Patent Application
20220362906
In semiconductor fabrication, integrated circuits and semiconducting devices are formed by sequentially forming features in sequential layers of material in a bottom-up manufacturing method. The manufacturing process utilizes a wide variety of deposition techniques to form the various layered features including various etching techniques such as anisotropic plasma etching to form device feature openings followed by deposition techniques to fill the device features. In order to form reliable devices, close tolerances are required in forming features including anisotropic etching techniques which rely heavily on layer planarization to form consistently deep anisotropically etched features.
In addition, excessive degrees of surface nonplanarity will undesirably affect the quality of several semiconductor manufacturing processes including, for example, photolithographic patterning processes, where positioning the image plane of the process surface within an increasingly limited depth of focus window is required to achieve high resolution semiconductor feature patterns.
Chemical mechanical polishing (CMP) is increasingly being used as a planarizing process for semiconductor device layers. CMP planarization is typically used several different times in the manufacture of a multi-level semiconductor device, including planarizing levels of a device containing both dielectric and metal portions to achieve global planarization for subsequent processing of overlying levels. A conventional CMP device includes a rotating polishing pad. A problem with the CMP operation is that the polishing surface of the polishing pad can become uneven during wafer processing. An uneven polishing surface cannot polish a wafer properly and may result in uneven or defective wafer processing.
Aspects of some embodiments 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.
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 some embodiments of 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, some embodiments of 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.
Some embodiments of the present disclosure are directed to a CMP process. A surface profile of a polishing pad is measured and compared with a reference profile to generate a difference result. A conditioning parameter value is determined according to the difference result, and the polishing pad is conditioned using the conditioning parameter value. The conditioning parameter value is used to control the rate of the material removed from the polishing pad. Therefore, the profile of the polishing pad is controlled to approach the reference profile.
A CMP controller 116 may be a processor, any form of computer, or a circuit. Prior to wafer planarization, the slurry arm 106 dispenses slurry 111, which contains abrasive slurry particles, onto a polishing surface 112 of the polishing pad 104 before wafer planarization occurs. The controller 116 then rotates the platen 102 and the polishing pad 104 (for example, via a platen spindle 118) about a polishing pad axis 120 as shown by a first angular velocity arrow 122. As the polishing pad 104 rotates, the conditioner 110, which is pivoted via a scan arm 124 and rotated about a disk axis 142, moves over the polishing pad 104 such that a conditioning surface 126 of the conditioner 110 is in frictional engagement with the polishing surface 112 of the polishing pad 104. In this configuration, the conditioner 110 scratches or “roughs up” the polishing surface 112 continuously during polishing to help ensure consistent and uniform planarization.
The wafer carrier 108 includes a head 134, a membrane 135, and a retaining ring 136. The retaining ring 136 surrounds a wafer 137. The membrane 135 is disposed on a downward surface of the head 134 to press the wafer 137. The controller 116 also rotates the wafer 137 housed within the wafer carrier 108 about a wafer axis 129 (e.g., via a wafer carrier spindle 130) as shown by a second angular velocity arrow 132. While the dual rotations (represented as the angular velocity arrows 122, 132) occur, the wafer 137 is pressed into the slurry 111 and the polishing surface 112 with a downforce applied by the wafer carrier 108. The combination of the slurry 111, the dual rotations, and the down-force planarizes the lower surface of the wafer 137 until an endpoint for the CMP operation is reached.
In some CMP operations, the wafer 137 is housed within the wafer carrier 108 with upward suction so as to keep the wafer 137 raised above the lower face of the retaining ring 136. When the platen 102 and the polishing pad 104 are rotated, the wafer carrier 108 is lowered, the retaining ring 136 is pressed onto the polishing pad 104, with the wafer 137 recessed just long enough for the wafer carrier 108 to reach a polishing speed. When the wafer carrier 108 reaches the polishing speed, the wafer 137 is lowered facedown to contact the polishing surface 112 of the polishing pad 104 and/or the slurry 111, so that the wafer 137 is substantially flush with and constrained outwardly by the retaining ring 136.
