Apparatus for uniform chemical mechanical polishing by intermittent lifting and reversible rotation

Methods and apparatuses for evenly polishing the entire polishing surface of a sample are described. One polishing apparatus of the present invention comprises: a platen having an upper surface upon which the sample surface is to be polished; a sample holder disposed opposite to the platen's upper surface, at least one of the platen and the sample holder being rotated about a first axis to effect polishing; a positioning means for changing the distance between the sample holder and the platen in response to a control signal; and a controller providing said control signal to the positioning means to control the operation of the positioning means during a polishing cycle, wherein the controller causes the positioning means to change the distance intermittently during the polishing cycle. One method according to the present invention comprises: dispensing slurry upon a polishing pad; polishing the sample against the polishing pad; and intermittently changing the distance between the sample and the polishing pad during the polishing step.

FIELD OF THE INVENTION 
The present invention relates to chemical mechanical polishing. More 
specifically, the present invention relates to apparatuses and methods for 
uniformly polishing the surface of a sample. 
BACKGROUND OF THE INVENTION 
Chemical mechanical polishing (CMP) has been increasingly used in the 
semiconductor fabrication industry to planarize the surfaces of integrated 
circuit chips, thin-film substrates, and thick-film substrates one or more 
times during the fabrication process. For this purpose, two major 
objectives are sought: good local planarity of the polished surface in the 
vicinity of the integrated circuit chip, and good global planarity of the 
polished surface from one edge of the wafer (or substrate) to the other. 
It is known that the degree of hardness of the polishing pad affects both 
the local and global planarity. A hard polishing pad typically has good 
global planarity, but poor local planarity, whereas a soft polishing pad 
typically has good local planarity, but poor global planarity. 
The inventors have observed that the periphery of the wafer is polished 
more than the interior of the wafer. It was initially thought by the 
inventors that this effect was due to the leading edge of the wafer 
carrier digging into a soft polishing pad while it is being rotated during 
the polishing process. Attempts to remedy this problem by increasing the 
hardness of the pad have not been wholly successful. 
Accordingly, there is a need to address this uneven polishing problem. 
SUMMARY OF THE INVENTION 
In their invention, the inventors have recognized that by the time the 
polishing slurry reaches the inner portion of the wafer sample, the 
abrasive particles of the slurry are rubbed into finer sizes and/or 
pressed into pores in the polishing pad by the outer periphery of the 
wafer sample. Both of these effects reduce the polishing slurry's 
effectiveness in polishing the inner portion of the wafer sample. The 
inventors have observed that the uneven polishing problem is made worse by 
reducing the flow rate of slurry onto the platen, but only marginally 
improved by increasing the slurry flow rate. 
The present invention encompasses methods and apparatuses for evenly 
polishing the entire polishing surface of a sample by intermittently 
separating the polishing sample from the polishing pad during the 
polishing process, and preferably while slurry is being dispensed, and by 
intermittently reversing the rotation direction of either or both of the 
sample holder and the platen. The intermittent separation of the sample 
and the pad enables the interior of the polishing sample to be polished by 
fresh (i.e., unused) slurry, and the reversal of rotation directions helps 
to dislodge slurry particles that have been pressed into the pores of the 
polishing pad. 
Broadly stated, polishing apparatuses according to the present invention 
comprise a platen having an upper surface to which a polishing pad is 
attached and upon which the sample surface is to be polished, a sample 
holder disposed opposite to the platen's upper surface with at least one 
of the platen and the sample holder being rotated about a first axis to 
effect polishing, a slurry dispenser, and a positioner which changes the 
distance between the sample holder and the platen in response to a control 
signal. Polishing apparatuses according to the present invention may 
further comprise a controller which generates one or more of the following 
control signals: (1) a control signal to the positioner which is generated 
to cause the positioner to intermittently separate the polishing sample 
from the polishing pad a plurality of times during the polishing cycle, 
(2) a control signal to the motor assembly that rotates the sample carrier 
which is generated to cause the sample holder to intermittently reverse 
rotation directions at least once during the polishing cycle; and (3) a 
control signal to the motor assembly that rotates the platen which is 
generated to cause the platen to intermittently reverse rotation 
directions at least once during the polishing cycle. 
Broadly stated, methods according to the present invention comprise the 
steps of: dispensing slurry upon a polishing pad, polishing the sample 
against the polishing pad, and taking one or more of the following steps 
during the polishing step: (1) intermittently changing the distance 
between the sample and the polishing pad a plurality of times during the 
polishing step (e.g., polishing cycle), (2) intermittently changing the 
rotation direction of the sample a plurality of times during the polishing 
step, and (3) intermittently changing the rotation direction of the platen 
a plurality of times during the polishing step. 
Accordingly, it is an object of the present invention to evenly polish the 
entire polishing surface of a sample. 
