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  Polishing pad having a window with reduced surface roughnessUSPTO Application #: 20070037488Title: Polishing pad having a window with reduced surface roughness Abstract: The present invention provides a polishing pad for performing chemical mechanical planarization of semiconductor substrates. The polishing pad comprises a polishing pad body having an aperture formed therein and a window fixed in the aperture for performing in-situ optical measurements of the substrate. The window has a lower surface capable of transmitting light incident thereon. The lower surface has been treated by laser ablation to remove surface roughness present on the lower surface. (end of abstract) Agent: Rohm And Haas Electronic Materials Cmp Holdings, Inc. - Newark, DE, US Inventor: Alan H. Saikin USPTO Applicaton #: 20070037488 - Class: 451006000 (USPTO) Related Patent Categories: Abrading, Precision Device Or Process - Or With Condition Responsive Control, By Optical Sensor The Patent Description & Claims data below is from USPTO Patent Application 20070037488. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. Provisional Application Ser. No. 60/706,971 filed Aug. 10, 2005. FIELD OF THE INVENTION [0002] The present invention relates to polishing pads used for chemical-mechanical planarization (CMP), and in particular relates to such pads that have windows formed therein for performing optical end-point detection. BACKGROUND OF THE INVENTION [0003] In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting, and dielectric materials are deposited on or removed from a surface of a semiconductor wafer. Thin layers of conducting, semiconducting, and dielectric materials may be deposited by a number of deposition techniques. Common deposition techniques in modern processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and electrochemical plating (ECP). [0004] As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization. Planarizing a surface, or "polishing" a surface, is a process where material is removed from the surface of the wafer to form a generally even, planar surface. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization is also useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even surface for subsequent levels of metallization and processing. [0005] Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates such as semiconductor wafers. In conventional CMP, a wafer carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate urging the wafer against the polishing pad. The pad is moved (e.g., rotated) relative to the substrate by an external driving force. Simultaneously therewith, a chemical composition ("slurry") or other fluid medium is flowed onto the substrate and between the wafer and the polishing pad. The wafer surface is thus polished by the chemical and mechanical action of the pad surface and slurry in a manner that selectively removes material from the substrate surface. [0006] A problem encountered when planarizing a wafer is knowing when to terminate the process. To this end, a variety of planarization end-point detection schemes have been developed. One such scheme involves optical in-situ measurements of the wafer surface. The optical technique involves providing the polishing pad with a window transparent to select wavelengths of light. A light beam is directed through the window to the wafer surface, where it reflects and passes back through the window to a detector, e.g., an interferometer. Based on the return signal, properties of the wafer surface, e.g., the thickness of films (e.g., oxide layers) thereon, can be determined. [0007] While many types of materials for polishing pad windows can be used, in practice the windows are typically made of the same material as the polishing pad, e.g., polyurethane. For example, U.S. Pat. No. 6,280,290 discloses a polishing pad having a window in the form of a polyurethane plug. The pad has an aperture and the window is held in the aperture with adhesives. [0008] A problem with such windows arises when they have surface roughness. For example, polyurethane windows are typically formed by slicing a section from a polyurethane block. Unfortunately, the slicing process produces surface imperfections or roughness R on either side of the window 1 in polishing pad 10, as shown in FIG. 1. The depth of the roughness ranges from about 10 to about 100 microns. The roughness on the bottom surface scatter the light used to measure the wafer surface topography, thereby reducing the signal strength of the in-situ optical measurement system. The roughness on the upper surface do not tend to scatter light as much as the bottom surface roughness due to the presence of a liquid slurry and proximity of the upper surface to the wafer. [0009] Because of the loss in signal strength from scattering by the lower window surface, the measurement resolution suffers, and measurement variability is a problem. Accordingly, what is needed a polishing pad for chemical-mechanical planarization with an improved window having greater light transmission and less light scattering properties. SUMMARY OF THE INVENTION [0010] In one aspect of the invention, there is provided a polishing pad for performing chemical mechanical planarization of semiconductor substrates, the polishing pad comprising: a polishing pad body having an aperture formed therein; a window fixed in the aperture for performing in-situ optical measurements of the substrate, the window having a lower surface capable of receiving light incident thereon; and wherein the lower surface has been treated by laser ablation to remove surface roughness present on the lower surface. [0011] In another aspect of the invention, there is provided a polishing pad useful for chemical mechanical planarization, the polishing pad comprising: a polishing pad body having a window fixed therein for performing in-situ optical measurements of a substrate, the window having a lower surface capable of transmitting light incident thereon; wherein the lower surface has been treated by laser ablation to remove surface roughness present on the lower surface; and wherein the lower surface further comprises micro-lenses formed by the laser ablation. [0012] In another aspect of the invention, there is provided a polishing pad useful for chemical mechanical planarization, the polishing pad comprising: a polishing pad body having a window fixed therein for performing in-situ optical measurements of a substrate, the window having a lower surface capable of transmitting light incident thereon; and wherein the lower surface has been treated by laser ablation to form micro-lenses. [0013] In another aspect of the invention, there is provided a method of forming a polishing pad for chemical mechanical planarization of semiconductor substrates, the polishing pad comprising: providing a polishing pad body having an aperture formed therein; fixing a window in the aperture for performing in-situ optical measurements of the substrate, the window having a lower surface capable of receiving light incident thereon; and treating the lower surface by laser ablation to remove surface roughness present on the lower surface. [0014] In another aspect of the invention, there is provided a method of performing in-situ optical measurements of a substrate in a chemical-mechanical planarization (CMP) system, comprising: providing the CMP system with a polishing pad having a window, the window having a lower surface treated by laser ablation to remove surface roughness present on the lower surface; directing a first beam of light through the laser-ablation treated surface and the window to the substrate; and reflecting the first beam of light from the substrate to form a second beam of light that passes back through the window and the laser-ablation treated surface. BRIEF DESCRIPTION OF THE DRAWINGS [0015] FIG. 1 illustrates a conventional polishing pad with a window having a surface roughness; [0016] FIG. 2 illustrates a cross-sectional view of an embodiment of the window of the present invention having reduced surface roughness; [0017] FIG. 3 illustrates a cross-sectional view of another embodiment of the window of the present invention having micro-lenses formed therein; and [0018] FIG. 4 illustrates a cross-sectional view of a CMP system showing a polishing pad of the present invention having a window with a laser-ablation treated surface, a wafer residing adjacent the upper surface of the polishing pad, and the basic elements of an in-situ optical detection system. DETAILED DESCRIPTION OF THE INVENTION Continue reading... Full patent description for Polishing pad having a window with reduced surface roughness Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Polishing pad having a window with reduced surface roughness patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Polishing pad having a window with reduced surface roughness or other areas of interest. ### Previous Patent Application: Polishing pad having a sealed pressure relief channel Next Patent Application: Centerless grinder Industry Class: Abrading ### FreshPatents.com Support Thank you for viewing the Polishing pad having a window with reduced surface roughness patent info. 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