GaN Substrate Growth via Stepwise NH3:HCl Ratio Control
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Solution Overview
Problem
Conventional methods for fabricating gallium nitride substrates using hydride vapor phase epitaxy face challenges such as bowing and cracking due to lattice mismatch and stress between the sapphire substrate and the gallium nitride layer, leading to high defect density and non-uniform growth, which complicates the process and reduces the quality of the semiconductor device.
Innovation Solution
A method involving stepwise reduction of the ammonia gas to hydrogen chloride gas flow rate ratio during growth, combined with surface treatments and the formation of a buffer layer, to control stress and prevent poly gallium nitride growth at the edges, resulting in a substrate with reduced bowing and cracking, and improved crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the flow rate of ammonia gas is increased to promote gallium nitride growth, then growth speed is improved, but poly gallium nitride grows intensively at the edges and uniformity deteriorates
Solution Approach 1:
The patent applies dynamics by making the ammonia gas flow rate variable rather than constant. The flow rate is dynamically adjusted in multiple stages: initially set at a higher rate to promote rapid growth, then progressively reduced to prevent edge poly crystallization and achieve uniform thickness. This dynamic adjustment resolves the contradiction between growth speed and uniformity.
Solution Approach 2:
The patent implements periodic action through staged flow rate adjustments. The ammonia flow rate is changed at specific intervals during the growth process, with each stage having a distinct flow rate setting. This periodic modification of growth conditions allows the system to achieve both rapid initial growth and subsequent uniformity.
2Length of stationary object
If the growth thickness is increased to produce thick films, then film thickness is improved, but internal stress accumulates and cracking occurs
Solution Approach 1:
The patent uses dynamics by progressively reducing the ammonia flow rate as growth proceeds. This dynamic adjustment prevents excessive stress accumulation that would occur with constant high flow rates, enabling the formation of thick films without cracking while maintaining structural integrity.
Solution Approach 2:
The patent applies parameter changes by modifying the ammonia flow rate at different growth stages. This parameter adjustment controls the growth rate and stress distribution, allowing thick films to be formed with reduced internal stress and minimized cracking risk.
3Stability of the object's composition
If HCl is used to pretreat the sapphire substrate to form a buffer layer, then buffer layer formation is improved, but the substrate is damaged and crystal defects increase
Solution Approach 1:
The patent applies parameter changes by optimizing the HCl treatment conditions, specifically controlling the flow rate ratio of NH3 to HCl. By adjusting these parameters, the buffer layer forms effectively while minimizing substrate damage and crystal defects.
Solution Approach 2:
The patent uses an intermediary approach by introducing a buffer layer that mediates between the sapphire substrate and the gallium nitride film. This buffer layer, formed through controlled HCl treatment followed by NH3 exposure, reduces lattice mismatch and prevents direct harmful interactions between the substrate and the semiconductor layer.
4Device complexity
If the flow rate ratio of NH3 to HCl is not controlled, then process simplicity is maintained, but bowing and non-uniform growth occur
Solution Approach 1:
The patent applies dynamics by implementing a dynamic control strategy for the NH3:HCl flow rate ratio. Rather than using a fixed simple ratio, the ratio is adjusted in stages during growth to compensate for bowing and ensure uniform substrate flatness, accepting increased process complexity as necessary for quality control.
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 enables the growth of high-quality gallium nitride substrates with reduced defect density and uniform thickness, minimizing bowing and cracking, and allowing for the fabrication of thick, defect-free films suitable for semiconductor applications.
Implementation Method 1
allowing gallium nitride to grow on the sapphire substrate while lowering the flow rate ratio of ammonia gas to hydrogen chloride gas stepwise
Implementation Method 2
a container containing gallium is disposed in the reaction chamber, and hydrogen chloride gas supplied to the introduction chamber reacts with gallium contained in the container to generate gallium chloride gas
Data Source
AI summary
Disclosed a method of fabricating a gallium nitride substrate using hydride vapor phase epitaxy (HVPE), including a step of injecting ammonia (NH3) gas to perform first surface treatment on a sapphire substrate; a step of injecting ammonia gas and hydrogen chloride (HCl) gas to form a buffer layer on the sapphire substrate; a step of injecting ammonia gas to perform second surface treatment on the sapphire substrate; and a step of allowing gallium nitride (GaN) to grow on the sapphire substrate while lowering the flow rate ratio of ammonia gas to hydrogen chloride gas stepwise.