Inductor Array Wafer Bow Measurement
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Solution Overview
Problem
Existing methods for measuring film stress in micromechanical systems (MEMS) are limited, particularly when films are deposited on non-planar structures or within trenches or on sidewalls, as they rely on laser scanning which becomes ineffective with patterned wafers and cannot accurately measure stress in such configurations.
Innovation Solution
An inductor array is placed over or under the wafer to monitor eddy current coupling, using metallization and contact printer lithography techniques to form inductors on a glass substrate, which are encapsulated and connected to allow measurement of inductance changes to determine wafer bow and subsequently film stress, even on patterned or non-planar surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser scanning is used to measure wafer bow, then measurement is simple for flat wafers, but measurement becomes inaccurate or impossible for patterned wafers with features
Solution Approach 1:
The patent replaces the optical laser scanning system with an electrical measurement system using inductor arrays. Instead of using light to detect wafer bow, the invention uses eddy current coupling between inductors and the conductive wafer to measure bow, thereby avoiding the limitation of laser scattering off patterned features
Solution Approach 2:
The patent introduces an inductor array as an intermediary measurement device placed near the wafer surface. This array acts as a mediator that couples electrically to the wafer through eddy currents, allowing indirect measurement of wafer bow without direct optical contact that would be scattered by features
2Adaptability or versatility
If inductor array is placed near wafer to measure eddy current coupling, then stress measurement works for patterned wafers, but device complexity increases
Solution Approach 1:
The patent divides the measurement system into discrete inductor elements arranged in an array. Each inductor can be independently addressed and measured, allowing the complex measurement task to be broken down into simpler individual measurements that can be processed separately
Solution Approach 2:
The inductor array serves multiple functions: it acts as both the measurement probe and the structural reference for determining wafer bow. The same inductor elements that detect eddy currents also provide the geometric reference needed to calculate bow, eliminating the need for separate reference structures
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
Enables accurate measurement of film stress on patterned or non-planar MEMS wafers by mapping bow changes using eddy current coupling, facilitating in situ stress monitoring during deposition, thereby overcoming limitations of prior art techniques.
Implementation Method 1
monitoring the eddie current coupling of the inductors in the array with the wafer
Data Source
AI summary
In a MEMS wafer, film stresses are measured by placing an inductor array over or under the wafer and measuring inductance variations across the array to obtain a map defining the amount of bowing of the wafer.