Method and apparatus for conditioning a polishing pad

A method and apparatus for conditioning a polishing pad is described. The method includes steps of moving a cylindrical roller having an abrasive substance affixed to it against a moving polishing pad. The roller may be actively rotated or reciprocated at variable rates, while maintaining a pressure against the polishing pad. The apparatus includes a cylindrical roller attached to one or more pressure application devices mechanically connected to the roller.

FIELD OF THE INVENTION
 The present invention relates to a method and apparatus for conditioning a
 polishing pad. More particularly, the present invention relates to a
 method and apparatus for conditioning a polishing pad used in the chemical
 mechanical planarization of semiconductor wafers.
 BACKGROUND
 Semiconductor wafers are typically fabricated with multiple copies of a
 desired integrated circuit design that will later be separated and made
 into individual chips. A common technique for forming the circuitry on a
 semiconductor is photolithography. Part of the photolithography process
 requires that a special camera focus on the wafer to project an image of
 the circuit on the wafer. The ability of the camera to focus on the
 surface of the wafer is often adversely affected by inconsistencies or
 unevenness in the wafer surface. This sensitivity is accentuated with the
 current drive toward smaller, more highly integrated circuit designs.
 Semiconductor wafers are also commonly constructed in layers, where a
 portion of a circuit is created on a first level and conductive vias are
 made to connect up to the next level of the circuit. After each layer of
 the circuit is etched on the wafer, an oxide layer is put down allowing
 the vias to pass through but covering the rest of the previous circuit
 level. Each layer of the circuit can create or add unevenness to the wafer
 that is preferably smoothed out before generating the next circuit layer.
 Chemical mechanical planarization (CMP) techniques are used to planarize
 the raw wafer and each layer of material added thereafter. Available CMP
 systems, commonly called wafer polishers, often use a rotating wafer
 holder that brings the wafer into contact with a polishing pad moving in
 the plane of the wafer surface to be planarized. A polishing fluid, such
 as a chemical polishing agent or slurry containing microabrasives, is
 applied to the polishing pad to polish the wafer. The wafer holder then
 presses the wafer against the rotating polishing pad and is rotated to
 polish and planarize the wafer.
 With use, the polishing pads used on the wafer polishers become clogged
 with used slurry and debris from the polishing process. The accumulation
 of debris reduces the surface roughness and adversely affects polishing
 rate and uniformity. Polishing pads are typically conditioned to roughen
 the pad surface, provide microchannels for slurry transport, and remove
 debris or byproducts generated during the CMP process.
 One present method for conditioning a polishing pad uses a rotary disk
 embedded with diamond particles to roughen the surface of the polishing
 pad. Typically, the disk is brought against the polishing pad and rotated
 about an axis perpendicular to the polishing pad while the polishing pad
 is rotated. The diamond coated disks produce predetermined microgrooves on
 the surface of the polishing pad. Because the linear velocities of the
 leading, center and lagging portions of the disk are different, the rate
 of microgrooving is different. This non-uniform microgrooving has led some
 pad conditioner manufacturers to add a continuous oscillation motion to
 the rotational movement of the rotary disk pad conditioners. This extra
 movement can result in part of the wafer being exposed to freshly
 conditioned portions of the polishing pad and another part of the wafer
 being exposed to a used portion of the pad.
 Another apparatus and method used for conditioning a pad implements a
 rotatable bar on the end of an arm. The bar may have diamond grit embedded
 in it or high pressure nozzles disposed along its length. In operation,
 the arm swings the bar out over the rotating polishing pad and the bar is
 rotated about an axis perpendicular to the polishing pad in order to score
 the polishing pad, or spray pressurized water on the polishing pad, in a
 concentric pattern. These types of pad conditioners often do not provide
 uniform pad conditioning because they are only applied to a small portion
 of the width of the pad's surface at any given time. Thus, the pressure of
 the conditioner against the pad can vary.
