Bidirectional Grating Superposition for Overlay Metrology
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Solution Overview
Problem
Current semiconductor manufacturing processes face challenges in minimizing alignment and overlay errors as critical dimensions shrink, requiring improved methods for aligning successively patterned layers.
Innovation Solution
The method involves forming grating lines on a first layer, creating spacer gratings around them, and using a template mask to etch the second layer, resulting in cut spacer gratings that can be measured for alignment errors, enabling the formation of bi-directional cut spacer grating layers for precise overlay metrology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional alignment and overlay metrology methods are used, then existing processes can maintain current manufacturing capabilities, but alignment and overlay errors increase as critical dimensions shrink
Solution Approach 1:
The patent transitions from traditional single-direction alignment marks to bidirectional grating superposition patterns that provide alignment reference in both X and Y directions simultaneously. This dimensional enhancement allows metrology tools to measure overlay errors more accurately by comparing grating superposition positions along orthogonal axes, thereby improving measurement precision for shrinking critical dimensions.
Solution Approach 2:
The invention creates replicated grating patterns across multiple layers that can be superimposed and measured. By copying the grating design from one layer to another and measuring the relative position of these copies through optical interference patterns, the system achieves higher measurement precision without requiring new metrology hardware.
2Measurement precision
If specialized target designs and locations are used for each layer, then alignment and overlay measurements can be performed, but device complexity and process steps increase
Solution Approach 1:
The patent employs a universal grating pattern design that serves multiple functions: it acts as an alignment reference for the current layer, provides overlay measurement marks relative to previous layers, and maintains consistency across all lithographic layers. This multi-functionality eliminates the need for layer-specific specialized targets, reducing process complexity while maintaining measurement precision.
Solution Approach 2:
The invention merges the alignment mark function and overlay measurement function into a single grating superposition pattern. By combining these previously separate metrology requirements into one integrated structure, the process complexity is reduced as fewer distinct target designs and locations are needed across different layers.
3Adaptability or versatility
If more layers are patterned on a single wafer, then device functionality increases, but cumulative alignment and overlay errors increase
Solution Approach 1:
The bidirectional grating superposition patterns provide real-time feedback on alignment and overlay accuracy for each successive layer. By measuring the grating superposition positions after each lithographic exposure, the system can detect cumulative errors early and apply corrective adjustments to subsequent layers, thereby maintaining manufacturing precision even as the number of patterned layers increases.
Data Source
AI summary
Cut spacer reference marks, targets having such cut spacer reference marks, and methods of making the same by forming spacer gratings around grating lines on a first layer, and fabricating a template mask that extends across and perpendicular to such spacer gratings. Cut spacer gratings are etched into a second layer using the template mask to superimpose at least a portion of the spacer gratings of the first layer into the second layer.