Cmp Method and System with Nanobubble Cleaning

The semiconductor integrated circuit industry has experienced exponential growth. Technological advances in integrated circuit materials and design have produced generations of integrated circuits where each generation has smaller and more complex circuits than the previous generation. In the course of integrated circuit evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing integrated circuits.

Chemical mechanical planarization (CMP) is a process that has enabled the use of thin film materials that enable features of relatively small size. CMP can planarize the surface of a semiconductor wafer after thin film deposition and patterning processes. CMP utilizes chemical and mechanical processes to planarize the semiconductor wafer. While highly beneficial, chemical mechanical planarization can also be susceptible to equipment failure resulting in damaged semiconductor wafers.

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 apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Terms indicative of relative degree, such as “about,” “substantially,” and the like, should be interpreted as one having ordinary skill in the art would in view of current technological norms.

Embodiments of the present disclosure utilize a high-pressure rinse including nanobubbles during a pad dressing process of a CMP pad. CMP processes planarized a semiconductor wafer by pressing the exposed face of the rotating wafer onto a top surface of the rotating CMP pad. The pad dresser helps to remove debris that can become lodged in the pad. However, over time, the surface of the pad can become uneven, making it difficult for the pad dresser to remove debris particles. Embodiments of the present disclosure advantageously supply a high-pressure rinse including nanobubbles during the pad dressing process. The nanobubbles assist in dislodging debris particles from the pad. The nanobubbles can be generated prior to supplying the rinse to the pad or while the rinse is on the surface of the pad. This helps to ensure that debris particles are clean from the CMP pad. This further helps to ensure that debris particles do not damage wafers or become attached wafers during subsequent CMP processes. This helps prevent damage to integrated circuits that are formed from the wafers. Accordingly, embodiments of the present disclosure increase semiconductor wafer yields and reduce the need for technicians or experts to repair or replace damaged equipment.

As used herein in the context of CMP processes and systems, the term “pad dresser” is synonymous with the term “pad conditioner” and “dressing” is synonymous with “conditioning”. Other variations of the word “dress” are also synonymous with corresponding variations of the word “condition”, in the context of CMP processes and systems.

is a simplified side view a CMP system, in accordance with some embodiments.is a simplified side view of the CMP systemofduring a pad dressing process between CMP processes. The CMP systemincludes a platen, a CMP head, a slurry supply system, and a pad dresser. The components of the CMP systemcooperate to provide an efficient CMP process that reduces the potential for damage to semiconductor wafers.

In one embodiment, the platenis a flat circular surface. The platenis configured to rotate during CMP processes. A driveshaftis coupled to the platen. The driveshaftis configured to rotate the platenduring a CMP process. A CMP padis positioned on a top surface of the platen. When the platenrotates, the CMP padrotates as well.

The platenmay rotate with a rotational velocity of between 20 RPM and 40 RPM, though other rotational velocities can be utilized without departing from the scope of the present disclosure. The platencan be coupled to a shaft that drives the rotation of the CMP platen. The platenmay have a diameter of about 50 cm to 75 cm, though platens of other sizes can be utilized without departing from the scope of the present disclosure.

The CMP systemincludes a CMP pad. The CMP padis positioned on top of the platen. The CMP padmay be circular and may have a diameter that is substantially identical to the diameter of the platen. The CMP padmay be coupled to the platenby fasteners, by suction (i.e., pressure differential), by electrostatic force, or in any suitable way. When the platenrotates, the CMP padalso rotates. The rotation of the CMP padis one of the factors that planarizes the semiconductor wafer, as will be described in more detail below.

The CMP padcan be made of a porous material. In one example, the CMP padis made from a polymeric material having a pore size between 20 micrometers and 50 micrometers. The CMP padmay have a roughness of about 50 μm. Other materials, dimensions, and structures of a CMP padcan be utilized without departing from the scope of the present disclosure. The CMP padmay be substantially rigid. As will be shown and described in more detail below, the CMP padincludes pores or cavities in which debris particles can become lodged.

