`Barber et al.
`
`USOO6342134B1
`(10) Patent No.:
`US 6,342,134 B1
`(45) Date of Patent:
`Jan. 29, 2002
`
`(54) METHOD FOR PRODUCING
`PIEZOELECTRIC FILMS WITH ROTATING
`MAGNETRON SPUTTERING SYSTEM
`
`5,702,573 A * 12/1997 Biberger et al. ....... 204/192.12
`5.830,327 A 11/1998 Kolenkow ............. 204/192.12
`5,935,641. A * 8/1999 Beam, III et al. .......... 427/100
`6,001.227 A 12/1999 Pavate et al. .......... 204/298.12
`OTHER PUBLICATIONS
`
`(*) Notice:
`
`7
`
`(56)
`
`(75) Inventors: Bradley Paul Barber, Chatham, NJ
`(US); Ronald Eugene Miller,
`Vossen et al., “Thin Film Processes", pp. 48, Dec. 1978.*
`Riegelsville, PA (US)
`* cited by examiner
`(73) Assignee: Agere Systems Guardian Corp.,
`Primary Examiner Nam Nguyen
`Orlando, FL (US)
`Assistant Examiner-Steven H. VerSteeg.
`Subject to any disclaimer, the term of this
`(74) Attorney, Agent, or Firm-Lowenstein Sandler PC
`patent is extended or adjusted under 35
`(57)
`ABSTRACT
`U.S.C. 154(b) by 0 days.
`A quality-assurance method is described that is useful in the
`(21) Appl. No.: 09/503,225
`fabrication of piezoelectric films of electronic devices, par
`ticularly resonators for use in RF filters. For example, the
`(22) Filed:
`Feb. 11, 2000
`(51) Int. Cl." ................................................ C23C 14/34 R E. tests E. sh
`of
`method COmorSeS determining the Surface roughneSS Of an
`(52) U.S. Cl. ....... 361933, it92.22. deposited and achieving a Surface roughness for the insu
`• al- as
`•-1s
`26/25 35
`lating layer that is Sufficiently low to achieve the high
`quality piezoelectric film. According to one aspect of the
`invention, the low Surface roughness for the insulating layer
`(58) Field of Search ....................... 20, 1922, 1923,
`is achieved with use of a rotating magnet magnetron System
`204/192.18, 192.22, 1923; 427/8: 216/38;
`29/25.35
`for improving the uniformity of the deposited layer. Accord
`ing to other aspects of the invention, the high-quality piezo
`electric film is assured by optimizing deposition parameters
`including determination of a “croSS-Over point' for reactive
`gas flow and/or monitoring and correcting for the surface
`roughness of the insulating layer pre-fabrication of the
`piezoelectric film.
`7 Claims, 4 Drawing Sheets
`
`References Cited
`U.S. PATENT DOCUMENTS
`:
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`2- . 12
`
`Cai C a
`
`SN' t al - - - - - - - 3.5.7.
`A
`:
`5,651,865 A * 7/1997 Sellers .................. 510
`5,683,558 A * 11/1997 Sieck et al. ............ 204/192.12
`5,693,197 A 12/1997 Lal et al. ................. 204/192.2
`
`ROTAING MAGNET
`MAGNETRON
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`CONDUCTIVE
`TARGET
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`POSITION SUBSTRATE
`ONTO PLATEN
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`FLOW NOBLE GAS
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`BEGIN MAGNET ROTATION
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`INCREMENT REACTIVE
`GAS 1. SCCM
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`ATTAINC OSSOWER POINT
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`INCREASE REACTIVEGAS
`FLOW RATE 3 SCCM
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`T FILMONTO
`MONITOR AFER
`
`:
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`FINE ADJ
`PULSE WIDTH
`
`COARSE ADJ st
`ATTAIN DESIRED INDEX
`REACTE FLOWGAS
`OFREFRACTION
`
`ADJUST
`
`
`|S FREOUENCY
`FOR STABILIY
`
`INCREASE RF BIAS
`
`Increas Fes
`
`ATTAIN DESIRED
`TENSILE STRESS
`
`REDUCE NOBLE
`GAS FLOW
`
`DECREASE
`PRESSRE
`
`INCREASE
`POWER
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`ATAINDESIPED
`SURFACE ROUGHNESS
`—-
`DEPOSIE HIGHQUALTY
`INSULATING FILM
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`Samsung Electronics Co., Ltd. v. Demaray LLC
`Samsung Electronic's Exhibit 1005
`Exhibit 1005, Page 1
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`U.S. Patent
`U.S. Patent
`
`Jan. 29, 2002
`Jan. 29, 2002
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`Sheet 1 of 4
`Sheet 1 of 4
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`US 6,342,134 B1
`US 6,342,134 B1
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`Ex. 1005, Page 2
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`Ex. 1005, Page 2
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`U.S. Patent
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`Jan. 29, 2002
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`Sheet 2 of 4
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`US 6,342,134 B1
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`FIG 2
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`3OO
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`28O
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`-2.
