a-C:F Carbon: A Robust Low-K Material

Peter Singer, Editor-in-Chief -- Semiconductor International, 10/1/1998

Fairchild Technolgies (Fremont, Calif.) received an award from SEMATECH honoring its achievements in standards criteria on the PR800 cluster tool for photoresist processing, including 40% improvement in CD control and 20% improvement in coat uniformity. Fairchild also opened a new facility in Fremont.

Mattson Technology (Fremont) announced a strategic relationship with Sandia National Laboratories to license advanced technology for Mattson's rapid thermal processing system, the Aspen RTP. The agreement resulted from a preliminary joint development project that extended over the past year, along with a concurrent global joint development program.

Rockwell Automation, a business of Rockwell International based in Milwaukee, Wis., plans to acquire Anorad Corp. (Hauppauge, N.Y.), a manufacturer of microposition equipment.

Peter Singer, Editor-in-Chief

  a-C:F Carbon: A Robust Low-K Material

At the upcoming International Electron Devices Meeting (IEDM), to be held in San Francisco, Calif., Dec. 6-9, Bell Labs researchers will report new insights into a promising a low-k material - fluorinated amorphous carbon (a-C:F) - that they claim has resulted in a "robust" film with good thermal stability, k<2.8 and "materials and electrical properties that meet stringent requirements for device integration. At IEDM, researchers from NEC and Applied Materials also will report on the successful integration of "highly stable" a-C:F film in a 0.18 µm CMOS process.

The Bell Labs researchers said a-C:F films are attracting attention because of their unique amorphous C-C crosslinked structure and the same C-F bonds found in low-k organic polymer PTFE or Teflon. "The strong C-F bonds decrease the dielectric constant, and the C-C crosslinked structure maintains the thermal stability," said W. Zhu and coworkers in a paper preprint.

At Bell Labs, a-C:F films were deposited by co-sputtering from Teflon and graphite targets. The researchers said that although the sputtering process is intrinsically difficult for gap-fill applications, it can fit nicely in the damascene integration flow, which eliminates the gap-fill requirement of low-k materials. Also, the results of fundamental understanding obtained are applicable to any deposition method (including CVD), as long as it produces a-C:F with the proper carbon structure.

With a substrate temperature of 350°C, films containing 45% fluorine with a dielectric constant of 2.7 were deposited successfully. These films are thermally stable up to 425°C (weight loss <3%).

The NEC and Applied Materials work focused in general on the integration of a-C:F in a 0.18 µm CMOS process and more specifically on two different annealing processes. The films, deposited by HDPCVD, were annealed using post and cap annealing. Post annealing, they said, has the advantage of reducing residual gas in a-C:F IMD, thus improving thermal stability. The cap anneal test was performed in order to simulate subsequent thermal exposure. The end result was 22% improvement in RC delay (measured by a ring oscillator) compared to SiO₂ film.

  Motorola Develops 0.18 µm Cu Process

Motorola will discuss details of a high-performance 0.10 µm CMOS process with six levels of scaled copper interconnects at the upcoming IEDM.

On the front end, the Motorola used CMP planarized shallow trenches with optimized high-energy retrograde well profiles to provide good electrical isolation down to active spacings of 0.175 µm. Dual-gate poly transistors with 3.0 nm physical gate oxides were formed using retrograde channel doping, shallow As and BF₂ source/drain extensions and tilt B and P halos. Reduced thermal cycles were employed to mitigate transient enhanced diffusion effects.

On the back end, scaled interconnects with a low-k (k <3.5) dielectric material were integrated into the process, with >15% linear shrink compared to the previous copper process.