Integrated Circuit Inspection via Wavelength Width Adjustment
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Solution Overview
Problem
The existing method for inspecting integrated circuits using laser light is hindered by interference from the rear face of the semiconductor substrate, which lowers the signal-to-noise ratio and is difficult to stabilize due to variations in optical distances caused by temperature changes.
Innovation Solution
Adjusting the wavelength width of the light irradiating the integrated circuit to inhibit interference from the rear face, allowing for accurate detection of signal information by ensuring the coherence length is shorter than the optical path length difference between the circuit and the rear face, and adjusting the irradiation position to go through the depletion layer for precise analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser light with narrow wavelength width is used to irradiate the integrated circuit, then the resolution and signal detection capability is improved, but interference from the rear face of the semiconductor substrate increases, lowering the signal-to-noise ratio
Solution Approach 1:
The patent changes the wavelength width parameter of the light source from narrow (laser) to broad (superluminescent diode). This parameter change fundamentally alters the coherence properties of the light, reducing the coherence length to be shorter than the optical path difference between the circuit and rear face, thereby eliminating interference while maintaining detection capability.
2Measurement precision
If the optical path length is increased to improve signal collection, then the detection sensitivity is improved, but the interference from the rear face becomes more significant and harder to stabilize due to temperature variations
Solution Approach 1:
The patent changes the spectral width parameter of the light source to create incoherent light with short coherence length. This ensures that even when optical path length is increased for better signal collection, the interference condition cannot be met because the coherence length is shorter than the optical path difference, thus stabilizing the measurement against temperature variations.
3Object-affected harmful factors
If a broad wavelength spectrum is used to reduce interference, then the signal-to-noise ratio is improved, but the resolution for detecting fine circuit features deteriorates
Solution Approach 1:
The patent optimizes the center wavelength and spectral width of the superluminescent diode to achieve a balance: the broad spectrum reduces interference while the appropriate center wavelength maintains sufficient resolution for detecting fine circuit features. The key is that the coherence length is reduced below the interference threshold while the wavelength remains suitable for optical detection.
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 improves the accuracy of integrated circuit inspection by reducing noise interference and stabilizing the signal, enabling better detection of circuit states.
Implementation Method 1
a light source 4 that emits light L having a center wavelength of 1310 nm and a wavelength width of 55 nm
Implementation Method 2
the position where the light L irradiates the integrated circuit 20 is adjusted by the scan optical system 8 such that the circuit portion 22 is irradiated with the light L through a depletion layer formed in the silicon substrate 21
Implementation Method 3
the light L reflected by the integrated circuit 20 passes through the image-forming optical system 11... the photosensor (light detection unit) 12 detects the light L from the integrated circuit 20
Data Source
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AI summary
An apparatus for inspecting an integrated circuit is an apparatus for inspecting an integrated circuit having a semiconductor substrate and a circuit portion formed on a front face side of the semiconductor substrate. The apparatus comprises a light generation unit for generating light for irradiating the integrated circuit, a wavelength width adjustment unit for adjusting the wavelength width of the light irradiating the integrated circuit, an irradiation position adjustment unit for adjusting the irradiation position of the light irradiating the integrated circuit, and a light detection unit for detecting the light from the integrated circuit when the light from the light generation unit irradiates the circuit portion through a rear face of the semiconductor substrate.