3D NAND Stack Assembly with Sequential Sacrificial Replacement
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Solution Overview
Problem
Current methods for forming memory devices, particularly three-dimensional NAND memory devices, face challenges in supporting the weight of the stack during fabrication, which can lead to buckling, bending, or collapsing of the structure due to insufficient support during the replacement of sacrificial materials in a single fabrication step.
Innovation Solution
The method involves using two different sacrificial materials to support a stack of alternating levels, where channel-material-pillars extend through the stack, and these sacrificial materials are sequentially replaced with conductive materials to form a laminate structure with alternating conductive and insulative levels, providing substantial support throughout the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sacrificial materials are replaced in a single fabrication step, then the fabrication process is simpler and faster, but the stack structure becomes unstable and may buckle, bend, or collapse due to insufficient support
Solution Approach 1:
The patent divides the single-step sacrificial material replacement into multiple sequential steps, with each step replacing one type of sacrificial material while leaving others in place to provide structural support. This segmentation allows the stack to maintain stability throughout the fabrication process while still achieving complete replacement of all sacrificial materials.
Solution Approach 2:
The patent performs preliminary actions by selectively removing only certain sacrificial materials in early fabrication steps while retaining others to provide temporary support structures. These retained sacrificial materials serve as preliminary support that prevents buckling and bending during subsequent processing steps, before being removed in later steps.
2Reliability
If multiple sacrificial materials are used to support the stack, then structural stability is improved, but the fabrication process complexity increases
Solution Approach 1:
The patent uses different sacrificial materials as intermediary support structures that facilitate the fabrication process. Each sacrificial material type serves as a temporary intermediary that provides specific support functions during particular fabrication steps, enabling complex stack formation while managing process complexity through systematic material replacement.
Solution Approach 2:
The patent applies different sacrificial materials at different locations within the stack structure, with each material type providing localized support where needed. This local differentiation allows for optimized structural stability in specific regions while maintaining overall process manageability through targeted replacement sequences.
Data Source
AI summary
Some embodiments include a method of forming an integrated assembly. Laterally alternating first and second sacrificial materials are formed over a conductive structure, and then a stack of vertically alternating first and second levels is formed over the sacrificial materials. The first levels include first material and the second levels include insulative second material. Channel-material-openings are formed to extend through the stack and through at least some of the strips. Channel-material-pillars are formed within the channel-material-openings. Slits are formed to extend through the stack and through the sacrificial materials. The first sacrificial material is replaced with first conductive material and then the second sacrificial material is replaced with second conductive material. At least some of the first material of the stack is replaced with third conductive material. Some embodiments include integrated assemblies.