PVD DEPOSITION METHODS AND APPLICATIONS •Cristian P. LUNGU •National Institute for Laser, Plasma and Radiation Physics, Magurele-Bucharest, ROMANIA PVD Parameters ] Structure ] Properties Outline •Physical vapor deposition •Combinatorial PVD techniques •DCA 2173 Combinatorial PVD machine •PVD process parameters ... thin film properties •Thin film growth: PVD Parameters ] Structure ] Annealed structure ] Properties I II Pure and mixed films preparation using thermionic vacuum arc method Thin Film Deposition (a compilation from literature) PVD: Physical Vapor Deposition IBAD: Ion Beam Assisted Dep. CVD: Chemical Vapor Deposition PE: Plasma Enhanced MO: Metal-Organic Additive Methods Deposition from vapor Deposition from liquids CVD Sputtering Evaporation Laser ablation PECVD MOCVD Sol-Gel Electro-deposition PVD plasma2 Sputtering (magnetron) Sputter-down configuration Substrate Power Supply N S N S N S Magnetron Design reduced field strength less balanced Position of the magnetic 'Null Point' and strength of the magnetic field define the degree of balance or unbalance of a magnetic system. The "ease" of electron release from the magnetic trap is determined mainly by the geometrical position of the null point of the magnetic field. If Z is large (i.e. ≥W) then the chance of an electron escaping is low and hence the magnetron is well balanced. Magnetron Sputtering Cathode Magnetic materials Max. rate (balanced) K1 Sputtering of Magnetic Materials figure3 Fe used_3 Sputtering process •momentum transfer process oinvolves top 10 Å omodel as hard sphere collisions for energies < 50 keV •95% of incident energy goes into target oè COOL the target (RF: avoid long periods with high reflected power) •5% of incident energy is carried off by target atoms ofor typical energies of 5-100 eV •target atoms eject with a non-uniform distribution ocosine distribution (like a surface source) Sputter processes (at the target) SPUTTERED PARTICLES BACKSCATTERED PARTICLES SECONDARY ELECTRONS •target atoms ejected •target ions ejected (1 - 2 %) •electrons emitted ohelps keep plasma going • •Ar+ ions reflected as Ar neutrals •Ar buried in target •photons emitted Target – Substrate Transport •Target atoms pass through Ar gas and plasma environment oone Ar+ ion for every 10,000 Ar neutrals oelectrons in plasma collide with Ar neutrals to form ions and more electrons •Target atoms collide with Ar atoms, Ar+ ions and electrons otreat as random walk "diffusion" through gas otarget atoms lose energy (down to 1-10 eV) ochemical reactions may occur in gas onot a line of sight process (unless pressure reduced) ocan coat around corners Arrival at the substrate •Adding to film: •impingement (deposition) on surface sticking coefficient typically not 1 •Removing from film: •reflection of impinging atoms •desorption (evaporation, resputtering) from surface Outline •Physical vapor deposition •Combinatorial PVD techniques •DCA 2173 Combinatorial PVD machine •PVD process parameters •Thin film growth Combinatorial technique •Method based on the creation of sets of materials (“materials libraries”) processed under identical, controlled conditions having regularly varying compositions. • Co-deposition Wedges In-situ masking Wang et al., Science, Vol 279, 1712, 1998 Combinatorial methods •Precursor deposition using shadow masks •Controlled thermal diffusion _ stoichiometric compounds In-situ Masking In-situ mask handling: • mask rotation • mask removal • replace / change 4-D shutter movements Precursor/Mask Technique ü Good for studies of dopants ü Large variety of different materials on a single wafer Ñ Method very complex for gradients Ñ Complex mask handling Ñ Mixing of the elements has to be performed in an additional process step _ adds problems of uniformity and reproducibility Combinatorial methods •Composite targets (Hanak, RCA) ûComposition variation fixed by