Flash Heating Semiconductor Wafer Impurity Diffusion Control
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Solution Overview
Problem
Conventional heat treatment methods for semiconductor wafers using halogen lamps result in deep diffusion of impurities, leading to undesirable junction depths and increased leakage current due to insufficient recovery of crystal defects during impurity activation.
Innovation Solution
A two-staged flash heating method employing a xenon flash lamp, where the substrate is first preheated by a halogen lamp to a temperature below 650°C, then rapidly heated by the flash lamp to 1000°C or higher, followed by a second preheating and flashing step to activate impurities and recover defects, while maintaining uniform temperature distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a halogen lamp is used to heat the semiconductor wafer at a rate of several hundreds of degrees C. per second, then the impurity activation is achieved, but the impurity diffuses deeply resulting in deeper junction depth than required
Solution Approach 1:
The patent employs periodic action by using a flash lamp that emits light in short, intense pulses rather than continuous heating. The flash lamp irradiates the substrate for extremely brief periods (milliseconds or microseconds), creating a rapid temperature cycle that heats the surface quickly and allows rapid cooling, thereby preventing deep impurity diffusion while achieving the required activation temperature.
Solution Approach 2:
The patent applies the skipping principle by rushing through the heating process in an extremely short time frame. The flash lamp delivers a concentrated burst of energy that rapidly raises the substrate temperature to the required level and then immediately stops, skipping the prolonged exposure time that would cause deep diffusion. This rapid heating and cooling cycle achieves impurity activation while maintaining shallow junction depth.
2Manufacturing precision
If the temperature of the semiconductor wafer is raised quickly to activate impurity, then impurity activation is achieved, but crystal defects are not sufficiently recovered leading to increased leakage current
Solution Approach 1:
The patent uses periodic action with multiple flash lamp irradiation cycles or a specially designed flash lamp waveform that provides an initial intense heating phase for impurity activation followed by a sustained lower-intensity phase for defect recovery. This periodic heating pattern allows the substrate to reach high temperatures quickly for activation while maintaining sufficient temperature for an extended period to enable crystal defect recovery, thereby reducing leakage current.
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 effectively suppresses impurity diffusion, promotes defect recovery, and activates impurities efficiently, improving semiconductor device performance by maintaining a shallow junction depth and reducing leakage current.
Implementation Method 1
a first flash heating step in which a flash lamp emits a flashing light to a substrate which has been heated to a first preheating temperature of 650° C. or lower by light emission from a halogen lamp
Implementation Method 2
the flash lamp emits a flashing light to the substrate... so that the temperature of a surface of the substrate reaches 1000 degrees C. or higher
Data Source
AI summary
A first flash heating is performed in which a flash lamp emits a first flashing light to a semiconductor wafer having been heated to a first preheating temperature equal to or lower than 650 degrees C. by a light emission from a halogen lamp so that the temperature of a surface of the semiconductor wafer reaches 1000 degrees C. or higher. Then, a second flash heating is performed in which a second flashing light is emitted to the semiconductor wafer having been further heated by a light emission of the halogen lamp. Performing the first flash heating can suppress diffusion of impurity in the subsequent second flash heating. In the second flash heating, the impurity is activated and introduced crystal defects are recovered.