Metrology module with non-flat mirror for chemical mechanical polishing systems

Abstract

A metrology module for use with a substrate processing system includes a camera for scanning a substrate and a light source configured to direct light toward the substrate at a non-zero incidence angle. The module also includes a reflector having a non-flat mirror configured to reflect light to the camera. The non-flat mirror is configured to receive light reflected from the substrate at a consistent reflected angle.

Description

PATENTAttorney Docket No.: 44025295WO01METROLOGY MODULE WITH NON-FLAT MIRROR FOR CHEMICAL MECHANICAL POLISHING SYSTEMS BACKGROUNDField

[0001] Embodiments of the present disclosure generally relate to electronic device manufacturing, and in particular, to chemical mechanical polishing (CMP) systems and methods used in a semiconductor device manufacturing processes. In particular, embodiments of the present disclosure generally relate to a metrology module for CMP systems.Description of the Related Art

[0002] An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a semiconductor substrate. A variety of fabrication processes require planarization of a layer on the substrate. For example, one fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. For example, a metal layer can be deposited on a patterned insulative layer to fill trenches and holes in the insulative layer. After planarization, the remaining portions of the metal in the trenches and holes of the patterned layer form vias, plugs, and lines to provide conductive paths between integrated circuits (ICs) on the substrate. As another example, a dielectric layer can be deposited over a patterned conductive layer, and then planarized to enable subsequent photolithographic steps.

[0003] Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier head. The exposed surface of the substrate, the surface with the layer deposition, is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to urge it against the polishing pad. A polishing slurry with abrasive particles is typically supplied to the surface of the polishing pad and spreads in between the substrate and the polishing pad. ThePATENTAttorney Docket No.: 44025295WO01polishing pad and the carrier head each rotate at a constant rotational speed and the abrasive slurry removes material from one or more of the layers in a planar fashion.

[0004] Many CMP processes include an endpoint detection (EPD) step. EPD is performed to identify whether the polishing process has reached the desired endpoint; that is, whether the surface uniformity, profile, and / or material removal have met the expected requirements. For example, EPD may involve measurement of the thickness of a material on the substrate. The measured thickness is then compared to the expected thickness.

[0005] Optical measurement systems have been used to measure the thickness of the material. In one example, the optical measurement system includes a camera designed to measure thin film interference which can be used to determine thickness. The camera lens collects light rays reflected from the surface of the substrate to form an image of the substrate. The angle at which the light rays hit the surface is the angle of the incidence. One challenge encountered by these optical measurement systems is the camera collects light rays in a broad range of angle of incidence. The broad range of angle of incidence can cause color distortions in the formed image.

[0006] There is, therefore, a need for an improved metrology module for measuring film thickness in a CMP system.SUMMARY

[0007] In some embodiments, a metrology module for use with a substrate processing system includes a camera for scanning a substrate and a light source configured to direct light toward the substrate at a non-zero incidence angle. The module also includes a reflector having a non-flat mirror configured to reflect light to the camera. The non-flat mirror is configured to receive light reflected from the substrate at a consistent reflected angle.

[0008] In some embodiments, an apparatus for polishing a substrate includes a polishing platen having a polishing pad disposed thereon and a substrate carrier for urging a substrate against the polishing pad. The apparatus also includes a metrology module for measuring the substrate either before or after the substrate is polished. The metrology module has a camera for scanning the substrate and a light sourcePATENTAttorney Docket No.: 44025295WO01configured to direct light toward the substrate. The metrology module also has a nonflat mirror configured to reflect light to the camera. The non-flat mirror is configured to receive light reflected from the substrate at a consistent reflected angle.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of the present disclosure and are therefore not to be considered limiting of its scope, as the present disclosure may admit to other equally effective embodiments.

[0010] Figure 1 is a schematic top view of a chemical mechanical polishing (CMP) system, according to some embodiments.

[0011] Figure 2 is a schematic view of an exemplary metrology module, according to some embodiments.

