US20020137434A1

US20020137434A1 - Method and apparatus for measuring properties of a polishing pad

Info

Publication number: US20020137434A1
Application number: US10/101,605
Authority: US
Inventors: Bong Choi; Ju-hun Song; Tae-Jin Kim
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2001-03-22
Filing date: 2002-03-21
Publication date: 2002-09-26
Also published as: KR20020074869A; KR100432781B1

Abstract

A comprehensive measurement of properties of a polishing pad of a CMP apparatus is used to create a database by which the CMP apparatus can be maintained and the polishing process can be precisely controlled. The measuring apparatus includes a measuring table and a control section. The measuring table has a flat top surface on which the polishing pad is placed, a camera, a sensor for sensing the relative location of the top surface of the polishing pad, a bracket to which the camera and the sensor are fixed, and an X-Y drive for moving the bracket in X- and Y-directions orthogonal to each other. The control section controls the operation of the camera, the sensor and the X-Y drive, and processes signals from the camera and sensor, so that a profile of the surface of the polishing pad can be discerned and an image of the surface of the polishing pad can be produced. The control section also assigns values to the sensed data and displays the values of the measured data, graphs and a surface image of the polishing pad. The measuring apparatus can also measure the hardness of the polishing pad and the transmittance through a transparent window of the polishing pad.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for measuring various properties of a polishing pad. More specifically, the present invention relates to a method and apparatus for measuring various properties of a polishing pad used to carry out the chemical and mechanical polishing of semiconductor wafers.

2. Description of the Related Art

Recently, as the need arises for more highly integrated semiconductor devices, a multi-layered structure has been used to yield a higher number of semiconductor chips per wafer. The multi-layered structure has been realized through the use of a conductive wiring pattern electrically connecting a plurality of layers on a semiconductor wafer. A planarization process is required to form such a multi-layered structure.

Chemical mechanical polishing (hereinafter referred as CMP) is a known planarization technique for forming the above-mentioned multi-layered structure. In CMP, the wafer is polished by the motion of a polishing pad relative to the wafer while the wafer is under pressure and a polishing solution or a slurry is provided between the wafer and the polishing pad.

The polishing pad carries out two major functions. That is, the polishing pad simultaneously causes the wafer to mechanically abrade and facilitates a chemical reaction between the slurry and the wafer. To this end, the polishing pad causes the polishing solution or slurry to flow smoothly by means of many small pores and grooves open at the surface of the polishing pad. Also, the polishing pad removes reactants from the surface of the wafer by means of its foam cell walls. The small pores have diameters of about 30˜70 μm so that the slurry deposited on the surface of the wafer can be stored temporarily in the pores. Hence, the Material-Removal-Rate (hereinafter referred to as MRR), namely the rate of polishing as a function of the pressure between the wafer and the polishing pad, can be kept constant during the polishing process. Also, a Within-Wafer-Non-Uniformity (hereinafter referred to as WIWNU) of the MRR is kept to a minimum.

However, during the CMP process, an elastic deformation occurs in the polishing pad due to a stress concentration resulting from a difference in density or size of device patterns on the wafer. Generally, the larger the stress concentration, the higher the MRR is. The uniformity of the MRR is also influenced by the hardness of the polishing pad. Generally, though, a hard polishing pad has a good local planarizing characteristic for inner portions of a chip, but generates a defect on a surface of the chip.

The polishing pads used in CMP apparatus are generally classified into two types, namely a non-woven fabric type and a foamed cross-linked polymer type. The non-woven fabric type of polishing pad is manufactured by impregnating or coating a non-woven fabric (e.g., polyester felt) with a cross-linked polymer (e.g., polyurethane resin). On the other hand, the foamed cross-linked polymer type of polishing pad is manufactured, for the most part, by coating a non-woven fabric pad with foamed polyurethane.

Both types of polishing pads provide a great number of pores open over the entire surface of the polishing pad. As mentioned earlier, the pores temporarily store the polishing solution and provide the polishing solution for the surface of the wafer. Such polishing pads of a CMP apparatus are mainly used for polishing a glass substrate or a mono-crystalline silicon wafer. In addition, new polishing pads are continually being developed to provide better performance during the CMP process. For example, the IC-1000 (manufactured by Rodel Inc. U.S.A) has been recently used in CMP apparatus without producing scratches on the surface of the wafer and offers the same performance as the IC-60 (also manufactured by Rodel Inc. U.S.A.).

Now, again, the performance of a polishing pad is basically decided by the hardness, surface state and compressibility of the polishing pad as these characteristics relate to the material being polished.

As concerns hardness, if the hardness of the polishing pad is not uniform over the entire polishing pad, the magnitude of a load applied to the polishing pad varies at different portions of the polishing pad. Thus, the thickness of the polishing pad becomes non-uniform during the polishing process. Consequently, the wafer is not planarized correctly. Hence, polishing pads should have a hardness tailored to the particular polishing operation.

