Charge Protection Layer for GaN Devices
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Solution Overview
Problem
GaN devices experience threshold voltage shifts due to charging of the silicon nitride layer, leading to increased variation across the wafer and reduced yield, caused by charge traps and UV radiation exposure.
Innovation Solution
A charge protection layer comprising an oxide, such as metal oxide or silicon oxynitride, is applied to shield the surface protection layer from radiation with higher energy than the bandgap energy of silicon nitride, preventing additional charge carriers and defect formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon nitride surface protection layer is formed on the barrier region, then oxidation prevention is achieved, but charging occurs due to charge traps shifting threshold voltage
Solution Approach 1:
An oxide charge protection layer is introduced as an intermediary between the UV radiation environment and the silicon nitride surface protection layer. This intermediate layer absorbs UV photons through its wider bandgap, preventing direct charging of the silicon nitride layer while maintaining the oxidation protection function.
Solution Approach 2:
The solution employs a composite structure combining two different materials: an oxide material (such as silicon oxide or metal oxide) with wider bandgap for UV radiation protection, and silicon nitride with excellent oxidation barrier properties. The combination leverages the complementary strengths of both materials to simultaneously achieve radiation hardness and oxidation resistance.
2Productivity
If standard GaN processing steps with UV light are used, then device fabrication is achieved, but charging of the silicon nitride layer occurs
Solution Approach 1:
The oxide charge protection layer is formed on the surface before subsequent UV-exposing processing steps. This preliminary protective layer is in place during device fabrication, preventing charge trap formation in the silicon nitride layer during standard GaN processing operations that involve UV light exposure.
3Ease of operation
If UV light is present during device operation, then device functionality is maintained, but threshold voltage variation changes over time
Solution Approach 1:
The wider bandgap oxide material is utilized to convert the harmful UV radiation into a beneficial protective effect. The oxide layer absorbs the UV photons that would otherwise charge the silicon nitride layer, transforming the UV exposure from a harmful charging mechanism into a benign environment for device operation.
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 charge protection layer significantly reduces the negative impact of charging, stabilizing the threshold voltage and enhancing the reliability and yield of GaN devices by preventing charge trap formation and UV-induced shifts.
Implementation Method 1
The charge protection layer includes an oxide and shields the surface protection layer under the charge protection layer from radiation with higher energy than the bandgap energy of silicon nitride
Data Source
AI summary
A semiconductor device includes a III-nitride semiconductor substrate having a two-dimensional charge carrier gas at a depth from a main surface of the III-nitride semiconductor substrate. A surface protection layer is provided on the main surface of the III-nitride semiconductor substrate. The surface protection layer has charge traps in a band gap which exist at room temperature operation of the semiconductor device. A contact is provided in electrical connection with the two-dimensional charge carrier gas in the III-nitride semiconductor substrate. A charge protection layer is provided on the surface protection layer. The charge protection layer includes an oxide and shields the surface protection layer under the charge protection layer from radiation with higher energy than the bandgap energy of silicon nitride.