Research on deposition rate of TiZrV/Pd film by DC magnetron sputtering method

Research on deposition rate of TiZrV/Pd film by DC magnetron sputtering method 1 first-author 1 corresp Corresponding author: zhbo@ustc.edu.cn Corresponding author: zhbo@ustc.edu.cn zhbo@ustc.edu.cn 1 1 National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China An accelerator storage ring needs clean ultra-high vacuum. A TiZrV non-evaporable getter (NEG) film deposited on interior walls of the chamber can realize distributed pumping, effective vacuum improvement and reduced longitudinal pressure gradient. But accumulation of pollutants such as N 2 and O 2 , will decrease the adsorption ability of the NEG, leading to a reduction of NEG lifetime. Therefore, an NEG thin film coated with a layer of Pd, which has high diffusion rate and absorption ability for H 2 , can extend the service life of NEG and improve the pumping rate of H 2 as well. In this paper, with argon as discharge gas, a magnetron sputtering method is adopted to prepare TiZrV-Pd films in a long straight pipe. By SEM measurement, deposition rates of TiZrV-Pd films are analyzed under different deposition parameters, such as magnetic field strength, gas flow rate, discharge current, discharge voltage and working pressure. By comparing the experimental results with the simulation results based on Sigmund’s theory, the Pd deposition rate C can be estimated by the sputtered depth. TiZrV-Pd deposition rates magnetron sputtering method non-evaporable getter 1 Introduction 1 In order to reduce beam losses caused by residual gas scattering and to maintain a longer beam lifetime, a storage ring of a synchrotron facility needs clean ultra-high vacuum environment. The ways to obtain and maintain ultra-high vacuum are mainly through discrete distribution of vacuum pumps, such as sputtering ion pumps and titanium sublimation pumps. However, the synchrotron radiations and high energy particles bombarding the inner wall cause surface outgassing and a high dynamic gas load. Also, due to the limitation of gas conductance of the vacuum chamber, vacuum pressure near the vacuum pumps is much better than those in other areas. TiZrV non-evaporable getter (NEG) film deposited on inner walls of the chamber, can realize distributed pumping effectively, improving the vacuum by reducing both gas pressure and longitudinal gradient, TiZrV films, having low secondary electron yield and adsorbing vaious kinds of gases (O 2 , N 2 , CO and CO 2 ), have been widely applied in particle accelerator facilities. Nevertheless, after repeated exposure to air, TiZrV films will be polluted by N 2 , O 2 and so on, which reduces their absorbing behavior and service life. When the pressure is less than 1×10 −9 mbar, the main component of residual gas is H 2 . In order to obtain ultra-high vacuum (UHV), vacuum pumps with a high pumping speed to H 2 are needed. Therefore, C. Benvenuti et al . [ 1 1 ] proposed the use of a palladium (Pd) film featuring a high adsorption of H 2 on the NEG film. The Pd film protects the NEG film and prolongs its service life. M. Mura et al . [ 2 2 ] found that TiZrV-Pd films improved the adsorption factor for other gases, too. They applied TiZrV-Pd films to ion pumps and obtained better vacuum performance. C. Benvenuti et al . reported that TiZrV-Pd films improved the pumping speed for H 2 and CO, but not N 2 and CO 2 . The secondary electron yield of TiZrV-Pd films caused by synchrotron radiation was lower than TiZrV films. It has been reported that film-coating parameters in DC magnetron sputtering affects the film properties, such as film deposition rates and mechanical properties [ 3 3 , 4 4 ]. In this paper, we present a study on effects of magnetic field strength, gas flow rate, discharge current, discharge voltage and working pressure on deposition rate of TiZrV-Pd films, by a magnetron sputtering deposition method. 