Contact Air Gap Spacer Structure for Coupling Capacitance Reduction
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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.
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, which allows for self-aligned and controllable air gaps, reducing coupling capacitance and improving effective capacitance and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device geometry is shrunk to improve production efficiency and lower costs, then productivity increases, but coupling capacitance between interconnects increases degrading device performance
Solution Approach 1:
The patent extracts the harmful dielectric material between the contact plug and gate, replacing it with an air gap. By removing the solid dielectric material that causes coupling capacitance and substituting it with air (a vacuum-like environment), the harmful capacitive coupling is eliminated while maintaining the structural integrity needed for scaled device geometry.
Solution Approach 2:
The patent creates a porous structure by forming an air gap between the contact plug and gate. This air gap acts as a porous space filled with air rather than solid dielectric material, reducing the effective dielectric constant in the region between interconnects and thereby reducing coupling capacitance.
2Object-generated harmful factors
If low-k dielectric materials are used to reduce coupling capacitance, then device performance improves, but the materials are brittle, unstable, and difficult to fabricate
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 space, then selectively removed. This disposable sacrificial layer approach simplifies fabrication compared to directly depositing and patterning low-k dielectric materials, as the sacrificial material can be removed cleanly without affecting surrounding structures.
Solution Approach 2:
The patent introduces a sacrificial material as an intermediary substance that temporarily occupies the space where the air gap will eventually form. This intermediary material facilitates the creation of precise air gaps through selective removal, avoiding the need to directly manipulate fragile low-k dielectric materials during the critical gap formation step.
3Object-generated harmful factors
If air gaps are formed before contact plugs to reduce coupling capacitance, then device performance improves, but the air gaps are prone to damage during subsequent processing
Solution Approach 1:
The patent performs preliminary actions by forming the contact plug structure first with its protective cap, then creating the air gap afterward. This reverse sequence ensures that the contact plug is already in place and can protect the air gap from damage during subsequent processing steps, rather than having the fragile air gap present before the protective contact structure exists.
Solution Approach 2:
The patent provides beforehand cushioning by forming a cap structure on the contact plug before creating the air gap. This cap acts as a protective barrier that cushions and protects the subsequently formed air gap from damage during etching and other processing steps, ensuring the air gap maintains its integrity throughout manufacturing.
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, enhances device performance by improving effective capacitance and resistance, and prevents metal gate-to-S/D contact metal shorts while maintaining a reliable air gap seal.
Implementation Method 1
selectively removing dummy features using etch selectivity
Implementation Method 2
polymer capped dry etching method
Implementation Method 3
insulating materials with a relatively low dielectric constant (k), such as low-k dielectrics and 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.