| Copper(Cu)has been proposed as a well-known material for metallization in Si-based semiconductor devices because of its low resistivity,high chemical stability,and excellent electromigration resistance.Nowadays,magnetron sputtering is widely used for Cu films deposition.Nevertheless,the degree of ionization of the sputtered particles is relatively low in conventional magnetron sputtering,which leads to poor film adhesion,low density,and void formation because of the shadowing effect.These problems not only result in low yields and poor product quality,but also limit the application of Cu metallization in the microelectronics field.As a promising PVD technology,High Power Pulsed Magnetron Sputtering(HPPMS)can be considered as a good method to prepare Cu films.Due to the high plasma density in HPPMS,the metal ion-to-neutral ratio in the deposition flux reaches ~70% in the case of Cu.This will increase the possibility in controlling the microstructure,phases,and chemical composition of the growing films.So,in order to solve the problem of Cu films in its application,in this work HPPMS was utilized to prepare Cu films.The plasma characteristics during deposition were tailored,aiming at achieving a desired film.Meanwhile,the relationship between plasma characteristics and the Cu films was systematically studied.Firstly,the plasma composition and ionization rate in front of target and substrate were compared by optical emission spectroscopy during HPPMS discharge.It showed that,comparing Ar ions and Ar atoms,Ti ion and Ti atoms dominated the species on the target surface.However,the Ar species became dominant and the metal species became less in front of target.In front of substrate,the proportion of metal species became much less.Meanwhile,Ti films were prepared by HPPMS,and the films properties were tailored by adjusting peak power and average power.It was found the Ti films with compressive stress,small grain size and smooth surface can be achieved by increasing peak power at constant average power.On the contrary,with the increase of average power when the peak power was same,the ion-to-atom ratio had no remarkable change,but the number of metal ions and atom obviously increased.The films showed tensile stress,large grain size,rough surface and highly preferred(002)direction.Secondly,different combinations of frequency and pulse width at a constant duty cycle were used to modulate the deposition rate and Ti film properties.The results showed that for a constant duty cycle wider pulse width would be more effective on improving titanium deposition rate than increasing frequency.The pulse width also would affect the power utilization ratio.Especially for a high duty cycle of 4.8% and 5.6%,a wider pulse was favorable to make full use of power on films deposition,resulting in a higher normalized static deposition rate.Meanwhile,with increase in pulse width for a constant duty cycle,adatom mobility and the deposition rate increased,contributing to growth of crystallite size and higher surface roughness of Ti films.Thirdly,the substrate bias was regulated to control the species current and ion energy to optimize the quality of Cu films.It was found that both electrons and ions contributed to the overall species current on the substrate.Electrons dominated the species current at the beginning and positive ions contributed the majority at end of the pulse.As the substrate bias increased from –17.3 V(floating voltage)to –100 V,the electron current gradually decreased,while the ion current increased,eventually stabilizing at –50 V.However,the changes in the deposition rate,tensile stress and texture of Cu films deposited from floating voltage to –50 V showed little difference as opposed to those Cu films deposited in the range from –50 V to –100 V.Compared to the Cu films deposited at –50 V,the films deposited at –100 V exhibited a higher tensile stress and a highly preferred(111)texture.The electrical resistivity of the Cu films reached 1.79 μ?·cm at –100 V.Further,different HPPMS peak power was applied to prepare the Cu films with different thickness.Furthermore,Ti interlayer was used to improve the Cu films properties.The effect of thickness and Ti interlayer on the stress and structure properties of Cu films was investigated in detail.The results demonstrated that the high ion-to-atom ration can be obtained at a higher peak power.The films prepared at high peak power showed a higher tensile stress,larger grain size and lower electrical resistivity.Meanwhile,films with the thicker thickness exhibited lower stress and larger grain size,resulting in a better electrical conductivity and adhesion.Meanwhile,it was found the Cu films with Ti interlay exhibited low tensile stress,smooth surface,high hardness and good adhesion.Cu films with highly preferred orientation of(111)face can be obtained for different substrate materials when Ti interlayer was used.At last,bipolar pulse High Power Pulsed Magnetron Sputtering based on conventional HPPMS was put forward to deposit Cu films on silicon wafers.Positive kick pulses with different pulse width and magnitude were applied after the initial negative pulse to drive Cu ions to the substrate,improving the properties of Cu films.Compared to films deposited by conventional HPPMS,the Cu films prepared by modified HPPMS exhibited a higher deposition rate.Moreover,the increase in voltage and pulse width of kick pulse resulted in a reduction of tensile stress of the Cu films. |
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