Sacrificial Layer Stripping for GaN Semiconductor Substrates
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Solution Overview
Problem
The existing methods for growing nitride-based semiconductor materials, such as GaN, on substrates like sapphire or silicon carbide face challenges including high defect densities, poor thermal conductivity, and high costs, which degrade the performance and reliability of opto-electronic devices, particularly due to lattice mismatch and thermal stress issues during substrate removal.
Innovation Solution
A method involving the use of a sacrificial layer with a lower melting point than the substrate and semiconductor layers, allowing for thermal stripping of the substrate without damaging the semiconductor structure, thereby reducing manufacturing costs and thermal stress, and improving the quality of the semiconductor device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser lift-off technology is used to strip the sapphire substrate from the GaN layer, then the substrate can be removed to form freestanding bulk GaN, but thermal stress is introduced into the GaN layer and the interface between the sapphire substrate and the GaN layer is damaged
Solution Approach 1:
A sacrificial layer is introduced as an intermediary between the substrate and the GaN layer. This sacrificial layer has a melting point between that of the substrate and the GaN layer, allowing it to be selectively removed by thermal processing. The sacrificial layer acts as a mediator that enables substrate removal without directly exposing the GaN layer to the high thermal stresses of laser lift-off, thereby preserving the integrity of the GaN layer-substrate interface.
Solution Approach 2:
The invention changes the thermal parameters of the substrate structure by introducing a layer with intermediate melting point properties. By controlling the thermal processing temperature to be between the melting point of the sacrificial layer and the GaN layer, selective removal of the substrate is achieved while maintaining the structural integrity of the GaN layer, thus resolving the thermal stress problem.
2Manufacturing precision
If sapphire substrate is used for GaN layer growth, then epitaxial growth can be achieved, but large lattice and thermal-expansion coefficient mismatching results in high density of defects at the interface
Solution Approach 1:
The sacrificial layer serves as a buffer intermediary between the sapphire substrate and the GaN layer during the growth process. This intermediate layer compensates for the lattice and thermal-expansion coefficient mismatching, reducing the generation of dislocations and defects at the interface while still allowing epitaxial growth to proceed.
3Ease of manufacture
If sapphire substrate is used, then GaN layer growth is enabled, but the poor thermal conductivity of sapphire adversely impacts performance of opto-electronic devices
Solution Approach 1:
The sacrificial layer acts as a thermal management intermediary during the growth phase, enabling the use of sapphire substrate for its manufacturing advantages while preventing thermal conductivity issues from affecting the final device performance. By removing the sapphire substrate after growth through the sacrificial layer mechanism, the final structure achieves better thermal management without compromising ease of manufacture.
4Reliability
If silicon carbide substrate is used instead of sapphire, then lattice mismatch and thermal properties are improved, but high cost and small substrate size remain issues
Solution Approach 1:
The invention employs a disposable sacrificial layer that enables the use of cheaper sapphire substrates instead of expensive silicon carbide substrates. The sacrificial layer is removed after serving its purpose of enabling GaN growth on the低成本 substrate, effectively replacing the need for expensive silicon carbide substrates while maintaining good thermal and lattice matching properties.
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 effectively reduces manufacturing costs, minimizes thermal stress, and enhances the quality and reliability of semiconductor devices by allowing for the efficient separation of semiconductor structures from substrates without the drawbacks of traditional laser lift-off methods.
Implementation Method 1
The substrate is stripped from the stack of semiconductor layers by melting the sacrificial layer through performing a thermal process at a temperature greater than the second melting point and less than the first melting point and the third melting point
Implementation Method 2
performing a thermal process at a temperature greater than the second melting point
Data Source
AI summary
A method of forming a semiconductor structure is provided. The method includes providing a substrate with a first melting point. A sacrificial layer with a second melting point is forming over the substrate. The second melting point is less than the first melting point. A stack of semiconductor layers is formed over the sacrificial layer. The stack of semiconductor layers has a third melting point greater than the second melting point and a formation temperature less than the second melting point. A thermal process is performed at a temperature greater than the second melting point and less than the first melting point and the third melting point in order to melt the sacrificial layer such that the substrate is stripped from the stack of semiconductor layers.