target geometry ûDifferent sputter rates of different materials Ò _ Difficult control of stoichiometry üDirect mixing Combinatorial methods •Co-deposition TiPdCr TiNiCuPd TiNiAu Co-deposition Technique ü Direct mixing of the elements Ñ Large substrates needed Ñ Large-area uniformity required Ñ Precision control of stoichiometry is difficult Combinatorial methods •Layered wedge deposition Deposition of wedge-type films with movable shutters AxByCz AxByCzDconst. C B A DSC00135 Outline •Physical vapor deposition •Combinatorial PVD techniques •DCA 2173 Combinatorial PVD machine •PVD process parameters •Thin film growth DCA 2173 for Combinatorial PVD Loadlock •keeps the other chambers clean •designed for 4“ Si wafers •can also use 4“ diameter carriers –must keep small samples from sliding or blowing away! •sample thickness < 2 cm Load Lock open Mask Chamber •< 2x 10-9 mTorr •6 storage slots: masks or wafers •Place or remove masks •Rotation of masks: • 90° increments •Tolerances very close. Use with caution! Linear chamber K1 K1 open_2 K1 •Magnetically configurable cathodes –3x DC, pulsed, 5 kW –3x RF, 300 W, 13.56 MHz •Target-to-Substrate: 8.1 – 26.6 cm (13.8 cm) •Pressure: 1–28 mT (5 mT) •Gas: Ar, N2, O2, Xx •RT – 1000°C (25° C) •4-D shutters •±178° oscillation (static) •Bias: 0 – 50* W RF •Magnetic field: 0.7 T •Quartz crystal monitor Linear chamber K1 Quartz crystal Target Wafer / Substrate 4D shutters Source shutter (open) Main shutter K1 critical distances Wide upward diagonal Robot transfer height = 26.4 mm 4-D shutters = 138.3 mm Manipulator maximum = 185 mm Manipulator minimum = 0 mm Manipulator Target XTM/2 quartz crystal Target a Substrate maximum = 266.45 mm Target a Substrate minimum = 81.45 mm Diagonal hell nach unten Target a XTM/2 = 110.05 mm Target a Substrate with 4-D shutters £ 128.15 mm Co-sputter chamber K2 2173 control & K2 K2 •Magnetically configurable cathodes –2x DC, pulsed, 5 kW (1x) –3x RF, 300 W, 13.56 MHz •Target-to-Substrate: 19.5 cm to focal point •Pressure: 1–28 mT (5 mT) •Gas: Ar, N2, O2, Xx •RT – 1000°C (25° C) •4-D shutters •0 or 10 rpm rotation speed •Bias: 0 – 50* W RF • 0 – 500 V DC (0–3 mA) •Quartz crystal monitor Co-sputtering K2 critical distances Co-sputtering: (best mixing; best deposition rate) 5-cathodes aimed to the focal point and Substrate just below 4D shutters then Target a Wafer center = 195.3 mm Target a XTM/2 = 187 mm Single or Multilayers: (best uniformity) Each cathode aimed to wafer edge then Target a Substrate edge = 189 mm Outline •Physical vapor deposition •Combinatorial PVD techniques •DCA 2173 Combinatorial PVD machine •PVD process parameters •Thin film growth Process Parameters in PVD •Seed layer • •Pressure •Voltage (Power) •Temperature •Substrate bias •Target-to-Substrate distance •Target-to-Substrate angle (K2) •Substrate rotation/oscillation •Sputter gas •Magnetic field (K1) Target characterization Fe: DC, K1 Substrate Bias High negative bias Positive bias Parameters in PVD •Seed layer • •Pressure •Power •Temperature •Bias •Target-to-Substrate •Angle; rotation •Sputter gas •Magnetic field • •Induce preferred orientation •Adhesion to substrate •Deposition rate •Particle energy •Surface bombardment •Mean free path •Arrival angle •Surface diffusion length •Depth diffusion length Thin Film Property Optimization Parameters – Structure – Properties Microstructure effects for H-storage Outline •Physical vapor deposition •Combinatorial PVD techniques •DCA 2173 Combinatorial PVD machine •PVD process parameters ... ¹ Properties! •Thin film growth W. Espe and M. Knoll: Werkstoffkunde der Hochvakuumtechnik,(1936) S. Dushman: Scientific Foundation of Vacuum Techique, (1949) H. Mayer: Physik dünner Schichten, Teil I (1950) und II (1955) O. S. Heavens: Optical Properties of Thin Films (1955) L. Holland: Vacuum Deposition of Thin Films, (1956) M. Auwärter: Ergebnisse der