`H
`E - 4
`2O
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`110
`F-115
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`CRYO PUMP
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`27 O
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`Ex. 1005, Page 3
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`U.S. Patent
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`Jan. 29, 2002
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`Sheet 3 of 4
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`US 6,342,134 B1
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`FIG 3
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`CHAMBER
`PRESSURE
`(NT)
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`13
`15
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`17
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`19
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`21
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`23
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`25
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`NITROGEN GAS FLOW (SCCM)
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`FIG 4
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`24
`23
`22
`21
`2
`CHAMBER
`PRESSURE 1.9
`(MT)
`18
`17
`1.6
`1.5-seas
`14
`O
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`OXYGEN GAS FLOW (SCCI)
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`Ex. 1005, Page 4
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`U.S. Patent
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`Jan. 29, 2002
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`Sheet 4 of 4
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`US 6,342,134 B1
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`ROTATING MAGNET
`MAGNETRON
`
`FIG. 5
`
`CONDUCTIVE
`TARGET
`
`POSITION SUBSTRATE
`ONTO PLATEN
`
`FLOW NOBLE GAS
`
`BEGIN MAGNET ROTATION
`
`INCREMENT REACTIVE
`GAS 1. SCCM
`
`.
`
`ATTAIN CROSSOWER POINT
`
`INCREASE REACTIVE GAS
`FLOW RATE 3 SCCM
`
`DEPOSIT FILM ONTO
`MONITOR WAFER
`
`COARSE ADJ
`REACTIVE FOW GAS
`
`OF REFRACTION
`
`life ATTAIN DESIRED INDEX
`
`ADJUST PIS FREQUENCY
`FOR STABILITY
`
`INCREASE RF BIAS
`
`ATTAIN DESIRED
`TENSILE STRESS
`
`
`
`DECREASE
`PRESSURE
`
`ATTAIN DESIRED
`SURFACE ROUGHNESS
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`DEPOSIT HIGH QUALITY
`INSULATING FILM
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`FINE ADJ
`PULSE WIDTH
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`REDUCE NOBLE
`GAS FLOW
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`INCREASE
`POWER
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`Ex. 1005, Page 5
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`US 6,342,134 B1
`
`1
`METHOD FOR PRODUCING
`PIEZOELECTRIC FILMS WITH ROTATING
`MAGNETRON SPUTTERING SYSTEM
`
`RELATED APPLICATIONS
`This application is related to U.S. patent application Ser.
`No. 09/502,868, now abandoned titled “Method for Produc
`ing Devices Having Piezoelectric Films,” filed concomi
`tantly herewith by inventors Bower, Pastalan, and Ritten
`house and assigned to the present assignee (hereinafter the
`“Bower application”), which is incorporated herein by ref
`
`CCCC.
`
`FIELD OF THE INVENTION
`The invention relates to a method for producing electronic
`devices containing a piezoelectric film comprising use of a
`rotating magnetron Sputtering System. The invention is par
`ticularly useful in fabricating acoustic resonators and Semi
`conductor devices.