2 Experimental 1 2.1. The apparatus 2 This magnetron sputtering deposition method is shown schematically in Fig.1 Fig.1 . The coating system mainly includes a pipe-to-be-coated of Φ 86 mm×540 mm, molecular pump system, gas control system, discharge power supply, cathode wires, a sample holder and a solenoid. The cathode is of two types: twisted Ti, Zr and V wires in a total diameter of 2.5 mm, and a Φ 1 mm Pd wire. Details of the deposition system can be found in Ref. [ 5 5 ]. Film thickness was measured by a Sirion 200 Schottky field SEM (scanning electron microscope). 2.2. Methods 2 The deposition rate calculation and transport of sputtered particles from the target towards the walls have been discussed for decades [ 6 6 - 8 8 6-8 ]. The models based on continuum equations are developed to simulate the evolution of surfaces in three dimensions, and useful information is provided on morphology of step coverage for various amounts of surface diffusion and angular distributions [ 9 9 ]. Other models mainly rely on a kinetic Monte Carlo method. For example, the “Effective Thermalizing Collision” (ETC) approximation has successfully explained the Keller-Simmons (K-S) formula, using an empirical equation in classical magnetron sputtering deposition with a single gas [ 10 10 ]. However, the models are complicated, less portable and time-consuming. According to a comparison between experiment and simulation results, we found that the deposition rate of single component Pd metal film can be estimated by the sputtering depth for cylindrical pipe coating. 2.2.1. Depth sputtered off the Pd target and deposition rate of the Pd film 3 The depth sputtered from the Pd target, D , can be expressed as [ 11 11 ]: <math display="block" id="M1"><mrow><mi>D</mi><mo>=</mo><mfrac><mrow><mi>J</mi><mi>Y</mi><msup><mi>r</mi><mn>3</mn></msup><mi>t</mi></mrow><mrow><msub><mi>e</mi><mn>0</mn></msub></mrow></mfrac></mrow></math> where J is the beam current density, Y is the sputtering yield, t is the time of sputtering, r 3 is the volume of an atom of the target and e 0 is the electron charge. Certainties in Y lead to certainties in the thickness scale, D . There are a number of predictive relations to calculate Y , based on Sigmund’s theory [ 12 12 ]. In this article, we used Eq. (2) developed by Matsunami et al . [ 13 13 ] and Eq. (3), which was improved later from Eq. (2) by Yamamura and Tawara [ 14 14 ]. <math display="block" id="M2"><mrow><mi>Y</mi><mtext>=</mtext><mfrac><mrow><mtext>0</mtext><mtext>.042</mtext><mi>Q</mi><msup><mi>α</mi><mtext>*</mtext></msup></mrow><mrow><msub><mi>U</mi><mtext>0</mtext></msub></mrow></mfrac><mfrac><mrow><msub><mi>S</mi><mtext>n</mtext></msub><mo stretchy="false">(</mo><mi>E</mi><mo stretchy="false">)</mo></mrow><mrow><mn>1</mn><mo>+</mo><mn>0.35</mn><msub><mi>U</mi><mn>0</mn></msub><msub><mi>s</mi><mtext>e</mtext></msub><mo stretchy="false">(</mo><mi>ε</mi><mo stretchy="false">)</mo></mrow></mfrac><msup><mrow><mo stretchy="false">(</mo><mn>1</mn><mo>−</mo><msup><mrow><mo stretchy="false">(</mo><mfrac><mrow><msub><mi>E</mi><mrow><mtext>th</mtext></mrow></msub></mrow><mi>E</mi></mfrac><mo