Backside Metal Line Patterning for Tight N2P Contact Spacing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
As nanosheet technology scales down, forming backside contacts with sufficient spacing becomes challenging due to interference between devices, and existing lithographic processes limit the spacing and increase resistance in backside interconnects.
Innovation Solution
A subtractive etch process is used to form backside metal lines with the widest part at the bottom surface and narrowest at the top, allowing for sub-lithographic spacing and repair of miss-alignment errors through a conductive metal liner and dielectric fill layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lithographic printing is used to form backside contacts, then manufacturing process is simple, but spacing between contacts is limited and cannot achieve tight N2P space
Solution Approach 1:
The patent inverts the conventional patterning approach by using a subtractive etch process instead of additive lithography. A continuous metal layer is formed first, then trenches are etched to separate it into individual backside contacts. This inversion allows spacing to be defined by the etch process rather than lithographic limits, enabling tight N2P spacing while maintaining manufacturing feasibility.
Solution Approach 2:
The continuous metal layer is segmented into individual backside contacts through the formation of trenches. This segmentation approach allows each contact to be precisely positioned and sized independently, achieving the required tight spacing between N-type and P-type contacts without being constrained by lithographic resolution.
2Manufacturing precision
If subtractive etch process is used to form backside metal lines, then sub-lithographic patterning is achieved, but miss-alignment errors occur
Solution Approach 1:
A repair liner is formed preliminarily to cover the entire surface before the subtractive etch process. This preliminary protective layer prevents miss-alignment errors during etching, ensuring that even if the etch process deviates slightly, the underlying metal layer remains protected and can be recovered, thus maintaining contact alignment reliability.
Solution Approach 2:
The repair liner acts as a cushioning layer that compensates for potential miss-alignment in the subtractive etch process. By having this protective layer in place beforehand, any etching errors are prevented from causing actual damage to the metal contacts, thereby ensuring reliable alignment.
3Productivity
If device density is increased to fit more devices in smaller area, then productivity is improved, but interference between devices increases and contact formation becomes harder
Solution Approach 1:
The patent moves the contact formation process to the backside of the device, utilizing the vertical dimension to separate contact formation from the frontside device structures. This dimensional transition allows high device density on the frontside while maintaining adequate spacing for backside contact formation, thus resolving the interference issue without compromising productivity.
Data Source
AI summary
A microelectronic structure including a first nanosheet transistor including a first backside metal line that has a first width as measure along a bottom surface of the first backside metal line and the first backside metal line has a second width as measure along a top surface of the first backside metal line. A second backside metal line that includes a second backside contact that is connected to the second source drain and the second backside metal line has a third width as measure along a bottom surface of the second backside metal line. The second backside metal line has a fourth width as measure along a top surface of the second backside metal line. The first width is larger than the second width and the third width is larger than the fourth width.