USOO8721847B2

(12) United States Patent (10) Patent No.: US 8,721,847 B2

Chang et al. (45) Date of Patent: *May 13, 2014
(54) HOMING OF ARBITRARY SCAN PATH OF A (56) References Cited
ROTATING MAGNETRON
U.S. PATENT DOCUMENTS
(75) Inventors: Yu Chang, San Jose, CA (US); William 4,714,536 A 12/1987 Freeman et al.
Kuang, Sunnyvale, CA (US); Ronald D. 5,762,766 A 6/1998 Kurita et al.
DeDore, Scotts Valley, CA (US); 5,944,968 A 8/1999 Kobayashi et al.
Jitendra R. Bhimjiyani, Cupertino, CA 6,852,202 B2 2/2005 Miller et al.
(US); Wesley W. Zhang, Sunnyvale, CA 8,021,527 B2
2003. O136901 A1
9, 2011 Miller et al.
7/2003 Ohtomo et al.
(US) 2003/0217914 A1 11/2003 Miller et al.
2004/0050690 A1 3/2004 Green et al.
(73) Assignee: Applied Materials, Inc., Santa Clara, 2005/0211548 A1 9/2005 Gung et al.
CA (US) 2011/0297538 A1* 12/2011 Miller et al. ............. 204298.16
OTHER PUBLICATIONS
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35 Miller et al., U.S. Appl. No. 13/213,367, filed Aug. 19, 2011,
U.S.C. 154(b) by 38 days. response with claims filed Jul. 29, 2013.
This patent is Subject to a terminal dis
claimer. * cited by examiner
(21) Appl. No.: 13/347,030 Primary Examiner — Rodney McDonald
(74) Attorney, Agent, or Firm — Charles S. Guenzer
(22) Filed: Jan. 10, 2012 (57) ABSTRACT
(65) Prior Publication Data A control system and method for controlling two motors
US 2012/O1038OO A1 May 3, 2012 determining the azimuthal and circumferential position of a
magnetron rotating about the central axis of the Sputter cham
ber in back of its target sputtering and capable of a nearly
Related U.S. Application Data arbitrary scan path, e.g., with a planetary gear mechanism. A
system controller periodically sends commands to the motion
(63) Continuation of application No. 1 1/948,118, filed on controller which closely controls the motors. Each command
Nov.30, 2007, now Pat. No. 8,114,256. includes a command ticket, which may be one of several
values. The motion controller accepts only commands having
(51) Int. Cl. a command ticket of a different value from the immediately
C23C I4/35 (2006.01) preceding command. One command selects a scan profile
(52) U.S. Cl. stored in the motion controller, which calculates motor sig
USPC ............ 204/192.13; 204/192.12; 204/298.03; nals from the selected profile. Another command instructs a
204/298.19; 204/298.2 dynamic homing command which interrogates sensors of the
(58) Field of Classification Search position of two rotating arms to determine if the arms in the
USPC ............... 204/298.03, 298.19, 298.2, 192.12, expected positions. If not, the arms are rehomed.
204/192.13
See application file for complete search history. 10 Claims, 7 Drawing Sheets

Mechatrolink
-58

156 36 14

50

Motion
Controller

Air

152 t
Diet System
Controller
U.S. Patent May 13, 2014 Sheet 1 of 7 US 8,721,847 B2

Mechatrolink

15O

Controller * St
4lut |E - Y1

22 18
48

33% 80
62 6) N-1;
%.
88
152
System
Dnet Controller

FIG 1
U.S. Patent May 13, 2014 Sheet 2 of 7 US 8,721,847 B2

FIG 2
U.S. Patent May 13, 2014 Sheet 3 of 7 US 8,721,847 B2

S.

s
U.S. Patent May 13, 2014 Sheet 4 of 7 US 8,721,847 B2

118

FIG 4
U.S. Patent May 13, 2014 Sheet 5 Of 7 US 8,721,847 B2
U.S. Patent May 13, 2014 Sheet 6 of 7 US 8,721,847 B2

80H)------—
401 NA4
NCY |\ \Y A NNY4
O HAIAH Y 'W | Y | | 'W ||
-40 | | | | |A| \| A H
-BOIN. . . . . . .
Time RC
U.S. Patent May 13, 2014 Sheet 7 Of 7 US 8,721,847 B2

2OO

2O2

Move M2 2O4.
(To Ignite Position)
Move M2 2O6
(To Initial Position)
Run Profile
FIG 9
 US 8,721,847 B2
1. 2
HOMING OF ARBTRARY SCAN PATH OF A spins about an pivotaxis at an end of the inner arm and has a
ROTATING MAGNETRON magnetron mounted on its end offset from the pivotaxis. The
described PMR system includes a planetary gear mechanism
RELATED APPLICATION with a Sun gear fixed at the target center and coupled to a gear
rotating on the pivotaxis and Supporting the second aim. The
This application is a continuation of Ser. No. 1 1/948,118, planetary gear mechanism produces a multi-lobed scan pat
filed Nov.30, 2007, issue fee paid and incorporated herein by tern in which the radial extent of the scan pattern and the
reference. number of lobes is established by the lengths of the two arms
FIELD OF THE INVENTION 10
and the gear ratio of the gear mechanism. Although this scan
pattern has been quite effective in advanced sputtering appli
The invention relates generally to sputtering of materials. cations, the lobed scan pattern may not be the optimal one and
In particular, the invention relates to the control of the scan it is desired to change the scan pattern without changing
path of a magnetron in back of a plasma sputtering target. physical parts of the scan mechanism.
15
BACKGROUND ART SUMMARY OF THE INVENTION

