Kathleen A. Dunn

Evolution of the nanostructure of deposits grown by electron beam induced deposition

Environmental scanning electron microscopy (ESEM) was used to perform electron beam induced deposition (EBID) using a WF6 precursor. The deposits consist of WO3 nanocrystals embedded in an amorphous matrix. Oxide formation is attributed to residual oxidizers present in the ESEM chamber during EBID. Under conditions of fixed low electron flux, the WO3 grain size and the degree of deposit crystallinity increase with time. These changes correlate with the degree of electron energy deposition into the material during growth, indicating that electron beam induced modification of as-grown material is significant in controlling the nanostructure and functionality of materials fabricated by EBID.

Electron postgrowth irradiation of platinum-containing nanostructures grown by electron-beam-induced deposition from Pt(PF3)4

The material grown in a scanning electron microscope by electron beam-induced deposition (EBID) using Pt(PF3)4 precursor is shown to be electron beam sensitive. The effects of deposition time and postgrowth electron irradiation on the microstructure and resistivity of the deposits were assessed by transmission electron microscopy, selected area diffraction, and four-point probe resistivity measurements. The microstructure, notably the platinum nanocrystallite grain size, is shown to evolve with electron fluence in a controllable manner. The resistivity was observed to decrease as a result of postgrowth electron irradiation, with the lowest observed value of 215±15????cm. The authors demonstrate that electron beam-induced changes in microstructure can be caused using electron fluences similar to those used during the course of EBID and suggest that the observed effects can be used to tailor the microstructure and functionality of deposits grown by EBID in situ without breaking vacuum.

Interfacial mixing and internal structure of Pt-containing nanocomposites grown by room temperature electron beam induced deposition

Material grown by room temperature electron beam induced deposition (EBID) using (CH3)3CH3C5H4Pt precursor consists of platinum nanocrystals embedded in an amorphous matrix. The crystallites are shown to intermix with the amorphous oxide on a Si substrate. The extent of intermixing scales with the electron energy density delivered to the material during growth. Dependencies on electron flux, fluence, and exposure time indicate that the intermixing process is athermal, electron-activated, and rate limited by mass transport inside the solid. Furthermore, the degree of deposit crystallinity is shown to scale with the electron flux and fluence used for EBID. We discuss mechanisms behind the observed changes in nanostructure and implications for the growth of functional materials by EBID.

ZERO THICKNESS DIFFUSION BARRIERS AND METALLIZATION LINERS FOR NANOSCALE DEVICE APPLICATIONS

A robust diffusion barrier and metallization liner technology are critical for the realization of a functional and reliable interconnect structure. While copper barrier materials and processes have evolved significantly since the onset of copper-based metallization, the extendibility of existing barrier/liner solutions for use in emerging nanoscale interconnect structures faces a number of significant challenges related to the continued scaling of IC feature sizes. A key element in addressing these challenges includes developing an understanding of the mechanisms that lead to barrier failure and subsequent interconnect reliability deficiencies, and identifying how such mechanisms differ in the nanoscale regime from their counterparts at the microscale regime. In this respect, it is important that these distinctions serve as baseline in establishing the factors that determine the relevance and applicability of potential barrier solutions. Furthermore, it is critical to understand how these factors have evolved as barrier layers scaled to thicknesses of a few atoms. Accordingly, the current report outlines short- and long-term trends for these technologies.

Direct-write 3D nanolithography at cryogenic temperatures

Direct-write three-dimensional nanolithography is demonstrated using cryogenic electron beam-induced deposition (EBID). Cryogenic cooling and an electron beam were used to condense and expose the precursor methylcyclopentadienyl(trimethyl)platinum (MeCpPtMe(3)). The exposure process was modeled by Monte Carlo simulations of electron-condensate interactions, which were used to develop two approaches for the fabrication of three-dimensional self-supporting structures with incorporated gaps. Vertical and lateral resolutions of approximately 150 and 22 nm are demonstrated, and underlying mechanisms that limit resolution and throughput are identified. Resolution can be traded off for condensate exposure efficiency, which is shown to be up to four orders of magnitude greater than that of conventional, room temperature EBID.

