EDP 93- EDP Etch Process

Table of Contents

LNF Supported Processes

EDP Etch

General Information

Definitions

EDP Etch Procedure

Hazards

LNF Supported Processes

EDP Etch

General  Information

EDP, (Ethylene Diamine Pyrocatechol) also known as Ethylene Diamine - Pyrocatechol – Water (EPW), Si etch is used to anisotropically etch Si for selective micromachining and to release devices.  It is NOT a CMOS-compatible process.  It is generally preferred for undercutting cantilevers.  It tends to leave a smoother finish than other etches, since faster etching of convex corners produces a polishing action.

The basic chemistry of EDP etching includes the following steps:

1.- Ionization of the Ethylenediamine:

NH2(CH2)2NH2 + H2O  NH2(CH2)2NH3+ + OH-

2.- Oxidation-Reduction (oxidation of Silicon):

Si + 2OH- + 4H2O →Si(OH)62- + 2H2(g)

3.- Chelation of the hydrous Silica:

Si(OH)62- + 3C6H4(OH)2 → [Si(C6The etch rate of the Si in the <100> face is faster than in the <111> face, anisotropy: (111):(100) ~ 1:35.

• Typical etch rates for (100) silicon:

EDP does not attack oxide or nitride at any appreciable rate, making them good masks for this process. The etching virtually stops when it encounters a heavily doped boron (B) layer (reduces the etch rate about 50 times). The etch rate for EDP at 110°C (probe temperature) is about 80 μ/hr (~1.3 μ/min).

EDP etching is readily masked by SiO2, Si3N4, Au, Cr, Ag, Cu, and Ta. But EDP can etch Aluminum! This is why it is not a good idea to use Al foil to cover the EDP. LNF provides a glass water cooled condenser lid for this effect. The purpose of the condenser is to restrict the leakage of corrosive fumes.  

• EDP is very corrosive, very carcinogenic, and should never be allowed near mainstream electronic micro-fabrication.

Definitions

• PPE: Personal protective equipment
• DI: Deionized water

EDP Etch Procedure

Materials:

Scale

Beakers (only from EDP cabinet) for measuring ethylene diamine

Small graduated cylinder (from EDP cabinet) for measuring DI water

Spatula for Pyrazine

Plastic weigh boats (1 large, 1 small) for measuring dihydroxide benzene & pyrazine

Teflon sample carrier (from EDP cabinet)

Funnel (EDP cabinet)

Glass waste bottles with waste label- pre written labels are in the EDP drawer

Reflux condenser to keep volatile ingredients from evaporating.

It is recommended you set up all materials above before you starting the solution mixing, while gloves are still clean.

Chemicals:

Ethylene diamine (NH2-CH2-CH2-NH2) CAS # 37164-19-5

1,2 Dihydroxide Benzene (C6H4(OH)2) CAS #120-80-9 (a.k.a Catechol)

Pyrazine (C4H4N2) CAS  #290-37-9

DI water

Prepare the EDP mixture:

Wear proper PPE: apron, double nitrile gloves under Trionic gloves. We recommend nitrile on top of Trionic that will be disposed immediately after handling chemicals or samples exposed to chemicals, safety glasses and face mask.  Acid sleeves are optional, but if you would like to wear them for extra protection, they are available on the supply rack. They should be put on over new, uncontaminated Trionic gloves. Put on the gloves first, then put on the acid sleeves.  Do not tuck the acid sleeves into the gloves, otherwise chemicals can drip down the sleeve into the glove.

Choose a glass beaker large enough for your sample and sample holder.

Measure the amount of liquid you need to cover completely your sample. All the measurements must be done in the hood.

Choose from the table the amount of EDP mixture you will prepare, start adding DI first:

Time to heat ~ 20 min

When all the chemicals are added the mixture is a brownish liquid. The 1,2 Dihydroxide Benzene salt has an amber color when is freshly opened, this doesn’t mean it is not effective.