Sputtering, alternatively called physical vapor deposition A system and method control two motors causing the
(PVD), is the most prevalent method of depositing layers of movement of a magnetron along a nearly arbitrary path on the
metals and related materials in the fabrication of semiconduc back of a sputtering target. A system controller periodically
tor integrated circuits. The commercially most important sends command to a motion controller which interprets those
form of sputtering is plasma sputtering using a magnetron in commands and accordingly drives the two motors.
back of the Sputtering target to increase the density of the According to one aspect of the invention, each command
plasma and increase the Sputtering rate. A typical magnetron includes a command ticket which can assume one of several
includes a magnetic pole of one magnetic polarity Surround 25 acceptable values as well as a possible no-operation value.
ing another magnetic pole of the opposed magnetic polarity. The system controller may resend commands with the same
A gap of nearly constant width and forming a closed loop value of the command ticket but changes the value for a new
separates the two poles and sets up a closed plasma track command. The motion controller does not change its control
adjacent the Sputtering face of the target. of the motors upon receipt of a command unless that com
Magnetron Sputtering was originally used to deposit a 30 mand includes a command ticket with an acceptable value
nearly planar and relatively thick layer of a metal Such as other than that of the previously received command.
aluminum, which was thereafter etched into a pattern of hori According to another aspect of the invention, plural scan
Zontal interconnects. A typical magnetron used for this type ning profiles of a magnetron Scanning path are stored in the
of Sputtering has a relatively large kidney shape with the motion controller. One command is a profile command select
closely adjacent poles positioned near the periphery of the 35 ing one of the stored profiles. Upon receipt of the profile
pattern. The magnetron extends from about the center of the command, the motion controller controls the motors to
target to near its usable periphery and is rotated about the execute the selected profile.
target center to produce uniform Sputtering of the target and According to yet another aspect of the invention, the sys
hence sputter deposition on the wafer. The large size of the tem includes two sensors which can detect when respective
magnetron can produce fairly uniform target erosion and 40 arms or other members of the scan mechanism pass nearby.
uniform thickness of the sputtered layer deposited on the One command is a dynamic homing command. Upon receipt
wafer. of the dynamic homing command, the motion controller
More recently, however, magnetron Sputtering has been causes the arms to move along preselected paths and deter
extended to deposit thin, nearly conformal layers into high mines if the sensors detect the arms at the expected times. If
aspect-ratio holes formed in dielectric layers, such as Vias for 45 not, the control system rehomes the scan mechanism.
Vertical interconnects or trenches for capacitive memories.
Examples of such sputtered layers include a barrier layer of BRIEF DESCRIPTION OF THE DRAWINGS
for example, tantalum and tantalum nitride, to prevent migra
tion of metal into the underlying dielectric or a copper seed FIG. 1 is a schematic cross-sectional view of a sputter
layer to act as plating electrode and nucleation layer for 50 chamber including an embodiment of the motor control sys
copper later filled into the via hole by electrochemical plating tem for an epicyclic magnetron scanning mechanism.
(ECP). Sputtering into such deep and narrow holes relies in FIG. 2 is an orthographic view of a universal magnetron
part on a large fraction of Sputtered atoms being ionized in a Scanning mechanism.
high-density plasma adjacent the target, which can be FIG. 3 is a cross-sectional view of part of the magnetron
achieved by a small magnetron which concentrates the target 55 scanning mechanism of FIG. 2.
power to a small area of the target, thus producing a high FIG. 4 is a plan view of reservoir top wall on which the
power density and corresponding adjacent high-density magnetron scanning mechanism is mounted and providing
plasma region. It has been found that Small magnetrons mounting holes for optical sensors associated with it.
scanned near the periphery of the target effectively can none FIG. 5 is diagram of an embodiment of a motor control
theless produce a nearly uniform sputter deposition over the 60 circuit according to the invention.
entire wafer because the sputtered ions diffuse toward the FIG. 6 is a plan view of a complex profile for a magnetron
center of the wafer as they travel from the target to the wafer. Scanning pattern.
However, it is sometimes desired to sputter a wider bandon FIG. 7 is a graph illustrating the angle and radius of the
the target with a smaller magnetron. Miller et al. describe a magnetron following the profile of FIG. 6.
planetary magnetron (PMR) system in U.S. Pat. No. 6,852, 65 FIG. 8 is a schematic plan view of a model of the scanning
202, incorporated herein by reference. In the PMR system, an mechanism used to explain the operation of Some of the
inner arm is rotated about the target center and an outer arm commands.
 US 8,721,847 B2
3 4
FIG. 9 is a flow diagram of one method of operating the the clamp ring 74 or pedestal 72 and the shield 76. Other
scanning mechanism with one command protocol consistent shield configurations may include an electrically floating sec
with the invention. ondary shield inside the primary shield 76 and perforations
through portions of the primary shield 76 protected by the
DETAILED DESCRIPTION OF THE PREFERRED 5 secondary shield to promote gas flow into the processing area.
EMBODIMENTS A DC power supply 80 negatively biases the target assem
bly 18 with respect to the grounded shield 76 and causes the
Miller et al. (hereafter Miller) describe a two-shaft epicy argon working gas to be excited and discharge into a plasma.
clic magnetron scan mechanism in U.S. patent application The magnetron 42 concentrates the plasma and creates a high
