Patent Application
20060276111
1. Field of the Invention
Embodiments of the present invention generally relate to an element for conditioning a polishing surface in an electrochemical mechanical processing system.
2. Description of the Related Art
Electrochemical mechanical processing (ECMP) is one process commonly used in the manufacture of high-density integrated circuits. ECMP is utilized to remove conductive material from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion compared to conventional chemical mechanical processing (CMP). The electrochemical dissolution is performed by applying a bias between an electrode and the substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. ECMP processes can be utilized to deposit material on the substrate by reversing the polarity of the bias.
In order to achieve desirable polishing results, the polishing surface of the polishing pad must be conditioned periodically to remove any accumulated polishing by-products on the pad surface and/or to refresh the surface of the pad due to wear of the pad material. Typically, a polishing surface conditioner is utilized to condition the surface of the pad. In one embodiment, the polishing surface conditioner includes a replaceable conditioning element, such as a diamond disk, coupled to a conditioning head that is movable over the polishing surface. The diamond disk is lowered into contact with the polishing surface while being rotated. The conditioning head is generally swept across the rotating polishing surface to allow the diamond disk to condition a predefined area.
In one conditioning process, typically performed on polyurethane polishing pads traditionally utilized in conventional CMP systems, the polishing surface conditioner is configured to restore the fluid retention characteristics of the polishing surface and to remove embedded material from the polishing surface. In another conditioning process, typically performed on fixed abrasive polishing materials, the polishing surface conditioner is configured to expose abrasive articles disposed within structures comprising the abrasive polishing material, while removing asperities from the upper surface of the polishing material and leveling the structures on the polishing surface to a uniform height.
However, ECMP processing pads are generally softer and more delicate than the pads utilized in CMP systems. For example, ECMP processing pads may have a conductive surface or have conductive regions disposed on the surface. The conductive regions may be formed, for example, by conductive particles disposed in a binder. The conductive surface of the processing pad is typically softer than the polyurethane polishing pads used in CMP processes.
In addition, rough conditioning may lead to alteration of the resistance of the conductive regions, leading to process variability and reduced process control. Rough conditioning processes may also leave portions of the conductive particles raised above the processing pad surface, leading to scratches or other damage of the substrate being processed.
Thus, care must be exercised while conditioning the polishing material to avoid gouging or otherwise damaging the polishing material. Once the polishing material is damaged, the polishing material must be discarded (i.e., not used for polishing) to prevent damaging the substrate being processed, thereby reducing the number of substrates that may be polished per unit quantity of polishing material and resulting in decreased throughput and increased costs.
Therefore, there is a need for an improved conditioning element.
Embodiments of a conditioning element for conditioning a processing pad are provided herein. In one embodiment, a conditioning element for conditioning a processing pad includes a body having a face. A plurality of diamond particles are disposed on the face and define a conditioning surface. The diamond particles are of a type selected from the group of very blocky (4D), blocky (3D), and irregular (2D), and have a shape ratio less than or equal to 1.2. In one embodiment, the diamond particles have an average size of between about 85 and about 115 μm. In one embodiment, the size of the diamond particles may have a standard of deviation that is less than about 5 μm. In one embodiment, the diamond particles may have a spacing of greater than 400 μm.
In another embodiment, a conditioning element for conditioning a processing pad includes a circular body having a face and a plurality of diamond particles disposed in an annular pattern on the face and defining an annular conditioning surface. The diamond particles are of a type selected from the group consisting of very blocky (4D), blocky (3D), and irregular (2D), and have a shape ratio less than or equal to 1.2. The diamond particles have an average size of between about 85 and about 115 μm and the standard of deviation of the size of the diamond particles is less than about 5 μm.
