Abstract: An enhanced protective coating to prevent interaction between constituents of the environment and devices that can be damaged by those constituents. This coating is provided by applying a synergistic combination of diffusion barrier and physical barrier materials. These materials can be, for example, in the form of a plurality of layers of a diffusion barrier and a physical barrier, with these barrier layers being alternated. Further protection in certain instances is provided by including at least one layer of a getter material to actually react with one or more of the deleterious constituents. The coating is illustrated by using alternating layers of an organic coating (such as Parylene-C™) as the diffusion barrier, and a metal coating (such as aluminum) as the physical barrier. For best results there needs to be more than one of at least one of the constituent layers.

Abstract: The interconnects in a semiconductor device contacting metal lines comprise a low resistance metal, such as copper, gold, silver, or platinum, and are separated by a material having a low dielectric constant, such as benzocyclobutene or a derivative thereof. A tri-layer resist structure is used, together with a lift-off process, to form the interconnects. The low dielectric constant material provides a diffusion barrier to the diffusion of the low resistance metal. The tri-layer resist comprises a first layer of a dissolvable polymer, a second layer of a hard mask material, and a third layer of a resist material. The resulting structure provides an integrated circuit with increased speed and ease of fabrication.

Abstract: A novel submicron process sequence was developed for the fabrication of CoSi/sub 2//n/sup +/-Si, CoSi/sub 2//p/sup +/-Si ohmic contacts and multilevel interconnects with copper as the interconnect/via metal and titanium as the diffusion barrier. SiO/sub 2/ deposited by plasma enhanced chemical vapor deposition (PECVD) using TEOS/O/sub 2/ was planarized by the novel technique of chemical-mechanical polishing (CMP) and served as the dielectric. The recessed copper interconnects in the oxide were formed by chemical-mechanical polishing. (dual Damascene process). Electrical characterization of the ohmic contacts yielded contact resistivity values of 10/sup -6//spl Omega/-cm/sup 2/ or less. A specific contact resistivity value of 1.5/spl times/10/sup -8//spl Omega/-cm/sup 2/ was measured for metal/metal contacts. >

Abstract: A capacitor and electrode structure comprising a PZT ferroelectric layer 17 with a primary component (Pb) and secondary component (Ti), a lower electrode layer 16 formed on the underside of the ferroelectric layer and made up of a special element (Pt) and Ti, and compounds thereof, and a diffusion barrier layer 18 which is formed on the underside of the lower electrode layer and which functions as a diffusion barrier with respect to Pb The capacitor and the electrode structure, which may be a component of a semiconductor memory device, suppress fluctuations in the composition of the ferroelectric layer in PZT, etc, so as to maintain the intended performance of the PZT ferroelectric layer, thereby simplifying and stabilizing film fabrication, and preventing the degradation of electrical characteristics and adverse effects on lower layers

Abstract: Thin TiN layers have been successfully produced on Si and SiO2 by reactive evaporation combined with rapid thermal annealing. Results of composition, resistivity, and stress measurements on these layers are reported. The TiN layers have a resistivity around 40 μΩ cm and a high stress of between 1 and 6 GPa. The composition ratio of nitrogen to titanium, measured by elastic recoil detection (ERD), combined with time‐of‐flight, was found to vary between 0.8 and 1.0 depending on the deposition conditions. In addition to the stoichiometry determination, ERD also clearly shows the presence of a TiSi2 layer between the TiN and the Si substrate. It is also shown that good TiN layers can be produced by reactive evaporation for nitrogen partial pressures between 1.0 and 2.0×10−5 mbar and for titanium evaporation rates between 0.3 and 0.5 nm/s.

