Self-Aligned Deposition Process for Ultrathin Electroless Barriers and Copper Films on Low-k Dielectric Films

Abstract

A self-aligned, integrated plating technique based on plasma physics and colloidal-related chemistry is proposed to fabricate patterns of ultrathin ͑р20 nm͒ Co-based barriers and copper films in a selective manner on dielectric ͑HOSP™ and SiO 2 ) films using electroless plating. High-resolution X-ray absorption spectroscopy, transmission electron microscopy, and atomic force microscopy reveal that, once properly pretreated by a gaseous plasma (O 2 or H 2 /N 2 ) and hydrogen peroxide (H 2 O 2 ) in a basic aqueous solution, the dielectric films can adsorb highly populated metallic ͑Ni͒ precipitates of sizes approximately from 2 to 4 nm to catalyze the deposition of electroless Co-based barriers. Finally, the capability of this technique to fabricate ''self-aligned'' patterns of barrier and copper is demonstrated and the importance of the plasma pretreatment and hydrogen peroxide ͑in SC-1 solution͒ is discussed.One solution to improve the performance of microprocessors is the implementation of copper as the interconnect metal and low dielectric constant ͑low-k͒ films as the isolating medium, enabling chips to operate with low resistance-capacitance ͑RC͒ delay and cross-talk noise, and reduced power comsuption. 1 Currently, the copper wire is deposited primarily by electrochemical plating such as electroplating and electroless plating. 2,3 However, because copper is highly diffusive and drifting in the surrounding dielectrics even at low temperatures ͑ϳ200°C͒, 4,5 a highly conducting diffusion/drift barrier layer with substantially reduced thickness typically less than ϳ20 nm must be used to separate the Cu and dielectric films. 6 Apart from sputter and chemical vapor deposited transition metal nitride/ carbide thin films ͑TiN, TaN, TiSiN, TaC͒, 7-10 electrolessly plated metal-based ͑Ni-and Co-͒ barriers are receiving extensive attention because of their proven barrier properties of Cu for dielectric layers and Si, improved gap-filling capability, reduced electrical resistivity, and simplified process flow for Cu deposition. 3,11,12 However, due to the dissimilar surfaces of the substrates ͑dielec-tric and nitride/carbide barriers͒ generally lacking catalytic properties, a seeding treatment or surface modification must be invoked to initiate the deposition of electroless barriers or Cu. Traditionally, predeposition of catalyst is obtained by sensitizing and activating in tin-palladium colloidal solutions, 12 activating in tin-free PdCl 2 acidic solutions, 13 or UV-inducing copolymer-grafting molecular modification, 14 thereby forming disjointed catalytic sites on the surface to be metallized. ͑See Ref. 15 for the general methods to form seed layers for the fabrication of copper circuits.͒ However, the major challenge of using electroless plating for circuit fabrication has been the selective patterning of the seed layer, which is further complicated by the requirement of an underlying diffusion barrier. 15,16 In this regard, we present the design of a simple ͑all-electrochemical integrated͒ process using a seeding pr...

Crystalline and Amorphous Electroless Co-W-P Coatings

“…4,5 In addition, similar studies are the focus of research in many parts of the world. [5][6][7][8] Extensive investigations of the structure of electroless deposited Co 0.9 W 0.02 P 0.08 films and their evolution with thermal annealing have been conducted. [7][8][9] The request of alternatives for electrodeposited chromium brings another aspect of interest in electrodeposited Co-W-P alloy.…”

Characterization of Ultrathin Electroless Barriers Grown by Self-Aligned Deposition on Silicon-Based Dielectric Films

“…16,17 The authors recently developed an electrochemically integrated, selfaligned deposition process for selectively growing metallic ͑nickel͒ seeding particles on silicon-based low-k dielectric layers to induce sequential growth of ultrathin ͑ϳ20 nm͒ electroless Co-W-P barriers and copper films, greatly simplifying the metallization process. 21 As illustrated schematically in Fig. 1, the underlying concept is to exploit plasma treatment in conjunction with colloidal-related chemistry to generate surface active sites that adsorb positively charged metal ions onto negatively charged low-k dielectric films, and then to reduce them to neutral atoms.…”