Papers by Author: James C. Sung

Abstract: Due to the continual improvement of CMP technologies, and the need for polishing delicate wafers at high speed, graphite impregnated pads (GiP) dressed by brazed organic dia mond disks (BODD) can double the throughput of wafer-pass at the reduced cost of ownership (CoO). The increased polishing rate is due to the act of nano graphite particles that absorb slurry. The nano graphite particles coated with chemical and abrasive can achieve high removal rate without causing scratches on the wafer. In addition, nano graphite particles do not stick to wafer surfaces, so they can be cleaned easily. BODD can uniquely dress GiP to create slurry channels so the pore free pad is not bottlenecked by slurry supply. This paper also demonstrated the low stress polishing by applying ultrasound during the CMP process.

Abstract: Diamond disks are indispensable for dressing CMP pads in the manufacture of semiconductors. Conventional diamond disks contain one type of diamond grits, with the aim to achieve two different functions, viz. glaze shaving and asperities grooving. Cocktail diamond disks are made by assembling brazed diamond pallets that contain different types of diamond crystals. Thus, the pad can be dressed clean, and at the same time, asperities may polish wafers fast without damaging.

Abstract: Sintered polycrystalline diamond cubicles were oriented to make CMP pad conditioners. The dressing experiments demonstrated the capability of fast pad cutting and efficient removal of glazed layer that is formed by polishing wafers with slurry on dressed pad.

Abstract: Current polishing pads cannot polish a workpiece without using slurry with free abrasive. The new slurry is required to be continually poured into the working area, so more than half of the slurry may be lost from the table without contacting the wafer surface; this leads to economic and environmental problems. In the current work, the fixed abrasive pad was used, where nano-sized diamond abrasives were embedded in the polishing pad; distilled water, rather than slurry, was used. The effect of various fixed abrasive pad designs on polishing characteristics during silicon wafer polishing was investigated. Moreover, the primary function of fixed abrasive was to remove the rough parts of silicon wafer as they were being polished. Consequently, it needed to disperse the nano-sized abrasives into the pad material with high hardness value; this way, working abrasives are not pressed into the pad material. Furthermore, with the use of a pad conditioner, the interior working abrasives were exposed to the pad surface. As a result, the best outcome of using the fixed abrasive pad with a nano-sized diamond was a surface roughness of Ra 0.47 nm.

Abstract: Diamond pad conditioner or dresser can determine the efficiency of chemical mechanical polishing (CMP) processes and the quality of polished wafers. Conventional diamond pad conditioners are made by adhering discrete diamond grits on a flat substrate. The size distribution of diamond grits coupled with the deformation of the substrate often make the tips of diamond grits lying at different heights. Instead of attaching individual diamond grits to a metal substrate, a revolutionary design of pad conditioners is based on carving a structure out of sintered polycrystalline diamond (PCD) matrix. The PCD dresser is manufactured by wire electro discharge machining to form cutting pyramids of a specific size with a designed shape. The dressing characteristics of pad surface textures are studied by comparison with conventional diamond pad conditioner. Experimental results indicate that the PCD dresser can dress asperities of the pad more uniformly than the conventional diamond dresser due to PCD dresser having identically shaped tip and the same height diamond. In addition the cutting rate of PCD dresser for IC1000 pad not only is reduced by about 30% but also it can dress pad more effectively than conventional diamond dresser.

Abstract: Diamond grits synthesized under ultrahigh pressure have been commercially manufactured since 1957. Most of the diamond grits are for sawing rocks (granite, marble) and concrete. In 2004, more than 4 billion carats (800 tons) of diamond saw grits were produced worldwide. About 3/4 of total production was made in China, but the Chinese diamond grits tend to be smaller in size (<40 mesh) and with inferior quality, so their total value accounts for only 1/4 of the world sales (about $600 millions). The ultrahigh pressure process for synthesizing diamond grits is due to make a quantum leap: the raw materials will incorporate diamond seeds with a predetermined pattern. The result is doubling the diamond yield with a narrower size distribution. Moreover, the shape of diamond crystals can be precisely tuned. For example, diamond octahedra or diamond cubes, that are not available today, can be mass-produced. The new technology is now being implemented worldwide so the future diamond grits will have improved quality at reduced prices.

