NEC Electronics Announces Development of Novel Resistivity Measurement Technique for High Reliability in Automotive Applications in the 32-nm Node and Beyond

Verification of CoWP Identified as a Viable Candidate for Interconnect Cap Layers

NEC Electronics has developed a novel measurement technique that will enable a dramatic increase in the reliability of automotive LSI devices manufactured with next-generation 32-nanometer (nm) node processes. The technique provides accurate measurements of resistance in the interconnects that connect transistors in LSI devices, even at the very small scales that will be found in next-generation devices. Using this technique, NEC Electronics has verified that metal-capping layers can extend the lifetime of the interconnects in next-generation automotive LSI devices, and has identified cobalt tungsten phosphorus (CoWP) as the leading material candidate for use in those layers.

The LSI devices in today's automobiles are fabricated with advanced semiconductor processes, in design rules ranging from 90 to 65 nm. Within the industry, however, the development focus has already shifted to the next generation. In the 32-nm node, which is expected to appear around 2012, the reliability of interconnect has emerged as a major issue. Devices in this generation will use copper interconnect, which was first adopted in the 150-nm generation. However, two problems need to be solved before copper interconnect can meet the stringent safety requirements of automotive applications.

The first problem stems from the fact that, in the 32-nm generation, the width of copper interconnects shrinks to about 50 nm, which is approximately equal to the mean free path of electrons in a material. Electron scattering tends to occur at the surface of copper and also at crystal grain boundaries, resulting in increased resistance. The second problem stems from the fact that next-generation LSI devices will be both smaller and faster. The density of the current flowing through the interconnects will increase, causing a decrease in the electromigration lifetime of the interconnect.

NEC Electronics has used its new measurement technique to show that both problems can be overcome by covering the copper interconnect with a CoWP cap layer. Scientifically, valid data from the measurements show that a CoWP cap not only ensures high reliability but also suppresses resistance due to electron scattering.

The results of the measurements and details of the new measurement technique follow:

1) NRR indicator of interconnect resistivity

To measure the influence of the transition to 32-nm-node technology on interconnect resistivity, NEC Electronics devised a technique that uses data from measurements at ultra-low temperatures (under 20K) to obtain a Normalized Residual Resistivity (NRR) indicator.

A significant advantage of this technique is that it allows the influence of impurity concentrations and electron scattering on resistivity to be determined very accurately, without being affected by the dimensions of the sample. By comparing the relationship between NRR and electromigration lifetimes for different processes, it is possible to identify processes that allow electromigration lifetimes to be increased without increasing resistivity. As the technologies for the next generation are developed, this technique can predict the influence of the process on interconnect reliability regardless of process dimensions. This will make it possible to develop highly reliable interconnect technologies for the 32-nm node and beyond.

2) Verification of cobalt tungsten phosphorus (CoWP) as a viable cap material

To achieve high reliability in the 32-nm node and beyond, it will also be necessary to suppress copper diffusion at the boundary between the interconnect and cap dielectrics. One method to suppress diffusion is to dope the impurities, creating a copper alloy. Another method is to cover the copper interconnect with a cap layer. It is believed that a cap layer of CoWP will dramatically increase the electromigration lifetime of copper interconnect, making it a leading candidate for use in next-generation automotive LSI devices.

NEC Electronics used its NRR technique to measure the effectiveness of CoWP cap layers. The results indicate that a CoWP cap does in fact suppress copper diffusion at the interface between the cap and the copper interconnect. Without introducing impurities in the copper interconnect, and without increasing resistivity, a CoWP cap suppresses diffusion at the surfaces of copper interconnect, which is the main cause of degradation in copper interconnect. This makes CoWP superior to rival materials and an ideal candidate for further research into next-generation interconnect configurations and process technologies.

These results are important because they enable an intelligent choice between candidate process technologies for highly reliable automotive ICs in the 32-nm node and beyond. NEC Electronics believes that the new measurement technique has succeeded in indicating the direction of development work in CMOS process technology. The new technique also has important implications for research efficiency and production management.

NEC Electronics will announce its new measurement technique at the International Electron Devices Meeting 2006 (IEDM 2006), to be held over three days starting December 11 in San Francisco (USA).

About NEC Electronics

NEC Electronics Corporation (TSE: 6723) specializes in semiconductor products encompassing advanced technology solutions for the high-end computing and broadband networking markets, system solutions for the mobile handset, PC peripherals, automotive and digital consumer markets, and platform solutions for a wide range of customer applications. NEC Electronics Corporation has 25 subsidiaries worldwide including NEC Electronics America, Inc. (www.am.necel.com) and NEC Electronics (Europe) GmbH (www.eu.necel.com). For additional information about NEC Electronics worldwide, visit www.necel.com.