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FORMATION OF THERMALLY STABLE Ta2O5 FILMS

IP.com Disclosure Number: IPCOM000042040D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Dishon, G: AUTHOR [+3]

Abstract

This article describes processes for the formation of thin Ta2O5 films with excellent thermal stability and low leakage characteristics which can be formed even on silicon substrates. For dynamic random-access memory (RAM) and other capacitor applications, it would be highly desirable for many reasons to have available a high capacitance density technology based on the use of high dielectric constant materials as opposed to simply decreasing film thicknesses. One such obvious material is Ta2O5 which has been used extensively for thick film applications. Its use in thin film applications, e.g., storage capacitor in a FET (DRAM) has been hampered by the tendency for reaction with the underlying silicon, and instability when subjected to temperatures above 500ŒC or so.

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FORMATION OF THERMALLY STABLE Ta2O5 FILMS

This article describes processes for the formation of thin Ta2O5 films with excellent thermal stability and low leakage characteristics which can be formed even on silicon substrates. For dynamic random-access memory (RAM) and other capacitor applications, it would be highly desirable for many reasons to have available a high capacitance density technology based on the use of high dielectric constant materials as opposed to simply decreasing film thicknesses. One such obvious material is Ta2O5 which has been used extensively for thick film applications. Its use in thin film applications, e.g., storage capacitor in a FET (DRAM) has been hampered by the tendency for reaction with the underlying silicon, and instability when subjected to temperatures above 500OEC or so. It has been erroneously assumed that thermal instability in the form of excessive leakage current, e.g., > 10 A/cm2 is in some way due to interfacial reaction and crystallization of the Ta2O5 . One problem in pursuing the dielectric constant capability of a dielectric is that when two capacitors are in series, the net capacitance where C1 and C2 are the capacitances of the separate capacitors, is degraded. Consider SiO2 with the dielectric constant of 4 and Ta2O5 with a dielectric constant of approximately 24. Suppose it is desired to have a 100 ~ Ta2O5 film but have a 17 ~ SiO2 film in series. Since C1 = C2, in this case we have

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Let us keep C2 (the Ta2O5 film) the same, but now reduce the thickness of the SiO2 to 8 ~. The value To carry it a little further, reduce the SiO2 thickness to 4 ~. Suppose we work on the opposite side, e.g., C1 < C2, e.g., the SiO2 thickness = 34 ~: In other words, for two capacitors in series, the net capacitance appr...