CMP METHOD AND SYSTEM WITH NANOBUBBLE CLEANING

Description

BACKGROUND

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.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

FIG. 1A is a simplified side view of a CMP system during a CMP process of a wafer, in accordance with some embodiments.

FIG. 1B is a simplified side view of the CMP system of FIG. 1A during a pad dressing process between CMP processes, in accordance with some embodiments.

FIG. 1C-1E are simplified cross-sectional views of a portion of a CMP pad, in accordance with some embodiments.

FIG. 2A is a simplified side view of a CMP system during a CMP process of a wafer, in accordance with some embodiments.

FIG. 2B is a simplified side view of the CMP system of FIG. 2A during a pad dressing process between CMP processes, in accordance with some embodiments.

FIG. 3 is a block diagram of a CMP system, in accordance with some embodiments.

FIG. 4A is a side view of a CMP system, in accordance with some embodiments.

FIG. 4B is an enlarged cross-sectional view of the CMP system of FIG. 4A, in accordance with some embodiments.

FIG. 4C is a top view of a dresser head of the CMP system of FIGS. 4A and 4B, in accordance with some embodiments.

FIGS. 5A and 5B are graphs associated with generation of nanobubbles, in accordance with some embodiments.

FIGS. 6A-6C are cross-sectional views of a wafer at various stages of processing, in accordance with some embodiments.

FIG. 7 is a flow diagram of a method for operating a CMP system, in accordance with some embodiments.

DETAILED DESCRIPTION

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.

FIG. 1A is a simplified side view a CMP system 100, in accordance with some embodiments. FIG. 1B is a simplified side view of the CMP system 100 of FIG. 1A during a pad dressing process between CMP processes. The CMP system 100 includes a platen 102, a CMP head 106, a slurry supply system 110, and a pad dresser 112. The components of the CMP system 100 cooperate to provide an efficient CMP process that reduces the potential for damage to semiconductor wafers.

In one embodiment, the platen 102 is a flat circular surface. The platen 102 is configured to rotate during CMP processes. A driveshaft 119 is coupled to the platen 102. The driveshaft 119 is configured to rotate the platen 102 during a CMP process. A CMP pad 104 is positioned on a top surface of the platen 104. When the platen 102 rotates, the CMP pad 104 rotates as well.

The platen 102 may 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 platen 102 can be coupled to a shaft that drives the rotation of the CMP platen 102. The platen 102 may 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 system 100 includes a CMP pad 104. The CMP pad 104 is positioned on top of the platen 102. The CMP pad 104 may be circular and may have a diameter that is substantially identical to the diameter of the platen 102. The CMP pad 104 may be coupled to the platen 102 by fasteners, by suction (i.e., pressure differential), by electrostatic force, or in any suitable way. When the platen 102 rotates, the CMP pad 104 also rotates. The rotation of the CMP pad 104 is one of the factors that planarizes the semiconductor wafer 108, as will be described in more detail below.

The CMP pad 104 can be made of a porous material. In one example, the CMP pad 104 is made from a polymeric material having a pore size between 20 micrometers and 50 micrometers. The CMP pad 104 may have a roughness of about 50 μm. Other materials, dimensions, and structures of a CMP pad 104 can be utilized without departing from the scope of the present disclosure. The CMP pad 104 may be substantially rigid. As will be shown and described in more detail below, the CMP pad 104 includes pores or cavities in which debris particles can become lodged.

The slurry supply system 110 supplies a slurry 123 onto the rotating pad 104 during the CMP process. The slurry 123 can 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 108. Accordingly, the compounds in the slurry 123 are selected based on the material or materials of the surface features of the semiconductor wafer 108 to be planarized. The slurry supply system 110 can include a tank 124 that holds the slurry 123, a slurry arm 121 that delivers the slurry onto the pad 104 during the CMP process, and a tube or hose 122 that supplies the slurry 123 from the slurry tank 124 to the slurry arm 121. The slurry arm 121 is one example of a dispensing arm.

In some embodiments, the pad dresser 112 dress the pad 104 during the CMP process. In other words, while the slurry arm 121 delivers the slurry 123 onto the platen 104 and while the CMP head 106 presses the wafer 108 onto the CMP pad 104, the pad dresser operates to dresser or dress the pad.