Abstract: Titanium is being investigated as the adhesion promoter and diffusion barrier between silicon dioxide and copper in a copper metallization scheme. Chemical-mechanical polishing (CMP) is being used to define the inlaid copper interconnections. An investigation into the CMP of titanium has revealed an interaction between the presence of copper ions in the polish slurry and the polish rate of titanium. The polish rate of titanium increases dramatically when copper ions are present in the slurry from the previous copper polish step. In this paper, we present and discuss the results of these investigations

Abstract: Chemical plating techniques have been used in silicon processing for many years for junction delineation and ohmic contact formation. In recent years, interest in this area has been renewed because of the potential use of electroless copper deposition for ultra-large-scale integration (ULSI) metallization and for the formation of thin metal etch masks for deep-ultraviolet lithography. Good deposition selectivity, low operating temperature, high copper purity, good filling characteristics, and planar topography have been among the many advantageous attributes reported from early investigations.In the June 1993 issue of the MRS Bulletin on Copper Metallization, Cho et al. gave an exposition on the use of electroless copper for VLSI. More comprehensive reviews of the electrochemical fundamentals can be found in References 8,9, and 10. This article summarizes the current understanding of various chemical and material aspects of this deposition method in an attempt to give an overview of the film growth characteristics for thin film applications. Because of length limitations, only selected topics are included. The emphasis is on the initiation conditions and the resultant microstructure and properties obtained. We also discuss special considerations for fine pattern formation.The information presented here applies primarily to electroless copper deposition on metals and metal silicides since these are the typical substrate surfaces for metallization in contact vias of ULSI circuits. Strictly speaking, metallization of upper-level interconnects occurs mostly on a dielectric base. However, since copper systems usually require a diffusion barrier to shield the copper from diffusing into the silicon, we can treat the deposition process startingfrom this layer onward.

Abstract: A physical vapour deposition diffusion barrier coating, based on amorphous alumina, offers the possibility to reduce the interdiffusion between the MCrAlY overlay and the Ni-base material occurring at elevated temperatures. The barrier function depends on the high temperature stabilization of the dense, amorphous structure. The coating contains nitrogen against the crystallization of alumina phases. Owing to the fact that todays MCrAlYs need diffusion bonding for a satisfactory adhesion, the barrier is deposited as X-Al-O-N, with X as a reactive element forming a diffusion bond layer with the Ni-base and MCrAlY during the first thermal treatment. The paper reviews several high temperature tests in which the barrier function of the alumina based coating was proved. The bonding effect of the chosen X element is explained. The influence of a deposition parameter variation on the formation of the reactive bonding zone is investigated. With this diffusion barrier, the temperature level of the first stage turbine blade could be increased up to 1100°C in the MCrAlY-Ni-base interface.

Abstract: The lifetime of thermal barrier coatings (TBCs) is limited by two main failure mechanisms, namely (i) thermal expansion mismatch between bond coat and top coat and (ii) bond coat oxidation. Both of these can cause failure of the ceramic top coat. Developments of recent years show that bond coats with higher oxidation resistance tend to have better coating system cyclic lives. In this paper the properties of a three-layer TBC consisting of an MCrAlY bond coat, an Al 2 O 3 diffusion barrier (2–5 μm) and a ZrO 2 -Y 2 O 3 top coat are presented. The diffusion barrier is applied by the r.f. physical vapour deposition process, the bond coat and top coat by plasma spraying. By the use of a diffusion barrier the bond coat oxidation can be strongly reduced in the tested temperature range from 1173 to 1373 K. The oxidation kinetics are influenced by the thickness of the diffusion barrier, the temperature of oxidation and the bond coat composition. TBC systems with high oxidation resistance show the best ceramic-bond coat interface strength.

Abstract: A structural model for the Al/SiO2 interface system after an oxidation–reduction reaction is proposed. Thermal dependence of the initial stages of the Al/SiO2 interface formation process is investigated by in situ x‐ray photoemission spectroscopy analysis and secondary ion mass spectrometry measurements of depth profiles. An abrupt interface without any reaction is confirmed when the interface is formed at room temperature. During Al deposition on SiO2 at substrate temperatures beyond 300 °C, oxidation–reduction reaction occurs that produces Al2O3 and reduces metallic Si at the interface. The reduced Si spreads throughout the entire Al layer uniformly and the thin Al2O3 layer acts as a diffusion barrier that limits the reaction in the very vicinity of the interface. This suggests a distinct layer ordering of the reacted system, Al(Si)/Al2O3/SiO2.

