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Methods for a Cu ABM to reduce low-k dielectric delamination

IP.com Disclosure Number: IPCOM000101592D
Publication Date: 2005-Mar-16
Document File: 9 page(s) / 196K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed are methods for the copper (Cu) alternative bump metallurgy (ABM) to reduce low-k dielectric delamination. Benefits include improved functionality, improved performance, and improved reliability.

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Methods for a Cu ABM to reduce low-k dielectric delamination

Disclosed are methods for the copper (Cu) alternative bump metallurgy (ABM) to reduce low-k dielectric delamination. Benefits include improved functionality, improved performance, and improved reliability.

Background

      Low-k dielectrics, such as carbon-doped oxide (CDO), can delaminate and result in device failure. This problem is especially significant for porous polymer-type low-k dielectric materials. Delamination is typically caused by the concentration of stress under the Cu pad after chip joining ((see Figure 1). A feasible solution is required for improved reliability and for the implementation of lead-free solder, which is expected to replace conventional tin-lead (SnPb) solder.

General description

              The disclosed methods are for Cu ABM. The first method forms a cavity in the Cu bump. The second method forms a cavity below the Cu bump. In both cases, the cavity is filled with a low-rigidity material. As a result, the bump is flexible enough to accommodate the coefficient of thermal expansion (CTE) mismatch stress, thereby reducing low-k delamination.

Advantages

              The disclosed method provides advantages, including:

•             Improved functionality due to forming a cavity inside or below a bump to fill with a more flexible material

•             Improved performance due to improving the CTE mismatch

•             Improved reliability due to improving the elasticity of the Cu bump and preventing delamination

Detailed description

      The disclosed methods are for Cu ABM and form a cavity either inside or below a Cu bump and fills it with a more flexible material. As a result, the resultant bump is very flexible and much less rigid than the pure Cu bump (Cu has an elastic modulus of about 130 GPa, 6 times higher than a Pb-3Sn die bump).

The first design is shown in Figure 2, in which a cavity forms inside a Cu ABM.

      Under the action of external forces due to CTE mismatch, the cavity wall Cu and low rigidity material function as three elastic springs to accommodate the CTE mismatch stresses (see Figure 3). The elastic springs represent the cavity wall and the low-rigidity material in parallel. Critical parameters include t1 and t2 for the cavity. Much less stress is transferred to the interlayer dielectric (ILD) region (see Figure 1 and 2). The dimensions of the cavity and cavity filling materials must be optimized based on modeling and experimentation (see Figure 4).

      The cavity can be fabricated using standard photolithography, Cu plating, and chemical-mechanical polishing. Thes...