Hai-Sheng Lu

Cu adhesion on tantalum and ruthenium surface: Density functional theory study

This work reports a first-principles study of copper adhesion on Ta(110) and Ru(0001) surface with the density functional theory. Adsorption energy, electron density difference, and geometrical structures of Cu on pure, oxygen, and nitrogen doped Ta(110), Ru(0001) surfaces, and Ru doped Ta(110) surface were investigated. By analyzing the calculated results and the existing experimental results, it is found that although Ta has stronger chemical interaction with Cu, its larger lattice mismatch with Cu, and easy oxidation and nitridation make Ta a poorer Cu adhesion layer in comparison with Ru. The adhesion ability of Cu on Ta can be improved by doping Ru in Ta. The agglomeration of Cu on Ta or Ru is also studied. The calculation results show that Cu adsorbed on Ta(110) surface is more likely to be desorbed and agglomerated on the top of the second Cu atom layer. The substitutional oxygen O Ta in Ta will stimulate the agglomeration of Cu on the Ta surface.

Effect of rapid thermal annealing on optical and interfacial properties of atomic-layer-deposited Lu2O3 films on Si (100)

Lu2O3 films have been grown on Si(100) by atomic layer deposition using Lu(iPrO)3 (iPrO=OCH(CH3)2) and H2O. Optical properties and surface/interface evolution of the Lu2O3/Si system during rapid thermal annealing process have been studied using spectroscopic ellipsometry. The refractive index at 632.8 nm and optical band gap for as-deposited sample are determined to be 1.88 and 4.88 eV, respectively. It is revealed that interfacial Lu-silicate growth upon annealing is the dominant factor affecting the refractive index and optical band gap of Lu2O3 films. For all samples, the surface roughness decreases with increasing annealing temperature.

Chemical-vapor-deposited graphene as charge storage layer in flash memory device

We demonstrated a flash memory device with chemical-vapor-deposited graphene as a charge trapping layer. It was found that the average RMS roughness of block oxide on graphene storage layer can be significantly reduced from 5.9 nm to 0.5 nm by inserting a seed metal layer, which was verified by AFM measurements. The memory window is 5.6 V for a dual sweep of ±12 V at room temperature. Moreover, a reduced hysteresis at the low temperature was observed, indicative of water molecules or -OH groups between graphene and dielectric playing an important role in memory windows.

The thermal and electrical properties of CoMo alloys as copper adhesion/barrier layers

CoMo alloys as copper diffusion barriers were investigated in this work. The thermal stability was studied after annealing, which was measured by FPP, XRD, SEM and AES. According to the electrical test, we carried out a new p-cap structure to measure. The breakdown electrical field and C-V properties were measured at 150°C. Both the thermal test and electrical results show CoMo is a potential diffusion barrier.

Investigation of Co/TaN bilayer as Cu diffusion barrier

The diffusion barrier properties of Co/TaN bilayer as Cu adhesion layer/diffusion barrier on the Si and low k (k=2.5) substrates were investigated. The barrier was prepared by using ion-beam sputtering technique. The barrier property was investigated by sheet resistance, X-ray diffraction (XRD), and Auger electron spectroscopy (AES) and electrical measurements. No obvious Cu diffusion and agglomeration was observed after annealing at 500°C for 30 min. Results show that Co/TaN has a good potential as cost effective adhesion/diffusion stack in copper metallization.

Investigation of ultra-thin Al 2 O 3 film as Cu diffusion barrier on low-k (k=2.5) dielectrics

Ultrathin Al<inf>2</inf>O<inf>3</inf> films were deposited by PEALD as Cu diffusion barrier on low-k (k=2.5) material. The thermal stability and electrical properties of the Cu/low k system with Al<inf>2</inf>O<inf>3</inf> layers with different thickness were studied after annealing. The AES, TEM and EDX results revealed that the ultrathin Al<inf>2</inf>O<inf>3</inf> films are thermally stable and have excellent Cu diffusion barrier performance. The electrical measurements of dielectric breakdown and TDDB tests further confirmed that the ultrathin Al<inf>2</inf>O<inf>3</inf> film is a potential Cu diffusion barrier in the Cu/low-k interconnects system.

Density Functional Theory Study of Cu Adhesion on Rh, Ir, Pd, Ta, Mo, Ru, Co, and Os Surfaces

In this work, first-principles calculation based on the density functional theory was applied to study Cu adhesion on the surfaces of Rh(111), Ir(111), Pd(111), Ta(110), Mo(110), Co(0001), Os(0001), and Ru(0001), on which the adsorption energy, electron density difference, and geometrical structures of Cu were investigated. The analysis of the calculated and experimental results shows that the atomic chemical interaction, surface lattice mismatch, and crystal lattice type have marked effects on Cu adhesion on glue layers. Cu atoms on all the metal surfaces studied in this work are more likely to form the fcc structure with a quasi-(111) orientation. The coupling effect of the large surface lattice mismatch and the lattice type difference between Cu and the metal surface can greatly reduce Cu adhesion ability. Among all the studied metals, Ir and Os showed comparable adhesion ability to Ru and can be considered as promising Cu glue layers for Cu interconnects.

Direct Growth of Al2O3 on Black Phosphorus by Plasma-Enhanced Atomic Layer Deposition

Growing high-quality and uniform dielectric on black phosphorus is challenging since it is easy to react with O2 or H2O in ambient. In this work, we have directly grown Al2O3 on BP using plasma-enhanced atomic layer deposition (PEALD). The surface roughness of BP with covered Al2O3 film can reduce significantly, which is due to the removal of oxidized bubble in BP surface by oxygen plasma. It was also found there is an interfacial layer of POx in between amorphous Al2O3 film and crystallized BP, which is verified by both X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) measurements. By increasing temperature, the POx can be converted into fully oxidized P2O5.

Direct copper electrodeposition onto cobalt adhesion layer in alkaline bath

The direct electroplating of copper film on an ultrathin cobalt film in the alkaline bath was investigated. The plating bath consists of CuSO4·5H2O and ethylenediamine. It is found that the ethylenediamine can well stop the cobalt reaction with copper ion and make the copper deposition on cobalt possible. The experimental results show that the copper films on the cobalt have a high preferential (111) orientation, very low surface roughness and low resistivity.

Surface modification of porous low-k material by plasma treatment and its application on reducing the damage from sputtering and CMP process

The influence of CH<inf>4</inf>, H<inf>2</inf>, NH<inf>3</inf> and He plasma on the properties of porous low-k material is studied. It is found that the H<inf>2</inf>, He, NH<inf>3</inf> plasma can cause huge carbon depletion in the porous low-k material, and change the low-k surface from hydrophobic to hydrophilic, which will induce moisture uptake into the low-k material during the CMP process, and results in the increase of the k value and leakage current. The CH<inf>4</inf> plasma can make low-k material more resist against moisture uptake and keep the k value and leakage current of low-k films stable.