Chemical Mechanical Polishing System with Conditioning Ring

Chemical mechanical polishing (“CMP”) is used in the manufacture of integrated circuits. A combination of chemical and mechanical forces is used to provide a level surface on the top layer of a semiconducting wafer substrate.

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The system may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Numerical values in the specification and claims of this application should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value. All ranges disclosed herein are inclusive of the recited endpoint.

The term “about” can be used to include any numerical value that can vary without changing the basic function of that value. When used with a range, “about” also discloses the range defined by the absolute values of the two endpoints, e.g. “about 2 to about 4” also discloses the range “from 2 to 4.” The term “about” may refer to plus or minus 10% of the indicated number.

The present disclosure relates to structures which are made up of different layers. When the terms “on” or “upon” are used with reference to two different layers (including the substrate), they indicate merely that one layer is on or upon the other layer. These terms do not require the two layers to directly contact each other, and permit other layers to be between the two layers. For example all layers of the structure can be considered to be “on” the substrate, even though they do not all directly contact the substrate. The term “directly” may be used to indicate two layers directly contact each other without any layers in between them. In addition, when referring to performing process steps to the substrate or upon the substrate, this should be construed as performing such steps to whatever layers may be present on the substrate as well, depending on the context.

The term “wafer substrate”, as used herein, refers to a substrate or to the combination of a substrate and any layers upon the substrate.

The present disclosure relates to chemical mechanical polishing (CMP) systems. CMP is used to planarize the surface of a wafer using relative motion between the wafer and a rotating CMP polishing pad to which a slurry is applied. Downward pressure is applied to push the wafer against the polishing pad, and elevated elements are worn down to obtain a surface with low surface roughness. This improves within die (WiD), within-wafer (WiW), and wafer-to-wafer (WtW) uniformity which is desired.

The condition of the polishing pad is a large factor in the performance of the CMP process. Polishing pads with different hardness, roughness, and/or porosity can result in wafers with different performance/yield. The polishing pad surface typically includes grooves and asperities which can become blocked or glazed by debris and byproducts produced during CMP. Thus, regular “dressing” of the polishing pad is performed to remove worn surface material and restore a desired uniform texture to the polishing pad surface. A pad conditioner pushes downward against the polishing pad using a disk with an abrasive surface for this purpose. However, the use of the pad conditioner is restricted at the perimeter of the polishing pad due to the down force, which can cause error alarms by tilting the polishing pad and thus changing the force applied to the wafer substrate that is being polished. This will also cause the polishing pad profile to include a step height near the perimeter, where the pad height is greater than the pad height where the pad conditioner can be used. This can cause wafer slip out, where the wafer substrate escapes from the wafer carrier.

In the present disclosure, a new system is provided in which the pad conditioner disk is replaced with a conditioning ring. The conditioning ring has a diameter that is equal to or greater than the radius of the polishing pad. The conditioning ring is thus able to condition the polishing pad from the center to the edge simultaneously, increasing the uniformity of the polishing pad height across its radius and also reducing conditioning time. The down force of the pad conditioner at the perimeter/edge is also reduced so as to avoid error signals.

is a side view of a CMP system, according to some embodiments of the present disclosure.is a plan view of the CMP system. It is noted that not all components are illustrated in both figures.

Referring to both figures, the CMP systemincludes a housingthat contains a chamberfor providing a sealed environment for the various components. One or more load ports (not shown) can be coupled to the wall of the chamberto permit wafer substrates to enter and exit the CMP systemusing a robotic wafer transfer system. A dooris illustrated which permits access to the chamber. A wafer load/unload stationis shown, where the wafer substrateis placed.

Continuing, the CMP systemincludes a polishing platen. The platen is in the form of a flat plate having an upper surface. The platen is attached to a shaft, which is coupled to a motor (not shown) for rotating the platen.

