Variable Width Contact Via for 3D Memory Void Prevention
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Solution Overview
Problem
Three-dimensional memory devices face challenges with high aspect ratio contact via structures, leading to void formation at the junction between vertically adjacent tiers due to conformal fill of metallic materials, which affects the reliability and efficiency of the memory device.
Innovation Solution
The implementation of contact via structures with variable widths, specifically designed to gradually widen at the joint region between tiers, reduces or eliminates voids by using local widening of the contact via cavity, ensuring a more conformal fill and enhancing the connection between tiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conformal fill of metallic materials is used in high aspect ratio contact via structures, then the contact via structure can be formed, but voids form at the junction between vertically adjacent tiers
Solution Approach 1:
The contact via cavity is designed with variable width, being wider at the joint region between tiers and narrower at other regions. This local variation in geometry ensures that the metallic fill material can properly conform and connect adjacent tiers without forming voids, while maintaining the necessary high aspect ratio for vertical integration.
Solution Approach 2:
The cross-sectional width of the contact via cavity is changed as a function of vertical position. The cavity width parameter is increased at the joint region to facilitate proper metal fill and connection, then reduced in other regions to maintain aspect ratio and device density. This parameter modulation resolves the void formation issue.
2Reliability
If the contact via cavity width is increased at the joint region, then void formation is reduced, but the device area increases
Solution Approach 1:
The contact via cavity exhibits local quality variation with width being non-uniform along the vertical axis. The width is selectively increased only at the critical joint region where void formation occurs, while remaining narrow in other regions. This localized geometric modification achieves reliability improvement without proportionally increasing the overall device footprint.
Solution Approach 2:
Instead of increasing the contact via width uniformly in the horizontal plane (which would increase device area), the solution introduces vertical dimensionality by varying the width as a function of height. The variable width profile along the vertical axis allows void prevention at the joint region while maintaining compact horizontal dimensions.
Data Source
AI summary
Devices are formed on a substrate. A first-tier alternating stack of first insulating layers and first spacer material layers having first stepped surfaces and a first retro-stepped dielectric material portion are formed over the substrate. A sacrificial contact via structure is formed through the first retro-stepped dielectric material portion. A second-tier alternating stack of second insulating layers and second spacer material layers is formed with second stepped surfaces. A second retro-stepped dielectric material portion including a doped silicate glass liner and a silicate glass material portion is formed over the second stepped surfaces. Memory stack structures are formed through the second-tier alternating stack and the first-tier alternating stack. A contact via cavity is formed down to the sacrificial contact via structure. The doped silicate glass liner is recessed and the sacrificial contact via structure is removed, to form a contact via structure in the contact via cavity.