These and other objects of the present invention will become apparent to 
those skilled in the art from the following detailed description of the 
invention, the accompanying drawings, and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a mixed block-schematic diagram of an exemplary polishing 
apparatus 100 according to the present invention. Polishing apparatus 100 
comprises a platen 110, a polishing pad 112 disposed on platen 110, and a 
slurry dispenser 115 which dispenses slurry onto pad 112. The polishing 
surface of a sample is polished upon the upper surface of platen 110 by 
being polished against polishing pad 112 or an equivalent thereof for 
purposes of polishing a sample. To hold the polishing sample, apparatus 
100 further comprises a sample holder 215 which holds a polishing sample 
220 (best shown in FIGS. 2 and 3), and a positioner 120 which holds sample 
holder 215 opposite to platen 110, and which moves it and polishing sample 
220 to contact the sample to the polishing pad on platen 110. As is common 
in the wafer polishing art, sample holder 215 holds sample 220 against its 
surface though the use of a vacuum, which is supplied to holder 215 by a 
vacuum source 144 through a conduit 146. Referring to FIG. 2, which shows 
a cross-sectional view of positioner 120, the vacuum is provided from 
conduit 146 to sample holder 215 by a tube 205 which passes through a 
rotating shaft 241 of positioner 120. The upper end of tube 205 is coupled 
to conduit 146 through a rotating fluid coupling 260. The lower end of 
tube 205 is coupled to a connecting space 230 within sample holder 215, 
which is in turn coupled to a plurality of vacuum ports 225 formed from 
connecting space 230 to the holding surface of sampled holder 215. Vacuum 
source 144 creates a negative pressure within tube 205, connecting space 
230 and vacuum ports 225. When the suction force on a sample 220 due to 
the negative pressure within vacuum ports 225 exceeds the weight of sample 
220, then sample 220 is held in contact with the sample holder 215, as 
shown in FIG. 2. 
Referring back to FIG. 1, polishing apparatus 100 further comprises a 
controller 130, a first motor drive assembly 132, and a second motor drive 
assembly 134. Motor drive assemblies 132 and 134 rotate platen 110 and 
positioner 120, respectively, about first and second axes, respectively. 
Motor drive assemblies 132 and 134 are responsive to direction control 
signals received from controller 130 and rotate platen 110 and positioner 
120, respectively, in either the clockwise or counterclockwise direction 
based on the direction control signals they receive. Platen 110 and/or 
positioner 120 are rotated about a first axis, such that one of the platen 
and the positioner is rotated with respect to the other, to effect 
polishing a sample held by the sample holder 215. Motor drive assemblies 
132 and 134 are also responsive to ON/OFF control signals from controller 
130 which instruct the motor drive assemblies whether or not to turn their 
respective components. These signals, for example, enable one of the 
platen or the sample holder to remain fixed while the other rotates. 
Referring to FIG. 2, positioner 120 comprises a rotating outer frame 240 
which receives sample holder 215, and a rotating shaft 241 which is 
attached to, or integrally formed with, housing 240. As described in 
greater detail below, shaft 241 is rotated by motor drive assembly 134, 
which in turn drives housing 240. To rotate sample holder 215, housing 240 
comprises a plurality of pin members 242 which fit into corresponding 
apertures 217 having slightly larger diameters. The pin members 242 lock 
the rotational motion of sample holder 215 to that of housing 240, but 
enable sample holder 215 to freely move in the vertical axis, and to tilt 
in the horizontal axes at small angles if polish sample 220 is tapered. If 
desired, apertures 217 may be lined with TEFLON sleeves to reduce 
friction. Also if desired, pin members 242 may include ball-shaped ends to 
enable a greater range of horizontal tilt. In such a case, apertures 217 
may be lined with needle bearings or roller bearings. 
Positioner 120 further comprises a course position adjuster 280, which is 
described in greater detail below, and a fine position adjuster, which is 
generally indicated at number 200 in FIG. 2. Fine adjuster 200 preferably 
comprises an expandable fluid chamber 235 positioned above sample holder 
215. The volume of fluid chamber 235 is defined by the upper surface of 
sample holder 215, the lower surface of outer frame 240, and the inner 
sidewalls of frame 240. An O-ring 236, or sealing member, is disposed 
between sample holder 215 and the inner sidewalls of frame 240 in a 
grooved recess of holder 215. O-ring 236 makes chamber 235 substantially 
air-tight, but enables sample holder 215 to freely move in the vertical 
axis and to tilt in the horizontal axes. When a fluid having a pressure 
greater than atmospheric pressure is coupled to chamber 235, sample holder 
215 is pushed toward platen 110, and chamber 235 expands. When the 
pressuring fluid is decoupled from chamber 235, a plurality of springs 245 
disposed between sample holder 215 and housing 240 push sample holder 215 
away from platen 110. In the down position, the downward pressure exerted 
on the upper surface of holder 215 by the fluid plus the gravitation force 
(i.e., weight) of sample holder 215 and sample 220 equals the upward force 
applied by springs 245 plus the upward force applied to sample 220 by the 
polishing pad. 
