Substrate belt polisher

This invention relates to a flexible membrane polishing belt against which a substrate, for example a semiconductor wafer, is polished using chemical mechanical polishing principles. A fluidized layer is provided on a surface of a polishing member backing assembly which urges the moving polishing membrane toward the substrate held in a polishing head to be polished. The linear motion of the belt provides uniform polishing across the full width of the belt and provides the opportunity for a chemical mechanical polishing to take place. Several configurations are disclosed. They include belts which are wider than the substrate being polished, belts which cross the substrate being polished, but which provide relative motion between the substrate and the polishing belt, and polishing belt carriers having localized polishing areas which are smaller than the total area of the substrate to be polished. Only a small area on the surface of the substrate is in contact with polishing membrane but the motion of the carrier with respect to the substrate is programmed to provide uniform polishing of the full substrate surface, as is each configuration described.

FIELD OF THE INVENTION 
The present invention relates to the field of chemical mechanical 
polishing. More particularly the present invention relates to apparatus 
and methods for chemical mechanical polishing of substrates used in the 
manufacture of integrated circuits. 
BACKGROUND OF THE INVENTION 
Chemical mechanical polishing is a method of planarizing or polishing 
semiconductor and other types of substrates. At certain stages in the 
fabrication of devices on a substrate, it may become necessary to polish 
the surface of the substrate before further processing may be performed. 
One polishing process, which passes a conformable polishing pad over the 
surface of the substrate to perform the polishing, is commonly referred to 
as mechanical polishing. Mechanical polishing may also be performed with a 
chemically active abrasive slurry, which typically provides a higher 
material removal rate and a higher chemical selectivity between films of 
the semiconductor substrate than are possible with mechanical polishing. 
When a chemical slurry is used in combination with mechanical polishing, 
the process is commonly referred to as chemical mechanical polishing, or 
CMP. 
Prior art CMP process typically include a massive rotating platen 
containing colloidal particles in an alkaline slurry solution. The 
substrate to be polished is held against the polishing platen by a 
polishing head or carrier which can be moved in an x-y direction over the 
plane of the platen from a position near its outside diameter to a 
position close to its center. The platen is several times larger than the 
substrate to be polished. The substrate is rotated independently while 
pressure is maintained between the substrate and the polishing pad. 
The rate of material removal from the substrate in CMP is dependent on 
several factors including, among others, the chemicals and abrasives used 
in the slurry, the surface pressure at the polishing pad/substrate 
interface and the net motion between the substrate and the polishing pad. 
Generally, the higher the surface pressure and net motion at the regions 
of the substrate which contact the polishing pad, the greater the rate of 
removal of material from the substrate. It should be appreciated that 
equipment capable of performing this process is relatively massive and 
difficult to control to the precision necessary to consistently remove an 
equal amount of material on all areas of the substrate. 
Using a large polishing pad of CMP processing creates several additional 
processing limitations which lead to non-uniformities in the polished 
substrate. Because the entire substrate is rotated against the polishing 
pad, the entire surface of the substrate is polished to a high degree of 
flatness as measured across the diameter of the substrate. However, where 
the substrate is warped, the portions of the substrate which project 
upwardly due to warpage tend to have higher material removal rates than 
the remainder of the substrate surface. Furthermore, as the polishing pad 
polishes the substrate, material removed from the substrate forms 
particulates which may become trapped in the pad, as the polishing slurry 
dries on the pad. When the pad becomes filled with particulates and the 
slurry dries in the pad, the polishing surface of the pad glazes and its 
polishing characteristics change. Unless the user constantly monitors the 
removal rate of the polishing pad with each substrate, or group of 
substrates, and adjusts the slurry, load, position, and/or rotational 
speed of the polishing pad to maintain the desired material removal rate, 
the amount of material removed by the polishing pad from each substrate 
consecutively processed thereon will decrease. 
SUMMARY OF THE INVENTION 
The present invention provides methods and apparatus for polishing 
substrates where the polishing pad is a flexible membrane strip or belt 
(preferably continuous) which moves linearly between adjacent support 
rollers to provide uniform polishing of the substrate in contact with the 
moving membrane. In one embodiment a flexible polishing membrane has a 
substrate holder (polishing head), holding a substrate for polishing on a 
first side of the linearly moving membrane and a membrane backing member 
on a second side of the linearly moving membrane. The substrate holder and 
the membrane backing member are collectively configured to provide a set 
of clamping forces to urge the substrate and the first side of said 
membrane into contact with one another for polishing. 
In one embodiment the membrane backing member is a flat surface having 
generally equally distributed fluid holes therein. The holes face the back 
of the flexible polishing membrane such that when the membrane backing 
member is brought into close proximity to the flexible membrane and fluid 
(liquid or gas) is flowing out from the holes a fluid layer is formed 
between the surface of the backing member and the second side of the 
flexible membrane (belt). Clamping forces urging the belt and backing 
member together are generally uniformly resisted by the intervening fluid 
layer which provides a nearly uniform pressure between the membrane and 
backing member. The uniform pressure on the backside (second side) of the 
membrane is substantially transferred through the membrane to provide 
uniform mechanical abrasion over the surface of the substrate being 
polished by rubbing against the first side of the membrane. The set of 
forces urging the substrate and membrane against one another can be varied 
in conjunction with, or independently of, any adjustment in the speed at 
which the membrane moves relative to the substrate being polished. 
Preferably the substrate is fixed in the substrate holder at a location 
generally closely adjacent to the path of the freely moving membrane 
(belt). The backing member is supported by an urging member whose force 
can be adjusted. In one example, the force supplied by the urging member 
on the backing member is provided by a bellows assembly having bellows 
whose internal pressure is controlled to maintain a pre-set force on the 
back of the membrane regardless of dimensional variations in the surface 
of the substrate and in the thickness of the membrane belt and any liquids 
or slurries on its surface. 
Alternately, the backing member can be held fixed while the substrate 
holder and substrate can be urged by an adjustable urging member whose 
force can be adjusted. Similar to the urging member discussed above for 
the backing member, the force supplied by the urging member on the 
substrate member is provided by a bellows assembly having bellows whose 
internal pressure is controlled to maintain a pre-set force on the 
membrane regardless of dimensional variations. 
As a third alternative, adjustable urging forces can be provided to both 
the substrate holder and to the membrane backing member. However the 
balancing of such forces would have to be controlled carefully to assure 
that nearly central alignment of the flexible membrane between its 
adjacent rollers (pulleys) is maintained. 
Polishing of wafers as described above is done by a belt which is generally 
wider and longer than the size of a single substrate (wafer). Polishing 
contact takes place over the whole surface of the wafer at once, as the 
belt is generally in contact with the full width and length of the 
substrate's surface at one time. If the wafer were held stationary 
relative to the belt, then anomalies or imperfections in the polishing 
membrane (belt) would be transferred to the wafers surface. To avoid or 
reduce the possibility that any such anomalies would form the substrate is 
slowly rotated and is also oscillated from side to side to distribute the 
effect of any such anomalies over a larger area. 
