Plasma Processing Apparatus Endpoint Detection Using Signal Filtering
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Solution Overview
Problem
Conventional plasma processing techniques face challenges in accurately detecting the end point of etching due to fluctuations in film thickness and adhesion of deposits, leading to reduced detection accuracy and yield, especially when gradual changes in plasma characteristics occur over time.
Innovation Solution
The use of an IIR filter to detect and remove the baseline component from light emission signals, combined with a Kalman filter and smoother to reduce noise and extract the change component, allowing for precise detection of etching end points even with gradual baseline changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional detection methods are used to monitor light emission intensity during etching, then end point detection can be performed, but detection accuracy decreases due to noise and baseline fluctuations in the signal
Solution Approach 1:
The patent extracts and removes the baseline component from the light emission signal using an IIR filter. By separating the baseline (gradual changes) from the actual etching signal, the method eliminates the harmful baseline fluctuations that reduce detection accuracy, allowing for more reliable end point detection.
Solution Approach 2:
The patent implements a feedback mechanism where the detected baseline component is continuously subtracted from the original signal to generate a corrected signal. This feedback loop continuously adjusts the detection signal by removing accumulated baseline drift, maintaining detection accuracy throughout the etching process.
2Measurement precision
If digital filtering is applied to reduce noise in light emission data, then noise components can be suppressed, but gradual baseline changes may also be removed along with the noise
Solution Approach 1:
The patent segments the light emission signal into two distinct components: the baseline component (gradual changes) and the etching signal component (actual process information). By using an IIR filter to detect and separate these components, the method can selectively remove noise while preserving the baseline information needed for accurate end point detection.
Solution Approach 2:
The patent extracts only the noise components from the signal while leaving the baseline intact. The IIR filter is configured to identify and remove only the random noise fluctuations, whereas the systematic baseline drift is preserved and separately handled through subtraction, preventing loss of important baseline information.
3Illumination intensity
If the aperture ratio of the detection system is increased to enhance signal strength, then reaction products can be easily detected, but the amount of change in the reference waveform increases making detection more difficult
Solution Approach 1:
The patent introduces a reference waveform as an intermediary element to compare against the etching waveform. By using the reference waveform captured at different aperture ratios, the system can normalize and compensate for the increased waveform change amplitude, allowing accurate detection despite the larger signal variations caused by high aperture ratios.
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 end point detection and processing yield by effectively filtering out baseline components and isolating change components, even when baseline gradients change gradually, ensuring precise timing and reduced residual film thickness variations.
Implementation Method 1
detecting a change in an intensity of light emission from the processing chamber during processing of a wafer
Implementation Method 2
detecting a baseline component of the first signal by using an IIR (infinite impulse response) filter on the first signal from which the noise components have been reduced
Implementation Method 3
reducing noise components by using a Kalman filter from the first signal indicating the intensity of light emission
Implementation Method 4
processing a film on a substrate-like sample by using plasma formed inside a processing chamber
Data Source
AI summary
A plasma processing apparatus includes: a detector configured to detect a change in an intensity of light emission from plasma formed inside a processing chamber; and a unit configured to adjust conditions for forming the plasma or processing a wafer arranged inside the processing chamber using an output from the detector, wherein the detector detects a signal of the intensity of light emission at plural time instants before an arbitrary time instant during processing, and wherein the adjusting unit removes the component of a temporal change of a long cycle of the intensity of light emission from this detected signal and detects the component of a short temporal change of the intensity of light emission, and adjusts the conditions for forming the plasma or processing a wafer arranged inside the processing chamber based on the short temporal change of the detected intensity of light emission.