Abstract: Copper is known to diffuse in dielectrics subjected to high electrical bias at temperatures as low as 100 degree(s)C. Also, it does not adhere to the interlayer dielectrics like SiO2 and polymers. In addition, copper corrodes readily in the corrosive environments. These properties of copper have inhibited the early acceptance of copper as the interconnection metal in the high performance integrated electronic circuit/devices. We have investigated the use of possible diffusion barrier (DB) and adhesion promoter (AP) materials in the conventional layered structures which lead to an increase in the total interconnection resistance negating the advantages of copper. Also, since the subquarter micron circuits necessitates the need of < 10 nm thick DBAP material, such layered structures are generally not stable under the interconnection processing, chip packaging, and/or actual use conditions. In this paper, we present results of our study of the electrically stable and corrosion resistant doped copper as the interconnection material. Al, Mg, and Ta, all of which have considerably higher free energy of formation for their oxides compared to that for Cu or Si oxides, have been added as the dopant in concentration range of 0.5 - 10 atomic percent in copper. Resistivity, adhesion to dielectric surfaces, effect of annealing to temperatures as high as 800 degree(s)C on such properties, corrosion resistance in air, and I-V/C-V characteristics of the metal/SiO2/Si capacitors have been investigated. It is found that addition of such dopants provides the necessary passivation. Doped films are very smooth even after anneals to temperatures as high as 800 degree(s)C. They did not lose adherence to SiO2 substrates after such anneals as demonstrated by the adhesive tape-peel tests. Preliminary indications are that doping has reduced the overall stress in the film. There is a small increase in the resistivity of copper, caused by the addition of these dopants. For example, for Cu with Mg (less than 2 atomic percent) the resistivity remains at or below 2 (mu) (Omega) cm. These results are compared with layered Al/Cu, Mg/Cu, Ti/Cu and TiN/Cu and show that doped films of copper satisfy all the reliability requirements at a small sacrifice of the resistivity in a manner similar to Al containing small amounts of copper.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Abstract: Most Ni-based metal matrix composites (MMC) studied to date were reinforced with ductile refractory metal fibers, mostly W or W-alloys. However, Ni embrittles and weakens cold-drawn W fibers by (1) forming intermetallic phases at the fiber-matrix interface and (2) inducing recrystallization of W at temperatures as low as 950 C by rapid grain-boundary diffusion. To prevent these problems, ceramic coatings with low solubility, reactivity, and diffusion coefficients for both W and Ni can be applied at the interface. However, ceramic coatings are brittle, and typically exhibit a large mismatch of coefficient of thermal expansion with Ni; therefore, these coatings tend to crack when the composite is subjected to thermal cycling. To prevent cracking of the diffusion barrier, ductile, metallic coatings can be used. Rhenium is an attractive candidate for W fibers in a Ni matrix, since it exhibits high-temperature strength significantly higher than W, while retaining excellent ductility at all temperatures, even after recrystallization. Also, its coefficient of thermal expansion is between those of W and Ni. Diffusion in the Re-W system at the potential use temperatures of Ni-based MMC (1,200--1,500 K) is negligible due to the very high melting points of both W and Re (3,695 K and 3,459more » K, respectively). Furthermore, Re additions have been found to improve the mechanical properties of both W and Ni. Finally, the Ni-Re phase diagram shows a simple peritectic system with no intermetallic present. However, one potential drawback is the relatively high solubility of each metal in the other. The authors present an experimental investigation of diffusion phenomena in the Ni-Re system. The parameters controlling diffusion (activation energy and frequency factor) of each metal into the other are determined in order to predict long-term diffusion behavior at elevated temperatures and to assess the suitability of Re diffusion coatings for W fibers in Ni-based matrices.« less

