Chemical mechanical polishing system with polishing pad height measurement sensor system

Abstract

A chemical mechanical polishing (CMP) system for semiconducting wafer substrates includes a polishing pad mounted upon a platen, a wafer carrier configured to hold a substrate on its backside and press the substrate against the polishing pad, and a pad conditioner that includes a conditioning disk and a conditioner head that holds the conditioning disk. The system also includes at least one polishing pad height measurement sensor to measure the profile of the polishing pad. The height measurement sensor can be mounted upon the wafer carrier or the pad conditioner, and is used to produce a uniform height across the surface of the polishing pad.

Description

BACKGROUND

[0001] 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.BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

[0003] FIG. 1A is a side view of a CMP system, in accordance with some embodiments of the present disclosure.

[0004] FIG. 1B is a plan view of the CMP system showing only some components.

[0005] FIG. 2A is a perspective view of a first embodiment of a height measurement sensor system mounted upon a pad conditioner head, in accordance with some embodiments of the present disclosure. Here, the sensor system is formed from a plurality of sensors. FIG. 2B is a plan view of the height measurement sensor system.

[0006] FIG. 3A is a perspective view of a second embodiment of a height measurement sensor system mounted upon a pad conditioner head, in accordance with some embodiments of the present disclosure. Here, the sensor system is an annular sensor. FIG. 3B is a plan view of the height measurement sensor system.

[0007] FIG. 4A is a side view of another embodiment showing a pad conditioner with a gimbal system, in accordance with some embodiments of the present disclosure.

[0008] FIG. 4B is a side view of another embodiment showing a pad conditioner with an electronic level, in accordance with some embodiments of the present disclosure. FIG. 4C is a plan view of the pad conditioner with an electronic level.

[0009] FIG. 5 is a flow chart illustrating a method for leveling a polishing pad, in accordance with some embodiments.

[0010] FIG. 6A is an illustrative side view of a polishing pad prior to conditioning, showing protrusions beyond a height specification. FIG. 6B is an illustrative side view of the polishing pad after conditioning. The protrusions are no longer present.

[0011] FIG. 7A is a graph showing polishing pad height versus polishing pad radius for multiple wafer substrates. FIG. 7B is a graph showing pad height range versus wafer count. These show the use of a “flat loss” pad profile for identifying protrusions.

[0012] FIG. 8A is a graph showing polishing pad height versus polishing pad radius for multiple wafer substrates. FIG. 8B is a graph showing pad height range versus wafer count. These show the use of a “flat” pad profile for identifying protrusions.

[0013] FIG. 9 is a flow chart illustrating a method for planarizing a top layer of a wafer substrate, in accordance with some embodiments.

[0014] FIG. 10A is a side view of a substrate with two layers thereon, prior to CMP.

[0015] FIG. 10B is a side view of a substrate with two layers thereon, after CMP has planarized the top layer.

[0016] FIG. 11A illustrates a first process that includes ex-situ pad conditioning, in accordance with some embodiments. FIG. 11B illustrates a second process that includes ex-situ pad conditioning, in accordance with some embodiments. FIG. 11C illustrates a third process that includes in-situ pad conditioning, in accordance with some embodiments. FIG. 11D illustrates a fourth process that includes in-situ pad conditioning and ex-situ pad conditioning, in accordance with some embodiments. FIG. 11E illustrates a fifth process that includes ex-situ pad conditioning and in-situ pad conditioning, in accordance with some embodiments. FIG. 11F illustrates a sixth process that includes ex-situ pad conditioning and in-situ pad conditioning, in accordance with some embodiments.

[0017] FIG. 12A is a graph showing pad loss profile versus wafer radius in an open-loop control system. FIG. 12B is a graph showing pad loss profile versus wafer radius in a closed-loop control system.DETAILED DESCRIPTION

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The term “wafer substrate”, as used herein, refers to a substrate or to the combination of a substrate and any layers upon the substrate.

[0024] 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.

[0025] 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.

