`
`EXPRESS MAIL LABEL NO.
`ED475251649US
`
`Electronic Version 1.2.8
`
`Stylesheet Version 1.0
`
`High Deposition Rate Sputtering
`
`Background of Invention
`
`[0001]
`
`Sputtering is a well—known technique for depositing films on substrates.
`
`Sputtering is the physical ejection of atoms from a target surface and is sometimes
`
`referred to as physical vapor deposition (PVD). ions, such as argon ions, are
`
`generated and then directed to a target surface where the ions physically sputter
`
`target material atoms. The target’ material atoms ballist-ically flow to a substrate
`
`where they deposit as a film of target material.
`
`[0002]
`
`Diode sputtering systems include a target and an anode. Sputtering is achieved
`
`in a diode sputtering system by establishing an electrical discharge in a gas
`
`between two parallel—plate electrodes inside a chamber. A potential of several
`
`kilovolts is typically applied between planar electrodes in an inert gas atmosphere
`
`(e.g., argon) at pressures that are between about 10 '1 and 10 '2 Torr. A plasma
`
`discharge is then formed. The plasma discharge is separated from each electrode by
`
`what is referred to as the dark space.
`
`[0003]
`
`The plasma discharge has a relatively constant positive potential with respect to
`
`the target. ions are drawn out of the plasma, and are accelerated across the cathode
`
`dark space. The target has a lower potential than the region in which the plasma is
`
`formed. Therefore, the target attracts positive ions. Positive ions move towards the
`
`target with a high velocity. Positive ions then impact the target and cause atoms to
`
`physically dislodge or sputter from the target. The sputtered atoms then propagate
`
`to a substrate where they deposit a film of sputtered target material. The plasma is
`
`replenished by electron~ion pairs formed by the collision of neutral molecules with
`
`secondary electrons generated at the target surface.
`
`file://C:\EFS Data\ZON—003\embedded\ZON—003EFSFinal.xml
`
`EX 121 8
`
`1 1/14/2002
`
`EX 1218
`
`
`
`rag: A. U1. )0
`
`[0004]
`
`Magnetron sputtering systems use magnetic fields that are shaped to trap and
`
`to concentrate secondary electrons, which are produced by ion bombardment of the
`
`target surface. The plasma discharge generated by a magnetron sputtering system
`
`is located proximate to the surface of the target and has a high density of electrons.
`
`The high density of electrons causes ionization of the sputtering gas in a region
`
`0
`
`that is close to the target surface.
`
`[0005]
`
`One type of magnetron sputtering system is a planar magnetron sputtering
`
`system. Planar magnetron sputtering systems are similar in configuration to diode
`
`sputtering systems. However, the magnets (permanent or electromagnets) in planar
`
`magnetron sputtering systems are placed behind the cathode. The magnetic field
`
`lines generated by the magnets enter and leave the target cathode substantially
`normal to the cathode surface. Electrons are trapped in the electric and magnetic]
`
`fields. The trapped electrons enhance the efficiency of the discharge and reduce the
`
`energy dissipated by electrons arriving at the substrate.
`
`[0006]
`
`Conventional magnetron sputtering systems deposit films that have relatively
`
`low uniformity. The film uniformity can be increased by mechanically moving the
`
`substrate and/or the magnetron. However, such systems are relatively complex and
`
`expensive to implement. Conventional magnetron sputtering systems also have
`
`relatively poor target utilization. The term "target utilization" is defined herein to be
`
`a metric of how uniform the target material erodes during sputtering. For example,
`
`high target utilization would indicate thatthe target material erodes in a highly
`
`uniform manner.
`
`[0007]
`
`in addition, conventional magnetron sputtering systems have a relatively low
`
`deposition rate. The term "deposition rate" is defined herein to mean the amount of
`
`material deposited on the substrate per unit of time. In general, the deposition rate
`
`is proportional to the sputtering yield. The term "sputtering yield" is defined herein
`
`to mean the number of target atoms ejected from the target per incident particle.
`
`Thus, increasing the sputtering yield will increase the deposition rate.
