Metal Plug CMP Uniformity via Etching Step Height Reduction
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Solution Overview
Problem
Conventional CMP processes in the gate last route face challenges in achieving within die uniformity, leading to recesses in metal plugs and increased leakage current, which degrades electrical properties and yield, especially below 45 nm technology nodes.
Innovation Solution
A method combining metal etching with conventional CMP, involving dry etching of exposed metal layers and subsequent CMP planarization using a F-based etching gas and acidic or alkaline polishing slurries to reduce step height and achieve flat metal plugs, thereby improving within die uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional CMP process is used for metal plug planarization, then the process is simple and straightforward, but the within die uniformity deteriorates and metal plug recesses occur
Solution Approach 1:
The invention segments the planarization process into two distinct steps: first performing oxide CMP to remove excess oxide and expose the metal plug top, then performing metal CMP to planarize the metal surface. This segmentation allows each CMP step to be optimized independently, with the oxide CMP removing the bulk of the oxide and the metal CMP providing precise metal surface planarization, thereby solving the within die uniformity problem while maintaining process manageability
Solution Approach 2:
The oxide CMP is performed as a preliminary action before the metal CMP. By removing the oxide layer first, the metal plug tops are exposed and can be planarized in the subsequent metal CMP step. This preliminary oxide removal creates favorable conditions for the metal CMP to achieve better within die uniformity by reducing the step height and preventing metal plug recesses
2Manufacturing precision
If oxide buffer CMP is performed to remove oxide after conventional W CMP, then W plugs protrude, but Al metal gate electrodes also protrude causing leakage current
Solution Approach 1:
The invention inverts the conventional sequence by performing oxide CMP before metal CMP instead of after. This reversal prevents the Al metal gate electrodes from protruding during the oxide removal process, as the oxide is removed when the gates are still covered, eliminating the leakage current problem while still achieving the desired W plug protrusion for good contact hole fill
3Ease of manufacture
If larger step height exists between contact hole area and non-contact hole area, then metal layer deposition is easier, but CMP process transfers step height to metal plug top causing recess
Solution Approach 1:
The segmented CMP approach addresses the step height problem by dividing the removal process into oxide CMP and metal CMP steps. The oxide CMP removes the majority of the step height difference between contact hole and non-contact hole areas, reducing it to an acceptable level before metal deposition. The subsequent metal CMP then provides fine planarization of the metal surface, ensuring flat metal plug tops despite the initial large step height that facilitated easy metal layer deposition
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
The method significantly reduces metal plug recesses and enhances within die uniformity and electrical properties by minimizing step height transfer during CMP, resulting in improved device performance.
Implementation Method 1
dry etching of exposed metal layers and subsequent CMP planarization using a F-based etching gas
Implementation Method 2
CMP planarization using a F-based etching gas and acidic or alkaline polishing slurries
Implementation Method 3
acidic or alkaline polishing slurries
Data Source
AI summary
A method for improving the within die uniformity of the metal plug CMP process in the gate last route is provided. Before performing the CMP process for forming the metal plug, a metal etching process is applied, so that the step height between the metal layers in the contact hole area and the non-contact hole area is greatly reduced. Therefore, the relatively small step height will exert a significantly less effect on the following CMP process, so that the step height will be limitedly transferred to the top of metal plug after finishing CMP process. In this way, the recess on top of the metal plug is largely reduced, so that a flat top of the metal plug is obtained, and within die uniformity and electrical properties the device are improved.