BEOL Copper CMP Dendrite Prevention via Nblok Cap
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Solution Overview
Problem
The exposure of copper to interlayer dielectric (ILD) during chemical mechanical planarization (CMP) leads to dendrite formation and subsequent issues like shorting and Time Dependent Dielectric Breakdown (TDDB) in semiconductor devices, particularly with the use of low-k dielectric materials, which existing methods struggle to address effectively in high-volume manufacturing.
Innovation Solution
A novel CMP integration scheme that involves copper deposition, recessing copper structures using controlled etch, depositing an Nblok cap layer to prevent copper exposure to ILD, and subsequent CMP to remove overburden and liner, thereby preventing dendrite formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If copper CMP is performed after BEOL processing, then copper overburden is removed and planarization is achieved, but residual copper exposure to ILD causes dendrite formation
Solution Approach 1:
A cap layer is deposited over the copper structures before CMP processing. This cap layer acts as an intermediary barrier that prevents copper exposure to ILD during CMP, thereby eliminating dendrite formation while maintaining planarization quality. The cap layer is temporarily present during the harmful process and then removed or retained as appropriate.
Solution Approach 2:
The cap layer is deposited in advance before the CMP process begins. This preliminary action prepares the copper structures by covering them with a protective layer that prevents harmful interactions during the subsequent CMP step, thereby preventing dendrite formation before it can occur.
2Reliability
If cap layer deposition is added to prevent dendrite formation, then dendrite issues are eliminated, but process complexity and queue time increase
Solution Approach 1:
The cap layer deposition is merged with existing process flows in the BEOL fabrication sequence. By integrating the cap layer step into the established process architecture and using standard deposition and removal techniques, the additional reliability benefit is achieved with minimal increase in overall process complexity.
3Reliability
If cap layer is deposited and then removed by CMP, then copper protection is achieved, but additional CMP steps and queue time are required
Solution Approach 1:
The cap layer removal is performed rapidly using optimized CMP parameters that enable quick elimination of the cap layer material. This rushing through the removal step minimizes the time the cap layer remains in the process, thereby reducing queue time while still achieving the protective function during the critical CMP window.
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 eliminates dendrite formation and improves TDDB performance by ensuring copper is not exposed to ILD during CMP, making it suitable for all metal layers in the BEOL stack and facilitating the use of ultra-low-k materials across various technology nodes.
Implementation Method 1
This residual copper can result in formation of dendrites due to copper oxidation
Implementation Method 2
chemical mechanical planarization (CMP)
Implementation Method 3
performing a copper deposition process to fill the trench or via with copper, which can be performed by fill, plating or electroless deposition
Data Source
AI summary
Disclosed herein are various methods of forming copper-based conductive structures on integrated circuit devices by performing a copper deposition process to fill the trench or via with copper, which can be performed by fill, plating or electroless deposition. Copper clearing of copper overburden is performed using CMP to stop on an existing liner. Copper in the trenches or vias is recessed by controlled etch. An Nblok cap layer is deposited to cap the trenches or vias so that copper is not exposed to ILD. Nblok overburden and adjacent liner is then removed by CMP. Nblok cap layer is then deposited. The proposed approach is an alternative CMP integration scheme that will eliminate the exposure of copper to ILD during CMP, will prevent any dendrite formation, can be used for all metal layers in BEOL stack, and can be utilized for multiple layers, as necessary, whenever copper CMP is desired.