`
`‘Brief Description of Drawings
`
`file://C:\EFS Data\ZON—O03\embedded\ZON—003EFSFina1.xml
`
`1 1/14/2002
`
`Page 2 of 56
`
`Page 2 of 56
`
`
`
`rug: 3 U1 :0
`
`[0008]
`
`This invention is described with particularity in the detailed description. The
`
`above and further advantages of this invention may be better understood by
`
`referring to the following description in conjunction with the accompanying
`
`drawings, in which like numerals indicate like structural elements and features in
`
`various figures. The drawings are not necessarily to scale, emphasis instead being
`
`placed upon illustrating the principles of the invention.
`
`[0009]
`
`FIG.
`
`1 illustrates a cross—sectional view of a known magnetron sputtering
`
`apparatus having a pulsed power source.
`
`[0010]
`
`FIG. 2 illustrates a cross—sectional view of a prior art cathode assembly having a
`
`cathode cooling system.
`
`[001 I]
`
`FIG. 3 illustrates a known process for sputtering material from a target.
`
`[00] 2]
`
`FIG. 4 illustrates a cross—sectional view of an embodiment of a magnetron
`
`sputtering apparatus according to the present invention.
`
`[0013]
`
`FIG. 5A through FIG. SD illustrate cross~sectional views of the magnetron
`
`sputtering apparatus of FIG. 4.
`
`[0014]
`
`FIG. 6 illustrates graphical representations of the applied voltage, current, and
`
`power as a function of time for periodic pulses applied to the plasma in the
`
`magnetron sputtering apparatus of FIG. 4.
`
`[0015]
`
`FIG. 7A through FIG. 7D illustrate various simulated magnetic field distributions
`
`proximate to the cathode assembly for various electron EXB drift currents in a
`
`magnetically enhanced plasma sputtering apparatus according to the invention.
`
`[0016]
`
`FIG. 8 illustrates a graphical representation of sputtering yield as a function of
`
`temperature of the sputtering target.
`
`.
`
`[0017]
`
`FIG. 9 illustrates a process for sputtering material from a target according one
`
`embodiment of the present invention.
`
`[0018]
`
`FIG. 10 illustrates a cross-sectional view of a cathode assembly according to
`
`one embodiment of the invention.
`
`file://CA:\EFS Data\ZON~003\embedded\ZON~O03EFSFinal.xm1
`
`‘
`
`1 1/ 14/2002
`Page 3 of 56
`
`Page 3 of 56
`
`
`
`rage 4 U1 :0
`
`[0019]
`
`FIG. ii is a flowchart of an illustrative process of enhancing a sputtering yield
`
`of a sputtering target according to the present invention.
`
`Detailed Description
`
`[0020]
`
`The sputtering process can be quantified in terms of the sputtering yield. The ‘
`
`term "sputtering yield" is defined herein to mean the number of target atoms
`
`ejected from the target per incident particle. The sputtering yield depends on
`
`several factors, such as the target species, bombarding species, energy of the
`
`bombarding ions, and the angle of incidence of the bombarding ions. in typical
`
`known sputtering processes, the sputtering yield is generally insensitive to target
`
`temperature.
`
`[0021]
`
`The deposition rate of a sputtering process is generally proportional to the
`
`sputtering yield. Thus, increasing the sputtering yield typically will increase the
`
`deposition rate. One way to increase the sputtering yield is to increase the ion
`
`density of the plasma so that a larger ion flux impacts the surface of the target. The
`
`density of the plasma is generally proportional to the number of ionizing collisions
`
`in the plasma.
`
`[0022]
`
`Magnetic fields can be used to confine electrons in the plasma to increase the
`
`number of ionizing collisions between electrons and neutral atoms in the plasma.
`
`The magnetic and electric fields in magnetron sputtering systems are concentrated
`
`in narrow regions close to the surface of the target. These narrow regions are
`
`located between the poles of the magnets used for producing the magnetic field.
`
`Most of the ionization of the sputtering gas occurs in these localized regions. The
`
`location of theionization regions causes non—uniform erosion or wear of the target
`
`that results in poor target utilization.
`
`[0023]
`
`increasing the power applied between the target and the anode can increase the
`
`production of ionized gas and, therefore, increase the target utilization and the
`
`sputtering yield. However, increasing the applied power can lead to undesirable
`
`target heating and target damage. Furthermore, increasing the voltage applied
`
`between the target and the anode increases the probability of establishing an
`
`undesirable electrical discharge (an electrical arc) in the process chamber. An
`
`undesirable electrical discharge can corrupt the sputtering process.
