GaN Schottky Diode Mesa Growth for Low-Leakage Sidewalls
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Solution Overview
Problem
Existing methods for selective area processing of GaN power electronic devices, such as dry etching and ion implantation, introduce damage and defects, leading to high leakage currents and reduced device performance.
Innovation Solution
The silicon nitride shadowed selective-area growth (SNS-SAG) method is developed, which forms a bilayer mask with an undercut region to shadow the semiconductor substrate from plasma, allowing for epitaxial growth without sidewall damage and defects, resulting in smooth and defect-free sidewalls and reduced leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If dry etching via ICP-RIE is used for selective vertical epitaxial processing, then material can be selectively removed, but crystalline defects form along sidewalls and bottom surfaces leading to high leakage current
Solution Approach 1:
A bilayer mask consisting of a first dielectric layer and a second dielectric layer is introduced as an intermediary structure. The first dielectric layer is selectively etched to form an undercut region that shadows the sidewalls during epitaxial growth, preventing poly-GaN formation. This mask structure mediates between the etching process and the growth process, enabling selective material removal without sidewall damage.
Solution Approach 2:
The bilayer mask with undercut region is formed before the epitaxial growth process. This preliminary action creates shadowed regions that protect the sidewalls from plasma exposure during subsequent growth, preventing the formation of crystalline defects before they can occur.
2Ease of manufacture
If ion implantation is used for selective vertical epitaxial processing, then doping can be achieved, but crystalline defects occur in the bulk requiring annealing
Solution Approach 1:
The patent replaces ion implantation (a mechanical bombardment process) with in-situ doping during epitaxial growth. By incorporating dopants directly into the growing crystal structure, the mechanical damage associated with ion implantation is eliminated, achieving doping without bulk crystalline defects.
3Ease of manufacture
If conventional epitaxial growth is performed without shadowing, then material growth occurs uniformly, but poly-GaN forms on mask sidewalls introducing roughness and defects
Solution Approach 1:
The bilayer mask structure creates asymmetric exposure during epitaxial growth. The undercut region in the first dielectric layer causes the plasma to be blocked from reaching the sidewalls, while the top surface remains exposed for uniform growth. This asymmetric geometry enables selective growth protection without compromising overall growth uniformity.
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
SNS-SAG significantly reduces leakage current by more than four orders of magnitude, enabling high-performance GaN power electronic devices with improved reliability and efficiency.
Implementation Method 1
a plasma source is configured to deposit a crystalline gallium nitride material
Implementation Method 2
crystalline semiconductor material is epitaxially grown on the exposed portion of the semiconductor substrate
Implementation Method 3
forming a bilayer mask with an undercut region to shadow the semiconductor substrate from plasma
Data Source
AI summary
A method of fabricating a power semiconductor device includes forming a bi layer mask on a semiconductor substrate, where the bilayer mask comprises a first dielectric layer on the semiconductor substrate and a second dielectric layer on the first dielectric layer. The first and second dielectric layers are through-etched to define an exposed portion of the semiconductor substrate. The first dielectric layer is selectively etched to form an undercut region of the bi layer mask. A crystalline semiconductor material is epitaxially grown on the exposed portion of the semiconductor substrate, and a polycrystalline semiconductor material is deposited on the second dielectric layer of the bilayer mask. After the epitaxial growth, the bilayer mask and the polycrystalline semiconductor material are removed from the semiconductor substrate, leaving behind a mesa comprising the crystalline semiconductor material on the semiconductor substrate. Advantageously, a sidewall of the mesa is substantially smooth and/or defect-free.