A. Mallikarjunan

β-phase tungsten nanorod formation by oblique-angle sputter deposition

We report the creation of an unusual simple cubic β-phase W(100) nanorods with a pyramidal tip having four (110) facets using an oblique-angle sputter deposition technique with substrate rotation (also known as glancing-angle deposition). During the oblique-angle deposition, both β-phase W(100) and α-phase W(110) islands exist at the initial stages of growth. The β-phase W(100) islands grow taller due to the lower adatom mobility on these islands. The taller islands survive in the competition and form isolated nanorods in the later stages of growth. This is in contrast to the sputter deposition at normal incidence, where only the thermodynamically stable bcc α-phase W(110) polycrystalline films were formed when the film grows to a certain thickness.

Metal drift behavior in low dielectric constant organosiloxane polymer

Metal drift into a low dielectric constant (low κ) hybrid organosiloxane (OS) polymer has been investigated using metal/OS/SiO2/Si capacitors. Compared to Cu, Al gate metal capacitors showed larger flatband voltage shifts in the capacitance–voltage (C–V) curves upon bias temperature stressing (BTS). To elucidate the mechanism and source of this bias instability, further BTS experiments were performed with gate metals tantalum and platinum. It is suggested that all these metals, except Pt, drift into the dielectric and the extent of drift appears to be directly related to the metal’s tendency to oxidize. The calculations, assuming singly ionized metal species, show that the charges/cm2 entering the dielectric fall in the order Pt<Cu<Ta<Al. A mechanism is proposed linking the presence of oxygen in OS to the ionization of the metals, and consequent drift through the dielectric under applied electric fields.

Mobile Ion Detection in Organosiloxane Polymer Using Triangular Voltage Sweep

The triangular voltage sweep (TVS) technique has been traditionally used for mobile ion detection in gate oxides. In this paper, we present and discuss the results of TVS measurements on plasma enhanced chemical vapor deposited (PECVD) silicon oxide and a low dielectric constant hybrid organosiloxane polymer (HOSP). A variety of gate metals were studied to detect and separate mobile ion effects associated with the metal For the PECVD oxide, no peak was detected with Al gate metal, whereas a large peak was detected with Cu; allowing us to correlate the observed peak to mobile copper ions. TVS traces revealed no peak for Pt/HOSP capacitors but peaks were detected with Cu, Ta, and Al capacitors. Thus, the appearance of mobile ion peaks in the TVS traces correlated well with the previously published bias-temperature stressing (BTS) induced instability of these capacitors, where the Hatband voltage shifts during BTS were in the order Pt < Cu < Ta < Al, with no shift observed for Pt capacitors. The effects of temperature, voltage sweep rate, and bias hold time were also investigated for Al/HOSP and Cu/HOSP capacitors. Cu peaks were one to two orders of magnitude smaller than Al peaks under all conditions investigated. It was concluded that the peaks originate from the gate metal.

Supercritical carbon dioxide extraction of porogens for the preparation of ultralow-dielectric-constant films

Supercritical carbon dioxide extraction of poly(propylene glycol) porogen from poly(methylsilsesquioxane) (PMSSQ) cured to temperatures adequate to initiate matrix condensation, but still below the decomposition temperature of the porogen, is demonstrated to produce nanoporous, ultralow-dielectric-constant thin films. Both closed and open cell porous structures were prepared simply by varying the porogen load in the organic/inorganic hybrid films. 25 and 55 wt % porogen loads were investigated in the present work. Structural characterization of the samples conducted using transmission electron microscope, small angle x-ray scattering, and Fourier transform infrared spectroscopy, confirms the extraction of the porogen from the PMSSQ matrix at relatively low temperatures (⩽200 °C). The standard thermal decomposition process is performed at much higher temperatures (typically in the range of 400 °C–450 °C). The values of dielectric constants and refractive indices measured are in good agreement with the stru...

Molecular Caulking A Pore Sealing CVD Polymer for Ultralow k Dielectrics

Porosity has been introduced in existing low-k interlayer dielectrics to further reduce their dielectric constant. It is desirable to deposit a metallic layer on top of the porous dielectric by chemical vapor deposition (CVD). However this presents the challenge of preventing the precursor from penetrating into the porous dielectric and depositing metal within this insulating layer. In the present paper a low-k CVD polymer capping (Molecular Caulking) is deposited at room temperature onto the porous ultralow k dielectric methyl silsesquioxane. Experiments show that the Molecular Caulking prevents precursor penetration during subsequent metallorganic CVD. In addition, while the Molecular Caulking itself slightly penetrates into the methyl silsesquioxane, it does not appreciably increase surface roughness or film dielectric constant.

