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Environmental & Advanced Material

2002-6 (Vol.38, No.1)

2002-6 (Vol.38, No.1) Contents

1. Preface (40 KB): ---[Koichi Niwa, Senior Vice President Fujitsu Laboratories Ltd. ]

Advanced materials - Materials technology which supports high-end device -

2. High-Performance Resist Materials for ArF Excimer Laser and Electron Beam Lithography (180 KB): High-performance resist materials for ArF (argon fluoride) excimer laser ( λ= 193 nm) and electron beam (EB) lithography for fabricating 100 nm-level and beyond ULSIs have been developed. For the base polymers of the ArF resists, a novel methacrylate was employed as a base polymer whose ester groups have chromophores with a low extinction coefficient at 193 nm. A polycyclic hydrocarbon substituent, called adamantyl, and lactone substituents were introduced for acid-labile ester groups in the methacrylate polymer. The alicyclic group provides superior sensitivity, resolution, and dry-etch resistance, while the lactone groups afford compatibility with a standard TMAH (tetramethylammonium hydroxide) developer, good resolution, and adhesion to Si substrates. For the base polymer of the EB resist, the above-mentioned adamantyl methacrylate unit was applied in a vinylphenol copolymer. By optimizing the compositions of these resists and the process conditions, we achieved a 100 nm line and space pattern by ArF excimer laser lithography and a 59 nm hole pattern by EB lithography. ---[Koji Nozaki, Ei Yano ]

3. A Study of Current Multilevel Interconnect Technologies for 90 nm Nodes and Beyond (269 KB): Technology trends of interconnects differ from those of transistors in that the performance of interconnects decreases as they are scaled down to satisfy stricter limits on line width and inter-line horizontal space. As interconnects follow this reverse scaling, the number of interconnects has been increased to realize a lower sheet resistance and higher reliability. A maximum of 10 levels of Cu interconnects is anticipated for 90 nm-generation logic devices that enter the gigahertz band. Cu/Low-k multilevel interconnect technology is an established technology that reduces wiring capacitance and therefore delay times. The incompatibilities between Cu interconnect processes and the material characteristics of Low-k have been investigated. This paper describes the current status and issues of Cu interconnects in system LSI and Cu/Low-k multilevel interconnects for 90 nm. ---[Takayuki Ohba ]

4. Decoupling Capacitor with Low Inductance for High-Frequency Digital Applications (140 KB): Because of the rapid progress of LSI technology, the operating frequency of LSIs is increasing and the power supply voltage is decreasing. To use high-performance LSIs effectively, new decoupling capacitors that can suppress the switching noise generated by LSIs and stabilize the supply voltage are required. We have developed a capacitor which can satisfy these requirements around the 300 MHz frequency range by using a (Ba,Sr)TiO₃ (BST) Chemical Solution Deposition (CSD) film and fine-pitch electrode structure. Two 200 nm-thick BST dielectric layers are deposited on an Si wafer with an Au-base electrode. The solder bump terminal for mounting to the circuit board is formed on the top Cr/Pt/Au electrode. The developed capacitor has a capacitance density of 2 µF/cm², an inductance of 30 pH, a resonant frequency around 230 MHz, and a breakdown voltage of 10 V. This paper describes the material technology of the dielectric BST film and thin-film electrode of the new capacitor. ---[Yoshihiko Imanaka, Takeshi Shioga, John D. Baniecki]

5. High-Temperature Superconducting Materials for High-Performance RF Filters (131 KB): This paper describes the development of high-Tc, superconducting YBCO films for high-performance RF filters. The use of a high-Q filter is expected to provide high selectivity and high sensitivity in the base stations of mobile telecommunication systems. We fabricated 2 GHz-band microstripline resonators by pulsed laser deposition of YBCO films and used them to study the relationships between the Q, microstructure, and film-thickness of YBCO films. A resonator consisting of 0.9 µm-thick epitaxial YBCO films on both sides of an MgO single-crystal substrate achieved an unloaded Q of 8 × 10⁴ at 70 K, which is about 10 times higher than the Q of conventional filters. A 2 GHz-band microstripline bandpass filter using the high-quality films demonstrated superior characteristics with a very low insertion loss and steep cutoffs. ---[Akihiko Akasegawa, Kazunori Yamanaka, Teru Nakanishi, Manabu Kai ]

6. High Ionic Conducting Polymer with Polysaccharide and its Applications (96 KB): Polysaccharide polymers such as cyanoethylpullulan, cyanoethylcellulose, and acetylcellulose were examined for use as matrix polymers in gel-electrolytes (ionic conducting polymers). Using cyanoethylpullulan matrix polymer, an excellent gelelectrolyte which provided a high ionic conductivity of up to 2.4 × 10^-3 S/cm at ambient temperature and good mechanical strength was obtained. In one of our applications of the newly developed gel-electrolyte, we used it to fabricate rechargeable lithium ion polymer batteries. These batteries showed good electrochemical properties, for example, a high charge/discharge efficiency and high discharge current density. ---[Fumio Takei, Hiroaki Yoshida, Norio Sawatari]