Ser. No. 11/924,573, filed Oct. 25, 2007, now issued as U.S. 10 density plasma (HDP) region 82 underneath the magnetron
Pat. No. 8,021.527, and incorporated herein by reference 42 inside the main chamber 12. The positively charged argon
particularly for the detailed mechanism and scan patterns ions are attracted to the target assembly 18 with sufficient
available. According to Miller, a sputter chamber 10 sche energy to sputter the metal from the target assembly 18. The
matically illustrated in the cross-sectional view of FIG. 1 sputtered metal deposits on and coats the Surface of the wafer
includes a conventional main chamber 12 generally symmet 15 70. Preferably for sputter depositing into deep and narrow
ric around a central axis 14 and Supporting a target assembly holes, an RF power supply 84 is connected to the pedestal
18through an adapter 20 and an isolator 22. The target assem electrode 72 through a capacitive coupling circuit 86, which
bly 18 may be formed from the material to be sputtered or acts as a high-pass filter, to create a negative DC self bias on
may include a target tile facing the interior of the chamber the wafer 70 with respect to the plasma. The self bias is
body 12 and bonded to a backing plate extending laterally effective at accelerating positive metalions or possibly argon
over the isolator 22. ions toward the wafer 70 in perpendicular trajectories that
The sputter chamber 10 also includes an epicyclic scan more easily enter high-aspect holes. The self bias also imparts
actuator 26 located in the back of the target assembly 18 and a high energy to the ions, which may be controlled to differ
including an inner rotary shaft 28 and a tubular outer rotary entiate sputter deposition on the wafer 70 and sputter etching
shaft 30, which are coaxial and arearranged about and extend 25 of the wafer 70. A computer-based system controller 88 con
along the central axis 14 and can rotate about it. A first motor trols the vacuum pump 60, the argon mass flow controller 66,
32 is coupled to the inner rotary shaft 28 by a drive gear 34 or the power supplies 80, 84 and the drive circuits for the mag
other mechanical means such as a belt wrapped around two netron motors 32, 36 according to the desired sputtering
pulleys to rotate it. A second motor 36 is similarly coupled to conditions and scan patterns input to the system controller 88
the outer rotary shaft 30 through another drive gear 38 or 30 through a recordable medium such as a CDROM inserted into
mechanical means to rotate it independently of the rotation of it or equivalent communication lines.
the inner rotary shaft 28. The rotary shafts 28, 30 are coupled A more realistic version of the epicyclic scan actuator 26
to an epicyclic mechanism 40, which Supports a magnetron and attached magnetron 42 is incorporated into a mechanism
42 through a mount 44 and scans it over the back of the target illustrated in the orthographic view of FIG. 2 in what is
assembly 18 in a nearly arbitrary pattern determined by the 35 referred to as a universal magnetron motion (UMM) mecha
rotations of the rotary shafts 28, 30. The principal embodi nism 100. The UMM mechanism 100 is supported on a flange
ment of the Miller epicyclic mechanism 40 is a planetary gear 102, which is supported on and sealed to a top wall of the
system which differs from the PMR mechanism by a sun gear cooling reservoir. A derrick 104 Supported on the flange 102
which is rotated by the inner rotary shaft 28 rather than being outside of the reservoir supports a vertical actuator 106 which
fixed, as is described in more detail by Miller and will be 40 can vertically move a slider which rotatably supports the
described in lesser detail below. The magnetron 42 typically rotary shafts 28, 30 and the motors 32, 36 coupled to them
includes a magnetic yoke 46 Supporting and magnetically through ribbed belts 108, 110.
coupling an inner pole 48 of one magnetic polarity along the A sectioned side view of FIG. 3 illustrates a cooling reser
central axis 14 and an outer pole 50 of the opposed magnetic voir 114 formed in back of the target assembly 18 by a
polarity and Surrounding the inner pole 48. The magnetron 42 45 reservoir sidewall 116 and a reservoir top wall 118 on which
and large portions of the epicyclic mechanism 40 are disposed the actuator flange 102 is Supported. A water-sealed gearbox
in an unillustrated cooling reservoir of recirculating chilled 120 and its counterweight 122 are fixed to the lower end of the
sealed to the back of the target or its backing plate in order to outer rotary shaft 30 inside the reservoir 114. A sun gear 124
maintain the target assembly 18 at a reasonably low tempera is fixed to the lower end of inner rotary shaft 28 inside of the
ture. 50 case 120 but is also captured between two sets of bearings. A
Returning to the main chamber 12, a vacuum pump 60 follower gear 126 is rotatably supported between another two
pumps the interior of the main chamber 12 through a pumping sets of bearings inside the gearbox 120 and is coupled through
port 62. A gas source 64 Supplies a sputter working gas. Such an unillustrated idler gear to the sun gear 124. A shaft 128 of
as argon, into the chamber 12 through a mass flow controller the follower gear 126 passes through a rotary seal on the
66. If reactive sputtering is desired, for example, of a metal 55 bottom of the gearbox 120 and is fixed to a magnet arm 130
nitride, a reactive gas, such as nitrogen in the example, is also such that the magnet arm 130 is rotated by the follower gear
Supplied. 126. The magnetron 42 and its counterweight 132 are fixed to
A wafer 70 or other substrate is supported on a pedestal 72 opposed ends of the magnetarm130. The gearbox 120 acts as
configured as an electrode in opposition to the target assem an inner arm and the magnet arm 130 acts as the outer arm
bly 18. A clamp ring 74 may be used to hold the wafer 70 to 60 which in conjunction with the Sun and follower gears 124,126
the pedestal 72 or to protect the pedestal periphery. However, act as a planetary gear mechanism.
many modern reactors use electrostatic chucks to hold the The two separately controlled rotary shafts 28, 30 allow the