 SUMMARY
 According to a first aspect of the invention, an elongated pad conditioning
 member comprising an abrasive substance is positioned around a shaft. The
 shaft has an axis substantially parallel to a plane of a polishing pad.
 The axis of the elongated pad conditioning member is positioned at greater
 than 180.degree. to the direction or vector of travel of the polishing
 pad. A motor is connectable to the elongated pad conditioning member. The
 motor is configured to variably rotationally reciprocate the exterior
 circumference of the elongated pad conditioning member at varying speeds
 about the shaft.
 In a further aspect of the invention, a roller has an axis of rotation
 oriented substantially parallel to a polishing plane of the polishing pad.
 Additionally, the axis of rotation of the elongated pad conditioning
 member is positioned at greater than 180.degree. to a direction of travel
 of the polishing pad. A motor is attachable to the roller providing
 continuous powered rolling. The motor is configured to continuously roll
 the outer circumference of the roller at variable speeds about the axis of
 rotation of the roller.
 According to another aspect of the present invention, a method of
 conditioning a polishing pad includes the steps of providing a polishing
 pad conditioner having a cylindrical roller with a longitudinal rotational
 axis, positioning the polishing pad conditioner adjacent the polishing pad
 so that the longitudinal rotational axis of the roller is oriented
 substantially parallel to the polishing pad, positioning the polishing pad
 conditioner so that the longitudinal rotational axis of the roller is not
 oriented at right angles to a vector or direction of travel of the
 polishing pad, and moving the roller against the polishing pad while the
 polishing pad is moving. A pressure is maintained against the polishing
 pad with the cylindrical roller. The roller is rotationally reciprocated
 about the longitudinal axis at variable speeds by a motor. In an
 alternative embodiment, the roller is continuously rotated about the
 longitudinal axis at variable speeds by a motor.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
 FIGS. 1 and 2 illustrate a presently preferred embodiment of a pad
 conditioner 10 according to the present invention. The pad conditioner 10
 includes a roller 12 having a cylindrical outer circumference 14 and first
 and second ends 16, 18. An abrasive substance, such as a diamond grit 22,
 is embedded in a strip 24 affixed along a longitudinal portion of the
 outer circumference 14 of the roller 12. The diamond grit 22 may have a
 density of 50 to 200 grit. Preferably, the diamond grit is dispersed
 randomly along the strip 24. The strip 24 may have any desired width. In
 another embodiment, a brush 26 is longitudinally disposed on the outer
 circumference 14 of the roller 12 on an opposite side of the roller from
 the abrasive material. The brush 26 may be made of a commonly available
 material such as nylon. For simplicity, FIGS. 1 and 2 illustrate the
 embodiment of the pad conditioner 10 having both a strip 24 of diamond
 grit 22 and a longitudinally disposed brush 26, however in a preferred
 embodiment the pad conditioner preferably only has the abrasive substance
 on the roller.
 The roller 12 preferably includes a coaxially disposed shaft 20 extending
 through the length of the roller. Alternatively, the shaft may be two
 separate coaxial segments extending partway in from each of the ends 16,
 18 of the roller 12. In yet another embodiment, the shaft 20 may extend
 only partly into one of the ends 16, 18 of the roller. As shown in FIGS. 1
 and 2, connectors 28 on either end 16, 18 of the roller hold the shaft 20.
 A sealed motor 30 connects the outer circumference 14 of the roller to the
 shaft 20. Preferably, the shaft is maintained in a fixed position and the
 motor rotates the outer circumference 14 of the roller 12 about the shaft
 20. In other embodiments, the motor may be positioned outside of the
 roller 12 and connected to the shaft 24 by a commonly available linkage
 mechanism such as a chain and sprocket assembly. The motor of the
 embodiment of FIGS. 1 and 2 is designed to rotationally reciprocate the
 outer circumference 14 of the roller 12 about the axis of the roller. The
 frequency and magnitude of the oscillations may be adjusted. Although any
 of a number of commonly available motors may be used to rotationally
 oscillate the roller, the motor is preferably a sealed motor such that
 slurry and debris do not damage the motor. A sealed motor also prevents
 oils and other contaminants from escaping the motor and adversely
 affecting the polishing ability of the polishing pad.
