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`US. Patent
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`Feb. 24, 2004
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`Sheet 1 0f 2
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`US 6,695,954 B2
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`US. Patent
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`Feb.24,2004
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`Sheet2 0f2
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`US 6,695,954 B2
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`US 6,695,954 B2
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`1
`PLASMA VAPOR DEPOSITION WITH COII.
`SPUTTERING
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This is a continuation of my application Ser. No. 08/971,
`867, filed Nov. 19, 1997 now US. Pat No. 6,375,810,
`entitled PLASMA VAPOR DEPOSITION WITH COIL
`SPUTTERING, which is a eontinuation-in-part of applica-
`tion Ser. No. 08/907382, filed Aug. 7, 1997, now abandoned
`entitled PLASMA VAPOR DEPOSITION WITH COIL
`SPUTTERING, Attorney Docket l957/PVD/DV.
`BACKGROUND OF THE INVENTION
`
`The present invention relates to the deposition of layers,
`or films, of metals and metal compounds on a workpiece, or
`substrate, during fabrication of integrated circuits, display
`components, etc.
`In connection with the fabrication of
`integrated circuits, the substrate may be constituted by one
`or more semiconductor wafers, while in the case of fabri-
`cation of a display, such as a liquid crystal display,
`the
`substrate may be one or more glass plates. The substrate
`could also be a hard disc that will be used for data storage,
`or read/write heads for a disc drive.
`It
`is known to deposit
`layers on such substrates by
`processes such as physical vapor deposition. By way of
`example, as described in copending application Ser. No.
`08/680,335 abandoned , filed .lul. 10, 1996 (Attorney Docket
`No. 1390CIP/PVD/DV), entitled “Coils for Generating a
`Plasma and for Sputtering” by Jaim Nulman et al., which is
`assigned to the assignee of the present application and
`incorporated herein by reference in its entirety, processes of
`this type may be performed in apparatus including a depo-
`sition chamber which contains a target, a coil and a support
`for the substrate. The target is made of a material such as a
`metal which will form a metal layer or the metal component
`of a metal compound layer. The coil will be supplied with an
`RF current that will generate, within the chamber, an RF
`electromagnetic field.
`When a gas is introduced into the chamber at an appro-
`priate pressure, a dense plasma (10I '—10'3 ions/cm") may be
`ignited inside the chamber by the RF electromagnetic field.
`The target may be associated with a magnetic field produc-
`ing device, such as a magnetron, and may be biased by a DC
`or RI" voltage applied to the target from a voltage source.
`The magnetic field traps electrons, while the DC bias voltage
`on the target attracts ions to the target. These ions dislodge,
`or sputter, atoms or clusters of atoms of material from the
`target. The sputtered atoms travel toward the support and a
`certain proportion of these atoms are ionized in the plasma.
`The support provides a surface for supporting the substrate
`and may be biased, usually by an AC source,
`to bias the
`substrate with a polarity selected to attract ionized target
`material to the substrate surface. The bottom coverage of
`high aspect ratio trenches and holes on the substrate can be
`improved by this substrate bias. Alternatively, the chamber
`may sputter target material without an RF coil or other
`devices for generating an ionizing plasma such that substan-
`tially all the material deposited is not ionized,
`Although the RF electromagnetic field is generated by
`applying an alternating RF current to the coil, a DC potential
`may be induced in the coil as described in the aforemen-
`tioned copending application Ser. No. 08/680,335. This
`potential which may be referred to as a self bias, combines
`
`with the RF potential on the coil. The combined DC and RF
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`
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`potentials have the net e ect of attracting ions from the
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`plasma to the coil. If the coil is made of the same material
`as the target, the coil can constitute an additional source of
`deposition material which will be sputtered from the coil by
`ions attracted from the plasma to be deposited on the
`substrate.
`
`If a film consisting essentially of only the sputtered
`material is to be formed on a substrate, then the gas within
`the chamber is preferably nonreactive with respect to the
`sputtered atoms. If, on the other hand, a compound film
`formed by a chemical reaction of the target material with
`another constituent is to be formed, the gas introduced into
`the chamber may have a composition selected to react with
`the sputtered target material ions and atoms to form mol—
`ecules of the compound, which are then deposited on the
`substrate. Alternatively, the gas may react with the target
`material while or after it is deposited.