The pad dresser 112 includes a pad dresser head 126 coupled to a pad dresser arm 128. During a CMP process, the bottom surface of the pad dresser head 126 is placed in contact with the top surface of the CMP pad 104. The pad dresser head 126 rotates during the CMP process. The dresser arm 128 sweeps the pad dresser head 126 across the top surface of the CMP pad 104 in a selected pattern. The bottom surface of the pad dresser head 126 includes hard particles embedded therein to help dress the pad.

The CMP head 106 is coupled to and suspended by a driveshaft 120. The driveshaft 120 can rotate the CMP head 106 during the CMP process. Furthermore, the driveshaft 120, or a component coupled to the driveshaft 120 can lower the CMP head 106 in order to place the semiconductor wafer 108 in contact with the CMP pad 104 during the CMP process.

During the CMP process, the top surface of the rotating CMP pad 104 experiences wear from the planarization process. The top surface of the rotating pad 104 may wear out unevenly such that depressions, valleys, and peaks may form in the CMP pad 104. The pad dresser 112 includes a rotating pad dresser head that is pressed downward onto the rotating CMP pad 104. 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 104. In particular, the rotating pad dresser head includes hard protruding particles 131 or materials. In one example, the particles 131 of the pad dresser include a diamond material lodged in the downward facing surface. The rotating head of the pad dresser 112 sweeps across the surface of the rotating CMP pad 104 in a pattern selected to maintain a substantially even top surface of the CMP pad 104 during the CMP process. Accordingly, the pad dresser 112 removes or prevents the formation of depressions, ridges, valleys, or uneven features on the surface of the rotating CMP pad 104.

During the CMP process, the CMP head 106 places the downward facing surface of the semiconductor wafer 108 into contact with the rotating CMP pad 104. The CMP head 106 may also rotate the semiconductor wafer 108 during the CMP process. Surface features of the downward facing surface of the semiconductor wafer 108 are 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 pad 104 rubbing down the bottom facing surface of the semiconductor wafer 108. 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 108. 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 108. The result of the CMP process is that the exposed bottom facing surface of the semiconductor wafer 108 becomes substantially planar.

In some embodiments, slurry arm 121 is positioned upstream from the CMP head 106. The slurry arm 121 supplies the slurry 123 onto the rotating pad 104 during the CMP process. In particular, the slurry arm 121 has a plurality of nozzles or apertures that each output the slurry 123 onto the pad 104. The slurry arm 121 can 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 head 126 is positioned downstream from the CMP head 106. Accordingly, the rotation of the pad 104 carries the slurry from the CMP head 106 to the pad dresser head 126. In one example, the pad dresser head 126 travels through a dresser scanning width less than the diameter of the pad 104. The pad dresser head 126 moves 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 123. Rotation of the pad 104 carries some of the used slurry 123 back into contact with the wafer held by the CMP head 106. Accordingly, some of the impurities and debris and the used slurry may come into contact with the wafer held by the CMP head 106. The slurry 123 generally follows a spiral pattern and is forced to the edge of the pad 104 due to the rotational motion of the pad 104. The slurry arm 121 constantly supplies fresh slurry 123 during the CMP process.

While the CMP process may be generally effective, several problems may arise that can damage the equipment of the CMP system 100 and the semiconductor wafer 108. For example, it is possible that debris particles from the wafer 108, the pad 104, or the pad dresser 112 may become lodged in the pores or cavities of the pad 104. For example, it is possible that some of the surface material of the pad dresser 112 may break off or otherwise become dislodged from the pad dresser 112. This results in pad dresser debris on the rotating CMP pad 104. The debris can include grains, particles, shards, or fragments of the material from the pad dresser 112. In one example, the debris includes diamond material. The rotating CMP pad 104 may carry the pad dresser debris into contact with the semiconductor wafer 108. The contact of the pad dresser debris with the semiconductor wafer 108 can scratch, fracture, or otherwise damage the semiconductor wafer 108. If the semiconductor wafer 108 is damaged by the pad dresser debris, then the semiconductor wafer 108 may need to be scrapped. Additionally, the CMP pad 104 may also be damaged when the pad dresser debris comes between the surfaces of the CMP pad 104 and the semiconductor wafer 108. This can result in a CMP pad 104 that 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 wafer 108 or the CMP pad 104. 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 104, the rotation of the CMP pad 104 causes the slurry to flow toward the outer perimeter of the CMP pad 104 and off of the CMP pad 104. Nevertheless, it is possible that some portion of the slurry may not quickly flow off of the CMP pad 104. 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 wafer 108 or the CMP pad 104.

