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 is used to deposit very thin and uniform layers of different materials, by use of thermal ALD or PEALD (Plasma Enhanced Atomic Layer Deposition).

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

When a sample is loaded into the reactor chamber, it will take some time before it reaches the desired temperature. Thus, it is important to include a temperature stabilization time in the deposition recipes.

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

Different precursor lines are connected to the reactor chamber through separate precursor inlets. At the moment the available precursors are TMA, TiCl₄, SAM24, TEMAHf, H₂O and NH₃, and soon O₃ will also be available. These precursor lines are all purged with a constant flow of nitrogen.

The liquid precursor sources TMA, TiCl₄ and H₂O are stored in bottles located in a side cabinet on the left side of the machine. When the TMA and TiCl₄ precursors are not in use, the manual valves have to be closed. The powder precursors SAM24 and TEMAHf are stored in bottles located in a big cabinet below the ALD chamber. These precursors are heated by heating jackets, and users should not open and close the manual valves. O3 is generated by use of an ozone generator that is located in the E-rack at the right side of the machine.

A remote plasma generator is connected to the upper part of the reactor chamber. Different precursor gases are connected to this plasma generator through the same gas inlet. At the moment the available plasma precursor gases are N₂, O₂ and NH₃, and soon H₂/N₂ will also be available. The plasma gas inlet is constantly purged with argon. The plasma gasses can also be used as precursors for thermal ALD if the power to the plasma generator is not turned on.

The plasma generator is separated from the reactor chamber by a plasma cone (or chamber lid). The argon flow through the plasma gas inlet ensures that the plasma cone remains clean.

The plasma cone is not heated, and thus is will affect the temperature uniformity in the reactor chamber, and it will affect the gas flows and increase the necessary purge time. For that reason it is possible to mount a thermal lid between the plasma cone and the reactor chamber. However, it is quite time consuming to install the thermal lid as it requires that the machine is cooled to room temperature and vented. Furthermore, it is not possible to run plasma processes with the thermal lid installed.

The precursor pulse time is controlled by special ALD valves that allow very short precursor pulses to be introduced into the ALD reactor chamber and at the same time allow a constant nitrogen or argon flow. Thus, nitrogen and argon are always flowing through the ALD valves into the chamber, independent on whether a precursor pulse is introduced or not.

At the moment it is possible to deposit Al₂O₃, TiO₂, HfO₂, SiO₂, AlN and TiN in the ALD. In order to deposit good quality nitride layers with low sheet resistance, the amount of oxygen has to be very low. Thus, the ALD reactor chamber has to be passivated before nitride depositions can be done, and oxides and nitrides cannot be deposited at same time.

Samples are loaded through a load lock. 6" and 8" wafers can be loaded directly in the load lock, while 4" wafers and smaller samples have to be placed on a 6" carrier plate or a 6" silicon dummy wafer with an etched recess. It is only possible to load one wafer or carrier plate at a time by use of the load lock.

The plasma cone is opened and closed, when samples are transferred between the load lock and the reactor chamber. Two buttons on the load lock are used to insert and retract the load lock arm from the reactor chamber. A window on the front side of the machine makes it possible to keep an eye on the reactor chamber and the sample during loading and unloading.

It is also possible to load a minibatch directly holder into ALD through a door on the left side of the reactor chamber. However, a training is needed in order to use the minibatch holder, and for nitride depositions the minibatch holder cannot be used as it requires that the machine is vented, and thus a possible nitride passivation will be ruined. Furthermore, the minibatch holder is not useful for plasma process, as the ALD material will only be deposited on the top sample(s).

The ALD is controlled by use of a computer with a touch screen that is situated next to the machine.

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,!! ALD1 skal ændres når ALD2 siden bliver klar

Process information

• Standard recipes on the ALD2 tool
• Advanced recipes involving fabrication of multilayers done on ALD1]
• Al₂O₃ deposition using ALD1
• TiO₂ deposition using ALD1

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). Result from ALD1 TiO2: 0.041 - 0.061 nm/cycle (Using the "TiO2" recipe, depending on the temperature). Result from ALD1
	Thickness	Al2O3: 0 - 100 nm
Process parameter	Temperature	Al2O3: 150 - 350 oC
	Precursors	TMA - Trimethylaluminium TiCl4 - Titaniumtetrachloride H2O - Water O3 - Ozone NH3 - Ammonia SAM24 - Bis(diethylamono)silane TEMAHf - Tetrakis(ethylmethylamino)hafnium
	Plasma precursors	N2 O2 NH3 (4% H2 in N2) will be installed later
Substrates	Batch size	Small 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)