wafer 70 against the pedestal 72. An electrically grounded magnetron 42 to be scanned in a nearly arbitrary pattern.
shield 76 supported on the adapter 20 protects the chamber However, this wide control requires that the two motors 32,36
walls and sides of the pedestal 72 from sputter deposition and 65 be closely controlled together. That is, for many more com
also acts as an anode in the plasma discharge. The working plicated scan patterns, the rotation of one motor must be
gas enters the main processing area through a gap 78 between closely synchronized with that of the other motor. If the
 US 8,721,847 B2
5 6
timings of the rotary shafts 28, 30 begin to drift apart, for an optical sensor, such as an Omron E3T-SR21, which both
example, if one of the ribbed belts 108, 110 slips, the scan emits a beam of light and receives a reflected beam from the
pattern rapidly degrades. reflector 142 associated with the magnet arm 130 to establish
A further problem with the independent control of the two a position of the magnet arm 130. Similarly, the motor drive
rotary shafts 28, 30 is that their relative rotation phase needs 5 156 for the gearbox 120 drives the associated motor 36, also
to be established and maintained. Following the Miller a servo motor, over a drive line 170 and receives a feedback
design, as illustrated in the plan view of FIG. 4, the top signal from the encoder of the servo motor 36 over a feedback
reservoir wall 118 includes a central aperture 134 around line 172. The motor 36 for the gearbox 120 will be referred to
which the actuator flange 102 is sealed and passing the rotary as M1. The gearbox motor drive 156 also receives over a
shafts 28, 30 into the reservoir 114. The top reservoir wall 118 10 detection line 176 from a sensor 174 such as the previously
also includes a first sensor aperture 136 offset from the central described optical sensor a detected reflected beam from the
axis 14 for a gearbox sensor and a second aperture 138 at a reflector 140 associated with the gearbox 120 to establish an
different radius from the central axis 14 for a magnet arm angular position of the gearbox 120.
sensor. In this design, the sensor apertures 136, 138 are One mode of controlling the scan paths through the control
located 15° apart at two different radii with respect to the 15 circuitry 160 of FIG.5 includes instructing each of the motors
central axis 14. The sensors which are inserted into the sensor 32.36 to rotate at respective rotation rates once the associated
apertures 136, 138 enable a homing function to establish and arms have been positioned with the desired phase between
then monitor the rotation state of the two planetary arms. The them. For example, if the arm motor 32 is instructed to be
sensors optically sense reflectors 140, 142, shown in FIG. 3, stationary while the gearbox motor 36 rotates at a set rotation
mounted respectively on tops of the counterweights 122 and rate, the resulting scan path is that of the previously described
132, which are respectively angularly fixed with respect to the PMR scan system with a fixed Sun gear. In another example,
gearbox 120 and magnet arm 130. if the arm and gearbox motors 32, 36 are instructed to rotate
Once the two arms have been homed, the timing or relative at the same rate in the same direction, the magnetron traces a
phase of their rotations needs to be maintained. In one circular path about the target center 14 with the radius deter
embodiment for improving the synchronism, a computer 25 mined by the initial phase between the two arms.
based motion controller 150, shown in FIG. 1, is interposed Both of these simple patterns could be easily achieved with
between the system controller 88 and the motors 32, 36 driv the use of the intermediate motion controller 150. However,
ing the rotary shafts 28, 30. For example, a DeviceNet (Dnet) the relatively slow cycle time of the Dnet controller 58 creates
communication link 152 transfers commands from the sys difficulties with more complex scan patterns. For example, a
tem controller 88 to the motion controller 150. The Dnet 30 scan pattern 180 illustrated in FIG. 6 includes a generally
communication system is a well known industrial computer circular scan about the target center 14 near the target periph
ized control system demonstrating high reliability and rug ery and two smaller, somewhat circular scans offset from the
gedness. The motion controller 150 in turn controls two center 14, all to be performed in a few seconds. A similar scan
motor drives 154, 156 over a communication link 158, for pattern is portrayed in the graph of FIG. 7 in which trace 182
example, based on the well known Mechatrolink. In general, 35 plots the angular position in degrees of the center of the
the motion controller 150 sends different sets of motion con magnetron as a function of time and trace 184 plots its radial
trol signals to the two motor drives 154, 156 indicating the position in units of 0.1 inch (2.54 mm). The angle trace 182
respectively required motion of the two motors 32, 36. The shows the points of a profile. The radius trace 182, though
motor drives 154, 156 respectively drive the two motors 32. illustrated as continuous, includes corresponding profile
36 with the required phase between the rotations of the motors 40 points. This complex scan pattern needs closer control than
32, 36. that afforded by the Dnet communication protocol when the
The system controller 88 sequentially polls the various rotation rate is in the typical range of 60 rpm.
elements under its control by transmitting the current control In one embodiment of the invention, the system controller
setting to the respective element. The polling period is on the 88 periodically polls the motion controller 150 on a somewhat
order of a second or somewhat less, which is not satisfactory 45 coarse time scale while the motion controller 150 much more
for direct Dnet control of the two motor drives 154, 156. tightly and quickly controls the motor drives 154, 156. The
Instead, the motion controller 150 receives the current Dnet polling may include both commands to the motion controller
control setting, interprets it, and accordingly performs rapid 150 and interrogations of it to determine status of the ele
