Flash Lamp Annealing for Impurity Diffusion Control
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Solution Overview
Problem
Conventional flash lamp annealing technologies are unable to control impurity diffusion effectively, which is crucial for optimizing the performance of semiconductor devices like CMOS, where precise control of impurity diffusion and activation is required.
Innovation Solution
A thermal processing method that involves irradiating a substrate with light to maintain a surface temperature at a diffusion temperature for a predetermined time to control impurity diffusion, followed by raising the temperature to an activation temperature to activate the impurities, with a cap film preventing desorption and maintaining impurity concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional annealing is performed for several seconds or longer to activate implanted impurities, then impurity activation is achieved, but impurities deeply diffuse by heat causing junction depth much larger than required
Solution Approach 1:
The patent employs flash lamp annealing which provides periodic, extremely short-duration light pulses (microseconds to milliseconds) to heat the substrate surface. This periodic thermal action activates impurities while limiting diffusion time, thereby achieving impurity activation without excessive junction depth increase
Solution Approach 2:
The flash lamp annealing process rushes through the heating process in an extremely short time (microseconds to milliseconds), skipping the prolonged thermal exposure that would cause deep diffusion. This allows the system to achieve impurity activation before significant thermal diffusion can occur
2Length of moving object
If flash lamp annealing is used to reduce impurity diffusion to the extent possible, then junction depth is controlled, but impurity diffusion cannot be controlled appropriately for optimizing device performance
Solution Approach 1:
The patent introduces dynamic control of the flash lamp parameters including pulse duration, pulse interval, and number of pulses. This dynamic adjustment allows the system to optimize both junction depth control and impurity diffusion control for different device requirements, enhancing adaptability
Solution Approach 2:
The patent changes multiple parameters including light pulse duration, pulse interval, number of pulses, and substrate temperature. By adjusting these parameters, the system can achieve appropriate impurity diffusion control while maintaining junction depth control, optimizing device performance
3Reliability
If the substrate is heated to high temperature for impurity activation, then impurity activation occurs, but impurities desorb from the surface and concentration decreases
Solution Approach 1:
The patent uses multiple continuous light pulses with appropriate intervals to maintain the substrate at activation temperature without excessive heating. This continuous controlled action achieves impurity activation while preventing the temperature excursions that would cause impurity desorption
Solution Approach 2:
The patent employs a cap film formed on the substrate surface before annealing. This cap film acts as a protective layer that prevents impurity desorption during high-temperature processing, cushioning against the harmful effect of temperature-induced desorption
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 method allows for precise control of impurity diffusion and activation, enhancing the performance of semiconductor devices by optimizing the overlapping length of source-drain extension under the gate, while preventing impurity desorption and concentration decrease.
Implementation Method 1
irradiating a substrate with light to maintain, for a predetermined time, a surface temperature of the substrate at a diffusion temperature
Implementation Method 2
diffusion of impurities occurs
Implementation Method 3
irradiating the substrate with light after the step (a) to rise the surface temperature of the substrate to an activation temperature at which activation of the impurities occurs
Implementation Method 4
a cap film is formed on a region in which the impurities are introduced on a surface of the substrate. Desorption of the impurities from the surface of the substrate in heating processing can be prevented
Data Source
AI summary
When an insulated gate bipolar transistor is incorporated in a drive circuit of a flash lamp, so that a light emission pattern of the flash lamp is freely defined, a temperature change pattern of a surface of a semiconductor wafer that receives the emission of flash light can be adjusted. The length of diffusion of impurities can be controlled by rising a surface temperature of the semiconductor wafer from a preheating temperature to a diffusion temperature through emission of flash light and maintaining the surface temperature at the diffusion temperature for a time period not shorter than 1 millisecond and not longer than 10 milliseconds. Subsequently, the impurities can be activated by rising the surface temperature of the semiconductor wafer from the diffusion temperature to an activation temperature.