Self-aligned via formation at metal line ends
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Solution Overview
Problem
In semiconductor device metallization processes, forming vias at the ends of metal lines is challenging due to alignment issues, particularly with lithography, which can result in variations in via critical dimension (CD) and misalignment or cutting off of vias.
Innovation Solution
The method involves patterning metal lines using alternating hardmasks for even and odd lines, cutting and enlarging mask windows to form T-shaped cavities, filling these cavities with a gap fill dielectric, and recessing the metal lines to create self-aligned vias at line ends, ensuring consistent via formation without CD variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lithography alignment is used to form vias at metal line ends, then via placement can be achieved, but via critical dimension (CD) variation and misalignment occur due to finite overlay shift
Solution Approach 1:
The hardmask is patterned with the metal lines in advance, and the via openings are defined by the hardmask pattern itself rather than by a separate lithography alignment step. This preliminary patterning establishes the reference framework before via formation, eliminating overlay shift issues.
Solution Approach 2:
The hardmask structure serves dual purposes: it defines the metal line pattern and simultaneously defines the via opening positions and dimensions. The via CD is self-determined by the hardmask geometry and etch parameters, not by separate lithography alignment, making the process self-aligning and eliminating overlay-dependent CD variation.
2Ease of manufacture
If separate lithography alignment is used for via formation, then via placement is possible, but process complexity increases due to multiple alignment steps
Solution Approach 1:
The via opening definition function is merged with the hardmask patterning function. The same hardmask that defines metal line positions also defines via opening positions, eliminating the need for separate via alignment lithography steps and reducing overall process complexity.
Solution Approach 2:
The hardmask layer performs multiple functions: it serves as the patterning mask for metal lines, as the positional reference for via formation, and as the template for defining via critical dimensions. This multi-functionality consolidates multiple process steps into fewer operations.
Data Source
AI summary
Techniques for self-aligned top via formation at line ends are provided. In one aspect, a method of forming self-aligned vias at line ends includes: patterning (even/odd) metal lines including using a (first/second) hardmask; cutting the hardmask and a select metal line, even or odd, using a cut mask having a window that exposes the hardmask over a cut region of the select metal line; enlarging the window to expose the hardmask on either side of the cut region; selectively etching the hardmask using the enlarged window to form a T-shaped cavity within the cut region; filling the T-shaped cavity with a gap fill dielectric; removing the hardmask; and recessing the metal lines, wherein the gap fill dielectric overhangs portions of the select metal line that, by the recessing, form the self-aligned vias at ends of the metal lines. A structure is also provided.