To avoid excess polishing at the edges of the substrate from the natural 
bowing of the flexible membrane when it is subjected to pressure from one 
side, a perimeter or fence ring is provided around the substrate. The 
perimeter ring, made of a highly abrasion resistant material such as 
Delrin or Ultra High Molecular Weight plastics, such as polyethylene, 
provide an artificial extension of the edge of the substrate. The 
transition between the edge of the substrate and the inside diameter of 
the perimeter ring is flat. The edge effect which causes additional wear 
at locations where the membrane bends because it is displaced from its 
natural course by the action of either the membrane backing member or the 
substrate support head, occurs only at the outer edges of the perimeter 
ring. The edge of the substrate is therefore insulated from edge effects 
by the perimeter ring which acts as a buffer. 
Polishing as described herein is preferably done in a horizontal plane, but 
can be performed in a vertical orientation, or at any other angle where 
the substrate can be held for engagement and dis-engagement with the 
flexible polishing membrane. 
Polishing wafer can also be done by using flexible polishing membranes 
which provide coverage less than the full area of the wafer. One example 
of such a configuration provides for a flexible polishing membrane which 
has a width whose dimension is less than the diameter of a substrate to be 
polished. The substrate is mounted in a holding fixture which faces a 
narrow circulating belt. The belt is moved back and forth transversely 
across the substrate to provide polishing of the full width of the 
substrate. The substrate and/or the belt rotating mechanism can be slowly 
rotated to further avoid the localized effect of belt anomalies or 
imperfections from being detected in the final finish polished substrate. 
Still other polishing configurations reduce the contact area between the 
flexible polishing membrane and the surface of the substrate to a small 
fraction of the area of the surface of the wafer. A set of two or more 
small rollers cause a narrow belt to rotate in a belt carrier unit. The 
unit is then manipulated to move relative to the surface of the substrate 
to evenly polish each unit of area on the surface. For example when the 
substrate is rotating independently from the movement of the belt carrier 
unit, the higher surface velocity of the substrate near its circumference 
must be taken into account by providing a lower dwell time at the 
perimeter while compensating for the lower surface velocity near the 
center of the substrate by providing a longer dwell time for the belt 
carrier unit. 
In another embodiment, the apparatus includes a rotating plate on which the 
substrate is held, and polishing arm which is located adjacent the plate 
and is moved across the surface of the substrate as the substrate rotates 
on the rotating plate. The polishing arm includes a polishing pad on the 
end thereof, which is preferably variably loadable against the surface of 
the substrate as different areas of the substrate are polished thereby. 
The speed of rotation of the substrate may be varied, in conjunction with, 
or independently of, any adjustment of the polishing pad against to 
control the rate of material removed by the polishing pad as it crosses 
the substrate. The polishing arm includes a cartridge of polishing pad 
material in tape form, a discrete length of which is exposed over the 
lower tip of the of the polishing arm to contact the substrate for 
polishing. The tape of polishing pad material may be moved over the 
polishing arm tip to continuously provide a new polishing pad surface as 
the substrate is processed, or may be moved to provide a discrete new 
section of polishing pad tape to polish each new substrate or allow the 
movement of the tape to move together with the arm to provide polishing. 
In another arm based configuration, the polishing pad may be offset from 
the polishing arm, and the polishing arm may be rotated over the rotating 
substrate to cause the polishing pad to contact the rotating substrate as 
the polishing pad also rotates about the axis of the polishing arm. 
The mechanical abrading of the surface of a substrate being polished is 
performed by placing a slurry of colloidal particles on the surface of the 
polishing membrane to act as the agent for polishing. This slurry is messy 
and must be kept wet to remain fluid to avoid excessive build up of 
particles and the polishing anomalies that such buildups may create. 
Deionized water is therefore run onto the belt along with the slurry to 
maintain its fluid state and replenish the abrasive colloidal members. An 
option to a stream of de-ionized water is to run the belt (continuous 
flexible membrane) through a bath of fluid and/or to condition the surface 
of the belt by winding the path of the belt over a conditioning/idler 
pulley. The surface of the pulley would include a grooved surface pattern 
such as knurling to allow a nonuniform build-up of caked on slurry to be 
knocked off or distributed by the pattern (usually regular) on the surface 
of the conditioning idler pulley. While not presently available, a dry 
belt which would provide the same or a very similar abrading action would 
be preferred to eliminate the mess and complications associated with the 
use of slurry. As far as is known no dry-type continuous belts for CMP are 
presently available. 
In CMP the chemical part of the activity is performed by providing 
typically an alkali (reducing) solution such as NaOH to the surface of the 
substrate during processing. The alkali solution causes softening of the 
surface of the substrate. The softened layer can then be more easily 
removed by the mechanically abrasive colloidal particles in the slurry. 
The depth of softening of the surface by the alkali solution is dependent 
on the time of contact between the solution and the surface. The 
introduction and removal of alkali solution must be carefully controlled 
to avoid over or under polishing the surface of the substrate. The 
chemical treatment provides for removal of the surface layer of the 
substrate to a uniform depth, rather than a strictly mechanical 
planarization which when planarizing substrates with high and low points 
takes more from high points and less from low points thereby increasing 
the possibility that layers of material which have been uniformly 
deposited over underlying undulating layers will be breached and the 
substrate features damaged or rendered less reliable as a result of the 
build up of manufacturing tolerances. 
A method according to the present invention includes the nearly 
theoretically ideal arrangement where the surface of the substrate being 
processed is uniformly exposed to an abrasive agent with a uniform force 
between the membrane carrying the abrasive and the substrate. The method 
includes the method steps of: holding a substrate to be processed in close 
proximity to a linearly moving membrane

DETAILED DESCRIPTION 
Chemical mechanical polishing (CMP) involves polishing a substrate surface 
by using a chemical (e.g. an alkaline solution) to react with the surface 
to be polished and then abrading the surface by mechanical means. A 
uniform distribution of the chemical and a uniform application of the 
abrading agent will result in a generally smooth, but not necessarily 
planar surface which is compatible with subsequent substrate processing 
steps. 
A continuous belt sanding device can contact the substrate with a spatially 
uniform pressure to uniformly abrade the surface to be polished. A 
continuous belt, subject to variations in properties across its width, 
provides uniform abrasion (wear pattern) across the substrate surface. 
Uniform abrasion is achieved when an equal net length of a polishing 
membrane (or belt) travels past each unit of surface area on the surface 
of the substrate and the abrasive media is evenly distributed on the 
polishing membrane. If a large width of the substrate is being swept by a 
single pass of the belt, then it is possible that some variation in 
abrasion might be detected when an abrasive track (assuming parallel 
imaginary tracks on a continuous belt) moves over a longer length of the 
substrate (for instance between its leading and trailing edges near the 
centerline of a circular wafer) when compared to a similar track moving 
over a shorter length of substrate (for instance near the edge of a 
circular wafer). This potentially very slight variation is explained by 
the fact that colloidal abrasive particles present in the slurry and 
become contaminated with removed material as they move across the 
substrate so that the belt's abrasive efficiency decreases with a longer 
contact surface. 
A configuration according to the invention executing the principle of 
uniform pressure over the surface of the substrate with a uniform belt 
contact distance across the wafer is shown in FIG. 1. The perspective view 
of FIG. 1 shows a configuration including a flexible membrane (polishing 
belt) 60 (usually an unimpregnated polyester material to which abrasive 
particles are added in use) routed around three rollers 68, 70, 72. A 
substrate (wafer) holder (polishing head) assembly 30 includes a fixed 
support 32 connected to a cantilevered arm 34. The cantilevered arm 34, as 
shown in FIG. 1, rigidly supports a polishing head shaft 38 which can be 
rotated by a rotation mechanism (not shown) and whose vertical motion can 
be adjusted by a vertical adjustment mechanism (not shown). Alternatively, 
the fixed support 32 can include hinged or pivoting features to raise or 
pivot the polishing head assembly 30 so that the substrate 50 being 
polished (not shown in FIG. 1 as it is on the underside of the polishing 
head assembly 30) can be loaded and unloaded to access polishing 
operations on the belt 60. 
