Anisotropic Deposition Research Articles

Design issues in ionized metal physical vapor deposition of copper

The filling of deep vias and trenches with metal for interconnect layers in microelectronic devices requires anisotropic deposition techniques to avoid formation of voids. Ionized metal physical vapor deposition (IMPVD) is a process which is being developed to address this need. In IMPVD, a magnetron sputter deposition source is augmented with a secondary plasma source with the goal of ionizing a large fraction of the metal atoms. Application of a bias to the substrate results in an anisotropic flux of metal ions for deposition. The ion flux also contributes to “sputter back” of metal deposits on the lip of the via which could lead to void formation. In this article, we describe and present results from a two-dimensional plasma model for IMPVD using a dc magnetron and an inductively coupled auxiliary ionization source. The scaling of copper IMPVD is discussed as a function of buffer gas pressure, sputter source, and source geometry. We show that the deposition rate of metal on the substrate will be reduced as pressure increases due to the increase in diffusive losses. We also show that the sputtering of the auxiliary coils can be a significant issue in IMPVD systems, which must be addressed in tool design.

Further evidence for inclination shallowing in red beds

Red beds and related shallow marine siliciclastic sediments within the extensional Catalan Neogene basins offer a unique opportunity to study the relationship between sediment anisotropy, remanence acquisition and inclination shallowing. On the basis of the dominant fabric features, sedimentary facies are grouped into laminated, massive and bioturbated. The bulk susceptibility appears to be dominated by paramagnetic phyllosilicates and clay minerals. The magnetic susceptibility fabric is dominantly foliated while the degree of anisotropy is very variable and is dependent on the facies type. Strong foliation dominates in the laminated sediments whereas weak anisotropy characterizes the bioturbated and massive mass‐flow facies. Moreover, we observe a correlation between facies type and remanence inclination. The undisrupted thinly laminated facies provides the most biased inclination values: 20° as opposed to 60° of the expected geomagnetic field. Steeper inclinations are reported from bioturbated muds, while the best record of the geomagnetic inclination is found in the weakly anisotropic mass flow deposits.

Characterization and Fabrication of Chimney-Shaped Metal Field Emitters

A novel fabrication technology has been successfully developed for chimney-shaped metal field emitters in order to improve the electrical characteristics of field-emission devices. This technology is based on anisotropic dry etching and sputtering deposition of metal film as well as wet etching of the attached silicon. It enables easy fabrication of chimney-shaped field emitters with excellent uniformity and high reproducibility. The anode current of the chimney-shaped Cr field emitter array (FEA) is 36.3 µA at the applied voltage of 1100 V and the threshold voltage V T, defined as that for which the anode current I a reaches 1 µA is 787 V. The chimney-shaped Cr FEA emits a current thirty times higher than that from the cone-shaped Cr-clad FEA at the applied voltage of 1100 V. This can be attributed to the presence of many sharp tips along the edge of the chimney-shaped emitter. The degradation phenomenon is not observed because compensation occurs between these many sharp tips. Another merit of this technique is that only one photolithography mask is needed during processing.

Catalytic effects of metal carbides, oxides and Ni single crystal on the vapor growth of micro-coiled carbon fibers

Micro-coiled carbon fibers were prepared by the impurity-activated chemical vapor deposition using the powders of metal carbides, metal oxides, and a Ni single crystal. The catalytic effect of these impurities on the coil yield and morphology were examined, and the growth mechanism is discussed. The pre-oxidized Ti plate, Ti 2O 3 and TiC powders, and a Ni single crystal as well as various metal powders provided the micro-coiled carbon fibers. For the Ni single crystal, the Ni(100) crystal gave the highest coil yield followed by Ni(111)and then Ni(110). It is considered that the anisotropic deposition rate of a carbon among the Ni single crystal planes is the driving force of the coiling of carbon fibers to form the coiled fibers.

The Anisotropic Plasma-Enhanced Chemical Vapor Deposition SiO2/Spin-on Glass Process for 0.35 µm Technology

A new plasma enhanced chemical vapor deposition (PECVD) oxide is proposed to form an anisotropic SiO2 film with ultra low sidewall step coverage for the intermetal dielectric (IMD) process. This oxide is named anisotropic plasma oxide (APO). In the APO technology, the anisotropic deposition is achieved by reducing the O2/TEOS (tetraethylorthosilicate) feed ratio in current PECVD process. The APO sidewall step coverage can be lowered to 20% compared to 65% for the conventional PECVD oxide. Reflective index, measured by ellipsometry method, indicates that the APO film is Si-rich. High deposition rate and low film stress show the APO is suitable to the IC production. This technology is successfully applied to the 0.5 µm 16 M dynamic random access memory (DRAM) products and is expected to apply to 0.35 µm ULSI technology.

