Self-Aligned Contact Air Gap Structure for Lower Coupling Capacitance
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Solution Overview
Problem
The increasing complexity in semiconductor manufacturing due to shrinking device geometry leads to increased coupling capacitance between interconnects, which degrades device performance, and existing low-k dielectric materials are brittle, unstable, and difficult to fabricate, while air gaps formed before contact plugs are prone to damage during processing.
Innovation Solution
Forming air gaps after the formation of contact plugs by selectively removing dummy features using etch selectivity and a polymer capped dry etching method to create self-aligned, larger volume air gaps, thereby reducing coupling capacitance and improving effective capacitance and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device geometry is scaled down to improve production efficiency and lower costs, then manufacturing productivity increases, but coupling capacitance between interconnects increases degrading device performance
Solution Approach 1:
The patent extracts the problematic dielectric material between the contact plug and gate, replacing it with an air gap. By removing the solid dielectric material and creating a void space filled with air (or vacuum), the coupling capacitance is significantly reduced since air has a much lower dielectric constant than conventional dielectric materials.
Solution Approach 2:
The patent creates a porous structure in the form of an air gap between the contact plug and gate. This air gap acts as a porous region with extremely low dielectric constant, effectively reducing the coupling capacitance between adjacent interconnect structures while maintaining the scaled-down geometry.
2Object-generated harmful factors
If low-k dielectric materials are used to reduce coupling capacitance, then device performance improves, but fabrication difficulty increases due to brittleness, instability, and process sensitivity
Solution Approach 1:
The patent uses a sacrificial material (such as silicon nitride or silicon oxide) that is temporarily deposited to define the air gap region, then selectively removed. This sacrificial approach allows for precise air gap formation without requiring direct deposition or handling of fragile low-k materials, simplifying the fabrication process.
Solution Approach 2:
The patent introduces a sacrificial material as an intermediary substance that facilitates air gap formation. This sacrificial layer is deposited, patterned, and then selectively removed to create the air gap. The intermediary approach avoids direct manipulation of problematic low-k materials while achieving the same capacitance reduction effect.
3Object-generated harmful factors
If air gaps are formed before contact plug formation, then coupling capacitance is reduced, but the air gaps are damaged during subsequent processing
Solution Approach 1:
The patent performs preliminary actions by forming the contact plug first, then subsequently creating the air gap around it. This reverse sequence ensures that the contact plug is already in place and can serve as a structural anchor, preventing air gap collapse during processing while still achieving capacitance reduction.
Solution Approach 2:
The patent inverts the conventional sequence by forming the air gap after contact plug formation rather than before. This inverted approach allows the contact plug to provide structural support during air gap creation, preventing damage while achieving the same electrical isolation effect.
4Object-generated harmful factors
If contact metal dimension is increased to improve device performance, then effective resistance improves, but contact area shrinks due to scaling
Solution Approach 1:
The patent extends the contact metal laterally beyond the gate width in the horizontal dimension, creating an L-shaped or extended contact structure. This dimensional extension allows the contact metal to maintain adequate cross-sectional area for low resistance while accommodating the scaled-down contact opening area, effectively decoupling the contact area constraint from the resistance requirement.
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 effectively reduces coupling capacitance between metal stacks and contact plugs, maintains a controllable air gap volume, and prevents metal gate-to-S/D contact metal shorts, while allowing for an increased contact metal dimension without shrinking the contact metal, thus enhancing device performance.
Implementation Method 1
selectively removing dummy features using etch selectivity
Implementation Method 2
a polymer capped dry etching method to create self-aligned, larger volume air gaps
Data Source
AI summary
A method of forming a device includes providing a transistor having a gate structure and a source/drain structure adjacent to the gate structure. A cavity is formed along a sidewall surface of a contact opening over the source/drain structure. After forming the cavity, a sacrificial layer is deposited over a bottom surface and along the sidewall surface of the contact opening including within the cavity. A first portion of the sacrificial layer along the bottom surface of the contact opening is removed to expose a portion of the source/drain structure. A metal plug is then formed over the portion of the exposed source/drain structure. A remaining portion of the sacrificial layer is removed to form an air gap disposed between the metal plug and the gate structure. Thereafter, a seal layer is deposited over the air gap to form an air gap spacer.