The flexible polishing membrane 60 moves in a right to left longitudinal 
direction between the top two rollers, i.e. from roller 70 to roller 72. 
As the flexible membrane (belt) 60 moves, an abrasive slurry containing 
colloidal abrasive particles of SiO.sub.2 is distributed over the width of 
the belt 60 by a slurry distribution manifold 74. Abrasive slurry is 
thereby placed on the flexible membrane 60 as it moves towards the 
polishing head 30. As the abrasive slurry on the polishing membrane 30 
contacts the substrate held by the polishing head 30, mechanical abrasion 
polishing of the substrate occurs. The chemical, e.g., NaOH, used to 
control the polishing rate can be part of the slurry or can be applied to 
the polishing membrane and substrate at another location in the cycle of 
the belt, e.g., by using spray nozzles (not shown). 
It is important to provide an uniform belt pressure across the surface area 
of the substrate being polished. It is generally not sufficient to place 
the polishing head 30 against a belt 60 and rely only on the tension of 
the belt 60 between rollers 70 and 72 to assure uniform polishing of the 
substrate surface. Instead, a flexible membrane backing assembly 62 (shown 
in dashed lines in FIG. 1) is provided at a location adjacent to the belt 
60 directly opposite to the polishing head 30 on top of the belt. The 
moving belt is sandwiched between the head 30 and the membrane backing 
assembly 62. The backing assembly 62, when in contact with the belt, 
assists in providing a uniform contact pressure between the belt 60 and 
the substrate 50. 
The membrane backing assembly 62 includes a fixed support member (membrane 
backing support bridge) 64 and a generally flat-topped membrane backing 
faceplate assembly 66. The membrane backing faceplate assembly 66 provides 
a uniform pressure to the underside of the moving belt 60 so that a 
uniform abrading pressure is applied over the surface of the substrate by 
uniformly pressing the polishing belt 60 upwards, with a small or 
negligible displacement, toward the fixed polishing head 30 which is 
located immediately adjacent to the path of the continuous belt 60. 
A cross section of the substrate polishing location as shown in FIG. 1 is 
shown in FIGS. 2 and 3. FIG. 3 is a closeup view of the configuration 
around one side of the polishing membrane 30. FIG. 4 shows a perspective 
exploded view of the details of the polishing head 30 and the membrane 
backing assembly 62. The polishing head 30 is supported by a lateral 
cantilever support 34. A continuous upper bridge support 36 shown in FIG. 
2 presents an example of an alternate support scheme for the polishing 
head (also shown for example by the bridge support 186 in FIG. 15). In 
either of these configurations, although not shown in the Figures, the 
substrate 50 and polishing head 30 may be rotated by a rotating mechanism. 
The substrate 50 and polishing head 30 can also be oscillated laterally 
(up and down as shown in FIG. 5) across the width of the belt 60. Such 
rotation and oscillatory movement prevents any surface defect or anomaly 
in the polishing belt 60 from creating a corresponding anomaly the surface 
of the substrate 50 being polished. Slow rotation of the polishing head 30 
(providing a diametral speed which is less than 1/100th of the 
translational speed of the belt 60) distributes the action of a defect on 
the surface of the belt over the surface of the substrate to help minimize 
its effect. If the polishing head moves at a rate of 100 ft/min then the 
rotation of the polishing head for an eight inch wafer should be about 1 
rpm or provide a 100:1 ratio between the movement of the belt versus the 
movement related to the rotation of the substrate. Under these conditions, 
belt or backing assembly defects located far from the center of a 
stationary rotating substrate are well distributed, while those which are 
closer to the center of the substrate are less well distributed. If a 
defect were to be located at the center of the substrate, rotation alone 
would cause no distribution of the defect. Therefore, to avoid the 
deleterious effects of such defects, the polishing head 30 is oscillated 
from side to side in an oscillatory motion. To prevent the polishing head 
30 from coming off the belt 60 during such sideways oscillation, the belt 
60 is wider than the polishing head 30 by a dimension at least equal to 
the full amplitude of the oscillation. This necessitates that the membrane 
backing assembly 62 also be wide enough or move together with the 
polishing head 30 to maintain uniform pressure on the bottom of the belt 
60 opposite the polishing head throughout the extremes of sideways 
oscillatory travel. In the configuration as shown in FIGS. 1-6, the 
polishing belt 60 and membrane backing assembly are wider than the 
substrate 50. 
Increased abrasion at the edge of the substrate (edge effects) can result 
from bowing of the flexible membrane outside the area clamped between the 
polishing head 30 and the membrane backing assembly 62. Edge effects can 
also result from the perimeter (edge) having to ride over or break down 
(cause distribution of) areas where slurry and/or the colloidal abrasive 
particles have built up and are not evenly distributed. It is preferable 
to eliminate the possibility of such edge effects. The configurations of 
FIGS. 1-6 include a retaining (edge--surface conditioning) ring 52. The 
retaining ring 52 surrounds the substrate 50 and prevents it from sliding 
out from under the polishing head 30. The retaining ring 52 and substrate 
are collectively held (or in other configurations pressed) against the 
moving belt 60. The thickness of the retaining ring 52 is generally equal 
to the thickness of the substrate being polished 50 together with any 
backing pad (e.g., item 46 in FIGS. 2-4). The retaining ring 52 is 
attached to the bottom of a main polishing head member 40 so that pressure 
on the polishing head 50 is uniformly distributed to both the substrate 50 
and the retaining ring 52. The presence of a retaining ring 52 requires 
that a larger diameter polishing head 30 be used. This in turn requires 
that the width of the polishing membrane 60 also be increased to prevent 
any part of the head 30 from coming off the polishing belt 60 during 
sideways oscillatory motion. The substrate retaining ring 52 is attached 
to the holding assembly backing plate by screws or generally mechanical 
holding mechanisms. The ring 52 can be released and replaced when the wear 
is excessive. 
The polishing head 30 includes a vacuum manifold 42 to distribute vacuum to 
vacuum holes 44 in the bottom of the main head member 40. The vacuum 
supply to the vacuum manifold 42 is through the polishing head shaft 38 to 
a rotatable coupling at the top of the shaft (not shown). The pattern of 
vacuum holes 44 on the bottom side of the main head member 40 partially or 
fully matches (a partial match utilizes some of the holes to retain the 
elastomer pad against the main head member) a pattern of holes 48 in the 
substrate backing pad 46 (preferably an elastomeric pad) to provide a 
conformable surface which can help to seal the vacuum passages against the 
substrate 50 during substrate loading and unloading operations and against 
which the substrate 50 can be pressed for polishing. Other arrangements 
for holding the wafer utilizing an elastomeric pad may be provided. They 
include placing an elastomer without holes across larger holes in the main 
head member 40. Pulling a vacuum partially pulls the elastomer into the 
larger holes and creates inverted craters in the elastomer, which when in 
contact with a wafer, act as suction cups to hold the wafer. When vacuum 
is pulled in the vacuum manifold 42, the substrate is held to the bottom 
surface of the polishing head 30 inside a cavity formed by the retaining 
ring 52. Vacuum pressure to the vacuum manifold 42 is controlled to allow 
loading and unloading of the substrate from the polishing head when the 
polishing head 30 is shifted to the loading or unloading position (for 
example as shown by dashed lines 30a and 34a in FIG. 6). These vacuum 
passages can also be pressurized to assist in release of the substrate 50 
from the polishing head 30 or in other configurations to assist in 
pressing the substrate uniformly toward the moving belt. 
