ENGS 194 Lab - MOSFET Fabrication

Fall Term, 1995


Lab group:

Course Professor:


Objective:

To fabricate various semiconductor devices, including enhancement mode N-channel MOSFETS, using the Solid State Lab at Thayer School of Engineering. To familiarize ourselves with all aspects of semiconductor device fabrication, such as: oxidation, photolithography, wet etching, metal deposition, ion implantation and annealing.

Timeline

Week 1: Wafer clean and oxidation

  1. Received eight (8) silicon wafers.
  2. Performed RCA cleaning.
  3. Wet thermal oxidation in Thermco atmospheric diffusion furnace.

Week 2: Oxide measurement and Photomask #1

  1. Predicted oxide thickness:
  2. Measured thickness with optical ellipsometer
  3. Exposed wafers to Photomask #1: MOAT isolation definition
  4. Etched wafers

Week 3: Thin gate oxidation and polysilicon deposition

Tuesday group: Thin gate oxidation

Our group: Electron Beam Deposition of Polysilicon

  1. Polysilicon deposition using Varian Electron Beam evaporator

Week 4: Polysilicon oxidation and annealing; Photomask #2

Tuesday group: RCA clean, measurement, and annealing

Our group: Polysilicon oxidation and Photomask #2

  1. Examined wafers:
  2. Oxidized polysilicon using rapid thermal annealer
  3. Exposed wafers to Photomask #2: Gate definition
  4. Etched polysilicon

Week 5: No lab

Week 6: Implant activation and drive-in; Isolation Oxide; Photomask #3

Tuesday group: Implant activation and drive-in; Isolation Oxide

Our group: Photomask #3: Contact definition

  1. Exposed wafers to Photomask #3: Contact definition

Week 7: Metal Deposition

  1. Electron beam deposition of aluminum using Varian electron beam evaporator
  2. Alpha-step measurements made of polysilicon and aluminum thickness

Week 8: Photomask #4: Metal definition; Forming gas anneal

Tuesday group: Photomask #4: Metal Definition

Our group: Strip photoresist; Forming Gas Anneal

  1. Observed etched isolation oxide
  2. Stripped photoresist
  3. Forming Gas Anneal


Results

Unfortunately, the devices we made did not function. We determined that the Aluminum layer was overetched, so that contact is not made with the substrate.