The Anisotropic Deposition of Doped Silicate Glass

In this letter we present initial results for the anisotropic deposition of doped silicate glass. The deposition was performed in a previously described low pressure chemical vapor deposition reactor by the reaction of tetraethylorthosilicate, triethyl borate, phosphine, and oxygen. The depositions were performed over a nominal temperature range of 973 to 1023 K. Results presented here indicate that the glass deposits anisotropically over polysilicon structures on silicon substrates favoring high surface density corners to lower surface density flat areas of the silicon substrates.

Anisotropic Deposition of Electroless Nickel: Bevel Plating

Wet chemical processes such as etching or plating are generally isotropic. Although anisotropic wet etching can be achieved using single‐crystalline substrates or a duplex resist, anisotropic metal deposition seems a difficult task. However, we show here that anisotropic deposition of Ni has been accomplished in an acid electroless Ni bath to which an appropriate level of Pb2+ has been added. Since the edges of a given pattern experience an additional contribution from nonlinear diffusion, mass transport to these edges is enhanced compared to the bulk of a substrate. As a result the surface concentration of the adsorbed stabilizer is also higher at the edges. By choosing the proper Pb2+ concentration, the edges can be selectively poisoned: bevels can be grown with an angle that is a function of the stabilizer concentration in the electrolyte. That the Pb2+ stabilizer inhibits the cathodic partial reaction (metal deposition itself), but not the oxidation of the reducing agent has been verified with cyclic voltammetry at a rotating‐disk electrode, carried out in the vicinity of the plating potential. The process can be used to deposit metal pyramids onto the Al bond pads of an integrated circuit. This morphology is useful for the direct mounting of an integrated circuit onto a conductor pattern (flip chip).

Simulation of vapor diffusion in anisotropic particulate deposits

Abstract In this study we determine the effective diffusivity tensor of computer-generated, particulate, anisotropic deposits. Deposits of polydispersed, spherical particles were generated by several algorithmic models, which simulate different deposition conditions. Depending on the nature of the arriving particle trajectories (diffusive/deterministic), the angle of incidence and the subsequent motion after they establish contact with an already deposited particle, both the deposit anisotropy and final solid fraction can be varied. Monte Carlo simulations of vapor molecules diffusing through cubic samples extracted from the generated deposits provided accurate estimates of their effective diffusivity tensor and associated tortuosities. The effective diffusivities were directly determined over the entire Knudsen number range, assuming self-diffusion in a constant pressure pure gas that consists of hard-sphere elastic molecules with exponentially distributed free-paths. In the continuum limit the effective diffusivities of the porous solids considered here could be closely correlated with porosity alone. Archie's power law [eq. (17)] with an exponent m = 1.45 fitted our computational results accurately. In the Knudsen limit on the other hand the details of the local microstructure became important and so an accurate prediction/correlation of the effective diffusivity required higher order information. An interpolation based on the experimentally measured effective diffusivities in the two Knudsen limits (Scott and Dullien, 1962) was used to correlate the diffusivities in the transition regime. For the deposits analyzed here the diffusivity properties became anisotropic only in the high Knudsen regime, that is, when diffusing molecule/solid interactions dominate. In the Knudsen limit we have also found significant “rectification” effects. Specifically, the transmission probability as determined by the test-molecule method could be up to 25% higher when the molecules diffused away from the target than when they diffused towards the target. Such “rectification” effects are attributed to the tree-like microstructures of the deposits.

