The STS Pegasus 4 is a Deep Reactive Ion Etch (DRIE) tool manufactured by SPTS Technologies. It is used for fast, high aspect ratio anisotropic etching of 4" (100 mm) silicon wafers using the Bosch process. It is also capable of slow, controlled etching with minimal undercut, sidewall roughness, and notching; sub-micron feature etching has been demonstrated down to 100 nm linewidth. Etch rate varies with feature size and density, so a characterization run is strongly recommended with any new mask.
|STS Pegasus 4|
|Manufacturer||SPTS Technologies Ltd.|
|Mask Materials||PR, SiO2|
|Sample Size||100 mm|
|Gases Used||Ar, C4F8, O2, SF6|
|Supported Processes||Supported processes|
|User Processes||User processes|
- High etch rates ~15 µm/min
- Nearly vertical sidewalls ~89°
- High selectivity to photoresist and SiO2
- 1550 L/sec Mag 2000 CTS Turbo Pump
- 2-250 mTorr
- Fast acting VAT pendulum valve
- Allows fast switching of BOSCH recipes (~1.5 seconds minimum)
- 100 mm Wafer
- 0-20 Torr Backside He Cooling
- -20°C to 20°C
- 120°C Walls
- Aluminum Walls
- 5 kW, 13.56 Mhz ICP coil
- 300 W, 13.56 Mhz platen
- 500 W, 380 kHz platen with pulsed power supply
- 10 A inner electromagnet
- 30 A outer electromagnet
The STS Pegasus 4 is equipped to handle 4” (100 mm wafers) up to 3 mm thick. All smaller samples must be mounted to a carrier wafer. All standard major and minor flats and full-round wafers are allowed.
If your sample and process meet any of the following criteria, you MUST mount your sample to a 4” carrier wafer:
- Sample size is smaller than a 4” (100 mm) wafer
- Substrate material is non-conducting (e.g. glass)
- Sample thickness is less than 100 μm
- Remaining thickness after etch is less than 100 μm
For all standard (Bosch process) recipes, an SiO2 coated carrier is required, unless otherwise instructed by a tool engineer. For non-bosch process recipes, create a helpdesk ticket and staff will help you determine the appropriate material.
The STS Pegasus 4 is designated as a Semi-Clean class tool. A full list of approved materials is included at the end of this section. In addition to the restrictions in this list, materials can be classified into four categories, detailed below: materials that may be etched, materials that can be used as masks, etch stop materials, and buried materials. Use of any material outside of these conditions requires approval by the LNF staff via a helpdesk ticket.
The STS Pegasus 4 is intended for etching single crystal silicon. While it is capable of etching silicon dioxide, silicon nitride, and poly-silicon, there are other tools at the LNF with better performance for these materials. There are certain restrictions for where these materials may be deposited, as detailed in the approved materials list.
This includes any material that will be exposed to the plasma for the majority of the process. The most common mask materials are photoresist and silicon dioxide. Silicon nitride is also allowed, although it has not been characterized. There are certain restrictions for where these materials may be deposited, as detailed in the approved materials list.
Etch stop materials
This includes any material that will be exposed briefly to the plasma. All materials listed in the approved materials list on the wiki are allowed, including approved mounting materials.
These materials may be present on the sample, but may not be exposed to the plasma. They may be covered by the mask or on the back of the sample, provided that the sample is mounted to a carrier wafer. Materials listed in the approved materials list on the wiki are allowed.
Below is a list of approved materials for the tool. Approved means the material is allowed in the tool under the conditions described above. If a material is not listed, please create a helpdesk ticket or email firstname.lastname@example.org for any material requests or questions.
The primary recipes for the STS Pegasus 4 are used for deep silicon etching. There are four main Bosch process recipes with varying properties. The tool also has an oxynitride etch that may be used to etch a mask layer prior to the Si etch, but this may be performed by other tools more effectively. There is also a thinning recipe designed to quickly etch a wafer without a mask. More details on supported processes can be found on the Processes page.
In addition to these, this tool has a number of user-created recipes for specific processes. Some of these recipes are documented on STS Pegasus 4 User Processes. For more information, please contact the tool engineers via the helpdesk ticket system.
Standard operating procedure
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Follow this procedure to receive authorization to run supported processes. Practicing with an authorized user or staff member prior to checkout is strongly encouraged.
- Complete the sample mounting course. If you have already completed this for another tool, you do not need to complete it again.
- Read through the User Manual above.
- Accurately complete the checkout quiz. You may retake as necessary until all answers are correct.
- Complete the process request form.
- Create a helpdesk ticket requesting a checkout session.
- Authorization will be provided pending successful completion of the quiz and demonstration of proper tool use in the presence of a tool engineer.
In order to provide reliable operating conditions, maintenance is performed regularly on the tool including inspecting and cleaning the chamber. The following regular maintenance is performed on the STS Pegasus 4:
- General tool check
- Qualification wafer run
- Check wafer centering
- Wipe down chamber walls
- Clean process kit, clamping ring
- Plasma clean and condition
- Change and clean source ceramics
- Refurbish turbo pump
- Clean APC valve, foreline valve, baratron valve
After any chamber maintenance, the etch rate of the standard recipes is checked, as described below.
LNF Recipe 1, 2, 3
To verify the condition of the tool an etch is performed on recipe 1, 2 and 3, rotating each week. The etch rate is measured on a 100 μm wide trench in 5 locations. The average of this is shown below.