Plasma Etching Endpoint Detection Using Interference Light
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Solution Overview
Problem
Conventional methods for accurately measuring the etching endpoint and controlling the thickness and etching depth in semiconductor manufacturing face challenges due to noise interference, variations in etching speed, and degradation of etching devices, leading to incorrect measurements and potential waste of semiconductor wafers.
Innovation Solution
The method involves obtaining a time differential waveform of interference patterns at multiple wavelengths, comparing them to standard patterns to estimate the etching amount, and using a correction coefficient to adjust for changes in plasma radiation, allowing for real-time measurement and control of etching depth and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If time supervision method is used to control etching process, then process control is simple, but measurement precision of remaining thickness is poor due to etching speed variations
Solution Approach 1:
The patent replaces the mechanical/time-based supervision method with an optical measurement system using interference light. Instead of monitoring etching time and assuming constant speed, the system directly measures the physical thickness of the remaining film through optical interference patterns, eliminating the need to assume constant etching speed and providing accurate real-time thickness measurement.
Solution Approach 2:
The patent introduces interference light as an intermediary to measure film thickness. The interference light reflects off the film surface and provides optical information about the remaining thickness, serving as a mediator between the etching process and the measurement system, enabling non-contact, high-precision thickness monitoring without being affected by etching speed variations.
2Measurement precision
If emission spectroscopy is used to detect etching endpoint, then etching depth can be measured, but measurement precision deteriorates when aperture ratio decreases and emission intensity becomes weak
Solution Approach 1:
The patent introduces interference light from an external light source as an intermediary to measure film thickness. This external light source provides strong, controllable illumination that reflects off the film surface and provides optical information about the remaining thickness, replacing the weak emission spectroscopy signal with a strong reflection-based interference signal that is not limited by the small aperture ratio.
Solution Approach 2:
The patent changes the measurement parameter from detecting weak emission intensity to measuring strong reflection-based interference patterns. By using an external light source and measuring reflected interference light, the system transforms the measurement from a low-signal emission detection to a high-signal reflection measurement, significantly improving the signal-to-noise ratio and measurement precision.
3Measurement precision
If standard spectral interferometer is used to measure remaining layer thickness, then measurement accuracy is high, but productivity decreases due to excessive etching and wafer rejection
Solution Approach 1:
The patent performs preliminary, real-time thickness measurement during the etching process using interference light, rather than waiting until after etching is complete. By continuously monitoring the remaining film thickness in real-time, the system can stop etching at the precise target thickness, preventing both under-etching and over-etching, and eliminating the need to discard wafers with excessive etching.
Solution Approach 2:
The patent implements a feedback control system where the interference light measurement provides real-time information about the remaining film thickness, which is fed back to control the etching process. This closed-loop feedback enables dynamic adjustment of the etching process to achieve the target thickness precisely, preventing over-etching and reducing wafer rejection rates while maintaining high measurement accuracy.
4Measurement precision
If multiple wavelengths are used to obtain time differential waveform, then noise interference is reduced, but device complexity increases
Solution Approach 1:
The patent uses a single spectroscope that can analyze multiple wavelengths simultaneously, making the device multi-functional. Instead of requiring separate measurement systems for each wavelength, the single spectroscope processes the entire spectrum, extracting time differential waveform information from multiple wavelengths to improve signal-to-noise ratio while avoiding the complexity of multiple independent measurement devices.
Solution Approach 2:
The patent combines multiple wavelength measurements into a single integrated measurement system. By using a single spectroscope to capture and analyze light across multiple wavelengths simultaneously, the system merges what would otherwise require multiple separate devices into one unified instrument, reducing overall system complexity while benefiting from the noise-reduction advantages of multi-wavelength analysis.
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 enables accurate online measurement and control of etching amounts, reducing waste and ensuring precise semiconductor layer formation by minimizing noise interference and accounting for etching speed variations and device degradation.
Implementation Method 1
a light source for emitting light; means for obtaining a time differential waveform of interference patterns
Data Source
AI summary
A plasma processing apparatus is provided using a method of measuring the thickness of a processed material, by which the actual remaining thickness or etching depth of a processed layer can be correctly measured online. The plasma processing apparatus includes a detector 11 for detecting interference light of multiple wavelengths from a surface of a sample during processing, pattern comparing means 15 for comparing actual deviation pattern data on the interference light obtained at a given time during processing and a plurality of standard deviation patterns corresponding to two or more thicknesses of the film, and calculating a deviation, the standard deviation patterns corresponding to interference light data of multiple wavelengths obtained, before the processing of the sample, for processing of another sample, deviation comparing means 115 for comparing the deviation between the data and a predetermined deviation and outputting data on a thickness of the film of the sample at that time, remaining-thickness time-series data recording means 18 for recording, as time series data, the data on the thickness of the film, and an endpoint decision unit 230 for deciding completion of a predetermined amount of etching by using the data on the thickness of the film.