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

Feedback to this page: click here

DRIE-Pegasus 2

Unless otherwise stated, all content on this page was created by Jonas Michael-Lindhard, DTU Nanolab

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

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 a wide 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 much fewer processes are allowed. As such, the instrument will not be released for general use for a wide range of applications.

Whereas Pegasus 1 and 3 are intended to serve as stable platforms with limited or no changes in hardware, Pegasus 2 has been 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 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.

7: Currently valid from May 17 2023 onwards

Item	The currently applied modification	Comments
Available gasses and gas chemistry	Available gasses: SF6-1: 1200 sccm SF6-2: 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)	Only SF6 and O2 are used for Si, PR, and Cr etch. The rest is only make-up
Plasma source heaters	The following heaters in the plasma source are off: 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. The absence of fluorocarbons in the plasma makes it unnecessary to maintain a high temperature on the chamber walls in order to reduce polymer condensation (see below). Always make sure that the temperature settings in the recipes are not enabled. Click here to have more information.
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.
Recipes	Do not run any recipes from the folder called 'z-Archive'.	The configuration of Pegasus 2 has changed over time (hence this table) so there is a large number of recipes that are no longer working. Also, some inappropriate settings in the some recipes (mainly with respect to the pressure control) have been identified. This is why it was decided that all existing (by autumn 2022) recipes be relocated to the folder called 'z-Archive' from which they must serve only as backup. To run a recipe in the z-Archive folder, it must be verified by the dry etch group and copied to another folder (typically user\group\****).
Etch of chromium and silicon nitrides	Recipes for etching chromium and silicon nitrides have been developed.	Etching the two materials is only allowed for processes in combination with other Pegasus 2 specific recipes such as the CORE recipe. Always consult with Nanolab staff.
Electrostatic clamping and helium backside cooling are again mandatory.	The processes run in Pegasus 2 operate at such low powers that they do not require very efficient cooling. It has therefore been decided that the following options/procedures Electrostatic clamping of carriers/substrates The Helium backside cooling is kept at 5 Torr instead of the usual 10 Torr on the other Pegasus tools. Using bonding procedures such as droplets of Galden oil to increase thermal contact between chips and carrier will no longer be required.	So far we have not seen any changes in the results but if you do, please contact Nanolab staff.
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.	See the papers in the section below.

Publications on the CORE process

The CORE process is described in detail in the publications below:

Nguyen, V. T. et al.

On the formation of black silicon in SF6-O2 plasma: The clear, oxidize, remove, and etch (CORE) sequence and black silicon on demand

2020 Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, 38(4), [043004].

https://doi.org/10.1116/6.0000196

Vy Thi Hoang Nguyen et al.

The CORE Sequence: A Nanoscale Fluorocarbon-Free Silicon Plasma Etch Process Based on SF6/O2 Cycles with Excellent 3D Profile Control at Room Temperature

2020 ECS J. Solid State Sci. Technol. 9 024002

https://doi.org/10.1149/2162-8777/ab61ed

Vy Thi Hoang Nguyen et al.

Ultrahigh aspect ratio etching of silicon in SF₆-O₂ plasma: The clear-oxidize-remove etch (CORE) sequence and chromium mask

2020 Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, 38(5), [053002]

https://doi.org/10.1116/6.0000357

Vy Thi Hoang Nguyen et al.

Cr and CrO_x etching using SF₆ and O2 plasma

2021 Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, 39(3), [032201]

https://doi.org/10.1116/6.0000922

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
• The ORE process with Al2O3 mask
• Nanoscale silicon nitride etch with SF6