[0026] FIG. 1A is a side view of a CMP system 100, according to some embodiments of the present disclosure. FIG. 1B is a plan view of the CMP system. It is noted that not all components are illustrated in both figures.

[0027] Referring to both figures, the CMP system 100 includes a housing 110 that contains a chamber 112 for providing a sealed environment for the various components. One or more load ports (not shown) can be coupled to the wall of the chamber 112 to permit wafer substrates to enter and exit the CMP system 100 using a robotic wafer transfer system. A door 114 is illustrated which permits access to the chamber 112. A wafer load / unload station 116 is shown, where the wafer substrate 200 is placed.

[0028] Continuing, the CMP system 100 includes a polishing platen 120. The platen is in the form of a flat plate having an upper surface. The platen is attached to a shaft 124, which is coupled to a motor (not shown) for rotating the platen.

[0029] A polishing pad 130 is 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 surface 132 of 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.

[0030] The wafer carrier 140 includes a carrier head 142 which is attached to a carrier body 144. The carrier head 142 is rotatable relative to the body 144. The body 144 is best seen in FIG. 1B, and is attached to a robotic arm 150 for moving the wafer carrier between the load / unload station 116 and the platen 120, as indicated in FIG. 1A. The wafer carrier 140 can also be moved up-and-down relative to the polishing pad 130, both for transport and for applying a desired amount of force to press the wafer against the polishing pad 130, as indicated in FIG. 1B. One or more motors (not shown) may be present for rotating the carrier head, moving the carrier head, and / or moving the robotic arm.

[0031] The wafer substrate 200 can be picked up by the carrier head 142, for example using a vacuum to suck and hold the wafer substrate upon the carrier head 142. A flexible membrane 152 is located between the wafer substrate 200 and the carrier head 142. The membrane can be inflated and used to press the wafer against the polishing pad 130. 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.

[0032] An annular retaining ring 154 is present along the perimeter of the carrier head to retain the wafer substrate and prevent it from spinning off the wafer carrier 140. 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.

[0033] Continuing, a slurry dispenser 160 is present for applying slurry to the polishing pad 130 during 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.

[0034] As illustrated here, the slurry dispenser 160 includes an arm 162 and one or more nozzles 164 for 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 FIG. 1A.

[0035] The CMP system 100 also includes a pad conditioner 170, which is used to condition the polishing pad 130. 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.

[0036] The pad conditioner 170 includes a conditioner head 172 which is attached to a conditioner body 174. The conditioner head 172 is rotatable relative to the body 174. The body 174 is attached to a movable arm 190 which can move between the center of the polishing pad and the perimeter of the polishing pad, as indicated in FIG. 1A. The pad conditioner 170 can also be moved up-and-down relative to the polishing pad 130 for applying a desired amount of force to the polishing pad 130, as indicated in FIG. 1B. A pad conditioning disk 180 is affixed to the underside of the conditioner head 172. 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.

[0037] A controller 192 is 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.

[0038] 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.

[0039] During the CMP process, the polishing pad 130 rotates along with the platen 120. The carrier head 142 also rotates, causing the wafer substrate to rotate. The polishing pad 130 and the carrier head 142 may 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 pad 130 and the carrier head 142. 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.

[0040] During a pad conditioning process, the pad conditioning disk 180 contacts the surface 132 of the polishing pad 130. Both the polishing pad 130 and the pad conditioning disk 180 rotate. Again, they may rotate in the same direction or in opposite directions. The pad conditioner 170 also applies a downward force to the pad conditioning disk 180 to press the disk against the polishing pad. The pad conditioner 170 also sweeps back and forth across the surface 132 of the polishing pad, so that the protrusions or cutting edges of the conditioning disk 180 move relative to the surface 132. 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.

[0041] 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 conditioner 170 is usually movable between a pad conditioning position over the polishing pad 130, and a home position where the pad conditioner is away from the polishing pad.

