Abrading – Abrading process – Abradant supplying
Reexamination Certificate
1999-11-22
2001-11-13
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
Abradant supplying
C451S165000, C451S041000, C451S289000, C451S102000, C451S099000, C366S114000
Reexamination Certificate
active
06315644
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART STATEMENT
This invention relates to an apparatus and a process for supplying an abrasive to an apparatus for polishing the surface of an object to be polished or workpiece such as wafer to be used as substrate or wafer coated with an insulation membrane or metal membrane to be treated by CMP (chemical and mechanical polishing) in the manufacture of semiconductors.
An advance in the LSI technology has rapidly generated a tendency toward device miniaturization and multi-level wiring in semiconductor integrated circuit. Multi-level wiring in integrated circuit has caused an extremely large increase in unevenness of the surface of semiconductors. In the manufacture of semiconductors, such steps as the manufacture of wafers for semiconductor use and the manufacture of semiconductor integrated circuits by printing circuits on wafers require a planarization technique for flattening the wafers to be used as substrate, the insulation membranes and metal membranes covering a part of the circuits printed on the wafers, and metal wirings. In particular, CMP is available as one of such planarization techniques applicable to an insulation membrane or metal membrane covering a part of the circuit on a wafer or to metal wiring. For example, the CMP technique is applied with the use of an apparatus for polishing the surface of interlayer insulation membranes and oxidation membranes for trench use (SiO
2
) with abrasives, an apparatus for polishing metal wirings and metal membranes (W, Al, Cu) with abrasives, or an apparatus for polishing polysilicon for use in trench and gate electrode with abrasives.
Abrasives useful for polishing the aforementioned workpiece are usually dispersions of abrasive particles based on silica (precipitated silica, fumed silica, colloidal silica, synthetic silica, etc.), alumina, cerium oxide, and zirconia in a variety of dispersion media, the choice depending on the kind of workpiece, the stage of use in the manufacture of semiconductors, and the polishing performance.
In order to polish the surface of workpiece with precision to a specified level, it is extremely important for the abrasive particles to be dispersed homogeneously and stably in a dispersion medium. To satisfy this requirement, a variety of dispersion media have been worked out by adding a third component to a base; for example, a dispersion medium for silica-based abrasive particles was devised by adding a surfactant to an aqueous solution of an electrolyte such as KOH and NH
4
OH and another dispersion medium for alumina-based abrasive particles by adding a surfactant or oxidizing agent to an aqueous solution of H
2
O
2
.
Abrasive particles to be used for polishing the workpiece in the manufacture of semiconductors, however, are extremely fine in the range from 0.01 to 50 &mgr;m and adjusted to have an extremely rigid particle size distribution. A delicate change in the chemical composition of dispersion medium as a result of evaporation while the container is opened in use, a change in temperature during storage of the abrasives, and other factors cause abrasive particles to undergo agglomeration with ease to form abnormally agglomerated particles of a large diameter in excess of a specified range of particle size distribution.
Such abnormally agglomerated particles, when formed in the abrasive, affect the polishing performance against the workpiece to such an extent as to change the polishing speed and cause damages such as scratches on the surface of the workpiece. As a result, they give polished products of inferior quality and lower the yield of acceptable products.
To deal with the case such as the aforementioned, a conceivable procedure would be to remove those particles which are larger than the standard particle diameter (that is, abnormally agglomerated particles and foreign particles) by filtration immediately before the abrasive is put to use. This procedure of filtering the abrasive immediately before use would be desirable as it is able to remove particles larger than the standard diameter with certainty and prevent the generation of polished products of inferior quality as much as possible. In practice, however, the filter clogs in a short time of use and needs to be replaced frequently, which makes it difficult to apply filtration on a commercial scale.
Now, the formation of abnormally agglomerated particles cannot be confirmed unless the surface condition of the product coming out of the polishing step is examined and judged and, moreover, the evaluation of whether the abrasive particles satisfy the standard particle diameter or not immediately before use of the abrasive is unrealistic costwise on a commerical scale.
Still more, it is desirable from the viewpoint of minimizing the manufacturing and transportation cost to prepare abrasives in high concentration and dilute to a specified concentration at time of use. However, agglomeration tends to occur more easily as the concentration becomes higher and, under the present conditions, the reduction of cost by this approach is difficult to accomplish.
OBJECT AND SUMMARY OF THE INVENTION
The present inventors have conducted studies to solve the aforementioned problems relating to abrasives, found surprisingly that an abrasive in which abnormally agglomerated particles have formed after preparation is sonicated by ultrasonic wave thereby nearly selectively deagglomerating the abnormally agglomerated particles without affecting the average particle diameter and particle size distribution of the abrasive particles obtained at the time of preparation (abrasive particles before agglomeration) and restoring the abrasive to have roughly the same average particle diameter and particle size distribution obtained at the time of preparation, and completed this invention.
Accordingly, an object of this invention is to provide an apparatus for supplying an abrasive for use in the manufacture of semiconductors which is capable of supplying an abrasive containing as little as possible of abnormally agglomerated particles to the surface of the workpiece and improving the yield of polished products in the manufacture of semiconductors.
Another object of this invention is to provide a process for supplying an abrasive for use in the manufacture of semiconductors which is capable of supplying an abrasive containing as little as possible of abnormally agglomerated particles to the surface of the workpiece and improving the yield of polished products in the manufacture of semiconductors.
Thus, this invention relates to an apparatus for supplying an abrasive for use in the manufacture of semiconductors comprising a storage tank which stores an abrasive for use in the manufacture of semiconductors and a supply line which guides the abrasive from the storage tank to a nozzle for supplying the abrasive to the workpiece, with a device for furnishing ultrasonic wave provided on the aforementioned storage tank or supply line for the purpose of sonicating the abrasive.
Furthermore, this invention relates to a process for supplying an abrasive for use in the manufacture of semiconductors wherein the abrasive is sonicated by ultrasonic wave before it is supplied to the workpiece.
An abrasive to which this invention is applicable is a dispersion in a specified dispersion medium of extremely fine abrasive particles which are used in surface polishing of the workpiece in the manufacturing step of semiconductors and are normally in the range from 0.01 to 50 &mgr;m and, hence, it is composed of abrasive particles and a dispersion medium. Such abrasive may be prepared in a composition either with a concentration applicable as prepared to the polishing of the workpiece or with a high concentration requiring proper dilution immediately before use.
There is no specific restriction to abrasive particles constituting the abrasive and the following known particles may be cited as examples; silica-based particles such as precipitated silica, fumed silica, colloidal silica and synthetic silica, alumina-based particles, cerium oxide-based p
Cho Toshitsura
Iwashiro Akira
Banks Derris H.
Birch & Stewart Kolasch & Birch, LLP
McDonald Shantese
Tama Chemicals Co. Ltd.
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