Porous Semiconductor Lift-Off Structure for Low-Stress Detachment
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Solution Overview
Problem
The production of semiconductor components, particularly thin-film components like GaN-based optoelectronic components, faces challenges during the laser lift-off process due to high-power density requirements, which can damage epitaxial layers and result in increased fragility and risk of fracture, especially for small dimensions or large chips with insufficient optical or thermal contrast.
Innovation Solution
A method involving an auxiliary carrier with a doped semiconductor material and an undoped semiconductor material, where the first layer is electrochemically porosified to reduce adhesion, allowing for simpler detachment using lower laser intensity and mechanical methods, such as stamping, by creating a porous structure that maintains mechanical stability while reducing material volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high-power density laser is used for lift-off, then detachment is achieved, but epitaxial layers are damaged and electronic structure is influenced
Solution Approach 1:
A porous layer is introduced between the sapphire substrate and the epitaxial GaN layer. This porous layer absorbs laser energy and facilitates detachment while protecting the epitaxial layers from damage. The porous structure allows for energy dissipation and reduces the harmful effects of high-power density laser irradiation on the sensitive epitaxial regions.
Solution Approach 2:
The porous layer acts as an intermediary between the sapphire substrate and the epitaxial GaN layer. It mediates the detachment process by providing a controlled interface that can be selectively removed or modified, enabling separation without direct high-power laser exposure to the epitaxial layers.
2Force
If high-power density is applied over entire chip for large chips, then detachment is achieved, but risk of fracture increases
Solution Approach 1:
The porous layer provides a mechanically compliant interface that distributes stress during detachment. For large chips, this porous structure prevents stress concentration that would lead to fracture, allowing safe detachment even when high-power density must be applied across the entire chip area.
3Object-affected harmful factors
If buffer layers are made thicker to prevent damage, then electronic structure is protected, but manufacturing complexity increases
Solution Approach 1:
Instead of increasing buffer layer thickness, a porous layer is introduced as a protective interface. This approach provides equivalent or superior protection to the epitaxial layers while maintaining simpler buffer layer structures and reducing overall device complexity.
4Force
If LLO method is used for small μ-LEDs, then detachment is achieved, but selective detachment becomes difficult due to optical focusing limits
Solution Approach 1:
The porous layer provides a distinct optical and physical interface that enhances selectivity for small μ-LEDs. The porous structure's optical properties differ from both the sapphire substrate and epitaxial layers, enabling precise laser targeting and selective detachment of individual small devices even when optical focusing is limited.
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 simplifies detachment processes, decreases the risk of damage, and allows for stress-reduced lift-off of semiconductor bodies, even for large chips, by reducing the adhesion force and maintaining sufficient mechanical stability, enabling efficient production with lower energy input.
Implementation Method 1
The first layer is electrochemically porosified in a subsequent step, wherein a degree of porosity is at least 20% by volume
Implementation Method 2
the epitaxially grown GaN boundary layer with respect to the (sapphire) substrate is decomposed by laser irradiation with a suitable wavelength
Implementation Method 3
a high-power density is necessary for a laser lift-off in order to vaporize the epitaxial GaN boundary layer
Implementation Method 4
a degree of porosity is at least 20% by volume... the holding force between the sapphire substrate and the layers which are part of the component is reduced
Data Source
AI summary
In an embodiment a method for producing a semiconductor body includes providing an auxiliary carrier, depositing a layer sequence on the auxiliary carrier having a first layer including a doped semiconductor material and a second layer including an undoped semiconductor material on the first layer, performing an electrochemical porosification of the first layer, wherein a degree of porosity is at least 20% by volume, forming a functional semiconductor body on the second layer and detaching the semiconductor body from the auxiliary carrier.