Thickness Measuring Apparatus Using Spectral Interference
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Solution Overview
Problem
Existing thickness measuring apparatuses for plate-shaped workpieces, such as wafers, are inefficient in measuring thickness over a wide area as they require scanning light over the entire surface and computing thicknesses at multiple points, reducing efficiency.
Innovation Solution
A noncontact thickness measuring apparatus using a white light source, dispersing means to generate spectral light, a two-dimensional image sensor to detect return light, and a computing section to calculate thicknesses across a two-dimensional area, applying spectral interference waveforms and accounting for refraction angles to determine actual thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If light is scanned on the entire surface of the wafer to measure thickness at multiple points, then the measurement coverage is improved, but the measurement efficiency deteriorates due to sequential computation at each point
Solution Approach 1:
The patent transitions from one-dimensional point-by-point measurement to two-dimensional area measurement by applying spectral light to illuminate a wide area of the wafer surface simultaneously. The two-dimensional image sensor captures thickness information across the entire illuminated area in a single shot, converting sequential measurement into parallel measurement through dimensional expansion.
Solution Approach 2:
The patent merges multiple measurement points into a single wide-area measurement by using spectral interference patterns that encode thickness information from multiple locations simultaneously. The spectral light reflects from different thickness regions and creates a composite interference pattern that contains all thickness data, which is then decoded to retrieve individual thickness values at multiple points without sequential scanning.
2Measurement precision
If a contact type measuring unit using probe is used, then the measurement precision is improved, but the workpiece surface quality deteriorates due to probe contact damage
Solution Approach 1:
The patent replaces the mechanical contact measurement system (probe touching the wafer surface) with an optical non-contact measurement system. Spectral light is used to measure thickness through optical interference patterns, eliminating mechanical contact entirely. This substitution maintains measurement precision while removing the harmful mechanical contact that causes surface damage.
Solution Approach 2:
The patent changes the measurement parameter from mechanical contact force to optical spectral interference. By using the wavelength-dependent interference pattern of spectral light reflecting from the wafer surfaces, the system measures thickness through optical parameters rather than mechanical contact, achieving precise measurement without physical damage to the workpiece surface.
3Object-affected harmful factors
If a noncontact type measuring unit with spectral light is used, then the workpiece surface quality is improved by avoiding contact damage, but the measurement efficiency deteriorates when measuring wide areas due to sequential point measurement
Solution Approach 1:
The patent expands the measurement from one-dimensional scanning to two-dimensional area capture by using spectral light to illuminate and measure a wide area of the wafer simultaneously. The two-dimensional image sensor array captures interference patterns from multiple locations at once, converting time-consuming sequential scanning into instantaneous parallel measurement across the entire illuminated area.
Solution Approach 2:
The patent applies spectral light to the wide area of the wafer before measurement begins, creating a pre-established interference pattern that contains all thickness information. The two-dimensional image sensor then captures this pre-prepared pattern in a single shot, eliminating the need for sequential point-by-point measurement and significantly improving wide area measurement efficiency.
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 efficient measurement of thickness across a wide area of a workpiece in a single operation, improving processing efficiency by providing accurate thickness data for processing apparatuses.
Implementation Method 1
dispersing means producing time differences corresponding to wavelengths of light components of the white light emitted from the white light source, thereby generating spectral light
Implementation Method 2
a two-dimensional image sensor having a photodetecting area for detecting return light obtained by reflecting the spectral light on the upper surface of the workpiece and the lower surface of the workpiece
Implementation Method 3
multiplying the temporary thickness by a cos θ, where θ is a refraction angle of the spectral light applied to the upper surface of the workpiece and advancing in the workpiece toward the lower surface thereof
Data Source
AI summary
A thickness measuring apparatus includes a white light source for emitting white light, a dispersing mechanism for producing time differences corresponding to the wavelengths of light components of the white light to thereby generate spectral light, the spectral light being applied to the workpiece and then reflected on the upper surface and the lower surface of the workpiece to obtain return light, a two-dimensional image sensor having a photodetecting area for detecting the return light, the photodetecting area including a plurality of pixels, a storing section for storing the intensity of the return light detected by the plural pixels according to wavelength with time difference, the intensity of the return light detected by each pixel being stored as a spectral interference waveform, and a thickness computing section for computing the thickness of the workpiece from the spectral interference waveform stored in the storing section.