[0042] Referring again to FIG. 1A, the polishing pad 130 may have a diameter 135 of from about 700 millimeters (mm) to about 800 mm. The wafer substrate 200 may have a diameter 205 ranging from about 150 mm to about 450 mm, or even higher. Thus, the wafer carrier 140 may have a diameter 145 of 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 disk 180 may have a diameter 185 of about 100 mm to about 110 mm. Other ranges and values for these various diameters are also within the scope of this disclosure.

[0043] 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 in FIG. 1A and FIG. 1B, two such sensor systems are present. A first height measurement sensor system 220 is mounted upon the pad conditioner 170. A second height measurement sensor system 230 is mounted upon the wafer carrier 140. In particular embodiments, the height measurement sensor system 220, 230 is mounted upon a rotatable component, such as the pad conditioner head 172 or the wafer carrier head 142.

[0044] As better seen in FIG. 1B, in some particular embodiments, the height measurement sensor system 220 comprises a plurality of sensors. Here, eight such sensors 222 are 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.

[0045] Referring now to FIG. 2A and FIG. 2B, some additional aspects of the pad conditioner 170 can be seen, in accordance with some first embodiments. FIG. 2A is a perspective view, and FIG. 2B is a plan view. In FIG. 2A, the pad conditioning disk 180 is visible on the underside of the conditioner head 172. Also visible are five sensors 222 spaced about the perimeter of the conditioner head. All eight sensors 222 of the height measurement sensor system 220 are visible in FIG. 2B. The body 174 is visible above the head 172, and does not spin or rotate. The sensors 222 of the height measurement sensor system rotate along with the conditioner head 172. When the sensors are mounted to the head of the wafer carrier, they will also rotate along with the carrier head.

[0046] Different second embodiments are illustrated in FIG. 3A and FIG. 3B. Here, the height measurement sensor system 220 is in the form of an annular ultrasonic sensor or infrared sensor. The pad conditioning disk 180 is visible on the underside of the conditioner head 172, with the annular sensor 220 running around the perimeter of the conditioner head. Again, the sensor 220 will 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.

[0047] FIGS. 4A-4C illustrate another embodiment of a pad conditioner 170. As best seen in FIG. 4A, a gimbal system 224 is present between the pad conditioner body 172 and the pad conditioner head 174. 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 disk 180 that 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.

[0048] As best seen in FIG. 4B and FIG. 4C, an electronic level 226 is present upon the pad conditioner head 172, 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. Sensors 222 of the height measurement sensor system are illustrated here. It should be noted the various features separately described in FIGS. 1A-4C can be combined in any desired manner, or certain features may be removed as well.

[0049] FIG. 5 is a flow chart illustrating a method 300 for leveling a polishing pad, in accordance with some embodiments. Reference to the plan view of FIG. 1B may be helpful for better understanding.

[0050] The polishing pad leveling method of FIG. 5 is 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 step 305 of FIG. 5, 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.

[0051] Next, in step 310 of FIG. 5, 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 system 220 is mounted on the pad conditioner 170 and / or the wafer carrier 140, and located over the polishing pad 130 and not contacting the polishing pad 130. The height measurement sensor system 220 is 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 190. In this way, the pad height can be measured along the entire radius of the polishing pad.

[0052] 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.

[0053] 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.

[0054] 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

[0055] 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.

[0056] While described above with the height measurement sensor system being mounted upon only the pad conditioner 170, the height measurement sensor system may also be mounted upon only the wafer carrier 140, 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.

[0057] 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 130. 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.

[0058] Then, in step 315 of FIG. 5, 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.

[0059] If any protrusions are identified, then the method proceeds to step 320. If no protrusions are identified, then the wafer count is reset to zero and the method goes back to step 305. For example, referring now to FIG. 6A, dotted line 134 identifies the height specification for polishing pad 130. In this example, five protrusions 136 are greater than the permitted height range.

[0060] Continuing, in step 320 of FIG. 5, 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.

[0061] Then, in step 325 of FIG. 5, the polishing pad 130 is 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 system 220 can 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 FIG. 6B, after the conditioning step, there are no longer any protrusions over dotted line 134.

[0062] 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.

