Aluminum nitride thin films deposited by hydrogen plasma enhanced and thermal atomic layer deposition

Plasma enhanced atomic layer deposition (PE-ALD) of aluminum nitride (AlN) thin films often utilizes NH3 or a mixture of N2 and H2 as a plasma source. However, the possibility of separating the activation step from the nitridation step by using H2 alone as the plasma source has never been explored. In this paper, we study the deposition of AlN by PE-ALD by using trimethylaluminum, H2 plasma and NH3 for deposition temperatures below 400 °C. The self-limiting ALD growth was achieved between 325 °C and 350 °C. As a comparison, AlN was also deposited by thermal ALD (T-ALD), where surface reactions between TMA and NH3 occurred with reasonable growth rates only at temperatures above 400 °C. The PE-ALD films showed low oxygen (1.5 at.%) and carbon contaminations (1 at.%). The T-ALD films contained carbon (5 at.%) mainly attributed to the presence of C Al bonds that was insignificant in PE-ALD films. The flow rate of H2 used in H2 plasma was found to have a significant impact on the preferred orientation of AlN films, where higher H2 flow rate promoted the (002) preferred orientation. Besides, the electrical resistivities were probed to be 108 Ω cm, as expected in an insulating material. As an example, AlN was used to infiltrate porous sintered silicon carbide (SiC). Both AlN deposited by PE-ALD and by T-ALD operating with exposure mode deposited at 400 °C were attempted. Even though, there is a greater risk for TMA precursor to decompose at 400 °C, infiltration of AlN was more successful by T-ALD operating with exposure mode.