Rotating belt wafer edge cleaning apparatus

An apparatus for cleaning edges and/or bevel areas of substrates. In one embodiment, the present invention provides a cleaning mechanism that cleans particles off the edge of the wafer based upon friction at the contact point between the wafer and a rotating belt.

FIELD OF THE INVENTION 
The present invention relates to the field of semiconductor wafer 
processing; more particularly, the present invention relates to cleaning 
the edges and/or bevel areas of semiconductor wafers. 
BACKGROUND OF THE INVENTION 
Semiconductor manufacturers use semiconductor wafers as the base for 
manufacturing integrated circuits. In one step of the manufacturing 
process, the wafers are put through chemical mechanical polishing (CMP). 
CMP is becoming the main planarization technology for both dielectric and 
metal layers. For the CMP of dielectric layers, such as BPSG, BPTEOS, and 
PECVD Oxides (often referred to as the ILD0, ILD1, ILD2. . . layers, 
respectively), a fumed silica-based slurry is normally used. Other 
slurries, such as dispersed silica, fumed or dispersed allumina, are also 
being used for CMP of both oxides and metals (such as tungsten (W), copper 
(Cu), aluminum (al), and titanium (Ti)). When the CMP process is 
completed, the wafers' surfaces are covered in particles, referred to as a 
slurry residue. At later steps in the process flow, some of this slurry 
residue is redistributed across the front of the wafer, thereby resulting 
in a loss in die yield and/or device performance. To prevent the slurry 
redistribution, all surfaces of a wafer must be free of contamination. 
Different post CMP cleaning methods have been introduced in the last few 
years. These include cleaning the wafers in wet stations using 
conventional wet cleaning methods, such as SC1, HF and megasonic cleaning. 
Other cleaning methods in use are based on scrubbing wafers with brushes 
of various kinds and configurations using DI water or a combination of DI 
with chemicals such as Ammonia and Citric acid. 
One system used to remove wafer contaminants is a double sided scrubber. In 
a double sided scrubber, a semiconductor wafer is scrubbed simultaneously 
on both sides by brushes. Since the wafer is being scrubbed simultaneously 
on both sides by the brushes, there must be a way of holding the wafer in 
place and rotating the wafer so the entire surface of the wafer is 
cleaned. A mechanism used for this purpose is commonly referred to as a 
roller. 
Today, double sided scrubbers are usually automated and comprise a conveyor 
type mechanism, rollers, and brushes. In general, the wafer lies flat on 
the conveyor mechanism and the conveyor mechanism moves the wafer into the 
brushes. While being scrubbed, the wafer is supported (or held 
horizontally) by the conveyor mechanism, brushes, rollers, or a 
combination thereof. FIG. 1 illustrates a conventional double sided wafer 
scrubber. Referring to FIG. 1, a wafer 102 is being scrubbed by brushes, 
one of which is shown as brush 110 and the other being beneath wafer 102 
and directly below brush 110. Rollers 108 rotate wafer 102 so the entire 
wafer surface may be cleaned. Each of brushes 110 is rotated about its 
central axis by a motor 106. The rotary motion of rollers 108 is then 
transferred to wafer 102 when the edge of each of rollers 109 comes into 
contact with the outer edge of wafer 102. 
Although conventional brush cleaning systems can effectively clean the 
front and backs of semiconductor substrates, such systems fail to provide 
a sufficient amount of mechanical energy at the edge/bevel to remove 
contamination. 
The present invention provides an apparatus that cleans the edge of 
substrates, including the bevel area when present. 
SUMMARY OF THE INVENTION 
An apparatus for cleaning edges and/or bevel areas of substrates is 
described. In one embodiment, the present invention provides a cleaning 
mechanism that cleans particles off the edge of the wafer based upon 
friction at the contact point between the wafer and a rotating belt.

DETAILED DESCRIPTION 
An apparatus for cleaning edges of contaminated substrates is described. 
The cleaning process may be used in double sided scrubber systems or other 
systems, such as, for instance, chemical mechanical polishing systems or 
flat panel display manufacturing systems. In the following description, 
numerous specific details are set forth such as rotation speeds, 
chemicals, pressures, etc., in order to provide a thorough understanding 
of the present invention. It will be apparent, however, to one skilled in 
the art that the present invention may be practiced without these specific 
details. In other instances, well-known components, structures and 
techniques have not been shown in detail in order to avoid obscuring the 
present invention. 
The present invention provides a method and apparatus that cleans the edge 
of substrates, including the bevel area when present. In the present 
invention, particles are removed from the edge and/or bevel area (or any 
other surface sloping from the edge to the top or bottom of the substrate) 
using an edge scrubbing mechanism that may be incorporated into a scrubber 
tool. 
