Specific Process Knowledge/Thermal Process/Furnace: Multipurpose annealing

From February 2024: RESIST PYROLYSIS FURNACE

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The Multipurpose annealing furnace

Multipurpose Annealing Furnace. Positioned in cleanroom B-1. Photo: DTU Nanolab internal

Boat with wafers for the Multipurpose Annealing Furnace. Photo: DTU Nanolab internal

The Multipurpose Annealing Furnace it made by ATV Technologie, and it was installed in the cleanroom in 2015.

The purpose of the Multipurpose Annealing Furnace is annealing and dry oxidation of different samples and resist pyrolysis. Annealing and resist pyrolysis can be done in vacuum or at atmospheric pressure, in a N₂ or H₂ atmosphere or a mixture of the two gasses.

All process gasses (except purge nitrogen) are heated, before they are introduced into the furnace at the door side.

Is is possible to change all quartz ware in the furnace (the furnace tube, the door sealing and the wafer boat). At the moment Nanolab has two different sets of quartz ware:

• Metal: Dedicated for different samples that cannot be RCA cleaned. Also samples with metals are allowed in the furnace, when this quartz set is mounted
• Resist pyrolysis: Dedicated for resist pyrolysis.

Please note that all new materials have to be approved by the Thin Film group (thinfilm@nanolab.dtu.dk) before they are allowed in the furnace.

The furnace tube is heated by use of 12 long heaters situated along the furnace tube and combined in three groups (top, bottom left and bottom right) and two flat heaters situated in the ends of the furnace tube. The this way the temperature will be very uniform everywhere in the furnace tube. The heating can be done very fast, up to 30 ^oC/min. For atmospheric pressure processes the maximum temperature is 1100 ^oC, and for vacuum processes the maximum temperature is 1050 ^oC.

The furnace body surrounding the furnace tube consists of a top and bottom half-shell. To cool down the furnace (when the temperature is below 800 ^oC), the top half shelf can be lifted up, and cooling fans will then flow air from the surroundings around the furnace tube to cool it down. However, for safety reasons, the cooling fans will not the activated when there is hydrogen in the furnace, and cooling will then be very slow.

It is not possible to open the furnace when the temperature is above 300 ^oC.

For resist pyrolysis, samples with different resist layers are heated up to maximum 1100 ^oC in a nitrogen atmosphere. At high temperatures carbon is formed by pyrolysis of the resist. In this way conductive structures can be made from a resist patterned sample. If oxygen from the air or from outgassing of the resist is present in the furnace, the resist layer will be removed, thus it is important to evacuate the furnace and flush it with nitrogen, before a high temperature for resist pyrolysis is obtained. Pyrolysis of a large amount of resist may also be a problem due to resist outgassing.

The user manual, technical information and contact information can be found in LabManager:

Furnace: Multipurpose annealing

Process information

• Oxidation: look at the Oxidation page
• Annealing: look at the Annealing page
• Results from the Multipurpose Anneal Furnace acceptance test
• Pyrolysis

Overview of the performance of the ATV furnace and process related parameters

Purpose		Dry oxidation of silicon Annealing in N2, H2 or a mixture of the two gasses Pyrolysis of different resists
Performance	Film thickness	Dry oxidation: 50 Å to ~200 nm SiO2 (it takes too long to grow a thicker oxide layer)
Process parameter range	Process Temperature	No vacuum: 25 oC - 1100 oC Vacuum: 25 oC - 1050 oC
	Process pressure	1 atm Vacuum down to ~0.1 mbar (depends on gas flow)
	Gasses on the system	N2: 20 slm O2: 10 slm H2: 5 slm (max 2 slm for vacuum processes) N2 mix : 10 slm (for H2-N2 gas mixture)
Substrates	Batch size	1-30 50 mm, 100 mm or 150 mm wafers per run 1-50 200 mm wafers per run (not possible with all quartz sets) Smaller samples (placed on Si carrier wafers)
	Substrate materials allowed	Depends on the quartz set