Wafer Edge Shape Scanning Without Focus Adjustment
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Solution Overview
Problem
Existing edge shape measurement techniques for semiconductor wafers face challenges such as difficulty in focusing on the wafer end surface due to its small curvature, leading to diffused light and inaccurate measurements, and issues with focal position adjustment when using a line-shaped focus, which complicates accurate edge shape determination.
Innovation Solution
An edge shape measurement apparatus and method that utilize a displacement sensor rotated around a predetermined point inside the wafer as a center, measuring distances without focusing, by scanning with a multicolor confocal displacement sensor that tracks light wavelengths to determine edge shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If confocal optical system is used to measure wafer end surface, then measurement capability is provided, but focusing becomes difficult due to small curvature of wafer end surface
Solution Approach 1:
The patent replaces the mechanical focusing adjustment system with an optical wavelength selection system. Instead of mechanically moving the focal point to match the wafer surface curvature, the system uses a light source that emits multiple wavelengths and selects the wavelength whose focal point coincides with the measurement point on the wafer end surface. This substitution eliminates the need for mechanical focusing adjustment while maintaining measurement capability.
Solution Approach 2:
The patent changes the optical parameter (wavelength) to adapt to different focal depths. By varying the wavelength of light, the focal point position changes, allowing the system to match the focal point with points at different depths on the curved wafer end surface without mechanical adjustment. This parameter change enables automatic adaptation to the wafer's small curvature.
2Measurement precision
If line-shaped focal point is used inside wafer end surface, then edge shape can be acquired, but focal position adjustment becomes difficult and accurate measurement is compromised
Solution Approach 1:
The patent replaces the mechanical focal position adjustment mechanism with an optical wavelength selection mechanism. Instead of mechanically positioning a line-shaped focal point, the system uses wavelength selection to achieve the same effect. The light source emits multiple wavelengths, and by selecting appropriate wavelengths, the system creates focal points at different positions along the optical axis, eliminating the need for complex mechanical adjustment mechanisms.
3Measurement precision
If focal point is placed on wafer end surface, then distance measurement is possible, but reflected light becomes diffused due to small curvature
Solution Approach 1:
The patent changes the wavelength parameter to optimize both focal point positioning and light concentration. By selecting wavelengths that correspond to focal points at specific positions on the wafer end surface, the system ensures that light is concentrated at the focal point rather than diffused. The wavelength selection enables precise control of where the light focuses, maintaining high intensity even on surfaces with small curvature.
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 the edge shape of wafers without focusing, allowing for precise scanning and determination of edge characteristics.
Implementation Method 1
a technique of irradiating a wafer end surface as a measurement target with measuring light using a confocal optical system, positioning a focus of the measuring light with a focal position adjustment device, and detecting a defocusing amount
Implementation Method 2
the reflected light is diffused
Data Source
AI summary
There is provided an edge shape measurement apparatus and a method of measuring an edge shape capable of accurately measuring the edge shape of a wafer without focusing when scanning with the displacement sensor. The displacement sensor configured to measure the edge shape of the wafer having a plate like shape is provided, and is configured to rotationally be driven taking a predetermined point inside the wafer as a rotational center in a plane which includes the rotational center and is perpendicular to upper and lower surfaces of the wafer while keeping a constant radius with the rotational center, and is configured to measure a distance to a point on a surface of the wafer located on a straight line connecting the rotational center and the displacement sensor by a rotational angle.