US20130217306A1

US20130217306A1 - CMP Groove Depth and Conditioning Disk Monitoring

Info

Publication number: US20130217306A1
Application number: US13/397,845
Authority: US
Inventors: Jiann Lih Wu; Bo-I Lee; Soon Kang Huang; Chi-Ming Yang; Chin-Hsiang Lin
Original assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Current assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Priority date: 2012-02-16
Filing date: 2012-02-16
Publication date: 2013-08-22
Also published as: TW201334916A; KR20130094676A; TWI522204B

Abstract

Some embodiments relate to a chemical mechanical polishing (CMP) system. The CMP system includes a polishing pad having a polishing surface, and a wafer carrier to retain a wafer proximate to the polishing surface during polishing. A motor assembly rotates the polishing pad and concurrently rotates the wafer during polishing of the wafer. A conditioning disk has a conditioning surface that is in frictional engagement with the polishing surface during polishing. A torque measurement element measures a torque exerted by the motor assembly during polishing. A condition surface analyzer determines a surface condition of the conditioning surface or the polishing surface based on the measured torque. Other systems and methods are also disclosed.

Description

BACKGROUND

Over the last four decades, the density of integrated circuits has increased by a relation known as Moore's law. Stated simply, Moore's law says that the number of transistors on integrated circuits (ICs) doubles approximately every 18 months. Thus, as long as the semiconductor industry can continue to uphold this simple “law,” ICs double in speed and power approximately every 18 months. In large part, this remarkable increase in the speed and power of ICs has ushered in the dawn of today's information age.
Unlike laws of nature, which hold true regardless of mankind's activities, Moore's law only holds true only so long as innovators overcome the technological challenges associated with it. One of the advances that innovators have made in recent decades is to use chemical mechanical polishing (CMP) to planarize layers used to build up ICs, thereby helping to provide more precisely structured device features on the ICs.
To limit imperfections in planarization, improved planarization processes are described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a CMP system in accordance with some embodiments.

FIG. 2 is a top view of a CMP system having a polish pad that includes a series of concentric grooves, and a groove depth measurement element traversing over the polish pad.

FIG. 3 is a cross sectional side view of FIG. 2's CMP system.

FIG. 4 shows a block diagram of another CMP system in accordance with some embodiments.

FIG. 5 is a flow diagram illustrating a method of performing a planarization process in accordance with some embodiments.

