Kenneth P. Rodbell

Mechanisms for microstructure evolution in electroplated copper thin films near room temperature

We present a model which accounts for the dramatic evolution in the microstructure of electroplated copper thin films near room temperature. Microstructure evolution occurs during a transient period of hours following deposition, and includes an increase in grain size, changes in preferred crystallographic texture, and decreases in resistivity, hardness, and compressive stress. The model is based on grain boundary energy in the fine-grained as-deposited films providing the underlying energy density which drives abnormal grain growth. As the grain size increases from the as-deposited value of 0.05–0.1 μm up to several microns, the model predicts a decreasing grain boundary contribution to electron scattering which allows the resistivity to decrease by tens of a percent to near-bulk values, as is observed. Concurrently, as the volume of the dilute grain boundary regions decreases, the stress is shown to change in the tensile direction by tens of a mega pascal, consistent with the measured values. The small ...

Measurement of the flux and energy spectrum of cosmic-ray induced neutrons on the ground

New ground-based measurements of the cosmic-ray induced neutron flux and its energy distribution have been made at several locations across the United States using an extended-energy Bonner sphere spectrometer. The data cover over twelve decades of neutron energy, from meV to GeV. An expression to scale the flux to other locations has been developed from a fit to the altitude dependence of our measurements and an expression from the literature for the geomagnetic and solar-activity dependence of neutron monitor rates. In addition, an analytic expression is provided which fits the neutron spectrum above about 0.4 MeV. The neutron flux is important for estimating the soft-error rate in computer memories and recent computer logic devices.

Electromigration and stress-induced voiding in fine Al and Al-alloy thin-filmed lines

Physical phenomena underlying failure due to electromigration and stress-induced voiding in fine Al and Al-alloy thin-film conducting lines are examined in the context of accelerated testing methods and structures. Aspects examined include effects due to line isolation (the absence of reservoirs at conductor ends), solute and precipitate phenomena, conductor critical (Blech) length, microstructure, film deposition conditions, and thermal processing subsequent to film deposition. Emphasis is on the isolated, submicron-wide, Al(Cu)-based thin-film interconnection lines of IBM VLSI logic and memory chips.

Correlation of texture with electromigration behavior in Al metallization

Aluminum films deposited at three different conditions, such that texture is the only microstructural variable, were tested for electromigration behavior. Texture analysis shows that random and (111) fiber texture components are present in the films deposited by both partially ionized beam (PIB), physical vapor deposition and sputtering. Two parameters are required to properly quantify the texture: (111) volume fraction and the distribution (half‐width) of the (111) fiber component. As the (111) texture becomes stronger, the median time to failure increases, while the failure standard deviation decreases. Previous texture correlations are based on incomplete information, so they cannot predict electromigration behavior in all cases.

TEXTURE IN MULTILAYER METALLIZATION STRUCTURES

The effects of thin Ti, TiN, or Ti/TiN underlayers on the development of the crystallographic texture and the grain structure are explored. Metal layers ∼0.5 μm in thickness of Al‐0.5Cu or of Cu are deposited on these underlayers and on amorphous SiO2 as a reference. A strongly textured underlayer such as Ti〈0002〉 or Ti〈0002〉/TiN〈111〉 induces a similarly strong 〈111〉 texture in the AlCu. In copper with 〈111〉, 〈200〉, and random texture components, an underlayer induces a stronger 〈111〉 component compared to an analogous film deposited on SiO2. A nearly random texture in TiN significantly weakens the texture in subsequent metal films. Grain size distributions in all AlCu films are monomodal reflecting a process of normal grain growth. The grain size distribution for Cu sometimes deviates from lognormal. The bimodal distribution implies that grain growth is abnormal even though the median grain size does not exceed a low multiple of the film thickness.

