WW SPECIFICATION
`
`EXPRESS MAIL LABEL NO.
`ED475251649US
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`Electronic Version l.2.8
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`Stylesheet Version 1.0
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`High Deposition Rate Sputtering
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`Background of invention
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`[0001]
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`Sputtering is a well—known technique for depositing films on substrates.
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`Sputtering is the physical ejection of atoms from a target surface and is sometimes
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`referred to as physical vapor deposition (PVD). ions, such as argon ions, are
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`generated and then directed to a target surface where the lens physically sputter
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`target material atoms. The target material atoms ballist-ically flow to a substrate
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`where they deposit as a film of target material.
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`[0002]
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`Diode sputtering systems include a target and an anode. Sputtering is achieved
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`in a diode sputtering system by establishing an electrical discharge in a gas
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`between two parallel—plate electrodes inside a chamber. A potential of several
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`kilovolts is typically applied between planar electrodes in an inert gas atmosphere
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`(e.g., argon) at pressures that are between about 10 ‘1 and 10 '2 Torr. A plasma
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`discharge is then formed. The plasma discharge is separated from each electrode by
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`what is referred to as the dark space.
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`[0003]
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`The plasma discharge has a relatively constant positive potential with respect to
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`the target. ions are drawn out of the plasma, and are accelerated across the cathode
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`dark space. The target has a lower potential than the region in which the plasma is
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`formed. Therefore, the target attracts positive ions. Positive ions move towards the
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`target with a high velocity. Positive ions then impact the target and cause atoms to
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`physically dislodge or sputter from the target. The sputtered atoms then propagate
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`to a substrate where they deposit a film of sputtered target material. The plasma is
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`replenished by electron-ion pairs formed by the collision of neutral molecules with
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`secondary electrons generated at the target surface.
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`file://C:\EFS Data\ZON—O03\embedded\ZON—003EFSFina].xml
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`GILLETTE 1015
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`1 1/ 14/2002
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`GILLETTE 1015
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`[“4554 U]. )0
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`[0004]
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`Magnetron Sputtering systems use magnetic fields that are shaped to trap and
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`to concentrate secondary electrons, which are produced by ion bombardment of the
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`target surface. The plasma discharge generated by a magnetron sputtering system
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`is located proximate to the surface of the target and has a high density of electrons.
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`The high density of electrons causes ionization of the sputtering gas in a region
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`~
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`that is close to the target surface.
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`[0005]
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`One type of magnetron sputtering system is a planar magnetron sputtering
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`system. Planar magnetron sputtering systems are similar in configuration to diode
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`sputtering systems. However, the magnets (permanent or electromagnets) in planar
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`magnetron sputtering systems are placed behind the cathode. The magnetic field
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`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}
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`fields. The trapped electrons enhance the efficiency of the discharge and reduce the
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`energy dissipated by electrons arriving at the substrate.
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`[0006]
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`Conventional magnetron sputtering systems deposit films that have relatively
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`low uniformity. The film uniformity can be increased by mechanically moving the
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`substrate and/or the magnetron. However, such systems are relatively complex and
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`expensive to implement. Conventional magnetron sputtering systems also have
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`relatively poor target utilization. The term "target utilization“ is defined herein to be
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`a metric of how uniform the target material erodes during sputtering. For example,
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`high target utilization would indicate thatthe target material erodes in a highly
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`uniform manner.
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`[0007]
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`in addition, conventional magnetron sputtering systems have a relatively low
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`deposition rate. The term "deposition rate" is defined herein to mean the amount of
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`material deposited on the substrate per unit of time. In general, the deposition rate
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`is proportional to the sputtering yield. The term "sputtering yield" is defined herein
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`to mean the number of target atoms ejected from the target per incident particle.
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`Thus, increasing the sputtering yield will increase the deposition rate.
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`[Brief Description of Drawings
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`file;//C:\EFS Data\ZON—003\embedded\ZON—003EFSFinal.xml
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`rags 3 or 30
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`{0008]
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`This invention is described with particularity in the detailed description. The
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`above and further advantages of this invention may be better understood by
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`referring to the following description in conjunction with the accompanying
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`drawings, in which like numerals indicate like structural elements and features in
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`various figures. The drawings are not necessarily to scale, emphasis instead being
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`placed upon illustrating the principles of the invention.
