Patent Application
20090318060
Embodiments of the present invention generally relate to an apparatus and method for conditioning a polishing surface in an electrochemical mechanical processing system.
Chemical Mechanical Polishing (CMP) is a process widely used in the manufacture of semiconductor devices. Layers and structures are deposited and formed on a semiconductor substrate by various processes. Usually, these formation processes result in a surface that is not planar, or certain features formed in the substrate being covered and needing to be exposed. CMP is a process by which material is removed from the surface of a substrate to make it more planar (sometimes this process is referred to as Chemical Mechanical Planarization) and to expose desireable features.
During the CMP process, a polishing pad is used to remove material from the substrate, which is the mechanical aspect of the process. The pad abrades the surface of the substrate, usually with the help of an abrasive composition applied to the pad. The abrasive composition may include components selected to enhance the removal process chemically, providing the chemical aspect of the process. Some variations additionally use electrochemical means to enhance the process further (Electrochemical Mechanical Planarization or Polishing). As material is removed from the substrate, it collects on the pad and builds up in the abrasive composition. Also, as the pad is used its abrasive quality diminishes due to wear. Buildup of polishing byproduct material, and wear on the polishing pad requires that the pad be conditioned to restore its polishing capability. New pads must also be conditioned before they can be beneficially used.
Pad conditioning generally involves scouring the pad with an abrasive article to remove material that may be fouling the abrasive surface of the pad and to restore roughness to the pad. A conditioning pad contacts the polishing pad, abrading material from the pad and cutting grooves and features into the surface of the pad to restore roughness.
It is a constant challenge in the semiconductor industry that devices formed on semiconductor substrates grow smaller and denser over time. As devices grow smaller, all processes involved in forming the devices are challenged to produce these devices reliably. CMP processes are no exception. The smaller devices are more delicate, the layers to be removed from the substrates are thinner, the layers beneath that need to be preserved are thinner, and the features to be exposed by polishing are smaller and more easily damaged. The tolerance for variation in all processes is less, and new methods are required to meet these tolerances.
Thus, there is a continuing need for a method and apparatus for conditioning a polishing pad that yields uniform pad performance over the life of the conditioning pad as successive polishing pads are conditioned.
Embodiments disclosed herein provide a method of conditioning a polishing element, comprising contacting a surface of a conditioning element with a surface of the polishing element; applying a conditioning force to the conditioning element over a conditioning time; moving the conditioning element with respect to the polishing element; measuring the frictional force between the conditioning element and the polishing element; adjusting the conditioning time; and adjusting the conditioning force. The conditioning time may be limited to a fraction of the time the polishing element is used to polish a substrate, and may be adjusted together with, or separate from, the down force.
Other embodiments provide a method of conditioning a polishing element, comprising disposing an abrasive conditioning element at an end of a conditioning arm rotatably coupled to an actuator at a pivot point; using the actuator to sweep the conditioning arm across the polishing element while the abrasive conditioning element contacts a surface of the polishing element to remove material from the polishing element; applying a downward force to the abrasive conditioning element; measuring the torque applied to the pivot point by the actuator; comparing the measured torque to a standard value; adjusting the amount of material removed from the surface of the polishing element by the abrasive conditioning element. Adjusting the material removal may be accomplished by adjusting the conditioning time, the contact force between the conditioning element and the polishing element, or the rate of movement of the conditioning element with respect to the polishing element.
Other embodiments provide a method of removing material from a surface of a process element, comprising contacting an abrasive element with the surface of the process element; applying a contacting force to the abrasive element; translating the abrasive element across the surface of the process element during a processing time; monitoring the translation force required to translate the abrasive element across the surface of the process element; using a controller to adjust the processing time and contacting force based on comparison of the measured translation force with a standard.
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 embodiments, some of which are 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.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
The invention generally provides an apparatus and methods for conditioning a polishing pad for a planarization process. Embodiments described herein relate to a conditioning disk for conditioning, which includes scoring and/or dressing, a polishing surface of a polishing pad used in a CMP process. A conditioning disk generally comprises an annular body disposed on a backing plate. The backing plate is adapted to be coupled to a conditioning head assembly that is used to urge the conditioning disk against the polishing surface of the polishing pad. The annular body comprises a polycrystalline diamond covering or coating that is adapted to refresh, score, or condition the polishing surface when in contact with the polishing surface. In some embodiments, the polycrystalline diamond covering is machined to include a plurality of substantially identical structures which condition the polishing surface of the polishing pad. The size, pitch, and height of the plurality of structures are controlled with tight tolerances to enhance the cut rate without adversely increasing surface roughness of the polishing surface, and to prevent clogging or accumulation of polishing by-products, such as metal particles and/or portions of the polishing surface that may be spent and/or torn away from the polishing surface.