and nearly continuous control of the motor drives 154, 156. ments associated with it. An example of a command format
A motor control circuitry 160 is shown in more detail in the 50 for a command sent from the system controller 88 to the
schematic diagram of FIG. 5. The motion controller 150, motion controller 150 is presented in TABLE 1. The com
which may be a Yaskawa MP2300, is powered by a 24VDC mand consists of 8 bytes each of 7 bits.
supply and communicates with the system controller 88 over
the Dnet communication link 152. Each of the motor drives TABLE 1
154, 156, which may be a respective Yaskawa SGDS 55
Byte Bit-7 Bit-6 Bit-S Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
08A12A, communicates with the motion controller 150 over
a Mechatrolink communication link 158. Each of the motor O Command Ticket Command Code
drives 154, 156 is powered from a 208 VAC supply required 1. Enable Hard
for the motors 32.36 and also from a 24VDC supply needed Stop
2 Command Data
for the sensors. The motor drive 154 for the magnet arm 130 60
3 Command Data
drives the associated motor 32, which in this embodiment is a 4 Command Data
servo motor, over a drive line 162 and receives a feedback 5 Command Data
signal from the encoder of the servo motor 32 over a feedback 6 Spare
7 Spare
line 164. The motor 32 for the magnet arm 130 will be
referred to in the software explanation as the M2 motor. The 65
arm motor drive 154 also receives a detection signal from a Two bits of the 0 byte present the command ticket. The
sensor 166 over a detection line 168. The sensor 166 may be command ticket accommodates the difference between the
 US 8,721,847 B2
7 8
relatively infrequent polling between the system controller 88 ciated reflectors 142,140. This command may be issued prior
and the much quicker and tighter control of the motor drives to continued production operation. An illustrative example of
154,156 taking into account that the polling includes the most the homing procedure is illustrated at the 3 o'clock position in
recent command even if that command is already being the schematic plan view of FIG. 8, in which an inner arm 190
executed. The command code may assume any of four values rotates about the central axis 14 of the target assembly 18 and
00, 01, 10, 11. The 00 command ticket is a NOP, that is, to be an outer arm 192 rotates about a pivotaxis 194 near the distal
ignored. Both the system controller 88 and the motion con end of the inner arm 190 and supporting an unillustrated
troller 150 keep track of the sequence of commands which magnetron near the distal end of the outer arm 192. The inner
have recently been sent. The system controller 88 in each arm 190 corresponds to the gearbox 120, the outer arm 192
polling period sends a command. If the command is the same 10 corresponds to the magnet plate 130, and the pivot axis 194
as in the last polling period, the command ticket remains the corresponds to the axis of the shaft of the follower gear 126.
same. If the command changes from the last polling period, The sensors 166, 174 are positioned over the rotatable arms
the system controller 88 changes the command ticket to a new 190, 192. The inner sensor 174 will trigger for every rotation
of the outer rotary shaft30. The object is to position the arms
value among the three active values 01, 10, 11. The command 15 190, 192 under their respective sensors 174, 166 to initialize
ticket values do not necessarily have to cycle regularly their positions. The outer sensor 166 will trigger for every
through the three allowed values. That is, a command ticket of rotation of the inner rotary shaft 28 but only when the two
01 or 11 following a previous command ticket of 11 will be arms 190, 192 are aligned. The figure assumes that the home
interpreted as a new command ticket to be processed. On the position in the one in which the arms 190, 192 in their home
other end, when the motion controller 150 receives a com positions are parallel with maximal extent of the outer arm
mand with a command ticket of the same value as the last
192 and does not include the complexity of the planetary gear
receive command ticket, it is basically ignored since the com mechanism of FIGS. 2-4 that the sensors 166, 174 are not
mand has already been processed. arranged along a single radius and that the reflectors 140, 142
The 6-bit COMMAND CODE instructs the motion con
troller 150 to perform one of many operations, several of associated with the arms 190, 192 may be located at different
which will be described later.
25 angular positions, for example, on the counterweights located
across the central axis 14.
An active ENABLE bit turns on both the M1 and M2 servo
drives. The ENABLE bit should be turned inactive whenever
The homing procedure first begins with the motion con
drive engagement is undesirable, such as when changing troller 150 instructing the gearbox motor 36 to rotate the inner
parts or when a hardware interlock indicates an operational arm 190 until the inner sensor 174 indicates its underlying
problem. An active HARD STOP bit acts an EMO, that is, position. The sensor detection may be slow so that it is nec
stop operation as quickly as possible. The motors are stopped essary for the procedure to hunt for the inner home position by
at their maximum deceleration. The HARD STOP overrides subsequent back and forth movement of the inner arm 190
the ENABLE. across the position of the inner sensor 174 until an inner home
position is established. Then, with the inner arm parked in its
The command contains 4 bytes of command data, the for 35 home position, the motion controller instructs the arm motor
mat of which depends upon the command. There are 2 bytes 32 to rotate the outer arm 192 until the outer sensor 166
of spare formatting in the command protocol awaiting further indicates its underlying position. Again, hunting for the outer
development of the protocol. home position may be required. The result is the illustrated
An initial and exemplary set of command codes are present home positions of the two arms 190, 192 from which all
in TABLE 2. Although the command code is defined by six 40 Subsequent movement is referenced.
bits, the tabulated 16 command codes are numbered in hexa A ''2''' command code indicates a ROTATE command,
