Direct bond copper process

Silicon chip on direct-bond-copper substrate. (From Krum, A., Course Notes, UCLA Extension, Engineering 881.152, Power Hybrids Design and Processing, April 3-6,1995, Los Angeles, CA. With permission.)... 

A 0.008 in. thick copper conductor with the same length and width as the thick-film conductor described above is fabricated using the direct bond copper (DEC) process. The resistance is calculated using Equation 8.4 and found to be 16.9 mO ... 

Thick-fihn, thin-film, and copper metallization processes are available for aluminum nitride. Certain of these processes, such as direct bond copper (DEC), require oxidation of the surface to promote adhesion. For maximum thermal conductivity, a metallization process should be selected that bonds directly to AIN to eliminate the relatively high thermal resistance of the oxide layer. 

Cations and anions that adsorb by forming short directional bonds with the surface cannot be considered to be indifferent in character. These ions actually alter the surface charge by the very process of adsorption, and their bonding is classified as chemical adsorption (or chemisorption) in this text. Examples of chemisorption include copper and phosphate adsorption on iron oxides ... 

When aluminum nitride (AIN) is bonded to copper with the DBC process, the surface of the ceramic first needs to be converted with heat and oxygen to alumina. This results in a thin layer (1-2 /xm) of oxygen-bearing alumina. The cross section of copper direct bonded to AIN is shown in Figure 8.11 [11]. The oxidized AIN is then placed in the furnace with the copper foil in the same maimer as with alumina and beryllium oxide. The process flow for DBC on AIN is shown in Figure 8.12. 

In this manner, a film of copper from 5 to 25 mils thick can be bonded to a substrate and a metallization pattern formed by photolithographic etching. For subsequent processing, the copper is usually plated with several hundred microinches of nickel to prevent oxidation. ITie nickel-plated surface is readily solderable, and aluminum wire bonds to nickel is one of the most reliable combinations. Aluminum wire bonded directly to copper is not as reliable and may result in failure on exposure to heat and/or moisture. ... 

Bonding of wafers using direct copper-to-copper interconnections is one of the most well-developed approaches to 3D integration, with Tezzaron producing product prototypes at this time [39-42]. Furthermore, Intel has reported a copper-bonding process compatible with 65-nm technology on 300-mm wafers [37,38]. 

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