`
`15
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`2
`reactive Sputter deposition techniques have been used. Sput
`ter deposition involves a vacuum deposition proceSS in
`which a Sputtering target is bombarded with ions, and the
`atoms of the target material are mechanically ejected from
`the target and deposited onto a nearby Substrate. In reactive
`Sputtering, a reactive gas is introduced into the deposition
`chamber and reacts with the target material to produce a film
`that is Sputtered onto the Substrate, either directly or upon
`further reaction with freed target material. In DC reactive
`Sputtering, a direct current electrical potential is applied
`within the Sputtering chamber in which a reactive Sputtering
`process is carried out. However, typical Sputtering and
`reactive Sputtering techniques, including DC reactive
`Sputtering, often do not provide adequate deposition rates. A
`pulse DC Sputtering method for efficiently depositing thin
`films of piezoelectric materials. Such as aluminum nitride
`(AIN), e.g., with improved control over the direction and
`delivery of the reactive gas, is described in U.S. patent
`application Ser. No. 09/145,323, to Miller et al., “Pulse DC
`Reactive Sputtering Method for Fabricating Piezoelectric
`Resonators, filed Sep. 1, 1998, assigned to the present
`assignee and incorporated herein by reference. In Miller et
`al., the quality of the piezoelectric films is improved with the
`techniques used to deposit the films, i.e., the pulse width of
`the positive portion of the applied Voltage is adjusted based
`on its effect on the desired film constituency, StreSS, and
`teXture.
`Magnetron Sputtering Systems are known in which
`magnetically-enhanced targets are used to confine the
`plasma discharge along a particular path and enhance the
`flow of target material. See, e.g., U.S. Pat. No. 5,830,327 to
`Kolenkow, “Methods and Apparatus for Sputtering with
`RotatingMagnet Sputter Sources”; U.S. Pat. No. 5,693,197
`to Lal et al., “DC Magnetron Sputtering Method and Appa
`ratus’: and U.S. Pat. No. 5,378,341 to Drehman et at,
`“Conical Magnetron Sputter Source,” all of which are incor
`porated herein. Use of magnetron Sputtering has been
`problematic, however, for depositing Silicon dioxide films.
`Because Silicon dioxide is a good insulator, a film Suffi
`ciently thick to cause arcing problems is rapidly formed at
`certain areas of the target, i.e., Splats or regions of Silicon
`dioxide may be deposited on the target Surface So that it is
`not uniformly biased, and eventually, the target may become
`coated to the point where it is no longer conductive and the
`deposition may stop. Thus, magnetron reactive Sputtering
`has not been conventionally used to deposit quality Silicon
`dioxide films. See, e.g., U.S. Pat. No. 5,683,558 to Sieck et
`al., “Anode Structure for Magnetron Sputtering Systems,” at
`col. 1, lines 53-55 (“The arcing associated with silicon
`dioxide has prevented planar magnetron reactive Sputtering
`from being efficiently utilized to deposit quality Silicon
`dioxide films”). Additionally, previous methods of deposit
`ing insulating films (including piezoelectric films) have
`involved use of RF Sputtering utilizing fixed magnets.
`AS may be appreciated, those in the field of communica
`tions Systems and components continue to Search for new
`methods for increasing System performance and integration.
`In particular, it would be advantageous to provide new
`methods for improving the quality of piezoelectric films. A
`high-quality AlN piezoelectric film deposited on a reflecting
`multi-layer acoustic mirror Stack is a method to produce
`high-quality, RF front-end filters for GHz applications.
`These objectives and further advantages of this invention
`may appear more fully upon considering the detailed
`description given below.
`SUMMARY OF THE INVENTION
`Summarily described, the invention embraces a quality
`assurance method for use in the fabrication of piezoelectric
`
`BACKGROUND OF THE INVENTION
`Communications Systems typically include a variety of
`devices (e.g., filters, mixers, amplifiers, integrated circuits,
`and So forth). Communications Systems are useful for trans
`mitting information (e.g., voice, video, data) relayed by
`means of wireleSS links, twisted pair, optical fibers, and So
`forth. AS wireleSS communications Systems become more
`advanced, Signals are being transmitted at higher frequen
`cies (e.g., PCS, ISM, etc). AS Systems are continually
`developed in response to market pressures, the demand for
`increased performance and reduced size intensifies. Market
`forces demand increased integration and reduction of com
`ponent size.
