(12) United States Patent
`US 6,277,249 B1
`(10) Patent N0.:
`(45) Date of Patent:
`Gopalraja et al.
`Aug. 21, 2001
`
`USOO6277249B1
`
`(54)
`
`(75)
`
`INTEGRATED PROCESS FOR COPPER VIA
`FILLING USING A MAGNETRON AND
`TARGET PRODUCING HIGHLY ENERGETIC
`IONS
`
`Inventors: Praburam G0palraja, Sunnyvale;
`Jianming Fu, San Jose; Fusen Chen,
`Saratoga; Girish Dixit, San Jose;
`Zheng Xu, Foster City; Sankaram
`Athreya, Sunnyvale; Wei D. Wang,
`Santa Clara; Ashok K. Sinha, Palo
`Alto, all of CA (US)
`
`(73) Assignee: Applied Materials Inc., Santa Clara,
`CA (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/518,180
`
`(22)
`
`Filed:
`
`Mar. 2, 2000
`
`Related US. Application Data
`
`(63)
`
`(51)
`
`Continuation—in—part of application No. 09/490,026, filed on
`Jan. 21, 2000.
`
`Int. Cl? ........................... C23C 14/35; c23c 14/00;
`c23c 14/34
`
`................................ 204/192.12; 204/298.19;
`(52) US. Cl.
`204/298.2; 204/298.21; 204/298.22; 204/298.16;
`204/298.17; 204/298.18; 204/298.12; 204/192.17;
`204/192.15
`
`(58) Field of Search ............................ 204/298.19, 298.2,
`204/298.21, 298.22, 298.16, 298.17, 298.18,
`298.12, 192.12; 192.15; 192.17
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,069,770 * 12/1991 Glocker ........................... 204/192.12
`
`5,178,739
`1/1993 Barnes et al.
`..... 204/192.12
`.................. 204/298.17
`5,482,611
`1/1996 Helmer et al.
`
`FOREIGN PATENT DOCUMENTS
`
`W0 00/48226
`A1
`
`8/2000 (W0) ............................. H01J/37/34
`
`OTHER PUBLICATIONS
`
`Kitamoto et al., “Compact sputtering apparatus for depos-
`iting Co—Cr alloy thin films in magnetic disk,” Proceedings:
`The Fourth International Symposium on Sputtering &
`Plasma Processes, Kanazawa, Japan, Jun. 4—6, 1997, pp.
`519—522.
`
`(List continued on next page.)
`
`Primary Examiner—Mark F. Huff
`Assistant Examiner—Daborah Chacko-Davis
`
`(74) Attorney, Agent, or Firm—Charles S. Guenzer
`
`(57)
`
`ABSTRACT
`
`A target and magnetron for a plasma sputter reactor. The
`target has an annular trough facing the wafer to be sputter
`coated. Various types of magnetic means positioned around
`the trough create a magnetic field supporting a plasma
`extending over a large volume of the trough. For example,
`the magnetic means may include magnets disposed on one
`side within a radially inner wall of the trough and on another
`side outside of a radially outer wall of the trough to create
`a magnetic field extending across the trough,
`to thereby
`support a high-density plasma extending from the top to the
`bottom of the trough. The large plasma volume increases the
`probability that
`the sputtered metal atoms will become
`ionized. The magnetic means may include a magnetic coil,
`may include additional magnets in back of the trough top
`wall to increase sputtering there, and may include confine-
`ment magnets near the bottom of the trough sidewalls. The
`magnets in back of the top wall may have an outer magnet
`surrounding an inner magnet of the opposite polarity. The
`high aspect ratio of the trough also reduces asymmetry in
`coating the sidewalls of a deep hole at the edge of the wafer.
`An integrated copper via filling process includes a first step
`of highly ionized sputter deposition of copper, a second step
`of more neutral, lower-energy sputter deposition of copper
`to complete the seed layer, and electroplating copper into the
`hole to complete the metallization.
`
`(List continued on next page.)
`
`27 Claims, 11 Drawing Sheets
`
`180
`
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`
`
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`142
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`190
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`TSMC et al. v. Zond, Inc.