After CMP, the wafer carrier 108 and the wafer 137 are lifted, and a post-CMP cleaning operation is performed. For example, the polishing pad 104 is subjected to a high-pressure spray of deionized water to remove slurry residue and other particulate matter from the polishing pad 104. Other particulate matter may include wafer residue, CMP slurry, oxides, organic contaminants, mobile ions and metallic impurities. The wafer 137 is then referred to a polished wafer.
The CMP system 100 also includes a sensor 128 disposed on the scan arm 124 for measuring a profile of the polishing pad 104. The profile includes thicknesses at various locations. In some embodiments, the sensor 128 detects the distance from the sensor 128 to the polishing surface 112 of the polishing pad 104. The thickness of the polishing pad is calculated by subtracting the measured distance from a known distance between the sensor 128 and the bottom of the polishing pad 104. The sensor 128 can be configured to take measures at incremental radial positions across the polishing pad 104 when the scan arm 124 moves. In other words, the length of the scan arm 124 may be long enough to move the sensor 128 across the polishing pad 104. By moving the sensor 128 across the rotating polishing pad 104, the thicknesses of all location of the polishing pad 104 can be measured.
The sensor 128 can detect the thickness of the polishing pad 104 in various different ways. In some embodiments, multiple sensors 128 are disposed on the scan arms 124, and each sensor 128 detects the thickness of the polishing pad 104 at different locations. In some embodiments, the sensor 128 is disposed on the conditioner 110. In some embodiments, the sensor 128 is disposed on another movable device/unit/apparatus for detecting the thickness of the polishing pad 104 at various locations. In some embodiments, multiple sensors 128 may be mounted in a fixed manner across the radius or diameter of the polishing pad 104. Each sensor 128 may be mounted over a different radial position of the polishing pad 104. Since there are multiple sensors 128, distance measurements can be made simultaneously without needing to move the sensors 128. Since the sensors 128 are not coupled to a moving mechanism, there is less chance of positional errors due to the movement of the sensors 128. In some embodiments, the sensors 128 may be mounted in a staggered manner, in which each sensor 128 has a different radial position over the polishing pad 104. As the polishing pad 104 rotates, the system can take thickness measurements, so as to record the thicknesses for all areas of the polishing pad 104.
In some embodiments, the thicknesses for different radial positions across the polishing pad 104 are measured. The measurements may be averaged to determine the thickness of each concentric circular area of the polishing pad 104. By combining all of the average thickness measurements across the polishing pad 104, a polishing pad profile may be generated. A new polishing pad 104 has a uniform profile and a planar polishing surface initially. As the polishing pad 104 wears, the thickness of the polishing pad 104 will decrease. Since the polishing pad 104 rotates, it will wear in a circular pattern around the center of rotation. In some embodiments, the thicknesses for locations all over the polishing pad 104 are detected. The thicknesses for the entire polishing pad 104 can then be mapped in a grid of such as a X, Y coordinate system or a polar coordinate system.
Various polishing pad thickness detection methods are applicable to embodiments of the disclosure. For example, in some embodiments, the controller 116 may take multiple thickness measurement readings and discard the higher and lower readings and average the remaining readings. Thus, any individual measurement errors in the sensor detection will be filtered out. Since the surface of the polishing pad is not perfectly smooth, an average of many measurements may produce a relatively accurate indication of the pad thickness.
In some embodiments, a closed loop control is performed to monitor and adjust the surface profile of the polishing pad. Any suitable control method is applicable to the closed loop control. For example, proportional-integral-derivative (PID) feedback control, PI control or P control may be adopted. In general, after the difference result 313 is calculated, the controller 116 makes appropriate correction to the conditioning parameter value in order to reduce the difference between the surface profile 311 and the reference profile 312. The controlling mechanism will be described below. In some embodiments, a multi-loop closed loop control may be adopted. For example, an inner loop controls one of the downforce value and the sweeping speed value, and an outer loop controls the other one of the downforce value and the sweeping speed value.
