Putting the Pedal to the Metal

Without an effective metal layer, any integrated circuit is just a bunch of separate transistors. Novellus Inova Physical Vapor Deposition (PVD) tools are designed for depositing metal films, both copper or aluminum, which form the conductors to interconnect the transistors on the wafer. "As you go to lower node steps 90 nm, 65 nm and so on, the line density goes up," says Dhairya Shrivastava, the director of systems engineering at Novellus. "With thinner lines, we have to be able to deposit thinner metal films. The challenge is to deposit thinner and thinner films inside high-aspect-ratio features."

The Inova NExT PVD tool was developed to address the high-aspect-ratio features in 65 nm and smaller nodes. Two items from the development of the next generation product provide behind-the-scenes insight.

The first key aspect involves materials. Since the process deposits a metal target onto the wafer in a chamber, there are other chamber parts that get coated with metal. Over time, this impacts performance and requires maintenance, otherwise, after a certain thickness, the film starts peeling off and causes defects on the wafer. As a result, PVD modules use shields that are changed at a certain interval.

"We used to have seven shields in the original design and through some creative thinking, we reduced it to two," says Shrivastava. The seven shields were made of stainless steel and were quite heavy. In addition to reducing the number of shields, the next generation PVD approach changed the maintenance philosophy. Previously, the stainless steel shields had to be removed, sent to a supplier to strip the metal, and then reinstalled in a specific orientation. The two replacement shields are made of aluminum and are disposable. In addition to the significantly reduced logistics with the disposable shields, the time between maintenance is the same or even longer.

The second key aspect involves motion control. In the process module, the wafer enters and rests on a platform, called a pedestal. After the robot has put the wafer on

the pedestal, the pedestal moves up to the process position. "Earlier we used to have 160 parts and that has been reduced to 110 parts," says Shrivastava. "We reduced the cost by more than 50 percent."

The original design used a gear head, a separate motor, brake, belt and pulley, and a motion controller. "We went with smart motor technology, where all of these things are built in, and a direct drive," says Shrivastava. "We simplified the design significantly."

Novellus took advantage of the latest available motor control technology to improve the equipment that will make the next generation of semiconductors. In addition to improved performance on several parameters including reduced parts count, lower maintenance and reliability issues, the smaller form factor improved accessibility during maintenance.

For more information about Novellus Inova contact Richard Weinberg, product manager, PVD Products, e-mail: [email protected], http://rbi.ims.ca/4925-502.

For more information about Novellus tools in semiconductor technology, http://rbi.ims.ca/4925-503.