Method and apparatus for controlling planarizing characteristics in mechanical and chemical-mechanical planarization of microelectronic substrates

A method and apparatus for mechanical and/or chemical-mechanical planarization of microelectronic substrates. In one embodiment, an apparatus for controlling the planarizing characteristics of a microelectronic substrate has a carrier that may be positioned with respect to a polishing medium of a planarizing machine to move with respect to a microelectronic substrate during planarization. The apparatus may also have a modulator with a contact element, and the modulator may be attached to the carrier to position at least a portion of a contact element in front of a leading edge of the substrate by a selected distance during planarization. In operation, the modulator causes the contact element to selectively engage a region of the planarizing surface to modulate the contour of the planarizing surface during planarization.

TECHNICAL FIELD

The present invention relates to mechanical and chemical-mechanical planarization of microelectronic substrates. More particularly, the present invention relates to controlling the planarizing characteristics of a microelectronic substrate.

BACKGROUND OF THE INVENTION

Mechanical and chemical-mechanical planarization processes remove material from the surface of semiconductor wafers, field emission displays and many other microelectronic substrates to form a flat surface at a desired elevation.FIG. 1schematically illustrates a planarizing machine10with a platen or base20, a carrier assembly30, a polishing pad40, and a planarizing solution44on the polishing pad40. The planarizing machine10may also have an under-pad25attached to an upper surface22of the platen20for supporting the polishing pad40. In many planarizing machines, a drive assembly26rotates (arrow A) and/or reciprocates (arrow B) the platen20to move the polishing pad40during planarization.

The carrier assembly30controls and protects a substrate12during planarization. The carrier assembly30generally has a substrate holder32with a pad34that holds the substrate12via suction, and an actuator assembly36typically rotates and/or translates the substrate holder32(arrows C and D, respectively). However, the substrate holder32may be a weighted, free-floating disk (not shown) that slides over the polishing pad40.

The polishing pad40and the planarizing solution44may separately, or in combination, define a polishing environment that mechanically and/or chemically removes material from the surface of the substrate12. The polishing pad40may be a conventional polishing pad made from a relatively compressible, porous continuous phase matrix material (e.g., polyurethane), or it may be an abrasive polishing pad with abrasive particles fixedly bonded to a suspension medium. In a typical application, the planarizing solution44may be a chemical-mechanical planarization slurry with abrasive particles and chemicals for use with a conventional non-abrasive polishing pad, or the planarizing solution44may be a liquid without abrasive particles for use with an abrasive polishing pad. To planarize the substrate12with the planarizing machine10, the carrier assembly30presses the substrate12against a planarizing surface42of the polishing pad40in the presence of the planarizing solution44. The platen20and/or the substrate holder32then move relative to one another to translate the substrate12across the planarizing surface42. As a result, the abrasive particles and/or the chemicals in the polishing environment remove material from the surface of the substrate12.

Planarizing processes must consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns on the substrate. As the density of integrated circuits increases, the uniformity and planarity of the substrate surface is becoming increasingly important because it is difficult to form sub-micron features or photo-patterns to within a tolerance of approximately 0.1 μm when the substrate surface is not uniformly planar. Thus, planarizing processes must create a highly uniform, planar surface on the substrate.

In the competitive semiconductor and microelectronic device manufacturing industries, it is also desirable to maximize the yield of individual devices or dies on each substrate. Typical semiconductor manufacturing processes fabricate a plurality of dies (e.g., 50-250) on each substrate. To increase the number of dies that may be fabricated on each substrate, many manufacturers are increasing the size of the substrates to provide more surface area for fabricating additional dies. Thus, to enhance the yield of operable dies on each substrate, planarizing processes should form a planar surface across the substrate surface.

In conventional planarizing processes, however, the substrate surface may not be uniformly planar because the rate at which material is removed from the substrate surface (the “polishing rate”) typically varies from one region on the substrate to another. The polishing rate is a function of several factors, and many of the factors may change throughout the planarizing process. For example, some of the factors that effect the polishing rate across the surface of the substrate are as follows: (1) the distribution of abrasive particles and chemicals between the substrate surface and the polishing pad; (2) the relative velocity between the polishing pad and the substrate surface; and (3) the pressure distribution across the substrate surface.

One particular problem with conventional planarizing devices and methods is that the deviation of the surface uniformity in a perimeter region of the substrate is generally much greater than that of a central region. In conventional planarizing processes, the polishing rate in a 5-15 mm perimeter region at the substrate edge is generally higher than the polishing rate in a central region. One reason for the difference in the polishing rate is that the relative velocity between the substrate and the polishing pad is generally higher in the perimeter region of the substrate than the central region. Another reason for the difference in the polishing rate is that the edge of the substrate wipes a significant amount of the planarizing solution off of the polishing pad before the planarizing solution can contact the central region. Conventional planarizing devices and methods, therefore, typically produce a non-uniform, center-to-edge planarizing profile across the substrate surface.