Referring to FIG. 1, the pressurizing fluid for chamber 235 is provided by 
a source 142, which may for example comprise a pump or compressor. In a 
preferred embodiment, the pressurizing fluid is in the gaseous state and 
may, for example, comprise compressed air. Source 142 is coupled to 
chamber 235 through a pressurizing valve 136 and a conduit 137, as shown 
in FIG. 1, and further through a rotary coupling 265 and a bore 210 
through shaft 241, as shown in FIG. 1. A side port 211 couples bore 210 to 
rotary coupling 265. Valve 136 is opened to couple fluid to chamber 235 to 
move sample holder 215 toward platen 110 until a desired position is 
achieved, and then valve 136 is closed to maintain the desired position. 
The desired position corresponds to a pressure per square centimeter 
within the chamber, and typically the process designer specifies the 
pressure per square centimeter (or other square unit) rather than the 
position. Once valve 136 is closed, the pressure per square centimeter 
within conduit 137 will be the same as the pressure per square centimeter 
within chamber 235 of finer adjuster 200. Thus, the desired pressure may 
be determined by measuring the pressure within conduit 137, and apparatus 
100 includes a pressure sensor 135 for this purpose. 
FIG. 3 shows positioner 120 with chamber 235 in a pressurized state. Tube 
205 preferably comprises a flexible plastic tubing which flexes in 
response to the height changes of sample holder 215 (in this case, the 
length of tube 205 is as long as required for holder 215 to be in the 
fully-down position, and tube 205 relaxes and bows inside bore 210 when 
holder 215 is in the up position). Some fluid leakage may occur through 
rotary coupling 265 and O-ring 236, but valve 136 may be periodically 
opened and closed to replace lost fluid. 
To cause sample holder 215 to move away from platen 110, apparatus 110 
includes a pressure release valve 138 coupled to conduit 137, as shown in 
FIG. 1, which releases the pressurized fluid from the expansion chamber. 
When pressure is released, the springs move sample holder 215 away from 
platen 110. Sensor 135 provides a measurement signal to controller 130, 
and controller 130 provides control signals to valves 136 and 138, as 
shown in FIG. 1. In this way, positioner 120 causes sample holder 215 and 
sample 220, as held by sample holder 215, to move between the up and down 
positions in response to control signals from controller 130. By 
monitoring the valve from pressure sensor 135 while filling chamber 235 
with pressurizing fluid, valve 136 may be closed, or otherwise operated, 
to provide a desired amount of pressure between polish sample 220 and 
platen 110. 
Referring to FIG. 2, motor drive assembly 134 comprises a motor 250 which 
is attached to a stationary housing 252 by a bracket 251. A motor gear 253 
is attached to the shaft of motor 250, and motor gear 253 engages with a 
ring gear 254 which is attached (e.g., press fitted) on a drive 
cylindrical 255. Drive cylinder 255 surrounds a portion of shaft 241 and 
is spaced therefrom by a sleeve bearing 256. A set of deep-groove bearings 
257 attaches drive cylinder 255 to stationary housing 252, and enables 
drive cylinder 255 to rotate as it is being driven by motor 250 and ring 
gear 254. Drive cylinder 255 rotates shaft 241 and, at the same time, 
enables shaft 241 to move in the vertical direction by an amount 
sufficient to lower housing 240 to near contact with platen 110 and to 
raise it away from platen 110. The drive is accomplished by one or more 
keys 258, each of which securely fits into a keyset 259 of drive cylinder 
255 and a keyset 249 of shaft 241. Keyset 249 has a longer length than key 
258, which enables shaft 241 to freely move in the vertical direction as 
it is being rotated by drive cylinder 255 and keys 258. A cap member 262 
may be used to lock key 258 to keyset 259. 
It may be appreciated that motor drive assemblies other than that shown in 
FIG. 2 may be used in practicing the present invention. The only feature 
of the drive assembly 134 required by some of the embodiments of the 
present invention is that the rotation direction be reversible. While 
conventional CMP equipment is not designed to allow the user to reverse 
the rotation of the motor drive, many of these systems employ DC motors 
for motor 250, which can be reversed in direction by reversing the 
polarity of the applied voltage to the motor. The standard electrical 
coupling to the DC motor is replaced by one specifically designed to 
enable application of reverse polarity. An exemplary voltage drive circuit 
for DC motors is described in greater detail below with reference to FIG. 
8. Many AC motors may also be similarly reversed by reversing the hot and 
neutral lines to the motor. While reversing the motor polarity is the more 
preferred way of achieving reverse rotation, it may be appreciated that 
reverse rotation may be achieved by mechanical components which enable the 
motor to only rotate in one direction. For example, an idler gear may be 
interposed between motor gear 253 and ring gear 254. 
