SiC Ohmic Contact via Nitrogen Doping and Radical Etching
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Solution Overview
Problem
Conventional methods for manufacturing silicon carbide semiconductor devices require a high-temperature annealing step, leading to the generation of carbon byproducts and peeling off of electrode materials, which contaminate the manufacturing line and impose restrictions on wafer processing, particularly affecting the formation of Schottky barrier diodes where the rectifying function of barrier metal layers is compromised.
Innovation Solution
A method involving thermal oxidation to form a thermal oxide film with high nitrogen concentration on an SiC substrate, followed by radical exposure to remove Si-N and C-N bonded bodies, allowing for the formation of a highly-concentrated n-type SiC layer without the need for high-temperature annealing, enabling the formation of an ohmic electrode layer at a lower temperature or omitting the annealing step altogether.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-temperature annealing step is performed to form an ohmic electrode layer on SiC layer, then a favorable contact between SiC layer and electrode layer is ensured, but carbon byproducts and peeled-off electrode material are generated causing contamination and manufacturing restrictions
Solution Approach 1:
The invention changes the temperature parameter from high-temperature annealing (950°C or above) to low-temperature annealing (700°C or below), fundamentally altering the thermal conditions to eliminate carbon byproduct generation while maintaining ohmic contact quality through nitrogen-doped highly-concentrated n-type SiC layer formation
Solution Approach 2:
The invention performs preliminary nitrogen introduction into the SiC layer before electrode formation, creating a highly-concentrated n-type SiC layer with nitrogen donors that pre-establish the electrical conditions necessary for favorable ohmic contact, eliminating the need for subsequent high-temperature annealing that would cause contamination
2Reliability
If a high-temperature annealing step is performed to form an ohmic electrode layer, then good adhesion between electrode layers is achieved, but various restrictions are imposed on wafer processing steps
Solution Approach 1:
The invention reduces the annealing temperature parameter from 950°C or above to 700°C or below, which eliminates the restrictions on wafer processing steps while maintaining adequate adhesive properties through the nitrogen-doped highly-concentrated n-type SiC layer that facilitates lower-temperature processing
Solution Approach 2:
The invention replaces the expensive and restrictive high-temperature annealing process with a cheaper, more flexible low-temperature annealing process enabled by nitrogen doping, allowing greater adaptability in wafer processing sequences including the ability to form barrier metal layers before ohmic electrode layers
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 eliminates the need for high-temperature annealing, preventing contamination and wafer processing restrictions, while ensuring a favorable ohmic junction between the SiC substrate and the ohmic electrode layer, maintaining the rectifying function of barrier metal layers and improving the reliability of silicon carbide semiconductor devices.
Implementation Method 1
forming a thermal oxide film on one surface of an SiC substrate by thermal oxidation at a temperature of 1150° C. or above in a gas atmosphere including molecules which contain nitrogen and oxygen
Implementation Method 2
one surface of the SiC substrate is exposed to radicals so that Si—N bonded bodies and C—N bonded bodies which are formed on one surface of the SiC substrate in the course of introducing highly-concentrated nitrogen into one surface of the SiC substrate are removed
Data Source
AI summary
A method for manufacturing a semiconductor device includes forming a thermal oxide film on one surface of an SiC substrate by thermal oxidation at a temperature of 1150° C. or above in a gas atmosphere including nitrogen and oxygen, and introducing highly-concentrated nitrogen to one surface of the SiC substrate while forming the thermal oxide film; forming a highly-concentrated n-type SiC layer on one surface of the SiC substrate such that the thermal oxide film is removed from one surface of the SiC substrate by etching and, thereafter, one surface of the SiC substrate is exposed to radicals so that Si—N bonded bodies and C—N bonded bodies on one surface of the SiC substrate are removed while leaving nitrogen introduced into a lattice of SiC out of highly-concentrated nitrogen introduced into one surface of the SiC substrate; and forming an ohmic electrode layer on one surface of the SiC substrate.