Decoupled Via Fill Process for High Aspect Ratio Interconnects
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Solution Overview
Problem
Traditional dual damascene interconnect processes face challenges with gap fill and electromigration in high aspect ratio vias due to non-conformal deposition techniques, leading to issues like trench overhang, pinched-off openings, and inadequate barrier and seed layer formation, as well as defects from selective electroless approaches.
Innovation Solution
A decoupled via fill process is implemented, where a conformal barrier layer is used to isolate lower and upper trench metals, with non-selective deposition of metals to fill the via and trench separately, preventing intermixing and void formation, and enhancing electromigration performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If line-of-sight PVD process is used to deposit barrier/adhesion and seed layers, then deposition is simple and direct, but trench overhang occurs leading to pinched-off openings and inadequate gap fill
Solution Approach 1:
The patent segments the trench fill process into multiple stages: first depositing barrier/adhesion and seed layers using PVD, then performing electroplating to fill the trench. This segmentation allows each process to optimize for its specific function, avoiding the limitations of a single line-of-sight approach.
Solution Approach 2:
The patent performs preliminary deposition of barrier/adhesion and seed layers using PVD before the main electroplating fill. This preliminary action prepares the trench walls with appropriate layers that prevent overhang and ensure proper copper adhesion, enabling subsequent complete gap fill.
2Productivity
If device dimensions are scaled down to narrower features, then device density increases, but aspect ratio becomes more aggressive causing PVD overhang and plating pinching
Solution Approach 1:
The patent changes the deposition parameters by switching from pure line-of-sight PVD to a combination of PVD and electroplating. This parameter change allows the process to handle higher aspect ratios and narrower features by using electroplating's ability to conformally coat vertical walls without overhang.
Solution Approach 2:
The patent introduces an intermediary electroplating process between the PVD deposition and the final trench fill. This intermediary step uses electroplating to uniformly fill the trench and via openings, compensating for the overhang issues created by PVD in high aspect ratio structures.
3Manufacturing precision
If selective electroless deposition is used to fill vias, then via fill is improved, but defects intrinsic to imperfect selectivity occur
Solution Approach 1:
The patent uses electroplating, which is a self-service process where copper ions are reduced and deposited directly onto the seed layer without requiring selective chemical reactions. This eliminates the selectivity issues and associated defects of electroless deposition, as the process naturally fills only the conductive regions with proper seed layers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves gap fill margin, reduces defects, and enhances electromigration performance by using dual metals with scaled thin conformal barriers, achieving better line and via resistance and RC performance.
Implementation Method 1
a first barrier layer is conformally deposited onto the bottom and sidewalls of the trench
Implementation Method 2
a first metal fill is blanket deposited into the trench
Data Source
AI summary
Techniques are disclosed for providing a decoupled via fill. Given a via trench, a first barrier layer is conformally deposited onto the bottom and sidewalls of the trench. A first metal fill is blanket deposited into the trench. The non-selective deposition is subsequently recessed so that only a portion of the trench is filled with the first metal. The previously deposited first barrier layer is removed along with the first metal, thereby re-exposing the upper sidewalls of the trench. A second barrier layer is conformally deposited onto the top of the first metal and the now re-exposed trench sidewalls. A second metal fill is blanket deposited into the remaining trench. Planarization and/or etching can be carried out as needed for subsequent processing. Thus, a methodology for filling high aspect ratio vias using a dual metal process is provided. Note, however, the first and second fill metals may be the same.