Cap Layer Sealing Air Gaps in Semiconductor Devices
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Solution Overview
Problem
Air gap structures in semiconductor devices are prone to damage during etching processes, leading to potential leakage between conductors due to their exposure, which compromises the reduction of undesirable device capacitance achieved by using air gaps.
Innovation Solution
A method is developed to form cap layers that seal the openings of air gaps, specifically by etching back the upper ends of contact etch stop layers and liner layers to widen the gap openings and then forming a cap layer using a second contact etch stop layer that partially fills the gaps, creating a funnel-shaped seal to protect the air gaps from further damage during subsequent etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If air gap structures are used to reduce device capacitance, then device capacitance is reduced, but the air gap structures are damaged during etching processes leading to conductor leakage
Solution Approach 1:
A cap layer is formed over the air gap structure before subsequent etching processes. This preliminary protective action prevents the air gap structure from being damaged during later etching steps, thereby maintaining both the capacitance reduction benefit and the structural integrity. The cap layer is specifically designed to protect the air gap while allowing necessary etching operations to proceed on other device regions.
Solution Approach 2:
The cap layer acts as an intermediary protective element between the air gap structure and the etching process. It mediates the interaction by providing a protective barrier that prevents direct contact between the etchant and the air gap structure, thus preventing damage while allowing the etching process to continue for other device components.
2Loss of energy
If the air gap structure is exposed to enable capacitance reduction, then device capacitance decreases, but leakage between conductors occurs when etching damages the air gap structure
Solution Approach 1:
The cap layer is formed in advance before etching operations that could potentially damage the air gap structure. This preliminary protection ensures that the air gap structure remains intact, preventing conductor leakage while maintaining the exposed configuration needed for capacitance reduction.
Solution Approach 2:
The cap layer provides beforehand cushioning or protection for the air gap structure. By placing this protective layer in advance, the patent cushions the air gap structure against potential damage from subsequent etching processes, thereby preventing the harmful effect of conductor leakage while preserving the capacitance reduction benefit.
3Reliability
If protective measures are added to air gap structures, then air gap integrity is maintained, but device complexity increases
Solution Approach 1:
The cap layer is applied selectively and locally only where air gap structures are present and need protection. This localized approach maintains air gap integrity without adding complexity to the entire device structure. The protective measure is concentrated precisely where needed rather than being applied universally across all device components.
Data Source
AI summary
A method of forming a cap layer for sealing an air gap is provided. The method includes forming a line feature over a substrate, forming a contact etch stop layer (CESL) on a sidewall of the line feature, forming a sacrificial layer on a sidewall of the CESL, forming a liner layer on a sidewall of the sacrificial layer, removing the sacrificial layer to form an air gap which is bordered at the CESL and the liner layer and which is adjacent to the line feature, etching back upper ends of the CESL and the liner layer to widen an opening of the air gap, and forming a cap layer to seal the opening of the air gap thus widened.