Abstract: The failure mechanism of the TiN/TiSi2 bilayers as diffusion barriers between Cu and n+Si was investigated. The TiN/TiSi2 bilayers were formed by either annealing Ti (50 nm)/n+Si via various rapid thermal processes or reactively sputtering TiN (50 nm) on TiSi2. The degradation study of the Cu/TiN/TiSi2/n+Si contact system was undertaken by scanning electron microscopy, cross‐section transmission electron microscopy (XTEM), secondary‐ion‐mass spectrometry (SIMS), and diode leakage current and contact resistance measurements. Leakage current measurements indicated no deterioration of n+‐p diode junctions up to 475 °C for 30 min in a N2 ambient. For the sintering temperature at 500 °C, the leakage current increased abruptly and SIMS profiles revealed a large amount of Cu atoms diffusing into the junctions of n+‐p diodes. XTEM showed that the small pyramidal‐shaped Cu3Si crystallite (with a size 0.25 μm) precipitated in the n+Si substrate. The formation of Cu3Si increased the occupied volume, then generated t...

Abstract: The in situ mechanical properties of the fibers, matrices and interfaces in an Al2O3 fiber-reinforced β-21S Ti alloy have been evaluated by using two nanoscale indentation tests. The Al2O3 fibers were coated with a refractory metal and Y2O3 duplex coating which served as a diffusion barrier during the HIPing used to produce the metal matrix composites. The hardness of the fibers, interfaces and matrix were obtained by performing a series of indentations across the fiber/matrix interface. The hardness decreases from the Al2O3 fiber to the Ti matrix. Additionally, by doing fiber pushout tests, the interfacial shear strength, interfacial frictional stress and mode II interfacial fracture energy were obtained. Scanning electron microscopy and X-ray mapping were used for microstructural and chemical analysis. The mechanical properties of the interfaces were related to their chemical composition. The interfacial fracture was found to occur at the interface between the refractory metal and the Y2O3. The mode II interfacial fracture energy in this system is more than two orders of magnitude lower than the interfacial fracture energy of Ti/Al2O3 without the diffusion barrier.

Abstract: We studied interfacial reactions in Co/amorphous Si(a‐Si) multilayers by transmission electron microscopy. We found that an intermixed layer of amorphous cobalt silicide formed in the as‐deposited state. To explain the solid‐state amorphization reaction, two parameters were used. They were the thermodynamic driving force (heat of formation) and the interfacial energy. The initial amorphization reaction in Co/a‐Si multilayers was thermodynamically and kinetically favored. However, the formed amorphous interlayer remained about 1 nm thick and did not grow thicker with increasing modulation period and annealing temperature. The reason for this phenomenon was that the amorphous interlayer acted as a diffusion barrier to impede the amorphization reaction in Co/a‐Si multilayers. Co2Si phase was always the preferred phase in the crystallization process for different average compositions of the multilayers. The mechanism that controlled the phase selection in Co/a‐Si interfacial reaction was interpreted by using ...

Abstract: This invention relates to integrated circuits which are protected from the environment. Such circuits are sealed by applying a diffusion barrier metal layer to the bond pads and one or more passivation layers to the remainder of the circuit.

Abstract: It is proposed that the plasma enhanced chemical vapor deposited tungsten nitride (PECVD‐W–N) thin film is used as a diffusion barrier to prevent the interdiffusion between Al and Si during postannealing process. The atomic concentration of N in W–N film deposited with NH3/WF6 partial pressure ratio of 0.5 is about 33 at. % and its resistivity is 90–110 μΩ cm. The Rutherford backscattering spectrometry, Auger electron depth profiles, x‐ray diffraction, and scanning electron micrographs show that 900 A PECVD‐W67N33 film interposed between Al and Si is more impermeable than PECVD‐W film due to N atoms and it also keeps its chemical integrity during the postfurnace annealing at 600 °C for 30 min in Ar ambient.