A polishing pad for polishing an insulating film should have a hard and rough surface to remove a reactant of the insulation film produced as the result of the chemical etching of the film by means of the slurry. In the case of polishing a metal such as aluminum, a ductile polishing pad is preferably used because the aluminum is prone to being damaged and contaminated due to its own ductility. When such a ductile polishing pad is used for polishing process, the RMM is about 3,000 Å/min and the selectivity of aluminum with respect to an oxide is about 40:1. On the other hand, a hard polishing pad is advantageous when polishing a hard metal such as tungsten. In the case of polishing tungsten, the RMM is about 2,000 Å/min and the selectivity with respect to an oxide is about 20:1. When polishing copper, a polishing pad having a medium hardness should be used. In this case, the RMM is about 4,000 Å/min and the selectivity thereof with respect to an oxide is about 100:1

Generally, the lower the density of the polishing pad is, the higher the MRR is. Also, the larger the compressibility is, the higher the MRR is.

As concerns compressibility, the extent to which a polishing pad will deform under compression has a direct effect on the evenness of the wafer and uniformity of a residual thin film of the wafer. With this in mind, a hard polishing pad, i.e., having a small compressive deformability, should be used when polishing a stepped surface of a wafer. For instance, an IC-1000 polishing pad, manufactured by Rodel Inc. U.S.A., is usually used in this case. Also, a second generation IC-series pad, namely the IC-1400 polishing pad, offers an extended lifetime and improvement in the uniformity of the surface of a wafer. The IC-1400 polishing pad has a structure of two layers—a surface layer and a lower layer. The surface layer is formed using the IC-1000 polishing pad, and the lower layer is made of an independent foamed material serving as a buffer layer to improve water permeability and a slight change of a compressive characteristic of the polishing pad, thereby increasing the uniformity of the surface of the wafer. Furthermore, a surface of the second generation polishing pad has concentric grooves formed therein.

The Q-2000 polishing pad (also a trade name of Rodel Inc. U.S.A.) has been developed for the purpose of decreasing a dependency of the polishing pad on the conditioner to improve a local planarity of the wafer. This pad, too, has a structure consisting of two layers. The surface layer thereof comprises a foamed polymer sheet having a high degree of hardness, and in which grooves are formed to ensure a smooth and uniform flow of the slurry.

As described above, the polishing pads are designed and selected for use based on the type and surface characteristics of the material to be polished. Because the polishing pads play a very important role in the CMP process, a strict management of the maintenance and deployment of the polishing pads is required in fabricating semiconductor devices.

To this end, the polishing pads are periodically replaced according to product specifications provided by the manufacturer. The product specifications are conservative in their approach to preventing a polishing pad from damaging a wafer. The reliance on the product specifications to manage the replacement of the polishing pads increases the manufacturing cost of the semiconductor devices because the polishing pad is sometimes replaced even if the used polishing pad is still functional. Furthermore, the end user of a CMP apparatus generally buys the polishing pad with the CMP apparatus from the manufacturer, and operates the CMP apparatus according to specifications provided by the manufacturer. Then, after the useful life of the polishing pad has expired, the end user mounts a new polishing pad to the apparatus. However, because the characteristics of the replacement polishing pad may differ slightly from the characteristics described in the specifications, operating the CMP apparatus according to the specifications usually results in a processing error. That is, a wafer can be damaged by a polishing pad even when the replacing of the polishing pads are being scheduled according to the product specifications of the manufacturer.

Meanwhile, the polishing pad has a transparent window by which the polishing of the wafer can be monitored. Accordingly, when to end the CMP process can be determined by monitoring the surface state of the wafer through the transparent window.

Now, when foreign material becomes lodged in the pores of the polishing pad, such foreign material may microscopically scratch the surface of the wafer. Furthermore, the gaps between adjacent pores and/or the depths of the pores are altered and made irregular by the foreign material. Hence, the condition of the slurry is changed by these changes in the gaps and/or depths of the pores which, in turn, leads to changes in the efficacy of the CMP process. Another problem that sometimes occurs is that the light transmittance through the transparent window of the polishing pad changes. When this occurs, the end point of the polishing process cannot be detected accurately. Thus, the wafer may be polished excessively or insufficiently.

As described above, the planarization of the wafer is influenced during the CMP process by various properties of the polishing pad; these properties include the surface profile, hardness, distribution and uniformity of the pores, and the degree of transparency of the window. Accordingly, such properties of the polishing pad need to be measured precisely if a wafer is to be sufficiently and uniformly polished.

U.S. Pat. No. 5,934,974, issued to Tzeng Huey-Ming, discloses a technique of measuring the degree of wear of a polishing pad by using a non-contact laser sensor. According to the patent, a device is mounted on a CMP apparatus to measure the thickness of the polishing pad during the polishing process without interrupting the process. Although the device can be easily adapted for use with a belt type of CMP apparatus, it is difficult to incorporate the device into a rotary type of CMP apparatus.

U.S. Pat. No. 5,974,679, issued to Birang, et al, discloses a technique of measuring a surface profile of the polishing pad by bringing a sensor into contact with a surface of the polishing pad. In this system, the sensor is part of a measuring apparatus mounted on a rotary plate of the CMP apparatus for measuring the thickness of the polishing pad. According to the Birang et al. patent, the measuring apparatus can measure the surface profile of the polishing pad only when the CMP apparatus stops because, as mentioned above, the measuring apparatus is mounted on the rotary plate of the CMP apparatus.

Japanese Patent Laid-open Publication No. 8-61949 discloses a technique of measuring the profile of a polishing pad by using a laser sensor and simultaneously measuring the profile of the rotary plate using an excess current sensor.