In some embodiments, a previous profile of the polishing pad serves as the reference profile, and thus a thickness tendency is maintained. For example, assume that the profile 304 is the current surface profile, and the profile 302 is the reference profile. A current thickness tendency of the surface profile at a first location is calculated by applying a high pass filter to the thicknesses of the surface profile around the first location. For example, the high pass filter may be written as [−1, 0, 1], in which the middle coefficient “0” corresponds to the thickness where the high pass filer is applied, and the left coefficient “−1” corresponds to the left thickness in the profile, and the right coefficient “1” corresponds to the right thickness in the profile. When this high pass filter is applied to the location j, the current thickness tendency is tcur,j+1−tcur,j−1, where tcur,j+1 is the thickness of the current profile at location (j+1), and so on. A reference thickness tendency of the reference profile at the first location is calculated by applying the same high pass filter to the thicknesses of the reference profile around the first location. For example, when this high pass filter is applied to the location j of the reference profile 302, the reference thickness tendency is tcur−k,j+1−tcur−k,j−1, where k is a positive integer which may be 1, 5, 10, or any other suitable number. The conditioning parameter value with respect to the first location is determined so that the current thickness tendency approaches the reference thickness tendency. For example, when the current thickness tendency is greater than the reference thickness tendency, it means the surface profile around the location j increases faster, and therefore the downforce value of the conditioner at the location j may be increased, or the sweeping speed value of the conditioner at the location j may be decreased. Note that the high pass filter [−1, 0, 1] is just an example, and the coefficients and the size of the filter are not limited in the disclosure. For example, the filter may be [−1, 1] where either coefficient could correspond to the thickness where the filter is applied. Alternatively, the filter may be [1, 0, 0, 0, −1] where the leftmost or right most coefficient corresponds to the thickness where the filter is applied.
The thickness tendency calculation is independent with respect to various locations. To be specific, a first current thickness tendency of the surface profile at a first location (e.g. location j) may be calculated. A second current thickness tendency of the surface profile at a second location (e.g. location j+1) may be calculated. A first reference thickness tendency of the reference profile at the first location j is calculated. A second reference thickness tendency of the reference profile at the second location (j+1) is calculated. The conditioning parameter value with respect to the first location j is determined according to the first current thickness tendency and the first reference thickness tendency. The conditioning parameter value with respect to the second location (j+1) is determined according to the second current thickness tendency and the second reference thickness tendency. In particular, the conditioning parameter value with respect to the location j may be different from the conditioning parameter value with respect to the location (j+1).
In some embodiments, the conditioning parameter value is controlled such that the difference between the surface profile of the polishing pad and the reference profile is within a predetermined range. For example, the surface profile includes thicknesses tcur,j and tcur,ref; the reference profile includes thicknesses tcur−k,j and tcur−k,ref in which ref indicates any location other than the location cur, and 0≤k≤cur. For example, when k=cur, the reference profile is a profile of a new polishing pad prior to processing a wafer; when k<cur, the reference profile is a profile of the polishing pad after processing at least one wafer. In some embodiments, the location ref is 350 mm where the smallest thickness occurs. The following equations (1) to (3) are performed.
