WO2023126760A1

WO2023126760A1 - Pad conditioning disk with compressible circumferential layer

Info

Publication number: WO2023126760A1
Application number: PCT/IB2022/062478
Authority: WO
Inventors: Matthew C. FRITZ
Original assignee: 3M Innovative Properties Company
Priority date: 2021-12-31
Filing date: 2022-12-19
Publication date: 2023-07-06
Also published as: TW202339903A

Abstract

Pad conditioning disks are described. In particular, pad conditioning disks includes discrete abrasive elements and a circumferential compressible layer are described. When uncompressed, the maximum height of the circumferential compressible layer is greater than the maximum height of the discrete abrasive elements, which may provide more even wafer removal rates for in-situ polishing processes.

Description

PAD CONDITIONING DISK WITH COMPRESSIBLE CIRCUMFERENTIAL LAYER

Background

A certain class of pads are used for the chemical-mechanical polishing of semiconductor wafers to a high degree of flatness and smoothness. These pads (CMP pads) are rotated and contacted with a semiconductor surface in conjunction with a slurry to abrade material from the wafer and create a polished surface. Exposure to both the abrasive slurry and the wear of the abrasive process itself can cause the topography of the CMP pad to shift with use. In order to provide consistent, and desirable polishing performance, those CMP pads often undergo conditioning (either in-situ or ex-situ) with a conditioning disk. Use of a conditioning disk (which is also rotated and contacted to a surface, except in this case to the surface of the CMP pad) may be used to restore the working surface of the CMP pad to near its original surface geometry.

Summary

In one aspect, the present disclosure relates to a pad conditioning disk. The pad conditioning disk includes a substantially circular carrier layer, at least one discrete abrasive element disposed nearer to an edge than a center of the carrier layer, and at least one circumferential compressible layer at least partially surrounding the at least one discrete abrasive element. The at least one discrete abrasive element has a maximum height hi above the carrier layer and the at least one circumferential compressible layer has a maximum height I12 above the carrier layer. When uncompressed, I12 > hi.

Brief Description of the Drawings

FIG. 1 is a schematic top plan view of an exemplary pad conditioning disk including a slurry distribution ring.

FIG. 2 is a schematic top plan view of an exemplary pad conditioning disk including a slurry distribution ring and channels.

FIG. 3 is a schematic elevation cross-section of a portion of an exemplary pad conditioning disk including a slurry distribution ring and channels.

Detailed Description

For pad conditioning processes, especially in-situ pad conditioning processes, the semiconductor wafer, pad conditioning disk, and CMP pad have surfaces in at least indirect contact with each other. For example, slurry may be dispensed on the pad in order to polish the surface of the semiconductor wafer, while the pad conditioning disk is in contact with a different portion of the pad. As the pad rotates relative to the wafer, and the conditioning disk sweeps and rotates relative to the pad, the slurry passes on the pad to both the wafer and the pad conditioner. Therefore, characteristics of the pad conditioning disk may influence polishing outcomes of the semiconductor wafer. The dynamic forces of the complicated rotation system may cause slurry to drift or accumulate toward the center of the pad, concentrating the abrasive slurry away from the edge and leading to uneven wafer removal rates.

Surprisingly, by using a circumferential, compressible layer as a slurry distribution ring, the motion of the pad conditioning disk may be leveraged to more desirably and evenly distribute slurry on the surface of a CMP pad. When uncompressed, the height of the slurry distribution ring is higher than the maximum height of discrete abrasive elements positioned on the carrier. And, when compressed until the maximum height of the discrete abrasive elements are in desired contact pressure (downforce) with the pad, the restoring force from the compressible slurry distribution ring may keep the ring in excellent contact with the CMP pad even through variations with the pad surface topography, while itself providing minimal wear on the CMP pad.

FIG. 1 is a schematic top plan view of an exemplary pad conditioning disk including a slurry distribution ring. Pad conditioning disk 100 includes carrier layer 110, discrete abrasive elements 120, and slurry distribution ring 130. Slurry distribution ring includes openings 132 for the discrete abrasive elements.