The conditioning device 215 is disposed proximate each polishing station 220A-220C and is adapted to condition the polishing material 225 disposed on each platen 230. Each conditioning device 215 is adapted to move between a position clear of the polishing material 225 and platen 230 as shown in
The polishing material 225 includes a polishing surface that may be at least partially conductive. Examples of polishing material 225 may include a combination of dielectric and conductive materials, or may be entirely dielectric or entirely conductive. In one embodiment, the polishing material 225 may include dielectric or conductive materials having conductive elements disposed therein. The conductive elements may be flakes, particles, and the like that are disposed in a dielectric or conductive material, such as a polymer material. Examples of conductive materials used as conductive elements and/or the conductive material are copper, carbon based materials, gold, platinum, silver, tin, zinc, nickel, cobalt, and combinations thereof, among other conductive materials that are resistant to polishing chemistry. Carbon-based material includes carbon black, graphite, and carbon particles. Examples of conductive carbon-based materials include carbon powder, carbon fibers, carbon nanotubes, carbon nanofoam, carbon aerogels, graphite, and combinations thereof. In one embodiment, a conductive polishing material may include conductive foils, polymers polymer materials with conductive materials disposed therein, conductive meshes, conductive flakes, conductive fibers, or a fabric of interwoven conductive fibers. The conductive materials, fibers, or fabric may be disposed in a polymeric material.
The pad dresser 210 is coupled to the conditioning head assembly 302 and may be selectively pressed against the polishing material 225 while rotating to condition the polishing material 225. The pad dresser 210 includes a backing plate and a conditioning surface. The backing plate and/or the conditioning surface are typically round, disk-shaped, or annular to facilitate rotation of the pad dresser 210 and enhance conditioning of the polishing material 225 and/or control of the conditioning process. In most embodiments, the polishing material 225 comprises a polishing pad having a polishing surface 370 and an attachment portion 372 that attaches to the backing plate 230.
During polishing, a substrate (not shown) is urged against the polishing material 225, with a downward force calculated to achieve a desired removal rate. The polishing material 225 may rotate on the platen 230 to translate the ridges and grooves of the polishing material across the substrate surface. The abrasive elements of the polishing material scour and abrade material from the substrate surface, and the resistance force applied by the substrate surface on each abrasive element of the polishing material generates a frictional force between the substrate and the polishing material. The substrate may also be rotated to increase removal rate. As one or both of the platen 230 and substrate are rotated, conductive material is removed from the face of the substrate by electrochemical and mechanical forces.
Before, during, or after the polishing process, the polishing surface 276 may require conditioning of the pad polishing surface in order to maintain predefined processing results. Conditioning may create, reform, and/or clear grooves and/or asperities in the polishing surface 276. In another application, conditioning of the polishing surface 276 refreshes the polishing surface 276. Refreshing may include at least one of exposing new or unused material on the polishing surface 276, removing polishing by-products, removing spent or torn portions of the polishing surface 276, and/or removal or minimization of oxides disposed in or on the polishing surface 276. The conditioning of the polishing surface 276 may be performed prior to polishing with a new polishing pad, during the polishing process to maintain and/or enhance surface roughness and removal rate of the polishing surface 276, or post-processing to prepare the polishing surface 276 for a new substrate to be polished.
A conditioning element such as those described herein is urged against the polishing surface. The conditioning element and the polishing surface may rotate, and the conditioning element may sweep across the polishing surface, as described above. Downward force is applied to the conditioning element to generate a desired amount of scouring, grooving, and roughening of the polishing surface. The interaction of abrasive elements of the conditioning element with the polishing surface generates a frictional force that is overcome by operation of the actuator 310. A sensor 312 monitors the frictional force by measuring the torque generated on the support member 304 by the actuator 310, and may provide that measurement to controller 314 configured to generate a control signal to the actuator 310. The controller 314 may also be configured to adjust the pressure inside the expandable cavity 390 to control the downward force applied to the conditioning element.
