`
`VAPOR DEPOSITION
`
`(PVD) PROCESSING
`
`Film Formation, Adhesion, Surface Preparation
`
`and Contamination Control
`
`OUHYRATE
`”m":
`1:):
`
`6i“? $1“
`
`"“057
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`“GUI
`
`by
`Donald M. Mattox
`
`NOYES PUBLICATIONS
`
`Samsung Electronics Co., Ltd. v. Demaray lLC
`Samsung Electronic's Exhibit 1032
`Exhibit 1032, Page 1
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`
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`Copyright © 1998 by Noyes Publications
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`No part ofthis book may be reproduced or utilized
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`in any form or 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.
`
`
`
`Handbook of physical vapor deposition (PVD) processing / by
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`
`
`Donald M. Mattox.
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`
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`p.
`cm.
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`
`Includes bibliographical references and index.
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`
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`
`
`ISBN 03155-14220
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`
`I. Title.
`I. Vapor—plating"Handbooks, manuals. etc.
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`T8695.M38
`1998
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`671.735.4021
`97-44664
`ClP
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`
`Ex. 1032, Page 2
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`Ex. 1032, Page 2
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`228 Handbook of Physical Vapor Deposition (PVD) Processing
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` M:7t-
`.\..\..\,/..\{.._/;/E:/x/
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`vxvvav
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`m
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`cm 0 man vow.-
`MOIITOI
`A0! “WHY
`
`- mun VOLTAGE +
`sun“
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`cartoon!
`
`GROUND WILD
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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 cannot be used to sputter dielectric target
`materials, since charge buildup on the cathode surface will prevent bom—
`bardment of 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
`bombardment of 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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`4
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`Ex. 1032, Page 3
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`Low-Pressure Plasma Processing Environment 229
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`The suppression of arcs generated in the DC discharge (arc sup-
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`pression) are important to obtaining stable performance of the DC power
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`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 charging is 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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`bombard the 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 bombardment will
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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
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`varied.l47] 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 the relative voltages being
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`variable as well as the duration time.[431 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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`_.r..mm,mmm,r.
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`Ex. 1032, Page 4
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`Ex. 1032, Page 4
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`a. Contlnuous Dc
`b. Unipolar Pulsed DC
`6. Blpolar Pubed Dc
`(1. Asymmetric Bipolar Pulsed as
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`Figure 4-7. DC waveforms.
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`Pulsed DC power can be obtained by switching a continuous DC
`or sinewave power supply with auxiliary electronicsm] or can be obtained
`from a specially designed pulsed power supply that generally allows more
`flexibility as to waveform. The pulsed power supply generally incorpo-
`rates arc suppression that operates by turning off the voltage or by applying
`a positive voltage when the arc initiates. Pulsed plasmas are also of interest
`in plasma etching and plasma enhanced CVD (PECVD).[5°'
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`4.4.4 Magnetically Confined Plasmas
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`Balanced Magnetrons
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`In surface magnetron plasma configurations 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 of the 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 normal to 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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`___-
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`Ex. 1032, Page 5
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`6
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`Physical 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 French call it, 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 gaseous
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`material accelerated in an electric field.[°a] Sputtering was first 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—
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`chemical sputtering” have been associated with the process whereby bom—
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`bardment of the target surface with a reactive species produces a volatile
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`speciesm This process is now often termed “reactive plasma etching” or
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`“reactive ion etching” and is important in the patterning of thin filmsm
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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
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`(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 developed for 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 energy is transferred when 0050 = l ( zero degrees)
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`andM =M. Therefore matching the atomic mass of the bombarding ion to
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`the target atom is important to 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 (4O amu) is used for inert gas sputtering since it 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 are 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 number of atoms ejected to
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`the number of 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 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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`material is removed from the target layer-by-Iayer. This allows the deposi-
`tion of some rather complex alloys such as WzTi for semiconductor
`metallization,[36l Al:Si:Cu for semiconductor metallization,[37l and M(eta1)-
`Cr—Al-Y alloys for aircraft turbine blade coatings.
`
`6.5.2 Reactive Sputter Deposition
`
`Reactive sputter deposition from an elemental targetlgsnm] relies
`on: (a) the reaction of the depositing species with a gaseous species, 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., N2, 02) 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=l4,
`0:16) and are thus not effective in sputtering. It is therefore desirable to
`have a heavier inert 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?” Poisoning of a target surface greatly reduces the 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 much that
`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 of reactive gas flow,[9°]‘[93l or by impedance of
`the plasma discharge. Figure 6-8 shows the 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. When the 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 where the partial pres-
`sure of nitrogen during deposition is 2 x 10‘4 Torr and the 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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`Continuously Increasing Flow
`———>
`
`0 timum
`OSerating
`Conditions
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`2a
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`al-
`
`u iE 8C0O
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`)
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`O E z
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`__..>
`Nitrogen Flow
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`Figure 6-8. Nitrogen partial pressure and flow conditions for the reactive sputter deposi-
`tion of TiN with constant target power (adapted from Ref. 5]).
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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, changes in the area or rate of the film being
`deposited will change the reactive gas availability and the film properties.