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`TSMC et al. v. Zond, Inc.
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`

`

`US 6,277,249 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`.................. 204/298.19
`4/1996 Bourez et a1.
`5,512,150 *
`12/1996 Lantsman ............. 204/19233
`5,589,041
`5,685,959 * 11/1997 Bourez et a1.
`..
`204/298.2
`5,685,961
`11/1997 Bourez et a1.
`..
`.
`
`5,865,961
`2/1999 Yokoyama ........... 204/19212
`
`..... 204/19212
`5,897,752 *
`4/1999 Hong et a1.
`.
`
`6/2000 Miyaura .......................... 204/192. 12
`6,080,284
`OTHER PUBLICATIONS
`
`.. 204/1922
`
`Yamazato et al., “Preparation of T1N thin Films by facing
`targets magnetron sputtering,” Proceedings: The Fourth
`International Symposium on Sputtering & Plasma Pro-
`cesses, Kanazawa, Japan Jun. 4—6, 1997, pp. 635—638.
`
`Musil et al., “Unbalanced magnetrons and new sputtering
`systems With enhanced plasma ionization,” Journal of Vac-
`cum Science and Technology A, vol. 9, No. 3, May/Jun.
`1991, pp. 1171—1177.
`
`Matsuoka et al., “Dense plasma production and film depo-
`sition by new high—rate sputtering using an electric mirror,”
`Journal of Vacuum Science and TechnologyA, vol. 7, No. 4,
`Jul/Aug. 1989, pp. 2652—2657.
`
`Ivanov et al., “Electron energy distribution function in dc
`magnetron sputtering discharge,” Vacuum, vol. 43, No. 8,
`1992, pp. 837—842.
`
`* cited by examiner
`
`GILLETTE-1109 / Page 2 of 22
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`GILLETTE-1109 / Page 2 of 22
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`

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`US. Patent
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`Aug. 21, 2001
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`Sheet 1 0f 11
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`US 6,277,249 B1
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`GILLETTE-1109 / Page 3 of 22
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`GILLETTE-1109 / Page 3 of 22
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`US. Patent
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`Aug. 21, 2001
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`US 6,277,249 B1
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`GILLETTE-1109 / Page 4 of 22
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`GILLETTE-1109 / Page 4 of 22
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`US. Patent
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`Aug. 21, 2001
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`Sheet 3 0f 11
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`US 6,277,249 B1
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`GILLETTE-1109 / Page 5 of 22
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`GILLETTE-1109 / Page 5 of 22
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`US. Patent
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`Aug. 21, 2001
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`Sheet 4 0f 11
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`US 6,277,249 B1
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`GILLETTE-1109 / Page 6 of 22
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`GILLETTE-1109 / Page 6 of 22
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`US. Patent
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`Aug. 21, 2001
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`Sheet 5 0f 11
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`GILLETTE-1109 / Page 7 of 22
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`GILLETTE-1109 / Page 7 of 22
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`

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`US. Patent
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`Aug. 21, 2001
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`Sheet 6 0f 11
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`US 6,277,249 B1
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`GILLETTE-1109 / Page 8 of 22
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`GILLETTE-1109 / Page 8 of 22
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`

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`Aug. 21, 2001
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`GILLETTE-1109 / Page 9 of 22
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`Aug. 21, 2001
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`GILLETTE-1109 / Page 10 of 22
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`Aug. 21, 2001
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`Sheet 9 0f 11
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`US 6,277,249 B1
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`200
`
`
`
`2.0
`
`1.5
`
`SPUTTERING
`
`YIELD
`
`1,0
`
`0.5
`
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`
`GILLETTE-1109 / Page 11 of 22
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`GILLETTE-1109 / Page 11 of 22
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`

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`US. Patent
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`Aug. 21, 2001
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`Sheet 10 0f 11
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`US 6,277,249 B1
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`GILLETTE-1109 / Page 12 of 22
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`GILLETTE-1109 / Page 12 of 22
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`Aug. 21, 2001
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`Sheet 11 0f 11
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`US 6,277,249 B1
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`230
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`232
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`234
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`236
`
`238
`
`PATTERNED
`INTER—METAL
`
`DIELECTRIC
`
`SPUTTER DEPOSIT
`BARRIER
`
`HIGH ENERGY
`IONIZED COPPER
`
`SPUTTER
`
`NEUTRAL LOW ENERGY
`COPPER SPUTTER
`DEPOSITION
`
`ELECTRO CHEMICAL
`PLATE COPPER
`
`FIG. 16
`
`GILLETTE-1109 / Page 13 of 22
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`GILLETTE-1109 / Page 13 of 22
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`

`

`US 6,277,249 B1
`
`1
`INTEGRATED PROCESS FOR COPPER VIA
`FILLING USING A MAGNETRON AND
`TARGET PRODUCING HIGHLY ENERGETIC
`IONS
`
`RELATED APPLICATION
`
`This application is a continuation in part of Ser. No.