Referring to FIG. 2, shaft 241 is moved in the vertical direction by course 
positioner 280. A ring member 281 is attached to shaft 241, such as by hot 
press fitting, and provides a point at which positioner 280 may move shaft 
241. Below ring member 281 is a stationary platform 284 which is coupled 
to ring member 281 by a thrust bearing 283. Thrust bearing 283 enables 
ring member 281 to freely rotate with respect to stationary platform 284, 
and enables platform 284 to move upward to move both ring member 281 and 
shaft 241 upward in the vertical direction against their weight. When 
platform 284 moves down, ring member 281 and shaft 241 move down as well, 
due to their weight. Stationary platform 284 is raised and lowered by a 
lever 286, which is attached at a fulcrum member 287. The far end of lever 
286 is moved by a motor 288, which has a worm gear drive on its shaft. A 
corresponding nut member 289 is provided in the far end of lever 286 to 
receive the worm gear. Nut member 289 has a gimbal attachment to lever 286 
which enables it to keep level with the worm gear drive while lever 386 
sweeps through its arc of motion. 
It may be appreciated that other course positioning means may be employed, 
such as that shown in U.S. Pat. No. 5,441,444 to Nakajima. The present 
invention does not require course positioner 280 since the positioning 
used by the present invention is provided by fine positioner 200. However, 
one may use course positioner 280 as a replacement or supplement to fine 
positioner 200 to provide the position changing used in the present 
invention. 
Referring now to FIGS. 1 and 5, based on a sequence of control 
instructions, such as those shown in FIG. 5, controller 130 issues control 
signals to motors 132 and 134 which control the rotational speed and/or 
direction of the motors. The control signals cause motors 132 and 134 to 
intermittently vary the rotational speed and direction of platen 110 and 
sample holder 215, respectively. Controller 130 also provides control 
signals to pressurizing valve 136 and release valve 138 to intermittently 
change the distance between the sample holder 215 and platen 110 during a 
polishing cycle. In response to the control signals received from 
controller 130, pressurizing valve 136 and release valve 138 cause a 
change in the distance between the platen and the sample holder 215. 
FIG. 4 shows a block diagram of an exemplary controller 300 according to 
the present invention which may be used to implement controller 130. 
Controller 300 comprises a processing unit 305, a memory unit 315, a timer 
320 and a user interface unit 325. Processing unit 305 includes 
analog/digital (A/D) converter 310. At port 331 processing unit 305 is 
supplied with information about the pressure within the positioner from 
sensor 135. Ports 332 and 333 are used to supply signals to control 
pressurizing valve 136 and release valve 138, respectively. Ports 334 and 
335 are used to send ON/OFF signals and motor direction signals, 
respectively, to motor drive assembly 132, which drives platen 110. 
Similarly, ports 336 and 337 are used to send ON/OFF signals and motor 
direction signals, respectively, to motor drive assembly 134, which drives 
positioner 120 and sample holder 215. Memory unit 315 stores a sequence of 
instructions on the rotation speeds and directions of motor drive 
assemblies 132 and 134, the position of positioner 120, and the time 
period during which certain of the instructions are in effect. The 
instructions are configured by the machine operator to any desired form 
through user interface unit 325, which may comprise a simple operating 
system, such as the Disk Operating System (DOS), running a text editor and 
an execution program. The text editor is used to input the desired 
sequence of instructions into a text file, and the execution program reads 
the text file and generates control signals at ports 332-337 to implement 
the user's instructions. Such text editors are readily available on DOS 
and other operating systems, and the execution steps of an exemplary 
execution program, which may be written in the BASIC language or another 
computer programming language, are described below with reference to FIG. 
6. 
Timer 320 of controller 300 provides an electronic signal representative of 
time which is used by the execution program to time the length of the 
instructions. For ease of use, timer 320 is preferably a count-down timer. 
After being initially set with a value representing a desired number of 
seconds for the time period, a countdown timer counts down one second at a 
time to a value of zero, at which point it stops. The value of timer 320 
may be read by processor 305 at any time. If desired, timer 320 may count 
down in other time units, such as for example tenths of seconds. 
Processing unit 305 generates control signals at output ports 332 to 337 in 
response to the sequence contents of memory unit 315, the output of timer 
320, and the output of pressure sensor 135, as provided in digital form by 
A/D converter 310. Thus, at selected times, as determined by the timer 
320, processing unit 305 sends the appropriate signals to the pressure 
valve, the release valve, the platen motor and the positioner/sample motor 
in response to the signal received from the pressure sensor via terminal 
331 and the corresponding control signals stored in memory unit 315. 
FIG. 5 shows an exemplary sequence of instructions to be followed by an 
execution program of controller 305. These instructions are held in memory 
315, and the instructions may be of two types: a settings-control (S.C.) 
instruction, and a flow-control (F.C.) instruction. Instructions 1-4 and 
6-9 in FIG. 5 are settings-control (S.C.) instructions, and instructions 5 
and 10 are flow-control (F.C.) instructions. An S.C. instruction specifies 
the settings of motor assemblies 132 and 134 and positioner 120 for a 
specified period of time. F.C. instructions enable the user to selectively 
repeat one or more groups of S.C. instructions, and to formally end a file 
of S.C. instructions at any point. The execution program reads these 
instructions from the user's file, and executes them, preferably one at a 
time, and preferably starting with the first instruction. The user's file 
may have any number of these instructions. 
