Stair-Step Etch Selectivity in SiO2/SiN Bilayer Stacks
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Solution Overview
Problem
The challenge in semiconductor wafer processing is to efficiently form stair-step structures with high selectivity and vertical profile angles in stacks of silicon oxide (SiO2) and silicon nitride (SiN) bilayers, while maintaining fast throughput and minimizing line edge roughness and corner faceting, especially as the industry moves towards higher bilayer counts.
Innovation Solution
A method involving multiple etching cycles with specific gas compositions and biases in a plasma processing chamber, where SiO2 and SiN layers are alternately etched using hydrofluorocarbon-based gases with sulfur hexafluoride and nitrogen trifluoride, and oxygen, respectively, under controlled conditions to achieve high selectivity and vertical profiles without polymer tapering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional etching methods are used to form stair-step structures, then the structures can be formed, but line edge roughness increases and corner faceting occurs
Solution Approach 1:
The patent applies periodic action by implementing multiple alternating etching cycles that switch between different gas chemistries (hydrofluorocarbon-based for SiO2, oxygen-based for SiN). Each cycle etches one material type then the other, creating a periodic pattern of etching and protection that maintains vertical profiles and reduces line edge roughness while achieving the desired stair-step structure efficiently
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting gas composition, pressure, and power settings between etching cycles. The gas chemistry is changed from hydrofluorocarbon-based to oxygen-based depending on which layer is being etched, and parameters like pressure and RF power are optimized for each specific etching step to maintain vertical sidewalls and reduce corner faceting
2Manufacturing precision
If selectivity is increased for etching SiO2 and SiN layers, then etching precision improves, but processing time increases
Solution Approach 1:
The patent applies segmentation by dividing the etching process into distinct segments or cycles, where each cycle is dedicated to etching a specific material layer (SiO2 or SiN) using optimized gas chemistry. This segmentation allows high selectivity to be achieved for each material type independently without requiring overly conservative process parameters that would slow down the overall process
Solution Approach 2:
The patent maintains continuity of useful action by implementing alternating etching cycles that continuously progress the stair-step structure formation. Rather than using single long etching steps with frequent interruptions, the process continuously alternates between etching SiO2 and SiN layers, maintaining high throughput while achieving the required selectivity through gas chemistry optimization
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 enables faster processing with reduced line edge roughness and corner faceting, maintaining vertical profiles and high selectivity, even at higher bilayer counts, thus improving the efficiency and quality of stair-step structure formation.
Implementation Method 1
generating a plasma from the SiO2 etching gas
Implementation Method 2
generating a plasma from the SiN etching gas
Implementation Method 3
an inert bombardment gas
Data Source
AI summary
A method for forming a stair-step structure in a stack on a substrate is provided. The method comprises at least one stair step cycle. Each stair step cycle comprises trimming the mask and etching the stack. Etching the stack is provided in a plurality of cycles wherein each cycle comprises etching a SiO2 layer and etching a SiN layer. Etching a SiO2 layer comprises flowing a SiO2 etching gas into the plasma processing chamber, wherein the SiO2 etching gas comprises a hydrofluorocarbon, an inert bombardment gas, and at least one of SF6 and NF3, generating a plasma from the SiO2 etching gas, providing a bias, and stopping the SiO2 layer etch. The etching a SiN layer comprises flowing a SiN etching gas into the plasma processing chamber, comprising a hydrofluorocarbon and oxygen, generating a plasma from the SiN etching gas, providing a bias, and stopping the SiN layer etch.