[0012] Figure 3 is a side view of an exemplary metrology module, according to some embodiments.

[0013] Figure 4 is a top view of the exemplary metrology module of Figure 3.

[0014] Figure 5 is a perspective view of a non-flat mirror attached to a reflector support, according to some embodiments.

[0015] Figure 6 is a schematic view of the non-flat mirror of Figure 5 and some mirror angles.

[0016] Figure 7 is an exemplary image of a substrate formed using a non-flat mirror, according to some embodiments.

[0017] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It isPATENTAttorney Docket No.: 44025295WO01contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0018] Embodiments herein generally relate to chemical mechanical polishing (CMP) systems, and in particular, to metrology modules used with CMP systems. In one embodiment, a metrology module for use with a substrate processing system includes a camera for scanning a substrate and a light source configured to direct light toward the substrate at a non-zero incidence angle. The module also includes a reflector having a non-flat mirror configured to reflect light to the camera. The non-flat mirror is configured to receive light reflected from the substrate at a consistent reflected angle. One benefit of a consistent reflected angle is more reliable thickness measurements can be obtained.

[0019] Figure 1 illustrates a schematic top view of a chemical mechanical polishing (CMP) system 100. The CMP system 100 generally includes a factory interface module 102, an input module 104, a polishing module 106, and a cleaning module 108. These four major components are generally disposed within the CMP system 100.

[0020] The factory interface module 102 includes a support to hold a plurality of cassettes 110, a housing 111 that encloses a chamber, and one or more interface robots 112. In some embodiments, a metrology module 210 is connected to the factory interface module 102. In some embodiments, the metrology module 210 is part of the factory interface module 102. The interface robot 112 generally provides the range of motion required to transfer substrates between the cassettes 110 and one or more of the other modules of the CMP system 100. An exemplary substrate is a silicon wafer with one or more layers deposited thereon.

[0021] Unprocessed substrates are generally transferred from the cassettes 110 to the input module 104 by the interface robot 112. The input module 104 generally facilitates transfer of a substrate between the interface robot 112 and a transfer robot 114. The transfer robot 114 transfers the substrate between the input module 104 and the polishing module 106. In some embodiments, the interface robot 112 transfers thePATENTAttorney Docket No.: 44025295WO01substrate to the metrology module 210 before the input module 104. The metrology module 210 can measure a thickness profile of the substrate before the substrate enters the input module 104, as will be discussed in more detail below,

[0022] The polishing module 106 generally comprises a transfer station 116, one or more polishing stations 118, and one or more non-contact cleaning units 140. The transfer station 116 is disposed within the polishing module 106 and is configured to accept the substrate from the transfer robot 114. The transfer station 116 transfers the substrate to at least one carrier head 124 of a polishing station 118 that retains the substrate during polishing.

[0023] The polishing stations 118 each includes a rotatable disk-shaped platen on which a polishing pad 120 is situated. The platen is operable to rotate about an axis. The polishing pad 120 can be a two-layer polishing pad with an outer polishing layer and a softer backing layer. The polishing stations 118 each further includes a dispensing arm 122, to dispense a polishing liquid, e.g., an abrasive slurry, onto the polishing pad 120. In the abrasive slurry, the abrasive particles can be silicon oxide, but some polishing processes use cerium oxide abrasive particles. Each polishing station 118 can also include a conditioner head 123 to maintain the polishing pad 120 at a consistent surface roughness.

[0024] The polishing stations 118 each includes at least one carrier head 124. The at least one carrier head 124 is operable to hold a substrate against the polishing pad 120 during a polishing operation. Following the polishing operation performed on a substrate, the at least one carrier head 124 transfers the substrate back to the transfer station 116.

[0025] The transfer robot 114 then removes the substrate from the polishing module 106 through an opening connecting the polishing module 106 with the remainder of the CMP system 100. The transfer robot 114 removes the substrate in a horizontal orientation from the polishing module 106 and transfers the substrate to the cleaning module 108.

