Microstructure Study Of Sputtered Silver Thin Films Biology Essay
The effects of deposition parametric quantities on microstructure, grain size and crystallographic orientation of Ag thin movies with assorted thicknesses by X-ray diffraction and scanning negatron microscopy ( SEM ) of samples has been studied. The influences of substrate and tempering temperature on microstructure, orientation and grain size fluctuations have been investigated. The consequences show that, grain size additions with movie thickness and substrate temperature and the produced Ag movies exhibit ( 111 ) extremum as preferable growing orientation in all instances. Grain size fluctuation with deposition temperature has been explained by structural zone theoretical account ( SZM ) .
In recent old ages thin metal movies specially silver movies attracted great involvement, due to their alone micro-electronic and optical belongingss ( lowest electrical electric resistance a‰?1.6I?I©.cm and the highest coefficient of reflection a‰? 95 % in seeable and IR part of spectrum ) [ 1,2,3 ] . Ag reflects heat on automotive glazing, and for windscreen merely silver can be employed as the reflecting metal bed because of its low light soaking up compared whit Au, Cr, Cu, aˆ¦and other baronial metals [ 4,5 ] . Silver thin movies exhibit sufficient long-run chemical stableness besides Ag is normally used in surface-enhanced sprinkling because of its unsmooth surface due to its high coefficient of reflection and energy-saving application like solar control system for heat rejection [ 6,7 ] . Since the physical belongingss of Ag movies were found to be strongly dependent on their denseness, microstructure and morphology, assortment of methods have been proposed for the deposition of Ag thin movies [ 8,9 ] . But some of the methods used are good merely for little size substrate, and some are non suited to accomplish a good homogeneousness of the movie bed belongingss across the whole deposition breadth, which is really of import for most optical and electrical applications. Besides since Ag is a baronial metal, these movies sometimes exhibit hapless adhesion to some metals, semi-conductors and specially insulators like glass [ 10,11 ] . Magnetron sputtering which has been employed in this work has many advantages compared with other methods of coating, high deposition rate, and really good homogeneousness of movie and really suited for surfacing big countries. Since high energy atoms ejected from sputtering mark arrive at the substrate surface with a average energy much higher than other methods of PVD. This kinetic energy can heighten the interaction between condensed species, and substrate surface taking to much better adhesion, and high packing denseness of atoms in the movies. Besides heat burden of the substrate is little compared to that in vaporization procedures, which can be of import for deposition on plastic and substrate stuffs with really low runing points, which may deform ( polycarbonate, Personal computer ) due to heat from high temperature of vaporization beginnings [ 12 ] . Recently considerable plants have been directed toward elaborate apprehension of metal-semiconductor systems with big lattice mismatch such as Al/Si, Cu/Si, Ag/Si, aˆ¦ , for both cardinal and practical application [ 13,14,15,16 ] . The metal-semiconductor systems have possible in production of stable Schottky barriers, and carry oning electrodes in big graduated table integrated circuits [ 17 ] and for this ground in this work deposition of Ag on glass and Si has been compared.Since in many applications in different engineerings, the distribution of grain size and crystalline orientation every bit good as their fluctuations strongly can impact the assorted belongingss public presentation, dependability and stableness of thin movies in optical and electrical devices. In this work the influence of different deposition parametric quantity ( movie thickness, substrate, tempering temperature ) on microstructure and morphology of Ag thin movies have been investigated. For surfacing metals by sputtering the structural zone theoretical account ( SZM ) , dwelling of three zones separated by two boundary temperature proposed by Movchan [ 18 ] , for polycrystalline movie construction has been refined by Thronton [ 18 ] , in which an extra zone ( passage zone, T ) appears between zone I and zone II. In our earlier plants on residuary emphasis in Cu and Ti thin movies at different substrate temperature the consequences showed good understanding with SZM [ 19 ] . In present work besides this theoretical account has been employed for description of the consequence of deposition temperature. Although many plants have been carried on Ag thin movies, but either movie thickness has been really low, so discontinuous movies take topographic point or movie thickness scope is really limited [ 20,21,22,23 ] .To the best of our cognition comparing of tempering and substrate temperatures effects on different substrate stuffs has non been reported.
