Control of Photocorrosion in the Copper Damascene Process

Abstract

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...

Electrochemical Deposition of Buried Contacts in High-Efficiency Crystalline Silicon Photovoltaic Cells

“…In an active semiconductor device such as a PV cell, photocorrosion phenomena may be observed. 34 A further consequence of the numerous handling steps is an increased risk of mechanically damaging the silicon nitride antireflection coating on the front of the PV cell, leading to metal clusters forming on the front of the cell and reduced cell performance. It is therefore likely that a further increase in overall cell performance can be achieved in an optimized and automated production process.…”

Galvanic cell formation: a review of approaches to silicon etching for sensor fabrication

“…Galvanic cell formation is sometimes encountered in open-circuit etching of semiconductors when a metal or another conductor on the wafer also comes into contact with solution. Such effects may lead to unexpected and, in some cases, unwanted results [3]. This paper may help to explain such effects.…”

“…Four holes are involved in this reaction (2) The oxide is, in fact, more complicated than that suggested by (2) [8], [60]. The oxide is dissolved chemically by HF (3) This reaction is mass-transport controlled and its rate depends on the hydrodynamics of the system. In the steady-state, the rates of reaction (2) and (3) are equal.…”

Post‐CMP Cleaning

“…The corrosion inhibitor also helps in avoiding the so-called photoinduced corrosion (Figs. 16.18 and 16.19) [57]. This photoassisted corrosion mechanism results in catastrophic displacement of Cu from the lines connected to the p-doped regions to the lines connected to the n-doped regions as in a solar cell.…”

“…Figure 16.23 shows the typical map of watermark defects and the image of watermarks. Most of the watermarks have a shape of circular droplet of water and dried solute can be seen in defect images [57].…”