Hillocks which grow on aluminum integratedhyphen;circuit films during the contact alloying process present processing and reliablity problems. Layered Al/Alhyphen;O films, deposited by periodically introducing controlled amounts of oxygen into the aluminumhyphen;deposition chamber, are shown to provide dramatic improvements in posthyphen;anneal filmhyphen;surface topography. Aluminum films, unlayered Alhyphen;O films, and layered Al/Alhyphen;O films were deposited on thermallyhyphen;oxidized silicon wafers in anehyphen;beam system to thicknesses of approximately 1 mgr;m at a rate of 25thinsp;Aring;/s. The films were photolithographically patterned into arrays of 100times;100hyphen;mgr;m bond pads and 7hyphen;mgr;m lines, and annealed in forming gas for 20 min at 530thinsp;deg;C. After these anneals, both aluminum films and unlayered Alhyphen;O films with oxygen concentrations less than approximately 6 at.percnt; had surface protrusions (hillocks and/or whiskers) approximately 1 mgr;m in height. Protrusion density was on the order of 105cmminus;2. Alhyphen;O films with oxygen concentrations greater than 6 at.percnt; displayed blistering and had resistivities greater than twice those of aluminum films. Layered Al/Alhyphen;O films with a structure consisting of four layers of 1000hyphen;Aring; Al/1000hyphen;Aring; Alhyphen;O topped with 2000thinsp;Aring; of Al had no protrusions with heights greater than 0.5 mgr;m for oxygen concentrations in Alhyphen;O layers ranging from 1.5 to 6 at.thinsp;percnt;. Overall compositehyphen;film resistivities ranged from approximately 15ndash;45percnt; higher than aluminum films over this oxygenhyphen;concentration range. Both film surface roughness and the density of hillocks with heights less than 0.5 mgr;m decreased with increasing oxygen concentrations. The thickness of the top Al layer was an important layering parameter; 1hyphen;mgr;m hillocks appearing on bond pads of films with top Al layers either less than approximately 1500thinsp;Aring; or greater than approximately 3000thinsp;Aring; thick. However, the 7hyphen;mgr;m lines were hillock free even for such nonhyphen;optimum layering structures. Al/Alhyphen;O layering also yielded dramatic improvement in posthyphen;530thinsp;deg;Chyphen;anneal topography for films deposited at 4thinsp;Aring;/s in an Shyphen;Gunreg;magnetron sputtering system. The Shyphen;Gun layered films had a generally higher density of short (thinsp;les;thinsp;0.5 mgr;m) hillocks than theehyphen;beam layered films.
展开▼