DETAILED DESCRIPTION

The present disclosure will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures are not necessarily drawn to scale. It will be appreciated that this detailed description and the corresponding figures do not limit the scope of the present disclosure in any way, and that the detailed description and figures merely provide a few examples to illustrate some ways in which the inventive concepts can manifest themselves.
Conventional CMP techniques lack real-time feedback to adequately account for changes in the surface condition of polishing pads and/or conditioning disks. For example, an overly worn conditioning disk can cause wafers to be planarized more slowly and/or less uniformly, relative to a new conditioning disk. Thus, it is imperative to be able to monitor the surface condition of polishing pads and/or conditioning disks so they can be changed at an optimum time that strikes a good balance between maximizing the useful lifetime of the pad/disk, maximizing wafer throughput, and maximizing wafer surface uniformity.
FIG. 1 shows a block diagram of a CMP system 100 in accordance with some embodiments of the present disclosure. The CMP system 100 includes platen 102, polishing pad 104, slurry arm 106, wafer carrier 108, and conditioning disk 110. In some embodiments, this CMP system can process wafers that are 450 mm in diameter, however it is also applicable to other wafer sizes.
Prior to wafer planarization, slurry arm 106 dispenses slurry 111, which contains abrasive slurry particles, onto polishing surface 112 of polishing pad 104 before wafer planarization occurs. Motor assembly 114, under control of CMP controller 116, then rotates the platen 102 and polishing pad 104 (e.g., via platen spindle 118) about a polishing pad axis 120—as shown by first angular velocity arrow 122. As polishing pad 104 rotates, conditioning disk 110, which can be pivoted via scan arm 124 and rotated about disk axis 142, traverses over polishing pad 104 such that conditioning surface 126 of conditioning disk 110 is in frictional engagement with polishing surface 112 of polishing pad 104. In this configuration, conditioning disk 110 scratches or “roughs up” polishing surface 112 continuously during polishing to help ensure consistent and uniform planarization. Motor assembly 114 also concurrently rotates a wafer housed within wafer carrier 108 about wafer axis 128 (e.g., via wafer carrier spindle 130)—as shown by second angular velocity arrow 132. While this dual- rotation 122, 132 occurs, the wafer is “pressed” into slurry 111 and polishing surface 112 with a down-force applied by wafer carrier 108. The combination of abrasive slurry 111, dual rotation (122, 132), and down-force planarizes the lower surface of the wafer until an endpoint for the CMP operation is reached.
To remedy shortcomings of conventional CMP systems, CMP system 100 includes a surface condition analyzer 136 to determine surface condition(s) of polishing pad 104 and/or conditioning disk 110 in real-time during polishing. In some cases, a feedback path 138 provides for real-time adjustment of CMP process parameters 140 based on the measured surface condition(s). In this way, the disclosed CMP techniques facilitate consistent and uniform planarization of wafers. Also, because the real-time measurement limits downtime for the CMP system 100 in that wafers can be continuously processed and polishing pads 104 and conditioning disks 110 are replaced at precisely the time they are spent, these techniques can also significantly improve manufacturing throughput while at the same time maximizing the useful lifetime of polishing pads 104 and conditioning disks 110.
To determine a surface condition of polishing pad 104, the polishing pad 104 includes a number of grooves (e.g., 134 a, 134 b) in the polishing surface 112. As the polishing pad 104 becomes more worn, the polishing surface 112 is worn down, thereby reducing the depth of the grooves. In this way, the groove depths correspond to the condition of the polishing pad 104. To take advantage of this behavior, a depth measurement element 142, such as an acoustic transducer, measures the groove depths of the respective grooves in real-time during polishing of the wafer. The depth measurement element 142 can be arranged on a scan arm (not shown) to diametrically scan over the polishing surface 112 during polishing to measure these groove depths. The surface condition analyzer 136 can compare the respective measured groove depths to a predetermined groove depth threshold, and the CMP controller 116 can notify a CMP operator when the polishing pad 104 has reached the end of its useful life based on the measured groove depths.
To determine a surface condition of conditioning disk 110, CMP system 100 includes a torque measurement element 144 to measure a torque exerted by the motor assembly 114 during polishing. A surface condition analyzer 136 then determines the condition of conditioning surface 126 (and possibly the polishing surface 112 to some extent) based on the measured torque. In making this determination, the surface condition analyzer 136 makes use of the fact that measured torque is proportional to the amount of friction between the engagement and conditioning surfaces 126, 112. Because the amount of friction measured is set by the conditioning surface's ability to “rough up” the polishing surface 112, the measured torque corresponds generally to the overall condition of the conditioning surface 126. For example, assuming equal slurry compositions, temperatures, angular velocities, etc.; more measured torque generally corresponds to more friction between the conditioning surface 126 and polishing surface 112, which generally corresponds to a less worn (e.g., newer) conditioning surface 126. Conversely, a lower torque generally corresponds to smoother (e.g., older) conditioning surface 126.