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`[0009]
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`FIG.
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`1 illustrates a cross—sectional view of a known magnetron sputtering
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`apparatus having a pulsed power source.
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`[0010]
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`FIG. 2 illustrates a cross—sectional view of a prior art cathode assembly having a
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`cathode cooling system.
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`[00] I]
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`FIG. 3 illustrates a known process for sputtering material from a target.
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`[00] 2]
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`FIG. 4 illustrates a cross—sectional view of an embodiment of a magnetron
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`sputtering apparatus according to the present invention.
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`[0013]
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`FIG. 5A through FIG. SD illustrate cross~sectional views of the magnetron
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`sputtering apparatus of FIG. 4.
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`[0014]
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`FIG. 6 illustrates graphical representations of the applied voltage, current, and
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`power as a function of time for periodic pulses applied to the plasma in the
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`magnetron sputtering apparatus of FIG. 4.
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`[0015]
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`FIG. 7A through FIG. 7D illustrate various simulated magnetic field distributions
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`proximate to the cathode assembly for various electron ExB drift currents in a
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`magnetically enhanced plasma sputtering apparatus according to the invention.
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`[0016]
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`FIG. 8 illustrates a graphical representation of sputtering yield as a function of
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`temperature of the sputtering target.
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`.
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`[0017]
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`FIG. 9 illustrates a process for sputtering material from a target according one
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`embodiment of the present invention.
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`[0018]
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`FIG. IO illustrates a cross-sectional view of a cathode assembly according to
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`one embodiment of the invention.
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`file://C‘:\EFS Data\ZON~003\embedded\ZON~OO3EFSFinal.xm1
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`raga 1+ UL 30
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`[0019]
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`FIG. ii is a flowchart of an illustrative process of enhancing a sputtering yield
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`of a sputtering target according to the present invention.
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`Detailed Description
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`[0020]
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`The sputtering process can be quantified in terms of the sputtering yield. The '
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`term "sputtering yield" is defined herein to mean the number of target atoms
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`ejected from the target per incident particle. The sputtering yield depends on
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`several factors, such as the target species, bombarding species, energy of the
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`bombarding ions, and the angle of incidence of the bombarding ions. in typical
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`known sputtering processes, the sputtering yield is generally insensitive to target
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`temperature.
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`[0021]
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`The deposition rate of a sputtering process is generally proportional to the
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`sputtering yield. Thus, increasing the sputtering yield typically will increase the
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`deposition rate. One way to increase the sputtering yield is to increase the ion
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`density of the plasma so that a larger ion flux impacts the surface of the target. The
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`density of the plasma is generally proportional to the number of ionizing collisions
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`in the plasma.
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`[0022]
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`Magnetic fields can be used to confine electrons in the plasma to increase the
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`number of ionizing collisions between electrons and neutral atoms in the plasma.
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`The magnetic and electric fields in magnetron sputtering systems are concentrated
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`in narrow regions close to the surface of the target. These narrow regions are
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`located between the poles of the magnets used for producing the magnetic field.
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`Most of the ionization of the sputtering gas occurs in these localized regions. The
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`location of theionization regions causes non—uniform erosion or wear of the target
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`that results in poor target utilization.
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`[0023]
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`increasing the power applied between the target and the anode can increase the
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`production of ionized gas and, therefore, increase the target utilization and the
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`sputtering yield. However, increasing the applied power can lead to undesirable
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`target heating and target damage. Furthermore, increasing the voltage applied
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`between the target and the anode increases the probability of establishing an
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`undesirable electrical discharge (an electrical arc) in the process chamber. An
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`undesirable electrical discharge can corrupt the sputtering process.