In all of the conventional techniques described above, a measuring device mounted on the CMP apparatus itself is used to scan the polishing pad in the radial direction to detect a profile of the polishing pad in one direction.

However, a typical CMP apparatus does not have enough space to accommodate such measuring devices. Also, the mounting structure for the measuring devices complicates the overall structure of the CMP apparatus. Furthermore, the conventional measuring devices can only measure the surface profile or thickness of the polishing pad. That is, the conventional measuring devices can not conduct a comprehensive measurement of the properties of the polishing pad.

SUMMARY OF THE INVENTION

Accordingly, an object of present invention is to overcome the aforementioned problems and limitations of the prior art.

More specifically, an object of the present invention is to provide a method of and apparatus for measuring and discerning properties of a polishing pad, such as the profile, surface state, hardness and transmittance through the transparent window thereof, before and/or after the polishing pad is used in a CMP apparatus.

A further object of the present invention is to provide a method of and apparatus for measuring and discerning properties of a polishing pad to produce data by which the CMP process can be maintained and managed efficiently.

A still further object of the present invention is to provide a method of and apparatus for discerning the wear of a used polishing pad to provide data useful for estimating the optimal operating parameters of the CMP apparatus.

The apparatus for measuring properties of a polishing pad according to the present invention includes a measuring table and a control section. The measuring table has a flat table top on which the polishing pad is placed. A camera for taking a picture of the top surface of the polishing pad, and a proximity sensor for measuring profile of the top surface of the polishing pad, are fixed to a bracket. Drive means move the bracket along the directions of X and Y axes in a plane above the polishing pad. The control section includes a control system for controlling the movement of the camera and the sensor along directions of the X and Y axes, as well as the operation of the camera and the sensor. Accordingly, the profile of the surface of the polishing pad can be discerned, and an image of the surface of the polishing pad can be produced. The control system also includes a display having a screen on which measured values, graphs and images can all be displayed

The table top is an upper plate that is precision-made to have a high degree of surface flatness so that it will affect the measurements of the surface profile of the polishing pad as little as possible. On the other hand, the upper plate has a plurality of holes formed at a central portion thereof. A vacuum pump communicates with the holes to produce suction by which the polishing pad is fixed to the upper plate. Therefore, vibrations and the like will not disturb the polishing pad when the polishing pad is being measured.

The sensor for sensing the profile of the polishing pad is preferably a non-contacting laser sensor.

The apparatus for measuring properties of the polishing pad may further include a hardness-measuring sensor for measuring the hardness of the polishing pad and a transmittance sensor for measuring the transmittance through a transparent window in the polishing pad. These sensors may also be mounted by the bracket to the drive means. Preferably, however, the transmittance sensor is fixed to the upper plate so as to overhang the edge of the upper plate.

The transmittance sensor may comprise a light-receiving element that is disposed coplanar with the top surface of the upper plate, and a light-emitting element that is disposed a predetermined distance above the light-receiving element so that the polishing pad may be inserted between the light-receiving element and the light-emitting element.

The drive means includes a Y-axis linear drive mechanism and an X-axis linear drive mechanism. The Y-axis linear drive mechanism comprises a Y-axis carrier extending along a first side of the upper plate, a Y-axis guide rail extending parallel to the Y-axis carrier along a second side of the top surface of the upper plate, a Y-axis slider supported by the Y-axis carrier so as to be movable longitudinally therealong, and a Y-axis guide rail slider supported by the Y-axis guide rail so as to be movable longitudinally therealong. The X-axis linear drive mechanism comprises an X-axis carrier disposed above the top surface of the upper plate and having opposite ends respectively mounted to the Y-axis slider and the Y-axis guide rail slider; and an X-axis slider supported by the X-axis carrier so as to be movable longitudinally therealong. The bracket to which the sensors are mounted is fixed to the X-axis slider so as to move therewith.

A respective feed screw or linear motor is connected each of the X-axis slider and Y-axis slider for moving the same along the X-axis and Y-axis carriers.

In a method of measuring properties of a polishing pad of a CMP apparatus according to the present invention, the polishing pad is placed on the table top and fixed thereto using a vacuum. The polishing pad is then scanned in the directions of the X and Y axes to locate the center of the polishing pad. Once the center of the polishing pad is located, the hardness thereof is measured and a value of the hardness is displayed on the screen. Next, a profile of the polishing pad is discerned by moving the proximity sensor over the polishing pad in the direction of the Y axis, and the profile is displayed in the form of a graph on the screen. In addition, the surface of the polishing pad is scanned with the camera while pictures of the surface of the polishing pad are taken. These pictures are then used to display an image of the surface of the polishing pad on the screen.

