Laser Annealed Junction Depth Control via Substrate Preamorphization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current laser annealing methods for forming shallow melt junctions in semiconductor and solar cell workpieces are limited by the high cost and expense of using short wavelength lasers, as longer wavelength lasers are not effectively absorbed by transparent thin workpieces, leading to inefficiencies and increased thermal budgets.
Innovation Solution
The method involves preamorphizing the substrate to alter its absorption characteristics, allowing the use of longer wavelength lasers for laser melt annealing, which reduces costs and enables the formation of shallow melt junctions by increasing absorption of laser energy at specific depths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If short wavelength lasers are used to form shallow melt junctions, then junction depth control and activation are improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the optical parameter (absorption coefficient) of the silicon substrate by introducing dopant atoms through ion implantation. This parameter change enables the substrate to absorb longer wavelength laser energy, allowing the use of cheaper lasers while maintaining shallow junction formation capability. The dopant concentration is specifically controlled to optimize absorption without excessive dopant loss.
Solution Approach 2:
The patent performs preliminary dopant implantation into the silicon substrate before laser annealing. This preliminary action modifies the substrate's absorption characteristics, enabling it to absorb longer wavelength laser energy. The pre-implanted dopant serves dual purposes: enhancing absorption and providing the dopant source for shallow junction formation during subsequent laser processing.
2Ease of manufacture
If longer wavelength lasers are used to reduce cost, then manufacturing cost decreases, but absorption by thin workpieces is insufficient
Solution Approach 1:
The patent modifies the optical absorption parameter of the silicon workpiece by introducing dopant atoms through ion implantation. This changes the absorption coefficient at longer wavelengths, enabling efficient energy coupling between the laser and the workpiece. The modified parameter allows longer wavelength lasers to be effectively absorbed and utilized for melt annealing.
3Manufacturing precision
If laser power density is increased to control junction depth, then junction depth precision is improved, but workpiece damage increases
Solution Approach 1:
The patent changes the optical absorption parameter of the substrate through dopant implantation, enabling better coupling of laser energy at lower power densities. This parameter modification allows precise control of melt depth through absorption characteristics rather than relying solely on high power density, thereby reducing workpiece damage while maintaining junction depth precision.
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 enables the use of cheaper, longer wavelength lasers for forming shallow junctions with controlled depth, reducing thermal budget and dopant loss, while maintaining high activation and quality of workpieces, thus making the process more economical and efficient.
Implementation Method 1
Due to the changes in the absorption characteristics of the substrate, longer wavelength lasers may be used for the anneal
Implementation Method 2
Laser energy of a sufficient energy is absorbed into the workpiece to thermally melt the workpiece
Implementation Method 3
Laser energy is absorbed in the solid source and also the workpiece
Implementation Method 4
the dopant is implanted into the workpiece, such as using an ion beam
Data Source
AI summary
Methods of enabling the use of high wavelength lasers to create shallow melt junctions are disclosed. In some embodiments, the substrate may be preamorphized to change its absorption characteristics prior to the implantation of a dopant. In other embodiments, a single implant may serve to amorphize the substrate and provide dopant. Once the substrate is sufficiently amorphized, a laser melt anneal may be performed. Due to the changes in the absorption characteristics of the substrate, longer wavelength lasers may be used for the anneal, thereby reducing cost.