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`rust: J oi 30
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`[0024]
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`Pulsing the power applied to the plasma can be advantageous since the average
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`discharge power can remain low while relatively large power pulses are periodically
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`applied. Additionally, the duration of these large voltage pulses can be preset so as
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`to reduce the probability of establishing an electrical breakdown condition leading
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`to an undesirable electrical discharge. However. very large power pulses can still
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`result in undesirable electrical discharges and undesirable target heating regardless
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`of their duration.
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`[0025]
`
`FlG.
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`1 illustrates a cross—sectional view of a known magnetron sputtering
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`apparatus 100 having a pulsed power source 102. The known magnetron sputtering
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`apparatus 100 includes a vacuum chamber 104 where the sputtering process is
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`performed. The vacuum chamber 104 is positioned in fluid communication with a
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`vacuum pump 106 via a conduit 108. The vacuum pump 106 is adapted to evacuate
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`the vacuum chamber 104 to high vacuum. The pressure inside the vacuum chamber
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`104 is generally less than lOOPa during operation. A feed gas source 109, such as
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`an argon gas source, is coupled. to the vacuum chamber 104 by a gas inlet 110. A
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`valve 112 controls the gas flow from the feed gas source 109.
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`[0026]
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`The magnetron sputtering apparatus 100 also includes a cathode assembly 114
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`having a target 116. The cathode assembly 114 is generally in the shape of a
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`circular disk. The cathode assembly 114 is electrically connected to a first output
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`118 of the pulsed power supply 102 with an electrical transmission line 120. The
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`cathode assembly 1 14 is typically coupled to the negative potential of the pulsed
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`power supply 102. In order to isolate the cathode assembly 114 from the vacuum
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`chamber 104, an insulator 122 can be used to pass the electrical transmission line
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`120 through a wall of the vacuum chamber 104. A grounded shield 124 can’ be
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`positioned behind the cathode assembly 1 14 to protect a magnet 126 from
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`bombarding ions. The magnet 126 shown in HQ.
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`1
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`is generally shaped in the form
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`of a ring that has its south pole 127 on the inside of the ring and its north pole 128
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`on the outside of the ring. Many other magnet configurations can also be used.
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`rage o 0130
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`[0027]
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`An anode 130 is positioned in the vacuum chamber 104 proximate to the
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`cathode assembly 114. The anode 130 is typically coupled to ground. A second
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`output 132 of the pulsed power supply 102 is also typically coupled to ground. A
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`substrate 134 is positioned in the vacuum chamber 104 on a substrate support 135
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`to receive the sputtered target material from the target 1 16. The substrate 134 can
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`be electrically connected to a bias voltage power supply 136 with a tranSmission »
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`line 138. In order to isolate the bias voltage power supply 136 from the vacuum
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`chamber 104, an insulator 140 can be used to pass the electrical transmission line
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`138 through a wall of the vacuum chamber 104.
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`[0028]
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`In operation, the pulsed power supply 102 applies a voltage pulse between the
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`cathode assembly 114 and the anode 130 that has a sufficient amplitude to ionize
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`the argon feed gas in the vacuum chamber 104. The typical ionization process is
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`referred to as direct ionization or atomic ionization by electron impact and can be
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`described as follows:
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`[0029]
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`Ar+e“-9Ar++2e‘
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`[0030]
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`where Ar represents a neutral argon atom in the feed gas and e ‘ represents an
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`ionizing electron generated in response to the voltage pulse applied between the
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`cathode assembly 114 and the anode 130. The collision betWeen the neutral argon
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`atom and the ionizing electron results in an argon ion (Ar + ) and two electrons.
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`[0031]
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`The negatively biased cathode assembly 1 14 attracts positively charged ions
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`with sufficient acceleration so that the ions sputter the target material from the
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`target 116. A portion of the sputtered target material is deposited on the substrate
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`134.
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`[0032]
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`The electrons, which cause the ionization, are generally confined by the
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`magnetic fields produced by the magnet 126. The magnetic confinement is
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`strongest in a confinement region 142 where there is relatively low magnetic field
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`intensity. The confinement region 142 is substantially in the shape of a ring that is
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`located proximate to the target material. Generally, a higher concentration of
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`positively charged ions in the plasma is present in the confinement region 142 than
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`elsewhere in the chamber 104. Consequently, the target 116 is eroded more rapidly
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`IGSU l U1 JU
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`in areas directly adjacent to the higher concentration of positively charged ions. The
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`rapid erosion in these areas results in undesirable non—uniform erosion of the
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`target 116 and. thus relatively poor target utilization.
