Lun-Lun Chen

Nitrided Tetragonal

Employment of a tetragonal ZrO2 film as the charge-trapping layer for nonvolatile memory was investigated and the NH3 nitridation effect of the ZrO2 film on memory performance was also explored in this letter. The permittivity of the tetragonal ZrO2 film is slightly reduced from 38.7 to 36.9 after nitridation; nevertheless, nitridation introduces more trapping sites and passivates the grain boundary channel which results in a high operation speed in terms of 2.6-V flatband voltage shift by programming at +10 V for 10 ms and a good retention characteristic with 20.2% charge loss after ten-year operation at 125degC, both are superior to that without NH3 nitridation. Most importantly, the process is fully compatible with existent ULSI technology and paves the way to adopt a high-permittivity crystalline dielectric as the charge-trapping layer for future high-performance nonvolatile memory.

\hbox{ZrO}_{2}

A Ge-stabilized tetragonal ZrO2 dielectric with a permittivity (κ) value of 36.5 has been obtained by annealing a ZrO2/Ge/ZrO2 laminate at 500u2009°C and it is a more reliable approach toward stabilizing a tetragonal ZrO2 film. However, metal-insulator-metal (MIM) capacitors with the sole tetragonal ZrO2 film as an insulator achieve a high capacitance density of 27.8u2002fF/μm2 at the price of a degraded quadratic voltage coefficient of capacitance (VCC) of 81u2009129u2002ppm/V2 and unacceptably high leakage current. By capping an amorphous La-doped ZrO2 layer with a κ value of 26.3 to block grain boundaries-induced leakage paths of the crystalline ZrO2 dielectric, high-performance MIM capacitors in terms of a capacitance density of 19.8u2002fF/μm2, a VCC of 3135u2002ppm/V2, leakage current of 6.5×10−8u2002A/cm2 at −1 V, as well as a satisfactory capacitance change of 1.21% after ten-year operation can be realized.

as the Charge-Trapping Layer for Nonvolatile Memory Application

CF4 plasma treatment on germanium (Ge) surface is proposed in this work to alleviate the strong Fermi level pinning between metal/Ge, and its effectiveness is also explored for n- and p-type Ge wafers. It is found that samples with CF4 plasma treatment reveal conduction behavior transition between Schottky and ohmic characteristics, a metal-work-function-dependent Schottky barrier height as well as modulated contact resistance, and these results confirm the depinning of Fermi level. This depinning can be explained by the effective capability in passivating dangling bonds at Ge surface through fluorine atoms and the formation of Ge-F binding with partial ionic property, both of which are helpful in decreasing the number of surface states and consequently release the pinning effect.

High-performance metal-insulator-metal capacitor with Ge-stabilized tetragonal ZrO2/amorphous La-doped ZrO2 dielectric

A Ge-stabilized tetragonal ZrO2 (t-ZrO2) film formed by incorporating Ge atoms thermally driven from an underlying Ge layer into a ZrO2 film was investigated as the gate dielectric for Ge metal-oxide-semiconductor (MOS) capacitors fabricated on a Si substrate. A sole t-ZrO2 film on Ge is not eligible for the gate dielectric because of the poor interface quality. By using a thermally-grown ultrathin GeO2 film as an interfacial layer, the t-ZrO2/GeO2/Ge stack shows improved interface characteristics and a permittivity (κ) value of 36.6 for the t-ZrO2. In addition, the stack also demonstrates good leakage current since the amorphous GeO2 layer terminates grain boundary channels in the crystalline ZrO2. Further leakage current suppression can be achieved by a H2 annealing of the t-ZrO2/GeO2/Ge stack since the defects at grain boundaries can be effectively passivated, which makes a leakage current of 1.08×10−6u2002A/cm2 at VFB−1u2002V for effective oxide thickness of 1.66 nm and paves an alternative avenue to develop ...

Impact of fluorine treatment on Fermi level depinning for metal/germanium Schottky junctions

A cubic ZrO2 film formed by annealing of amorphous ZrON has been investigated as the charge-trapping layer for nonvolatile memory. The memory with a nitrogen-stabilized cubic ZrO2 film shows promising performance in terms of 3.81-V hysteresis memory window by ± 7-V program/erase voltage and 1.98-V flatband-voltage shift by programming at +7 V for 10 ms. As compared to that with an amorphous ZrON film, the improved performance is due to the greatly enhanced κ-value of 32.8 and the increased trapping sites provided by grain boundaries. Additionally, it shows 28.6% charge loss after ten-year operation at 85°C. Although it is worse than that with an amorphous ZrON film, it is advantageous over an atomic-layer-depositiongrown tetragonal ZrO2 film in terms of reduced leakage current. Improved retention can be accomplished by passivation of grain boundaries and/or high- κ double quantum barrier as the tunnel and blocking dielectric.

