A complete abrasive‐free process for fabricating copper damascene interconnection has been developed. The process is a combination of newly developed abrasive‐free polishing (AFP) of Cu and dry etching of a barrier metal layer. A new aqueous chemical polishing solution and a polyurethane polishing pad produce complete stop‐on‐barrier characteristics of Cu polishing. The AFP provides a very clean, scratch‐free, anticorrosive polished surface, and the total depth of erosion and dishing is reduced to less than one fifth of that produced by conventional slurries, even after 100% overpolishing. The barrier metal is successfully dry etched by using SF6 gas at a high selectivity ratio (more than 10) of barrier metal to SiO2 . It was found that the developed AFP significantly reduces both Cu line resistance and its deviation. Moreover, AFP can also contribute to cost reduction of chemical mechanical polishing and help solve environmental problems related to waste slurries. © 2000 The Electrochemical Society. All rights reserved.
Copper (Cu) corrosion during chemical mechanical polishing (CMP) was controlled in order to improve the Cu damascene interconnect process. Slurry chemical corrosion was found to be enhanced when the slurry was diluted by deionized (DI) water during rinsing just after CMP. Since the corrosion inhibitor, benzotriazole (BTA), reduces the Cu removal rate, adding it to the rinse solution prevents chemical corrosion more effectively than adding it to the slurry. On the other hand, galvanic corrosion occurs at the interface between Cu and the barrier metal, and it can be prevented by selecting appropriate barrier metals. Because the difference between the electrochemical potentials of Cu and the barrier metal is small in the slurry, refractory metals such as Ta, TaN, and TiN were found to be appropriate barrier metals. On the other hand, W, WN, and Ti have large potential differences, so galvanic corrosion was clearly observed when Cu/W damascene interconnects were fabricated.
The use of highly packed multilevel interconnections with low resistance and low parasitic capacitance has attracted much attention as a method for increasing operating speed of ultralarge scale integrated circuits (ULSIs). 1 Copper (Cu) metallization has been intensively studied for increasing current density as well as reducing the resistance of interconnections and is going to be put to practical use. 2,3 The damascene process is expected to be very promising for producing fine Cu lines, 4 and the key to establishing this process is chemical mechanical polishing (CMP) of Cu and barrier metals. Slurries for Cu CMP usually contain an oxidizer, abrasive powder, etching chemicals of Cu or Cu oxide, and an inhibitor when necessary. 5,6 Kaufman et al. proposed a mechanism of tungsten CMP, a mechanism thought to be common to many kinds of metals, i.e., oxidation of the metal surface, removal of the oxide on protruding areas by abrasive particles in the slurry, and reoxidation of the exposed metal surface. 7 In order to provide damascene metal lines of high accuracy and at a high yield, the optimization of chemical characteristics of slurries and the CMP conditions have been investigated for achieving a large removal rate while suppressing dishing and erosion. 8 The Cu films, however, are very quick to corrode or be etched, especially in a wet-chemical environment. Two types of corrosion are known to occur during Cu CMP. One is chemical corrosion due to the chemical reaction of Cu with chemicals in the slurry, and the other is galvanic corrosion that occurs when two electrochemically different metals are electrically connected and exposed to the same electrolyte. Since these types of corrosion would result in pattern defects and loss of metal thickness (resistance increase), the chemicals of the Cu CMP slurry must be chosen carefully.This paper reports on the investigation of corrosion induced by Cu CMP slurries and describes a new mode of corrosion called pattern-specific corrosion. This paper also clarifies that this corrosion is due to photoillumination during interconnection fabrication; 9 thus, it may also be called photocorrosion. 10 Experimental CMP conditions and slurries.-A dead-weight-type CMP apparatus with an 18 in. diam platen was used with a grid-grooved, foamed polyurethane polishing pad (IC1000, Rodel Co.). The linear velocity of the wafer center to the polishing pad was varied from 25 to 50 m/min, and the down forces were varied from 140 to 210 g/cm 2 (13.7-21.6 kPa). Two kinds of alumina-based slurries were prepared. Slurry A is a mixture of hydrogen peroxide solution (H 2 O 2 , 30 wt % in water) and a commercially available, alumina abrasive suspension (QCTT1010, Rodel). The hydrogen exponent pH of the suspension is about 4.5. Though the suspension is an old one, it was chosen because it has been widely used as the standard suspension commercially available. The recommended mixing ratio of QCTT1010 to H 2 O 2 is 7:3 (volume ratio). Slurry B is a mixture of H 2 O 2 and an experimental alumina abrasiv...
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