United States Patent [i9]
`Pavate et al.
`
`US006001227A
`[ii] Patent Number:
`[45] Date of Patent:
`
`6,001,227
`Dec. 14,1999
`
`[54] TARGET FOR USE IN MAGNETRON
`SPUTTERING OF ALUMINUM FOR
`FORMING METALLIZATION FILMS
`HAVING LOW DEFECT DENSITIES AND
`METHODS FOR MANUFACTURING AND
`USING SUCH TARGET
`
`[75]
`
`Inventors: Vikram Pavate; Keith J. Hansen, both
`of San Jose; Glen Mori, Pacifica;
`Murali Narasimhan; Seshadri
`Ramaswami, both of San Jose; Jaim
`Nulman, Palo Alto, all of Calif.
`
`[73] Assignee: Applied Materials, Inc., Santa Clara,
`Calif.
`
`[21] Appl. No.: 08/979,192
`Nov. 26, 1997
`Filed:
`[22]
`Int. Cl.6 ................................................. C23C 14/34
`[51]
`[52] U.S. Cl................................ 204/298.12; 204/298.13;
`204/298.16; 204/298.21; 148/237; 420/528
`[58] Field of Search ....................... 204/298.12, 298.13,
`204/298.16, 298.19, 298.21; 148/237; 420/528
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`9/1993 Parker .................................... 204/298.2
`5,242,566
`5,268,236 12/1993 Dumont et al.............................. 428/636
`6/1994 Tepman ................................ 204/192.12
`5,320,728
`9/1995 Satou et al............................. 204/298.13
`5,447,616
`1/1996 Fukuyo et al......................... 204/298.13
`5,486,815
`9/1998 Dunlop et al................................. 419/61
`5,809,393
`
`FOREIGN PATENT DOCUMENTS
`0 466 617 Al 1/1992 France .
`31 21 389
`8/1982 Germany .
`9/1996 Germany .
`196 09 439
`
`OTHER PUBLICATIONS
`
`PCT Notification of Transmittal of the International Search
`Report from the International Searching Authority at the
`European Patent Office dated Mar. 16, 1999, 7 pages.
`
`G.T. Murray, Preparation and Characterization of Pure Met­
`als, Cubberley et al: “Metals Handbook, 9th Edition, vol. 2,
`Properties and Selection: Nonferrous Alloys and Pure Met­
`als. ” Apr. 27, 1983, American Society for Metals, Oh, US
`XP002094554 86, pp. 709-713.
`Abstract for JP 06-280005, Patent Abstracts of Japan, Oct.
`1994.
`Abstract for JP 03-064447, Patent Abstracts of Japan, Mar.
`1991.
`Derwent Abstract for JP 52-14519, Aug. 1993.
`Abstract for JP 06-017246, Patent Abstracts of Japan, Jan.
`1994.
`A.S. Pokrovskaya-Soboleva, A.L. Shapiro, T.S. Borisova,
`L.K. Mazurova, V.I. Razgulayeva, “Electric Strength of
`Vacuum Gap With Electrodes Made of Carbographite Mate­
`rials”, Proceedings of the Sixth International Symposium on
`Discharges and Electrical Insulation in Vacuum, Swansea,
`UK, Jul. 1974, pp. 86-91.
`
`Primary Examiner—Alan Diamond
`Attorney, Agent, or Firm—Fliesler, Dubb, Meyer & Lovejoy
`ABSTRACT
`
`[57]
`
`Improved targets for use in DC_ magnetron sputtering of
`aluminum or like metals are disclosed for forming metalli­
`zation films having low defect densities. Methods for manu­
`facturing and using such targets are also disclosed. Conduc­
`tivity anomalies such as those composed of metal oxide
`inclusions can induce arcing between the target surface and
`the plasma. The arcing can lead to production of excessive
`deposition material in the form of splats or blobs. Reducing
`the content of conductivity anomalies and strengthening the
`to-be-deposited material is seen to reduce production of such
`splats or blobs. Other splat limiting steps include smooth
`finishing of the target surface and low-stress ramp up of the
`plasma.
