Epitaxial Substrate Barrier Layer for HEMT Sheet Resistance
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Solution Overview
Problem
Existing epitaxial substrates for HEMTs with high-resistance Si-single crystal substrates face challenges in accurately measuring sheet resistance due to reduced rear surface resistance, leading to inaccurate measurements and increased process complexity.
Innovation Solution
A method involving the formation of a barrier layer against impurity diffusion on one surface of the high-resistance Si-single crystal substrate, followed by epitaxial growth of III-nitride layers on a buffer layer, allowing for accurate non-contact measurement of sheet resistance without contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a high-resistance Si-single crystal substrate is used for HEMT fabrication, then energy loss in high-frequency region is reduced, but the resistance of the rear surface becomes low due to impurity diffusion during epitaxial growth
Solution Approach 1:
A barrier layer is introduced as an intermediary between the high-resistance Si substrate and the III-nitride layers. This barrier layer prevents direct diffusion of III elements into the substrate while allowing the epitaxial growth to proceed, thus maintaining high rear surface resistance while enabling the use of high-resistance substrates for low energy loss
Solution Approach 2:
The barrier layer is formed on the substrate surface before the epitaxial growth of III-nitride layers. This preliminary action prevents impurity diffusion during the subsequent growth process, ensuring that the substrate's high resistance is maintained throughout device fabrication
2Productivity
If non-contact resistance measurement method is used for HEMT characterization, then wafer can be reused and in-plane distribution can be measured, but measurement accuracy is compromised when rear surface resistance is low
Solution Approach 1:
The barrier layer acts as an electrical isolator between the substrate and the III-nitride device structure. This allows the substrate to be electrically isolated from the measurement circuit, enabling accurate non-contact sheet resistance measurements even when the substrate's rear surface resistance changes during processing
Solution Approach 2:
The barrier layer creates a localized high-resistance region at the substrate interface while maintaining the overall device functionality. This localized modification allows the substrate to serve dual purposes: as a mechanical support and as an electrical isolator for accurate measurements
3Measurement precision
If a step of removing the rear surface of the Si substrate is added to solve measurement accuracy problem, then measurement accuracy is improved, but the number of process steps increases and workability deteriorates
Solution Approach 1:
The barrier layer is formed on the substrate surface before any other processing steps. This preliminary formation of the barrier layer prevents the need for subsequent substrate removal steps, as the barrier layer itself provides the necessary electrical isolation for accurate measurements
Solution Approach 2:
Instead of removing the substrate's rear surface to improve measurement accuracy, the invention extracts the problematic diffusion path by introducing a barrier layer. This eliminates the need for destructive substrate removal while maintaining measurement accuracy
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
Enables precise and efficient measurement of sheet resistance in HEMTs by preventing impurity diffusion and maintaining high resistivity, thereby improving the accuracy and workability of the epitaxial substrate production process.
Implementation Method 1
III elements to be p-type carriers diffuse into the Si-single crystal substrate through the rear surface of the Si-single crystal substrate
Implementation Method 2
a buffer is provided between the channel layer 22 and the substrate 21, and this buffer is made to serve as an insulating layer
Implementation Method 3
a method of measuring the sheet resistance by an electromagnetic induction method is generally used
Data Source
AI summary
To provide an epitaxial substrate for electronic devices, in which current flows in a lateral direction, which enables accurate measurement of the sheet resistance of HEMTs without contact, and to provide a method of efficiently producing the epitaxial substrate for electronic devices, the method characteristically includes the steps of forming a barrier layer against impurity diffusion on one surface of a high-resistance Si-single crystal substrate, forming a buffer as an insulating layer on the other surface of the high-resistance Si-single crystal substrate, producing an epitaxial substrate by epitaxially growing a plurality of III-nitride layers on the buffer to form a main laminate, and measuring resistance of the main laminate of the epitaxial substrate without contact.