520.495/580.495 Microfabrication Laboratory

Laboratory Assignment #6

Objectives:

I) To post-process the exposed aluminum pads and plate them with gold.

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 under the hood this week as plating requires multiple solutions at high temperatures. DO NOT forget to label ALL containers.

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:  

Gold plating aluminum pads

 

Step 1 – Techni En Zincate

  1. Fill a glass beaker with 375mL H2O
  2. Add 175mL of the Zincate Solution
  3. Keep the solution at room temperature
  4. Immerse the wafer(s) for 30 seconds
  5. The aluminum should be turn  noticably greyer

 

Step 2 – Alkaline Electroless Nickel Strike

  1. Fill a plastic beaker with 380mL H2O
  2. Add 90mL of Technic 9109A
  3. Add 30mL of Technic 9109B
  4. * Test that the pH is 9.5-10
  5. Heat the solution to 110 oF
  6. Immerse the wafers for 15 minutes

 

Step 3 – Techni En 9185

  1. Fill a plastic beaker with 400mL H2O
  2. Add 75mL 9185B
  3. Add 25mL 9185A
  4. Heat to 190oF
  5. ** Test that the pH is 4.8-4.9
  6. Immerse the wafers for 15minutes

 

Step 4 – Oromerse SO

1.       Fill a glass beaker with 467 mL of Oromerse SO part A

2.      Add 33mL of Oromerse SO part B

3.      Heat to 158o-164o

4.      Test that the pH is 8.8-9.0

5.      Immerse the wafers for 20 minutes

 

Notes: Checking the pH should be done with older solutions. With fresh solutions (less than two days old) pH checking is not necessary.

 

*  If the pH is too low, raise with a solution of one part ammonium, one part water

If the pH is too high, lower with a solution of 10% sulfuric acid in water

 

** If the pH is too low, raise with a solution of 10% sodium hydroxide in water

If the pH is too high, lower with citric acid.

YOU HAVE NOW FINISHED PROCESSING THE WAFERS!

III. Postlab Work:

  1. What is the thickness of the gold plated on top of the deposited metal patterns? Characterize it at a single point per DNA microchip pattern on the wafer.