Multiple Patterning Method for Integrated Circuit Memory Lines
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Solution Overview
Problem
The challenge in integrated circuit fabrication is that reducing the pitch of integrated circuits to sub-lithographic dimensions creates compatibility issues with accessing the lines, as the masks used for defining plugs are lithographically sized, and misalignment requirements increase the needed sizes for access areas, limiting the density of the circuit.
Innovation Solution
A quadruple patterning method is employed, where a set of line patterns with different pitches in the X and Y directions are formed, allowing for the creation of supplemental features and contact pickup areas, enabling the use of conventional or larger contact pads for electrical access, while maintaining sub-lithographic dimensions for the X direction lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pitch of integrated circuits is reduced to sub-lithographic dimensions, then the density of the circuit is increased, but the compatibility with access elements such as vertical plugs is compromised due to lithographic mask size requirements and misalignment tolerances
Solution Approach 1:
The patent divides the pitch reduction problem into two independent directional components: X-direction lines maintain sub-lithographic pitch for high density, while Y-direction lines maintain lithographic pitch for access compatibility. This segmentation allows each direction to be optimized independently, resolving the contradiction between density and accessibility.
Solution Approach 2:
The patent applies different pitch characteristics to different spatial locations and directions: sub-lithographic pitch is applied locally to X-direction lines where density is critical, while lithographic pitch is applied to Y-direction lines where access element compatibility is critical. This local differentiation resolves the universal contradiction.
2Productivity
If the pitch between lines is reduced below lithographic minimum, then more lines can be packed in the same area, but the masks used to define access plugs require larger sizes due to misalignment allowances
Solution Approach 1:
The patent segments the line orientations into X-direction (for density) and Y-direction (for access), allowing sub-lithographic pitch only where it serves density purposes without forcing access areas to be larger than necessary.
Solution Approach 2:
The patent creates an asymmetric pitch structure where X-direction spacing differs from Y-direction spacing, with X-direction having tighter sub-lithographic pitch and Y-direction having wider lithographic pitch. This asymmetry optimizes both density and access area size simultaneously.
3Ease of manufacture
If conventional photolithographic equipment is used, then the manufacturing process is simpler, but the minimum pitch that can be produced is limited to approximately double the minimum feature width
Solution Approach 1:
The patent segments the pitch requirements by direction, applying sub-lithographic pitch only to X-direction lines where precision is critical for density, while using standard lithographic pitch for Y-direction lines where conventional equipment suffices, thus balancing manufacturing simplicity with precision where needed.
Solution Approach 2:
The patent applies enhanced manufacturing precision locally to X-direction lines through sub-lithographic pitch while maintaining standard manufacturing processes for Y-direction lines, resolving the contradiction between overall process simplicity and local precision requirements.
Data Source
AI summary
An integrated circuit memory comprises a set of lines each line having parallel X direction line portions in a first region and Y direction line portions in a second region. The second region is offset from the first region. The lengths of the X direction line portions are substantially longer than the lengths of the Y direction line portions. The X direction and Y direction line portions have respective first and second pitches with the second pitch being at least 3 times larger than the first pitch. Contact pickup areas are at the Y direction line portions. In some examples, the lines comprise word lines or bit lines. The memory can be created using multiple patterning methods to create lines of material and then the parallel X direction line portions and parallel Y direction line portions.