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`[0033]
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`Dramatically increasing the power applied to the plasma can result in more
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`uniform erosion of the target 116 and higher sputtering yield. However, the amount
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`of applied power necessary to achieve this increased uniformity can increase the
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`probability of generating an electrical breakdown condition that leads to an
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`undesirable electrical discharge between the cathode assembly l l4 and the anode
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`130 regardless of the duration of the pulses. An undesirable electrical discharge will
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`corrupt the sputtering process and cause contamination in the vacuum chamber
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`104. Additionally, the increased power can overheat the target and cause target
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`damage.
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`[0034]
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`Sputtering yields are generally determined experimentally. The yield
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`dependence on the bombarding ion energy approximately exhibits a threshold that
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`is between about lO—SOeV, followed by a nearly linear range that extends to several
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`hundred eV. At higher energies, the dependence is less than linear. Sputtering
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`processes are generally most energy efficient when the ion energies are within the
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`linear range.
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`[0035]
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`Sputtering systems are generally calibrated to determine the deposition rate
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`under certain operating conditions. The erosion rate of the target 116 can be
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`expressed by the following equation:
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`R zkfl’flA/msn
`p
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`[0035]
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`where k is a constant, jis the ion current density in mA/cm 2 , Yis the
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`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
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`proportional to the sputtering yield Y.
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`[0037]
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`RC. 2 illustrates a cross—sectional view of a prior art cathode assembly l 14‘
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`having a cathode cooling system. The cathode assembly 114' includes target 116'.
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`The cathode cooling system also includes a conduit 150 that contains a fluid 152
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`for conducting heat away from the cathode assembly i 14'. The fluid 152 can be a
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`rug: 0 01' :0
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`liquid coolant or a gas, for example.
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`[0038]
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`in operation, ions 154 in a plasma impact a surface 156 of the target 116'. The
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`impact of the ions 154 generates heat 158 at the surface 156. Additionally, the
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`impact of the ions 154 eventually dislodges atoms 160 from the surface 156 of the
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`target 116' causing sputtering. The heat 158 that is generated by the ion impact
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`radiates through the cathode assembly 114'. The cathode assembly 114' is in
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`thermal communication with the conduit 150. The fluid 152 absorbs the heat 158
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`and transfers it away from the cathode assembly 1 14'.
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`[0039]
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`FIG. 3 illustrates a known process for sputtering material from a target 116'. An ,
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`ion 154 having a mass Mi and a velocity vi impacts a target particle 162 having a
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`mass Mt which is initially at rest on the surface 156 of the target 116'. The ion 154
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`impacts the surface 156 at normal incidence. The momentum from the ion 154
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`transfers to the target particle 162 driving the target particle 162 into the target
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`116'.
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`[0040]
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`Thus, the ejection of a sputtered particle 164 from the target 1 14' generally
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`requires a sequence of collisions for a component of the initial momentum vector to
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`change by more than ninety degrees. Typically, an incident ion 154 experiences a
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`cascade of collisions and its energy is partitioned over a region of the target surface
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`156. However, the sputtering momentum exchange occurs primarily within a region
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`extending only about ten angstroms below the surface 156. The incident ion 154
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`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
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`or more of its neighbors. The primary knock~on is driven into the target 114',
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`where it can be reflected and sometimes returned to the surface 156 to produce
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`sputtering by impacting the rear of a surface atom 170.
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`[0041]
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`A fraction of the kinetic energy of the incident ion 154 is transferred to the
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`target particle 162. This kinetic energy transfer function can be expressed as
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`follows:
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`4M.M,
`5=———~———2—
`(Mi-+16)
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`[0042]
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`The Sputtering yield Y can be eXpressed as foliows, assuming perpendicular ion
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`incidence onto a substantially planar surface 156:
`
`1 “5&7 U1 JU
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`Y=k ng—Xa
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`E M/ J
`U
`( M-
`
`’
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`[0043]
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`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
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`ion 154, [is the kinetic energy of the incident ion 154, and U is the surface binding
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`energy for the target material. For most sputtering materials, the mass dependence
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`of e or does not vary greatly from one material to another. The primary material—
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`sensitive factor is the surface binding energy, and this has only a first power
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`dependence.
