Two-Step Via Structure for Low-Resistance Metal Filling
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Solution Overview
Problem
Via resistance increases as via bottom widths are made smaller in advanced technology nodes, and there is a challenge in maintaining effective metal filling and reducing bridging in conductive layers of semiconductor devices.
Innovation Solution
Implementing two-step via structures with increased via widths to reduce via resistance and improve metal filling, while keeping contact areas small to prevent bridging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If via bottom widths are made smaller to scale down devices, then device scaling is achieved, but via resistance increases
Solution Approach 1:
The via structure is segmented into multiple portions with different widths. The via includes a first portion with a first width and a second portion with a second width that is greater than the first width. This segmentation allows the via to have both small contact areas (first portion) and increased volume (second portion) to reduce resistance.
Solution Approach 2:
Different portions of the via have different local properties. The first portion has a smaller width optimized for contact area, while the second portion has a larger width optimized for volume and resistance reduction. This local quality variation resolves the contradiction between small dimensions and low resistance.
2Reliability
If via widths are increased to reduce via resistance, then via resistance decreases, but contact areas increase causing bridging
Solution Approach 1:
The via is divided into portions with different widths. The first portion maintains a small width to prevent bridging, while the second portion has an increased width to reduce resistance. This segmentation allows simultaneous optimization for both resistance reduction and bridging prevention.
Solution Approach 2:
The via structure implements local quality variation where different sections have different widths suited for their specific functions. The narrower section prevents bridging while the wider section reduces resistance, resolving the contradiction between these two requirements.
3Ease of manufacture
If conventional via structures are used in advanced technology nodes, then manufacturing is simpler, but metal filling becomes ineffective
Solution Approach 1:
The via structure is segmented into portions with different widths, creating a two-step via structure. This segmentation improves metal filling by providing varied geometries that facilitate complete filling while maintaining compatibility with existing manufacturing processes.
Solution Approach 2:
The via structure transitions from a uniform cross-section to a multi-level cross-section with different widths at different heights. This dimensional change improves metal filling effectiveness by creating geometric variations that enhance material deposition and filling.
Data Source
AI summary
A method includes forming a first etch stop layer (ESL) over a conductive feature, forming a first dielectric layer on the first ESL, forming a second ESL on the first dielectric layer, forming a second dielectric layer on the second ESL, forming a trench in the second dielectric layer, forming a first opening in a bottom surface of the trench extending through the second dielectric layer, and forming a second opening in a bottom surface of the first opening. The second opening extends through the first dielectric layer and the first ESL. The second opening exposes a top surface of the conductive feature. The method further includes widening the first opening to a second width, filling the trench with a conductive material to form a conductive line, and filling the second opening and the first opening with the conductive material to form a conductive via.