To reduce such center-to-edge planarizing profiles, several existing polishing pads have holes or grooves that transport a portion of the planarizing solution below the substrate surface during planarization. A Rodel IC-1000 polishing pad, for example, is a relatively soft, porous polyurethane pad with a number of large slurry wells approximately 0.05-0.10 inches in diameter that are spaced apart from one another across the planarizing surface by approximately 0.125-0.25 inches. During planarization, small volumes of slurry are expected to fill the large wells, and then hydrodynamic forces created by the motion of the substrate are expected to draw the slurry out of the wells in a manner that wets the substrate surface. However, even IC-1000 pads may produce significant center-to-edge planarizing profiles indicating that the perimeter of the substrate presses some of the slurry out of the wells ahead of the center of the substrate. U.S. Pat. No. 5,216,843 describes another polishing pad with a plurality of macro-grooves formed in concentric circles and a plurality of micro-grooves radially crossing the macro-grooves. Although grooved pads may improve the planarity of the substrate surface, substrates planarized with such pads still exhibit non-uniformities across the substrate surface indicating a non-uniform distribution of planarizing solution and abrasive particles under the substrate.

Other techniques for reducing the center-to-edge planarizing profile reduce the differences in the relative velocity between the perimeter and central regions. For example, one existing planarizing machine holds the polishing pad stationary and orbits the substrate in an eccentric pattern across the polishing pad. In another related planarization process, the substrate is held in a precession wafer holder that allows the substrate to precess with respect to the wafer holder during planarization. Although reducing the difference in the relative velocity across the substrate surface reduces the center-to-edge planarizing profile, existing planarizing machines may still produce significant deviations in the surface uniformity between the perimeter region and the central region.

In light of the results of conventional planarizing devices, the deviation of the surface uniformity in the perimeter region may be so great that it impairs or ruins dies formed in the perimeter region. Thus, because a defective 5-15 mm perimeter region affects a larger surface area and more dies on a 12-inch substrate than an 8-inch substrate, the center-to-edge planarizing profile significantly impacts the yield of larger substrates.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for mechanical and/or chemical-mechanical planarization of microelectronic substrates. In one embodiment in accordance with the principles of the present invention, an apparatus for controlling the planarizing characteristics of a microelectronic substrate has a carrier that may be positioned with respect to a polishing medium of a planarizing machine. The carrier may be a substrate holder of the planarizing machine or another carrier independent from the substrate holder that moves with respect to a microelectronic substrate during planarization of the substrate. The apparatus may also have a modulator attached to the carrier, and the modulator may have a contact element for engaging the polishing medium. The modulator, for example, may be attached to the carrier to position at least a portion of the contact element in front of a leading edge of the substrate by a selected distance during planarization. In operation, the contact element selectively engages a portion of the planarizing surface proximate to the leading edge of the substrate to modulate the contour of the planarizing surface of the polishing medium.

In one particular embodiment in which the carrier is a substrate holder, the modulator is attached to the substrate holder to position the contact element superadjacent to an exposed portion of a standing wave that forms at the leading edge of the substrate during planarization. The contact element operates by engaging the exposed portion of the standing wave in a manner that modulates the contour of a residual portion of the standing wave under a perimeter region of the substrate. For example, the modulator may be a passive modulator in which the contact element has a bottom surface with a desired contour to attenuate or shift the residual portion of the standing wave. In another embodiment, the modulator may be an active modulator having an actuator that carries the contact element and a controller coupled to the actuator. The controller may be programmed to drive the actuator in a manner that selectively moves a bottom surface of the contact element against the exposed portion of the standing wave. The particular motion of the actuator may be selected to continually shift a pressure point of the residual portion of the standing wave and/or attenuate the residual portion of the standing wave. For example, the active modulator may move the contact element against the exposed portion of the standing wave in a manner that oscillates a pressure point of the residual portion of the standing wave under the perimeter region of the substrate to average the effect of the pressure point over a larger surface area on the substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an apparatus and method for mechanical and/or chemical-mechanical planarization of substrates used in the manufacturing of microelectronic devices. Many specific details of certain embodiments of the invention are set forth in the following description and inFIGS. 2-5Bto provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments and may be practiced without several of the details described in the following description.

FIG. 2is a schematic view of a planarizing machine100in accordance with one embodiment of the invention. The planarizing machine100includes a carrier assembly130and an active modulator170for controlling the planarizing characteristics of a microelectronic substrate12. The features and advantages of the modulator170are best understood in the context of the structure and operation of the planarizing machine100. Thus, the general features of the planarizing machine100will be described initially.

