CHEMICAL MECHANICAL PLANARIZATION APPARATUS AND METHOD

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 63/693,264, filed Sep. 11, 2024, the entirety of which is incorporated herein by reference.

BACKGROUND

As the complexity of integrated semiconductor chips grows, it has become necessary to build multiple layers of conductors and insulation to permit the interconnect of devices on and in the silicon chip. This multiplicity results in an uneven surface as the layers are built. In order to enable further processing, it becomes necessary to planarize the surface of the in-process wafer. This planarization is done using Chemical Mechanical Planarization (hereinafter “CMP”). The method involves a combination of both mechanical and chemical processes to remove unwanted material and render the surface of the process wafer flat and ready to continue processing of additional layers of material.

The CMP process is done using machines that use a relatively large rotating table upon which a polishing pad of relatively porous felt or rubber like material is placed, usually glued in place. The substrates to be polished are placed polished side down on the pad using holders of various types. The table is rotated which can rotate the wafer holder or the wafer holder can be independently caused to rotate. The wafer to be polished is small in comparison to the polishing pad on the rotating table. As the table rotates, a polishing slurry is introduced onto the top of the table. The polishing slurry becomes interposed between the pad and the wafer which has the desired effect of polishing the wafer and rendering the surface of the wafer flat.

In lens polishing, the more or less opposite approach is taken. The lens is rotated, and the polishing pad is typically smaller and caused to move both rotationally about its own axis and with respect to the surface of the lens to be polished in such a way as to polish away unwanted material. A surfeit of relatively dilute slurry acting as the polishing agent may be continuously pumped into play between the lens and the polishing pad.

SUMMARY

In one aspect, the invention may be a polishing apparatus comprising: a rotatable polishing pad having an axial center of rotation; a slurry delivery conduit configured to introduce polishing slurry through said axial center of rotation; and wherein the slurry is dispensed directly beneath the rotating pad to enable localized polishing of a substrate surface.

The polishing pad may have a diameter less than 50 mm to enable high-resolution planarization of localized substrate regions.

The slurry delivery conduit may be integrated within a rotary union to maintain continuous flow during pad rotation.

The slurry may injected at a controlled flow rate synchronized with pad rotation speed to optimize material removal rate and uniformity.

The substrate may comprise silicon carbide (SiC), germanium (Ge), or other advanced semiconductor materials requiring localized planarization.

The polishing pad pressure may controlled by the upward loading of the object being polished.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a wafer polishing apparatus in accordance with an embodiment of the present invention;

FIG. 2 is a perspective view of a polishing assembly of the wafter polishing apparatus of FIG. 1;

FIG. 3 is a side view of the polishing assembly of FIG. 2;

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is a close-up view of area V of FIG. 4;

FIG. 6 is a close-up view of area VI of FIG. 3;

FIG. 7 is a close-up top perspective view of the wafer polishing apparatus of FIG. 1; and

FIG. 8 is a top plan view of the wafter polishing apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the exemplified embodiments. Accordingly, the invention expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto.

Referring to FIG. 1, a wafer polishing apparatus 100 is illustrated. The wafer polishing apparatus 100 may include a process bowl 110. The process bowl 110 may have an open top end. A wafer 10 may be supported in the process bowl 110. The wafer 10 may be supported by a support member, which may be a holder or a chuck. The holder may be configured to rotate the wafer 10 during polishing, although this may not be required in all embodiments. The holder or chuck may hold or support the wafer with vacuum, pins, clamps, or the like.

The wafer polishing apparatus 100 may include a polishing assembly 200. The polishing assembly 200 may comprise a polishing arm 210 and a polishing pad 220. The polishing arm 210 may extend over at least a portion of the open top end of the process bowl 110. The polishing arm 210 may be attached at only one end such that the polishing arm 210 is positioned over the process bowl 110 in a cantilevered manner. The polishing pad 220 may be coupled to a distal portion of the polishing arm 210. The polishing pad 220 may be located in a position that enables the polishing pad 220 to directly contact the wafer 10 supported in the process bowl 110 to perform polishing thereon.

FIGS. 2-5 further illustrate the wafer polishing apparatus 100. The polishing arm 210 may define an interior cavity that houses a driver gear 211, a driven gear 212, and a chain 213 coupling the driver gear 211 to the driven gear 212. The driver gear 211 may be coupled to a motor 214 to rotate the driver gear 211. The polishing arm 210 may be configured to rotate about a first rotational axis A-A. This may allow the distal end of the polishing arm 210 and the polishing pad 220 attached thereto to swing in a pivoting or arcuate motion along at least a portion of the wafer 10 located below the polishing pad 220. The polishing pad 220 may be configured to rotate about a second rotational axis B-B. The second rotational axis B-B may be a central axis of the polishing pad 220 that extends vertically and intersects the top and bottom surfaces of the polishing pad 220.

The polishing pad 220 may be coupled to the polishing arm 210 by a post 230. A fluid passageway (also referred to herein as a slurry delivery conduit) 240 may extend through the driven gear 212, through the post 230, and through the polishing pad 220. In an alternative embodiment, the fluid passageway or slurry delivery conduit 240 may extend through the polishing pad 220 without also extending through the driven gear 212 and the post 230. The fluid passageway 240 may extend through a central portion of the polishing pad 220 (i.e., through the axial center of rotation of the polishing pad 220). Thus, a portion of the fluid passageway 240 that extends through the polishing pad 220 may be elongated along the second rotational axis B-B. An inlet conduit 235 may extend through an opening in a top end of the polishing arm 210. The inlet conduit 235 may be fluidly coupled to the fluid passageway 240. A polishing slurry may be fluidly coupled to the inlet conduit 235 by one or more conduits or tubes or the like. The fluid passageway 240 may be located and configured to deliver a fluid (i.e., the polishing slurry) through an opening in the bottom of the polishing pad 220 that is aligned with the center of rotation of the polishing pad 220.

