Study On The Structure And Performance Of The ?-Al₂O₃ Films By Reactive Sputtering At Low Temperature

?-Al₂O₃ films exhibit good high-temperature hardness,low friction coefficient,good chemical inertness,dielectric and anti-permeation properties,which have great potential to be used in many applications such as machine processing industry,electronics and tritium permeation barriers.Nowadays,the single phase?-Al₂O₃ films are fabricated by chemical vapor deposition in commercial scale,but the high substrate temperature of over 1000?greatly limits the choice of substrate materials and results in poor adhesion,which has a negative impact on the practical performance of the?-Al₂O₃ films.However,due to the polymorphism of alumina,decreasing the substrate temperature is always accompanied by the formation of?or other metastable phases,and only the thermodynamically stable?-Al₂O₃ is considered the best to meet the application demands.Thus,the low temperature deposition of the?-Al₂O₃ film is a preferred purpose for many researchers.Considering the hysteresis effect during the deposition of alumina films in reactive sputtering,all film samples were prepared by radio frequency magnetron sputtering?RFMS?.The films deposited by sputtering the Al and?-Al₂O₃ targets at 550?on?-Al₂O₃ substrate exhibit?phase only,which indicates that the homogeneous substrate can suppress the formation of?phase.The film deposited from Al target at 550?on Si?100?is composed of?-??-and amorphous Al₂O₃ while that deposited from?-Al₂O₃ target at the identical temperature exhibits?-Al₂O₃ and amorphous,which is attributed to the?nucleus developed from the?-Al₂O₃ clusters.With the increase of the substrate temperature,the content of amorphous phase decrease and that of?-Al₂O₃ increase,which improves the mechanical property and the resistivity whereas the permittivity of the films has a tendency to decrease.In order to investigate the influence of the?-Al₂O₃ seeds on the formation of alumina films,the?-Al₂O₃ powder-ethanal suspension were prepared with different concentration and then dropped on the substrate.After the ethanal evaporated,the?-Al₂O₃ seeds were distributed on the substrate.The alumina films were deposited from Al target at a temperature in the range of500?⁶00?.The measurements show that increasing the concentration of the suspension can increase the distribution density of the?-Al₂O₃ seeds on substrate,which can enhance the promotion on the nucleation of?-Al₂O₃ and suppress the formation of?or other metastable phases.Therefore,the required temperature for the formation of single phase?-Al₂O₃ film is reduced.In view of the influences of the?-Al₂O₃ target and seeds on the formation of the alumina films,the isostructural?-Cr₂O₃ with corundum structure can induce the heteroepitaxial growth of the?-Al₂O₃ at low temperature.The Al_100-xCr_x?x=10,20,30?alloy targets were used to fabricate the Al-rich Al-Cr-O films at a substrate temperature in the range of 500?⁶00?.With the Cr content in the target increased,the proportion and distribution density of?-Cr₂O₃in films increase,which can enhance the promotion on the nucleation of the?-Al₂O₃ and reduce the required temperature for the formation of single phase?-type Al-Cr-O film.The increased content of?-Cr₂O₃ leads to an improvement of the mechanical property.The Al-Cr-O film deposited from Al₇₀Cr₃₀ target at 550?is composed of single phase?-?Al,Cr?₂O₃.The hardness of the?-?Al,Cr?₂O₃ films reaches to 28.3 GPa and the permittivity is 8.9.According to the assumption that the sputtered species developed form the?-Al₂O₃ target include?phase nucleus,we fabricated the Al/?-Al₂O₃ composite target?15 wt%?-Al₂O₃?.The alumina films were deposited from the Al/?-Al₂O₃ target at the deposition temperature in the range of 450?⁵50?.As the temperature increased,the content of the?and amorphous phases decreased and that of the?-Al₂O₃ increased significantly.Consequently,the mechanical property and the resistance of the films improved whereas the permittivity decreases.The nanocrystalline alumina film deposited at 550?displays single?-Al₂O₃.The hardness of the single phase?-Al₂O₃ film reaches to 23.8 GPa,which is similar to that of sintered alumina ceramic,and the permittivity is 7.6.