Preparation Of Metal Carbide (W-C,Ta-C) Thin Films And Study On Their Microstructure And Electrical Properties

When the metal-oxide-semiconductor field effect transistor（MOSFET）was first manufactured in the 1960s,aluminum（Al）was used as the gate electrode.However,due to the low melting point of Al,it was not suitable for the process,so it was replaced by n⁺doped polycrystalline silicon.However,with the scaling of MOSFET,a series of new problems appeared,such as boron penetration,gate depletion and Fermi level pin-ning.As a result,polycrystalline silicon electrodes are no longer suitable for electrodes.Therefore,in order to solve the above problems,metal gate must be used as the elec-trode of MOSFET.Metal carbide is one of the most promising candidate materials for metal gate because it has excellent properties and can meet the requirements of metal gate.In this paper,W-C and Ta C thin films were deposited on Si（100）and Si/Si O₂substrates by non-reactive magnetron co-sputtering at room temperature and argon at-mosphere from pure W,Ta and C targets simultaneously.Then,the prepared sample is subjected to heat treatment under high vacuum in order to improve the crystallinity of the film.The main purpose of this work is to study the effects of deposition methods,film thickness and annealing process on the film structure and electrical properties.When all the samples are prepared,they are measured。The measurements include,the crystal structure of the thin film is characterized by grazing incidence X-ray diffrac-tion（GIXRD）.The surface morphology and thickness of the film were characterized by scanning electron microscope（SEM）.The surface morphology and roughness of the film were measured by atomic force microscope（AFM）.X-ray photoelectron spectros-copy（XPS）is used to characterize the chemical bond state and chemical percentage of elements in the film.The chemical structure of the sample was measured using a Raman spectrometer（Raman）and the present compounds were identified.The resistivity of the thin film layer was measured with a four-point probe.First of all,for W-C thin films,the experimental results show that the growth rate of the thin films is about 5.46 nm/min,and the thin films grows like spherical structure.When the annealing temperature is 700℃and 800℃respectively,and the atomic ratio is W/C=1.18,hexagonal phase W₂C is formed,and the grain size of the film is 8.1 nm and 11.7 nm respectively at these two temperatures.The resistivity of the film is rela-tively high,which may be caused by the excessive carbon in the film（as can be seen from Raman spectrum）not bonding with tungsten atoms.Secondly,for Ta-C thin films,the experimental results show that the growth rate of the thin films is about 6.7 nm/min,and the thin films are growth like spherical.The atomic percentage of elements in the film is very sensitive to the deposition power,and even a small increase in the deposition power of Ta will lead to an increase in Ta content.However,the slight change of Ta content does not lead to the change of film structure and surface morphology.The annealing temperature did not change the microstructure of the film,but resulted in slight changes in the grain size（ranging from 7.0 nm to 9.1nm）and surface roughness of the film.The resistivity of the deposited Ta C film shows randomness with the change of annealing temperature,which may be caused by the deposition method.However,when the thickness increases from 79.2 nm to 134 nm,the resistance of the film decreases first and then increases.The minimum resistivity of the film is 235.2μΩ.cm,which was occurs at the thickness of 79.2 nm.Finally,the depos-ited Ta C film shows good thermal stability and low enough resistivity,which can be used for gate electrode applications.