Electroless Deposition of Thin-Film Cobalt-Tungsten-Phosphorus Layers Using Tungsten Phosphoric Acid (H[sub 3][P(W[sub 3]O[sub 10])[sub 4]]) for ULSI and MEMS Applications

Abstract

This paper describes an electroless deposition method for the formation of thin metallic films that contain mainly cobalt with significant amount of tungsten ͑up to ϳ11 atom % ͒ and phosphorus ͑in the range of 1-3 atom % ͒. The Co͑W, P͒ films can be applied for microelectronics multilevel metallization or for ultralarge-scale integrated ͑ULSI͒ and microelectromechanical systems ͑MEMS͒ applications. The film was deposited from an aqueous electrolyte that contained tungsten phosphoric acid, H 3 ͓P͑W 3 O 10 ͒ 4 ͔, as a source for tungsten. Cobalt sulfate was used as a source for the cobalt ions and sodium hypophosphite as the reducing agent and a source for phosphorus. The Co͑W, P͒ thin films from solutions with tungsten phosphoric acid were studied and compared to Co͑W, P͒ films that had been obtained from solutions wherein the tungsten was supplied by tungstate ions. The use of tungsten phosphoric acid allowed higher tungsten content and lower deposition rate when compared to solutions with Na 2 WO 4 and (NH 4 ͒ 2 WO 4 . The deposition with tungsten phosphoric acid was studied for 20-200 nm thick layers and was found to be reproducible. The deposited layers were bright colored and their specific resistance was in the range of 48-90 ⍀ cm. The process parameters of typical solutions are presented and discussed. The film sheet resistance, composition, and surface morphology are presented for various solutions and process conditions. The deposition process involves several reactions that occur simultaneously and are described in this work. Finally, various applications are proposed for copper metallization as a barrier layer, to confine the copper, or as a capping layer to prevent copper oxidation and improve adhesion of the inlaid copper to upper interlevel dielectric layers.

Characteristics of electrodeposited CoWP capping layers using alkali-metal-free precursors

“…Various metallic films have been proposed as capping/barrier layers, including NiReP [7], CoWP [8][9][10][11][12][13], CoWB [14], NiWB [15], NiCoP [16], CoMoP [17], and so on. These films were formed by using wet chemical methods such as electroless and electro plating.…”

Integration of Low‐ k Dielectric Films in Damascene Processes

“…It can be easily understood that a Cu/metal interface will demonstrate stronger adhesion properties than at the Cu/dielectric barrier interface. SAB techniques based on selective CVD [69,70], electroless deposition [71][72][73][74][75][76], or copper surface modifi cation [77,78] have been studied. However, when SABs are integrated as a stand-alone process above the Cu lines prior the SiOC dielectric deposition, i.e., without any low-k dielectric liner, via over-etching cannot be prevented for misaligned vias.…”

Electrodeposition of CoWP film

“…One of the problems for the use of copper is its oxidation and diffusion into SiO 2 layers, which degrade the electrical performance of the microelectronic devices [14][15][16]. To prevent copper from oxidation and diffusion, barrier/capping layers with dielectric/metallic materials have been introduced [17][18][19][20][21][22][23][24]. The barrier/capping layers should be stable at temperature up to 400 • C and the thickness of the films should be between 50 and 150 nm.…”