Chemical Mechanical Polishing System with Polishing Pad Height Measurement Sensor System

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 “fromto.” 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 wafer is typically fixed in position. If the surface of the wafer is not parallel to the surface of the polishing pad, an uneven polishing pad surface texture can result. This is known as underdressing or overdressing, and can impact the polishing behavior on subsequent wafers. Controlling the height profile or the thickness profile of the polishing pad and its topography is thus significant in the CMP process.

In the present disclosure, a new system is provided that reduces the surface roughness (Ra) of the CMP polishing pad. This can mitigate dishing and erosion due to protrusions extending above the surface of the CMP polishing pad. At least one height measurement sensor system is used to measure the height profile of the CMP polishing pad. Protrusions can then be identified and reduced so as to meet a polishing pad height specification.

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 carrierincludes 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 diskis affixed to the underside of the conditioner head. The conditioning disk includes diamond particles which are embedded within a matrix. One or more motors (not shown) may be present for rotating the carrier head, 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 diskcontacts the surfaceof the polishing pad. Both the polishing padand the pad conditioning diskrotate. Again, they may rotate in the same direction or in opposite directions. The pad conditioneralso applies a downward force to the pad conditioning diskto press the disk against the polishing pad. The pad conditioneralso sweeps back and forth across the surfaceof the polishing pad, so that the protrusions or cutting edges of the conditioning diskmove relative to the surface. This motion 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 conditioneris usually 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 polishing padmay have a diameterof from about 700 millimeters (mm) to about 800 mm. The wafer substratemay have a diameterranging from about 150 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. The pad conditioning diskmay have a diameterof about 100 mm to about 110 mm. Other ranges and values for these various diameters are also within the scope of this disclosure.

The polishing pad is desirably uniform in its height or thickness from the center of the polishing pad to the perimeter/edge of the polishing pad. To measure and control the profile of the polishing pad, i.e. its thickness and topography, at least one height measurement sensor system is present in the CMP system. As illustrated inand, two such sensor systems are present. A first height measurement sensor systemis mounted upon the pad conditioner. A second height measurement sensor systemis mounted upon the wafer carrier. In particular embodiments, the height measurement sensor system,is mounted upon a rotatable component, such as the pad conditioner heador the wafer carrier head.

As better seen in, in some particular embodiments, the height measurement sensor systemcomprises a plurality of sensors. Here, eight such sensorsare illustrated. In particular embodiments, 2 to 8 sensors are used. As the number of sensors increases above 8, the improvement in measurement is not significant. The sensors are usually evenly spaced about the perimeter of the pad conditioner or the wafer carrier. In particular embodiments, the sensors are ultrasonic sensors or infrared sensors. Briefly, an ultrasonic sensor emits a sound wave and calculates distance based on the time needed for the sound wave to be reflected back to the sensor. Similarly, an infrared sensor emits a light signal and calculates distance based on the time needed for the light signal to be reflected back to the sensor. Thus, the distance between the polishing pad and the height measurement sensor system can be detected, to create a height profile of the polishing pad. An ultrasonic sensor may be useful for CMP processes involving metals and may be less sensitive to noise, and thus may be suitable in more applications than infrared sensors.

Referring now toand, some additional aspects of the pad conditionercan be seen, in accordance with some first embodiments.is a perspective view, andis a plan view. In, the pad conditioning diskis visible on the underside of the conditioner head. Also visible are five sensorsspaced about the perimeter of the conditioner head. All eight sensorsof the height measurement sensor systemare visible in. The bodyis visible above the head, and does not spin or rotate. The sensorsof the height measurement sensor system rotate along with the conditioner head. When the sensors are mounted to the head of the wafer carrier, they will also rotate along with the carrier head.

