SiC Device Annealing for Threshold Voltage Stability
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Solution Overview
Problem
Silicon carbide semiconductor devices experience significant threshold voltage variation due to trap formation at the interface between the silicon carbide substrate and the gate oxide film, which is not effectively reduced by existing annealing methods, especially when exposed to high temperatures during subsequent processing steps.
Innovation Solution
A method involving a three-step annealing process for a silicon carbide substrate, where the first step is performed in an oxygen atmosphere, followed by a second step at 1300°C or more in an atmosphere containing nitrogen or phosphorus atoms to reduce trap density, and a third step in an inert gas to diffuse excess gases and minimize trap formation, thereby reducing threshold voltage variation and preventing substrate softening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If annealing is performed in a hydrogen atmosphere to reduce threshold voltage variation, then threshold voltage stability is improved temporarily, but the effect is lost when the substrate is exposed to high temperature in subsequent processing steps
Solution Approach 1:
The patent changes the annealing atmosphere from hydrogen to nitrogen or phosphorus-containing atmosphere, and adjusts the temperature parameter to 1300°C or higher. This parameter change creates a more stable annealing effect that persists through subsequent high-temperature processing steps, resolving the contradiction between temporary stability and lasting durability.
Solution Approach 2:
The patent converts the potentially harmful high-temperature exposure that previously destroyed the annealing effect into a beneficial step by performing annealing at 1300°C or higher in nitrogen/phosphorus atmosphere. This high-temperature annealing not only reduces trap density effectively but also stabilizes the threshold voltage against subsequent thermal processing, turning the harmful high-temperature exposure into a beneficial annealing treatment.
2Reliability
If high temperature annealing is performed to reduce trap density, then threshold voltage variation is reduced, but substrate softening may occur
Solution Approach 1:
The patent optimizes the annealing temperature parameter to be 1300°C or higher but控制在 below the substrate softening point. This precise parameter control allows effective trap density reduction while preventing substrate softening, resolving the contradiction between threshold voltage stability and substrate structural integrity.
Solution Approach 2:
The patent uses nitrogen or phosphorus-containing atmosphere as an inert environment for high-temperature annealing. This inert atmosphere prevents unwanted chemical reactions and substrate damage at high temperatures, enabling effective trap reduction while maintaining substrate structural integrity.
3Reliability
If nitrogen or phosphorus atoms are introduced to reduce trap density, then threshold voltage stability is improved, but excess gas diffusion must be controlled
Solution Approach 1:
The patent segments the annealing process into distinct stages: first introducing nitrogen or phosphorus atoms to reduce trap density, then performing a separate diffusion step in inert gas to remove excess atoms. This segmentation allows independent optimization of each step, improving threshold voltage stability while simplifying process control.
Solution Approach 2:
The patent performs the diffusion step immediately after the nitrogen/phosphorus introduction step, maintaining continuous processing without interruption. This continuity ensures that excess gas atoms are removed promptly while the substrate is still in the optimal state, effectively reducing trap density without requiring complex intermediate handling or storage steps.
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 method effectively reduces threshold voltage variation in silicon carbide semiconductor devices, maintaining stability even after prolonged stress application and high-temperature exposure, with a difference in threshold voltage remaining within ±0.2 V over 1000 hours, and ensures the device operates as a normally off type without substrate softening.
Implementation Method 1
a first heating step of heating the silicon carbide substrate in an atmosphere of oxygen
Implementation Method 2
a second heating step of heating the silicon carbide substrate to a temperature of 1300° C. or more and 1500° C. or less in an atmosphere of gas containing nitrogen atoms or phosphorus atoms
Implementation Method 3
an atmosphere of gas containing nitrogen atoms or phosphorus atoms
Implementation Method 4
a third heating step of heating the silicon carbide substrate in an atmosphere of a first inert gas
Data Source
AI summary
A method for manufacturing a silicon carbide semiconductor device includes the following steps. A silicon carbide substrate is prepared. A first heating step of heating the silicon carbide substrate in an atmosphere of oxygen is performed. A second heating step of heating the silicon carbide substrate to a temperature of 1300° C. or more and 1500° C. or less in an atmosphere of gas containing nitrogen atoms or phosphorus atoms is performed after the first heating step. A third heating step of heating the silicon carbide substrate in an atmosphere of a first inert gas is performed after the second heating step. Thus, the silicon carbide semiconductor device in which threshold voltage variation is small, and a method for manufacturing the same can be provided.