Wednesday, April 26, 2006

Reliability Challenges in Roadmap: Opportunities for Mechanics

Starting from 1998, the microelectronics industry has coordinated an international effort in producing the International Technology Roadmap for Semiconductors (ITRS) as the worldwide consensus on the main trends of technology spanning across 15 years into the future. The participation of experts from Europe, Japan, Korea, Taiwan, and USA ensures that the ITRS is a valid source of guidance for the integrated circuit (IC) industry and the worldwide market. Full revisions of the ITRS were produced in 1999, 2001, 2003, and 2005, with updates in even-numbered years (2000, 2002, 2004). The latest revision, ITRS 2005, consists of an executive summary (101 pages) and 15 Working Group Reports on specific areas (each from 25 to 76 pages).

Among many grand challenges listed in the Roadmap, reliability, both electrical and mechanical, is identified as a key challenge for future technologies in areas ranging from frond-end processes to interconnect and to packaging. Modeling and Simulation, as a crosscut topic, emphasizes more predictive physical models and more efficient simulations to achieve design-for-reliability (DFR). To highlight the principal reliability challenges and to identify the research needs for reliability physics and reliability engineering, an accompanying document, Critical Reliability Challenges for the International Technology Roadmap for Semiconductors, was published in 2003 by the Reliability Technical Advisory Board (RTAB) of SEMATECH (an industry consortium). As stated in the document, “the development of semiconductor technology in the next 7 years will bring a broad set of reliability challenges at a pace that has not been seen in the last 30 years.” Consequently, “a failure mechanism-driven approach must be employed, identifying the potential failures and evaluating their kinetics and impact based on the specific application conditions and requirements of each market segment.”

What can we read from the Roadmap?

We, as applied mechanicians, are well trained dealing with stress concentration, fracture, delamination, and many other deformation and defect mechanisms. These constitute a major portion of the mechanical reliability issues in the Roadmap. Stress and defect play important roles in determining electrical reliability as well. It is noted in the Roadmap that “Meeting reliability specification is a critical customer requirement and failure to meet reliability requirements can be carastrophic.” This in turn requires an in-depth knowledge of the physics of relevant failure modes and powerful engineering capabilities for design-for-reliability, building-in-reliability, and reliability qualification tests. Introduction of new materials and processes, highly complex integrated structures, and continuously shrinking feature sizes bring out the paramount needs for new discoveries and major breakthroughs in reliability physics and reliability engineering. On the other hand, the Roadmap notes insufficient R&D resources in the industry, and promotes cooperation and the most efficient use of existing resources. Together, great opportunities are open for applied mechanicians, most in academia. Several successful stories have been told with mutual benefits to the industry and the academia. The technical committee on Integrated Structures of Applied Mechanics Division is to forge more interactions across the traditional boundary between academia and industry. A time has arrived that the impact of mechanics can shape the future of the technology roadmap.

Here is a short and incomplete list of reliability challenges from the 2005 Roadmap. For more details, read the Roadmap!

· Timely assurance of the reliability of process integration with new materials and structures, including high-k gate dielectric, metal gate electrodes, ultra-thin body (UTB) fully depleted (FD) silicon-on-insulator (SOI) transistors, and multi-gate structures.

· Achieving necessary reliability of interconnects, including copper/low-k, porous low-k, and beyond (e.g., nanowires, nanotubes, optical interconnects).

· Chip-package interaction and its impact on interconnect reliability; co-design of interconnects and packaging.

· Impact of increasing wafer size, lead-free solder joints, 3D packaging, and organic substrates/devices on thermomechanical reliability of assembly and packaging.

· Design and test for reliability

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