Horizontal high temperature rotating graphite drum furnace for ALD and LPCVD on particles and powders
Jonas Sundqvist Ph.D.
Conformal ALD and CVD on particles have been demonstrated numerous times using different technologies. ALD that in most cases have superior conformal properties as compared to PVD and CVD has been realized, for instance, using the following reactor technologies:
- Fluidized bed
- Rotating drum
- Vibrating belt
- Tubular reactors
At Fraunhofer IKTS Thin Film Group, an existing R&D LPCVD/ALD high-temperature Furnace platform has been equipped with a rotating particle processing drum. The modular high temperature rotating graphite drum furnace can be operated in LPCVD and ALD mode, i.e., continuous co-injections of precursors or time-resolved pulsing in ALD mode for conformal coating of particles and powders.
The furnace is designed for developing functional thin films, especially protective coatings and diffusion barrier for hard metal powders such as tungsten carbide (WC), cubic boron nitride (c-BN) that is widely used as an abrasive material and LiNi0,5Mn1,5O4 (LNMO) powder used in lithium ion battery cathode materials for operation at higher voltage (4.7 V).
The rotating drum has been manufactured in graphite allowing high temperature operation up to the maximum of 1050°C that the outer Inconel furnace with quartz insert can operate at. The ALD/LPCVD furnace have been qualified for two basic processes that are interesting for the applications mentioned above:
Process 1 : Titanium nitride (TiN) using TiCl4 and NH3 as precursors. This process is well known and understood for as well thermally activated ALD >300 °C and thermal CVD and pulsed CVD >400°C
Process 2 : Aluminium oxide (Al2O3) using either TMA or in-situ generated AlCl3 and water as precursors. AlCl3 can preferably be used in CVD process mode up to the maximum furnace temperatures whereas, TMA is employed for low temperature ALD in the range of 80 to 400 °C .
Results from the two processes will be presented, showing basic process window characteristics as well as elemental analysis and particle cross-section analysis.