`09/490,026, filed Jan. 21, 2000.
`
`FIELD OF THE INVENTION
`
`The invention relates generally to a plasma sputter reac-
`tor. In particular, the invention relates to the sputter target
`and associated magnetron used in a sputter reactor and to an
`integrated via filling process using sputtering.
`
`BACKGROUND ART
`
`A semiconductor integrated circuit contains many layers
`of different materials usually classified according to whether
`the layer
`is a semiconductor, a dielectric (electrical
`insulator) or metal. However, some materials such as barrier
`materials, for example, TiN, are not so easily classified. The
`two principal current means of depositing metals and barrier
`materials are sputtering, also referred to as physical vapor
`deposition (PVD), and chemical vapor deposition (CVD).
`Of the two, sputtering has the inherent advantages of low
`cost source material and high deposition rates. However,
`sputtering has an inherent disadvantage when a material
`needs to filled into a deep narrow hole, that is, one having
`a high aspect ratio, or coated onto the sides of the hole,
`which is often required for barrier materials. Aspect ratios of
`3:1 present challenges, 5:1 becomes difficult, 8:1 is becom-
`ing a requirement, and 10:1 and greater are expected in the
`future. Sputtering itself is fundamentally a nearly isotropic
`process producing ballistic sputter particles which do not
`easily reach the bottom of deep narrow holes. On the other
`hand, CVD tends to be a conformal process equally effective
`at the bottom of holes and on exposed top planar surfaces.
`Up until the recent past, aluminum has been the metal of
`choice for the metallization used in horizontal interconnects.
`
`Vias extending between two levels of copper can also be
`formed of copper. Contacts to the underlying silicon present
`a larger problem, but may still be accomplished with copper.
`Copper interconnects are used to reduce signal delay in
`advanced ULSI circuits. Due to continued downward scal-
`
`ing of the critical dimensions of microcircuits, critical elec-
`trical parameters of integrated circuits, such as contact and
`via resistances, have become more difficult to achieve. In
`addition, due to the smaller dimensions, the aspect ratios of
`inter-metal features such as contacts and vias are also
`
`increasing. An advantage of copper is that it may be quickly
`and inexpensively deposited by electrochemical processes,
`such as electroplating. However, sputtering or possibly CVD
`of thin copper layers onto the walls of via holes is still
`considered necessary to act as an electrode for electroplating
`and as a seed layer for the electroplated copper. The dis-
`cussion of copper processes will be delayed until later.
`The conventional sputter reactor has a planar target in
`parallel opposition to the wafer being sputter deposited. A
`negative DC voltage is applied to the target sufficient to
`ionize the argon working gas into a plasma. The positive
`argon ions are attracted to the negatively charged target with
`sufficient energy to sputter atoms of the target material.
`Some of the sputtered atoms strike the wafer and form a
`sputter coating thereon. Most usually a magnetron is posi-
`tioned in back of the target
`to create a magnetic field
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`adjacent to the target. The magnetic field traps electrons,
`and,
`to maintain charge neutrality in the plasma, the ion
`density also increases. As a result, the plasma density and
`sputter rate are increased. The conventional magnetron
`generates a magnetic field principally lying parallel to the
`target.
