AVS 46th International Symposium
    Electronic Materials and Processing Division Wednesday Sessions
       Session EM+NS-WeM

Paper EM+NS-WeM9
Failure Analysis of Sub 1/4-Micron Contacts by Means of TEM-EELS

Wednesday, October 27, 1999, 11:00 am, Room 6C

Session: Nano-characterization of Molecules, Materials, and Devices
Presenter: F. Yano, Hitachi Ltd., Japan
Authors: F. Yano, Hitachi Ltd., Japan
Y. Nakamura, Hitachi Ltd., Japan
T. Aoyama, Hitachi Ltd., Japan
Y. Mitsui, Hitachi Ltd., Japan
Correspondent: Click to Email
Although TEM-EELS (Transmission Electron Microscope-Electron Energy Loss Spectroscopy) has practically been used for elemental analysis for nanometer area, its full potential, we believe, is achieved when it is used for chemical analysis just like ESCA. This paper uncovers our experience of thermally stable contact development, in which our advanced TEM-EELS@footnote 1@ has revealed reactions in the contact during thermal process, which have detrimentally increased its resistivity.@footnote 2,3@ The contact holes are filled with sputtered Ti, which is annealed to form TiSi@sub 2@, CVD-TiN and CVD-W. Alathough the contact resistivity was low enough just after contact processes, it became higher after thermal process. The resistivity was varied 10@super 2@ to 10@super 6@ @ohm@ depending on the process conditions. Chemical analysis of loss energies showed that Si substrate in the contact is fully covered with SiO@sub 2@ in the fatal worst case. Even somewhat better cases, TiSi@sub 2@ formation was partial and still SiO@sub 2@ was formed. In other cases, TiO@sub x@ was also observed. These oxidized layers clearly increased resistivity. However, the mechanism of oxidation was unclear, especially the origin of the oxygen was, because neither oxygen nor water was applied. To clarify the mechanism, we made a model, in which residual TiCl@sub x@ on CVD-TiN forms titanium acid gel (TiO@sub x@(H@sub 2@O)@sub n@) which works as a water reservoir. During thermal process, the water in the gel is released, which goes through TiN grain and finally oxidizes silicon at the interface of TiN and Si substrate. To prove this model, the relation between the amount of residual Cl and the contact resistivity was measured. The results supported the model above, i.e., the more Cl observed, the higher the resistivity is. Based on this mechanism, all cases of high resistivity failures in the thermally stable contact were explained. Chemical analysis by TEM-EELS will be a key technique for failure analysis of 1/4-micron devices and after. @FootnoteText@ @footnote 1@ T. Sekiguchi, et al., Jpn. J. Appl. Phys., vol. 37 (1998) L694. @footnote 2@ Y. Mitsui, et al., Ext. Abst. IEDM (1998) 329.@footnote 3@ Y. Nakamura, et al., Proceedings of Advanced Metallization Conference, Colorado (1998) 661.