Silver thin movies has been deposited on Si and glass substrate under assorted experimental conditions, a vacuity system ( Hind High Vacuum, H.H.V ) , with basal force per unit area of 10-6 mbar was employed, therefore the background force per unit area prior to silver coating was around this value. Circular Ag mark phonograph record with 125mm diameter and 3mm thickness was made of pure Ag ( 99.9 % ) . For plasma formation research class Ar ( 99.99 % ) was used in force per unit area scope of 2A-10-2 – 2A-10-1 mbar. To change the deposition rate discharge current was changed from 0.2 to 1.2 A, while Ar force per unit area was kept changeless, electromotive force alterations was in scope of 300-450 Volts, depending on Ar force per unit area. For sputtering the optimal distance between Ag mark and substrate ( glass, Si ) was found to be 10 centimeter and this distance was kept fixed for all samples in this work. Deposition rate and movie thickness were measured by usage of vibrating quartz crystal thickness proctor, Ag movie with assorted thickness ( 50-1000nm ) with optimal surfacing rate of 4.2nm/s were deposited. The substrates were fixed on chromium steel steel holder, which could be heated to a set temperature as required in each tally of coating. The substrate temperature ( Ts ) was controlled by programmed thermoregulators and digital thermocouples fixed inside holes on the surface of substrate holders. Just before usage of substrates they were cleaned and made ready for deposition so the native oxide on the surface of substrate was later removed. Si ( 100 ) P type wafer was cut to required dimensions ( 1A-1cm ) and round glass substrate with 2 centimeters diameter and 1mm thickness were used for surfacing Ag. Before start surfacing discharge was runned for few proceedingss and the produced plasma was checked by spectrometer with high deciding power, the shutter was removed when merely line spectra belonging to Ag and Ar atoms and ions were observed and no set spectra due to taint was observed ( this checking was carried out via window of sing port of vacuum chamber ) . For tempering the Ag movie samples a vacuity and gas flow ( Ar ) oven was employed. To look into the effects of deposition parametric quantities on microstructure, crystallographic orientation and grain size surveies, X-ray diffraction ( theoretical account PW30 Philips ) was used. Scaning negatron microscopy ( SEM ) of the produced Ag thin movies besides was carried out ( Model VEGA/XMU ) to give better position and information.
consequence & A ; DISCUSSION
Silver ( FCC, baronial metal ) was coated on glass and Si substrate with deposition rate of 4.2 nm/s at room temperature ( 25oC ) , Fig ( 1a, B ) show XRD form of Ag/Si and Ag/glass severally for different Ag movie thickness.
Fig1. XRD form of Ag thin movies for different Ag movie thickness ( a ) Ag/Si, ( B ) Ag/Glass
In both instances ( 111 ) of Ag extremum is really intense compared with ( 200 ) extremum, which exhibit that ( 111 ) is the preferable orientation for both substrate used. Since effectual manner of cut downing electron migration in metallic movies Cu, Al, Au, Ag, aˆ¦ is production of thin movies with strong ( 111 ) orientation [ 4 ] , so these consequences can be really of import in that regard. ( 111 ) orientation in thin metal movies can heighten their electromigration lifetime, as an of import characteristic for device applications, so fluctuation of ( 111 ) strength ( I111 ) and ( 200 ) ( I200 ) against thickness of Ag was plotted for both Ag/Si, Ag/glass samples, Figs ( 2a, B ) .
Fig2. Variation strength ( 111 ) , ( 200 ) against Ag thickness for ( a ) Ag/Si, ( B ) Ag/Glass
Intensity of ( 111 ) extremum additions much sharper than strength of ( 200 ) extremum with movie thickness and for both substrates this rise of strength is really similar, which means different type of substrate do non alter this state of affairs. For computation of grain size and analyzing its fluctuation with the deposition parametric quantities, Scherrer equation has been used [ 24 ] .
( 1 )
Where D is grain size diameter, is X-ray wavelength ( ) , is the Brrage angle, B is the full half breadth of peak upper limit and K is a dimensionless invariable which for metal movies normally is taken as unity [ 24 ] . Although this equation for exact computation grain size is non really suited and equal, but for comparing the consequences is good plenty particularly when SEM of the samples besides is carried out. When fluctuation of grain size versus Ag thickness was plotted ( Fig 3 ) , grain growing for Ag/Si sample with silver thickness can be observed, while for Ag/glass after certain Ag thickness, a crisp rise of grain is happened, followed by fast decrease of grain growing for 700nm thickness of Ag. SEM images of these samples besides showed this state of affairs, for Ag movie with 750nm thickness many big grain can be observed while for lower and higher thickness of Ag really smooth movie with little grains is obtained, Figs ( 4a, B, degree Celsius ) .
Fig3. Grain size of Ag movies versus the movies thickness
Fig4.Electron micrographs from Ag movies on Si at different thickness: ( a ) 250nm, ( B ) 750nm, ( degree Celsius ) 1000nm
To look into the consequence of substrate temperature on microstructure, preferable orientation and grain growing fluctuation, Ag movies with movie thickness of 250nm with surfacing rate of 4.2nm/s were deposition on Si and glass substrate at different deposition temperatures. Fig ( 5a, B ) show XRD form of the Ag samples ( Ag/Si, Ag/Glass ) for different substrate temperatures, in both instances ( 111 ) extremum is once more the preferable orientation. Fig ( 6 ) gives secret plan of grain size fluctuation against reduced temperature ( ) , ( where TS is substrate temperature, and TM is the runing point temperature of surfacing stuff, both in Kelvin grade ) .
Fig5. XRD form of Ag movies deposited at assorted substrate temperature for, ( a ) Ag/Si, ( B ) Ag/Glass
Fig6. Grain size of Ag movies as a map reduced temperature ( Ts/Tm ) .
