Specific Process Knowledge/Thin film deposition/ALD Picosun R200

ALD1

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ALD - Atomic layer deposition

ALD1, positioned in cleanroom F-2.

The ALD1 (Picosun R200 ALD) tool is used to deposit a very thin layer of Al₂O₃, TiO₂ (amorphous or anatase) and HfO₂ on different samples. Layer can be up to 100 nm thick, see the table below.

Each process is using two different precursors. The reaction takes place in cycles. During each cycle, a very short pulse of each precursor is introduced into the ALD reaction chamber in turns, and in-between each precursor pulse the chamber is purged with nitrogen. All reactions have to take place on the sample surface, thus it is very important that each precursor is removed from the chamber before the next one is introduced. In that way, materials can be deposited atomic layer by atomic layer by ALD.

In order to ensure that the ALD reactor has the same temperature everywhere, it has a dual chamber structure. The inner chamber is the reactor chamber, and the outer chamber is a vacuum chamber that is isolating the reactor from room air. The space between the two chambers is called an intermediate space (IMS), and this is constantly purged with nitrogen. A sample holder is placed in the reactor chamber.

When the reactor chamber is heated up or cooled down, it will take some time before the sample holder and the sample reaches the desired temperature. Thus, it is important to include a temperature stabilization time in the process recipes.

The ALD deposition takes place in the reactor chamber. All precursor and nitrogen carrier gas lines are connected to the reactor chamber through separate gas lines. The precursor pulse time is controlled using special ALD valves, that allow very short precursors pulses to be introduced into the ALD reactor and at the same time allow a constant nitrogen purge.

The ALD reaction takes place under vacuum, thus a vacuum pump is connected to the bottom of the ALD reactor chamber. The pump is located in the basement.

The liquid precursors (H₂O, TMA, TiCl₄ and TEMAHf) are located in the cabinet below the ALD chamber. When these precursors are not in use, the manual valves have to be closed. Only four of the precursors (normally ₂O, TMA, TEMAHf and TiCl₄) can be connected at the same time. Ozone is generated by use of an ozone generator that is located on the side of the machine.

It is possible to change the sample holder, so that ALD deposition can take place on different samples, e.g. a small wafer batch (up to five wafers at a time) or a number of smaller samples. Samples are loaded manually into the sample holder by use of a tweezer. However, for some materials the uniformity will only be good for the top sample(s) in a minibatch holder.

A short presentation with some information about the ALD tool can be found here.

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

ALD1 info page in LabManager,

Process information

• Standard recipes on the ALD 1 tool
• Advanced recipes involving fabrication of multilayers
• Al₂O₃ deposition using ALD 1
• TiO₂ deposition using ALD 1
• ZnO deposition using ALD 1. Obsolete - ZnO should now be deposited in ALD2
• Al-doped ZnO (AZO) deposition using ALD 1. Obsolete - AZO should now be deposited in ALD2
• HfO₂ deposition using ALD 1

Equipment performance and process related parameters

Equipment		ALD1
Purpose	ALD (atomic layer deposition) of	Al2O3 (amorphous) TiO2 (amorphous or anatase) HfO2 (polycrystalline)
Performance	Deposition rates	Al2O3: ~ 0.075 - 0.097 nm/cycle (Using the "Al2O3" recipe, depending on temperature) TiO2: 0.041 - 0.061 nm/cycle (Using the "TiO2" recipe, depending on temperature) HfO2: 0.0827 nm/cycle
	Thickness	Al2O3: 0 - 100 nm TiO2: 0 - 100 nm HfO2: 0 - 100 nm As the purpose of ALD 1 is to deposit very thin and uniform layers, the allowed deposition thickness is limited to 100 nm, and it is not allowed to do more depositions on the same sample(s) to deposit thicker layers than 100 nm. Deposition of thicker layers is not allowed, because this will occupy the machine for long time and thus make it available for less users. Long depositions also cause issues and with flakes and particles, which means that the chamber and the pump line will have to be cleaned or changed quite often. Furthermore, the delivery time on precursors is usually quite long. So when you make a sample design, you should avoid steps, where you need to deposit thicker layers than 100 nm with ALD, or you can consider, if the same material can be deposited using other machines in the cleanroom.
Process parameter range	Temperature window	Al2O3: 150 - 300 oC Amorphous TiO2: 100 - 150 oC Anatase TiO2: 300 - 350 oC HfO2: 150 - 350 oC
	Precursors	TMA TiCl4 H2O O3 O2 - Not available at the moment TEMAHf
Substrates	Batch size	1 200 mm wafer 1-5 100 mm wafers 1-5 150 mm wafers Several smaller samples
	Allowed materials	Silicon Silicon oxide, silicon nitride Quartz/fused silica Al, Al2O3 Ti, TiO2 Other metals (use dedicated carrier wafers) III-V materials (use dedicated carrier wafers) Polymers (depending on the melting point/deposition temperature, use carrier wafers)