Multi-Stage Etch Stop Layers for Precise Contact Hole Formation
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Solution Overview
Problem
The challenge in fabricating VLSI circuits lies in the unreliable contact etch process due to uncertain plasma etch rates in small openings, varying dielectric stack thicknesses, and inaccurate endpoint detection, leading to excessive overetching necessary for reliable electrical connections.
Innovation Solution
A multi-stage contact etch process with a controlled etch stop layer, comprising a conformal layer of silicon carbide nitride, silicon oxynitride, or silicon carbide, provides differential etch selectivity to accurately form contact holes, minimizing overetching and ensuring reliable electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If substantial overetch is used to assure reliable contact connection, then electrical connection reliability is improved, but manufacturing precision deteriorates due to excessive material removal
Solution Approach 1:
The etch stop layer is divided into multiple layers with different etch rates (first etch stop layer with higher etch rate, second etch stop layer with lower etch rate). This segmentation allows the etching process to be controlled in stages, first removing the upper layer quickly then slowing down at the second layer, providing precise depth control while ensuring complete penetration for reliable electrical connection.
Solution Approach 2:
The multi-layer etch stop structure acts as an intermediary mechanism between the etching process and the final contact hole depth. By introducing these intermediate layers with different etch characteristics, the system achieves both the necessary overetch for reliability and the precision for controlled material removal, resolving the contradiction between the two opposing requirements.
2Loss of time
If endpoint detection techniques are used to estimate contact hole depth, then manufacturing time is reduced, but measurement precision deteriorates due to inaccuracy in small openings
Solution Approach 1:
The etch stop layers are designed to provide self-indicating etch endpoints through their differential etch rates. As the etching process progresses, the transition from etching the first etch stop layer to the second etch stop layer creates a naturally detectable endpoint signal, eliminating the need for complex external endpoint detection techniques and providing accurate depth control without additional measurement time.
3Productivity
If plasma etch rate is increased to improve productivity, then manufacturing precision deteriorates due to uncertainty in small opening etching
Solution Approach 1:
Different regions of the etch stop structure have different etch rates tailored to specific process requirements. The first etch stop layer has a higher etch rate for efficient material removal in early stages, while the second etch stop layer has a lower etch rate for precise depth control in later stages. This local variation in etch characteristics allows high productivity overall while maintaining precision where needed.
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 multi-stage etch process enhances etch and overetch control, reducing manufacturing defects and improving electrical performance by precisely forming contact holes without excessive overetching, thus ensuring reliable contact connections.
Implementation Method 1
the plasma etch rate in small openings is inherently uncertain
Data Source
AI summary
A semiconductor device including a contact plug formed in a contact hole using a multi-stage contact etch process. The semiconductor device comprises a source/drain region over a semiconductor substrate, an oxide layer extension extending from the source/drain region toward a gate dielectric layer, and a contact plug extending through a dielectric layer over the source/drain region, the contact plug extending through a first etch stop layer and a second etch stop layer to a horizontal remaining portion of the oxide layer extension.