The slurry supply systemsupplies a slurryonto the rotating padduring the CMP process. The slurrycan include a solution of water and one or more corrosive compounds. The corrosive compounds are selected to chemically etch or remove one or more materials on the surface of the semiconductor wafer. Accordingly, the compounds in the slurryare selected based on the material or materials of the surface features of the semiconductor waferto be planarized. The slurry supply systemcan include a tankthat holds the slurry, a slurry armthat delivers the slurry onto the padduring the CMP process, and a tube or hosethat supplies the slurryfrom the slurry tankto the slurry arm. The slurry armis one example of a dispensing arm.

In some embodiments, the pad dresserdress the padduring the CMP process. In other words, while the slurry armdelivers the slurryonto the platenand while the CMP headpresses the waferonto the CMP pad, the pad dresser operates to dresser or dress the pad.

The pad dresserincludes a pad dresser headcoupled to a pad dresser arm. During a CMP process, the bottom surface of the pad dresser headis placed in contact with the top surface of the CMP pad. The pad dresser headrotates during the CMP process. The dresser armsweeps the pad dresser headacross the top surface of the CMP padin a selected pattern. The bottom surface of the pad dresser headincludes hard particles embedded therein to help dress the pad.

The CMP headis coupled to and suspended by a driveshaft. The driveshaftcan rotate the CMP headduring the CMP process. Furthermore, the driveshaft, or a component coupled to the driveshaftcan lower the CMP headin order to place the semiconductor waferin contact with the CMP padduring the CMP process.

During the CMP process, the top surface of the rotating CMP padexperiences wear from the planarization process. The top surface of the rotating padmay wear out unevenly such that depressions, valleys, and peaks may form in the CMP pad. The pad dresserincludes a rotating pad dresser head that is pressed downward onto the rotating CMP pad. The rotating pad dresser head includes or is coated with a hard, durable material that can effectively sand down the surface of the CMP pad. In particular, the rotating pad dresser head includes hard protruding particlesor materials. In one example, the particlesof the pad dresser include a diamond material lodged in the downward facing surface. The rotating head of the pad dressersweeps across the surface of the rotating CMP padin a pattern selected to maintain a substantially even top surface of the CMP padduring the CMP process. Accordingly, the pad dresserremoves or prevents the formation of depressions, ridges, valleys, or uneven features on the surface of the rotating CMP pad.

During the CMP process, the CMP headplaces the downward facing surface of the semiconductor waferinto contact with the rotating CMP pad. The CMP headmay also rotate the semiconductor waferduring the CMP process. Surface features of the downward facing surface of the semiconductor waferare planarized during the CMP process. The planarization is achieved by both mechanical and chemical processes. The mechanical aspect of the planarization is achieved by the physical effect of the CMP padrubbing down the bottom facing surface of the semiconductor wafer. The mechanical aspect of the planarization is akin to a very fine sanding process. The chemical aspect of the planarization is achieved by the chemical effect of the slurry on the materials of the surface features of the semiconductor wafer. The compounds in the solution of the slurry etch or otherwise react with and remove the materials of the surface features of the semiconductor wafer. The result of the CMP process is that the exposed bottom facing surface of the semiconductor waferbecomes substantially planar.

In some embodiments, slurry armis positioned upstream from the CMP head. The slurry armsupplies the slurryonto the rotating padduring the CMP process. In particular, the slurry armhas a plurality of nozzles or apertures that each output the slurryonto the pad. The slurry armcan supply the slurry with a total flow rate between 100 mL/minute and 500 mL/minute, though other slurry flow rates can be utilized without departing from the scope of the present disclosure.

In some embodiments, the pad dresser headis positioned downstream from the CMP head. Accordingly, the rotation of the padcarries the slurry from the CMP headto the pad dresser head. In one example, the pad dresser headtravels through a dresser scanning width less than the diameter of the pad. The pad dresser headmoves back and forth through the scanning width while rotating. The scanning width has a value between 15 cm and 30 cm, though other values can be used without departing from the scope of the present disclosure.