`Much effort has been expended to allow sputtering to
`effectively coat metals and barrier materials deep into nar-
`row holes. High-density plasma (HDP) sputtering has been
`developed in which the argon working gas is excited into a
`high-density plasma, which is defined as a plasma having an
`ionization density of at least 101lcm'3 across the entire
`space the plasma fills except the plasma sheath. Typically, an
`HDP sputter reactor uses an RF power source connected to
`an inductive coil adjacent to the plasma region to generate
`the high-density plasma. The high argon ion density causes
`a significant fraction of sputtered atoms to be ionized. If the
`pedestal electrode supporting the wafer being sputter coated
`is negatively electrically biased, the ionized sputter particles
`are accelerated toward the wafer to form a directional beam
`
`that reaches deeply into narrow holes.
`HDP sputter reactors, however, have disadvantages. They
`involve a relatively new technology and are relatively
`expensive. Furthermore, the quality of the sputtered films
`they produce is often not
`the best,
`typically having an
`undulatory surface. Also, high-energy ions, possibly the
`argon ions attracted as well to the wafer, tend to damage the
`material already deposited.
`Another sputtering technology, referred to as self-ionized
`plasma (SIP) sputtering, has been developed to fill deep
`holes. See, for example, US. patent application Ser. No.
`09/373,097 filed Aug. 12, 1999 by Fu and US. patent
`application Ser. No. 09/414,614 filed Oct. 8, 1999 by Chiang
`et al. Both of these patent applications are incorporated by
`reference in their entireties. In its original implementations,
`SIP relies upon a somewhat standard capacitively coupled
`plasma sputter reactor having a planar target in parallel
`opposition to the wafer being sputter coated and a magne-
`tron positioned in back of the target to increase the plasma
`density and hence the sputtering rate. The SIP technology,
`however, is characterized by a high target power density, a
`small magnetron, and a magnetron having an outer magnetic
`pole piece enclosing an inner magnetic pole piece with the
`outer pole piece having a significantly higher total magnetic
`flux than the inner pole piece. In some implementations, the
`target is separated from the wafer by a large distance to
`effect
`long-throw sputtering, which enhances collimated
`sputtering. The asymmetric magnetic pole pieces causes the
`magnetic field to have a significant vertical component
`extending far towards the wafer, thus enhancing and extend-
`ing the high-density plasma volume and promoting transport
`of ionized sputter particles.
`The SIP technology was originally developed for sus-
`tained self-sputtering (SSS) in which a sufficiently high
`number of sputter particles are ionized that they may be used
`to further sputter the target and no argon working gas is
`required. Of the metals commonly used in semiconductor
`fabrication, only copper is susceptible to SSS resulting from
`its high self-sputtering yield.
`The extremely low pressures and relatively high ioniza-
`tion fractions associated with SSS are advantageous for
`filling deep holes with copper. However,
`it was quickly
`realized that the SIP technology could be advantageously
`applied to the sputtering of aluminum and other metals and
`even to copper sputtering at moderate pressures. SIP sput-
`tering produces high quality films exhibiting high hole
`filling factors regardless of the material being sputtered.
`
`GILLETTE-1109 / Page 14 of 22
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`

`US 6,277,249 B1
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`3
`Nonetheless, SIP has some disadvantages. The small area
`of the magnetron requires circumferential scanning of the
`magnetron in a rotary motion at the back of the target. Even
`with rotary scanning, radial uniformity is difficult to achieve.
`Furthermore, very high target powers have been required in 5
`the previously known versions of SIP. High-capacity power
`supplies are expensive and necessitate complicated target
`cooling. Lastly, known versions of SIP tend to produce a
`relatively low ionization fraction of sputter particles, for
`example, 20%. The non-ionized fraction has a relatively
`isotropic distribution rather than forming a forward directed
`beam as the ionized particles are accelerated toward a biased
`wafer. Also, the target diameter is typically only slightly
`greater than the wafer diameter. As a result, those holes
`being coated located at the edge of the target have radially
`outer sidewalls which see a larger fraction of the wafer and
`are more heavily coated than the radially inner sidewalls.
