Professor James Economy's Group
New Low-k Porous Materials for Interconnects
Planned increases in IC performance, such as faster clock speeds and lower power consumption, require the use of low-k materials for interconnects in chip manufacturing. Implementation of low k dielectrics can reduce RC delay, power dissipation, crosstalk noise and number of metal lever. Dense low-k materials with k values in the range of 2.8-3.0 are in manufacturing at the 90 nm node (see Figure 1). The International Technology Roadmap for Semiconductors indicates that porous low-k materials with k < 2.4 will be required for the 65 nm node by 2006. Low-k dielectric materials alone is expected to grow from $16 million in 2002 to nearly $400 million in 2006.
Poly(m-diethynyl benzene) is a good candidate as a low-k dielectric because it has low dielectric constant (k=2.7), high thermal stability (> 450°C), relatively low moisture pick-up and capability of planarizing over complex geometries. However, its low solubility in most common spin-coating solvents and tendency to crack due to its easy crystallizing limit its application as a low-k material in microelectronic devices. We modified its chemical structure by copolymerizing diethynyl benzene with triethynyl benzene. As a result, the new polymers display greatly improved solubility in common spin-coating solvents, such as THF, NMP and cyclohexanone. The bulk dielectric constant of this material is 2.7, which can be lowered to 2.3 by adding porogens to form porous structure. Characterization of other properties and further modification of its structure to improve its properties is underway.
Figure. Cross-section of seven-lever 90 nm node interconnect *
* Ref. http://www.eeel.nist.gov/812/conference/Presentations/Ho.pdf/copper.pdf