As set forth previously, there is a particular risk that debris particles from either the wafer, the crystallized slurry, the pad dresser 112, or the pad itself can become lodged in the cavities or pores of the CMP pad 104. 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 pad 104 will only be effective at planarizing the wafer 108. A second risk is that lodged debris particles will scratch or otherwise damage the wafer 108. A third risk is that the debris particles in the cavities can become attached to the wafer 108. Each of these risks can result in scrapped wafers or damaged equipment.

In some embodiments, the CMP system 100 utilizes the pad dresser 112 to remove debris particles from the cavities or pores of the pad 104 between CMP processes. In particular, the CMP system 100 sprays a high presser rinsing fluid 127 onto the pad 104 while the wafer 108 is not present in while the pad dresser 112 moves back and forth across the pad. Nanobubbles 130 are generated in the rinsing fluid to assist in removing debris particles from the pores or cavities of the pad 104.

FIG. 1B illustrates a pad dressing process, in accordance with some embodiments. After a CMP process has been performed on the wafer 108, the wafer 108 and the CMP head 106 are removed from the pad 104. The slurry arm 121 is then utilized to provide the high-pressure rinsing fluid 127 onto the pad 104.

In some embodiments, the system 100 includes an ultrasonic tank 125. In FIG. 1B, the ultrasonic tank 125 is shown as being coupled to the hose or tube 122 in order to deliver the rinsing fluid 127 onto the pad 104. In such an example, valves can be operated to prevent the slurry 123 from entering the tube 122 and to enable the rinsing fluid 127 to enable the tube 122. Accordingly, though not shown, the system 100 can include one or more valves.

In some embodiments, the ultrasonic tank 125 supplies rinsing fluid 127 to the slurry arm 121 via a separate tube or connection. Various schemes, components, and configurations can be utilized to alternately supply rinsing fluid 127 and slurry 123 to the slurry arm 121 without departing from the scope of the present disclosure.

In some embodiments, the ultrasonic tank includes an ultrasonic generator 141. The ultrasonic generator 141 generates 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 nanobubbles 130 in the rinsing fluid 127. As will be set forth in more detail below, the nanobubbles 130 help to remove debris particles from pores or cavities in the pad 104 during 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 pad 104 to 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, N₂, CO₂, or other gases without departing from the scope of the present disclosure.

Nanobubbles 130 can be highly beneficial in dislodging debris particles due to the properties of the nanobubbles. Nanobubbles 130 remain suspended in the rinsing fluid for a relatively long durations of time. This enables the nanobubbles 130 to disperse throughout the rinsing fluid 127. Furthermore, nanobubbles 130 remain stable in the rinsing fluid until they interact with debris particles to dislodge them. Furthermore, the nanobubbles 130 continue to transfer gas to the rinsing fluid 127 until they collapse.

In one embodiment, the generation of the nanobubbles includes injection of a surfactant into the rinsing fluid 127. 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 tank 125 includes a heater 143 and a cooler 145. The heater 143 can be utilized to selectively raise the temperature of the rinsing fluid 127. The cooler 145 can be utilized to selectively lower the temperature of the rinsing fluid 127. In this way, the temperature of the rinsing fluid can be carefully controlled.

FIGS. 1C-1E each include a simplified side view of a portion of pad 104, as well as an enlarged view of a portion of the pad 104. In FIG. 1C, the pad 104 is relatively new. The large portion of FIG. 1C illustrates that the pad 104 includes pores or cavities 151. The pores or cavities 151 add asperity to the pad that helps to planarize the wafer 108 during CMP processes.

