R. S. Johnson

Physical and electrical properties of noncrystalline Al2O3 prepared by remote plasma enhanced chemical vapor deposition

Noncrystalline Al2O3 dielectric films have been synthesized by remote plasma enhanced chemical vapor deposition (RPECVD) and deposited on (i) H-terminated Si(100) and (ii) on SiO2 prepared by remote plasma assisted oxidation and RPECVD on Si(100) substrates using organometallic source gases injected downstream from a He/O2 plasma. Chemical composition and morphology of the Al2O3 films and their interfaces have been studied by Auger electron spectroscopy (AES), Fourier transform infrared spectroscopy, nuclear resonance profiling (NRP), and x-ray diffraction (XRD). Previous studies in which Al2O3 was deposited by thermal CVD, rapid thermal CVD, (RTCVD), direct PECVD, and physical vapor deposition generally resulted in relatively thick SiO2 or Al-silicate interfacial layers which impact adversely on the highest attainable capacitance. In line AES and NRP indicate the as-deposited RPECVD films are fully oxidized on deposition, and their interfaces can be chemically abrupt with Si oxide or Al silicate interfac...

Heavy-ion-induced breakdown in ultra-thin gate oxides and high-k dielectrics

Presents experimental results on single-event-induced breakdown in sub-5-nm plasma-enhanced SiO/sub 2/, nitrided SiO/sub 2/, Al/sub 2/O/sub 3/, HfO/sub 2/, and Zr/sub 0.4/Si/sub 1.6/O/sub 4/ dielectrics typical of current and future-generation commercial gate oxides. These advanced oxides are found to be quite resistant to ion-induced breakdown. Radiation-induced soft breakdown was observed in some films with 342 MeV Au (LET=80 MeV/mg/cm/sup 2/) but not 340 MeV I (LET=60 MeV/mg/cm/sup 2/). The critical voltage to hard breakdown was found to scale with the square root of the physical oxide thickness, not with the energy stored on the gate capacitance. Alternative dielectrics with equivalent oxide thickness substantially below their physical thickness were found to exhibit significantly higher voltage to hard breakdown than SiO/sub 2/ counterparts. All of the samples reached ion-induced hard breakdown at applied voltages well above typical operating power-supply voltages; these findings bode well for the use of advanced commercial integrated circuits in space systems.

Electronic structure of noncrystalline transition metal silicate and aluminate alloys

A localized molecular orbital description ~LMO! for the electronic states of transition metal ~TM! noncrystalline silicate and aluminate alloys establishes that the lowest conduction band states are derived from d states of TM atoms. The relative energies of these states are in agreement with the LMO approach, and have been measured by x-ray absorption spectroscopy for ZrO2 ‐ SiO2 alloys, and deduced from an interpretation of capacitance‐voltage and current‐voltage data for capacitors with Al2O3 ‐T a 2O5 alloy dielectrics. The LMO model yields a scaling relationship for band offset energies providing a guideline for selection of gate dielectrics for advanced Si devices.

New approach for the fabrication of device-quality Ge/GeO2/SiO2 interfaces using low temperature remote plasma processing

It has been shown that low temperature (300 °C) remote plasma enhanced processing can separately and independently control interface formation and bulk oxide deposition on silicon substrates. Plasma processing is followed by a low thermal budget thermal anneal, e.g., 30 s at 900 °C. In this article, this process has been modified and applied to germanium substrates to determine if it can provide a successful pathway to device-quality Ge–dielectric interfaces. The new process also employs a three-step process: (i) an O2/He plasma-assisted, predeposition oxidation of the germanium surface to form a superficial germanium–oxide passivating film, (ii) deposition of a SiO2 bulk film by remote plasma-enhanced chemical vapor deposition from SiH4 and O2, and (iii) a postdeposition anneal for chemical and structural relaxation. The resulting interfaces are improved by the predeposition, plasma-assisted oxidation step, but are still far too defective for device applications.