`Thus, it is important to use the same fixture, 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 mass spectrometry techniquesl91H931
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`
`
`Ex. 1032, Page 9
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`340 Handbook of Physical Vapor Deposition (PVD) Processing
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`Since gas pressure is important to 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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`m
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`‘
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`Controllers
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`-
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`Nah Vacuum We)
`vmu Conduct-nu By—Pnss
`Roughlng Pump“)
`Rouonlng VIM
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`
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`Figure 6-9. Typical reactive sputter deposition system.
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`In some reactive 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 some cases.
`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 number of
`processes including:
`
`' Dissociation of molecular species to more chemically reactive
`radicals (e.g., N2 + e'—> 2N° and NH3 + e‘ —>N° + 3H°)
`
`° Production of new molecular species that are more
`chemically reactive and/or more easily absorbed on surfaces
`(e.g., 02 + e'—-> 20° then 0° + 02 —> 03)
`
`Ex. 1032, Page 10
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`Physical Sputtering and Sputter Deposition 341
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`- Production ofions—recombination at surfaces releases energy
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`0 Adding internal energy to atoms and molecules by creating
`metastable excited states—de—excitation at surfaces releases
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`energy
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`- Increasing the temperature of the gas
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`- Generating short wavelength photons (UV) that can
`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
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`plasma and its 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
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`the target.
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`substrate surface to activate reactive gases and provide ions for concurrent
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`bombardment. This can be done using an unbalanced magnetron configura—
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`tion, application of an rf to the target, or by establishing a separate auxiliary
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`plasma over the substrate surface.
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`The reaction probability is also a function of the surface coverage.
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`For example, it is easier for an oxygen species to react with a pure titanium
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`surface than with a Ti01‘9 surface. Figure 6-10 shows the effect of reactive
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`nitrogen availability on the electrical resistivity of TiNX 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
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`bombardment of the depositing/reacting species by energetic ions acceler-
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`ated from the plasma (“sputter ion plating” or “bias sputtering”). Concur-
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`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
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`is obtained by having the surface at a negative potential (applied bias or self-
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`bias) so that ions are accelerated from the plasma to the surface. Figure 6-
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`11 shows the relative effects of deposition temperature and applied bias on
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`the electrical resistivity (normalized) of a TiNX film.l94] The lowest resistiv-
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`ity is attained with both a high deposition temperature and concurrent
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`bombardment although a low-temperature deposition with concurrent bom-
`bardment comes close.
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`Ex. 1032, Page 11
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`Ex. 1032, Page 11
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`342 Handbook ofPhysical Vapor Deposition (PVD) Processing
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`easssfiiéfiii
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`002
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`on: O0.
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`013 0.“ w m m 0.10
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`0."
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`RESISTIVITY(tin-cm)
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`0
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`on
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`REACTIVE NITROGEN AVAILABILITY
`(partial pressure - microns)
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`Figure 6-10. TiN resistivity as a function of nitrogen content (nitrogen availability during
`deposition). (Adapted from Ref. 94.)
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`veslstlvlty
`Normalized
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`IIIO=UV
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`Blassw
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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), TiCxNy (bronze, rose, violet, or
`black as x and y are varied) and ZrN (brass). Coatings such as TiN and
`(Ti,Al)C,‘Ny are used as wear-resistant coatings on tools, molds, and other
`surfaces. Reactive deposition is used to produce oxide films such as ZrO2 and
`TiOZ, which are used to form anti-reflection and band-pass coatings on optical
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`_..4‘
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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 SiOLs, 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. However it 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 (C2H2) or
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`methane (CH4) for carbon, silane (SiH4) for silicon, and diborane (BzHa)
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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
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`such as the carbides, borides, and silicides.l95l 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
`little TiC.
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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 over a 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 feet or more in length. In such an application, it may
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`be easier to use quasi—reactive sputtering from a compound target.
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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
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`reactive gas in a plasma is 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
`Structures
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`Layered structures can be deposited by passing the substrate in
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`front of several sputtering targets sequentially. For example, X-ray diffrac-
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`tion films are formed by depositing thousands of alternating layers of high-
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`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 of the 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
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`Ion 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 gridless 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
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`such as with the MetaModeTM deposition configurationlwl]
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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 ofien the plasma volume is 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
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`density between the target and the substratelm] Magnetic fields in the
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`vicinity of the substrate can also be used to enhance reactive gas ionization
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`and bombardment. For example using a magnetic field (100G) in the
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`vicinity of the substrate, the ion flux was increased from 0.1 ma/cm2 to 2.5
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`ma/cm2 in the unbalanced magnetron reactive sputter deposition ofA1203 . [103]
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`6.7
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`TARGETS AND TARGET MATERIALS
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`For demanding applications, a number of sputtering target proper-
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`ties must be controlled in order to have reproducible processing.“041 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
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`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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`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 conformal targets 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 planar target, the hollow cylindrical target, the post cathode,
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`the conical target, and the rotating cylindrical targetllomlom
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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 have tiles 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 backseattering does not give
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`“cross-talk” between the 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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`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 cathodelm] This can be due to 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 depending of the position of the fixture, particularly if the fixture
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`has a potential on it.
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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 which it 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 front of the first target and then in front of the substratelmg]
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`Ex. 1032, Page 15
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`Ex. 1032, Page 15
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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 may be difficult 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 tendency to 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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`When using alloy or compound targets 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;
`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 some cases, 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
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`of this problem are:
`ferroelectric films of BaTiO3,[“3] superconducting
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`films such as YBaZCu3O7, and magnetic materials such as GbTbFelll‘” In
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`the case of alloy depositio