7. Epitaxial Ferroelectric Thin Films on Silicon Substrates for Future Electronic Devices (166 KB): A lead lanthanum zirconate titanate ((Pb_1-2/3yLa_y)(Zr_1-xTi_x)O₃, PLZT) thin film with a thin-film bottom electrode of strontium ruthenium oxide (SrRuO3, SRO) can be grown epitaxially on a (001) silicon substrate. Ceria (CeO₂) and yttria-stabilized zirconia (YSZ) were used as a buffer layer. This paper discusses the orientation and domain structure of PLZT thin films on an SRO/CeO₂/YSZ buffer layer. All oxide thin films of the PLZT/SRO/CeO₂/YSZ heteroepitaxial structure were oriented toward (001). The CeO₂ and YSZ grew epitaxially with a cube-on-cube alignment with the diamond structure of the silicon. The PLZT and SRO thin film rotates 45° in-plane with respect to the fluorite structure of CeO₂. The remanent polarization of a PbLa_0.03Zr_0.45Ti_0.55O₃ epitaxial thin film is 10 µC/cm² and is smaller than that of a (001)-oriented epitaxial PLZT thin film with a platinum bottom electrode on a magnesia (MgO) substrate. The profiles of the reciprocal space mapping reveal that the PLZT epitaxial thin films were distorted into a pseudocubic structure by the tensile stress from the silicon substrate. ---[Masao Kondo, Kenji Maruyama, Kazuaki Kurihara ]

8. Simple Micro-Lens with Polymer-Filled Trench in Slab Waveguide (136 KB): We have developed a new micro-lens array that is integrated into silica slab waveguides. This paper reports the design, material, fabrication, and performance of this new array. The micro-lens has a concave trench filled with a low refractive index polymer. The array has a low insertion loss (0.5 dB), low crosstalk (< -40 dB), and stable characteristics. Our experiments indicate that the micro-lens is suitable for use in two-dimensional optical switches of advanced photonic networks. ---[Koji Tsukamoto, Akio Sugama, Yukiko Wakino, Tomoko Miyashita, Masayuki Kato ]

Characterization technology - Advanced characterization technology for nanometer scale evaluation -

9. Direct Observation of Potential Distribution across PbZr_xTi_1-xO₃ Thin Films Using Off-Axis Electron Holography (390 KB): This paper describes how we used off-axis electron holography to observe the potential distribution across a ferroelectric PbZr_xTi_1-xO₃ (PZT) capacitor and the surrounding electric field created by spontaneous polarization of polycrystalline PZT (poly-PZT) thin film. We produced equi-phase contour maps of the incident electron beam. Because the phase of the beam was shifted according to the electric field strength in the PZT thin film, these contour maps can be used to visualize the electric field. This is the first electron-holographic representation of the electric field of a poly-PZT thin film of a ferroelectric memory device.---[Koichiro Honda ]

10. Characterization of Ultra-Shallow Implants Using Low-Energy Secondary Ion Mass Spectrometry: Surface Roughening under Cesium Bombardment (157 KB): Surface roughening caused by low-energy Cs⁺ bombardment was studied to obtain more reliable ultra-shallow arsenic depth profiles and to provide important information for the modeling and process control of advanced CMOS design. Ultra-shallow arsenic implantation distributions and narrowly spaced antimony delta markers in silicon were used to explore surface roughening caused by low-energy Cs⁺ bombardment (0.25 to 1 keV) at impact angles between 0° (normal incidence) and 75°. The surface roughening was observed at oblique incidence. The roughening degraded the depth resolution and gave rise to a severe profile shift. In addition, another profile shift was observed at near normal incidence. This shift seems to be correlated to the amount of Cs accumulated in and on the sample. Impact angles of 45 to 50° (0.25 keV), 50 to 55° (0.5 keV), and 55 to 60° (1 keV) should be used to avoid the surface roughening and profile shift. The use of these conditions enables us to evaluate arsenic depth profiles more correctly and provide important information for forming reliable ultra-shallow junctions. ---[Yuji Kataoka, Mayumi Shigeno, Yoko Tada, Kazutoshi Yamazaki, Masataka Kase]