`
`file://C :\EFS Data\ZON-O03\embedded\ZON-003EFSFina1.xml
`
`1 1/ 1 4/2002
`Page 4 of 56
`
`Page 4 of 56
`
`
`
`rage J 01 30
`
`[0024]
`
`Pulsing the power applied to the plasma can be advantageous since the average
`
`discharge power can remain low while relatively large power pulses are periodically
`
`applied. Additionally, the duration of these large voltage pulses can be preset so as
`
`to reduce the probability of establishing an electrical breakdown condition leading
`
`to an undesirable electrical discharge. However. very large power pulses can still
`
`result in undesirable electrical discharges and undesirable target heating regardless
`
`of their duration.
`
`[0025]
`
`FIG.
`
`1 illustrates a cross—sectional view of a known magnetron sputtering
`
`apparatus 100 having a pulsed power source 102. The known magnetron sputtering
`
`apparatus 100 includes a vacuum chamber 104 where the sputtering process is
`
`performed. The vacuum chamber 104 is positioned in fluid communication with a
`
`vacuum pump 106 via a conduit 108. The vacuum pump 106 is adapted to evacuate
`
`the vacuum chamber 104 to high vacuum. The pressure inside the vacuum chamber
`
`104 is generally less than 100Pa during operation. A feed gas source 109, such as
`
`an argon gas source, is coupled. to the vacuum chamber 104 by a gas inlet 110. A
`valve 112 controls the gas flow from the feed gas source 109.
`
`[0026]
`
`The magnetron sputtering apparatus 100 also includes a cathode assembly 114
`
`having a target 116. The cathode assembly 114 is generally in the shape of a
`
`circular disk. The cathode assembly 114 is electrically connected to a first output
`
`118 of the pulsed power supply 102 with an electrical transmission line 120. The
`
`cathode assembly 1 14 is typically coupled to the negative potential of the pulsed
`
`power supply 102. In order to isolate the cathode assembly 114 from the vacuum
`
`chamber 104, an insulator 122 can be used to pass the electrical transmission line
`
`120 through a wall of the vacuum chamber 104. A grounded shield 124 can’ be
`
`positioned behind the cathode assembly 1 14 to protect a magnet 126 from
`
`bombarding ions. The magnet 126 shown in H6. 1
`
`is generally shaped in the form
`
`of a ring that has its south pole 127 on the inside of the ring and its north pole 128
`
`on the outside of the ring. Many other magnet configurations can also be used.
`
`file://C:\EFS Data\ZON—O03\embedded\ZON—003EFSFinal.xm1
`
`1 1/14/2002
`Page 5 of 56
`
`Page 5 of 56
`
`
`
`ragc: 0 U1 no
`
`[0027]
`
`An anode 130 is positioned in the vacuum chamber 104 proximate to the
`
`cathode assembly 114. The anode 130 is typically coupled to ground. A second
`
`output 132 of the pulsed power supply 102 is also typically coupled to ground. A
`
`substrate 134 is positioned in the vacuum chamber 104 on a substrate support 135
`
`to receive the sputtered target material from the target 1 16. The substrate 134 can
`
`be electrically connected to a bias voltage power supply 136 with a transmission »
`
`line 138. In order to isolate the bias voltage power supply 136 from the vacuum
`
`chamber 104, an insulator 140 can be used to pass the electrical transmission line
`
`138 through a wall of the vacuum chamber 104.
`
`[0028]
`
`In operation, the pulsed power supply 102 applies a voltage pulse between the
`
`cathode assembly 114 and the anode 130 that has a sufficient amplitude to ionize
`
`the argon feed gas in the vacuum chamber 104. The typical ionization process is
`
`referred to as direct ionization or atomic ionization by electron impact and can be
`
`described as follows:
`
`[0029]
`
`Ar+e"—9Ar++2e’
`
`[0030]
`
`where Ar represents a neutral argon atom in the feed gas and e ‘ represents an
`
`ionizing electron generated in response to the voltage pulse applied between the
`
`cathode assembly 114 and the anode 130. The collision between the neutral argon
`
`atom and the ionizing electron results in an argon ion (Ar + ) and two electrons.
