A Thermal Model for the Initiation of Programming in Metal‐to‐Metal Amorphous‐Silicon Antifuses

Abstract

An antifuse is a programmable element which normally resides in a high-resistance state called the "OFF-state." It can be switched into a low-resistance state called the "ON-state" by the application of a high-voltage pulse. [1][2][3] We have previously reported on the energy considerations during the growth of a molten filament in metalto-metal amorphous-silicon antifuses, 4 and on the ON-state reliability of amorphous-silicon antifuses. 5 In this paper, we present a thermal model for the initiation of programming in these antifuses.The antifuses studied in this work are located in the via between two metal layers. The bottom metal electrode is Al-Si-Cu/TiW and the top metal electrode is Ti/TiW/Al-Si-Cu. The via is circular with diameter ranging from 0.5 to 2 m. The amorphous-silicon layer is deposited by plasma-enhanced chemical vapor deposition (PECVD) of SiH 4 at 400ЊC. The amorphous-silicon layer thickness ranges from 500 to 1500 Å. ExperimentalThe dependence of the current I af in the antifuse on the applied voltage V app is shown in Fig. 1. The amorphous-silicon antifuse is initially in the OFF-state. In this state, its resistance R OFF is on the order of several megaohms. It is programmed to a low-resistance state (ON-state) by applying a voltage across its electrode pads through a series resistance R ser . The voltage is applied using the HP4145B semiconductor parameter analyzer. The current through the antifuse is measured using the same HP4145B. The current at the initiation of programming is denoted by I pf and the corresponding voltage is V pf . The series resistance R ser controls the programming current I pp and the final ON-state resistance R ON . The resistance in the ON-state is on the order of 25 to 200 ⍀ and it depends on the programming conditions. 3,6,7 The programming voltage V pp and the series resistance R ser control the programming conditions. Without the series resistance, there is no control of the power dissipated in the antifuse during programming. 8 Programming under these conditions leads to a much lower ON-resistance as shown in Fig. 2. In this figure, seven devices were measured for each data point. In the case with no series resistance, the standard deviation ranged from a low value of 0.61 ⍀ to a high value of 0.88 ⍀. In the case where R ser ϭ 760 ⍀, the standard deviation of the antifuse ON-resistance ranged from a low value of 3.86 ⍀ to a high value of 7.05 ⍀.Before programming, the applied voltage appears entirely across the antifuse as R OFF >> R ser . In the ON-state, most of the voltage drop appears across the series resistance because R ON << R ser . This type of A thermal model for the initiation of programming in metal-to-metal amorphous-silicon antifuses is described. The current and field crowding at the edges of the via cause the temperature at the via corners to increase due to Joule heating. Programming is initiated when the temperature at the via edges reaches the melting temperature of amorphous silicon. The model presented in this work explains how the thickne...