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| == Optical Endpoint detection systems ==
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| During a process, the plasma dissociates the gas molecules present in the process chamber into reactive species that emit light at certain wavelengths. This means that the light coming from the process chamber will be a spectrum in which elements of both process gases and process reactants are found. By analyzing the spectrum we can keep track of when certain species change concentration, i.e. when, for instance, the etch of a thin layer is complete. This is the end point of the etch hence the name.
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| The DRIE-Pegasus, the ICP Metal Etcher and the III-V ICP are all equipped with a Verity SD1024 Spectrometer and the SpectraView software package. The SpectraView software enables you to monitor any number of any wavelength in the 200-800 nm range and do complicated mathematical analysis of the spectra.
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| === Setting up the OES system ===
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| '''Start up:'''
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| # Double click the SpectraView icon on the Verity EPD computer and the software will start.
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| # In the system window in the left side there is a list of configuration files. If it's not open, select View\System Window in the menu.
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| # Double click the configuration file you wish to use. If you need to create one that is not already there, select an existing one and save using a different name.
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| '''The configuration file:'''
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| The configuration file holds the information of what to monitor; i.e. what wavelengths and what to do with their signals.
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| To set up the configuration file you will need to know the emission wavelengths the elements or compounds you're looking for. To find this information use the help files: From the Menu go to: Help \SpectraView Manual -> Appendix D Wavelengths by emission species. It is also the intention to build up a knowledge base in LabAdviser so you may find information there as well.
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| The configuration file has a number of headings:
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| ; Setup:
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| : Usually, one should not edit this. If, however, the process is longer than 10 minutes, you will have to extend the 10 minute time out.
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| ; Data Sources:
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| : There is only one possible input (the optical fiber) so do not edit this.
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| ; Regions:
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| : Press Insert to add a region to monitor. Use an appropriate names and different colors for every region you add. For instance, call the 261.7 nm AlCl line 'AlCl_261' as name and the range og 261 to 262.5 nm, see image below. The range may be set in units of a half nanometer.
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| ; Variables:
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| : Only for advanced configuration files. Do not edit.
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| ; Equations:
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| : Determines what to do with the data from each region. Press Insert and select 'Region Equation'. Here, select <ul> <li> Appropriate names and colors as with regions.</li> <li> Spectrum: Only one choice.</li> <li> Region according to name.</li> <li> Operation: Typically one will choose 'Max' to find the peak within each region, see image below. Other possibilities are Sum, Average, Min or Median. </li> </ul>
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| ; Snapshot:
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| : The possibility of taking snapshots of the whole spectrum after certain time - this is not necessary.
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| ; Graphs:
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| : What plots to be displayed. Select <ul> <li> Spectral Graphs: This will show the spectrum (typically from 200 nm to 80 nm) of light during the process.</li> <li> Trend Graphs: Select which equations to be displayed. These graphs will enable you to monitor the development of the Peaks relevant for you as you etch your sample.</li> <li> Sequence, Reprocess and Properties: Beyond the scope of this manual </li> </ul>
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| === Processing ===
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| Once the configuration file has been set up, it must be activated. To do so, right-click on the configuration file in the System window that you wish to use and select 'Set as Current'.
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| To start monitoring click one of three buttons marked by a yellow square above.
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| ; M - Monitor:
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| : The system will monitor the Graphs (Spectral and Trend) that have been set up in the configuration file. Panels with these Graphs will pop up. The data will not be stored. It is very useful to click the 'Tile' option under Window settings.
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| ; C - Capture:
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| : In addition to the monitoring described above the data will be stored on the hard drive. This enables you to analyse the data afterwards.
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| ; P - Processing:
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| : In addition to the monitoring and capturing of the data as described above, this mode will also feed an end point to the SPTS operator computer. It is, however, advised not to use this mode as it doesn't work for several reasons: <ul> <li> It requires that an endpoint has been defined in the configuration file under 'Sequence' which is beyond the scope of this manual. </li><li> It requires that the etch recipe on the SPTS computer has been set up for it. </li></ul>
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| === Limitations ===
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| The endpoint detector may seem to be powerful tool - but it has some drawbacks. Below are listed some points that is maybe worth considering:
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| ; The etch process parameters:
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| : The intensity of the plasma relies heavily on process parameters such as RF powers, pressure and gas flows. It is clear that if these parameters are low, the intensity of the plasma is low and therefore the signal to noise ratio will be low.
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| ; The intensity of the species to monitor:
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| : The concentration of some etch product in the plasma is strongly dependent on the area that is etched. Are you etching small holes on a small chip lying on a carrier, the signal you are looking for is infinitely smaller than if you etch large areas on an entire wafer. The same applies to (high/low) etch rates.
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Techniques, hardware and challenges common to all dry etch tools
This page contains information that is common to dry etch instruments.