The membrane backing assembly 62 faces the underside of the polishing 
membrane 60. The top surface of the assembly 62 is generally square or 
rectangular and is located to oppose the polishing head 30, so that the 
moving polishing belt is clamped between the two. The membrane backing 
assembly 62 includes the horizontally extending fixed support member 
(bridge) 64 supporting a vertically extending fixed support frame (a 
perimeter wall--forming an open box) consisting of a series of sidewalls, 
e.g. 96, 98, over which a generally horizontally extending faceplate 76 
floats. The faceplate 76 is allowed to float vertically, but is retained 
horizontally, by the fixed sidewalls, e.g., 96,98. The sidewalls, e.g., 
96,98 can be seen in FIGS. 2 and 4. An extendible bellows 100 flexibly 
connects the membrane backing support 64 to the floating faceplate 76. The 
bellows 100 can be pressurized to a fixed pressure or the pressure within 
the bellows can be controlled to provide a pre-set variable or pre-set 
constant vertical force (as seen in FIGS. 2 and 3) on the bottom of the 
moving flexible membrane (belt) 60. 
A rubbing plate (not shown), commonly used in belt sanders, can be molded 
over the top of the floating faceplate 76 to provide a flat surface 
against which generally uniform rubbing can take place. The faceplate 76 
with a top surface in contact and rubbing against the bottom of the 
flexible polishing membrane 60 wears both elements over time and either 
the membrane or the top of the backing plate would have to be replaced 
periodically. Many defects in the surface of the backing plate present at 
installation or which form later would tend to displace the flexible 
membrane unevenly and tend to cause uneven wear on the surface of the 
substrate being polished. To eliminate this wear between the bottom of the 
flexible membrane 60 and the top of the face 78 of the floating faceplate 
76, a pressurized fluid of either gas or liquid is provided through the 
holes 80 of the faceplate 76 and provides a uniform fluid bed or film of 
gas or liquid which acts as a nearly friction free buffer between the back 
of the flexible membrane 60 and the upper surface of the floating backing 
faceplate 76. The passage of fluid at the surface holes of the floating 
backing plate member provide a generally uniformly pressurized fluid layer 
between the back of the membrane and top of the backing plate assembly 
which therefore evenly pressurizes the back of the moving flexible 
membrane 60. The fluid or gas creating this layer is continuously 
replenished so that the thickness of the layer remains generally constant 
as the liquid or gas escapes sideways. 
A set of small fluid holes 80 in the top of the faceplate membrane surface 
78 provide for fluid (gas or liquid) passage from the faceplate fluid 
manifold cavity 82 to its surface 78 in contact with the moving belt 60. 
The fluid layer (illustrated by arrows 108 showing fluid flow) is thereby 
created between the moving polishing belt 60 and top surface 78 of the 
faceplate 76. The fluid can be either a gas or a liquid. The need to 
re-capture expended liquid weighs in favor of using a compressible gas. 
However, the containment used to capture the slurry could also be used to 
capture a liquid used in producing the fluid layer on the faceplate. 
Fluid, either gas or liquid, is provided to the faceplate manifold 82 
through a flexible hose 102 which is routed through the bellows 101 (or 
could be routed outside the bellows) such that fluid reaching the manifold 
enters a fluid feed opening 86 and is distributed within the manifold 82 
as shown by the arrows 110. The bellows top flange 101a (FIG. 4) is fixed 
to and sealed against the faceplate back surface 84. Faceplate side 
surfaces 88, 90 face adjacent fixed sidewalls 96, 98 to prevent the 
faceplate 76 from being displaced sideways. 
Since liquid slurry is present on the top of the flexible membrane (belt), 
it is important that the area around the bellows does not become plugged. 
Therefore, a labyrinth-type vertically moving skirt seal 92, 93, 94 is 
provided around the edge of the floating faceplate 76 to prevent any 
liquid, such as the slurry or pressurized liquid flowing from faceplate 
fluid holes 80, from flowing into the box-like container inside the 
sidewalls 96, 98 and restricting the vertical motion of the bellows 100. 
The sidewalls of the box-shaped member enclosing the bellows also act as a 
guide to prevent sideways motion of the floating member backing plate. The 
friction generated when the floating piece rubs against the stationary 
piece can adversely affect the uniformity of polishing. The two surfaces 
can be coated with a friction reducing coating (such as PTFE). 
Alternately, the two surfaces may be separated by using a fluid passing 
nozzle configuration which interposes a fluid layer between the floating 
and stationary pieces. These configurations easily accommodate variations 
in the thickness of the slurry or the thickness of the belt 60 as the belt 
moves over the substrate being polished to enhance the ability of the 
membrane backing assembly 62 to move very rapidly according to the 
instantaneously encountered dimension. 
Since the floating faceplate 76 is facing the moving belt 60, the belt 60 
tends to pull the floating faceplate 76 in the direction that the belt is 
moving. The moving belt 60 will also have a hydrodynamic (aerodynamic) 
effect in that the fluid at the leading edge of the floating membrane 
backing plate will tend to be sucked away and cause the belt 60 to touch 
the faceplate 76 at its leading edge. The hydrodynamic effect can be 
compensated for by adding fluid holes at the leading edge of this 
interface. Alternately, a curved transition could be provided so that the 
belt 60 sucks enough air towards the fluid layer that undesirable touching 
does not occur. 
The leading edge of the floating faceplate 76 can also be slightly rounded 
to avoid excessive wear that might be experienced as a result of the 
membrane catching on a sharp corner of such a leading edge. 
The size and number of fluid holes 80 ideally should provide a bed or film 
of fluid behind the polishing membrane so that the substrate 50 is evenly 
and uniformly polished. The pattern of holes 80 in the rectangular 
floating faceplate 76 covers nearly the full width of the belt. However, 
when unopposed by a polishing head 30 the moving belt 60 tends to bow up 
as shown by the dashed lines 61 in FIG. 3. 
The floating faceplate 76 as shown in FIG. 2 and 3 can either have a 
labyrinth skirt seal extension (e.g., 91, 93) whose top surface is planar 
with the top surface 78 of the faceplate 76 or can be offset slightly 
(e.g. 91a) as shown in FIG. 7. 
FIG. 4 shows an exploded view of the items discussed above for FIGS. 1-3. 
