Self-Aligned Contact Air Gaps After Plug Fill for IC Capacitance
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Solution Overview
Problem
The increasing coupling capacitance between interconnects in semiconductor IC devices due to shrinking device geometry is not effectively reduced by existing low-k dielectric materials, which are brittle, unstable, and difficult to fabricate, and 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, ensuring self-aligned and precisely controllable air gaps that extend above the top surfaces of metal gates, thereby reducing coupling capacitance and improving device reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If low-k dielectric materials are used between S/D contact plugs and nearby gates to reduce coupling capacitance, then coupling capacitance is reduced, but the materials are brittle, unstable, difficult to deposit, and sensitive to processes such as etching, annealing, and polishing
Solution Approach 1:
The patent removes the problematic low-k dielectric material entirely from the region between the contact plug and gate. Instead, it forms an air gap by selectively removing dummy features, thereby eliminating the material reliability issues while achieving the desired capacitance reduction through the air interface.
Solution Approach 2:
The patent changes the dielectric parameter from low-k material (with its associated reliability problems) to air (k=1.0). This parameter change achieves superior capacitance reduction while avoiding the brittleness, instability, and process sensitivity of low-k dielectric materials.
2Object-affected harmful factors
If air gaps are formed before contact plugs to reduce coupling capacitance, then coupling capacitance is reduced, but the air gaps are prone to damage during subsequent processing
Solution Approach 1:
The patent inverts the conventional sequence by forming the air gap after the contact plug is already in place. This reversal ensures that the air gap is not exposed to damaging processes such as etching and deposition that occur during contact plug formation, thereby protecting air gap integrity while still achieving capacitance reduction.
Solution Approach 2:
The patent performs preliminary actions by forming the contact plug and its protective structures (such as liner layers and fill materials) before creating the air gap. This preliminary preparation ensures that when the air gap is formed by removing dummy features, the surrounding structures are already in place to protect against damage.
3Productivity
If device geometry is shrunk to increase functional density, then production efficiency increases and costs are lowered, but coupling capacitance between interconnects increases
Solution Approach 1:
The patent introduces air gaps as intermediary structures between the contact plugs and gates. These air gaps act as mediators that reduce the electromagnetic coupling between adjacent interconnects, allowing the device geometry to be shrunk for higher density without suffering from increased coupling capacitance.
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 reliability, and allows for optimal AC/DC gain without potential air gap damages, improving the fabrication process by avoiding issues like punch-through and short circuits.
Implementation Method 1
a dummy feature over the S/D feature and between the gate stack and the contact hole. The method further comprises forming in the contact hole a contact plug that is electrically coupled to the S/D feature, and, after forming the contact plug, selectively removing the dummy feature to form an air gap
Data Source
AI summary
In one example aspect, a method for integrated circuit (IC) fabrication comprises providing a device structure including a substrate, a source/drain (S/D) feature on the substrate, a gate stack on the substrate, a contact hole over the S/D feature; and a dummy feature over the S/D feature and between the gate stack and the contact hole. The method further comprises forming in the contact hole a contact plug that is electrically coupled to the S/D feature, and, after forming the contact plug, selectively removing the dummy feature to form an air gap that extends higher than a top surface of the gate stack. The method further comprises forming over the contact plug a seal layer that covers the air gap.