Pad conditioning disk 100 may be overall any suitable shape and size, and may be designed to be compatible with suitable polishing machines or other equipment. The pad conditioning disk may include suitable mechanical or adhesive means for attachment to an arm or other mounting point. Carrier layer may be any suitable material and thickness. In some embodiments, carrier layer 100 may be formed from materials including metals or metal alloys, polymeric materials or blends, or other suitable substrates. In some embodiments, the material of the carrier layer may be selected to be chemically resistant or to resist tarnishing or other degradation under typical use conditions. For example, in some embodiments, the carrier layer may be or include stainless steel. In some embodiments the carrier may be substantially rigid and inflexible under normal operating conditions. In some embodiments, the carrier layer may be flexible or conformable under normal operating conditions. Like the dimensions of the overall pad conditioning disk, the carrier layer may have its shape and size dictated by compatibility with particular machines and applications. In some embodiments, the carrier layer may be substantially circular in order to more easily facilitate low-vibration rapid rotation. The carrier layer may include one or more mounting regions particularly adapted for disposing one or more discrete abrasive elements. These regions may be include raised or lowered regions of the carrier (machined, etched, or otherwise formed) or roughened areas to improve adhesion or attachment.

Discrete abrasive elements 120 are attached to or disposed on the carrier layer. In some embodiments, the at least one discrete abrasive element is attached by the use of a suitable adhesive. The adhesive may be selected for the appropriate compatibility of the adhesive with the carrier layer and the discrete abrasive element and other characteristics, such as the ability to provide a permanent or removable/repositionable adhesion, chemical resistance, adhesion under a range of normal use temperatures, and the like. While adhesives enable a significant class of mounting mechanisms for the discrete abrasive elements, the method of attachment is not limited. Other options, such as welding (including ultrasonic welding), or mechanical attachment (such as hook-and-loop) are contemplated for attachment of the discrete abrasive elements.

The discrete abrasive elements include a base including a working surface with a plurality of microfeatures. Being discrete, these abrasive elements do not form a continuous surface on the carrier of the pad conditioning disk. The discrete abrasive elements are disposed nearer to an edge than a center of the carrier layer. In some embodiments, the discrete abrasive elements are spaced equally around a circumference of the pad conditioning disk. For example, in some embodiments, including the one shown in FIG. 1, there are five discrete abrasive elements spaced approximately 72 degrees apart at substantially a same radius from the center of the pad conditioning disk. However, the number of discrete abrasive elements is not limited, and can be adjusted based on the desired application and use. In some embodiments, there may be as few as one or as many as sixteen discrete abrasive elements. In some embodiments, these discrete abrasive elements may appear as a disc or a puck disposed on the carrier. In some embodiments, each of the discrete abrasive elements includes a working surface with a plurality of microfeatures. In some embodiments, the microfeatures are precisely shaped features. These microfeatures may be formed by a variety of suitable processes, including micromachining, waterjet cutting, injection molding, extrusion, microreplication, or ceramic die pressing. In some embodiments, the discrete abrasive elements include a superabrasive grit in a metal matrix, ceramic bodies including ceramic material in an amount of at least 85% by weight, and ceramic bodies including a diamond coating. Example of superabrasive grit include cubic boron nitride (CBN) and chemical vapor disposition (CVD) diamond. Examples of other coatings and more details of the general properties and formation of precisely shaped microfeatures are described in U.S. Patent No. 10,710,211 (Lehuu et al.), which is hereby incorporated by reference.

