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Analysis Technologies for Robust Fujitsu Products

FSTJ 2010-7 Cover Image

2010-7 (Vol.46, No.3)

This special issue represents only a few of the analytical technologies being developed in the Fujitsu Group. This issue also introduces technologies playing an important role in radiation measurement and environmental monitoring.

2010-7 (Vol.46, No.3) Contents

1. Preface (502 KB)
Analytical technologies are not just for enhancing the performance and reliability of Fujitsu Group products, but also play an important role as basic technologies in the quest to make our planet a safe and secure place. In particular, they will play an important role in environmental load reduction, which is considered to be a major corporate issue in the 21st century. ---[Ei Yano, Member of the Board, President of Device & Materials Laboratories, Fujitsu Laboratories Ltd.]
2. High-Precision Evaluation of Ultra-Shallow Impurity Profiles by Secondary Ion Mass Spectrometry (1.32 MB )
As complementary metal oxide semiconductor (CMOS) processes evolve and device structures become finer, semiconductor manufacturers are having to form transistor gates with thin films 1–3 nm thick and ultra-shallow junctions of 40 nm or less. For better reliability and performance, these device structures must be controlled at the nanometer level. This requires the nanometer-level analysis and evaluation of the profiles of elements in thin films and the profiles of impurities in ultra-shallow junctions. Secondary ion mass spectrometry (SIMS) is ideal for analyzing compositions and impurity profiles. Although the latest developments in SIMS equipment do enable nanometer-level element profile analysis, this analysis method works by exploiting complex physical phenomena, so it is important to optimize the analysis conditions in order to obtain the profiles precisely. In this paper, we discuss the latest achievements in our study of analysis conditions where high precision is obtained by considering factors that degrade precision in the SIMS analysis of element profiles across surface regions ranging from 3–5 to 10–20 nm from the surface. ---[Yoko Tada, Kunihiro Suzuki, Yuji Kataoka]
3. Two-Dimensional Carrier Profiling by Scanning Tunneling Microscopy and Its Application to Advanced Device Development (860 KB)
A high-resolution two-dimensional (2D) carrier profiling technique has been desired to optimize the dopant profile around the source/drain and extension region in transistors to enhance electrical characteristics when scaling the gate length down to less than 50 nm. At Fujitsu Semiconductor Ltd., high spatial resolution of about 1 nm has been achieved by scanning tunneling microscopy to enable the 2D carrier profiling technique to be applied to the development of scaled transistors beyond the 90-nm technology node. The dependence of the 2D carrier profile on process conditions was found to agree well with that of electrical characteristics. On the basis of such profiles, the dopant profile in scaled transistors has been optimized. The technique also enables an evaluation of dopant distribution fluctuations that cause variability in transistor performance. The dopant profile around the extension region was found to depend on the gate line edge roughness. On the basis of the measured results, various methodologies for suppressing transistor performance variability have been proposed. ---[Hidenobu Fukutome]
4. Application of Scanning Nonlinear Dielectric Microscopy to Measurement of Dopant Profiles in Transistors (1.09 MB )
This paper presents results obtained when using scanning nonlinear dielectric microscopy (SNDM) to measure dopant profiles in transistors. Secondary ion mass spectrometry (SIMS) measurements of an epitaxial multilayer film on a standard sample and SNDM measurements of the sample surface showed that it was possible to obtain a uniform concentration region with a thickness of approximately 4–5 µm in each layer. An SNDM signal with a one-to-one correspondence to the dopant quantity was obtained. In real devices, dopant concentration profiles could be obtained as two-dimensional images by applying calibration curves from the standard sample to cross-sectional observations of n- and p-channel transistors. ---[Koichiro Honda]
5. Atomic-Resolution Imaging and Analysis with Cs-Corrected Scanning Transmission Electron Microscopy (1.49 MB )
Advances in nanotechnology and electronic device miniaturization are making atomic-level control of structure and composition increasingly important. To promote research and development in this field, it is essential to develop technology for measuring the structures, compositions, and properties of materials and devices with atomic resolution. Scanning transmission electron microscopy (STEM), which is a high-spatial-resolution imaging technique, combined with analytical equipment has been used in various fields such as research and development. However, conventional STEM equipment suffers from probe size limitations and a drop in electron-beam current due to the effects of spherical aberration (Cs) in the magnetic lens. Recently, though, Cs-correction technology has been developed, and the Cs corrector has been mounted on commercial STEM equipment. This technology is proving to be exceptionally effective in enabling imaging and analysis at even higher resolutions. In this paper, we describe the principles for increasing resolution by applying Cs-correction technology and present examples of atomic-resolution STEM measurements. ---[Yasutoshi Kotaka, Takashi Yamazaki, Yuji Kataoka]
6. Analysis of Insulating Materials and Deep Interfaces by Auger Electron Spectroscopy (874 KB)
