Silicon Substrates with Compressive Stress for GaN Heterostructures
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Solution Overview
Problem
The mismatch in lattice constant and thermal expansion coefficients between semiconductor substrates and epitaxial layers, such as GaN, leads to excessive stress, causing bending or cracking of heterostructures during cooling, which reduces component yield and increases processing difficulties.
Innovation Solution
The use of a diffusion layer formed by doping the substrate with p-type or n-type dopants, combined with a buffer layer and/or a protective layer, to induce a pre-bend or reduce stress in the substrate before epitaxial deposition, allowing for the growth of a substantially flat heterostructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon substrate is used for GaN epitaxial growth, then the cost is low, but the large lattice constant difference (17%) and thermal expansion coefficient difference (46%) cause excessive tensile stress leading to bending or cracking
Solution Approach 1:
A diffusion layer is formed in the silicon substrate before GaN epitaxial growth to pre-induce compressive stress that counteracts the tensile stress generated during cooling. This preliminary stress compensation prevents bending and cracking, maintaining heterostructure integrity while using low-cost silicon substrates
Solution Approach 2:
The diffusion layer modifies the physical parameters of the silicon substrate by introducing dopants that create compressive stress. This changes the stress state from purely tensile to a balanced state with compressive pre-stress, enabling reliable GaN growth on silicon without requiring expensive alternative substrates
2Manufacturing precision
If a sapphire substrate is used for GaN epitaxial growth, then the lattice mismatch (16%) and thermal expansion coefficient difference (34%) are reduced, but the cost increases significantly
Solution Approach 1:
The invention uses inexpensive silicon substrates with a diffusion layer instead of expensive sapphire substrates. The diffusion layer acts as a stress-compensating interface that enables reliable GaN growth on silicon, making the cheaper substrate viable despite its larger lattice mismatch
Solution Approach 2:
The diffusion layer serves as an intermediary between the silicon substrate and GaN epitaxial layer. It mediates the stress relationship by introducing compressive pre-stress that compensates for the thermal and lattice mismatch, enabling successful growth on silicon without requiring sapphire substrates
3Reliability
If a SiC substrate is used for GaN epitaxial growth, then the lattice mismatch (3.5%) and thermal expansion coefficient difference (25%) are minimized, but the cost becomes too high for routine commercial use
Solution Approach 1:
The invention replaces expensive SiC substrates with low-cost silicon substrates by introducing a diffusion layer that provides stress compensation. This makes routine commercial production economically viable while maintaining acceptable stress management through the engineered diffusion layer
4Device complexity
If no diffusion layer is formed, then the manufacturing process is simple, but the heterostructure exhibits bending with the GaN layer having a concave primary surface
Solution Approach 1:
A diffusion layer is formed in the silicon substrate before GaN epitaxial growth to pre-induce compressive stress that counteracts the tensile stress generated during cooling. This preliminary stress compensation prevents bending and cracking, maintaining heterostructure integrity while using low-cost silicon substrates
Solution Approach 2:
The diffusion layer is localized in specific regions of the silicon substrate to create targeted stress compensation. By controlling the spatial distribution of dopants in the diffusion layer, the patent achieves local stress management that maintains overall heterostructure flatness without requiring complex global modifications
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 mitigates stress-induced bending and cracking, enhancing the yield and reliability of semiconductor devices by creating a flat heterostructure with reduced manufacturing costs.
Implementation Method 1
heating the substrate at a temperature between about 1200° C. and 1300° C. in the presence of p-type or n-type dopants to form a diffusion layer extending from the first primary surface a depth into the substrate
Implementation Method 2
the differences in lattice constant and thermal expansion coefficient the formed heterostructure may exhibit a bending/bowing
Data Source
AI summary
A heterostructure including: a substrate having a first primary surface, a second primary surface, and a diffusion layer extending a depth into the substrate from the first primary surface; and an epitaxial layer disposed on the second primary surface of the substrate is disclosed along with methods for production of the same.