Wafer Internal Crack Detection Using Near Infrared Light
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Solution Overview
Problem
Existing methods struggle to clearly detect internal cracks in wafers, particularly those with surface acoustic wave devices on lithium tantalate or lithium niobate substrates, due to interference from surface roughness during the grinding process.
Innovation Solution
An internal crack detection method using near infrared light with a wavelength of 1000 to 1500 nm is applied to both a reference wafer and a target wafer, with images recorded before and after processing. The difference in images is analyzed to isolate and detect internal cracks, allowing for clear identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If visible light is applied to the back side of the substrate to image the substrate, then cracks generated in the substrate can be imaged, but surface roughness such as tearing generated on the back side is also imaged, making it difficult to clearly detect the cracks
Solution Approach 1:
The patent changes the wavelength parameter of the light from visible light (500-700 nm) to near-infrared light (700 nm to 1.5 μm). This parameter change allows the light to penetrate the substrate and reach the front side devices while still enabling crack detection, effectively filtering out the harmful surface roughness interference that plagues visible light imaging.
Solution Approach 2:
The patent introduces near-infrared light as an intermediary that can pass through the substrate material without being significantly scattered or absorbed by the surface roughness. This intermediary light source enables indirect observation of cracks by transmitting through the substrate and reflecting off the crack surfaces, bypassing the interference problem of direct visible light imaging.
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 effectively differentiates between internal cracks and surface roughness, enabling precise detection of cracks in wafers, even after grinding, thereby improving the quality of devices by identifying potential defects.
Implementation Method 1
applying near infrared light having a transmission wavelength to a reference wafer
Data Source
AI summary
A method for detecting an internal crack in a wafer includes a first image recording step of applying near infrared light having a transmission wavelength to a reference wafer having the same configuration as a target wafer to be subjected to the detection of the internal crack, thereby obtaining a first image of the reference wafer having no internal crack and then recording the first image, a processing step of processing the target wafer, a second image recording step of applying the near infrared light to the target wafer, thereby obtaining a second image of the processed target wafer and then recording the second image, and an internal crack detecting step of removing the same image information between the first image and the second image from the second image to obtain a residual image, thereby detecting the residual image as the internal crack in the target wafer.