Raised Doped Crystalline Structures for III-N Transistors
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Solution Overview
Problem
The challenge in semiconductor device technology is to achieve low contact resistance and sheet resistance for non-silicon semiconductor materials, particularly in III-N materials, where damaged surfaces during recess etching lead to polycrystalline microstructure and high dislocation densities, resulting in poor device performance.
Innovation Solution
The use of an amorphous growth mask to hinder nucleation on damaged surfaces, allowing single crystalline doped semiconductor material to regrow from undamaged seeding surfaces, thereby forming a raised doped crystalline structure that wraps around the recess or crystalline body, ensuring improved crystallinity and reduced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If recess etching is performed on non-silicon semiconductor materials, then contact structures can be formed, but the surface becomes damaged leading to polycrystalline microstructure and high dislocation densities
Solution Approach 1:
A mask layer is deposited over the recessed region before epitaxial growth occurs. This preliminary masking action prevents doped material from nucleating on the damaged recess sidewalls, ensuring that single crystalline material only grows from the undamaged seed layer surface, thereby maintaining high crystalline quality while still enabling contact structure formation
Solution Approach 2:
The mask layer serves as an intermediary element that selectively blocks doped material from contacting the damaged recess sidewalls. This intermediary prevents the harmful interaction between the damaged surface and the doped material, allowing the epitaxial growth to proceed with high crystalline quality while still forming the necessary contact structures
2Reliability
If doped material is grown on damaged surfaces, then contact resistance can be reduced, but polycrystalline microstructure and high dislocation densities result
Solution Approach 1:
The mask layer creates a local quality distinction by allowing doped material to grow only on the undamaged seed layer surface while blocking growth on the damaged recess sidewalls. This selective local growth ensures that the contact region maintains single crystalline quality with low dislocation densities, while still achieving the necessary electrical contact properties
Solution Approach 2:
The damaged recess sidewalls, which would normally lead to poor crystalline quality, are converted into a beneficial configuration by using them as the target for metal contact deposition. The damage is hidden from the epitaxial growth process while still serving the functional purpose of contact formation, thus converting a harmful feature into a beneficial one
3Reliability
If single crystalline doped material is regrown from undamaged seeding surfaces, then contact resistance and sheet resistance are reduced, but additional process steps are required
Solution Approach 1:
The mask layer serves multiple functions: it acts as a barrier during epitaxial growth to prevent polycrystalline formation, serves as a template for subsequent metal contact deposition, and can be selectively removed to define contact regions. This multi-functionality reduces the need for additional separate process steps, making the added complexity worthwhile given the significant improvement in sheet resistance and contact quality
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 results in significantly lower contact resistance and sheet resistance, enhancing the overall performance of semiconductor devices by promoting lateral growth of high-quality, single crystalline doped material that interfaces effectively with the two-dimensional electron gas (2DEG).
Implementation Method 1
The use of an amorphous growth mask to hinder nucleation on damaged surfaces, allowing single crystalline doped semiconductor material to regrow from undamaged seeding surfaces
Implementation Method 2
a raised doped crystalline material disposed on the top surface of the device material, and wrapping around the sidewall of the device material
Data Source
AI summary
Semiconductor devices including an elevated or raised doped crystalline structure extending from a device layer are described. In embodiments, III-N transistors include raised crystalline n+ doped source/drain structures on either side of a gate stack. In embodiments, an amorphous material is employed to limit growth of polycrystalline source/drain material, allowing a high quality source/drain doped crystal to grow from an undamaged region and laterally expand to form a low resistance interface with a two-degree electron gas (2DEG) formed within the device layer. In some embodiments, regions of damaged GaN that may spawn competitive polycrystalline overgrowths are covered with the amorphous material prior to commencing raised source/drain growth.