Specific Process Knowledge/Thermal Process/Furnace: Multipurpose annealing

Feedback to this page: click here

This page is written by DTU Nanolab internal

The Resist Pyrolysis furnace (from February 2024)

Resist Pyrosysis furnace. Positioned in cleanroom B-1. Photo: DTU Nanolab internal

Boat with wafers for the Resist Pyrolysis furnace. Photo: DTU Nanolab internal

The Resist Pyrolysis furnace it made by ATV Technologie, and it was installed in the cleanroom in January 2015.

In November 2024 the furnace was repaired by ATV Technologie. At the repair, the whole furnace body was changed, and all heaters were replaced. Also, the process exhaust flow was decreased by changing a valve in the exhaust line.

Until February 2024, the furnace was named "Multipurpose Anneal furnace", and then it became the "Resist Pyrolysis furnace".

The Resist Pyrolysis furnace is a research tool. It means, that it is mainly available for users working on certain research projects, especially in the Biomaterial Microsystems Group at DTU Nanolab.

The furnace is mainly being used for resist pyrolysis. It can also be used for annealing in nitrogen (N₂) (or forming gas, i.e. up to 4% H₂ mixed with N₂, but this has not been tested) and oxidation with oxygen (O₂), but O₂ is mostly used for cleaning of the furnace after resist pyrolysis processes.

For resist pyrolysis, samples with different resist layers are heated up to maximum 1050 ^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.

Process steps can run either at atmospheric pressure or in vacuum. A small N₂ or O₂ flow (up to 2 SLM) can be applied in vacuum steps.

The quartz parts in the furnace (the furnace tube, the door sealing and the wafer boat) can be changed, depending on what processes and samples the furnace is used for, but it has been decided that a quartz set for resist resist pyrolysis will be mounted in the furnace all the time. This limits the number of materials that are allowed in the furnace.

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

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

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. This ensures that the temperature will be very uniform everywhere in the furnace tube. The heating can be done very fast, up to 30 ^oC/min. The maximum allowed process temperature is normally 1050 ^oC, however up to 1100 ^oC without vacuum is possible. The maximum allowed process time at 1050 ^oC is 3 hours.

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 and not for processes with H₂), 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.

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

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

Resist Pyrolysis furnace

Process information

• Oxidation: look at the Oxidation page
• Annealing: look at the Annealing page
• Results from the Resist Pyrolysis furnace acceptance test
• Resist pyrolysis

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

Purpose		Pyrolysis of different resists Annealing in N2 Annealing in forming gas (up to 5% H2 mixed with N2) - Not tested Dry oxidation of silicon
Performance	Film thickness	Dry oxidation of silicon: 50 Å to ~200 nm SiO2 (it takes too long to grow a thicker oxide layer)
Process parameter range	Process temperature	No vacuum: Room temperature - 1100 oC - Normally maximum 1050 oC allowed Vacuum: Room temperature - 1050 oC Standby: Down to room temperature
	Process time	Maximum 3 hours at 1050 oC
	Process pressure	Atmospheric pressure Vacuum: Pressure down to ~0.1 mbar (gas flow dependent)
	Gases on the system	Atmospheric pressure: N2: 20 SLM - Maximum 10 SLM recommended (to protect the heaters) O2: 10 SLM H2: 5 SLM - Not allowed N2 mix: 10 SLM (for forming gas, i.e. up to 5% H2 mixed with N2) - Not tested Vacuum: N2: 2 SLM O2: 2 SLM H2: Not allowed N2 mix : Not allowed
Substrates	Batch size	1-30 50 mm, 100 mm or 150 mm wafers per run Smaller samples (placed horizotally on a Si carrier wafer)
	Substrate materials allowed	Normally only samples for resist pyrolysis approved by Nanolab