Mechanistic Understanding of the Stress-Induced Failure of Si 3 N 4 Metal-Insulator-Metal Capacitors
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Mechanistic understanding of the stress-induced failure of Si3N4 Metal-Insulator-Metal Capacitors
Dongwoo Suh, Bongki Mheen, Seung-Yun Lee, Kyu-Hwan Shim, and Jin-Yeong Kang
Compound Semiconductor Research Department, Microelectronics Technology Laboratory Electronics and Telecommunications Research Institute, Taejon 305-600, Republic of Korea
ABSTRACT
The failure of Si3N4 metal-insulator-metal (MIM) capacitors fabricated by plasma enhanced chemical vapor deposition (PECVD) was investigated using cross-sectional transmission electron microscopy (XTEM) and residual stress analysis.
As a result we noted that the failure of the Si3N4
MIM capacitors originated from the microvoids formed over the Si3N4 dielectric and the TiN interlayer. The microvoid of the MIM capacitor, particularly in case of having a very thin Si3N4 of less than 50 nm-thick, caused it to leak out much of the current to the extent of a few microamperes even at bias of 3 volts. The formation of microvoids was explained by the residual stress of the constituent layers at a mechanistic point of view.
The stress analysis showed that the absolute stress normalized by the
thickness of the Si3N4 layer should be less than 31 MPa/nm to avoid microvoiding.
In this research it
was noted in conclusion that the stress state of not only the dielectric but also the interlayer should be taken into account for the successful design of high capacitive Si3N4 MIM capacitors.
L6.15.1
INTRODUCTION As the application of active electronic devices expands over the range of giga hertz, passive devices such as capacitor, inductor, resistor, and so forth, have been required to be equipped with high performance in that frequency range to keep pace with those.
As for capacitor, Si3N4 metal-insulator-
metal (MIM) structure has been widely adopted up to date because not only the dielectric characteristic of Si3N4 is superior to that of conventional SiO2 but also the capacitance is independent of the applied bias [1].
The capacitance of an MIM capacitor is expressed as below
C
= ε
o
ε
r
A d
(1)
where εo and εr are permittivity of free space and relative dielectric constant (Si3N4: 7.5, SiO2: 3.9), A is the capacitance area and d is the dielectric thickness. According to equation (1), it is necessary to decrease the dielectric thickness in order to increase the capacitance. As the silicon nitride becomes thin, however, the capacitor is ready to be electrically broken down by the concentrated electric field particularly at hillocks [2,3].
So an interlayer as a diffusion barrier should be placed between the
Si3N4 and the aluminum electrode layers to suppress the formation of the hillocks.
Among the
candidates of the interlayer TiN has been extensively adopted because of excellent stability against the diffusion of silicon and aluminum [4]. Most of the explanations on the breakdown of the Si3N4 MIM capacitor resort to the stress of the capacitor using Raman spectroscopy or optical laser technique [5,6]. While such approaches explain the breakdown based on the
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