Two-Stage Light Irradiation for Wafer Annealing Depth Control
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Solution Overview
Problem
Conventional heat treatment methods for semiconductor wafers using halogen lamps result in deep diffusion of ions, leading to unintended junction depth and potential damage during rapid temperature rises, while xenon flash lamps can cause surface damage with prolonged irradiation.
Innovation Solution
A two-stage light irradiation method where a peak emission output is followed by a supplemental irradiation with reduced output, maintaining surface temperature and avoiding excessive heating, allowing for ion activation and defect restoration without damaging the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If halogen lamps are used for rapid thermal annealing, then the substrate temperature can be raised rapidly, but ions are deeply heat-diffused causing junction depth to increase
Solution Approach 1:
The light irradiation is divided into two distinct stages: a first stage with high emission output for rapid heating, and a second stage with reduced emission output for controlled cooling and defect restoration. This segmentation allows the system to achieve both rapid temperature rise and precise junction depth control by separating the heating function from the cooling/annealing function.
Solution Approach 2:
The light emission follows a periodic waveform pattern with a peak emission followed by a reduced emission phase. This periodic action enables the substrate to experience rapid heating during the peak phase while preventing excessive heat diffusion during the reduced emission phase, thereby controlling junction depth while maintaining fast processing speed.
2Speed
If xenon flash lamps are used for extremely short-time irradiation, then surface temperature rises rapidly for ion activation, but defects at depth cannot be restored
Solution Approach 1:
The light irradiation continues through two stages: the first stage provides rapid surface heating for ion activation, and the second stage maintains extended irradiation with reduced output to allow heat diffusion to deeper regions. This continuous two-stage action ensures both rapid surface heating and sufficient time for defect restoration at depth, combining the advantages of fast processing with complete annealing.
3Reliability
If prolonged light irradiation is used to restore defects at depth, then defect restoration improves, but surface temperature becomes excessively high causing damage
Solution Approach 1:
The light emission output is adjusted differently for different time periods: high output during the first stage for rapid surface heating, and reduced output during the second stage for controlled heat diffusion. This local quality adjustment in the emission profile allows deep defect restoration while preventing surface overheating and damage.
Solution Approach 2:
The emission output parameter of the light source is dynamically changed between two stages: a peak emission output for rapid heating followed by a reduced emission output for controlled cooling. This parameter change enables the system to achieve both deep defect restoration and surface temperature control, preventing surface damage while ensuring complete annealing.
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 activates implanted ions and restores defects at depth without surface damage, ensuring precise temperature control within the semiconductor wafer.
Implementation Method 1
heating a substrate by light irradiation of the substrate
Implementation Method 2
The wavelength of the light emitted from xenon flash lamps is shorter than that of the light emitted from conventional halogen lamps, and it almost coincides with a fundamental absorption band of a silicon semiconductor wafer. Thus, when a semiconductor wafer is irradiated with the flash light emitted from xenon flash lamps, the temperature of the semiconductor wafer can be raised rapidly
Data Source
AI summary
In light-irradiation heating with a total irradiation time of one second or less, two-stage irradiation is performed, including a first stage of light irradiation of a semiconductor wafer, which irradiation produces an output waveform that reaches a peak at a given emission output; and a second stage of supplemental light irradiation of the semiconductor wafer, which irradiation is started after the peak, producing an emission output smaller than the above given emission output. The emission output in the second stage is two thirds or less than the above given emission output at the peak. The first-stage light-irradiation time is between 0.1 and 10 milliseconds, and the second-stage light-irradiation time is 5 milliseconds or more. This allows the temperature of the semiconductor wafer even at a somewhat greater depth below the surface to be raised to some extent while allowing the surface temperature to be maintained at a generally constant processing temperature.