`
`[0031]
`
`The negatively biased cathode assembly 1 14 attracts positively charged ions
`
`with sufficient acceleration so that the ions sputter the target material from the
`
`target 116. A portion of the sputtered target material is deposited on the substrate
`
`134.
`
`[0032]
`
`The electrons, which cause the ionization, are generally confined by the
`
`magnetic fields produced by the magnet 126. The magnetic confinement is
`
`strongest in a confinement region 142 where there is relatively low magnetic field
`
`intensity. The confinement region 142 is substantially in the shape of a ring that is
`
`located proximate to the target material. Generally, a higher concentration of
`
`positively charged ions in the plasma is present in the confinement region 142 than
`
`elsewhere in the chamber 104. Consequently, the target 116 is eroded more rapidly
`
`file://C:\EFS Data\ZON-003\embedded\ZON—003EFSFina1.xm1
`
`1 1/ 14/2002
`Page 6 of 56
`
`Page 6 of 56
`
`
`
`IGSU I U1 JU
`
`in areas directly adjacent to the higher concentration of positively charged ions. The
`
`rapid erosion in these areas results in undesirable non—uniform erosion of the
`
`target 116 and. thus relatively poor target utilization.
`
`[0033]
`
`Dramatically increasing the power applied to the plasma can result in more
`
`uniform erosion of the target 116 and higher sputtering yield. However, the amount
`
`of applied power necessary to achieve this increased uniformity can increase the
`
`probability of generating an electrical breakdown condition that leads to an
`
`undesirable electrical discharge between the cathode assembly 114 and the anode
`
`130 regardless of the duration of the pulses. An undesirable electrical discharge will
`
`corrupt the sputtering process and cause contamination in the vacuum chamber
`
`104. Additionally, the increased power can overheat the target and cause target
`
`damage.
`
`[0034]
`
`Sputtering yields are generally determined experimentally. The yield
`
`dependence on the bombarding ion energy approximately exhibits a threshold that
`
`is between about 10—30eV, followed by a nearly linear range that extends to several
`
`hundred eV. At higher energies, the dependence is less than linear. Sputtering
`
`processes are generally most energy efficient when the ion energies are within the
`
`linear range.
`
`[0035]
`
`Sputtering systems are generally calibrated to determine the deposition rate
`
`under certain operating conditions. The erosion rate of the target 116 can be
`
`expressed by the following equation:
`
`R = k~——~JYMi:s/mm
`P
`
`[0035]
`
`where k is a constant, /is the ion current density in mA/cm 2 , -)’is the
`
`sputtering yield in atoms/ion, and Mis the atomic weight in grams, and p is the
`3
`density in gm/cm of the target material. The deposition rate is generally
`
`proportional to the sputtering yield Y.
`
`[0037]
`
`H6. 2 illustrates a cross—sectional view of a prior art cathode assembly 114‘
`
`having a cathode cooling system. The cathode assembly 114' includes target 116'.
`
`The cathode cooling system also includes a conduit 150 that contains a fluid 152
`
`for conducting heat away from the cathode assembly 1 14'. The fluid 152 can be a
`
`file://C:\BFS Data\ZON-O03\embedded\ZON-003EFSFinal.xml
`
`11/14/2002
`Page 7 of 56
`
`Page 7 of 56
`
`
`
`rage o 01' no
`
`liquid coolant or a gas, for example.
`
`[0038]
`
`in operation, ions 154 in a plasma impact a surface 156 of the target 116'. The
`
`impact of the ions 154 generates heat 158 at the surface 156. Additionally, the
`
`impact of the ions 154 eventually dislodges atoms 160 from the surface 156 of the
`
`target 116' causing sputtering. The heat 158 that is generated by the ion impact
`
`radiates through the cathode assembly 114'. The cathode assembly 114' is in
`
`thermal communication with the conduit 150. The fluid 152 absorbs the heat 158
`
`and transfers it away from the cathode assembly 1 14'.
`
`[0039]
`
`FIG. 3 illustrates a known process for sputtering material from a target 116'. An ’
`
`ion 154 having a mass Mi and a velocity vi impacts a target particle 162 having a
`
`mass Mt which is initially at rest on the surface 156 of the target 116'. The ion 154
`
`impacts the surface 156 at normal incidence. The momentum from the ion 154
`
`transfers to the target particle 162 driving the target particle 162 into the target
`
`H6‘.
