Good Diffusion Barrier Research Articles

Co-sputtered TiB 2 as a diffusion barrier for advanced microelectronics with Cu metallization

Titanium boride thin films were deposited from separate Ti and B targets by magnetron co-sputtering and the conditions for obtaining good diffusion barrier properties were evaluated. The best diffusion barrier properties against Cu penetration were obtained when the film was amorphous and deposited with RF bias. Auger electron spectroscopy (AES) and plan-view scanning electron microscopy (SEM) revealed that Cu penetration into amorphous titanium boride is appreciably greater in the unbiased specimen. The as-deposited amorphous film has a resistivity of 450–500 μΩ · cm, but after following annealing at ∼ 723°C for 1 h a substantial decrease in resistivity was obtained while the structure of the boride remained amorphous. The amorphous boride is stable up to 890°C. The crystallization temperature can be decreased by RF bias application, and under these conditions microcrystalline TiB 2 can be formed already at ∼ 400°C. Crystalline TiB 2 has a strong (001) preferred orientation. TiSi 2 (C-54) is also formed during annealing at temperatures exceeding 765°C as a result of the reaction of titanium boride containing free Ti with the silicon substrate.

Alteration of oxidation behaviour of silicon carbide by aluminium implantation

Surface modification of ceramics by ion implantation is a fruitful area of research, giving the prospect of improving their surface-sensitive properties such as oxidation and wear resistance, hardness, and fracture toughness, while retaining the desirable bulk properties. In the case of oxidation, the surface chemistry of ceramics can be so tailored as to favour conditions for enhanced oxidation stability. These conditions include formation of an oxide barrier layer, neutralization of detrimental effects of bulk or environmental impurities, and modification of oxide defect concentration and conductivity. The effects of ion implantation on the oxidation behaviour of ceramics, mainly silicon nitride and silicon carbide, have been shown to be complex [1, 2]. Noda et al. [1] investigated the oxidation behaviour of sintered silicon nitride implanted with chromium to doses in the range 1 × 10175 × 1017 ions/cm 2 at 200 keV. It was shown that, at temperatures up to 1100 °C, a stable chromia layer was preferentially formed and acted as a good diffusion barrier to inward diffusion of oxygen and outward diffusion of impurity cations present in the sintered specimens. Chromium implantation markedly increased the oxidation resistance of silicon nitride. Above 1100 °C, little difference was observed in the oxidation behaviour between the implanted and unimplanted specimens due to rapid vaporization of chromium oxide. Studies of chromium-implanted silicon carbide by McHargue et al. [2] yielded an opposite outcome, however. It was revealed that silicon carbide implanted with chromium to doses in the range 6.2 × 1015-2.7 × 1016 ions/cm 2 at 95-280 keV exhibited significantly faster chemical-etching and oxidation rates than unimplanted samples~ These results were attributed to the amorphization of SiC by chromium implantation [2]. The adverse effect of implantation-induced structural changes on oxidation was also shown by Due t al. [3] in their oxidation studies of self-implanted single crystal silicon carbide at 1100 °C. Documented studies which investigate the potential of ion implantation to improve the oxidation resistance of silicon carbide and silicon nitride ceramics have been focused on using chromium as the dopant [1, 2]. In principle, any dopant may be considered to have a potentially beneficial effect on the oxidation stability if the dopant preferentially

Preparation and microstructure of reactively sputtered Ti 1− xZr xN films

Thin films of Ti 1− x Zr x N with various x have been deposited by reactively sputtering with a segmental TiZr target in an ArN 2 mixture under different conditions of total pressure and applied substrate bias. The thin films are characterized from the macro and micro points of view with the use of Auger electron spectroscopy, X-ray diffraction, electron probe microanalysis and high resolution field emission scanning electron microscopy. It has been found that the microstructure of the films depends strongly on the deposition conditions such as substrate position, total pressure and applied substrate bias, whereas it is less sensitive to the composition X. Ti 1− x Zr x N films are suggested to act as a good diffusion barrier.