The planarizing machine100may have a platen or a support table110carrying an underpart112at a work station or a planarization station where a section “A” of a planarizing medium100is positioned. The underpart112may be a substantially incompressible support member attached to the table110to provide a flat, solid surface to which a particular section of the polishing medium140may be secured during planarization. In other applications, however, the underpart112may be a compressible pad to provide a more conformal polishing medium. The planarizing machine110100also has a plurality of rollers to guide, position, and hold the polishing medium140over the underpart112. In one embodiment, the rollers include a supply roller120, first and second idler rollers121a and121b, first and second guide rollers122a and122b, and a take-up roller123. The supply roller120carries an unused portion of the polishing medium140, and the take-up roller123carries the used portion of the polishing medium140. The supply roller120and the take-up roller123are driven rollers to sequentially advance the unused portion of the polishing medium140onto the underpart112. As such, an unused section of the planarizing medium may be quickly substituted for a worn, used section to provide a consistent surface for planarizing the substrate. The first idler roller121a and the first guide roller122a position the polishing medium140slightly below the underpart112so that the supply and take-up rollers120and123stretch the polishing medium140over the underpart112to hold it stationary during planarization.

The planarizing machine100also has a carrier assembly130to translate the substrate12across a planarizing surface150of the polishing medium140. In one embodiment, the carrier assembly130has a substrate holder132to pick up, hold and release the substrate12at appropriate stages of the planarization process. The carrier assembly130may also have a support gantry134carrying an actuator136so that the actuator136can translate along the gantry134. The actuator136preferably has a drive shaft137coupled to an arm assembly138that carries the substrate holder132. In operation, the gantry134raises and lowers the substrate12, and the actuator136orbits the substrate12about an axis B-B via the drive shaft137. In another embodiment, the arm assembly138may also have an actuator (not shown) to drive a shaft139of the arm assembly138and thus rotate the substrate holder132about an axis C—C in addition to orbiting the substrate holder132about the axis B—B.

The modulator170may be an active modulator170with a contact element172, an actuator174carrying the contact element172, and a controller180coupled to the actuator174. In one embodiment, the actuator174is attached to the substrate holder132to position at least a portion of the contact element172in front of leading edge of the substrate12during planarization. For example, the actuator174and the contact element172may surround the substrate12so that a portion of the contact element172is positioned superadjacent to an area on the polishing medium140in front of a leading edge of the substrate12irrespective of the direction that the substrate holder132is moving. The contact element172may accordingly be a carrier ring that contains the substrate12within the substrate holder132. As discussed in further detail below, the contact element172selectively engages the planarizing surface150to modulate the contour of the planarizing surface150under a perimeter region of the substrate12.

FIG. 3is a partial schematic cross-sectional view of the substrate holder132showing a portion of the active modulator170in greater detail. The actuator174may be a single linear displacement device or a plurality of displacement devices embedded in the substrate holder132in a ring around the substrate12. The contact element172may thus be a ring configured to position a bottom surface173of the contact element172superadjacent to a portion of the planarizing surface150. In one particular embodiment, the actuator174is a piezoelectric ring driven by electric signals from the controller180. The contact element172may accordingly be a metal, ceramic or other type of ring attached to the piezoelectric actuator174.

One aspect of the invention is the discovery that a leading edge14of the substrate12having a motion “M” forms a standing wave152in the planarizing surface150of the polishing medium140. The particular waveform of the standing wave152is a function of several factors, such as the pad type, substrate structure, planarizing solution, downforce, relative velocity and other factors. The standing wave152shown inFIG. 3is a schematic representation of a standing wave that does not necessarily represent the waveform of an actual standing wave. As such, the amplitude and wave length of the standing wave152shown inFIG. 3are exaggerated for illustrative purposes. Additionally, a planarizing solution is not shown on top of the planarizing surface150for purposes of clarity, but it will be appreciated that a planarizing solution is typically dispensed onto the planarizing surface150during planarization.

In operation, the controller180drives the actuator174to move the contact element172vertically and/or horizontally with respect to an exposed portion154of the standing wave152. For example, in one possible application of the active modulator170, the actuator174may hold a bottom surface173of the contact element172in engagement with the planarizing surface150(not shown inFIG. 3) at a set position with respect to the exposed portion154of the standing wave152to alter a residual portion of the standing wave156with respect to the substrate12. In another possible application of the active modulator170, the actuator174may continuously move the contact element172in engagement with the planarizing surface150to continuously alter the contour of the planarizing surface150in a manner that produces a plurality of different waveforms on the planarizing surface150instead of the standing wave152. In still another possible application of the active modulator170, the actuator may move the contact element172into engagement with the planarizing surface150at a selected frequency, amplitude and phase with respect to the standing wave152to cancel the standing wave152on the planarizing surface150. Thus, the controller180may be programmed to selectively operate the active modulator170in a desired manner according to the particular application.