[0063] The “flat loss” pad profile for determining whether pad conditioning is needed is described in more detail with reference to FIG. 7A and FIG. 7B. FIG. 7A 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. FIG. 7B 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.

[0064] The “flat” pad profile for determining whether pad conditioning is needed is described in more detail with reference to FIG. 8A and FIG. 8B. FIG. 8A 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. FIG. 8B 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 1-4, the range of heights was greater than 0.4 mils, but for wafers 5-12, the range of heights was 0.4 mils or lower.

[0065] In the particular example illustrated in FIG. 8B, if the leveling method of FIG. 5 was performed after every 5 or 10 wafers (i.e. the set point in step 305 is >5), no pad conditioning would occur because the range of heights is within the height specification when the identification step 315 is 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, step 305 of FIG. 5 may be performed multiple times before step 310 is performed. Similarly, steps 310 and 315 may be performed multiple times before conditioning steps 320 and 325 are performed.

[0066] FIG. 9 is a flow chart illustrating a method 350 for planarizing a top layer of a wafer substrate, in accordance with some embodiments. Reference to the plan view of FIG. 1B and to the side views of FIG. 10A and FIG. 10B may be helpful for better understanding.

[0067] Referring initially to FIG. 10A, an example is shown of a substrate 200 having a frontside 202 and a backside 204. A first layer 210 is present upon the frontside 202, and a second layer 212 covers the first layer 210. The second layer is the top layer 218 of the substrate, or put another way is the outermost exposed layer of the frontside of the substrate. The second layer includes the step height 213 of the first layer 210, and can be thinner over the edges of the first layer. This can be undesirable for high-resolution photolithography which requires height differences to be minimized for accurate printing. Thus, to obtain a level surface, the second layer is deposited to an initial thickness 215 that is greater than the final desired thickness, and CMP is performed to remove the step height.

[0068] The substrate 200 may be, for example, a wafer made of a semiconducting material. Such semiconductor materials can include silicon, for example in the form of crystalline Si. In alternative embodiments, the substrate can be made of other elementary semiconductors such as germanium, or may include a compound semiconductor such as silicon carbide (SiC), gallium arsenide (GaAs), gallium carbide, gallium phosphide, indium arsenide (InAs), indium phosphide (InP), silicon germanium, silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide. In particular embodiments, the substrate is silicon.

[0069] The first layer 210 and the second layer 212 can be a dielectric layer, an electrically conductive layer, a diffusion barrier layer, or any other layer that is useful in a semiconductor device or integrated circuit. Examples of dielectric materials may include silicon dioxide (SiO2), silicon nitride (Si3N4), silicon carbide (SiC), hafnium dioxide (HfO2), zirconium dioxide (ZrO2), aluminum oxide (Al2O3), silicon oxynitride (SiOxNy), hafnium oxynitride (HfOxNy) or zirconium oxynitride (ZrOxNy), or hafnium silicates (ZrSixOy) or zirconium silicates (ZrSixOy) or silicon carboxynitride (SiCxOyNz), or hexagonal boron nitride (hBN). Other dielectric materials may include tantalum oxide (Ta2O5), nitrides such as silicon nitride, polysilicon, phosphosilicate glass (PSG), fluorosilicate glass (FSG), undoped silicate glass (USG), high-stress undoped silicate glass (HSUSG), and borosilicate glass (BSG). Examples of electrically conductive materials may include metals such as copper, aluminum, nickel, chromium, gold, germanium, silver, titanium, tungsten, platinum, tantalum, ruthenium, cobalt, rhenium, palladium, or zirconium; composites like TiN, WN, or TaN; or alloys thereof; electrically conductive polymers; and carbon nanotubes. A diffusion barrier layer prevents metals from diffusing into a dielectric layer. Examples of suitable materials that act as a diffusion barrier can include Ti, Ta, Ru, TiN, TaN, or WN.