The polishing head main member 40 has a series of holes 44 on its lower 
surface. A retaining ring 52, preferably made of Delrin, surrounds the 
bottom edge of the polishing head main member 40. A flexible elastomer 
backing pad 46 has holes 48 whose locations correspond to the holes 44 in 
the polishing pad main member. The backing pad 46 is placed in the cavity 
at the bottom of the polishing head and acts as a compliant member to the 
extreme local pressures that would be present if a hard metal surface 
pressed a silicon substrate against an abrasive medium. The substrate 50 
is then sandwiched between the flexible membrane 60 and the bottom of the 
polishing head assembly 30 (including, but not limited to items 40, 52, 46 
and 48). On the bottom of the moving flexible membrane 60, the faceplate 
76 is supported by bellows 100 attached by flanges 101a, 101b and held in 
a particular alignment with the bottom of the moving polishing belt 60 by 
a perimeter wall including sidewalls 96, 98. The perimeter wall sits on 
support member 64. 
A schematic top view of the substrate 50 and its retaining ring 52 are 
shown in FIG. 5. Arrows 58 show the direction of travel of the moving belt 
60. The wave pattern 56 around the centerline 60a of the moving membrane 
60 shows the oscillating action of the center 54 of the substrate 
retaining ring assembly (which also correlates to the centerlines of the 
polishing head assembly). 
A top view of the configuration of FIGS. 1-4 is shown in FIG. 6. While the 
polishing head 30 and the cantilevered arm 34 appear to show a fixed 
orientation in FIGS. 1-4, loading and unloading of the polishing head must 
generally take place by moving the belt 60 relative the polishing head 30. 
The dashed lines 30a, 34a in FIG. 6 show one example of such a location 
for loading and unloading of a substrate from the polishing head 30. While 
not shown in the drawings, as discussed above, the polishing head 30 can 
be configured to rotate about its own axis 30b and the cantilevered arm 34 
may oscillate across the polishing belt 30. 
FIG. 7 is a configuration according to the invention showing in which the 
polishing head 30 would be positioned against a substrate 50. A three 
roller 68, 70, 72 arrangement is provided around which the flexible 
membrane 60 is wound. A tensioning roller 114 is provided which can also 
act as a surface conditioner for the polishing surface of the flexible 
polishing membrane 60. The tensioning/conditioning roller 114 (for 
example, made of a ceramic or a hard plastic material to avoid 
contaminating the substrate 50 being polished by introducing conductive or 
abrasive contaminants) may have a knurled pattern in its surface to 
actively displace and distribute colloidal particles of slurry which have 
become aggregated on and attached themselves to the flexible moving 
membrane 60. As shown in FIG. 7, a slurry introduced by droplets 75 is 
distributed over the width of the moving belt 60 by a manifold 74 situated 
upstream from the substrate 50 being polished. The membrane backing 
faceplate assembly 66 is situated opposite the substrate 50 being 
polished. The polishing membrane 60 is routed through a bath 117 of liquid 
having a liquid level 118, such as de-ionized water or an alkaline 
solution, to assist in maintaining moisture on the belt. The small arrows 
104, 106 (also seen in FIGS. 2 and 3) show fluid (such as slurry) escaping 
from the surface of the belt 60. The take-up roller 70 and drive roller 72 
(identified by the drive arrow 73) include surface linings 70a and 72a, 
respectively, on their surface. These linings are made of elastomers such 
as neoprene and rubber or other material generally used in the art. 
FIG. 8 shows another orientation according to the invention. The location 
of the substrate 50 alone represents the location of the polishing head 30 
(which is not shown) on the inside of the belt 60. In this configuration 
the substrate is shown and polishing occurs on the inside surface of the 
moving belt 60a. The three rollers 120, 124, and 126 and a tensioning 
roller 122 are located so that the actual drive 120 and guide rollers 124, 
126 condition the surface of the belt 60a which is the polishing the wafer 
while new colloidal particles to abrade the substrate are added by the 
manifold 74. The membrane backing faceplate assembly 66 in this 
configuration is located below the belt 60a. 
FIG. 9 shows the orientation of rollers as shown in FIG. 8, but the 
membrane backing assembly 66 pressurizing the belt is shown above the belt 
and the tensioning roller 122 acts as conditioning roller in this 
instance. New droplets of colloidal slurry are added in this configuration 
to the surface of the moving belt 60b as the moves down the right hand 
path between rollers 124 and 126 
FIG. 10 shows an alternative arrangement in which a moving belt 60c 
circulates around two rollers 130, 134. The substrate polishing position 
is shown by the location of substrate 50. The membrane backing faceplate 
assembly 66 is shown with variable tensioning 136 of the belt 60c between 
the two rollers 130, 134 relative to the fixed support 132. 
The tension of the belt 60, 60a, 60b, 60c in any of these configurations 
should be great enough to provide the motive force (frictional force) 
between the rollers and the belt to drive the belt even at the most 
aggressive abrasion conditions. The force attempting to restore the belt 
to its natural path tends to wear the retaining ring 52 and tends to 
over-polish the edge of the substrate. Therefore, the tension should not 
be so great as to excessively wear the belt or to provide rapid wear of 
the edge of the retaining ring if the substrate being polished is slightly 
displaced from the line directly between adjacent belt rollers. 
FIG. 11 shows a configuration according to the invention including four 
rollers 138, 140, 144, 146. The drive roller 146 is tensioned by a 
tensioning roller 142. The polishing location is on the belt 60d between 
the top two rollers 140, 148. Gravity influences the membrane polishing 
belt if it is on a horizontal plane. In an alternate configuration, shown 
by a dashed line 150 a substrate may be polished on a side of the 
arrangement. This configuration would eliminate the effect of gravity on 
the polishing belt 60d. A spray nozzle 152 can spray chemical solutions 
and/or slurry onto the belt as it approaches the substrate 50 being 
polished. 
FIG. 12 shows a wide flexible polishing membrane 60e having two polishing 
positions identified by substrates 50a and 50b. The locations of membrane 
backing assemblies 62a, 62b (shown in dashed lines) are opposite the 
positions 50a, 50b at which polishing can take place. In this 
configuration each substrate 50a, 50b being polished has its own separate 
track on the surface of the belt 60e. Another configuration with a 
reliable belt membrane could have the tracks on which polishing takes 
place overlaps or coincide, so long as polishing performance 
specifications are maintained. 
FIG. 13 shows an alternate arrangement according to the invention. The 
substrate 50c in FIG. 13 is held in a generally fixed position, either 
stationary or rotating slowly, in a faceup orientation with respect to the 
polishing belt 60f and its carrier (items including rollers 160, 162, and 
narrow belt backing assembly 164). A set of two rollers 160, 162 (as shown 
in FIG. 13, although more are possible) move polishing belt 60f. Polishing 
belt 60f is narrower than the substrate 50c surrounded by a retaining ring 
52a. The belt carrier mechanism includes a backing assembly 164 which 
moves with the rollers as the rollers move from side to side. While a 
single linear side to side movement is shown in FIG. 13 by arrows 166, it 
is possible the that the membrane polishing assembly (carrier) will rotate 
as well as translate, instead of or in addition to the substrate rotating 
providing a similar polishing effect as when the substrate alone rotates. 
Alternatively, the substrate could move laterally with respect to the 
belt. 
FIG. 14 is a closeup view of the membrane backing assembly showing a series 
of bellows 174, 176 which are equally pressurized to provide a generally 
uniform pressure to the backside of the moving flexible membrane 60f so 
that polishing across the width of the substrate is generally uniform. 
FIG. 15 shows another embodiment according to the invention. A substrate 
50d is retained within a retaining ring 52b and a flexible polishing 
membrane 60g is wound around a series of rollers which provide a belt 
polishing contact area much smaller than the area of the substrate 50d. 
