520.495/580.495 Microfabrication Laboratory

Laboratory Assignment #6

Objectives:

I) Use the mask aligner with the second mask to open the cuts in the polysiloxane film..

II) Etch polysiloxane until metal patterns are exposed..

NOTE: We will continue processing the same TWO student wafers per section.

Preliminaries:

1. All the cleaning procedures (except using spin/rinse/dryer) should be done in the hood. Aprons, protective sleeves, gloves, face shield, lab coat, and goggles must be worn during cleaning procedures. Wear plastic disposable gloves at all times. Be especially careful when working with HF.

2. Transfer wafers with tweezers;  try to grasp the wafer at the same place each time, usually at the flat edge.

I. Prelab Work:

As usual, draw the process flow diagram for the steps that we will take this week in the lab.

II. Lab Work:

A.  Photolithography using passivation cuts (C) mask

  1. Fill a 1000ml beaker with 800ml of Xylene; this will be the negative photoresist developer. Fill a 2000 ml beaker with 1500 ml of de-ionized water for rinsing the wafers following development.
  2. Set wafer on to the chuck of the photo mask aligner, and align the wafer with the mask. Make sure that you have mask (C) on the aligner and that the mask is oriented the proper way. Set exposure timer at 60 seconds. Turn away from the aligner during exposure.
  3. Develop the photoresist by immersing the wafer in the developer for approximately 60 seconds. (IMPORTANT: Do not over develop. Rinse the wafer by first immersing the wafer in the beaker of DI water for 5 minutes and then again under running de-ionized water at the sink. Dry the wafer using the filtered nitrogen gun, and inspect the wafer under the microscope.

B.  Polysiloxane etching

  1. Prepare 800 ml of buffered HF in a 1000 ml plastic beaker.
  2. Also fill two 2000 ml beakers with deionized water to use as rinse.
  3. Load wafers into a carrier and immerse in the buffered HF for approximately 1 minute. Take the wafers out and rinse well with DI water.
  4. Check to see if the etching has reached the metal patterns. Make sure that you test in four points on the wafer. If the metal patterns are not exposed continue the buffered HF etching monitoring the process every 30 seconds  until you are confident that the metal patterns are exposed. It takes about 3 minutes to etch through the polysiloxane layer.
  5. Keep the KTFR photoresist on the sensor for extra passivation and protection

YOU HAVE NOW FINISHED PROCESSING THE WAFERS!

III. Postlab Work:

  1. What is the thickness of polysiloxane on top of the deposited metal patterns? Characterize it at five points on the wafer (four at the corners and one in the middle).