Laboratory: A Typical Oxidation Process

Thermal Oxidation For Silicon Dioxide (SiO2) Film Formation The setup comprises a resistance heated furnace, a cylindrical fused-quartz tube containing Si wafers held vertically in slotted quartz boat, and a source of either dry oxygen or water vapor. Several dozen wafers typically stand vertically ~ 1 cm apart and are oxidized simultaneously. Temperature is controlled to within ± 1 °C.

At the wafer surface Si combines with oxygen to form the oxide Si (solid) + O2 (gas) SiO2 (Solid) Or Si (solid) + 2H2O (gas) SiO2 (solid) + 2H2 (gas) Si is consumed in this process, and subsequently Si surface recedes from its original location. However, the volume of grown oxide is larger than that of consumed Si (consumed Si volume/grown oxide volume ~ 0.44); i. e., the net effect is an increase in thickness. 900 °C to 1200 °C 900 °C to 1200 °C

The basic structural unit of thermal oxide is a Si atom surrounded tetrahedrally by four oxygen atoms. The Si-O and O-O internuclear distances are 1.6 Å and 2.27 Å, respectively. SiO2 or silica has several crystalline structures (the dominant one is quartz), and an amorphous structure. Amorphous oxide has a density of ~ 2.2 gm/cm3, whereas quartz has a density of ~ 2.7 gm/cm3. Thermally grown oxides are usually amorphous.

- Inspect furnace.

- Inspect gas lines to the furnace.

- Set oxide growth temperature.

- Prepare wafers and load them into the quartz boat.

- With boat loader, return wafers in boat to the furnace.

- Shut oven door.

- Set oxidation mode (dry or wet) and gas flow in standard cubic centimeter minute.

- Check gas flow (typically ~ 2.5 sccm).

- After oxidation cool gradually and remove wafers from furnace.

- Put wafers in wafer boxes and store them in the clean room.