[0026] The cleaning module 108 generally includes one or more cleaning devices that can operate independently or in concert. For example, the cleaning module 108PATENTAttorney Docket No.: 44025295WO01can include, from top to bottom in Figure 1, a resist removal module 128, an input module 129, one or more brush or buffing pad module 131 , 132, a megasonic cleaner 133, and a drying module 134. Other possible cleaning devices include chemical spin cleaners and jet spray cleaners (not shown). A transport system, e.g., an overhead conveyor 130 that supports robot arms, can walk or run the substrate from cleaning device to cleaning device. The one or more brush or buffing pad module 131, 132 directly contacts the substrate. The modules 131, 132 may be a brush scrubbing module using a rotating brush to scrub the substrate surface. The substrate can be transferred to the megasonic cleaner 133 in which high frequency vibrations produce controlled cavitation in a cleaning liquid to clean the substrate. Alternatively, the megasonic cleaner 133 can be positioned before the brush or buffing pad module 131 , 132. A final rinse can be performed in a rinsing module before being transferred to the drying module 134. In some embodiments, the cleaned substrate can be transferred to the metrology module 210 to be measured again. Thereafter, the interface robot 112 returns the substrate to one of the cassettes 110.

[0027] The CMP system 100 includes a controller 160, which generally includes one or more processors, memory, and support circuits. The one or more processors may include a central processing unit (CPU) and may be one of any form of a general purpose processor that can be used in an industrial setting. The memory, or non-transitory computer-readable medium, is accessible by the one or more processors and may be one or more of memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits are coupled to the one or more processors and may comprise cache, clock circuits, input / output subsystems, power supplies, and the like. The various methods disclosed herein may generally be implemented under the control of the one or more processors by the one or more processors executing computer instruction code stored in the memory as, for example, a software routine. When the computer instruction code is executed by the one or more processors, the one or more processors controls the CMP system 100 to perform processes in accordance with the various methods disclosed herein.PATENTAttorney Docket No.: 44025295WO01

[0028] Figure 2 illustrates an exemplary metrology module 210, according to some embodiments. The metrology module 210 can be used to measure the thickness profile of a substrate 201 either before the substrate 201 enters the input module 104 or after the substrate 201 leaves the cleaning module 108. The metrology module 210 is configured to reflect light from the substrate 201 to the camera 241 at a constant angle of incidence.

[0029] In this example, the metrology module 210 includes a light source 220, a reflector 230, and a light receiver 240. Circuitry is provided to send and receive signals between the controller 160 and the light source 220 and the light receiver 240.

[0030] The substrate 201 is positioned below and laterally between the light source 220 and the reflector 230. In some embodiments, the light source 220 is oriented to direct light 222 onto the exposed surface of the substrate 201 at a non-zero angle of incidence (AOI). The angle of incidence can be, for example, from 0° to 90°, from 5° to 65°, or from 10° to 50°. In some examples, the AOI is from 10° to 40°, such as 15°, 20°, 25°, 30°, or 35°.

[0031] In some embodiments, the light source 220 is configured to emit white light. In one example, the white light emitted includes light having wavelengths of 200-800 nanometers. Any suitable light source capable of emitting white light is contemplated. Exemplary light sources include an array of white-light light emitting diodes (LEDs), a xenon lamp, a xenon mercury lamp, a mercury lamp, tungsten lamp, or monochromatic light.

[0032] The light source can illuminate a substantially linear elongated region that spans the width of the substrate 201 ( / '.e. , z direction). In some examples, the light source 220 can include optics, such as a beam expander, to spread the light from the light source 220 onto the elongated region. In some embodiments, the light source 220 can include a linear array of light sources. The light source 220 itself, and the region illuminated on the substrate 201, can be elongated and have a longitudinal axis parallel to the surface of the substrate 201.

