Semiconductor Dopant Activation via Pulsed Laser
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing semiconductor device producing methods face challenges in activating dopants on the rear surface of a semiconductor substrate without causing temperature rises on the already formed surface structure, which can lead to damage.
Innovation Solution
A semiconductor device producing method that uses a combination of quasi-continuous wave and pulsed laser beams with specific wavelength and pulse width configurations to selectively activate dopants on one side of the substrate, controlling the temperature rise on the opposite side to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser irradiation is performed on the rear surface to activate dopants, then dopant activation is achieved, but the front surface temperature rises causing damage to the surface structure
Solution Approach 1:
The patent employs periodic pulsed laser irradiation instead of continuous wave irradiation. By controlling the pulse width to 10 ns to 1 ms and setting appropriate pulse intervals, the laser energy is delivered in discrete bursts that allow heat to dissipate between pulses, preventing cumulative temperature rise on the front surface while still achieving sufficient thermal diffusion for dopant activation during each pulse period.
Solution Approach 2:
The patent changes the temporal parameters of laser irradiation by using pulsed waves with controllable pulse widths (10 ns to 1 ms) and adjustable pulse intervals. This parameter control allows optimization of the thermal diffusion depth and peak temperature profile, enabling dopant activation at the rear surface while limiting the integrated heat exposure that causes front surface temperature rise.
2Quantity of substance
If high concentration dopants are implanted to ensure sufficient activation, then dopant concentration is improved, but crystallinity recovery becomes difficult without melting the substrate
Solution Approach 1:
The patent utilizes the phase transition of the semiconductor substrate from solid to liquid and back to solid through controlled laser heating. By delivering laser pulses with sufficient energy density to melt the substrate locally (phase change to liquid) and then allowing rapid cooling (phase change back to solid), the patent achieves complete crystallinity recovery and full dopant activation even for high concentration implants, as the melting process resets the crystal structure.
Solution Approach 2:
The periodic pulsed laser irradiation creates repeated cycles of heating, melting, and cooling. Each pulse creates a transient liquid phase that enables complete dopant activation, followed by rapid solidification that restores crystallinity. The pulse interval is controlled to allow sufficient cooling between pulses, preventing excessive heat accumulation while maintaining the phase transition mechanism for each individual pulse.
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 effectively suppresses temperature rises on the opposite surface during dopant activation, ensuring the integrity of the formed surface structure while achieving complete dopant activation and recrystallization without surface melting.
Implementation Method 1
activating the dopants by the irradiation with a laser beam
Implementation Method 2
it is possible to sufficiently recover the crystallinity of an amorphized portion and sufficiently activate the implanted dopants
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A first laser pulse emitted from a semiconductor laser oscillator and having a first pulse width is entered onto a second surface of a semiconductor substrate in which a semiconductor device is formed on a first surface and dopants are added to a surface layer portion on the second surface side. A second laser pulse having a second pulse width less than or equal to 1/10 of the first pulse width is entered on an incident area of the first laser pulse in an overlapping manner. The relative positional relationship on a time axis between falling time of the first laser pulse and rising time of the first laser pulse is set such that the temperature of the first surface, which rises due to the incidence of the first laser pulse and the second laser pulse, does not exceed an allowable upper limit value which is predetermined.