Dry Etching Method for High Aspect Ratio Holes
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Solution Overview
Problem
Existing dry etching methods for semiconductor manufacturing, particularly for three-dimensional NAND flash memories, face challenges in achieving high aspect ratio etching without anomalies in shape and excessive deposition on etch stop layers, with limited control over the etching rate ratio of silicon nitride (SiN) to silicon oxide (SiOx) and insufficient selectivity to the mask.
Innovation Solution
A dry etching method using a plasma etching agent containing C3F6 and a hydrogen-containing saturated fluorocarbon, along with an oxidizing gas, under a negative direct-current self-bias voltage, to control the SiN/SiOx etching rate ratio within 0.90 to 1.5 and suppress excessive deposition on the etch stop layer, ensuring high selectivity and uniformity in etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a mixed gas containing CF gas and CHF gas is used to simultaneously etch SiN and SiOx layers, then the etching speed increases, but excessive deposition occurs on the etch stop layer and mask selectivity deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the etching gas by using C3F6 (hexafluoropropene) instead of conventional CF4 or CHF3, and controls the specific ratio of C3F6 to C4F6 (hexafluorobutadiene) between 5:95 to 45:55. This parameter change modifies the plasma chemistry to reduce excessive fluorocarbon deposition while maintaining high etching rates for both SiN and SiOx layers.
Solution Approach 2:
The patent employs a composite gas system combining C3F6 and C4F6 in specific proportions. This composite approach leverages the complementary properties of both gases: C3F6 provides high etching rate and good anisotropy, while C4F6 contributes to side wall protection and shape control, achieving a balance between productivity and deposition control.
2Productivity
If the etching rate of SiN layer is excessively high compared to SiOx layer, then the etching process is faster, but isotropic etching occurs causing anomaly in etching shape
Solution Approach 1:
The patent adjusts the gas composition parameters to achieve a balanced etching rate ratio between SiN and SiOx layers. By controlling the C3F6:C4F6 ratio and optimizing other process parameters, the patent maintains the SiN etching rate within a specific range relative to SiOx, preventing excessive anisotropic etching that would cause shape anomalies while still achieving high productivity.
3Ease of manufacture
If conventional CF gas is used to etch SiN layer, then the process is simple, but the etching rate is slow causing deposition on SiN layers
Solution Approach 1:
The patent changes from conventional CF4 gas to C3F6 (hexafluoropropene) as the primary fluorocarbon source. This parameter change significantly increases the etching rate of SiN layers while maintaining process simplicity. The unique molecular structure of C3F6 provides both high reactivity with SiN and controlled deposition characteristics.
4Manufacturing precision
If separate etching operations are performed on SiN and SiOx layers, then the etching selectivity is improved, but the number of process steps significantly increases
Solution Approach 1:
The patent merges the etching of SiN and SiOx layers into a single simultaneous etching process using a optimized gas mixture of C3F6 and C4F6. This merging is achieved by adjusting the gas composition and process parameters to achieve appropriate etching rate ratios, eliminating the need for multiple separate etching steps while maintaining good selectivity and control.
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 and minimizes fluorocarbon deposition, enabling the formation of through holes with high aspect ratios without shape anomalies, ensuring good electrical characteristics and efficient semiconductor manufacturing.
Implementation Method 1
plasmatizing a dry etching agent to generate a plasma and etching the laminated film by the plasma
Implementation Method 2
etching the laminated film by the thus-generated plasma under a bias voltage of 500 V or higher
Implementation Method 3
the dry etching agent contains C3F6, a hydrogen-containing saturated fluorocarbon, and an oxidizing gas
Data Source
AI summary
A dry etching method according to the present disclosure is for forming a through hole in a laminated film of silicon oxide layers and silicon nitride layers on a substrate in a direction vertical to the laminated film by plasmatizing a dry etching agent to generate a plasma and etching the laminated film by the plasma through a mask having a predetermined opening pattern under a negative direct-current self-bias voltage whose absolute value is 500 V or greater, wherein the dry etching agent contains at least C3F6, a hydrogen-containing saturated fluorocarbon represented by CxHyFz and an oxidizing gas, and wherein the volume of the hydrogen-containing saturated fluorocarbon contained in the dry etching agent is in a range of 0.1 to 10 times the volume of C3F6 contained in the dry etching agent.