Electron trapping in noncrystalline remote plasma deposited Hf-aluminate alloys for gate dielectric applications

The physical and electrical properties of noncrystalline Hf-alumiunate alloys, (HfO2)x(Al2O3)1−x, were investigated. Characterization by Auger electron spectroscopy and Fourier transformation infrared spectroscopy confirm these alloys are homogeneous and pseudobinary in character, displaying increased thermal stability against crystallization with respect to the respective end-member oxides. Capacitance–voltage and current density-voltage data as a function of temperature demonstrate that the Hf d states of these alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset energy of HfO2 with respect to Si. This work also provides additional insight into a previously reported study of Ta-aluminate alloys with localized electron traps associated with d states of the Ta atoms.

Electron traps at interfaces between Si(100) and noncrystalline Al2O3, Ta2O5, and (Ta2O5)x(Al2O3)1−x alloys

The physical and electrical properties of noncrystalline Al2O3, Ta2O5, and their alloys, (Ta2O5)x(Al2O3)1−x, are investigated. Characterization by Auger electron spectroscopy and Fourier transformation infrared spectroscopy confirm these alloys are homogeneous with pseudobinary in character, and display increased thermal stability. Capacitance–voltage and current density–voltage data as a function of temperature demonstrate that the Ta d states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta2O5 with respect to Si.

Characteristics of metalorganic remote plasma chemical vapor deposited Al2O3 gate stacks on SiC metal–oxide–semiconductor devices

Metalorganic remote plasma chemical vapor deposited SiO2/Al2O3 stacks were deposited on 6H p-type silicon SiC to fabricate a high-k gate stack SiC metal–oxide–semiconductor capacitors. Capacitance–voltage (C–V) and current–voltage (I–V) measurements were performed. C–V characteristics showed excellent properties at room and higher temperatures. Samples exhibited a slight negative flatband shift from which the net oxide charge (Qox) was calculated. Low leakage currents were observed even at high temperatures. I–V characteristics of Al2O3 were superior to those observed on AlN and SiO2 dielectrics on SiC.

Electron trapping in non-crystalline Ta- and Hf-Aluminates for gate dielectric applications in aggressively scaled silicon devices

Abstract The physical and electrical properties of non-crystalline Ta- and Hf-alumiunates, (Ta 2 O 5 ) x (Al 2 O 3 ) 1− x and (HfO 2 ) x (Al 2 O 3 ) 1− x , respectively, were studied. As-deposited films were homogeneous and pseudo-binary in character with increased thermal stability with respect to the respective end-member oxides. Capacitance–voltage and current density–voltage data as a function of temperature demonstrate that the Ta and Hf d-states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta 2 O 5 and HfO 2 with respect to Si. This work correlates the studies of Ta- and Hf-aluminates to develop a qualitative conduction band energy level scheme for the two alloys where the interfacial electrical properties are dominated by electron traps of the respective transition metal atoms, and/or or network defects associated with the alloy.

Spectroscopic evidence for a network structure in plasma-deposited Ta2O5 films for microelectronic applications

Based on the bond-ionicity definition of Pauling, gate dielectric materials are grouped into three categories with increasing bond ionicity, continuous random networks, crn’s, modified crn’s with ionic components, mcrn’s, and random closed packed ionic structures, rcpis’s. Using this classification scheme, fully oxidized Ta2O5 films prepared at low temperature, ∼300 °C, have mcrn’s, and are expected to have similar bonding arrangements and thermal stability to non-crystalline Al2O3 and SiO2-rich, Zr silicate alloys. This is verified by combining previously published Raman data with more recent FTIR and EXAFS results.

Simplified bond-hyperpolarizability model of second harmonic generation: Application to Si-dielectric interfaces

We show that the anisotropies of second-harmonic-generation (SHG) intensities of singular and vicinal (111) and (001)Si–dielectric interfaces can be described accurately as dipole radiation originating from the anharmonic motion of bond charges parallel to the bond directions. This simplified bond-hyperpolarizability model not only provides a simpler and mathematically more efficient representation of SHG, but also allows a direct physical interpretation at the bond level, which was lacking in previous approaches. Application to oxidized and nitrided Si–SiO2 interfaces provides new insight into bonding that occurs at these interfaces as well as the origin of SHG.