`
`[0040]
`
`Thus, the ejection of a sputtered particle 164 from the target 1 14' generally
`
`requires a sequence of collisions for a component of the initial momentum vector to
`
`change by more than ninety degrees. Typically, an incident ion 154 experiences a
`
`cascade of collisions and its energy is partitioned over a region of the target surface
`
`156. However, the sputtering momentum exchange occurs primarily within a region
`
`extending only about ten angstroms below the surface 156. The incident ion 154
`
`generally strikes two lattice atoms 166, 168 almost simultaneously. This low energy
`knock-on receives a side component of momentum and initiates sputtering of one
`
`or more of its neighbors. The primary knock~on is driven into the target 114',
`
`where it can be reflected and sometimes returned to the surface 156 to produce
`
`sputtering by impacting the rear of a surface atom 170.
`
`[0041]
`
`A fraction of the kinetic energy of the incident ion 154 is transferred to the
`
`target particle 162. This kinetic energy transfer function can be expressed as
`
`follows:
`
`4M.M,
`z:=———-————2-
`(M,-+M.)
`
`file://C:\EFS Data\ZON-O03\embedded\ZON—003EFSFina1.xml
`
`1 1/ 14/2002
`Page 8 of 56
`
`Page 8 of 56
`
`
`
`[0042]
`
`The sputtering yield Y can be expressed as follows, assuming perpendicular ion
`
`incidence onto a substantially planar surface 156:
`
`1 GEM? U1 JU
`
`_
`
`E
`
`Y—k xr-:x—L7><a(
`
`M
`
`[0043]
`
`where k is a constant, e is the energy transfer function, a is a near—linear
`
`function of the ratio of the mass of the target atom 162 to the mass of the incident
`
`ion 154, [is the kinetic energy of the incident ion 154, and U is the surface binding
`
`energy for the target material. For most sputtering materials, the mass dependence
`
`of e or does not vary greatly from one material to another. The primary material-
`
`sensitive factor is the surface binding energy, and this has only a first power
`
`dependence.
`
`[0044}
`
`At energies above 20—30eV, heavy particles can sputter atoms from a surface of
`
`a target. The sputtering yield increases rapidly with energy up to a few hundred eV,
`
`with 500-1 00OeV argon ions being typically used for physical sputtering. Above a
`
`few hundred eV, there is a possibility that ions 154 will be implanted in the target
`
`116'. This can especially occur at energies over 1keV.
`
`[0045]
`
`FIG. 4 illustrates a cross—sectional view of an embodiment of a magnetron
`
`sputtering apparatus 200 according to the present invention. The magnetron
`
`, sputtering apparatus 200 includes a chamber 202, such as a vacuum chamber. The
`
`chamber 202 is coupled in fluid communication to a vacuum system 204 through a
`
`vacuum valve 206. In one embodiment, the chamber 202 is electrically coupled to
`
`ground potential.
`
`[0046]
`
`The chamber 202 is coupled to a feed gas source 208 by one or more gas lines
`
`207. In one embodiment, the gas lines 207 are isolated from the chamber and other
`
`components by insulators 209. Additionally. the gas lines 207 can be isolated from
`
`the feed gas source using in—line insulating couplers (not shown). A gas flow
`
`control system 210 controls the gas flow to the chamber 202. The gas source 208
`
`can contain any feed gas. For example. the feed gas can be a noble gas or a mixture
`
`of noble gases. The feed gas can also be a reactive gas, a non—reactive gas, or a
`
`mixture of both reactive and non—reactive gases.
`
`file://C:\EFS Data\ZON—003\embedded\ZON—OO3EFSFinal.xm1
`
`11/14/2002
`
`Page 9 of 56
`
`Page 9 of 56
`
`
`
`{K155 1U U1 JU
`
`[0047]
`
`A substrate 211 to be sputter coated is supported in the chamber 202 by a
`
`substrate support 212. The substrate 211 can be any type of work piece such as a
`
`semiconductor wafer. In one embodiment. the substrate support 212 is electrically
`
`coupled to an output 213 of a bias voltage source 214. An insulator 215 isolates the
`
`bias voltage source 214 from a wall of the chamber 202. In one embodiment, the
`
`bias voltage‘ source 214 is an alternating current (AC) power source, such as a radio
`
`frequency (RF) power source. In other embodiments (not shown), the substrate
`
`support 212 is coupled to ground potential or is electrically floating.