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`[0044]
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`At energies above 20—30eV, heavy particles can sputter atoms from a surface of
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`a target. The sputtering yield increases rapidly with energy up to a few hundred eV,
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`with 500—1000eV argon ions being typically used for physical sputtering. Above a
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`few hundred eV, there is a possibility that ions 154 will be implanted in the target
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`116'. This can especially occur at energies over ikeV.
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`[0045]
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`FIG. 4 illustrates a cross—sectional view of an embodiment of a magnetron
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`sputtering apparatus 200 according to the present invention. The magnetron
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`, sputtering apparatus 200 includes a chamber 202, such as a vacuum chamber. The
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`chamber 202 is coupled in fluid communication to a vacuum system 204 through a
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`vacuum valve 206. In one embodiment, the chamber 202 is electrically coupied to
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`ground potential.
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`[0046]
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`The chamber 202 is coupled to a feed gas source 208 by one or more gas iines
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`207. In one embodiment, the gas iines 207 are isolated from the chamber and other
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`components by insulators 209. Additionally. the gas lines 207 can be isolated from
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`the feed gas source using in—line insulating couplers (not shown). A gas flow
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`control system 210 controls the gas flow to the chamber 202. The gas source 208
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`can contain any feed gas. For example. the feed gas can be a noble gas or a mixture
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`of noble gases. The feed gas can also be a reactive gas, a non—reactive gas, or a
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`mixture of both reactive and non—reactive gases.
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`[3155 IU U). JU
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`[0047]
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`A substrate 211 to be sputter coated is supported in the chamber 202 by a
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`substrate support 212. The substrate 211 can be any type of work piece such as a
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`semiconductor wafer. In one embodiment. the substrate support 212 is electrically
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`coupled to an output 213 of a bias voltage source 214. An insulator 215 isolates the
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`bias voltage source 214 from a wall of the chamber 202. In one embodiment, the
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`bias voltage source 214 is an alternating current (AC) power sourC'e, such as a radio
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`frequency (RF) power source. In other embodiments (not shown), the substrate
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`support 212 is coupled to ground potential or is electrically floating.
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`[004 8]
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`The magnetron sputtering apparatus 200 also includes a cathode assembly 216.
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`In one embodiment, the cathode assembly 216 includes a cathode 218 and a
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`sputtering target 220 composed of target material. In one embodiment, the cathode
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`218 is formed of a metal. In one embodiment, the cathode 218 is formed of a
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`chemically inert material, such as stainless steel. The sputtering target 220 is in
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`physical contact with the cathode 218. In one embodiment, the sputtering target
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`220 is positioned inside the cathode 218 as shown in FIG. 4. The distance from the
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`sputtering target 220 to the substrate 211 can vary from a few centimeters to about
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`one hundred centimeters.
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`[0049]
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`The target material can be any material suitable for sputtering. For example, the
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`target material can be a metallic material, polymer material, superconductive
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`material, magnetic material including ferromagnetic material, non-magnetic
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`material, conductive material, non—conductive material, composite material, reactive 1
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`material, or a refractory material.
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`[0050]
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`The cathode assembly 216 is coupled to an output 222 of a matching unit 224.
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`An insulator 226 iSolates the cathode assembly 216 from a grounded wall of the
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`chamber 202. An input 230 of the matching unit 224 is coupled to a first output
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`232 of a pulsed power supply 234. A second output 236 of the pulsed power supply
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`234 is coupled to an anode 238. An insulator 240 isolates the anode 238 from a
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`grounded wall of the chamber 202. Another insulator 242 isolates the anode 238
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`from the cathode assembly 216.
