Pulsed Laser Annealing Silicon Wafer Dopant Activation
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Solution Overview
Problem
The existing laser annealing methods for silicon wafers face challenges in efficiently eliminating end-of-range (EOR) defects and disorder caused by proton implantation, particularly due to high annealing temperatures and energy density requirements, which limit the activation of dopants and increase costs and complexity.
Innovation Solution
A laser annealing method that uses a pulsed laser with controlled pulse width and energy density to heat the silicon wafer without melting the surface, allowing for efficient activation of dopants and reduction of EOR defects, while maintaining a temperature below the melting point of silicon to prevent damage to the element structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high annealing temperature is used to eliminate EOR defects, then EOR defects are reduced, but dopant activation efficiency decreases due to complex defect recovery
Solution Approach 1:
The patent applies periodic pulsed laser irradiation to heat the silicon wafer surface rapidly to high temperatures for short durations, enabling EOR defect elimination without prolonged exposure that would cause complex defect recovery. The pulsed heating cycles allow the surface to reach annealing temperatures while the bulk remains cooler, resolving the contradiction between high temperature treatment and dopant activation efficiency.
2Length of stationary object
If laser energy density is increased to activate dopants deeper in the wafer, then dopant activation depth increases, but surface melting occurs causing disorder
Solution Approach 1:
The patent uses selective laser wavelengths that penetrate to different depths in silicon, applying local heating at specific depths rather than uniform surface heating. By choosing appropriate laser wavelengths, the energy is deposited at the desired depth to activate dopants without melting the surface, thus achieving deep dopant activation while preventing surface disorder.
3Reliability
If multiple proton implantation steps are performed to form field stop layer without disorder, then disorder is reduced, but process complexity and time increase
Solution Approach 1:
The patent extracts the disorder-generating step (multiple proton implantation cycles) by using a single implantation step followed by laser annealing. The laser annealing selectively activates dopants and eliminates EOR defects without generating the turbulent crystal state that causes disorder, thus achieving high-quality field stop layers while simplifying the overall process.
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 reduces EOR defects and improves element characteristics by activating dopants without the need for high-energy lasers, allowing for a more efficient and cost-effective process with reduced disorder in the silicon wafer.
Implementation Method 1
laser annealing by irradiating a silicon wafer with a pulsed laser beam
Implementation Method 2
heat the silicon wafer without melting the surface
Implementation Method 3
controlled pulse width and energy density to heat the silicon wafer without melting the surface
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
Prepared is a silicon wafer in which an element forming a complex defect that serves as a donor by being activated is implanted in an outer layer portion on one outer surface. The element is activated by causing a pulsed laser beam having a wavelength within a range of 690 nm to 950 nm to be incident onto a laser irradiation surface that is the outer surface of the silicon wafer in which the element is implanted. When the element is activated, the pulsed laser beam is caused to be incident onto the silicon wafer with a pulse width and a pulse energy density of the pulsed laser beam on condition that at least the element in a part of a region to a depth of 40 m from the outer surface is activated without melting the laser irradiation surface.