Self-Aligned BEOL Interconnect Patterning With Subtractive Metal Etch
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The complexity of microelectronic device fabrication has increased due to the need for precise alignment and etching of features with decreasing sizes, making it challenging to achieve accurate alignment of layers during back-end-of-line (BEOL) processes.
Innovation Solution
A 2-dimensional self-aligned scheme with a subtractive metal etch is employed, utilizing a silicon nitride hard mask layer as a chemical mechanical polishing stop and subsequent self-aligned double patterning processes to align vias with both metal layers, followed by gap-filling and etching to form interconnects with precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching and alignment methods are used in BEOL processes, then the fabrication process is simpler, but the alignment accuracy and precision of etching operations deteriorate as device features are reduced in size
Solution Approach 1:
The fabrication process is divided into distinct segments: forming a patterned layer with first features, forming a second patterned layer with second features, and performing subtractive metal etching. Each segment serves a specific function in achieving overall alignment accuracy, allowing complex alignment tasks to be broken down into manageable steps that can be optimized independently.
Solution Approach 2:
The method performs preliminary patterning actions to create alignment reference features before the final etching step. The first patterned layer and second patterned layer are formed in advance to establish precise alignment relationships, enabling subsequent etching operations to achieve high accuracy without requiring complex real-time alignment systems.
2Manufacturing precision
If device feature sizes are reduced to achieve higher integration, then the density and capacity improve, but the alignment difficulty and etching precision requirements increase
Solution Approach 1:
The alignment system is self-aligning, where the first patterned layer and second patterned layer automatically establish their relative positions through the subtractive metal etching process. The method uses the structure itself as the alignment reference, eliminating the need for external alignment marks or complex alignment equipment, thereby achieving high etching accuracy even at reduced feature sizes.
Solution Approach 2:
The method transitions from two-dimensional planar alignment to three-dimensional self-aligned structures by forming patterned layers at different levels and using vertical etching. This dimensional approach allows alignment to be achieved through vertical stacking and self-registration rather than relying solely on lateral alignment, enabling precise etching at smaller feature dimensions.
3Adaptability or versatility
If multiple material layers and complex device structures are introduced to achieve desired device functionality, then the device performance improves, but the alignment difficulty increases
Solution Approach 1:
The subtractive metal etching process serves multiple functions simultaneously: it removes metal to create interconnect structures, establishes alignment between different patterned layers, and defines feature geometries. This multi-functional approach allows complex device structures with multiple material layers to be fabricated while maintaining alignment precision through a single integrated process step.
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 method enables accurate alignment and formation of interconnects between metal layers with reduced widths, suitable for ultra-small pitch patterning, improving the precision and efficiency of BEOL processes.
Implementation Method 1
depositing a first oxide layer over a patterned hard mask layer
Implementation Method 2
Plasma dry etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers
Implementation Method 3
The second portion of the via is gap-filled with a gapfill metal
Data Source
AI summary
Embodiments of the present disclosure generally relate to layer stacks produced during back-end-of-line (BEOL) process flows. In one or more embodiments, the layer stack is disposed on a substrate and contains a first hard mask layer disposed on a first metal layer, one or more low-k material layers disposed over the first hard mask layer, a second metal layer disposed over the one or more low-k material layers and the first hard mask layer, a second hard mask layer disposed over the second metal layer, and an oxide layer disposed over the second hard mask layer. The second metal layer, the second hard mask layer, and the oxide layer are patterned and form a plurality of features. A gapfill interconnect metal is connected to the first metal layer and the second metal layer and is disposed through the first hard mask layer and the one or more low-k material layers.