TSMC : Foundry Watch

Low-K Dielectrics: Key to Success at 90 Nanometers and Beyond

As the semiconductor industry's process technology leader, TSMC has frequently spearheaded advancements by skillfully leveraging its own R&D resources and the world-class expertise of its material suppliers, IC designers or service alliance partners. These collaborative efforts were never more apparent than TSMC's recent successful deployment of low-K technology at nanometer nodes.

At today's scaled down IC processes geometries (i.e.; 0.13-micron and below), integration of new thin layers of low-K insulation dielectric film material and copper interconnects is a prerequisite to improved transistor performance that can move electronic signals at multi-gigahertz speeds. The superior properties of low-K material are key to insulating each transistor and adjoining circuits from each other, thus minimizing the delay and "drag" on signals traveling through microscopic wires.

While the rest of the foundry industry wrestled unsuccessfully with the many issues of low-k qualification at 0.13-micron, TSMC conducted and completed unprecedented qualifications at the process, product and package levels, and now offers low-K insulation and copper interconnects with the world's most advanced process technologies. These breakthroughs have made it possible to more than double effective chip performance while substantially reducing overall power consumption.

The road to success was circuitous, and the challenges many. Ultimately, the integration of low-K intermetal dielectric (IMD) hinged on partnerships with an ASIC vendor who was familiar with the product aspects of a competitive manufacturable interconnect infrastructure, and a material vendor who thoroughly understood the vagaries of low-K film.

In the material selection process, TSMC determined that the mechanical strength of Applied Materials' Black Diamond CVD low-K film - four times the hardness of spin-on approaches - made it resistant to fracture and damage during critical CMP and packaging. Further tests demonstrated thermal expansion properties comparable to copper, solving heat-related shrinkage, expansion, and thermal cycling issues. With 100% better thermal conductivity than spin-on films, Black Diamond proved to dissipate heat effectively, eliminating copper electromigration. The film also exhibited stability throughout the manufacturing process, including resistance to moisture and plasma attack.

ASIC vendor LSI Logic also played a major role as it worked with TSMC to overcome Cu/low K integration challenges for their Gflx (110nm) ASIC technology. Performance improvements were dramatic, from 8% to 13% depending on the interconnect length of the critical data path. In addition, low-K technology provided better signal integrity due to lower cross-talk coupling. Both LSI Logic and TSMC took added extensive packaging qualification with its assembly vendors before announcing the qualification of its low-K process.

Other lightning-fast TSMC-manufactured designs followed. ATI's Radeon 9600XT graphics accelerator, Agere's DSP16411 chip and Altera's leading FPGAs all now deliver the low-K benefit of faster operation to performance-hungry users.

Today, TSMC is the leading high volume producer that wafers combine copper and low-K dielectric film. The company ship more than 10,000 wafers last year and has shipped an additional 10,000 wafers in the first quarter of this year. Yields on these wafers and their manufacturing cycle times now rival those of wafers using traditional dielectrics. As the only foundry company to successfully qualify all-copper and low-K chips at 0.13-micron, TSMC finds itself in the unique position of having a lot of experience and no new materials to qualify at 90nm.

As a consequence, TSMC is the first foundry to complete 90-nanometer process and product qualifications, and package evaluation for large die sizes.

Ongoing development and collaboration by chipmakers worldwide will enable low-K technology to successfully overcome challenges that for many years were daunting for some companies and unsolvable for others. But it will also take teamwork, perseverance, and collective innovation for top semiconductor companies to gain market advantage with low K technology in a broad spectrum of products. With TSMC blazing a low-K dielectric trail with its industry partners, the precedent for success has been established at 90nm and beyond.