Selective and Blanket Electroless Copper Deposition for Ultralarge Scale Integration

Abstract

Electroless Cu thermodynamics, electrochemistry, mechanism, kinetics, and mass transport are reviewed. Electroless Cu deposition is a thermodynamically favorable and kinetically inhibited process, with two electrochemical reactions including anodic oxidation of a reducing agent and cathodic reduction of metal ions occurring simultaneously, with a multistep catalytic redox mechanism, an Arrhenius type of rate equation, and mass-transport limited reaction in narrow and deep features such as subhalf micron trenches and vias of high aspect ratios (>3). Selective and blanket electroless Cu deposition from formaldehyde-based solutions with ethylenediaminetetraacetic acid as a complexing agent was investigated for trench/via filling applications. A single-wafer electroless Cu deposition system with up to 8 in. wafer capability has been designed and manufactured. An electroless Cu deposition solution and operation conditions have been optimized to obtain electroless Cu films at high deposition rate (-75 to 120 nm/mm), with low resistivity (p <2 pSi cm), low surface roughness (R, -10 to 15 nm for -1.5 .Lm thick deposits) and good electrical uniformity (std dev <3% for 6 in. wafers and 5 to 7% for 8 in. wafers). A novel dry seeding method on sputtered Cu/Al bilayers has been developed to provide protection of Cu catalytic properties from passivation by using an Al sacrificial layer and to obtain uniform initiation and blanket growth of electroless Cu by in situ Al dissolution in the plating bath. Electroless Cu films blanket deposited on sputtered Cu/Al seed layer were conformal with 100% step coverage. A novel wet seeding method has been developed with Cu contact displacement deposition on a TiN diffusion barrier to provide selective and blanket electroless copper plating. Subhalf micron (down to 0.3 p.m) trenches and vias of high aspect ratios (up to 5:1) were completely filled for both blanket and selective electroless deposition modes. IntroductionCopper is being considered to replace current Al metallization in ultralarge scale integrated (ULSI) technology because of lower resistivity, potentially higher resistance to electromigration, and stress-induced voiding. Cu can be

Electroless deposition of copper in acidic solutions using hypophosphite reducing agent

“…Thin film copper deposition technologies for ultra-large scale integrated technology (ULSI) are being intensively investigated and electroless-plating is one of the routes explored [1][2][3][4][5][6][7][8][9]. Indeed copper offers low specific resistance and high resistance to electromigration [2,3].…”

Electroless Cu deposition process on TiN for ULSI interconnect fabrication via Pd/Sn colloid activation

“…The appropriate pH of the plating bath should range from 11.5 to 12.5, as suggested by the study of Dubin and Shcham-Diamond. 7 Figure 4 illustrates that both the pH of the plating solution and the resistivity of the deposit gradually decrease with increasing temperature. The existence of other impurities usually results in the elevation of resistivity of the deposit.…”

“…The Al sacrificial layer is removed when dipping into the alkaline electroless deposition solution and the exposed Cu seed can serve as a catalyst for subsequent deposition of Cu. Dubin et al 7,8 formed 25-nm Ti, 40-nm TiN, or 40-nm Ta as a barrier layer and sputtered Cu seed as an activation layer for subsequent electroless plating, which comprised TMAH as a pH adjuster. The concentration of each component was also optimized by correlating it with the deposition rate and resistivity.…”

Fabrication of microelectrodes deeply embedded in LiNbO3 using a femtosecond laser

“…femtosecond laser machining [15][16][17][18][19] and good via and trench filling ability of electroless copper deposition [20,21] have been proved. By combining the advantages of these two techniques, geometry-controllable and void-free microelectrodes deeply embedded in LiNbO 3 are demonstrated.…”