Group III Nitride Layer Growth on Silicon With Nitridation Stages
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Solution Overview
Problem
Existing methods for fabricating Group III nitride devices on foreign substrates, such as silicon, face challenges in achieving high crystallinity and reducing defects due to lattice mismatch, thermal expansion mismatch, and chemical incompatibility, leading to suboptimal performance in power electronic applications.
Innovation Solution
A method involving Metal Organic Vapour Phase Epitaxy (MOPVE) processing is used, where a substrate is subjected to a nitrogen-containing gas followed by a Group III element-containing gas in specific temperature and time sequences, including nitridation, conversion, bulk growth, and desorption processes, to form a Group III nitride layer with improved crystallinity and reduced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a Group III nitride layer is fabricated on a foreign substrate using conventional epitaxial growth methods, then the device can be manufactured, but the crystallinity is poor and defects are high due to lattice mismatch and thermal expansion mismatch
Solution Approach 1:
The conventional single-step epitaxial growth process is segmented into multiple distinct stages: nitridation stage (forming SiN layer), conversion stage (converting SiN to AlN), desorption stage (removing unwanted byproducts), and bulk growth stage (growing high-quality AlN layer). Each stage is performed at optimized temperatures and with specific gas compositions, allowing precise control over the layer formation process and significantly improving crystallinity while reducing defects
Solution Approach 2:
Before the bulk growth of the Group III nitride layer, preliminary actions are performed including nitridation of the substrate surface to form a SiN layer, followed by conversion to AlN, and desorption of byproducts. These preliminary steps prepare a clean, crystalline substrate surface that enables subsequent high-quality epitaxial growth, addressing the crystallinity and defect issues before the main growth process begins
2Productivity
If the substrate temperature is maintained at high levels throughout the epitaxial growth process, then the growth rate is faster, but the crystallinity deteriorates due to unwanted byproduct formation and poor surface preparation
Solution Approach 1:
The growth process uses periodic action by cycling through distinct temperature stages: a first high temperature for nitridation, a second lower temperature for conversion and desorption to remove byproducts, and then returning to high temperature for bulk growth. This periodic temperature variation allows the system to achieve both high growth rates and high crystallinity by optimizing conditions for each specific phase of the process
Solution Approach 2:
The process dynamically changes multiple parameters including substrate temperature, gas composition, and pressure at different stages. Temperature is varied between high and low values, gas composition is changed from nitrogen-only to mixed gases, and these parameter changes are coordinated to optimize both growth rate and crystallinity at each phase, resolving the contradiction between speed and quality
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 results in Group III nitride layers with enhanced crystallinity and reduced defects, providing a superior substrate for subsequent epitaxial growth and improving the performance of devices like transistors and light emitting diodes.
Implementation Method 1
a nitridation process in which nitrogen gas and no Group III element-containing gas is supplied to the apparatus and substrate
Implementation Method 2
the apparatus is configured for MOPVE (Metal Organic Vapour Phase Epitaxy) processing
Implementation Method 3
after the conversion process a desorption process is carried out by increasing the second substrate temperature to a third substrate temperature that is greater than the second substrate temperature
Data Source
AI summary
A method of fabricating a Group III nitride layer on a substrate includes placing a substrate having a growth surface in a chamber of an apparatus configured for MOPVE (Metal Organic Vapour Phase Epitaxy) processing. A nitrogen-containing gas and no Group III element-containing gas is then supplied for a first time period. After expiry of the first time period, the supply of the nitrogen-containing gas is stopped. A Group III element-containing gas and no nitrogen-containing gas is then supplied to the apparatus for a second time period. After expiry of the second time period, the supply of the Group III element-containing gas to the apparatus is stopped for a third time period. After expiry of the third time period, the Group III element-containing gas and the nitrogen-containing gas is supplied to the apparatus and a Group III nitride layer is formed on the growth surface of the substrate.