Study on the Structure and Performance of the α-Al2O3 Films by Reactive Sputtering at Low Temperature

Author:Cheng Zuo Tian

Supervisor:zhou ke zuo qiu wan qi


Degree Year:2019





α-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 phaseα-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 theα-Al2O3 films.However,due to the polymorphism of alumina,decreasing the substrate temperature is always accompanied by the formation ofγor other metastable phases,and only the thermodynamically stableα-Al2O3 is considered the best to meet the application demands.Thus,the low temperature deposition of theα-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 andα-Al2O3 targets at 550℃onα-Al2O3 substrate exhibitαphase only,which indicates that the homogeneous substrate can suppress the formation ofγphase.The film deposited from Al target at 550℃on Si(100)is composed ofα-、γ-and amorphous Al2O3 while that deposited fromα-Al2O3 target at the identical temperature exhibitsα-Al2O3 and amorphous,which is attributed to theαnucleus developed from theα-Al2O3 clusters.With the increase of the substrate temperature,the content of amorphous phase decrease and that ofα-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 theα-Al2O3 seeds on the formation of alumina films,theα-Al2O3 powder-ethanal suspension were prepared with different concentration and then dropped on the substrate.After the ethanal evaporated,theα-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 theα-Al2O3 seeds on substrate,which can enhance the promotion on the nucleation ofα-Al2O3 and suppress the formation ofγor other metastable phases.Therefore,the required temperature for the formation of single phaseα-Al2O3 film is reduced.In view of the influences of theα-Al2O3 target and seeds on the formation of the alumina films,the isostructuralα-Cr2O3 with corundum structure can induce the heteroepitaxial growth of theα-Al2O3 at low temperature.The Al100-xCrx(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 ofα-Cr2O3in films increase,which can enhance the promotion on the nucleation of theα-Al2O3 and reduce the required temperature for the formation of single phaseα-type Al-Cr-O film.The increased content ofα-Cr2O3 leads to an improvement of the mechanical property.The Al-Cr-O film deposited from Al70Cr30 target at 550℃is composed of single phaseα-(Al,Cr)2O3.The hardness of theα-(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 theα-Al2O3 target includeαphase nucleus,we fabricated the Al/α-Al2O3 composite target(15 wt%α-Al2O3).The alumina films were deposited from the Al/α-Al2O3 target at the deposition temperature in the range of 450℃550℃.As the temperature increased,the content of theγand amorphous phases decreased and that of theα-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 singleα-Al2O3.The hardness of the single phaseα-Al2O3 film reaches to 23.8 GPa,which is similar to that of sintered alumina ceramic,and the permittivity is 7.6.