Plasma Etching Sequence for Uniform Tungsten Removal in Deep Trenches
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Solution Overview
Problem
Existing plasma etching methods struggle to achieve uniform etching of tungsten films in deep trenches with a depth of 12 μm or more, leading to significant variations in etching amounts across different layers.
Innovation Solution
A multi-step plasma processing method involving alternating deposition and etching steps using specific gas mixtures and radio frequency power application, including a second etching step with RF-bias, to uniformly etch tungsten films in deep trenches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If isotropic etching is used to remove tungsten films laterally, then uniform etching can be achieved in shallow trenches, but etching uniformity deteriorates in deep trenches with depth of 12 μm or more
Solution Approach 1:
The etching process is divided into multiple sequential etching steps (first, second, third etching steps) with different gas compositions and conditions. Each step targets specific depth ranges of the deep trench, with earlier steps handling upper portions and later steps handling deeper portions, thereby achieving uniform etching throughout the entire 12 μm depth
Solution Approach 2:
The patent changes multiple process parameters across different etching steps including gas composition (switching between CF4-based and C4F8-based gases), radio frequency bias application (applying or not applying RF bias), and pressure conditions. These parameter changes optimize etching performance for different depth regions, maintaining uniformity throughout the deep trench structure
2Quantity of substance
If the number of stacked layers is increased to 200 layers or more for higher integration, then memory capacity is improved, but etching uniformity across the stacked structure deteriorates
Solution Approach 1:
The etching of 200+ stacked tungsten layers is performed in multiple sequential steps rather than a single step. Each etching step removes a controlled portion of the stacked layers, ensuring that etching reaches uniformity throughout the entire stack height. The multi-step approach prevents the uniformity deterioration that would occur in a single-step process for such high layer counts
Solution Approach 2:
The patent employs continuous processing where deposition and etching steps are repeated in sequence to build and then selectively remove portions of the stacked structure. This continuous alternation of deposition and etching maintains control over the stacked film structure while achieving uniform lateral etching across all 200+ layers
3Quantity of substance
If a two-step processing method (anisotropic etching followed by isotropic etching) is used, then tungsten at groove bottom can be removed, but etching uniformity in lateral direction deteriorates in deep trenches
Solution Approach 1:
Instead of using only two steps, the patent divides the etching process into three or more sequential etching steps, each with optimized gas composition and parameters. This further segmentation allows better control over the etching front progression through the deep trench, maintaining lateral uniformity while achieving complete tungsten removal from the groove bottom
Solution Approach 2:
The patent introduces additional parameter changes between etching steps, including switching gas types (CF4 to C4F8 mixtures), adjusting radio frequency bias conditions, and modifying pressure settings. These parameter changes optimize the etching characteristics for different depth regions, ensuring both complete tungsten removal and uniform lateral etching in deep trenches
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 method achieves uniform etching across the depth of the trench, reducing etching amount variations to within acceptable limits, ensuring consistent film removal even in high-aspect-ratio structures.
Implementation Method 1
a first etching step of etching the tungsten film after the first depositing step; a second etching step of etching the tungsten film by using a mixed gas containing a Cl2 gas, an N2 gas, a CF4 gas and a C4F8 gas after the second depositing step
Implementation Method 2
in the anisotropic etching step, ions are perpendicularly incident on a sample to remove the tungsten at the groove bottom by generating plasma
Implementation Method 3
by generating plasma and applying radio frequency power to the sample
Data Source
AI summary
A plasma processing method for uniformly removing a processing target film in a lateral direction even when a depth of a trench is increased, in particular, a method for plasma-etching a tungsten film of a stacked film formed by alternately stacking an insulating film and the tungsten film. The method includes: a first depositing step of depositing a film; a first etching step of etching after the first depositing step; a second depositing step of depositing a film; a second etching step of etching using a mixed gas after the second depositing step; and a third etching step of etching after the second etching step, the second depositing step being performed after the first depositing step and the first etching step are repeated a predetermined number of times, and the second depositing step, the second etching step, and the third etching step are repeated a predetermined number of times.