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Nguyen Van Hieu (promotion date: 19 March 2004)

Multilevel Interconnect Reliability

Promotion date: 19 March 2004

Nguyen van Hieu

Studies in my thesis are about reliability of the multilevel interconnects. It can be recognized that in the computer processors, there is a dense array of narrow, thin-film metallic conductors that serve to transport current between the various devices on the chip. These metallic conductors are called multilevel interconnects. My study focused on the failures due to electro-thermomechanical stresses. Because there is a very high density grid of connectors on a chip, even on different levels, you want to improve on the reliability of the connections.

You are from Vietnam, how did you come to do a PhD at this university?

I knew this university through ITIMS (International Training Institute for Materials Science), where I got the MSc. Degree and worked for few years. ITIMS was established in December 1992 by the Ministry of Education and Training of Vietnam with help of the Universities of Amsterdam and Twente. During I was working for ITIMS, I received scholarship for a short traineeship at UT, then I applied for the Ph.D at semiconductor component group.

What was your thesis about?

Studies in my thesis are about reliability of the multilevel interconnects. It can be recognized that in the computer processors, there is a dense array of narrow, thin-film metallic conductors that serve to transport current between the various devices on the chip. These metallic conductors are called multilevel interconnects. My study focused on the failures due to electro-thermomechanical stresses. Because there is a very high density grid of connectors on a chip, even on different levels, you want to improve on the reliability of the connections. The metal line is extremely thin and very vulnerable due to the high current density and the temperature of the chip itself. These can result in failure in the chip due to “electromigration”, “thermomigration”, and “fatigue of metal”. Electromigration is a diffusion of metal atoms due to “electron wind”, thermomigration is a diffusion of metal atoms due to a present of temperature gradient, and fatigue failure is due to thermal cycling when the chip subjected to a large “on-off” electrical current. Failure mechanisms can be extrusion short-circuit, or open circuit, or cracking of the thin films (metal films or dielectric films).

Is it already applied in a real chip?

Not yet at moment, because I've just finished the work. However, results about the relation between electromigration and interconnect layout can be used soon; they were well verified through simulations and experiments. My research was very close to practical application in industry and in fact I was financed by industry (FOM and Philips).

And you were allowed to publish the results?

Yes, they allowed me to publish. Sometimes the results of a particular research are kept as company secrets, but that wasn’t the case here. So I could do the PhD.

What are you going to do after this?

I will go back to Vietnam and will work for ITIMS. They said I could come back whenever I wanted. It is not clear at moment what I will do; I think that I will work on a research program about sensor technology. Otherwise, I may be responsible for the clean-room. That allows me to remain in contact with my group here.

I would also like to apply at the university as a lecturer. I would like to teach besides doing research. In teaching I can put something I learned of the Dutch educational system into practice. Here the students are expected to work for themselves and not just to sit back and listen to their instructors. I am sure that a more active approach results in a better understanding.

So you have been here for 5 years including the grant?

Yes, and I enjoyed it very much. The Dutch people are very nice and I enjoyed playing football in the third team of FC Drienerlo. The professors are very easy to talk to and allow you to work independently, but were helpful nonetheless. As long as you get results.

Have you been back to Vietnam during those five years?

Yes, twice. When I was married and had a little son. I am very much looking forward to seeing my family and my friends again.