In another embodiment, a conditioning element for conditioning a processing pad includes a disk-shaped body having a face and a plurality of diamond particles disposed on the face and defining a conditioning surface having a flatness of between about −10 and about 50 μm. The diamond particles are of a type selected from the group consisting of very blocky (4D), blocky (3D), and irregular (2D), and have a shape ratio less than or equal to 1.2. The diamond particles have an average size of between about 85 and about 115 μm and the standard of deviation of the size of the diamond particles is less than about 5 μm. The diamond particles have a spacing of greater than 400 μm and a distribution of between about 251 and about 261 particles per square cm. The diamond particles protrude between about 35 and about 65 μm from the face of the body and an uppermost portion of each of the diamond particles are leveled to within a range of between about 30 and about 50 μm.
In another aspect of the invention, a method of conditioning a processing pad is provided. In one embodiment, the method includes providing a conditioning element having a plurality of diamond particles disposed on a face of the conditioning element and defining a conditioning surface, wherein the diamond particles are of a type selected from the group consisting of very blocky (4D), blocky (3D), and irregular (2D), and have a shape ratio less than or equal to 1.2; and pressing the conditioning element against a processing surface of the processing pad with a force of less than about 2 pounds per square inch while rotating the conditioning element and the processing pad.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIGS. 3A-C respectively depict sectional side, bottom, and detail views of one embodiment of a conditioning element; and
FIGS. 4A-C depict various abrasive particle types suitable for forming a conditioning surface on the conditioning element.
To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures.
A conditioning element suitable for use in ECMP systems is provided herein. Specifically, the conditioning element is suitable for conditioning processing pads having conductive surfaces that are more delicate than the pads typically used in traditional CMP systems, e.g., polyurethane pads. The conductive surface of the pads may be partially conductive or fully conductive. The term fully conductive refers to, for example, a pad surface that comprises conductive particles or elements, such as tin, disposed in a binder. Examples and descriptions of suitable fully conductive pads and other pads suitable for use in ECMP systems are described in U.S. Pat. No. 6,561,873, issued May 13, 2003 to Tsai, et al. and entitled, “Method and Apparatus for Enhanced CMP Using Metals Having Reductive Properties,” U.S. patent application Ser. No. 10/455,895, filed Jun. 6, 2003 by Hu, et al. and entitled, “Conductive Polishing Article for Electrochemical Mechanical Polishing,” and U.S. patent application Ser. No. 10/140,010, filed May 7, 2002 by Hu, et al. and entitled, “Conductive Polishing Article for Electrochemical Mechanical Polishing,” all of which are incorporated herein be reference.
A controller 160 is provided to facilitate control and integration of the system 100. The controller 160 typically comprises a central processing unit (CPU), memory, and support circuits (not shown). The controller 160 is coupled to the various components of the system 100 to facilitate control of, for example, the planarizing, conditioning, and transfer processes.
In one embodiment, the factory interface 104 includes an interface robot 110 adapted to transfer substrates from one or more substrate storage cassettes 112 to a first transfer station 114. A second robot 116 is positioned between the factory interface 104 and the polisher 108 and is configured to transfer substrates between the first transfer station 114 of the factory interface 104 and a second transfer station 118 disposed on the polisher 108. The cleaner 106 is typically disposed in or adjacent to the factory interface 104 and is adapted to clean and dry substrates returning from the polisher 108 before being returned to the substrate storage cassettes by the interface robot 110.
The polisher 108 includes at least one polishing station 126 and a transfer device 120 disposed on a base 140. In the embodiment depicted in
The transfer device 120 supports at least one polishing head 124 that retains the substrate during processing. In the embodiment depicted in
The second transfer station 118 includes a load cup 142, an input buffer 144, an output buffer 142 and a transfer station robot 148. The input buffer 144 accepts a substrate being transferred to the polisher 108 from the second robot 116. The transfer station robot 148 transfers the substrate from the input buffer 144 to the load cup 142. The load cup 142 transfers the substrate vertically to the polishing head 124, which retains the substrate during processing. Polished substrates are transferred from the polishing head 124 to the load cup 142, and then moved by the transfer station robot 148 to the output buffer 142. From the output buffer 142, polished substrates are transferred to the first transfer station 114 by the second robot 116 and then transferred through the cleaner 106. One second transfer station 118 that may be adapted to benefit from the invention is described in U.S. Pat. No. 6,156,124, issued Dec. 5, 2000 to Tobin and entitled, “Wafer Transfer Station for a Chemical Mechanical Polisher,” which is incorporated by reference in its entirety.
