SiC Device Ohmic Electrodes Top-Hat Laser Annealing
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Solution Overview
Problem
The formation of ohmic electrodes on silicon carbide (SiC) semiconductor devices using laser annealing results in surface unevenness and stress concentration, leading to reduced element strength and reliability due to the high temperature treatment required for alloy layer formation.
Innovation Solution
A SiC semiconductor device with ohmic electrodes scattered on the surface to have unevenness heights less than 1.0 μm, utilizing a top-hat type laser for laser annealing to minimize surface irregularities and maintain a bending strength of 1000 MPa or more, thereby improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser annealing is used to form ohmic electrodes on SiC substrate, then alloy layer formation and ohmic contact are achieved, but surface unevenness and stress concentration occur leading to reduced element strength
Solution Approach 1:
The patent changes the laser beam profile parameter from conventional Gaussian distribution to top-hat (flat-top) distribution. This parameter change allows the laser energy to be uniformly distributed across the irradiation area, preventing excessive energy concentration at the beam center that causes deep melting and surface unevenness. The uniform energy distribution achieves sufficient alloy layer formation for ohmic contact while minimizing surface deformation and maintaining element strength.
Solution Approach 2:
The patent employs periodic pulsed laser annealing instead of continuous laser irradiation. By using short-duration pulses with appropriate intervals, the process allows heat diffusion between pulses, preventing excessive heat accumulation that leads to deep melting and surface unevenness. The periodic action maintains ohmic contact quality through sufficient thermal cycles while controlling surface deformation to preserve element strength.
2Reliability
If high temperature treatment is applied for alloy layer formation, then ohmic contact resistance is reduced, but surface unevenness increases and element strength decreases
Solution Approach 1:
The patent modifies the thermal processing parameters by using top-hat laser beam profile with controlled pulse duration and energy density. This creates a more uniform temperature distribution across the treatment area, achieving sufficient alloy layer formation for low contact resistance while preventing excessive localized heating that causes surface unevenness and strength reduction. The parameter optimization ensures bending strength remains above 1000 MPa.
Solution Approach 2:
The patent uses periodic pulsed high temperature treatment instead of continuous heating. The pulsed regime allows controlled heat diffusion and cooling cycles, achieving necessary alloy layer formation for ohmic contact while preventing excessive heat accumulation that leads to surface deformation and strength loss. This periodic thermal action maintains both low contact resistance and high bending strength.
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
The approach effectively suppresses the decrease in element strength and enhances the reliability of SiC semiconductor devices by maintaining a high bending strength and minimizing surface unevenness through controlled laser annealing with a top-hat type laser.
Implementation Method 1
irradiating a laser beam on the metal thin film to perform laser annealing
Implementation Method 2
laser annealing for reacting the metal thin film with Si or C in SiC
Implementation Method 3
performing a laser annealing to react the metal thin film with Si or C in SiC
Implementation Method 4
forming at least one of metal silicide and metal carbide
Data Source
AI summary
A silicon carbide semiconductor device includes: a silicon carbide semiconductor substrate that has a front surface and a rear surface; and a plurality of ohmic electrodes that are in ohmic contact with a surface of silicon carbide on at least one of the front surface and the rear surface of the silicon carbide semiconductor substrate. The plurality of ohmic electrodes are scattered on the surface of the silicon carbide to provide a concavity and convexity. The concavity and convexity has a height due to the ohmic electrodes less than 1.0 μm.