Multilayer planarization of polymer dielectrics

Polymers are widely used in the microelectronics industry as thin-film interlevel dielectrics layers between metal lines, as passivation layers on semiconductor devices and in various packaging applications. As multiple layers of polymer and patterned metal are constructed, the ability of these polymers to planarize topographical features becomes increasingly important. In this study, the degree of planarization (DOP) for five commercially available polymers has been examined for three different structural configurations with the intent of simulating practical applications. Specifically, this study investigates single layer planarization, multiple coat planarization, and planarization of metal lines patterned on a polymer base. This study also examines the effects of orientation of the metal structure to polymer flow during spin casting and location on the wafer. The polymers are selected to investigate different polymer chemistries frequently used in the microelectronics industry. The underlying structures were fabricated using standard photolithography and electroplating techniques. Feature dimensions include 25-200 μm line spacings and widths with the polymer overcoat thickness being twice the height of the underlying structures     

Variable frequency microwave curing of photosensitive polyimides

Variable frequency microwave (VFM) curing was investigated as a means of rapid curing of two photosensitive polyimides. The properties of two polymers, PI 2734 and Ultradel 7501, cured by convective heating and VFM curing were compared. The results of this study indicate that rapid VFM curing of these polymers is feasible. Complete imidization was possible. The most significant differences in properties between VFM and thermally cured films were in the electrical properties due to the slow evolution of chemical products     

Electron beam enhanced multilayering and planarization inpreimidized polyimides

High-density packaging and interconnection applications frequently involve the use of polyimide-based materials as interlevel dielectrics for multilevel interconnection schemes. Surface planarity after each polymer layer is very important to the fabrication of multilayer structures. Highly nonplanar surfaces were observed in a multilayer test structure, fabricated using a thermally cured polyimide (Ultradel 7501). In this study, the effect of a novel cure technique involving electron beam (e-beam) exposure on multilayering and planarization behavior in Ultradel 7501 is investigated. Planarization measurements were conducted on different feature sizes and at various locations on the wafer in order to investigate the effect of solvent exposure, time and area of contact between multiple layers. The degree of planarization was found to improve from -206% for a thermally cured case to +15% for an e-beam cured sample. Analysis of the solvent induced polymer swelling and its effect on multilayer planarization of Ultradel 7501 is presented     

Longitudinal Evaluation of a GIS Laboratory in a Transportation Engineering Course

This paper focuses on the potential impact of student-centered feedback for enhancing the learning experience of civil engineering students that used a geographic information system (GIS) based tutorial in a transportation engineering course. The tutorial was implemented in a laboratory environment developed as a self-guided activity supported by a web-based learning system. The formative research proposed in this study includes a series of four successive implementations of this laboratory. Students’ performance, beliefs, and perceptions were monitored by using a mixed-methods design approach and weaknesses identified from early implementations were addressed before the next implementation of the laboratory activity. The students’ performance was found to improve when the GIS web-based tutorial was complemented with an instructor-driven short introduction that anchored the laboratory activity in traffic safety. In addition, students’ feedback in both quantitative and qualitative format indicated weaknesses related to the difficulty of the laboratory and usability factors such as speed and size of data uploading. As these weaknesses were addressed, students’ positive input regarding the overall GIS laboratory experience significantly increased. This positive input was fully backed up by students’ feedback indicating major strengths of the GIS laboratory for professional growth and future career development in civil and transportation engineering. Finally, students’ inputs in the latest implementations provided valuable suggestions for future potential improvements regarding how to better integrate the GIS laboratory in course-related activities such as term projects.     

Ferroelectric,piezoelectric and electrostrictive properties of Sn4+‐modified Ba0.7Ca0.3TiO3 lead‐free electroceramics

Lead‐free Ba_0.7Ca_0.3Ti_1?xSn_xO₃ (x=0.00, 0.025, 0.050, 0.075, and 0.1, abbreviated as BCST) electroceramic system was prepared by the solid‐state reaction method and its ferroelectric, piezoelectric, and electrostrictive properties were investigated. X‐ray diffraction shows that the compositions with x≤0.05 exhibit a tetragonal crystal structure having P4mm symmetry; while the compositions x=0.075 and 0.1 exhibit a mixed P4mm+Amm2 phase coexistence of tetragonal and orthorhombic and P4mm+Pmm pseudo‐cubic lattice symmetries, respectively, at room temperature. The dense microstructure having relative density ~90%‐92% and average grain size in the range ~2.36 μm to 8.56 μm was observed for BCST ceramics. Temperature‐dependent dielectric measurements support the presence of phase coexistence and show the decrease in Curie temperature (T_C) with Sn⁴⁺ substitution. The dielectric loss (tan δ) values in the temperature range (?100°C to 150°C) was observed to be <4%, for all BCST ceramics. The BCST compositions exhibit typical polarization‐electric field (P‐E) hysteresis and electric field induced strain (S‐E) butterfly loop, which confirms the ferroelectric and piezoelectric character. The compositions x=0.025, 0.05 and 0.075 show the peaking behavior of displacement current density () to an applied electric field () (J‐E) which implies the saturation state of polarization. The maximum electrostrictive coefficient (Q₃₃) value of 0.0667 m⁴/C² was observed for x=0.075 and it is higher than some of the significant lead‐based electrostrictive materials. The compositions x=0.05 and 0.075 exhibit the notable electrostrictive properties that may be useful for piezoelectric Ac device applications. The observed results are discussed and correlated with the structure‐property‐composition.     

Silver metallization for advanced interconnects

Silver metal has the highest room-temperature electrical conductivity of any substance; however, it has found limited acceptance in the electronic industry (e.g., silver filled epoxy) due to the high rate of metal corrosion and migration causing dendrites and electrical failures. With decreasing transistor feature sizes, device-operating voltages have scaled down considerably. In this paper, the reliability of silver and potential benefits of silver metallization are discussed in terms of future trends in microelectronic interconnections. Experimental data supports existing reliability models indicating that electrochemical migration failure modes may not be operative at low voltages. Silver metal corrosion and migration are studied under accelerated test conditions to obtain a qualitative understanding of the failure mechanism     

Disseminated histoplasmosis and Wegener's granulomatosis

Disseminated histoplasmosis is an unusual complication in endemic areas and has been reported in patients with an immunodeficient state, either from human immunodeficiency virus (HIV) infection or transplantation. In the non-HIV population, rare cases of disseminated histoplasmosis have been reported in patients with leukemia and Hodgkin's disease and patients receiving steroid therapy for various diseases. We report a case of disseminated histoplasmosis in a patient with Wegener's granulomatosis.