Microstructural descriptors characterizing granular deposits

AbstractQuantitative results are presented on mean coordination number and coordination number distribution, contact normal distribution and fabric tensor of simulated anisotropic granular deposits with resulting solid fractions between ca. 15% for ballistic deposits and 58%, corresponding to a random loose packing. The deposits, generated by the capture of uniform size spherical particles arriving normal to a target, were simulated using a simple algorithmic model.We focus on microstructural quantities which explicitly take into account the discrete nature of the granules comprising the deposit. Such measures are important in determining the heat transport properties of the deposits for Fourier conduction through the solid phase, as well as their mechanical and sintering properties. The variation of mean coordination number with deposit solid fraction was successfully correlated using a unit‐cell model (Eq. 13). This correlation, in conjunction with entropy maximization arguments (after Nayak and Tien, 1978) has been further used to predict the coordination number distribution. The usefulness of the results reported here is illustrated by computing an upper bound to the deposit effective thermal conductivity (Jagota and Hui, 1990) and comparing it to both ‘exact’ simulation results (Tassopoulos and Rosner, 1991b) and experimental data (Koh, 1971).

Formation of crystalline tripalmitin-rich spicules in isolated hepatocytes.

Conditions were developed for rapid deposition of triglyceride in isolated rat hepatocytes. Liver cells from fasted rats were incubated for 90 min at 37 degrees C with 3.0 mM palmitic or oleic acid, 4% bovine serum albumin, 20 mM glucose, 10 mM lactate, and 1 mM pyruvate. When oleic acid was used, numerous cytoplasmic lipid droplets were produced. When hepatocytes were incubated with palmitic acid, similar amounts of triglyceride were synthesized but instead of lipid droplets, a vast accumulation of peculiar spicules permeated the cytoplasm. These inclusions appeared in myriads of swirled threads, thick elongated angular plates, and needles, some of which exhibited longitudinal osmiophilic bands of 250 A thickness. These structures were associated with smooth endoplasmic reticulum. The cells appeared otherwise normal. Polarized light microscopy at 37 degrees C revealed a multiplicity of brilliant white inclusions between crossed polars in cells incubated with palmitic acid. These birefringent structures exhibited 90 degrees periodicity between both maximum brilliance and extinction, indicative of anisotropic crystalline deposits. Molecular species analysis of triglycerides in cells incubated with palmitic acid, together with data on [1-14C]palmitic acid incorporation, demonstrated an almost exclusive synthesis of tripalmitin. Spicules isolated from homogenized hepatocytes displayed needles containing longitudinal single and double osmiophilic bands of 110 A and 260 A thickness, respectively, and lipid spicular aggregates. The isolated spicules were almost pure tripalmitin by analysis. These observations document the formation and development of crystalline triglyceride in living cells and may provide a unique system for the study of cellular lipid synthesis, transport and deposition.

Spin-polarized fuel in high gain ICF targets

The use of spin-polarized D-T can reduce the input energy requirement of an inertially confined fusion (ICF) target by nearly a factor of two. Two-dimensional (2-D) computer simulations indicate that the effects due to anisotropic burn product emission and deposition are negligible.

An electron diffraction study of ω‐tricosenoic acid Langmuir‐Blodgett films

Abstract ω‐Trieosenoie‐ acid is a promising new material for Langmuir-Blodgett (LB) films. This paper reports an investigation of the packing of molecules of this acid in LB films using the techniques of high-energy transmission and reflection electron diffraction. The four distinct packing arrangements that have been observed are all different from that of the bulk crystal, and the one adopted by the film is determined both by the substrate and the deposition conditions used. In three of the four arrangements, the long aliphatic chains are packed at maximum density, while in the fourth an unusual packing of the molecules is reported in which their chain axes lie in the plane of the LB film. In addition, two of the four arrangements are observed to give rise to anisotropic deposition.

Calcium oxalate crystals within ocular tissues; a clinicopathologic and histochemical study.

For a number of years, pathologists at the Armed Forces Institute of Pathology had recognized nonstaining anisotropic crystalline deposits within certain ocular tissues and had recorded the lesions in which they occurred under the tentative heading of protein crystals in the Registry of Ophthalmic Pathology. The chemical nature of the crystals, however, remained unknown. We became curious about them early in 1954, when the studies to be reported herein were initiated. A new histochemical procedure devised by Johnson1furnished strong presumptive evidence that they contained calcium oxalate. The occurrence of these deposits was recognized in two main types of cases, one of which was phacolytic glaucoma. Hence, brief mention was made of their presence in the sclerotic nuclei of Morgagnian cataracts in the paper on phacolytic glaucoma by Flocks, Littwin, and Zimmerman.2 Independently, and without knowledge of our interest in these crystals, Dr. David G. Cogan and his