[0033] In some embodiments, the light receiver 240 is a camera 241 that is sensitive to light from the reflector 230. The camera 241 includes an array of detectorPATENTAttorney Docket No.: 44025295WO01elements. For example, the camera 241 can include a charge-couple device (CCD) array. In some examples, the array is a single row of detector elements. In one example, the camera 241 is a linescan camera. The row of detector elements can extend parallel to the longitudinal axis of the elongated region illuminated by the light source 220.

[0034] The reflector 230 is configured to project a field of view of the substrate 201 onto the array of detector elements of the light receiver 240, e.g., the camera 241. The field of view can be long enough to view the entire width of the substrate 201 , e.g. , 150 to 300 mm long. The camera 241 can be configured such that individual pixels correspond to a region having a length equal to or less than about 0.5 mm. For example, assuming that the field of view is about 200 mm long, and the light receiver 240 includes 1024 elements, then an image generated by the linescan camera can have pixels with a length of about 0.5 mm. To determine the length resolution of the image, the length of the field of view (FOV) can be divided by the number of pixels onto which the FOV is imaged to arrive at a length resolution.

[0035] In some embodiments, as shown in Figures 3 and 4, the metrology module 210 includes a support structure 250 for supporting the light source 220, the reflector 230, and the light receiver 240. Figure 3 is a side view of the support structure 250 with one of two support arms 260 removed. Figure 4 is a top view of the support structure 250. The support structure 250 positions the light source 220, the reflector 230, and the light receiver 240 above the substrate 201. In this embodiment, the support structure 250 includes a base 252 disposed on a stand 255. The light receiver 240 is disposed on the stand 255. One support arm 260 is disposed on each side of the stand 255 and extends toward the substrate 201. The support arms 260 suspend the light source 220 and the reflector 230 above the substrate 201.

[0036] In some embodiments, the light receiver 240 is a line-scan camera. The light source 220 and the reflector 230 are movable relative to the substrate 201 such that the imaged area can scan across the width ( / '.e. , z direction) of the substrate 201. In particular, the relative motion can be in a direction parallel to the surface of the substrate 201.PATENTAttorney Docket No.: 44025295WO01

[0037] In this example, a reflector support 236 is provided to retain the reflector 230 in position relative to the substrate 201 and the light receiver 240. Each end of the reflector support 236 is attached to a support arm 260. In this embodiment, the reflector support 236 is configured to position the reflector 230 at a mirror angle “0” (theta) relative to a vertical axis (i.e., y axis) that is perpendicular to the surface of the substrate 201. In some embodiments, the mirror angle 0 is selected so that the reflector 230 receives reflected light at the same angle as the light directed toward the substrate 201 , specifically, the AOI. In this example, the light source 220 is arranged to direct light to the substrate 201 at an AOI of 20°. The reflector support 236 positions the reflector 230 at a mirror angle 0 of 55° so that the reflector 230 receives reflected light from the substrate 201 at a reflected AOI of 20°. The mirror angle 0 may be any suitable angle that enables the reflector 230 to receive reflected light at the same AOI as the light directed toward the substrate 201. In some examples, the mirror angle 0 is in a range from 0° to 90°, from 15° to 80°, from 25° to 75°, or from 30° to 70°. Exemplary mirror angles include 35°, 40°, 45°, 50°, 55°, 60°, or 65°.

[0038] In some embodiments, the reflector 230 is a non-flat mirror 330, as shown in Figure 5. The mirror 330 is shown with its backside attached to the reflector support 236. The front side of the mirror 330 is the reflector side 331 , which reflects light from the substrate 201 to the light receiver 240, such as a linescan camera 241. The mirror 330 has a width (i.e. , along the z axis) that is bi-sected by centerline 311. The mirror 330 has a length having an upper edge 321 and a lower edge 322.