Single-Event Upsets and Multiple-Bit Upsets on a 45 nm SOI SRAM

Experimental results are presented on single-bit-upsets (SBU) and multiple-bit-upsets (MBU) on a 45 nm SOI SRAM. The accelerated testing results show the SBU-per-bit cross section is relatively constant with technology scaling but the MBU cross section is increasing. The MBU data show the importance of acquiring and analyzing the data with respect to the location of the multiple-bit upsets since the relative location of the cells is important in determining which MBU upsets can be corrected with error correcting code (ECC) circuits. For the SOI SRAMs, a large MBU orientation effect is observed with most of the MBU events occurring along the same SRAM bit-line; allowing ECC circuits to correct most of these MBU events.

Low Energy Proton Single-Event-Upset Test Results on 65 nm SOI SRAM

Experimental results are presented on proton induced single-event-upsets (SEU) on a 65 nm silicon-on-insulator (SOI) SRAM. The low energy proton SEU results are very different for the 65 nm SRAM as compared with SRAMs fabricated in previous technology generations. Specifically, no upset threshold is observed as the proton energy is decreased down to 1 MeV; and a sharp rise in the upset cross-section is observed below 1 MeV. The increase below 1 MeV is attributed to upsets caused by direct ionization from the low energy protons. The implications of the low energy proton upsets are discussed for space applications of 65 nm SRAMs; and the implications for radiation assurance testing are also discussed.

On the use of alloying elements for Cu interconnect applications

To address the future use of alloying elements for Cu interconnect applications in integrated circuits, first, available bulk experimental data such as residual resistivity per at. % solute and binary phase diagrams are used to arrive at a set of 24 potential elements. Next, experimental results in thin films and lines allow the authors to arrive at a smaller set that includes ten elements, namely, Pd, Au, Al, Ag, Nb, Cr, B, Ti, In, and Mn, with higher priority and six, namely, Zn, V, C, Mg, P, and Sn with lower priority for further studies. These additional studies are needed before a strong case for or against alloying additions to Cu can be made. The available thin film and line data are summarized in a series of tables that should prove useful for the readers. In particular, the thin film data allow the authors to obtain an effective average residual resistivity (EARR) per at. % solute that combines the effects of impurity scattering, second phase precipitates, and grain size refinement resulting from...

Porosity in plasma enhanced chemical vapor deposited SiCOH dielectrics: A comparative study

The low dielectric constant (k) of plasma enhanced chemical vapor deposited SiCOH films has been attributed to porosity in the films. We have shown previously that the dielectric constant of such materials can be extended from the typical k values of 2.7–2.9 to ultralow-k values of k=2.0. The reduction in the dielectric constants has been achieved by enhancing the porosity in the films through the addition of an organic material to the SiCOH precursor and annealing the films to remove the thermally less-stable organic fractions. In order to confirm the relation between dielectric constant and film porosity the latter has been evaluated for SiCOH films with k values from 2.8 to 2.05 using positron annihilation spectroscopy, positron annihilation lifetime spectroscopy, small angle x-ray scattering, specular x-ray reflectivity, and ellipsometric porosimetry measurements. It has been found that the SiCOH films with k=2.8 had no detectable porosity, however the porosity increased with decreasing dielectric con...

The role of texture in the electromigration behavior of pure aluminum lines

The effects of microstructure on electromigration behavior were evaluated in three nominally 1 μm thick pure aluminum films, which were tested at temperatures from 423 to 523 K. The three Al films had essentially the same grain structure but different variants of an 〈111〉 texture. Texture had a very strong effect on the electromigration behavior in ∼2 μm wide polycrystalline lines, where both a reduced fraction of randomly oriented grains and a tighter 〈111〉 distribution increased the electromigration lifetime. The apparent activation energy for electromigration decreased as the texture strengthened. The near bamboo microstructure of 0.5 μm narrow lines showed extensive orientation clustering with an unusually high proportion of low angle boundaries in the most strongly 〈111〉 textured film. The electromigration damage in both 2 and 0.5 μm wide lines was correlated with the types of flux divergence sites in each film. The texture impacts the character of the grain boundaries and interfaces which control th...