`For example, plasma and nonionizing plasma sputtering
`deposition processes of the type described above can be used
`to deposit either a pure metal or metal alloy, such as
`titanium,
`tantalum, aluminum, copper, aluminum-copper,
`etc., or a metal compound, such as titanium nitride (TiN),
`aluminum oxide (A1203), etc. Also, other non metallic
`materials may be deposited such as silicon and silicon
`dioxide. For deposition of a pure metal or metal alloy, the
`target, and possibly the coil, will be made of this metal and
`the plasma gas is preferably a non-reactive gas, i.e. a gas
`such as argon, helium, xenon, etc., which will not react with
`the metal. For deposition of a metal compound, the target,
`and possibly the coil, will be made of one component of the
`compound,
`typically the metal or metal alloy, and the
`chamber gas will include a reactive gas composed of, or
`containing,
`the other component or components of the
`compound, such as nitrogen or oxygen. The sputtered metal
`reacts with gas atoms or molecules to form the compound,
`molecules of which are then deposited on the substrate. In
`the same manner, a nonmetallic target material may be
`sputtered in a nonreactive environment to deposit relatively
`pure target material onto the substrate. Alternatively, the
`target material may be sputtered in a reactive environment to
`produce on the substrate a layer of a compound of the target
`material and a reactive component. Hereinafter, a compound
`formed of a target or coil material and a reactive component
`will be referred to as a reaction compound, whether the
`sputtered material is metallic or otherwise.
`One factor determining the performance of such apparatus
`is the density of gas, and hence the density of the plasma, in
`the chamber. A relatively dense plasma can provide an
`increased ionization rate of the sputtered material atoms,
`thus improving bottom coverage of trenches and holes on
`the substrate. However, under high pressure conditions,
`material sputtered from the target
`tends to be deposited
`preferentially in a central region of the substrate support
`surface. Such nonuniformity can often increase at higher
`deposition rates or higher pressures.
`This nonuniformity is disadvantageous because the thick-
`ness of the deposited layer preferably should correspond to
`a nominal value, within a narrow tolerance range, across the
`entire support surface. Therefore, when the substrate is, for
`example, a wafer which will ultimately be diced into a
`plurality of chips, and there is a substantial variation in the
`thickness of the layer across the wafer surface, many of the
`chips may become rejects that must be discarded.
`As described in the aforementioned copending applica-
`tion Ser. No. 08/680,335, it has been recognized that mate-
`rial sputtered from the coil may be used to supplement the
`deposition material sputtered from the primary target of the
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`US 6,695,954 B2
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`3
`chamber. Because the coil can be positioned so that material
`sputtered from the coil tends to deposit more thickly at the
`periphery of the wafer, the center thick tendency for material
`sputtered from the primary target can be compensated by the
`edge thick tendency for material sputtered from the coil. As
`a result, uniformity can be improved.
`The quantities of material sputtered from the coil and the
`target are a function of several factors including the DC
`power applied to the target and the RF power applied to the
`coil. However, the freedom to adjust these and other factors
`may be limited in some applications by the requirements of
`other process parameters which are often interdependent.
`Thus, a need exists for further control over the quantity of
`material sputtered from the coil to facilitate further increases
`in the degree of uniformity of deposition that may be
`achieved.
`
`In addition, when such apparatus is used to deposit a
`reaction compound layer, some of the reaction compound
`typically also coats the target and the coil. For example,
`when titanium nitride is deposited in a chamber having a
`titanium metal target in a nitrogen atmosphere,
`titanium
`nitride typically coats the target and coil. Therefore, if it
`were then attempted to deposit a pure target material layer,
`i.e., a layer of just titanium, in the same apparatus,
`the
`reaction compound molecules of titanium nitride would
`likely also be sputtered from the target, and also from the
`coil, and thus could contaminate the titanium metal layer,
`Therefore,
`it has generally not been practical to sputter
`deposit a metal or metal alloy layer from a target of the same
`material immediately after having deposited a metal com-
`
`pound layer in the same apparatus.
