Fiche de révision : Wafer Etching Fundamentals

📋 Course Outline

1. Etching Role and Definition
2. Wet and Dry Etching
3. Dry Etching Equipment and Objective
4. Pre-Start and System Startup
5. Wafer Loading and Recipe Selection
6. Automatic Process and Shutdown
7. Wet Resist and Oxide Etching

📖 1. Etching Role and Definition

🔑 Key Concepts & Definitions

• Etching : The process of removing material uniformly from a wafer or locally removing it to delineate a microcircuit pattern.

📝 Essential Points

• Etching combined with photolithography creates oxide openings for diffusion or implantation, and repeated etching and patterning forms semiconductor components, polysilicon, metallization layers, and passivation openings for bonding pads.

• The dry-etching objective is to transfer the photolithographic pattern to the wafer by removing oxide that is not covered by photoresist.

💡 Memory Hook

Patterned protection causes selective material removal

📖 2. Wet and Dry Etching

★ Must-know

📌 Wet chemical etching dissolves material directly in a solvent or converts it into a soluble compound, whereas dry etching removes material through momentum transfer from ionized gases in a plasma.

Further detail

• Dry etching uses gases rather than the liquid chemicals used in wet chemical etching.

📖 3. Dry Etching Equipment and Objective

★ Must-know

• The dry-etching equipment is a Samco reactive ion etcher, and the principal sample is an oxidized wafer with a patterned surface.

Further detail

• CF4 is used for silicon oxide etching, O2 is used to ash or remove photoresist after etching, and bent tweezers are used for wafer handling.

📖 4. Pre-Start and System Startup

📝 Essential Points

• Before startup, the operator switches on the wall and rear power if the system is off, opens the processed chilled water and compressed-air valves, verifies minimum nitrogen pressure of 1.2 bar, and checks that SF6, CHF3, O2, and CF4 are open at about 1.2 bar.

• System startup consists of pressing the green ON button, pressing the System Start Up soft key, and waiting for the pumps to start.

• The turbo molecular pump must reach its normal operating speed of 48000 rpm before the Main Menu appears, which takes about six minutes.

📖 5. Wafer Loading and Recipe Selection

★ Must-know

• To load a wafer, the operator selects Auto Mode, presses Sample Set to vent the chamber, opens the lid with both Open/Close buttons simultaneously, places the wafer in the correctly sized four-inch or six-inch tray, and closes the lid using both buttons until two short beeps are heard.

• After loading, pressing Process returns the system to the Auto Mode screen, where the operator selects Recipe and chooses a standard recipe numbered 1–5 or a custom recipe numbered 6–10 before pressing Decide.

Further detail

• Recipe process times can be edited through Conf Para, Change Time Setting, the arrow keys, and ENT to save each changed value, followed by Change Time Setting and OK to return to Auto Mode.

📖 6. Automatic Process and Shutdown

★ Must-know

📌 Open to ATM restores atmospheric pressure after processing, whereas Hold VAC keeps the chamber under vacuum until the operator vents it.

• When Hold VAC is selected, the operator presses Purge, waits about 1.5 minutes for venting, opens the lid, removes the wafer, and either loads another wafer and presses Process or presses Vacuum to place the machine in standby.

• The chamber should be maintained in a vacuum state whenever possible to prevent contamination, including after removing a wafer in Open to ATM mode by pressing Vacuum to evacuate the chamber.

• To shut down the system, the operator ensures that the chamber is pumped down to at most $3\times10^{-3}\ \mathrm{Pa}$, presses the red OFF button, and leaves system power on until the turbo pump has stopped after about seven minutes.

Further detail

📌 Hold VAC is recommended when the system is seldom used, while Open to ATM is recommended when the operator is waiting at the system for process completion.

• The standard recipes include O2 cleaning for 5 minutes, silicon etching with CF4 and O2 at 4.0 Pa and 300 W for 2 minutes at approximately 750 Å/min, and silicon dioxide etching with CHF3 at 2.3 Pa and 130 W for 4 minutes at approximately 500 Å/min.

📖 7. Wet Resist and Oxide Etching

★ Must-know

• Wet resist stripping is performed in a fume hood with the ventilator and light on:

  • the resist-coated wafer carrier is immersed in stripper
  • transferred through rinse bath 1 and rinse bath 2 for full cycles
  • dried with a nitrogen gun
  • and the gloves are washed before removal

• Wet oxide etching requires chemical gloves, checking the BOE tank, setting up the BOE-PVDF tank and rinse controller, observing the oxide color, immersing the oxidized wafer in BOE for about one minute, rinsing it, and drying it with a nitrogen gun.

Further detail

• The wet-etching equipment includes a wet bench, oxidized and resist-coated wafers, BOE containing HF for silicon oxide etching, Teflon and glass beakers, bent tweezers, and acetone for photoresist removal after etching.

📊 Synthesis Tables

Wet and Dry Etching Comparison