Capacitive Wafer Bow Measurement With Air-Float Support
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Solution Overview
Problem
Existing methods for determining wafer bow, such as laser interferometry, require complex hardware and software, reducing measurement throughput and are not effective in minimizing alteration of wafer stresses caused by substrate holders.
Innovation Solution
A system using a capacitor array with electrodes and air flow to measure capacitance across the wafer surface, allowing for contactless and simultaneous measurement of wafer bow without gravitational influence, enabling precise 3D mapping and correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser interferometry is used to determine wafer bow, then measurement precision is improved, but device complexity increases and measurement throughput decreases
Solution Approach 1:
The patent replaces the complex mechanical laser interferometry system with a capacitive sensing system. Instead of using lasers, mirrors, and interferometric optics, the invention uses simple capacitive sensors that measure changes in capacitance caused by wafer bow, thereby reducing device complexity while maintaining measurement capability
Solution Approach 2:
The patent creates a simplified measurement model by placing capacitive sensors at multiple locations on the wafer surface. These sensors collectively capture the wafer bow profile through electrical measurements, providing a simplified copy or representation of the physical deformation without requiring complex optical measurement systems
2Ease of operation
If traditional substrate holders are used to support the wafer, then ease of operation is improved, but stress alteration of the wafer increases
Solution Approach 1:
The patent employs a pneumatic substrate holder that uses air pressure to support the wafer. By applying uniform air pressure through porous surfaces or arrays of small holes, the wafer is held in a stress-free state during measurement, eliminating the mechanical contact stresses that would otherwise be introduced by traditional clamping or gripping mechanisms
Solution Approach 2:
The patent introduces air as an intermediary medium between the substrate holder and the wafer. This air cushion or air bearing allows the wafer to be supported without direct mechanical contact, thereby preventing stress alteration while still providing stable positioning and support during the measurement process
3Object-generated harmful factors
If contactless measurement method is used, then stress alteration is minimized, but measurement precision may be affected
Solution Approach 1:
The patent changes the measurement parameter from optical displacement (as in laser interferometry) to electrical capacitance. By measuring capacitance changes at multiple sensor locations, the system achieves precise wafer bow measurement through a contactless electrical field interaction that does not introduce mechanical stress or require physical contact with the wafer surface
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances measurement throughput and precision in determining wafer bow, minimizing stress alteration and facilitating accurate processing by providing a 3D model for wafer correction.
Implementation Method 1
an air flow system including a plurality of air outlets in the support surface which are configured to output air for elevating the wafer above the substrate holder
Implementation Method 2
A capacitor array unit including a plurality of electrodes laterally spaced from one another in the capacitor array unit, each electrode facing the support surface and being spaced a respective fixed distance from the support surface such that each electrode can form a capacitor with an opposing area of a wafer elevated by the substrate holder
Data Source
AI summary
An apparatus for measuring bow of a wafer includes a substrate holder including a support surface configured to support a wafer, and an air flow system including a plurality of air outlets in the support surface which are configured to output air for elevating the wafer above the substrate holder. A capacitor array unit including a plurality of electrodes laterally spaced from one another in the capacitor array unit, each electrode facing the support surface and being spaced a respective fixed distance from the support surface such that each electrode can form a capacitor with an opposing area of a wafer elevated by the substrate holder.