Semiconductor Inspection Noise Subtraction via Frequency Band Segmentation
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Solution Overview
Problem
In optical probing technology for semiconductor device inspection, the small modulation signal leads to challenges in signal-to-noise ratio (S/N) due to shot noise and excess noise, making it difficult to achieve high precision and reducing measurement efficiency.
Innovation Solution
A semiconductor device inspection system that generates measurement and reference signals based on detection signals in specific frequency bands, where the reference frequency band is set to a level 3 decibels higher than the white noise level, allowing for the calculation of an analysis signal that removes shot noise and excess noise, thereby reducing measurement time and improving precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the scan time is extended or the quantity of light is increased to secure sufficient S/N, then the measurement precision is improved, but the measurement time is increased
Solution Approach 1:
The frequency spectrum is segmented into multiple bands, with at least one band dedicated to capturing noise characteristics. This allows simultaneous measurement of both signal and noise components, enabling noise subtraction to improve precision without extending scan time or increasing light quantity.
Solution Approach 2:
A noise signal serving as an intermediary is introduced through the noise frequency band. This noise signal characterizes the noise component and is used to subtract noise from the measurement signal, thereby improving measurement precision without requiring extended scan time or increased light quantity.
2Measurement precision
If the quantity of light is increased to improve S/N ratio, then the measurement precision is improved, but the shot noise and excess noise components increase proportionally
Solution Approach 1:
The noise component is extracted from the total detection signal by isolating it in a separate noise frequency band. This extracted noise signal is then subtracted from the measurement signal, removing shot noise and excess noise components that would otherwise degrade measurement precision.
Solution Approach 2:
The harmful noise components (shot noise and excess noise) are converted into a useful reference signal by capturing them in the noise frequency band. This noise reference signal is then used to subtract noise from the measurement signal, transforming the harmful noise into a beneficial tool for noise cancellation.
3Device complexity
If separate timing detection is used for measurement and reference signals, then the device complexity is reduced, but the measurement precision decreases due to noise variation
Solution Approach 1:
The measurement signal and noise reference signal are merged into a single detection process occurring at the same timing. The detection unit simultaneously captures both signals in different frequency bands, eliminating timing variations and improving measurement precision without significantly increasing device complexity.
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
The system effectively reduces measurement time and enhances the precision of measurement results by isolating noise components, allowing for more accurate inspection of semiconductor devices.
Implementation Method 1
light emitted from a light source is irradiated an integrated circuit, and the light reflected by the integrated circuit is detected by an optical sensor to acquire a detection signal
Data Source
AI summary
A semiconductor device inspection system (1) includes a laser beam source (2), for emitting light, an optical sensor (12) for detecting the light reflected by the semiconductor device (10) from the light and outputting a detection signal, a frequency band setting unit (16) for setting a measurement frequency band and a reference frequency band with respect to the detection signal, a spectrum analyzer (15) for generating a measurement signal and a reference signal from the detection signals in the measurement frequency band and the reference frequency band, and a signal acquisition unit (17) for calculating a difference between the measurement signal and the reference signal to acquire an analysis signal. The frequency band setting unit (16) sets the reference frequency band to a frequency domain in which a level of the detection signal is lower than a level obtained by adding 3 decibels to a white noise level serving as a reference.