In addition, the transparent window of the polishing pad may be aligned with the transmittance sensor so that the transmittance through the transparent window is measured. Likewise, the measured value of the transmittance through the transparent window is displayed on the screen.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention will become more apparent from the following detailed description thereof made in conjunction with the accompanying drawings, of which: [0039]
FIG. 1 is a schematic diagram of a rotary CMP apparatus; [0040]
FIG. 2 is a plan view of a polishing pad of the rotary CMP apparatus shown in FIG. 1; [0041]
FIG. 3 is a perspective view of measuring apparatus for measuring properties of a polishing pad according to the present invention; [0042]
FIG. 4 is a perspective view of a measuring table of the measuring apparatus according to the present invention; [0043]
FIG. 5 is a perspective view of a sensor array fixed to an X-axis slider of the measuring table; [0044]
FIG. 6 is a perspective view of a transmittance sensor of the measuring table for measuring the transmittance of a transparent window of the polishing pad; [0045]
FIG. 7 is a block diagram of a control section of the measuring apparatus according to the present invention; [0046]
FIG. 8 is a flowchart of the overall operation of the measuring apparatus according to the present invention; [0047]
FIGS. 9 and 10 are flowchart of a subroutine in which the measuring apparatus detects a center of the polishing pad according to the present invention; [0048]
FIGS. [0049] 11 to 14 are front views of a display screen of the control section of the measuring apparatus according to the present invention; and
FIG. 15 is a graph illustrating a surface profile of the polishing pad measured by means of a laser sensor according to the present invention.[0050]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. [0051]
Referring to FIG. 1, a CMP apparatus includes a [0052] rotary platen 10 and a polishing pad 12 attached to the top surface of the rotary platen 10. As the polishing process progresses, the pores of the polishing pad are clogged with residual material generated by the polishing process. If left unchecked, the essential function of the pores, e.g., of storing polishing slurry, would be degraded. To counteract this problem, a conditioner head 14 is supported at the periphery of the polishing pad 12 in contact with the polishing pad 12. The conditioner head 14 comprises a nickel plate having diamond particles electro-deposited on a surface thereof. The conditioner head 14 thus produces fine cuts in the surface of the polishing pad 12 to expose new pores that can then store the slurry.
A [0053] rotary head 16 is supported at the periphery of the polishing pad 12, symmetrically to the conditioner head 14 with respect to the center of the polishing pad. The rotary head 16 produces a vacuum by which a wafer 18 is adhered to the bottom surface thereof. The rotary head 16 moves the wafer 18 adhered thereto downward to press the wafer 18 against the polishing pad 12. The rotary head 16 also rotates eccentrically relative to the polishing pad 12 so that the wafer 18 makes contact with the polishing pad 12 over an area wider than that of just the wafer 18. The slurry constituting a polishing solution is supplied through a nozzle 20 situated above the polishing pad 12.
In addition, the [0054] polishing pad 12 and the wafer 18 are rotated in directions opposite to each other while the polishing solution is supplied between the polishing pad 12 and the wafer 18 so as to polish the wafer 18.
The pores that are formed in a surface of the [0055] polishing pad 12 have diameters of about 30˜70 μm so as to be capable of accommodating the slurry, of rendering the MRR (Material Removal Rate) constant and of minimizing the WIWNU (Within Wafer Non-Uniformity).
FIG. 2 is a plan view of the [0056] polishing pad 12. The polishing pad 12 is in the form of a disc and has a transparent window 12 a at a location where the wafer is brought into contact with the rotary head 16. The polishing pad 12 also has a plurality of concentric circular grooves 12 b. Laser light is transmitted to the surface of the wafer 18 through the transparent window 12 a, and is then reflected by the wafer 18. The reflected light is transmitted back through the window 12 a and is then received in a light sensor (as illustrated back in FIG. 1). The concentric grooves 12 b provide space for storing and supplying the slurry. Accordingly, the shape and a distribution of the grooves 12 b as well as those of the pores are very important factors affecting the polishing characteristics of the polishing pad 12. In particular, these factors dictate the uniformity of contact between the slurry and the surface of the wafer 18.
FIG. 3 shows a measuring apparatus for measuring and discerning properties of the [0057] polishing pad 12, namely, the surface profile, surface state, hardness and transmittance of a transparent window thereof. As will be described in further detail later on, the properties of the polishing pad, 12 before and after use in the CMP apparatus, can be filed in a database. The measuring apparatus of the present invention basically includes a measuring table 100 and a control section 200.
The [0058] control section 200 is in the form of a cabinet. A monitor 202 is disposed at the top of the control section 200 and a first tray 204 for supporting a keyboard 208 and a second tray 206 for supporting a mouse 210 are mounted at an intermediate portion of the control section 200. A disc driver 212 for driving a data disc on which data is recorded, for example, a floppy disc, an optical disc or the like, is located at the center of a lower portion of the control section 200. The control section 200 also includes a computer processor, an interface circuit board and a power supply.
The measuring table [0059] 100 basically comprises an XY-carrier 110 to which a plurality of sensors are mounted, an additional transmittance sensor 120, and a vacuum pump 130 disposed at the bottom of the measuring table 100. Referring also now to FIG. 4, the XY-carrier 110 is installed on an upper plate 102 of the measuring table 100. The transmittance sensor 120 is fixed to the front of the upper plate 102. The upper plate 102 of the measuring table 100 is made by a precision machine-process so as to possess a high degree of surface flatness. A pad-accommodating section on which the polishing pad 12 is placed is formed at the center of the top surface of the upper plate 102, and a plurality of vacuum holes 104 are formed in the pad-accommodating section. The vacuum pump 130 is connected to the plurality of vacuum holes 104 to produce a vacuum by which the polishing pad 12 is adhered to the upper plate 102 of the measuring table.
The XY-[0060] carrier 110 comprises X-axis and Y-axis linear drive mechanisms. The Y-axis linear drive mechanism includes a Y-axis carrier 111, a Y-axis slider 112, a Y-axis guide rail 114, and a Y-axis guide rail slider 115. The X-axis linear drive mechanism includes an X-axis carrier 116 and an X-axis slider 117. The Y-axis carrier 111 extends along the left edge of the upper plate 102 of the measuring table 100 (in the direction of a Y axis). The Y-axis guide rail 114 extends along the right edge of the upper plate 102 of the measuring table parallel to the Y-axis carrier 111. The Y-axis carrier 111 carries the Y-axis slider 112 in the direction of the Y axis. The Y-axis guide slider 115 is guided for movement along the Y-axis guide rail in the direction of the Y axis.
One end of the [0061] X-axis carrier 116 is fixed to the Y-axis slider 112 and the other end of the X-axis carrier is fixed to the Y-axis guide slider 115. As a result, the X-axis carrier 116 can traverse the measuring table 100.
