| As an important method of films deposition,the magnetron sputtering has been widely used in the industrial application and the scientific research.According to the mechanism on magnetron discharge,the cathode sheath near the target plays an important role in controlling the ions towards the cathode target and maintaining the magnetron discharge.Thus,the sheath property is paid more attentions.However,when the sheath property is experimentally diagnosed using the probe,some problems are raised.As a result,a non-invasive plasma diagnosis method is needed.Recently,the plasma impedance monitor(PIM),which is a non-invasive plasma diagnosis method and is carried out by a radio-frequency voltage-current(?-?)probe system,has been used in the plasma processing.In this method,the radio-frequency(RF)discharge plasma can be modelled using an equivalent circuit proposed by Schneider,which consists of two sub-circuits in series representing the plasma body and the electrode sheath.The plasma body includes the plasma resistance Rv due to the electron collisions with gas atoms and Rst due to the stochastic electron heating on the oscillating plasma boundaries,as well as the capacitance Co accounting for the displacement current and the plasma inductance L0 due to the electron inertia in the RF field.The electrode sheath includes the parallel sheath capacitance C'sh determining the effective sheath width ds,and the parallel sheath resistance R'sh due to the ion acceleration power in the sheath.Therefore,by the plasma impedance measurement,the non-invasive diagnosis method on the sheath can be developed.In this thesis,the equivalent circuit model of discharge plasma was analyzed for the radio-frequency(RF)and very-high-frequency(VHF)magnetron discharges,the plasma impedance characteristics of RF and VHF magnetron discharges with Ag,Cu and Al targets were measured using plasma impedance monitor method,and the non-invasive diagnosis method on the sheath was developed.The effect of discharge frequency(2 MHz,13.56 MHz,27.12 MHz,and 60 MHz)and discharge pressure(1.0 Pa,3.5 Pa,5.0 Pa,7.5 Pa,and 10.0 Pa)on impedance characteristics were discussed.The sheath thickness of 13.56 MHz magnetron discharge and its change with sputtering power and discharge pressure were obtained.The major results are as follows.(1)According to the discharge frequency ?(13.56 MHz,27.12 MHz and 60 MHz)and the electrou plasma frequency ?pe calculated using ?pe2=e2n/(?0m),the comparison between ? and ?pe was made.It is found that for the 13.56 MHz magnetron discharge,at the discharge pressure of 1-10 Pa,the condition of ?<?Cpe is satisfied.So the capacitance C0 accounting for the displacement current and the plasma inductance L0 due to the electron inertia can be neglected.The equivalent circuit proposed by Schneider can be simplified as the "capacitance sheath model".However,for the 27.12 MHz and 60 MHz magnetron discharges,the condition of ?<<?pe is not satisfied.So,the plasma inductance L0 due to the electron inertia can not be neglected.(2)The discharge frequency(2 MHz,13.56 MHz,27.12 MHz,and 60 MHz)has obvious influence on the impedance characteristics of Ag,Cu and Al targets magnetron sputtering.For the 2 MHz magnetron discharge,the change of real part R with the discharge current shows a relationship of R?I-1,which is completely different from that of 13.56 MHz,27.12 MHz,and 60 MHz discharge,indicating that the plasma resistance Rv and Rst make the main contribution to the impedance characteristics.For the 27.12 MHz magnetron discharge,the imaginary part X decreases to 0 from a negative value(capacitive reactance),and then becomes a positive value(inductive reactance)with the discharge current increase.For the 60 MHz magnetron discharge,the imaginary part X shows a positive value(inductive reactance).The results indicate that the electron inertia makes the main contribution to the impedance characteristics at the 27.12 MHz and 60 MHz magnetron discharges.(3)The discharge pressure(1.0 Pa,3.5 Pa,5.0 Pa,7.5 Pa,and 10.0 Pa)also has influence on the impedance characteristics of Ag,Cu and Al targets magnetron discharge.The increase of discharge pressure can lead to the increase of absolute value of impedance |Z|,real part R,and imaginary part X.The effect of discharge pressure on impedance characteristics is also related to the discharge frequency.For the 13.56 MHz magnetron discharge,at the discharge pressure of 1.0-7.5 Pa,the discharge pressure has influence on the absolute value of impedance |Z| and imaginary part X.While at the discharge pressure of 7.5-10.0 Pa,the discharge pressure has influence on the real part R.For the 27.12 MHz magnetron discharge,the increase of discharge pressure can lead to the evolution of imaginary part X from the negative value(capacitive reactance)to the positive value(inductive reactance).The current at the point of X=0? decreases with the pressure increase.(4)For the 13.56 MHz magnetron discharge,because the condition of ?<?pe is satisfied,the equivalent circuit can be simplified as the "capacitance sheath model".Therefore,the sheath thickness ds can be calculated from the imaginary part X of impedance according to the equation of X=(Cs?)-1 and Cs=?0Sds-1.At the pressure of 3.5 Pa,with the sputtering power increase from 44 W to 192 W,the sheath thickness ds decreases from 0.111 mm to 0.052 mm for Ag target,from 0.115 mm to 0.070 mm for Al target,and from 0.118 mm to 0.085 mm for Cu target,respectively.The change of pressure also has influence on the sheath thickness ds.At the sputtering power of 50 W and 200 W,the increase of pressure from 1.0 Pa to 10.0 Pa leads to the decrease of sheath thickness ds from 0.113 mm to 0.102 mm and from 0.059 mm to 0.040 mm,respectively.In conclusion,the impedance characteristics of radio-frequency(2 MHz,13.56 MHz and 27.12 MHz)and very-high-frequency(60 MHz)magnetron discharge can be investigated by a voltage-current probe technology.The sheath property can be experimentally diagnosed using the non-invasive plasma impedance monitor method. |
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