Specific Process Knowledge/Thermal Process/Oxidation

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Oxidation

At DTU Nanolab we have seven furnaces for thermal oxidation of silicon samples: Boron Drive-in + Pre-dep furnace (A1), Gate Oxide furnace (A2), Phosphorous Drive-in furnace (A3), Anneal-oxide furnace (C1), Anneal-Bond furnace (C3), Al-Anneal furnace (C3) and Multipurpose Annealing furnace.

Thermal oxidation can take place either by a dry process or by a wet process, depending on what furnace that is used for the oxidation. The film quality for a dry oxide is better than the film quality for a wet oxide with regards to density and dielectric constant. However, the oxidation rate is slow for dry oxidation.

• Dry oxidation is used to grow 5 nm - 300 nm of oxide in the furnaces: A1, A2, A3, C1, C3, C4 and Multipurpose Anneal furnace.
• Wet oxidation is used to grow up to 3 µm of oxide in the furnaces: A1, A3, C1 and C3.

Wafers with oxide layers thicker than >3 µm can normally not be made in the cleanroom and will have to be bought (but check the wafer shop first - there might be some on stock). It is NOT allowed to oxidize the same wafers two time to get a thicker layer than 3 µm without approval

Thermal oxidation can done at temperatures up to 1150 C (but only 1100 C in C1 furnace and 1050 C the Multipurpose Anneal furnace). At these very high temperatures, the quartz tube in the furnaces might start to deform, so therefore the oxidation times are restricted:

• Maximum allowed oxidation time at 1150 C: 8 hours
• Maximum allowed oxidation time at 1100 C: 23 hours (this will result in ~3 um wet oxide)

The standard recipes, quality control limits and results for the Boron Drive-in + Pre-dep furnace (A1) and the Phosphorus Drive-in furnace (A3) can be found here:

• Standard recipes, QC limits and results for the Boron Drive-in + Predep furnace (A1)
• Standard recipes, QC limits and results for the Phosphorus Drive-in furnace (A3)

The wet oxidation rates for the Anneal-Bond furnace (C1) can be found here:

• Wet oxidation in Anneal-oxide furnace (C1)

Standard recipes in the oxidation furnaces

The steps in the standard oxidation recipes in the A-stack furnaces (A1, A2 and A3) and the C-stack furnaces (C1, C3 and C4) can be found here:

• Specific Process Knowledge/Thermal Process/Oxidation/Standard oxidation recipes

Comparison of the seven oxidation furnaces

	Boron Drive-in + Pre-dep furnace (A1)	Gate Oxide furnace (A2)	Phosphorous Drive-in furnace (A3)	Anneal Oxide furnace (C1)	Anneal Bond furnace (C3)	Multipurpose Annealing furnace
Generel description	Dry and wet oxidation. Boron pre-deposition and boron drive-in of boron are also done in the furnace.	Dry oxidation of gate oxide and other very clean oxides.	Dry and wet oxidation. Phosphorous drive-in is also done in the furnace.	Dry and wet oxidation of 100 mm and 150 mm wafers. Oxidation of new wafers without RCA cleaning. Oxidation and annealing of wafers from the LPCVD furnaces and PECVD4.	Dry and wet oxidation and annealing of wafers from Wafer Bonder 02 and from PECVD4 and PECVD3.	Dry oxidation and annealing of almost all materials.
Oxidation method	Dry: O2 Wet: Torch	Dry: O2	Dry: O2 Wet: Torch	Dry: O2 Wet: Steamer	Dry: O2 Wet: Bubbler	Dry: O2
Annealing gas	N2	N2	N2	N2	N2	N2 H2
Process temperature	900 oC - 1150 oC	900 oC - 1150 oC	900 oC - 1150 oC	900 oC - 1100 oC	900 oC - 1150 oC	Vacuum: 20 oC - 1050 oC No vacuum: 20 oC - 1100 oC
Substrate and batch size	1-30 50 mm wafers 1-30 100 mm wafers	1-30 50 mm wafers 1-30 100 mm wafers	1-30 50 mm wafers 1-30 100 mm wafers	Small samples on a carrier wafer, horizontal 1-30 50 mm wafers 1-30 100 mm wafers 1-30 150 mm wafers	Small samples on a carrier wafer, horizontal 1-30 50 mm wafers 1-30 100 mm wafers	1-30 50 mm, 100 mm or 150 mm wafers 1-50 200 mm wafers Small samples on a carrier wafer, horizontal
Allowed materials	All wafers have to be RCA cleaned, except boron pre-doped wafers from the same furnace.	All wafers have to be RCA cleaned.	All wafers have to be RCA cleaned, except phosphorous pre-doped wafers from furnace A4.	All processed wafers have to be RCA cleaned, except wafers from LPCVD furnaces and PECVD4.	All processed wafers have to be RCA cleaned, except for wafers from Wafer Bonder 02 and from PECVD4 and PECVD3.	Depends on the furnace quartz set: Metal: Almost all materials, permission is needed Resist pyrolysis

