P Type Regrown Channel Layer for Threshold Voltage Stability
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Solution Overview
Problem
Conventional silicon carbide MOSFETs with N type regrown channels experience fluctuations in threshold voltage due to temperature variations and manufacturing processes, leading to undesirable conduction at room and elevated temperatures, which complicates achieving high conductivity without deteriorating threshold voltage control.
Innovation Solution
A semiconductor device with a P type regrown channel layer divided into sections of varying conductivity types, where the channel layer is epitaxially grown with non-uniform doping concentrations and retrograde doping profiles, allowing for better control over threshold voltage and conduction across the semiconductor body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an N type regrown channel layer is used to improve channel mobility, then channel conductivity is improved, but threshold voltage control deteriorates due to fluctuations from scattered carriers during manufacturing
Solution Approach 1:
The patent changes the doping type parameter from N type to P type for the regrown channel layer. This parameter change fundamentally alters the carrier behavior and threshold voltage characteristics, allowing for stable threshold voltage control while maintaining good channel conductivity through the P type doping profile
Solution Approach 2:
The patent applies different doping concentrations at different locations within the channel layer. The P type regrown channel layer has a doping profile that varies from the source region through the channel to the drift region, with higher doping near the source and lower doping toward the drift region, optimizing both conductivity and threshold voltage control locally
2Reliability
If the threshold voltage is reduced by about 1 volt through N type regrown layer to improve conduction, then channel conductivity is improved, but device performance stability deteriorates due to undesirable variations at room and elevated temperatures
Solution Approach 1:
The patent changes the conductivity type parameter from N type to P type in the regrown channel layer. This fundamental parameter change reverses the threshold voltage shift direction and stabilizes the threshold voltage across temperature ranges, eliminating the undesirable variations that occur with N type doping
Solution Approach 2:
The patent inverts the conventional approach by using P type doping instead of N type doping for the regrown channel layer. This inversion of the doping type fundamentally changes the electrical characteristics, stabilizing the threshold voltage while maintaining conduction efficiency across different operating temperatures
3Ease of manufacture
If conventional double diffusion techniques are used to form DMOSFETs, then manufacturing process is simplified, but channel mobility remains poor leading to very high on-resistance
Solution Approach 1:
The patent applies a preliminary epitaxial growth step to form the P type regrown channel layer before final device fabrication. This preliminary action creates a pre-doped channel structure that eliminates the need for complex post-growth doping steps, maintaining manufacturing simplicity while achieving low on-resistance
Solution Approach 2:
The patent changes the channel doping approach from post-growth ion implantation to pre-growth epitaxial doping. This parameter change in the manufacturing process allows for better dopant distribution and higher channel mobility, reducing on-resistance while keeping the overall process complexity manageable
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 P type regrown channel layer maintains a stable threshold voltage, ensuring the device remains normally off at zero gate bias across a wide temperature range and provides controlled current responses, reducing channel resistance and reverse leakage current.
Implementation Method 1
The innovative features of this invention are useful in several different semiconductor devices and are particularly effective in MOSFET designs... Transistors formed by the new method include a regrown P type epitaxial layer for the channel layer
Data Source
AI summary
The invention is a device for controlling conduction across a semiconductor body with a P type channel layer between active semiconductor regions of the device and the controlling gate contact. The device, often a MOSFET or an IGBT, includes at least one source, well, and drift region. The P type channel layer may be divided into sections, or divided regions, that have been doped to exhibit N type conductivity. By dividing the channel layer into regions of different conductivity, the channel layer allows better control over the threshold voltage that regulates current through the device. Accordingly, one of the divided regions in the channel layer is a threshold voltage regulating region. The threshold-voltage regulating region maintains its original P type conductivity and is available in the transistor for a gate voltage to invert a conductive zone therein. The conductive zone becomes the voltage regulated conductive channel within the device.