Abstract: Aluminizing of nickel alloy 718 was studied in order to reveal the effect of combined alloy additions on aluminide growth kinetics, as opposed to pure metal substrates. The low activity pack process was used and treatment was carried out at 1273 K using ammonium fluoride activator and Ni-50 wt% Al powder as an aluminium source for treatment times of 1, 2, 4 and 8 h. The aluminide coatings varied between 40 and 110 Μm in thickness. The microstructures consisted of a NiAl phase with a fine grain size containing small secondary-phase particles at the grain boundaries. The interface between the coating and the substrate was lined by a lamellar layer exhibiting a two-phase structure, which was enriched in chromium and niobium in addition to containing iron and nickel. Weight gain measurements indicated parabolic growth up to 2 h, beyond which the growth rate slowed down. Microstructures and composition profiles revealed that the interlayer, which was enriched in elements insoluble in NiAl, posed a barrier to interdiffusion of the reacting species and slowed down the growth kinetics of the aluminide.

Abstract: Pd-Ge based ohmic contact to n-GaAs with a TiW diffusion barrier was investigated. Electrical analysis as well as Auger electron spectroscopy and the scanning electron microscopy were used to study the contact after it was subjected to different furnace and rapid thermal annealing and different aging steps. All analyses show that TiW can act as a good barrier metal for the Au/Ge/Pd/n-GaAs contact system. A value of 1.45 × 10−6 Ω-cm2 for the specific contact resistance was obtained for the Au/TiW/Ge/Pd/n-GaAs contact after it was rapid thermally annealed at 425°C for 90 s. It can withstand a thermal aging at 350°C for 40 h with its ρc increasing to 2.94 × 10−6Ω-cm2 and for an aging at 410°C for 40 h with its ρc increasing to 1.38 × 10−5 Ω-cm2.

Abstract: A method of applying a continuous stable intermetallic diffusion barrier layer to a high temperature metallic article is described. In many instances, protective coatings are incompatible with the material of the substrate to which they are applied. Such incompatilibility is overcome in the invention through in situ formation of an intermediate stable diffusion barrier layer by sequential deposition and subsequent reaction of suitable metals to form a continuous intermetallic layer. A conventional overlay coating may then be applied to the intermetallic layer without risk to the underlying substrate. The invention also contemplates creation of unitary diffusion barriers from multi-layer deposits; deposition of plural diffusion barriers, and formation of complete protective systems comprising substrate, diffusion barrier(s) and overlay coating prior to heat treatment in situ.

Abstract: Au-Zn/Au and X/Au-Zn/Y/Au metallizations (where X=Au, Cr or Ni is a nucleation layer and Y=Cr or Ni is a diffusion barrier), formed by vacuum evaporation of Au-Zn (10 wt%) alloy, were studied for the preparation of ohmic contacts to p-type InP. The metallurgical and electrical properties of such contacts were investigated as a function of deposition parameters (especially the deposition rate of Au-Zn alloy) and alloying conditions. The role of the nucleation layer X on the InP surface and of the barrier layer Y between the Au-Zn and the outer Au layer in contact formation is also discussed.

Abstract: Ruthenium dioxide (RuO2) thin films are evaluated as bottom electrode for dielectric SrTiO3. It was found that a RuO2 (50nm) / Ru (20nm) barrier layer on a Si substrate is effective as an oxygen barrier layer and as a metal diffusion barrier layer for sputter deposited SrTiO3 films at substrate temperature of 450°C. To test suitability for high temperature processes, RuO2/Ru electrodes were annealed in air at 600°C. 100nm-thiick RuO2 was sufficient to prevent oxygen diffusion. After annealing in the same condition, the leakage current of sputter deposited SrTiO3 (150nm) on RuO2(50nm) / Ru(50nm) was 7.6 × 10 −9 (A/cm2) at 2V.