e
j
=t
cur,j
−t
cur−k,j (1)
e
ref
=t
cur,ref
−t
cur−k,ref (2)
d
j
=e
j
−e
ref (3)
In the equation (1), a first thickness difference ej between the current thickness tcur,j and the reference thickness tcur−k,j is calculated. In the equation (2), a second thickness difference eref between the current thickness tcur,ref and the reference thickness tcur−k,ref is calculated. Note that both of the current thickness tcur,j and the reference thickness tcur−k,j are at the location j, and both of the current thickness tcur,ref and the reference thickness tcur−k,ref are at the location ref. In the equation (3), a third thickness difference dj between the thickness difference ej and the thickness difference eref is calculated. The controller 116 determines whether the third thickness difference dj is in a pre-determined range (e.g. 0 to ±R mm, in which R may be 0.1, 0.2, 2, 3, 4 mm, or any other suitable value). If the third thickness difference dj is not within the pre-determined range, the controller 116 modifies the conditioning parameter value with respect to the location j according to the third thickness difference dj. For example, when the thickness difference dj is greater than 0.2, then the downforce value of the conditioner at the location j may be increased, or the sweeping speed value of the conditioner at the location j may be decreased. If the thickness difference dj is in the pre-determine range, the controller 116 adopts the default conditioning parameter value or the latest conditioning parameter value with respect to the location j to control the conditioner. In some embodiments, the thickness difference dj is inputted to the closed loop control to control the conditioning parameter value with respect to the location j.
Note that the equations (1) to (3) may be applied to every location j of the polishing pad. Accordingly, the conditioning parameter value with respect to the location j is determined independently. For example, the conditioning parameter value with respect to a first location may be different from the conditioning parameter value with respect to a second location in which the first location is different from the second location.
In some embodiments, the equation (1) is performed but not the equations (2) and (3). The thickness difference ej means the “thickness loss”. The controller 116 determines if the thickness difference ej is in a pre-determined range (e.g. 0 to ±R mm, in which R may be 0.1, 0.2, 2, 3, 4 mm, or any other suitable value). If the thickness difference ej is not in the pre-determined range, the controller 116 modifies the conditioning parameter value with respect to the location j according to the thickness difference ej. For example, if the thickness difference ej is smaller than −0.5, the controller 116 decreases the downforce value or increases the sweeping speed value of the conditioner with respect to the location j. If the thickness difference ej is in the pre-determine range, the controller 116 adopts the default conditioning parameter value or the latest conditioning parameter value with respect to the location j to control the conditioner. In some embodiments, the thickness difference ej is inputted to a closed loop control to control the conditioning parameter value with respect to the location j.
In some embodiments, the reference thickness Tcur−k,j and the reference thickness tcur−k,ref in the equations (1) to (3) may be replaced with other thicknesses. For example, the reference thickness Tcur−k,j may be replaced with the thickness t0,j of a new polishing pad at the location j, and the reference thickness Tcur−k,j may be replaced with the thickness t0,ref of the new polishing pad at the location ref. In some embodiments, the reference thickness Tcur−k,j may be replaced with an average of multiple thicknesses of the polishing pad at the location j corresponding to multiple polished wafers. In other words, the reference profile is an average profile of multiple profiles of the polishing pad after processing multiple wafers. For example, an average of the multiple thicknesses ta
In some embodiments, the current thickness at another location serves as the reference profile. To be specific, the surface profile includes a current thickness tcur,j, and the reference profile includes another current thickness tcur,ref in which the location j is different from the location ref. A thickness difference between the current thickness tcur,j and the current thickness tcur,ref is calculated as the following equation (4).
se
j
=t
cur,j
−t
cur,ref (4)
The controller 116 determines if the thickness difference sej is in a pre-determined range (e.g. 0 to ±R mm, in which R may be 0.1, 0.2, 2, 3, 4 mm, or any other suitable value). If the thickness difference sej is not in the pre-determined range, the controller 116 modifies the conditioning parameter value with respect to the location j. For example, if the thickness difference sej is greater than 0.4 mm, the controller 116 increases the downforce value or decreases the sweeping speed value of the conditioner with respect to the location j. If the thickness difference sej is in the pre-determine range, the controller 116 adopts the default conditioning parameter value or the latest conditioning parameter value with respect to the location j to control the conditioner. In these embodiments, the reference profile is a “flat profile” in which the thicknesses of the polishing pad are uniform. In some embodiments, the thickness difference sej is inputted to a closed loop control to control the conditioning parameter value with respect to the location j.