In FIG. 1C, because the pad 104 is relatively new, the surface of the pad 104 is relatively flat as can be seen in the upper portion of FIG. 1C. During pad dressing processes, the pad dresser is able to apply a substantially even downward force on the flat surface of the pad 104. The result is that debris particles 153 can be efficiently removed from the cavities 151.

FIG. 1D illustrates a pad 104 that has gone through a large number of CMP processes. The upper portion of FIG. 1D illustrates that the top surface of the pad 104 has become curved, though the curvature is exaggerated in FIG. 1D. The result is that the pad dresser 112 does not apply an even downward force on the pad 104. In the absence of nanobubbles 130 in the rinsing fluid 127, debris particles 153 can become lodged in the pores or cavities 151. If not addressed, this can result in damage to the wafer 108 as described previously.

FIG. 1E illustrates a pad 104 that has gone three large number of CMP processes and is curved, in a manner similar to FIG. 1D. As before, the pad dresser 112 may not be able to apply and even downward force on the curved surface of the pad 104. However, in FIG. 1E, rinsing fluid 127 including nanobubbles 130 is utilized during the pad dressing process. The nanobubbles 130 get below the debris particles 153 and assist in dislodging them. The result is that the pad dressing process effectively removes debris particles 153 from the cavities or pores 151 and the pad 104. This helps ensure that wafers 108 are not damaged during subsequent CMP processes.

In some embodiments, the nanobubbles 130 are generated after the rinsing fluid has been dispensed onto the pad 104. In some embodiments, the pad dresser 112 includes one or more ultrasonic generators that generate ultrasonic waves. The ultrasonic waves cause nanobubbles 130 to form in the rinsing fluid 127 that has seeped into the cavities 151. As described previously, by selecting the frequency of the ultrasonic waves, nanobubbles can be generated in the rinsing fluid 127 at selected depths within the pad 104.

FIG. 2A and 2B are side views of a CMP system 100, in accordance with some embodiments. In FIG. 2A, a CMP process is being performed. In FIG. 2B, a pad dressing process is being performed. Many aspects of the CMP system 100 of FIGS. 2A and 2B are substantially similar to those of FIGS. 1A and 1B.

However, in FIGS. 2A and 2B, the pad dresser arm 128 includes an interior fluid channel and a plurality of outlets 133. A tube 157 is coupled between the ultrasonic fluid tank 125 and the dresser arm 128. The ultrasonic fluid tank 125 includes the rinsing fluid 127 the ultrasonic generator 141, the heater 143, and the cooler 145. The dresser arm 128 is one example of a dispensing arm.

In FIG. 2A, a CMP process is performed. In particular slurry 123 is provided from the slurry tank 124 onto the pad 104 via the slurry arm 121. The rotating wafer 108 expressed in contact with the rotating pad 104 during the CMP process. The dresser head 126 sweeps across the pad 104 during the CMP process.

In FIG. 2B, a pad dressing process is performed. The wafer 108 and the CMP head 106 have been removed. During the pad dressing process, the ultrasonic tank 125 generates nanobubbles 130 in the rinsing fluid 127. The rinsing fluid 127, including the nanobubbles 130, is supplied via the outlet 133 in the dresser arm 128 onto the pad 104. The CMP head 126 sweeps across the surface of the pad 104 as described previously. As described previously, the nanobubbles 130 in the rinsing fluid 127 help to dislodge debris particles from the pad 104.

In some embodiments, the dresser arm 128 is between 25 cm and 50 cm above the pad 104. In some embodiments, the slurry arm 121 is between 25 cm and 50 cm above the pad 104. A distance in this range can result in good slurry distribution on the CMP pad 104. Other configurations of a slurry supply system 110 and a pad dresser 112 that dispenses the rinsing fluid 127 can be utilized without departing from the scope of the present disclosure.

FIG. 3 is a block diagram of a CMP system 300, in accordance with some embodiments. The CMP systems 100 of FIGS. 1A-1B and 2A-2B may be a subset of the CMP system 300. The CMP system 300 includes a plurality of load/unload port 160. The CMP system includes a driveway for passed through 162, a CMP chamber including four CMP platens 102 and to wafer load cups 164, and a wafer cleaning system 166.