Slurry distribution ring 130 is also attached to the carrier layer by any suitable means and is positioned circumferentially on the pad conditioning disk. Slurry distribution ring 130 at least partially surrounds the discrete abrasive elements (including completely surrounding the discrete abrasive elements, as illustrated in FIG. 1). In some embodiments, slurry distribution ring 130 is compressible. In some embodiments, slurry distribution ring 130 may include more than one layer: a top layer and a base layer, where at least the base layer is compressible. In these multi-layer embodiments, different layers may provide different functionality to the overall mechanical performance of the slurry distribution ring. For example, the top layer may include a chemically resistant or low-friction material in order to operate in contact pressure with the CMP pad or to prolong disk life under conditions present at the interface between the conditioning disk and the CMP pad. In some embodiments, this top layer may include one or more of nylon, polyetheretherketone (PEEK), polycarbonate, polystyrene, or polyphenylene sulfide. In some embodiments, the top layer may include one or more surface modifications or coatings. In some embodiments, the top layer may itself not be compressible, but the base layer is and therefore the entire slurry distribution ring construction is compressible. In these multi-layer embodiments, the base layer may be a compressible material, such as a foam (open- or closed-celled), elastomer, rubber, or the like. In some embodiments, the slurry distribution ring may include a mechanical spring mechanism to provide the desired compression and restoring force.

The slurry distribution ring is provided circumferentially near the edge of the pad conditioning disk (carrier). In some embodiments, at least 90 degrees of arc at a particular radius includes the slurry distribution ring. In some embodiments, at least 180 degrees of arc at a particular radius includes the slurry distribution ring. In some embodiments, at least 270 degrees of arc at a particular radius includes the slurry distribution ring. In some embodiments, at least 300 degrees of arc at a particular radius includes the slurry distribution ring. In some embodiments, 360 degrees of arc at a particular radius includes the slurry distribution ring. In some embodiments, the slurry distribution ring may be formed from several discrete pieces collectively covering at least 90, 180, 270, or 300 degrees of arc.

Slurry distribution ring 130 includes openings 132 to accommodate the discrete abrasive elements. The spacing from the slurry distribution ring to the discrete abrasive element may be design dependent: in some embodiments, the space may be minimized in order to prevent the accumulation of slurry within the gap. In some embodiments, the slurry distribution ring immediately adjacent to the discrete abrasive element may be sloped, curved, stepped, or beveled in order to provide a smoother transition between the slurry distribution ring and the discrete abrasive elements.

As illustrated more specifically in FIG. 3, both the top of the discrete abrasive elements and the slurry distribution ring have a maximum height with reference to the surface of the carrier layer, and, when uncompressed, the height of the slurry distribution ring is greater than the height of the top of the discrete abrasive elements. In some embodiments, this difference in height may be several micrometers. In some embodiments, this difference in height may be several millimeters. Any suitable difference is height may be designed, depending on the particular application. In some embodiments, the difference in height is selected such that when the pad conditioning disk is exposed to typical process downforce (e.g., from about 1 to about 10 pounds), the slurry distribution ring compresses such that the heights of the slurry distribution ring and the tops of the discrete abrasive elements are substantially equal.

FIG. 2 is a schematic top plan view of an exemplary pad conditioning disk including a slurry distribution ring and channels. Pad conditioning disk 200 includes carrier layer 210, discrete abrasive elements 220, and slurry distribution ring 230. Slurry distribution ring includes openings 232 for the discrete abrasive elements and channels 234.

As in FIG. 1, the carrier layer, discrete abrasive elements, and slurry distribution are substantially the same and may be formed from similar materials. However, FIG. 2 illustrates an exemplary modification wherein slurry distribution ring 230 includes channels 234 in addition to openings 232.

As illustrated in FIG. 2, channels 234 may include straight channels or curved channels. Channels may be a portion wherein the slurry distribution ring is not present (either not being placed there or having been, e.g., removed, ablated, or etched) or where the slurry distribution ring has a secondary height smaller the height of the rest of the slurry distribution ring (either having been formed that way or having material removed to create such channels). In some embodiments, this channel height is also less than the maximum height of the top of the discrete abrasive elements. The presence of channels 234 may be, depending on the application and desired performance characteristics, modified and tuned to obtain a desired balance between slurry retention and distribution: in some embodiments controlling the rate at which slurry is released from the pad conditioning disk. The number, shape, and spacing of channels 234 may vary, including even within the same pad conditioning disk.