Referring to FIG. 5, the first field of each instruction specifies the type 
of instruction, S.C. or F.C. The second field of an S.C. instruction 
indicates the time period over which the instruction's settings are to be 
used, and the third field thereof indicates whether sample holder 120 is 
to be dis-engaged (e.g., intermittently lifted) from platen at the 
beginning of the S.C. instruction for a short period of time. The 
remaining fields of an S.C. instruction give the ON/OFF states and 
direction states for motor assemblies 132 and 134 during the instruction. 
The abbreviation C.W. indicates clockwise rotation and C.C.W. indicates 
counter-clockwise rotation. The second field of a flow-control (F.C.) 
instruction indicates the type of flow control operation, such as an 
instruction to repeat a previous set of S.C. instructions, or an 
instruction to stop the machine, which disengages the sample holder from 
the platen. A repeat F.C. control instruction is show at instruction #5 in 
FIG. 5. The third field of this F.C. instruction indicates the instruction 
at which the repeat operation is to start from, and the fourth field 
indicates how many times the repeat operation is to be done. In simple 
terms, F.C. instruction #5 specifies that S.C. instructions #1 through #4 
are to be repeated two times before proceeding to instruction #6. An "end" 
F.C. instruction, such as shown at instruction #10, causes controller 300 
to end the polishing process regardless of any instructions that may 
follow in the user's file. 
FIG. 6 is a flow diagram of the exemplary steps which the execution program 
of controller 300 may use to read and execute the instructions provided in 
the user's file, such as that shown in FIG. 5. As shown in FIG. 6, the 
process starts at block 500 and proceeds to block 502, where a program 
register "RECORD COUNTER" in controller 300 is set to a value of 1. This 
register will be used to keep track of the current instruction that is 
being read from the instruction memory and executed by processor 300. At 
block 506, the current instruction is read from memory using the value of 
the RECORD COUNTER register. If the current instruction is a flow control 
(F.C.) instruction, then the execution program takes branch 510 to block 
511, otherwise, it takes branch 540 to block 542. At block 511, if the 
instruction is an end instruction, the polishing process is ended at block 
512, otherwise the execution program proceeds to block 514, where it 
determines whether or not the instruction is a repeat instruction. If the 
instruction is not a repeat instruction, the execution program presumes 
the instruction is in error, ignores it, and then proceeds to block 560 
(via point A) to obtain the next instruction. (If new F.C. instructions 
are added, the processing of these new instructions may occur at point A.) 
If the instruction is a repeat instruction, the execution program proceeds 
to block 516, where it determines whether this is the first time through 
block 516 for the current instruction. If it is the first time through, 
the execution program proceeds to block 518, where it sets a register 
variable "REPEAT COUNTER" to the number of times indicated in the fourth 
field of the repeat instruction. If it is not the first time through, the 
execution program proceeds to block 520, where it decrements the current 
value of the register variable REPEAT COUNTER by one. Both of blocks 518 
and 520 proceed to block 522, where the execution program determines 
whether the register variable REPEAT COUNTER equals zero. If REPEAT 
COUNTER equals zero, then the execution program proceeds to block 560 to 
obtain the next instruction following the current instruction (e.g., to 
get instruction #6 after passing through instruction #5 for the last 
time). If REPEAT COUNTER is not zero, the execution program proceeds to 
block 524, where it sets the variable register RECORD COUNTER to the value 
in the third field of the repeat instruction, which is the identity (e.g., 
number) of the instruction from which the repeating operation is to start. 
From Block 524, the execution program goes to block 506 to determine the 
instruction type of repeat instruction now held by RECORD COUNTER. 
The settings-control (S.C.) instructions are processed by the execution 
program starting at block 542, as indicated above. At block 542, it is 
determined whether the record is an S.C. instruction. If the instruction 
is not an S.C. instruction, the execution program presumes the instruction 
is in error, ignores it, and then proceeds to block 560 (via point A) to 
obtain the next instruction. If the record is an S.C. instruction, the 
execution program proceeds to block 544, where it reads; from the third 
field of the instruction whether there should be a disengagement of the 
sample holder from the platen (e.g., whether the sample holder should be 
intermittently lifted) at the beginning of the instruction. If so, the 
sample holder is disengaged at block 546. In either case, the execution 
program proceeds to block 548, where the appropriate changes in the motor 
state and direction are set for both the positioner motor and the platen 
motor, and where the time period for the instruction is loaded into timer 
320. Exemplary steps for block 548 are described below with reference to 
FIG. 7. After executing the steps of block 548, motor assemblies 132 and 
134 are set in motion according to the settings of the S.C. instruction. 