The action of the pad dresser can generate particles and debris that mix with the used slurry. Rotation of the padcarries some of the used slurryback into contact with the wafer held by the CMP head. Accordingly, some of the impurities and debris and the used slurry may come into contact with the wafer held by the CMP head. The slurrygenerally follows a spiral pattern and is forced to the edge of the paddue to the rotational motion of the pad. The slurry armconstantly supplies fresh slurryduring the CMP process.

While the CMP process may be generally effective, several problems may arise that can damage the equipment of the CMP systemand the semiconductor wafer. For example, it is possible that debris particles from the wafer, the pad, or the pad dressermay become lodged in the pores or cavities of the pad. For example, it is possible that some of the surface material of the pad dressermay break off or otherwise become dislodged from the pad dresser. This results in pad dresser debris on the rotating CMP pad. The debris can include grains, particles, shards, or fragments of the material from the pad dresser. In one example, the debris includes diamond material. The rotating CMP padmay carry the pad dresser debris into contact with the semiconductor wafer. The contact of the pad dresser debris with the semiconductor wafercan scratch, fracture, or otherwise damage the semiconductor wafer. If the semiconductor waferis damaged by the pad dresser debris, then the semiconductor wafermay need to be scrapped. Additionally, the CMP padmay also be damaged when the pad dresser debris comes between the surfaces of the CMP padand the semiconductor wafer. This can result in a CMP padthat needs to be scrapped or repaired. Either of these occurrences leads to high costs in terms of time, resources, and money in order to fix the damage or scrap the semiconductor waferor the CMP pad. Furthermore, CMP processes may be interrupted for a period of time while repairs are made.

Another potential problem is the crystallization of the slurry during the CMP process. When the slurry is provided onto the surface of the rotating CMP pad, the rotation of the CMP padcauses the slurry to flow toward the outer perimeter of the CMP padand off of the CMP pad. Nevertheless, it is possible that some portion of the slurry may not quickly flow off of the CMP pad. This portion of the slurry may crystallize. The crystallized portion of the slurry can have a similar effect as the pad dresser debris. Accordingly, the crystallized portion of the slurry can damage the semiconductor waferor the CMP pad.

As set forth previously, there is a particular risk that debris particles from either the wafer, the crystallized slurry, the pad dresser, or the pad itself can become lodged in the cavities or pores of the CMP pad. The cavities help provided asperity that makes the planarization process effective. If the cavities fill up with debris particles, there are multiple risks. A first risk is that the padwill only be effective at planarizing the wafer. A second risk is that lodged debris particles will scratch or otherwise damage the wafer. A third risk is that the debris particles in the cavities can become attached to the wafer. Each of these risks can result in scrapped wafers or damaged equipment.

In some embodiments, the CMP systemutilizes the pad dresserto remove debris particles from the cavities or pores of the padbetween CMP processes. In particular, the CMP systemsprays a high presser rinsing fluidonto the padwhile the waferis not present in while the pad dressermoves back and forth across the pad. Nanobubblesare generated in the rinsing fluid to assist in removing debris particles from the pores or cavities of the pad.

illustrates a pad dressing process, in accordance with some embodiments. After a CMP process has been performed on the wafer, the waferand the CMP headare removed from the pad. The slurry armis then utilized to provide the high-pressure rinsing fluidonto the pad.

In some embodiments, the systemincludes an ultrasonic tank. In, the ultrasonic tankis shown as being coupled to the hose or tubein order to deliver the rinsing fluidonto the pad. In such an example, valves can be operated to prevent the slurryfrom entering the tubeand to enable the rinsing fluidto enable the tube. Accordingly, though not shown, the systemcan include one or more valves.

In some embodiments, the ultrasonic tanksupplies rinsing fluidto the slurry armvia a separate tube or connection. Various schemes, components, and configurations can be utilized to alternately supply rinsing fluidand slurryto the slurry armwithout departing from the scope of the present disclosure.

In some embodiments, the ultrasonic tank includes an ultrasonic generator. The ultrasonic generatorgenerates soundwaves with very high frequencies. The soundwaves can have frequencies between 10 kHz and 10 MHz, though other frequencies can be utilized without departing from the scope of the present disclosure. Soundwaves in this frequency range are able to effectively generate large numbers of nanobubbles. The ultrasonic waves generate nanobubblesin the rinsing fluid. As will be set forth in more detail below, the nanobubbleshelp to remove debris particles from pores or cavities in the padduring a pad dressing process.

