HANDBOOKOF PHYSICAL
`VAPOR DEPOSITION
`(PVD) PROCESSING
`Film Formation, Adhesion, Surface Preparation
`
`and Contamination Control
`
`TARGET
`
`SUBSTRATE
`a,
`Crasia)
`1?——
`
`SUBSTRATE
`
`by
`Donald M. Mattox
`
`NOYES PUBLICATIONS
`
`SamsungElectronics Co., Ltd. v. Demaray LLC
`SamsungElectronic's Exhibit 1032
`Exhibit 1032, Page 1
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`

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`Copyright © 1998 by Noyes Publications
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`Nopart ofthis book may be reproduced orutilized
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`in any formor by any means, electronic or
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`mechanical, including photocopying, recording or
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`by any information storage and retrieval system,
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`without permission in writing from the Publisher.
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`Library of Congress Catalog Card Number: 97-44664
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`ISBN: 0-8155-1422-0
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`Printed in the United States
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`Published in the United States of America by
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`Noyes Publications
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`169 Kinderkamack Rd., Park Ridge, NJ 07656
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`1098765432
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`Library of Congress Cataloging-in-Publication Data
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`
`Mattox, D. M.
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`
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`Handbook of physical vapor deposition (PVD) processing / by
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`Donald M. Mattox.
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`em.
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`Includes bibliographical references and index.
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`ISBN 0-8155-1422-0
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`
`1. Vapor-plating--Handbooks, manuals, etc.
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`TS695.M38
`1998
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`671.7'35--de21
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`I. Title.
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`97-44664
`cIP
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`Ex. 1032, Page 2
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`Ex. 1032, Page 2
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`

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`228 Handbook of Physical Vapor Deposition (PVD) Processing
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`CAGE
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`ooh!it§Sei*A°
`L eeclee ey e
`ee
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` ROTATING
`eeUSCATHODE
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`+jHiak voLT- [J
`AGE SUPPLY
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`MONITOR
`—|HIGH VOLTAGE|+
`SUPPLY
`
`GROUND BHIELD
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`Figure 4-6. Barrel ion plating system configuration with a triode DC discharge.
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`The DC diode discharge cannotbe used to sputter dielectric target
`materials, since charge buildup on the cathode surface will prevent bom-
`bardmentof the surface.
`If there are reactive gases in the plasma their
`reaction with the target surface can lead to the formation of a surface that
`has a different chemical composition than the original surface. This
`change in composition leads to “poisoning”of the cathode surface and thus
`changes the plasma parameters.
`In the extreme, poisoning will cause
`bombardmentof the cathode to cease due to surface charge buildup. If an
`insulating surface forms on the DC cathode, charge buildup will cause
`arcing over the surface.
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`Ex. 1032, Page 3
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`

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`Low-Pressure Plasma Processing Environment 229
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`The suppression of arcs generated in the DC discharge (are sup-
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`pression) are important to obtaining stable performance of the DC power
`supplies particularly when reactively sputter depositing dielectric films.°!
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`Arcing can occur anytime a hot (thermoelectron emitting) spot is formed or
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`when surface chargingis different over surfaces in contact with the plasma.
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`Arc suppression is obtained by momentarily turning off the power supply
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`or by applying a positive bias when an arc is detected.
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`Pulsed DC
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`When a continuous DC potential is applied to a metal electrode
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`completely covered with a dielectric material, the surface of the dielectric
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`is polarized to the polarity, and nearly the voltage,of the metal electrode. If
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`the surface potential is negative, ions are accelerated out of the plasma to
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`bombardthe surface giving sputtering, secondary electron emission, “atomic
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`peening,” and heating. However, since the secondary electron emission
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`coefficient is less than one the surface will buildup a positive surface
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`charge and the bombardment energy will decrease then bombardmentwill
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`crease. This problem can be overcome by using a pulsed DC rather than a
`continuous DC.
