Double-Side Polished Wafer Scratch Inspection via UV Absorption
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for detecting scratches on high-quality, transparent, double-side polished single crystal silicon carbide wafers are inaccurate and subjective, especially when the wafers are transparent in visible and UV frequencies, leading to potential costly reworks and quality control issues.
Innovation Solution
A method and apparatus that utilize a radiation source with wavelengths absorbed by the wafer, combined with a UV-absorbing background material and filters, to direct and detect scattered radiation, allowing only wavelengths absorbed by the wafer to pass, thereby identifying scratches on the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If visible light is used to inspect the wafer surface, then the inspection process is simple, but the scratches cannot be detected due to the transparent nature of the wafer
Solution Approach 1:
The patent changes the wavelength parameter of the inspection light from visible light to ultraviolet light. Since silicon carbide wafers are transparent to visible light but absorb UV radiation at wavelengths below their bandgap energy, using UV light enables scratches to be detected through absorbed radiation rather than reflected or transmitted light, thus resolving the contradiction between operational simplicity and detection accuracy.
Solution Approach 2:
The patent exploits the wavelength-dependent absorption properties of the wafer material. By selecting UV wavelengths that are absorbed by the wafer (below the bandgap), the inspection method creates a contrast where scratches appear as dark regions against a lighter background, enabling detection without requiring the wafer to be opaque.
2Measurement precision
If UV radiation below the bandgap wavelength is used, then scratches can be detected through absorption, but the wafer appears transparent and does not provide sufficient contrast
Solution Approach 1:
The patent converts the wafer's transparency, which initially prevents scratch detection, into a beneficial property. By using UV radiation below the bandgap wavelength, the wafer absorbs the radiation uniformly, creating a dark background. Scratches, which scatter light, appear as lighter regions against this dark background, enabling detection. The transparency that caused the problem becomes the basis for the solution through wavelength-selective absorption.
3Adaptability or versatility
If double-side polished wafers are inspected, then both surfaces can be examined, but the scratches on either surface cannot be discriminated from the opposite surface flaws
Solution Approach 1:
The patent introduces UV radiation below the bandgap wavelength as an intermediary that interacts differently with scratches on the front surface versus the back surface. Radiation absorbed by scratches on the front surface does not reach the detector, while radiation from the back surface can pass through the front surface. This creates a asymmetric detection pattern that allows identification of scratch location on either 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
This approach provides an efficient and accurate method for identifying scratches on semiconductor wafers, preventing costly reworks by ensuring precise detection before device preparation, and ensuring the quality of epitaxial layers and resulting devices.
Implementation Method 1
directing radiation from the radiation source that has wavelengths that will be absorbed within the wafer by the fundamental absorption of the wafer
Implementation Method 2
positioning a semiconductor wafer for illumination by a radiation source and adjacent a background material that will absorb radiation from the radiation source
Implementation Method 3
detecting radiation scattered on the surface of the wafer and filtered, by position, to thereby identify the location of the scratches on the surface of the wafer
Data Source
AI summary
The invention is a method of inspecting a semiconductor wafer surface for scratches. The method includes positioning a semiconductor wafer for illumination by a radiation source and adjacent a background material that will absorb radiation from the radiation source, directing radiation at a surface of the wafer from the radiation source that has a wavelength that will be absorbed by the fundamental absorption of the wafer, filtering or otherwise limiting the radiation to allow only radiation having wavelengths that are absorbed by the fundamental absorption of the wafer to pass, and detecting radiation scattered on the surface of the wafer and filtered, by position, to thereby identify the location of the scratches on the surface of the wafer, while the absorption of the background material prevents other radiation from the source from interfering with the detection of the scratch-scattered radiation.