Gold Etch¶

Standard Operating Procedure:

To remove gold from a substrate – patterned or unpatterned.

Substrate, glass beaker (for etchant), glass beaker (for rinse) and stainless steel tweezers

Gold Etchant TFA [contains: iodine, potassium iodide]

The etch rate will approximately double with every 10°C increase in temperature; stirring or agitation will increase the etch rate.
The etch rate will be reduced by approximately 50% by adding 1 part DI water to 2 parts etchant.
Recommended Operating Temperatures: 20-80°C (30-40°C most common)
Etch Rate at 25°C: 28Å/sec
Select Compatible Materials: Chromium, silicon, nichrome, titanium, titanium-tungsten alloy
Select Incompatible Materials: Aluminum, nickel, copper, silver, gallium arsenide, germanium
Compatible Plastics: HDPE, PP, Teflon, PFA, PVC

Trionic gloves on top of nitrile gloves, apron, safety glasses and face-shield

Get two glass beakers that will fit your samples for processing from the “Caustics Supplies” drawer in the glassware rack to the left of the hood – one should be labeled “Water Only” and the other should be labeled “Gold Etchant Only”.
Rinse both beakers with DI water prior to beginning the process.
Stand the beaker labeled “Water Only” to be used for rinsing the sample on a cleanroom wipe in the hood and fill it with DI water so that the water level will cover the entire substrate.
Blow the beaker labeled “Gold Etchant Only” semi-dry and place it on a cleanroom wipe in the hood.
Carefully pour the Gold Etchant into the “Gold Etchant Only” beaker so that there is enough liquid to cover your submerged sample.
If you plan to heat the etch, place the beaker of Gold Etchant on the hotplate and bring it up to temperature, setting the hotplate temperature to at least 10°C higher than your target temperature. You will need to monitor the temperature of the etchant with a glass thermometer placed in the etchant in order to be accurate.
Calculate the etch time for your sample. You will need to know the thickness of your gold layer. At 25°C, the gold will etch at a rate of approximately 28 Å/sec.
Place your sample into the etchant using tweezers and soak it for the appropriate amount of time calculated in the previous step. Agitation of the etchant will help to accelerate the etch.

When the etch is complete, remove your sample from the etchant with tweezers and transfer the sample carefully to the DI water rinse beaker. Make sure to leave the tweezers in the rinse beaker as well.
Let the sample and tools soak in DI water for 1 minute.
Remove the sample from the rinse beaker with the tweezers.
Rinse the sample with DI water in the hood sink, holding it in the water stream for approximately 10 seconds or more.

After the water rinse is finished, blow the sample dry with the N2 gun.
After getting most of the water off, you can dry the samples more in an oven or on a hotplate, if allowable for your sample.
Inspect sample for traces of un-etched gold. If features are small, use an optical microscope. DO NOT use a microscope, or any other equipment in the facility while wearing the hood PPE. If more etch time is required, place wafer back into the etchant for another 30 seconds while agitating. Repeat rinse and dry procedures.

The etchant may be used for multiple etches. For temporary storage (\<1 day), place a watch glass over the etchant beaker and store on fab wipes in the back of the hood. Make sure there is a label with your name, the date and chemical contents next to it, and leave the Badger slot for the hood enabled while your chemicals remain in the hood.
Dump the etchant waste into the waste container designated for “Gold Etchant” in the back of the hood. Note that this gold etchant is not an acid or caustic. DO NOT pour waste into a waste container for acids or caustics.
Rinse the beaker with DI water multiple times (typically 3 times or more) in the sink and then blow it as dry as possible with the nitrogen gun. DO NOT pour rinse water in the waste containers.
Dump the DI rinse beakers into the sink in the hood. DO NOT pour rinse water in the waste containers.
Rinse the beaker with DI water multiple times (typically 3 times or more) in the sink and then blow it as dry as possible with the nitrogen gun.
Return all glassware to its proper storage location.
Wipe up any splashes or drops of fluid in the hood with chemical wipes and dispose of them in the trash.
Store the Gold Etchant in the Oxidizers Cabinet.
Inspect all of the PPE to ensure it did not come in contact with the etchant before returning it to its storage location.

Skin: Remove contaminated clothing, rinse affected area with water for at least 15 minutes. Wash skin with soap and water. If there is any irritation, get immediate medical attention.
Eye: Immediately flush with water for at least 15 minutes while lifting upper and lower eyelids occasionally. Get immediate medical attention.
Ingestion: Drink water or milk unless victim is unconscious. Induce vomiting if help is not immediately available. Get immediate medical attention.
Inhalation: Remove to fresh air. Resuscitate if necessary. Take care not to inhale any fumes released from the victim’s lungs. Get immediate medical attention.

If a small spill occurs and is fully contained within the hood:

Wipe up the spill using appropriate wipes and dispose of them in the designated waste container.
If wipes are insufficient, use the absorbent pads stored in the bottom right corner of the hood.
If you are unsure how to clean up the material or feel uncomfortable doing so, notify staff immediately.

If the spill requires use of an absorbent pillow from the spill kit:

Notify staff immediately.
If the spill occurs after hours, contact cleanroom staff and post a message on Slack to alert other users not to use the hood until it has been properly cleaned and cleared by staff.

If a spill occurs outside the hood:

Notify cleanroom staff immediately.
Evacuate the immediate area (typically the entire bay containing the hood).
If the spill occurs after hours, contact cleanroom staff and post a message on Slack to alert others. The cleanroom will remain closed until staff can safely manage the spill.