A polishing padis attached to the upper surface of the platen. This attachment is typically performed by adhesive, mechanical, or vacuum means. The polishing pad is commonly made from materials that are soft enough not to substantially scratch the wafer, but hard enough to push abrasive particles in the slurry against the wafer to cause mechanical polishing. Examples of such materials may include polyurethane and polyester. The upper surfaceof the polishing pad may also include high-aspect grooves and asperities between the grooves. The polishing pad has a surface roughness (Ra), which is used for polishing of the wafer substrate. The texture, composition, and/or the structure of the polishing pad may vary depending on the material that is being polished.

The wafer carrier(also known as a polishing head) includes a carrier headwhich is attached to a carrier body. The carrier headis rotatable relative to the body. The bodyis best seen in, and is attached to a robotic armfor moving the wafer carrier between the load/unload stationand the platen, as indicated in. The wafer carriercan also be moved up-and-down relative to the polishing pad, both for transport and for applying a desired amount of force to press the wafer against the polishing pad, as indicated in. One or more motors (not shown) may be present for rotating the carrier head, moving the carrier head, and/or moving the robotic arm.

The wafer substratecan be picked up by the carrier head, for example using a vacuum to suck and hold the wafer substrate upon the carrier head. A flexible membraneis located between the wafer substrateand the carrier head. The membrane can be inflated and used to press the wafer against the polishing pad. Vacuum is generally not applied during the polishing process. In some embodiments, the membrane can be made from a silicone, although other materials may also be used.

An annular retaining ringis present along the perimeter of the carrier head to retain the wafer substrate and prevent it from spinning off the wafer carrier. The retaining ring is typically formed from a wear-resistant material. Examples of suitable materials may include polyphenylene sulfide (PPS), polyetheretherketone (PEEK), or other polymers. In use, the retaining ring surrounds the circumference of the wafer substrate.

Continuing, a slurry dispenseris present for applying slurry to the polishing padduring the CMP process. The slurry is a mixture of abrasive particles and fluids. If desired, the fluids may be reactive with the top layer of the wafer substrate, which can aid in the CMP process. The abrasive particles mechanically polish the top layer of the wafer substrate. The abrasive particles may be, for example, silica, aluminum oxide ceria, silicon carbide, zirconium oxide, iron oxide, zinc oxide, or titanium dioxide. Other chemicals may also be present in the slurry, such as an oxidizer, a chelator, a surfactant, a corrosion inhibitor, a removal rate enhancer, etc. The composition of the slurry may vary depending on the material that is being polished.

As illustrated here, the slurry dispenserincludes an armand one or more nozzlesfor dispensing the slurry. The slurry is usually dispensed near the center of the polishing pad, and then travels outwards due to centrifugal forces from rotation of the platen and polishing pad. The arm may also move between the center of the polishing pad and the perimeter of the polishing pad, as indicated in.

The CMP systemalso includes a pad conditioner, which is used to condition the polishing pad. The removal rate of a polishing pad will decrease over time due to surface degradation, also known as glazing. The pad conditioner removes the glazed surface of the polishing pad, uncovering fresh pad material, and also creates grooves and asperities to provide a more uniform and stable removal rate over time and over the entire surface of the polishing pad.

The pad conditionerincludes a conditioner headwhich is attached to a conditioner body. The conditioner headis rotatable relative to the body. The bodyis attached to a movable armwhich can move between the center of the polishing pad and the perimeter of the polishing pad, as indicated in. The pad conditionercan also be moved up-and-down relative to the polishing padfor applying a desired amount of force to the polishing pad, as indicated in. A pad conditioning ringis affixed to the underside of the conditioner head. One or more motors (not shown) may be present for rotating the carrier head and the conditioning ring, moving the carrier head, and/or moving the movable arm.

A controlleris used to control the various components, and to measure various conditions within the chamber for the CMP process. The system may also include sensors (not shown) for monitoring applicable parameters. For example, such sensors may include those for tracking the slurry flow rate, the down force of the wafer carrier and/or the pad conditioner, the rotation speed of the platen/wafer carrier/pad conditioner, the dwell time of the wafer carrier/pad conditioner, the temperature of the wafer substrate, etc. The controller can also determine whether to activate or deactivate the system, how/when to move the wafer carrier and/or the pad conditioner, control the motion of any automated handling system that may be present, etc. It is noted that these various parameters may not have to be held steady during operation, and could be changed by the controller operating a computer program which alters their setpoints as appropriate. The controller may also include a user interface for communicating with operators.