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`Pulsed DC uses a potential operating in the range 50-250 kHz
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`where the voltage, pulse width,off time (if used), and pulse polarity can be
`varied.'*7] The voltage rise and fall is very rapid during the pulse. The
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`pulse can be unipolar, where the voltage is typically negative with a no-
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`voltage (off) time, or bipolar where the voltage polarity alternates between
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`negative and positive perhaps with an off time. The bipolar pulse can be
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`symmetric, where the positive and negative pulse heights are equal and the
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`pulse duration can be varied or asymmetric with therelative voltages being
`variable as well as the duration time.!48] Figure 4-7 shows some DC
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`waveforms. Generally in asymmetric pulse DC sputter deposition, the
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`negative pulse (e.g., -400 V) is greater than the positive pulse (e.g,. +100
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`V) and the negative pulse time is 80-90% of the voltage cycle and the
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`positive pulse is 20-10% of the voltage cycle.
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`In pulse DC sputtering, during the positive bias (and off-time),
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`electrons can move to the surface from the plasma and neutralize any
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`charge build-up generated during the negative portion of the cycle. During
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`the negative portion of the cycle, energetic ion bombardment can sputter
`dielectric surfaces.
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`rereeeeeeaeeee
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`Ex. 1032, Page 4
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`Ex. 1032, Page 4
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`

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`a. Continuous DC
`b. Unipolar Pulsed DC
`c. Bipolar Pulsed DC
`d. Asymmetric Bipolar Pulsed DC
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`Figure 4-7. DC waveforms.
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`Pulsed DC powercan be obtained by switching a continuous DC
`or sinewave powersupply with auxiliary electronics!*! or can be obtained
`from a specially designed pulsed powersupply that generally allows more
`flexibility as to waveform. The pulsed power supply generally incorpo-
`rates arc suppressionthat operates by turningoff the voltage or by applying
`a positive voltage whenthe arcinitiates. Pulsed plasmasarealsoofinterest
`in plasma etching and plasma enhanced CVD (PECVD).'°!
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`4.4.4 Magnetically Confined Plasmas
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`Balanced Magnetrons
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`In surface magnetron plasmaconfigurations the electric (E) (vec-
`tor) and magnetic (B) (vector) fields are used to confine the electron path to
`be near the cathode (electron emitting) surface. An electron moving with a
`component of velocity normal to the magnetic field will spiral around the
`magnetic field lines and its direction will be confined by the magnetic field.
`The frequency of the spiraling motion and the radius ofthe spiral will
`depend on the magnetic field strength. The interaction of an electron
`with the electric and magnetic fields depends on the magnitude and
`vector orientation of the fields (E x B). For example, if the magnetic
`field is parallel to a surface and the electric field is normalto the surface an
`electron leaving the surface will be accelerated away from the surface and
`will spiral around the magnetic field. There will also be a resulting motion
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`Page 5 of 20
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`a]
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`Ex. 1032, Page 5
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`

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`6 P
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`hysical Sputtering and
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`Sputter Deposition
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`(Sputtering)
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`6.1
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`INTRODUCTION
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`The physical sputtering (sputtering) process, or pulvérisation as
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`the Frenchcallit, involves the physical (not thermal) vaporization of atoms
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`from a surface by momentum transfer from bombarding energetic atomic-
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`sized particles. The energetic particles are usually ions of a gascous
`material accelerated in an electric field.4! Sputtering wasfirst observed
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`by Grove in 1852 and Pulker in 1858 using von Guericke-type oil-sealed
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`piston vacuum pumps. The terms “chemical sputtering” and “electro-
`chemical sputtering” have beenassociated with the process whereby bom-
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`bardmentof the target surface with a reactive species producesa volatile
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`species.'] This process is now often termed “reactive plasma etching”or
`“reactive ion etching” andis important in the patterning ofthin films.!!