 The pad conditioner 10 also includes a pressure control system 32. As shown
 in FIG. 3, the pressure control system 32 includes pressure control
 devices 34, such as air cylinder and piston assemblies, attached to each
 end 16, 18 of the roller 12 via load cells 36. Each load cell 36 is
 electrically connected to a central controller 38 over a feedback line 37
 (FIG. 3). The central controller 38 determines the adjustments necessary
 to each end of the roller in order to maintain a desired pressure of the
 roller against the polishing pad being conditioned. The controller 38
 maintains the desired pressure on each end of the roller by controlling
 two proportional control valves 40, each connected to a respective one of
 the pressure application devices 34 via a control line 41. Each pressure
 application device 34 is therefore independently controllable by the
 central controller 38 to provide a uniform pressure across the polishing
 pad. The feedback loop created by the signals coming from the load cells
 36 to the controller enables the pad conditioner 10 to maintain highly
 accurate pressure control at each end of the roller. A command line 39
 connects the central controller 38 to a host computer (not shown) that can
 adjust the operational parameters of the pad conditioner 10, such as
 pressure threshold and speed of rotational oscillation.
 In one embodiment, the central controller 38 may be an embedded processor,
 such as a Zilog Z 180 or a Motorola HC11, running standard PID software.
 The pressure application devices may be hydraulic or pneumatic cylinder
 and piston assemblies. A lead screw or other actuator may also be used as
 the pressure application device 34. The load cells may be pressure
 transducers such as Sensotec Model 31/1429-04 available from Sensotec in
 Columbus, Ohio.
 FIG. 4 illustrates one environment in which a preferred embodiment of the
 rotary pad conditioner may operate. In FIG. 4, the rotary pad conditioner
 10 is positioned on a support member 42 attached to a frame 43 of a wafer
 polisher 44. The wafer polisher 44 may be a linear belt polisher having a
 polishing pad 46 mounted on a linear belt 48 that travels in one
 direction. The pressure application device 34, shown as a cylinder and
 piston assembly in this embodiment, acts both to provide the downforce for
 the roller against the polishing pad and to extend and retract the roller
 from the pad. In one embodiment, the pressure application device may
 provide a downward pressure in the range of 0-10 p.s.i. The wafer polisher
 44 may be a linear belt polisher such as the TERES.TM. polisher available
 from Lam Research Corporation of Fremont, Calif. The alignment of the pad
 conditioner 10 with respect to the polishing pad 46 is best shown in FIGS.
 4 and 5. Preferably, the axis of rotation (i.e. the longitudinal axis of
 the shaft) for the roller 12 on the pad conditioner 10 is parallel to the
 polishing pad 46 and the roller is aligned such that its axis of rotation
 is also perpendicular to the direction of motion of the polishing pad 46.
 Although the pad conditioner may have a roller length that is less than
 the width of the polishing pad, the length of the roller is preferably
 substantially equal to or greater than the width of the polishing pad to
 allow for an even pressure profile across the entire polishing pad.
 FIGS. 6 and 7 show an alternative embodiment of the pad conditioner 110. In
 the embodiment of FIGS. 6 and 7, the pad conditioner 110 includes a roller
 bath 50 sized to receive a portion of the outer circumference 114 of the
 roller 112. The roller bath 50 is preferably movable so that it can be
 positioned under the roller 112 as desired. The purpose of the roller bath
 is to periodically rinse the diamond grit 22 and/or the brush 26 on the
 roller 112. The roller bath includes a tub 52 having a liquid reservoir 54
 and an opening 56 sized to receive a portion of the outer circumference
 114 of the roller 112. The roller bath 50 may also include one or more
 spray nozzles 113 to spray the roller 112 with deionized water or other
 suitable rinsing fluid. The roller bath 50 may be movably connected to the
 rest of the pad conditioner 110 or the polisher by an actuator 116 such as
 a pneumatic piston and cylinder assembly. Preferably, the roller bath is
 controllable to move under or away from the roller 112. One suitable
 liquid for the liquid reservoir 54 is deionized water. As will be apparent
 to those of skill in the art, other liquids may be used.
