Defect States Due to Silicon Dangling Bonds at the Si(100)/SiO 2 Interface and the Passivation by Hydrogen Atoms
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C. KANETA*, T. TERAKURA**b
YAMASAKI*,
T. UCHIYAMA**,
T.
UDA**
2
AND K.
*Fujitsu Laboratories Limited, 10-1 Morinosato-Wakamiya, Atsugi, 243-0197, Japan, [email protected]
**JRCAT-ATP, 1-1.-4 Higashi, Tsukuba, 305-8562, Japan
***JRCAT- NAIR, 1-1-4 Higashi, Tsukuba, 305-8562, Japan ABSTRACT The defect states due to the Si dangling-bonds at the Si(100)/SiO 2 interface is investigated by employing the first-principles method based on the density functional theory. Two
prototypes of the defects at the interface are considered. One exists on one end of a Si-Si dimer. On the other hand, the other exists on an edge of a Si-O-Si bridge. The electronic
structures for these systems were calculated to investigate the interface states. For the former, two defect states strongly localizing on the silicon dangling bond at the interface appear in the band gap. The latter defect also generates two defect states. But the upper level is in the conduction band, while the lower level is in the band gap. It is also shown that the interface states completely disappear by introducing a H atom into the interface and terminating the
dangling bonds. Our results suggest the silicon dangling-bond on a Si-Si dimer with no adjacent
O atoms as a candidate for the Pbl center. INTRODUCTION
Interface states or traps are exceedingly harmful to the performance and the reliability of the MOS (metal-oxide-semiconductor) devices. The Si dangling-bond (SDB) defects, the typical
intrinsic defects at the Si/SiO2 interface, have been considered to be one of the origins of the
interface states or traps. They have been called Pb centers, a generic name for different SDB defects. In the Si(100)/SiO 2 interface, Pbo and Pbl centers have been known as these types of defects [I]. A high correlation between the interface state density obtained by the capacitance voltage (CV) measurement and the level density of Pb0 and Pbl centers by the electron paramagnetic resonance (EPR) measurement has been shown on (100) wafers [2].
The Pbo is modeled as a °Si-Si3 defect. (The symbol 9 represents an unpaired Si bond.) The Pbl had been tentatively assigned to °Si-Si 20, but recent findings suggest that it exists on a Si-Si dimer and contains no 0 atoms [3]. To understand the electronic properties of various types of the SDB defects is important for the SiISiO 2 interface engineering. We investigate the interface states due to the two prototypes of SDB defects at the Si(l00YSiO 2. We also show the passivation of the interface states by the H atom. METHODOLOGY
The stable atomic configurations of SDB defects at the Si(100)/Si0 2 interface and their electronic structures are investigated using the first-principles method [4] based on the density functional theory [5]. Only valence electrons are explicitly considered. To account for the core-valence interactions, we use a norm-conserving pseudopotential for Si atoms, and ultrasoft pseudopotentials [6] for 0 and H atoms, respectively. The generalized gradient correction [7] is added to the local density app
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