A polishing fluid delivery system 102 includes at least one polishing fluid supply 150 coupled to at least one polishing fluid delivery arm assembly 152. Generally, each polishing station 126 is equipped with a respective delivery arm assembly 152 positioned proximate to a respective platen 130 to provide polishing fluid thereto during polishing. In the embodiment depicted in
The platen 130 of each polishing station 126 supports a polishing material 128. During processing, the substrate is held against the polishing material 128 by the polishing head 124 in the presence of polishing fluid provided by the delivery system 102. The platen 130 rotates to provide at least a portion of the polishing motion imparted between the substrate and the polishing material 128. Alternatively, the polishing motion may be imparted by moving at least one of the polishing head 124 or polishing material 128 in a linear, orbital, random, rotary or other motion.
The polishing material 128 may be comprised of a foamed polymer, such as polyurethane, or may be a fixed abrasive material. Fixed abrasive material generally includes a plurality of abrasive elements disposed on a flexible backing. In one embodiment, the abrasive elements are comprised of geometric shapes formed from abrasive particles suspended in a polymer binder. The polishing material 128 may be in either pad or web form.
A conditioning mechanism 134 is disposed proximate each polishing station 126 and is adapted to condition the polishing material 128 disposed on each platen 130. Each conditioning mechanism 134 is adapted to move between a position clear of the polishing material 128 and platen 130 as shown in
A conditioning element 208 is coupled to the bottom of the conditioning head assembly 202, for example, to a backing plate 250, and may be selectively pressed against the platen 130 while rotating to condition the polishing material 128. The conditioning element 208—and the backing plate 250—are typically round, or disk-shaped, to facilitate smooth rotation of the conditioning element 208 and enhance control of the process.
The elevation of the conditioning element 208 is generally controlled by pressurizing or venting an expandable cavity 290 partially bounded by a diaphragm 240 disposed in conditioning head assembly 202. A spring 242 disposed in the conditioning head assembly 202 provides an upward bias that assists in the retraction of the conditioning element 208 when the cavity 290 behind the diaphragm 240 is vented. Although the conditioning head assembly 202 depicted in
The support member 204 houses a drive shaft 214 coupling a motor 216 disposed below the base 140 to a pulley 218 disposed adjacent a first end 220 of the arm 206. A belt 222 is disposed in the arm 206 and operably couples the pulley 218 and the conditioning head assembly 202, thereby allowing the motor 216 to selectively rotate the conditioning element 208. While a belt 222 is shown in
A control fluid conduit 224 connected to a fluid control system 226 is routed through the support member 204 and arm 206, and is coupled to the conditioning head assembly 202. The fluid control system 226 includes a gas supply and various control devices (i.e., valves, regulators and the like) that facilitate the application and/or removal of fluid pressure to the motion of the conditioning head assembly 202. In one embodiment, the fluid control system 226 provides air or nitrogen to control the elevation of the conditioning element 208 relative to the platen 130, and to control the pressure applied by the conditioning element 208 against the polishing material 128 during conditioning.
The body 310 may have one or more threaded holes 322 formed in the back 320 to facilitate coupling to the backing plate 250 via screws, threaded extensions, or the like. In the embodiment depicted in FIGS. 3A-B, three threaded holes 322 are formed along a diameter of the body 310. Alternatively or in combination, one or more threaded holes 326 may extend partially through the body 310 from the back 320 along a periphery of the body 310 to facilitate coupling to the backing plate 250 via screws, threaded extensions, or the like. In the embodiment depicted in FIGS. 3A-B, three threaded holes 326 are substantially evenly spaced near a peripheral edge of the body 310. In addition, one or more apertures 324 may be formed in the back 320 of the body 310 to facilitate alignment with a feature, such as a locating pin (not shown) that extends from the backing plate 250 of the conditioning head assembly 202. In the embodiment depicted in FIGS. 3A-B, two apertures 324 are disposed on opposing sides of the body 310.