Although the present invention is described in conjunction with the 
scrubbing of a wafer, it will be appreciated that any similarly shaped, 
i.e. generally flat, substrate, may be processed by the methods and 
apparatuses of the present invention. Further, it will be appreciated that 
reference to a wafer or substrate may include a bare or pure semiconductor 
substrate, with or without doping, a semiconductor substrate with 
epitaxial layers, a semiconductor substrate incorporating one or more 
device layers at any stage of processing, other types of substrates 
incorporating one or more semiconductor layers such as substrates having 
semiconductor on insulator (SOI) devices, two or multiple substrates 
bonded to each other, or substrates for processing other apparatuses and 
devices such as flat panel displays, multichip modules, etc. 
FIGS. 2A and 2B illustrate a wafer edge cleaning device in one embodiment 
of the present invention. As shown, the edge 203 of a rotating wafer 202 
is cleaned by positioning a rotating belt 206 adjacent to the wafer edge 
203 such that an abrasive outer surface 208 of the belt slides across the 
edge surface. The frictional forces generated between the outer surface 
208 of belt 206 and edge 203 result in the removal of contaminates 
residing at the contact points at the belt/edge interface. The relative 
velocity difference between belt 206 and wafer 202 also contributes to the 
removal of particles from the edge surface. The inner surface 209 of belt 
206 is acted upon by the outer surfaces 214 and 216 of rollers 210 and 
212, respectively. Each of rollers 210 and 212 have an axis of rotation 
218 and 220, respectively. The location of axis 218 is fixed, whereas axis 
220 is permitted to move along a path 222 as roller 220 is pivoted in an 
upward direction about fixed axis 218. A motor (not shown) is coupled to 
roller 210 to provide rotational movement to the roller. The resistance 
between the outer surface 214 of roller 210 and inner surface 209 of belt 
imparts the rotational movement of roller 210 to belt 206. 
As shown in FIG. 2A and 2B, the edge 203 of wafer 202 is cleaned by placing 
the wafer adjacent edge cleaning apparatus 200 and pivoting roller 220 in 
an upward direction about axis 218 so that the outer surface 208 of belt 
206 contacts the edge 203 of wafer 202. In one embodiment, belt 206 
comprises an elastomer material that is stretched to fit over rollers 210 
and 212. Alternatively, roller 220 may be slidably mounted. In such an 
embodiment, belt 206 is placed around the outer surfaces of the rollers 
and the tension of belt 206 is adjusted by slidably adjusting the position 
of roller 220. The outer surface 208 of belt 206 is textured such that 
sufficient frictional forces are produced at the belt/wafer edge interface 
to remove contaminates from the wafer edge during cleaning. The surface 
roughness of surface 208 is selected to facilitate the removal of unwanted 
particles from the wafer's edge without damaging the wafer itself. In some 
instances, the texture of belt 206 may vary along the circumference of the 
belt. In this manner, one portion of the belt may be used for removing one 
type of contaminate while another portion of the belt may be used to 
remove another type of contaminate. 
FIG. 3A illustrates another method of cleaning the edge of a wafer. As 
shown in FIG. 3A, rollers 210 and 212 are attached to support structure 
300 at axis 218 and 220. In lieu of using a pivoting action to bring the 
belt 206 into contact with wafer edge 203, the lateral movement of support 
structure 300 is used to position the edge cleaning apparatus. In 
addition, rollers 210 and 212 may be spring mounted to structure 300 by 
springs 310 and 312. By spring mounting rollers 210 and 212 to structure 
300, the amount of force exerted upon edge 203 by belt 206 is more 
accurately controlled. 
In one embodiment, the width of belt 206 is approximately 0.5 inches. The 
outer surface 208 of belt 206 may comprise PVA, nylon, or polyurethane. 
With reference to FIGS. 4A and 4B, a belt-type edge cleaning apparatus 400 
in another embodiment of the present invention is shown. The belt-type 
edge cleaning apparatus 400 is similar to the edge cleaning apparatus 200 
of FIGS. 2A and 2B, however, apparatus 400 includes three rollers instead 
of two. Edge cleaning apparatus 400 includes a belt 406 having an inner 
surface 409 and an outer surface 408. Belt 406 is held in position and 
rotated by three rollers 410-412. Each of rollers 410-412 has an axis of 
rotation 416, 417 and 418, respectively. Additionally, wafer 402 is 
rotated about an axis of rotation. Axis 416 is stationary, whereas axes 
417 and 418 are permitted to move generally in the direction indicated in 
FIG. 4B as the belt assembly is pivoted upward about axis 416. A motor 
(not shown) is coupled to roller 410 to provide rotational movement to 
belt 406. As shown in FIG. 4B, the edge 403 of wafer 402 is cleaned by 
placing the edge of wafer 402 in proximity to rotating belt edge cleaning 
apparatus 400 and pivoting apparatus 400 upward about stationary axis 416 
to engage the outer surface 408 of belt 406 against wafer edge 403. In one 
embodiment, axes 416, 417 and 418 are oblique to the rotational axis of 
the wafer 402. 
