In-situ Etch Depth Measurement via Interferometric Reference
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Solution Overview
Problem
Existing methods for measuring the etching depth in glow discharge spectrometry are inaccurate due to sensitivity to plasma chamber expansion and require optical windows that reduce optical emission signal collection, limiting accuracy to above one micron.
Innovation Solution
A system using a light source, optical splitter, and interferometric beam recombination to measure etching depth by comparing the phase shift between a zone exposed to the plasma and a protected zone, allowing for accurate depth measurement insensitive to plasma chamber expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical methods (chromatic confocal sensor, triangulation sensor, two-wave laser interferometer) are used to measure etching depth, then depth measurement capability is provided, but measurement precision deteriorates due to sensitivity to plasma chamber expansion and heating, limiting accuracy to above one micron
Solution Approach 1:
The patent introduces a reference surface that is not exposed to the plasma as an intermediary reference point. By comparing the position of the eroded surface against this stable reference surface using interferometric measurement, the system eliminates the harmful effect of plasma chamber expansion, achieving sub-micron measurement precision
Solution Approach 2:
The patent segments the sample surface into two distinct zones: a first zone exposed to plasma for etching and a second zone protected from plasma as a reference. This segmentation allows differential measurement between the eroded region and the stable reference region, isolating the etching depth measurement from chamber expansion effects
2Ease of operation
If optical window is used in plasma chamber to allow optical beam passage, then optical access is provided, but optical emission signal collection is reduced
Solution Approach 1:
The patent changes the spatial arrangement by positioning the optical beam path in a different dimension - using the sample holder flange and peripheral regions rather than the central optical axis. This allows optical access through the chamber periphery without interfering with the central plasma emission collection path
Solution Approach 2:
The patent segments the optical paths into two separate channels: one for plasma emission collection through the lens system and another for depth measurement through the sample holder flange. This spatial segmentation allows both functions to operate simultaneously without mutual interference
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
Achieves accurate etching depth measurement with an error of the order of the light source wavelength, enabling precise analysis of sample composition as a function of depth rather than time, while maintaining optical emission signal integrity.
Implementation Method 1
an optical recombination device adapted to recombine the first reflected beam and the second reflected beam and to form an interferometric beam
Implementation Method 2
the first incident beam towards the first zone along the first optical path and the second incident beam towards the second zone along the second optical path, so as to form a first reflected beam by reflection on the first zone and, respectively, a second reflected beam by reflection on the second zone
Implementation Method 3
The plasma extracts atoms from the surface of the sample, and places them in ionized or excited electronic states
Implementation Method 4
The glow discharge spectrometry consists in exposing a limited zone of a face of a sample to an etching plasma
Implementation Method 5
The nature of these atoms is determined by analysis of their emission spectrum in the plasma
Data Source
AI summary
A glow discharge spectrometry system includes a glow discharge lamp suitable for receiving a solid sample (10) and forming a glow discharge etching plasma (19). The system (100) for measuring in situ the depth of the erosion crater generated by etching of the sample (10) includes an optical separator (3), optical elements (4) suitable for directing a first incident beam (21) toward a first zone (11) of the sample, the first zone being exposed to the etching plasma, and a second incident beam (22) toward a second zone (12) of the same side of the sample, the second zone being protected from the etching plasma, respectively, and an optical recombining device (3) suitable for forming an interferometric beam (30) so as to determine the depth (d) of the erosion crater.