The body 310 may be fabricated from any process compatible material, such as metals, alloys, ceramics, and the like. In one embodiment, the body comprises stainless steel. The body 310 may further comprise multiple layers that together form the conditioning element 208. For example, an upper layer 311 may have the conditioning surface 300 formed thereon and may be bonded or otherwise secured to a base layer 309 to form the body 310 of the conditioning element 208. Optionally, a protective coating may be formed over at least a portion of the face 301 of the body 310. The coating protects the body 310 from exposure to the process chemistry (e.g., slurry and/or electrolyte) to extend the useful life of the conditioning element 208. The protective coating may comprise an extremely hard material such as diamond, diamond-like carbon (e.g., α-carbon), cubic boron nitride, and the like.
Although the conditioning element 208 may be any shape, it is practical and convenient to have a circular, or disk-shaped conditioning element. In one embodiment suitable for conditioning ECMP pads, such as ECMP pads used to process 200 and 300 mm substrates, the conditioning element 208 has a diameter between about 100 and about 110 mm. In one embodiment, the conditioning element 208 has a diameter of about 108 mm. The conditioning element 208 is generally stiff or rigid enough to minimize flexing under processing conditions. The rigidity of the conditioning element 208 may be obtained by material selection and/or the thickness of the conditioning element 208. For example, the conditioning element 208 may have a thickness of between about 6 and about 7 mm.
The conditioning surface 300 may cover the entire face 301 of the conditioning element 208. Alternatively, the conditioning surface 300 may cover only a portion of the face 301. In the embodiment depicted in
A recessed area 304 is disposed within center of the annular portion 302 to ensure that only the conditioning surface 300 contacts the material to be conditioned during processing. Optionally, one or more of an outer edge 306 and an inner edge 308 of the annular portion 302 may be relieved, such as by a radius, bevel, chamfer, and the like. The relieved edges reduce the likelihood that any sharp burrs or edges may scratch or gouge the material to be conditioned.
The conditioning surface 300 generally comprises particles 350, also referred to as grit, of an extremely hard material, such as diamond, that is securely embedded in or bonded to the body 310. The particles 350 may be embedded or bonded to the body 310 by suitable methods. To reduce the likelihood of damaging the material being conditioned, the particles 350 may be arranged on the conditioning surface 300 and may be excluded from any relieved edges 306, 308 and recessed areas 304 of the conditioning element 208.
FIGS. 4A-C depict suitable diamond particle types for use in the conditioning element 208. Specifically,
After being secured to the body 310, about 50 percent of the diamond particles 350 generally protrude above the face 301 of the body 310. In one embodiment, the diamond particles 350 protrude between about 35 to about 65 μm above the face 301. To facilitate the uniformity of the exposed surface of the diamond particles 350 above the face 301, the diamond particles 350 may have a uniform shape distribution. The uniformity of the diamond particles 350 is typically measured by a shape ratio. The shape ratio compares the height and the width of the diamond particles 350. Having a ratio near 1 ensures that the diamond particles 350 will extend the same distance above the face 301 of the body 310 no matter which way the particles are oriented during fabrication. For example, the diamond particles 350 may be dispersed onto the face 301 of the body 310 and fall in a random configuration. Diamond particles having a similar size as well as a shape ratio near 1 will have a similar height regardless of the orientation of the particles upon coming to rest on the face 301. In one embodiment, the shape ratio of the diamond particles 350 is between about 1 and about 1.2.
To further facilitate the uniformity of the protrusion of the diamond particles 350 above the face 301, the diamond particles 350 may be leveled, or controlled (e.g., the height of the tips of the diamond particles 350 may be leveled to be more uniform). In one embodiment, the tips of the diamond particles 350 are leveled to have a maximum tip-to-tip variation of between about 30 to about 50 μm. In addition, the conditioning surface 300 has a flat profile, for example as measured in multiple locations by a 2 mm diameter probe, ranging from about −30 to about 30 μm.
