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Rhodium film and method of formationRelated Patent Categories: Semiconductor Device Manufacturing: Process, Coating With Electrically Or Thermally Conductive Material, To Form Ohmic Contact To Semiconductive MaterialRhodium film and method of formation description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060160344, Rhodium film and method of formation. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to the field of semiconductor integrated circuits and, in particular, to a novel method for forming high quality rhodium (Rh) films. BACKGROUND OF THE INVENTION [0002] Thin film technology in the semiconductor industry requires thin deposition layers, increased step coverage, large production yields, and high productivity, as well as sophisticated technology and equipment for coating substrates used in the fabrication of various devices. For example, process control and uniform film deposition directly affect packing densities for memories that are available on a single chip or device. Thus, the decreasing dimensions of devices and the increasing density of integration in microelectronics circuits require greater uniformity and process control with respect to layer thickness. [0003] Various methods for depositing thin films of complex compounds, such as metal oxides, ferroelectrics or superconductors, are known in the art. Current technologies include mainly RF sputtering, spin coating processes, and chemical vapor deposition (CVD), with its well-known variation called rapid thermal chemical vapor deposition (RTCVD). These technologies, however, have some disadvantages. For example, the RF sputtering process yields poor conformality, while the spin deposition of thin films is a complex process, which generally involves two steps: an initial step of spinning a stabilized liquid source on a substrate usually performed in an open environment, which undesirably allows the liquid to absorb impurities and moisture from the environment; and a second drying step, during which evaporation of organic precursors from the liquid may leave damaging pores or holes in the thin film. Further, both CVD and RTCVD are flux-dependent processes requiring uniform substrate temperatures and uniform distribution of the chemical species in the process chamber. [0004] Promising candidates for materials for capacitor electrodes in IC memory structures include noble metals, such as platinum (Pt), palladium (Pd), iridium (Ir), ruthenium (Ru), rhodium (Rh) and osmium (Os), as wells as their conductive oxides (for example, ruthenium oxide (RuO.sub.2), iridium oxide (IrO.sub.2) or osmium oxide (OsO.sub.2), among others). Although the above-mentioned noble metals are all physically and chemically similar, platinum (Pt) is most commonly used because platinum has a very low reactivity and a high work function that reduces the leakage current in a capacitor. Platinum is also inert to oxidation, thus preventing oxidation of electrodes which would further decrease the capacitance of storage capacitors. The use of platinum as the material of choice for capacitor electrodes poses, however, problems. One of them arises from the difficulty of etching and/or polishing platinum. [0005] Recently, particular attention has been accorded to rhodium (Rh) as an alternative material to platinum because rhodium has excellent electrical properties which are the result of good electrical conductivity, good conductivity, good heat-transfer properties and high work function. Rhodium films are currently deposited by sputtering, CVD or RTCVD, among others. Although the CVD processing technologies afford good step coverage, as the geometries of the future generations of semiconductors become extremely aggressive, these processing technologies will not be able to afford better step coverage, that is a high degree of thickness and/or uniformity control over a complex topology for thin films of such future generation of semiconductors. [0006] Accordingly, there is a need for an improved carbon-free rhodium film with good step coverage and improved electrical properties, as well as a new and improved method for forming such continuous and smooth rhodium films with good step coverage. BRIEF SUMMARY OF THE INVENTION [0007] The present invention provides a novel method for the formation of rhodium films with good step coverage which may be used as top and/or lower plate electrodes for a capacitor. Rhodium films are formed by a low temperature atomic layer deposition technique using a rhodium gas precursor followed by an oxygen exposure. The invention provides, therefore, a method for forming smooth and continuous rhodium films which also have good step coverage. BRIEF DESCRIPTION OF THE DRAWINGS [0008] FIG. 1 is a conventional time diagram for atomic layer deposition gas pulsing. [0009] FIG. 2 is an elevation view of an atomic layer deposition (ALD) apparatus used for the formation of a rhodium film according to the present invention. [0010] FIG. 3 illustrates a schematic cross-sectional view of a DRAM device on which an upper capacitor rhodium plate will be formed according to a method of the present invention. [0011] FIG. 4 illustrates a schematic cross-sectional view of the DRAM device of FIG. 4 at a stage of processing subsequent to that shown in FIG. 4. [0012] FIG. 5 is an ink copy of a scanning electron microscopic (SEM) micrograph of a rhodium film deposited by a method of the present invention. [0013] FIG. 6 is an illustration of a computer system having a memory device including a rhodium film formed according to a method of the present invention. DETAILED DESCRIPTION OF THE INVENTION [0014] In the following detailed description, reference is made to various specific embodiments in which the invention may be practiced. These embodiments are described with sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be employed, and that structural, logical, and electrical changes may be made. [0015] The term "substrate" used in the following description may include any semiconductor-based structure. Structure must be understood to include silicon, silicon-on insulator (SOI), silicon-on sapphire (SOS), doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. The semiconductor also need not be silicon-based. The semiconductor could be silicon-germanium, germanium, or gallium arsenide. When reference is made to a substrate in the following description, previous process steps may have been utilized to form regions or junctions in or on the base semiconductor or foundation. [0016] The term "rhodium" is intended to include not only elemental rhodium, but rhodium with other trace metals or in various alloyed combinations with other metals as known in the semiconductor art, as long as such rhodium alloy is conductive. [0017] The present invention provides a novel method for the formation of carbon-free rhodium films with good step coverage which could be used, for example, as top and/or lower plate electrodes for capacitors, as fuse elements or as seed layers for electroplating. According to an exemplary embodiment of the invention, rhodium films are formed by a low temperature atomic layer deposition technique using a gas precursor of dicarbonyl cyclopentadienyl rhodium (I) [CpRh(CO.sub.2)] in an oxygen exposure. The invention provides, therefore, a method for forming smooth and continuous rhodium films which also have good step coverage and reduced carbon content. [0018] Continuous and smooth rhodium films formed according to embodiments of the present invention employ atomic layer deposition (ALD) processes for achieving good step coverage. For a better understanding of the formation of the ultra-uniform thin rhodium layers according to the present invention, the ALD technique will be outlined below. [0019] Generally, the ALD technique proceeds by chemisorption at the deposition surface of the substrate. The ALD process is based on a unique mechanism for film formation, that is the formation of a saturated monolayer of a reactive precursor molecules by chemisorption, in which reactive precursors are alternately pulsed into a deposition chamber. Each injection of a reactive precursor is separated by an inert gas purge or a pump cycle. Each injection also provides a new atomic layer on top of the previously deposited layers to form a uniform layer of solid film. This cycle is repeated according to the desired thickness of the film. 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