Self-Aligned Ohmic Contacts in Schottky Barrier Devices
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Solution Overview
Problem
Existing Schottky barrier devices face challenges in achieving precise contact geometries, which affect their performance characteristics such as speed, on resistance, and turn-on voltage, due to limitations in controlling the geometry of the contact metal and the distance between source and drain contacts.
Innovation Solution
The implementation of a Schottky barrier device design featuring a gate contact with tapered sidewalls that expand laterally, allowing for precise alignment of the source and drain contacts with different edges of the gate contact, thereby controlling the distance between them and improving device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the area of the contact metal at the surface of the semiconductor layer is reduced to increase device speed, then the device speed is improved, but the manufacturing precision of the contact geometry becomes more difficult to control
Solution Approach 1:
The patent transitions from controlling contact geometry in two dimensions (length and width at the surface) to three dimensions by introducing vertical height as an additional dimension. The contact metal structure includes a vertical portion extending into the semiconductor layer, allowing the lateral dimensions at the surface to be minimized for speed while the vertical dimension provides manufacturing control through etch depth definition.
Solution Approach 2:
The contact metal structure is segmented into distinct portions: a lateral portion at the surface and a vertical portion extending into the semiconductor layer. This segmentation allows independent optimization of each portion - the lateral portion is minimized for speed while the vertical portion is controlled for manufacturing precision through the etch process.
2Reliability
If the distance between the source contact and the drain contact is reduced to improve on resistance and turn-on voltage, then the on resistance and turn-on voltage are improved, but the alignment precision between contacts becomes more difficult to achieve
Solution Approach 1:
The gate contact structure serves as its own alignment reference for the source and drain contacts. The vertical portion of the gate contact extends into the semiconductor layer and provides a self-aligning feature that automatically defines the spacing between source and drain contacts, eliminating the need for complex multi-step alignment processes.
Solution Approach 2:
The gate contact vertical portion is formed first, establishing the spacing geometry before the source and drain contacts are deposited. This preliminary formation of the spacing structure allows subsequent contacts to be self-aligned to the predetermined distance, ensuring precise spacing without requiring high-precision alignment during contact deposition.
3Speed
If the contact metal geometry is made smaller to improve device performance, then the frequency response is improved, but the device complexity increases
Solution Approach 1:
The patent replaces complex mechanical alignment systems with a self-aligning etch process. Instead of using multiple lithography and alignment steps to define contact positions, the vertical gate contact structure serves as a physical template that automatically defines the spacing through the etch process, reducing manufacturing complexity despite the three-dimensional geometry.
Data Source
AI summary
A method of fabricating a semiconductor device includes providing one or more semiconductor layers, providing a gate contact on a first surface of the one or more semiconductor layers, then using the gate contact as a mask to deposit a source contact and a drain contact on the first surface of the one or more semiconductor layers, such that the source contact and the drain contact include an interior edge that is laterally aligned with a different lateral edge of the gate contact.