Epitaxial Sacrificial Layer Composition Profile for Crack-Free Lift-Off
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Solution Overview
Problem
During the process of isolating a substrate from a semiconductor layer using a sacrificial layer, the crystal face orientation dependency of the etching rate can lead to uneven etching, causing the sacrificial layer and semiconductor layer to be connected at a subtle region, resulting in cracks in the semiconductor layer when the substrate is detached.
Innovation Solution
An epitaxially-grown substrate is designed with a sacrificial layer that includes a mixed-crystal semiconductor with varying Al or In composition ratios in the thickness direction, where the local maximum value of the composition ratio is positioned inside the sacrificial layer, away from the surfaces. This variation in composition ratio creates a differential etching rate, allowing for controlled separation of the substrate from the semiconductor layer without causing cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sacrificial layer is used to isolate the substrate from the semiconductor layer, then the substrate can be separated from the semiconductor layer, but uneven etching due to crystal face orientation dependency causes the sacrificial layer and semiconductor layer to remain connected at subtle regions, leading to cracks in the semiconductor layer
Solution Approach 1:
The sacrificial layer is designed with non-uniform Al composition distribution, where the Al composition ratio varies in the thickness direction with a local maximum value positioned inside rather than at the surfaces. This creates regions of different etching rates within the layer, allowing the central high-Al region to etch faster and form isolation paths that prevent crack propagation, while the lower-Al regions near the surfaces maintain structural integrity.
Solution Approach 2:
The Al composition ratio in the sacrificial layer is varied as a gradient parameter through the thickness direction. By controlling the Al composition ratio to have a local maximum inside the layer rather than at the surfaces, the etching rate is modulated spatially, enabling controlled separation that prevents semiconductor layer cracking while achieving complete substrate isolation.
2Reliability
If the sacrificial layer has uniform composition, then the structure is simple to manufacture, but the etching rate is uniform causing incomplete separation and potential cracking
Solution Approach 1:
The sacrificial layer incorporates spatially varying Al composition ratios, with the ratio changing in the thickness direction and exhibiting a local maximum at an internal position. This non-uniform composition creates localized differences in etching behavior, enabling the central region to etch more rapidly and form effective isolation paths that ensure complete substrate separation.
Solution Approach 2:
The sacrificial layer functions as a composite structure with varying AlGaAs composition ratios throughout its thickness. By integrating regions of different Al compositions within a single continuous layer, the structure achieves both the simplicity of a single-layer fabrication process and the functional complexity of differentiated etching rates, ensuring reliable substrate isolation.
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
The controlled etching process, facilitated by the varying composition ratios in the sacrificial layer, effectively suppresses the occurrence of cracks in the semiconductor layer during substrate isolation, ensuring a stable and reliable semiconductor device manufacturing process.
Implementation Method 1
At a location of the sacrificial layer indicating a local maximum value of a composition ratio of Al or In, the etching rate with respect to an acidic etchant or an alkaline etchant is relatively large.
Data Source
AI summary
An epitaxially-grown substrate includes: a substrate made of a III-V-group compound semiconductor containing Ga or In as a III-group element; a sacrificial layer epitaxially grown on the substrate; and a semiconductor layer epitaxially grown on the sacrificial layer. The sacrificial layer includes a layer made of a mixed-crystal semiconductor containing Al or In as a III-group element, a composition ratio of Al or In varies in a thickness direction, and a location indicating a local maximum value of the composition ratio of Al or In is positioned inside other than a lower surface and an upper surface of the sacrificial layer.