Based on the measured condition of conditioning surface 126, the CMP controller 116 can make real-time changes to CMP process parameters during polishing in some embodiments. For example, as the conditioning surface 126 becomes more worn (as indicated by less friction and less measured torque), the CMP controller 116 can apply more down-force to the conditioning disk 110 (and/or more up-force from the platen 102) so there is greater frictional engagement between the conditioning surface 126 and polishing surface 112. The CMP controller 116 can also apply more down-force to the wafer via the wafer carrier 108, can increase the platen's angular velocity 122, can increase the wafer's angular velocity 132, can alter the composition of slurry 111, and/or can increase the temperature of the slurry 111 to increase the polish rate to offset the change in conditioning surface 126. Other changes to CMP process parameters 140 could also be made.
In addition, in some embodiments, the surface condition analyzer 136 can compare the measured torque to some predetermined torque threshold for a given set of CMP process parameters 140, wherein the predetermined torque threshold corresponds to a torque at which the conditioning disk 110 is to deemed “spent”. For example, for a given slurry composition, temperature, angular velocities, etc.; if the torque falls below some predetermined torque threshold (indicating conditioning surface 126 is too worn), the conditioning disk 110 is deemed spent. Thus, the CMP controller 116 can notify a CMP operator that it is time to replace the conditioning disk 110.
FIGS. 2-3 illustrate a more detailed view of one example of how groove depths can be measured for a polishing pad 200. FIG. 2 's polishing pad 200 includes a number of grooves 202 a, 202 b, which have lower surfaces 204 a, 204 b that are recessed relative to polishing surface 206. Although only two grooves are shown, it will be appreciated that any number of grooves ranging from one to hundreds or thousands of grooves can be included on the polishing pad 200, depending on the relative sizes of polishing pad and respective groove widths. A depth measurement element 208, such as an acoustic transducer, measures groove depths of the respective grooves in real-time during wafer polishing. The depth measurement element 208 can be arranged on a scan arm (not shown) to diametrically scan over the polishing pad 200 during polishing—as shown by arrow 210.
In embodiments where depth measurement element 208 is an acoustic transducer, the acoustic transducer transmits an acoustic pulse or wave 214 and subsequently measures a reflected acoustic pulse or wave 216 which is based on the transmitted acoustic pulse or wave. Often, this measurement is carried out while a liquid 212, such as deionized water or slurry for example, is present on the polishing pad 200 to help limit attenuation of the propagating acoustic pulse or wave. To measured the groove depth, the acoustic transducer can analyze a time between transmission of the pulse or wave 214 and reception of the reflected pulse or wave 216; or can measure a phase difference between the transmitted pulse or wave 214 and received pulse or wave 216. Thus, to measure a first polishing pad thickness t1, the acoustic transducer will measure a first distance dl based on the time or phase difference between the transmitted and reflected waves or pulses. As the acoustic transducer continues its scan, it will see a change in the time or phase difference as it starts to pass over groove. In particular, it will see a longer time delay between transmitted and reflected pulses or waves or a corresponding change in phase difference, which is indicative of a second distance d1. By taking the difference between d1 and d2, the acoustic transducer can determine the corresponding groove depth.
If a measured groove depth is less than some predetermined groove depth, it can indicate the polishing pad is spent. Hence, in such an instance, a CMP controller can notify a CMP operator so the CMP operator can replace the polishing pad 200 with a new polishing pad. Further, in some embodiments it is possible that the polishing ability of the polishing pad 200 changes as the pad wears. Because of this, monitoring the groove depth in real-time allows the CMP system to account for changes in the polishing characteristics of the polishing pad 200 as it wears. For example, as the polishing surface becomes more worn (as indicated by diminished groove depths), the CMP controller 116 can apply more down-force to the wafer via the wafer carrier 108, can increase the platen's angular velocity 122, can increase the wafer's angular velocity 132, can alter the composition of slurry 111, and/or can increase the temperature of the slurry 111 to increase the polish rate or otherwise change the CMP parameters to offset the change in polishing surface.
FIG. 4 show a cross-sectional side view of another CMP station 400 in accordance with some embodiments. CMP station 400 comprises platen 402, polishing pad 404 supported by platen 402, wafer carrier 406 to hold wafer 408 proximate to polishing pad 404 during polishing, and conditioning disk 422 having conditioning surface 424. Wafer carrier 406 includes an annular retaining ring 410, inside of which a pocket 412 houses wafer 408. A plurality of concentric, variable-pressure elements (PE) 414 a-414 c are included on wafer carrier 406. The variable pressure elements 414, which are proximate to pocket 412, exert independent amounts of suction or pressure onto corresponding concentric regions on the back-side of the wafer 408 a. Corresponding concentric surfaces on the front of the wafer 408 b may be called “to-be-polished” wafer surfaces.