In some embodiments, nanobubbles have diameters or width dimensions between 50 nm and 300 nm. Nanobubbles with these dimensions can effectively dislodge debris particles from the CMP padto further reduce the probability of damage to a wafer or CMP equipment. The nanobubbles can be formed from a gas injected into the rinsing fluid. In some embodiments, the nanobubbles are air bubbles. Alternatively, the nanobubbles can be generated from argon, helium, N, CO, or other gases without departing from the scope of the present disclosure.

Nanobubblescan be highly beneficial in dislodging debris particles due to the properties of the nanobubbles. Nanobubblesremain suspended in the rinsing fluid for a relatively long durations of time. This enables the nanobubblesto disperse throughout the rinsing fluid. Furthermore, nanobubblesremain stable in the rinsing fluid until they interact with debris particles to dislodge them. Furthermore, the nanobubblescontinue to transfer gas to the rinsing fluiduntil they collapse.

In one embodiment, the generation of the nanobubbles includes injection of a surfactant into the rinsing fluid. The surfactant can be selected to provide particular characteristics to the nanobubbles. For example, larger surfactants can render larger nanobubbles. Furthermore, anionic surfactants can result in a tunable zeta potential. The zeta potential corresponds to propensity for the surface of the bubble to carry an electrostatic charge. In negative charge can be imparted via an anionic a surfactant such as sodium lauryl sulfate. A positive charge can be imparted via cationic surfactant such as cetyltrimethylammonium chloride. Other surfactants that can be utilized include for the nanobubbles include Siegel tried field on the in bromide or sodium dodecyl sulfate. In some embodiments, the rinsing fluid includes deionized water mixed with the surfactant.

In some embodiments, the nanobubble penetration depth is tunable. For example, waves with ranges between 4 MHz and 6 MHz can result in penetration down to 5-7 cm of pad thickness. Soundwaves between 0.5 and 1.5 MHz can result in penetration down to 25-35 cm of pad thickness. Other ranges and depths can be utilized without departing from the scope of the present disclosure.

In some embodiments, the ultrasonic tankincludes a heaterand a cooler. The heatercan be utilized to selectively raise the temperature of the rinsing fluid. The coolercan be utilized to selectively lower the temperature of the rinsing fluid. In this way, the temperature of the rinsing fluid can be carefully controlled.

each include a simplified side view of a portion of pad, as well as an enlarged view of a portion of the pad. In, the padis relatively new. The large portion ofillustrates that the padincludes pores or cavities. The pores or cavitiesadd asperity to the pad that helps to planarize the waferduring CMP processes.

In, because the padis relatively new, the surface of the padis relatively flat as can be seen in the upper portion of. During pad dressing processes, the pad dresser is able to apply a substantially even downward force on the flat surface of the pad. The result is that debris particlescan be efficiently removed from the cavities.

illustrates a padthat has gone through a large number of CMP processes. The upper portion ofillustrates that the top surface of the padhas become curved, though the curvature is exaggerated in. The result is that the pad dresserdoes not apply an even downward force on the pad. In the absence of nanobubblesin the rinsing fluid, debris particlescan become lodged in the pores or cavities. If not addressed, this can result in damage to the waferas described previously.

illustrates a padthat has gone three large number of CMP processes and is curved, in a manner similar to. As before, the pad dressermay not be able to apply and even downward force on the curved surface of the pad. However, in, rinsing fluidincluding nanobubblesis utilized during the pad dressing process. The nanobubblesget below the debris particlesand assist in dislodging them. The result is that the pad dressing process effectively removes debris particlesfrom the cavities or poresand the pad. This helps ensure that wafersare not damaged during subsequent CMP processes.

In some embodiments, the nanobubblesare generated after the rinsing fluid has been dispensed onto the pad. In some embodiments, the pad dresserincludes one or more ultrasonic generators that generate ultrasonic waves. The ultrasonic waves cause nanobubblesto form in the rinsing fluidthat has seeped into the cavities. As described previously, by selecting the frequency of the ultrasonic waves, nanobubbles can be generated in the rinsing fluidat selected depths within the pad.

are side views of a CMP system, in accordance with some embodiments. In, a CMP process is being performed. In, a pad dressing process is being performed. Many aspects of the CMP systemofare substantially similar to those of.