`
`
`Some e orts have been made to deal with this drawback
`by sputtering away the metal compound layer coating on the
`target, and covering over the metal compound layer coating
`on the coil with a layer of the metal sputtered from the target,
`this procecure being known as “pasting”. However, such
`attempts have generally been found to be unacceptably
`costly and time—consuming, and otherwise unsatisfactory.
`Therefore, facilities in which layers of a metal and layers
`of a compound of that metal are to be deposited on substrates
`are typically equipped with two apparatuses, each for depos-
`iting a respective type of layer. This, of course, may entail
`twice the investment cost associated with one apparatus.
`Moreover, in production systems having multiple chambers
`coupled to a central transfer chamber, valuable perimeter
`space of the transfer chamber is occupied by an extra
`chamber that could otherwise be used by another chamber to
`increase throughput or provide additional processes.
`BRIEF SUMMARY OF THE INVENTION
`
`
`
`It is an object of the present invention to alleviate the
`above difficulties.
`
`A more specific object of the invention is to improve the
`uniformity with which a layer of material is deposited on a
`substrate.
`
`Another object of the invention is to achieve such
`improvement in uniformity without any significant increase
`in the cost or complexity of the deposition apparatus.
`Still another object of the invention is to improve depos-
`ited film uniformity while, at the same time, improving
`apparatus throughput.
`Still another object of the invention is to improve depos—
`ited film uniformity while at the same time reducing the cost
`and complexity of the deposition apparatus.
`Still another object of the invention is to allow added
`control of the rate of deposition of material on a substrate.
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`A further specific object of the invention is to facilitate
`deposition of a layer of a target material such as an elemental
`metal or metal alloy in a single deposition apparatus a short
`time after completion of deposition of a layer of a reaction
`compound of the target material and another constituent.
`A still more specific object of the invention is to rapidly
`remove reaction compound material which has been depos—
`ited on the target or coil in a deposition chamber subsequent
`to a reaction compound layer deposition process and prior to
`a target material layer deposition process which does not
`include a reactive constituent.
`The above and other objects are achieved, according to
`the present invention, by a method and apparatus for sputter
`depositing a layer on a substrate in which following depo-
`sition of a layer of reaction compound formed from con-
`stituents which includes a reactive material and a material
`sputtered from a target or coil, a layer of material sputtered
`from the same target or coil may be deposited in the same
`chamber in which the subsequent layer is substantially free
`of contamination by the reaction compound or the reactive
`material.
`In the illustrated embodiment,
`this may be
`achieved by removing the reactive material from the sputter
`chamber following the deposition of the reaction compound,
`introducing a non—reactive gas into the enclosure, and sput—
`tering substantially all reaction compound from the target or
`coil which provided the source of the sputtered material. As
`a consequence, the same chamber is then ready to deposit
`another layer except that the layer may be a layer consisting
`essentially of only material sputtered from the source. In this
`manner, a chamber may be used to deposit a metal com-
`pound such as titanium nitride and then after sputter
`cleaning, be ready to deposit a layer of relatively pure
`titanium in the same chamber without substantial contami-
`nation by titanium nitride.
`This aspect of the invention is particularly applicable to
`apparatus which includes a chamber containing a sputtering
`target and a plasma generating coil. According to the
`invention, a suitable voltage is applied to the coil, while the
`chamber is filled with a non-reactive gas and does not
`contain any substrate,
`to produce a plasma which will
`rapidly splitter deposited metal compound material from the
`target, and possibly also from the coil.
`The above and other objects are further achieved, accord-
`ing to the present invention, by a method and an apparatus
`for depositing a layer of a material which contains a metal
`on a workpiece surface in which both RF energy is supplied
`to a coil
`to generate a plasma to ionize the deposition
`material, and a separate DC bias is applied to the coil to
`control
`the coil sputtering rate.
`In the illustrated
`embodiment, a DC voltage source is coupled to the coil
`through an RF filter to provide a DC bias potential which is
`different in magnitude from the coil DC self bias potential
`which results from the applied RF power. In this manner, the
`coil bias potential and hence the coil sputtering rate may be
`controlled with a degree of independence from the RF power
`applied to the coil.