In an embodiment, at least a portion of the fluid passageway or slurry delivery conduit 240 bay be located within a rotary union 242. This may facilitate maintaining a continuous flow of the polishing slurry even during rotation of the rotatable polishing pad.

As shown in FIG. 5, the system may include a source of a polishing fluid 300. The source of the polishing fluid 300 may be fluidly coupled to the inlet conduit 235. The polishing fluid may be any chemical mechanical planarization slurry now known or later discovered, including without limitation slurries that contain particles composed of alumina, silica, and ceria which are suspended in an acidic or basic solution. The slurry may include nano-sized abrasives dispersed in an acidic or basic solution. The polishing fluid may be introduced into the inlet conduit 235 (such as by pumping, pressurization and valves, or the like) whereby the polishing fluid flows from the inlet conduit 235 to the fluid passageway 240. The fluid passageway 240 may comprise an outlet 241 at a bottom end 221 of the polishing pad 220. Thus, the polishing slurry may be configured to flow through the fluid passageway 240 and through the opening/passageway in the polishing pad 220 for dispensing onto the wafer 10.

In an embodiment, the polishing slurry may be configured to be injected from the outlet 241 at the bottom end 221 of the polishing pad 220 at a controlled flow rate. In an embodiment, the controlled flow rate may be synchronized with a speed of rotation of the rotary pad 220 during use. That is, the polishing pad 220 may be rotated at a rotational speed, which may be constant or varied during a polishing operation. The flow rate of the dispensing of the polishing slurry may be synchronized to the rotational speed of the polishing pad 220. Thus, as the rotational speed of the polishing pad 220 increases, the flow rate of the dispensing of the polishing slurry through the outlet 241 in the bottom end 221 of the polishing pad 220 also increases. As the rotational speed of the polishing pad 220 decreases, the flow rate of the dispensing of the polishing slurry through the outlet 241 in the bottom end 221 of the polishing pad 220 also decreases. The bottom end 221 of the polishing pad 220 may comprise grooves to enhance the polishing effect.

Referring to FIG. 7, the polishing pad 220 may have a smaller diameter than the wafer 10. In an embodiment, the polishing pad may have a diameter of 50 mm or less for a 300 mm diameter wafer. In an embodiment a ratio of the diameter of the wafer 10 to the diameter of the pad 220 may be in a range of 2:1 to 10:1, or in a range of 3:1 to 9:1, or in a range of 4:1 to 8:1, or in a range of 5:1 to 7:1. In an embodiment, the ratio of the diameter of the wafer 10 to the diameter of the pad 220 may be at least 2:1, or at least 3:1, or at least 4:1, or at least 5:1. Thus, the polishing pad 220 may be a small pad that is used to polish the wafer 10 during use. The wafer 10 may be rotated as noted above. The polishing pad 220 may be rotated about the second rotational axis B-B. In some embodiments, one of the wafer 10 or the polishing pad 220 is rotated, but not both. In other embodiments, both the wafer 10 and the polishing pad 220 are rotated. In some embodiments, there is relative rotation between the polishing pad 220 and the wafer 10. In accordance with the invention described herein, the polishing slurry is introduced axially through the fluid passageway 240 and then through a hole (i.e., the outlet 241) in the polishing pad 220. This permits fresh polishing slurry to be introduced directly where it is needed at the polishing pad/wafer interface.

The wafer 10 may be a substrate. The wafer 10 may be a semiconductor wafer or substrate. The wafer 10 may comprise silicon carbide (SiC), germanium (Ge), or other advanced semiconductor materials requiring localized planarization. In an embodiment, the pressure applied by the polishing pad 220 onto the wafer 10 may be controlled by an upward loading of the wafer or substrate 10 being polished. That is, the support holding the wafer 10 may apply an upward force onto the wafer 10, thereby pressing the wafer 10 into contact with the polishing pad 220. The support holding the wafer 10 may be capable of moving upwardly and downwardly towards and away from the polishing pad 220 while supporting the wafer 10 to achieve the desired pressure of the polishing pad 220 onto the wafer 10. Alternatively, the polishing assembly 200 may be configured to move the polishing pad 220 downwardly to apply a desired force onto the wafer 10. In either case, the bottom end 221 of the polishing pad 220 should be in contact with the top surface of the wafer 10 during a polishing process.

In an embodiment, the bottom end 221 of the polishing pad 220 may be angled relative to a horizontal plane, and relative to a surface of the wafer 10 that is being treated. Specifically, the bottom end 221 of the polishing pad 220 may lie in a plane that is oriented at an oblique angle relative to a horizontal plane and relative to the surface of the wafer 10 that is being treated. In an alternative embodiment, the bottom end 221 of the polishing pad 220 may lie in a horizontal plane.

As compared to conventional CMP processes described in the background, the mechanism of polishing of the wafer in accordance with the invention described herein is reversed. The wafer becomes the “Table” and the pad becomes the small object wherein the relative motion as between the surfaces has the effect of polishing and therefor planarizing the surface of the wafer.

While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. It is to be understood that other embodiments may be utilized, and structural and functional modifications may be made without departing from the scope of the present invention. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims.