Electroless Cu for VLSI

Abstract

Interconnection technology is a key factor in the continual advancement of integrated systems. The rapid increase in device density and circuit complexity through scaling demands a similar increase in the interconnection density. Traditionally, this is achieved by reducing the metal pitch as well as gradually increasing the number of interconnection levels. As the width and spacing of interconnections are scaled down to submicron dimensions at the chip level and micron dimensions at the board level, signal delay, crosstalk, electromigration, and stress-induced migration become important concerns.Cu holds promise as an alternative metallization material to Al alloy due to its low resistivity and ability to reliably carry high-current densities. Cu has a bulk resistivity of 1.68 μΩ-cm, whereas Al has a bulk resistivity of 2.65 μΩ-cm. The only metal with a resistivity lower than Cu is Ag. Since Cu has a melting point and atomic weight both higher than Al, it is expected to have better resistance to electromigration, although properties such as grain structure and resistance to corrosion at high temperatures may also affect electromigration characteristics.

Grain nucleation and texture analysis of electroless copper deposition on a palladium seed layer

“…The electroless copper solution was composed of: 1 with glyoxylic acid substituting for formaldehyde. 12,13 Small samples (1 × 1 cm) were exposed to differing bath conditions of pH, temperature, dilution, and time.…”

“…The standard aluminum copper alloy interconnects are incapable of meeting several imminent needs. [1][2][3][4] First, Al-Cu interconnects are susceptible to electromigration due to the higher current densities found in ULSI circuits. 1,5,6 Second, fast switching devices require resistivities below those possible in Al-Cu alloys.…”

“…[1][2][3][4] First, Al-Cu interconnects are susceptible to electromigration due to the higher current densities found in ULSI circuits. 1,5,6 Second, fast switching devices require resistivities below those possible in Al-Cu alloys. 4,7,8 Aluminum alloys also exhibit thermally induced internal stresses which may have significant effects on mechanical stability and reliability, causing stress voiding in multilevel interconnects.…”

High rate of copper electrodeposition from the hexafluorosilicate bath

“…Electrodeposited copper is used in multilayer coatings, and serves as an underlayer before zinc or tin electrodeposition (aiming to alloy them into brass and bronze afterwards). In recent decades electrodeposited copper has been employed in electronics for developing interconnects in ultra largescale integrations (ULSI), as copper possesses higher electrical conductivity, compared to previously used aluminum [2][3][4][5]. Electrodeposited copper is also used in the fabrication of light emitting diodes (LEDs) devices as a supporting metal [6].…”

Evaluation of the initial growth of electroless deposited Co(W,P) diffusion barrier thin film for Cu metallization

“…However, difficulties of implementing Cu metallization include the drift of Cu ions into the inter-level dielectrics (ILDs), the fast diffusion of Cu in Si as well as the creation of electrically active deep level in the energy band gap [1]. Therefore, developing a new diffusion barrier layer between Cu and Si or a new ILD is technologically important [2][3][4][5].…”