Wafer Shape Metrology for Target-Free Post-Bond Overlay
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Solution Overview
Problem
Conventional methods for measuring post-bonding overlay between semiconductor wafers require metrology targets, which can complicate the bonding process and limit measurement density, especially when placed on carrier wafers.
Innovation Solution
A wafer metrology system that performs stress-free shape measurements on individual wafers and post-bonded pairs, using a controller to predict overlay between features based on shape data and provide feedback or feedforward adjustments to process tools, potentially eliminating the need for targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If metrology targets are placed on carrier wafers to measure post-bonding overlay, then overlay measurement can be performed, but additional processing is required and measurement density is limited
Solution Approach 1:
The patent extracts the metrology target requirement from the measurement process by using the wafer shape itself as the measurement reference. Instead of placing external targets on the wafer, the system uses the natural shape features and bonding interface geometry to determine overlay, thereby eliminating the need for additional target placement processing
Solution Approach 2:
The wafer shape measurement system serves multiple functions: it characterizes the wafer shape before bonding, measures the bonding interface geometry, and determines overlay alignment all in one process. This multi-functional approach replaces the separate target placement and measurement steps required by conventional methods
2Measurement precision
If metrology targets are placed on carrier wafers to measure post-bonding overlay, then overlay measurement can be performed, but measurement density is limited
Solution Approach 1:
The patent transitions from point-based target measurements to surface-based shape measurements. By utilizing the entire wafer surface geometry and bonding interface shape rather than discrete target points, the system achieves much higher measurement density and more comprehensive overlay characterization across the wafer area
3Measurement precision
If conventional overlay measurement methods are used, then overlay can be measured, but the bonding process is complicated by target placement requirements
Solution Approach 1:
The patent removes the metrology target placement step from the bonding process flow by using the wafer's inherent shape features as measurement references. This extraction of the target requirement simplifies the bonding process while maintaining overlay measurement capability
Solution Approach 2:
The wafer itself provides the measurement reference through its shape characteristics and bonding interface geometry, eliminating the need for external targets. The bonding process and measurement process are integrated, with the bonded wafer pair's shape serving as the measurement standard
Data Source
AI summary
A wafer shape metrology system includes a wafer shape metrology sub-system configured to perform one or more stress-free shape measurements on a first wafer, a second wafer, and a post-bonding pair of the first and second wafers. The wafer shape metrology system includes a controller communicatively coupled to the wafer shape metrology sub-system. The controller is configured to receive stress-free shape measurements from the wafer shape sub-system; predict overlay between one or more features on the first wafer and the second wafer based on the stress-free shape measurements of the first wafer, the second wafer, and the post-bonding pair of the first wafer and the second wafer; and provide a feedback adjustment to one or more process tools based on the predicted overlay. Additionally, feedforward and feedback adjustments may be provided to one or more process tools.