Specific Process Knowledge/Thin film deposition/ALD2 (PEALD)

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ALD - Atomic layer deposition

Picosun R200 PEALD, positioned in cleanroom F-2.

The ALD2 (atomic layer deposition) tool from Picosun R200 with plasma capability is used to deposit a very thin layer of Al₂O₃, TiO₂ (amorphous or anatase), SiO₂, HfO₂, TiN and AlN.

Each process is using two different precurcors. 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 precurcor is removed from the chamber before the next one is introduced. In that way the ALD layer will be deposited atomic layer by atomic layer.

In order to ensure that the ALD reactor has the same temperature eveywhere, it has a dual chamber structure. The inner chamber is the ALD reactor with the sample holder, 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). The IMS is connected to a nitrogen carrier gas line.

When the reactor chamber is heated up or cooled down, it will take some time before the sample holder and the sample reach 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 percursors pulse time is controlled using special ALD valves, that allow very short precursors pulses to be introduced into the ALD reactor and a 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. The pump is located in the basement.

The liquid precursors (TMA, TiCl₄ and H₂O) are located in the cabinet below the ALD chamber. When the TMA and TiCl₄ precursors are not in use, the manual valves have to be closed. 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 or a number of smaller samples. Samples are loaded manually into the sample holder by use of a tweezer.

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:

ALD Picosun R200 info page in LabManager,

Process information

• Standard recipes on the ALD tool
• Advanced recipes involving fabrication of multilayers
• Al₂O₃ deposition using ALD
• TiO₂ deposition using ALD

Equipment performance and process related parameters

Equipment		ALD2 (PEALD)
Purpose	ALD (atomic layer deposition) of	Al2O3 TiO2 (amorphous or anatase) SiO2 HfO2 TiN AlN
Performance	Deposition rates	Al2O3: ~ 0.075 - 0.097 nm/cycle (Using the "Al2O3" recipe, depending on the temperature) TiO2: 0.041 - 0.061 nm/cycle (Using the "TiO2" recipe, depending on the temperature)
	Thickness	Al2O3: 0 - 100 nm
Process parameter range	Temperature	Al2O3: 150 - 350 oC
	Precursors	TMA TiCl4 H2O O3 O2
Substrates	Batch size	Samples and single wafers are loaded through the load lock 100 mm and smaller are loaded on a carrier plate (150 mm) 150 mm or 200 mm wafer don't need the carrier plate Up to 5 wafers when doing thermal ALD of oxides wafer size 100 mm, 150 mm and 200 mm
	Allowed materials	Silicon Silicon oxide, silicon nitride Quartz/fused silica Al, Al2O3 Ti, TiO2 Other metals (use dedicated carrier wafer) III-V materials (use dedicated carrier wafer) Polymers (depending on the melting point/deposition temperature, use carrier wafer)