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Stable Gate MOSFET Structures

IP.com Disclosure Number: IPCOM000078718D
Original Publication Date: 1973-Feb-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 78K

Publishing Venue

IBM

Related People

Li, PC: AUTHOR [+4]

Abstract

The advantage of the dense structure of silicon nitride film has been frequently utilized, as passivation in silicon integrated circuit technology. One of its most important usages is the Si-SiO(2)-Si(3)N(4) silicon sandwich insulator gate structure for a metal-oxide semiconductor field-effect transistor (MOSFET). The silicon nitride film in this structure has demonstrated the ability to reduce the probability of the gate short, the penetration of sodium ion. However, recently, such advantages from Si(3)N(4) has been somewhat overshadowed by the disadvantage that such structure experiences a long-term electrical stability problem, namely the shift of threshold voltage under the voltage stressing.

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Stable Gate MOSFET Structures

The advantage of the dense structure of silicon nitride film has been frequently utilized, as passivation in silicon integrated circuit technology. One of its most important usages is the Si-SiO(2)-Si(3)N(4) silicon sandwich insulator gate structure for a metal-oxide semiconductor field-effect transistor (MOSFET). The silicon nitride film in this structure has demonstrated the ability to reduce the probability of the gate short, the penetration of sodium ion. However, recently, such advantages from Si(3)N(4) has been somewhat overshadowed by the disadvantage that such structure experiences a long-term electrical stability problem, namely the shift of threshold voltage under the voltage stressing.

The hereinafter described gate structures overcome the disadvantage. The preferred gate structures are: (a) polysilicon - SiO(2) - silicon (bromide) or (chloride) oxynitride - SiO(2)- Si; and (b) metal-silicon (bromide) oxynitride - SiO(2) - Si.

The silicon (bromide) oxynitride film, like the silicon nitride film, is a dense structure. A comparison of properties between these two films is shown in Table
1. The SiO(2) - silicon (bromide) oxynitride interface states and the trapping centers in silicon (bromide) oxynitride, are substantially lower than those in the SiO(2)-Si(3)N(4) interface state and in the Si(3)N(4)itself. Therefore, the use of silicon (bromide) oxynitride in the above structures not only maintain the advantage of silicon nitride, but also reduce the stability problem. Table I Silicon Nitride Silicon (Bromide) Oxynitride Breakdown v/cm 10/7/ 10/7/ Dielectric constant (relative) 5.5 5 - 6.5 Etchant Phosphorous acid Phosphorous acid Preparation method Chemical vapor Chemical vapor deposition deposi...