Auger electron spectroscopy (AES) is a powerful tool for investigating the composition of minute particles and thin films as well as the compositional distribution of elements in the depth direction of multilayered films and metallic-bonded interfaces. However, non-conductive materials are generally difficult to analyze because of the charge-up phenomenon generated by the exciting electron beam. Furthermore, in a "depth profiling" analysis performed simultaneously with sputter etching, if the target analysis site is deep beneath the sample surface, the depth resolution is degraded by effects such as surface roughness and mixing, so precise evaluation is difficult. To solve these problems, we have investigated an AES analysis technique that uses a thin sample processed by a focused ion beam. It enables measurement free from charge-up even if the sample is composed of insulating material and achieves depth profiling with outstanding resolution even at analysis sites (such as interfaces) deep within the sample. ---[Michiko Sato, Shiori Shirai, Yoshihiko Seyama, Toru Itakura]
7. Materials Analysis Using Synchrotron Radiation and Neutron Beams (988 KB)
To develop high-performance and high-reliability products that do not contain any hazardous substances, Fujitsu uses many analysis techniques and various types of equipment. To add to these, we have been developing materials analysis techniques using synchrotron radiation and neutron beams, which cannot easily be handled by general analysis equipment. For this analysis, we make use of national public research facilities. In this paper, we introduce the "SUNBEAM" beamline constructed by a consortium of 13 companies at the SPring-8 synchrotron radiation facility managed by RIKEN and give examples of how Fujitsu Laboratories is applying this beamline to materials analysis. We also introduce two future analysis technologies: analysis using the X-ray free electron laser now under construction at SPring-8 and neutron beam analysis at the Japan Proton Accelerator Research Complex (J-PARC) built in Tokaimura, Ibaraki prefecture, by the Japan Atomic Energy Agency (JAEA). ---[Naoki Awaji, Kenji Nomura, Shuuichi Doi]
8. Radiation Measurement Technologies for Evaluating Soft Errors (729 KB)
Two radiation measurement technologies for estimating and lowering the occurrence rate of "soft errors" are introduced. Radiation such as fast neutrons (generated by cosmic rays) and α-rays (generated by the impurities in materials composing LSIs) cause incorrect operations—known as soft errors—in computer systems. Since soft errors undermine the reliability of mission-critical products such as backbone servers, it is necessary to estimate and reduce their occurrence rate. To enable experimental measurements of neutron and α-ray dose rates, my coworkers and I have developed and utilized a vacuum α-ray tracking method—for measuring the amount of α-rays with high sensitivity—as well as a cosmic ray neutron spectrometer. With these two technologies, it has become possible to measure the radiation dose rate in low-α-ray-emitting materials, which has been impossible until now, and the neutron dose rate in arbitrary environments such as mountainous regions and to estimate the soft error rate accurately. Moreover, these technologies make it possible to select materials with low α-ray emissivity and choose environments with a low neutron dose rate, thereby contributing to improvements in computer system reliability. ---[Ryozo Takasu]
9. Evaluation of Devices and Materials by Transmission Electron Microscopy (1.63 MB )
With the components of cutting-edge devices becoming smaller and more complicated and their constituent materials becoming more multilayered and diversified, nanometer-order structural control has recently become indispensable. To improve the performance and reliability of manufactured products like these devices, nanometer-order evaluation technology is therefore essential. As examples, this paper introduces four techniques for materials and device analysis that utilize transmission electron microscopy (TEM): three-dimensional observation by electron tomography for evaluating device features controlled at the nanometer-level, electron holography for visualizing information about the electric and magnetic fields of devices at the nanometer-level, high-resolution TEM observation and electron-energy-loss spectroscopy for analyzing the crystal structure and composition of nanostructure multilayers, and high-angle annular dark-field scanning transmission electron microscopy for observing the atomic arrangement of ordered alloys and analyzing heteroepitaxial interface structures. ---[Toyoo Miyajima, Ryoji Ito, Koichiro Honda, Mineharu Tsukada]
10. Compact Sensor for Environmental Monitoring (1.02 MB )
This report describes a simple means of detecting trace amounts of gaseous substances in the atmosphere. In the fabrication processes for semiconductor LSIs, production defects occur if gas phase contaminants in the atmosphere stick to the wafer being processed. To overcome this problem, I have developed and am currently applying a contamination sensor that uses a quartz crystal microbalance (QCM) to detect such contamination. The detection system using this sensor has high sensitivity and is well suited to tracking the time-varying concentration of an atmospheric contaminant. Investigating the behavior of contaminants in a semiconductor LSI fabrication plant makes it possible to identify contamination sources and eliminate them. Therefore, this sensor system should be effective in lowering production costs and improving product quality. Moreover, the sensor is compact, so it can be easily installed, for example, at various locations around a plant and in the wafer container. Besides being compact, the QCM controller is easy to use and offers outstanding portability: it simply needs to be plugged into the universal serial bus (USB) port of a device such as a notebook computer. As a result of these features, it is likely that this sensor will not only be used in semiconductor fabrication plants but also be applied to other kinds of environmental measurement. ---[Ryozo Takasu]
11. Evaluation and Analysis Technologies for Printed Wiring Board Materials (794 KB)
