Laser Doping of SiC Substrates via Pulse Scanning
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Solution Overview
Problem
Conventional ion injection methods for doping silicon carbide (SiC) with impurities result in heat damage and defects, leading to decreased electric properties, and existing laser doping methods face challenges in achieving optimal fluence and homogeneity for efficient impurity introduction.
Innovation Solution
A laser irradiation method using a pulse laser beam with photon energy greater than the bandgap energy of the semiconductor substrate, where the irradiation object with an impurity source film is moved at a calculated scanning speed relative to the irradiation region, ensuring fluence thresholds for ablation and surface protection are met, allowing for efficient impurity doping without surface damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional ion injection method is used to dope SiC with impurities, then impurity injection can be performed with precise depth control, but heat damage occurs and defects are formed which decrease electric properties
Solution Approach 1:
The patent replaces the conventional ion injection method (mechanical/physical bombardment) with a laser-based doping method. The laser beam provides energy to the impurity source film, causing ablation and introducing impurities into the SiC substrate without the mechanical damage and heat damage associated with ion injection. This substitution maintains depth control capability while eliminating the harmful thermal effects that create defects and reduce electric properties.
Solution Approach 2:
The patent changes the fundamental parameter of the doping process from ion beam energy to laser fluence (energy per unit area). By controlling laser fluence and the number of irradiation pulses, the method achieves precise depth control of impurity concentration while avoiding the thermal damage thresholds that plague conventional ion injection. The laser parameters can be adjusted independently to optimize both precision and material integrity.
2Object-affected harmful factors
If laser doping method is used to introduce impurities from impurity source film, then surface damage can be avoided, but achieving optimal fluence and homogeneity for efficient impurity introduction is challenging
Solution Approach 1:
The patent employs periodic laser irradiation with multiple pulses rather than a single continuous beam. By controlling the number of pulses and the interval between them, the method achieves uniform impurity distribution through repeated, controlled ablation events. This periodic action allows heat to dissipate between pulses, preventing surface damage while ensuring homogeneous impurity introduction throughout the target region.
Solution Approach 2:
The patent introduces dynamic control elements including moving the irradiation object relative to the laser beam, adjusting laser fluence, and varying the number of irradiation pulses. These dynamic parameters work together to optimize impurity distribution homogeneity while maintaining surface integrity. The relative motion between beam and substrate ensures uniform energy distribution, preventing localized overheating and achieving consistent doping across the entire irradiation area.
3Productivity
If high fluence laser beam is used to efficiently introduce impurities, then doping efficiency improves, but surface damage occurs to the semiconductor substrate
Solution Approach 1:
The patent segments the total laser energy delivery into multiple discrete pulses rather than delivering all energy in a single high-fluence burst. This segmentation allows the impurity source film to be progressively ablated and impurities to be introduced efficiently, while the lower fluence of individual pulses prevents surface damage. The cumulative effect of multiple pulses achieves high doping efficiency without exceeding the damage threshold of the semiconductor substrate.
Solution Approach 2:
The patent uses the impurity source film as a protective cushion between the laser beam and the semiconductor substrate. The source film absorbs the laser energy and undergoes ablation, shielding the underlying substrate from direct exposure to high fluence. This beforehand cushioning allows efficient impurity introduction through the ablated material while the substrate surface remains protected from damage, as the energy is consumed by the sacrificial source film layer.
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 introduces impurities into the semiconductor substrate with improved homogeneity and reduced surface damage, enabling efficient doping of SiC while maintaining the integrity of the semiconductor surface.
Implementation Method 1
irradiating the irradiation object with a pulse laser beam... first fluence being equal to or larger than a threshold at or beyond which ablation potentially occurs to the impurity source film
Implementation Method 2
first fluence being equal to or larger than a threshold at or beyond which ablation potentially occurs to the impurity source film
Implementation Method 3
pulse laser beam having photon energy larger than the bandgap energy of the semiconductor substrate
Data Source
AI summary
A laser irradiation method of irradiating, with a pulse laser beam, an irradiation object in which an impurity source film is formed on a semiconductor substrate includes: reading fluence per pulse of the pulse laser beam with which a rectangular irradiation region set on the irradiation object is irradiated and the number of irradiation pulses the irradiation region is irradiated, the fluence being equal to or larger than a threshold at or beyond which ablation potentially occurs to the impurity source film when the irradiation object is irradiated with pulses of the pulse laser beam in the irradiation pulse number and smaller than a threshold at or beyond which damage potentially occurs to the surface of the semiconductor substrate; calculating a scanning speed Vdx; and moving the irradiation object at the scanning speed Vdx relative to the irradiation region while irradiating the irradiation region with the pulse laser beam at the repetition frequency f.