 Referring to FIG. 8, a preferred method of conditioning a polishing pad
 utilizing the pad conditioners 10, 110 described above is set forth below.
 The pad conditioner controller 38 receives a signal to begin conditioning
 the pad 46 and instructs the roller 12 to align the strip 24 of grit 22
 toward the pad (at step 60). The controller 38 controls the proportional
 control valves 40 to activate the pressure application devices 34
 connected to the ends 16, 18 of the roller and lower the roller against
 the polishing pad (at step 62). The polishing pad 46 is preferably already
 moving when the roller contacts the pad. In one embodiment, the pad 46 is
 moving linearly on a belt 48 or strip. In other embodiments, the pad may
 be moving in a circular direction on a rotating disk support.
 While the roller is lowered, the motor 30 begins to rotationally
 reciprocate the roller about the shaft 20 (at step 64). The roller is
 preferably reciprocated so as to rotate the grit 22 back and forth against
 the pad. The rotational amount of the reciprocation may be adjusted. A
 preferred rotational amount is the circumferential width of the strip 24
 so that the grit 22 is in continuous contact with the pad. The frequency
 of reciprocation is adjustable through controlling the motor. One suitable
 strip width for the strip of grit is 1 inch and a suitable reciprocation
 frequency is 10 r.p.m. for a 14 inch roller having a 2 inch diameter. In
 other embodiments, the width of the grit, or other abrasive, may be
 narrower or wider and the reciprocation adjusted to suit the roller size,
 abrasive type and amount, and desired conditions. In another embodiment,
 the entire outer circumference 14 of the roller may be coated in an
 abrasive and continuously rotate in one direction.
 An advantage of the presently preferred pad conditioner is that a varying
 grit profile is presented to the pad because of the rotational
 reciprocation and the random distribution of grit on the strip of abrasive
 attached to the roller. Thus, uniform grooves in the pad are avoided and a
 more even overall roughness may be created on the pad. In another
 preferred embodiment, the pad conditioning process may also include the
 step of moving the polishing pad from side to side as illustrated by the
 arrow designated "belt steering" in FIG. 5.
 In addition to reciprocating the roller, the pad conditioner 10 maintains a
 constant pressure between the roller and pad (at step 66). The load cells
 36 at each end of the roller each generate a signal proportional to the
 pressure applied by the air cylinder and piston of the pressure
 application device 34. The load cells send their separate signals to the
 controller 38 which can individually adjust the pressure applied at the
 two ends of the roller. The continuous feedback of sensed pressure,
 coupled with individual control for each end of the roller permit a
 substantially even pressure against the pad. Irregularities and variations
 are sensed and compensated for by the controller through the feedback
 system.
 After the pad and roller have been in contact for a desired amount of time,
 the pressure application devices 34 retract the roller. If the pad
 conditioner includes a brush 26, the central controller 38 instructs the
 motor 30 to rotate the roller until the brush is aligned over the
 polishing pad 46. The roller is again lowered against the pad and
 rotationally reciprocated. The reciprocating action of the brush against
 the pad helps to remove loose slurry and debris generated by the first
 part of the pad conditioning process.
