ALD1

Feedback to this page: click here

This page is written by DTU Nanolab internal

ALD - Atomic layer deposition

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. The layer can be up to 100 nm thick, see the table below.

Each process uses 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 turn. Between each precursor pulse, the chamber is purged with nitrogen. All reactions must take place on the sample surface; therefore, it is crucial that each precursor is removed from the chamber before the next one is introduced. In that way, materials can be deposited atomically, layer by layer, by ALD.

To ensure the ALD reactor maintains a uniform temperature throughout, it features a dual-chamber structure. The inner chamber is the reactor chamber, and the outer chamber is a vacuum chamber that isolates the reactor from room air. The space between the two chambers is referred to as an intermediate space (IMS), which is constantly purged with nitrogen. A sample holder is placed in the reactor chamber.

When the reactor chamber is heated or cooled, it will take some time for the sample holder and the sample to reach the desired temperature. Therefore, it is essential to incorporate a temperature stabilization period into 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 enable the introduction of very short precursor pulses into the ALD reactor while maintaining 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 (usually H₂O, TMA, TEMAHf, and TiCl₄) can be connected at the same time. Ozone is generated using an ozone generator 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 using 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

Recipes

Process details

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
Performance	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. The deposition of thicker layers is not allowed, as this would occupy the machine for an extended period, thereby reducing its availability to fewer users. Long depositions also cause issues, and with flakes and particles, this means that the chamber and the pump line will need to be cleaned or replaced quite often. Furthermore, the delivery time on precursors is usually quite long. When creating a sample design, it is advisable to avoid steps that require depositing thicker layers than 100 nm using ALD. Alternatively, consider whether 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
Process parameter range	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 1-3 200 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)