Relationship of aluminum grain size to the grain size of polycrystalline silicon produced by the aluminum induced crystallization of amorphous silicon

The aluminum-induced crystallization and layer exchange process shows great promise for converting a-Si into large-grained poly-Si for solar cell applications. To investigate the relationship between the grain size of Al and the final grain size of poly-Si, a series of samples were deposited by RF magnetron sputtering 165 nm of Al onto SiN/SiO2 coated (100) silicon substrates. The Al grain size was varied by vacuum annealing prior to the deposition of 195 nm of a-Si. Completion of the layer exchange process resulted in poly-Si films which were then characterized with plan view TEM. The average Si grain size was found to increase as a function of increasing Al grain size, consistent with the grain-boundary nucleation model for this process. The largest average Si grain size of 4.9±1.92µm corresponded to the Al sample which was annealed for 24 hours at 550°C. The microstructure of the poly-Si film can therefore be manipulated by altering the properties of the as-deposited Al layer with an isothermal anneal.

Rapid trench initiated recrystallization and stagnation in narrow Cu interconnect lines

Understanding and ultimately controlling the self-annealing of Cu in narrow interconnect lines has remained a top priority in order to continue down-scaling of back-end of the line interconnects. Recently, it was hypothesized that a bottom-up microstructural transformation process in narrow interconnect features competes with the surface-initiated overburden transformation. Here, a set of transmission electron microscopy images which captures the grain coarsening process in 48 nm lines in a time resolved manner is presented, supporting such a process. Grain size measurements taken from these images have demonstrated that the Cu microstructural transformation in 48 nm interconnect lines stagnates after only 1.5 h at room temperature. This stubborn metastable structure remains stagnant, even after aggressive elevated temperature anneals, suggesting that a limited internal energy source such as dislocation content is driving the transformation. As indicated by the extremely low defect density found in 48 nm trenches, a rapid recrystallization process driven by annihilation of defects in the trenches appears to give way to a metastable microstructure in the trenches.

Metallization of a Genetically Engineered Polypeptide

Recently, well-ordered biological materials have been exploited to pattern inorganic nanoparticles into linear arrays that are of particular interest for nanoelectronic applications. In this work, a de novo designed E. coli-expressed polypeptide (previously shown to form highly rectilinear, β-sheet-containing structures) operates as a template for divalent metal cations. EDX and TEM analysis verify the attachment of platinum ions to the histidine-rich fibril surface, which was designed specifically to facilitate attachment of chemical moieties. Following chemical reduction, TEM further confirms the formation of localized zero-valent metal aggregates with sub-nanometer interparticle spacing.

Correlating surface segregation and microstructural evolution of electrochemically deposited copper

Electroplating bath additives become problematic when incorporated into electrochemically deposited copper as impurities. The surface segregation of these impurities during spontaneous microstructural transformation was monitored by secondary ion mass spectrometry and found to be no different than the surface chemistry of the non-transforming plated samples or even sputtered copper. The results show that microstructural transformation of electroplated copper progresses despite the presence of impurities, suggesting foreign constituents are not in fact responsible for grain boundary pinning in these films.

Role of Temperature and Duration of the Crystallization Anneal in the Texture Development of YBCO Prepared by TFA-MOD

The preparation of thin film Y1Ba2Cu3O7-x by metalorganic deposition using trifluoroacetic acid and metal acetates (TFA-MOD) has gained attention in recent years as a less expensive alternative to high vacuum synthesis. In this method, a sol-gel precursor containing the metal cations is converted to YBCO via a three-stage heat treatment consisting of calcining, firing, and oxygenation. The focus of this study was to optimize the process conditions during the firing heat treatment to obtain strongly textured, high-Jc YBCO. Samples were prepared by depositing the metalorganic precursor onto lang100rang SrTiO3 substrates by dip coating. To ensure that film characteristics were attributable only to the crystallization anneal (i.e. firing), all other process steps were standardized based on earlier reports. The role of firing temperature was then investigated in the range of 700degC to 830degC with the duration held to four hours. After identifying the optimal processing temperature (in this case, 800degC) the duration was investigated in the range of one to six hours. A narrow processing window for obtaining a high degree of c-axis texturing was thereby identified and resulted in Jc values as high as 2.19 MA/cm2 for the film fired for 4 hours at 800degC.