Ta-Hsun Yeh

Amorphouslike chemical vapor deposited tungsten diffusion barrier for copper metallization and effects of nitrogen addition

In this article, we propose an amorphouslike chemical vapor deposited tungsten (CVD-W) thin film as a diffusion barrier for copper metallization. Experimental results gave no evidence of interdiffusion and structural change for Cu/amorphouslike CVD-W/Si samples annealed up to 675 °C for 30 min in N2. At higher temperatures (700 °C), Cu penetration results in the formation of η′′-Cu3Si precipitates at the CVD-W/Si interface. This is due to the crystallization of the amorphouslike CVD-W film above 650 °C, rendering the grain-boundary structure and, hence, fast pathways for Cu diffusion. The Cu/amorphouslike CVD-W/p+n diodes, thus, sustain large increases in reverse leakage current. In addition, the effects of nitrogen addition by using an in situ nitridation on the amorphouslike CVD-W film are also discussed. The effectiveness of the nitrided barrier is attributed to the blocking of the grain boundaries in the tungsten film by nitrogen atoms. This slows down Cu diffusion significantly. Physical and chemical...

Nitridation of fine grain chemical vapor deposited tungsten film as diffusion barrier for aluminum metallization

A novel tungsten nitride (WNx) film for diffusion barrier applications has been prepared by nitridation of a fine grain chemical vapor deposited tungsten (CVD-W) film. The fine grain CVD-W is deposited at 300 °C in a low pressure chemical vapor deposition reactor with a SiH4/WF6 flow rate of 12.5/5 sccm under a total gas pressure of 100 mTorr. The subsequent nitridation process is executed in nitrogen plasma at 300 °C without breaking vacuum. The thickness of WNx layer as examined by secondary ion mass spectroscopy is 50 nm after 5 min exposure to nitrogen plasma. X-ray photoelectron spectroscopy spectra shows that the atomic ratio of tungsten to nitrogen in WNx layer is 2:1. According to the analysis by Auger electron spectroscopy and the measurement of n+p junction leakage current, the Al/WNx/W/Si multilayer maintains excellent interfacial stability after furnace annealing at 575 °C for 30 min. The effectiveness of W2N barrier is attributed to stuffing grain boundaries with nitrogen atoms which eliminat...

Highly selective etching for polysilicon and etch‐induced damage to gate oxide with halogen‐bearing electron‐cyclotron‐resonance plasma

The investigations of polysilicon etching with three halogen‐bearing plasmas (SF6, Cl2, and HBr) in an electron‐cyclotron‐resonance reactor have been made. We examine the etching characteristics which include etching rate, anisotropy, and selectivity based on the discussions of the chemical and electrical properties of the F, Cl, and Br radicals. It was found that the degree of anisotropy strongly depends on the deposition of a silicon halide film on sidewall and on the spontaneous etching properties of three halogen plasma mixtures. The selectivity to oxide is related to the amount of silicon halides that are produced during etching poly‐Si and the electrically polarized level of these products when they adsorb on the oxide surface. We find that the selectivity on oxide is approximately infinite for the HBr system and over 90 for the Cl2 system. In addition, the effects of oxygen addition, microwave power, and rf power are also investigated. It was found that the maximum etching rate and selectivity of S...

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.

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.

Thermal Stability of Amorphous-like WNx/W Bilayered Diffusion Barrier for Chemical Vapor Deposited-Tungsten/p+-Si Contact System

The barrier characteristics of tungsten nitride/tungsten (WNx/W) bilayer formed by an in situ nitridation on a thin chemical vapor deposited amorphous-like tungsten (CVD a-W) film in CVD-W/Si contact system have been investigated. The thickness of WNx layer after a 5 min of N2 plasma exposure at 300°C approximated 50 nm and the atomic ratio of W to N in WNx layer was 2:1. In the CVD-W/a-WNx/a-W/Si multilayered sample, no discernible tungsten silicide was detected by X-ray diffractometer (XRD) at W/Si interface after annealing at 750°C. Meanwhile, with the Rutherford backscattering spectroscopy (RBS) analysis and the measurement of p+n junction leakage current, the CVD-W/a-WNx/a-W/Si multilayer maintained the integrity of interface and the CVD-W/a-WNx/a-W/p+n diode kept the reverse leakage current density less than 9×10-9 A/cm2 while the post annealing was carried out at 700°C for 30 min. As the experimental results, the effectiveness of amorphous-like WNx/W bilayered diffusion barrier is attributed to stuff grain boundary with N atoms as well as to eliminate the rapid diffusion paths by using CVD a-W material.

The influence of precleaning process on the gate oxide film fabricated by electron cyclotron resonance plasma oxidation

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.