Study On The Self Forming Barrier Layer Of Copper Alloy And Its Performance Improvement

Copper has been extensively accepted as an advanced interconnect material in ultra-large-scale integrated?ULSI?devices because of the better electromigration resistance and lower resistivity.Unfortunately,Cu inter-diffuses easily with dielectric materials such as SiO₂ even at low annealing temperature which results in the deterioration of the device performance.So it is necessary to insert a diffu sion barrier to prevent the inter-diffusion.As the device's critical dimensions are scaled down to nanometer scale,the traditional diffusion barriers lead to a significant increase in the resistivity of the Cu interconnects.So it is essential to find an ultrathin Cu diffusion barrier which displays low resistivity.However,it is often difficult to achieve with the current technology.To address this problem,a barrier-less or barrier-free Cu-alloy metallization process has been proposed for the fabrication of Cu interconnects.In this study,Cu?X?films?M=V?Co?C etc.?were deposited by magnetron sputtering with optimizing parameters.The effects of process parameters on the diffusion barrier properties and thermal stability of copper alloy interconnect systems are analyzed from three aspects: the optimization of the process parameters,the doping of the alloys and the improvement of the properties of small molecules.The research results could provide a guideline for the design and the development of new materials for Cu interconnects of integrated circuits.Effects of the Sputtering parameters,the alloying content and the annealing conditions on the texture of Cu?V?films and the thermal stability of Cu?V?interconnection system were investigated.The?111?texture of the copper alloy films,as the increase of sputtering power,sputtering pressure and the target base distance increases first and decreases subsequently.When the sputtering power is 90 W,the sputtering pressure is 0.5 Pa and the distance between the target and the substrate is 60 mm,the Cu?111?texture of Cu?V?alloy film is the most obvious and the Cu?V?system has the best diffusion barrier property and thermal stability.The?111?texture increases with the increase of annealing temperature.The influence of alloy content on the?111?texture of Cu?V?thin films which sputtered on SiO₂/Si substrate has been studied.The?111?texture increases with the increase of the alloy content.The choice of the doping concentration should also consider the influence of the resistivity.In the technology of self-forming diffusion barrier of copper alloy,the field assisted annealing process is introduced.In the ordinary vacuum annealing process,a certain negative voltage is applied.Negative bias will provide more energy to the diffusion of copper alloy elements to the interface between the film and the substrate.Compared with ordinary annealing at the same annealing temperature,the alloying elements at the interface are increased after field assisted annealing.The thickness and quality of the self-forming diffusion barrier are improved.As the experimental results,the field annealing process has a positive effect on improving the diffusion barrier property and the thermal stability of the system,reducing the resistivity of the film and improving the conductivity of the system.The effects of different alloying elements on the diffusion barrier properties and thermal stability of Cu?M?/SiO₂/Si interconnect system were analyzed.The potential possibility of Zr as alloying elements was evaluated.After annealing,Zr atoms can diffuse to the Cu/SiO₂ interface and form an effective ZrO₂ barrier layer,can effective block of Cu to the direction of the dielectric layer diffusion.The interfacial adhesion between Cu film and SiO₂ substrate was significantly improved.The thermal stability of Cu/SiO₂ thin film system is improved.The application of Co element in the self-forming barrier of copper alloy was proposed.After annealing at 500?,In Cu?Co?/SiO₂/Si system,no Cu3 Si phase compounds with high resistance were detected.Co elements precipitate at the surface of the thin film and the interface between the film and the substrate,forming a Co enriched self-forming barrier with a thickness of about 15-20 nm,which has a good blocking effect on inhibiting the diffusion of copper and silicon.In addition,the resistivity of Cu?Co?alloy film can still keep low value after annealing at 500?.Cu?Co?alloy thin film has great application prospect in the future to improve the reliability of copper metal interconnect system.The properties of Cu?V?alloy films were investigated to evaluate its potential use as self-forming diffusion barrier in copper metallization.After annealed at 500 °C,the resistivity of the Cu?V?films reduced to 3.1?W·cm,there is no obvious increase in resistivity.XRD suggest that Cu alloy film has preferential?111?crystal orientation and no extra peak corresponding to Cu and Si even after annealed at 500 °C.After annealing,the interface of Cu?V?/SiO₂/Si multilayer system is clearly defined.V atoms are observed at the surface of the Cu?V?films and the interface of the Cu?V?and SiO₂/Si.A self-formed thin layer is observed at the interface between Cu alloy and the SiO₂/Si substrate,which hinders the interaction between Cu thin film and silicon dioxide substrate.After annealing,the MOS capacitor structure still has low leakage current.Adding small amounts of V to Cu film can improve the barrier performance and thermal stability compared with pure Cu contact s ystems.The Cu?V?alloy system has been greatly improved by the addition of C and N element in the Cu?V?thin film.The resistivity of copper alloy thin film can be reduced by adding some C atoms.At the same temperature,compared with the Cu?V?/SiO₂/Si system,the intensity of Cu?111?diffraction peak in Cu?V-C?/SiO₂/Si system increases.A large amount of doped metal elements and C elements are assembled at the interface between copper alloy and substrate,forming a dense diffusion barrier,resulting in Cu content change curve at the boundary of the interface is steep,the diffusion of Cu to the substrate is reduced.The introduction of N element significantly reduces the leakage of MOS capacitor and gets better interface characteristics.The diffusion barrier property and thermal stability of the alloy film with N element has been greatly improved at high temperature.