`In another aspect of the invention, the coil may be shaped
`and positioned to permit use as the sole source of sputtered
`material within said chamber while maintaining good uni—
`formity. As a consequence, in some applications, the need
`for a separate target and associated magnetron may be
`eliminated,
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWINGS
`
`MG. 1 is a simplified, elevational, cross-sectional View of
`deposition apparatus constructed according to one embodi-
`ment of the invention.
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`US 6,695,954 B2
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`5
`FIG. 2 is a circuit diagram illustrating electrical systems
`associated with the apparatus of FIG, 1.
`FIG. 3 is a view similar to that of FIG. 1 showing another
`embodiment of deposition apparatus according to the inven—
`tion.
`FIG. 4 is a cross-sectional view of another embodiment of
`a coil which may be employed in apparatus according to the
`present invention.
`DETAILED DESCRIPTION OF EMBODIMENTS
`
`FIG. 1 shows the basic components of one embodiment of
`a deposition apparatus constructed according to a first pre-
`ferred embodiment of the invention.
`
`The illustrated apparatus includes a deposition chamber 2,
`a sputtering target 4, a plasma generating coil 6 and a
`workpiece support 8, all of which are disposed within
`chamber 2. Outside of chamber 2, and above target 4, there
`is provided a magnetic field generating assembly, such as a
`magnetron, 10. Target 4 is made of a conductive material, for
`example a metal, such as titanium, which is to be sputtered
`and then deposited on a workpiece provided on a workpiece
`support surface 14 of workpiece support 8. Other materials
`which are currently deposited in such apparatus include
`metals and alloys such as aluminum, copper,
`tantalum,
`aluminum—copper alloys and metal compounds such as
`titanium nitride and tantalum nitride.
`
`In order to make possible the generation of a plasma
`within chamber 2, a suitable quantity of an ionizable gas,
`such as argon, is introduced into the chamber through a port
`15 and RF power is supplied to coil 6 from an RF power
`supply 16 via an appropriate matching network 20. One end
`of coil 6 is connected to matching network 20 and the other
`end of coil 6 is connected to ground via a DC blocking
`capacitor 22 (FIG. 2). The RF power supplied to coil 6
`results in the generation of an electromagnetic field that
`produces a plasma. Assembly 10 also contributes to genera-
`tion of a plasma within chamber 2. In the absence of RF
`current in coil 6, a plasma of lower density can also be
`generated in the vicinity of target 4 and magnetron 10 by
`applying a DC or RF voltage to target 4.
`Under these conditions, a material to be deposited on a
`substrate disposed on surface 14 will be sputtered from
`target 4, at least partially ionized in the plasma field and
`directed to the workpiece.
`The sputtering of material from target 4 is aided by
`biasing target 4, by means of a biasing voltage source 24,
`such as a DC source, with a polarity to attract ions in the
`plasma. The attracted ions impact on target 4 and dislodge
`atoms or clusters of atoms of the material making up target
`4.
`
`Aproportion of the atoms sputtered from target 4 will be
`ionized in the plasma to become, in the case of a metal,
`positive ions. In order to promote deposition of these posi-
`tive ions on the workpiece surface, workpiece support 8 is
`connected to a suitable bias voltage source 26 such as an AC
`source. In the illustrated embodiment, sources 24 and 26
`cause a negative bias to develop on the target 6 and the
`substrate 14, respectively.
`Since it is often desired to be able to move workpiece
`support 8 vertically within chamber 2, while the interior of
`chamber remains sealed, workpiece support 8 may be
`coupled to chamber 2 by an appropriate bellows 28.
`When the only voltage applied to coil 6 is an alternating
`RF voltage, it is believed that a DC self bias is inherently
`induced on coil 6 across blocking capacitor 22. In the
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`illustrated embodiment, this bias will have a negative polar—
`ity and can be of the order of —100 volts. If coil 6 is made
`of a sputterable material, then ions in the plasma will be
`attracted to coil 6 as a result of the DC self bias and these
`ions will sputter, or dislodge, atoms or clusters of atoms of
`material from the surface of coil 6. Therefore, by making
`coil 6 of the same material as target 4, the rate of generation
`of material for deposition on the workpiece surface can be
`increased. Still further, the target and coil 6 provide spatially
`separated sources of sputter material, which can be used to
`improve film properties.
