Protective Oxide Layer Prevents Contact-to-Gate Shorts in Semiconductor Devices
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Solution Overview
Problem
As semiconductor devices miniaturize, the decreasing pitch and distance between MOSFETs lead to issues such as contact shorting during fabrication, particularly due to overetching of the isolation layer during the formation of contact plugs next to the gate structure, which can result in contact-to-gate short circuits.
Innovation Solution
A semiconductor device design that incorporates a protective oxide layer with high etching selectivity over the etch stop layer to prevent overetching of the isolation layer, allowing for the reduction of the etch stop layer thickness while preventing oxygen penetration and substrate oxidation, thereby avoiding contact-to-gate short issues by forming a contact plug that partially overlaps the gate structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the etch stop layer thickness is reduced to enable contact plug formation next to the gate structure, then the distance between MOSFETs decreases and device density increases, but the isolation layer becomes vulnerable to overetching which causes contact-to-gate short circuits
Solution Approach 1:
A protective oxide layer is introduced as an intermediary between the etch stop layer and the isolation layer. This protective layer acts as a mediator that prevents the etching process from damaging the isolation layer while allowing the etch stop layer to be sufficiently thin for high-density device layout. The protective oxide layer is selectively removed in contact regions to enable proper electrical connections.
Solution Approach 2:
The protective oxide layer is formed in advance before the isolation layer etching process. This preliminary protective coating prevents overetching of the isolation layer during subsequent processing steps, ensuring that the isolation layer maintains its integrity even when the etch stop layer is made very thin to achieve higher device density.
2Reliability
If the etch stop layer is made thinner to prevent overetching of the isolation layer, then contact-to-gate shorting is prevented, but oxygen penetration increases causing substrate oxidation
Solution Approach 1:
The protective oxide layer serves as a dual-function intermediary: it protects the isolation layer from overetching while simultaneously acting as a barrier that prevents oxygen from penetrating through the thin etch stop layer to oxidize the substrate. This mediator layer resolves both concerns by providing both mechanical protection and chemical barrier functions.
Solution Approach 2:
The structure employs a composite material approach by stacking multiple layers with different functions: the etch stop layer (for dimensional control), the protective oxide layer (for isolation protection and oxygen barrier), and the isolation layer (for electrical isolation). This composite structure achieves both thin etch stop layer benefits and substrate protection.
3Productivity
If the distance between MOSFETs is decreased to increase device density, then wafer capacity increases, but contact shorting during fabrication becomes more likely
Solution Approach 1:
The fabrication process is segmented into multiple precise steps with the protective oxide layer providing a temporary protective barrier during critical etching operations. This segmentation allows for safer processing at reduced pitch by introducing intermediate protective measures that can be selectively removed, enabling higher wafer capacity without compromising contact isolation reliability.
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
The solution effectively prevents contact-to-gate short circuits and reduces contact resistance by maintaining the integrity of the isolation layer and substrate during the etching process, ensuring reliable electrical connections without oxidizing the substrate.
Implementation Method 1
A protective oxide layer with high etching selectivity over the etch stop layer is formed
Implementation Method 2
preventing oxygen penetration and substrate oxidation
Data Source
AI summary
A semiconductor device includes a substrate, a source/drain region, an etch stop layer, an oxide layer, an interlayer dielectric layer, and a contact plug. The source/drain region is in the substrate. The etch stop layer is over the source/drain region. The oxide layer is over the etch stop layer. The interlayer dielectric layer is over the oxide layer. The contact plug is electrically connected to the source/drain region through the interlayer dielectric layer, the oxide layer, and the etch stop layer.