Examples of alternate roller carriers are illustrated in FIG. 16 and 17. 
Such carriers are attached and guided by a carrier linkage (or mechanism) 
184 connected to, for example, a bridge support 186. Carrier linkage 184 
causes the roller carrier to move across the surface of the substrate 50d 
in a pre-programmed pattern, possibly rotary, to provide uniform polishing 
of the substrate 50d surface. The retaining ring 52b, similar to the 
retaining rings discussed above, minimizes edge effects which cause 
differential polishing at the perimeter. 
An urging linkage, as provided, for example, in the linkage 184, can be 
provided to attempt to provide uniform polishing pressure as the 
pre-programmed polishing path is carried out by the carrier assemblies. 
A series of three rollers and a carrier are shown in FIG. 15 and 16. A 
centralized pivoting frame 188 equalizes the pressure on the substrate 
between the two rollers so that generally equal polishing occurs within 
the region covered by the belt between the rollers. Because the distance 
between the rollers 194 and 196 is small, the polishing belt path 192 
generally maintains contact with the surface of the substrate 50d as long 
as the each of the rollers 194, 196 also do. A backing plate assembly may 
be placed between the rollers 194, 196 to provide uniform pressure the 
polishing belt path 192 
When a carrier according to FIG. 17 is used, a very small area (almost a 
line contact) is made between the roller 202 and belt 60h at the location 
200 in contact with the substrate 50d. The carrier 190 moves in a 
pre-programmed manner over the surface of the substrate as guided by the 
carrier links 198 to the support bridge 186. The configuration of FIG. 17 
is more like the stylus or cutter tool of a lathe. If there is relative 
rotation between the substrate and the carrier, the polishing program 
directing the movement of the carrier takes into account the fact that 
surface speed of a rotating substrate is greater the larger the distance 
from the center of rotation. The polishing program makes accommodations so 
that the center of the substrate is not polished any more or less than any 
of the regions away from the center. Alkaline solution and colloidal 
particles can be introduced by mounting a slurry and/or alkaline solution 
drip to the carriers so that fluid is introduced ahead of the locations 
where the polishing roller carrier is about to travel. 
FIGS. 18, 19, 20, 21, 22, 23, 24 and 25 schematically show a variety of 
arrangements of the polishing head, the substrate, and the polishing 
membrane backing assembly (faceplate), according to the invention. In each 
configuration the substrate 210 to be polished is located above the 
polishing belt 212 and a fixed support is provided both above and below 
the belt, but there are variations in the assemblies in the supports and 
the belt. 
FIG. 18 shows a vertically fixed gimbaled 216 polishing head 214, and the 
backing faceplate 218 is supported by a set of fixed or variable spring 
members 222,223 from a lower fixed support 220. Only rubbing contact is 
provided between the backing faceplate 218 and the bottom of the belt 212. 
FIG. 19 shows a configuration like FIG. 18, except that a backing faceplate 
244 provides a fluid layer contact between the bottom of the belt 212 and 
the top of the faceplate 224. 
FIG. 20 inverts the fixed and spring elements of FIG. 18. The polishing 
head 214 in this configuration is urged by fixed or adjustable spring 
members 226, 227 toward the polishing belt 212. A bottom faceplate 218 
which rubs the belt 212 is vertically fixed by the gimbaled support 228. 
FIG. 21 is a variation of the configuration of FIG. 20 in which a two piece 
polishing head 230, 232 having a fluid layer interface assures a uniform 
pressure across the head on the belt 212. 
FIG. 22 is a variation of the configuration of FIG. 21 in which a bellows 
224 replaces the spring members of FIG. 21. The bellows pressure may be 
controlled, or the bellows may be closed and provide a reduced force at 
greater extensions and a greater force on compression. 
FIG. 23 is variation of the configuration of FIG. 22 in which a polishing 
head 236 provides fluid force directly to one side of the wafer being 
polished without any intervening elements. This arrangement provides 
uniform pressure over each unit of substrate area urging the substrate 
toward to belt 212 for polishing. 
FIG. 24 shows a configuration similar to that shown in FIG. 19 with the 
addition of sidewalls 238, 240, sidewalls 238, 240 each have friction 
reducing inserts 242, 244, respectively, to reduce the friction caused by 
any vertical motion between the backing faceplate 224 and the sidewalls 
238, 240. 
FIG. 25 shows a configuration according to the invention similar to that 
shown in FIG. 24. A bellows element, as explained for FIG. 22 above, is 
interposed between the backing faceplate 218 and the fixed support 220. 
Fluid nozzles 246, 248 are provided to separate the backing faceplate from 
the side walls. 
Use of the configurations as described above includes a method according to 
the invention including the steps of: holding a substrate 50 in contact 
with linearly moving flexible polishing membrane 60 and providing a 
generally uniform pressure to the substrate 50 to accomplish generally 
uniform polishing across the area of the substrate 50. The step of 
applying uniform pressure is accomplished by pressurizing a bellows 234 
(FIG. 22). Bellows 234 can be positioned between a substrate holder fixed 
support 32 and the substrate holder 30. The pressure within the bellows 
234 is controlled to be generally uniform. 
Bellows 100 can also be positioned between which is used as a member 
intermediate the membrane backing support bridge 64 and the side of the 
polishing membrane 60 opposite the substrate 50 being polished. The 
backing faceplate 78 includes a series of holes 80 in its surface through 
which pressurized fluid flows to create a fluid layer. 108 separating the 
polishing membrane 60 from the surface of the backing faceplate 78. 
The substrate 50 can be rotated during polishing and can be moved in an 
oscillatory motion generally perpendicular to the relative motion between 
the belt 60 and the substrate 50. 
An alternate method according to the invention includes the steps of: 
holding a substrate 50 in contact with the flexible polishing membrane 60 
opposite a backing faceplate position (corresponding to the membrane 
backing assembly 62) behind the flexible membrane 60 and moving the 
polishing membrane 60 in a generally linear path past the substrate 50 to 
polish the substrate 50. A further additional steps may include: providing 
a clamping force to urge the substrate 50 and the backing faceplate 78 
toward the other and in contact with the flexible membrane 60, and or 
reconditioning the flexible membrane 60 (e.g., by the rollers 114, 122) as 
it is moved toward the polishing location where the substrate 50 is 
polished. 
Referring to FIG. 26, another chemical mechanical polishing apparatus 
according to the present invention generally includes a base 310 for 
rotatably supporting a rotating plate 312 therein, and a moveable tubular 
polishing arm 314 suspended over the rotating plate 312 and supported in 
position on a cross arm 316. Cross arm 316 is maintained on the base 310, 
and over the plate 312, by opposed uprights 315, 315a which extend 
upwardly from the base 310. The rotating plate 312 preferably includes a 
conformable pad 334 fixed to its upper surface. A substrate 318 having an 
upper surface 319 to be polished, is placed on the conformable pad 334 
with its upper surface 319 exposed opposite the plate 312. The conformable 
pad 334 is wetted, so that surface tension will adhere the substrate 318 
to the conformable pad 334 to maintain the substrate in position on the 
conformable pad 334 as the substrate 318 is polished. The tubular 
polishing arm 314, with a polishing pad 320 located over the lower open 
end 328 thereof, is moved generally radially across the upper surface 319 
of the substrate 318 to perform the polishing. The polishing pad 320 is 
preferably continuously moved linearly across the rotating upper surface 
319 of the substrate 318, from the edge to center thereof, until the 
polishing end point is reached. The polishing pad 320 is preferably five 
to fifty millimeters wide. Therefore, when a five, six, seven or eight 
inch (125-200 mm) substrate is located on the plate 312 the surface area 
of the polishing pad 320 is substantially smaller than the overall 
substrate area to be polished, generally at least three times smaller, and 
preferably at least 10 times smaller. The polishing pad 320 material is 
preferably a polyurethane impregnated polyester felt such as IC 1000, or 
Suba IV, both of which are available from Rodel, Inc. of Newark, Pa. To 
provide controllable substrate surface material removal rate across the 
entire substrate 318, the polishing arm 314 and cross arm 316 are provided 
with apparatus to control the positioning, and load, of the polishing arm 
314 and polishing pad 320 with respect to substrate upper surface 319. 
