Ag Seed-Layer Formation by Electroless Plating for Ultra-Large-Scale Integration Interconnection

Abstract

A high density of Pd catalytic particles is an important factor for obtaining a uniform and continuous Ag seed layer in electroless plating. Adequate surface pretreatment is critical for the formation of such a Pd catalytic particle population. In this study, electroless plating of Ag thin films on TiN substrates was performed using Sn sensitization and Pd activation as pretreatment methods. Sn surface sensitization improves surface wetting and aids in the formation of a Pd catalytic layer in surface-oxidative Pd activation. The Pd activation supported by Sn sensitization also accelerated the formation of a continuous thin Ag film. Furthermore, a thin Ag seed layer deposited on a patterned structure showed excellent conformality. © 2008 The Electrochemical Society. ͓DOI: 10.1149/1.2948365͔ All rights reserved.Manuscript submitted March 26, 2008; revised manuscript received May 29, 2008. Published July 8, 2008 Because chip size has shrunk in ultra-large-scale integration, resistance-capacitance delay has become a critical factor that limits the overall performance of devices.1 Ag is considered to be the ultimate interconnection material in the metallization process of the semiconductor industry due to its very low resistivity, low diffusivity into silicon, and its high resistance against oxidation. 2-4Electroless plating is the autocatalytic process of depositing a metal in the absence of an external source of electric current. In electroless plating, electrons generated by oxidation of a reducing agent on the catalytic surface reduce metal ions.5 Once a continuous metal layer is formed, the metal layer itself acts as a catalyst. [6][7][8][9][10] Electroless plating has high potential for use in the metallization process, especially for the formation of a seed layer for electroplating, due to excellent step coverage, simple processing, low resistivity of the deposited film, and no requirement for an external current supply.11-13 Most work in electroless plating has focused on using this method to form a seed layer for complementary metal oxide semiconductor interconnection. However, there have been few reports about bottom-up filling by Ag electroplating.14,15 Furthermore, no research investigating the use of an electroless plated Ag seed layer for bottom-up filling has been done.In electroless plating, pretreatment steps, where the catalytic particle layer is generated, are very important for obtaining smooth and continuous film morphology. 16 In this study, Pd is adopted as the catalytic material. Pd activation involves the formation of catalytic Pd particles by the reduction of Pd on the substrate surface using electrons generated by the oxidation of the substrate. To obtain a continuously even Ag film, a high density of Pd particles is critical. Sn sensitization is a surface-wetting process that improves the hydrophilic character of various surfaces [17][18][19][20][21][22][23] by the adsorption of colloidal particles a few nanometers in size. In one study, after Sn sensitization, the sample was immersed in a...

Tin Sensitization for Electroless Plating Review

“…Increasing HCl concentration (from 30 to 90 mL/L) did not affect the contact angle as drastically (the contact angle changed less than 10 • ). 17 A minimum contact angle of 20 • was measured for 45 mL/L HCl at 7.0 g/L SnCl 2 . During the exposure time for sensitization, the contact angle decreased in the initial 3-5 min, then stabilized after 5 min.…”

“…During the exposure time for sensitization, the contact angle decreased in the initial 3-5 min, then stabilized after 5 min. 17 Increasing the tin(IV) chloride concentration in the tin(II) and tin(IV) sensitization solution was reported to decrease the minimum contact angle, but not until the contact angle reached a certain value, such as 53 • for the AZ-1350 resist. 16 Addition of aged tin(IV) chloride solution into conventional tin sensitization solution (SnCl 2 -HCl) was studied in detail by contact angle, UV spectral absorption, conductance, and nephelometric measurements of the solutions.…”

Fabrication methods of 3D periodic metallic nano/microstructures for photonics applications

“…Electroless deposition is a wet chemical process where metal is deposited onto the dielectric samples via the redox process i.e. metal ions are reduced via the reduction reaction and deposited onto the sample surface . In general, the dielectric sample to be coated is immersed into the aqueous solution of the corresponding metal salt combining with a reduction reaction catalyst.…”

Electroless Gold Plating on Aluminum Patterned Chips for CMOS-Based Sensor Applications

“…This process has been studied as a replacement of physical vapor deposition of the metal seed layer on a substrate that has a poor step coverage before electroplating some metal interconnects in ultralarge-scale integrated circuit technology. [20][21][22] Although the Au ELP technique has long been known, the traditional Au ELP on the Al surface has complicated steps, and to the best of our knowledge, the formed Au surface has not yet been utilized in the sensor applications. In this research, we have studied selective Au ELP on Al patterns with Pd activation to decrease the contact resistance between single-walled carbon nanotubes ͑SWCNTs͒ and Al contact pads.…”