Procedure for Stamping on SiO2 Wafers

Hamza Aziz

The stamping procedure can be divided into four sub-procedures:

1. Wafer Cleaning
2. Metal Deposition
3. Stamping
4. Etching

A. Wafer Cleaning?

1. Take Silicon dioxide wafers and put them in isopropanol solution and ultrasonicate for 5 minutes.
2. After ultrasonication, take wafers out of the solution and wash them with nanopure water then isopropanol.? Dry the wafer with argon, or compressed air can.

(Optional)

1. Place the ultrasonicated wafers in a clean, dry vial and put 1 part Conc. hydrogen peroxide then 2 parts Conc. H2SO4 (this solution is called Pirahna solution).
2. Place a micro stirring bar inside the vial and put the vial in a water beaker on the hot plate.
3. Heat the water up to boiling temperature while stirring the Pirahna solution.? Let this go on for about 10-15 minutes.
4. Drain the Pirahna into the acid waste bottle.
5. Take the wafers out and wash them with nanopure water and then dry them.?Rinse the vial thoroughly with water before throwing it away.

B. Metal Evaporation

1. Take wafers and load them onto the holder in the evaporator
2. Take the vacuum down to about 1x10-5 and deposit 3 nm of titanium on the wafer.
3. After depositing titanium, deposit 50-100nm of Ag at the same vacuum.

C. Stamping?

1. Prepare a .5mM alkanethiol solution, using octadecanethiol and ethanol.? Solutions of lesser concentrations can also be used, i.e .25mM.? The solution has to be stirred for a while before the alkanethiol dissolves.
2. Hold the stamp from the sides and clean the surface with ethanol or isopropanol using a swab.? Try not to touch the surface while cleaning.? Dry the stamp.??
3. Gently coat the stamp surface with alkanethiol using the swab.??
4. Dry the stamp for approx. 1 min. in gas.
5. Place wafer on a level surface.? The best thing is to put the wafer on top of another wafer.? This would guarantee a flat surface and prevent the PDMS from touching the table.
6. Do not press down upon the PDMS because it would distort the features and could possibly coat the whole surface.
7. Let the stamp sit for 10-15 sec., then take it off and let the wafer dry.

D. Etching

1. Prepare a 20mL Silver etching solution (.3806g of K2S2O3, 0.0660g of K3Fe(CN)6, and 0.0084g of K4Fe(CN)6 and pour nanopure water to make 20mL solution.
2. Pour solution in a 20mL vial and cover the vial with aluminum foil.
3. Uncover the vial before use. Put a stirring bar in the solution and the put the setting for 300rpm.
4. Pick up the wafer and dip it in the etchant for 16 seconds (for a 50nm thick Ag layer) then take the wafer out and wash with water and dry with argon.
5. Then wash the wafer in HF for 15 seconds
6. Then again wash it in the Ag etchant until all of the silver is gone.