`Resonators such as Bulk Acoustic Wave (BAW) resona
`tors are important components in the fabrication of bandpass
`filters and other related semiconductor devices. The BAW
`resonator is a piezoelectric resonator that essentially com
`prises a film of piezoelectric material (e.g., a crystalline AlN
`film), deposited between at least two electrodes. Upon
`application of Voltage to Such a structure, the piezoelectric
`material will vibrate in an allowed vibrational mode at a
`certain frequency. Piezoelectric resonators are thus useful in
`discriminating between Signals based on frequency diversity
`(e.g., a bandpass filter), and in providing stable frequency
`Signals (e.g., as in a frequency Stabilizing feedback element
`in an oscillator circuit).
`Typically, the performance and resonant frequency of the
`piezoelectric resonator will depend upon the composition,
`thickness, and orientation of the piezoelectric material. The
`resonant frequency of a piezoelectric material is typically
`inversely proportional to its thickness, thus, for piezoelectric
`resonators to operate at high frequencies {e.g., frequencies
`greater than ~700 Megahertz (MHz) up to 10 Gigahertz (10
`GHz), the thickness of the piezoelectric film must be
`reduced to a thin film (e.g., having a thickness ranging from
`about 500 nm to about 10 um). The coupling between
`electrical and mechanical energy of a piezoelectric resonator
`is dependent on the crystalline orientation of the atoms
`comprising the piezoelectric film. The induced Strain (i.e.,
`stress wave) in a piezoelectric film in response to applied
`voltage (i.e., electric field) can only occur from the advan
`tageous alignment of the crystalline axis within the piezo
`electric film. An example of an advantageous film orienta
`tion is <002> of AlN perpendicular to the substrate.
`Piezoelectric film quality may be affected by the method
`used to form the film. Typically, Sputter deposition or
`
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`Ex. 1005, Page 6
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`US 6,342,134 B1
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`3
`films for electronic devices, particularly resonators. The
`method comprises determining the Surface roughness of an
`insulating layer on which the piezoelectric film is to be
`deposited and achieving a Surface roughness for the insu
`lating layer that is Sufficiently low to achieve the high
`quality piezoelectric film. According to one aspect of the
`invention, the low Surface roughneSS for the insulating layer
`is achieved with use of a rotating magnet magnetron System
`for improving the uniformity of the deposited layer. Accord
`ing to other aspects of the invention, the high-quality piezo
`electric film is assured by optimizing deposition parameters
`or monitoring and correcting for the Surface roughness of the
`insulating layer pre-fabrication of the piezoelectric film.
`
`15
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`25
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`For a better understanding of the invention, an exemplary
`embodiment is described below, considered together with
`the accompanying drawings, in which:
`FIG. 1 is a perspective Schematic illustration of an acous
`tic resonator;
`FIG. 2 is a Schematic diagram of a reactive Sputtering
`arrangement with rotating magnetrons for use in performing
`the inventive method;
`FIG. 3 is a representative graph illustrating determination
`of the cross-over point for AlN; and
`FIG. 4 is a representative graph illustrating determination
`of the cross-over point for SiO2; and
`FIG. 5 is a block diagram showing Steps for performing
`an exemplary inventive method.
`It is to be understood that these drawings are for the
`purposes of illustrating the concepts of the invention and are
`not to Scale.
`
`4
`num (Al) or a metal Stack using titanium and Al. Besides use
`of Al and/or Ti/Al, other metals having a low sheet resis
`tance and low Surface roughneSS may be used for fabricating
`the electrodes 130, 135. Previous stacked metal electrodes
`often have comprised Ti/TiN/Al as the composition of
`choice.