Ge-stabilized tetragonal ZrO2 as gate dielectric for Ge metal-oxide-semiconductor capacitors fabricated on Si substrate

Abstract-The combination of tetragonal ZrO₂ (t-ZrO₂) and amorphous Al₂O₃ was explored as the gate dielectric for Si-based MOS devices. Because of the absence of a ZrSiO₄ and/or ZrSi interfacial layer, the thermally stable t-ZrO₂/Al₂O₃/Si stack is more eligible than the Al₂O₃/t-ZrO₂/Si stack for the gate dielectric since it demonstrates larger capacitance, smaller hysteresis, better frequency dispersion, lower leakage current, and more robust reliability. By employing additional NH₃ plasma nitridation to well passivate the grain boundaries of the t-ZrO₂ film, without compromising its κ-value, a greatly reduced leakage current of 2.9 × 10^-8 A/cm² can be achieved at gate bias of flatband voltage (V_fb)-1 V with an effective oxide thickness of 1.64 nm, which paves a new way to develop a high-performance crystalline gate dielectric for advanced MOS devices.

Nonvolatile Memory With Nitrogen-Stabilized Cubic-Phase

By adopting an amorphous Y2O3 passivation layer, which provides a wide band gap and well passivates Ge surface without the presence of GeOx, a high-permittivity (κ) crystalline ZrO2/Y2O3 stack was explored as the gate dielectric for Ge metal-oxide-semiconductor (MOS) devices on Si substrate. The crystalline ZrO2 is a Ge stabilized tetragonal/cubic dielectric with the κ value of 36.1 and was formed by depositing a ZrO2/Ge/ZrO2 laminate and a subsequent 500u2009°C annealing. The high-κ crystalline ZrO2/Y2O3 gate stack shows promising electrical characteristics in terms of low interface trap density of 5.8×1011u2002cm−2u2009eV−1, negligible hysteresis, and leakage current of 5.6×10−4u2002A/cm2 at gate bias of flatband voltage (VFB) 1 V for equivalent oxide thickness of 1.13 nm. This gate stack not only demonstrates the eligibility for advanced Ge MOS devices but introduces a more reliable process to form a high-κ crystalline gate dielectric.

\hbox{ZrO}_{2}

Metal-insulator-metal (MIM) capacitors with crystalline-TiO₂/SiO₂ stacked dielectric are explored in this letter. The crystalline TiO₂ possesses a high permittivity while the SiO₂ provides a negative quadratic voltage coefficient of capacitance (<i>VCC</i>-α) to cancel out the positive <i>VCC</i>-α from the crystalline TiO₂. These desirable properties render MIM capacitors with high performance in terms of a capacitance density of 11.9 fF/μm² with a <i>VCC</i>-α of 90 ppm/V². With additional N₂ plasma treatment on the crystalline TiO₂, because of the effective passivation of grain-boundary-related defects and, consequently, a lower leakage current by a factor of 50, the <i>VCC</i>-α can be further lowered to 30 ppm/V² with slight degradation in capacitance density to 11.2 fF/μm², which well meets the requirement in 2018 set by ITRS.

as Charge-Trapping Layer

Metal-insulator-metal (MIM) capacitors with single TiO₂ and a TiO₂/Y₂O₃ stack as an insulator are explored in this letter. It is found that, at the process temperature higher than 400°C, TiO₂ MIM capacitors demonstrate a high capacitance density at the price of an unacceptably high leakage current and voltage coefficient of capacitance (VCC). On the other hand, with the process temperature of 500°C, TiO₂/Y₂O₃ MIM capacitors display desirable characteristics in terms of a large capacitance density of 32.2 fF/μm², a low VCC of 3490 ppm/ V², small frequency dispersion, and a low leakage current of 4.5 × 10^-9 A/cm² at -1 V. The Y₂O₃ film not only provides a high dielectric-electrode band offset but also possesses high thermal stability against crystallization; both are important to suppress leakage current. In addition, the Y₂O₃ film prevents a TiO₂ film from crystallization at 500°C due to the increased entropy caused by incorporated Y atoms, and the amorphous TiO₂ film offers a high κ value to achieve a large capacitance density without sacrificing leakage current and VCC.

Tetragonal

Resistive random access memory (RRAM) cells with a thin oxygen-deficient ZrTiOx, film topped by a Ti oxygen- gettering layer and a Pt electrode were fabricated on n-Ge layer, and the switching mechanism, as well as electrical characteristics, was explored. The RRAM cells demonstrate a stable bipolar switching behavior without the requirement of a forming process. Because of the existence of a larger amount of interface traps which would trap carriers and help build a favorable electric field for the drift of oxygen vacancies, the RRAM cells possess lower SET and RESET voltages compared to those fabricated on n-Si layer. With many promising properties such as a large sensing margin of 300 times, a high operation speed of 250 ns, a robust endurance of 105 cycles, and a long data retention time of up to 10 years, the ZrTiOx-based RRAM cells exhibit a promising perspective as nonvolatile memory devices for Ge-based technology.