Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
2000-05-04
2001-10-09
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C106S003000, C438S692000, C438S693000, C451S041000
Reexamination Certificate
active
06299659
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polishing-material composition that allows highly accurate surfaces to be obtained at high efficiency by polishing. More specifically, the invention relates to a polishing-material composition suitable for polishing steps on insulating films such as silicon dioxide films, silicon nitride films and organic films used in manufacturing processes for LSI devices.
BACKGROUND ART
With the recent remarkable progress in computer-related technology there have been, year by year, advancements in the integration of LSI devices, while the memory capacities of magnetic disks are constantly on the increase; one of the fundamental techniques on which this progress has been based is polishing processing.
In manufacturing processes for LSI devices, polishing techniques for interlayer insulating films have been introduced and are beginning to be employed in practice for the major object of alleviating the problem on depth of focus in the photolithography step that occurs with refinement of design rules. There are also being seen more and more applications of polishing processing techniques such as embedded metal polishing (the Damascene method) for formation of fine wiring and the Shallow Trench Isolation method aimed at achieving separation of elements on narrower surface areas than by the conventional LOCOS (Local Oxidation of Silicon) method, as indispensable elemental technologies for the manufacture of next generation LSI devices. In this field, which involves polishing to miniature elements and wiring structures, high accuracy of finished surfaces is of course a requirement, but high efficiency and stability of the polishing process is also desired.
Polishing interlayer insulating film and Shallow Trench Isolation have been primarily studied using a slurry suspended silicon dioxide fine powder obtained by a gas phase method in an alkaline aqueous solution or a slurry suspended cerium oxide powder in water, whereas metal polishing has been primarily studied using a slurry suspended silicon dioxide powder, also obtained by a gas phase method, or aluminum oxide powder in water, with addition of an oxidizing agent such as iron nitrate or hydrogen peroxide. However, it has not yet been possible to achieve a level which satisfies all of the standpoints of surface-accuracy (or finishing level), polishing rate and stability of polishing rate. In order to achieve a high surface-accuracy it is necessary for the polishing-material particles to have a fineness on the order of submicrons, but smaller polishing-material particles generally result in a slower polishing rate. Thus, there has been a trade-off between surface-accuracy and polishing rate, and it has not generally been easy to achieve both.
Alkaline slurries suspended silicon dioxide fine powders have been used to achieve high surface-accuracy in polishing interlayer insulating film, which has been the most practiced method of polishing for LSI device manufacturing processes, but the low polishing rate has been an inconvenience. The polishing rate generally increases gradually from the start of polishing, tending to stabilize after the course of a given time of usually a few minutes or more; however, since the machining thickness is at most about 1 &mgr;m for polishing in LSI device manufacturing processes, the polishing time most often is on the order of a few minutes. In other words, since the polishing is completed within a start-up region wherein polishing rate is still unstable, a considerable burden has existed in detecting the end point.
In contrast, cerium oxide slurries are advantageous for achieving both surface-accuracy and polishing rate in polishing interlayer insulating film and Shallow Trench Isolation method, but the polishing rate tends to increase with longer polishing time as in the case of silica slurries, and since the higher polishing rate makes it more difficult to detect the end point, this has constituted an obstacle against their practical implementation.
In the Shallow Trench Isolation method, a silicon nitride film is situated under the silicon dioxide film to be polished so that polishing is carried out with the silicon nitride film as a stopper, and therefore it has been necessary to have a fast polishing rate for the silicon dioxide film and a slow polishing rate for the silicon nitride film, or in other words, to have a high “selectivity ratio” which is the value of the polishing rate for the silicon dioxide film divided by that for the silicon nitride film; however, a problem has existed in that both silicon dioxide slurries and cerium oxide slurries have “selectivity ratios” of as low as about 2-6.
As explained above under “Background Art”, it has been strongly desired to realize higher levels of both surface-accuracy and polishing rate, as well as stability of polishing rate, than is currently achieved in polishing steps on insulating films such as silicon dioxide films, silicon nitride films and organic films in manufacturing processes for LSI devices.
The present invention provides a polishing-material composition that can overcome the problems referred to above.
DISCLOSURE OF THE INVENTION
As a result of diligent research aimed at solving the aforementioned problems, the present inventors have discovered a polishing-material composition for polishing LSI devices characterized by a polishing-material composition containing water and cerium oxide which has been surface treated with a coupling agent, the maximum value being no greater than about 5 &mgr;m and the average value being about 0.01 to about 1.0 &mgr;m in the secondary particle size distribution of the cerium oxide; the polishing-material composition for polishing LSI devices characterized in that the primary crystal size of the cerium oxide is about 0.005 to about 0.5 &mgr;m; the polishing-material composition for polishing LSI devices characterized in that the cerium oxide concentration in the polishing-material composition is about 0.01-about 10 wt %; and the polishing-material composition for polishing LSI devices characterized in that the coupling agent is at least one coupling agent selected from among silane coupling agents, titanate coupling agents, zirconate coupling agents, aluminum coupling agents and phosphate coupling agents.
In polishing steps for LSI device insulating films, polishing-material compositions using silicon dioxide as the abrasive grains and polishing-material compositions using manganese dioxide as the abrasive grains have been studied in addition to cerium oxide but, for the present invention, the abrasive grains have been limited to cerium oxide. According to the invention, minimal improvement in polishing performance is achieved when silicon dioxide or manganese dioxide is used as the abrasive grains, and it is not possible to reach a satisfactory level desired for polishing LSI device insulating films.
According to the invention it is possible to realize a high level of both surface-accuracy (or surface finishing level) and polishing rate, as well as stabilization of polishing rate, by creating a condition where the polishing-material particles are strongly held in a polishing-pad during polishing. The polishing-pad is entirely made of resin, and the main polishing-pads used in polishing steps for LSI devices that require high accuracy are dry independent pore-type polyurethane pads produced by casting or slicing (such as “IC1000” by Rodel, Inc.), or nonwoven types prepared by impregnating polyurethane into polyester fibers and dry-foaming (such as “Suba400” by Rodel, Inc.), or two-layer types that are laminates of these two types of pads (such as “IC1000/Suba400” by Rodel, Inc.). Fluorine resin-based pads are also being investigated. Thus, while the pad material is an organic compound, the abrasive grain material used for the invention, i.e. cerium oxide, is an inorganic compound. Surfaces of inorganic compounds such as metal oxides usually have low affinity for and are poorly compatible with the surfaces of organic compounds. It was therefore considered that if
Ichikawa Kagetaka
Kido Takanori
Tsujino Fumio
Uotani Nobuo
Marcheschi Michael
Showa Denko K.K.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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