Evaluation of Ta, Ti and TiW encapsulations for corrosion and diffusion protection of Cu interconnects

Using Auger electron spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy and sheet resistance measurements the properties of sputtered thin film Ta, Ti and TiW as humidity-induced corrosion barriers for Cu substrates have been evaluated. Ta/Cu/Ta, Ti/Cu/TiN and TiW/Cu/TiW sandwich structures processed on SiO 2 substrates were thermally stressed in 100% relative humidity (2 atm) at 120 °C for 72 h. While Ta and Ti films made excellent humidity-induced corrosion barriers, with smooth surfaces, TiW was destroyed, transforming Cu to Cu 2O and CuO. A comparative study showed Ta and TiW to be good diffusion barriers for Cu. Titanium broke down as a diffusion barrier by reacting with Cu at about 300 °C.

Recent Advances in the CVD of Metal Nitrides and Oxides

AbstractUse of metal-organic precursor materials has permitted thermal CVD of many metal nitrides at remarkably low temperatures and without corrosive by-products. Metallic TiN, VN, Nb3N4 and Mo2N3; semiconducting GaN and Sn3N4; and insulating AIN, Zr3N4, Hf3N4 and Ta3N5 can be deposited at temperatures typically in the range 100 to 400 C. Deposits free of carbon are obtained by transamination reactions of metal dialkylamido precursors with a sufficiently large excess of ammonia. The resulting TiN films are good diffusion barriers, and provide low contact resistance between metals and silicon.Transparent semiconducting oxide films, such as SnO2, ZnO and TiO2, are often made by MOCVD for use in solar cells, energy-efficient window coatings and electro-optical displays. These wide band-gap semiconductors can be doped to n-type conductivity by a variety of dopant elements. Fluorine is the dopant which produces materials with the highest electron mobility, conductivity and transparency, by substituting for oxygen. Certain organic fluorine compounds have been found to be very effective fluorine dopants for these CVD reactions, yielding films with very shallow donors having nearly 100 % electrical activity.Precursors for the CVD of alkaline earth metal oxides, particularly barium, lack the volatility and stability needed for reproducible deposition of superconducting, ferroelectric or magnetic oxides. Use of ammonia or volatile amines as carrier gases greatly enhances the volatility and stability of betadiketonates of barium, strontium and calcium, providing high and stable transport rates for source temperatures below 100 C, even for non-fluorinated ligands.

Stability of Ultra-Thin Gate Oxides with Boron Doped Polysilicon Gate Structures After Rapid Thermal Annealing

ABSTRACTWe report a systematic study of dopant diffusion behavior for thin gate oxides and polysilicon implanted gate structures. Boron behavior is emphasized and its behavior is compared to that of As+ and BF2+. Dopant activation is achieved by rapid thermal annealing. Test structures with 100 Å, 60 Å and 30 Å gate oxides and ion implanted polysilicon gate electrodes were fabricated and characterized after annealing by SIMS, SEM, TEM, and C-V rpeasurements. For arsenic implanted structures, no dopant diffusion through a gate oxide of 30 Å thickness and an annealing condition as high as 1 100*C/1Os was observed. For boron implanted structures, as indicated by SIMS depth profiling, structures annealed at 1000*C/10s exhibit a so-called critical condition for boron diffusion through a 30 Å gate oxide. Boron dopant penetration is clearly observed for 60 Å gate oxides at an annealing condition of 1050 0C/10s. The flatband voltage shift can be as high as 0.56 volts as indicated by C-V measurements for boron penetrated gate oxides. However, 100 Å gate oxides are good diffusion barriers for boron at an annealing condition of 1100°C/10s. For BF2 implanted structures, the diffusion behavior is consistent with behavior reported in the literature.

Formation of TiN by nitridation of magnetron sputtered Ti films using microwave plasma CVD

The formation of a TiN z /TiSi x bilayer by microwave-assisted nitrogen plasma nitridation of titanium film with changing microwave power has been studied. Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy were used to characterize the formation of TiN z /TiSi x bilayer and to examine the barrier properties. The results show that the nitrided and silicided Ti layers grow in thickness and increase in concentration according to microwave power increase, and that the samples treated above the power of 200 W have good film properties, and that the TiN z /TiSi x /Si structure has good diffusion barrier properties up to ∼500° C for 30 min heat treatment.