The printed wiring board (PWB) is a vital component of electronic equipment. Today, with product diversification and a shorter development cycle being dominant trends, it is essential to develop PWBs that satisfy performance and reliability requirements as quickly as possible. It has therefore become important to correctly select and appropriately use PWB materials that suit objectives from among the many commercially available materials. Over the last ten years, Fujitsu has been independently evaluating insulation materials for PWB use and has been comparing those results with the results of evaluating PWBs themselves while performing tests and accumulating data. We are currently developing evaluation technologies for determining whether new insulation materials can achieve the performance demanded of PWBs used in a variety of Fujitsu products. Among these technologies, we introduce ones that target thermomechanical properties, heat resistance, and transmission properties and mention their future directions. ---[Daisuke Mizutani]
12. Interconnection Evaluation Technology for Printed Wiring Boards (848 KB)
As a developer of world-class products including server and network devices, Fujitsu recognizes the printed wiring board (PWB) as a core component among the various components of those products. One basic element supporting high-quality PWBs is through-hole interconnection reliability. Existing methods for evaluating interconnections typically involve temperature cycle tests that subject the PWB to low and high temperatures. We have developed an evaluation technique that applies current to interconnections and wiring patterns to heat the PWB's interior and generate a temperature rise. This technique can apply a temperature load closer to actual conditions than temperature cycle tests can, enabling evaluation in one-fifth the time. In this paper, we introduce this new through-hole interconnection evaluation technique. ---[Mitsuhiko Sugane, Yoshihiro Morita]
13. Simulation Method for Connector Packaging (1.20 MB )
There is a growing demand for technology that can analyze and test contact reliability with high accuracy in high-pin-count flat packaging such as sockets for central processing units (CPUs) and application specific integrated circuits (ASICs) and in card edge connectors for modular products. We have developed simulation technology for visualizing the behavior of individual contacts, which cannot be obtained empirically. This technology lets engineers test connections in connector packaging and clarify their behavior, enabling the mechanism behind stable contacts to be determined from the desktop without the need to perform numerous experiments. This paper introduces two key examples of applying this technology. First, for land grid array (LGA) connections having a high mating pressure, we clarified the behavior of individual contacts and tested long-term connection reliability while taking into account the package and system (board) displacement over time. Next, for connector packaging for module boards that must secure a mechanical board while also achieving electrical stability in the same contacts, we tested connection safety by clarifying the mechanism of module-board slippage due to vibration during equipment transport. ---[Makoto Sakairi, Tadashi Tateno, Akira Tamura]
14. Analysis of Ion Implantation Profiles for Accurate Process/Device Simulation:
Ion Implantation Profile Database Based on Tail Function
(2.58 MB )
In the design of very-large-scale integrated circuit (VLSI) devices, accurate prediction of the doping profiles resulting from ion implantation, a standard method for doping impurities in VLSI processes, is essential. This is done by obtaining analytical expressions for the secondary ion mass spectrometry (SIMS) data of ion implantation profiles, and these analytical formulas are used to compile an ion implantation profile database. The profiles of arbitrary implantation conditions can be generated using interpolated parameter values. The functions used to express these ion implantation profiles include Gaussian, joined half Gaussian, Pearson, and dual Pearson functions. In addition to these, my coworkers and I have proposed a new tail function. This tail function has fewer parameters than the dual Pearson function, which is currently the standard function used in general-purpose simulators, and it is better able to specify an arbitrary profile using a unique set of parameters. We used this function to construct an ion implantation database comprising approximately 1000 smaller databases. By linking this database with a single additional parameter, we were also able to predict the amorphous layer thickness under a wide range of implantation conditions. ---[Kunihiro Suzuki]
15. Analysis of Ion Implantation Profiles for Accurate Process/Device Simulation:
Analysis Based on Quasi-Crystal Extended LSS Theory
(2.32 MB )
Ion implantation profiles are sometimes needed in cases where the implantation conditions are not covered by existing databases or novel materials are being used. Although profiles can be derived by Monte Carlo simulation, it can take a long time to trace the trajectories of tens of thousands of ions. My coworkers and I have proposed an extended LSS (Lindhard, Scharff, and Schiøtt) theory that predicts profiles almost instantaneously but with comparable precision to Monte Carlo simulation. Although it works for profiles in amorphous layers, it cannot predict profiles in the crystalline materials used in practice. Therefore, we proposed a quasi-crystal extended LSS theory (QCLSS) in which parameters corresponding to the characteristic channeling phenomena in crystalline materials are implemented with a semi-empirical model and linked to the extended LSS theory. This can provide nearly instantaneous predictions of the implantation profiles of novel ion species in novel crystalline substrates. By applying the QCLSS theory to Si1–xGex substrates (which have recently been the focus of much study), we constructed a database for the implantation of B, As, and P ions in substrates with arbitrary values of composition ratio x. ---[Kunihiro Suzuki]