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`Sputter deposition, which is often called just sputtering (a poor use
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`of the term), is the deposition of particles whose origin is from a surface
`(target) being sputtered. Sputter deposition of films was first reported by
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`Wright in 1877 and was feasible because only a relatively poor vacuum is
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`needed for sputter deposition. Edison patented a sputter deposition process
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`for depositing silver on wax photograph cylinders in 1904. Sputter deposi-
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`tion was not widely used in industry until the need developedfor reproducible,
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`Ex. 1032, Page 6
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`Ex. 1032, Page 6
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`Physical Sputtering and Sputter Deposition 321
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`Figure 6-2. Collision of particles.
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`The maximum energyis transferred when cos@ = | ( zero degrees)
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`and M,=M,. Therefore matching the atomic mass of the bombarding ion to
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`the target atom is importantto the sputtering yield. This makes krypton (84
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`amu), xenon (131 amu) and mercury (201 amu) ions attractive for sputter-
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`ing heavy elements, and light ions such as nitrogen (14 amu) unattractive.
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`This advantage is typically outweighed by other considerations such as
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`cost of the sputtering gas, health concerns or the desire to perform “reactive
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`sputter deposition” of oxides and nitrides.
`It is interesting to note that
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`much of the early work on sputtering was done using mercury ions.
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`Typically argon (40 amu) is usedforinert gas sputtering sinceit is
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`a relatively inexpensive inert gas. Mixtures of argon and nitrogen, argon
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`and oxygen or argon and methane/acetylene are used for sputtering in
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`reactive sputter deposition.
`In some cases, energetic ions of the target
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`material can bombard the target producing “self-sputtering.” This effect is
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`important in ion plating using ionized condensable ions(“film ions”) formed
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`by arc vaporization or by post-vaporization ionization of sputtered or
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`thermally evaporated atoms.
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`6.2.2 Sputtering Yields
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`The sputtering yield is the ratio of the numberof atoms ejected to
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`the numberof incident bombarding particles and depends on the chemical
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`bonding of the target atoms and the energy transferred by collision. The
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`Ex. 1032, Page 7
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`Ex. 1032, Page 7
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`338 Handbook of Physical Vapor Deposition (PVD) Processing
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`materialis removed from the target layer-by-layer. This allows the deposi-
`tion of some rather complex alloys such as W:Ti for semiconductor
`metallization,!8Al:Si:Cu for semiconductor metallization,7) and M(etal)-
`Cr-Al-Y alloys for aircraft turbine blade coatings.
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`6.5.2 Reactive Sputter Deposition
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`Reactive sputter deposition from an elementaltarget!8*1(89) relies
`on: (a) the reaction of the depositing species with a gaseousspecies, such as
`oxygen or nitrogen, (b) reaction with an adsorbed species, or (c) reaction
`with a co-depositing species such as carbon to form a compound. The
`reactive gas may be in the molecular state (e.g., N,, O,) or may be
`“activated” to form a more chemically reactive or more easily adsorbed
`species. Typically, the reactive gases have a low atomic masses (N=14,
`O=16) andare thus not effective in sputtering. It is therefore desirable to
`have a heavierinert gas, such as argon,to aid in sputtering. Mixing argon
`with the reactive gas also aids in activating the reactive gas by the Penning
`ionization/excitation processes.
`Typically, a problem in reactive sputter deposition is to prevent the
`“poisoning” of the sputtering target by the formation of a compound layer
`on its surface.5!) Poisoning ofa target surface greatly reducesthe sputter-
`ing rate and sputtering efficiency. This problem is controlled by having a
`high sputtering rate (magnetron sputtering) and controlling the availability
`of the reactive gas, such that there will be enough reactive species to react
`with the film surface to deposit the desired compound,but not so muchthat
`it will unduly poison the target surface.