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`l’dsC l 1 U1 JU
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`[005i]
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`In one embodiment (not shown), the first output 232 of the pulsed power
`supply 234 is directly coupled to the cathode assembly 2I6. In one embodiment
`
`I
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`(not shown), the second output 236 of the pulsed power supply 234 and the anode
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`238 are both coupled to ground. In one embodiment (not shown), the first output
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`232 of the pulsed power supply 234 couples a negative voltage impulse to the
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`cathode assembly 216. In another embodiment (not shown), the second output 236
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`of the pulsed power supply 234 couples a positive voltage impulse to the anode
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`238.
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`[0052]
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`In one embodiment, the pulsed power supply 234 generates peak voltage levels
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`of between about SW and about 30kV. In one embodiment, operating voltages are
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`generally between about 50V and IkV. In one embodiment, the pulsed power supply
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`234 sustains discharge current levels that are on order of about IA to 5,000A
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`depending on the volume of the plasma. Typical operating currents varying from
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`less than about one hundred amperes to more than a few thousand amperes
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`depending on the volume of the plasma. In one embodiment, the power pulses have
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`a repetition rate that is below IkHz. In one embodiment. the pulse width of the
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`pulses generated by the pulsed power supply 234 is substantially between about
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`one microsecond and several seconds.
`
`[0053]
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`The anode 238 is positioned so as to form a gap 244 between the anode 238
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`and the cathode assembly 216 that is sufficient to allow current to flow through a
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`region 245 between the anode 238 and the cathode assembly 216. In one
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`embodiment, the gap 244 is between approximately 0.3cm and 10cm. The surface
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`area of the cathode assembly 216 determines the volume of the region 245. The
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`gap 244 and the total volume of the region 245 are parameters in the ionization
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`process as described herein.
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`[0054]
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`An anode shield 248 is positioned adjacent to the anode 238 and functions as
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`an electric shield to electrically isolate the anode 238 from the plasma. In one
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`embodiment, the anode shield 248 is coupled to ground potential. An insulator 250
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`is positioned to isolate the anode shield 248 from the anode 238.
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`rage 1/. UL JD
`
`[0055]
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`The magnetron sputtering apparatus 200 also includes a magnet assemny 252.
`
`In one embodiment, the magnet assembly 252 is adapted to create a magnetic field
`
`254 proximate to the cathode assembly 2i6. The magnet assembly 252 can include
`
`permanent magnets 256, or alternatively, electro—magnets (not shown). The
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`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]
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`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
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`direct different types of sputtered target materials to the substrate 212.
`
`[0057}
`
`In one embodiment, the magnetron sputtering apparatus 200 is operated by
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`generating the magnetic field 254 proximate to the cathode assembly 216. In the
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`embodiment shown in FIG. 2, the permanent magnets 256 continuously generate
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`the magnetic field 254. In other embodiments, electro—magnets (not shown)
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`generate the magnetic fieId 254 by energizing a current source that is coupled to
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`the electrowmagnets. In one embodiment, the strength of the magnetic field 254 is
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`between about fifty gauss and two thousand gauss. After the magnetic field 254 is
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`generated, the feed gas from the gas source 208 is supplied to the chamber 202 by
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`the gas flow control system 210.
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`[0058]
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`In one embodiment, the feed gas is supplied to the chamber 202 directly
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`between the cathode assembly 216 and the anode 238. Directly injecting the feed
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`gas between the cathode assembly 216 and the anode 238 can increase the flow
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`rate of the gas between the cathode assembly 216 and the anode 238. Increasing
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`the flow rate of the gas allows longer duration impulses and thus, can result in the
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`formation higher density plasmas. The flow of the feed gas is further discussed
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`herein.
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`rage 1.) 01 30
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`[0059]
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`in one embodiment, the pulsed power supply 234 is a component of an
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`ionization source that generates the weakly-ionized plasma. The pulsed power
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`supply applies a voltage pulse between the cathode assembly 216 and the anode
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`238. ln one embodiment, the pulsed power supply 234 applies a negative voltage
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`pulse to the cathode assembly 216. The amplitude and shape of the voltage pulse
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`are such that a weakly—ionized plasma is generated in the region 246 between the
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`anode 238 and the cathode assembly 216.