Abstract: A DRAM cell structure comprises a self-aligned surface strap (38) between a trench capacitor (10) and a diffusion region (20) where the strap comprises polysilicon coated with an electrically conductive liner diffusion barrier material (36) in order to prevent diffusion from the strap to an active region of the device. The preferred diffusion barrier materials are TiN and TaN.

Abstract: An amorphized tungsten nitride diffusion barrier is compared with that of polycrystalline tungsten nitride preventing the diffusion of copper into Si during post annealing processes at 600–800 °C for 30 min. Experimental evidence such as RBS, TEM, XRD measurements shows that the amorphized tungsten nitride layer perfectly blocks the expeditious diffusion of the Cu film due to the amorphous grain boundaries stuffed with N impurities.

Abstract: The thermal stabil i ty of Cu/CoSi2 contacted p+n shallow junction diodes with and without TiW diffusion barr ier was investigated with respect to metal lurgical reaction and electrical characteristics. Without the diffusion barrier, the Cu (2000 A)/CoSi2 (700 ,~)/p+n diodes (with a junction depth of 0.2 v~m measured from the silicide surface) were able to sustain a 30 s rap id thermal annealing (RTA) in N2 ambient up to 450~ without losing the integri ty of the devices characteristics. The Cu3Si phase was observed at the CoSi2/Si interface after 500~ annealing; the phase penetra ted through the CoSt2 layer causing a catastrophic change in layer structure after 700~ annealing. With the addi t ion of a 1200 A thickness of TiW diffusion barr ier between Cu and CoSt2, the junction diodes were able to sustain the RTA treatment up to 775~ without degrading the basic electrical characteristics, and no metal lurgical reaction could be observed even after an 800~ annealing. Copper has been regarded as a potential metallization material in deep submicron integrated circuits because of its low resistivity (1.67 ~12-cm for bulk) and superior high electromigration resistance. I'2 However, copper forms Cu-Si compounds at very low temperatures (200~ 3-7 The high diffusivity of Cu will also introduce deep level traps in Si that deteriorate the device performance. ~ To make the Cu as an interconnect metal for Si devices, the thermal reaction of Cu with the underlayer materials and devices must be carefully evaluated. Since silieides have been widely used as contact materials in ultralarge scale integrated (ULSI) circuits, many studies have been made on Cu/silieide systems and their diffusion barriers properties. 9-15 It has been reported that Cu reveals different reaction behavior with different silieides) 6 Copper was found to diffuse across the silicide layer and form the Cu-Si compound below the silieide layers in the Cu/CrSi2/Si and Cu/CoSi2/Si systems; on the other hand, Si is the dominant diffusing species and diffuses out to react with Cu to form Cu~Si in the Cu/TiSi2/Si structure. Apart from the interdiffusion through the silieide layer, Cu was also found to react with the silicide layer in the Cu/ TiSi2/Si system. 16 Because the reaction in the Cu/silieide/Si structure is so complicated and always occurs at relatively low temperature, a more detailed understanding on the reaction mechanism is desirable, and an effective diffusion * Electrochemical Society Active Member. barrier layer is required for the application of the Cu/sili-

Abstract: Reliability of Ti–Pt–Au and Ti–Mo–Au systems has been investigated for GaAs integrated circuit first‐level metallizations on semi‐insulating GaAs substrates and second‐level metallizations on interlayer SiO2 films using Auger depth profile analysis, residual resistance examination and temperature storage step‐stress testing. Auger analysis and residual resistance examination showed significant reaction between first‐level Ti–Pt–Au and GaAs substrates during metallization processes, while Ti–Mo–Au system with the electron‐beam evaporated Mo film showed higher thermal stability because the Mo film acted as a good diffusion barrier between GaAs and Au. The second‐level Ti–Pt–Au on SiO2 was found to be free from the reaction with GaAs substrates, and its degradation was ascribed to interdiffusion of composite metals. The resistance increase in step‐stress testing for the second Ti–Pt–Au was analyzed on the basis of a new diffusion‐controlled model, and long‐term reliability was estimated. A mean time to failu...