Chii-Horng Li

The relaxation phenomena of positive charges in thin gate oxide during Fowler-Nordheim tunneling stress

In this study, new relaxation phenomena of positive charges in gate oxide with Fowler-Nordheim (FN) constant current injections have been investigated and characterized. It was found that the magnitudes of applied gate voltage shifts (/spl Delta/V/sub FN/) during FN injections, after positive charges relaxed or discharged, have a logarithmic dependence with the relaxation time for both injection polarities. The results can derive the relationship of transient discharging currents, that flow through the oxides after removal of the stress voltage, with the relaxation time. We have shown that the current has a 1/f dependence for both injection polarities which can be also derived from the tunneling front model. The effects of oxide fields (lower than the necessary voltage for FN tunneling) and wafer temperatures (373 and 423 K) for the relaxation of positive charges are also studied.

Self-Organized Nanomolecular Films on Low-Dielectric Constant Porous Methyl Silsesquioxane at Room Temperature

By dipping in a silanisation solution, a hydrophobic self-organized nanomolecular film (SOM) was successfully grown on the surface of dry-etched porous methyl silsesquioxane (DE-PMSQ). The reaction was spontaneous at room temperature. The moisture adsorption on the DE-PMSQ was avoided and the surface of the SOM/DE-PMSQ was rather smooth. Leakage current and dielectric constant measurements of DE-PMSQ and SOM/DE-PMSQ samples also showed consistent behavior. As a result, it is promising to use the low-k PMSQ as an inter-metal dielectric with hydrophobic SOM grown on DE-PMSQ.

Interface characteristics of selective tungsten on silicon using a new pretreatment technology for ULSI application

The characteristics of selective tungsten film on silicon strongly depend on the surface properties of the underlying substrate. In this work, a new pretreatment process prior to selective tungsten film deposition has been developed. A CF/sub 4//O/sub 2/ mixed plasma modification procedure and a subsequent O/sub 2/ plasma ashing step combine to achieve efficient surface precleaning. The damage and contamination induced by reactive ion etching (RIE) are thus eliminated. Concurrently, a subsequent anhydrous HF cleaning was used to remove the native oxide on silicon as well as to obtain a fluorine-passivated silicon surface which can avoid reoxidation during the transport of wafers. This new pretreatment technology produces tungsten films that retain superior physical properties within the aspects of deposition rate, film morphology, and selectivity. Also, excellent interface characteristics with low silicon consumption, low contact resistance, low contact leakage current, and fewer impurities of fluorine, oxygen, and carbon within the interfacial region are obtained.

Influences of damage and contamination from reactive ion etching on selective tungsten deposition in a low‐pressure chemical‐vapor‐deposition reactor

Reactive ion etching (RIE) used in contact hole formation can result in damage and contamination of the underlying silicon substrate. In this work, influences of these phenomena on selective tungsten deposition in a low‐pressure chemical‐vapor‐deposition reactor have been studied. The damage was generated because of ion bombardment and radiation‐induced bonding changes in silicon lattices. It causes large Si consumption, rough W/Si interface during tungsten deposition, and large leakage current of W/Si Schottky structure. Simultaneously, contamination occurred with two forms of residual layers and impurity permeation layers in fluorocarbon‐based RIE chemistries. The CF4/CHF3/O2 RIE of oxide produces the SiFxCyOz complex layers deposited on the sidewall and on the Si surface as well as the embedding of impurities such as F and C in the Si substrate. The creep‐up, selectivity loss, lateral encroachment, high W film resistivity, and rough W/Si interface have been observed in the contaminated samples. Accordi...

A new simple and reliable method to form a textured Si surface for the fabrication of a tunnel oxide film

In this work, a textured Si surface was formed with a new simple and reliable method for tunnel oxide fabrication. First, a thin poly-Si layer (12 nm thick) was deposited on Si surface and a 30-nm thick dry oxide film was then grown in O/sub 2/ ambient. This oxide film was served as a sacrificial oxide. The poly-Si film and Si substrate were both oxidized during thermal oxidization. After stripping this sacrificial oxide, a textured Si surface was obtained. Tunnel oxide grown on this textured Si surface has asymmetrical J-E characteristics, less interface states generation and better reliability (larger Q/sub bd/) as compared to those of normal oxide.

