buildup while maintaining processing efficiency.
2Loss of time
If rapid thermal processing is used to reduce processing time, then thermal cycles can be completed in minutes, but temperature spikes and poor uniformity occur
Solution Approach 1:
The patent incorporates real-time temperature monitoring using optical pyrometry or other non-contact sensing methods during microwave processing. This feedback is used to dynamically adjust microwave power levels and pulse timing to maintain uniform temperature distribution across the wafer batch. The closed-loop control prevents temperature spikes and ensures consistent processing conditions throughout the rapid thermal cycle.
Solution Approach 2:
The patent uses dynamic control of microwave power delivery with varying pulse widths, duty cycles, and power levels during the processing cycle. This dynamic adjustment allows the system to rapidly heat the wafers uniformly while preventing localized overheating. The processing parameters are continuously optimized during the cycle to maintain temperature uniformity despite the rapid heating rates.
3Reliability
If high thermal budget annealing is applied to activate dopants, then dopant activation is achieved, but dopant diffusion increases and junction depth increases
Solution Approach 1:
The patent uses rapid microwave annealing to quickly pass through the temperature range where dopant diffusion occurs. By heating rapidly to the required activation temperature and maintaining it for a brief period, the system achieves dopant activation before significant diffusion can occur. This 'rushing through' the critical temperature zone minimizes unwanted dopant migration while ensuring complete activation.
Solution Approach 2:
The patent changes the fundamental heating parameters by using microwave energy with specific frequency, power level, and pulse characteristics rather than conventional thermal conduction. This parameter change enables volumetric heating that reaches the required temperature uniformly throughout the wafer thickness rapidly, achieving dopant activation with minimal thermal exposure time and thus minimal diffusion.
4Reliability
If conventional thermal processing is used for nickel silicide formation, then phase transformation occurs, but temperature monitoring and phase control become difficult
Solution Approach 1:
The patent replaces conventional contact-based temperature measurement with non-contact optical pyrometry during microwave processing. This allows real-time temperature monitoring without physical interference with the microwave field or the nickel-silicon system. The optical method provides continuous temperature data throughout the phase transformation process, enabling precise control of the silicide formation and phase evolution.
Solution Approach 2:
The patent uses optical radiation as an intermediary to monitor temperature during the microwave heating process. The optical pyrometer detects thermal radiation emitted by the nickel-silicon system, providing indirect but accurate temperature measurement without introducing physical probes that would interfere with the microwave energy coupling or the phase transformation process.
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
This approach enables rapid, low-thermal-budget processing with in-situ feedback, ensuring minimal deformation and improved process control, achieving consistent and repeatable results in semiconductor device fabrication.
Implementation Method 1
a first noncontacting thermal measurement device positioned to measure temperature on a first area of the semiconductor
Implementation Method 2
a second noncontacting thermal measurement device positioned to measure temperature on a second area of the semiconductor
Implementation Method 3
Method and apparatus for controlled thermal processing... heating source
Data Source
AI summary
A materials processing system comprises a thermal processing chamber including a heating source, a first noncontacting thermal measurement device positioned to measure temperature on a first area of the material being processed, and, a second noncontacting thermal measurement device positioned to measure temperature on a second area of the material being processed, the first device being relatively more sensitive to changes in surface emissivity than the second device. By comparing the outputs of the two devices, emissivity changes can be detected and used as a proxy for some physical change in the workpiece and thereby determine when the desired process has been completed. The system may be used to develop a process recipe, or it may be part of a system for real-time process control based on emissivity changes. Applicable processes include heating, annealing, dopant activation, silicide formation, carburization, nitridation, sintering, oxidation, vapor deposition, metallization, and plating.