FIG. 3 is a schematic elevation cross-section of a portion of an exemplary pad conditioning disk including a slurry distribution ring and channels. Pad conditioning disk 300 includes carrier layer 310, discrete abrasive elements 320, and slurry distribution ring 330. Slurry distribution ring includes openings 332 for the discrete abrasive elements and channels 334. FIG. 3 includes elements as described above for FIG. 1 and FIG. 2, except that exemplary relative heights of the discrete abrasive elements, slurry distribution ring, and channels are shown as hi, h2, and he, respectively. As can been seen from the illustration, pad conditioning disk 300 — not subject to downforces or any compression — shows, h2 > hi > he.

Examples

To investigate the effect of exemplary embodiments including a compressible circumferential slurry distribution ring, the following examples were prepared:

Comparative Example 1

The abrasive elements were prepared as described in U.S. Pat. No. 9,965,664 (Lehuu et al.) — hereby incorporated by reference in its entirety — for Example 10, differing only in abrasive feature geometries as follows: number of primary features per element: 0.60 (3 per 5); primary feature height: 120 micrometers, offset height: 75 micrometers, truncation depth of primary microfeatures: 10 micrometers; aspect ratio: 0.50. The offset height between the primary and secondary abrasive features is defined as the height difference between the primary feature and secondary feature. The aspect ratio is defined as the feature height divided by its base width. The truncation depth of the primary feature is defined by the depth from which the theoretical peak would have been formed if the sides of the pyramid would have been allowed to converge to a point. Each abrasive element had precisely shaped features having at least one primary feature height, which was higher and offset to either a secondary level of features or a flat base region between the features. Five abrasive elements were prepared for each Example and assembled into an abrasive article. The assembly process was developed such that the tallest, precisely shaped features on each element, all having the same design feature height, would become planar. A planar sapphire surface was used as an alignment plate. The elements were placed onto the alignment plate such that the major surfaces having precisely shaped features were in direct contact with the alignment plate (facing down) with their second flat, major surfaces facing upwards, rotating as necessary to align the orientation as desired. The abrasive elements were arranged in a circular pattern, such that their center points were positioned along the circumference of a circle with a radius of about 1.75 inch (44.5 mm) and spaced apart equally at about 72° around the circumference. A fastening element was then applied to the exposed surface of the abrasive elements in the center region. The fastening element was an epoxy adhesive available under the trade designation 3M SCOTCH-WELD EPOXY ADHESIVE DP420 from 3M Company, St. Paul, Minnesota. A circular, stainless steel carrier, having a diameter of 4.25 inch (108 mm) and a thickness of 0.22 inch (5.64 mm) was then placed face down on top of the fastening element (the back side of the carrier is machined, such that, it may be attached to the carrier arm of a REFLEXION polisher). A 10 lb (4.54 kg) load was applied uniformly across the carrier's exposed surface and the adhesive was allowed to cure for about 4 hours at room temperature.

Comparative Example 2

To a pad conditioning disk made as in Comparative Example 1 was added a 5 -lobe shaped spacer made of polymethyl methacrylate (PMMA), as described in U.S. Patent Publication No. 2019-0337119 Al, which is hereby incorporated by reference. The spacer was bonded to the carrier using 3M VHB tape. The thickness of the spacer was 3 mm and the chord length of each arc was 47.2 mm.

Example 1

To a pad conditioning disk made as in Comparative Example 1 was added a polyetheretherketone (PEEK) ring cut to completely surround each discrete abrasive element. The ring had an inner radius of approximately 3 inches and an outer radius of approximately 4 inches. The ring was placed on a similarly cut (thought slightly undersized) ring of 3M BUMPON SJ5816 cushioning material cut from rollstock and adhered to the stainless steel carrier. The PEEK ring was placed and adhered on the top surface of the cushioning material. As configured, the PEEK ring had a maximum height with reference to the stainless steel carrier approximately 50 micrometers above the maximum height of the tips of the discrete abrasive element.

