Nitride Semiconductor Buffer Layer Stress Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing nitride semiconductor substrates with GaN deposited on Si single crystal substrates face challenges in achieving high crystallinity and reducing leakage current due to poor flatness of the AlN layer, which affects stress control and dislocation issues in the AlGaN layer, and the relationship between Al composition and carbon concentration is not well established.
Innovation Solution
A nitride semiconductor substrate with a buffer layer comprising a single-layered first initial layer of AlN and a second initial layer of AlzGa1-zN (0.12≤z≤0.65) is formed on a silicon single crystal substrate, with controlled carbon concentrations within specific ranges to enhance crystallinity and reduce leakage current, and a multilayer buffer structure is used to relax stress and improve surface flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the temperature of AlN layer formation is increased to improve crystal quality and surface flatness, then crystallinity and surface flatness are improved, but etching on Si proceeds quickly and the formation rate is limited
Solution Approach 1:
The buffer layer is divided into multiple segments: a first buffer layer (AlN) in contact with Si substrate, and a second buffer layer (AlGaN) on top. This segmentation allows each layer to be optimized independently - the AlN layer provides the high temperature stability needed for good crystallinity while the AlGaN layer compensates for stress and improves flatness, resolving the contradiction between formation rate and surface quality.
Solution Approach 2:
The patent uses a composite buffer structure combining AlN and AlGaN materials. The AlN layer forms a stable base with high crystallinity at elevated temperatures, while the AlGaN layer with lower Al composition provides stress relief and surface flatness improvement. This composite approach enables achieving good surface flatness without requiring excessively high formation temperatures that would cause rapid Si etching.
2Reliability
If carbon doping is increased to compensate electrons and increase resistance in AlGaN layer, then resistance is improved, but crystal quality deteriorates
Solution Approach 1:
Carbon doping is applied locally and selectively in the AlGaN buffer layer rather than uniformly throughout the entire device structure. The patent specifies that the AlGaN layer should have appropriate Al composition (0.1≤x≤0.6) to widen the band gap sufficiently, and carbon should be doped at appropriate concentrations to compensate electrons without exceeding levels that would damage crystal quality. This localized control of carbon doping achieves the desired resistance increase while preserving crystal quality.
Solution Approach 2:
The patent optimizes multiple parameters simultaneously: Al composition (x) in AlxGa1-xN is set between 0.1 and 0.6 to achieve sufficient band gap widening, carbon concentration is controlled to provide electron compensation without excessive doping, and layer thickness is optimized. By changing these parameters within specific ranges, the patent achieves high resistance through electron compensation while avoiding crystal quality deterioration that would result from excessive carbon doping.
3Reliability
If AlN layer is formed to provide high resistance and wide band gap, then resistance is improved, but the layer causes stress control issues and dislocation problems when deposited on Si substrate
Solution Approach 1:
The AlGaN layer acts as an intermediary between the Si substrate and the high-Al-content AlN layer. The AlGaN buffer layer with lower Al composition (x=0.1-0.6) provides a transition zone that reduces lattice mismatch and thermal stress between the Si substrate and the AlN layer. This intermediary layer prevents dislocation propagation and stress concentration, allowing the AlN layer to maintain its high resistance and wide band gap properties without causing stress control issues.
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 substrate achieves high crystallinity and reduced leakage current, enabling high withstand voltage and improved crystal quality, particularly suitable for lateral semiconductor devices.
Implementation Method 1
vapor depositing a 100 nm-thick AlN single crystal layer
Implementation Method 2
metal organic chemical vapor deposition (MOCVD)
Data Source
AI summary
A nitride semiconductor substrate can effectively reduce leakage current in the vertical direction. The nitride semiconductor substrate comprises a buffer layer and an operation layer, both of which are made of nitride semiconductor, deposited on a silicon single crystal substrate, wherein the buffer layer comprises a single-layered first initial layer in contact with the silicon single crystal layer, and a single-layered second initial layer in contact with the first initial layer, the first initial layer is made of AlN, the second initial layer is made of AlzGa1-zN (0.12≤z≤0.65), and in an X-Y graph where the X-axis denotes z×100 and the Y-axis denotes carbon concentration in the second initial layer, X ranges from 12 to 65 and Y is within a range between Y=1E+17×exp(−0.05×X) and Y=1E+21×exp(−0.05×X).