`Therefore, the sidewalls of the edge holes are asymmetri-
`cally coated.
`Other sputter geometries have been developed which
`increase the ionization density. One example is a multi-pole
`hollow cathode target, several variants of which are dis-
`closed by Barnes et al. in US. Pat. No. 5,178,739. Its target
`has a hollow cylindrical shape, usually closed with a circular
`back wall, and is electrically biased. Typically, a series of
`magnets, positioned on the sides of the cylindrical cathode
`of alternating magnetic polarization, create a magnetic field
`extending generally parallel
`to the cylindrical sidewall.
`Helmer et al. in US. Pat. No. 5,482,611 disclose a hollow
`cathode target in which an axially polarized tubular magnet
`surrounds the sides of the hollow cathode and extend in back
`
`10
`
`15
`
`20
`
`25
`
`30
`
`of the cathode back wall to create a generally axial magnetic
`field but which forms a cusp at the cathode back wall.
`Another approach uses a pair of facing targets facing the
`lateral sides of the plasma space above the wafer. Such 35
`systems are described, for example, by Kitamoto et al. in
`“Compact sputtering apparatus for depositing Co—Cr alloy
`thin films in magnetic disks,” Proceedings: The Fourth
`International Symposium on Sputtering & Plasma
`Processes, Kanazawa, Japan, Jun. 4—6, 1997, pp. 519—522, 40
`by Yamazato et al. in “Preparation of TiN thin films by
`facing targets magnetron sputtering, ibid., pp. 635—638, and
`by Musil et al. in “Unbalanced magnetrons and new sput-
`tering systems with enhanced plasma ionization,” Journal of
`Vacuum Science and TechnologyA, vol. 9, no. 3, May 1991, 45
`pp. 1171—1177. The facing pair geometry has the disadvan-
`tage that the magnets are stationary and create a horizontally
`extending field that is inherently non-uniform with respect to
`the wafer.
`
`Musil et al., ibid., pp.1174, 1175 describe a coil-driven 50
`magnetic mirror magnetron having a central post of one
`magnetic polarization and surrounding rim of another polar-
`ization. An annular vault-shaped target is placed between the
`post and rim. This structure has the disadvantage that the soft
`magnetic material forming the two poles, particularly the 55
`central spindle, are exposed to the plasma during sputtering
`and inevitably contaminate the sputtered layer. Furthermore,
`the coil drive provides a substantially cylindrical geometry,
`which may not be desired in some situations. Also,
`the
`disclosure illustrates a relatively shallow geometry for the 60
`target vault, which does not take advantage of some possible
`beneficial effects for a concavely shaped target.
`It is thus desired to combine many of the good benefits of
`the different plasma sputter reactors described above while
`avoiding their separate disadvantages.
`Returning now to copper processing and the structures
`that need to be formed for copper vias, it is well known to
`
`65
`
`4
`those in the art that in a typical copper interconnect process
`flow, a thin barrier layer is first deposited onto the walls of
`the via hole to prevent copper from diffusing into the
`isolating dielectric layer separating the two copper levels
`and also to prevent
`intra/intermetal electrical shorts. A
`typical barrier for copper over silicon oxide consists of a
`combination of Ta/TaN, but other materials have been
`proposed, such as W/WN and Ti/TiN among others. In a
`typical barrier deposition process, the barrier layer is depos-
`ited using PVD to form a continuous layer between the
`underlying and overlying copper layers including the contact
`area at the bottom of the via hole. Thin layers of these barrier
`materials have a small but finite transverse resistance. A
`
`structure resulting from this copper interconnect process
`flow produces a contact having a finite characteristic resis-
`tance (known in the art as a contact or via resistance) that
`depends on the geometry. Conventionally, the barrier layer
`at the bottom of the contact or via hole contributed about
`30% of the total contact or via resistance.
`
`As a result, there is a need in the art for a method and
`apparatus to form a contact between underlying and over-
`lying copper layers having a low contact resistance without
`unduly complicating the process.
