Box-in-Box Overlay Mark Orientation for DRAM Accuracy
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Solution Overview
Problem
The existing box-in-box overlay mark designs face challenges in overlay measurement accuracy due to imperfect alignment and optical impacts from dense parallel narrow trenches in the inner-box trenches, which are limited by lithography and metrology tool resolution, leading to reduced accuracy in DRAM word-line processes.
Innovation Solution
A modified box-in-box overlay mark with dense narrow trenches in the inner and outer box regions oriented at an angle different from the x- and y-directions, allowing the linear photoresist patterns to be wider than the trenches and improving position determination accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dense parallel narrow trenches are used in the inner box region to satisfy design rules, then the trenches can be formed within lithography resolution limits, but the overlay measurement accuracy is reduced due to optical impacts from the trenches
Solution Approach 1:
The patent extracts the problematic dense parallel narrow trenches from the inner box region by repositioning them to the outer box region only. This removes the source of optical interference while preserving the necessary structure for overlay measurement. The inner box region is left with only the photoresist patterns, eliminating the harmful interaction between trenches and measurement signals.
Solution Approach 2:
The patent changes the spatial arrangement by moving the dense narrow trenches from the inner box region to the outer box region, effectively using the outer region as a separate functional zone. This dimensional reorganization allows the trenches to exist without interfering with the inner box measurement patterns, resolving the optical interference problem.
2Ease of manufacture
If the outer box is defined by oxide spacer without transfer to substrate, then the outer box structure can be formed for overlay marking, but the chop layer photoresist cannot be properly registered to the pitch reduction layer
Solution Approach 1:
The patent performs preliminary action by forming the dense narrow trenches in the outer box region before the final overlay measurement process. This preliminary structure provides a stable reference framework that enables proper registration of subsequent layers, including the chop layer photoresist to the pitch reduction layer, without requiring the outer box to be transferred to the substrate.
Data Source
AI summary
A box-in-box overlay mark is described, including an inner box region and an outer box region surrounding the same, dense narrow trenches in the previous layer in the inner box region and the outer box region, x- and y-directional linear photoresist patterns defining a rectangle over the narrow trenches in the inner box region, and x- and y-directional linear patterns defining another rectangle in the outer box region. At least the narrow trenches in the inner box region are orientated in a direction different from the x-direction and the y-direction. The linear photoresist patterns are defined in or from a photoresist layer for defining a current layer, each of which is wider than each of the narrow trenches. The linear patterns are defined in or from the previously layer, each of which is wider than each of the narrow trenches.