Oxidation curves

Color chart for oxide/nitride thickness

• View oxide/nitride color vs thickness/angle

Generic calculator for wet/dry oxide thickness calculation

The following links give an approximate oxide time/thickness based on a general formula:

• Know thickness - calculate oxidation time

• Know time - calculate oxide thickness

Deal-Grove parameters

By Kasper Reck-Nielsen February 2015

The following table contains linear and parabolic parameters for use in the Deal-Grove model for thermal oxidation. The parameters are obtained a least squares fit to data available in the furnace logbooks. Information on wafer orientation and doping concentration, which is not available in the logbooks, has not been included in calculating the parameters.

	Anneal Oxide			Anneal Bond			Boron Drive-in			Gate Oxide			Phosphor Drive-in
Recipe	B [µm2/h]	B/A [µm/h]	RMSE [nm]	B [µm2/h]	B/A [µm/h]	RMSE [nm]	B [µm2/h]	B/A [µm/h]	RMSE [nm]	B [µm2/h]	B/A [µm/h]	RMSE [nm]	B [µm2/h]	B/A [µm/h]	RMSE [nm]
DRY900	0.000408	0.107	Too little data	0.0660	0.272	31	0.000390	0.154	Too little data	0.0028	0.079	4 (limited data)	0.0507	0.884	Too little data
DRY1000	-	-	-	-	-	-	0.465	0.838	20	-	-	-	0.641	1.45	41
DRY1050	0.0111	0.526	27	-	-	-	0.0129	0.330	8	0.022	0.505	3 (limited data)	0.0134	0.362	6
DRY1100	0.020	0.930	10	-	-	-	0.0212	0.736	23	-	-	-	0.0313	0.553	14
WET950	-	-	-	-		-	0.0716	1.25	12	-	-	-	0.110	1.17	11
WET1000	0.192	1.54	44	-		-	0.192	1.80	29	-	-	-	0.195	2.49	22
WET1050	0.487	0.965	29	0.477	0.899	Too little data	0.455	1.33	16	-	-	-	0.448	1.73	12
WET1100	0.580	1.43	8	-	-	-	0.519	1.186	3	-	-	-	0.403	9.05	7

Wet Oxidation on <100>

The curves below are based on measurements in our specific furnaces and give more accurate results. We will still recommend to make minimum one test run if the thickness is very important.

• Wet oxidation
• 
  A1 Furnace <100>-Si Wet Oxidation
• 
  A3 Furnace <100>-Si Wet Oxidation

Dry Oxidation on <100> and <111> wafer

• Dry oxidation
• 
  Dry oxide on <100> wafer. The y-axis is in Å and the x-axis is in minutes.
• 
  Dry oxide on <111> wafer. The y-axis is in Å and the x-axis is in minutes.

Breakdown voltage measurements

Breakdown measurements have been down for A1 Boron Drive-in and Pre-dep furnace and the A3 Phosphorus drive-in furnaces in November 2021. The results can be found on this page:

• Specific Process Knowledge/Thermal Process/Oxidation/Breakdown voltage measurements