US 20050191945 A1
A porous polishing pad for use chemical/mechanical planarization of semiconductor wafers is provided with a transparent section formed in a section of the porous polishing pad by direct injection of a polymeric material into a modified portion of the pad. The modified section may be either a low density area, or may be created by removing a complete vertical section of the pad. The injected polymer forms an integral window with the pad by flowing into the matrix of the pad at the pad/window interface. No additional reinforcement is required to hold the window in place; however, adhesive and/or another impervious layer may be attached behind the window for additional support. In an alternative embodiment, a separate and distinct window-plug is inserted into a cutout section of the pad, and bonded to the pad by one or more binding film layers on the back, non-working surface of the pad.
1. A polishing pad for use in chemical mechanical polishing of substrates, said polishing pad having a polishing surface, comprising:
a porous fibrous matrix;
a binder for binding said fibers;
said fibrous matrix forming a porous structure by which polishing slurry and polishing debris during chemical mechanical polishing of substrates are temporarily stored for subsequent rinsing away, and for enhanced flow-distribution of the polishing slurry;
said fibrous matrix comprising an end-point-detection transparent window section for allowing light beams from an end-point detection apparatus to pass therethrough.
2. The polishing pad for use in chemical mechanical polishing of substrates according to
3. The polishing pad for use in chemical mechanical polishing of substrates according
4. The polishing pad for use in chemical mechanical polishing of substrates according
5. The polishing pad for use in chemical mechanical polishing of substrates according
6. The polishing pad for use in chemical mechanical polishing of substrates according
7. The polishing pad for use in chemical mechanical polishing of substrates according
8. The polishing pad for use in chemical mechanical polishing of substrates according
said fibrous matrix comprising a front working surface for use in polishing and a back surface for mounting to a platen of a CMP apparatus;
said polishing pad further comprising a reinforcing impervious layer attached to said back surface for providing structural integrity to said window-plug in said fibrous matrix; said reinforcing impervious layer having a cutout in alignment with said cutout section of said fibrous matrix for allowing the light beam from an end-point-detection device to pass therethrough; said cutout being of less cross-sectional area than the juxtapositioned portion of said window-plug thereat in order to form an overlapping section of said reinforcing impervious layer that overlaps said juxtapositioned portion of said window-plug;
said overlapping section of said reinforcing impervious layer being fused to said juxtapositioned portion of said window-plug for bonding said reinforcing impervious layer to said juxtapositioned portion of said window-plug;
said reinforcing impervious layer also being fused to said back surface of said fibrous matrix.
9. The polishing pad for use in chemical mechanical polishing of substrates according
Priority of provisional application No. 60/365,100 filed on Mar. 18, 2002 is herewith claimed. The present application is also, a continuation-in-part of U.S. patent, application Ser. No. 10/349,201, filed on Jan. 22, 2003.
The present invention is related to polishing of materials, in particular to the chemical mechanical polishing (CMP) of integrated circuits. Specifically, a method for placing a transparent section in a polishing pad is described. In particular, the present invention is directed to forming or placing an end-point detecting, laser-transparent window in a CMP polishing pad disclosed in above-mentioned parent application Ser. No. 10/349,201, or the porous polishing pad disclosed in commonly-owned U.S. patent application. No. 10/087,223, filed on Mar. 1, 2002, which applications are incorporated by reference herein. The CMP porous polishing pads disclosed therein are made of a matrix of porous paper-making fibers that is impregnated and bound together with a thermoset resin. Such a polishing pad is a matrix of absorbent cellulose fibers, for example, and are impregnated with a thermoset resin, preferably phenolic, is densified, and cured to provide a rigid, yet porous structure. The porous CMP polishing pads thereof are made by a wet-laid, specialty paper-making process.
In the field of semiconductor manufacture, numerous integrated circuits are produced on wafers through layers of wiring devices. During the process of forming layers and structures, the topography of the surface becomes increasingly irregular. The prevailing technology for planarizing the surface is chemical mechanical polishing (CMP). In effect, this process polishes the top layer of an integrated circuit prior to the depositing of another layer.
