Specific Process Knowledge/Thermal Process/A1 Bor Drive-in furnace

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Boron Drive-in and Pre-dep furnace (A1)

Boron Drive-in and Pre-dep furnace (A1). Positioned in cleanroom B-1/ Photo: DTU Nanolab internal

The Boron Drive-in and Pre-dep furnace (A1) is a Tempress horizontal furnace for thermal oxidation of silicon wafers. Also boron pre-deposition/doping is done in this furnace. Furthermore, the furnace is used for boron drive-in after the pre-deposition or after boron ion implantation.

The furnace is mostly used for wet and dry thermal oxidation of silicon wafers. The oxidation recipes are named e.g. "WET1000" and "DRY1000", where "WET" or "DRY" indicates whether it is a wet or dry oxidation process, and the number indicates the oxidation temperature.

The purpose of the boron doping is to make conductive structures, etch stop layers etc. For pre-deposition of silicon wafers, boron-nitride source wafers are used as doping source. There are only a few source wafers available, i.e. it is not possible to dope an entire batch of 30 wafers, but both sides of the source wafers are available for doping. It is necessary to activate the source wafers before use by heating them for 1 hour at the temperature needed during the pre-deposition (but never at a temperatures lower than 1050 C). During the pre-deposition a boron phase layer is created on the silicon wafers. This layer can be removed in BHF, if argon is used instead of nitrogen for the pre-deposition (at temperatures higher then 1050 C), otherwise the wafers have to be oxidized before the BHF etch. When the boron phase layer has been removed, the wafers can go directly into the furnace again for a drive-in process with or without an oxide growth.

The Boron Drive-in and Pre-dep furnace is the top furnace tube in the furnace A-stack positioned in cleanroom B-1. The furnaces in the A-stack are the cleanest of all furnaces in the cleanroom. Please be aware of that all wafers have to be RCA cleaned before they enter the furnace, and please check the cross contamination information in LabManager, before you use the furnace. Before boron pre-deposition, also the source wafers and a dedicated carbide boat have to be RCA cleaned.

The user manual, quality control instruction and results, technical information and contact information can be found in LabManager:

Boron Drive-in and Pre-dep furnace (A1)

Process knowledge

• Oxidation: look at the Oxidation page
• Boron drive-in: look at the Dope with Boron page
• Boron doping: look at the Dope with Boron page.

Quality Control - Parameters and Limits

Quality control (QC) for the processes "Wet1050" and "Dry1050"

The QC procedure for the Boron Drive-in + Pre-dep furnace (A1) The newest QC data for wet and dry oxide QC Recipe: WET1050 DRY1050 H2 flow 3 slm 0 slm O2 flow 2 slm 5 slm Temperature 1050 oC 1050 oC Oxidation time 30 min 100 min QC limits Thickness Non-uniformity (both over a single wafer and over the boat) DRY1050 107.3 nm - 113.3 nm 3.2 % WET1050 298.2 nm - 305.5 nm 3.7 % Numbers from March 2020

Overview of the performance of the Boron Drive-in and Pre-dep furnace and some process related parameters

Purpose	Thermal oxidation of Si wafers Boron pre-deposition/doping of Si wafers Oxidation of boron phase layers Driving-in pre-deposited or ion-implanted boron	Thermal oxidation: Dry oxidation using O2 Wet oxidation using H2O vapour Boron pre-deposition/doping: Boron-nitride wafers are used as doping source. This is a solid doping source containing B2O3 Driving-in pre-deposited or ion-implanted boron Dry or wet oxidation recipes are normally used for this purpose
Performance	Film thickness	Dry oxide: ~ 0 nm - 300 nm (it takes too long to grow a thicker oxide) Wet oxide: ~ 0 nm - 3 µm (23 hours wet oxidation at 1100 oC for Si[100] wafers)
Process parameter range	Process Temperature	800-1150 oC
	Process pressure	1 atm (no vacuum)
	Gasses on the system	N2 O2 H2 (in a torch, H2 and O2 burns into H2O vapour for wet oxidation)
Substrates	Batch size	1-30 100 mm wafers (or 50 mm wafers) per run
	Substrate materials allowed	Silicon wafers (RCA cleaned) Boron-nitride source wafers for boron pre-deposition/doping