Cu passivation: A method of inhibiting copper-polyamic acid interactions

The use of passivation metals to protect Cu from interacting with polyamic acid precursor has been investigated by means of cross-sectional transmission electron microscopy, Rutherford backscattering spectroscopy, and resistivity measurements. Palladium or platinum, each 100 nm in thickness, was electron-beam evaporated onto Cu surface. Although not a good diffusion barrier against Cu outdiffusion, these metals can still effectively inhibit the Cu-polyamic acid interactions and, consequently, prevent the formation of Cu oxide precipitates in the polymer film. The trade-off is that, since Pd and Pt both diffuse into Cu and form solid solution alloys, the resistivity of Cu is raised significantly due to the enhanced electron-impurity scattering. In contrast, Cr serves both as a passivation metal and a good diffusion barrier without raising Cu resistivity. This is probably due to the lack of mutual solubility between Cr and Cu.

Electrical degradation of Al/TiW/CoSi2 shallow junctions

TiW barrier properties have been investigated by electrical testing of shallow CoSi2 junctions. Rutherford backscattering and Auger analyses have been used to study Al(0.5% Cu)/TiW/CoSi2/Si structure. Based on the electrical data, it was demonstrated that 900 Å of TiW will serve as a good diffusion barrier up to 475 °C/30 min. The junctions failed at 450 °C when TiW thickness was reduced to 450 Å. The electrical data show the stress of TiW film does not show any significant effects on its properties. Furthermore, shallower junctions (i.e., p+n ) are more vulnerable to barrier failure.

Rapid thermal annealing of YBaCuO thin films sputtered on [formula omitted] substrates

We have determined the rapid thermal annealing (RTA) conditions that optimize both the surface quality and the superconducting properties of YBaCuO films deposited on silicon-based substrates. This process has allowed a very thin nitride layer (45Å) to be a good diffusion barrier; silica acting as a sticking layer. A T(onset) in the 87–91 K range has been obtained, with T( R = 0) ∼- 60 K and Jc ∼- 500 A.cm −2 at T(R = 0) 2 . Repeated RTA cycles might by a way to improve these figures.

WSi x refractory gate metal process for GaAs MESFETs

A co-sputtering process is characterized which allows the deposition of WSi 0.4 layers for Schottky gates of GaAs self-aligned MESFETs. The process parameters were optimized to yield films with low stress, good adhesion and a high interface stability during 800°C n + implant activation anneal. The good diffusion barrier properties of the Schottky metal can be attributed to the amorphous nature of the film. This implies a natural explanation of the optimum film composition. Employing various analytical methods the gate metal/GaAs interface was characterized after 800°C anneal. I− V diode measurements were performed to obtain contact electrical properties such as barrier height and ideality factor. MESFETs with different channel implants down to 10 keV were fabricated to confirm the good stability of the Schottky contact.

Low temperature epitaxial NiSi2 formation on Si(111) by diffusing Ni through amorphous Ni–Zr

Although amorphous alloys are known to be good diffusion barriers, amorphous nickel-zirconium is shown to react with Si at relatively low temperatures. Diffusion of Ni at 350°C through an amorphous Ni–Zr buffer layer leads to the formation of epitaxial NiSi2 on single crystal silicon substrates. Interplay of mobility and thermodynamics is applicable for epitaxial silicide nucleation and growth. Also, a one-step annealing process in oxygen ambient leads to bilayer formation of NiSi2/ZrO2 structures on silicon substrates.

