GaN Semiconductor Wafer Bow Reduction via Doped Silicon Substrate
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Solution Overview
Problem
Gallium nitride (GaN) semiconductor devices face issues with wafer damage and deformation due to lattice and thermal expansion mismatches with heterogeneous substrates, leading to non-uniform light emission and increased production costs.
Innovation Solution
A silicon-based substrate doped with boron and germanium at high concentrations is used, combined with a buffer layer and nitride stack, to reduce wafer bow and enhance light emission uniformity, incorporating a masking layer and intermediate layers to manage stress and defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN thin films are grown on heterogeneous substrates (sapphire, SiC, Si), then device manufacturing is enabled, but lattice mismatch causes defects and thermal expansion mismatch causes wafer bow and cracks
Solution Approach 1:
The patent introduces an AlN buffer layer as an intermediary between the silicon substrate and the GaN-based nitride semiconductor layer. This buffer layer acts as a mediator that reduces the lattice mismatch and thermal expansion coefficient difference between the silicon substrate and GaN, thereby decreasing defect density while enabling device manufacturing on cost-effective silicon substrates
Solution Approach 2:
The patent changes the thermal and structural parameters of the substrate system by selecting silicon with specific properties and using AlN buffer layers with controlled thickness and composition. This parameter optimization reduces both dislocation density and wafer bow, achieving low defect density (below 10^8/cm²) while maintaining manufacturing feasibility
2Manufacturing precision
If buffer layers and GaN thin films are made thicker to reduce defect density below 10^8/cm², then manufacturing precision improves, but compressive stress increases causing plastic deformation of silicon substrates
Solution Approach 1:
The patent optimizes the thickness parameters of buffer layers and GaN films to achieve the minimum required thickness for defect reduction while staying below the threshold that would cause excessive compressive stress. By carefully controlling these dimensional parameters, the patent reduces defect density below 10^8/cm² without causing plastic deformation or hardening of the silicon substrate
Solution Approach 2:
The patent applies partial compression - using just enough compressive stress to reduce defect density to the required level (below 10^8/cm²) but not excessive compression that would cause substrate deformation. This controlled partial action achieves the necessary precision while maintaining substrate strength
3Manufacturing precision
If substrate thickness is increased to reduce wafer bow and temperature non-uniformity, then manufacturing precision improves, but substrate cost increases and plastic deformation is not completely prevented
Solution Approach 1:
The AlN buffer layer serves as a thermal and structural intermediary that improves temperature uniformity during MQW growth and reduces wafer bow without requiring increased substrate thickness. This mediator layer achieves precision improvements while maintaining cost-effectiveness by avoiding the need for thicker, more expensive substrates
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 effectively reduces wafer deformation, improves light emission uniformity, and lowers production costs by minimizing substrate warping and defects, thereby enhancing the yield and quality of GaN-based semiconductor devices.
Implementation Method 1
a silicon-based layer doped with boron (B) and germanium (Ge)
Implementation Method 2
a compressive stress is applied in order to compensate for a tensile stress due to the mismatch in thermal expansion coefficients
Implementation Method 3
a bow of a wafer itself increases due to a mismatch in thermal expansion coefficients between GaN thin films and heterogeneous substrates
Implementation Method 4
many defects may occur on grown GaN thin films due to a mismatch in lattice constants between GaN thin films and heterogeneous substrates
Data Source
AI summary
A gallium nitride based semiconductor device includes a silicon-based layer doped simultaneously with boron (B) and germanium (Ge) at a relatively high concentration, a buffer layer on the silicon-based layer, and a nitride stack on the buffer layer. A doping concentration of boron (B) and germanium (Ge) may be higher than 1×1019/cm3.