`The appropriate gas composition and flow for reactive sputter
`deposition can be established by monitoring the partial pressure of the
`reactive gas as a function ofreactive gas flow,°!-3] or by impedance of
`the plasma discharge. Figure 6-8 showsthe effect of reactive gas flow on
`the partial pressure of the reactive gas in the reactive sputter deposition of
`TiN. Under operating conditions of maximum flow and near-minimum
`partial pressure, the deposit is gold-colored TiN and the sputtering rate is
`the same as metallic titanium. At higher partial pressures, the sputtering
`rate decreases and the film is brownish. As the target is poisoned, the
`deposition rate decreases. Whenthe nitrogen availability is decreased, the
`target is sputter-cleaned and the deposition rate rises.
`The gas composition should be determined for each deposition
`system and fixture geometry. A typical mixture for reactive sputter
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`Ex. 1032, Page 8
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`

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`Physical Sputtering and Sputter Deposition 339
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`deposition might be 20% nitrogen and 80% argon wherethe partial pres-
`sure of nitrogen during deposition is 2 x 104 Torr andthe total gas flow is 125
`sccm. Gases mixtures are typically controlled using individual mass flow
`meters On separate gas sources though specific gas mixtures can be purchased.
`Figure 6-9 depicts a typical reactive sputter deposition system.
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`
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`Optimum
`Operating
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`Conditions
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`Continuously Increasing Flow
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`>
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`2a
`3-
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`a o
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`s=&C
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`c®o
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`So
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`==
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`—_—>
`Nitrogen Flow
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`Figure 6-8. Nitrogen partial pressure and flow conditionsfor the reactive sputter deposi-
`tion of TiN with constant target power(adapted from Ref. 51).
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`In reactive deposition, the reactive gases are being pumped(‘“get-
`ter pumping”) by the depositing film material. Since the depositing film is
`reacting with the reactive gas, changesin theareaorrate ofthe film being
`deposited will change the reactive gas availability and the film properties.
`Thus,it is important to use the samefixture, substrate, and vacuum surface
`areas as well as deposition rate, in order to have a reproducible reactive
`sputter deposition process. Changes in the geometry (loading factor) or
`deposition rate will necessitate changes in gas flow parameters.) The gas
`density (partial pressure) of the reactive gas in the plasma can be monitored by
`optical emission spectroscopy or massspectrometry techniques.01H931
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`Ex. 1032, Page 9
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`

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`340 Handbookof Physical Vapor Deposition (PVD) Processing
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`Since gas pressure is importantto the properties of the sputter depos-
`ited film it is important that the vacuum gauge be periodically calibrated and
`located properly and pressure variations in the chamber be minimized.
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`Optical Emission
`Spectrometer
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`Hi-Vac Valve
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`High Vacuum Pump(s)
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`tose Flow
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`Variable Conductance By-Pass
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`Roughing Pump(s)
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`Roughing Valve
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`Figure 6-9. Typical reactive sputter deposition system.
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`In somereactive deposition configurations,the inert gas is injected
`around the sputtering target and the reactive gas is injected near the
`substrate surface. This inert “gas blanket”over the target surface is helpful
`in reducing target poisoning in somecases.
`In reactive deposition, the depositing material must react rapidly
`or it will be buried by subsequent depositing material. Therefore, the
`reaction rate is an important consideration. The reaction rate is determined
`by the reactivity of the reactive species, their availability, and the tempera-
`ture of the surface. The reactive species can be activated by a numberof
`processes including:
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`¢ Dissociation ofmolecular species to more chemically reactive
`radicals (e.g., N, + e— 2N° and NH; + e& N° + 3H?)
`¢ Production of new molecular species that are more
`chemically reactive and/or more easily absorbed on surfaces
`(e.g., O, + e— 20° then O° + O, > O;)
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`Ex. 1032, Page 10
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`

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`Physical Sputtering and Sputter Deposition 341
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`energy
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`° Production ofions—recombinationat surfaces releases energy
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`* Adding internal energy to atoms and molecules by creating
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`metastable excited states—de-excitation at surfacesreleases
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`e Increasing the temperature of the gas
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`e Generating short wavelength photons (UV) that can
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`stimulate chemical reactions
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`° Generating energetic electrons that stimulate chemical reactions
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`* Ions accelerated from the plasma to the surface promotes
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`chemical reactions on the surface (bombardment enhanced
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`chemical reactions)
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`The extent to which a plasma can activate the reactive gases and
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`provide ions for concurrent bombardment depends on the properties of the
`plasmaandits location.
