Oxidation


Process Notes:

(0) Use the below attached Job Request Form to request a furnace job.

(1)   Two Thermal Oxidation types:

  • WET from Pyrogenic steam (2 H2+ O2 => 2 H2O)
  • DRY from Pure Oxygen (O2)

 

(2)   Historically, the Deal-Grove Model (DGM ) was the 1st to find widespread acceptance regarding  the thermal oxidation process. See  http://en.wikipedia.org/wiki/Thermal_oxidation and http://en.wikipedia.org/wiki/Deal-Grove_model  for more details.

However, the original DGM did not explain or fit all the experimental data.

 

(3)   The DGM was refined later with the addition of the Massoud Model (MM) for thin oxides and also the addition of the Doping Acceleration Model (DAM). On-line calculators exist with these refinements:

See  http://www.lelandstanfordjunior.com/  for example.

 

(4)   Recently, the DGM was rebutted in several papers and a power law proposed that fits the oxidation data better than DGM from very thin to very thick, without add-on patches, and also explains many facts about thermal oxidation that the DGM failed to account for.  

 

(5)   Empirically, we see a much better fit to the data in our WETOX tube using the power law than the DGM. However, this data was collected using only solvent pre-oxidation cleans on lightly doped N-type (100) silicon wafer, for a dry oxidation at 1100 C.  The DGM is satisfactory for WET oxidations giving thick oxides. Note that the total recipe time is the sum of the oxidation step soak time, plus the recipe base time (which includes push/pull, ramp-up/down, stabilisations, etc. except the soak time). The breakdown is as follows:

 

T (C)

Base Time

Max Ox Time*

Max Ox Thickness (approximations)

C

minutes

minutes

Dry (nm)

Wet (nm)

900

155

325

  62

  536

1000

195

285

163

1036

1100

235

245

250

1387

 

 

                  (*) For a Maximum Total Time of 8 hrs = 480 minutes

Oxidation times smaller than 10 minutes should be avoided for repeatability.

(6)   To summarize dry oxidation rates are influenced by 1st order and 2nd order parameters:

  • 1st order = Temperature, Ambient (Wet or Dry)
  • 2nd order = Surface crystallographic orientation,  Doping Level, Pre-oxidation Cleans

 

(7)   Regarding electrical quality of the thermal oxides, the pre-oxidation cleanliness of the silicon surface is critical, as well as that of the oxidation tube, the oxidizing gases, the quartzware, the handling equipment, etc.  Lifetime killers such as Fe, Cu, Au, etc. must be in extremely low concentrations (<< 1ppb) in the Silicon.