Patent Application
20240391051
The present invention relates to a retaining ring used for chemical mechanical polishing.
In semiconductor fabrication, chemical mechanical polishing (CMP) is used for planarization of semiconductor wafers that may be used for the fabrication of integrated circuits, including very large scale integrated (VLSI) circuits and ultra large scale integrated (ULFI) circuits. Chemical mechanical polishing is employed to remove material from a deposited layer on a wafer substrate. In a typical CMP process, the wafer is exposed to an abrasive medium under controlled chemical, pressure, velocity, and temperature conditions. The abrasive medium may include slurry solutions containing small abrasive particles, such as silicon dioxide, and chemically reactive substances, such as potassium hydroxide. Typical chemical mechanical polishing processes include a carrier head that holds a wafer against a polishing pad. One or both of the polishing pad or carrier head may rotate to affect the polishing of the wafer.
Generally, carrier heads include a retaining ring used to hold the wafer within a given boundary. In general, known retaining rings are formed either completely of a metal construction or a metal backing with a ring portion of polymer or silicon dioxide. The ring portion typically contacts the polishing pad or surface and the semiconductor wafer. This contact, combined with the rotation and abrasives previously mentioned, generates heat and results in an increase in temperature. Over time, this increase in temperature can have adverse effects on the process, retaining ring, pad, and ultimately, the wafer substrate.
Conventional retaining rings attempt to mitigate this heat generation by incorporating low levels of lubricants into the retaining ring polymer such as polytetrafluoroethylene (PTFE), carbon, polyimide (PI), boron nitride and other constituents to help mitigate the heat generation. These filler systems do have an incremental impact on the heat generation, but due to the thermally insulative nature of thermoplastic polymers, the ring will continue to see increased temperature at the interface location with the pad.
Increases in thermal temperature can negatively impact the CMP process in several different areas, including increased wear rate of the CMP ring and the CMP pad which can cause variation in the CMP process and lead to lower yields and increase consumable costs. However, perhaps the largest issue associated with thermal increase is the formation of an inner grove defect that can develop as the wafer being polished cuts into the inside diameter of the CMP ring. The adoption of new technology wafers that have a reduced thickness only serves to exaggerate the inner groove formation, as the increasingly thin edge of the wafer impacts the inside diameter of the ring. This impact occurs very close to the wear surface between the ring and the pad which is the exact area that experiences elevated temperature during the CMP process. The elevated temperature of the ring in this localized area inherently softens the thermoplastic polymer and reduces the impact and wear resistance, increasing the likelihood of the inner groove formation. This inner groove formation is detrimental to the CMP process and can cause wafer damage, poor yields and dramatically reduced consumable life.
For many years, wafers used in semiconductor manufacturing were almost always made of silicon. Silicon is a relatively soft material. In recent years, especially as demand for chips suitable for use in electric vehicles has greatly increased, wafers for certain applications have increasingly been made from gallium arsenide (GaAs) or silicon carbide (SiC). Gallium arsenide and silicon carbide are both extremely hard materials. For this reason, wafers made of GaAs and SiC wear out traditional CMP rings much faster than wafers made of silicon.
Accordingly, one aspect of the present invention is to provide a thermoplastic based retaining ring that is thermally conductive and can transfer heat away from the interface region. The retaining ring utilizes unique filler systems that allow the thermoplastic polymer to conduct the heat away from the surface contact area and transfer it into and away from the ring, thus maintaining a consistently lower temperature at the contact area between the ring and pad. Lower operating temperatures will retard the wear rate of the ring and pad, resulting in better process uniformity, increased consumable life and better process yield. In addition to these benefits, lower temperatures at the wear surface also maintains the original impact strength of the material, which reduces the formation of the inner groove formation, maintaining process consistency and increasing yield.
The process life of the retaining ring is also a key performance indicator, since a ring that has increased wear resistance and hence longer life, will dramatically reduce consumable costs, and increase machine uptime, yield rates and process consistency. The forementioned material compositions used to produce the retaining ring was developed to increase wear performance in addition to its thermally conductive characteristics. Wear studies have shown that this novel thermally conductive retaining ring composition also increases the life of the retaining ring by 300-400% under standard CMP operating conditions.
These and other advantages of the invention will become more apparent and more readily appreciated from the following detailed description of the exemplary embodiments of the invention taken in conjunction with the accompanying drawings where:
With reference to
Due to the heat and pressure generated by the CMP processing, wear is imparted on the inside edge of the retaining ring 100 by the wafer W during the CMP processing.
