A correlation study of layer growth rate, thickness uniformity, stoichiometry, and hydrogen impurity level of ALD grown HfO2 thin films

Hafnium oxide was deposited from tetrakis(dimethylamino)hafnium (TDMAHf) and water by atomic layer deposition (ALD) on heated 400 Si wafers covered with native oxide in the temperature range from 100 C to 350 C. Optimized self-limiting ALD reaction and smallest hydrogen impurity level have been realized for a substrate temperature of 300 C. The stoichiometry of deposited films and hydrogen impurity level were measured by elastic recoil detection analysis. The hafnium to oxygen ratio showed the expected 1:2 value. Besides hydrogen, no other impurities could be detected. Furthermore, a strong correlation between the growth rate per cycle (GPC), film uniformity and level of hydrogen impurities was observed. Based on this result, the easily accessible GPC can be used as a first indication for the hydrogen impurity level in ALD grown thin films. Furthermore, the characterization of the crystal structure showed the appearance of some crystallites in an amorphous matrix already for a growth temperature of 250 C and a pure crystalline layer at a growth temperature of 350 C. The increased crystallinity with increasing growth temperature was attributed to a higher seed concentration and a constant crystal size.