SiC Substrate GaN Device Cl-AlN Buffer Parasitic Capacitance
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Solution Overview
Problem
The high cost of semi-insulating SiC substrates hinders the widespread use of GaN-based semiconductor devices, and the use of conductive SiC substrates increases parasitic capacitance, which is detrimental for high-speed operations, while existing crystal growth methods like MOCVD have low growth speed and potential chlorine contamination issues.
Innovation Solution
A method involving the growth of a thick Cl-containing AlN layer by H-VPE on a conductive SiC substrate, followed by a Cl-free AlN layer and device constituent layers grown by MOCVD, which reduces parasitic capacitance and chlorine contamination by using a combination of hydride vapor phase epitaxy (H-VPE) and metal organic chemical vapor deposition (MOCVD) techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a semi-insulating SiC substrate is used, then parasitic capacitance is suppressed and device performance is improved, but the substrate cost increases significantly
Solution Approach 1:
An AlN layer is introduced as an intermediary between the conductive SiC substrate and the GaN-based device layers. This AlN layer acts as a mediator that blocks parasitic capacitance and prevents chlorine diffusion, allowing the use of cheaper conductive substrates while achieving performance comparable to expensive semi-insulating substrates
Solution Approach 2:
The invention changes the electrical parameter of the substrate interface by introducing the AlN layer, which has different electrical properties than the SiC substrate. This parameter change effectively suppresses parasitic capacitance without requiring expensive semi-insulating substrate material
2Ease of manufacture
If a conductive SiC substrate is used, then substrate cost is reduced, but parasitic capacitance increases and device performance deteriorates
Solution Approach 1:
The AlN layer serves as a protective intermediary that decouples the electrical characteristics of the conductive substrate from the device layers, allowing cost-effective substrate selection without sacrificing device performance
3Ease of manufacture
If MOCVD is used for crystal growth, then process maturity is high and equipment is available, but growth speed is low and chlorine contamination occurs
Solution Approach 1:
The crystal growth process is segmented into two distinct stages: first using H-VPE for rapid initial layer formation, then transitioning to MOCVD for subsequent layer growth. This segmentation allows each method to be used in its optimal performance range
Solution Approach 2:
A preliminary AlN layer is grown by H-VPE before the main device layers are deposited by MOCVD. This preliminary action creates a foundation layer that enables faster overall production while preventing chlorine contamination in the subsequent MOCVD growth stages
4Productivity
If H-VPE is used for crystal growth, then growth speed is high, but chlorine contamination is introduced
Solution Approach 1:
The chlorine introduced by H-VPE is converted into a beneficial barrier function. The Cl-containing AlN layer formed by H-VPE acts as a diffusion barrier that prevents subsequent chlorine contamination from MOCVD processes, transforming the harmful chlorine into a protective element
Solution Approach 2:
The H-VPE growth of Cl-containing AlN is performed as a preliminary step before MOCVD processing. This preliminary action intentionally introduces chlorine to create a protective barrier layer that will prevent harmful chlorine diffusion in later processing 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
This approach allows for the formation of GaN-based semiconductor devices with reduced parasitic capacitance and extended device lifetime by blocking chlorine diffusion and improving crystal quality, enabling high thermal conductivity and high breakdown voltage performance at a lower cost.
Implementation Method 1
an AlN layer containing Cl and formed on the conductive SiC substrate
Implementation Method 2
A method called hydride vapor phase epitaxy (H-VPE) has been under research recently, which method grows nitride semiconductor by reacting HCl and group III metal to form metal chloride which is further reacted with ammonia or the like to form nitride semiconductor
Implementation Method 3
hydride vapor phase epitaxy (H-VPE) has been under research recently, which method grows nitride semiconductor by reacting HCl and group III metal
Implementation Method 4
Metal organic chemical vapor deposition (MOCVD) is mainly used as a crystal growth method for the GaN based compound semiconductor
Implementation Method 5
A high thermal conductivity of SiC is considered to contribute to this performance
Implementation Method 6
GaN has a wide band gap of 3.4 V allowing a high voltage operation
Data Source
AI summary
A compound semiconductor device includes: a conductive SiC substrate; an AlN buffer layer formed on said conductive SiC substrate and containing Cl; a compound semiconductor buffer layer formed on said AlN layer which contains Cl, said compound semiconductor buffer layer not containing Cl; and a device constituent layer or layers formed above said compound semiconductor buffer layer not containing Cl.