Laboratory A Typical Oxidation Process Thermal Oxidation For

Laboratory: A Typical Oxidation Process

Thermal Oxidation For Silicon Dioxide (Si. O 2) 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) + O 2 (gas) 900 °C to Si. O 2 (Solid) 1200 °C Or Si (solid) + 2 H 2 O (gas) 900 °C to Si. O 2 (solid) + 1200 °C 2 H (gas) 2 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.

• 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. • Si. O 2 or silica has several crystalline structures (the dominant one is quartz), and an amorphous structure. • Amorphous oxide has a density of ~ 2. 2 gm/cm 3, whereas quartz has a density of ~ 2. 7 gm/cm 3. • 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.