 Following a conditioning or brushing of the pad, the pad conditioner may
 clean itself off in the roller bath. The roller bath moves underneath the
 roller and the air cylinders of the pressure application devices lower at
 least a portion of the roller into the liquid reservoir. The motor
 reciprocates the roller to loosen and dislodge slurry or debris. The one
 or more spray 113 nozzles in the tub may also activate to further clean
 the grit. If both the abrasive grit and the brush require cleaning, then
 the roller rotates until the brush is aligned over the liquid reservoir in
 the tub and the cleaning process is repeated for the brush.
 Another embodiment of the polishing pad conditioner 200 is shown in FIGS.
 9-12. In this embodiment, the pad conditioner 200 has a passively
 rotatable roller 202 consisting of a precision ground stainless steel
 cylinder, plated with an abrasive substance such as diamonds, that is
 rigidly coupled to a shaft 204 via set screws. Diamonds corresponding to
 100 grit (163 microns) size are preferably deposited and plated over the
 roller such that the entire surface of cylinder is uniformly covered with
 sharp diamond pyramids oriented normal to the surface of the cylinder. The
 shaft 204 may be made from 440C stainless steel, hardened to a Rockwell
 hardness of 50 to 55 and machined to close tolerances so that resulting
 radial run-out is less than 0.0001 inch. Two bearings 208 support the
 shaft 204. The bearings 208 may be commercially available bearings such as
 those having a classification of ABEC 4 or higher. Two brackets 210 mount
 securely to a plate 212 and support the resulting assembly.
 FIG. 10 shows the cross-sectional view of the pad conditioner 200. The
 brackets 210, plate 212 and attached roller 202 are preferably movable by
 a commercially available double acting cylinder 214 with cushioned pads on
 both sides. One suitable double acting cylinder with cushioned pads is the
 AV 1.times.2"-B available from PHD, Inc. of Fort Wayne, Ind. The shaft 216
 of the cylinder 214 is guided by a linear bearing 218 to achieve smooth
 system operation and limit friction. A mounting block 222 serves as an
 attachment block for cylinder 212. The mounting block 222 securely bolts
 to an alignment plate 226 with four bolts 224. In addition to containing
 the linear bearing 218 for the cylinder shaft 216, the mounting block 222
 contains linear bearings 220 that slidably guide two guide shafts 232
 positioned on either side of the cylinder shaft 216. During operation, the
 cylinder 214 is subject to various loads, such as normal, side and torsion
 loads. In order to compensate for this loading, the two guide shafts 232
 are securely attached to the plate 212 with Allen-head screws 234. Each
 guide shaft 232 is mounted on linear guide bearings 220 and is free to
 slide in a direction parallel to the cylinder shaft 216 via. The shaft 216
 of the double acting cylinder 214 is also securely attached to the plate
 210 with an Allen-head screw 236 in order to increase the system's
 mechanical stability and resistance to side loads. Suitable guide shafts
 232 may be 0.500 inch diameter precision-ground and hardened metal shafts.
 To counterbalance the weight of the system, two compensating springs 228
 are added to the assembly. Preferably, the springs are mounted coaxially
 around each of the guide shafts between a slide bushing 230 and the
 mounting block 222. Required counterbalance force is adjusted by moving
 the two sliding bushings 230 to compress the spring 228 the desired
 amount. The mounting plate 226 allows alignment of the roller 202 to the
 surface of the belt pad and attaches the pad conditioner assembly 200 to
 the frame of the wafer polisher 44 (FIGS. 4-6).
 Precise downforce control on the roller is achieved by using a continuous
 automated downforce controller 237 as shown in FIG. 11. In the idle state
 of operation a first valve 238 is turned ON and a second valve 240 is
 turned OFF. This action provides a necessary retracting force to cylinder
 212. Pressure that is available to the supply side of the first valve 238
 is regulated by a first pressure regulator 239 in the range of 1 to 10
 pounds per square inch (p.s.i.). During operation, the second valve 240 is
 ON and the first valve 238 is OFF. Pressure that is available to the
 supply side of the second valve 240 is regulated by a second pressure
 regulator 242 in the range of 5 to 20 p.s.i. Pressure at the second valve
 240 is continuously controlled by an electro-pneumatic regulator 244 and
 monitored by a pressure sensor 246. Both the electro-pneumatic regulator
 244 and pressure sensor 246 are in closed loop control mode via a
 controller 248. The regulator 244 may be a Pressure Control Valve ITV 2000
 available from SMC Corp. of Tokyo, Japan. The pressure sensor 246 may be a
 ThruTube transducer and the controller may be a Multi-Channel Digital
 Controller Model LR3400 both available from Span Instruments, Inc. of
 Plano, Tex.
