Covalent Nitrides for Maskless Laser Writing of Microscopic Metal Lines
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COVALENT NITRIDES FOR MASKLESS LASER WRITING OF MICROSCOPIC METAL LINES LEON MAYA Chemistry Division, Oak Ridge National Laboratory, P.O.B. 2008, Oak Ridge, TN 378316119. ABSTRACT Selected covalent metal nitrides with limited thermal stability, such as Sn 3N4, Cu3 N, and Ni 3N, were prepared in a glow discharge system by reactive sputtering in a nitrogen plasma. These compounds were characterized by chemical analysis and their thermal behavior These materials established by temperature-programmed thermal decomposition. decompose into the elements with the rate reaching a maximum at 615, 465, and 405 *C for Sn, Cu, and Ni respectively. The feasibility of using these coatings to generate metal lines by maskless laser writing was explored. Conducting metal lines, a few micron in width, could be generated with each of these nitrides. The resistivities of the metal lines were within an order of magnitude of those of the bulk metals for Cu and Ni and somewhat more for Sn. INTRODUCTION Metallization of electronic components to produce electrical contacts in integrated circuits is an important step in the manufacture of these devices. Metallizations are performed by depositing the metal uniformly and subsequently creating a pattern through the use of masks and etchings. Current technology involves deposition of aluminum for MOS and PtSi, Ti, W, Au, and TiN for bipolar devices. The deposition is accomplished by evaporation of the metal or by sputtering of the more refractory materials. A new trend in the manufacture of microelectronic devices that obviates the need for multiple steps to create metallic or insulating patterns, as well as accomplishing semiconductor doping, is the use of direct maskless laser writing. In this process a focused pulsed or CW laser beam effects photolytic or pyrolytic transformations on species present in the substrate or immediately above in the vapor phase. Representative of this trend are studies [1-5] that have examined different applications of this technique. The present study was undertaken to establish the feasibility of utilizing the relatively low thermal stability of a number of metal nitrides to generate metallic lines by maskless laser writing. RESULTS AND DISCUSSION Preparation and characterization of the nitrides: Films of each nitride were deposited by reactive sputtering in a nitrogen plasma which was generated by a potential drop of about 400 V and a 10 mA current between two stainless steel electrodes. The cathode made contact with a thin foil of the metal to be sputtered while the second electrode, at ground, acted as a pedestal to hold the substrate to be coated. In a typical run, lasting 20 h, a flow of 20 sccm ultrapure nitrogen was passed through the system while holding a pressure of 2 torr. The amount deposited was established by weighing in a microbalance. The films were characterized by FTIR, XRD, Temperature Programmed Thermal Decomposition, (TPTD), four probe electrical resistivity, and direct chemical analysis. The TPTD was conducted in an enclosed tube, placed in
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