Diffusion and Adhesion of Cu/Parylene

ABSTRACTThe combination of Cu and parylene (poly-p-xylylene) for metallization and insulator in integrated circuit or packaging multilayer interconnection systems gives one of the lowest resistance and capacitance values per unit length. In this paper we present a detailed study of the diffusion characteristics of Cu in parylene-n (PA-n) substrates. PA-n was vapor-deposited and Cu metallization performed at room temperature using the Partially Ionized Beam (PIB) technique. Rutherford Backscattering (RBS) technique has been used to study the diffusion of Cu in PA-n substrate after annealing the samples to elevated temperatures in vacuum. We found no sign of Cu diffusion after the Cu/PA-n sample was annealed at 300°C for 6 hours. Diffusion occurs at 350 °C. However, preannealed PA-n substrate prior to Cu deposition can prevent the diffusion even at a temperatures above 350°C. Also we found that amorphous carbon and chromium are good diffusion barriers of Cu on PA-n. The dry adhesion between PA-n deposited on Al, Cu and Ag was found to be good. The adhesion of these PIB deposited metals on PA-n in high vacuum was also very good.

Characterization of WSix gate metal process for GaAs MESFET's

A WSi 0.4 cosputtering process has been developed to provide a gate metallization for GaAs self-aligned MESFET devices. The deposition parameters were optimized to produce films with good interface stability during 800°C n + implant activation anneal. The importance of the amorphous structure to serve as a good diffusion barrier is emphasized. Various analytical methods are employed to characterize the gate metal/GaAs interface. I–V diode measurements were used to characterize contact electrical properties such as barrier height and ideality factor. MESFET's with a very shallow channel implant (10 keV) were fabricated with a K-value of 510 mS/V·mm, thus the good stability of the Schottky contact to GaAs was confirmed.

Interdiffusion of an Au/Ni/Cr multilayer metallization on silicon substrates

The Au/Ni/Cr multilayer metallization is widely used in silicon devices for interconnections. The interdiffusion behaviour within the metallization and with the silicon substrate is of great practical importance. Sheet resistivity measurements and the Auger electron spectroscopy profiling technique have been used to study the interdiffusion behaviour and the effectiveness of the chromium and nickel layers as diffusion barriers. Interdiffusion became dramatic with an increase in the annealing temperature. At 250°C there was almost no interdiffusion. When the annealing temperature was increased above 450°C interdiffusion was observed to occur significantly. Chromium was found to be a good diffusion barrier for interdiffusion between gold and silicon. For a thin chromium layer 35nm thick, it remained effective until 450°C. Its thermal stability was limited by the out-diffusion of chromium through the gold overlayer. Contrary to previous expectations, nickel was not an effective diffusion barrier for interdiffusion between gold and silicon. It was only useful for improving the solderability of the metallization. Interdiffusion between gold and silicon and out-diffusion of chromium through gold were found to be responsible for the increase of the sheet resistivity and detrimental to the solderability of the metallization. The out-diffusion of silicon was the dominating process of interdiffusion between gold and the silicon substrate.

Non-alloyed ohmic contacts on rapid thermally Zn diffused GaAs

Rapid thermal diffusion of zinc into undoped semi-insulating GaAs substrates from spin-on zinc silica film is performed in A.G. Associates Heat pulse 410 system with tungsten-halogen lamps as the heat source. The Zn diffused layers were electrically characterised by Van der Pauw measurements and showed the formation of p + layer. The surface morphology of the diffused layers were observed by optical microscope and scanning electron microscope. The depth profiling of diffused layers by secondary ion microscopy showed considerable diffusion of Si along with Zn. Radio frequency sputter depositing Si 3N 4 was found to be a good diffusion barrier for Zn diffussion. Non-alloyed ohmic contact with low contact resistivity was implemented on these Zn diffused layers.