decimal and require only four bits. which instructs the two motors 32, 36 to rotate at the samerate
TABLE 2
in the same direction. For a planetary gear system, equal
rotation means that the two arms 190,192 rotate in parallel so
COM 45 that, as illustrated in the 12 o'clock position in FIG. 8, the two
CODE DEFINITION arms 190, 192 remain aligned. If the ROTATE command is
NOP
issued while the arms 190, 192 are out of phase, that is, not
HOME aligned, the Subsequent synchronous rotation maintains the
ROTATE phase between the arms 190,192 during subsequent rotation.
STOP 50 A '3” command code indicates a STOP command, which
MOVEM2
PROFILE
stops the rotations of the motors 32, 36 if they are indeed in
CONFIRMHOME
motion.
SPIN M2 A “4” command code indicates a MOVE M2 command,
STOP SPIN M2 which causes the motor 32 to move the outer aim 130 to a
MOVEM1 55 phase angle, specified in the data field of the command, rela
CLEARAL.ARM
SET ROTATION ACCEL tive to the angular position of the gearbox 120. For example,
SET MOVEM2 ACCEL ifa MOVEM2 command were issued after the arms had been
SET MOVEM2 SPEED positioned in the 12 o'clock position of FIG. 8 such that the
SET SPIN M2 ACCEL
GET
outer arm 192 would move in a retrograde motion to a new
60 angular position relative to the inner arm 190, a resultant
positioning is shown in the 9 o'clock position in which the
A “0” command code indicates a NOP, that is, to be outer arm 192 is now perpendicular to the inner arm 190 with
ignored. its distally supported magnetron well inside the periphery of
A “1” command code indicates a HOME command to the target assembly 18.
establish initial conditions for the angular positions of both 65 A “5” command codes indicates a PROFILE command,
the motors 32, 36 and hence of the magnet arm and the which greatly facilitates the control of complex scan patterns
gearbox with the use of the sensors 166, 174 and their asso with a relatively slow system controller 88. The scan pattern
 US 8,721,847 B2
10
180 of FIG. 6 can be decomposed into a number of sections profiles may be pre-loaded into the motion controller 150 to
190 connected between adjacent profilepoints 192. The PRO be selected by the system controller 88.
FILE command in essence allows the motion controller 150 One process for scanning a magnetron in accordance with
to consult a locally stored profile pattern based on the profile a stored profile is illustrated in the flow diagram of FIG. 9. In
points 192 to instruct the motors 32, 36 to cause the magne step 200, the HOME command causes both motors and their
tron to be scanned along the desired profile 180. associated arms to home to their home positions. It is not
Multiple profiles may be pre-loaded in the motion control necessary that the home positions correspond to maximal
ler 150. Two bytes of command data in the data command extent of the arms, only that their positions be known. In step
may be used to select which of the stored profiles is to be used. 202, the ROTATE command causes both motors and hence
Two more bytes of command data may be used to indicate a 10 their arms in the case of a planetary gear mechanism to rotate
profile factor, which represents the total run time of the pro at a same rate, for example, 60 Hz, thus producing a circular
file, for example, in millisecond. scan of the magnetron about the central axis. In step 204, the
MOVE M2 command instructs the outer arm to move the
The profiles may be stored in the memory of the motion magnetronto a position facilitating ignition of the plasma, for
controller 150 in various forms. However, one convenient 15 example, near the chamber wall at the target periphery. Once
format illustrated in TABLE3 for a scan pattern similar to that system controller 118 has caused the plasma to be ignited and
of FIGS. 6 and 7 includes a series of except for the first entry, has changed the target power to the desired level begin sput
paired values of time, for example, enumerated in seconds, tering, in step 206, a MOVEM2 command instructs the outer
and a phase angle of the outerarm 192 relative to the inner aim arm to move to an initial position. In step 208, a PROFILE
190. Other scan patterns are also stored in the motion con command instructs the movement of the magnetron accord
troller 150. ing to a designated scan path for a designated length of time.
At the completion of the PROFILE step 208, the system
TABLE 3 controller 118 causes the plasma is extinguished so that sput
401 O
tering is stopped and control returns to the ROTATE step 202.
O O 25 During this period, the wafer processed according to the
O.OO2S O profile is removed from the chamber and replaced by a fresh
O.OOS O wafer. Generally, sputtering uniformity is improved if the
0.0075 O
O.O1 O
magnetron is returned at the end of the profile to the same
radial position as at the beginning of the profile, that is, the
30 same phase between the arms as specified in the second
O.13 O
column of the profile table.
O.1325 2O
It is desirable that the scan pattern, for example, of FIG. 6
O.13S 78 or 7 be triggered by the PROFILE command and not be
0.1375 176 referenced to a set angular position on the target assembly 18
35 so that the start azimuth is randomized. The traces 182, 184 of
FIG. 7 can be referenced to an initial angular position at time
O.995 36OOOO equal to Zero and change from the actual angular occurring at
0.9975 36OOOO that time. Typically, azimuthal angle during processing of a
1. 36OOOO wafer is not important as long as properaveraging is achieved,
40 but it is desired that the target sputtering be azimuthally
The first entry in the table indicates the number of position averaged to prevent local over Sputtering, for example,
data to follow in the table. In the remainder of the table, the between the areas of the illustrated tracks if they were
first column indicates a time, for example, in seconds with a repeated for each wafer.
A “6” command code indicates a CONFIRMHOME com
total elapsed time of is with a constant time difference in 2.5 45 mand, which is somewhat similar to a HOME command but
ms between the entries, and the second column indicates a is performed on the fly, that is, while the arms are rotating at