The positioning of the polishing arm 314, with respect to the substrate 
318, is provided by a linear positioning mechanism 322 formed as an 
integral part of the cross arm 316. In one embodiment, as shown in FIG. 
26, the linear positioning assembly 322 includes an internally-threaded 
slide member 323, and cross bar 316 includes mating threads to receive 
slide member 323 thereon. A secondary cross bar 317 is attached to 
uprights 315, 315a generally parallel to cross bar 316. Slide member 323 
is received on cross bar 316, and secondary cross bar 317 projects through 
slide member 323 to prevent its rotation with respect to cross bar 316. A 
stepper motor 321 is coupled to the cross bar 316 at upright 315 to rotate 
the cross bar 316 in discrete angular steps. In this configuration, the 
slide member 323, and polishing arm 314 with the polishing pad 320 
attached to the lower open end 328 thereof, may be moved axially across 
the substrate 318 in increments as small as 0.01 mm by rotating the cross 
bar 316 in discrete small arcuate steps by stepper motor 321. Other drive 
means, such as a linear actuator, a geared tape pulley, or other precision 
positioning mechanism may be easily substituted for this polishing arm 314 
drive system. 
Referring still to FIG. 26, linear positioning assembly 322 precisely 
aligns the cross arm 316 over the substrate 318 to move the polishing arm 
314 from the edge to the center of the substrate 318. As polishing pad 320 
moves from the edge to the center of the substrate 318, the substrate 318 
rotates on plate 312, and thus the polishing pad 320 contacts and polishes 
all areas of the substrate 318. To polish the center of the substrate 318 
where the relative motion between the polishing pad 320 and the substrate 
318 is at its minimum, the polishing arm may vibrate or rotate to create 
motion between the polishing pad 320 and the substrate 318 center. 
To rotate the polishing arm 314, a servo motor 325 is coupled to slide 
member 323, and a drive shaft 327 extends from motor 325 into slide member 
323 to engage the upper end of polishing arm 314. The upper end of 
polishing arm 314 is received in a rotary union at the base of slide 
member 323, which allows polishing arm 314 to rotate and also permits the 
transfer of liquids or gasses from slide member 323 into the hollow 
interior of the polishing arm 314. To provide vibratory motion, an offset 
weight may be coupled to the motor drive shaft 327. As the motor rotates, 
this offset weight causes the motor 325, and thus slide member and 
polishing arm attached thereto, to vibrate. 
To partially control material removal rate of polishing pad 320, the load 
applied at the interface of the polishing pad 320 and substrate upper 
surface 319 is also variably maintained with load mechanism 324 which is 
preferably an air cylinder, diaphragm or bellows. Load mechanism 324 and 
is preferably located integrally with polishing arm 314 between cross arm 
316 and substrate 318. The load mechanism 324 provides a variable force to 
load the polishing pad 320 against the substrate 318, preferably on the 
order of 0.3 to 0.7 Kg/cm.sup.2. A load cell 326, preferably a pressure 
transducer with an electric output, is provided integrally with polishing 
arm 314, and it detects the load applied by the polishing pad 320 on 
substrate upper surface 319. The output of the load cell 326 is preferably 
coupled to the load mechanism 324 to control the load of the polishing pad 
320 on the substrate upper surface 319 as the polishing pad 320 actuates 
across the substrate 318. 
To provide the slurry to the polishing pad 320, the slurry is preferably 
passed through the polishing arm 314 and out the open end 328 of polishing 
arm 314 to pass through the polishing pad 320 and onto the substrate. To 
supply slurry to the polishing arm, a slurry supply tube 332 is connected 
to slide member 323, and passages within the slide member 323 direct the 
slurry from the supply tube 332 through the rotary union and into the 
hollow interior of polishing arm 314. During polishing operations, a 
discrete quantity of chemical slurry, selected to provide polishing 
selectivity or polishing enhancement for the specific substrate upper 
surface 319 being polished, is injected through tube 332, slide member 323 
and arm 314, to exit through polishing pad 320 to contact the substrate 
upper surface 319 at the location where polishing is occurring. 
Alternatively, the slurry may be metered to the center of the substrate 
318, where it will flow radially out to the edge of the rotating substrate 
318. 
Referring now to FIG. 27, to rotate the plate 312 and the substrate 318 
located thereon, a motor 336 is coupled to the underside of the plate 312 
with a drive shaft. Motor 336 rotates the plate 312, and is preferably a 
variably speed direct current motor, such as a servo-motor, which may 
selectively provide variably substrate 318 rotation speeds during 
polishing operations. 
Referring again to FIG. 26, to polish a substrate 318 with the CMP 
apparatus of the present invention, the substrate 318 is loaded onto pad 
334, and the plate 312 is rotated to the proper polishing speed by the 
motor 336. The slide member 323 of the linear positioning mechanism 322 
moves polishing arm 314 from a position beyond the substrate radial edge 
to a position adjacent the substrate edge to begin polishing the substrate 
upper surface 319. As the polishing arm 314 is moved to contact the 
substrate edge, the polishing pad 320 is passed over a reconditioning 
blade 338 maintained on base 310 to remove any particulates which may have 
collected in polishing pad 320 during previous polishing with the 
polishing pad 320. Blade 338 is preferably a sharp blade, and as polishing 
pad 320 is brought across it, the fibers of the pad are raised and 
particulates trapped therein are removed. Other reconditioning apparatus, 
such as diamond wheels or stainless wire brushed may also be used to 
recondition the polishing pad. Once polishing pad 320 is brought into 
contact with the outer edge of the substrate 318, chemical slurry is 
pumped through the tube 332 and out through polishing pad 320, and 
polishing arm 314 is rotated and/or vibrated. As the substrate 318 rotates 
under the polishing pad 320, slide member 323 moves the polishing arm 314 
and polishing pad 320 from the substrate edge and across the substrate 
upper surface 319 to the center of the substrate 318. As the polishing pad 
320 is controllably varied by load mechanism 324 to compensate for the 
decrease in net motion between the polishing pad 320 and substrate upper 
surface 319 which occurs as the polishing pad 320 approaches the center of 
the substrate 318. Further, the speed of rotation of plate 312, and thus 
the net motion between polishing pad 320 and the substrate 318, may be 
varied in conjunction with, or independently of, the relative radial 
position of polishing pad 320 on substrate 318 by varying the motor 336 
speed. Once the polishing end point is reached, the chemical slurry stops 
flowing, the rotation and/or vibration stops, and the slide member 323 
moves polishing arm 314 across reconditioning blade 338 and back to its 
original position adjacent the upright 315. To properly position polishing 
arm 314 for the next substrate 318 to be polished, a zero position stops 
342 extends from upright 315, generally parallel to cross arm 316, and 
slide member 323 stops moving when it engages zero position stop 342. When 
the next substrate 318 is positioned on the plate 312, and the next 
polishing cycle begins, the polishing pad 320 will again cross the 
reconditioning blade 338 to raise fibers in the polishing pad 320 and 
remove particulates which may have collected in polishing pad 320 as a 
result of accumulated substrate polishing. Alternatively, the polishing 
pad 320 may be replaced after each polishing cycle. 