Testing

Next, Example 1 and the Comparative Examples were tested on an Applied Materials 300 mm REFLEXION polishing tool. The machine was used under the following conditions. The conditioning cycle was run using a copper removal slurry (PL 1076 from Fujimi Corporation, Kiyosu, Aichi, Japan) at 5 lbs ( 1.13 kg) of downforce with the conditioner speed of 87 rpm and a pad speed of 93 rpm. The conditioner arm sweep recipe had a start position of 2.5 inch (2.5 cm) and an end position of 13.5 inch (32.4 cm). The sweep was divided into 13 zones which had the following relative dwell times respectively: 1.00, 1.00, 1.00, 1.00, 1.00, 1.00, 1.00, 1.00, 1.00, 1.00, 1.20, 1.70 and 2.50. The cycle time was 19 sweeps per minute. A pad for a copper removal process was used. The polish downforce for a Cu- blanket wafer was 1.2 psi with a head speed of 87 rpm and a platen speed of 93 rpm. Slurry flow rate was 250 ml/min and the head sweep was 10 sweeps per minute through 10 zones. For break-in, each conditioner was run twice in randomized order for 15 minutes with deionized water and 5 thermal oxide blanket wafers and 1 copper blanket wafer. Measurements with a FLIR A655SC infrared camera were made after completion of the final sweep during the 1 minute process period. The difference between the local temperature minimum at the radius where slurry is being dispensed and the maximum temperature in the direction towards the center of the pad from where the minimum temperature of the slurry was observed and reported in Table 1. The larger the drop, the stronger the indication that slurry is accumulating and remaining unmixed with the warmer slurry present in other parts of the pad. This may lead to uneven removal rates at different locations on the wafer. Minimal temperature drops were indicative of good mixing and more even removal rates, as confirmed by post-polishing examination of the copper thickness on the wafer surface.

Claims

What is claimed is:

1. A pad conditioning disk, comprising: a substantially circular carrier layer; at least one discrete abrasive element disposed nearer to an edge than a center of the carrier layer; at least one circumferential compressible layer at least partially surrounding the at least one discrete abrasive element; wherein the at least one discrete abrasive element has a maximum height hi above the carrier layer; wherein the at least one circumferential compressible layer has a maximum height I12 above the carrier layer; and wherein, when uncompressed, I12 > hi.

2. The pad conditioning disk of claim 1, wherein the at least one circumferential compressible layer covers at least 300 degrees of arc of the substantially circular carrier layer at at least one radius r.

3. The pad conditioning disk of claim 1, wherein the at least one circumferential compressible layer covers 360 degrees of the substantially circular carrier layer at at least one radius r.

4. The pad conditioning disk of claim 1, wherein the at least one circumferential compressible layer defines at least one channel from the center of the carrier layer to the edge of the carrier layer wherein the height is less than I12.

5. The pad conditioning disk of claim 4, wherein the at least one circumferential compressible layer defines at least one channel from the center of the carrier layer to the edge of the carrier layer wherein the height is less than hi.

6. The pad conditioning disk of claim 4, wherein the at least one channel is straight.

7. The pad conditioning disk of claim 4, wherein the at least one channel is curved.

8. The pad conditioning disk of claim 1, wherein the at least one circumferential compressible layer includes a foam layer.

9. The pad conditioning disk of claim 8, wherein the at least one circumferential compressible layer includes a top layer. The pad conditioning disk of claim 9, wherein the top layer includes one or more of nylon, poly etheretherketone, polycarbonate, polystyrene, or polyphenylene sulfide. The pad conditioning disk of claim 1, wherein the at least one circumferential compressible layer includes a spring mechanism.

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