Ultra-high Aspect Ratio Dielectric Etch via Carbon Mask Trimming
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Solution Overview
Problem
Plasma etching of semiconductor devices faces challenges with increasing ultra-high aspect ratio features, particularly due to twisting issues caused by asymmetric fluorocarbon polymer deposition, which affects the precision and alignment of features as aspect ratios exceed certain thresholds.
Innovation Solution
A method involving a carbon-based mask for selective etching of dielectric layers, where a fluorocarbon polymer is initially deposited and then selectively removed using a trimming gas to reshape the mask, followed by repeated etching cycles to maintain precision and reduce twisting, utilizing a plasma processing chamber with controlled RF energy and gas flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the aspect ratio of features is increased to meet ultra-high density design requirements, then the device density is improved, but twisting occurs particularly near the bottom of the feature
Solution Approach 1:
The patent applies preliminary action by depositing fluorocarbon polymer on the mask surface before the etching process begins. This pre-deposited polymer layer serves as a protective barrier that prevents asymmetric deposition during etching, thereby preventing twisting even at ultra-high aspect ratios of 30:1 or higher
Solution Approach 2:
The fluorocarbon polymer acts as an intermediary substance between the etchant and the mask. By introducing this intermediate layer, the patent prevents direct interaction that would cause asymmetric deposition, thereby maintaining feature alignment precision while achieving high device density
2Speed
If continuous etching is performed to complete the ultra-high aspect ratio feature, then the etching speed is maintained, but asymmetric fluorocarbon polymer deposition causes twisting
Solution Approach 1:
The patent implements periodic action by interrupting the continuous etching process with intermediate steps of fluorocarbon polymer deposition and removal. This periodic intervention prevents asymmetric deposition from causing twisting, while the overall etching speed is maintained through optimized cycle timing
Solution Approach 2:
By depositing fluorocarbon polymer on the mask before etching begins and maintaining its presence throughout the process, the patent preliminarily protects against asymmetric deposition. This preliminary protective measure enables continuous etching at high speed without sacrificing alignment precision
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 twisting and maintains high aspect ratios, allowing for precise etching of features with aspect ratios up to 40:1, improving the alignment and spacing of semiconductor device components.
Implementation Method 1
A plasma processing chamber comprises a chamber wall forming a plasma processing chamber enclosure
Implementation Method 2
the selectively etching provides a net deposition of a fluorocarbon based polymer on the carbon based mask
Implementation Method 3
providing a trimming gas, comprising an oxygen containing gas for ashing the fluorocarbon polymer
Implementation Method 4
a first RF excitation source providing a signal with a RF frequency between 1 MHz and 5 MHz, a second RF excitation source providing a signal with a RF frequency between 10 MHz and 40 MHz
Data Source
AI summary
A method for etching an ultra high aspect ratio feature in a dielectric layer through a carbon based mask is provided. The dielectric layer is selectively etched with respect to the carbon based mask, wherein the selective etching provides a net deposition of a fluorocarbon based polymer on the carbon based mask. The selective etch is stopped. The fluorocarbon polymer is selectively removed with respect to the carbon based mask, so that the carbon based mask remains, using a trimming. The selectively removing the fluorocarbon polymer is stopped. The dielectric layer is again selectively etched with respect to the carbon based mask, wherein the second selectively etching provides a net deposition of a fluorocarbon based polymer on the carbon based mask.