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The STS APS DGRIE (STS Glass Etcher) is an ICP RIE tool manufactured by SPTS Technologies. It is used for anisotropic etching of silicon-based dielectrics (silicon dioxide, silicon nitride, glass, and quartz). It can etch thin film oxide and nitride up to 8 μm thick with 90° ± 0.5° sidewall angles. Very deep (100 μm) etches have been performed on fused silica and quartz substrates. Sub-micron feature etching has also been demonstrated (down to 100 nm linewidth). The tool will only accept 6” wafers - all smaller samples must be mounted to a carrier wafer.

STS APS DGRIE
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Equipment Details
Manufacturer SPTS Technologies Ltd.
Model APS
Technology DRIE
Materials Restriction Semi-Clean
Material Processed SiO2
Fused silica
Borosilicate glass
Quartz
Mask Materials SPR 220
KMPR
Polysilicon
Sample Size 150 mm
Gases Used Ar, He, C4F8, O2, SF6, CF4, H2
Equipment Manual
Overview System overview
Operating Procedure User manual
Supported Processes Supported Processes
User Processes User Processes
Maintenance Maintenance

Contents

Announcements

  • [2019-11-18] If you are processing samples through the STS Glass Etcher that will later be processed in CMOS clean furnaces, we are now requiring a double pre-furnace clean before your furnace run. The first clean would be in RCA-81 and the second would be in PFC-01. We will continue to investigate other cleaning methods and strategies to improve upon our tool and material segregation policy in the future. Please submit a Helpdesk ticket for the Glass Etcher if this new policy poses issues to your process so we can work with you to resolve them.

Capabilities

The STS APS system is designed for deep glass RIE and high aspect ratio thin film silicon-based dielectric etching at submicron resolution.

  • SiO2 films
    • Up to 8 μm
    • 0.26 μm/min
    • 2.5:1 selectivity to PR
    • Feature sizes down to 100 nm
  • Fused silica, quartz, glass substrates
    • 100 μm depth
    • ~0.5 μm/min
    • Up to 5:1 selectivity to KMPR/SU-8
    • Feature sizes > 20 μm

System overview

Hardware details

  • Gases
  • Pressure
    • 1550 L/sec Mag 2000 CTS Turbo Pump
    • 2-250 mTorr
    • Fast acting VAT pendulum valve
  • Chuck
    • 150 mm Wafer
    • 0-20 Torr Backside He Cooling
    • -20°C to 20°C
  • Chamber
    • 120°C Walls
    • Aluminum Walls
  • RF
    • 2500 W, 13.56 Mhz Coil
    • 1000 W, 13.56 Mhz Platen

Substrate Requirements

The STS APS DGRIE is equipped to handle 6” (150 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.

Sample mounting

See also: Sample mounting

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 6” (150 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
Etch depth must be calculated for the deepest feature. An etch rate test should be performed to determine this for each process and mask design.

For most standard recipes, a bare Si carrier is recommended, unless otherwise instructed by a tool engineer. If you are unsure what carrier to use, create a helpdesk ticket and staff will help you determine the appropriate material.

Material restrictions

The STS APS DGRIE 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.

Samples that will later be processed in a CMOS clean furnace will require two PFC steps prior to the furnace step. The first should be performed in RCA Bench 81 and the second in PFC Bench 01.

Materials etched

This tool is intended for etching silicon dioxide and silicon nitride. There are certain restrictions for where these materials may be deposited, as detailed in the approved materials list.

Mask materials

This includes any material that will be exposed to the plasma for the majority of the process. The most common mask material is photoresist. Poly/amorphous silicon can also be used. 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.

Buried 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.

Approved materials

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 info@lnf.umich.edu for any material requests or questions.

Supported processes

The primary recipes for the STS Glass Etcher are used for oxide/quartz/silica etching. The uk submicron etch is designed for thin-film (up to 8 μm) etching of oxide. Feature sizes can range from 100 nm to a full wafer. The Fused silica etch is designed for deep etching of fused silica, quartz, and glass. More details on the 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 APS DGRIE User Processes. For more information, please contact the tool engineers via the helpdesk ticket system.

For all process questions, fill out the process request form and create a helpdesk ticket.

Standard operating procedure

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Checkout procedure

  1. Complete the sample mounting course. If you have already completed this for another tool, you do not need to complete it again.
  2. Read through this page and the User Manual above.
  3. Complete the process request form.
  4. Create a helpdesk ticket requesting training and attend an introductory training session with a tool engineer.
  5. Practice with your mentor or another authorized user until you are comfortable running the tool on your own.
  6. Schedule a checkout session with a tool engineer via the helpdesk ticket system. If this checkout is successful, the engineer will authorize you on the tool.

Maintenance

In order to provide reliable operating conditions, maintenance is performed weekly on the tool including inspecting and cleaning the chamber. The following regular maintenance is performed on the STS Pegasus 6:

  • Weekly
    • Inspect chamber
    • Wipe down chamber walls
    • Clean clamping ring
    • Clean process kit
    • Plasma clean and condition
  • Monthly
    • Check wafer centering
  • Annually
    • Clean source ceramics and upper chamber
    • Clean APC valve, foreline valve, baratron valve
  • Biennially
    • Refurbish turbo pump

After any chamber maintenance, the etch rate of the uk submicron etch is checked to verify the condition of the tool.To verify the condition of the tool The etch is run for 2 minutes on a 6" oxide coated wafer and the etch rate is measured in 25 locations. The average of this is shown below.