Specific Process Knowledge/Etch/DRIE-Pegasus/Pegasus-2

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DRIE-Pegasus 2

The DRIE-Pegasus 2 operator station and load lock in the DTU Nanolab cleanroom A-1

The user manual(s), user APV(s), technical information and contact information can be found in LabManager:

Equipment info in LabManager

Restricted usage on a dedicated research tool

In general, the dry etch tools at DTU Nanolab are free to use for users with proper training. The users have freedom to etch the approved materials and substrates within the rules specified in manuals, LabAdviser and cross contamination sheets. At the same time, the instruments are set up to meet the broadest range of etch demands in this way ensuring that most dry etch applications can be covered. Indeed, for most of the instruments there is a continuous tug of war between providing flexibility (for instance allowing mask materials that do not form any volatile etch products with the gas chemistry available in the process chamber) while ensuring process chamber cleanliness.

Pegasus 2 stands out as it is a dedicated research tool where the research group of professor Henri Jansen [1] has freedom to explore the conventions of dry etching. This requires that a very strict control be applied to the process chamber in terms of the range of processes and substrates used. As such, the instrument will not be released for general use for a wide range of applications.

Whereas most dry etch tools are intended to serve as stable platforms with limited or no changes in hardware, Pegasus 2 will be subject to experiments. For instance, as of the end of 2020 the instrument has been set up to run the CORE process. This means that comparing to DRIE-Pegasus 1 and DRIE-Pegasus 3, Pegasus 2 and its allowed usage have been modified (this list is not complete - see the complete list in the table below). For instance:

1. The C₄F₈ MFC has been disconnected to maintain a carbon-free (carbon containing masks are allowed) chamber.
2. The RF generator supplying the power to the coil has been disconnected thus allowing only processes driven by the platen generator.

This kind of experiment will not be allowed on other dry etch tools as it is obvious that this is incompatible with running any of the usual Bosch processes.

Therefore, you should always make sure that whatever process you may want to run on Pegasus 2 is allowed or even possible. The table below should provide this information. If you want to get access to the tool, then talk to professor Henri Jansen and the dry etch group.

Current setup and rules on Pegasus 2

Click here to access older configurations.

The current configuration is set up for nanoscale etching using the CORE recipe.

Currently valid from September 13 2021 onwards

Item	The currently applied modification	Comments
Available gasses and gas chemistry	Available gasses: SF6: 50 sccm O2: 50 sccm Ar: 283 N2: 500 sccm He: 11 sccm Not available: C4F8 (H2 currently fitted but closed) : 0 sccm CO2: (It is not in the software)	OnlySF6 and O2 are used for Si, PR, and Cr etch. The rest is only make-up
Plasma source heaters	Applies to Plenum Heater Inner Heater Magnetic Confinement Heater Chamber Heater	The temperature on the heaters in the plasma source are set to 20 degrees with a high tolerance. This essentially corresponds to powered off compared to default Pegasus temperatures which are in the 120-140 degrees range. Always make sure that the temperature settings in the recipes are not enabled. Click here to have more information.
RF power and pressure settings	All recipes run without coil power, very low platen power and low pressures	None of the recipes use coil power in order to prevent aluminium fluoride formation at the aluminium oxide dome. These particles may drop on the wafer or chuck and cause abnormalitites. Most of the recipes rely on very low pressure and low power - 0.2 mTorr and 10 Watt platen power is not an error and easily supports the plasma.
Carbon free plasmas	The process chamber does not have any carbon containing etch gasses. Therefore, polymer build-up on the chamber walls is not an issue. The 'carbon free' policy does not, however, apply to the choice of masking materials and CSAR, AZ and DUV resists are allowed.
Chamber conditioning and cleaning	Running long oxygen cleans is not necessary and must be avoided. Neither are shorter cleans between wafers.	The absence of carbon containing etch gasses ensures that the process chamber is kept clean.
Approved recipes	The 'std' folder holds the list of currently allowed recipes	Recipes in other folders may no longer be safe to run.
Etch of nickel and chromium	Recipes for etching nickel and chromium have been developed	The cross contamination consequences have yet to be determined
Background knowledge required for safe operation	The users and supervisors of Pegasus-2 must carefully read the 4 papers listed in the comments in order to have a correct understanding of the etch process and experimental procedure and how it relates to the Bosch etch performance.	Papers: On the formation of black silicon in SF6-O2 plasma: The clear, oxidize, remove, and etch (CORE) sequence and black silicon on demand The CORE Sequence: A Nanoscale Fluorocarbon-Free Silicon Plasma Etch Process Based on SF6/O2 Cycles with Excellent 3D Profile Control at Room Temperature Ultrahigh aspect ratio etching of silicon in SF6-O2 plasma: The clear-oxidize-remove etch (CORE) sequence and chromium mask Cr and CrOx etching using SF6 and O2 plasma
List of approved recipes	The list of currently approved recipes is: A gentle barc etch The ORE t1 resist mask Strip resist and barc A polysilicon etch for hard masks Cr etch The CORE Si etch with Cr hard mask

Process information

New recipes are being developed all the time and the total number of recipes on the tool is huge. However, as the configuration of the instrument changes over time a vast majority of the recipes may no longer be safe to run. Unless you have specific permission to run other recipes, the only recipes that you can safely run are the ones in the 'std' folder as shown above in the table. If you have your own recipe folder, always verify that the recipe you want to run is present in the 'std' folder.

Previous work on Pegasus 2

• Nanoscale silicon etching with SF6 and O2 (the CORE process)
• Black silicon on Demand