`Since coils, such as coil 6, may be dimensioned and
`positioned so as to be outside the periphery of workpiece
`support surface 14, it has been found that sputtered material
`originating from coil 6 will tend to be deposited thicker in
`the peripheral region of the workpiece support surface than
`in the center region. This is beneficial because in many
`installations, and particularly those operating with high
`pressures, material sputtered from target 4 tends to be
`deposited thicker in the central region of the workpiece
`support surface than in the peripheral region. Thus,
`the
`sputtering of deposition material from coil 6 can help to
`counteract the tendency of material sputtered from target 4
`to be deposited to a greater thickness in the central region of
`the workpiece support surface.
`To obtain the best deposition uniformity, the coil sputter-
`ing rate is preferably sufficiently high relative to the target
`sputtering rate to compensate for any deposition nonunifor-
`mity of material from the target. One way this might be
`achieved is to reduce the target sputtering rate. But a lower
`target sputtering rate usually results in a lower deposition
`rate on the substrate, and therefore a lower system through—
`put. Another approach is to increase the coil sputtering rate
`by increasing RF power level. However, the optimum value
`of the RI" power applied to the coil is a function of several
`process parameters and chamber design considerations.
`Hence, in many applications a particular RF power level
`which may provide a useful self bias on the coil 6 to provide
`a desired coil sputtering rate, may have a disadvantageous
`effect on these other factors or may be higher than that which
`may be provided by the particular system. Thus, the RF
`power level which provides the best uniformity of deposi-
`tion may not be appropriate for the particular chamber or
`may adversely affect other film properties.
`In accordance with one aspect of the invention, the coil
`sputtering rate may be controlled with a degree of indepen-
`dence of the RF power level. In the illustrated embodiment,
`not only is RF energy supplied to the coil to generate a
`plasma to ionize the deposition material, but a separate DC
`bias is also applied to the coil to separately control the coil
`bias level and hence control the coil sputtering rate. As a
`result, one need not be limited to the DC self bias which is
`created when only an alternating RF current is applied to the
`coil.
`
`Thus, according to the invention, the DC bias on coil 6 is
`altered, independently of the magnitude and frequency of
`the RF power delivered by supply 16, by also connecting
`coil 6 to a DC voltage source 30. Preferably, an RF blocking
`filter 32 is connected between coil 6 and DC voltage source
`30. Such an RF blocking filter, when designed properly, can
`eliminate or reduce substantially RF current flowing to the
`DC source 30. Filter 32 provides a negligibly small DC
`impedance between source 30 and coil 6 so that coil 6 will
`be placed at a DC bias essentially equal to the voltage
`provided by voltage source 30. While voltage source 30 is
`represented schematically by a battery, it will be appreciated
`that any suitable DC voltage source can be employed and the
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`US 6,695,954 B2
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`7
`output voltage thereof can be adjusted to produce the desired
`level of DC bias on coil 6.
`While the RF generator 16 and matching network 20 are
`preferably coupled to one end of the coil 6, the DC source
`30 and RF filter 32 may be coupled to the coil anywhere
`along its length. For example, as shown in FIG. 2, the DC
`source 30 and filter 32 may be coupled to end of coil 6 to
`which is the end to which the blocking capacitor 22 is
`coupled which is opposite to the end to which RF generator
`16 is coupled.
`As an alternative to the arrangement illustrated in FIG. 1,
`it will be appreciated that a separate voltage source 30 need
`not be provided and RF filter 32 could, instead, be connected
`between coil 6 and the DC voltage source 24. Since there is
`no DC path from coil 6 to ground, the current flow between
`voltage source 30 and coil 6 will be a function primarily of
`the sputtering current as ions impact the coil 6 and secondary
`electrons are emitted into the plasma. Therefore, voltage
`source 30, or voltage source 24, if used in place of source 30,
`preferably should be capable of producing a sufficiently high
`output current to accommodate the anticipated sputtering
`rate.