At 404, the measured torque is compared to a standard value, which may be a target value. The standard value is determined by the amount of friction desired between the conditioning element and the polishing surface. The frictional force is related to the effectiveness of conditioning. A high frictional force indicates material is being removed from the polishing surface at a high rate, but too high a removal rate results in reduced pad life. A low frictional force may indicate the polishing surface is not being roughened enough to provide effective processing of substrates.
At 406, an adjustment is made based on the comparison above. One adjustment is to the conditioning time. When the conditioning time has elapsed, conditioning may be interrupted by lifting the conditioning element off the polishing surface, even though polishing of a substrate is ongoing. If the frictional force is high, the polishing surface may be effectively conditioned in a shorter time, so the conditioning time is reduced to avoid excessive wear on the polishing surface and the conditioning element. If low, the conditioning time may be lengthened to achieve the desired results. The conditioning time will generally be controlled between 50% and 100% of the polishing time for a substrate. Conditioning of the polishing surface may take place exclusively while a substrate is being processed, or may proceed between processing of substrates. In some embodiments, conditioning may be continuous as substrates are positioned on the apparatus, processed, and removed from the apparatus. In other embodiments, conditioning may start before, during, or after polishing, and may end before, during, or after polishing.
In some embodiments, it may be necessary to increase or reduce the conditioning vigor by more than is possible through adjustments to conditioning time. At 408, the downforce may also be adjusted to increase or reduce the frictional force. Effective and reproduceable conditioning of a polishing surface results.
At 504, the measured frictional force is compared to a standard value. The standard value is determined by the desired rate of material removal from the polishing surface, and the desired scoring and grooving of the surface. If the measured value deviates from the standard value, an adjustment is made at 506. The conditioning time may be adjusted at 506 to increase or decrease material removal from the polishing surface. Adjustments to the conditioning time are generally bounded by upper and lower limits, which may be determined by polishing time of a substrate, or by other process considerations such as platen rotation speed or arm sweep speed. For example, it may be advantageous to ensure conditioning time is long enough to encompass coverage of the entire width of the platen by the conditioning element in at least one sweep. In some processes, conditioning time may be required to complete more than one sweep. As described above in connection with method 400, conditioning may begin before, during, or after polishing, and may end before, during, or after polishing. The conditioning time may be shorter than, equal to, or longer than the polishing time. It is generally preferred that conditioning begins at the same time polishing begins, and ends at the same time polishing ends, or before.
In the event the desired conditioning effectiveness cannot be achieved by the adjustment of 506, the downforce may be adjusted at 508. The pressure inside the conditioning head may be adjusted to provide more or less force on the conditioning element. In some embodiments, the downforce and the conditioning time may be adjusted together or simultaneously. For example, if the measured frictional force indicates a material removal rate that is too high, the conditioning time and downforce may both be reduced at the same time. If the removal rate is too low, both may be increased at the same time.
In some embodiments, the contact time may be limited. For example, when substrates are not being processed on the polishing surface, conditioning may be interrupted. In some embodiments, it may be desireable to condition the polishing surface when a substrate is disposed thereon and being processed. In other embodiments, it may be useful to limit the contact time to a fraction of the time the substrate is processed on the polishing surface. For example, in some embodiments the contact time may be between about 50% and about 100% of the polishing time. In embodiments wherein the conditioning element is translated across the polishing surface, it may be desireable to require that the contact time be no less than the time required to translate the conditioning element across the entirety of one dimension of the polishing surface. In an embodiment in which the polishing surface is an annular or disk-shaped surface, and the conditioning element is translated from an inner radius to an outer radius of the polishing surface, or from an outer radius to an inner radius of the polishing surface, it may be advantageous to require that the contact time be no less than the time required to translate the conditioning element from the inner to the outer radius, or vice versa, to ensure the entire polishing surface is conditioned.
In other embodiments, other variables may be adjusted to achieve effective conditioning results over the life of a conditioning element. In some embodiments, the conditioning element may rotate, and the rate of rotation may be adjusted. In other embodiments, the rate the conditioning element is translated across the polishing surface may be adjusted. In still other embodiments, the conditioning element may be translated and rotated according to specified patterns, which may be adjusted to affect the amount of material removed from the polishing pad.
While the foregoing is directed to embodiments of the 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.
This application claims benefit of U.S. provisional patent application Ser. No. 61/074,956, filed Jun. 23, 2008, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61074956 | Jun 2008 | US |