`A copper layer used to form an interconnect is conve-
`niently deposited by electrochemical deposition,
`for
`example, electroplating. As is well known, an adhesion or
`seed layer of copper is usually required to nucleate an
`ensuing electrochemical deposition on the dielectric side-
`walls as well as to provide a current path for the electro-
`plating. In atypical deposition process, the copper seed layer
`is deposited using PVD methods, and the seed layer is
`typically deposited on top of the barrier layer. A typical
`barrier/seed layer deposition sequence also requires a pre-
`clean step to remove native oxide and other contaminants
`that reside on the underlying metal that has been previously
`exposed in etching the via hole. The pre-clean step, for
`example, a sputter etch clean step using an argon plasma, is
`typically performed in a process chamber that is separate
`from the PVD chamber used to deposit the barrier and seed
`layers. With shrinking dimension of the integrated circuits,
`the efficacy of the pre-clean step, as well as sidewall
`coverage of the seed layer within the contact/via feature
`becomes more problematical.
`As a result, the art needs a method and apparatus that
`improves the pre-clean and deposition of the seed layer.
`SUMMARY OF THE INVENTION
`
`The invention includes a magnetron producing a large
`volume or thickness of a plasma, preferably a high-density
`plasma. The long travel path through the plasma volume
`allows a large fraction of the sputtered atoms to be ionized
`so that their energy and directionality can be controlled by
`substrate biasing.
`In one embodiment of the invention, the target includes at
`least one annular vault on the front side of the target. The
`backside of the target includes a central well enclosed by the
`vault and accommodating an inner magnetic pole of one
`polarity. The backside of the target also includes an outer
`annular space surrounding the vault and accommodating an
`outer magnetic pole of a second polarity. The outer magnetic
`pole may be annular or be a circular segment which is
`rotated about the inner magnetic pole.
`In one embodiment, the magnetization of the two poles
`may be accomplished with soft pole pieces projecting into
`the central well and the outer annular space and magneti-
`cally coupled to magnets disposed generally behind the well
`
`GILLETTE-1109 / Page 15 of 22
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`US 6,277,249 B1
`
`5
`and outer annular space. In a second embodiment, the two
`poles may be radially directed magnetic directions. In a third
`embodiment, a magnetic coil drives a yoke having a spindle
`and rim shape.
`In one advantageous aspect of the invention, the target
`covers both the spindle and the rim of the yoke as well as
`forming the vault, thereby eliminating any yoke sputtering.
`According to another aspect of the invention, the relative
`amount of sputtering of the top wall or roof of the vault
`relative to the sidewalls may be controlled by increasing the
`magnetic flux in the area of the top wall. An increase of
`magnetic flux at the sidewalls may result in a predominantly
`radial distribution of magnetic field between the two
`sidewalls, resulting in large sputtering of the sidewalls.
`One approach for increasing the sputtering of the top wall
`places additional magnets above the top wall or roof with
`magnetic polarities aligned with the magnets just outside of
`the vault sidewalls. Another approach uses only the top wall
`magnets to the exclusion of the sidewall magnets. In this
`approach,
`the back of the target can be planar with no
`indentations for the central well or the exterior of the trough
`sidewalls. In yet another approach, vertically magnets are
`positioned near the bottom of the vault sidewalls with
`magnetic polarities opposed to the corresponding magnets
`near the top of the vault sidewalls, thereby creating semi-
`toroidal fields near the bottom sidewalls. Such fields can be
`
`adjusted either for sputtering or for primarily extending the
`top wall plasma toward the bottom of the trough and
`repelling its electrons from the sidewalls. A yet further
`approach scans over top wall a small, closed magnetron
`having a central magnetic pole of one polarity and a sur-
`rounding magnetic pole of the other polarity.
`The target may be formed with more than one annular
`vault on the side facing the substrate. Each vault should have
`a width of at least 2.5 cm, preferably at least 5 cm, and more
`preferably at least 10 cm. The width is thus at least 10 times
`and preferably at least 25 times the dark space, thereby
`allowing the plasma sheath to conform to the vault outline.