In addition, the X-axis linear drive mechanism and the Y-axis linear drive mechanism comprise feed [0062] screws 116 b and 111 b that are rotated by stepper motors 116 a and 111 a, respectively (briefly refer to FIG. 7). The X-axis slider 117 and the Y-axis slider 112 are threaded to the feed screws 116 b and 111 b, respectively, so as to move in the direction of the axis X and the Y axis when the feed screws 116 b and 11 b are rotated by the stepper motors 116 a and 111 a. Alternatively, the X-axis linear drive mechanism and the Y-axis linear drive mechanism may comprise the stators of linear motors, and the X-axis slider 117 and the Y-axis slider 112 may respectively be integrated with the respective movers of the linear motors. In any case, the X-axis carrier 116 is moved in the direction of the Y axis, and the X-axis slider 117 is moved in the direction of the X axis. In this way, the X-axis slider 117 can be scanned across the pad-accommodating portion of the upper plate 102 in an XY-plane defined by the X and Y axes of the measuring table 100.
Referring to FIG. 5, a [0063] bracket 118 is mounted to the X-axis slider 117, and a camera 140, a laser sensor 150 and a hardness-measuring sensor 160 are fixed to the X-axis slider 117 by bracket 118.
Referring to FIG. 6, the [0064] transmittance sensor 120 for measuring the transmittance through the transparent window 12 a of the polishing pad 12 includes a light-receiving element 122 and a light-emitting element 124. The light-receiving element 122 is mounted to one end of a first holding arm 121, the other end of which is fixed to the top portion of the measuring table 100. The light-emitting element 124 is attached to an end portion of a second holding arm 123 disposed above and in parallel with the first holding arm 121 as spaced a predetermined distance therefrom. The first and second holding arms 121 and 123 have lengths that are sufficient to extend from an edge of the polishing pad 12 to the center of the transparent window 12 a of the polishing pad 12. The light-receiving element 122 and the light-emitting element 124 are positioned such that an extension of the top surface of the upper plate 102 of the measuring table 100 lies between the light-receiving sensor 122 and the light-emitting sensor 124. In particular, the light-receiving sensor 122 lies coplanar with the top surface of the upper plate 102.
Accordingly, when the transmittance through the [0065] transparent window 12 a is to be measured, the polishing pad can be supported on the top surface of the upper plate 102 with the transparent window 12 a disposed in the path of light transmitted to the light-receiving element 122 from the light-emitting element 124 (FIG. 7).
The [0066] camera 140 is, for example, a CCD (charge coupled device) camera having a high resolution and a high magnification. Such a camera is suitable for observing the surface of the polishing pad 12 using the naked eye. The camera 140 can also search for foreign matter in the grooves or the pores of the polishing pad 12.
The [0067] laser sensor 150 is a common sensor widely used for measuring the interference of laser light. More specifically, the laser sensor 150 directs a laser onto the surface of the polishing pad 12 and detects the interference pattern of light reflected by the surface of the polishing pad 12. Hence, the relative position of the surface of the polishing pad can be detected, whereby the surface profile of the polishing pad 12 can be discerned.
The hardness-measuring [0068] sensor 160 is a common sensor widely used for measuring hardness.
Referring now especially to FIG. 7, the [0069] control section 200 comprises a control system that may include a personal computer, the sensors and camera connected to the personal computer through an interface board. In this case, each of the sensors and the camera can communicate with the interface board through an RS232 serial bus or a USB (universal serial bus).
Specifically, the [0070] control section 200 includes a microcomputer 218, a memory 216 including a DRAM, a SRAM and an EPROM, a keyboard 208, a mouse 210, a hard disc driver 216, a floppy disc driver 212, a CD-ROM driver 214 and a monitor 202. The microcomputer 218 is connected through a system bus to a hardness-measuring sensor interface 220, a laser sensor interface 222, a camera interface 224, a motor operating portion 226 and a transmittance sensor interface 228.
As shown in FIG. 7, the profile, the surface state and the hardness of the [0071] polishing pad 12 are measured while the polishing pad 12 is adhered by a vacuum to a central portion (position A in FIG. 7) of the upper plate 102 of the measuring table 100. On the other hand, the transmittance through the transparent window 12 a is measured while the polishing pad 12 is positioned on the measuring table 100 with the transmittance sensor 120 aligned with the transparent window 12 a (position B in FIG. 7).
The operation of the measuring apparatus will now be described in more detail with reference to FIGS. [0072] 8-14.
Referring to FIG. 8, at first, the control system of the [0073] control section 200 is initialized (step S1). In this step, the motors 111 a, 116 a are first initialized and then the sensors 120,140, 150 and 160 are initialized using the initialization screen shown in FIG. 11. Referring to FIG. 11, when the motors are initialized, the current X-axis and Y-axis positions of the motors are input, and “X-axis motor homing”, “Y-axis motor homing”, “motor initialization” and “manual motor movement” actions are performed. Also, when a sensor is initialized, a current sensor reading is input and then a “sensor initialization” action is performed.
Furthermore, the environment is set up by inputting reference values before the properties of the polishing pad are measured. In order to set up the environment, a pad data reference value, a hardness reference value and a transmittance reference value of the polishing pad are inputted using the environment setup screen shown in FIG. 12, and then a “setup reference value” action is performed. [0074]
When the system initialization is completed, a project start screen is displayed on the [0075] monitor 202, as shown in FIG. 13 (step S2). The project start screen includes an image display window for displaying images taken by the CCD camera 140, a data display window for displaying the pad data and a graph display window for displaying a graph of the surface profile of the pad.
The image display window includes an image display region, a “CCD” button for selecting the CCD camera, a “previous” button for selecting a previous image, a “delete” button for deleting a current image and a “next” button for selecting a next image. [0076]
The data display window has a display portion for displaying information pertaining to the polishing pad such as its serial number, pad data, reference value of the hardness, measured value of the hardness, error of the hardness, reference value of the transmittance through the window, measured value of the transmittance and error of the transmittance. Furthermore, the data display window has a key pad portion including various buttons such as a “serial number” button, a “reading pad” button, a “measuring hardness” button, a “measuring transmittance” button, a “transmittance reference value” button, a “hardness reference value” button, a “save” button, a “preview” button and a “print” button. [0077]
Each measuring mode can be selected using the project start screen (steps S[0078] 3-S6).
Firstly, when the “measuring transmittance” button is pressed after the [0079] transparent window 12 a of the polishing pad 12 is aligned with the transmittance sensor 120 (step S3), the transmittance sensor 120 measures the transmittance through the transparent window 12 a (step S7). A transmittance signal generated by the transmittance sensor is transferred through the transmittance sensor interface 228 to the microcomputer 218. The transmittance signal is converted into the measured value by the microcomputer 218 and compared with the transmittance reference value to calculate the error of the transmittance. Then, the error and the measured value of the transmittance are displayed on the screen of the data display window.