In some embodiments, an average of multiple current thicknesses serves as the reference profile. To be specific, the sensor 128 detects the thicknesses tcur,m, where m∈ C, and C denotes an area of the polishing pad. Note that the area C may represent the whole polishing pad 104 or a portion of the polishing pad 104. The controller 116 calculates an average thickness tcur,avg according to the following equation (5).
The controller 116 calculates the thickness difference as tcur,j−tcur,avg. The controller 116 also determines whether the thickness difference tcur,j−tcur,avg is within a pre-determined range. If the thickness difference is not within the pre-determined range, the controller 116 modifies the conditioning parameter value with respect to the location j. For example, if the thickness difference tcur,j−tcur,avg is greater than 0.4 mm, the controller 116 increases the downforce value or decreases the sweeping speed value of the conditioner with respect to the location j. If the thickness difference tcur,j−tcur,avg is in the pre-determine range, the controller 116 adopts the default conditioning parameter value or the latest conditioning parameter value with respect to the location j to control the conditioner. In some embodiments, the thickness difference tcur,j−tcur,avg is inputted to a closed loop control to control the conditioning parameter value with respect to the location j.
In some embodiments, a closed loop control is performed in the operation 405. The closed loop control may be performed in an in-situ mode or an ex-situ mode. In other words, the closed loop control may be performed simultaneously with the CMP operation, before the CMP operation, and/or after the CMP operation. In some embodiments, the chemical mechanical polishing operation is performed using the polishing pad after conditioning the polishing pad. In some embodiments, the CMP operation is performed using the polishing pad in which the chemical mechanical polishing operation and conditioning the polishing pad are performed at least partially simultaneously. In some embodiments, the CMP operation is performed using the polishing pad prior to measuring the surface profile of the polishing pad.
Referring to
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Those who are in the art should be able to appreciate the embodiments of
In some embodiments, the CLC is performed for every wafer. In some embodiments, the CLC is performed for every N wafers, where N is a positive integer greater than 1.
In some embodiments, the system detects the rotational position of the polishing pad, and a polar coordinate system may be the preferred means for defining the locations of the polishing pad associated with the thickness measurements. In other embodiments, the sensor(s) measures the thicknesses of the stationary polishing pad. The sensor may record one or more thicknesses and then be moved to a new position and stopped to measure additional thicknesses. The thicknesses of the entire polishing pad or representative locations of the polishing pad can be measured in a sequential manner. In these embodiments, the sensors may associate the thicknesses measurements of the polishing pad with X, Y location coordinates.
Different types of sensors can be used to measure the polishing pad thickness. Sensors suitable for polishing pad metrology include: laser, chromatic white light, inductive, CETR pad probe, ultrasonic, etc. The sensor(s) can be moved over the polishing pad in order to detect the pad thickness. The thickness detection can be performed during wafer processing or in between the processing of wafers. In some embodiments, the detection of the polishing pad thickness is performed when the polishing pad is covered with slurry, however other embodiments, the pad thickness detection is performed on a dry pad which requires the removal of the slurry.
Laser sensors direct a laser light at the polishing pad surface and the reflected light is detected. Based upon the reflected light, the distance between the sensor and the surface can be precisely calculated. Because the speed of light is constant, a pulse of laser light can be precisely and the system can detect the time it takes a light pulse to contact the surface being measured and receive the rebounded pulse. Alternatively, the light based distance measurement will be based upon interferometry. While the laser beam will most easily detect a clean polishing pad that has the slurry cleaned from the surface, it is also possible to detect the polishing pad thickness by directing the laser beam through a thin layer of slurry to the surface of the polishing pad and detecting the reflected light.
In some embodiments, a chromatic white light can be used to detect thickness of the polishing pad. A beam of light can be directed at the polishing pad and the reflected images are detected by a sensor, the diameter of the white light is substantially larger than that of a laser beam. Thus, fewer measurements may be required to determine the thicknesses of an entire polishing pad.
The proximity detector comprises an oscillating circuit composed of a capacitance in parallel with an inductance that forms the detecting coil which produces a magnetic field. The current flowing through the inductive loop changes when the sensor is in proximity to other objects and the change in current can be detected. By measuring the change in current, the distance to the object can be determined.