`The invention also includes a two-step sputtering process,
`the first producing high-energy ionized copper sputter ions,
`the second producing a more neutral, lower-energy sputter
`flux. The two-step process can be combined with an inte-
`grated copper fill process in which the first step provides
`high sidewall coverage and may break through the bottom
`barrier layer and clean the copper. The second step com-
`pletes the seed layer. Thereafter, copper is electrochemically
`deposited in the hole.
`After forming a first level of metal on a wafer and pattern
`etching a single or dual damascene structure for a second
`level of metal on the wafer, the wafer is processed in a PVD
`cluster tool to deposit a barrier layer and a seed layer for the
`second metal level.
`
`Instead of using a pre-clean step (for example, a sputter
`etch clean step), in accordance with one aspect of the present
`invention, a simultaneous clean-deposition step (i.e., a self-
`cleaning deposition step) is carried out. The inventive self-
`cleaning deposition is carried out using a PVD definition
`chamber that produces high-energy ionized material.
`In
`accordance with one embodiment of the present invention,
`the high-enrgy ions physically remove material on flat areas
`of a wafer. In addition, the high-energy ions can dislodge
`material from a barrier layer disposed at the bottom of a
`contact/via feature. Further, in accordance with one embodi-
`ment of the present invention, wherein an initial thickness of
`the barrier layer is small, the high-energy ions can removed
`enough material from the barrier layer to provide direct
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`
`contact between a seed layer and the underlying metal (for
`example, between a copper underlying layer and a copper
`seed layer). In addition to providing direct contact between
`the two copper layers, the inventive sputtering process also
`causes redeposition of copper over sidewalls of the contact/
`via to reinforce the thickness of the copper seed layer on the
`sidewall. This provides an improved path for current
`conduction, and advantageously improves the conformality
`of a layer subsequently deposited by electroplating.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic cross-sectional view of a first
`
`embodiment of a magnetron sputter reactor of the invention
`using a stationary, circularly symmetric magnetron.
`FIG. 2 is a schematic cross-sectional diagram illustrating
`the collimating function of the target of the invention.
`FIG. 3 is a schematic cross-sectional view of a second
`
`embodiment of a magnetron sputter reactor of the invention
`using a rotating, segmented magnetron with vertically mag-
`netized magnets.
`FIG. 4 is a schematic cross-sectional view of a third
`
`embodiment of a magnetron sputter reactor of the invention
`using a rotating, segmented magnetron with radially mag-
`netized magnets.
`FIG. 5 is a schematic cross-sectional view of a fourth
`
`embodiment of a magnetron sputter reactor of the invention
`using an electromagnetic coil.
`FIG. 6 is a cross-sectional view of a fifth embodiment of
`
`a magnetron of the invention using additional magnets at the
`roof of the trough to increase the roof sputtering.
`FIG. 7 is a cross-sectional view of a sixth embodiment of
`
`a magnetron of the invention using only the trough magnets.
`FIG. 8 is a cross-sectional view of a seventh embodiment
`
`of a magnetron of the invention using additional confine-
`ment magnets at the bottom sidewall of the trough.
`FIG. 9 is a cross-sectional view of an eighth embodiment
`of a magnetron of the invention using a closed magnetron
`over the trough roof and separate magnets for the trough
`sidewalls.
`
`FIGS. 10—12 are cross-sectional view of ninth through
`eleventh embodiments of magnetrons of the invention.
`FIG. 13 is a graph of sputtering yield as a function of
`copper ion energy.
`FIGS. 14 and 15 are cross-sectional views illustrating the
`effects of high-energy ionized sputter deposition.
`FIG. 16 is a flow diagram of an integrated copper via fill
`process.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The invention uses a complexly shaped sputter target and
`a specially shaped magnetron which have the combined
`effect of impressing a magnetic field producing a thick
`region of relatively high plasma density. As a result, a large
`fraction of the atoms sputtered from the target can be ionized
`as they pass through the plasma region. Ionized sputtered
`particles can be advantageously controlled by substrate
`biasing to coat the walls of a deep, narrow hole.