`Notably, it would be advantageous to non-destructively
`predict and assure the quality of the piezoelectric film 120
`before the film is deposited. Traditionally, methods for
`determining the quality of the piezoelectric films have been
`applied after the piezoelectric films 120 are deposited (e.g.,
`X-ray diffraction) but these methods may destroy or damage
`the devices. Additionally, it would be advantageous to avoid
`use of collimated metals (i.e., metals deposited with a
`collimator) in order to eliminate film thickness non
`uniformity associated with collimated depositions. To avoid
`Such non-uniformities, this invention provides an inventive
`process to produce a high-quality piezoelectric film without
`use of the collimator. The inventive method is advantageous
`in that high-quality piezoelectric films can be fabricated
`when there is a decrease in the process window for depos
`iting textured Ti-Al, and the quality of the piezoelectric
`film can be assured pre-fabrication, i.e., before the piezo
`electric film is deposited. This is accomplished by fabricat
`ing insulating layerS 125 having a Surface roughness that is
`Sufficiently low to assure the high-quality piezoelectric film
`(e.g. <10 A), non-destructively evaluating these layers, and
`further Smoothing them, if necessary. This method also
`reliably predicts the quality of the piezoelectric film before
`it is deposited.
`According to one aspect of the invention, a process
`involving use of rotating magnet magnetrons and pulsed DC
`power Supplies is applied to deposit the insulating layers
`and/or piezoelectric film. Rotating magnet magnetrons are
`used to provide film thickneSS uniformity, and Such rotating
`magnet magnetrons are made possible in that process param
`eters are optimized to achieve a high deposition rate and
`correct index of refraction. According to another aspect of
`the invention, the proceSS comprises determination of a
`“cross-over point” such that the target will remain effective
`in emitting atoms and resisting the deposition of materials
`thereon. The “cross-over point” is defined as the point at
`which a pressure increase in the chamber 210 (see FIG. 2)
`becomes non-linear with the flow of reactive gasses, and is
`further defined below. Additionally, the process makes use
`of the recognition that the quality of the piezoelectric film
`can be improved by addressing the Surface roughness of the
`layerS on which the piezoelectric film is deposited, i.e.,
`providing an underlying insulating layer having a relatively
`Smooth Surface produces a higher quality piezoelectric film.
`Thus, according to another aspect of the invention, the
`Surface roughness of the insulating layers are monitored and
`Smoothed, if necessary, before the piezoelectric film is
`deposited.
`Notably, the contemporaneously-filed Bower application
`referenced above (which is assigned to the present assignee
`and incorporated herein), describes the recognition that the
`Surface roughness of the electrode underlying the piezoelec
`tric film (FIG. 1, 135) affects the quality of the piezoelectric
`film 120. The Bower application thus describes a method of
`making a device having a piezoelectric film comprising
`controlling the Surface roughness of the metal layer, which
`may include controlling the Surface roughness of the insu
`lating layers 125 underlying the metal layer 135. The Bower
`method comprises use of textured titanium (and a collimator
`in the deposition process), which increases the System
`tolerance or process window for Surface roughness. In other
`
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`DETAILED DESCRIPTION OF THE
`INVENTION
`Although specific features and configurations are dis
`cussed below, it should be understood that these examples
`are for purposes of illustration only. One skilled in the
`relevant art will recognize that other Steps, configurations
`and arrangements may be used without departing from the
`Spirit and Scope of the invention.
`The invention pertains to a method for obtaining high
`quality piezoelectric films. FIG. 1 is a perspective Schematic
`illustration of an acoustic resonator, which may be fabri
`cated using the inventive method. The resonator 100 com
`prises a substrate 110, a film or layer 120 of piezoelectric
`material, and a means for retaining acoustic energy in the
`piezoelectric film, Such as a Bragg reflecting region 125,
`between the Substrate 110 and film 120. Alternative to the
`reflecting region 125, a layer of air (not shown) may be used
`to suspend the film 120 above the substrate 110. A bottom
`electrode 135 and top electrode 130 are disposed on opposite
`surfaces of the piezoelectric film 120.