[0070] In step 355 of FIG. 9, and referring back to FIG. 1B, the wafer substrate 200 is mounted upon a wafer carrier 140. The backside 204 is proximate the wafer carrier head 142, and the frontside 202 of the wafer substrate faces the polishing pad 130 of the CMP system 100. In step 360, the wafer substrate 200 is pushed against the polishing pad 130 by the wafer carrier 140. In step 365, the polishing pad polishes the wafer substrate. At the same time, the polishing pad 130 is conditioned by the pad conditioner 170. This concurrent polishing of the wafer substrate and the conditioning of the polishing pad is referred to herein as in-situ conditioning. Once completed, in step 370, the wafer substrate is removed from contact with the polishing pad. The resulting structure is shown in FIG. 10B. The step height is no longer present, and the final thickness 217 of the second layer is less than the initial thickness 215 as shown in FIG. 10A.

[0071] Various combinations of ex-situ pad conditioning and in-situ pad conditioning are contemplated. Some combinations are schematically illustrated in FIGS. 10A-10F.

[0072] In the first combination shown in FIG. 11A, an ex-situ pad conditioning process is performed upon the CMP system in step 400. This is done as described above in FIG. 5. Next, in step 410, a CMP process is performed upon the top layer of a wafer substrate. Then, in step 415, a post-CMP cleaning process is performed. This may be done, for example, using a washing fluid (which does not contain abrasive particles) that is sprayed on one or both sides of the wafer substrate to remove debris. Rotating scrubber brushes may also be used, if desired.

[0073] In the second combination shown in FIG. 11B, the same three steps 400, 410, 415 are performed. In step 420 of FIG. 11B, the wafer count, or in other words the number of wafer substrates that have passed through the CMP system, is compared to a threshold value, which can be any desired value. After the threshold value is reached, in step 425, another ex-situ pad conditioning process is performed upon the CMP system.

[0074] In the third combination shown in FIG. 11C, an in-situ pad conditioning process and CMP process are concurrently performed in step 405. Then, in step 415, a post-CMP cleaning process is performed.

[0075] In the fourth combination shown in FIG. 11D, the same steps 405, 415, of FIG. 11C are performed. In step 420 of FIG. 11D, the wafer count is compared to a threshold value. After the threshold value is reached, in step 425, another ex-situ pad conditioning process is performed upon the CMP system.

[0076] In the fifth combination shown in FIG. 11E, an ex-situ pad conditioning process is performed upon the CMP system in step 400. Next, an in-situ pad conditioning process and CMP process are concurrently performed in step 405. Then, in step 415, a post-CMP cleaning process is performed.

[0077] In the sixth combination shown in FIG. 11F, the same three steps 400, 405, 415 of FIG. 11E are performed. In step 420 of FIG. 11F, the wafer count is compared to a threshold value. After the threshold value is reached, in step 425, another ex-situ pad conditioning process is performed upon the CMP system.

[0078] The different combinations described above are generally discussed with respect to only one protrusion. For example, the conditioning process may take longer than the CMP process to perform, and so may span both an ex-situ conditioning process and an in-situ conditioning process. Alternatively, multiple protrusions may be treated at different times, for example removing one protrusion using an ex-situ conditioning process and removing another protrusion using an in-situ conditioning process. Any such combinations are contemplated as falling within the scope of the present disclosure.

[0079] The CMP systems having the height measurement sensor system(s) of the present disclosure have several advantages. The texture of the polishing pad is better controlled, to be more uniform. The surface roughness of the polishing pad is reduced. As a result, dishing and erosion on the wafer substrate is reduced. This results in improved WID, WiW, and WtW uniformity and improved die yield and improved IC device performance. The service lifetime of the polishing pad is also extended.

[0080] Some embodiments of the present disclosure thus relate to methods for leveling a polishing pad. A height profile of the polishing pad is created using at least one height measurement sensor system. At least one protrusion from a polishing pad height specification is identified. At least one polishing parameter for the at least one protrusion is determined. The polishing pad is then conditioned based on the at least one polishing parameter to reduce the height of the at least one protrusion. The at least one height measurement sensor system is mounted upon a pad conditioner or a wafer carrier.