phase angle between the outer arm and the inner arm, for operational rates to determine that synchronization has not
example, in units of milli-degrees. The table may be extended been lost between the motors because of belt slippage or other
for longer scan times, for example, a typical 4S. The indicated reasons. The operation on the fly is quicker than the home
pattern controls the magnetron to first scan in a generally 50 operation, for example, 2 or 3 seconds versus 1 minute for the
circular pattern near the periphery of the target before chang HOME command and also indicates if there is a problem with
ing to a more complex pattern, which ends up with another loss of the original homing position.
outer circular scan. The operation of the CONFIRM HOME command
The motion controller 150 normalizes the 1-sec period of assumes that the motors and arms are synchronously rotating
the stored trajectory according to the profile factor included in 55 according to the ROTATE command. The M2 motor 32 is
the data field of the PROFILE command. The rotation rate of instructed to move the magnetarm130 to a position where its
the inner arm 190, to which the rotation of the outer arm 192 reflector 142 should pass under the associated sensor 166.
is referenced by the PROFILE command, may be set by a The magnet arm sensor 166 should be triggered once per
preceding ROTATE command. The motion controller 150 revolution with a few degrees of the rotary position based on
may perform a calculation from the profile table to determine 60 the previous homing operation. If not, an alarm is flagged and
at what rate the motor for the outer arm 182 needs to rotate to trouble shooting is required. The magnet aim sensor 166
move the magnetron from the previous position in the profile should similarly be triggered once every revolution. If not, an
table to the next position. The rotation rate set by the ROTATE alarm is flagged and a HOME command is issued to rehome
command determines the length of time for the scan pattern the motor drives 154, 156. If homing is confirmed for two
set by the PROFILE command. More complicated paths 65 consecutive rotations, the magnet arm 130 is returned to its
between two or more neighboring points on the selected original position and rotation continues until instructed oth
profile may be calculated. Significantly different multiples erwise.
 US 8,721,847 B2
11 12
A “7” command code indicates a SPIN M2 command, controlled to effect a nearly arbitrary scanning pattern, par
which allows the magnet arm 130 to rotate at a different rate ticularly if the motors need to be asynchronously operated.
and even direction than the gearbox 120, that is, to rotate The motors may be of types other than servo motors. The
asynchronously. Its four bytes of date specify the speed of the communication links are not limited to the types described,
M2 motor 32 for the magnet art 130. The speed date is signed 5 but the invention provides significant advantages when the
and a negative value indicates reverse or retrograde rotation communication link to the motors operates significantly
relative to the gearbox 120. faster than the link to the host controller.
An “8” command code indicates a STOP SPIN M2 com The invention thus allows the magnetron to be scanned in
mand, which stops the asynchronous spinning of magnet arm complex patterns without a significant upgrade or even modi
130 resulting from the SPIN M2 command. Instead, the M2 10 fication of the system controller. The invention also provides
motor 32 is instructed to rotate or at least place the magnet an efficient procedure for confirming the homing condition of
arm 130 in synchronism with the gearbox 120, that is, accord the motor magnetron without impacting the throughput of the
ing to the any previously issued ROTATE command. The system.
phase between the two motions is indicated by the angle data
included in the STOP SPIN M2 command. 15 The invention claimed is:
A '9' command code indicates a MOVE M1 command, 1. A control mechanism for controlling the movement of a
which instructs the M1 motor 32 to rotate or move the gearbox magnet assembly in a sputter chamber, comprising:
to a position indicated by the data of the MOVE M1 com a magnet assembly;
mand. This is a static operation. The state of the other, M2 a scanning mechanism including a first arm rotatable about
motor 36 does not matter. 2O a central axis and a second arm mounted on the first arm
An 'A' command code indicates a CLEARALARM code, and rotatable about a pivot axis located on the first arm
which instructs the motion controller 150 to clear any previ and Supporting the magnet assembly at a position on the
ously issued alarm flags and return to normal operation. second arm thereby allowing azimuthal and radial
A command code “B” indicates SET ROTATION ACCEL, movement of the magnet assembly about the central
which sets the ROTATION acceleration for both motors 25 axis;
according its included data. This command should be sent two motors differentially and mechanically coupled to the
before any ROTATION command is sent and remains inforce two arms;
thereafter. a first reflector disposed on the first arm and a second
“C” and “D' command codes indicate respectively a SET reflector disposed on the secondarm away from the pivot
MOVEM2 ACCEL command and a SET MOVEM2 SPEED 30 axis;
command, which set the acceleration and speed applied in the a first optical sensor positioned at a first radial distance
MOVE M2 command in moving the magnet arm 130 to a from the central axis and operatively associated with the
position specified in the latter command. first reflector;
Similarly, an “E” command codeindicates a SET SPIN M2 a second optical sensor positioned at a second radial dis
ACCEL, which sets the acceleration used in the SPIN M2 35 tance from the central axis different than the first radial
command instructing the asynchronous spin rate of the mag distance and operatively associated with the second
net arm 130. reflector; and
An “F” command code indicates a GET command, in a controller responsive to outputs of the first and second
which the system controller 88 interrogates the motion con optical sensors and controlling the two motors to control