Plasma surface modification for ion penetration barrier in organosiloxane polymer

Low dielectric constant (low-κ) hybrid organosiloxane polymer (HOSP) displayed larger instability with Al compared to Cu capacitors when investigated using the bias temperature stressing (BTS) and triangular voltage sweep (TVS) techniques. We attributed this instability to ion penetration from the gate metal. As SiO2 is a well-known barrier against Al penetration, an attempt was made to create a SiO2-like surface on HOSP using different plasma treatments. The plasma conditions were selected to minimize bulk damage to the polymer. While N2O and O2 plasmas caused bulk electrical damage, N2 and Ar plasma treatments dramatically reduced ion penetration from the Al gate into HOSP. This was seen from the decrease in the BTS C–V shift as well as the TVS ion peak area. A short (1 min) low-power (30 W) N2 plasma treatment was effective as an aluminum ion penetration barrier, without significantly increasing the refractive index or dielectric constant value of HOSP. Formation of a SiO2-like surface was confirmed fr...

Hindered Copper Ion Penetration in Parylene-N Films

Recently, it has been suggested that the existence of certain oxygen-containing chemical groups at copper/polymer interfaces aids copper ionization and its subsequent diffusion into these polymers. In the present study, poly(paraxylylene-N) or Parylene-N was selected for copper diffusion studies. It was demonstrated that no copper ion penetration was detected in the Parylene-N films under bias temperature stressing conditions of 150°C and 0.5 MV/cm. The present finding suggests that one may control copper penetration by employing dielectrics or passivation layers devoid of oxygen in the multilevel interconnect metallization scheme.

Supercritical CO2 Extraction of Porogen Phase: An Alternative Route to Nanoporous Dielectrics

We present a supercritical CO{sub 2} (SCCO{sub 2}) process for the preparation of nanoporous organosilicate thin films for ultra low dielectric constant materials. The porous structure was generated by SCCO{sub 2} extraction of a sacrificial poly(propylene glycol) (PPG) from a nanohybrid film, where the nanoscopic domains of PPG porogen are entrapped within the crosslinked poly(methylsilsesquioxane) (PMSSQ) matrix. As a comparison, porous structures generated by both the usual thermal decomposition (at ca. 450 C) and by a SCCO{sub 2} process for 25 wt% and 55 wt% porogen loadings were evaluated. It is found that the SCCO{sub 2} process is effective in removing the porogen phase at relatively low temperatures (< 200 C) through diffusion of the supercritical fluid into the phase-separated nanohybrids and selective extraction of the porogen phase. Pore morphologies generated from the two methods are compared from representative three-dimensional (3D) images built from small angle x-ray scattering (SAXS) data.

Separation of copper ion-induced and intrinsic polymer instabilities in polyarylether using triangular voltage sweep

A low dielectric constant polyarylether (PAE) polymer was investigated for resistance to copper drift. Positive bias-temperature stressing (BTS) of metal/PAE/SiO2/Si capacitors led to large initial flat-band voltage shifts toward the left-hand side in the capacitance–voltage curve for all gate metals investigated (Pt, Al, and Cu). Upon triangular voltage sweep (TVS) testing, Pt/PAE/SiO2/Si capacitors exhibited no peak, whereas a single peak (indicative of mobile ions) was seen for Cu/PAE/SiO2/Si capacitors. The results indicate that an intrinsic polymer instability source, such as polarization (under bias), was the major cause for the BTS instability of the polymer. From TVS studies, Cu+ ion drift could be characterized in the temperature range of 150–250 °C, and mobility of Cu+ in PAE was extracted from Hillen’s analysis. A combination of BTS and TVS techniques is thus more useful for characterization of copper drift, and helps to resolve the intrinsic polymer effect from that of metal drift-related inst...

Correlation Between Bond Cleavage in Parylene N and the Degradation of Its Dielectric Properties

Parylene, a chemical vapor deposited polymer, is shown here to have limited stability when annealed and/or bias temperature stressed. Parylene N thin films were preannealed at 250, 300, and 350°C for 30 min and then bias temperature stressed at 150°C and 0.5 MV/cm for 0, 30, 60, and 90 min. An order of magnitude increase in leakage current was observed for films preannealed at 300°C compared to the 250°C films but a precipitous increase was observed for the 350°C samples, which lead to shorting. Further, an electron spin resonance signal was observed for films annealed at 350°C without bias.