Copper has attracted attention as a new interconnection material for metalization because of its lower bulk resistivity and higher resistance to electro migration than Al and its alloys. However, Cu diffusion into Si and SiO2 during annealing degrades the reliability of VLSL devices. A barrier layer is therefore important in realizing Cu interconnection technology. Tantalum (Ta) thin films are very stable barrier film against Cu diffusion. The sensitivity and depth resolution of the SIMS technique make it an attractive tool for monitoring Cu diffusion. In this study, Cu/Ta/SiO2/Si samples were heat treated at 400 degrees C-850 degrees C, and analyzed by a Cameca IMS 6f SIMS instrument with oxygen beam under various conditions. Specially, the use of a rotating stage on SIMS provides significant improvement in depth resolution for polycrystalline metal film samples.
Secondary ion mass spectrometry (SIMS) depth profiling is an important technique for the characterization of ultra shallow junctions, thin gate oxides and other interfacial layers in modern wafer fabrication. In this study, a CAMECA IMS 6f SIMS instrument is used to study the various factors that may affect the depth resolution in ultra shallow depth profiling of a B delta doped Si standard sample. Several analyses using 0.5-2.0 keV O2+ have been performed with and without oxygen flooding and sample rotation. The roughening of the sputtered crater bottom is one factor that degrades the depth resolution in low energy depth profiling, and both oxygen flooding and sample rotation are shown to suppress surface roughening. In addition, the depth resolution is found to be sensitive to other factors such as ion beam mixing and as a result, impact energies as low as 0.5 keV may be needed to achieve optimum depth resolution.
Tantalum (Ta) thin films of 35 nm thickness were investigated as diffusion barriers as well as adhesion- promoting layers between Cu and SiO2 using x-ray diffractometry (CRD), Scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). After annealing at 600 degrees C for 1h in vacuum, no evidence of interdiffusion was observed. However, XPS depth profiling indicates that elemental Si appears at the Ta/SiO2 interface after annealing. In- situ XPS studies show that the Ta/SiO2 interface was stable until 500 degrees C, but about 32 percent of the interfacial SiO2 was reduced to elemental Si at 600 degrees C. Upon cooling to room temperature, some elemental Si recombined to form SiO2 again, leaving only 6.5 percent elemental Si. Comparative studies on the interface chemical states of Cu/SiO2 and Ta/SiO2 indicates that the stability of the Cu/Ta/SiO2/Si system may be ascribed to the strong bonding of Ta and SiO2 due to the reduction of SiO2 through Ta oxide formation.
This paper repots the effect of a flash copper layer, sandwiched between a copper film deposited by metal-organic chemical vapor deposition (MOCVD) and a TaN barrier metal, on copper diffusion through TaN barrier to Si substrate. The structures studied include a Cu film deposited by MOCVD, a thin layer of flash Cu and a TaN barrier layer deposited by ionized metal plasma (IMP), and SiO2 grown on SI substrate. It is found that for the structure of CVD Cu/TaN/SiO2/ Si which has no flash Cu layer, the Cu could diffuse through the 25-nm thick barrier layer at an annealing temperature of 600 degrees C. However, by depositing a flash CU layer between the CVD Cu film and the TaN barrier, the Cu diffusion can be significantly reduced. In addition to Cu, the diffusion of Ta and oxygen, and the interaction between them at different temperatures are also examined. Our observations provide useful information on Cu moralization for deep sub-micron integrated circuits.
In this study, we have simulated the melt front and temperature distribution profiles for pre-amorphized Si during laser irradiation. The simulation data show that theoretically, it is possible to melt the whole amorphous layer without melting the underlying crystalline substrate. On the other hand, ultra-shallow p+/n junctions were formed by ultra-low energy boron ion implantation into pre- amorphized silicon substrates. Dopant activation was achieved via spike rapid thermal annealing (RTA) and pulsed excimer laser annealing. Secondary ion mass spectrometry analyses show that a step-like dopant profile can be obtained with a single-pulse laser irradiation. Such a profile is in sharp contrast with the boron concentration profile that is obtained after spike RTA. The cross- sectional transmission electron microscopy images show that the entire pre-amorphized layer has been recrystallized to single-crystalline Si after laser annealing. The results clearly indicate the advantages of employing laser anneal as compared to RTA in the fabrication of highly activated and abrupt ultra-shallow junctions.
KEYWORDS: Copper, Silicon, Annealing, Metalorganic chemical vapor deposition, Crystals, Chemical vapor deposition, Resistance, Metals, Diffusion, Chemical species
We report the properties of the copper films deposited by metal-organic chemical vapor deposition (MOCVD) and the interaction between the copper film and its neighbor layer in the Cu/TaN/SiO2/Si structures upon annealing in a furnace in a nitrogen environment. It is found that the sheet resistance of the copper film slightly decreases as the annealing temperature increases up to 500 degrees C and the increases drastically with the further increase of the annealing temperature. From x-ray diffraction, both CuTa10O26 and TaSi2 can be observed in the MOCVD Cu/TaN/SiO2/Si structures at an annealing temperature of 600 degrees C, indicating an interact between the Cu film and the layer underneath. For the structures which have a deposited flash Cu layer between the CVD Cu film and TaN barrier, however, the TaSi2 cannot be observed. SIMS analysis indicates that the addition of the flash Cu layer also impacts Cu diffusion across the barrier metal due likely to the change in the crystallographic plane of the Cu films.
A comparative study on GaN/sapphire has been performed by transmission electron microscopy (TEM) and IR reflectance (IR). TEM observations reveal that both the undoped and Si doped GaN epilayers have large density of threading dislocations. Dislocations in the undoped GaN tend to from open core structure, while dislocation lines in the Si-doped GaN are very sharp and the strain contrast is much more confirmed. It is believed that Si-doping causes the increase in undoped GaN to much more confirmed dislocation lines. Frank dislocation loops are also found lined up at a depth of about 110 +/- 10 nm from the interface. High resolution TEM study also reveals that the GaN buffer layer grown at low temperature has transformed into its thermodynamically stable wurtzite structure during the high temperature post- buffer GaN epilayer growth process. The comparative IR reflectance hows the corresponding behavior. The interference fringes of the Si doped sample, compared with the undoped ones, shows a contrast damping and reflectance reduction behavior, suggesting the presence of a transition/defect layers near the interface.
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