Next, the [0080] polishing pad 12 is placed at the center of the measuring table 100, and then is fixed to the measuring table 100 using the vacuum produced by vacuum pump 130. After the polishing pad 12 is fixed to the measuring table 100, the XY-carrier 110 is moved in the directions of the X and Y axes to scan the surface of the pad 12 with the camera 140 and the sensors 150,160 in a plane defined by the X and Y axes. At this time, signals produced by the camera 140 and the sensors 150, 160 are processed to discern the surface profile and state of the polishing pad 12 and to measure the hardness of the polishing pad 12 (S8-S10). In particular, when the hardness mode is selected (step S4), the hardness of the polishing pad 12 is measured (step S8). When the pad-reading mode is selected (step S5), the surface profile of the polishing pad 12 is read (step S9). When the CCD mode is selected (step S6), a picture of the polishing pad 12 is taken (step S10).
Referring to FIG. 9, the [0081] microcomputer 218 performs the homing of the X-axis motor 116 a and the Y-axis 111 a motor to search out the center of the polishing pad 12 placed on the measuring table 100. To detect the position of the center of the polishing pad 12, the X-axis motor 116 a is operated to move the X-axis slider 117 along the X-axis carrier 116 to a center point along the axis X (step S12). When the movement to is completed (step S13), the Y-axis motor 111 a is operated to move the X-axis carrier 117 along the Y-axis carrier 111 to the point where the axis Y starts on the polishing pad 12 (step S14). The point where the axis Y starts is checked (step S15) and then, the Y-axis motor 111 a accurately moves the X-axis carrier 116 in the direction of the Y axis (step S16). The starting point of the axis Y is detected during the accurate movement of the X-axis carrier 117 in step S16 (step S17).
Referring to FIG. 10, once the starting point of the axis Y is detected (step S[0082] 17 in FIG. 9), the Y-axis motor 111 a is operated to accurately move the X-axis carrier 117 along the Y-axis carrier 111 to a point where the Y axis ends on the polishing pad 12 (step S18). The end point is checked (step S19), and then the Y-axis motor 111 a accurately moves the X-axis carrier 116 in the direction of the Y axis (step S20). The end point along the Y axis is detected during the accurate movement of the X-axis carrier 116 in step S20 (step S21). When the end point along the Y axis is detected at step S21, a center point along the Y axis is calculated based on the starting point and the ending point along the Y axis. Then the X-axis carrier 116 is moved along the Y-axis carrier 111 to the center point along the Y axis (step S22). When the movement of the X-axis carrier 116 to the center point along the Y axis is completed (step S23), the center of the polishing pad 12 has been found.
When the movement of the [0083] X-axis slider 117 to the center of polishing pad 12 is completed, the “measuring hardness” button is clicked (step S4) so that the hardness-measuring sensor 160 measures the hardness of the polishing pad 12 at its central portion (step S8). A hardness signal generated by the hardness-measuring sensor 160 is transferred through the hardness-measuring sensor interface 220 to the microcomputer 118. The hardness signal is converted into a measured value by means of the microcomputer 218 and compared with the reference value of the hardness to calculate the error of the hardness. Then, the error and the measured value of the hardness are displayed on the screen of the data display window.
When the “reading pad” button is pressed on the project start screen (step S[0084] 5), the laser sensor 150 measures the surface profile of the polishing pad 12 (step S9). The laser sensor 150 measures the surface profile of the polishing pad while accurately moving from the center of the polishing pad 12 to the outer peripheral edge of the polishing pad. Accordingly, a profile signal generated by the laser sensor 150 is transferred to the microcomputer 118. The microcomputer 118 converts the profile signal into digital data and displays the digital data as a graph on the project start screen shown in FIG. 13.
FIG. 15 is an exemplary graph of a surface profile of the polishing pad measured by the [0085] laser sensor 150 according to the present invention. A plurality of peaks 300 regularly arranged at a low portion of the graph in FIG. 15 correspond to the grooves formed in the surface of the polishing pad. According to the present invention, the measuring of the profile of the polishing pad serves as a two-dimensional examination by which the distance between adjacent grooves and the depths of the grooves can be determined. Accordingly, a polishing pad whose grooves have an irregular depth and spacing can be detected, thereby insuring that the only polishing pads that are used are those that will supply the slurry uniformly over the surface of the wafer.
When the “CCD” button is clicked on the project start screen (step S[0086] 6), a surface image of the polishing pad is displayed (step S10). Therefore, an operator can observe an enlarged image of the surface of the polishing pad as scanned by the laser sensor 150, can capture important ones of these images and can save the images in a database.
The measured data of the polishing pad according to the above-mentioned procedure and screen images of the polishing pad are filed in the database according to the serial number of the polishing pad and are thus saved on the hard drive. As shown in FIG. 14, the measured data and screen images of the polishing pad filed in the database can be searched on the basis of measured data or serial number of the polishing pad. [0087]
As described above, the measuring apparatus according to the present invention can measure the profile, the hardness, the transmittance of the transparent window and the surface state of the polishing pad, wherein the properties of each polishing pad can be exactly observed. Accordingly, when the polishing pad is mounted in the CMP apparatus, the polishing process can be set up based on the actual characteristics of the polishing pad. As a result, the polishing process can be carried out under conditions that minimize the number of polishing defects in the wafer. [0088]
Furthermore, the presence of foreign matter in the pores and grooves of the polishing pad is easily discerned from the displayed image of the surface of the polishing pad. Therefore, measures can be taken to prevent micro-scratches from being produced in the wafer. In addition, the measured hardness of the polishing pad can be used to ensure that the polishing pad is suitable for the particular material layer of the wafer to be polished. [0089]
Also, because the transmittance through the transparent window of the polishing pad can be measured, an excessive or insufficient polishing of the wafer can be prevented. [0090]
Furthermore, operating characteristics of the CMP apparatus can be estimated from the wear exhibited by its polishing pad as discerned using the present invention. Therefore, a schedule for replacing the polishing pads can be accurately determined. Moreover, using such information, the CMP apparatus can be set-up to optimize the efficacy of the polishing pads and prolong the useful life thereof. Accordingly, the present invention contributes to reducing the manufacturing cost of the semiconductor devices. [0091]
Finally, although the present invention has been described in connection with the preferred embodiments thereof, the present invention is not so limited. Rather, various changes and modifications can be made to the preferred embodiments by one skilled in the art within the spirit and scope of the present invention as hereinafter claimed. [0092]