Turning now to FIG. 5A, edge cleaning apparatus 500 is shown incorporated 
into a double sided scrubber 500. As illustrated in FIG. 5A, wafer 502 is 
cleaned by a top-side brush 504 and a bottom-side brush 506 as it moves 
through the scrubber (from left to right). Edge rollers 510 are provided 
to rotate wafer 502 in a counter-clockwise direction as indicated. Motors 
512 are coupled to edge rollers 510 to provide rotational movement to the 
wafer. A rotating belt edge cleaning apparatus 600 is provided along side 
wafer 502. As wafer 502 moves through scrubber 500, edge cleaning 
apparatus 600 is rotated upward such that belt 606 is pressed against 
wafer edge 503. Hence, as wafer 502 moves through the double sided 
scrubber system, top-side and bottom-side brushes 504 and 506 clean the 
top and bottom surfaces of wafer 502, while rotating belt 606 removes 
contaminates along the edge and bevel areas of the wafer. A motor 602 is 
coupled to stationary roller 604 to provide rotational movement to the 
edge cleaning belt 601. 
One benefit of the present invention lies in the combined use of top-side 
and bottom-side brushes 504 and 506 and edge cleaning apparatus 600 to 
clean all of the exposed areas of the wafer which may be contaminated with 
slurry particles. This includes the top surface, bottom surface and the 
edge/bevel areas of the wafer. Another benefit of the present invention is 
that the rotating edge cleaning apparatus 600 may be integrated into 
current double-side scrubber mechanism with minimal design changes to the 
scrubber system. In addition, since the rotation of the edge cleaning 
apparatus is independent of the wafer rotation, the relative velocity of 
the edge cleaning apparatus may be varied without affecting the cleaning 
of the top-side and bottom-side surfaces of the wafer. 
To further facilitate particle removal, a water jet 535 may be used to 
propel water into or near the point of contact between rotating belt 606 
and wafer edge 503, as shown in FIG. 5B. The water jet may be positioned 
such that the direction of water flows from a plane aligned with the 
rotational axis of the wafer and contact points between the wafer and the 
edge cleaning apparatus. In such a case, the water may simply carry the 
particles away that are removed from the wafer by the edge cleaning 
apparatus or may, if at sufficient pressure, cause removal of particles by 
itself. Note that the water jet is held in place by a support structure 
which is well-known in the art. In one embodiment, the water jet is held 
in place above the wafer. Such a jet may be as simple as a barbed coupling 
with reducing barb to increase the velocity of the created stream. In one 
embodiment, the barbed coupling is 1/8" to 1/16" in diameter. In another 
embodiment, the jet may include a nozzle that produces a fanned, knife 
edge pattern. Water jets are well-known in the art. Note also that jets 
that spray other chemicals may be used, instead of water, to facilitate 
particle removal. 
Rotating belt 606 may be cleaned occasionally to remove build-up of 
particles. In one embodiment, the scrubber may flow DI water or a 
combination of DI water and a chemical such as NH.sub.4 OH or NH.sub.4 
OH/H.sub.2 O.sub.2 mixture through itself. In an alternate embodiment, the 
edge cleaning apparatus may be cleaned by spraying DI or a combination of 
DI and a chemical such as NH.sub.4 OH or NH.sub.4 OH/H.sub.2 O.sub.2 onto 
belt 606 during wafer cleaning to reduce particle build-up. 
In one embodiment, a splash shield (not shown) may be provided around the 
rotating belt edge cleaning apparatus 600 to minimize the dispersion of 
water, chemicals and contaminates from the surface of belt 606 to other 
areas of the scrubber system. 
Another benefit of the present invention lies in the ability to use 
different types of materials to facilitate the cleaning of a variety of 
contaminates from the edge or bevel area of a wafer. Materials of 
different textures may single belt within a single belt, or may be 
incorporated into a plurality of rotating belt edge cleaning devices. In 
this manner, one material may be used for removing one type of contaminate 
while another material may be used to remove another type of contaminate. 
FIG. 6 illustrates an embodiment of the present invention wherein a 
plurality of rotating belt edge cleaning apparatus are used to 
sequentially clean the an edge 703 of wafer 702. As wafer 702 rotates, a 
first rotating belt edge cleaning apparatus 710 containing a first belt 
712 of a given texture that cleans particles from edge. The edge of the 
wafer is then rotated toward a second rotating belt edge cleaning 
apparatus 714. Edge cleaning apparatus 714 includes a second belt 716 that 
contains an outer surface having a different texture or abrasiveness than 
the first belt 712. 
Another important feature of the present invention lies in the ability to 
readily interchange belts of varying types into the edge cleaning 
apparatus. As a result, a standard rotating edge cleaning design may be 
used when cleaning any of a variety of contaminates from the edge or bevel 
area of a wafer. Moreover, it is important to note that materials of 
different textures may be attached to the outer surface of the edge 
cleaning belt to enhance the belt's particle removal capability. 
Thus, a method and apparatus for cleaning edges of substrates, such as 
wafers, is disclosed.