`
`30 Claims, 5 Drawing Sheets
`
`Page 1 of 14
`
`APPLIED MATERIALS EXHIBIT 1040
`
`

`

`U.S. Patent
`
`Dec. 14,1999
`
`Sheet 1 of 5
`
`6,001,227
`
`155a
`
`152a
`
`PVD Al
`
`155
`
`SUBSTRATE 152
`
`CHUCK
`
`140
`
`V
`GND
`
`FIG. 1
`
`Page 2 of 14
`
`

`

`U.S. Patent
`
`Dec. 14,1999
`
`Sheet 2 of 5
`
`6,001,227
`
`S ft
`o O m
`H Qi Q
`%
`
`FIG. 2
`
`FIB CROSS SECTION OF Al Cu DEFECT ON INTERCONNECT LEVEL
`
`Page 3 of 14
`
`

`

`U.S. Patent
`
`Dec. 14,1999
`
`Sheet 3 of 5
`
`6,001,227
`
`300
`
`BASIC PROCESS
`
`IMPROVEMENTS
`
`321
`
`322
`
`323
`
`324
`
`326
`
`327
`
`328
`
`FIG. 3
`
`Page 4 of 14
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`

`

`U.S. Patent
`
`Dec. 14,1999
`
`Sheet 4 of 5
`
`6,001,227
`
`ATMOSPHERE -440-
`H2 O2 H2O
`
`HEAT SOURCE
`-420-
`
`FIG. 4A
`
`FIG. 4B
`
`Page 5 of 14
`
`

`

`U.S. Patent
`
`SPLAT FORMATION THROUGH TARGET LIFE
`(200 MM WAFER)
`
`PROCESS CONDITIONS
`10.6 Kw, 22 mT, 52 mm SPACING
`
`Dec. 14,1999
`
`PROPOSED CERTIFICATION LIMIT FOR SPLAT DENSITY
`
`NOTE: EACH DATA POINT REPRESENTS
`AN AVERAGE DENSITY OF 45 WAFERS
`
`10
`
`8 -■
`
`6 --
`
`4 --
`
`2 --
`
`Sheet 5 of 5
`
`6,001
`
`0
`
`FIG. 5
`
`100
`
`200
`
`300
`
`400
`500
`TARGET LIFE IN KWHRS
`
`600
`
`700
`
`800
`
`Page 6 of 14
`
`

`

`1
`TARGET FOR USE IN MAGNETRON
`SPUTTERING OF ALUMINUM FOR
`FORMING METALLIZATION FILMS
`HAVING LOW DEFECT DENSITIES AND
`METHODS FOR MANUFACTURING AND
`USING SUCH TARGET
`
`BACKGROUND
`1. Field of the Invention
`The invention relates generally to physical vapor deposi­
`tion (PVD) of metal films. The invention relates more
`specifically to DC magnetron sputtering of metals such as
`aluminum (Al) or aluminum alloys onto semiconductor
`substrates and the like for forming fine pitch metallization
`such as the electrically-conductive interconnect layers of
`modern integrated circuits.
`2. Cross Reference to Related Patents
`The following U.S. patent(s) is/are assigned to the
`assignee of the present application, and its/their disclosures
`is/are incorporated herein by reference:
`(A) U.S. Pat. No. 5,242,566 issued Sep. 7, 1993 to N.
`Parker; and
`(B) U.S. Pat. No. 5,320,728 issued Jun. 14, 1994 to A.
`Tepman.
`3. Description of the Related Art
`The electrically-conductive interconnect layers of modern
`integrated circuits (IC) are generally of very fine pitch (e.g.,
`10 microns or less) and high density (e.g., hundreds of lines
`per square millimeter).
`A single, small defect in the precursor metal film that
`ultimately forms a metallic interconnect layer of an IC can
`be so positioned as to seriously damage the operational
`integrity of the IC. As such it is desirable to form metal films
`with no defects or as few, minimally sized defects as
`possible.