`
`FIG. 2 is a circuit diagram illustrating one example of
`circuitry employed for supplying RF current and a DC bias
`voltage to coil 6. Here coil 6 is represented by its equivalent
`circuit, which is a series arrangement of an inductance and
`a resistance.
`
`Matching network 20 is a conventional network which
`includes two adjustable capacitors and an inductor. As is
`known, the purpose of circuit 20 is to match the output
`impedance of RF power supply 16 to the impedance of the
`load to which it is connected. In addition, the DC blocking
`capacitor 22 connected between coil 6 and ground serves to
`prevent flow of a DC current from coil 6 to ground. To
`improve deposited layer uniformity, RI" frequency and
`power levels may be periodically altered during deposition.
`In addition, impedances of the components of the matching
`network and blocking capacitor may be periodically varied
`during deposition.
`Filter 32 is constructed, in a conventional manner, of
`impedances such as capacitors and inductors,
`to block
`transmission of RF power from coil 6 to voltage source 30.
`In the embodiment shown in FIG. 1, if it is desired to
`reduce the rate at which metal is sputtered from target 4 in
`order to improve the deposited layer thickness uniformity
`across the substrate surface, this can be achieved by reduc-
`ing the DC power applied to target 4.
`Since plasma generating coil 6 can be converted into an
`effective source of sputtered material by application thereto
`of a suitable DC bias potential, then, according to a further
`feature of the present
`invention,
`the possibility exists of
`completely eliminating target 4 and its associated assembly
`10 and using the coil as the sole source of sputtering
`material.
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`However, if the coil is to be used as the only sputtering
`material source, then it would be desirable to configure the
`coil to produce sputtered material in such a manner that the
`resulting layer deposited on the workpiece will have a
`substantially uniform thickness across the workpiece surface
`area. For example, coil 6 could be replaced by a flat
`multi-turn coil, as represented by coil 36 in FIG. 3. Apart
`from the dilIerent configuration of the coil and the elimina-
`tion of target 4, assembly 10 and voltage supply 24,
`the
`apparatus shown in FIG. 3 may be identical to that shown in
`FIG. 1 and described above.
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`is believed that the rate of production of sputtered
`It
`material can be readily controlled by adjusting the level of
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`voltage produced by source 30. Thus, source 30 is preferably
`an adjustable voltage source.
`When target 4 is no longer needed as a sputtered material
`source, the system designer has greater freedom to select the
`configuration of the plasma generating coil. Herctofore, it
`was considered preferable to construct the coil in such a
`manner as to not obstruct the movement of sputtered mate—
`rial from the target 4 to the workpiece. When target 4 is no
`longer provided, this limitation no longer exists. In addition,
`when a target is no longer present, one has greater freedom
`to select the height of the coil above workpiece support
`surface 14. Depending on the shape of processing chamber
`2 and the configuration of the plasma generating coil, it may
`be found to be preferable to move the coil either up or down
`relative to the height which the coil would have in that
`chamber when a separate target 4 is also provided. However,
`as a general rule, displacing the coil upwardly may result in
`ionization of a higher percentage of the sputtered material
`prior to reaching the substrate surface and thus could
`increase the percentage of the deposited material reaching
`the bottoms of grooves in the substrate. Furthermore, elimi-
`nation of target 4 and magnetic field generating assembly 10
`could represent a substantial simplification of the design of
`the apparatus and provide a corresponding reduction in the
`cost of manufacturing the apparatus.
`The coil configuration shown in FIG. 3 thus represents
`one of many possibilities made available by the present
`invention.
`
`Another preferred form of construction for a coil which
`could serve as a sole source of sputtered material according
`to one aspect of the invention is coil 46 shown in FIG. 4 and
`is wound to conform to a dome shape. In certain apparatus
`configurations,
`this shape could be found to result in a
`deposited layer having a particularly high uniformity. FIG.
`4 illustrates a non-inverted dome shape. It is anticipated that
`dome shapes which are inverted may be utilized as well.
