Two-Step Flash Annealing for Wafer Heating Without Shattering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional lamp annealers used for ion activation in semiconductor wafers face challenges in achieving shallow junctions due to deep diffusion of implanted ions, leading to increased sheet resistance values and potential wafer shattering from sudden thermal expansion during high-energy light irradiation.
Innovation Solution
A heat treatment method involving a two-step photo-irradiation process with a first step of weak irradiation followed by a second step of intense irradiation, where the substrate is preheated with a low light-emission output and then subjected to a higher peak output, and optionally including a buffer irradiation step to manage temperature increases, using a flash lamp with power supplied from multiple capacitors to control the light-emission output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If flashes of light with greater irradiation energy are emitted within an extremely short period of time to further increase surface temperature, then sheet resistance value is reduced and ion activation is improved, but thermal stress causes the semiconductor wafer to shatter
Solution Approach 1:
The light emission is divided into multiple pulses instead of a single flash. The first pulse has a first light-emission output and the second pulse has a second light-emission output that peaks higher than the first. This segmentation allows the surface temperature to be increased in controlled steps, achieving lower sheet resistance values while preventing thermal stress-induced shattering by avoiding sudden temperature jumps.
Solution Approach 2:
The first light-emission pulse serves as a preliminary action that preheats the semiconductor wafer surface before the second, higher-intensity pulse is applied. This preliminary heating reduces the thermal shock when the second pulse is emitted, allowing the wafer to withstand the higher peak temperature needed for optimal ion activation without shattering.
2Manufacturing precision
If xenon flash lamps are used to raise surface temperature rapidly within several milliseconds, then ion activation is achieved without deep diffusion, but the lamps and driving circuits experience increased load and shortened lifetime
Solution Approach 1:
The single high-energy flash is segmented into multiple pulses with controlled durations. By distributing the total energy across multiple shorter pulses rather than one extremely intense flash, the peak power demand on the lamps and driving circuits is reduced, thereby extending their operational lifetime while still achieving the required surface temperature for proper ion activation depth control.
3Device complexity
If halogen lamps are used for heat treatment, then equipment complexity is lower, but ion diffusion becomes deep and junction depth control is poor
Solution Approach 1:
Instead of using continuous illumination from halogen lamps, the invention employs periodic pulsed light emission from flash lamps. This periodic action with extremely short duration (several milliseconds or less) enables rapid heating that achieves ion activation before significant thermal diffusion can occur, thereby improving junction depth control while maintaining relatively simple equipment architecture.
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 allows for further increase in surface temperature of the substrate while preventing shattering, reducing thermal damage and extending the lifespan of flash lamps and their driving circuits by managing instantaneous temperature increases.
Implementation Method 1
raising only the surface temperature of an ion-impregnated semiconductor wafer within an extremely short period of time (several milliseconds or less) by irradiating the surface of the semiconductor wafer with flashes of light from xenon flash lamps
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 the fundamental absorption band of a silicon semiconductor wafer. Thus, when a semiconductor wafer is irradiated with the flashes of light emitted from xenon flash lamps, the temperature of the semiconductor wafer can be raised rapidly with only a small amount of light transmitted through the semiconductor wafer.
Data Source
AI summary
Two-step photo-irradiation heat treatment is performed so that a total photo-irradiation time is not more than one second and that a first step of photo-irradiation of a semiconductor wafer is performed with a light-emission output that averages out at a first light-emission output and a second step of photo-irradiation of the semiconductor wafer is performed in accordance with an output waveform that peaks at a second light-emission output that is higher than both average and maximum light-emission outputs in the first step. Performing preliminary photo-irradiation with a relatively low light-emission output in the first step and then performing intense photo-irradiation with a higher peak in the second step enables the surface temperature of a semiconductor wafer to increase further with a smaller amount of energy than in conventional cases, while preventing the semiconductor wafer from shattering.