LIMITATION OF THE TIN TI LAYER FORMED BY THE RAPID THERMAL HEAT-TREATMENT OF PURE TI FILMS IN AN NH3 AMBIENT IN FABRICATION OF SUBMICROMETER CMOS FLASH EPROM ICS/

It Is essential to have a suitable refractory metal or compound as a g lue layer in fabrication of integrated circuits (IC's) with submicrome ter dimensions, Presently, the reactively sputtered (in N-2 ambient) T iN film is being widely used due to its simplicity of deposition, Howe ver, a major shortcoming of this method of TiN film formation is the g eneration of a rather large number of particles during the sputtering process, which in turn leads to a significant loss in the number of go od devices, A much cleaner (from the particle generation point of view ) TiN formation process, which requires less process steps to form the Ti/TiN, is the rapid thermal heat treatment of a pure Ti film in an N H3 ambient. In this study, the technical feasibility and limitation of the TiN film formed by the rapid thermal heat treatment (RTHT) in an ammonia ambient for the fabrication of 0.85-mu m CMOS hash electricall y programmable read only memory (EPROM) integrated circuits having a c ontact aspect ratio of approximately 1.5, were investigated, When the as-deposited thickness of the Ti film was less than 130 Angstrom, all memory contacts exhibited an ''electrically open'' contact signature ( >4750 Omega/contact). Transmission electron microscopy (TEM) cross sec tion examination of a failed contact chain structure indicated that th e failure mechanism could be a physical separation at the W-plug/silic on interface. For the Ti films with thickness between 130 and 240 Angs trom, the contact resistance dropped to a value between 59 and 68 Omeg a/contact. Furthermore, the contact failure rate (contacts exhibiting ''electrically open'' signature) decreased as the thickness of the Ti film increased, In this case, the failure mechanism appeared to be the direct contact between the TiN layer and the silicon at the contact i nterface, This condition was created during the multistep nitridation process where approximately 240 to 250 Angstrom of the Ti film was con verted to TiN, For the memory devices having Ti films thicker than 240 Angstrom, all memory contacts were electrically and mechanically stab le, and exhibited equivalent or higher circuit yields compared to devi ces having a sputter deposited TiN/Ti bilayer film (control group).