Contact Anneal

The aluminum anneal is used to reduce contact resistance at the aluminum-silicon interface.

During processing, any exposed silicon will rapidly oxidize (native oxide). This oxide can increase the resistance of the contacts to the wafer.

Annealing is used to reduce the contact resistance, as well as recrystallize the aluminum on the wafer. At elevated temperatures, aluminum will 'take' the oxygen away from the SiO₂ at the interface to form Al₂O₃. This aluminum oxide is then incorporated into the bulk of the aluminum, leaving the interface free of oxide.

Equipment

Lindbergh-Tempress 8500 manual anneal furnace chamber 8A

Supplies

N₂

Operating parameters

• Furnace temperature: 475°C
• N₂ flow: 100
• time: 10 minutes

Equipment/controls/tools locations

• Temperature controller: on the side of the furnace
• Gas panel: top rack in the back of the furnace
• Quartz handling: covered cart is to the left of the furnace, tongs are inside
• Boat: at the mouth of the furnace

Operating precautions

High temperatures

Use the high temperature gloves when handling hot equipment.

Contamination issues

• Quartware is easily contaminated by alkali ions. This leads to premature quartz failure (breakage) due to devitrification as well as unstable MOSFET V_t. Once quartz is contaminated, little can be done to remove the contamination.
• Always wear latex gloves when working with the furnace.
• N₂ should always be flowing in standby to minimize contamination by backstreaming of air in the room into the hot chamber.

Operating procedure

1. Adjust N₂ flow to 100 on the anneal furnace flowmeter if it is not there already.
   
   
2. Load your wafer into the annealing furnace for 10 at T = 475°C.
   
   
3. When the 10 minutes have elapsed, remove the wafer from the furnace and place it in your wafer carrier. Be sure that the boat pushrod is fully inserted into the quartz tube so that it will not be broken. Return the empty boat to the front of the furnace tube.