`
`[0060]
`
`The weakly—ionized plasma is also referred to as a pre—ionized plasma. In one
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`embodiment, the peak plasma density of the pre~ionized plasma is betWeen about
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`. 10 6 and 10 12 cm '3 for argon feed gas. in one embodiment, the pressure in the
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`chamber varies from about 10 '3 to lOTorr. The peak plasma density of the pre—
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`ionized plasma depends on the properties of the specific plasma processing system.
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`[0061]
`
`in one embodiment, the pulsed power supply 234 generates a low power pulse
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`having an initial voltage that is between about 100V and SW with a discharge
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`current that is between about 0.1A and 100A in order to generate the weakly—
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`ionized plasma. ln some embodiments the width of the pulse can be on the order of
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`0.1 microseconds to one hundred seconds. Specific parameters of the pulse are
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`discussed herein in more detail.
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`[0062]
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`in one embodiment, the pulsed power supply 234 applies a voltage between the
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`cathode assembly 216 and the anode 238 before the feed gas is supplied between
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`the cathode assembly 216 and the anode 238. in another embodiment, the pulsed
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`power supply 234 applies a voltage between the cathode assembly 216 and the
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`anode 238 after the feed gas is supplied between the cathode assembly 216 and the
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`anode 238.
`
`[0063]
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`In one embodiment, a direct current (DC) power supply (not shown) is used to
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`generate and maintain the weakly—ionized or pre—ionized plasma. in this
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`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
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`generates an initial voltage of several kilovolts between the cathode assembly 216
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`and the anode 238 in order to generate and maintain the pre—ionized plasma. The
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`initial voltage between the cathode assembly 216 and the anode 238 creates a
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`rust: 14 01 )0
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`plasma discharge voltage that is on the order of IOOV to IOOOV with a discharge
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`current that is on the order of 0.IA to IOOA.
`
`[0064]
`
`The direct current required to generate and maintain the pre—ionized plasma is
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`a function of the volume of the plasma. In addition, the current required to generate
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`and maintain the pre—ionized plasma is a function of the strength of the magnetic
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`field in the region 245. For example, in one embodiment, the DC power supply
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`generates a current that is on order of lmA to IOOA depending on the volume of
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`the plasma and the strength of the magnetic field in the region 245. The DC power
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`supply can be adapted to generate and maintain an initial peak voltage between the
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`cathode assembly 216 and the anode 238 before the introduction of the feed gas.
`
`[0065]
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`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
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`example, the weakly—ionized or pre—ionized plasma can be generated and
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`maintained using electron cyclotron resonance (ECR), capacitively coupled plasma
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`discharge (CCP), or inductively coupled plasma (ICP) discharge. AC power supplies
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`can require less power to generate and maintain a weakly—ionized plasma than a DC
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`power supply. In addition, the pre—ionized or weakly—ionized plasma can be
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`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
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`the region 245 and then diffuses into the region 245.
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`[0066]
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`Forming a weakly—ionized or pre—ionized plasma substantially eliminates the
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`probability of establishing a breakdown condition in the chamber 202 when high—
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`power pulses are applied between the cathode assembly 216 and the anode 238.
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`Uniformly distributing the weakly—ionized or pre—ionized plasma over the cathode
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`area results in a more uniform strongly ionized plasma when a high power pulse is
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`applied. The probability of establishing a breakdown condition is substantially
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`eliminated because the weakly—ionized plasma has a low—level of ionization that
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`provides electrical conductivity through the plasma. This conductivity greatly
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`reduces or prevents the possibility of a breakdown condition when high power is
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`applied to the plasma.
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`file://C:\EFS Data\ZON-003\embedded\ZON—OO3EFSFinal.xm1
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`[0067]
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`'Once the weakly—ionized plasma is formed, high—power pulses are then
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`generated between the cathode assembly 216 and the anode 238. In one
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`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 IkW to about lOMW. In one embodiment, the high—
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`power pulses are rapidly applied across the weakly—ionized plasma. In one
`
`embodiment, the high—power pulses are