11.Quantitative Ultra Shallow Dopant Profile Measurement by Scanning Capacitance Microscope (171 KB): This paper compares scanning capacitance microscope (SCM) signals of an n-MOS transistor implanted with arsenic ions at an energy as low as 5 keV with a vertical secondary ion mass spectroscopy (SIMS) profile of the same device. Then, it describes SCM measurement by the application of a DC voltage sufficient to compensate for the flat band shift caused by the interaction between the probe of a conductive scanning probe microscope (SPM) and a silicon surface. To acquire the exact impurity distribution beneath a silicon surface, the SIMS measurement was carried out at a primary ion energy of less than 1 keV. As a result, the calibration of SCM signals using SIMS data was accomplished in the ultra shallow region near the silicon surface. It was also confirmed that the formalism based on the depletion approximation applies in this region. Using this formalism, we show that, at concentrations around 10¹⁸ cm^-3, SCM enables quantitative two-dimensional dopant profiling near the source/drain extension at a resolution of better than 10 nm. Moreover, by optimizing the sample preparation and measurement conditions, it is also possible to analyze a sub-µm gate transistor with a 60 nm channel length and investigate the complex dopant distribution in the source/drain region, including the edge of the shallow trench isolation. ---[Yoshio Kikuchi, Tomohiro Kubo, Masataka Kase ]

12. Structural Characterization of Giant Magnetoresistance Multilayers with New Grazing Incidence X-ray Fluorescence (170 KB): We have developed a grazing incidence x-ray fluorescence (GIXRF) technique based on wavelength dispersive (WD) fluorescence equipment with high-brilliance synchrotron radiation x-rays at SPring-8. The technique has been successfully applied to the evaluation of the stratified structure of giant magnetoresistance (GMR) multilayers. Because of the good energy resolution and high count rate of the WD detector, high-quality data about the dependence of fluorescence intensities on the incident angle for the composition elements were obtained. An analysis program based on matrix formalism has been developed, and a good agreement between data and model calculations has been obtained. The results indicate that excessive thermal treatment causes a roughening of inter-layer interfaces, which degrades the magnetic properties of a GMR head. ---[Naoki Awaji ]

Environmental materials - Materials development to reduce environmental impact -

13. A Highly Reliable Halogen-Free Dielectric for Build-up Printed Circuit Boards (135 KB): We have developed a highly reliable halogen-free (HF) flame-resistant epoxy dielectric for build-up printed circuit boards (PCBs). This material does not generate environmentally hazardous products such as polybrominated dibenzodioxins/furans or hormone disruptive agents like bisphenol-A and its derivatives. The dielectric is composed as the flame of a mixture of a reactive type oligomeric organic phosphate and Al(OH)₃ resistant. High Cu conductor corrosion resistance under high-temperature, high-humidity bias conditions has been obtained due to a cross-linkable organic phosphate that reduces the free phosphate ion content. The newly developed dielectric has the thermal and mechanical properties required in mobile electronic devices such as hand phones and laptop PCs, for example, high flexibility and shock resistance. ---[Yasuhiro Yoneda, Daisuke Mizutani, Nawalage F. Cooray ]

14. Reliability of Solder Joints Assembled with Lead-Free Solder (120 KB): To protect the natural environment, we will introduce the use of lead-free solder instead of the current tin-lead solder in the assembly of printed circuit boards in electronics equipment. During the transition to lead-free soldering, these two types of solders will be used in combination in joints. After the transition, a new element, bismuth, from components will contaminate the lead-free solder joints. We investigated the two types of solder through dynamic mechanical examination and concluded that lead-free solder can be used in combination with the current tin-lead solder and on its own to form sufficiently reliable joints. ---[Masayuki Ochiai, Toshiya Akamatsu, Hidefumi Ueda]

15. Recycling Magnesium Alloy Housings for Notebook Computers (176 KB): Magnesium alloy housings are lightweight and strong, have excellent heat removal characteristics, and are in widespread use in portable personal computers and similar devices. Another characteristic of magnesium alloy is that it can be remelted for recycling. There are two ways to recycle magnesium alloy housings, one is for recycling excess material generated during the molding process and one is for recycling collected magnesium alloy housings that have been painted. In the first process, adjusting the composition of the magnesium alloy in the remelting process yields a material with the same strength and corrosion resistance as the virgin material, even after repeated recycling. In the second process, the paint is removed from the magnesium alloy housings by immersion in a solution. The alloy is then remelted without generating much gas or dust, and its composition is adjusted to produce a recycled material having the same performance as the virgin material. The technology for recycling excess material was first applied to the production of the Fujitsu PC FMV-BIBLO notebook computer, which was marketed in 1999. The technology for recycling painted magnesium alloy housings will be applied full-scale starting in fiscal 2002. ---[Koichi Kimura, Kota Nishii, Motonobu Kawarada ]

16. Biodegradable Packing Materials for LSIs (127 KB): In general, the plastic LSI packing material used to transport and mount LSIs is discarded after the LSIs have been removed from the material and mounted. We investigated ways to use biodegradable plastic to decrease the environmental load due to discarded plastic. We developed a biodegradable LSI-packing material that is also electro-conductive. This material protects LSIs against electrostatic discharge and is also decomposed in soil by natural microorganisms. Moreover, it does not produce harmful gasses when it is incinerated. This paper describes this biodegradable LSI packing material and how it has been put to practical use in LSI trays and embossed carrier tape. ---[Takafumi Hashitani, Ei Yano, Yukio Ando ]

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