1. Field of the Invention
The present invention relates to a slurry recycling apparatus and method for a chemical-mechanical polishing technique (hereinafter referred to as a CMP technique).
2. Description of the Related Art
A CMP technique is employed for polishing semiconductor wafers and for obtaining planer surfaces thereof.
To polish an object (particularly, the semiconductor wafer, etc.) with the CMP technique, the object is pressed against a polishing pad, and the object and the polishing pad are rotated and moved relatively. A chemical solution, that is, slurry for polishing is supplied onto the polishing pad so as the object to be polished.
A by-product, and changes in a chemical composition and a pH of the slurry which are produced and caused during the polishing process entail a drawback that the object is not satisfactorily polished. Therefore, slurry which has optimum chemical properties such as concentration, pH, etc. needs to be supplied onto the polishing pad.
For the above-described reasons, new slurry is always supplied onto the polishing pad, resulting in consuming a large amount of slurry. However, slurry is expensive, therefore, various techniques have been proposed for recycling used slurry.
In the technique disclosed in Unexamined Japanese Patent Application No. H2-257627, the slurry is recycled by an apparatus having a structure shown in FIG. 5.
As shown in FIG. 5, slurry used in a polisher 101 is collected into a tank 103 via a tube 102. After silica contained in the used slurry is removed therefrom by a centrifugal separator 104 connected to the tank 103, the slurry is supplied back to the tank 103.
In order to recycle the used slurry, undiluted slurry having a high concentration is supplied into the tank 103 from an undiluted slurry tank 105, whereas water, etc., is supplied from a solvent tank 106 into the tank 103. An amount of undiluted slurry and water, etc., to be supplied is controlled based on a concentration of the slurry in the tank 103. The concentration of the slurry in the tank 103 is measured by a ultrasonic propagation speed measuring device 107. The slurry recycled within the tank 103 is supplied to the polisher 101 via a tube 109 by a pump 108.
In the technique disclosed in Unexamined Japanese Utility Model Application KOKAI Publication No. H5-49257, the used slurry is collected into a recycled fluid storage tank. In this case, a flow rate and a concentration of the used slurry are measured. Based on this measured result, an amount of coolant (a surface-active agent, a rustproof agent, a fluid addition agent, etc.) is supplied into the recycled fluid storage tank. Hence, the used slurry is recycled in the recycled fluid storage tank, and the recycled slurry is supplied therefrom to a polisher.
In the technique disclosed in Japanese Patent Application No. H10-58314, the slurry is recycled by an apparatus having the structure shown in FIG. 6.
A semiconductor wafer is placed with force on a polishing pad 201 and is made to rotate by a carrier 203 which is mounted with a shaft 202. Slurry 204 is supplied onto the polishing pad 201 from a tube 205 and is applied to polish the semiconductor wafer so as to be caught by a catch ring 206. The used slurry caught by the catch ring 206 is collected in a manifold 208 via a tube 207. New slurry is supplied into the manifold 208 via a tube 209, chemical components for recycling is supplied via a tube 210 and nonionic water is supplied via a tube 211. The new slurry, chemical components and nonionic water are added to the used slurry in the manifold 208 so as the slurry to be recycled.
The recycled slurry heats up or cools down at a predetermined temperature by a heat switcher 212. Afterward, the recycled slurry is measured and analyzed by sensors 213 to 215. An amount of new slurry, chemical components and nonionic water to be supplied is controlled by the measured and analyzed results of the sensors 213 to 215.
Further, the recycled slurry is filtered by a filter 216 and supplied onto the polishing pad 201 via the tube 205.
In the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H10-118899, the used slurry is concentrated by means of a ultrafiltration (UF) unit employing a ultrafilter. In such a case, a concentration of the concentrated slurry is measured, and if the concentration thereof is equal to or above a predetermined value, an alkali agent or an acid is added to the concentrated slurry. The used slurry which has been recycled in such a manner is once stored in a polishing agent bath and supplied to a polishing apparatus.
However, the above-described techniques entail problems described below.
According to the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H2-257627, there is provided a single tank (tank 103) for collecting the used slurry. Thus, while the used slurry is being recycled, more used slurry is continuously supplied into the tank 103. That is, collection of the used slurry and adjusting (recycling) the concentration of the slurry are parallelly and continuously performed. Accordingly, the used slurry and the centrifuged slurry each having various concentrations exist within the tank 103. This causes a drawback that adjusting the concentration of the slurry delays and the concentration thereof is hardly stable.
In addition to the above, the slurry is supplied to the polisher 101 from the tank 103 containing the used slurry together with the recycled slurry, that is, adjusting the concentration of the slurry (recycling the slurry) and supplying the slurry are parallelly and continuously performed. Hence, the slurry which has not been satisfactorily recycled may be supplied to the polisher 101, therefore, the to-be-polished object is polished with a low degree of accuracy.
In the technique disclosed in Unexamined Japanese Utility Model Application KOKAI Publication No. H5-49257, the flow rate and the concentration of the slurry to be supplied into the recycled fluid storage tank are measured, however, the concentration of the slurry recycled in the recycled storage tank is not measured. As a result of this, the concentration of the recycled slurry is not recognized. That is, even if the concentration of the recycled slurry does not satisfy a predetermined value, the slurry concentration value is not detected. Therefore, the concentration of the slurry may become unstable.
In the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H10-58314, each amount of new slurry, chemical components and nonionic water to be supplied into the manifold 208 is adjusted on the basis of the chemical properties and the concentration of the already-recycled slurry. However, the concentration of the slurry to be collected into the manifold 208 from the catch ring 206 is not constant, so that the concentration and the chemical properties of the to-be-recycled slurry are not stable. Accordingly, the to-be-polished object may not be preferably polished.
In the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H10-118899, the used slurry is concentrated by means of the ultrafiltration unit, thus, the alkali agent contained in the slurry is removed. Thus, the alkali agent needs to be added to the concentrated slurry, and it is required to arrange an apparatus for monitoring the addition amount, etc. This entails a problem that the structure of the recycling apparatus becomes comnplicated.
The recycled slurry is once collected in the polishing agent bath, and its concentration is not checked therein. The concentration of the slurry supplied to the polisher changes, without being detected. Therefore, the to-be-polished object may not preferably be polished.