Self-Aligned Contact Opening via Lateral Etch
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Solution Overview
Problem
The challenge in forming borderless source/drain contacts in semiconductor devices is the significant dielectric cap loss during the contact etch process, which requires a thicker capping layer, leading to gate-to-source/drain shorts and increased complexity in replacement metal gate fill processes.
Innovation Solution
A method involving the formation of a vertical contact opening within an interlayer dielectric layer between gate stacks, with lateral removal of the dielectric layer between the gate stacks to create a contact hole without removing spacers or caps, using high-selectivity etching to silicon nitride spacers and caps, allowing for a self-aligned contact opening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional contact etch process is used to form borderless source/drain contacts, then the contact opening can be formed, but significant dielectric cap loss occurs leading to gate-to-S/D shorts
Solution Approach 1:
The patent transitions from a conventional vertical contact etch to a lateral contact etch approach. Instead of etching vertically through the dielectric cap to form the contact hole, the method forms a trench laterally adjacent to the gate stack and then removes the dielectric cap horizontally. This dimensional change eliminates cap loss during the opening formation process while maintaining gate-to-S/D isolation.
Solution Approach 2:
The patent performs preliminary actions by forming a trench in the interlayer dielectric adjacent to the gate stack before removing the dielectric cap. A spacer is also formed in advance to define the contact opening location. These preliminary structures guide the subsequent lateral cap removal process and ensure precise contact formation without damaging the gate stack.
2Reliability
If a thicker dielectric capping layer is formed to compensate for cap loss, then gate-to-S/D isolation is improved, but the gate height increases causing greater burdens to replacement metal gate fill
Solution Approach 1:
The patent extracts the dielectric cap removal process from the contact opening formation process. Instead of removing the cap vertically during etching (which causes loss), the method separates cap removal into a distinct lateral process step. This allows the cap to be removed cleanly without vertical erosion, maintaining thin cap thickness while ensuring complete isolation.
Solution Approach 2:
The patent changes the etch direction from vertical to lateral. The contact hole is formed by lateral removal of the dielectric cap from a trench, rather than vertical etching through the cap. This dimensional change eliminates the need for thicker caps to compensate for vertical etch loss, maintaining thin cap thickness and avoiding increased gate height.
3Reliability
If oxidation or selective dielectric growth techniques are used to form a thick capping layer, then gate-to-S/D isolation is achieved, but the manufacturing complexity and process difficulty increase
Solution Approach 1:
The patent inverts the conventional sequence and approach: instead of forming a thick cap to prevent shorts and then carefully etching through it, the method forms a thin cap, creates a lateral trench, and removes the cap horizontally. This inverted approach simplifies the process by eliminating the need for complex oxidation or selective growth techniques to achieve thickness.
Solution Approach 2:
The patent uses lateral etching instead of vertical etching to form the contact opening. This dimensional change allows the use of standard thin dielectric caps with conventional formation techniques, avoiding the need for complex oxidation or selective dielectric growth processes required to create and manage thick caps.
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 cap loss and maintains uniform cap heights, preventing gate-to-source/drain shorts while enabling a self-aligned contact opening, suitable for advanced semiconductor devices with tight pitch requirements.
Implementation Method 1
forming the vertical contact opening with a reactive ion etch
Implementation Method 2
laterally removing ILD between the two gate stacks from the vertical contact opening toward the spacers, to form a contact hole
Implementation Method 3
forming the vertical contact opening by etching with high selectivity to the spacers
Data Source
AI summary
A self-aligned source/drain contact formation process without spacer or cap loss is described. Embodiments include providing two gate stacks, each having spacers on opposite sides, and an interlayer dielectric (ILD) over the two gate stacks and in a space therebetween, forming a vertical contact opening within the ILD between the two gate stacks, and laterally removing ILD between the two gate stacks from the vertical contact opening toward the spacers, to form a contact hole.