Sacrificial Fin for Self-Aligned MOL Contact Alignment
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Solution Overview
Problem
As device dimensions decrease, forming individual components and electrical contacts in semiconductor devices becomes increasingly challenging due to scaling issues, particularly in lithography patterning, where there is no self-alignment in Middle-Of-The-Line (MOL) contacts, leading to potential shorts and increased complexity.
Innovation Solution
The method involves forming a sacrificial fin structure using Self-Aligned-Double-Patterning (SADP) to self-align the MOL contact, where a sacrificial fin is used to maintain a small critical dimension and separate the contact landing from the substrate, enabling precise placement and alignment of contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional lithography patterning is used for MOL contacts, then the fabrication process is simpler, but self-alignment is not achieved leading to potential shorts and reduced manufacturing precision
Solution Approach 1:
A sacrificial fin structure is introduced as an intermediary element to enable self-alignment of MOL contacts. The sacrificial fin is formed between the contact openings, serves as a reference structure during patterning, and is removed after alignment is achieved. This mediator allows the contact openings to self-align to the active fin without requiring complex lithography overlay control.
Solution Approach 2:
The sacrificial fin structure is formed in advance before the MOL contact openings are patterned. This preliminary structure provides a physical reference that guides the subsequent contact opening formation, ensuring self-alignment. The sacrificial fin is removed only after it has served its alignment purpose, allowing the contact openings to be precisely positioned relative to the active fin.
2Measurement precision
If device dimensions are decreased to achieve smaller features, then resolution is improved, but forming individual components and electrical contacts becomes more difficult
Solution Approach 1:
The sacrificial fin acts as a mediator that enables contact formation at reduced dimensions. By providing a physical reference structure, it allows standard lithography tools to achieve precise alignment even when the overall device dimensions are scaled down. The sacrificial fin's larger dimensions compared to the final contact size make it easier to form while still enabling precise contact placement.
Solution Approach 2:
The fin structure is segmented into an active fin and a sacrificial fin portion. The active fin maintains the small critical dimension for device performance, while the sacrificial fin portion provides a larger, easier-to-form reference structure for alignment. This segmentation allows the manufacturing process to work with larger, easier-to-manage dimensions for alignment while maintaining small final feature sizes.
3Manufacturing precision
If sacrificial fin is used for self-alignment, then contact alignment precision is improved, but the fabrication process becomes more complex
Solution Approach 1:
The sacrificial fin formation is merged with the existing fin formation process. The same epitaxial growth or deposition steps that create the active fin also create the sacrificial fin portion, eliminating the need for separate fabrication steps. The patternning and etching processes that define the active fin simultaneously define the sacrificial fin, combining multiple functions into unified process steps.
Solution Approach 2:
The sacrificial fin is created as a copy or replica of the active fin structure using the same fabrication processes. By copying the fin formation steps, the sacrificial fin automatically inherits the correct dimensions and positioning, ensuring self-alignment without requiring additional alignment steps or complex process control.
Data Source
AI summary
A method is presented for forming a self-aligned middle-of-the-line (MOL) contact. The method includes forming a fin structure over a substrate, depositing and etching a first set of dielectric layers over the fin structure, etching the fin structure to form a sacrificial fin and a plurality of active fins, depositing a work function metal layer over the plurality of active fins, depositing an inter-layer dielectric (ILD) and a second set of dielectric layers. The method further includes etching the second set of dielectric layers and the ILD to form a first, via portion and to expose a top surface of the sacrificial fin, removing the sacrificial fin to form a second via portion, and filling the first and second via portions with a conductive material to form the MOL contact in the first via portion and a contact landing in the second via portion.