`
`[004 8]
`
`The magnetron sputtering apparatus 200 also includes a cathode assembly 216.
`
`In one embodiment, the cathode assembly 216 includes a cathode 218 and a
`
`sputtering target 220 composed of target material. In one embodiment, the cathode
`
`218 is formed of a metal. In one embodiment, the cathode 218 is formed of a
`
`chemically inert material, such as stainless steel. The sputtering target 220 is in
`
`physical contact with the cathode 218. In one embodiment, the sputtering target
`
`220 is positioned inside the cathode 218 as shown in FIG. 4. The distance from the
`
`sputtering target 220 to the substrate 211 can vary from a few centimeters to about
`
`one hundred centimeters.
`
`[0049]
`
`The target material can be any material suitable for sputtering. For example, the
`
`target material can be a metallic material, polymer material, superconductive
`
`material, magnetic material including ferromagnetic material, non—magnetic
`
`material, conductive material, non—conductive material, composite material, reactive A
`
`material, or a refractory material.
`
`[0050]
`
`The cathode assembly 216 is coupled to an output 222 of a matching unit 224.
`
`An insulator 226 isolates the cathode assembly 216 from a grounded wall of the
`
`chamber 202. An input 230 of the matching unit 224 is coupled to a first output
`
`232 of a pulsed power supply 234. A second output 236 of the pulsed power supply
`
`234 is coupled to an anode 238. An insulator 240 isolates the anode 238 from a
`
`grounded wall of the chamber 202. Another insulator 242 isolates the anode 238
`
`from the cathode assembly 216.
`
`file://C:\EFS Data\ZON—003\embedded\ZON-003EFSFinal.xm1
`
`11/14/2002
`
`Page 10 of 56
`
`Page 10 of 56
`
`
`
`1"d5C L 1 U1 JU
`
`[005]]
`
`In one embodiment (not shown), the first output 232 of the pulsed power
`supply 234 is directly coupled to the cathode assembly 216. In one embodiment
`
`I
`
`(not shown), the second output 236 of the pulsed power supply 234 and the anode
`
`238 are both coupled to ground. In one embodiment (not shown), the first output
`
`232 of the pulsed power supply 234 couples a negative voltage impulse to the
`
`cathode assembly 216. in another embodiment (not shown), the second output 236
`
`of the pulsed power supply 234 couples a positive voltage impulse to the anode
`
`238.
`
`[0052]
`
`In one embodiment, the pulsed power supply 234 generates peak voltage levels
`
`of between about 5kV and about 30kV. In one embodiment, operating voltages are
`
`generally between about 50V and lkV. In one embodiment, the pulsed power supply
`
`234 sustains discharge current levels that are on order of about lA to S,000A
`
`depending on the volume of the plasma. Typical operating currents varying from
`
`less than about one hundred amperes to more than a few thousand amperes
`
`depending on the volume of the plasma. In one embodiment, the power pulses have
`
`a repetition rate that is below lkHz. In one embodiment. the pulse width of the
`
`pulses generated by the pulsed power supply 234 is substantially between about
`
`one microsecond and several seconds.
`
`[0053]
`
`The anode 238 is positioned so as to form a gap 244 between the anode 238
`
`and the cathode assembly 216 that is sufficient to allow current to flow through a
`
`region 245 between the anode 238 and the cathode assembly 216. In one
`
`embodiment, the gap 244 is between approximately 0.3cm and lOcm. The surface
`
`area of the cathode assembly 216 determines the volume of the region 245. The
`
`gap 244 and the total volume of the region 245 are parameters in the ionization
`
`process as described herein.
`
`[0054]
`
`An anode shield 248 is positioned adjacent to the anode 238 and functions as
`
`an electric shield to electrically isolate the anode 238 from the plasma. in one
`
`embodiment, the anode shield 248 is coupled to ground potential. An insulator 250
`
`is positioned to isolate the anode shield 248 from the anode 238.
