Mechanical Property Characterization Of Hign-k Ultra-thin Nanofilms By In-situ Nanoindentation

As microelectronics is transitioning into deep nanotechnology,the feature size of the FET device—the gate length is shrinking,and the thickness of the gate oxide dielectric layer is correspondingly reduced,which resulting in a sharp increase in gate leakage current and oxide dielectric breakdown.It has become a technical bottleneck for further shrinking the size of semiconductor devices.In order to break through this problem,researchers are studying high-k gate dielectric materials such as HfO₂ and Al₂O₃.They have higher dielectric constants than SiO₂ and excellent electrical properties,which can increase transistor drive current and transistor switching speed.In the technology node where metal oxide transistor devices are moving toward smaller sizes,it is expected that high-k materials such as HfO₂ and Al₂O₃ will replace traditional materials such as SiO₂,SiO_xN_y and Si₃N₄ as the new gate oxide dielectric materials for application and development in the semiconductor industry.At present,most of the reports have studied the electrical and optical properties of high-k gate dielectric nanofilms,but few studies have focused on the mechanical properties of them,especially those thickness are under 50 nm scale.In the field-effect transistor,a nanodevice with high precision,the gate dielectric film is subjected to external forces during operation,which may cause distortion of various types of signals,causing a certain degree of deformation and cracking of the film,further affecting other physical properties of the device.Accurately characterizing the mechanical properties of the film is necessary,and the results play a very important guiding role in the use of high-k gate dielectric materials.In this paper,the nanoindentation technique is used to test the high-precision mechanical properties of Al₂O₃ and HfO₂ ultra-thin films grown by atomic layer deposition?ALD?technique.The mechanical properties of Al₂O₃ and HfO₂ thin films were characterized and analyzed by results of the elastic modulus,Combined with the surface morphology and microstructure.The main research contents and results are as follows:1.Five Al₂O₃ nanofilms with thickness of 20-60 nm were deposited by atomic layer deposition?ALD?respectively.The surface roughness and microstructure of the deposited Al₂O₃ nanofilms were characterized by three dimensional optical microscopy and transmission electron microscopy.The force-displacement curves captured by a hybrid scanning electron microscope/scanning probe microscope?SFM/SPM?system were analyzed based on Hertz's theory of contact mechanics for the elastic modulus of Al₂O₃nanofilms.The J.Hay model was used to eliminate the influence of the substrate on the measurement results,and the errors in the model due to the different shapes of the indenter were corrected.The results show that,ALD Al₂O₃nanofilms is amorphous,and the surface roughness does not increase with the increase of thickness.The elastic modulus do not show obvious small size effect,and the measured value is175±10 GPa.Under the same indentation ratio,the smaller the film thickness is,the more obvious the substrate effect is.The measurement results before and after the removal of the substrate effect were observed under the same indentation ratio?indentation depth h/film thickness t=0.75?.The overall trend was that the smaller the film thickness,the more obvious the substrate effect.2.Three sets of HfO₂ films which above 20 nm was deposited on a silicon substrate at 200,250,and 300?by atomic layer deposition technique.The surface morphology of the three samples was observed under a 3D optical microscope from Bruker.The element mapping of the HfO₂ coating was observed using a Titan G2 spherical aberration correction analysis transmission electron microscope.Finally,the nanoindentation tests of three groups of sample films were carried out by the Bruker AFM's Peakforce mode and the hybrid SFM/SPM system.The elastic modulus values were obtained by using Hertz contact theory and the improved de-basement effect model,and the measurement results of the two experimental equipments were compared and analyzed.The experimental results show that the HfO₂ materials grown in the deposition temperature that below 300°C are amorphous,and the surface roughness of the samples has no obvious change trend.The elastic modulus values of the HfO₂ films grown at different deposition temperatures are closer.The numerical results obtained by the two experimental methods are relatively stable.The elastic modulus values obtained by the Bruker AFM and the hybrid SFM/SPM system are 152±14 and 203±12 GPa,respectively.After the de-base effect treatment,the calculation results of the hybrid SFM/SPM system have better corrections,which is closer to the reference value from existing research results.