`In many sputtering systems the plasma conditions
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`vary widely throughout the deposition chamber. This is particularly true for
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`the magnetron configurations where the sputtering plasma is confined near
`the target.
`In such a case, a plasma needs to be established near the
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`substrate surface to activate reactive gases and provide ions for concurrent
`bombardment. This can be done using an unbalanced magnetron configura-
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`tion, application ofan rfto the target, or by establishing a separate auxiliary
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`The reaction probability is also a function ofthe surface coverage.
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`surface than with a TiO, . surface. Figure 6-10 showsthe effectof reactive
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`nitrogen availability on the electrical resistivity of TiN, films. The films
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`have minimum resistivity when the composition is pure titanium and when
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`the composition is near TiN.
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`Another important variable in reactive deposition is concurrent
`bombardmentof the depositing/reacting species by energetic ions acceler-
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`ated from the plasma(“sputter ion plating” or “bias sputtering”). Concur-
`rent bombardment enhances chemical reactions and can densify the deposit-
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`ing film if unreacted gas is not incorporated into the deposit. Bombardment
`is obtained by havingthe surface at a negative potential (applied biasor self-
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`bias) sa that ions are accelerated from the plasma to the surface. Figure 6-
`11 showsthe relative effects of deposition temperature and applied bias on
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`the electrical resistivity (normalized) of a TiN, film.@! The lowestresistiv-
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`ity is attained with both a high deposition temperature and concurrent
`bombardmentalthough a low-temperature deposition with concurrent bom-
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`bardment comesclose.
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`Ex. 1032, Page 11
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`Ex. 1032, Page 11
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`

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`342 Handbook ofPhysical Vapor Deposition (PVD) Processing
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`°e888888&BSB 0
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`RESISTIVITY(\19-cm)
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`OOF
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`GO2
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`003
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`004
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`005 006 O07
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`008
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`009
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`010 ON
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`REACTIVE NITROGENAVAILABILITY
`(partial pressure - microns)
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`i
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`Figure 6-10. TiN resistivity as a function ofnitrogen content (nitrogen availability during
`deposition). (Adapted from Ref. 94.)
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`resistivity
`Normalized
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`Blas = OV
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`Blas = -300V
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`Figure 6-11. TiN resistivity as a function of deposition temperature and concurrent
`bombardment(adapted from Ref. 94).
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`Reactive deposition is used to produce colored wear-resistant
`decorative coatings such as TiN (gold), TiC,N, (bronze, rose, violet, or
`black as x and y are varied) and ZrN (brass). Coatings such as TiN and
`(T1,ADC,Ny are used as wear-resistant coatings on tools, molds, and other
`surfaces. Reactive deposition is used to produce oxide films such as ZrO, and
`TiO,, whichare used to form anti-reflection and band-passcoatings on optical
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`—
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`Ex. 1032, Page 12
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`Physical Sputtering and Sputter Deposition 343
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`components, indium-tin-oxide (ITO), is a transparent electrical conductor
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`and Si0,g, is a material of interest as a transparent, moisture-permeation-
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`barrier materials for packaging applications.
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`The co-depositing material for reactive deposition can be from a
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`second sputtering target. Howeverit is often in the form of a chemical
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`vapor precursor which is decomposed in a plasma and on the surface.
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`Chemical vapor precursors are such materials as acetylene (C,H,) or
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`methane (CH,) for carbon, silane (SiH,) for silicon, and diborane (B,H,)
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`for boron. This technique is thus a combination of sputter deposition and
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`plasma enhanced chemical vapor deposition and is used to deposit materials
`such as the carbides, borides, and silicides.!95! It should be noted that co-
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`deposition does not necessarily mean reaction. For example, carbon can be
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`deposited with titanium to give a mixture ofTi + C but the deposit may have
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`In reactive sputtering, the injection of the reactive gas is important
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`to insure uniform activation and availability over the substrate surface.