`A magnetron sputter reactor 10 of a first embodiment is
`illustrated in the schematic cross-sectional view of FIG. 1. It
`
`includes a specially shaped sputter target 12 and magnetron
`14 symmetrically arranged about a central axis 16 in a
`reactor otherwise described for the most part by Chiang et al.
`in the above referenced patent. The target 12 or at least its
`
`GILLETTE-1109 / Page 16 of 22
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`GILLETTE-1109 / Page 16 of 22
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`US 6,277,249 B1
`
`7
`interior surface is composed of the material to be sputter
`deposited. The invention is particularly useful for sputtering
`copper, but it may be applied to other sputtering materials as
`well. As is known, reactive sputtering of materials like TiN
`and TaN can be accomplished by using a Ti or Ta target and
`including gaseous nitrogen in the plasma. Other combina-
`tions of metal targets and reactive gases are possible. The
`target 12 includes an annularly shaped downwardly facing
`vault 18 facing a wafer 20 being sputter coated. The vault
`could alternatively be characterized as an annular roof. The
`vault 18 has an aspect ratio of its depth to radial width of at
`least 1:2 and preferably at least 1:1. The vault 18 has an
`outer sidewall 22 outside of the periphery of the wafer 20,
`an inner sidewall 24 overlying the wafer 20, and a generally
`flat vault top wall or roof 25 (which closes the bottom of the
`downwardly facing vault 18). The target 12 includes a
`central portion forming a post 26 including the inner side-
`wall 24 and a generally planar face 28 in parallel opposition
`to the wafer 20. The target 12 also includes a flange 29 that
`is vacuum sealed to the chamber body of the sputter reactor
`10.
`
`The magnetron 14 illustrated in FIG. 1 includes one or
`more central magnets 30 having a first vertical magnetic
`polarization and one or more outer magnets 32 of a second
`vertical magnetic polarization opposite the first polarization
`and arranged in an annular pattern. In this embodiment the
`magnets 30, 32 are permanent magnets, that is, composed of
`strongly ferromagnetic material. The inner magnets 30 are
`disposed within a cylindrical central well 36 formed
`between the opposed portions of the inner target sidewall 24
`while the outer magnets 32 are disposed generally radially
`outside of the outer target sidewall 22. A circular magnetic
`yoke 34 magnetically couples tops of the inner and outer
`magnets 30, 32. The yoke is composed of a magnetically soft
`material, for example, a paramagnetic material, such as
`$8410 stainless steel, that can be magnetized to thereby
`form a magnetic circuit for the magnetism produced by the
`permanent magnets 30, 32. Permanently magnetized yokes
`are possible but are difficult to obtain in a circular geometry.
`A cylindrical inner pole piece 40 of a similarly magneti-
`cally soft material abuts the lower ends of the inner magnets
`30 and extend deep within the target well 36 adjacent to the
`inner target sidewall 24. If the magnetron 14 is generally
`circularly symmetric,
`it is not necessary to rotate it for
`uniformity of sputter deposition. A tubular outer pole piece
`42 of a magnetically soft material abuts the lower end of the
`outer magnets 32 and extends downwardly outside of the
`outer target sidewall 22. The magnetic pole pieces 40, 42 of
`FIG. 1 differ from the usual pole faces in that they and the
`magnets 30, 32 are configured and sized to emit a magnetic
`field B in the target trough 18 that is largely perpendicular
`to the magnetic field of the corresponding associated mag-
`nets 30, 32. In particular, the magnetic field B is generally
`perpendicular to the target trough sidewalls 22,24.
`This configuration has several advantages. First, the elec-
`trons trapped by the magnetic field B, although gyrating
`about the field lines, otherwise travel generally horizontally
`and radially with respect tot he target central axis 16. The
`electrons strike the target sidewalls 22, 24 and are re-emitted
`at angles generally isotropic with respect to the magnetic
`field B. That is, electron loss is minimized, thus increasing
`the plasma density. Secondly, the depth of the m