[0081] Also disclosed in various embodiments are chemical mechanical polishing (CMP) systems comprising: a polishing pad; a pad conditioner; a wafer carrier; and at least one height measurement sensor system mounted upon a rotatable component of the pad conditioner or the wafer carrier.

[0082] Other embodiments disclosed herein relate to methods for planarizing a top layer of a wafer substrate. The top layer is pushed against a polishing pad using a wafer carrier to which the wafer substrate is attached. The polishing pad is in-situ conditioned using a pad conditioner while the top layer is being polished by the polishing pad. At least one height measurement sensor system is mounted upon the pad conditioner or the wafer carrier.

[0083] Also described in various embodiments herein are methods for operating a chemical mechanical polishing (CMP) system. At least one protrusion from a uniform polishing pad height specification of a polishing pad is identified based on data received from at least one height measurement sensor system mounted upon a pad conditioner or a wafer carrier. At least one polishing parameter is determined, and the polishing pad is conditioned based on the at least one polishing parameter to reduce a height of the at least one protrusion (i.e. ex-situ conditioning). A CMP process is then performed upon a wafer substrate. The wafer substrate is cleaned after the CMP process is complete.

[0084] Also disclosed are other methods. for operating a chemical mechanical polishing (CMP) system. At least one protrusion from a uniform polishing pad height specification of a polishing pad is identified based on data received from at least one height measurement sensor system mounted upon a pad conditioner or a wafer carrier. At least one polishing parameter is determined. The polishing pad is then in-situ conditioned based on the at least one polishing parameter to reduce a height of the at least one protrusion concurrently with a CMP process being performed upon a wafer substrate. The wafer substrate is then cleaned after the CMP process is complete. If needed, ex-situ conditioning of the polishing pad based on the first polishing parameter to reduce the height of the at least one protrusion may continue after the wafer substrate is cleaned.

[0085] Also disclosed are further methods for operating a chemical mechanical polishing (CMP) system. At least one protrusion from a uniform polishing pad height specification of a polishing pad is identified based on data received from at least one height measurement sensor system mounted upon a pad conditioner or a wafer carrier. At least one polishing parameter is determined. The polishing pad is then ex-situ conditioned based on the at least one polishing parameter to reduce a height of the at least one protrusion. A CMP process is begun upon a wafer substrate. Further in-situ conditioning of the polishing pad based on the at least one polishing parameter to reduce a height of the at least one protrusion continues concurrently with the CMP process being performed upon the wafer substrate. The wafer substrate is cleaned after the CMP process is complete.

[0086] Finally, other embodiments relate to further methods for operating a chemical mechanical polishing (CMP) system. A first protrusion and a second protrusion from a uniform polishing pad height specification of a polishing pad are identified based on data received from at least one height measurement sensor system mounted upon a pad conditioner or a wafer carrier. At least a first polishing parameter and a second polishing parameter are determined, one for each protrusion. In-situ conditioning of the polishing pad is performed based on the first polishing parameter to reduce a height of the first protrusion concurrently with a CMP process being performed upon a wafer substrate. The wafer substrate is cleaned after the CMP process is complete. Ex-situ conditioning of the polishing pad is then performed based on the second polishing parameter to reduce a height of the second protrusion.

[0087] The methods, systems, and devices of the present disclosure are further illustrated in the following non-limiting working examples, it being understood that they are intended to be illustrative only and that the disclosure is not intended to be limited to the materials, conditions, process parameters and the like recited herein.EXAMPLES

[0088] An experiment was performed in which open loop control was used without controlling the thickness of the polishing pad, and compared to an experiment in which closed-loop control was used to control the thickness of the polishing pad. 700 wafer substrates were run through each system.

[0089] FIG. 12A is a graph showing the results of the open loop control system, and FIG. 12B is a graph showing the results of the closed loop control system. In each graph, the y-axis is the pad loss profile, in mils. The y-axis is the radius from the center of the polishing pad, in inches. The legend provides the wafer count, i.e. W 19 is the 19th wafer run through the system, and W 600 is the 600th wafer run through the system.