stretchy="false">)</mo></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup><mo stretchy="false">)</mo></mrow><mi>s</mi></msup></mrow></math> <math display="block" id="M3"><mrow><mi>Y</mi><mtext>=</mtext><mfrac><mrow><mtext>0</mtext><mtext>.042</mtext><mi>Q</mi><msup><mi>α</mi><mtext>*</mtext></msup></mrow><mrow><msub><mi>U</mi><mtext>0</mtext></msub></mrow></mfrac><mfrac><mrow><msub><mi>S</mi><mtext>n</mtext></msub><mo stretchy="false">(</mo><mi>E</mi><mo stretchy="false">)</mo></mrow><mrow><mn>1</mn><mo>+</mo><mfrac><mrow><mi>W</mi><msup><mi>ε</mi><mrow><mo>−</mo><mn>0.2</mn></mrow></msup></mrow><mrow><mn>1</mn><mo>+</mo><msup><mrow><mo stretchy="false">(</mo><msub><mi>M</mi><mn>1</mn></msub><mo>/</mo><mn>7</mn><mo stretchy="false">)</mo></mrow><mn>3</mn></msup></mrow></mfrac><msub><mi>s</mi><mtext>e</mtext></msub><mo stretchy="false">(</mo><mi>ε</mi><mo stretchy="false">)</mo></mrow></mfrac><msup><mrow><mo stretchy="false">(</mo><mn>1</mn><mo>−</mo><msup><mrow><mo stretchy="false">(</mo><mfrac><mrow><msub><mi>E</mi><mrow><mtext>th</mtext></mrow></msub></mrow><mi>E</mi></mfrac><mo stretchy="false">)</mo></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup><mo stretchy="false">)</mo></mrow><mi>s</mi></msup></mrow></math> where, S n ( E ) is the nuclear stopping power per atom, U 0 is the surface binding energy per atom, Q = 0.47–4.6 in Eq. (2) and Q =0.54–2.62 in Eq. (3), W is obtained from a look-up table provided for 34 elements, M 2 is the target atom’s mass, M 1 is the incident ion mass, s is a constant, and s e ( ε ) is the inelastic electronic stopping power. In Eq. (2), <math display="block" id="M4"><mrow><msup><mi>α</mi><mtext>*</mtext></msup><mo>=</mo><mn>0.08</mn><mo>+</mo><mn>0.164</mn><msup><mrow><mo stretchy="false">(</mo><msub><mi>M</mi><mn>2</mn></msub><mo>/</mo><msub><mi>M</mi><mn>1</mn></msub><mo stretchy="false">)</mo></mrow><mrow><mn>0.4</mn></mrow></msup><mo>+</mo><mn>0.0145</mn><msup><mrow><mo stretchy="false">(</mo><msub><mi>M</mi><mn>2</mn></msub><mo>/</mo><msub><mi>M</mi><mn>1</mn></msub><mo stretchy="false">)</mo></mrow><mrow><mn>1.29</mn></mrow></msup></mrow></math> and <math display="block" id="M5"><mrow><msub><mi>E</mi><mrow><mtext>th</mtext></mrow></msub><mo>=</mo><mrow><mo>[</mo><mrow><mn>1.9</mn><mo>+</mo><mn>3.8</mn><mo stretchy="false">(</mo><msub><mi>M</mi><mn>1</mn></msub><mo>/</mo><msub><mi>M</mi><mn>2</mn></msub><mo stretchy="false">)</mo><mo>+</mo><mn>0.134</mn><msup><mrow><mo stretchy="false">(</mo><msub><mi>M</mi><mn>2</mn></msub><mo>/</mo><msub><mi>M</mi><mn>1</mn></msub><mo stretchy="false">)</mo></mrow><mrow><mn>1.24</mn></mrow></msup></mrow><mo>]</mo></mrow><msub><mi>U</mi><mn>0</mn></msub></mrow></math> In Eq. (3), http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10334279&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10334277&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=10334279&type= and <math display="block" id="M6"><mtable columnalign="left"><mtr><mtd><msub><mi>E</mi><mrow><mtext>th</mtext></mrow></msub><mo>=</mo><mrow><mo>[</mo><mrow><mn>1</mn><mo>+</mo><mn>5.7</mn><mo stretchy="false">(</mo><msub><mi>M</mi><mn>1</mn></msub><mo>/</mo><msub><mi>M</mi><mn>2</mn></msub><mo stretchy="false">)</mo></mrow><mo>]</mo></mrow><mo stretchy="false">(</mo><msub><mi>U</mi><mn>0</mn></msub><mtext>/γ),  </mtext><msub><mi>M</mi><mn>2</mn></msub><mo>></mo><msub><mi>M</mi><mn>1</mn></msub><mtext>,</mtext></mtd></mtr><mtr><mtd><mtext>     </mtext><mo>=</mo><mn>6.7</mn><mo stretchy="false">(</mo><msub><mi>U</mi><mn>0</mn></msub><mtext>/γ)</mtext><mi>，</mi><msub><mi>M</mi><mn>2</mn></msub><mo><</mo><msub><mi>M</mi><mn>1</mn></msub></mtd></mtr></mtable></math> where <math display="block" id="M7"><mrow><mtext>γ=</mtext><mfrac><mrow><mtext>4</mtext><msub><mi>M</mi><mn>1</mn></msub><msub><mi>M</mi><mn>2</mn></msub></mrow><mrow><msup><mrow><mo stretchy="false">(</mo><msub><mi>M</mi><mn>1</mn></msub><mtext>+</mtext><msub><mi>M</mi><mn>2</mn></msub><mo stretchy="false">)</mo></mrow><mtext>2</mtext></msup></mrow></mfrac></mrow></math> and, when E is in eV, <math display="block" id="M8"><mrow><mi>ε</mi><mtext>=</mtext><mfrac><mrow><mtext>0</mtext><mtext>.03255</mtext></mrow><mrow><msub><mi>Z</mi><mn>1</mn></msub><msub><mi>Z</mi><mn>2</mn></msub><msup><mrow><mo stretchy="false">(</mo><msub><mi>Z</mi><mn>1</mn></msub><msup><mrow/><mrow><mn>2</mn><mo>/</mo><mn>3</mn></mrow></msup><mo>+</mo><msub><mi>Z</mi><mn>2</mn></msub><msup><mrow/><mrow><mn>2</mn><mo>/</mo><mn>3</mn></mrow></msup><mo stretchy="false">)</mo></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></mrow></mfrac><mfrac><mrow><msub><mi>M</mi><mn>2</mn></msub></mrow><mrow><msub><mi>M</mi><mn>1</mn></msub><mtext>+</mtext><msub><mi>M</mi><mn>2</mn></msub></mrow></mfrac><mi>E</mi></mrow></math> According to Ref. [ 15 15 - 17 17 15-17 ], errors of the SEM measurements are about 5%. We compared the argon ion deposition yield of Pd film obtained by Eqs. (2) and (3) with the experimental data in energy range 350–700 eV. The deposition rate C is the film thickness ( T ) over the deposition time ( t ). Adopting Wolfram Mathematica software, deposition rate of Pd film for a cylindrical pipe was calculated by the two models. Under experimental conditions given in Table 1 Table 1 , seven Pd film samples were deposited on silicon substrates, and the film thicknesses were measured by SEM. In the film coating process, the discharge voltage fluctuated slightly. So, in the simulation, the discharge voltage was chosen at the relatively stable discharge voltage of the film coating process. The simulated and measured Pd film deposition rates are given in Fig.2(a) Fig.2(a) . 1 1 Samples 1 1 Discharge current (A) 1 1 Stable discharge voltage (V) 1 1 Working pressure (Pa) 1 1 Gas flow (sccm) 1 1 #1 1 1 0.02 1 1 385 1 1 2 1 1 2.0 1 1 #2 1 1 0.02 1 1 420 1 1 2 1 1 2.0 1 1 #3 1 1 0.02 1 1 440 1 1 2 1 1 3.0 1 1 #4 1 1 0.03 1 1 500 1 1 2 1 1 2.0 1 1 #5 1 1 0.03 1 1 690 1 1 2 1 1 2.0 1 1 #6 1 1 0.04 1 1 526 1 1 2 1 1 2.0 1 1 #7 1 1 0.04 1 1 548 1 1 5 1 1 2.0 In most cases, the error ranges −7% ~ 6% for the experimental results and the values calculated using Eq.(3), and 2% ~ 11% for the experimental results and the values calculated using Eq.(3), though the largest error is 16% for both models. M. P. Seah et al . considered effects of amorphization, damage and implanted ions occurring in the early stage of sputtering and used Q = 0.018/ r 3 , where r is the average interatomic spacing. With this improvement, the Pd film deposition rates calculated using Eq.(2) deviate by −2.5% ~ 20% from the experimental, as shown in Fig. 2(b) Fig. 2(b) ; while they are just −7.7% ~ 10% for the results calculated by Eq.(3). Particularly, for Samples 1, 5, 6 and 7, the errors are 0%, −1.6%, 0.8% and 1.6%, respectively; while for Samples 2, 3 and 4, the errors are −7.7%,−7.7% and 10%, respectively. Therefore, in most cases, the deposition rate ( C ) is basically the same as the depth sputtered ( D ), which can be used to estimate the Pd film thickness. 