 The controller 248 continuously exchanges downforce information such as set
 point values, pressure on/off commands, data on the difference between
 requested downforce and actual downforce, etc. with a process module
 controller (not shown) via a RS 232 link 250. Both valves 238, 240 are
 controlled by a pneumatic signal supplied by a 4-way/3 position solenoid
 controlled valve 252. Solenoids 254 and 256 get ON/OFF commands from the
 process module controller over digital I/O lines 258. In this manner, the
 system 200 achieves quick downforce response and feedback with a minimum
 of components. In one preferred embodiment, the process module controller
 may be a Pentium.RTM. based PC configured to allow direct analog/digital
 interface with controllers, motors, valves, and the like and is in
 communication with a wafer polishing system controller. The wafer
 polishing system controller may be an embedded PC such as the Pentium
 MMX.RTM. PCA-6153 Single Board Computer, commercially available from
 Advantech Technologies, Inc. of Santa Clara, Calif., used in the TERES.TM.
 wafer polisher available from Lam Research Corporation in Fremont, Calif.
 In a wafer polishing system using the pad conditioner 200 of FIGS. 9-11, a
 semiconductor wafer to be polished is brought under pressure on to the
 polishing pad. In a preferred embodiment, the wafer polishing system is a
 linear belt polisher, such as the TERES.TM. polisher available from Lam
 Research Corporation, with a polishing pad 46 mounted on the belt. The
 belt is preferably capable of moving with linear velocities ranging from
 50 to 1000 linear feet per minute. During polishing, the polishing pad
 conditioner 200 is lowered against the polishing pad by the cylinder and
 shaft 214, 216. The downforce controller 237 controls the cylinder 214 so
 that a constant pressure is continuously applied to hold the roller
 against the polishing pad. Although the cylinder may operate to apply
 pressures of 0.1 to 100 p.s.i. to the polishing pad surface, the cylinder
 preferably operates to produce a constant pressure in the range of 1 to 6
 p.s.i. during conditioning, and most preferably is operated to maintain a
 pressure of 1 p.s.i. at the surface of the polishing pad. The pad
 conditioner may be adjusted to continuously contact and condition the
 polishing pad, to contact the polishing pad only after a semiconductor
 wafer is polished on the wafer polisher, or to intermittently polish the
 polishing pad during a wafer polishing process.
 A plurality of discrete contacts between the diamond points embedded on the
 surface of the roller 202 form a single line of contact with the surface
 of the pad 46 and generate a multitude of micro-cuts in the pad as the
 roller is driven by the linear motion of the polishing pad attached to the
 belt. In this manner, the pad is conditioned by the action of the diamond
 grit removing a fine layer of material from the pad and exposing
 micro-pores on the top surface of the pad. The pores are cut by the
 passive rotating action of the roller as the downforce controller 237
 maintains the pressure of the roller against the pad 46. Although the
 roller is rotated by the movement of the pad at a rate that is
 substantially matched to the linear velocity of the pad, there may be some
 slip between the roller and pad. The slip of the roller with respect to
 the pad is kept constant by means of precision downforce control. A basic
 physical analysis of the cylindrical pad conditioner indicates that both
 V.sub.conditioner and V.sub.belt are related according to the relation:
 V.sub.conditioner =K .times.V.sub.belt, where K is a slip factor.