In some CMP processes, wafer 408 is held inside pocket 412 with upward suction applied to wafer's backside by variable pressure elements 414 so as to keep the wafer 408 raised above the lower face of retaining ring 410. Platen 402 is then rotated about platen axis 418, which correspondingly rotates polishing pad 404. Abrasive slurry 420 in then dispensed onto the polishing pad 404, and conditioning disk 422 is lowered onto polishing pad 404. A platen motor (not shown) then begins rotating wafer carrier 406 around platen axis 418. Meanwhile, wafer carrier 406 is lowered, retaining ring 410 is pressed onto polishing pad 404, with wafer 408 recessed just long enough for wafer carrier 406 to reach polishing speed. When wafer carrier 406 reaches wafer polishing speed, wafer 408 is lowered facedown inside pocket 412 to contact the surface of polishing pad 404 and/or abrasive slurry 420, so that the wafer 408 is substantially flush with and constrained outwardly by retaining ring 410. Retaining ring 410 and wafer 408 continue to spin relative to polishing pad 404, which is rotating along with platen 402. This dual rotation, in the presence of the downforce applied to wafer 408 and the abrasive slurry 420, cause the wafer 408 to be gradually planarized. During this planarization process, the surface condition of conditioning disk 422 and/or polishing pad 404 can be monitored in real-time, and CMP parameters can be adjusted based on the measured surface condition(s).
After CMP, wafer carrier 406 and wafer 408 are lifted, and polishing pad 404 is generally subjected to a high-pressure spray of deionized water to remove slurry residue and other particulate matter from the pad 404. Other particulate matter may include wafer residue, CMP slurry, oxides, organic contaminants, mobile ions and metallic impurities. Wafer 408 is then subjected to a post-CMP cleaning process.
FIG. 5 illustrates another method of planarization in accordance with some embodiments of the present disclosure. While this method and other methods disclosed herein may be illustrated and/or described as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the disclosure herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.
As FIG. 5 shows, method 500 starts at 502 when CMP process parameters are set for a CMP system. CMP process parameters can include, but are not limited to: a polish time for which wafers are to be polished, a down-force to be applied to a to-be-polished wafer surface relative to a polishing pad, a down-force to be applied to the conditioning surface, an angular velocity of the polish pad or wafer, a slurry composition or a slurry temperature. A wafer typically includes a number of electrical connections and electrical isolation regions that are established using alternating layers of conductors and insulators.
In step 504, the method provides an abrasive slurry on a polishing surface of the CMP system.
In 506, the method places a conditioning surface in frictional engagement with the polishing surface to condition the polishing surface. The conditioning surface typically has a hardness that is greater than that of the polishing surface. For example, in many embodiments the conditioning surface is a diamond encrusted surface.
In 508, the method places a to-be-polished wafer surface proximate to the conditioned polishing surface.
In 510, the method polishes the to-be-polished wafer surface while using the CMP process parameters.
In 512, during polishing of the wafer, the method measures a surface condition of the polishing surface and/or conditioning surface.
In 514, the method adjusts one or more CMP process parameters during polishing based on the measured surface condition.
Thus, it will be appreciated that some embodiments relate to a CMP system. The CMP system includes a polishing pad having a polishing surface, and a wafer carrier to retain a wafer proximate to the polishing surface during polishing. A motor assembly rotates the polishing pad about a polishing pad axis and concurrently rotates the wafer about a wafer axis during polishing of the wafer. A conditioning disk has a conditioning surface that is in frictional engagement with the polishing surface during polishing. A torque measurement element measures a torque exerted by the motor assembly during polishing. A condition surface analyzer determines a surface condition of the conditioning surface or the polishing surface based on the measured torque.
Other embodiments relate to a CMP system for polishing a wafer. This CMP system includes a platen arranged to rotate about a platen axis, and a polishing pad arranged over the platen. The polishing pad is arranged to rotate about the platen axis coincidentally with the platen, and includes a polishing surface having one or more grooves disposed therein. A depth measurement element measures groove depths of the respective grooves in real-time during polishing of the wafer. A feedback path adjusts a CMP process parameter in real-time based on the respective measured groove depths.
Another method relates to chemical mechanical polishing (CMP). In this method, a set of CMP process parameters are set. These CMP parameters are to be used to planarize one or more wafers. The method provides an abrasive slurry on a polishing surface of a CMP station. The method places a conditioning surface in frictional engagement with the polishing surface to condition the polishing surface. A to-be-polished wafer surface is placed proximate to the conditioned polishing surface. The to-be-polished wafer surface is then polished while employing the set of CMP process parameters. During polishing of the wafer, the method measures a surface condition of the polishing surface or conditioning surface. A CMP process parameter can be adjusted during polishing based on the measured surface condition.
Although the disclosure has been shown and described with respect to a certain aspect or various aspects, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the disclosure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several aspects of the disclosure, such feature may be combined with one or more other features of the other aspects as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.