`55
`The layer of piezoelectric material advantageously com
`prises AlN, but may be made of any suitable material that
`has piezoelectric qualities Sufficient for the particular reso
`nator application. Typical piezoelectric materials include,
`for example, quartz, Zinc oxide (ZnO), and ceramic mate
`rials such as lithium niobate (LiNbO), lithium tantalate
`(LiTaO), paratellurite (TeO2), and lead titanate Zirconate
`(PZT). The substrate typically is comprised of silicon but
`may be fabricated with other materials. Such as quartz,
`Sapphire, polysilicon, aerogel, and aluminum oxide (Al2O).
`Advantageously, with the invention, the electrodes and
`particularly the bottom electrode 135 may comprise alumi
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`US 6,342,134 B1
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`words, when the collimator is used, the insulating layerS 125
`do not have to be as Smooth as when the collimator is not
`used in order to achieve a high-quality piezoelectric film.
`The collimator also is known, however, for decreasing the
`thickneSS uniformity of the titanium layer.
`With this invention, a process is described for minimizing
`the Surface roughness of the underlying insulating layerS on
`which the electrode and piezoelectric films are deposited,
`and with the instant method, the use of a collimator is not
`required. The Surface roughness of the underlying layerS 125
`may be reduced to achieve a maximum texture for the
`piezoelectric films and optimal operation. of the resonator.
`For example, the insulating. layers should be fabricated So
`they have root mean Square (RMS) morphology reflecting a
`Surface roughness of about less than 10 Angstroms. The
`RMS value reflects a true average, absolute value for the
`deviation or difference in the Surface morphology from a
`mean value of Zero, the value of Zero reflecting a completely
`smooth surface. The RMS value is defined by the square root
`of the difference between the mean Square and the Square of
`the mean, or in other words, it is the normalized average
`value of the roughness relative to the median of the mea
`Sured roughness.
`A "high-quality piezoelectric film is defined herein as a
`film having a texture reflecting a good crystalline orientation
`of atoms, low stress (less than about 50 megaPascals
`{MPa), and appropriate index of refraction (approximately
`2.0, more preferably 2.07+0.005, and more preferably
`2.078+0.005). Film thickness uniformity advantageously is
`0.4% one Sigma, with a more preferred thickness uniformity
`of 0.2% one Sigma, with an even more preferred thickness
`uniformity of 0.1% three Sigma. Thus, the “quality” of a
`piezoelectric film as that term is used herein relates to at
`least one of the texture, StreSS, uniformity, and/or index of
`refraction of the piezoelectric film. The term “texture” as
`used herein is intended to describe the crystallographic
`alignment of grains in a polycrystalline film wherein "maxi
`mum texture' denotes a film having an alignment
`(orientation) of grains centered about a single direction at an
`angle subtended from (relative to) the growth direction. The
`texture and thus quality of the piezoelectric film can be
`defined by reference to its “rocking curve.” More
`Specifically, ideally crystallographic directions of the grains
`are centered about a single direction; as mentioned above,
`the performance of the piezoelectric film (e.g. in a piezo
`electric resonator), is dependent upon the crystalline orien
`tation of the atoms comprising the film. Typically, however,
`there will be a gaussian distribution of directions about
`which the grains are centered. The Smaller the distribution,
`the closer the film is to maximum texture. The distribution
`of grain directions may be plotted to define a peak, and the
`width of the peak at half its maximum height (full-width at
`half maximum) (FWHM), i.e., the “rocking curve” width,
`reflects a value for defining the quality of the film texture.
`The “rocking curve' width is thus the figure of merit for the
`film texture, i.e., the Smaller the distribution, the Smaller the
`rocking curve, and the closer the film is to maximum texture.
`The piezoelectric film advantageously is formed with a
`FWHM rocking curve of less than 3.5, with a more
`preferred low rocking curve being less than about 2.5, and
`more preferably less than 1.5° (FWHM).
`According to one aspect of the invention, a high-quality
`piezoelectric film may be fabricated by applying a rotating
`magetron and pulse DC reactive Sputtering process to fab
`ricate one or more layers of the piezoelectric device, includ
`ing the insulating layers (FIG. 1, 125), and/or the piezoelec
`tric film (FIG. 1, 120). FIG. 2 is a simplified, schematic
`
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`6
`representation of a rotating magnetron Sputtering apparatus
`for use in depositing the piezoelectric 120, the insulating
`layers 125, and the electrodes 130, 135 on the substrate 110.
