Novel Air-gap Formation Technology Using Ru Barrier Metal for Cu Interconnects with High Reliability and Low Capacitance

Development of air-gap etching process by a mask approach for characterization of intralayer and interlayer capacitances

“…It was reported that Ta has higher etching rate in the fluorine chemistry than Cu. 13) After the SiCOH removal step, the Cu surface was fully covered with a porous Cu polymer ("Cu+C+O" layer) and the surface of Cu was slightly higher than the barrier Ta=TaN. "Cu+C+N" and "Cu+C" were next to the "Cu+C+O" layer.…”

“…In the nonconformal CVD approach, an air-gap is formed by the pinch-off of the deposited CVD dielectric after air-gap etching. [11][12][13] The disadvantage of this method is that copper is exposed in the etching chemistry during etching and there is a risk of via landing on the air-gap area owing to via misalignment. The use of an air-gap mask could solve the above issues with a selective opening in a critical area for capacitance reduction.…”

“…20) With air-gap application, the intralayer capacitance could be decreased and this was fully discussed in the literature. [12][13][14]21,22) The interlayer capacitance is also part of the total interconnect capacitance and increases with increasing metal line width. The variation of interlayer capacitance which resulted from the air-gap mask approach should also be taken seriously.…”

Novel Air-gap Formation Technology Using Ru Barrier Metal for Cu Interconnects with High Reliability and Low Capacitance

“…We also found it difficult to keep the crosssectional shape of Cu wiring during the air-gap formation process in 140-nm-pitch interconnects when using a typical TaN/Ta barrier metal and a typical intermetal dielectric (IMD) etching condition. 20) Moreover there are very few reports on interconnect reliability issues such as timedependent dielectric breakdown (TDDB) life time, 18) electromigration (EM) lifetime and packaging reliability. 19) To improve TDDB and EM properties, CuAl or CuMn seed layers for a Cu electroplating process 6,8) and some barrier-metal materials have been investigated for Cu interconnects.…”

“…The previous paper on this technology was presented at the Advanced Metallization Conference Asian Session (ADMETA) in 2009. 20) This paper is a complete version of the presented paper with new data such as the observation results of surface roughness and additional reliability data EM lifetimes with failure analysis results. Basically, the electrical characteristics and reliability test results were compared between cases with and without air-gaps and the results for conventional TaN/Ta stacked barrier metals as reference structures.…”