[0039] The non-flat mirror 330 has a mirror angle 0 that is not constant across the width of the mirror 330. In some embodiments, the mirror angle 0 decreases from the centerline 311 out toward the two ends 324 of the mirror 330. In some embodiments, the change in mirror angle can be non-linear or linear. Figure 5 shows a non-flat mirror 330 having a non-linear change in mirror angle along the width of the mirror 360. As shown, the thickness of the upper edge 321 of the mirror 330 decreases from the centerline 311 out toward the ends 324. The change in thickness of the upper edge 321 is representative of a change in the mirror angle. In particular, as the mirror angle decreases, the thickness of the upper edge 321 also decreases. In Figure 5, the mirror angle at the centerline 311 is 55° and decreases to 45° at the end 324 of the mirrorPATENTAttorney Docket No.: 44025295WO01330. To accommodate the reduced mirror angle, the thickness of the upper edge 321 is reduced. In some examples, the change in mirror angle causes the reflector side 331 of the mirror 330 to have a “twisted” configuration. For example, the end 324 of the mirror 330 can be slightly twisted relative to the centerline 311 so that the end 324 has a mirror angle of 45°. In some embodiments, the thickness of the upper edge 321 remains constant while the mirror angle of the mirror 330 changes.

[0040] This change in mirror angle is further illustrated in Figure 6. Figure 6 is a partial schematic view of one half of the mirror 330. In this embodiment, the other half of the mirror 330 has the same configuration. Figure 6 shows the schematic view of the reflector side 331 and the mirror angles of the mirror 330, according to one embodiment. As shown, the mirror angle at the centerline 311 is 55°. The mirror angle decreases from the centerline toward the end of the mirror 330. The mirror angle at the end 324 of the mirror 330 is 45°. In this example, an end portion 337 of the mirror 330 at the end 324 has a constant mirror angle of 45°. As shown, the mirror angle decreases as the radial position increases toward the end 324. The mirror angle decrease is non-linear until it reaches a mirror angle of 45° at a radial position greater than 200 mm, which is also the beginning of the end portion 337. It must be noted the end portion 337 is optional. In this example, the mirror 330 is configured for a substrate 201 having a width of less than 400 mm, such as 300 mm. Thus, the end portion 337 of mirror 330 is not used to reflect light to the camera 241. In this example, the mirror angle at a radial position of 150 mm ( / .e., the edge of a 300 mm substrate such as substrate 201 ) is 51.7°. To achieve a constant reflected AOI, it must be noted that the mirror angles may be different based on factors such as the desired AOI, substrate size, the distance between the substrate 201 and the mirror 330, and other factors affecting the reflected AOI.

[0041] Referring back to Figure 6, the non-flat mirror 330 is configured to receive light from the substrate 201 at the same reflected angle across the width of the substrate 201. As shown in Figure 6, the light 301 reflected from the center position of the substrate 201 is received by the mirror 330 at a reflected angle of 20°. The light 301 is received at the centerline 311 of the mirror 330, which has a mirror angle of 55°, and reflected toward the camera 341. Similarly, the light 309 reflected from the edgePATENTAttorney Docket No.: 44025295WO01the substrate 201 is received by the mirror 330 at a reflected AOI of 20°. The light 309 is received at the 150 mm radial position of the mirror 330, which has an angle mirror of 51.7°, and reflected toward the camera 341. In this manner, the non-flat mirror 330 produces a consistent reflected AOI of 20° along the radial position of the mirror 330. As shown, the zero radial position corresponds to the centerline 311 of the mirror 330 and has a reflected AOI of 20°. The reflected AOI remains constant at 20° as the radial position increases toward the end 324. One benefit of the having a constant reflected AOI is that the colors of the light reflected from the substrate 201 are consistent. The consistent reflected colors lead to a more reliable thickness measurement of one or more layers of the substrate 201.

[0042] In some embodiments, when the camera 241 is a linescan camera, the camera 241 may image the substrate in a non-linear configuration. In some embodiments, the reflected light received by the camera 241 is sent as color data to the controller 160. The controller 160 is configured to receive the color data from the camera 241 and generate a 2-dimensional image of the substrate 201. Referring back to Figure 6, the camera 241 may image the center position of the substrate 201 at line 441. The camera 241 images the edge the substrate 201 at line 449, which is offset from line 441. For radial positions between the center position and the edge, the camera 241 will obtain the image along a line between lines 441 and line 449. The resulting line scanned by the camera 241 is a curved line. Figure 7 is an exemplary image 610 of a substrate 201 formed using a non-flat mirror 330. Although the formed image 610 of the round substrate 201 is non-uniform (e.g., not round), it is believed the benefits of obtaining a constant AOI, such as reliable thickness measurements, outweigh the resulting non-uniform image 610. In some embodiments, image processing can be performed on the non-uniform image 610 to produce a round image of a substrate 201.