2.2.2. Simulation and experimental results of deposition rate 3 The film thickness should be controlled in the coating process. In the early experiments, in order to obtain a preconceived film thickness, the film coating parameters were adjusted according to the film thickness measured by SEM. In practice, to save time and cost, we calculated film thickness with the following assumptions of the empirical formula: 1) During the experiment, the current value displayed on the discharge power supply is composed of electron current and ion current. When calculating the deposition rate of Pd films, ion current is needed. In order to simplify the calculation, assume that the value of ion current is equal to the discharge current; 2) The incident energy of Ar + is eU, where U is the cathode voltage; and 3) The Pd films and Pd target are of the same density. The atomic mass of Pd ( m Pd ) sputtered by the Ar + and thickness of the deposited Pd film ( h Pd ) can be calculated by: <math display="block" id="M9"><mrow><msub><mi>m</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>=</mo><mi>n</mi><mo>⋅</mo><msub><mi>η</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>⋅</mo><msub><mi>M</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>/</mo><msub><mi>N</mi><mtext>A</mtext></msub></mrow></math> <math display="block" id="M10"><mrow><msub><mi>h</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>=</mo><msub><mi>m</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>/</mo><mrow><mo>(</mo><mrow><msub><mi>ρ</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>⋅</mo><mi>s</mi></mrow><mo>)</mo></mrow><mo>=</mo><mi>n</mi><mo>⋅</mo><msub><mi>η</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>⋅</mo><msub><mi>M</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>/</mo><mrow><mo>(</mo><mrow><msub><mi>N</mi><mtext>A</mtext></msub><mo>⋅</mo><msub><mi>ρ</mi><mrow><mtext>Pd</mtext></mrow></msub><mo>⋅</mo><mtext>π</mtext><mi>d</mi></mrow><mo>)</mo></mrow></mrow></math> where, d =0.086 m is the pipe diameter; i is the current density in A; s is the surface area per unit length of the pipe in m 2 ; η Pd is the Pd sputtering yields of Ar + in certain energies; M Pd = 106.42 g/mol is molar mass of Pd; ρ Pd =12.2×10 6 g/m 3 is the density of Pd; N A =6.02×10 23 mol −1 is the Avogadro constant; n = i / e 0 = i ×0.625×10 19 is the number of incident Ar + ions on the target surface in unit time. The simulated and measured Pd film deposition rates are shown in Table 2 Table 2 . It can be seen that the the simulation results are about 50% less than the experimental results. This means that the Pd films differ obviously in density from the Pd target. So, the depth sputtered ( D ) off the Pd target and deposition rate ( C ) of Pd films can be happen to be very close. 1 1 Samples 1 1 #1 1 1 #2 1 1 #3 1 1 #4 1 1 #5 1 1 #6 1 1 #7 1 1 Simulated 1 1 49 1 1 67 1 1 76 1 1 119 1 1 134 1 1 162 1 1 165 1 1 Measured 1 1 104 1 1 116 1 1 120 1 1 150 1 1 188 1 1 244 1 1 253 3 Results and Discussion 1 The SEM was used to measure TiZrV-Pd film thicknesses deposited under different work pressures, gas flow rates, magnetic field strengths or discharge currents. In order to reduce the gas impurity effect on the film composition, the working pressure was just 1~20 Pa and the gas flow rate was just 1–5 sccm (standard cubic centimeter per minute). The discharge current was chosen based on considerations of film deposition rates. The magnetic field strength was measured by gaussmeter. The cross section morphology and surface topography of some TiZrV-Pd films are shown in Fig. 3 Fig. 3 . 