Hochvakuumtechnik und der Physik dünner Schichten, (1957) K. L. Chopra: Thin Film Phenomena, (1969) L. I. Maissel, R. Glang: Handbook of Thin Film Technology, (1970) H. Mayer: Physics of thin films Parts, I and II, (Complete bibliography), (1972) B. Lewis, J.C. Anderson: Nucleation and Growth of Thin Films (1978) Reference reviews - books HISTORY OF THIN FILMS GROWTH, TECHNIQUES, CHARACTERIZATION Péter B. Barna Research Institute for Technical Physics and Materials Science of HAS Budapest, Hungary Thin Film Growth •Steps in Film Formation 1.thermal accommodation 2.binding 3.surface diffusion 4.nucleation 5.island growth 6.coalescence 7.continued growth • Thin Film Growth •target atoms and ions impinge •electrons impinge •Ar atoms and residual molecules impinge oAr pressure typically 1 - 100 mTorr oAr may be incorporated into film o10-6 Torr: ~1 monolayer/s impinges a surface •energetic particles may modify growth •substrates heat up o100° – 200°C is possible (heat of condensation can also be significant) ofor a thermally isolated sample (no heat conduction) Thin Film Growth •Adding to film: •impingement (deposition) on surface •Removing from film: •reflection of impinging atoms •desorption (evaporation, resputtering) from surface Thin Film Growth Modes •Island growth (Volmer - Weber) • • • •form three-dimensional islands •conditions: ofilm atoms more strongly bound to each other than to substrate oand/or slow diffusion • island growth model â â Thin Film Growth Modes •Layer by layer growth (Frank van der Merwe) • • • •generally highest crystalline quality •conditions: ofilm atoms more strongly bound to substrate than to each other oand/or fast diffusion layer by layer growth model â â Thin Film Growth Modes •Mixed growth (Stranski - Krastanov) • • • • •initially layer-by-layer •then forms three dimensional islands • è change in energetics mixed growth model â â Microstructural Evolution Å ð nm nm ð µm P. Barna, et al. Conclusions on structure evolution in elemental thin films * correlation exists between grain size, grain morphology, surface topography and texture, these are developing together * the in-plane size (column diameter) and the orientation of crystals can be controlled by the temperature * the as-deposited structure has low thermal stability * the possible zones are: Zone I, Zone T and Zone II * in Zones I and II the structure and orientation are uniform along thickness, crystals penetrate through the film * no grain boundaries parallel to the substrate, i.e. no equiaxed grain morphology (Zone III ) can exist Ts is the deposition temperature and Tm is the melting point in K PVD Structure Zone Models •Movchan – Demchishin T/Tm : grain structure •Thornton Inert gas pressure •Messier Particle energy http://www.cerac.com/pubs/images/tszmodel.jpg Messier SZM Movchan-Demchishin: Evaporation Thornton: Sputtering Conclusions (P.B. Barna, M. Adamik, Thin Solid Films, 317(1998)27; I. Petrov, P.B. Barna, L. Hultman, J.E. Greene, J. Vac. Sci. Technol.,21(2003)S117) • The structure evolution in polycrystalline films (both elemental and multicomponent) can be described by a pathway (characteristic for every materials system) on the basis of the same fundamental phenomena of structure formation: nucleation, crystal growth, grain growth • The operation of every single fundamental phenomenon is related to a thermally activated atomic process (temperature dependence of the pathway) • The atomic processes are: adatom diffusion (Ts > ~ 0,05Tm) (nucleation) self surface diffusion (Ts > ~ 0,1Tm) (crystal growth, coalescence) bulk diffusion (Ts > ~ 0,3Tm) (grain growth) in multicomponent films additionally: chemical interaction among species including process induced segregation of excessive species resulting in delayed nucleation of secondary phase(s) •Fully acknowledge the contribution of Alan Savan, CAESAR, Germany Acknowledgment