`The apparatus includes a chamber 210 (e.g., a plasma
`chamber), and a pair of electrodes (the target 260 and anode
`ring 225) within the chamber. The electric potential applied
`to the electrodes may be controlled by a pulsed DC power
`Source 230 or other Suitable Source. Various Sources are
`provided for injecting gases into the chamber. A first flow
`control Source 240 injects noble gases into the chamber (e.g.,
`Ar, Ze, and Kr), and a second flow control source 250
`Supplies a reactive gas (O, N, etc.) into the chamber 210.
`The gases are Supplied via gas delivery port 245.
`A target material is positioned within the Sputtering
`chamber. The Substrate 110 is also positioned therein, and
`disposed Such that it is in communication with the target and
`gasses within the chamber. The target material 260 is
`mounted adjacent a rotating magnet assembly 280 which
`includes a magnet array to produce a magnetic field to
`penetrate the target material 260 and form an arc over its
`surface facing the substrate 110. A rotation motor 300 causes
`the rotating magnet assembly to rotate about an axis of
`rotation with respect to the target 260. The magnetic field
`generated acroSS target 260 helps to confine free electrons
`near the Surface of the target. The increased concentration of
`ions excited by these electrons at the target Surface increases
`the efficiency of the Sputtering process. The pressure within
`the chamber can be regulated with pressure regulators 240,
`250 and throttle valve 270. An RF power supply 235 applies
`a bias voltage to the substrate platen 115 to control tensile
`film StreSS.
`A high-quality film may be achieved with this apparatus,
`and various parameters can be applied to optimize the
`processing conditions. Applicants have discovered a method
`comprising optimization of the reaction parameters to
`achieve a high-deposition rate and correct index of refrac
`tion. The method includes a step of determining the “croSS
`over point” in the process. The “cross-over point” is defined
`as the point at which a pressure increase in the chamber 210
`becomes non-linear with the flow of reactive gases, and this
`point reflects a reactive gas flow rate that Strongly effects a
`reaction with the target material. For example, FIG. 3 is a
`representative graph illustrating determination of the croSS
`over point in a proceSS involving fabrication of an AlN
`piezoelectric film, in which the reactive gas comprises
`nitrogen and the target comprises aluminum. FIG. 4 is a
`representative graph illustrating determination of the croSS
`over point in a process involving fabrication of an SiO2
`layer, in which the reactive gas comprises oxygen and the
`target comprises Silicon.
`Referring to FIG. 3, the characteristic pressure-flow curve
`shows two asymptotic regimes. At low flow of reactive gas
`(to the left of the graph), all the nitrogen is being reacted
`with metallic aluminum So introduction of Small amounts of
`nitrogen does not increase the chamber pressure. AS the gas
`flow is increased, gas is present in the chamber that cannot
`react with metal, and the unreacted gas causes an increase in
`pressure in the chamber. At a very high flow rate (to the right
`of the graph), the target material becomes filly “poisoned” or
`coated with the reaction product (AIN) such that any further
`gas admitted into the chamber will not react with target
`material and will directly contribute to a pressure increase.
`The plot of pressure versus reactive gas flow (as in FIGS. 3
`and 4) shows a “cross-over curve” from the behavior of a
`metallic target fully consuming reactive gas to the behavior
`of a fully poisoned target showing increasing pressure with
`further admission of reactive gas.
`
`Ex. 1005, Page 8
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`
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`US 6,342,134 B1
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`8
`impact upon the texture of the piezoelectric films deposited
`thereon. AS applied to the insulating layers, additional
`parameters to consider are that a reduction in the Surface
`roughness of the resultant SiO2 films is achieved by increas
`ing the power and/or decreasing the pressure. According to
`the invention, these parameters may be adjusted and opti
`mized to achieve the highest deposition rate that produces
`films having the desired Surface roughness and index of
`refraction. Applying this evaluative process, films may be
`consistently produced that have the desired index of refrac
`tion and a surface texture of less than 25 A (RMS), and more
`preferably less than 10 A.