`Embodiments of the present invention which utilize a coil
`as the sole source of sputtering material should be expected
`to deliver such material to the workpiece at a lower rate than
`would occur if another target were also provided. However,
`in many cases, the layer which is to be deposited may be
`very thin and a lower sputtering and deposition rate would
`allow the thickness of such a layer to be more accurately
`controlled. Thus, for certain purposes, apparatus exhibiting
`a lower sputtering and deposition rate is desirable.
`On the other hand, when material is to be sputtered and
`deposited at a high rate, apparatus according to the invention
`which combines a separate target with a coil which is
`separately DC biased may be preferred. Because the depo-
`sition nonuniformity from target 4 alone may be aggravated
`at higher deposition rates in some applications, more coil
`sputtering may be needed to maintain good overall deposi—
`tion uniformity. Therefore, additional DC bias on the coil
`will be advantageous in such applications.
`Apparatus according to the invention can be employed for
`depositing metal layers, such as layers of titanium, tantalum,
`aluminum, etc., in which case the gas introduced to generate
`a plasma may be selected to not react with ions of the metal
`to be deposited. A typical gas employed for this purpose is
`argon.
`The invention can also be employed for forming layers of
`metal compounds, such as TiN, TaN, etc. In this case, the
`coil, and target, if provided, would be made of the metal
`component of such a compound, while the gas introduced
`into chamber 2 would be composed of or consist of another
`component, such as nitrogen.
`
`Page 7 of 12
`Page 7 of 12
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`

`US 6,695,954 B2
`
`9
`In general, embodiments of the invention will be operated
`to give the bias potential on the coil a magnitude which is
`greater than its DC self bias potential, A bias potential of
`greater magnitude will cause material to be sputtered from
`the coil at a higher rate. Furthermore, when a coil
`is
`employed as the sole source of sputtering material, material
`may be sputtered from the coil at a rate required by certain
`deposition operations even if the only DC bias on the coil is
`the self bias. Therefore, according to certain embodiments of
`the invention in which the coil is the sole source of split-
`tering material, voltage source 30 and blocking filter 32 are
`removed, so that the coil end which is remote from RF
`power supply 16 is connected only to capacitor 22.
`The parameters of the RF current supplied to a coil, the
`component values for the circuitry shown in FIG. 2,
`the
`temperature and pressure conditions within chamber 2 and
`all other operating parameters not specified herein would be
`selected according to principles known in the art.
`Similarly,
`the precise shape and dimensions of each
`plasma generating coil can be determined on the basis of
`principles known in the art. To cite one specific example, in
`apparatus according to the invention for depositing a layer
`on a workpiece in the form of a silicon wafer having a
`diameter of 8 inches, the coil could be constructed in the
`manner described in copending application Ser. No. 08/857,
`719, filed May 16, 1997, and entitled “Central Spiral Coil
`Design for Ionized Metal Plasma Deposition" (Attorney
`Docket No. 1752/PVD/DV). The plasma generating coils
`shown in the drawings of the present application are con-
`structed from stock having a circular cross section.
`However, coils employed in embodiments of the present
`invention can also be made from stock having other cross-
`sectional shapes, including square, rectangular, fiat ribbon,
`oval, etc. cross-sectional shapes. For those embodiments in
`which DC voltage source 30 is employed to increase the
`magnitude of the DC bias on the coil, i.e. to make that bias
`more negative, the coil is preferably provided with a cooling
`fluid channel and a cooling fluid, most commonly water, is
`caused to flow through the channel for cooling purposes.
`Apparatus of the type described above may be employed
`to form an elemental metal or metal alloy layer or a layer of
`other types of target material
`in which formation of a
`compound which includes the target material is not desired.
`In this case, the gas filling chamber 2 will preferably be a
`non-reactive gas, such as argon, helium, xenon, etc. If a
`metal reaction compound layer is to be deposited in such
`apparatus, chamber 2 may be filled through port 15 with an
`appropriate reactive gas which is ionized in the plasma and
`then combines with ions and atoms of the sputtered metal to
`form the compound. Typical metal compounds which are
`formed in this manner include 'l‘iN, 'l‘aN and A1203. In each
`case,
`the target will be made of the metal component or
`metal alloy component of such compound. When the com-
`pound is a