United States Patent
`
`[19]
`
`[11] Patent Number:
`
`6,001,227
`
`Pavate et al.
`
`[45] Date of Patent:
`
`Dec. 14, 1999
`
`US()()6()()1227A
`
`[S4] TARGET FOR USE IN MAGNETRON
`SPU'I'I‘ERING 0F 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, I’acifica;
`Murali Narasimhan; Seshadri
`Ramaswaml, both of San Jose; Jnlm
`Nulman, Palo Alto, all of Calif.
`
`I73] Assignee: Applied Materials, Inc., Santa Clara,
`Calif.
`
`[21]
`
`App]. No.:
`
`08/979,192
`
`[22
`
`Filed:
`
`Nov. 26, I997
`
`Int. Cl.“ .................................................... c23c 14/34
`[51]
`[52] us. Cl.
`................................ 204/298.12; 204,298.13;
`204/298.16; 204729321; 148/237; 420/528
`
`Field of Search ..........
`204,298.12. 298.13,
`204/298.16, 298.
`._ 8.21; 148/237; 420/528
`
`
`
`[58]
`
`[50]
`
`References Cited
`
`GT. Murray, Preparation and Characterimtion of Pure Met-
`als, Cubberley et a1: “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 (JO—280005, Patent Abstracts of Japan, Oct.
`1994.
`
`Abstract for JP (134164447, Patent Abstracts of Japan, Mar.
`1991.
`
`Derwem Abstract for JP 52—14519, Aug. 1993.
`
`Abstract for JP 06—017246, Patent Abstracts of Japan, Jan.
`1994.
`
`AS. Pokrovskaya—Soboleva, A.l.. Shapiro, TS Borisova,
`LK. Mazurova, V.l. 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. I974, pp. 86—91.
`
`Primary liraminer—Alan Diamond
`Attorney; Agent, or Hmi—Hiesler, Dubb, Meyer & Lovejoy
`
`U.S. PATENT DOCUMENTS
`
`[57]
`
`ABSTRACT
`
`5,242,566
`5,268,236
`5,320,728
`5,447,616
`5,436,315
`5,809,393
`
`9/1993 Parker .................................. 204/298.2
`1211993 Dumont ct al.
`428/030
`
`6/1994 Tepman
`204,192.12
`..
`9/1995 Satou et al.
`.. 204/’298.13
`
`1/1996 Fukuyo el al.
`204,298.13
`9/1998 Dunlop et al.
`............................ 419/61
`
`FOREIGN PATENT DOCUMENTS
`
`0 466 617 Al
`31 21 389
`196 (I9 439
`
`France .
`1/1992
`8/1982 Germany .
`9/1996 Germany .
`
`OTHER PUBLICATIONS
`
`PCT Notification of Transmittal of the International Search
`
`Report from the International Searching Authority at
`European Patent Oflice dated Mar. 16, 1999, 7 pages.
`
`the
`
`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
`
`in
`
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`m
`
`Samsung Electronics Co., ltd. v. Demaray LLC
`
`Samsung Electronic's Exhibit 1040
`Exhibit 1040, Page 1
`
`

`

`US. Patent
`
`Dec. 14,1999
`
`Sheet 1 of5
`
`6,001,227
`
`MN
`
`
`
`
`TARGET
`
`SHIELD
`
`+++++++
`+++++++
`+++++++
`
`'.'.va}u'.‘."155:'1
`
`SUBSTRATE
`
`152
`
`
`
`CHUCK
`
`140
`
`FIG. 1
`
`Ex. 1040, Page 2
`
`

`

`US. Patent
`
`Dec. 14, 1999
`
`Sheet 2 0f 5
`
`6,001,227
`
`305$.new?
`
`mommhzmoz.
`
`mOJ
`m30_<
`
`%% ._m>w._
`
`HOMZZOOKMHZZOHOmumO:0_<m0ZO_._.OmwmwOmomi
`
`
`
`
`
`ZO_wD._OZ_mO~_<Hwoms.OZEmtbaw._.<owk<z_0.m0mOAm:0_<
`
`
`
`
`
`NCE
`
`Ex. 1040, Page 3
`
`