`
`file://C:\EFS Data\ZON-003\embedded\ZON—0O3EFSFinal.xm1
`
`1 1/14/2002
`Page 1 1 of 56
`
`Page 11 of 56
`
`
`
`raga 1/. or JD
`
`[0055]
`
`The magnetron sputtering apparatus 200 also includes a magnet assembly 252.
`
`In one embodiment, the magnet assembly 252 is adapted to create a magnetic field
`
`254 proximate to the cathode assembly 216. The magnet assembly 252 can include
`
`permanent magnets 256, or alternatively, e|ectro—magnets (not shown). The
`
`configuration of the magnet assembly 252 can be varied depending on the desired
`
`shape and strength of the magnetic field 254. The magnet assembly can have either
`
`a balanced or unbalanced configuration.
`
`[0056]
`
`In one embodiment, the magnet assembly 252 includes switching electro-
`
`magnets. which generate a pulsed magnetic field proximate to the cathode
`‘assembly 216. In some embodiments, additional magnet assemblies (not shown)
`
`can be placed at various locations around and throughout the chamber 202 to
`
`direct different types of sputtered target materials to the substrate 212.
`
`[0057]
`
`In one embodiment, the magnetron sputtering apparatus 200 is operated by
`
`generating the magnetic field 254 proximate to the cathode assembly 216. In the
`
`embodiment shown in FIG. 2, the permanent magnets 256 continuously generate
`
`the magnetic field 254. In other embodiments, electro—magnets (not shown)
`
`generate the magnetic field 254 by energizing a current source that is coupled to
`
`the electro—magnets. In one embodiment, the strength of the magnetic field 254 is
`
`between about fifty gauss and two thousand gauss. After the magnetic field 254 is
`
`generated, the feed gas from the gas source 208 is supplied to the chamber 202 by
`
`the gas flow control system 210.
`
`[0058]
`
`In one embodiment, the feed gas is supplied to the chamber 202 directly
`
`between the cathode assembly 216 and the anode 238. Directly injecting the feed
`
`gas between the cathode assembly 216 and the anode 238 can increase the flow
`
`rate of the gas between the cathode assembly 216 and the anode 238. Increasing
`
`the flow rate of the gas allows longer duration impulses and thus, can result in the
`
`formation higher density plasmas. The flow of the feed gas is further discussed
`
`herein.
`
`file://C:\EFS Data\ZON—003\embedded\ZON—003EFSFinaI.xml
`
`1 1/ 14/2002
`Page 12 of 56
`
`Page 12 of 56
`
`
`
`rage 1.) 01 30
`
`[0059]
`
`in one embodiment, the pulsed power supply 2-34 is a component of an
`
`ionization source that generates the weakly-ionized plasma. The pulsed power
`
`supply applies a voltage pulse between the cathode assembly 216 and the anode
`
`238. in one embodiment, the pulsed power supply 234 applies a negative voltage
`
`pulse to the cathode assembly 216. The amplitude and shape of the voltage pulse
`
`are such that a weal<ly—ionized plasma is generated in the region 246 between the
`
`anode 238 and the cathode assembly 216.
`
`[0060]
`
`The weakly—ionized plasma is also referred to as a pre—ionized plasma. In one
`
`embodiment, the peak plasma density of the pre~ionized plasma is between about
`
`» i0 6 and 10 12 cm '3 for argon feed gas. in one embodiment, the pressure in the
`3
`
`chamber varies from about 10 '
`
`to 10Torr. The peak plasma density of the pre-
`
`ionized plasma depends on the properties of the specific plasma processing system.
`
`[0061]
`
`in one embodiment, the pulsed power supply 234 generates a low power pulse
`
`having an initial voltage that is between about 100V and 5kV with a discharge
`
`current that is between about 0.1A and 100A in order to generate the weakly-
`
`ionized plasma. in some embodiments the width of the pulse can be on the order of
`
`0.1 microseconds to one hundred seconds. Specific parameters of the pulse are
`
`discussed herein in more detail.