Claims

What is claimed is:

1. A chemical mechanical polishing (CMP) system, comprising:

a polishing pad having a polishing surface;

a wafer carrier to retain a wafer proximate to the polishing surface during polishing;

a motor assembly to rotate the polishing pad about a polishing pad axis and concurrently rotate the wafer about a wafer axis during polishing of the wafer;

a conditioning disk having a conditioning surface, wherein the conditioning surface is in frictional engagement with the polishing surface during polishing;

a torque measurement element to measure a torque exerted by the motor assembly during polishing; and

a condition surface analyzer to determine a surface condition of the conditioning surface or the polishing surface based on the measured torque.

2. The CMP system of claim 1, further comprising:

a feedback path to adjust a CMP process parameter in real-time during polishing of the wafer based on the surface condition determined by the condition surface analyzer.

3. The CMP system of claim 1, wherein the polishing pad includes a plurality of grooves in the polishing surface, the CMP system further comprising:

a depth measurement element to measure groove depths of the respective grooves during polishing of the wafer.

4. The CMP system of claim 3, wherein the depth measurement element comprises an acoustic transducer to measure the groove depths while a liquid is present on the polishing surface.

5. The CMP system of claim 3, wherein the depth measurement element is arranged on a scan arm to diametrically traverse over the polishing pad to measure the groove depths of the respective grooves.

6. The CMP system of claim 1, wherein the motor assembly rotates the polishing pad about a platen axis at a first angular velocity and rotates the wafer about a wafer carrier axis at an second angular velocity.

7. The CMP system of claim 6, further comprising:

a feedback path to adjust the first angular velocity or the second angular velocity based on the surface condition determined by the condition surface analyzer.

8. The CMP system of claim 1, wherein the conditioning surface has a hardness that is greater than a hardness of the polishing surface.

9. The CMP system of claim 8, wherein the conditioning surface is a diamond encrusted surface.

10. The CMP system of claim 2, further comprising:

a slurry dispenser to dispense an abrasive slurry onto the polishing surface;

wherein the feedback path is configured to adjust a slurry composition or slurry temperature based on the surface condition determined by the condition surface analyzer.

11. The CMP system of claim 2, wherein wafer carrier includes a plurality of concentric and variable down-force elements adapted to apply respective down-forces with respect to the polishing pad to concentric wafer regions;

wherein the feedback path is configured to adjust the respective down-forces based on the surface condition determined by the condition surface analyzer.

12. A chemical mechanical polishing (CMP) system for polishing a wafer, comprising:

a platen arranged to rotate about a platen axis;

a polishing pad arranged over the platen and arranged to rotate about the platen axis coincidentally with the platen, the polishing pad including a polishing surface having one or more grooves disposed therein;

a depth measurement element to measure groove depths of respective grooves in real-time during polishing of the wafer; and

a feedback path to adjust a CMP parameter in real-time based on the respective measured groove depths.

13. The CMP system of claim 12, wherein the depth measurement element comprises an acoustic transducer to measure the groove depths while a liquid is present on the polishing surface.

14. The CMP system of claim 13, wherein the liquid comprises slurry or deionized water.

15. The CMP system of claim 12, wherein the depth measurement element is arranged on a scan arm to diametrically traverse over the polishing pad to measure the groove depths of the respective grooves.

16. A method of chemical mechanical polishing (CMP), comprising:

setting a set of CMP process parameters to be used for planarizing one or more wafers;

providing an abrasive slurry on a polishing surface of a CMP station;

placing a conditioning surface in frictional engagement with the polishing surface to condition the polishing surface;

placing a to-be-polished wafer surface proximate to the conditioned polishing surface;

polishing the to-be-polished wafer surface while employing the set of CMP process parameters; and

during polishing of the wafer, measuring a surface condition of the polishing surface or conditioning surface.

17. The method of claim 16, further comprising:

adjusting a CMP process parameter during polishing based on the measured surface condition.

18. The method of claim 16, wherein the surface condition is measured by measuring a torque of a motor assembly used to move the polishing surface or wafer.

19. The method of claim 16, wherein polishing surface includes a number of grooves, and wherein the surface condition is measured by measuring depths of the respective grooves during polishing.

20. The method of claim 19, wherein the depths of the respective grooves are measured using an acoustic transducer.