`

`US. Patent
`
`Dec. 14, 1999
`
`Sheet 3 0f 5
`
`6,001,227
`
`321
`
`322
`
`323
`
`324
`
`326
`
`327
`
`328
`
`199
`
`301
`
`
`
`ACQUIRE RAW
`MATERIALS
`
`EXTRACT ALUMINUM
`BY PURIFYING RAW
`
`MATERIALS
`
`MELT AND CAST
`
`IN CRUCIBLE
`
`302
`
`303
`
`304
`
`305
`
`306
`
`307
`
`308
`
`W M
`
`INIMIZE INITIAL
`IMPURITIES, ESP.
`0, H, N, C, Si
`
`SELECT PURIFICATION
`PROCESS FOR MINIMAL
`
`INCLUSION OF Al203 OR
`OTHER ANOMALIES
`
`MELT‘S OXIDE SKIN
`
`1) MINIMIZE H2 ABSORB
`2) REDUCE CRUCIBLE INTRO OF
`C. N. O FLAKES INTO MELT
`3) MIN CONVECTIVE INCORP OF
`
`
`MECHANICAL
`DEFORMATION
`
`
`(FORGE/ROLL)
`
`
`
`MACHINING
`
`HIRE
`
`SURFACE
`TREATMENT
`
`
`
`PACKAGING/
`SHIPPING
`
`
`
`IGNITE PLASMA
`& MAINTAIN PVD
`
`PROCESS
`
`INCREASE STRENGTH/HARDNESS
`
`3) 250% OF [200] TEXTURE
`
`1) SMALL GRAIN SIZE (<100M)
`2) SOLID SOLUTION ADDENDS
`INDUCE 2ND PHASE
`
`PERCIPITATES (1 -10,u)
`
` SMOOTH INITIAL TARGET
`SURFACE TO AVG
`E ROUGHNESS OF <20“ INCH
`
`1) ULTRASONIC SURFACE
`CLEAN
`
`2) INERT GAS PACK
`
`(<2KW/SEC RAMP)
`
`REDUCE ELECTRO-
`MECHANICAL STRESS FROM
`RAPID PLASMA IGNITION
`
`FIG. 3
`
`Ex. 1040, Page 4
`
`

`

`U.S. Patent
`
`Dec. 14, 1999
`
`Sheet 4 0f 5
`
`6,001,227
`
`10.9
`
`‘\3*
`
`ATMOSPHERE 4M0-
`
`
`
`44
`
`
`CRUCIBLE
`410 Al MELT
`
`CONVECTION
`
`
`CURRENTS
`
`FLAKES
`415
`
`
`
`HEATSOURCE
`420
`
`FIG. 4A
`
`450a
`A|203
`
` 450b
`
`H2 BUBBLE
`
`OTHER ANOMALY
`450C
`
`FIG. 4B
`
`Ex. 1040, Page 5
`
`

`

`SPLAT FORMATION THROUGH TARGET LIFE
`
`(200 MM WAFER)
`
`PROCESS CONDITIONS
`
`10.6 Kw, 22 mT. 52 mm SPACING
`
`PROPOSED CERTIFICATION LIMIT FOR SPLAT DENSITY
`
`NOTE: EACH DATA POINT REPRESENTS
`
`AN AVERAGE DENSITY OF 45 WAFERS
`
`SPLATSPERWAFER(>1MICRON)
`
`100
`
`200
`
`300
`
`500
`400
`TARGET LIFE IN KWHRS
`
`600
`
`700
`
`800
`
`mamaSH
`
`
`
`6661‘71'33“
`
`S.I0S”WIS
`
`LZZ‘100‘9
`
`Ex. 1040, Page 6
`
`

`

`6,001,227
`
`1
`TARGET FOR USE IN MAGNETRON
`
`
`
`
`SPUTTERING 0F 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 (A1) 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
`
`
`
`
`
`
`
`
`
`
`is/are assigned to the
`The following US. patent(s)
`assignee of the present application, and its/their disclosures
`
`
`
`
`
`
`
`
`is/are incorporated herein by reference:
`
`
`
`
`
`
`
`
`
`
`
`(A) US. Pat. No. 5,242,566 issued Sep. 7, 1993 to N.
`Parker; and
`
`
`
`
`
`
`
`
`
`
`
`(B) US. 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 (1C) 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 1C. 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 EnduraTM system
`
`
`
`
`
`
`
`
`
`
`available from Applied Materials Inc. of California for
`
`
`
`
`
`
`
`
`
`
`
`sputtering aluminum (Al) or aluminum alloys onto semi-
`conductor wafers.
`
`Although such DCimagnetron 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
`
`
`
`
`
`
`
`DCimagnetron-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 DCimagnetron 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., A1203 precipitates)
`
`10
`
`U.)Ln
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`
`
`
`
`
`
`
`formed by trapped gas
`and nonconductive voids (e.g.,
`
`
`
`
`
`
`
`
`
`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., A1203 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 (A1203),
`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 (A1203), 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 DCimagnetron 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
`
`Ex. 1040, Page 7
`
`Ex. 1040, Page 7
`
`