 Experimentally, K has been found to range from 0.95 to 0.98 thus providing
 very close match between conditioning cylinder and belt pad. It is
 contemplated that rollers having a slip factor (K) less than 0.95 may also
 be used.
 Although the roller's orientation may be as shown in FIG. 12, where the
 axis of rotation is perpendicular to the velocity vector of the polishing
 pad, the roller is preferably maintained at a non-perpendicular angle with
 respect to the velocity vector of the polishing pad. When the roller is
 oriented as shown in FIG. 13, the cutting action of the diamond grit on
 the roller produces uniform cross-cuts on the pad and avoids prolonged
 contact time and linear scratches on the pad surface.
 If V.sub.belt (the velocity of the belt) determines time of the contact
 between each single diamond embedded in the roller and the pad material
 and V.sub.transverse determines cutting action of the single diamond
 against micro-contact area of the pad, then the relationship between the
 V.sub.belt and V.sub.transverse may be described as following:
 V.sub.transverse =tangent (90-.alpha.).times.V.sub.belt where .alpha. is
 the angle defined by the roller's rotational axis and the direction of
 rotation of the polishing pad. In one embodiment, V.sub.transverse may be
 in the range of 150 to 250 linear feet per minute, with corresponding
 values of alpha from 60 to 70 degrees.
 FIGS. 14, 14a, 15 and 15a illustrate another aspect of a pad conditioner
 300 according to presently preferred embodiment. This embodiment is
 capable of leaving marks not only along the direction of travel of the pad
 but also at a variety of angles to the direction of movement of the pad.
 In FIGS. 14 and 15, the pad conditioner 300 includes a roller 312 having a
 cylindrical outer circumference 314 and first and second ends 316, 318. An
 abrasive substance, such as a diamond grit is embedded in a strip affixed
 along a longitudinal portion of the outer circumference 314 of the roller
 312. In one preferred embodiment, a brush is longitudinally disposed on
 the outer circumference 314 of the roller 312 on an opposite side of the
 roller from the abrasive material. The diamond grit may have a density of
 50 to 200 grit. Preferably, the diamond grit is dispersed randomly along
 the strip. The strip may have any desired width. The brush may be of a
 commonly available material such as nylon. A belt 348, having a polishing
 pad mounted thereon or integrally formed therewith, travels in conjunction
 with the roller 312.
 The present embodiment of one aspect of the invention includes a roller 312
 having a shaft and a sealed motor. The roller 312 of the driven
 cylindrical pad conditioner 300 is placed not at a right angle with the
 direction of movement of the pad. That is, the roller 312 of the driven
 cylindrical pad conditioner 300 is positioned at a non-perpendicular angle
 with respect to the direction of movement of the pad. With the roller 312
 positioned not at a right angle to the pad, marks are left along the pad
 not only in the direction of movement of the pad but also at a variety of
 angles to the direction of movement. Marks on the pad will always be the
 result of speed of the conditioning V.sub.c. By changing the value of
 either the roller's 312 rotational speed or the belt speed, the direction
 of the vector V.sub.c will also be changed.
 The belt 348 travels with a velocity whose vector is indicated as V.sub.b
 in FIGS. 14 and 15. As shown in FIGS. 14 and 15, .omega. represents the
 rotational velocity of the conditioner whereas R indicates the radius of
 the conditioner. Multiplying .omega. by R gives the linear speed at the
 circumference of the conditioner, which is caused by the rotation of the
 shaft. Furthermore, the vector V.sub.c is the result of V.sub.b +.omega.R.
 By positioning the roller not at a right angle to the pad movement but
 rather at 90-.beta. degrees to it, a variety of marks at different angles,
 varying from zero to approximately 180-.beta. degrees, may be left on the
 pad. Here, .beta. the angle of the conditioner placed non-perpendicularly
 to the direction of pad movement. Also, a change in the rotational speed
 of the roller 312 influences the various angles of the marks that are left
 on the pad. These marks of various angles are advantageous at least
 because they allow for more accurate and variable planarization of
 semiconductor wafers. Further, the combination of varying the speed of the
 roller and positioning the roller not at right angles with the direction
 of travel of the pad allows for improvement of the removal rate and
 uniformity from the semiconductor wafer surface by the pad.