Abstract: Diamond grits in tools are typically held in a sintered matrix of metal powder (e.g. Co). The bonding between diamond and the matrix is essentially mechanical. As a result, most diamond grits are easily knocked out from the tool during cutting. The diamond industry has designed various metal coatings (e.g. Ti, Cr, Si) to improve the adherence of diamond grits in the matrix, but the improvements have been modest (e.g. up to 50% increase of tool life). A revolutionary “Active Braze Coated Diamond” (ABCD) is now being developed. The coating of ABCD is much thicker (e.g. 20 microns) than conventional ones (about 1 micron). The molten braze is wetted and reacted with diamond to form strong chemical bond at the interface so that the diamond does not become knocked out of tools. ABCD is coated with a nickel alloy that can form metallurgical diffusion bonds readily with the metal matrix of the tool. In essence, ABCD turns diamond into a metal grain so that the diamond tools can be made by conventional powder metallurgical process without being concerned about the poor bonding between matrix metal powder and the diamond as before.

Abstract: Kinik Company pioneered diamond pad conditioners protected by DLC barrier (DiaShield® Coating) back in 1999 (Sung & Lin, US Patent 6,368,198) and there has been no follower since then. Kinik's offered two varieties of DiaShield® Coatings: ultrahard tetrahedral amorphous carbon and superhard hydrogenated DLC. Kink also evaluated Cermet Composite Coating (CCC or C3, patent pending). C3 is unique that the coating composition grades from a metallic (e.g. stainless steel) under layer to a ceramic (e.g. Al2O3 or SiC) exterior. The metallic under layer can form metallurgical bond with metallic matrix on the diamond pad conditioner. The ceramic exterior is both wear and corrosion resistant. The gradational design of C3 coating will assure its strong adherence to the substrate because there is no weak boundary between coating and substrate. By dipping diamond pad conditioners of various designs in acidic solution (e.g. copper cleaning solution) for extended periods of time (e.g. 50 hours) the chemical inertness of various matrix materials are determined with the decreasing ranking as: hydrogenated DLC > C3 coating > tetrahedral amorphous carbon > sintered nichrome > brazed alloy > electroplated nickel.

Abstract: Although diamond tools have been used for over a century, the diamond grits distribution in the matrix is not uniform. This is because the large and light diamond grits tend to segregate from the small and heavy metal powder during the mixing process, hence diamond distribution in the diamond tools is intrinsically heterogeneous. As a result, the cutting performance of the diamond tools cannot be optimized. In 1997, Dr. James Chien-Min Sung applied two historical patents that can allow the design of diamond distribution according to a predetermined pattern. As the result, the life of diamond tools may be doubled; and the cutting speed, may also be twice as high. The three-dimensional saw segments with arrayed diamond grits were made back in 1999 with the improved performance as predicted. The Sung invention can allow the diamond tools industry to make ideal saw segment that has variable diamond size and diamond separation at different regions. Conventional diamond saws contain diamond grits that are distributed randomly in a metal matrix, as a result, their cutting speeds are slow and their sawing lives are short. In 1997, Dr. James C. Sung applied new patents that revealed revolutionary technology for making diamond tools with diamond grits set in a predetermined pattern. The diamond placement design was first appeared in a series of DiaGrid® products, such as wire saws and grinding wheels. In 1999, DiaGrid® pad conditioners was introduced and it has since become the world's standard for dressing pads, particularly those used for chemical mechanical planarization of semiconductor devices. In 2005, Shinhan adapted the idea and produced saw segments with diamond grits set in a predetermined pattern, their results confirmed that the sawing speed and the life were significantly improved over conventional designs.

Abstract: Amorphous diamond can emit electrons in vacuum when applied with an electrical field of only a few volts per micron. It is also extremely thermionic so the emitted current can increase millions times when heated to only a few hundreds degrees centigrade. As a result, amorphous diamond can be a thermal generator or a solar cell. The energy conversion efficiency can have much higher (e.g. 50%) than that (e.g. 15%) of silicon based solar cells that can absorb only a narrow spectrum of sun light. As a solar cell, amorphous diamond has another advantage that its radiation hardness is the highest of all materials, hence, its thermal electricity efficiency will not attenuate as does the solar cell based on photo electric semiconductorls. An immediate application of amorphous diamond is to coat it on electron emitting electrodes, such as that used as cold cathode fluorescence lamps (CCFL) that illuminate liquid crystal displays (LCD) for fornote books and television sets. Amorphous diamond can dramatically reduce the turn-on voltage to lit CCFL so the lamp life can be greatly extended. Moreover, the electrical current can be increased to enhance the brightness of the light.