`

`6,001,227
`
`3
`produce an essentially homogeneous distribution of metal
`
`
`
`
`
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`grains of diameters less than or equal to 100 ,u and second
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`phase precipitates of diameters in the range of about 1 to 10
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`[L and more than about 50% material having <200> texture;
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`(d) smoothing the initial target surface to an average rough-
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`ness of no more than about 20 microinches;
`(e) using
`ultrasonic cleaning to remove arc-inducing contaminants
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`from the initial target surface; and (f) shipping the cleaned
`target in an inert gas pack.
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`A method for operating a DCimagnetron PVD system in
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`accordance with the invention comprises the steps of: (a)
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`installing a new target having one or more of the following
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`characteristics: (a) essentially no dielectric inclusions such
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`as metal oxides (A1203), nitride precipitates, carbide
`precipitates, of sizes larger than about 1 micron in concen-
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`trations greater than 5,000 such inclusions per gram of target
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`material; (b) essentially no voids such as those caused by
`entrapped gas of sizes larger than about 1 micron in con-
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`centrations greater than 5,000 such voids per gram of target
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`material; (c) an essentially homogeneous distribution of
`metal grain size in the range of about 75 micron and 90
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`micron; and (d) an initial surface roughness of less than
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`about 20 microinches. A DCimagnetron PVD operating
`method in accordance with the invention further comprises
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`ramping plasma power at a rate of no more than 2 Kw per
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`second or less.
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`Other aspects of the invention will become apparent from
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`the below detailed description.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`The below detailed description makes reference to the
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`accompanying drawings, in which:
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`FIG. 1 is a schematic diagram of a DC sputtering mag-
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`netron;
`FIG. 2 is a micrograph showing a cross sectional side
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`View of an isolated ‘splat’ or ‘blob’ within the interconnect
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`structure of an integrated circuit;
`FIG. 3 is a flow chart showing steps taken in the manu-
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`facture and subsequent use of a target, including improve—
`ment steps in accordance with the invention;
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`FIGS. 4A and 4B respectively show cross sectional Views
`of a simple casting process and the resultant product for
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`purpose of explanation; and
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`FIG. 5 is a plot showing average splats number per wafer
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`over sampled groupings of 45 wafers each taken every 200
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`Kw hours of a sample target in accordance with the inven-
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`tion.
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`DETAILED DESCRIPTION
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`FIG. 1 shows a schematic diagram of a DC sputtering
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`magnetron system 100. A magnet 110 is positioned over a
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`portion of target 120. The target
`includes a deposition-
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`producing portion that
`is electrically conductive and is
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`composed of the to-be-sputtered material (e.g., a metal such
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`as aluminum). Target 120 is typically of a symmetrical form
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`such as a circular disk, but may have various bends or other
`features such as shown for adaptively fitting into a specific
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`DCimagnetron PVD system and for producing specific
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`distributions of electrical field intensity and gas flow in
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`accordance with design specifics of
`the receiving
`DCimagnetron PVD system. The target 120 is typically
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`structured for removable insertion into the corresponding
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`DCimagnetron PVD system 100. Targets are periodically
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`replaced with a new targets given that the PVD process
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`erodes away the to-be-deposited material of each target.
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`U.)Ln
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`4
`A switchng means 125 may be provided for selectively
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`connecting the target 120 to a relatively negative voltage
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`source 127. In general,
`the negative voltage source 127
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`provides a DC cathode voltage in the range of about —470 V
