Epitaxial layers with discontinued aluminium content for III-nitride semiconductor
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Solution Overview
Problem
The growth of III-nitride semiconductor devices on silicon substrates is hindered by significant lattice and thermal expansion coefficient mismatches, leading to dislocation density and wafer bow issues, which impede the production of high-quality devices with low manufacturing costs.
Innovation Solution
A semiconductor device structure incorporating a stack of III-nitride transition layers on a silicon substrate, with specific composition and thickness gradients, to modulate strain and reduce dislocation density, and a second III-nitride layer with a higher band gap energy, effectively mitigating the mismatch-induced stress and bow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN is grown on silicon substrate, then manufacturing cost is reduced and compatibility with modern Si processing is improved, but dislocation density increases and wafer bow occurs due to lattice and thermal expansion mismatch
Solution Approach 1:
The patent introduces an AlGaN buffer layer as an intermediary between the silicon substrate and the GaN epilayer. This buffer layer has a composition gradient (varying Al content) that provides a transition zone, mediating the lattice and thermal expansion mismatch between Si and GaN, thereby reducing dislocation density while maintaining cost advantages of Si substrates
Solution Approach 2:
The patent employs parameter changes by varying the aluminum composition ratio in the AlGaN buffer layer. The Al content is changed gradually through the buffer layer thickness, creating a composition gradient that adapts the lattice constant and thermal properties to reduce mismatch effects, thus improving manufacturing precision without sacrificing ease of manufacture
2Manufacturing precision
If GaN is grown on silicon carbide or sapphire substrate, then dislocation density is reduced, but manufacturing cost increases and processing difficulty increases
Solution Approach 1:
The patent uses a silicon substrate, which is inexpensive and readily available, as a replacement for expensive SiC or sapphire substrates. By compensating for the higher dislocation density through the AlGaN buffer layer design, the patent achieves acceptable device quality on cheap substrates, enabling cost-effective mass production
3Reliability
If thick GaN films are grown on silicon substrate, then device performance is improved, but wafer bow and cracking increase due to accumulated stress from material mismatch
Solution Approach 1:
The patent changes the composition parameter of the AlGaN buffer layer to control stress accumulation. By optimizing the Al content gradient, the buffer layer compensates for thermal expansion mismatch and reduces accumulated stress, allowing thick GaN films to be grown without excessive wafer bow or cracking
Solution Approach 2:
The AlGaN buffer layer serves as a cushioning layer grown beforehand to accommodate and distribute the stress that will accumulate during subsequent thick GaN film growth. This pre-prepared stress management structure prevents wafer bow and cracking before they occur during device fabrication
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 approach significantly reduces dislocation density to ≤1×10^9 cm^-2 and wafer bow to <30 μm, enhancing die yields to ≥75% and enabling the production of high-quality III-nitride semiconductor devices compatible with modern silicon processing.
Implementation Method 1
A stack of III-nitride transition layers is provided on the substrate. The stack of III-nitride transition layers may have a composition gradient and/or thickness gradient in the normal direction.
Implementation Method 2
The present invention relates to a semiconductor device and a manufacturing method thereof, and particularly to a semiconductor device with a Group-III nitride (hereinafter referred to as 'III-nitride') layer
Data Source
AI summary
The present invention provides a semiconductor device, comprising: a substrate (10); a stack of III-nitride transition layers (11) disposed on the substrate (10), the stack of III-nitride transition layers (11) maintaining an epitaxial relationship to the substrate (10); a first III-nitride layer (121) disposed on the stack of III-nitride transition layers (11); and a second III-nitride layer (122) disposed on the first III-nitride layer (121), the second III-nitride layer (122) having a band gap energy greater than that of the first III-nitride layer (121), wherein the stack of III-nitride transition layers (11) comprises a first transition layer (111), a second transition layer (112) on the first transition layer (111), and a third transition layer (113) on the second transition layer (112), and wherein the second transition layer (112) has a minimum aluminium molar ratio among the first transition layer (111), the second transition layer (112) and third transition layer (113). The present invention also relates to a method of forming such semiconductor device. The semiconductor device according to the present invention advantageously has a dislocation density less than or equal to 1×109 cm−2 in the first III-nitride layer (121).