Plasma Etching Method for 3D-NAND Recess Profile Control
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Solution Overview
Problem
In plasma etching of multilayer films for 3D-NAND flash memory, the challenge is to suppress the widening of the opening and tapering of deep holes while minimizing base loss and non-uniformity, which is difficult due to the varying deposition amounts of CF-based polymers in different etching processes.
Innovation Solution
A plasma processing method that alternately repeats a first over etching process with a low deposition amount of CF-based polymer and a second over etching process with a high deposition amount, adjusting the flow rate ratio of oxygen to fluorocarbon-based gases, to control the etching profile and prevent base silicon film etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the flow rate ratio of oxygen gas is reduced to increase CF-based polymer deposition amount, then the opening width is suppressed from increasing, but the lower end of the deep hole becomes tapered
Solution Approach 1:
The etching process is segmented into multiple distinct stages: main etching process, first over etching process, and second over etching process. Each stage has specific gas flow rate ratios and duration settings that address different aspects of the etching profile, thereby resolving the contradiction between opening width control and lower end shape prevention
Solution Approach 2:
The patent employs periodic alternation between different gas flow rate ratios during the over etching processes. The first over etching process uses a higher oxygen gas flow rate ratio, followed by the second over etching process with a reduced oxygen gas flow rate ratio, creating a periodic action that prevents both opening widening and lower end tapering
2Shape
If the time period for over etching process is increased to control lower end shape, then tapering is suppressed, but base loss increases
Solution Approach 1:
The patent dynamically adjusts the oxygen gas flow rate ratio during different phases of the etching process. By increasing the oxygen gas flow rate ratio in the first over etching process and then reducing it in the second over etching process, the system optimizes the balance between preventing lower end tapering and minimizing base loss
Solution Approach 2:
The patent changes multiple parameters including gas flow rate ratios, process duration, and gas composition between different etching stages. These parameter changes enable precise control over the etching profile while minimizing unwanted base loss
3Loss of substance
If the time period for main etching process is increased to suppress base loss, then base loss is reduced, but the lower end shape cannot be sufficiently controlled
Solution Approach 1:
The patent segments the etching process into distinct main etching and over etching phases, with the over etching phase specifically designed to control the lower end shape. This segmentation allows the main etching process to focus on depth control while the subsequent over etching processes address shape control
Solution Approach 2:
The patent performs preliminary etching in the main etching process to reach the desired depth, then applies subsequent over etching processes to refine the lower end shape. This preliminary action followed by refinement prevents both base loss and shape defects
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 suppresses base loss and non-uniformity while widening the bottom portion of the recess, ensuring precise etching profiles and improved electrical characteristics.
Implementation Method 1
performing a plasma etching process on a multilayer film formed on a target substrate with a patterned mask layer as a mask by generating plasma of a processing gas
Implementation Method 2
a deposition amount (adhesion amount) of a CF-based polymer needs to be large by reducing a flow rate ratio of an oxygen gas
Data Source
AI summary
A main etching process of forming a recess portion in a multilayer film having a laminated film where a first film and a second film having different relative permitivities are alternately formed on a base silicon film to a preset depth and an over etching process of forming the recess portion until the base silicon film is exposed are performed by introducing a processing gas including a CF-based gas and an oxygen gas and by performing a plasma etching process. In the over etching process, a first over etching process where a flow rate ratio of the oxygen gas to the CF-based gas is increased as compared to the main etching process and a second over etching process where the flow rate ratio of the oxygen gas to the CF-based gas is reduced as compared to the first over etching process are repeatedly performed two or more times.