`
`[0062]
`
`In one embodiment, the pulsed power supply 234 applies a voltage between the
`
`cathode assembly 216 and the anode 238 before the feed gas is supplied between
`
`the cathode assembly 216 and the anode 238. in another embodiment, the pulsed
`
`power supply 234 applies a voltage between the cathode assembly 216 and the
`
`anode 238 after the feed gas is supplied between the cathode assembly 216 and the
`
`anode 238.
`
`[0063]
`
`In one embodiment, a direct current (DC) power supply (not shown) is used to
`
`generate and maintain the weakly—ioni2ed or pre—ionized plasma. In this
`
`embodiment, the DC power supply is adapted to generate a voltage that is large
`
`enough to ignite the pre—ionized plasma. in one embodiment, the DC power supply
`
`generates an initial voltage of several kilovolts between the cathode assembly 216
`
`and the anode 238 in order to generate and maintain the pre—ionized plasma. The
`initial voltage between the cathode assembly 216 and the anode 238 creates a
`
`fi1e://C:\EFS Data\ZON—0O3\embedded\ZON-O03EFSFina1.xml
`
`11/14/2002
`
`Page 13 of 56
`
`Page 13 of 56
`
`
`
`rage 14 U1 )0
`
`plasma discharge voltage that is on the order of i0OV to lO00V with a discharge
`
`current that is on the order of O.lA to 100A.
`
`[0064]
`
`The direct current required to generate and maintain the pre—ionized plasma is
`
`a function of the volume of the plasma. ln addition, the current required to generate
`
`and maintain the pre—ionized plasma is a function of the strength of the magnetic
`
`field in the region 245. For example, in one embodiment, the DC power supply
`
`generates a current that is on order of lmA to 100A depending on the volume of
`
`the plasma and the strength of the magnetic field in the region 245. The DC power
`
`supply can be adapted to generate and maintain an initial peak voltage between the
`
`cathode assembly 216 and the anode 238 before the introduction of the feed gas.
`
`[0065]
`
`In another embodiment, an alternating current (AC) power supply (not shown) is
`
`used to generate and maintain the weakly~ionized or pre—ionized plasma. For
`
`example, the weakly—ionized or pre—ionized plasma can be generated and
`
`maintained using electron cyclotron resonance (ECR), capacitively coupled plasma
`
`discharge (CCP), or inductively coupled plasma (ICP) discharge. AC power supplies
`
`can require less power to generate and maintain a weakly—ionized plasma than a DC
`
`power supply. In addition, the pre—ionized or weakly—ionized plasma can be
`
`generated by numerous other techniques, such as UV radiation techniques, X—ray
`
`techniques, electron beam techniques, ion beam techniques, or ionizing filament
`
`techniques. in some embodiments, the weakly—ionized plasma is formed outside of
`
`the region 245 and then diffuses into the region 245.
`
`[0066]
`
`Forming a weakly—ionized or pre—ionized plasma substantially eliminates the
`
`probability of establishing a breakdown condition in the chamber 202 when high-
`
`power pulses are applied between the cathode assembly 216 and the anode 238.
`
`Uniformly distributing the weakly—ionized or pre—ionized plasma over the cathode
`
`area results in a more uniform strongly ionized plasma when a high power pulse is
`
`applied. The probability of establishing a breakdown condition is substantially
`
`eliminated because the weakly—ionized plasma has a low—level of ionization that
`
`provides electrical conductivity through the plasma. This conductivity greatly
`
`reduces or prevents the possibility of a breakdown condition when high power is
`
`applied to the plasma.
`
`file://C:\EFS Data\ZON-O03\embedded\ZON—OO3EFSFinaI.xm1
`
`1 1/14/2002
`Page 14 of 56
`
`Page 14 of 56
`
`
`
`rug: is or 30
`
`[0067]
`
`Once the weakly—ionized plasma is formed, high—power pulses are then
`
`generated between the cathode assembly 216 and the anode 238. In one
`
`embodiment, the pulsed power supply 234 generates the high—power pulses. The
`
`desired power level of the high—power pulse depends on several factors including
`
`the desired deposition rate, the density of the pre—ionized plasma, and the volume
`
`of the plasma, for example. In one embodiment, the power level of the high—power
`
`pulse is in the range of about lkw to about IOMW. In one embodiment, the high-
`
`power pulses are rapidly applied across the weakly—ionized plasma. In one
`
`embodiment, the high—power pulses are substantially