Vertical GaN Device Substrate Resistance Reduction
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Solution Overview
Problem
The ON resistance of vertical GaN-based semiconductor devices is high due to the resistance of the GaN-based semiconductor substrate, which is not effectively reduced by existing manufacturing methods.
Innovation Solution
A manufacturing method for a vertical GaN-based semiconductor device that includes forming a MIS structure, implanting n-type dopants in the back surface of the GaN-based semiconductor substrate, and annealing the substrate without a protective layer, using a laser beam to irradiate the back surface at a temperature between 1000° C to 1350° C, which reduces the nitrogen removal and activates the dopants, thereby lowering the ON resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional annealing methods are used on GaN-based semiconductor substrate, then dopant activation is achieved, but nitrogen is removed from the substrate causing degradation
Solution Approach 1:
The patent changes the annealing temperature parameter to a specific range (1000-1350°C) and uses laser beam parameters (wavelength, pulse duration, fluence) to achieve dopant activation while minimizing nitrogen removal. This optimized parameter combination resolves the contradiction between achieving dopant activation and preventing nitrogen loss.
Solution Approach 2:
The patent employs pulsed laser annealing instead of continuous heating, using periodic laser pulses to activate dopants. This periodic action allows the material to cool between pulses, reducing cumulative nitrogen removal while maintaining effective dopant activation through repeated thermal cycles.
2Reliability
If high doping concentration is applied to reduce substrate resistance, then ON resistance decreases, but device performance is degraded due to excessive doping
Solution Approach 1:
The patent applies different doping concentrations to different regions of the substrate. The back surface receives high doping concentration to reduce substrate resistance, while the front surface maintains lower doping concentration to preserve device performance. This local differentiation resolves the contradiction between reducing ON resistance and maintaining manufacturing precision.
Solution Approach 2:
The patent applies doping selectively to the back surface region that requires it for resistance reduction, rather than uniformly doping the entire substrate. This partial action approach reduces ON resistance where needed while avoiding excessive doping in regions where it would degrade performance.
3Stability of the object's composition
If protective layer is provided during annealing to prevent nitrogen removal, then nitrogen stability is improved, but dopant activation efficiency is reduced
Solution Approach 1:
The patent replaces conventional thermal field annealing with laser beam annealing. The laser provides highly localized and intense heating that activates dopants efficiently without requiring a protective layer, thus maintaining nitrogen stability while achieving high dopant activation efficiency.
Solution Approach 2:
The laser beam acts as an intermediary between the heat source and the substrate, providing controlled energy delivery that activates dopants without causing excessive nitrogen removal. This intermediary mechanism allows effective dopant activation without needing a protective layer to prevent nitrogen loss.
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 achieves a significant reduction in ON resistance by optimizing the doping concentration and carrier concentration distribution, resulting in a lower contact resistance and improved device performance.
Implementation Method 1
annealing the GaN-based semiconductor substrate may be performed by irradiating the back surface with a laser beam
Implementation Method 2
implanting n type dopants in a back surface of the GaN-based semiconductor substrate
Implementation Method 3
annealing the GaN-based semiconductor substrate
Data Source
AI summary
A manufacturing method of a vertical GaN-based semiconductor device having: a GaN-based semiconductor substrate; a GaN-based semiconductor layer including a drift region having doping concentration of an n type impurity, which is lower than that of the GaN-based semiconductor substrate, and is provided on the GaN-based semiconductor substrate; and MIS structure having the GaN-based semiconductor layer, an insulating film contacting the GaN-based semiconductor layer, and a conductive portion contacting the insulating film, the method includes: implanting an n type dopant in a back surface of the GaN-based semiconductor substrate after forming of the MIS structure, and annealing the GaN-based semiconductor substrate after the implanting of the n type dopant.