`The metal films of integrated circuits are typically formed
`by physical vapor deposition (PVD). One low cost approach
`uses a DC magnetron apparatus such as the Endura™ system
`available from Applied Materials Inc. of California for
`sputtering aluminum (Al) or aluminum alloys onto semi­
`conductor wafers.
`Although such DC_ magnetron PVD systems generally
`produce high quality metal films with relatively low defect
`densities, heretofore unexplained ‘blobs’ of extra material
`are occasionally observed in the deposited metal. These
`blobs can interfere with device formation and disadvanta-
`geously reduce mass production yield of operable devices.
`The present inventors have isolated such blobs in
`DC_ magnetron-formed aluminum films, have analyzed the
`composition and physical structures of such blobs, and have
`developed methods for minimizing the formation of such
`undesirable blobs.
`SUMMARY OF THE INVENTION
`The above-mentioned problems are overcome in accor­
`dance with the invention by providing an improved target for
`use in magnetron sputtering of aluminum, or of aluminum
`alloys or of like metals where the formed metal films having
`low defect densities.
`It has been determined that the microscopic make up of
`the target in a DC_ magnetron PVD system plays an integral
`role in the mechanisms that lead to blob formation.
`More particularly, nonhomogeneous structures within the
`target such as dielectric inclusions (e.g., A12O3 precipitates)
`
`6,001,227
`
`2
`and nonconductive voids (e.g., formed by trapped gas
`bubbles), when exposed as part of the target surface, are
`believed to create corresponding distortions in the electric
`fields that surround the target surface during the sputtering
`process. It is believed that large-enough distortions can
`evolve into points of field breakdown through which arcs of
`high current flow between the plasma and the target. Such
`arcing currents can result in localized melting of the target
`material and in the production of relatively large blobs of
`liquid material that splatter onto the wafer surface. The
`splattered material apparently draws back together on con­
`tact with the wafer surface, due to surface tension effects,
`and solidifies into the undesirable blob.
`In accordance with a first aspect of the invention, targets
`are manufactured so as to minimize the sizes and numbers
`of dielectric inclusions (e.g., A12O3 precipitates) and non­
`conductive voids (e.g., formed by trapped hydrogen
`bubbles).
`Blob formation is additionally believed to be due to
`stress-induced breakdown of the target material when the
`sputtering plasma is struck. The electric fields and currents
`which develop near the surface of the target as the plasma is
`ignited tend to generate mechanical stresses within the target
`material. Localized breakdown due to poor mechanical
`strength of the target local material is believed to be another
`source of blob generation.
`In accordance with a second aspect of the invention,
`targets are manufactured so as to homogeneously maximize
`the strength of the target material and thereby inhibit blob
`generation due to localized mechanical breakdown.
`A target in accordance with the invention essentially
`excludes dielectric inclusions such as metal oxides (A12O3),
`nitride precipitates, carbide precipitates, of sizes larger than
`about 1 micron in concentrations greater than 5,000 such
`inclusions per gram of target material. A target in accordance
`with the invention alternatively or further essentially
`excludes voids such as those caused by entrapped gas of
`sizes larger than about 1 micron in concentrations greater
`than 5,000 such voids per gram of target material. A target
`in accordance with the invention alternatively or further has
`an essentially homogeneous distribution of metal grain size
`in the range of about 75 micron and 90 micron. A target in
`accordance with the invention alternatively or further has an
`initial surface roughness of less than about 20 microinches.
`A DC_ magnetron PVD system in accordance with the
`invention comprises a target having one or more of the
`following characteristics: (a) essentially no dielectric inclu­
`sions such as metal oxides (A12O3), nitride precipitates,
`carbide precipitates, of sizes larger than about 1 micron in
`concentrations greater than 5,000 such inclusions per gram
`of target material; (b) essentially no voids such as those
`caused by entrapped gas of sizes larger than about 1 micron
`in concentrations greater than 5,000 such voids per gram of
`target material; (c) an essentially homogeneous distribution
`of metal grain size in the range of about 75 micron and 90
`micron; and (d) an initial surface roughness of less than
`about 20 microinches. A DC_ magnetron PVD system in
`accordance with the invention further comprises means for
`ramping plasma power at a rate of 2 Kw per second or less.
