Dual Flash Lamp Annealing for Uniform Wafer Heating
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Solution Overview
Problem
Conventional flash lamp annealing processes for semiconductor wafers face challenges such as long preheating times, non-uniform temperature distribution, and potential wafer cracking due to thermal stress, which hinder efficient impurity activation and increase processing time.
Innovation Solution
A heat treatment apparatus and method utilizing two xenon flash lamps, one irradiating the back surface and the other the surface of the semiconductor wafer, with overlapping emission times to achieve uniform heating and reduce thermal stress, allowing for rapid temperature elevation and uniform activation of impurities without deep diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If preheating is performed using a hot plate or halogen lamps before flash lamp annealing, then the substrate reaches a stable initial temperature, but the processing time increases significantly (one minute with hot plate, several seconds to ten seconds with halogen lamps)
Solution Approach 1:
The patent combines the preheating function and flash lamp annealing function into a single integrated process. The flash lamp system performs both preheating and rapid temperature elevation simultaneously, eliminating the need for separate preheating equipment (hot plate or halogen lamps) and reducing total processing time to several milliseconds while achieving uniform temperature distribution across the substrate surface.
Solution Approach 2:
The flash lamp system is designed to perform preliminary heating action directly on the substrate surface before the main annealing process. By using the flash lamp's initial light emission phase for preheating and the subsequent phases for rapid temperature elevation, the system accomplishes both preheating and annealing in one operation, reducing overall processing time while maintaining temperature stability.
2Productivity
If the substrate surface is irradiated with flashes of light to rapidly raise temperature, then impurity activation is achieved in extremely short time, but non-uniform temperature distribution occurs due to pattern-dependent light absorption
Solution Approach 1:
The patent segments the flash lamp system into multiple independently controllable light sources arranged in arrays. By dividing the illumination into multiple zones that can be controlled separately, the system compensates for pattern-dependent absorption variations across different regions of the substrate, achieving uniform temperature distribution while maintaining rapid heating capability.
Solution Approach 2:
The patent implements local quality control by allowing different regions of the flash lamp array to emit light with different intensities or timing. This enables targeted compensation for areas with higher light absorption due to patterns, ensuring uniform temperature elevation across the entire substrate surface while maintaining the rapid annealing process.
3Loss of time
If flash lamp annealing is performed without preheating, then processing time is reduced, but thermal stress causes wafer cracking
Solution Approach 1:
The patent uses periodic action by controlling the flash lamp emission in multiple sequential phases. The first phase provides gentle preheating to reduce thermal stress, while subsequent phases deliver rapid temperature elevation for annealing. This time-resolved control of light emission eliminates wafer cracking by ensuring gradual thermal expansion while maintaining overall processing time in the millisecond range.
Solution Approach 2:
The patent changes the temporal parameters of light emission from the flash lamp, using a multi-phase pulse structure instead of a single continuous pulse. By adjusting the duration, intensity, and timing of different emission phases, the system achieves both rapid processing and thermal stress management, preventing wafer cracking while maintaining high productivity.
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 significantly reduces processing time, prevents wafer cracking, and ensures uniform impurity activation by maintaining a uniform temperature distribution across the wafer surface, enhancing the efficiency and effectiveness of the annealing process.
Implementation Method 1
The wavelength of light emitted from the xenon flash lamp is shorter than that of light emitted from a conventional halogen lamp, and approximately coincides with a fundamental absorption band of a silicon semiconductor wafer. Thus, when a semiconductor wafer is irradiated with flashes of light emitted from the xenon flash lamp, the temperature of the semiconductor wafer can be raised rapidly
Implementation Method 2
when a semiconductor wafer is irradiated with flashes of light emitted from the xenon flash lamp, the temperature of the semiconductor wafer can be raised rapidly
Data Source
AI summary
A first flash heating is performed in which a lower flash lamp irradiates a back surface of a semiconductor wafer with flashes of light, so that heat conduction from the back surface to a surface of the semiconductor wafer raises the temperature of the surface from the room temperature to an intermediate temperature. Then, a second flash heating is performed in which an upper flash lamp irradiates the surface of the semiconductor wafer with flashes of light, to raise the temperature of the surface of the semiconductor wafer from the intermediate temperature to a target temperature. Since only the irradiation with flashes of light emitted from the lower flash lamp and the upper flash lamp is used to cause the semiconductor wafer having the room temperature to reach the target temperature, all heat treatments can be completed in an extremely short time of one second or less.