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`This can be difficult if, for instance, the film is being deposited overa large
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`area such as on 10' x 12' architectural glass panels where the sputtering
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`cathode can be twelve fect or more in length. In such an application, it may
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`be easier to use quasi-reactive sputtering from a compoundtarget.
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`In “quasi-reactive sputter deposition”the sputtering target is made
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`from the compound material to be deposited and a partial pressure of
`reactive gas in a plasmais used to make-up for the loss of the portion of the
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`gaseous constituent that is lost in the transport and condensation/reaction
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`processes. Typically the partial pressure of the reactive gas used in quasi-
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`reactive deposition is much less than that used for reactive deposition. For
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`example, the gas composition might be 10% oxygen and 90% argon.
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`6.5.3 Deposition of Layered and Graded Composition
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`Structures
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`Layered structures can be deposited by passing the substrate in
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`front ofseveral sputtering targets sequentially. For example, X-ray diffrac-
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`tion films are formed bydepositing thousandsof alternating layers of high-
`Z (W) and low-Z (C) material with each layer being about 30A thick.
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`Layered and graded composition structures can be deposited using
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`reactive deposition. The composition is changed by changing the availabil-
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`ity ofthe reactive gas. Thus one can form layers of Ti-TiN-Ti by changing
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`the availability ofthe nitrogen. Since nitrogen has been incorporated in the
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`Ex. 1032, Page 13
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`Ex. 1032, Page 13
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`348 Handbook ofPhysical Vapor Deposition (PVD) Processing
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`6.6.4 Ton and Plasma Sources
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`In some types of reactive sputter deposition, a few monolayers of a
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`pure metal are deposited and then the substrate is passed in front of a source
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`of the reactive species. By doing this repeatedly, a compound film can be
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`built-up. The source for reactive gas is generally a plasma source, such as
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`a gridiess end-Hall source, where the gas is activated and, in some cases,
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`reactive ions are accelerated to the substrate (Sec. 4.5.1). An easy configu-
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`ration for doing this is to mount the substrates on a drum and repeatedly
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`rotate them in front of the sputtering source and the reactive gas source
`such as with the MetaMode™deposition configuration.)
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`6.6.5 Plasma Activation Using Auxiliary Plasmas
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`Activation of the reactive species enhances chemical reactions
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`during reactive deposition. The plasma used in sputtering will activate the
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`reactive gases but often the plasma volumeis small or not near the substrate
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`surface. Configurations such as the unbalanced magnetron can expand the
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`volume. Auxiliary electron sources can be used to enhance the plasma
`density between the target and the substrate.!!°2] Magnetic fields in the
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`vicinity of the substrate can also be used to enhancereactive gas tonization
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`and bombardment. For example using a magnetic field (100G) in the
`vicinity of the substrate, the ion flux was increased from 0.1 ma/cm? to 2.5
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`ma/cm?in the unbalanced magnetronreactive sputter deposition ofAl,O,.0%!
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`6.7
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`TARGETS AND TARGET MATERIALS
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`For demanding applications, a numberof sputtering target proper-
`ties must be controlled in order to have reproducible processing.!°41 The
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`cost of large-area or shaped sputtering targets can be high. Sometimes by
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`using a little ingenuity, cheaper configurations can be devised such as
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`making large plates from overlapping mosaic tile, rods from stacked
`cylinders, etc. Conformal targets, which conform to the shape of the
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`substrate, may be used to obtain uniform coverage over complex shapes
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`and in some instances may be worth the increased cost.
