Combination Hardmask for High Aspect Ratio Etch Selectivity
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Solution Overview
Problem
Current etching techniques for high aspect ratio features in semiconductor devices face challenges in achieving sufficient vertical and radial selectivity, leading to issues with feature accuracy and contamination during the stacking process in 3D flash memory devices.
Innovation Solution
A method involving a combination hardmask is formed by layering carbon or silicon oxide and metal hardmasks, patterned and etched using specific gas plasmas, allowing for precise etching through the stack while minimizing contamination and improving selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single hardmask layer is used for etching high aspect ratio features, then the etching process is simple, but vertical and radial selectivity are insufficient leading to feature accuracy degradation and contamination
Solution Approach 1:
The single hardmask layer is segmented into multiple distinct layers: a first hardmask layer (e.g., silicon oxide) and a second hardmask layer (e.g., metal such as tungsten or titanium nitride). Each layer serves a specific function - the first layer provides vertical selectivity while the second layer provides radial selectivity and protects against sputtered metal contamination, thereby achieving high feature accuracy without excessive overall complexity
Solution Approach 2:
The patent employs composite material structure by combining different materials in the hardmask layers - specifically using materials with complementary properties such as silicon oxide (for vertical etch selectivity) and metal materials (for radial selectivity and contamination protection). This composite approach enables both vertical and radial selectivity to be achieved simultaneously, resolving the contradiction between manufacturing precision and device complexity
2Ease of manufacture
If conventional etching techniques are used, then the process is straightforward, but sputtered metal contamination occurs during the etching process
Solution Approach 1:
The second hardmask layer acts as an intermediary protective layer between the etching environment and the underlying structures. This metal-containing layer specifically protects against sputtered metal contamination during the etching process while allowing the etch to proceed through the first hardmask layer, thus maintaining ease of manufacture while eliminating contamination issues
Solution Approach 2:
The patent changes the material parameters of the hardmask structure by introducing a metal-containing second layer with specific properties (high sputter resistance, appropriate etch selectivity). This parameter change in material composition and structure effectively prevents sputtered metal contamination while maintaining a relatively simple two-step etching process
3Reliability
If a combination hardmask with multiple layers is used, then vertical and radial selectivity are improved, but the mask formation process becomes more complex
Solution Approach 1:
The mask formation process is segmented into distinct, optimized steps: forming the first hardmask layer with specific thickness and material properties for vertical selectivity, then forming the second hardmask layer with different material properties for radial selectivity. Each segment is independently optimized and controlled, which improves reliability while keeping the overall process manageable through clear separation of functions
Solution Approach 2:
The use of composite materials with complementary properties allows each layer to be optimized for its specific function. The first layer (e.g., silicon oxide) is optimized for vertical etch selectivity while the second layer (e.g., metal) is optimized for radial selectivity and contamination protection. This functional segmentation through composite materials achieves high reliability without requiring overly complex formation processes
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 both vertical and radial selectivity by up to 3-4 times, reducing faceting and sputtered metal contamination, thereby improving the accuracy and cleanliness of etched features in high aspect ratio semiconductor devices.
Implementation Method 1
forming the first hardmask layer etch gas into a plasma
Data Source
AI summary
A method for etching features in a stack is provided. A combination hardmask is formed by forming a first hardmask layer comprising carbon or silicon oxide over the stack, forming a second hardmask layer comprising metal over the first hardmask layer, and patterning the first and second hardmask layers. The stack is etched through the combination hardmask.