The controller may be implemented on one or more general purpose computers, special purpose computer(s), a programmed microprocessor or microcontroller and peripheral integrated circuit elements, an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FPGA, Graphical card CPU (GPU), or PAL, or the like. Such devices typically include at least memory for storing a control program (e.g. RAM, ROM, EPROM) and a processor for implementing the control program.

During the CMP process, the polishing padrotates along with the platen. The carrier headalso rotates, causing the wafer substrate to rotate. The polishing padand the carrier headmay rotate in the same direction (clockwise or counter-clockwise), or in opposite directions. As they rotate, slurry is deposited upon the polishing pad and flows between the polishing padand the carrier head. Through the chemical reaction between reactive chemicals in the slurry and the top layer of the wafer substrate, and further through mechanical polishing due to contact between the abrasive particles in the slurry and the fop layer of the wafer substrate, the top layer of the wafer substrate is planarized.

During a pad conditioning process, the pad conditioning ringcontacts the surfaceof the polishing pad. Both the polishing padand the pad conditioning ringrotate. Again, they may rotate in the same direction or in opposite directions. The pad conditioneralso applies a downward force to the pad conditioning ringto press the ring against the polishing pad. The rotational motion of the conditioning ring removes debris from the surface of the polishing pad and also creates new grooves and asperities, which prolongs the service lifetime of the polishing pad.

The pad conditioning process may occur when a wafer substrate is not being polished, i.e. an ex-situ process. Alternatively, during in-situ processing, pad conditioning can occur concurrently with the polishing of a wafer substrate. The pad conditionercan be movable between a pad conditioning position over the polishing pad, and a home position where the pad conditioner is away from the polishing pad.

Referring again to, the wafer substratemay have a diameterranging from about 150 millimeters (mm) to about 450 mm, or even higher. Thus, the wafer carriermay have a diameterof about 170 mm to about 470 mm, or in more specific embodiments from about 300 mm to about 320 mm for handling 300 mm wafer substrates. Other ranges and values for these various diameters are also within the scope of this disclosure.

Referring now to the plan view of, some additional aspects of the polishing padand the conditioning ringcan be seen, in accordance with some embodiments. Initially, the conditioning ring has an inner radiusand an outer radius, and a widthbetween the two radii. The outer radius is greater than the inner radius. The conditioning ring is not a disk where the surface area contacting the polishing pad is a circle, but instead has an annular shape. It is noted the terms “ring” and “radius” and “annular” should not be construed as requiring the conditioning ring to be circular, but only that the width is generally constant between the two radii.

In particular embodiments, the inner radiusis from about 300 mm to about 400 mm. In particular embodiments, the outer radiusis from about 350 mm to about 500 mm. The widthmay range from about 10 mm to about 200 mm. By way of comparison, the polishing padmay have a diameterof from about 700 millimeters (mm) to about 800 mm, or in other words a radius of about 350 mm to about 400 mm. Other ranges and values are also within the scope of this disclosure.

Due to the need to sweep the conventional pad conditioner back and forth across the radius of the polishing pad, the conditioning time at the edge of the polishing pad is 50% less than the other areas of the polishing pad. In addition, the edge of the polishing pad is often left unconditioned to reduce false arms due to a down force error being triggered. However, the conditioning ring can spend an equal amount of conditioning time at the edge of the polishing pad with a reduced likelihood of triggering a down force error.

Also illustrated here is debris, both inside the conditioning ring and outside of the conditioning ring. As previously mentioned, the diameter of the conditioning ring may be equal to or greater than the radius of the polishing pad. As illustrated in, then, the inner radiusof the conditioning also extends beyond and rotates outside the perimeter of the polishing pad, creating a space between the polishing pad and the conditioning ring. Put another way, some portion of the conditioning ring may be outside or beyond the perimeter of the polishing pad. Due to the motion of the conditioning ring, the debris will be moved to the perimeter of the polishing pad and off the polishing pad, whether located inside or outside of the conditioning ring.

