3D Memory Opening Layout for Better Lithography Focus Margin
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Solution Overview
Problem
Current three-dimensional memory devices face challenges in manufacturing due to the difficulty in simultaneously printing memory openings and support openings with high fidelity, especially with aggressive off-axis illumination, which affects the depth of focus and lithographic process window.
Innovation Solution
The solution involves forming memory openings in a first hexagonal array parallel to a horizontal direction and support openings in a second hexagonal array perpendicular to the first horizontal direction within an alternating stack of insulating and electrically conductive layers, using a specific lithographic pattern and exposure source to optimize the lithographic process and enhance focus margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If aggressive off-axis illumination is used to print memory openings and support openings simultaneously, then manufacturing complexity is reduced, but manufacturing precision deteriorates due to depth of focus issues
Solution Approach 1:
The patent divides the opening array into two distinct hexagonal arrays: memory openings arranged in a first hexagonal array and support openings arranged in a second hexagonal array. This segmentation allows each array type to be optimized independently for its specific function, enabling simultaneous printing with aggressive off-axis illumination while maintaining the precision needed for both memory and support structures
Solution Approach 2:
The patent transitions from conventional square or rectangular opening arrays to hexagonal arrays with specific nearest-neighbor directions. By arranging memory openings with nearest neighbors in a first horizontal direction and support openings with nearest neighbors in a second horizontal direction (at a different angle), the patent exploits geometric dimensionality to achieve better lithographic performance with off-axis illumination
2Device complexity
If conventional lithographic patterns are used for both memory and support openings, then process simplicity is maintained, but manufacturing precision suffers due to limited focus margin
Solution Approach 1:
The patent employs asymmetric hexagonal array configurations where memory openings and support openings have different orientations and spacing characteristics. The first hexagonal array for memory openings has nearest neighbors in a first horizontal direction, while the second hexagonal array for support openings has nearest neighbors in a second horizontal direction. This asymmetry optimizes the lithographic pattern for aggressive off-axis illumination, significantly enhancing the focus margin and manufacturing precision
Data Source
AI summary
An alternating stack of insulating layers and spacer material layers is formed over a substrate. The spacer material layers are formed as, or are subsequently replaced with, electrically conductive layers. Memory openings and support openings are formed through the alternating stack. The memory openings are arranged in a first hexagonal array having a nearest-neighbor direction that is parallel to a first horizontal direction, and the support openings are arranged in a second hexagonal array having a nearest-neighbor direction that is perpendicular to the first horizontal direction. Memory opening fill structures are formed within a respective one of the memory openings, and support pillar structures within a respective one of the support openings.