 Another aspect of the present invention includes a method of conditioning a
 polishing pad. The method includes providing a polishing pad conditioner
 having a cylindrical roller with a longitudinal rotational axis. The
 polishing pad conditioner is positioned adjacent the polishing pad so that
 the longitudinal rotational axis of the roller is oriented substantially
 parallel to the polishing pad. Further, the polishing pad conditioner is
 positioned so that the longitudinal rotational axis of the roller is not
 oriented at right angles to the direction of travel of the polishing pad.
 The roller is positioned against the polishing pad while the polishing pad
 is moving. A pressure is maintained against the polishing pad with the
 cylindrical roller. The roller is rotationally reciprocated about the
 longitudinal axis at variable speeds by a motor. According to this method,
 marks on the pad are produced at across or at various angles to the
 direction of movement of the pad. In yet a further embodiment, the roller
 312 continuously rotated about the longitudinal axis at variable speeds by
 a motor. Marks according to this further embodiment are also produced at
 various angles to the direction of movement of the pad.
 From the foregoing, a method and apparatus for conditioning a polishing pad
 has been described. One embodiment of the method includes the steps of
 positioning the pad conditioner over the polishing pad, moving a roller on
 the pad conditioner against the polishing pad while the pad is moving,
 rotationally reciprocating the roller of the pad conditioner about the
 rotational axis of a roller on the pad conditioner, and maintaining a
 pressure between the roller and polishing pad. If the pad conditioner also
 has a brush, the pad conditioner can then brush the pad by raising the
 roller and lowering it again after positioning a portion of the roller
 attached to a brush over the pad. To clean the pad conditioner after
 conditioning the pad, a roller bath is moved under the pad conditioner and
 the roller is rinsed with a liquid by reciprocating desired portions of
 the roller in the liquid. In a second embodiment, the method includes the
 steps of aligning a passively rotatable roller at angle with respect to
 the velocity vector of the polishing pad, pressing the roller into the
 polishing pad, and maintaining enough pressure to rotate the roller with
 the force of the moving pad.
 A pad conditioner is also disclosed having a roller aligned with its axis
 of rotation parallel to a pad. In one embodiment, the roller holds a strip
 of an abrasive substance such as a strip of diamond grit. In another
 embodiment, the roller holds both an abrasive substance and a brush. A
 motor connected to the roller is designed to rotationally reciprocate the
 roller. Pressure application devices connected to each end of the roller
 and a controller can maintain a desired pressure by the roller against the
 pad. The pad conditioner then lowers the roller until the brush reaches
 the pad. The brush acts to sweep the slurry and other debris from the
 newly roughened pad. The roller may reciprocate to assist the sweeping
 action, or the roller may simply hold the brush against the pad as it
 moves underneath it. The pad conditioner again retracts the roller after a
 desired time period. In another embodiment, a pad conditioner comprises a
 passive roller rotated by contact with the moving polishing pad. The
 passive roller is preferably angled with respect to the rotational
 direction of a linear polishing pad to improve pad conditioning. In yet a
 further embodiment, a pad conditioner comprises a variably rotational
 motorized roller. The variably rotational motorized roller may be a
 rotationally reciprocating roller or a continuously rotating roller where
 the reciprocation rate or rate of rotation is varied during conditioning
 of the polishing pad. The motorized roller is positioned at least
 180.degree. with respect to the direction of travel of the pad.
 It is intended that the foregoing detailed description be regarded as
 illustrative rather than limiting, and that it be understood that the
 following claims, including all equivalents, are intended to define the
 scope of this invention.