Liquid Support Substrate Holding for Metrology Sag
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Solution Overview
Problem
Conventional substrate holding mechanisms induce curvature in semiconductor wafers during metrology measurements, making it challenging to accurately measure shape characteristics like wafer curvature and z-height values due to gravitational bending.
Innovation Solution
A liquid support system is used with a specific gravity matching that of the substrate, allowing the substrate to float without sinking, combined with a vacuum chuck or edge supports to prevent lateral movement, ensuring uniform support and minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional substrate holding mechanisms (vacuum chuck or edge supports) are used, then substrate can be securely held for processing, but substrate experiences gravitational bending making shape measurement inaccurate
Solution Approach 1:
The patent applies Archimedes' principle by using a liquid support medium with specific gravity matched to the substrate material density. The substrate floats on the liquid, creating a buoyant force that counteracts gravitational bending. This allows the substrate to be held uniformly across its entire bottom surface without the edge-supported or center-supported configurations that cause warpage in conventional vacuum chucks or mechanical fixtures.
Solution Approach 2:
The patent uses a liquid (hydraulic medium) as the support mechanism instead of conventional pneumatic vacuum chucks or mechanical edge supports. The liquid provides uniform distributed support across the entire substrate bottom surface, eliminating the point or line contact that causes gravitational bending in traditional holding mechanisms.
2Measurement precision
If liquid support is used to eliminate gravitational bending, then shape measurement accuracy improves, but substrate may sink or move laterally
Solution Approach 1:
The patent precisely controls the specific gravity parameter of the liquid support medium to match the density of the substrate material. This parameter matching creates neutral buoyancy conditions where the substrate floats without sinking, achieving both measurement accuracy and positional stability. The liquid density is specifically selected or adjusted to equal the substrate density.
Solution Approach 2:
The liquid support medium serves multiple functions simultaneously: it provides uniform distributed support to eliminate gravitational bending, maintains substrate through-position via buoyancy, and allows for lateral positioning control. This single liquid medium replaces multiple conventional support mechanisms.
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
This approach enables precise measurement of substrate surface characteristics by eliminating gravitational sag and maintaining substrate stability, enhancing metrology precision and accuracy.
Implementation Method 1
By selecting a liquid having a same specific gravity as that of a given substrate being supported, the given substrate can float on the liquid without sinking
Data Source
AI summary
An apparatus and method for uniformly holding a substrate without flexure or bending of the substrate, thereby enabling accurate shape measurements of the substrate such as wafer curvature, z-height values and other surface characteristics. Techniques include using a liquid as a supporting surface for a substrate thereby providing uniform support. Liquid used has a same specific gravity of a substrate being supported so that the substrate can float on the liquid without sinking. Uniform support of the substrate enables precision metrology.