`Applying the realization that the piezoelectric film quality
`can be improved by providing a good Starting platform for
`the piezoelectric film (i.e., by providing an underlying
`insulating layer having a relatively Smooth Surface texture),
`the Surface roughness of the insulating layer may be mea
`Sured and if necessary, further processed to achieve optimal
`quality piezoelectric films. The Surface roughness of an SiO,
`film may be non-destructively measured by an Acoustic
`Force Microscope (AFM) located within the silicon labora
`tory in which the piezoelectric device is produced, e.g., a
`class 10 clean room where all Silicon fabrication takes place
`or other Silicon Fabrication Research Laboratory (SFRL). In
`other words, the Surface roughness of the insulating layer is
`measured in-situ during the fabrication. Further Smoothing
`can be achieved by chemical mechanical polishing and to a
`lesser extent with a hydrogen hotsputter etch process (HSE)
`(a patent on this process was filed in the United Kingdom by
`Trikon Technologies Inc. The Trikon process teaches a flow
`rate of hydrogen at 50 Scem. However, applicants have
`discovered that a reduction in the flow rate of hydrogen gas
`provides Significant advantages in producing films having
`the desired texture. For example, a reduction in hydrogen
`flow rate to 25 sccm (from the Trikon 50 sccm flow rate) has
`resulted in an improved Surface Smoothing capability that
`does not impact upon the overall thickness of the SiO film.
`The following examples will serve to further typify the
`nature of the invention but should not be construed as a
`limitation on the scope thereof, which is defined by the
`appended claims.
`
`15
`
`25
`
`35
`
`40
`
`7
`FIG. 5 is a block diagram showing illustrative steps of one
`aspect of the invention. The invention comprises use of the
`croSS-Over curve in optimizing the reactive Sputtering depo
`Sition process with use of rotating magnet magnetrons and
`pulsed DC power. The method includes a step of providing
`the target material within a Sputtering chamber, with the
`target material being oriented on a rotating magnet assembly
`for producing a magnetic field across the target material. A
`Substrate within the Sputtering chamber in open communi
`cation with the target, and a pair of electrodes (target and
`anode ring) are positioned within the Sputtering chamber. AS
`the proceSS begins, the magnet rotation begins and is Stabi
`lized at a level Sufficient to achieve uniform target erosion.
`A Suitable rotation Speed is 282 rpms. The cross-over point
`for the flow of a reactive gas into the Sputtering chamber is
`determined with appropriate Settings to the pulse frequency
`and pulse width. The noble gas is introduced into the
`Sputtering chamber, and then the reactive gas is added So that
`it reacts with a portion of the target material. The reactive
`gas is introduced incrementally into the Sputtering chamber
`So that the flow rate of the reactive gas is maintained at a rate
`corresponding Substantially to, but greater than, the flow rate
`at the croSS-Over point. A film is thus deposited on the
`Substrate as the chamber is maintained just above the
`cross-over point. Immediately below (less than 3 ScCm) the
`cross-over point will result in a metallic film. Above the
`croSS-Over point, the deposition rate decreases for at least 20
`Sccm and until the target is totally poisoned, becomes an
`insulator, and a plasma can no longer be maintained.
`AS the deposition process is carried out, a pulsed DC
`voltage is applied across the pair of electrodes (the target and
`anode ring) that are positioned within the Sputtering cham
`ber So that ions from the noble gas impinge upon the target
`material and eject atoms therefrom. Freed atoms of the target
`material react mostly at the target with the reactive gas to
`form a coating on the Substrate. Maintaining the flow rate
`near the croSS-Over point is effective in optimizing the
`deposition conditions, the target will continue to be conduc
`tive while depositing a coating on the Substrate, and poi
`Soning of the target itself is controlled. Additionally, various
`other aspects of the process may be managed to improve the
`deposition rate and overall quality of the deposited films. For
`example, the relevant parameters of the process may be
`monitored and adjusted, considering that the deposition rate
`is inversely proportional to the amount of reactive gas, the
`power Supply pulse width, and the deposition pressure, and
`is directly proportional to the power