3.1 The influence of working pressure on deposition rates 2 At discharge current of 0.2 A, magnetic field strength of 120 Gauss and gas flow rate of 2 sccm, the deposition rates of TiZrV films on silicon substrates was studied under working pressure of 1–20 Pa. The results are shown in Table 3 Table 3 . At 2 Pa, the deposition rate of TiZrV was the highest (266 nm/h), and the discharge voltage was the highest, too. 1 1 Samples 1 1 Working pressure (Pa) 1 1 Deposition rate (nm·h −1 ) 1 1 Discharge voltage (V) 1 1 #0610 1 1 1 1 1 260 1 1 394–365 1 1 #0311 1 1 2 1 1 266 1 1 427–436 1 1 #0527 1 1 5 1 1 147 1 1 334–319 1 1 #0604 1 1 10 1 1 170 1 1 350–314 1 1 #0612 1 1 20 1 1 139 1 1 350–329 At discharge current of 0.04 A, magnetic field strength of 175 Gauss and gas flow of 2.0 sccm, the deposition rates of Pd films on TiZrV film substrates was measured at working pressure of 2−20 Pa ( Table 4 Table 4 ). Again, at 2 Pa, the deposition rate of Pd film (244 nm/h) and the discharge voltage were the highest. 1 1 Samples 1 1 Working pressure (Pa) 1 1 Deposition rate (nm·h −1 ) 1 1 Discharge voltage (V) 1 1 #0227 1 1 2 1 1 244 1 1 530–523 1 1 #0618 1 1 5 1 1 166 1 1 437–548 1 1 #0508 1 1 10 1 1 186 1 1 456–527 1 1 #0620 1 1 20 1 1 166 1 1 464–573 3.2 The influence of gas flow on deposition rates 2 At discharge current of 0.25 A, working pressure of 2 Pa, and magnetic field strength of 123 Gauss, the deposition rates of TiZrV films on silicon substrate was studied at gas flow rate of 1, 3 and 4 sccm ( Table 5 Table 5 ). The highest deposition rate of TiZrV films was 278 nm/h at 1 sccm. The influence of gas flow on the deposition rates is closely related to the discharge voltage. High discharge voltage contributes to the improvement of the deposition rates of TiZrV films. This was found the same for Pd films, as shown in Table 6 Table 6 . At 2 sccm, the deposition rate of Pd films was the highest (240 nm/h). 1 1 Sample 1 1 Gas flow(Sccm) 1 1 Depositionrate (nm·h −1 ) 1 1 DischargeVoltage (V) 1 1 #0617 1 1 1 1 1 278 1 1 350–400 1 1 #0619 1 1 3 1 1 233 1 1 351–375 1 1 #0624 1 1 4 1 1 270 1 1 371–385 1 1 Sample 1 1 Gas flow(Sccm) 1 1 Depositionrate (nm·h −1 ) 1 1 Dischargevoltage (V) 1 1 #0606 1 1 1 1 1 177 1 1 424–458 1 1 #1225 1 1 2 1 1 240 1 1 664–697 1 1 #0611 1 1 3 1 1 160 1 1 440–446 1 1 #0613 1 1 4 1 1 146 1 1 436–465 1 1 #0225 1 1 5 1 1 210 1 1 571–574 3.3. The influence of magnetic field strength on deposition rates 2 At discharge current of 0.2 A, working pressure of 2 Pa, and gas flow of 2 sccm, the deposition rates of TiZrV films on silicon substrate was studied under magnetic field strengths of 82–177 Gauss ( Table 7 Table 7 ). At 82 Gauss, the highest deposition rate of TiZrV film was 500 nm/h. High discharge voltage increased the deposition rate of TiZrV film. This was found the same for Pd films ( Table 8 Table 8 ). The highest deposition rate of Pd films was 240 nm/h at 175 Gauss. 