Next, at block 550, the execution program determines whether the sample 
holder is to be disengaged at the beginning of the instruction, as 
specified in the third field of the S.C. instruction (this is the same 
determination as made in block 544). If so, the execution program proceeds 
to block 552, where it waits a few seconds before engaging the sample 
holder. This time delay, which may be between 2 and 10 seconds, enables 
motor assembly 134 to rotate platen 110 and cause fresh slurry to be 
spread over platen 110 before the sample holder is reengaged. From blocks 
550 and 552, the execution program proceeds to block 560, where the RECORD 
COUNTER is incremented to obtain the identity of the next instruction. 
Before proceeding from block 560 back to block 506, the execution program 
of processor 305 executes block 570, where it waits for timer 320 to count 
down the time period for the current instruction (e.g., wait for timer 320 
to reach zero). This time was set back in block 548. If the current 
instruction is a flow-control (F.C.) instruction, no time was entered in 
timer 320, and its value is already zero. Therefore, F.C. instructions do 
not incur a time delay at block 570. 
FIG. 7 shows a flow chart for exemplary detailed steps taken in block 548 
in setting the parameters for the current instruction. The process starts 
at 600 and ends at block 612. At 602, a motor "off" signal is sent to port 
334 if the direction of motor assembly 132 is to be reversed, a motor 
"off" signal is sent to port 336 if the direction of motor assembly 134 is 
to be reversed. Then there is a pause of approximately 3 seconds at 604 to 
enable each motor which is to be reversed to reduce its speed to zero. At 
block 606, new motor rotation directions are output to ports 335 and 337 
as specified by the S.C. instruction. Thereafter, at 608, a motor "on" 
signal is output to ports 334 and 336, if specified by the settings of the 
S.C. instruction, to begin rotation of the motor assemblies 132 and 134. 
At block 610, timer 320 is set with the time period in the second field of 
the S.C. instruction. 
In the polishing methods of the present invention, slurry is dispensed upon 
a polishing pad, which is preferably disposed on a platen, and thereafter, 
the sample is polished against the polishing pad. The sample is polished 
by rotating one of the polishing pad (by rotating the platen upon which 
the polishing pad is disposed) and the sample (by rotating the sample 
holder which holds the sample) with respect to the other about a first 
axis with the sample against the pad to effect polishing. 
In a preferred embodiment, the polishing pad (as well as the platen upon 
which the polishing pad is disposed) is rotated about a first axis which 
is substantially perpendicular to the upper surface (i.e., the polishing 
surface) of the platen and the polishing pad in either a clockwise or 
counterclockwise direction while the sample holder (as well as the sample 
held by the sample holder) is rotated about a second axis which is 
substantially perpendicular to the polishing surface of the sample in 
either a clockwise or counterclockwise direction. 
In a preferred embodiment the first and second axis are parallel. Also in a 
preferred embodiment, the polishing pad and the sample are rotated in 
opposite directions to more efficiently effect polishing. 
In one embodiment of the method of the present invention, the distance 
between the sample and the polishing pad is intermittently changed during 
the polishing step (e.g., polishing cycle) by intermittently moving the 
sample away from the polishing pad. In a preferred embodiment, the sample 
is periodically moved away from and towards the polishing pad every 15 to 
75 seconds during the polishing process. Also in a preferred embodiment, 
the rotational direction and/or speed of either the sample, the polishing 
pad, or both the sample and polishing pad is changed after the sample and 
polishing pad are moved away from one another and returned against one 
another. The motor speed may be changed by keeping a motor off during an 
S.C. instruction. Motor speed may also be changed by varying the magnitude 
of the voltage applied to a DC motor, and the chart of FIG. 5 may be 
expanded to include motor speeds as additional fields, and the execution 
program shown in FIG. 6 may be expanded to read these fields and generate 
appropriate control signals to the motor assemblies. For example, the DC 
motors may be controlled with the use of a programable DC voltage source. 
The addition of the speed fields enables the user to ramp the speeds 
during the polishing process by gradually incrementing (or decrementing) 
the speed values in the speed fields. 
In a preferred embodiment, the sample and polishing pad are moved away from 
each other, the direction of rotation of one or both of the polishing pad 
and the sample are changed, and the sample and polishing pad are returned 
against one another at least two times during the polishing process. 
In another embodiment, the rotational direction of one of or both the 
polishing pad and the sample is intermittently reversed. The rotational 
speed of one of or both the polishing pad and the sample may also 
intermittently changed, such as by turning off a motor assembly during an 
S.C. instruction, or by using speed fields as described above. In a 
preferred embodiment, at least one rotational direction is reversed 
periodically at a period of approximately 15 to 75 seconds. The rotational 
speed of the sample and/or polishing pad may be increased upon reversing 
the rotational direction of the sample and/or polishing pad. More 
specifically, the rotational speed is increased after moving the sample 
away from the polishing pad and before returning the sample toward the 
polishing pad. 