In most chemical-mechanical polishing, the working layer of an integrated circuit is exposed to a moving polishing pad and a chemical slurry solution. In some systems, the polishing pad, mounted on a platen, rotates about a fixed axis, while the wafer rotates and moves across the pad. Since material on the active layer is removed during the process, it is critical that the polishing process be terminated at the correct time. In order to control the end point of the polishing process, various methods have been developed. The most prevalent method has utilized laser interferometry which detects the end point of the polishing process, an example of which is disclosed in U.S. Pat. No. 6,280,289—Wiswesser, et al. In these systems, a laser is mounted in the platen and directed through the pad onto the surface of the wafer. A control system detects changes in the reflected signal to determine the end point.
In order for end-point detection to be carried out, the pad must have a section that is reasonably transparent to the wavelength of the laser being used. Most methods for producing a transparent region in the polishing pad involve inserting a formed, transparent plug into a hole in the pad. The plug is usually secured to the pad by an adhesive film onto the back, or rear, non-working side or surface of the polishing pad.
It is, therefore, the primary objective of the present invention to provide an end-point-detecting, laser-transparent window in a porous CMP polishing pad, and, in particular, for providing such a window in a porous polishing pad made of a fibrous matrix of paper-making fibers manufactured by a specialty, paper-making process and bonded by a thermoset resin.
According to present invention, a porous, wet-laid-manufactured polishing pad made of paper-making fibers bound by a thermoset resin is formed with a local transparent section. Transparency for purposes of the present invention is defined as sufficient light transmission such that the end-point detection system is able to function. Such a local transparent section is formed within the pad by either removing a section of the pad itself, or by creating a low density area in the paper-making fiber matrix. In either case, the pad is fixtured, or grasped, between two flat plates creating a mold with the local section. The local section is filled with a polymeric material that is injected under pressure into the region. The polymer may be a cured polymer that is heated to permit flow, or may be an uncured polymer that is mixed prior to injection into the local portion of the porous polishing pad. In either case, the polymer is subjected to pressure to permit flow. As the injected material flows into the matrix of the pad, a diffusion zone around the perimeter of the window is created, whereby the polymeric material bonds securely with the pad. The resulting region thereby is transparent to the laser emanating from the end-point detection system.
The types of materials suitable for the window include amorphous, semi-crystalline, crystalline or elastomeric polymers. Generally, polymers that exhibit low shrinkage and maintain clarity upon cooling, such as amorphous polymers, are the preferred choice.
A method for creating a transparent section of the invention in the polishing pad consists of partially or completely removing a section of the polishing pad, or creating a low density area in the desired region of the pad; forming a mold in the region by placing the pad between two flat surfaces; injecting the polymer in a liquid or semisolid state into the region; and allowing the assembly to cool and/or cure.
In a different embodiment, a separately-formed, stepped window-plug is inserted into the cutout or opening formed on the polishing pad, and retained therein by a first impervious layer, and a second adhesive layer.
The invention will be more readily understood with reference to the accompanying drawings, wherein:
Referring now to the drawings in greater detail,
In order to form a window that is transparent to the laser beam, or equivalent light beam, of a conventional end-point detection system (not shown) associated with a CMP apparatus, which window is preferably rectangular in shape, the pad 10 is placed in a fixture, or mold, consisting of two flat plates 14, 15 that may be heated, or may not be heated, as shown in
The integrity of the window of the polishing pad is formed by diffusion of the flowing polymer into the porous pad.
According to the invention, the window formed in the polishing pad preferably has an approximate opacity range of 0-70% (30-100% transmission) for a laser of a wavelength in the range 150-3500 nm. Most laser systems for end-point detection are approximately in the range of 600-700 nm.
While the above-description has been given with regard to the formation of a window in a porous pad, and in particular to the porous paper-making-fiber-matrix polishing pads disclosed U.S. patent application Ser. Nos. 10/087,223 and 10/349,201, other types of porous pads or non-porous pads may also be provided with the window of the present invention. Formation of the window of the invention in a nonporous pad is similar to first embodiment described above for a porous pad, where there is created a higher-density zone around the opening in the nonporous pad for the window, the diffusion zone thus being decreased or eliminated altogether at a high-density barrier, as described above. Further structural integrity may be achieved by attaching an adhesive layer, or other impervious layer, to the back of the window or nonporous pad, as described above. In this case the additional layer must be of sufficient clarity to allow proper functioning of the end-point detection.
While specific embodiments of the invention have been shown and described, it is to be understood that numerous changes and modifications may be made therein without departing from the scope and spirit of the invention as set forth in the appended claims.