In some embodiments, each wafer is received at one of the load/unload ports 160. Each wafer is then passed through the driveway for passed through 162 into the CMP chamber. In the CMP chamber, each wafer will be processed at two platens. Each wafer will be processed at either platens P1-1 and P2-1 (as shown by the path of travel arrow) or platens P1-2 and P2-2. For each platen 102, there is a respective CMP head 106, a slurry system 110, a pad dresser 112, and in ultrasonic generator to generate nanobubbles as described previously.

In some embodiments, each wafer 108 undergoes a CMP process including a first CMP step and the second CMP step. For example, a wafer 108 may be passed to the platen P1-1 two undergo the first CMP step and then to the platen P2-1 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 108. At each platen 102, a pad dressing processes performed between CMP processes (or steps), including generation of the nanobubbles 130 as described previously. After the CMP process, the wafer is passed through the wafer cleaning system 166 and then unloaded and one of the load/unload ports 160. A CMP system 300 can include other configurations without departing from the scope of the present disclosure.

FIG. 4A is a simplified side view of a CMP system 100, in accordance with some embodiments. Though not shown in FIG. 4A, the CMP system 100 can include the slurry supply system 110 and the CMP head 106. The CMP system 100 of FIG. 4A also includes a system (not shown) that dispenses rinsing fluid 127. In some embodiments, the slurry supply system 110 supplies the rinsing fluid 127 for the dressing process as described in relation to FIG. 1A and 1B. In some embodiments, the dresser arm 128 supplies the rinsing fluid 127 as described in relation to FIGS. 2A and 2B. Other systems, components, or configurations can be utilized to dispense the rinsing fluid 127 without departing from the scope of the present disclosure.

In FIG. 4A, the dresser head 126 generates ultrasonic vibrations during the pad dressing process while the rinsing fluid is being supplied onto the pad 104. The ultrasonic vibrations generated by the dresser head 126 generate nanobubbles 130 (not shown in FIG. 4A) in the rinsing fluid 127. As the rinsing fluid 127 has penetrated into the pores or cavities 151 of the pad 104, the generated nanobubbles assist in dislodging the debris particles from the pores or cavities 151. FIG. 4A also illustrates the hard particles or structures 131 that protrude from the dresser head 126.

As can be seen in FIG. 4A, the dresser head 126 includes a plurality of ultrasonic generators 170. The ultrasonic generators 170 are embedded in an array in the dresser head 126. During the pad dressing process, the ultrasonic generators 170 generate ultrasonic waves that results in nanobubbles 130, as described previously.

In some embodiments, the ultrasonic generators 170 can be selectively controlled to generate ultrasonic waves at various frequencies. In some embodiments, ultrasonic generators 170 near a center of the dresser head 126 generate ultrasonic waves at higher frequencies than do the ultrasonic generators 170 near the periphery of the dresser head 126. In one example, the ultrasonic generators 170 near the center of the dresser head 126 generate ultrasonic waves with a frequency between 4 MHz and 6 MHz, while the ultrasonic generators 170 near the periphery of the dresser head 126 generate ultrasonic waves of the frequency of 0.5 MHz and 1 MHz. Other frequencies and distributions of frequencies can be utilized without departing from the scope of the present disclosure.

In some embodiments, the ultrasonic generators 170 each correspond to a vibrator chip. Each vibrator chip can include a micro-electromechanical system (MEMS) chip. Each MEMS chip can generate ultrasonic waves as described previously. In some embodiments, the ultrasonic generators 170 include miniature motors that can generate ultrasonic waves. The ultrasonic generators 170 can include other types of devices without departing from the scope of the present disclosure.