Effects of gas ratio on electrical properties of electron‐cyclotron‐resonance nitride films grown at room temperature

The effects on the electrical properties of electron‐cyclotron‐resonance (ECR) nitride films grown at room temperature with different SiH4/N2 gas ratios from 7 sccm/43 sccm to 2 sccm/48 sccm are systematically investigated. Superior properties of the films with low bulk trap density 8×1017 cm−3, small trap cross section, high breakdown strength 12.12 MV/cm, and near‐stoichiometric refractive index 2.0 are obtained when the gas ratio SiH4/N2 is 5 sccm/45 sccm, the microwave power is 210 W, and the chamber pressure is 0.5 mTorr. With the microwave power, total gas flow rate, and total pressure unchanged, the decrease in SiH4/N2 ratio lower than 5/45 results in larger trap density and some lower breakdown strength. On the other side, increasing SiH4/N2 ratio results in higher hydrogen content, lower breakdown strength, and films which are easily degraded during consecutive voltage sweep. High microwave power will eliminate the weak bonds and strengthen the electrical stability of the high SiH4/N2 ratio film.

Charge Retention Loss in a

The charge loss mechanism in a hafnium oxide (HfO2 ) dielectric dot flash memory is investigated. We measure the temperature and time dependence of a charge loss induced gate leakage current in a large area cell directly. We find that (1) the charge loss is through a top oxide in the cell and (2) the stored charge emission process exhibits an Arrhenius relationship with temperature, as opposed to linear temperature dependence in a semiconductor-oxide-nitride-oxide-semiconductor flash memory. A thermally activated tunneling front model is proposed to account for the charge loss behavior in a HfO2 dot flash memory.

\hbox{HfO}_{2}

In this work, a simple and reliable method to fabricate a textured Si surface and the characteristics of oxides grown on the textured Si surface are proposed. The concept of different oxidation rates in poly-Si grain and grain boundaries has been used to form textured Si surface which does not need to etch the surface of Si wafer and is without the constraint of stopping the oxidation process on the poly Si/Si-substrate interface to get better electrical characteristics. Tunnel oxide grown on the textured single crystalline Si exhibits much better electrical characteristics and reliabilities than those of oxides grown on poly-Si substrate (thin poly-Si film on Si substrate) and on untextured single crystalline Si substrate.

Dot Flash Memory via Thermally Assisted Tunneling

The influence of the precleaning process on the characteristics of SiO 2 film grown by using electron cyclotron resonance (ECR) plasma oxidation at room temperature is presented in this work. We find that the growth rate, electrical properties, and reliability of the ECR plasma grown oxide is improved by this precleaning step. Two growth mechanisms are found which determine the electrical properties of the plasma grown oxide. The plasma damage is also discussed. We find that plasma oxidation produces little plasma damage in our experiments. Excellent ECR plasma grown silicon dioxide with good electrical properties and reliability characteristics are obtained by this precleaning technique.

The characteristics of tunnel oxides grown on textured silicon surface with a simple and reliable process

In this work, the thin tungsten film nucleated by an in situ SiH 4 -WF 6 gas-phase reaction in the low pressure regime (100 mTorr) was investigated and used as an adhesion layer to replace TiN in a blanket chemical vapor deposition of tungsten (CVD-W) process. The deposition rate, step coverage, and film resistivity were studied as a function of the process parameters. Deposition rates from 360 to over 3000 nm/min were observed and increased with increasing deposition pressure and temperature. Moreover, we found that the deposition rate fell to zero when the temperature was less than 150°C. Also, the gas-phase reaction vanished when the SiH 4 /WF 6 flow ratio was smaller than 1.6. On the other hand, the step coverage decreased with increasing deposition rate. Finally, the tungsten film resistivity was 167 μΩ-cm which was comparable to that of a sputtered TiN film (about 150 μΩ-cm) and also exhibited good adhesion ability on oxide when the temperature was higher than 200°C. Overall, the results indicate that this in situ gas-phase nucleated tungsten film is an attractive replacement for TiN film in the blanket CVD-W technique because of reduced process complexity, excellent step coverage, and low resistivity.