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 - 500°C
- N2 flow: 100
- time: 15 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
Vt. 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
- Adjust N2 flow to 100 on the anneal furnace flowmeter if it is not there already.
- Load your wafer into the annealing furnace for 15 minutes at T = 475°C.
- When the 15 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.
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