`A target manufacturing method in accordance with the
`invention comprises one or more of the following steps of:
`(a) obtaining purified aluminum having less than about 1
`ppm of hydrogen and less than about 10 ppm oxygen; (b)
`casting the purified aluminum using a continuous-flow cast­
`ing method wherein the melt skin is not exposed to an
`oxidizing atmosphere; (c) working the cast metal so as to
`
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`6,001,227
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`3
`produce an essentially homogeneous distribution of metal
`grains of diameters less than or equal to 100 /( and second
`phase precipitates of diameters in the range of about 1 to 10
`ii and more than about 50% material having <200> texture;
`(d) smoothing the initial target surface to an average rough­
`ness of no more than about 20 microinches; (e) using
`ultrasonic cleaning to remove arc-inducing contaminants
`from the initial target surface; and (f) shipping the cleaned
`target in an inert gas pack.
`A method for operating a DC_ magnetron PVD system in
`accordance with the invention comprises the steps of: (a)
`installing a new target having one or more of the following
`characteristics: (a) essentially no dielectric inclusions such
`as metal oxides (A12O3), nitride precipitates, carbide
`precipitates, of sizes larger than about 1 micron in concen­
`trations greater than 5,000 such inclusions per gram of target
`material; (b) essentially no voids such as those caused by
`entrapped gas of sizes larger than about 1 micron in con­
`centrations greater than 5,000 such voids per gram of target
`material; (c) an essentially homogeneous distribution of
`metal grain size in the range of about 75 micron and 90
`micron; and (d) an initial surface roughness of less than
`about 20 microinches. A DC_ magnetron PVD operating
`method in accordance with the invention further comprises
`ramping plasma power at a rate of no more than 2 Kw per
`second or less.
`Other aspects of the invention will become apparent from
`the below detailed description.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The below detailed description makes reference to the
`accompanying drawings, in which:
`FIG. 1 is a schematic diagram of a DC sputtering mag­
`netron;
`FIG. 2 is a micrograph showing a cross sectional side
`view of an isolated ‘splat’ or ‘blob’ within the interconnect
`structure of an integrated circuit;
`FIG. 3 is a flow chart showing steps taken in the manu­
`facture and subsequent use of a target, including improve­
`ment steps in accordance with the invention;
`FIGS. 4A and 4B respectively show cross sectional views
`of a simple casting process and the resultant product for
`purpose of explanation; and
`FIG. 5 is a plot showing average splats number per wafer
`over sampled groupings of 45 wafers each taken every 200
`Kw hours of a sample target in accordance with the inven­
`tion.
`
`DETAILED DESCRIPTION
`FIG. 1 shows a schematic diagram of a DC sputtering
`magnetron system 100. A magnet 110 is positioned over a
`portion of target 120. The target includes a deposition­
`producing portion that is electrically conductive and is
`composed of the to-be-sputtered material (e.g., a metal such
`as aluminum). Target 120 is typically of a symmetrical form
`such as a circular disk, but may have various bends or other
`features such as shown for adaptively fitting into a specific
`DC_ magnetron PVD system and for producing specific
`distributions of electrical field intensity and gas flow in
`accordance with design specifics of the receiving
`DC_ magnetron PVD system. The target 120 is typically
`structured for removable insertion into the corresponding
`DC_ magnetron PVD system 100. Targets are periodically
`replaced with a new targets given that the PVD process
`erodes away the to-be-deposited material of each target.
`
`4
`A switching means 125 may be provided for selectively
`connecting the target 120 to a relatively negative voltage
`source 127. In general, the negative voltage source 127
`provides a DC cathode voltage in the range of about -470 V
`to -530 V relative to the potential on an opposed anode
`(ground or GND in the illustrated example). The specific
`cathode voltage varies according to design. When switching
`means 125 is closed to connect the target 120 with negative
`voltage source 127, the target can act as a source of
`negatively charged particles such as 135 (e-) and 138 (Al-)
`which are discussed below. Because of this the target is also
`referred to as the cathode.
