Pt Film Growth with Tetra-Kis(Triflurophosphine)Platinum
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Y.-M. Sun, J. Lozano, N. Mettlach, J. G. Ekerdt, S. Madhukar' and R. L. Hance" and J. M. White Texas Materials Institute The University of Texas at Austin Austin, TX 78712 "Embedded Systems Technology Laboratories Motorola, Austin, TX 78721 ABSTRACT
Platinum film growth using Pt(PF 3)4 precursors was investigated. The study focused on three aspects of film growth: conformality, adhesion and selective growth. Pt(PF 3)4 deposited pure Pt films over a wide range of temperatures (-200 to 400 °C). At 200 °C, the step coverage for a via with an aspect ratio of three was poor. Lower growth temperatures showed a significant decrease in the growth rate. In addition, these films had poor adhesion to the substrate as indicated by separation between the Pt and the substrate in cross sectional scanning electron microscopy images. Oxygen addition during Pt film growth from Pt(PF 3)4 improved both film conformality and adhesion. With oxygen, the step coverage on the side wall was greater than 90 %. The dependence of the film growth rate on oxygen varied with the growth temperature: the growth rate decreased at 200 °C, while it changed slightly at 260 °C when oxygen was added. The substrate effect on the initial growth rate was studied on various substrates. The initial growth rate on metals is much faster than that on other substrates. The growth rate decreased on various substrates in the order of iridium > titanium nitride > barium strontium titanate > silicon nitride > silicon oxide. INTRODUCTION
The unique physical and chemical properties of noble metals, such as high melting temperatures, high oxidation resistance, and good electrical conductivity, make them ideal candidates for barrier and electrode materials in microelectronic devices [1-3]. Platinum, which has a high work function and excellent electrical properties, is one of the promising candidates. In most studies, the metal electrode has been deposited by ion sputtering methods [4-6]. Metalorganic chemical vapor deposition (MOCVD) may serve as a better way to form the electrodes. MOCVD has the advantages of relatively low deposition temperature, high growth rate, conformal growth and selective area growth [7]. Through a selective area growth process the difficulty of the dry etching step can be avoided. One potential precursor, Pt(PF3 )4 , is a liquid at room temperature and has a vapor pressure of 25 Torr at 25 °C. It is stable in dry air up to 130 °C, but decomposes at much lower temperatures if moisture is present. Rand et al. [8] reported the first MOCVD of platinum films using Pt(PF 3)4 at atmospheric pressure with a H2 carrier gas, substrate temperatures between 200 and 300 °C, and a source temperature of 0 °C. The film resistivity was 18 laiQ-cm as compared to 10 IIQ-cm for bulk platinum. Morabito and Rand [9] studied the depth profile of as-deposited platinum films on Si using Auger electron spectroscopy and secondary ion mass spectroscopy, and found that there was a high concentration (10-20 at. %) of phosphorus at the top surface, decreasing rapidly to -
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