Nitride Semiconductor Crystal Growth Suppressing Cracking via Substrate Etching
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Solution Overview
Problem
Nitride semiconductor crystal growth is hindered by cracking due to thermal stress caused by differences in thermal expansion coefficients between the seed crystal substrate and the grown nitride semiconductor layer, particularly evident in thick GaN layers grown on heterogeneous substrates like sapphire or SiC, limiting device thickness and yield.
Innovation Solution
Applying an etching action to the outer end of the seed crystal substrate during growth and using a container design that allows for a controlled etching environment adjacent to the seed crystal, with a weakening etching action with distance from the container's inner surface, to suppress the growth of stress-inducing crystal faces and reduce impurity concentration differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the nitride semiconductor layer thickness is increased to enable thicker device structures, then device functionality is improved, but cracking occurs due to thermal stress from thermal expansion coefficient differences
Solution Approach 1:
The patent changes the thermal parameter by heating the substrate to 700-1100°C during growth, which reduces the thermal expansion coefficient difference between the heterogeneous substrate and nitride semiconductor layer, thereby suppressing thermal stress and enabling thicker layers without cracking
Solution Approach 2:
The patent applies a preliminary etching action to the outer end of the seed crystal substrate before and during growth, which suppresses the formation of stress-inducing crystal faces at the periphery, preventing cracking that would otherwise occur in thick layers
2Manufacturing precision
If growth temperature is increased to improve crystal quality, then crystal structure is improved, but thermal stress increases leading to cracking
Solution Approach 1:
The patent optimizes the growth temperature range to 700-1100°C, which is high enough to produce high-quality crystal structures but controlled to minimize thermal expansion coefficient differences and resulting thermal stress
3Device complexity
If the seed crystal substrate is used without etching treatment, then growth process is simplified, but stress-inducing crystal faces form at the outer end causing cracking
Solution Approach 1:
The patent applies preliminary etching to the outer end of the seed crystal substrate before growth begins, which prevents the formation of stress-inducing crystal faces at the periphery that would cause cracking in thick layers
Solution Approach 2:
The patent maintains continuous etching action during the growth process by introducing etching gas throughout growth, ensuring that stress-inducing crystal faces are continuously suppressed as the layer thickens
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 method effectively suppresses cracking in nitride semiconductor crystals, enhancing yield and allowing for thicker, more uniform nitride semiconductor layers without warpage, suitable for applications in light emitting diodes and transistors.
Implementation Method 1
applying an etching action to an outer end of the seed crystal substrate during growth
Implementation Method 2
a vapor phase growth method, such as metal organic vapor phase epitaxy (MOVPE) or hydride vapor phase epitaxy (HVPE), is mainly used
Implementation Method 3
the nitride semiconductor is grown over the seed crystal substrate, by feeding an organometallic gas, such as trimethyl gallium (TMG), trimethyl aluminum (TMA) or the like, and ammonia
Implementation Method 4
cracking tends to occur when the thermal expansion coefficients of the seed crystal substrate and the nitride semiconductor layer grown thereover are significantly different
Implementation Method 5
Returning the temperature of the nitride semiconductor epitaxial wafer formed with the GaN layer over the heterogeneous substrate to room temperature causes stress due to a difference between thermal expansion coefficients
Data Source
AI summary
A nitride semiconductor crystal producing method, a nitride semiconductor epitaxial wafer, and a nitride semiconductor freestanding substrate, by which it is possible to suppress the occurrence of cracking in the nitride semiconductor crystal and to ensure the enhancement of the yield of the nitride semiconductor crystal. The nitride semiconductor crystal producing method includes growing a nitride semiconductor crystal over a seed crystal substrate, while applying an etching action to an outer end of the seed crystal substrate during the growing of the nitride semiconductor crystal.