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`to —530 V relative to the potential on an opposed anode
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`(ground or GND in the illustrated example). The specific
`cathode voltage varies according to design. When switching
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`means 125 is closed to connect the target 120 with negative
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`voltage source 127,
`the target can act as a source of
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`negatively charged particles such as 135 (e') and 138 (A1")
`which are discussed below. Because of this the target is also
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`referred to as the cathode.
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`A tubular gas-containment shield 130, usually of cylin-
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`drical shape, is provided below and spaced apart from the
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`target 120. Shield 130 is electrically conductive and is
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`generally coupled to ground (GND) or to another relatively
`positive reference voltage so as to define an electrical field
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`between the target 120 and the shield. Shield 130 has a
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`plurality of apertures 132 defined through it for admitting a
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`supplied flow of gas 131 such as argon (Ar) from the exterior
`of the shield 130 into its interior.
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`A workpiece-supporting chuck 140 is further provided
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`centrally below and spaced apart from the target 120, usually
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`within the interior of the shield 130. Chuck 140 is electri-
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`cally conductive and is generally also coupled to ground
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`(GND) or to another relatively positive reference voltage so
`as to define a further electrical field between the target 120
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`and the chuck.
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`A replaceable workpiece 150 such as a semiconductor
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`wafer is supported on the chuck centrally below the target
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`120. Workpiece 150 originally consists of a substrate 152
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`having an exposed top surface 152a. As PVD sputtering
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`proceeds, a metal film 155 having a top surface 1550 builds
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`up on the substrate 152. It is desirable that the build up or
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`deposition of the metal film 155 be uniform across the entire
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`top surface 152a of the substrate, but as explained herein,
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`anomalies sometimes interfere with homogeneous deposi-
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`tion.
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`Workpiece substrate 152 may include an insulative layer
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`composed for example of SiOz. In such cases, the metal film
`155 may be electrically insulated from chuck 140 and the
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`voltage of the metal film 155 will float to a slightly negative
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`level relative to the chuck’s voltage (e.g., GND).
`DCimagnelron operation initiates as follows. When
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`switching means 125 is closed,
`initial electric fields are
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`produced between the target 120 and the shield 130 and the
`chuck 140. Plasma igniting gas is introduced. The illustrated
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`assembly of FIG. 1 is usually housed in a low pressure
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`chamber 105 (partially shown) that maintains an internal
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`pressure in the range of about 2 to 5 Torr or lower. Some of
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`the supplied gas 131 that enters the interior of shield 130
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`disassociates into positively charged ions (AF) and nega-
`tively charged ions (Ar') when subjected to the initial
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`electric fields. One so-generated positive ion is shown at
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`133. Due to electrostatic attraction, ion 133 (Ar+) accelerates
`towards and collides with the bottom surface of the target at
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`first collision point, say 134. The point of collision is
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`denoted with an asterisk (“*”). This initial collision induces
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`emission of an electron (e') 135 from cathode 120. (A
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`particle of target material (Al) may also be dislodged by
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`collision 134.) The emitted electron 135 drifts down towards
`the more positive chuck 140. However, the magnetic fields
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`of magnet 110 give electron 135 a spiraling trajectory as
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`indicated at 136. Eventually electron 135 collides with a
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`molecule of the inflowing gas 131 (e.g., Arz). This second
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`collision (*) produces another positively charged ion 137
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`Ex. 1040, Page 8
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`Ex. 1040, Page 8
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`