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`Ex. 1032, Page 14
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`Ex. 1032, Page 14
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`

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`Physical Sputtering and Sputter Deposition 349
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`6.7.1 Target Configurations
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`Targets can have many forms. They may have to be of some
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`predetermined shape to fit supplied fixtures or be conformal to the sub-
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`strate shape. For example conformaltargets may be a sector of a cone for
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`coating a rotating cone, hemispherical to coat a hemisphere, axial rod to
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`coat the inside of a tube, etc. The targets may be moveable or be protected
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`by shutters to allow “pre-sputtering” and “conditioning” of the target
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`before sputter deposition begins. Common sputtering target configura-
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`tions are the planartarget, the hollow cylindrical target, the post cathode,
`the conical target, and the rotating cylindrical target.{101l!06]
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`A single target may be used to deposit alloys and mixtures by
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`having different areas of the target be of different materials. For example,
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`the mosaic target may havetiles of several materials, the rod target may
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`have cylinders of several materials, etc. The composition of the film can
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`then be changed by changing the area ratios. When using this type of
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`target, the pressure should be low so that backscattering does not give
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`“cross-talk” betweenthe target areas. If cross-talk occurs, the sputtering rates
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`may change as one material is covered by the other which has a lower
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`sputtering rate.
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`Multiple targets allow independent sputtering of materials and can
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`be used to allow deposition of layers, alloys, graded compositions, etc. If
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`both the targets and the substrates are stationary, the flux distribution from
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`each target must be considered. Often when using large area targets, the
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`substrates are rotated sequentially in front of the targets to give layered
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`structures and mixed compositions
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`Targets of different materials can have different plasma character-
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`istics in front of each cathode.!°7! This can be dueto differing secondary
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`electron emission from the target surfaces.
`If the substrates are being
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`rotated in front of the sputtering target(s), changes in the plasma may be
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`observed dependingofthe position of the fixture, particularly if the fixture
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`has a potential onit.
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`“Serial co-sputtering” is a term used for a deposition process
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`where material from one sputtering target is deposited onto another sputter-
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`ing target from whichit is sputtered to produce a graded or mixed composition.
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`Serial co-sputtering can be done continuously if the second target is periodi-
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`cally rotated in frontof the first target and thenin front of the substrate.U°8
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`Ex. 1032, Page 15
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`Ex. 1032, Page 15
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`

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`Physical Sputtering and Sputter Deposition 351
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`giving a porous material, and act as virtual leaks and contaminant sources.
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`Porous targets can adsorb contaminants such as water and introduce a
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`processing variable which maybedifficult to control. For materials with
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`poor thermal conductivity, thin targets are more easily cooled than thick
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`targets thus reducing “hot-spots” and the tendencyto fracture.
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`Targets which have been formed by vacuum melting (metals) or
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`chemical vapor deposition (metals, compounds) are generally the most
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`dense. Less dense targets are formed by sintering of powders in a gaseous
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`or vacuum atmosphere with hot isostatic pressing (HIP) producing the
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`most dense sintered product. Sintering sometimes produces a dense
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`surface layer (“skin”) but the underlying material may be less dense and
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`this material becomes exposed with use. In some cases,it may be useful to
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`specify the outgassing rate of the target as a function of temperature.
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`Whenusing alloy or compoundtargets care must be taken that the
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`target is of uniform composition, that is be homogeneous. This is particu-
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`larly a problem when sputtering magnetic alloy material such as Co,Cr,Ta;
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`Co,Ni,Cr,Ta; CoCr,Pt; Co,Fe,Tb; or Co,Cr,Ni,Pt where material distribu-
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`tion in the target is extremely important. In somecases, the composition of
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`the deposited material may be different from that of the target material in a
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`reproducible way due to preferential loss of material. Common examples
`of this problem are:
`ferroelectric films of BaTiO,,!!3! superconducting
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`films such as YBa,Cu,O,, and magnetic materials such as GbTbFe.!!!4] In
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`the case of alloy deposition, the change in composition may be compen-
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`sated for by changing the target composition so as to obtain the desired film
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`composition! !51
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`
`
`
`Second phaseparticles