`A tubular gas-containment shield 130, usually of cylin­
`drical shape, is provided below and spaced apart from the
`target 120. Shield 130 is electrically conductive and is
`generally coupled to ground (GND) or to another relatively
`positive reference voltage so as to define an electrical field
`between the target 120 and the shield. Shield 130 has a
`plurality of apertures 132 defined through it for admitting a
`supplied flow of gas 131 such as argon (Ar) from the exterior
`of the shield 130 into its interior.
`A workpiece-supporting chuck 140 is further provided
`centrally below and spaced apart from the target 120, usually
`within the interior of the shield 130. Chuck 140 is electri­
`cally conductive and is generally also coupled to ground
`(GND) or to another relatively positive reference voltage so
`as to define a further electrical field between the target 120
`and the chuck.
`A replaceable workpiece 150 such as a semiconductor
`wafer is supported on the chuck centrally below the target
`120. Workpiece 150 originally consists of a substrate 152
`having an exposed top surface 152a. As PVD sputtering
`proceeds, a metal film 155 having a top surface 155a builds
`up on the substrate 152. It is desirable that the build up or
`deposition of the metal film 155 be uniform across the entire
`top surface 152a of the substrate, but as explained herein,
`anomalies sometimes interfere with homogeneous deposi­
`tion.
`Workpiece substrate 152 may include an insulative layer
`composed for example of Si02. In such cases, the metal film
`155 may be electrically insulated from chuck 140 and the
`voltage of the metal film 155 will float to a slightly negative
`level relative to the chuck’s voltage (e.g., GND).
`DC_ magnetron operation initiates as follows. When
`switching means 125 is closed, initial electric fields are
`produced between the target 120 and the shield 130 and the
`chuck 140. Plasma igniting gas is introduced. The illustrated
`assembly of FIG. 1 is usually housed in a low pressure
`chamber 105 (partially shown) that maintains an internal
`pressure in the range of about 2 to 5 Torr or lower. Some of
`the supplied gas 131 that enters the interior of shield 130
`disassociates into positively charged ions (Ar+) and nega­
`tively charged ions (Ar-) when subjected to the initial
`electric fields. One so-generated positive ion is shown at
`133. Due to electrostatic attraction, ion 133 (Ar+) accelerates
`towards and collides with the bottom surface of the target at
`first collision point, say 134. The point of collision is
`denoted with an asterisk (“*”). This initial collision induces
`emission of an electron (e-) 135 from cathode 120. (A
`particle of target material (Al) may also be dislodged by
`collision 134.) The emitted electron 135 drifts down towards
`the more positive chuck 140. However, the magnetic fields
`of magnet 110 give electron 135 a spiraling trajectory as
`indicated at 136. Eventually electron 135 collides with a
`molecule of the inflowing gas 131 (e.g., Ar2). This second
`collision (*) produces another positively charged ion 137
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`5
`(Ar+) which accelerates towards and collides with the bot­
`tom surface of the target. This third collision produces yet
`another electron like 135, and a chain reaction is established
`leading to the creation of a sustained plasma 160 within the
`interior of the gas-containment shield 130. Plasma 160 is
`charged positive relative to the cathode 120 and begins to act
`like a floating anode. This changes the electric field distri­
`bution within the DC_ magnetron PVD system 100. At some
`point the electric field distribution stabilizes into a long term
`steady state.
`The ballistic collisions of massive particles such as 137
`(Ar+) with the bottom surface of the target 120 sometimes
`cause small particles of the target’s material to break off and
`move toward the underlying workpiece 150. An example of
`such an emitted target particle is shown at 138. The sizes and
`directions of the emitted target particles tend to produce a
`relatively uniform deposition of the emitted material (e.g.,
`aluminum) on the top surface (152a and later 155a) of the
`workpiece 150.
`On occasion, however, as explained above, the deposition
`is not uniform in that blobs or ‘splats’ appear on or within
`the deposited metal film 155. Some of the splats can have
`diameters as large as 500 microns, which is quite large in a
`world where operational features of the affected device have
`dimensions of 1 micron or less. Such splats are undesirable.