[0090] Comparing FIG. 12A to FIG. 12B, the pad loss is much higher on the edges compared to the center in the open loop control system of FIG. 12A. in contrast, in FIG. 12B, the pad loss is much more uniform.

[0091] The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and / or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.

Claims

1. A method for leveling a polishing pad of a chemical mechanical polishing (CMP) system for semiconducting wafer substrates, comprising:creating a height profile of the polishing pad using at least one height measurement sensor system;identifying at least one protrusion from a polishing pad height specification;determining at least one polishing parameter for the at least one protrusion; andconditioning the polishing pad based on the at least one polishing parameter to reduce a height of the at least one protrusion;wherein the at least one height measurement sensor system is mounted upon a pad conditioner or a wafer carrier.

2. The method of claim 1, wherein the at least one height measurement sensor system is mounted on a rotatable component of the pad conditioner or the wafer carrier.

3. The method of claim 1, wherein the at least one height measurement sensor system comprises a plurality of ultrasonic or infrared sensors.

4. The method of claim 3, wherein the ultrasonic or infrared sensors in the plurality are evenly spaced about a perimeter of the pad conditioner or the wafer carrier.

5. The method of claim 3, wherein the plurality of ultrasonic or infrared sensors contains from 2 to 8 sensors.

6. The method of claim 1, wherein the at least one height measurement sensor system comprises an annular ultrasonic or infrared sensor.

7. The method of claim 1, wherein a first height measurement sensor system is mounted upon the pad conditioner and a second height measurement sensory system is mounted upon the wafer carrier.

8. The method of claim 1, further comprising polishing a wafer substrate using the polishing pad, wherein the polishing pad is conditioned concurrently with or prior to the polishing of the wafer substrate.

9. The method of claim 1, wherein the at least one protrusion is identified by identifying a pad height that is outside of a specified range variation, or by identifying a pad height that is outside of a specified profile range.

10. The method of claim 1, wherein the at least one polishing parameter comprises a pad conditioner down force, a pad conditioner rotation speed, or a pad conditioner dwell time.

11. The method of claim 1, wherein the pad conditioner is gimbaled between a pad conditioner body and a pad conditioner head, and includes an electronic level on the pad conditioner head.

12. The method of claim 11, further comprising tilting the pad conditioner head to change an area of a pad conditioning disk that contacts the polishing pad.

13. A chemical mechanical polishing (CMP) system for semiconducting wafer substrates, comprising:a polishing pad;a pad conditioner;a wafer carrier; andat least one height measurement sensor system mounted upon a rotatable component of the pad conditioner or the wafer carrier.

14. The CMP system of claim 13, wherein the pad conditioner is mounted upon a movable arm that can move between a center and a perimeter of the polishing pad; andwherein the pad conditioner comprises a rotatable pad conditioner head and a pad conditioning disk affixed to an underside of the pad conditioner head.

15. The CMP system of claim 13, wherein the at least one height measurement sensor system comprises one or more ultrasonic or infrared sensors.

16. The CMP system of claim 13, wherein a first height measurement sensor system is mounted upon the pad conditioner and a second height measurement sensory system is mounted upon the wafer carrier.

17. The CMP system of claim 13, wherein the pad conditioner is gimbaled between a pad conditioner body and a pad conditioner head, and includes an electronic level on the pad conditioner head.

18. A method for planarizing a top layer of a wafer substrate, comprising:pushing the top layer against a polishing pad using a wafer carrier to which the wafer substrate is attached; andin-situ conditioning the polishing pad using a pad conditioner while the top layer is being polished by the polishing pad;wherein at least one height measurement sensor system is mounted upon the pad conditioner or the wafer carrier.

19. The method of claim 18, wherein the at least one height measurement sensor system is mounted on a rotatable component of the pad conditioner or the wafer carrier.

20. The method of claim 18, wherein the at least one height measurement sensor system is mounted on a rotatable pad conditioner head of the pad conditioner or upon a rotatable wafer carrier head of the wafer carrier.

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