Mechanical probes can also be used to detect the polishing pad thickness. The probe is generally an elongated structure having an end that contacts the polishing pad. By knowing the extension of the probe from a fixed point to the surface of the polishing pad, the thickness of the polishing pad can be determined. It can be difficult to use the mechanical probe during the CMP process since the movement of the polishing pad may cause damage to the probe. Thus, in some embodiments, the probes are used to measure stationary polishing pads. Since the probe can be pressed through the slurry, the sensor readings will not be influenced by the slurry.
An ultrasonic sensor determines the thickness of the polishing pad by interpreting the echoes from ultra high frequency sound waves. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object. By knowing the position of the sensor and receiver, the thickness of the polishing pad can be determined.
In some embodiments, a method includes measuring a first thickness of a polishing pad at a first location of the polishing pad and a second thickness of the polishing pad at a second location of the polishing pad; obtaining a first reference thickness of the polishing pad at the first location of the polishing pad, wherein the first reference thickness is an average thickness of multiple thicknesses at the first location of the polishing pad in multiple polishing processes; obtaining a second reference thickness of the polishing pad at the second location of the polishing pad, wherein the second reference thickness is an average thickness of multiple thicknesses at the second location of the polishing pad in multiple polishing processes; calculating a first thickness difference between the first thickness and the first reference thickness; calculating a second thickness difference between the second thickness and the second reference thickness; modifying a conditioning parameter value at the first location of the polishing pad according to the first thickness difference and the second thickness difference; and sweeping a conditioner across a surface of the polishing pad; and applying a downforce or a sweeping speed to the conditioner that urges the conditioner against the first location of the polishing pad according to the modified conditioning parameter value.
In some embodiments, a method includes measuring a first thickness tcur,j of a polishing pad at a first location of the polishing pad and a second thickness tcur,ref of the polishing pad at a second location of the polishing pad; obtaining a first reference thickness tcur−k,j of the polishing pad at the first location of the polishing pad and a second reference thickness tcur−k,ref of the polishing pad at the second location of the polishing pad; calculating a first thickness difference ej between the first thickness tcur,j and the first reference thickness tcur−k,j; calculating a second thickness difference eref between the second thickness tcur,ref and the second reference thickness tcur−k,ref; calculating a third thickness difference dj between the first thickness difference ej and the second thickness difference eref; modifying a conditioning parameter value at the first location of the polishing pad according to the third thickness difference dj; sweeping a conditioner across a surface of the polishing pad; and applying a downforce or a sweeping speed to the conditioner that urges the conditioner against the first location of the polishing pad according to the modified conditioning parameter value.
In some embodiments, a method includes measuring a first thickness tcur,j of a polishing pad at a first location of the polishing pad and a second thickness tcur,ref of the polishing pad at a second location of the polishing pad, wherein the second thickness tcur,ref is a smallest thickness of the polishing pad; calculating a thickness difference sej between the first thickness tcur,j and the second thickness tcur,ref; modifying a conditioning parameter value at the first location of the polishing pad according to the thickness difference sej; sweeping a conditioner across a surface of the polishing pad; and applying a downforce or a sweeping speed to the conditioner that urges the conditioner against the first location of the polishing pad according to the modified conditioning parameter value.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of some embodiments of the present disclosure. Those skilled in the art should appreciate that they may readily use some embodiments of 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 embodiments of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the embodiments of the present disclosure.
This application is a Continuation application of of U.S. application Ser. No. 16/141,680, filed on Sep. 25, 2018, now U.S. Pat. No. 11,389,928, issued on Jul. 19, 2022, which claims priority to U.S. Provisional Application Ser. No. 62/592,746, filed Nov. 30, 2017, which are herein incorporated by references.
| Number | Date | Country | |
|---|---|---|---|
| 62592746 | Nov 2017 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16141680 | Sep 2018 | US |
| Child | 17866538 | US |
