Patent Application
20250058429
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.
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 h1 above the carrier layer and the at least one circumferential compressible layer has a maximum height h2 above the carrier layer. When uncompressed, h2>h1.
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.
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
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
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
As in
As illustrated in
To investigate the effect of exemplary embodiments including a compressible circumferential slurry distribution ring, the following examples were prepared:
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.
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 A1, 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.
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.
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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/062478 | 12/19/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63295575 | Dec 2021 | US |
