Many researchers have used a dry etch gas mixture of Ar and Cl 2 to form patterned platinum structures for semiconductor processing applications. 1 This process invariably produces sidewall redepositions (SRDs) or "fences" on the features. 2,3 It is believed that these residues contain Pt, PtCl x , PtO y , TiO 2 , and organic material. The TiO 2 and organic species are believed to result from sputtering of the barrier layer and photoresist on the wafer surface during the etching. It is believed that an increase in Ar concentration in the gas mix helps achieve a better vertical profile on the structure. The solubility of the SRDs in aqueous solution decreases with an increase in Ar concentration in the gas mix. It has been shown that a 30% HCl solution can be used to dissolve some SRDs but that the composition of the etch gas influences the residue removal by this method. Specifically, complete elimination of Cl 2 from the dry etch gas mix results in "insoluble" SRDs. 3,4 If the amount of Cl 2 gas in the mix is less than 20%, SRDs formed on the features are difficult to dissolve. 5 Higher Cl 2 content in the dry etch gas mix results in SRDs which are soluble in dilute HCl solutions or water after etching and are soluble in 12 M HCl after oxygen plasma ashing. 1,4,9 The goal of this paper is to explain the process by which these SRDs can be removed using either a wet or a dry clean process. Wafers etched in an 80/20 Ar/Cl 2 gas mix to form patterned bottom platinum electrodes for an embedded DRAM-type (dynamic random access memory) application were obtained from Motorola. Significant amounts of SRDs were found on all the Pt structures on all the wafers. Previous work has shown that the 80/20 ratio of Ar/Cl 2 tends to produce "insoluble" SRDs. 5 In the present study we have used various techniques to identify a removal mechanism for the SRDs, including dry heating in various ambients and wet cleaning in aqueous solutions. Also, ultrasonic cleaning has been employed to aid in the removal of these SRDs. ExperimentalPatterned 200 mm wafers with features containing platinum SRDs were provided by Motorola. These features and the residues were subject to oxygen plasma ashing before they were made available for the cleaning studies. The photoresist used in the patterning of the features was IX500EL resist from JSR Electronics. The resist was nominally 1.1 m thick prior to patterning. Platinum features that were analyzed ranged from 5-8 m in size. Samples were analyzed by scanning electron microscopy (SEM) using a JEOL JSM-840 microanalyzer before being cleaned. A cross-sectional view of the layers present on a typical sample is shown in Fig. 1.A representative micrograph of a platinum feature with SRDs is shown in Fig. 2. The small black circle on this figure indicates the spot where an EDX (energy-dispersive X-ray) spectrum was taken. These spectra were used for purposes unrelated to this manuscript. In all SEM images in this manuscript, the light-colored material around the edges of the features is the SRD.Samples were t...
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