Paths to Smaller Features

Ruth DeJule, Associate Editor -- Semiconductor International, 8/1/1999

Optical lithography techniques are continually being explored to achieve smaller geometries while minimizing additional costs.

Mitsubishi Electronic Corp. has developed a coating, AZ R200, to improve the resolution of via holes. The process consists of simple coat, bake and rinse steps. After patterning of the photoresist, an acid is generated that diffuses from the exposed area into the wall of the unexposed area. The coating material is then cross-linked by this acid. Mitsubishi has demonstrated the material to shrink via holes by a factor of 2, from 0.2 mm to 0.1 mm, using existing 248 nm exposure tools and standard photoresists. Effectiveness also has been demonstrated in the i-line exposure range, shrinking 0.35 mm via holes to 0.2 mm. Clariant's AZ Electronic Materials Business is licensed to manufacture and sell the AZ R200 coating.

Contact holes smaller than 70 nm pose a particular challenge. Implementing chemical amplification of resist lines (CARL), a process developed by Siemens AG -- essentially combining top surface imaging (TSI) and bi-layer resist techniques -- has been incorporated into an advanced DUV, 193 nm, photoresist system developed at Infineon Technologies (Erlangen, Germany). The system includes a unique chemical biasing step for definition of very small trenches and contact holes.

Standard binary reticles and a 193 nm stepper with 0.60 NA produced 30 nm contact holes, 633 nm deep, in PETEOS oxide. OMEGA (Trikon, Newport, UK) and the Resist Test Center at International SEMATECH also participated in this project. Clariant is commercializing the CARL photoresist.