Current Leakage Screening for GaN-on-Silicon Epitaxial Wafers
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Solution Overview
Problem
Wide-bandgap semiconductor materials like GaN-on-Silicon face substantial lattice mismatch issues, leading to crystal defects and inefficiencies in power conversion due to current leakage, which existing quality control methods fail to reliably predict.
Innovation Solution
A quality control test is performed on a single substrate with an epitaxial layer by measuring current leakage through an ohmic contact, discarding the batch if the leakage exceeds a threshold, ensuring only high-quality substrates are used for device fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional quality control methods are used to detect crystal defects in GaN-on-Silicon substrates, then measurement precision may be adequate, but testing time and costs increase significantly
Solution Approach 1:
The patent performs a preliminary current leakage measurement on a single test substrate from the batch before committing to full batch fabrication. This early detection approach identifies defective batches upfront, preventing wasted fabrication time on substrates that will ultimately fail quality control.
Solution Approach 2:
The patent uses a simplified test structure that copies only the essential elements needed for leakage detection (substrate, epitaxial layer, and contact regions) without requiring complete device fabrication. This allows rapid assessment of batch quality using a minimal representative sample.
2Reliability
If comprehensive quality testing is performed on all substrates in a batch, then reliability improves, but productivity decreases due to extended testing time
Solution Approach 1:
The current leakage measurement is performed on a single test substrate early in the process flow, before full device fabrication begins. This preliminary quality gate determines whether the entire batch proceeds to fabrication, maintaining reliability while enabling rapid batch-level decision making.
Solution Approach 2:
Instead of testing every substrate individually, the patent applies partial action by testing only one representative substrate per batch. This single test provides sufficient statistical confidence to accept or reject the entire batch, balancing reliability requirements with productivity needs.
3Manufacturing precision
If full device fabrication is performed on all substrates before quality verification, then manufacturing precision can be optimized, but loss of substance increases due to wasteful processing of defective substrates
Solution Approach 1:
The patent performs quality verification through current leakage measurement before initiating the full device fabrication process. Defective batches are identified and discarded at this early stage, preventing waste of expensive fabrication resources and materials on substrates that would ultimately fail quality control.
Solution Approach 2:
The patent takes preliminary anti-action by discarding entire batches that fail the current leakage test before any device fabrication occurs. This prevents the harmful effect of processing defective substrates through the fabrication sequence, eliminating material waste at the source.
4Ease of manufacture
If existing quality control methods are used for GaN-on-Silicon substrates, then device fabrication can proceed, but reliability decreases due to undetected current leakage from lattice mismatch defects
Solution Approach 1:
The patent extracts the critical quality assessment function from the full device fabrication process by performing a dedicated current leakage measurement on a test substrate. This separate, focused test specifically targets the lattice mismatch defect issue in GaN-on-Silicon substrates, providing reliable detection without disrupting fabrication continuity.
Solution Approach 2:
The patent introduces an intermediary current leakage measurement step between substrate preparation and full device fabrication. This intermediary test acts as a quality gate that detects latent defects before they manifest in finished devices, ensuring reliability while maintaining manufacturing flow.
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 method significantly reduces testing time and costs while ensuring high yield and quality by identifying defective substrates early, reducing cycle time from weeks to days and preventing wasteful fabrication processes.
Implementation Method 1
measuring an electrical current leakage between the epitaxial layer and the substrate
Implementation Method 2
measuring an electrical current leakage between the epitaxial layer and the substrate through the ohmic contact
Data Source
AI summary
A method of fabricating a device involves forming a plurality of structures, such that each structure of the plurality includes a substrate and an epitaxial layer on the substrate. The epitaxial layer and the substrate have a lattice mismatch. The method further includes forming an electrical contact on the epitaxial layer of a selected structure of the plurality of structures and performing a current leakage measurement quality control test for the selected structure of the plurality of structures through the electrical contact. The method also involves forming a device on each of the remaining structures of the plurality of structures if the selected structure passed the leakage measurement quality control test or discarding each of the remaining structures of the plurality of structures if the selected structure did not pass the leakage measurement quality control test.