In the conventional art, the retaining ring 100 is made of a polymer, such as unfilled polyetheretherketone (PEEK). A lubricant, such as polytetrafluoroethylene (PTFE), carbon, polyimide (PI), and boron nitride, may be incorporated into the polymer. The lubricant incorporated into the conventional polymer is at a low level. One embodiment of the conventional art has boron nitride at 1%-2% by weight of the retaining ring 100. Even with the addition of lubricant, the retaining ring 100 of the conventional art is still thermally insulative, resulting in increased temperature at the interface location between the retaining ring 100 and the wafer W during CMP processing.
The retaining ring of the present invention is formed of a thermally conductive material that transfers heat away from an interface region between the wafer W and the inside edge of the retaining ring 100. The thermally conductive material is formed by adding a material filler, which is thermally conductive, to a base material when forming the retaining ring. It is believed that enough material filler is added to the base material so that the particles of the material filler in the retaining touch each other to create a heat path to transfer away the heat generated during the CMP processing, thereby presenting a crosslinked polymer.
In one embodiment, the thermal conductivity of the retaining ring in a through plane of the retaining ring is between 0.5 W/mk and 20 W/mk. In another embodiment, the thermal conductivity in the through plane of the retaining ring is between 10 W/mk and 20 W/mk. In another embodiment, the thermal conductivity in the through plane of the retaining ring is between 2.0 W/mk and 10 W/mk. In another embodiment, the thermal conductivity in the through plane of the retaining ring is between 1.0 W/mk and 5 W/mk.
In one embodiment, the thermal conductivity in plane, in flow, of the retaining ring is between 2.0 W/mk and 60 W/mk. In another embodiment, the thermal conductivity in plane, in flow, of the retaining ring is between 5.0 W/mk and 50 W/mk. In another embodiment, the thermal conductivity in plane, in flow, of the retaining ring is between 2.0 W/mk and 10 W/mk. In another embodiment, the thermal conductivity in plane, in flow, of the retaining ring is between 2.0 W/mk and 30 W/mk.
The base material may be a thermoplastic such as PEEK, polyphenylene sulfide (PPS), polyethylene terephthalate (PET), PI, polyamide-imide (PAI), aliphatic polyketone (PK), polyaryle ether ketones (PAEK), PTFE, polyphthalamide (PPA), liquid crystal polymers (LCP), polybutylene terephthalate (PBT), nylons such as PA6, PA66, PA12, thermoplastic polyurethane (TPU), rigid TPU, polyolefins, or similar polymers, and combinations thereof.
The material filler may be carbon, glass, polyimide, PAI, TiO2, ceramic, silica, alumina, boron nitride, diamond, aramid, aluminum oxide, aluminum nitride, pitch carbon fiber, polyacrylonitrile (PAN) carbon fiber, pitch graphite fiber, graphite fiber, graphite, and combinations thereof. In a preferred embodiment, the material filler is boron nitride. Boron nitride provides good wear properties, is thermally conductive, and electrically insulative.
The material filler may be between 5% and 70% by weight of the material of the retaining ring. In another embodiment, the material filler may be between 10% and 70% by weight of the material of the retaining ring. In another embodiment, the material filler may be boron nitride which is 20%-40% by weight of the material of the retaining ring. In another embodiment, the material filler may be boron nitride which is 20%-60% by weight of the material of the retaining ring. In another embodiment, the material filler may be boron nitride which is 30%-40% by weight of the material of the retaining ring. In another embodiment, the material filler may be boron nitride which is 25%-50% by weight of the material of the retaining ring.
As such, the material filler is a substantial portion of the material of the retaining ring of the present invention, thereby changing the properties of the material. The material composition used to produce the retaining ring 100 was originally developed to increase wear performance, with the unexpected additional benefit of its thermally conductive characteristics.
Thus, the thermoplastic polymer of the retaining ring 100 of the present invention is able to conduct the heat away from the surface contact area and transfer it into and away from the retaining ring, thus maintaining a consistently lower temperature at the contact area between the retaining ring 100 and the polishing pad 3. Lower operating temperatures will retard the wear rate of the retaining ring 100 and the polishing pad 3, resulting in better process uniformity, increased consumable life and better process yield. In addition to these benefits, lower temperatures at the wear surface also maintains the original impact strength of the material, which reduces the formation of the inner groove, maintaining process consistency and increasing yield.
The process life of the retaining ring 100 is also a key performance indicator, since a ring that has increased wear resistance and hence longer life, will dramatically reduce consumable costs, and increase machine uptime, yield rates and process consistency. The material composition used to produce the retaining ring 100 was developed to increase wear performance in addition to its thermally conductive characteristics. Wear studies have shown that this novel thermally conductive retaining ring composition, also increases the life of the retaining ring by 300-400% under standard CMP operating conditions.
As shown in
Although only certain embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiment without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
This application claims priority to U.S. Application No. 63/469,304, filed on May 26, 2023, the entire content and disclosure of which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 63469304 | May 2023 | US |