[0043] In some embodiments, the non-flat mirror 330 may be manufactured by depositing aluminum on the surface of a mirror substrate. The mirror substrate may be made from aluminum, plastic, glass, or any suitable mirror substrate. The mirror substrate may be manufactured using a computer numerical control (CNC) process such as a 3D interpolation CNC process or a ball mill CNC process. In anotherPATENTAttorney Docket No.: 44025295WO01example, the substrate may be manufactured using 3D printing. The 3D printed substrate may be polished after printing. Aluminum may be deposited on the surface of the substrate to form the reflective side.

[0044] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

PATENTAttorney Docket No.: 44025295WO01What is claimed is:

1. A metrology module for use with a substrate processing system, comprising:a camera for scanning a substrate;a light source configured to direct light toward the substrate at a non-zero incidence angle; anda reflector having a non-flat mirror configured to reflect light from the substrate to the camera, the non-flat mirror is configured to receive light reflected from the substrate at a consistent reflected angle.

2. The metrology module of claim 1 , wherein the non-flat mirror includes a plurality of mirror angles along a length of the non-flat mirror to reflect to the camera.

3. The metrology module of claim 2, wherein the plurality of mirror angles decrease from a centerline of the mirror to an end of the mirror.

4. The metrology module of claim 2, wherein a change of the plurality of mirror angles along the length of the non-flat mirror is non-linear.

5. The metrology module of claim 2, wherein the plurality of mirror angles is from 25° to 75°.

6. The metrology module of claim 1 , wherein the reflected angle is equal to the incidence angle.

7. The metrology module of claim 6, wherein the incidence angle is an angle from 10° to 50°.

8. The metrology module of claim 7, wherein the plurality of mirror angles is from 25° to 75°.

9. The metrology module of claim 1 , wherein the camera is a linescan camera.PATENTAttorney Docket No.: 44025295WO0110. The metrology module of claim 1 , wherein the light source emits white light.

11. An apparatus for polishing a substrate, comprising:a polishing platen having a polishing pad disposed thereon;a substrate carrier for urging a substrate against the polishing pad; and a metrology module for measuring the substrate either before or after the substrate is polished, the metrology module having:a camera for scanning the substrate;a light source configured to direct light toward the substrate; and a non-flat mirror configured to reflect light from the substrate to the camera, the non-flat mirror is configured to receive light reflected from the substrate at a consistent reflected angle.

12. The apparatus of claim 11 , wherein the non-flat mirror includes a plurality of mirror angles along a length of the non-flat mirror to reflect to the camera.

13. The apparatus of claim 12, wherein the plurality of mirror angles decrease from a centerline of the mirror to an end of the mirror.

14. The apparatus of claim 13, wherein the decrease of the plurality of mirror angles along the length of the non-flat mirror is non-linear.

15. The apparatus of claim 12, wherein the plurality of mirror angles is from 20° to 75°.

16. The apparatus of claim 12, wherein the reflected angle is equal to an incidence angle of the light from the light source to the substrate.

17. The apparatus of claim 12, further comprising a robot for transferring the substrate to or from the metrology module.

18. The apparatus of claim 12, wherein the metrology module is configured to measure a thickness of one or more layers on the substrate.PATENTAttorney Docket No.: 44025295WO0119. The apparatus of claim 12, further comprising a controller configured to receive color data from the camera and generate a 2-dimensional image of the substrate.

20. The apparatus of claim 12, wherein the reflected angle is an angle from 10° to 50°.

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