FIG. 4B is an enlarged cross-sectional view of a portion of the CMP system 100 of FIG. 4A, in accordance with some embodiments. FIG. 4B illustrates the cavities or pores 151 and the pad 104. FIG. 4B also illustrates particles 153 lodged in the pores 151. Rinsing fluid 127 has been dispensed onto the surface of the pad 104 and permeates the pores 151. FIG. 4B also illustrates the distribution of ultrasonic generators 170 within the dresser head 126. The ultrasonic generators 170 generate ultrasonic waves that penetrate into the pad 104 for the penetration depth based on the frequency of the ultrasonic waves, as described previously. The ultrasonic waves generate nanobubbles 130 in the rinsing fluid 127 of assist in dislodging the debris particles 153 from the cavities or pores 151.

FIG. 4C is a top view of a dresser head 126 of the pad dresser 112 of FIGS. 4A and 4B, in accordance with some embodiments. The ultrasonic generators 170 are dispersed at various distances from the center or rotational axis of the pad dresser head 126. The ultrasonic generators 170a are closest to the rotational axis of the pad dresser head 126. The ultrasonic generators 170b are second closest to the rotational axis of the pad dresser head 126. The ultrasonic generators 170c are second furthest from the rotational axis of the pad dresser head 126. The ultrasonic generators 170d are furthest from the rotational axis of the pad dresser head 126.

In one embodiment, the frequency of the ultrasonic waves generated by each group of ultrasonic generators 170a-d is based on the distance of that group from the rotational axis of the pad dresser head 126. In some embodiments, the ultrasonic generators 170a and 170b generate ultrasonic waves with a high frequency (e.g., between 4 MHz and 6 MHz), while the ultrasonic generators 170c and 170d generates ultrasonic waves with a lower frequency (e.g., between 0.5 MHz and 1.5 MHz). In some embodiments, each group of ultrasonic generators generates ultrasonic waves with a different frequency. Other distributions of ultrasonic generators 170 and the ultrasonic frequencies can be utilized without departing from the scope of the present disclosure.

FIG. 5A is a graph 500 illustrating the number of nanobubbles generated in a fluid over time for a first frequency of a first lower frequency (upper curve) and a second higher frequency (lower curve), in accordance with some embodiments. In the example of FIG. 5A, a larger number of nanobubbles are generated for the lower frequency than for the higher frequency, with the number of nanobubbles generated increasing over time for both cases. The X axis is time and the Y axis is the number of nanobubbles.

FIG. 5B is a graph 501 illustrating the radius of nanobubbles generated based on the surfactant concentration, in accordance with some embodiments. As can be seen in FIG. 5B, surfactant n8-COOH results in the generation of bubbles with a relatively smaller radius for surfactant concentrations around 10,000 mM (where mM is millimolar). Surfactant n12-COOH results in the generation of nanobubbles with a relatively larger radius for surfactant concentrations around 10,000 mM. The X axis is surfactant concentration and the Y axis is the radius of the nanobubbles.

FIG. 6A is a simplified cross-sectional view of a portion of a wafer 108, in accordance with some embodiments. The wafer 108 includes a semiconductor substrate 161. The semiconductor substrate can include silicon, silicon germanium, or other suitable semiconductor materials. The semiconductor fins or channel stacks 163 extend from the substrate 161. Though not shown in FIG. 6A, the channel stacks 163 can each include a plurality of separate channels of a transistor. The metal gate 165 may wrap around each of the channels in the configuration of a gate all around transistor. The metal gate 165 is shown as a single layer, but may include a plurality of metal layers and structures. The metal gate 165 can include tungsten, titanium, titanium nitride, tantalum nitride, cobalt, ruthenium, or other suitable conductive materials. The simplified view of FIG. 6A does not illustrate how the gate metal 165 may wrap around each of the channels. Furthermore, source/drain regions are not illustrated in FIG. 6A.

The fins or channel stacks 163 are separated from each other by shallow trench isolation 164. The shallow trench isolation 164 can include silicon oxide, silicon nitride, SiCN, SiCON, SiON, or other suitable dielectric materials.

A dielectric layer 167 has been formed on the metal gate 165. The dielectric layer 167 can include silicon nitride, silicon oxide, SiCN, SiCON, SiON, or other suitable dielectric materials.