Referring now toand, additional aspects of the pad conditionercan be seen, in accordance with some embodiments.is a plan view, andis a side cross-sectional view. In, the upper surface of the pad conditioner headis visible. The pad conditioner bodyis visible above the head, and does not spin or rotate. The location of the conditioning ringbelow the pad conditioner head is identified with dashed lines.

In, the conditioning ringis attached to the undersideof the conditioner head. The conditioning ring has a contact surfacewhich will contact the polishing pad. The contact surfaceis annular, and has an inner perimeterand an outer perimeter. The inner perimetercorresponds to the inner radius, and the outer perimetercorresponds to the outer radius. In this embodiment, the heightof the ring on the inner perimeterand the heightof the ring on the outer perimeterof the contact surfaceare generally equal when measured relative to the pad conditioner head.

is a side cross-sectional view of another embodiment of the conditioning ring. In this embodiment, the outer perimeteris rounded. Put another way, the heightof the outer perimeteris less than the heightof the inner perimeterwhen measured relative to the pad conditioner head. This may be useful when the pad conditionerand the polishing padare not flat relative to each other, for avoiding pad scratching that might otherwise occur.

is a plan view of an upper surfaceof the conditioning ring.is a plan view of the undersideof the pad conditioner head. Together, these two views show one way in which the conditioning ring can be attached to the pad conditioner head.

Referring first to, the conditioning ringmay extend downwards from a disk-shaped base. The upper surface of the base is illustrated as including a plurality of female members. Here, eight female members are illustrated and are evenly spaced about the perimeter of the base. The conditioning ring is outlined in dashed lines around the perimeter of the base. Referring to, the undersideof the pad conditioner head includes complementary male members. The location of the bodyis indicated in dashed lines. The female membersand the male membersengage each other to attach the conditioning ring to the pad conditioner head. Alternatively, the basemay have male members and the undersidemay have female members. Other mechanical or adhesive methods for joining the conditioning ring to the pad conditioner head may also be used.

andillustrate additional embodiments of the conditioning ring. In, the conditioning ringhas an elliptical shape. In, the conditioning ringhas a rectangular shape. It is noted that regardless of the shape, the conditioning ring still rotates about a center. With the shapes as illustrated inand, the length a is equal to or greater than the radius of the polishing pad, but the width b is not. More generally, then, the conditioning ring may have a shape that has a major axis length a and a minor axis width b, with the length being greater than or equal to the width. The length and width may independently range from about 300 mm to about 500 mm. In some particular embodiments, the ratio of the major axis length to the minor axis with is from about 1.3 to about 1.8. The widthof the conditioning ring is still from about 10 mm to about 200 mm.

illustrate some additional aspects of the conditioning ring.is a plan view of the contact surface. Here, the contact surface is an abrasive surface. This abrasive surface may be made, for example, by embedding diamond particles within a matrix, such as by brazing, electro-plating, or sintering. In, the contact surfacecomprises a brushing surface. Hairs or bristles are embedded within a matrix, and are used for sweeping debris. In, the conditioning ringcomprises an inner ringand an outer ring. The outer ringhas an abrasive contact surface as illustrated in, and the inner ringhas a brushing contacting surface as illustrated in. Their combined widthis from about 10 mm to about 200 mm. The ratio of their widths (inner ring widthto outer ring width) may range from about 0.1 to about 9, or in more particular embodiments from about 0.5 to about 2, or from about 0.9 to about 1.1. To be clear, the entire contact surface of the conditioning ring may be abrasive (as in), or the entire contact surface may be a brushing surface (as in), or the contact surface can be a combination of both surfaces. One type may be tailored to provide more cutting of the polishing pad or to better clean the surface of the polishing pad, respectively.

A rinse barmay be present within the CMP system for washing the conditioning ring, as illustrated in.is a plan view.is a side view of the rinse bar through line B-B of, andis a side view of the rinse bar through line C-C of.

