Thermal Oxidation

Pure Wafer thermal oxide furnaces are certified for growing oxide on wafers of 50.2 mm to 300 mm in diameter. We guarantee a ±5% percent industry-standard uniformity across every batch, but typically our processed wafers qualify at a far better rate, enabling us to meet the tightest of customer specifications. With our dry thermal oxidation method, we grow oxides of 500Å to 1000Å and our wet thermal oxidation process is applied for oxides of 1,000 to 100,000Å.

Capabilities
  • Thickness Range

    500Å - 10µm

  • Target thickness tolerance

    ± 5%

  • Within Wafer uniformity

    ± 3%

  • Metrology tool

    Filmetrics

  • Standard Process Temp

    1050°C

  • Diameters supported

    50mm to 300mm

  • Tool

    Horizontal Furnace

  • Deposition type

    Steam / Double Side Dep

1. Dry Versus Wet Thermal Oxidation

Table 1 below shows that Pure Wafer thermal oxidation processes uses wet oxidation for oxide thicknesses > 1000 Å and uses dry oxidation for oxide thicknesses < 1000 å. This is because wet oxidation has a much faster growth rate than dry, making wet oxide growth the preferred method for growing thick oxides. wet oxidation has a faster growth rate because water molecules are smaller than oxygen molecules and diffuse faster through silicon dioxide. however, the benefits of using dry oxidation are that although it has a slower growth rate, it is more controlled, more dense, and cleaner than wet oxidation. We can also grow any combination of dry and wet oxide for special applications.

Wet versus Dry Oxide Growth for Pure Wafer Thermal Oxide Process
Desired Oxide Thickness / Type of Thermal Oxidation
  • > 1000 Å

    Water Vapor (Wet)

  • < 1000 Å

    Molecular Oxygen (Dry)

2. Factors That Affect Thermal Oxidation
Orientation
Only affects oxide growth during the Linear (initial) Stage. A wafer with more atoms available for reaction with an oxidant will have a faster oxide growth rate. This allows silicon wafers with <111> orientation to be more readily available to react with an oxidant over <100> wafers, because <111> crystals run parallel to the wafer surface, whereas <100> crystals run angled to the wafer surface.
Dopants
Increase growth rate when present. N-type dopants increase growth rate during the Linear Stage and P-type dopants increase growth rate during the Parabolic Stage.
Chlorine
Can be added to improve cleanliness of oxide, increase growth rate during Parabolic Stage, and improve performance of overall device.
Pressure
As pressure increases, the oxide growth rate increases as well, during both Linear and Parabolic Stages of oxidation. When the pressure is increased, the temperature can be decreased, and the oxide growth rate can remain the same. For every 10 atm of pressure added, the temperature can be reduced by 30 °C while allowing the oxide growth rate to remain constant.
3. Annealing

The Annealing of wafers is a common practice that is used throughout the industry. Annealing is a high-temperature furnace operation that is commonly used to relieve stress in silicon. It can also be used for the activation of ion-implanted dopants. Further reasons for the use of Annealing are to reduce structural defects, and it also reduces interface charge at the silicon-silicon dioxide interface.  We have the capabilities to do Nitrogen Annealing. This is accomplished using pure nitrogen to flow through the furnace over the wafers. The furnace is then heated to a specific temperature for the desired amount of time.

Thermal Oxidation Picture 1
Thermal Oxidation Picture 2