Nitride Semiconductor Substrate Trench Stress Relief
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Solution Overview
Problem
The challenge lies in growing high-quality nitride semiconductor films like GaN on base substrates without warpage or cracks, particularly on silicon substrates, which are prone to thermal expansion issues and have low separation yields when used as substrates for devices like laser diodes or light-emitting diodes.
Innovation Solution
The solution involves forming trenches on the lower surface of the base substrate with varying pitches, widths, or depths that increase from the central portion to the peripheral portion to absorb and reduce stresses, thereby preventing warpage and cracks during nitride semiconductor film growth. This method allows for efficient growth on silicon substrates without the need for additional buffer layers or high-cost substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a GaN film is grown on a silicon base substrate, then production cost is reduced and separation time is shortened, but warpage or cracks occur due to differences in thermal expansion coefficient and lattice constant
Solution Approach 1:
The base substrate is divided into multiple regions by forming grooves or trenches at regular intervals. This segmentation allows the substrate to expand and contract independently in each segment, reducing thermal stress and preventing warpage and cracks during GaN film growth on silicon substrates.
Solution Approach 2:
Different regions of the base substrate are given different structural characteristics through the groove pattern. The grooved regions have reduced thickness or different mechanical properties compared to the non-grooved regions, creating local variations that accommodate thermal expansion differences and prevent overall substrate failure.
2Manufacturing precision
If a buffer layer is formed on a base substrate to reduce lattice strain, then GaN film growth quality is improved, but production cost increases and process complexity increases
Solution Approach 1:
The grooves or trenches are formed on the base substrate before growing the GaN film. This preliminary structural modification prepares the substrate to accommodate thermal stress during the subsequent film growth process, eliminating the need for additional buffer layers and reducing overall process complexity.
Solution Approach 2:
Instead of adding a buffer layer to manage stress, the invention extracts or removes material from the base substrate by forming grooves or trenches. This removal creates stress-relief structures that prevent warpage and cracks without requiring additional layers or materials.
3Force
If grooves are formed at regular intervals on a sapphire base substrate, then separation stress is reduced, but warpage or cracks still occur due to thermal expansion differences during GaN film growth
Solution Approach 1:
The groove parameters (depth, width, spacing, pattern) are optimized to specifically address thermal expansion differences during GaN film growth. By adjusting these parameters, the substrate can accommodate both separation stress and thermal stress, preventing warpage and cracks that occur with regular-interval grooves alone.
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 results in high-quality nitride semiconductor substrates free from warpage and cracks, enabling efficient separation of the base substrate and reducing production time and costs, while maintaining high yield and quality.
Implementation Method 1
the base substrate and the GaN film have different lattice constants and thermal expansion coefficients, which makes it difficult to grow epitaxially the GaN film on the base substrate
Data Source
AI summary
The present invention relates to a nitride semiconductor substrate such as gallium nitride substrate and a method for manufacturing the same. The present invention forms a plurality of trenches on a lower surface of a base substrate that are configured to absorb or reduce stresses applied larger when growing a nitride semiconductor film on the base substrate from a central portion of the base substrate towards a peripheral portion. That is, the present invention forms the trenches on the lower surface of the base substrate such that pitches get smaller or widths or depths get larger from the central portion of the base substrate towards the peripheral portion.