A layer 169 has been formed on the layer 167. The layer 169 can include amorphous silicon, a dielectric material, or other types of material. The dielectric layer 171 has been formed on the layer 169. The dielectric layer 171 can correspond to a hard mask layer. The hard mask layer can include silicon nitride, silicon oxide, SiCN, SiCON, SiON, or other suitable dielectric materials. A trench 177 has been formed through the layers 171, 169, 167, and 165. The trench separates portions of the metal gate 165 in order to electrically isolate the gate electrodes of various transistors. The trench 177 may be termed a cut metal gate trench.

A dielectric liner layer 173 has been formed on the sidewalls of the trench 177 and on the top surface of the layer 171. The dielectric liner layer 173 can include silicon nitride, silicon oxide, SiCN, SiCON, SiON, or other suitable dielectric materials. The dielectric layer 175 has been formed on the dielectric layer 173 and filling the trench 177. The dielectric layer 175 can include silicon nitride, silicon oxide, SiCN, SiCON, SiON, or other suitable dielectric materials. The various layers can be formed by thin film deposition processes or other deposition processes.

In FIG. 6B, a first CMP step of a CMP process has been performed. During the CMP process, the wafer 108 is held within the CMP head 110. The first CMP step rapidly the layers 175, 173, 171 and stops at the layer 169. The first CMP step may include a first type of slurry and first rotation and downward pressure parameters of the CMP head 102. The first CMP step corresponds to a bulk polishing with a higher removal rate to remove the dielectric layer 175 and the hard mask layer 171 with a high removal rate.

In FIG. 6C, a second CMP step of the CMP process has been performed. A second slurry different than the first slurry may be used during the second CMP step in order to remove the layers 169 and 167. Furthermore, the second CMP step removes a portion of the gate metal 165 and the fins or channel stacks 163 such that the metal gate 165 of each transistor is electrically isolated from the others. The second CMP step etches at a rate that is slower than the etching rate of the first CMP step. Furthermore, the second CMP step may utilize other rotation and downward pressure parameters of the CMP head 102. The second CMP step corresponds to a bulk polishing to achieve a smooth surface.

The CMP pads 104 on which the CMP steps are performed are dressed with a pad dressing process including generation of nanobubbles in a rinsing fluid, as described in relation to FIGS. 1A-5C. This results in the removal of debris particles from the cavities or pores of the pads prior to each CMP step. This further results in reduced damage to the wafer 108.

FIG. 7 is a flow diagram of a method 700, in accordance with some embodiments. The method 700 can utilize components, processes, and systems described in relation to FIGS. 1A-6C. At 702, the method 700 includes rotating a CMP pad positioned on a platen. One example of a CMP pad is the CMP pad 104 of FIG. 1A. One example of a platen is the platen 102 of FIG. 1A. At 704, the method 700 includes supplying a rinsing fluid onto the CMP pad while the CMP pad rotates. One example of a rinsing fluid is the rinsing fluid 127 of FIG. 1B. At 706, the method 700 includes generating nanobubbles in the rinsing fluid with ultrasonic waves. One example of nanobubbles are the nanobubbles 130 of FIG. 1B. At 708, the method 700 includes dressing the CMP pad with a CMP pad dresser while the rinsing fluid and the nanobubbles are present.

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.

In one embodiment, a method includes rotating a CMP pad positioned on a platen and supplying a rinsing fluid onto the CMP pad while the CMP pad rotates. The method includes generating nanobubbles in the rinsing fluid with ultrasonic waves and dressing the CMP pad with a CMP pad dresser while the rinsing fluid and the nanobubbles are present.

In one embodiment, a system includes a CMP platen, a CMP pad dresser head configured to dress a CMP pad on the CMP platen, and a rinsing fluid tank configured to hold a rinsing fluid. The system includes a dispensing arm configured to dispense the rinsing fluid onto the CMP pad while the CMP pad dresser head dresses the CMP pad and an ultrasonic generator configured to generate nanobubbles in the rinsing fluid while the CMP pad dresser head dresses the CMP pad.

In one embodiment, a device includes a CMP dresser head. The CMP dresser head includes a plurality of hard particles configured to dress a CMP pad during a CMP pad dressing process and an ultrasonic generator configured to generate ultrasonic waves during the CMP pad dressing process.

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.