Different second embodiments are illustrated inand. Here, the height measurement sensor systemis in the form of an annular ultrasonic sensor or infrared sensor. The pad conditioning diskis visible on the underside of the conditioner head, with the annular sensorrunning around the perimeter of the conditioner head. Again, the sensorwill rotate along with the conditioner head. Similarly, when the annular sensor is mounted to the head of the wafer carrier, it will also rotate along with the carrier head.

illustrate another embodiment of a pad conditioner. As best seen in, a gimbal systemis present between the pad conditioner bodyand the pad conditioner head. This permits the pad conditioner head to be tilted relative to the pad conditioner body. This may be useful for changing the surface area of the pad conditioning diskthat contacts the surface of the polishing pad. The range of tilt does not need to be very high. For example, the range of tilt may be less than 0.5 mils for the pad conditioning disk (which has a diameter of up to 110 mm). The sensors of the height measurement sensor system are not illustrated here.

As best seen inand, an electronic levelis present upon the pad conditioner head, which serves as a sensor for measuring the degree of tilt of the pad conditioner head. Here, the electronic level is present on an upper side of the pad conditioner head. The electronic level may be a conductive electronic level or a capacitive electronic level. The electronic level will also rotate along with the pad conditioner head. Sensorsof the height measurement sensor system are illustrated here. It should be noted the various features separately described incan be combined in any desired manner, or certain features may be removed as well.

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

The polishing pad leveling method ofis usually performed periodically after a given number of wafer substrates have been polished through the CMP system. Initially, the method might only be performed after a set number of wafer substrates have passed 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 leveling 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 leveling 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. This can be done, for example, when the height measurement sensor systemis mounted on the pad conditionerand/or the wafer carrier, and located over the polishing padand not contacting the polishing pad. The height measurement sensor systemis then used to measure the height of the polishing pad in a circle or annulus around the pad conditioner and/or the wafer carrier. The pad conditioner can be moved between the center and the perimeter of the polishing pad with side-to-side motion of the movable arm. In this way, the pad height can be measured along the entire radius of the polishing pad.

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 pad conditioner/wafer carrier and the platen do not need to be rotated to generate the height profile. It may be advantageous for only the polishing pad to be rotated during the height measurement, so that the sensors on the pad conditioner head are in a fixed position, which can produce more precise measurements. Rotation of the sensors may require additional factors to be considered. If more area coverage is needed, the pad conditioner can be moved between the center and the perimeter of the polishing pad by the movable arm.

In other embodiments, the pad conditioner head can rotate while the pad conditioner is moved between the center and the perimeter of the polishing pad by the movable arm. The platen remains fixed in place. This can expose the height measurement sensor system to a larger portion of the polishing pad over which the pad height is measured.

In other embodiments, the platen is rotated to move the pad conditioning disk below the height measurement sensor system while the pad conditioner is moved between the center and the perimeter of the polishing pad by the movable arm. The pad conditioner head does not rotate, but remains fixed in place. This is an alternative way for exposing the height measurement sensor system to a larger portion of the polishing pad

In still other embodiments, both the pad conditioner head and the platen rotate. Their rotation speeds do not need to be the same. During the rotation, the pad conditioner is moved between the center and the perimeter of the polishing pad by the movable arm. This exposes the height measurement sensor system to the entire surface of the polishing pad.

While described above with the height measurement sensor system being mounted upon only the pad conditioner, the height measurement sensor system may also be mounted upon only the wafer carrier, or two sensor systems may be used which are mounted upon both the pad conditioner and the wafer carrier. It is noted that the diameter of the wafer carrier is usually much larger than that of the pad conditioner, and so the degree of side-to-side motion may be smaller for the wafer carrier. Measurements from two sensor systems may be used to cover a larger surface area in a shorter amount of time, or for error-checking between the two sensor systems.

