Dry Etching Method for 3D NAND Laminated Films
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Solution Overview
Problem
Existing dry etching methods for semiconductor manufacturing, particularly in three-dimensional NAND flash memory production, face challenges in achieving sufficient etching selectivity and preventing excessive horizontal etching of silicon nitride (SiN) layers, leading to structural collapse and uneven etching shapes due to high aspect ratios and low etching rates.
Innovation Solution
A dry etching method using a plasma etching agent containing 1,3,3-tetrafluoropropene and a C2-C5 unsaturated perfluorocarbon, with a predetermined ratio, applied under a bias voltage of 500 V or higher, to control the etching rate ratio of SiN to SiOx within 0.90 to 1.5, ensuring high selectivity to the mask and preventing isotropic etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional CF-based gas is used for etching, then the etching process can be performed, but the etching rate of SiN is low and deposition occurs on SiN layers resulting in poor etching shape
Solution Approach 1:
The patent changes the chemical composition parameters of the etching gas from conventional CF-based gas to a mixed gas containing CHF3 and C3F8. This parameter change enables simultaneous achievement of high etching rate for SiN and SiO2 layers while preventing deposition on SiN layers, thereby resolving the contradiction between etching speed and etching shape precision
Solution Approach 2:
The patent uses a composite etching gas system combining CHF3 (providing high etching rate) and C3F8 (providing low deposition and good shape control). This composite gas approach allows the system to achieve benefits of both individual gases simultaneously, resolving the contradiction between fast etching and precise shape control
2Manufacturing precision
If multiple independent etching steps are performed on respective layers, then each layer can be etched separately, but the number of etching steps significantly increases with increase in number of layers
Solution Approach 1:
The patent merges multiple independent etching steps into a single plasma etching step by using a mixed gas of CHF3 and C3F8. This single step can simultaneously etch both SiN and SiO2 layers with appropriate selectivity, dramatically reducing the total number of etching steps required while maintaining manufacturing precision
Solution Approach 2:
The mixed gas etching system achieves multi-functionality by being able to etch different materials (SiN and SiO2) with different required selectivities in a single process step. This universal etching capability eliminates the need for multiple specialized etching steps for different layers
3Productivity
If a mixed gas containing CF-based gas and CHF-based gas is used for simultaneous etching, then different layers can be etched in one step, but the etching gas does not ensure sufficient etching selectivity to mask resulting in mask failure
Solution Approach 1:
The patent changes the gas composition from CF-based/CHF-based mixed gas to CHF3/C3F8 mixed gas. This parameter change provides sufficient etching selectivity to the mask while maintaining the ability to simultaneously etch different layers, resolving the contradiction between productivity and mask selectivity
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 method allows for precise control of the etching rate ratio, suppressing excessive isotropic etching of SiN layers and preventing structural collapse, even at high aspect ratios, while maintaining high etching selectivity and uniformity in the etched features.
Implementation Method 1
generating a plasma from a dry etching agent and etching the laminated film by the plasma
Implementation Method 2
etching the laminated film by the plasma through the mask under a bias voltage of 500 V or higher
Data Source
AI summary
Disclosed is a dry etching method for etching a laminated film of silicon oxide layers and silicon nitride layers on a substrate. The dry etching method includes providing a mask on the laminated film, generating a plasma from a dry etching agent and etching the laminated film by the plasma through the mask under a bias voltage of 500 V or higher to form a through hole in the laminated film vertically to the layers, wherein the dry etching agent contains at least C3H2F4, an unsaturated perfluorocarbon represented by CxFy and an oxidizing gas, and wherein a volume of the unsaturated perfluorocarbon contained in the dry etching agent is 0.1 to 10 times a volume of the C3H2F4 contained in the dry etching agent.