1 1 Samples 1 1 Magnetic field strength (Gauss) 1 1 Deposition rate (nm·h −1 ) 1 1 Discharge voltage (V) 1 1 #0409 1 1 82 1 1 500 1 1 606–658 1 1 #0402 1 1 93 1 1 490 1 1 508–561 1 1 #0331 1 1 107 1 1 317 1 1 394–471 1 1 #0311 1 1 123 1 1 266 1 1 427–436 1 1 #0521 1 1 177 1 1 240 1 1 381–308 1 1 Samples 1 1 Magnetic field strength (Gauss) 1 1 Deposition rate (nm·h −1 ) 1 1 Discharge voltage (V) 1 1 #0514 1 1 65 1 1 163 1 1 443–440 1 1 #0304 1 1 123 1 1 212 1 1 559–569 1 1 #1225 1 1 175 1 1 240 1 1 664–697 1 1 #0418 1 1 206 1 1 130 1 1 430–440 3.4. The influence of discharge current on deposition rates 2 At working pressure of 2 Pa, magnetic field strength of 175 Gauss and gas flow rate of 2 sccm, the deposition rates of TiZrV films on silicon substrate was studied under discharge currents of 0.10, 0.25 and 0.50 A ( Table 9 Table 9 ). At 0.5 A, the deposition rate of TiZrV thin film was the highest (316 nm/h). 1 1 Sample 1 1 Discharge current (A) 1 1 Deposition rate (nm·h −1 ) 1 1 Discharge voltage (V) 1 1 #1224 1 1 0.10 1 1 30 1 1 473–490 1 1 #0108 1 1 0.25 1 1 80 1 1 547–557 1 1 #0226 1 1 0.50 1 1 316 1 1 492–343 According to the magnetron sputtering model proposed by John A.Thornton [ 15 15 ], the averaged ion current J i _mean can be related to the discharge current ( I dc ) by: <math display="block" id="M11"><mrow><msub><mi>J</mi><mi>i</mi></msub><msub><mrow/><mrow><mo>_</mo><mtext>mean</mtext></mrow></msub><mo>=</mo><msub><mi>I</mi><mrow><mtext>dc</mtext></mrow></msub><mo>/</mo><mrow><mo>(</mo><mrow><mn>2</mn><mtext>π</mtext><mi>R</mi><mi>w</mi></mrow><mo>)</mo></mrow><mo>,</mo></mrow></math> where R is the average radius of high density plasma torus with a bright glow close to the cathode, and w is the width of high density plasma torus. Ions current increases with the discharge current. According to Eq.(15), film deposition rate R sput increases with ion current. Table 9 Table 9 shows positive relationship between the deposition rate and discharge current but it is not linear. Because when the discharge current increases, R and w will change slightly. In short, theoretical analysis is consistent with the experimental results. <math display="block" id="M12"><mrow><msub><mi>R</mi><mrow><mtext>sput</mtext></mrow></msub><mo>=</mo><msub><mi>γ</mi><mrow><mtext>sput</mtext></mrow></msub><msub><mi>J</mi><mi>i</mi></msub><msub><mrow/><mrow><mo>_</mo><mi>m</mi><mi>e</mi><mi>a</mi><mi>n</mi></mrow></msub><mo>/</mo><mrow><mo>(</mo><mrow><mi>e</mi><mi>n</mi></mrow><mo>)</mo></mrow></mrow></math> where γ sput ~1, n is the atomic density of target material. It was found the same results hold for the influence of discharge current on the deposition rates of Pd films. When the discharge current was 0.03 A, the deposition rate of Pd film was the highest, about 217 nm/h. 4 Conclusion 1 The experiment results show that magnetic field strength, gas flow, discharge current and working pressure will affect the deposition rates of TiZrV-Pd films. Adjusting the four parameters and other experimental conditions, the maximum deposition rate for TiZrV thin film was 490 nm/h, and it was about 240 nm/h for Pd film. The results meet the demand of actual coating requirement. Moreover, comparing the simulation results based on Sigmund’s theory and experimental results, the Yamamura and Tawaras model with Q = 0.018/ r 3 can be used to estimate, within 10% deviation from the SEM measurement results, the deposition rate of the Pd film by the depth sputtered from the Pd target in this experiment system. References C. Benvenuti , P. Chiggiato , F. Cicoira , et al ., Vacuum properties of palladium thin film coatings . Vacuum 73 ( 2004 ) 139 - 144 . 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(Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2017 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-017-0199-6 http://dx.doi.org/10.1007/s41365-017-0199-6 . 2017 Nuclear Science and Techniques 04 28