`FIG. 2 is a micrograph taken with a focused ion beam
`(FIB) microscope at a magnification sufficient to show an
`anomalous section of a 1 micron-thick aluminum line. The
`micrograph shows a cross sectional side view of an isolated
`‘splat’ or ‘blob’ within the interconnect structure of an
`integrated circuit. The splat diameter is approximately 5
`microns and the splat height is roughly 1.5 microns. In this
`particular case, the deposited metal film (155) is an alloy of
`aluminum and copper (AICu). The ‘splat’ is given its name
`because of the appearance that something had splattered
`onto the otherwise planar, PVD deposited metal film.
`In the captured splat of FIG. 2, an inclusion having a
`diameter of roughly 0.3 micron is seen within the body of the
`splat. Inclusions are not routinely observed in every splat.
`Inclusions such as the one shown in FIG. 2 were isolated and
`analyzed chemically. The analysis showed that such inclu­
`sions were composed primarily of the oxide, A12O3.
`The present inventors deduced that the A12O3 inclusion
`had come from the specific target (120) used in the PVD
`sputtering process, given that the feed gas consisted of
`relatively pure Ar, and the substrate had been cleaned, and
`there was nothing else in the DC_ magnetron PVD system
`that could act as a source of A12O3.
`The present inventors further deduced that the A12O3
`inclusion was a causal factor in the generation of the
`observed splat even though the splat is further defined by an
`excessive amount of AICu that appears to have splattered
`onto the forming metal film during the PVD process.
`Further questions remained, however. What was the spe­
`cific mechanism that made the A12O3 inclusion a causal
`factor in the generation of the observed splat? Why do many
`splats not include such A12O3 inclusions?
`It is believed that the correct answer lies in understanding
`how electrical fields are distributed within the
`DC_ magnetron system 100 (FIG. 1) after plasma 160
`reaches steady state stability, and how this stability can be
`temporarily disturbed.
`Referring to FIG. 1, as the plasma 160 reaches steady state
`stability, there develops between the bottom surface 120a of
`the target and a top boundary 160a of the plasma, an area
`that is essentially free of electrons or other charged particles.
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`6
`This charge-free region is referred to in the literature as the
`‘dark space’ or the ‘dead space’. Its extent is referenced in
`FIG. 1 as 170 (not to scale).
`A relatively large voltage differential develops between
`the top 120a and bottom 160a of the dark space 170.
`Target-emitted electrons such as 135 are believed to tunnel
`rather than to drift through the dark space 170 and to thereby
`maintain the relatively large voltage differential between the
`top and bottom of the dark space 170.
`A relatively homogenous distribution of electric field
`intensity is generally needed along planes 160a and 120a to
`maintain the continuity of the dark space 170. (Lower plane
`160a is referred to as a virtual anode surface.)
`It is believed that pinhole-like breaches in the continuity
`of the dark space 170 occur from time to time. A breach may
`occur because of a localized increase in electric field inten­
`sity. The latter causal effect may come about because a
`discontinuity develops in the localized conductivity of one
`or both of the cathode surface 120a or virtual anode surface
`160a. If the size of the breach is significant, a sudden rush
`of charged particles may pass through the breaching pinhole,
`from the plasma 160 into the target 120. In essence, an arc
`of current of relatively large magnitude, can pass between
`the plasma 160 and the target 120 at the point of breach of
`the dark space 170.
`If a sufficiently large arc is produced, a significant amount
`of heat may be generated at or around the arc-struck point of
`the target’s surface 120a. Localized temperature may rise
`sufficiently to melt an area about the arc-struck point. The
`molten target material can separate from the target and
`become drawn to the more positively charged chuck 140.
`When the molten target material hits the top surface 155a of
`the workpiece, it splatters, cools, and adheres to the top
`surface 155a as an anomaly.
`Computer simulations have shown that dropping a glob of
`molten metal onto a planar, solid metal surface produces a
`dome-shaped blob of material having ripples of the type
`seen in the ‘splat’ of FIG. 2 on the planar surface.