Claims

What is claimed is:

1. Apparatus for measuring properties of a polishing pad, comprising:

an upper plate having a flat top surface on which the polishing pad is to be placed;

a camera operative to produce signals representative of an image of a surface portion of the polishing pad;

a sensor operative to generate signals representative of a relative location of a surface portion of the polishing pad;

a bracket fixing said camera and said sensor in place above the top surface of said upper plate, whereby the camera is positioned to produce signals representative of an image of a top surface portion of the polishing pad and the sensor is positioned to generate signals representative of the relative location of a top surface portion of the polishing pad when the polishing pad is disposed on said upper plate;

X-axis and Y-axis linear drive mechanisms to which said bracket is connected, said linear drive mechanisms being operable to move said bracket, and the camera and sensor fixed in place by the bracket, in X- and Y-directions extending orthogonal to each other in a plane above the top surface of said upper plate, whereby the top surface of the polishing pad can be scanned by said camera and said sensor when the polishing pad is disposed on the top surface of said upper plate; and

a control system operatively connected to said camera so as to control the operation of said camera and receive the signals produced by said camera, operatively connected to said sensor so as to control the operation of said sensor and receive signals generated by said sensor, and operatively connected to said X-axis and Y-axis linear drive mechanisms so as to control the movement of said camera and said sensor in said X- and Y-directions, and

said control system including a processor configured to process said signals to produce data by which an image of and the profile of the top surface of a polishing pad disposed on the top surface of said upper plate can be discerned.