Generally, the location of each sensor relative to the polishing pad is known throughout the height measurement process. As a result, 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, a search for any protrusions from a polishing pad height specification is performed, and any such protrusions are identified. For example, the height specification may be a permitted range variation around a given pad height setpoint. As one example, the given pad height setpoint may be 1.2 mils, and the permitted range variation would be 0.2 mils. Then, the permitted pad heights would range from 1.0 mils to 1.4 mils, and any heights above 1.4 mils would be considered a protrusion. This could be described as a “flat loss” pad profile. Any pad height below 1.0 mils might trigger an alarm to determine the cause of such variations outside the height specification, or might cause the given pad height to be lowered so that other portions of the polishing pad are now considered a protrusion. As a result, a uniform polishing pad surface can be obtained. Alternatively, the height specification may be a permitted range of heights above the lowest point in the height profile. As one example, the lowest point on the polishing pad may be arbitrarily designated as having a height of 0.0 mils, and the permitted range of heights may be 0.4 mils. Then, any portion of the polishing pad with a height greater than 0.4 mils would be identified as a protrusion from the polishing pad height specification. This could be described as a “flat” pad profile. Again, the controller can be used to identify any protrusions.

If any protrusions are identified, then the method proceeds to step. If no protrusions are identified, then the wafer count is reset to zero and the method goes back to step. For example, referring now to, dotted lineidentifies the height specification for polishing pad. In this example, five protrusionsare greater than the permitted height range.

Continuing, in stepof, for each protrusion, at least one polishing parameter is determined. The polishing parameter(s) are used to reduce the height of the protrusion to fall within the height specification. 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. In embodiments where the pad conditioner is gimbaled, another polishing parameter may be the degree of tilt. Combinations of these parameters are also contemplated. This may be performed by the controller.

Then, in stepof, the polishing padis conditioned based on the at least one polishing parameter to reduce the height of the protrusion. The pad conditioner is brought into contact with the protrusion and then grinds the protrusion down. It is noted that a closed loop control system may be used. The height measurement sensor systemcan be used to measure the progress of the conditioning, and those measurements are returned to the controller, which can then adjust the polishing parameter(s) if desired based on the new measurements, so that the protrusion is reduced to fall within the height specification. The polishing pad may be rotating during this conditioning step, or may be stationary (i.e. not rotating), depending on the location of the protrusion (for example, localized versus being present at a given radius all the way around the polishing pad). It is again noted that this conditioning step may occur ex-situ without a wafer substrate being polished concurrently or in-situ while a wafer substrate is being polished concurrently. Referring now to, after the conditioning step, there are no longer any protrusions over dotted line.

In addition, the closed-loop feedback can be used to provide information on when the pad conditioning disk needs to be replaced. For example, when the conditioning is not progressing as expected, this may be an indication that the pad conditioning disk has been fully consumed and needs replacement.

The “flat loss” pad profile for determining whether pad conditioning is needed is described in more detail with reference toand.shows pad height versus radius for 12 sequential wafer substrates that have passed through the CMP system. As can be seen here (and as expected), the pad height at a given radius decreases with each wafer substrate.shows the pad height range versus wafer count. The pad height range is calculated as the difference between the highest height and the lowest height measured on the wafer substrate, regardless of location. The pad height setpoint is 1.2 mils, and the permitted range variation is 0.2 mils. The pad heights are outside of this permitted range variation, and so no pad conditioning is necessary.

The “flat” pad profile for determining whether pad conditioning is needed is described in more detail with reference toand.shows pad height versus radius for 12 sequential wafer substrates that have passed through the CMP system. Again, the pad height at a given radius decreases with each wafer substrate.shows the pad height range versus wafer count. Again, the pad height range is calculated as the difference between the highest height and the lowest height measured on the wafer substrate, regardless of location. The permitted range of heights is 0.4 mils. As seen here, for wafers-, the range of heights was greater than 0.4 mils, but for wafers-, the range of heights was 0.4 mils or lower.

In the particular example illustrated in, if the leveling method ofwas performed after every 5 or 10 wafers (i.e. the set point in stepis >5), no pad conditioning would occur because the range of heights is within the height specification when the identification stepis performed. However, if the leveling method was performed after every 1, 2, 3, or 4 wafers, then pad conditioning would have occurred sooner to bring the polishing pad within the height specification. Put another way, stepofmay be performed multiple times before stepis performed. Similarly, stepsandmay be performed multiple times before conditioning stepsandare performed.

is a flow chart illustrating a methodfor planarizing a top layer of a wafer substrate, in accordance with some embodiments. Reference to the plan view ofand to the side views ofandmay be helpful for better understanding.