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`6,001,227
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`5
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`(Ar+) which accelerates towards and collides with the bot-
`tom surface of the target. This third collision produces yet
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`another electron like 135, and a chain reaction is established
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`leading to the creation of a sustained plasma 160 within the
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`interior of the gas-containment shield 130. Plasma 160 is
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`charged positive relative to the cathode 120 and begins to act
`like a floating anode. This changes the electric field distri-
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`bution within the DCimagnetron PVD system 100. At some
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`point the electric field distribution stabilizes into a long term
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`steady state.
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`The ballistic collisions of massive particles such as 137
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`(Ar+) with the bottom surface of the target 120 sometimes
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`cause small particles of the target’s material to break off and
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`move toward the underlying workpiece 150. An example of
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`such an emitted target particle is shown at 138. The sizes and
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`directions of the emitted target particles tend to produce a
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`relatively uniform deposition of the emitted material (e.g.,
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`aluminum) on the top surface (152a and later 1550) of the
`workpiece 150.
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`On occasion, however, as explained above, the deposition
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`is not uniform in that blobs or ‘splats’ appear on or within
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`the deposited metal film 155. Some of the splats can have
`diameters as large as 500 microns, which is quite large in a
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`world where operational features of the affected device have
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`dimensions of 1 micron or less. Such splats are undesirable.
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`FIG. 2 is a micrograph taken with a focused ion beam
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`(FIB) microscope at a magnification sufficient to show an
`anomalous section of a 1 micron-thick aluminum line. The
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`micrograph shows a cross sectional side view of an isolated
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`‘blob’ within the interconnect structure of an
`‘splat’ or
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`integrated circuit. The splat diameter is approximately 5
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`microns and the splat height is roughly 1.5 microns. In this
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`particular case, the deposited metal film (155) is an alloy of
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`aluminum and copper (AlCu). The ‘splat’ is given its name
`because of the appearance that something had splattered
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`onto the otherwise planar, PVD deposited metal film.
`In the captured splat of FIG. 2, an inclusion having a
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`diameter of roughly 0.3 micron is seen within the body of the
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`splat. Inclusions are not routinely observed in every splat.
`Inclusions such as the one shown in FIG. 2 were isolated and
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`analyzed chemically. The analysis showed that such inclu-
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`sions were composed primarily of the oxide, A1203.
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`The present inventors deduced that the A1203 inclusion
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`had come from the specific target (120) used in the PVD
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`sputtering process, given that
`the feed gas consisted of
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`relatively pure Ar, and the substrate had been cleaned, and
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`there was nothing else in the DC magnetron PVD system
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`that could act as a source of A1203.
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`the A1203
`The present inventors further deduced that
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`inclusion was a causal
`factor
`in the generation of the
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`observed splat even though the splat is further defined by an
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`excessive amount of AlCu that appears to have splattered
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`onto the forming metal film during the PVD process.
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`Further questions remained, however. What was the spe-
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`cific mechanism that made the A1203 inclusion a causal
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`factor in the generation of the observed splat? Why do many
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`splats not include such A1203 inclusions?
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`It is believed that the correct answer lies in understanding
`how electrical
`fields are distributed within the
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`DCimagnetron system 100 (FIG. 1) after plasma 160
`reaches steady state stability, and how this stability can be
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`temporarily disturbed.
`Referring to FIG. 1, as the plasma 160 reaches steady state
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`stability, there develops between the bottom surface 120a of
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`the target and a top boundary 160a of the plasma, an area
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`that is essentially free of electrons or other charged particles.
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`10
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`U.)Ln
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`40
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`()0
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`6
`This charge-free region is referred to in the literature as the
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`‘dark space’ or the ‘dead space”. Its extent is referenced in
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`FIG. 1 as 170 (not to scale).
`A relatively large voltage differential develops between
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`the top 120a and bottom 160a of the dark space 170.
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`Target-emitted electrons such as 135 are believed to tunnel
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`rather than to drift through the dark space 170 and to thereby
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`maintain the relatively large voltage differential between the
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`top and bottom of the dark space 170.
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`A relatively homogenous distribution of electric field
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`intensity is generally needed along planes 160a and 120a to
`maintain the continuity of the dark space 170. (Lower plane
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`1600 is referred to as a virtual anode surface.)
`It is believed that pinhole-like breaches in the continuity
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`of the dark space 170 occur from time to time. Abreach may
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`occur because of a localized increase in electric field inten-
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`sity. The latter causal effect may come about because a
`discontinuity develops in the localized conductivity of one
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`or both of the cathode surface 120a or virtual anode surface
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`160a. If the size of the breach is significant, a sudden rush
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`of charged particles may pass through the breaching pinhole,
`from the plasma 160 into the target 120. In essence, an arc
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`of current of relatively large magnitude, can pass between
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`the plasma 160 and the target 120 at the point of breach of
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`the dark space 170.
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`If a sufficiently large arc is produced, a significant amount
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`of heat may be generated at or around the arc—struck point of
`the target’s surface 120a. Localized temperature may rise
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`sufficiently to melt an area about the arc-struck point. The
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`molten target material can separate from the target and
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`become drawn to the more positively charged chuck 140.
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`When the molten target material hits the top surface 15511 of
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`the workpiece,
`it splatters, cools, and adheres to the top
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`surface 155a as an anomaly.
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`Computer simulations have shown that dropping a glob of
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`molten metal onto a planar, solid metal surface produces a
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`dome—shaped blob of material having ripples of the type
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`seen in the ‘splat’ of FIG. 2 on the planar surface.
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`Re-consolidation of the splattered material occurs due to
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`surface tension and cooling of the splattered blob. The blob
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`of anomalous material re—consolidates and solidifies into the
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`rippled, dome-shaped form. This supports the present inven-
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`tors’ hypothesis that some splats are produced by a melting
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`of material on the target’s surface 120a.
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`The present inventors suspect that localized melting is not
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`the only mechanism by which nonhomogeneous deposition
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`of excessive target material occurs onto the workpiece
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`surface 155a. An arc—struck part of the target’s surface 120a
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`might be mechanically weak. The shock or resultant thermal
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`stress of a current arc may dislodge the mechanically weak
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`part from the target’s surface. The dislodged but not neces—
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`sarily molten material can then be drawn to the workpiece
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`top surface 155a to form a nonhomogeneous, excessive
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`deposition at the point of landing.
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`A1203 inclusions are electrically nonconductive or of high
`electrical resistance, and as such they define discontinuities
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`in the voltage distributing or conductive properties of the
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`target’s bottom surface 120a.
`Internal A1203 inclusions
`wi