When present, the rinse baris located to the side of the polishing pad, in a location that the conditioning ring passes over. As seen inand, the rinse bar includes one or more nozzlesthat each direct a streamof cleaning liquid against the contact surface. Depending on the location of the rinse bar, the rinse bar has a lengththat is less than or equal to the diameter of the conditioning ring.

andillustrate another embodiment of a CMP system, in accordance with some embodiments of the present disclosure. In this embodiment, the system includes a first platenwith a first polishing pad, and also includes a second platenwith a second polishing padthereon. Each platen is attached to a shaft,which can rotate, and can also move vertically up-and-down. The conditioning ringis located in a position and has a diameter sufficient to span both polishing pads,, and is able to condition both polishing pads. The conditioning ring can also be moved via the movable arm(see) as desired. In some embodiments, the two polishing pads can be concurrently conditioned. In such situations, the down force on each polishing pad can also be independently controlled by moving the respective platen vertically to control the down force. As illustrated here, the two polishing pads,and the conditioning ringare all rotating in the same direction. Rotation in the same direction reduces the degree of variation in the torque/friction between them compared to rotation in opposite directions and improves process control as well.

illustrates another embodiment of a CMP system, in accordance with some embodiments of the present disclosure. In this embodiment, the system includes four platens, each supporting a polishing pad,,,. The conditioning ringis located in a position and has a diameter sufficient to span all four polishing pads, and can condition all four polishing pads concurrently if desired. More generally, then, the CMP system may contain one pad conditioner with a conditioning ring thereon, and a plurality of polishing pads which can be conditioned by the pad conditioner. For example, different polishing pads are used for a bulk polish versus a buff polish.

illustrates another embodiment of a CMP system, in accordance with some embodiments of the present disclosure. In this embodiment, the system includes two wafer carriers,and one pad conditionerthat includes a conditioning ring. CMP can be concurrently performed using the two wafer carriers on the same polishing pad. This is possible because more of the polishing pad surfacecan be used, particularly near the edge of the polishing pad. The two wafer carriers are independent of each other.

is a flow chart illustrating a methodfor conditioning a polishing pad, in accordance with some embodiments. Reference to the plan view ofmay be helpful for better understanding.

The polishing pad conditioning method ofcan be performed periodically after a given number of wafer substrates have been polished through the CMP system. Thus, in stepof, the wafer count, or in other words the number of wafer substrates that have passed through the CMP system since the last conditioning was performed, is compared to the set number. For example, here the set number is 10. However, the set number can be any value, and could be as low as one (1). In other words, the polishing pad conditioning method may be performed as often as desired.

Next, in stepof, after the set number is reached, a height profile of the polishing pad is created. For example, as previously mentioned, the polishing pad includes grooves and asperities. As the polishing pad surface is worn down, the depth of the grooves is reduced and can serve as a proxy for the height of the polishing pad. A measurement element, such as an acoustic transducer or a laser, can measure the depths of the grooves across the polishing pad surface. The measurement element can be arranged on a scan arm (not shown) to scan the polishing pad surface. Other means for measuring the height of the polishing pad can also be used.

It is noted that due to the rotation of the polishing pad during CMP operation, the pad height at a given radius from the center of the polishing pad is usually uniform all the way around the polishing pad. Thus, in some embodiments, the platen does not need to be rotated to generate the height profile. In other embodiments, the platen is rotated to move the polishing pad surface past the measurement element.

With appropriate processing by the controller, a height profile can be generated for the polishing pad. The height profile may take the form of a curve showing the pad height versus radius, or can be a three-dimensional map showing the pad height across the entire polishing pad, as desired.

Then, in stepof, the controller can then compare the height profile to a desired height profile to determine whether conditioning is needed. Assuming conditioning is needed, then the method proceeds to step. If no conditioning is needed, then the wafer count is reset to zero and the method goes back to step.

Continuing, in stepof, at least one polishing parameter is determined. The polishing parameter(s) are used to dress the polishing pad to improve its uniformity and texture. In some particular embodiments, the polishing parameter may be one or more of the pad conditioner down force, the pad conditioner rotation speed, or a pad conditioner dwell time. Combinations of these parameters are also contemplated. This may be performed by the controller.