Ohmic Contact Formation on Thinned Silicon Carbide Substrates
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Solution Overview
Problem
Forming an ohmic contact on a thinned silicon carbide (SiC) semiconductor device is challenging due to the need for high temperatures, which can damage vulnerable structures, and current laser anneal methods often ablate deposited films, preventing complete silicide formation.
Innovation Solution
A method involving mechanical thinning of the SiC substrate, followed by a low-temperature alloy process to form a non-ohmic nickel silicide phase, and subsequent localized laser annealing to convert it into an ohmic nickel silicide phase, ensuring complete silicide formation without damaging existing electronic devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature annealing (>1000°C) is applied to form ohmic contact on thinned SiC substrate, then ohmic contact quality is improved, but deposited metal films are ablated and device-side structures are damaged
Solution Approach 1:
The patent applies preliminary low-temperature annealing (400-600°C) to form a non-ohmic nickel silicide phase (Ni2Si) before the final ohmic contact formation. This preliminary action creates a stable intermediate layer that prevents film ablation during subsequent high-temperature processing while still enabling eventual ohmic contact formation through controlled silicide phase transformation.
Solution Approach 2:
The patent changes the temperature parameter in stages: first applying low temperature (400-600°C) to form Ni2Si phase, then using localized high temperature (≥1000°C) laser annealing to transform Ni2Si to ohmic NiSi phase. This staged parameter change allows ohmic contact formation while controlling harmful film ablation through precise temperature and time management.
2Temperature
If wafer thickness is reduced to improve thermal performance, then heat dissipation is improved, but wafer strength during processing deteriorates
Solution Approach 1:
The patent performs all device-side processing and thickening operations while the substrate maintains its original greater thickness for structural strength. Only after device fabrication is complete does the patent thin the substrate to the target thickness range, ensuring the substrate has adequate strength throughout the critical fabrication processes.
Solution Approach 2:
The patent segments the thickness modification process into distinct stages: maintaining original thickness during device fabrication, then performing controlled thinning afterward. This segmentation allows the substrate to have appropriate thickness for each process stage - thick enough for strength during fabrication, thin enough for thermal performance in the final device.
3Temperature
If conventional laser annealing is used on thinned substrates, then localized heating is achieved, but deposited metal films are still ablated preventing complete silicide formation
Solution Approach 1:
The patent performs preliminary low-temperature annealing to form Ni2Si phase before applying high-temperature laser annealing. This preliminary action creates a more thermally stable intermediate silicide layer that absorbs and distributes laser energy more effectively, preventing direct ablation of the metal film during high-temperature processing while still enabling complete silicide formation.
Solution Approach 2:
The patent changes the laser annealing parameters by first using low temperature to form Ni2Si, then using controlled high-temperature laser annealing with optimized pulse duration and power density to transform Ni2Si to NiSi. This two-stage parameter approach ensures complete silicide formation while minimizing film ablation through precise energy control.
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 allows for reliable and cost-effective ohmic contact formation on thinned SiC substrates, improving thermal performance and device operation while mitigating heat transfer to delicate device-side structures.
Implementation Method 1
annealing the alloy layer at a second temperature range using localized heating by a laser beam to form an ohmic layer
Implementation Method 2
The non-ohmic nickel silicide phase is converted into an ohmic nickel silicide phase through localized melting
Data Source
AI summary
A silicon carbide semiconductor assembly and a method of forming a silicon carbide (SiC) semiconductor assembly are provided. The silicon carbide semiconductor assembly includes a semiconductor substrate and an electrode. The semiconductor substrate is formed of silicon carbide and includes a first surface, a second surface opposing the first surface, and a thickness extending therebetween. The method includes forming one or more electronic devices on the first surface and thinning the semiconductor substrate by removing the second surface to a predetermined depth of semiconductor substrate and leaving a third surface opposing the first surface. The method further includes forming a non-ohmic alloy layer on the third surface at a first temperature range and annealing the alloy layer at a second temperature range forming an ohmic layer, the second temperature range being greater than the first temperature range.