Method of forming noble metal contacts

#Miniaturization of the front-end of the wireless transceiver offers many advantages including cost, the use of smaller number of components and added functionality allowing the integration of more functions. Micro-electromechanical system (MEMS) is an enabling technology for miniaturization and offers the potential to integrate on a single die the majority of the wireless transceiver components, as described by a paper by D.E. Seeger, et al., presented at the SPIE 27th Annual International Symposium on Microlithography, Mar. 3-8, 2002, Santa Clara, Calif., entitled “Fabrication Challenges for Next Generation Devices: MEMS for RF Wireless Communications”.

#A micro-electromechanical system (MEMS) switch is a transceiver passive device that uses electrostatic actuation to create movement of a movable beam or membrane that provides an ohmic contact (i.e. the RF signal is allowed to pass-through) or a change in capacitance by which the flow of signal is interrupted and typically grounded.

#Competing technologies for MEMS switches include p-i-n diodes and GaAs MESFET switches. These, typically, have high power consumption rates, high losses (1 dB or higher insertion losses at 2 GHz), and are non-linear devices. MEMS switches on the other hand, have demonstrated insertion loss of less than 0.5 dB, are highly linear, and have very low power consumption since they use a DC voltage and an extremely low current for electrostatic actuation. These and other characteristics are fully described in a paper by G.M. Rebeiz, and J.B. Muldavin, “RF MEMS switches and switch circuits”, published in IEEE Microwave, pp. 59-71, December 2001.

#The accompanying drawings, which are incorporated in and which constitute a part of the specification, illustrate presently preferred embodiments of the invention and, together with the general description given above and the detailed description of the preferred embodiments given below; serve to explain the principles of the invention.

#FIGS. 1a-1f are schematic diagrams of a cross-section of a first embodiment of the invention illustrating the process steps detailing the formation of a raised noble contact fabricated by blanket noble deposition and chemical mechanical planarization.

#FIGS. 2a-2f are schematic diagrams of a cross-section of a second embodiment of the invention illustrating the process steps detailing the formation of a raised electrode fabricated by selective electroplating of the noble contact.

#The invention will now be described with reference to FIGS. 1 and 2 by first discussing the integration and fabrication of the lower switch contact.

#Two different approaches are used to deposit the contact material: blanket deposition methods and selective deposition methods. In one embodiment, a raised noble contact is formed by a blanket noble metal deposition and chemical mechanical planarization. A copper Damascene level is first embedded in silicon dioxide. The copper electrodes (11, 12, 13, and 14) are capped by a silicon nitride layer (10), typically, 500-1000 Å thick. Silicon oxide layer (20) having, preferably, a thickness of 1000-2000 Å is deposited thereon, is shown in FIG. 1a. Etching, preferably by way of photolithography and RIE (reactive ion etching) forms a contact pattern (15) into the oxide (20) and nitride layers (10) exposing copper (12), as shown in FIG. 1b. Next, a thin barrier layer is deposited by PVD, (physical vapor deposition) or CVD (chemical vapor deposition) such as Ta, TaN, W or dual layers, such as Ta/TaN, typically 50-700 Å thick (30, FIG. 1c). A blanket noble metal is deposited by PVD, CVD, or electroplating (40, FIG. 1c). The noble metal is shaped by a chemical-mechanical planarization process (CMP) stopping at the barrier metal Ta, TaN, W (30, FIG. 1d). Alternatively, if the noble metal CMP is not selective to the barrier layer metals the polish process can be stopped on the dielectric layer 20 which is not integral to the completed device. Noble metals that can be shaped by chemical-mechanical planarization (CMP) include Ru, Rh, Ir, Pt, and Re. Next, if required, the barrier metal (30) is removed in the field area by CMP stopping on silicon dioxide as shown in FIG. 1e. Silicon oxide (20) is removed by reactive ion etching stopping on silicon nitride (10) to yield a raised noble metal lower electrode (50, FIG. 1f).

#In another embodiment, the raised electrode is formed by selective electroplating the noble contact. Selective electrolytic plating in the presence of a barrier layer has been discussed in U.S. Pat. No. 6,368, 484 to Volant et al. and, more specifically, the selective electro-deposition of copper in Damascene features. The inventive method differs in that it forms a raised noble metal contact by selective electrodeposition through a mask.