However, in, the pad dresser armincludes an interior fluid channel and a plurality of outlets. A tubeis coupled between the ultrasonic fluid tankand the dresser arm. The ultrasonic fluid tankincludes the rinsing fluidthe ultrasonic generator, the heater, and the cooler. The dresser armis one example of a dispensing arm.

In, a CMP process is performed. In particular slurryis provided from the slurry tankonto the padvia the slurry arm. The rotating waferexpressed in contact with the rotating padduring the CMP process. The dresser headsweeps across the padduring the CMP process.

In, a pad dressing process is performed. The waferand the CMP headhave been removed. During the pad dressing process, the ultrasonic tankgenerates nanobubblesin the rinsing fluid. The rinsing fluid, including the nanobubbles, is supplied via the outletin the dresser armonto the pad. The CMP headsweeps across the surface of the padas described previously. As described previously, the nanobubblesin the rinsing fluidhelp to dislodge debris particles from the pad.

In some embodiments, the dresser armis between 25 cm and 50 cm above the pad. In some embodiments, the slurry armis between 25 cm and 50 cm above the pad. A distance in this range can result in good slurry distribution on the CMP pad. Other configurations of a slurry supply systemand a pad dresserthat dispenses the rinsing fluidcan be utilized without departing from the scope of the present disclosure.

is a block diagram of a CMP system, in accordance with some embodiments. The CMP systemsofmay be a subset of the CMP system. The CMP systemincludes a plurality of load/unload port. The CMP system includes a driveway for passed through, a CMP chamber including four CMP platensand to wafer load cups, and a wafer cleaning system.

In some embodiments, each wafer is received at one of the load/unload ports. Each wafer is then passed through the driveway for passed throughinto the CMP chamber. In the CMP chamber, each wafer will be processed at two platens. Each wafer will be processed at either platens P-and P-(as shown by the path of travel arrow) or platens P-and P-. For each platen, there is a respective CMP head, a slurry system, a pad dresser, and in ultrasonic generator to generate nanobubbles as described previously.

In some embodiments, each waferundergoes a CMP process including a first CMP step and the second CMP step. For example, a wafermay be passed to the platen P-two undergo the first CMP step and then to the platen P-to undergo the second CMP step of the CMP process. The overall CMP process results in the planarization and at least partially removal of one or more surface layers of the wafer. At each platen, a pad dressing processes performed between CMP processes (or steps), including generation of the nanobubblesas described previously. After the CMP process, the wafer is passed through the wafer cleaning systemand then unloaded and one of the load/unload ports. A CMP systemcan include other configurations without departing from the scope of the present disclosure.

is a simplified side view of a CMP system, in accordance with some embodiments. Though not shown in, the CMP systemcan include the slurry supply systemand the CMP head. The CMP systemofalso includes a system (not shown) that dispenses rinsing fluid. In some embodiments, the slurry supply systemsupplies the rinsing fluidfor the dressing process as described in relation to. In some embodiments, the dresser armsupplies the rinsing fluidas described in relation to. Other systems, components, or configurations can be utilized to dispense the rinsing fluidwithout departing from the scope of the present disclosure.

In, the dresser headgenerates ultrasonic vibrations during the pad dressing process while the rinsing fluid is being supplied onto the pad. The ultrasonic vibrations generated by the dresser headgenerate nanobubbles(not shown in) in the rinsing fluid. As the rinsing fluidhas penetrated into the pores or cavitiesof the pad, the generated nanobubbles assist in dislodging the debris particles from the pores or cavities.also illustrates the hard particles or structuresthat protrude from the dresser head.

As can be seen in, the dresser headincludes a plurality of ultrasonic generators. The ultrasonic generatorsare embedded in an array in the dresser head. During the pad dressing process, the ultrasonic generatorsgenerate ultrasonic waves that results in nanobubbles, as described previously.