troller 150 for the value of a piece of data specified in the data 40 relative angular positions of the first and second arms to
field of the GET command. The data may be identification of thereby control a path of the radial and azimuthal move
the motion controller 150, alarm state, or a current value of ment of the magnet assembly according to a selected one
control parameter being imposed on the motors. of a plurality of Such paths,
Even though the motion controller 150 allows complex wherein at least the second sensor is operative during
scanning patterns and rapid control of the servo motors, it also 45 execution of the selected one of the paths and the con
allows conventional scanning to be performed in which the troller responsive to the second sensor flags an invalid
servo motors are instructed to rotate at specified speeds for rotation condition of the first and second arms and the
relatively long periods of time which could be handled by first and second sensors are used to rehome the positions
system controller 88 alone. of the first and second arms.
The Dnet communication link 152 is bidirectional so that 50 2. The control mechanism of claim 1, wherein the first
the motion controller 150 not only receives instructions but reflector is disposed at the first radial distance from the central
also sends responses to the system controller 88. A response axis.
may be automatically returned after a command has been 3. The control mechanism of claim 1, wherein the second
received to inform the system controller 88 that the com radial distance is greater than the first radial distance.
manded action has been completed or perhaps that it failed 55 4. The control mechanism of claim 1, further comprising a
and accompanying data may confirm the desired operational magnet chamber sealable to a sputtering target affixable to a
parameters. The CONFIRMHOME command in particularis sputter chamber, wherein the magnet chamber includes an
expecting a response. A response may include an alarm fault upper wall facing the target and Supporting the first and sec
flag. The response may follow a GET command in which ond optical sensors and wherein the magnet chamber
requested data are returned to the system controller 88. 60 encloses the first and second arms and the magnet assembly.
A response format is similar to the command format of 5. The control mechanism of claim 1, wherein the first and
TABLE 1 but may belonger in some response types to accom second optical sensors are used to home the positions of the
modate two or more pieces of data sent to the system control first and second arms prior to execution of the selected one of
ler 88. The response advantageously includes the previously the paths.
described command ticket. 65 6. A sputter system, comprising:
The invention may be applied to other types of Scanning a vacuum chamber arranged about a central axis, including
mechanisms requiring two or more motors to be separately a pedestal for Supporting a substrate to be processed, and
 US 8,721,847 B2
13 14
configured to be fit with a sputter target assembly having 7. The sputter system of claim 6, wherein:
a front face including sputter material in opposition to the first optical sensor includes a first optical emitter and a
the pedestal; first optical detector optically couplable to the first opti
a magnet chamber fittable to a the target assembly and
including a top wall facing a back face of the target; 5 thecal emitter through the first reflector, and
second optical sensor includes a second optical emitter
a magnet assembly;
a scanning mechanism accommodated in the magnet and a second optical detector couplable to the second
chamber for scanning the magnet assembly about the optical emitter through the second reflector.
back side of the target assembly in radial and azimuthal 8. The sputter system of claim 6, wherein the controller is
directions about the central axis and including an inner 10 storable with a plurality of Scanning patterns for the move
member rotating about the central axis and an outer ment of the magnet assembly in the radial and azimuth direc
member Supported on and rotating about a pivot axis on tions and is capable of executing a selected one of the scan
the inner member, wherein the pivot axis is displaced ning patterns.
from the central axis and the magnet assembly is Sup 9. A control procedure for controlling a scanning path of a
ported on the outer member; magnet assembly mounted on an outer arm Supported on and
first and second motors driving the scanning mechanism to 15 rotatable about a pivot axis of an inner arm rotatable about a
effect the movement of the magnet assembly in the central axis displaced from the pivot axis, comprising the
radial and azimuthal directions; steps of:
a first reflector mounted on the inner member;
a first optical sensor mounted on the top wallata first radius optically detecting planetary positions of the inner and
from the central axis and capable of detecting the pres- 20 outer arms and in response thereto establishing initial
ence of the first reflector; relative rotary positions of the inner and outer arms;
a second reflector mounted on the outer member; thereafter moving the inner and outer arms to cause the
a second optical sensor mounted on the top wallata second magnet assembly to follow a first path having radial and
radius from the central axis different than the first radius azimuthal components about the central axis; and
and capable of detecting the second reflector, and 25 a Subsequent step of optically detecting a rotary position of
a controller responsive to the first and second optical detec at least the outerarm to determine ifreestablishing of the
tors and separately controlling the first and second relative planetary positions of the inner and outer arms is
motors and including a homing procedure to home the required.
positions of the inner and outer members and including 10. The control procedure of claim 9, further comprising
driving the scanning mechanism to move at least one of 30 selecting
the inner and outer members in a hunting motion in a radial andasazimuthal the first path one of a plurality of paths having
components about the central axis.
back and forth movement across the respective first and
second optical sensors. k k k k k