Novellus Improves Ashable Hard Masks

Novellus said it has developed a suite of ashable hard mask (AHM) PECVD films with ~25% greater etch selectivity and improved transparency. The platform integrates an EBR capability that completely removes the AHM film within a 1 mm transition zone.

Staff -- Semiconductor International, 11/24/2009

Novellus Systems Inc. (San Jose) said it has developed a suite of ashable hard mask (AHM) PECVD films with ~25% greater etch selectivity and improved transparency. The approach includes an integrated edge bevel removal (EBR) to improve throughputs.

Novellus claims improved etch selectivity with its multilayer films.

At <32 nm design rules, both logic and memory device makers require high-aspect-ratio (HAR) patterning. Compared with traditional photoresists, amorphous carbon films offer higher etch selectivity and superior mechanical properties, resulting in more accurate pattern transfers. Amorphous carbon films also are used for double patterning.

Although increasing the deposition temperature at <32 nm can improve the etch selectivity, it tends to reduce the AHM film's transparency, making alignment more difficult during the lithography steps. Novellus said its AHM films maintain transparency while supporting the higher selectivity needed for HAR patterning. Novellus said it has demonstrated yield improvements of ~7% when the new films are coupled with its integrated EBR technology.

Kevin Jennings, senior vice president for Novellus's PECVD business unit, said the films have high selectivity and low erosion rates, resulting in better critical dimension uniformity (CDU) for HAR features such as contacts. The AHM thickness at the wafer's edge impacts the die yield in that region, requiring a narrow transition zone from full AHM thickness to bare silicon where the AHM is completely removed.

The PECVD films have low erosion rates, resulting in better CDUs for contacts. (Source: Novellus Systems)

Novellus's Vector PECVD platform integrates an EBR capability that removes the AHM film within a 1 mm transition zone, and ensures that the edge die have the required AHM thickness necessary for CDU control, within 2 mm from the wafer's edge, Jennings said.

No additional bevel edge cleaning tools are required. Since the AHM removal is performed outside the deposition chamber, he said it provides improved process and particle control compared with other in-situ edge control techniques.

Jennings said conventional amorphous carbon films deposited at higher temperatures are prone to moisture absorption. The Vector platform improves the hermeticity, incorporating process interfaces that block moisture uptake.