CMOS Compatible Contact Layers in GaN Devices
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Solution Overview
Problem
III-V nitride-based semiconductor devices face high contact resistance due to Mg-H complexes in p-type GaN layers, and existing CMOS compatible contact methods using aluminum or high work function metals result in poor electrical characteristics and incompatibility with CMOS fabrication technology.
Innovation Solution
A method involving the deposition of a nickel layer on a p-type gallium nitride layer, followed by thermal treatment in an oxygen atmosphere and removal using a sulfuric acid and hydrogen peroxide solution, to facilitate the deposition of a CMOS compatible titanium aluminum titanium contact layer, enhancing electrical characteristics and compatibility with CMOS technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a metal electrode is directly contacted with a p-type GaN layer, then the contact structure is simple, but high contact resistance occurs due to Mg-H complexes passivating the Mg dopants
Solution Approach 1:
A nickel layer is introduced as an intermediary between the metal electrode and the p-type GaN layer. This nickel layer serves as a mediator that facilitates charge transfer and reduces contact resistance without requiring complex structural modifications. The nickel layer temporarily occupies the interface during fabrication and is subsequently removed, leaving an improved contact interface.
Solution Approach 2:
The nickel layer is deposited and thermally treated in advance before the final contact metal is applied. This preliminary action modifies the p-type GaN layer surface and reduces Mg-H complex formation at the interface, preparing the surface for better electrical contact. The thermal treatment at 350°C-500°C in oxygen atmosphere activates the nickel layer and modifies the underlying GaN layer properties.
2Ease of manufacture
If aluminum is used as a CMOS compatible contact material, then fabrication cost is reduced and CMOS compatibility is achieved, but adhesion to the p-type GaN layer is poor
Solution Approach 1:
The nickel layer acts as an adhesion promoter and intermediary between the aluminum contact metal and the p-type GaN layer. During the thermal treatment step, the nickel layer modifies the GaN surface properties, creating a more adhesive surface for the subsequent aluminum deposition. This intermediary approach maintains CMOS compatibility while significantly improving adhesion strength.
3Reliability
If an interfacial layer of high work function metals is fabricated on the p-type GaN layer, then contact resistance may be reduced, but the contacts have poor electrical characteristics and are not CMOS compatible
Solution Approach 1:
The nickel layer is deposited and thermally treated as a preliminary step to modify the p-type GaN layer surface properties and reduce contact resistance. After this preliminary treatment improves the electrical characteristics, the nickel layer is removed and a CMOS compatible aluminum layer is deposited. This sequence allows the benefits of high work function metal treatment to be achieved while maintaining CMOS compatibility in the final structure.
Solution Approach 2:
The nickel layer serves as a temporary processing layer that is discarded after fulfilling its function of reducing contact resistance and improving surface properties. The nickel layer is removed using an etchant after the thermal treatment, leaving the modified GaN layer ready for CMOS compatible aluminum contact deposition. This temporary use of non-CMOS compatible material enables subsequent CMOS compatible fabrication.
4Strength
If the nickel layer thickness is increased, then coverage and adhesion improvement may be enhanced, but etching time and process complexity increase
Solution Approach 1:
The nickel layer thickness is optimized to a specific range (5-15 nm) that provides sufficient coverage and adhesion improvement while maintaining etchability. This parameter optimization ensures that the layer is thick enough to fulfill its intermediary function but thin enough to be efficiently removed by the etchant, balancing adhesion enhancement with process efficiency.
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 approach reduces contact resistance and improves electrical characteristics, specifically lowering threshold voltages, and enables the use of CMOS compatible contact layers in semiconductor devices, reducing fabrication costs and enhancing compatibility with existing CMOS production lines.
Implementation Method 1
The GaN based structure is thermally treated at a temperature range of 350°C to 500°C in an oxygen atmosphere, upon the deposition of the Ni layer
Implementation Method 2
The GaN based structure is thermally treated at a temperature range of 350°C to 500°C in an oxygen atmosphere
Implementation Method 3
the Ni layer is removed using an etchant. Furthermore, a CMOS compatible contact layer is deposited on the p-type GaN layer, upon removal of the Ni layer
Implementation Method 4
removal using a sulfuric acid and hydrogen peroxide solution
Data Source
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AI summary
A method for fabricating Complementary Metal Oxide Semiconductor (CMOS) compatible contact layers in semiconductor devices is disclosed. In one embodiment, a nickel (Ni) layer is deposited on a p-type gallium nitride (GaN) layer of a GaN based structure. Further, the GaN based structure is thermally treated at a temperature range of 350°C to 500°C. Furthermore, the Ni layer is removed using an etchant. Additionally, a CMOS compatible contact layer is deposited on the p-type GaN layer, upon removal of the Ni layer.