To maintain satisfactory conditioning performance and to reduce the likelihood of damaging the conductive surface of the ECMP pad, the diamond particles 350 have a controlled distribution and spacing. In one embodiment, the diamond particles 350 have a distribution of between about 251 and 261 particles per square cm. The diamond particles 350 may have a diamond to diamond distance of between about 300 μm and about 600 μm. In another embodiment, the diamond particles 350 are spaced greater than about 400 μm apart. The distribution of the diamond particles 350 is also controlled during fabrication to be substantially uniform.
In one embodiment, the conditioning element 208 may have diamond particles 350 that are blocky and/or very blocky diamond particle types ranging in size from about 20 to about 180 μm and having an average size of between about 85 μm and about 115 μm. The standard of deviation between the diamond particles 350 is less than about 5 μm. The diamond particles 350 protrude between about 35 to about 65 μm above the face 301 and the shape ratio of the diamond particles 350 is less than about 1.2. The tips of the diamond particles 350 are leveled to have a maximum tip-to-tip variation of between about 30 to about 50 μm and the conditioning surface 300 has a flat profile ranging from about −30 to about 30 μm. The diamond particles 350 have a distribution of between about 251 and 261 particles per square cm and the diamond particles 350 have a diamond to diamond spacing that is greater than about 400 μm apart.
In operation, the conditioning element 208 as described above may be used to condition a fully conductive pad having a conductive processing surface comprising, for example, conductive particles disposed in a binder. The fully conductive pad is used as the polishing material 128 in the ECMP system 100 described with respect to
The cutting rate of the conditioning element 208 is less than about 0.5 mil/hour on the conductive surface of the ECMP processing pad. The low cutting rate of the conditioning element 208 is used to refresh the processing pad surface by removing byproduct from the polishing process without dressing the processing pad surface (i.e., removing a large quantity of polishing material to even the processing surface), as is typically done in conventional polishing pad conditioning processes. Utilizing a conditioning element 208 as described herein and having a low cutting rate, the conductive surface of the ECMP processing pad may have a uniform center-to-edge conductivity and remaining thickness after being conditioned ex-situ and/or in-situ by the conditioning element 208.
The conditioning element 208 is pressed against the polishing material 128 with a low down force, for example from about 0.5 pounds per square inch to about 2 pounds per square inch. The reduced pressure facilitates conditioning without damaging the conductive surface of the polishing material 128 and extending the life time of both the polishing material 128 and the conditioning element 208. The conditioning mechanism 134 may be set to a sinusoidal sweep of, for example, about 5 to about 15 cycles per minute over a range of between about 1.5 and about 13.5 inches. The conditioning head assembly 202 may rotate at about 95 rpm and the platen 130 may rotate at about 7 to about 30 rpm. Electrolyte may be provided at a flow rate of about 330 ml/min.
It is contemplated that other process conditions may be used as necessary to condition conductive pads as desired for particular processes. The conditioning process may be alternatively be performed on other polishing equipment or on conditioning equipment separate from the polishing equipment.
In addition, conditioning may be performed during an initial break-in period and/or periodically throughout the life of the processing pad. For example, an ECMP processing pad may be conditioned for an initial break-in period after installing the pad in the processing equipment and prior to processing any substrates. In one embodiment, a pad break-in process includes a high-pressure rinse with de-ionized (DI) water. The DI water rinse exposes some the conductive particles on the surface of the processing pad and facilitates uniform contact points on the pad.
After 10 hours of conditioning under the conditions described above, the conditioning element 208 was examined and found to have no conductive particles from the polishing material 128 (i.e., the ECMP pad) clogging the conditioning surface 300. In addition, no conductive flakes were observed on the conditioning surface 300. The polishing material 128 was uniformly conditioned from pad center to pad edge with no significant increase in the resistance of the conductive pad surface. No deep scratches were present on the pad surface and no conductive particles were protruding from the pad surface. Thus, a conditioning element has been described that is suitable for conditioning ECMP processing pads without significantly increasing the resistance of the conductive portions of the pad. In addition, the conditioning element may be used without scratching or otherwise damaging the processing pad.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
