Etching Method for NAND Flash Memory Side Wall Verticality
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Solution Overview
Problem
Existing etching methods for multi-layer films with alternately stacked silicon oxide and silicon nitride films, particularly in NAND type flash memory devices, face challenges in maintaining the verticality of side wall surfaces during the etching process, leading to potential clogging of mask openings and reduced throughput due to the mixing of processing gases.
Innovation Solution
A method involving alternating sequences of generating plasmas of fluorocarbon and hydrofluorocarbon gases, with specific gas ratios and periods, and inclusion of inert gases to prevent gas mixing, ensuring continuous plasma generation without gas replacement periods, thereby protecting side walls and improving verticality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single plasma processing gas is used for etching multi-layer films and thick oxide films simultaneously, then etching speed is improved, but side wall verticality deteriorates and mask openings may clog
Solution Approach 1:
The etching process is segmented into multiple steps with different processing gases: first step uses CF4-based gas for high-speed etching of the thick oxide film in the second region, while the second step uses C4F8-based gas for precise etching with good side wall protection in the first region. This segmentation allows each step to optimize for its specific function, resolving the contradiction between speed and precision.
Solution Approach 2:
The patent employs periodic alternation between two different plasma processing conditions. The first step (CF4-based) and second step (C4F8-based) are repeated in sequence, allowing the process to periodically switch between high-speed etching mode and high-precision mode. This periodic action enables both fast throughput and high verticality to be achieved over the complete etching cycle.
2Manufacturing precision
If gas replacement periods are introduced between different processing gases, then side wall protection is improved, but etching throughput is reduced
Solution Approach 1:
The patent eliminates idle gas replacement periods between etching steps by directly transitioning from CF4-based processing gas to C4F8-based processing gas without interrupting the plasma flow. This continuous action maintains high throughput while still achieving effective side wall protection through the alternating etching steps, as each step naturally deposits protective byproducts during the etching process itself.
3Productivity
If fluorocarbon gas is used for etching, then etching speed is improved, but deposition on mask increases causing openings to clog
Solution Approach 1:
The etching process segments the use of fluorocarbon gases into two distinct phases: CF4 in the first step provides high etching speed with controlled deposition, while C4F8 in the second step provides lower deposition rate with good side wall protection. This segmentation distributes the deposition burden and prevents excessive mask clogging while maintaining overall etching efficiency.
Solution Approach 2:
The patent changes the chemical composition parameters of the processing gas between steps. By switching from CF4 (higher fluorine content, faster etching) to C4F8 (lower fluorine content, slower etching but less deposition), the process dynamically adjusts gas parameters to match the specific etching requirements of each step, controlling mask deposition while maintaining throughput.
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 enhances the verticality of side wall surfaces, reduces mask clogging, and increases etching throughput by maintaining consistent plasma generation and controlling gas deposition on the mask.
Implementation Method 1
a first step of generating a plasma of a first processing gas which contains a fluorocarbon gas and a hydrofluorocarbon gas, in a processing container of a plasma processing apparatus
Implementation Method 2
etching of a multi-layer film configured by alternately stacking silicon oxide films and silicon nitride films is performed to form a deep hole in the multi-layer film
Implementation Method 3
Each of the plurality of sequences further includes between the first and second steps an intermediate step of generating a plasma of an inert gas which contains a helium gas
Data Source
AI summary
The etching method of one embodiment includes a first step of generating a plasma of a first processing gas containing a fluorocarbon gas and a hydrofluorocarbon gas in a processing container of a plasma processing apparatus, and a second step of generating a plasma of a second processing gas containing a hydrofluorocarbon gas and a nitrogen gas in the processing container. In the method, sequences each including the first step and the second step are performed. The plasma is continuously generated over the execution period for the first step and the execution period for the second step. In the second step, a ratio of the flow rate of a hydrogen gas to the flow rate of the second processing gas is set to be small in a period immediately before the execution period for the first step and a period immediately after the execution period for the first step.