2. Apparatus for measuring properties of a polishing pad as claimed in claim 1, wherein said upper plate has a plurality of vacuum holes extending through a central portion of the top surface thereof.

3. Apparatus for measuring properties of a polishing pad as claimed in claim 1, wherein said sensor is a non-contacting laser sensor.

4. Apparatus for measuring properties of a polishing pad as claimed in claim 1, and further comprising a hardness-measuring sensor operative to measure hardness of a polishing pad, said hardness-measuring sensor being supported by said X-axis and Y-axis linear drive mechanisms.

5. Apparatus for measuring properties of a polishing pad as claimed in claim 1, and further comprising a transmittance sensor operative to measure transmittance.

6. Apparatus for measuring properties of a polishing pad as claimed in claim 5, wherein said transmittance sensor includes a light-receiving element that is disposed coplanar with the top surface of said upper plate, and a light-emitting element that is disposed above the light-receiving element as spaced therefrom, whereby a polishing pad is insertable between the light-receiving element and the light-emitting element.

7. Apparatus for measuring properties of a polishing pad as claimed in claim 1, wherein said X-axis and Y-axis linear drive mechanisms comprise a Y-axis carrier extending along a first side of said upper plate, a Y-axis guide rail extending parallel to said Y-axis carrier along a second side of the top surface of said upper plate, a Y-axis slider supported by said Y-axis carrier so as to be movable longitudinally therealong, a Y-axis guide rail slider supported by said Y-axis guide rail so as to be movable longitudinally therealong, an X-axis carrier disposed above the top surface of said upper plate and having opposite ends respectively mounted to said Y-axis slider and said Y-axis guide rail slider; and an X-axis slider supported by said X-axis carrier so as to be movable longitudinally therealong between the opposite ends thereof, said bracket being fixed to said X-axis slider so as to move therewith.

8. Apparatus for measuring properties of a polishing pad as claimed in claim 7, wherein said X-axis and Y-axis linear drive mechanisms include a respective feed screw associated with each of said X-axis carrier and said Y-axis carrier.

9. Apparatus for measuring properties of a polishing pad as claimed in claim 1, wherein said control system includes a display comprising a screen, said processor and said display being operative to produce on said screen numeric displays pertaining to a polishing pad disposed on the top surface of said upper plate, a graph of the profile of the top surface of the polishing pad, and an image of the top surface of the polishing pad

10. A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus, comprising the steps of:

placing the polishing pad on a table top;

fixing the polishing pad to the table top using suction;

scanning a surface the polishing pad, fixed to the table top, in X- and Y-axis directions orthogonal to each other, and using data derived from said scanning to locate the center of the polishing pad;

once the center of the polishing pad is located, measuring the hardness of the polishing pad at the center of the polishing pad, and displaying a value of the hardness on a screen;

moving a sensor, aimed at the polishing pad fixed to the table top, in the direction of the Y-axis, and using signals from the sensor to discern a profile of the top surface of the polishing pad;

displaying the profile of the polishing pad on the screen;

scanning the surface of the polishing pad, fixed to the table top, with a camera to thereby take pictures of the surface of the polishing pad; and

displaying the pictures on the screen as an image of the surface of the polishing pad.

11. A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus as claimed in claim 10, and further comprising the steps of:

positioning a transparent window of the polishing pad adjacent a transmittance sensor for measuring transmittance;

measuring transmittance through the transparent window using the transmittance sensor; and

displaying a value of the transmittance on the screen.

12. A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus as claimed in claim 11, wherein the step of displaying the value of the transmittance on the screen comprises the substeps of:

calculating an error between the measured value and a standard value of the transmittance; and

displaying the measured value, the standard value and the error of the transmittance on the screen.

13. A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus as claimed in claim 10, wherein the step of displaying the value of the hardness of the polishing pad on the screen comprises the steps of:

calculating an error between the measured value and a standard value of the hardness of the polishing pad; and

displaying the measured value, the standard value and the error of the hardness on the screen.

14. A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus, comprising the steps of:

placing a polishing pad, having a transparent window, on a flat surface of a measuring table before the polishing pad is installed in a chemical and mechanical polishing apparatus;

with the polishing pad disposed on the flat surface, scanning the polishing pad with a sensor and using signals derived from the sensor to discern the surface profile of the polishing pad, measuring the hardness of the polishing pad, and measuring a transmittance through the transparent window of the polishing pad;

subsequently installing the polishing pad in the chemical and mechanical polishing apparatus, and polishing a wafer using the polishing pad;

subsequently removing the polishing pad from the chemical and mechanical polishing apparatus and placing the used polishing pad back on the flat surface of the measuring table;

with the used polishing pad disposed back on the flat surface, scanning the used polishing pad with the sensor and using signals derived from the sensor to discern the surface profile of the used polishing pad, measuring the hardness of the used polishing pad, and measuring the transmittance through the transparent window of the used polishing pad; and

filing values of the surface profile, hardness and transmittance of the polishing pad, before and after the polishing pad has been used to polish the wafer, in a database.

15. A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus, as claimed in claim 14, and further comprising using the database to create a schedule for the replacing of polishing pads in the chemical and mechanical polishing apparatus.

16. A method of measuring properties of a polishing pad of a chemical and mechanical polishing apparatus, as claimed in claim 14, and further comprising using the database to establish operating parameters of the chemical and mechanical polishing apparatus.