After 1 hr of heating you lose about 50 ml and the wafer could be exposed. Make sure you cover the beaker with the condenser and include a little extra solution to account for evaporation losses. Use the condenser provided, this helps to reduce the loss by evaporation and it helps to heat the liquid faster.

Please remember to:

• Wipe the outside of the lip of the bottle when done pouring
• To prevent spills, when measuring liquids with a graduated cylinder or other small beaker, first pour liquid from chemical bottle into a larger beaker, then carefully transfer desired amount into graduated cylinder or small beaker.
• Discard the weighing boats into the “EDP” trashcan
• If pyrazine becomes in contact with moisture it will become a solid
• Wipe down the scale after use
• Collect the first 3 rinses in the waste bottle using the funnel. It is convenient to place the waste bottle in the sink
• Connect the hoses for the reflux and open the DI water very slowly
• Remember when the reflux condenser is full of water is very heavy, please be careful
• The temperature probe must go through the hole in the condenser and it must touch the water but not any wall of the container. Make sure it is always in contact with the solution
• For small pieces use the 1 liter beaker and cover with small condenser.
• Over long etches the loss of solution can be a problem.
• The condenser is heavy when full, it will be difficult to remove if you let the mixture cool down.

Etching the Sample

Place the beaker with the mixture on the hot plate.

Turn the heater on: Choose the program that you like. Select the recipe by typing in the number for that recipe on the hot plate controller under the recipe edit page. The manual for the hot plate is in the logbook and LNF Wiki page for EDP Bench 93.

There are three heating recipes:

When the solution is at temperature slowly lift the reflux condenser and place the sample in the beaker; slowly replace the reflux.

Time your etch (rate is about 80 micron per hour)

If you don’t see bubbles during etch, it is probably not happening.

To stop etching: use timer. Go to timer/recipe – press pause reset alarm clear.

On the hot plate on the adjacent bench heat up water and cover with aluminum foil. This water is to rinse the wafer after etching is finished. Rinse until there is no coloration of the hot water. Put the rinse water in the waste bottles (you will need more than one). Use the hot water to rinse your plastic ware and glassware.

Cleaning and Waste Disposal

The used EDP solution needs to be collected as chemical waste. OSEH has done tests on the rinsates and determined that we must collect them if there is any coloration because it has enough bad carcinogens they need to be properly disposed.  Collect rinsate until there is no color in the liquid. You must pour it in labeled waste bottles; use funnel. Preprinted labels are in the drawer that says EDP. Rinse all labware used in hot water until no color leaches out. Note that EDP residue is initially clear, but darkens in color with time.  Wipe down bench surfaces and rinse labware thoroughly.

If you do not clean labware properly, the EDP will slowly evaporate and coat the inside of the cabinets, you will breathe that air when you open the cabinet next time. Your choice.

Hazards

Ethylene diamine (NH2-CH2-CH2-NH2) CAS # 37164-19-5: Flammable liquid.  Corrosive. Causes severe skin burns and eye damage.  Causes extreme damage to mucous membranes and respiratory system.  May cause allergic skin reaction.  May cause allergy, asthma symptoms, or breathing problems if inhaled. Can cause coughing, wheezing, laryngitis, shortness of breath, headache, nausea, or vomiting. Repeated exposure may cause asthma, dizziness, diarrhea, or abdominal pain.

1,2 Dihydroxide Benzene (C6H4(OH)2) CAS# 120-80-9 (a.k.a Catechol): Toxic. Toxic if inhaled or in contact with skin.  Is rapidly absorbed through skin.  Causes skin irritation and may cause allergic skin reaction. Confirmed animal carcinogen. Causes serious eye damage.  Toxic to aquatic life. May cause coughing, shortness of breath, nausea, headache and vomiting.

Pyrazine (C4H4N2) (CAS# 290-37-9?): Flammable solid. Keep away from heat, sparks, and flames.  Causes skin irritation and serious eye irritation.  May cause respiratory irritation.