FIG. 4Ais a schematic partial cross-sectional view illustrating the aforementioned possible application in which the contact element170172is held at a set position against the planarizing surface150. InFIG. 4A, the controller180drives the actuator174to position the bottom surface173of the contact element172a distance h1away from a reference height ho where the bottom surface173engages the exposed portion154of the standing wave152. The actuator174may hold the bottom surface173in this position such that the force exerted by the contact element172against the exposed portion154changes the residual portion156of the standing wave152with respect to the perimeter region15of the substrate12. Thus, in this possible application, the contact element172may be positioned to affect the boundary condition of the standing wave152in a manner that attenuates and/or changes the position of pressure points of the residual portion156with respect to the substrate12.

FIG. 4Bis another schematic cross-sectional view that, together withFIG. 4A, illustrates the aforementioned possible application in which the actuator174continuously moves the contact element172in engagement with the planarizing surface150to produce a plurality of different waveforms on the planarizing surface150. In this application, the actuator174may move the bottom surface173of the contact element172between the position h1(FIG. 4A) and a position h2(FIG. 4B) at one or more frequencies to continuously alter the waveform on the planarizing surface. As such, the standing wave152on the planarizing surface150will be replaced by a number of different waves in which the pressure points act on different radial positions of the substrate12. For example, if the actuator174moves the contact element172from the position h1to the position h2during planarization, a number of pressure points158and159may move with respect to the substrate. The actuator174, accordingly, may move the contact element172during planarization to change the radial locations of the pressure points with respect to the substrate12so that the effects of the pressure points may be spread across a larger surface area of the substrate12. In this application, therefore, the active modulator170is expected to reduce the concentration of a high pressure forces at relatively fixed radial positions on the substrate12.

To program the controller180to drive the actuator174, an operator may measure the planarity of the perimeter region15of a number of substrates that were planarized while holding the contact element172at a number of different set positions or moving the contact element172at a number of selected frequencies and amplitudes. Since the shape of the standing wave150152is a function of such factors as the pad type, substrate configuration, relative velocity, slurry distribution and down force, the particular position or movement of the contact element172may be determined empirically for each specific planarization process. Based upon the actual deviation in the surface uniformity of the perimeter region15, and also based upon the size of the perimeter region15, a person skilled in the art can determine the best position or motion of the contact element172to program into the controller180.

The planarizing machine100with the active modulator170is expected to reduce the deviation in the surface uniformity in the perimeter region of a microelectronic substrate. Unlike conventional devices and methods for reducing the edge effect in planarization, several embodiments of the present invention are expected to enhance the uniformity of the substrate surface by altering the pressure exerted against the perimeter region of the substrate. The contact element172, more particularly, may shift and/or attenuate the residual portion of the standing wave under the perimeter region15of the substrate12to reduce the concentration of high pressure points at substantially fixed radial positions on the substrate12. As a result, the modulator170is expected to limit large deviations in the surface uniformity to a region approximately 2-5 mm from the substrate edge as opposed to the 5-15 mm perimeter region produced by conventional devices. Moreover, compared to conventional systems, the modulator170is also expected to reduce the extent of the deviations in surface uniformity in the 2-5 mm perimeter region. Thus, the planarizing machine100with the active modulator170is expected to increase the yield of operable dies on each substrate.

FIGS. 5A and 5Bare partial schematic cross-sectional views of another embodiment of a modulator270for controlling the planarizing characteristics of microelectronic substrates. Referring to FIG. SA, the modulator270may be a passive modulator in which the contact element272is fixedly attached to or integrally formed with the substrate holder132. The contact element272may have a bottom surface273with a desired contour to modulate a residual portion156of the standing wave152on the planarizing surface150under the perimeter region15of the substrate12. As described above with respect to determining the waveform for moving the active contact element172, the contour of the bottom surface273may be determined empirically to shift or attenuate the residual portion156of the standing wave. Thus, the shape of the bottom surface273shown inFIGS. 5A and 5Bis for illustrative purposes, and it will be appreciated that other shapes may be used to adapt the contact element272to the specific planarizing process. The width of the contact element172and its distance from the leading edge14of the substrate12can also be determined empirically at different operating conditions such as wafer velocity.

FIG. 5Billustrates the operation of the passive modulator270in which the substrate holder132presses the bottom surface273against the exposed portion154of the standing wave152on the planarizing surface150. As described above, the shape of the bottom surface273may be configured either to attenuate and/or shift the residual portion156of the standing wave152. Unlike the active modulator170, however, the passive modulator270does not oscillate the pressure points of the residual portion156because the contact face273remains at the same elevation relative to the polishing pad140during planarization.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described above for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, the contact element172may be an integral part of the piezoelectric actuator174. Additionally, the shape of the bottom surface173of the contact element172may also be contoured as shown by the bottom surface273of the contact element272. Accordingly, the invention is not limited except as by the appended claims.