GaN Substrate Removal Using a Dissolvable Growth Restrict Mask
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Solution Overview
Problem
The challenge lies in efficiently removing GaN-based substrates from GaN-based semiconductor layers without damaging the semiconductor layers, particularly due to weak bonding at the GaN/sapphire interface and the high cost of GaN substrates, which are prone to bowing and curvature during epitaxial growth, leading to non-uniformity and yield reduction.
Innovation Solution
A method involving epitaxial lateral overgrowth (ELO) with a growth restrict mask, followed by dry etching, bonding to a support substrate, and dissolving the growth restrict mask using wet etching to easily remove the GaN-based substrate, allowing for recycling and reducing mechanical damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a mechanical removal method such as ultra-sonic removal is used to remove the substrate, then the substrate can be easily removed from the semiconductor layers, but the semiconductor layers may be damaged causing cracks
Solution Approach 1:
The patent replaces mechanical removal methods (ultra-sonic removal, cleaving) with a chemical dissolution process. The growth restrict mask is dissolved using chemical etchants, which automatically separates the substrate from the semiconductor layers without mechanical stress, thereby preventing cracks while achieving easy substrate removal.
2Stability of the object's composition
If GaN substrates are used to avoid bowing and curvature during epitaxial growth, then substrate stability is improved, but the substrate becomes difficult to remove due to lack of heterointerface
Solution Approach 1:
The patent introduces a growth restrict mask as an intermediary layer between the GaN substrate and the semiconductor layers. This mask enables easy removal by providing a dissolvable interface, while the GaN substrate itself remains stable during growth. The mask acts as a mediator that facilitates substrate removal without compromising substrate stability.
Solution Approach 2:
The patent changes the chemical parameters of the interface by using a growth restrict mask with different etching characteristics than the GaN substrate. The mask is designed to be soluble in specific chemical etchants, creating a parameter difference that enables selective removal of the mask and subsequent easy substrate separation, while the GaN substrate maintains its structural stability.
3Ease of operation
If the GaN/sapphire interface is used, then substrate removal is facilitated due to weak bonding, but mechanical damage may occur during removal
Solution Approach 1:
The patent replaces mechanical separation methods with chemical dissolution of the growth restrict mask. Instead of relying on weak bonding at the GaN/sapphire interface that requires mechanical force for separation, the mask is dissolved chemically, eliminating mechanical stress and preventing damage to the semiconductor layers while still achieving easy substrate removal.
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 method enables the efficient and cost-effective recycling of GaN-based substrates, maintaining high-quality semiconductor layers with reduced substrate strain and curvature, improving yield and reducing the risk of cracks, while allowing for the reuse of expensive GaN substrates.
Implementation Method 1
epitaxial lateral overgrowth (ELO) with a growth restrict mask
Implementation Method 2
followed by dry etching
Implementation Method 3
dissolving the growth restrict mask using wet etching
Data Source
AI summary
A method of removing a substrate, comprising: forming a growth restrict mask with a plurality of striped opening areas directly or indirectly upon a GaN-based substrate; and growing a plurality of semiconductor layers upon the GaN-based substrate using the growth restrict mask, such that the growth extends in a direction parallel to the striped opening areas of the growth restrict mask, and growth is stopped before the semiconductor layers coalesce, thereby resulting in island-like semiconductor layers. A device is processed for each of the island-like semiconductor layers. Etching is performed until at least a part of the growth restrict mask is exposed. The devices are then bonded to a support substrate. The GaN-based substrate is removed from the devices by a wet etching technique that at least partially dissolves the growth restrict mask. The GaN substrate that is removed then can be recycled.