Sapphire Substrate Warping Control via Laser-Reformed Domains
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Solution Overview
Problem
Sapphire substrates used in epitaxial growth of nitride semiconductor layers face significant warping issues due to thermal expansion differences, leading to poor layer quality, non-uniformity, and reduced yield, especially in large-diameter substrates, where precise control of warping is technically difficult using conventional polishing techniques.
Innovation Solution
The formation of reformed domain patterns within the sapphire substrate using a pulsed laser for multiphoton absorption, allowing for precise control of substrate warping and stress management, thereby minimizing warping behavior during layer growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional polishing techniques are used to control sapphire substrate warping, then manufacturing process simplicity is maintained, but manufacturing precision deteriorates due to inability to precisely control warping in large-diameter substrates
Solution Approach 1:
The invention applies preliminary action by forming reformed domain patterns within the sapphire substrate before epitaxial growth to pre-compensate for thermal expansion differences. The laser processing creates internal stress fields that counteract the warping forces generated during subsequent high-temperature growth, allowing precise warping control without complex polishing procedures.
Solution Approach 2:
The invention replaces the mechanical polishing system with a laser-based field processing system. Instead of using mechanical abrasion and complex tooling to control warping, the invention uses laser-induced reformed domains to create internal stress fields that actively compensate for thermal warping, achieving superior precision with a different physical mechanism.
2Strength
If sapphire substrate thickness is increased to reduce warping, then substrate strength is improved, but manufacturing precision deteriorates due to difficulty in controlling warping shape and amount
Solution Approach 1:
The invention applies local quality by creating reformed domain patterns at specific locations and depths within the substrate using laser processing. By controlling the laser parameters (energy density, scanning speed, pulse duration), different regions of the substrate acquire different stress characteristics, allowing precise control of warping shape and amount while maintaining overall substrate strength.
3Manufacturing precision
If epitaxial growth temperature is increased to improve layer quality, then layer purity is improved, but substrate warping increases due to thermal expansion differences
Solution Approach 1:
The invention applies preliminary anti-action by pre-forming reformed domain patterns that create internal stress fields opposing the thermal expansion forces. These pre-established stress fields act as a counterbalance during high-temperature epitaxial growth, allowing the substrate to maintain its shape despite the thermal gradients and expansion differences that occur at elevated growth temperatures.
4Manufacturing precision
If laser processing parameters are optimized to control warping, then manufacturing precision is improved, but use of energy increases due to multiple parameter adjustments
Solution Approach 1:
The invention applies parameter changes by systematically varying laser processing parameters (energy density, pulse duration, scanning speed, wavelength) to optimize the reformed domain formation. By carefully controlling these parameters, the invention achieves precise warping compensation while minimizing excess energy input, as the laser energy is concentrated in specific regions rather than uniformly heating the entire substrate.
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 enables the suppression of substrate warping, improvement in layer quality and uniformity, and increased yield of nitride semiconductor devices and bulk substrates, allowing for the growth of thick layers without cracking, even in large-diameter substrates.
Implementation Method 1
forming reformed domain patterns within a sapphire substrate for epitaxial growth of nitride semiconductor layers by means of multiphoton absorption of a pulsed laser
Data Source
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AI summary
[Purpose] In the field of sapphire substrates used chiefly for epitaxial growth of nitride semiconductor layers, to provide a sapphire substrate of which the shape and/or amount of warping can be controlled efficiently and precisely and of which substrate warping that occurs during layer formation can be suppressed and substrate warping behavior can be minimized, to provide nitride semiconductor layer growth bodies, nitride semiconductor devices, and nitride semiconductor bulk substrates using such substrates, and to provide a method of manufacturing these products. [Means of Resolution] Reformed domain patterns are formed within a sapphire substrate and the warp shape and/or amount of warping of the sapphire substrate are controlled by means of multiphoton absorption by condensing and scanning a pulsed laser through a polished surface of the sapphire substrate. When nitride semiconductor layers are formed using sapphire substrates obtained by means of this invention, substrate warping during layer formation is suppressed and substrate warping behavior is minimized so that layer quality and uniformity are improved and the quality and yield of nitride semiconductor devices is increased.