Patent Application
20150021498
The present invention relates generally to electronic device manufacturing, and more particularly to chemical mechanical polishing.
Within electronic device manufacturing, a planarization process may be used to remove various layers or films, such as silicon dioxide, silicon nitride, copper, or the like from a substrate (e.g., a patterned wafer). Planarization may be accomplished using a chemical mechanical polishing (CMP) process by applying an abrasive slurry between a polishing pad and the substrate surface to be polished (e.g., planarized). The substrate is received in a substrate holder that includes a retaining ring adapted to prevent the substrate from slipping out from between the holder and the polishing pad. Pressure is applied to force the substrate against the polishing pad and both the substrate holder and the polishing pad may be rotated to facilitate the material removal. Further, the holder may oscillate the substrate back and forth across the surface of the polishing pad.
During certain planarization processes, although sufficient material removal may be accomplished with existing processes, unwanted wear of the substrate holder may occur. Accordingly, improved polishing methods and apparatus are sought.
In a first aspect, a chemical mechanical polishing method is provided. The chemical mechanical polishing method includes providing a substrate retaining ring including a polymer ring having a polymer surface adapted to contact a substrate while in operation; and treating the surface of the polymer ring to attain an increased hardness of the surface as compared to other regions of the polymer ring.
In another aspect, a chemical mechanical polishing system is provided. The chemical mechanical polishing system includes a substrate held in a substrate holder having a substrate retaining ring, the substrate having a peripheral edge supported by the substrate retaining ring, the retaining ring having a polymer ring having a polymer contact portion in contact with at least a portion of the peripheral edge, wherein the polymer contact portion has a hardness that is greater than a remaining portion of the polymer ring.
In yet another aspect, a chemical mechanical polishing substrate holder is provided. The chemical mechanical polishing substrate holder includes a substrate retaining ring configured to support a peripheral edge of a substrate, the retaining ring including a polymer ring having a polymer contact portion adapted to contact at least a portion of the peripheral edge, wherein the polymer contact portion has a hardness that is greater than a remaining portion of the polymer ring.
Other features and aspects of the present invention will become more fully apparent from the following detailed description of example embodiments, the appended claims, and the accompanying drawings.
Embodiments described herein relate to systems and methods adapted to polish the surface and edge of a substrate. While the major surface of the substrate is polished directly by the pad, removal of material from the edge of the substrate can be influenced using the retaining ring of the substrate holder. Pressures applied to the polishing pad through the retaining ring can be selected so that the substrate edge removal rate is controlled. However, selecting relatively low pressures to reduce wear can be problematic. A retaining ring on a polishing head is subjected to at least two wear mechanisms: vertical wear and lateral wear. Vertical wear of the ring refers to wear normal to the lower contact surface between the ring and the polishing pad (i.e., the retaining ring surface facing the polishing pad). If possible, it would be desirable to reduce or avoid vertical wear by using lower pressures. Lateral, or horizontal, wear of the ring refers to wear from the substrate edge resulting from friction during polishing.
Lateral wear results in “notching” of the retaining ring if the pressure applied to the polishing pad through the retaining ring is too low. If notching is allowed to occur, the edge of the substrate may undesirably be subjected to the downward pressure from the retaining ring which affects substrate edge removal rates and risks substrate slipping. Increasing the pressure applied to the polishing pad through the retaining ring can effectively be used to remove or prevent notching but at the expense of increasing the amount of vertical wear. In other words, using a conventional substrate holder, it is necessary to have sufficient vertical wear to ensure that damage resulting from lateral wear (or wafer notching) is removed to provide proper retention of the substrate within the holder.
In some embodiments, the present invention reduces the need to apply a relatively large amount of pressure to the polishing pad through the retaining ring. By increasing the hardness of the inner diameter of the retaining ring, the retaining ring is better able to resist substrate notching, even at lower retaining ring pressures during substrate polishing. In some embodiments, the inner surface of the retaining ring is treated to achieve the increased hardness. For example, in the case where the retaining ring is constructed of a polymer material, the treatments can include ultraviolet (UV) light curing and bead blasting. Other methods such as cold rolling, vulcanization, application of a laminate, laser hardening, and electron beam curing can also be used. Other well-known hardening methods may be used for polymer rings and for retaining rings made of other materials. In some embodiments, the hardness and/or depth of the hardening is selected to ensure notching cannot occur at any practicable retaining ring pressure.
These and other aspects of embodiments of the invention are described below with reference to
The polishing pad 104 may be of conventional construction, and may comprise any suitable porous material such as a rigid micro-porous polyurethane pad. The polishing pad 104 may be mounted (e.g., adhered) onto a conventional platen 106 that may be rotated by a suitable motor (not shown) coupled to the platen 106 by shaft 107. In some embodiments, polishing pad 104 may have a shore D hardness per ASTM D2240 of between about 30 and about 70, and between about 52 and about 62 in some embodiments. The polishing pad 104 may have a pore size between about 30 and about 70 microns, and a porosity of between about 10% and about 50%, for example. Other hardness, pore sizes, and porosities may be used.
In some embodiments, the disc-shaped platen 106 may be rotated at between about 10 and about 200 RPM, between about 20 RPM and about 120 RPM, and between about 50 RPM and about 100 RPM in some embodiments while polishing, i.e., a material-removal process wherein the metal layer on the substrate 102 is planarized by using a slurry containing an abrasive and possibly an etchant.
The substrate 102 may be held in a substrate holder 108 including a retaining ring 110 (shown in cross-section). Prior art substrate holders (also referred to as retainers or carrier heads) are described in U.S. Pat. No. 8,298,047; U.S. Pat. No. 8,088,299; U.S. Pat. No. 7,883,397; and U.S. Pat. No. 7,459,057, issued to the present assignee, for example, and incorporated herein by reference. Other types of substrate holders may be used. Substrate holder 108 may be rotated and may also be scanned (e.g., oscillated) back and forth across the surface of the polishing pad 104 as the polishing pad 104 is being rotated in contact with the substrate 102. The holder oscillation rate may between about 0.1 mm/s and about 5 mm/s, for example. Other oscillation rates may be used. Substrate holder 108 may be rotated at between about 10 RPM to about 200 RPM.
Turning now to
In some embodiments, the greater hardness is provided by exposing the inner surface 202 to UV light for a sufficient time to cure and harden the inner surface 202 to a depth D. In such embodiments, the portions not to be hardened may be taped to prevent other regions of the polymer retaining ring 110 from being exposed to UV light and hardened in those regions. In alternative embodiments, greater hardness is provided by exposing the inner diameter to bead blasting for a sufficient time to compact and harden the inner surface 202 to a depth D.
The example method 600 includes providing a substrate retaining ring including a polymer ring for retaining a substrate within a CMP system (602). An inner surface of the retaining ring is treated to attain an increased or greater hardness relative to other portions of the ring (604). The treatment may include UV light curing, bead blasting, or other methods of hardening a surface. The hardened retaining ring is then used to retain a substrate within the CMP system while allowing the vertical pressure and thus, the vertical wear on the ring to be minimized (606).
Accordingly, while the present invention has been disclosed in connection with example embodiments thereof, it should be understood that other embodiments may fall within the scope of the invention, as defined by the following claims.
