Compatibility of the Low‐Dielectric‐Constant Poly(arylether) with the Electroless Copper Deposition Solution

Abstract

Multilevel metallization and the interlayer dielectric (ILD) have become the limiting factors in process integration and device performance. A new generation of low-dielectric-constant (low-k) materials are required to achieve advantages in high-speed, low dynamic power dissipation, and low-cross-talk noise. 1-2 To date, many new dielectric materials with dielectric constants smaller than that of conventional SiO 2 have been introduced. 3-6The present work was done in an attempt to evaluate the compatibility between a promising low-k ILD polymer and the electroless Cu deposition solution developed for subquartermicron interconnect applications. 7,8 The low-k polymer selected is the nonfluorinated poly(arylether), PAE-2. 5,9 PAE-2 exhibits a dielectric constant lower than that of SiO 2 , as well as good thermal stability. For exploring the compatibility of PAE-2 with the electroless Cu deposition solution, Fourier transform infrared (FTIR) spectroscopy and ellipsometry were employed to examine possible chemical and physical property changes of the low-k material before and after electroless Cu solution treatments at different solution temperatures and treatment times. Our results show that there is no chemical reaction between this low-dielectric-constant polymer and the electroless Cu deposition solution. However, a significant change in thickness as well as refractive index is induced by the electroless solution treatment. It is demonstrated that the thermal treatment can alleviate the electroless Cu solution-induced effects, as far as the glass transition temperature, the coefficient of thermal expansion, and refractive index are concerned.Experimental The electroless Cu deposition solution (pH 12.3-12.7 adjusted by tetramethylammonium (TMAH)) contained cupric sulfate, ethylenediaminetetraacetic acid (EDTA), formaldehyde, and additives. The additives, including RE-610, Triton, ® and 2,2Ј-dipyridyl, have more than a single effect and serve as surfactants (RE-610, Triton) to control surface tension, stabilizers (Triton, 2,2Ј-dipyridyl x ) to prevent the spontaneous decomposition of the plating solution and a ductility promoter (2,2Ј-dipyridyl) which prevents hydrogen inclusion in the deposit. 8 A detailed composition of the electroless Cu deposition solution is shown in Table I. Generally, the bath of the electroless Cu deposition solution employed in this work is operated at temperatures ranging between 50 and 80ЊC for Cu deposition. Therefore, 57 and 77ЊC were selected as low and high experimental temperatures at which the PAE-2 films supported on Si wafers were investigated. The dielectric samples were immersed in the electroless Cu solution at 57 and 77ЊC, for 5, 10, 15, and 20 min. During the immersion in the electroless Cu deposition solution under the real deposition conditions, Cu deposition did not occur because there was no seed layer initially deposited on the thin polymer films. However, the back side of the Si substrate was not protected by any other film (i.e., SiO 2 ) and slight Cu deposition was o...

Influence of Chemical Pretreatment of Epoxy Polymers on the Adhesion Strength of Electrochemically Deposited Cu for Use in Electronic Interconnections

“…A significant number of publications [15][16][17][18] focus on the influence of the plating bath composition on the properties of the electroless deposited copper and report changes in adhesion due to plating bath composition. The influence of the surface on which the electroless copper is plated on the adhesion strength is however not very clear in these cases.…”