FIG. 8 is a circuit diagram of an exemplary motor control circuit of the 
present invention. Motor control circuit 700 comprises ON/OFF control 
circuit 710 and rotation direction control circuit 750. ON/OFF control 
circuit 710 controls the ON/OFF state of motor M, such as motor 132 or 
134, whereas rotation direction control circuit 750 controls the direction 
in which motor M rotates. 
ON/OFF control circuit 710 receives a source of high-voltage power (e.g., 
50-110 VDC) for DC motor M at its power input terminals 701 and 702. As 
shown in FIG. 8, motor M is coupled to terminals 701 and 702 by way of a 
power switching transistor 730, and a double-pole, double-through (DPDT) 
switch 780. DPDT switch 780 is used to reverse the polarity of the voltage 
applied to motor M by exchanging the connections of the motor's terminals, 
thereby changing the motor's rotation direction. DPDT switch 780 will be 
described in greater detail below. Power switching transistor 730 is used 
to selectively close the circuit between the input terminals 701 and 702 
and DPDT switch 780 and motor M, and preferably comprises an n-channel 
FET. When power switching transistor 730 is in its ON (or conducting) 
state, power is delivered to motor M. When transistor 730 is in its OFF 
state, power is not delivered to motor M. A series combination of a 
free-wheeling diode 732 and resistor 733 is coupled across the terminals 
of motor M (to the left of DPDT switch 780) to provide a current 
conduction path for the inductive motor current whenever transistor 730 is 
turned off. Such freewheeling circuits are well known to the art, and 
readily implemented by those of ordinary in skill in the art. However, it 
is important to place the freewheeling circuit at the power side (shown as 
the left side in the figure) of DPDT switch 780 rather than the motor 
side, otherwise power will short through the freewheeling circuit which 
DPDT switch is reversed. 
The conduction state of power transistor 730 is determined by its gate 
voltage, which in turn is controlled by a signal provided at a port 716, 
which receives the ON/OFF control signal for the motor from controller 300 
(or 130). The voltage of the ON/OFF signal at port 716 is generally below 
12V, and typically 5 volts and less. At least 8 volts are required to be 
applied to the gate of transistor 730 to put the transistor in a fully 
conductive state (the threshold voltage of FET power transistors is 
typically around 4 volts for an n-channel FET). Accordingly, the signal 
from port 716 should be amplified before applying it to the gate of 
transistor 730. Also, because the ground reference for the signal at port 
716 may be different than the ground voltage at terminal 702, the signal 
should be translated so as to be referenced to the ground level provided 
at terminal 702. There are a number of ways of achieving the amplification 
and translation, one of which is illustrated below. The present invention 
is not limited to any particular way of achieving the aforementioned 
amplification and translation. 
To achieve translation to the ground reference of terminal 702, the signal 
at port 716 is provided to an opto-isolator (or opto-coupler) 722 by way 
of diode 718 and two resistors 719 and 720. Opto-isolator 722 comprises a 
light-emitting diode (LED) which emits light on the base of a 
photo-transistor 723 when sufficient voltage is applied to it. When the 
LED diode is lit, photo-transistor 723 is enabled to conduct current 
between its collector and emitter. When LED diode is not lit, no such 
current can be conducted. The signal is thereby transmitted from one 
circuit to another by light, and transistor 723 may be included in a 
circuit which has a different ground reference than the LED diode. In this 
case, transistor 723 is part of a circuit which is referenced to the 
ground provided by terminal 702. Resistor 719 limits the current that can 
pass through the LED diode, and diode 718 and resistor 720 improve the 
noise immunity of the circuit by increasing the threshold voltage needed 
by the ON/OFF signal at port 716 to light the LED diode. 
The signal from photo-transistor 723 is amplified by a circuit formed by a 
transistor 728 (Q1), and two resistors 724 and 726. Resistor 724 is 
coupled between the low voltage power (12V) provided by Zener diode 712 
and the collector of phototransistor 723, and forms a first inverting 
amplifier with transistor 723. The output of this first inverting 
amplifier, which is at the collector of transistor 723, is provided to the 
input of a second inverting amplifier formed by resistor 726 and 
transistor 728. The output of the second inverting input is at the 
collector of transistor 728, also indicated as node 734, and is provided 
to the gate of power transistor 730. Thus, the optical signal provided to 
the gate of photo-transistor 723 is sent through two inverting amplifiers, 
thereby causing power transistor 730 to turn on (positive gate voltage) 
when light is at the base of transistor 723, and causing transistor 730 to 
turn off when there is no light. 