`Re-consolidation of the splattered material occurs due to
`surface tension and cooling of the splattered blob. The blob
`of anomalous material re-consolidates and solidifies into the
`rippled, dome-shaped form. This supports the present inven­
`tors’ hypothesis that some splats are produced by a melting
`of material on the target’s surface 120a.
`The present inventors suspect that localized melting is not
`the only mechanism by which nonhomogeneous deposition
`of excessive target material occurs onto the workpiece
`surface 155a. An arc-struck part of the target’s surface 120a
`might be mechanically weak. The shock or resultant thermal
`stress of a current arc may dislodge the mechanically weak
`part from the target’s surface. The dislodged but not neces­
`sarily molten material can then be drawn to the workpiece
`top surface 155a to form a nonhomogeneous, excessive
`deposition at the point of landing.
`A12O3 inclusions are electrically nonconductive or of high
`electrical resistance, and as such they define discontinuities
`in the voltage distributing or conductive properties of the
`target’s bottom surface 120a. Internal A12O3 inclusions
`within the target become part of the target’s surface as the
`surface 120a is eroded away by ion bombardment to expose
`the previously internal inclusions.
`Abrupt changes in the localized intensity of electric fields
`neighboring the bottom surface 120a of the target can
`develop when sufficiently large A12O3 inclusions, or other
`forms of disruption in the electrical conductivity properties
`of the target’s bottom surface 120a become exposed. This
`
`Page 9 of 14
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`6,001,227
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`7
`can lead to breach of the dark space 170, arcing, and the
`production of molten blobs or mechanically-dislodged
`anomalies. In general, such regions of disruption in the
`electrical conductivity properties of the target’s bottom
`surface 120a are referred to herein as conductivity anoma­
`lies. A conductivity anomaly of relatively high electrical
`resistance is defined as a region having a resistivity at least
`100 times greater than a corresponding electrical resistivity
`of an anomaly-free representative portion of the to-be-
`deposited metal.
`In view of the above, and in accordance with one aspect
`of the invention, it is desirable to minimize the numbers and
`sizes of conductivity anomalies within the to-be-deposited
`material of the target 120. Aside from oxides such as A12O3
`conductivity anomalies can include nitride precipitates, car­
`bide precipitates, contaminants that produce cathodic vapor
`bursts, and voids in the metal, where the latter voids may be
`originally defined by trapped gas bubbles.
`It is to be understood that when the composition or other
`characteristics of the ‘target’ is discussed herein, that dis­
`cussion is primarily directed to portions of the target that are
`bombarded by plasma-produced ions and are possibly sub­
`jected to being struck by arcs and as a result producing
`anomalous depositions. Targets in general may have addi­
`tional portions that are adapted for replaceable receipt into
`and/or electrical coupling with the remainder of the
`DC_ magnetron PVD system. Those additional portions
`may not require special compositioning or structuring in
`accordance with the present invention in instances where
`those additional portions are not bombarded by plasma-
`produced ions.
`In accordance with another aspect of the invention, it is
`desirable to maximize the microhardness (and thereby the
`micro-strength) of the target material so that arc-struck parts
`of the target are prevented from being so mechanically weak
`as to allow arc-induced dislodging of such target parts.
`Disruptions in the uniformity of electric field intensity
`about the bottom surface 120a of the target can also come
`about due to excessive roughness in the initial form of that
`bottom surface 120a.
`In accordance with yet another aspect of the invention, it
`is desirable to minimize the roughness of the initial bottom
`surface 120a of the target so as to inhibit disruptions in the
`uniformity of electric field intensity about the dark space
`170.
`Disruptions in the uniformity of electric field intensity
`about the bottom surface 120a of the target can also come
`about due to excessive dirt being left on the initial form of
`that bottom surface 120a when the target is first used (burnt
`in). The dirt can induce arcing. The latter can produce pits
`or other unevenness in the target surface which then pro­
`duces yet more arcing.
