Laboratory Report 1 For this Lab Report, you will learn some of the basic MEMS fabrication processes, namely wafer cleaning, oxidation, photolithography and etching both oxide and silicon. DO NOT ATTEMPT ANY PROCEDURE BEFORE BEING PROPERLY TRAINED. Follow the procedures outlined in this document, and write the lab report following guidelines posted on the web (and distributed on the first day of class), making sure to answer all the questions in the reporting section for each step. Process Outline for Laboratory 1: 1. Step 1: Oxidation a. Sample cleaving b. Sample cleaning c. Thermal oxidation 2. Step 2: Photolithography and Oxide Etching a. Spinning photoresist b. Contact lithography c. Development d. Wet etching Silicon Dioxide with Hydrofluoric Acid (HF) 3. Step 3: Silicon Etching a. Wet etching Silicon with Potassium Hydroxide (KOH) STEP 1: Growing an Oxide Overview: Start with half of a 4in <100> Silicon wafer. Use a diamond tipped scribe to make a small scratch on the rough side of the wafer where you want to start the cleave. Flip the sample over and press the scribe down on the polished side where you made the scratch. This should crack the wafer along a crystal plane enabling you to cut the wafer (in a controlled manner) into smaller rectangular pieces. Thermal oxidation requires 2 steps of cleaning: a solvent based clean to remove the majority of contaminants and a Piranha acid clean to further remove organics to prevent contamination of the oxidation furnace. Finally, grow 300nm of “wet” thermal oxide on top of your silicon sample. This is done in an oxidation furnace at 900C with controlled gas conditions (H2O vapor and N2). Procedure: Sample Cleaving 1. Always wear latex or nitrile gloves while handling the chips. Do not touch samples with your bare hands; the oils from your skin are full of hydrocarbons which are unwanted impurities for all processes. 2. Take a <100> Silicon sample (half of a 4in wafer or so) and place it shiny side down on a cleanroom wipe. 3. Using the diamond tipped scribe, make a small scratch on the unpolished side of the wafer (perpendicular to a flat edge of the sample) where you want to start the cleave (try to get three ~1in x 2in rectangular samples out of the half wafer).4. Flip the sample over and put pressure on where you scratch the sample. The wafer should begin to crack along a crystal plane. Keep applying pressure until the crack cuts the sample in two. 5. Continue cleaving until you have the desired chips (you should have 2 chips 1in x 2in or (slightly) greater. 6. Scratch meaningful labels on the unpolished side of your samples. 7. Place them into sample carriers. Solvent Cleaning 1. Using tweezers, place your samples into the wafer boats designated for solvents. 2. Place the wafer boat into the acetone beaker then put the acetone beakers into the sonicator and run for 3 minutes. 3. Move the wafer boat into the isopropyl alcohol beaker and place in the sonicator for 3 minutes. 4. Fill a beaker with deionized water and put your wafer boat into the DI water and rinse with DI for 3 minutes 5. Remove boat from the DI water, place samples onto a new cleanroom wipe and blow dry your samples with the filtered N2 gun. 6. Place samples back into the wafer carriers. Note: 1. The cleaning solutions can be reused several times. All the groups will share the same set of cleaning solvents, so be careful not to contaminate the solutions. 2. In case the existing cleaning solvents need to be replaced, dispose them in the appropriate container- Do not pour solvents down the drain. 3. All beakers in the lab must be labeled correctly. Beakers are color coded to prevent cross-contamination, please do not use for other purposes. Acid Cleaning 1. Very slowly add 5 parts of H2SO4 to 1 part of H2O2. The mixture is self heating and attains a temperature of 80 degrees centigrade. When cool, the mixture may be re‐used by adding 5 ml of fresh H2O2. Heat to 80-100C 2. Place samples into a Teflon boat designated for Piranha. 3. Carefully place boat into the hot Piranha solution and leave for 10 minutes. 4. Remove boat and place in DI water for 3 minutes 5. Remove samples from boat, blow dry with N2 and place in your sample carrier 6. Take samples to the HF hood. 7. Put on the appropriate protective equipment (Nitrile (purple) or acid gloves, apron, and face shield). 8. Place samples in the Teflon boat for HF. 9. Dip in HF solution for 15 seconds to remove any native oxide. 10. Remove boat from HF and rinse with DI water for 3 minutes. 11. Blow dry with N2 and place samples in wafer carrier. Thermal Oxidation 1. Open the N2 valve at the back of the furnace till the flow meter reads 15 let the furnace purge for 10 minutes. Reduce gas flow to load or unload furnace. 2. Load the wafers on to the boat 3. Place the boat at the mouth of the furnace for 5 minutes. 4. Slowly push the boat in over a period of 3 minutes till you reach the flat zone. 5. Allow 5 minutes for the wafers to heat up to the furnace temperature. Nitrogen flow should be 15 for the duration of soak time. 6. Adjust gas flows for wet oxidation and leave the wafers for the desired time. 7. Slowly pull the wafers out of the furnace over a span of 3 minutes.8. Let the boat sit at the mouth of the furnace for 5 minutes. 9. Remove the boat from the furnace. Gently remove your samples from the boat. Let the boat cool for at least 20 minutes before moving the samples. Reporting: 1. Describe, in your own words, the procedure you used to clean the chips. Write down all the steps you preformed, including the details of the procedure, including details like the time you kept the chips in the ultrasonic cleaner, the exact temperature of the oven, the length of time the chip was blown dry and kept in the oven, etc… 2. Take a picture of your blank starting substrate showing the scribed alphabet. Write/label visible defects, if any. (Don’t forget scale bars on the image!!) STEP 2: OPTICAL LITHOGRAPHY and OXIDE ETCHING Overview: You will prepare the wafer for spinning on the positive photoresist (AZ 4110) including the dehydration bake and HMDS treatment. In brief, you will spin on AZ 4110 and then softbake the resist for 1 min. @ 85 deg C. Next, you will expose for the appropriate time using Mask-1. There is no alignment at this stage. Use the exposure times suggested by your TA. (20 sec. @ 7.5 mW/cm2) [The lamp is preset for