Selective Contact Opening Etch for Self-Aligned Source/Drain Contacts
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Solution Overview
Problem
As semiconductor devices shrink, forming conductive contacts to gate electrodes or source/drain regions becomes challenging due to increased feature density and decreased feature size, leading to difficulties in ensuring that contacts land on the intended target without simultaneously exposing unintended layers, which can result in shorts within the device.
Innovation Solution
A method involving a semiconductor substrate with a nitride etch stop layer over a gate electrode and a metal-based etch stop layer over a source/drain contact region, using a plasma etching process with a corrosive material and a fluorine-based reducing agent to selectively etch the metal-based etch stop layer, forming a passivation layer on the nitride etch stop layer to inhibit its etching and prevent exposure of the gate electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a plasma etching process is used to remove the metal-based etch stop layer, then the source/drain contact region can be exposed, but the nitride etch stop layer over the gate electrode may also be etched, causing electrical shorts
Solution Approach 1:
The patent modifies the chemical composition of the plasma etching process by incorporating fluorocarbon compounds (such as CF4, C4F8, or C4F6) alongside traditional corrosive etchants (such as Cl2, BCl3, or SiCl4). This parameter change in the etching chemistry creates a passivation effect on the nitride etch stop layer, reducing its etch rate while maintaining effective removal of the metal-based etch stop layer, thereby achieving the required selectivity and preventing electrical shorts
Solution Approach 2:
The fluorocarbon compounds act as an intermediary substance in the plasma etching process. They deposit a protective polymer layer on the nitride etch stop layer surface, which serves as a mediator that prevents direct contact between the corrosive etchant and the nitride layer, thus protecting it from etching while allowing the metal-based etch stop layer to be removed
2Productivity
If the minimum feature size is reduced to increase device density, then more components can be integrated, but the difficulty of ensuring contacts land on the intended target increases
Solution Approach 1:
The patent applies different etching rates to different regions of the substrate by utilizing the selective passivation effect. The fluorocarbon-based plasma creates a protective layer specifically on the nitride etch stop layer regions, while the metal-based etch stop layer regions are selectively removed. This local difference in etching behavior enables precise contact formation even at reduced feature sizes, maintaining manufacturing precision while increasing device density
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 allows for self-aligned contact formation to the source/drain contact region while maintaining the integrity of the gate etch stop layer, reducing the risk of electrical shorts and enabling the use of metal-based etch stop layers with desirable electrical properties, such as high breakdown voltage and low dielectric constant.
Implementation Method 1
etching the metal-based etch stop layer using a plasma etching process that selectively etches the metal-based etch stop layer
Implementation Method 2
a plasma etching process that selectively etches the metal-based etch stop layer until a surface of the source/drain contact region is exposed, at least a portion of the nitride etch stop layer remaining
Implementation Method 3
The plasma forms a passivation layer on a surface of the nitride etch stop layer, inhibiting etching of the nitride etch stop layer during exposure of the semiconductor substrate to the plasma
Implementation Method 4
exposing the semiconductor substrate to a plasma formed in a gas comprising a corrosive material and fluorocarbon
Data Source
AI summary
In certain embodiments, a method for processing a semiconductor substrate includes receiving a semiconductor substrate that includes a nitride etch stop layer aligned to a gate electrode and a metal-based etch stop layer aligned to a source/drain contact region. The method further includes selectively etching the metal-based etch stop layer, to remove the metal-based etch stop layer and expose a surface of the source/drain contact region, by exposing the semiconductor substrate to a plasma formed in a gas comprising a corrosive material and fluorocarbon.