`In accordance with yet a further aspect of the invention,
`it is desirable to minimize dirt on the initial bottom surface
`120a of the target so as to inhibit dirt-induced arcing.
`An aluminum target in accordance with the invention has
`one or preferably more of the following homogenous char­
`acteristics of Table 1:
`
`TABLE 1
`
`PROPERTY
`
`PREFERRED RANGE
`
`Dielectric Inclusion
`Content, where such
`
`less than about
`5000 inclusions per gram
`
`8
`
`TABLE 1-continued
`
`PROPERTY
`
`PREFERRED RANGE
`
`5
`
`10
`
`inclusions have widths of
`0.3 micron or more
`Hydrogen content
`Carbon content
`Oxygen content
`Nitrogen content
`Metal grain size
`
`(200) textured material
`(111) textured material
`Hardness
`
`Surface roughness
`
`15
`
`Alloy strengthening
`addend
`Alloy precipitate size
`Other impurities
`
`of target material
`
`less than about 0.5 ppm
`less than about 10 ppm
`less than about 10 ppm
`less than about 10 ppm
`less than about 100
`micron
`greater than 50%
`less than about 3%
`greater than about
`50 (Rockwell scale)
`less than about 20 micro-
`inches
`greater than about 0.5%
`Cu by weight
`about 5 microns or less
`less than about 10 ppm
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Looser requirements can also be adapted for Table 1. For
`example: the number of allowed inclusions per gram of
`target material can be widened to 7,500 or 10,000; the
`definition of to-be-limited inclusions can be broadened to
`those having widths of about 1 micron or more; and the
`allowed hydrogen content can be loosened to less than about
`1 ppm (parts per million).
`Another, more stringently-controlled, aluminum target in
`accordance with the invention has one or preferably more of
`the following characteristics of Table 2:
`
`TABLE 2
`
`PROPERTY
`
`PREFERRED RANGE
`
`Dielectric Inclusion
`Content, where such
`inclusions have widths of
`0.1 micron or more
`Hydrogen content
`Carbon content
`Oxygen content
`Nitrogen content
`Metal grain size
`
`(200) textured material
`(111) textured material
`Hardness
`
`Surface roughness
`
`Alloy strengthening
`addend
`Alloy precipitate size
`Other impurities
`
`less than about
`5000 inclusions per gram
`of target material
`
`less than about 0.75 ppm
`less than about 5 ppm
`less than about 10 ppm
`less than about 7 ppm
`between about 75 micron
`and 90 micron
`greater than 75%
`less than about 1%
`greater than about
`50 (Rockwell scale)
`less than about 16 micro­
`inches
`about 0.5% Cu by weight
`
`less than about 4 microns
`less than about 5 ppm
`
`Even tighter requirements can also be adapted for Table 2.
`For example: the number of allowed inclusions per gram of
`target material can be narrowed to 3,000 or 1,000; the
`definition of to-be-limited inclusions can be tightened to
`include those having have widths of about 0.5 micron or
`more; the allowed hydrogen content can be tightened to less
`than about 0.05 ppm (parts per million), the allowed initial
`surface roughness can be reduced to 10 microinches or less;
`and the required amount of <200> texture material can be
`raised to 90% or more.
`Referring to FIG. 3, the manufacturing steps by which
`targets in accordance with the invention can be realized are
`discussed.
`FIG. 3 is a flow chart showing steps taken in the manu­
`facture and subsequent use of a target in accordance with the
`
`Page 10 of 14
`
`

`

`9
`invention. The overall manufacture-and-use process is ref­
`erenced as 300.
`At step 301, the raw materials that will form the target are
`acquired through mining or other means. It is desirable to
`acquire the raw materials from appropriate sources so that
`the acquired raw materials have minimal amounts of initial
`impurities, particularly oxygen (O), hydrogen (H), nitrogen
`(N), carbon (C), and silicon (Si) in the recited order.
`Minimizing initial O content is especially desirable
`because such oxygen content can lead to later formation of
`undesirable metal oxides such as A12O3 inclusions. Mini­
`mizing N and C content is less but still desirable because the
`inclusion