For Ag/Si grain growing addition with decreased temperature, while for Ag/glass after a little addition for, a crisp rise of grain growing takes topographic point, followed by fast decrease at higher temperature. Since deposition of thin metal movies by sputtering on glass substrate obey the structural zone theoretical account, this behaviour of grain growing is due to alter of Thornton zones and besides it can be due to thermal grooving which Michigans and decreased growing of grains. SEM images of these samples besides show this state of affairs, in high substrate temperature big grains can be observed, Fig ( 7 ) . To analyze how annealing temperature can impact the structural and grain growing of Ag movies, two samples of Ag movies with 250nm thickness with 4.2nm/s surfacing rate were deposited on glass and Si at room temperature. Both of these samples were annealed up to temperature of 325oC in vacuity for 60 proceedingss Figs ( 8a, B ) show XRD form of Ag/glass, Ag/Si severally. Once once more ( 111 ) extremum is preferred orientation in both instances, secret plan of grain size fluctuation against tempering temperature has been given in Fig ( 9 ) .
Fig7. SEM image of Ag/Si movie on deposited 400K
Fig8. XRD form of Ag thin movies against tempering temperature ( a ) Ag/Si, ( B ) Ag/Glass
Fig9. secret plan of grain size as annealing temperature
For Ag/Si thin movie grain growing increases with temperature up to 250oC and so grain growing Michigans and even shows a small decrease at higher temperature. But for Ag/glass sample at low temperature grain size rises with temperature up to 150oC, so a sudden lessening occurs and after that remains approximately changeless at higher temperature. This is stating that in low temperature part for both samples grain rise takes topographic point, but at higher tempering temperatures big grains break to smaller one, but for Ag/glass this happens at lower temperature. This can be due to alter of adhesion force between thin movie ( Ag ) and substrate, which means a alteration of emphasis and strain between movie and substrate took topographic point at these tempering temperatures.
To compare the tempering and substrate temperature effects on microstructure of Ag thin movies which have been coated on Si, Fig ( 10 ) shows how grain growing takes topographic point for these samples with temperature. But for the annealed samples grain are larger which can be due to agglomeration of Ag mean while after temperature of 225oC this grain rise Michigans and demo a decrease at higher temperature. To see the consequence of different substrates, and surface status, 250nm Ag was coated on glass, and on smooth and unsmooth surface of Si, SEM pictures of these samples which have been coated under similar experimental status is shown in Figs ( 11a, B, degree Celsius ) on smooth surface of Si, really unvarying Ag thin movies with little grains can be observed, while for unsmooth surface of Si, larger grains with few agglomerations can be seen. But for glass substrate figure of big grains due to agglomeration is discernible which can be due to smoothness of glass surface, the grain growing from XRD consequences agree with these SEM observations.
Fig10. comparison grain size of tempering and deposition temperature of Ag/Si
Fig11. SEM image of Ag movies on different substrates ( a ) : on smooth surface of Si, ( B ) : Rough surface of Si, ( degree Celsius ) : Glass
SUMMERY & A ; CONCLUSION
For word picture of Ag thin movies coated on Si and glass substrate and analyzing the effects of deposition parametric quantities on microstructure and crystalline orientation and grain size fluctuations assorted silver thin movies under different conditions were investigated. Grain size for Ag/Si sample additions really small with movie thickness, but for Ag/glass grain growing is crisp and so at higher Ag thickness a decrease of grain size takes topographic point. This can be due to status and smoothness of glass surface compared with Si surface and besides adhesion of Ag to Si and glass is really different. Addition of movie thickness did non alter the preferable orientation ( ( 111 ) ) , besides extremum ( 111 ) was the intense extremum for both substrate which means preferable orientation is independent of used substrates. Changing deposition temperature was described by SZM, for Ag/glass samples, but Ag/Si did non obey this structural theoretical account. Increase of substrate temperature did non alter the preferable orientation for both substrates, but thermic rifling for Ag movies on glass takes topographic point, and besides for Ag/Si addition of ( 111 ) extremum strength is non the same for glass substrate which is formless stuff. For tempering temperature one time once more ( 111 ) is the preferable orientation, for Ag/Si grain growing with temperature is observed, which is due to enlargement and smaller grains get together to do larger grains. But for Ag/glass samples grain growing Michigans at higher tempering temperature and followed by a decrease which is due to interrupting of larger grains to smaller 1s, and this can happen because of alterations of adhesion force between thin movies ( Ag ) and substrate. Type and surface raggedness of substrate can change the growing of grains and agglomeration for Ag thin movies. At really low deposition rate adhesion of movie to substrate ( specially glass ) was non that good and really high deposition rate 14 nm/s produced formless Ag movie, so optimal rate of 4.2nm/s was used. Heating can better the adhesion of movie to substrate, specially for samples with higher deposition temperature which produces thin movies with good quality and stableness.