Stability of hydrogen in silicon nitride films deposited by low-pressure and plasma enhanced chemical vapor deposition techniques

Hydrogen concentration depth profiles in silicon nitride films deposited by low-pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) techniques were studied. Quantitative hydrogen profiling was carried out using the resonant nuclear reaction 15N+1H→12C+4He+γ ray. Hydrogen concentration in as-deposited LPCVD silicon nitride films was ∼2.5×1021 atoms/cm3 and was stable even after a furnace anneal at 450 °C in 3% H2/Ar for 30 min or a rapid thermal anneal at 1000 °C in oxygen for 30 s. These nitride films thus appear to be good hydrogen diffusion barriers. In contrast, hydrogen concentration in as-deposited PECVD silicon nitride films was ∼1.75×1022 atoms/cm3 and dropped to ∼7.5×1021 atoms/cm3 after rapid thermal annealing at 1000 °C in oxygen for 30 s. During high-temperature anneals, the hydrogen diffused from PECVD silicon nitride film into the underlying SiO2 layer. A comparison of the hydrogen concentration in these deposited oxides under the nitrides with those previously reported for as-deposited, but uncovered, SiO2 films points out that the observed threshold voltage shifts in nitride covered metal–oxide semiconductor capacitors are related to the loss of hydrogen from the silicon oxide during vacuum processing for nitride deposition and to the subsequent diffusion in SiO2 from the PECVD nitride films.

Screen-Printed Superconducting Y-Ba-Cu-O Thick Films on Various Substrates

Superconducting thick films of the Y-Ba-Cu-O system prepared by screen-printing and sintering on different substrates were investigated to study the effect of the substrate material on the superconducting properties of the films. These properties were determined by carrying out structural studies using SEM, EPMA and XRD and by determining the electrical resistivity. The effect of diffusion barrier layers between the film and the substrate on the superconducting properties of the film was also studied. The onset temperature of superconductivity inYBa2Cu3O7−δ(123) superconducting thick film was around 92 K on almost all the substrates. The substrate material had an influence on the temperature at which zero resistance (i.e. Tc) was attained. This varied from 85 K on yttrium stabilized zirconium oxide (YSZ) and nickel substrates down to below 70 K on other substrates. Nickel offered promise as being a good diffusion barrier between the substrate and the 123 superconducting thick film because the reactions between the film and nickel occurred slowly and did not impair the superconducting properties of the film. In the case of alumina substrates, there was a rapid reaction which took place at high annealing temperatures. A BaAl2O4phase was found between the film and the alumina substrate which promoted adhesion but resulted in poor superconducting properties of the film.

The deposition and film properties of reactively sputtered titanium nitride

Titanum nitride films were prepared by reactive d.c. magnetron sputtering from a titanium target in a working gas mixture of Ar + N 2. Film preparation was examined with respect to kinetics during reactive sputtering. Rutherford backscattering, Auger electron spectroscopy, transmission electron microscopy and electron diffraction were used to determine film composition, impurity levels and microstructure. The stoichiometric TiN films were found to possess a single-phase f.c.c. structure and demonstrated good diffusion barrier integrity in an Al/TiN/Si structure at temperatures below 550 °C. Interposition of a thin 60 Å titanium layer at the TiNSi interface yielded low contact resistance to p +- and n +-Si regions. The limitation of reactively sputtered TiN diffusion barrier layers was determined to be their effect on the electromigration of the overlying aluminum, an effect which has not previously been reported. The insertion of a TiN layer between the aluminum and the underlying SiO 2 shifted the electromigration failure mode from open- to short-circuit formation and reduced the median time to failure (MTF) by more than an order of magnitude. The MTF of the composite Al/TiN conductor was a factor of 5 less than that for a comparable Al/TiW conductor. Preliminary experimentation with layered Al/Ti conductors revealed the electromigration failure mode also to be short-circuit formation.

Glow Discharge Produce Amorphous Sic:H Thin Films

ABSTRACTAmorphous hydrogenated silicon carbide alloy films (a-SiC:H) were produced by the decomposition of methane and silane in a glow discharge deposition system. A deposition rate of 13 Å/sec was achieved for good quality films. Amorphous SiC:H films of p+type and n+type of a band gap of 1.86 eV and 1.8 eV and the activation energy of 0.4 eV and 0.23 eV, respectively were obtained. Results show that p+type and n+type a-SiC:H films can be good window layers and good diffusion barriers for indium in polyimide/metal/n-i-p(p-i-n)/ITO amorphous silicon solar cells.