Because resistor 714 and Zener diode 712 provide a limited amount of 
current (I.sub.MAX =(V.sub.MAIN -12V)/R.sub.714), the ordinary design care 
should be taken to ensure that the maximum amount of current drawn by 
transistor 728 (Q1) is not so large that the first inverting amplifier is 
not able to drive transistor 728 (Q1). This may be achieved by proper 
selection of values for resistors 724 and 726 based on the maximum current 
I.sub.MAX and the minimum current gain (.beta.) of transistor 728. The 
maximum current draw occurs when transistor 723 is off and transistor 728 
is on. The value of resistor 726 may be chosen assuming that the V.sub.CE 
of transistor 728 is zero, that resistor 726 passes all of I.sub.MAX, and 
that the voltage drop across resistor 726 under this condition is around 5 
volts. These assumed conditions are reasonable, and give a value for 
resistor 726 of R.sub.726 =5V/I.sub.MAX. The assumed conditions require a 
minimum base current of I.sub.MAX /.beta., which is supplied by resistor 
724. The value of resistor 724 is chosen such that it provides 2-3 times 
the minimum base current, assuming that the supply voltage is at 5V (thus 
R.sub.724 &lt;1/2*(5V-0.7V)/(I.sub.MAX /.beta.)). The value of I.sub.MAX is 
of course selected by choosing the value of resistor 714. I.sub.MAX should 
be chosen such that its magnitude is sufficient to charge the gate of 
transistor 730 in a reasonably short amount of time (usually less than 
10-50 microseconds), given the turn-on charge requirement of the 
transistor (usually around 100 nC). Exemplary component values are 
provided in FIG. 8. 
Direction control circuit 750 comprises DPDT switch 780, briefly described 
above, and controls the state of DPDT switch 780, which in turn controls 
the direction of the motor's rotation. Switch 780 has a winding 788 and 
two armatures 782 and 784, which toggle between respective upper and lower 
contacts. Armatures 782 and 784 normally rest against their respective top 
contacts when winding 788 is not energized, and toggle to their respective 
bottom contacts when winding 788 is energized. The top contact of armature 
782 is coupled to the positive terminal of motor M, and the bottom contact 
thereof is coupled to the negative terminal of motor M. The contacts of 
armature 784 are coupled in the opposite manner, the top contact being 
coupled to the negative terminal and the bottom contact being coupled to 
the positive terminal. Thus, when winding 788 is not energized, armature 
782 couples the motor's positive terminal to terminal 701 and armature 784 
couples the motor's negative terminal to power transistor 730 (and onto 
terminal 702 when transistor 730 is conducting). When winding 788 is 
energized, the reverse coupling occurs with armature 784 coupling the 
motor's positive terminal to power transistor 730 and armature 782 
coupling the motor's negative terminal to terminal 701. The reversal of 
voltage polarity to the motor, which occurs when winding 788 is energized, 
reverses the direction of the motor's rotation. 
Power to winding 788 is controlled by a resistor 776 and a transistor 770 
coupled in series with winding 788, the so-formed series combination being 
coupled between power terminals 701 and 702. Transistor 770 operates in a 
similar manner to power switch 730 (but at a much lower current level), 
causing current to flow through winding 788 when it is in an ON state, and 
blocking current flow when it is in an OFF state. Resistor 776 limits the 
current and voltage provided to winding 788. A series combination of a 
free-wheeling diode 772 and resistor 774 is coupled across the terminals 
of winding 788 to provide a current conduction path for the inductive 
winding current whenever transistor 770 is turned off. Such freewheeling 
circuits are well known in the art. 
The conduction state of transistor 770 is determined by its gate voltage, 
which in turn is controlled by a signal provided at a port 756, which 
receives the direction control signal for the motor from controller 300 
(or 130). The voltage of the direction signal at port 756 is generally 
below 12V, and typically 5 volts and less. Like the ON/OFF signal at port 
716, the direction signal at port 756 may have a different ground 
reference than that provided by ground 702. For design convenience, the 
same type of driver circuit used in ON/OFF control circuit 710 
(opto-coupler and two inverting amplifiers) is used in direction control 
circuit 750 to drive the gate of transistor 770 based on the signal at 
port 756. The topology of the drive circuit is the same, but some of the 
component values are different because a lower amount of current is 
required to turn on drive transistor 770. The reference numbers of the 
drive components are 752, 754, 758-760, 762-764, and 766-768, and may be 
readily corresponded to the drive components of ON/OFF control circuit 
710. Exemplary component values are shown in FIG. 8. 
In a preferred embodiment of the present invention, a first and second 
motor control circuits, such as motor control circuit 700, are coupled to 
the motors of drive assemblies 132 and 134, respectively. Therefore, the 
direction of rotation and the ON/OFF status of motors 132 and 134 are 
independently controlled by separate motor control circuits. 
While the present invention has been particularly described with respect to 
the illustrated embodiments, it will be appreciated that various 
alterations, modifications and adaptations may be made based on the 
present disclosure, and are intended to be within the scope of the present 
invention. While the invention has been described in connection with what 
is presently considered to be the most practical and preferred 
embodiments, it is to be understood that the present invention is not 
limited to the disclosed embodiments but, on the contrary, is intended to 
cover various modifications and equivalent arrangements included within 
the scope of the appended claims.