Multiheight Conductive Via Contacts for 3D NAND Interconnects
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Solution Overview
Problem
Current methods for forming multilevel interconnect structures in semiconductor devices face challenges in achieving high density without design restrictions and minimal processing complexity and cost, particularly in creating electrically conductive via contacts with varying heights in three-dimensional NAND memory devices.
Innovation Solution
The method involves forming a stack of alternating sacrificial layers and insulating layers over a substrate, using contact masks and over masks to create contact openings that extend perpendicular to the substrate, and depositing electrically conductive via contacts with self-aligned insulating liners for electrical isolation, allowing for the formation of terraced word lines and efficient interconnects across multiple levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional methods are used to form multilevel interconnect structures, then processing complexity and cost increase, but manufacturing precision and design flexibility are maintained
Solution Approach 1:
The contact mask is divided into multiple segments at different heights, with each segment defining contact openings for specific depth ranges. This segmentation allows selective formation of contacts at different levels without requiring complete etching through the entire stack, reducing processing complexity while maintaining precision through localized mask control
Solution Approach 2:
The patent introduces a vertical dimension to the mask structure by forming terraced regions at different heights. This multi-level mask approach enables precise control of contact openings at various depths within the alternating stack, achieving high manufacturing precision without increasing overall process complexity
2Adaptability or versatility
If contact openings are formed to varying depths to reach different sacrificial layers, then electrical isolation between contacts is compromised, but interconnect functionality is improved
Solution Approach 1:
Insulating liners are applied selectively to the sidewalls of contact openings at different heights, providing electrical isolation only where needed. This localized application of insulating material maintains electrical isolation reliability while allowing contacts at different depths to function independently without compromising interconnect versatility
Solution Approach 2:
The insulating liner acts as an intermediary barrier between conductive contacts at different levels. This intermediate layer prevents electrical interference between contacts while allowing each contact to maintain its functional connection to the appropriate sacrificial layer, thus preserving both isolation and interconnect functionality
3Manufacturing precision
If multiple etching steps are used to form contact openings at different levels, then manufacturing precision is improved, but processing complexity increases
Solution Approach 1:
Multiple contact openings at different depth levels are formed simultaneously in a single etching step using a terraced contact mask structure. This merging of multiple operations into one step achieves precise depth control for each contact level without increasing processing complexity, as the mask geometry itself defines the different etch depths
4Adaptability or versatility
If the number of wiring levels is increased for high density circuitry, then device functionality is improved, but manufacturing precision requirements become more stringent
Solution Approach 1:
The contact mask is segmented into multiple terraced levels, with each segment corresponding to a specific wiring level in the alternating stack. This segmentation enables precise formation of contacts for each wiring level independently, supporting increased device functionality while maintaining manufacturing precision through localized mask control at each level
Data Source
AI summary
A method of making multi-level contacts includes providing an in-process multilevel device having a device region and a contact region including a stack of alternating sacrificial layers and insulating layers located over a major surface of a substrate. A contact mask having contact mask openings is provided over the stack, and a first over mask having first over mask openings is provided over the contact mask. A subset of the contact mask openings is substantially aligned with the first over mask openings. Contact openings are formed through the stack, wherein each of the contact openings extends substantially perpendicular to the major surface of the substrate to a respective one of the sacrificial layers. A plurality of electrically conductive via contacts is formed in the plurality of the contact openings.