FIGS. 28 and 29 show a second embodiment of the polishing arm 314 useful 
with the chemical mechanical polishing apparatus of the present invention. 
In this embodiment, the polishing arm 314 includes a tubular roller 
support arm 346 which extends downwardly from the load member 324, and a 
roller member 348 which is attached to the lower terminus of roller 
support arm 346, by bearing plates 350. The plates 350 are located on 
opposite sides of the roller support arm 346 and extend downwardly 
therefrom to receive rotatable roller axle 352 extending from either end 
of the roller member 348. The roller member 348 preferably freewheels 
within the plates 350, although it may be coupled to a drive system to be 
positively rotated. To provide the polishing pad surface to polish the 
substrate 18, a cassette 354 is loaded on the upper end of the roller 
support arm 346 and a tape 356 of polishing pad material is looped over 
the roller 348 such that the ends thereof are wound between spools 358 in 
the cassette 354. The tape 356 of polishing material is preferably aligned 
on the substrate by aligning the axles 352 parallel to the radius of the 
substrate 318. The cassette 354 preferably includes an integral drive 
motor which rotates the spools 358 to provide a clean polishing pad 
surface at roller 348 as required. It also optionally includes a pair of 
reconditioning blades 360 which contact the polishing tape 356 surface to 
clean it of particulates which accumulate therein from substrate 
polishing. The tape 356 may be incrementally moved, to provide a clean 
polishing pad surface on roller 348 after each polishing cycle, or may be 
continuously or incrementally moved to provide a fresh, clean polishing 
pad surface at the polishing pad/substrate interface while each individual 
substrate 318 is being polished. To provide the fresh polishing pad 
material against the substrate 318, the roller 348 may alternatively by 
positively driven by a drive mechanism to move the tape 356 over the 
roller 348 and the substrate upper surface 319, and the reconditioning 
blade my be located adjacent roller 348. Polishing slurry may be provided, 
in metered fashion, through the hollow interior of the roller support arm 
346 to supply the polishing slurry directly at the polishing pad/substrate 
interface. 
Referring now to FIG. 30, an additional alternative embodiment according to 
the invention is shown. In this embodiment, polishing arm 314 extends 
downwardly from load mechanism 324 and terminates on secondary plate 380 
located above, and generally parallel to, the rotating plate 312. A pair 
of secondary polishing arms 384, each having a polishing pad 320 on the 
end thereof, extend downwardly from intermediate plate 380 to position the 
polishing pads 320 in position to engage the substrate upper surface 319. 
Secondary polishing arms 384 are preferably located adjacent the edge of 
intermediate plate 380, 180 degrees apart, and polishing arm 314 is 
preferably connected to the center of secondary plate 380. Thus, a 
polishing arm 314 is rotated by motor 325, secondary polishing arms 384 
traverse a circular path having a mean diameter equal to the linear 
distance between the centers of secondary polishing arms 384. As linear 
positioning assembly 322 moves polishing arm 314 over the substrate 318, 
and the secondary polishing arms 384 rotate about the longitudinal axis of 
the polishing arm 314, net movement will occur between the pads 320 and 
all areas of the substrate upper surface 319. 
To ensure even net relative motion between the polishing pads 320 and the 
substrate upper surface 19, the length of the span between the secondary 
polishing arms 384 on intermediate plate 380, in combination with the 
length of travel of the slide member to position the pads 320 from the 
edge to center of the substrate, should not exceed the radius of the 
substrate, and the rate in rpm, and direction, of rotation of both plate 
312 and polishing 314 must be equal. Preferably, the span between the 
centers of the two polishing pads 320 on the ends of secondary polishing 
arms 384 is 3 to 4 cm. Additionally, although two secondary polishing arms 
384 are shown, one, or more than two, polishing arms, or an annular ring 
of polishing pad material may be connected to the underside of the 
intermediate plate 80 without deviating from the scope of the invention. 
Referring now to FIG. 31, a schematic of the control system 370 for 
controlling the chemical mechanical polishing apparatus of the present 
invention is shown. The control system 370 includes a controller 372 which 
is coupled, by electrical cables, to load mechanism 324, load cell 326, 
plate drive motor 336, cross bar stepper motor 321 and motor 325. When the 
chemical mechanical polishing apparatus is first used, the controller 372 
signals the stepper motor 321 of the linear positioning mechanism 322 to 
rotate the threaded cross bar 316, and thus move the slide member 323 and 
polishing arm 314 attached thereto to the fully-retracted position 
adjacent to upright 15. As slide member 323 positions the polishing arm 
314 in the fully-retracted position, a signal member thereon, preferably a 
signal pin, touches the zero position stop 342 which sends a signal to the 
controller 372 indicating that the polishing arm 314 is in the fully 
retracted position. Controller 372 then actuates the stepper motor 321 to 
move polishing arm 314 to the edge of substrate upper surface 319. As 
polishing pad 320 is moving into position to engage the edge of substrate 
318, the controller 37 starts motor 336 to rotate substrate 318 at the 
desired speed. 
Once polishing pad 30 engages the edge of substrate 318, the controller 372 
further signals the load member 324 to create a bias force, or load, at 
the interface of the polishing pad 320 and the substrate upper surface 
319, signals motor 325 to vibrate and/or rotate polishing arm 314, and 
simultaneously starts the flow of the polishing slurry into polishing pad 
320. The controller 372 monitors and selectively varies the location, 
duration, pressure and linear and rotational relative velocity of the 
polishing pad 320 at each radial location on the substrate upper surface 
319 through the linear position mechanism 322, load member 324, motor 325 
and motor 336 until the polishing end point is detected. An end point 
detector, such as an ellipsometer capable of determining the depth of 
polishing at any location on the substrate 318, is coupled to the 
controller 372. The controller 372 may stop the movement of the linear 
position apparatus 322 in response to end point detection at a specific 
substrate radius being polished, or may cycle the linear position 
apparatus 322 to move polishing pad 320 back and forth over the substrate 
318 until the polishing end point is reached and detected at multiple 
points on substrate upper surface 319. In the event of a system breakdown, 
a stop 340 projects from upright 315a generally parallel to cross bar 316 
to prevent slide member 323 from travelling completely over the substrate 
318. Once polishing end point is reached, the controller 372 signals the 
load cell of lift polishing arm 314 off the substrate 318, stop delivery 
of the polishing slurry, and move slide member 323 back into engagement 
with zero position stop 342. The polished substrate 318 is then removed, 
and a new substrate 318 may be placed on plate 312 for polishing. 
While the invention has been described with regards to specific 
embodiments, those skilled in the art will recognize that changes can be 
made in form and detail without departing from the spirit and scope of the 
invention.