Tsuyoshi Fujimura

Design and measurements of test element group wafer thinned to 10 /spl mu/m for 3D system in package

We designed and measured test element group wafers thinned to 10 /spl mu/m for 3D system in package. The n-well p-Si diodes in 10 /spl mu/m thick wafer showed increasing of the reverse saturation current in comparison to the currents in 20 /spl mu/m, 30 /spl mu/m or 640 /spl mu/m thick wafer. While the pMOSFETs and nMOSFETs in 10 /spl mu/m thick wafer showed no degradation of mobility, sub-threshold swing and threshold voltage. Defects might be induced by mechanical stress during wafer back grinding process near wafer back side, within a few micron-meters from the wafer back surface.

Fabrication of Open-Top Microchannel Plate Using Deep X-Ray Exposure Mask Made with Silicon On Insulator Substrate

We propose a high-aspect-ratio open-top microchannel plate structure. This type of microchannel plate has many advantages in electrophoresis. The plate was fabricated by deep X-ray lithography using synchrotron radiation (SR) light and the chemical wet etching process. A deep X-ray exposure mask was fabricated with a silicon on insulator (SOI) substrate. The patterned Si microstructure was micromachined into a thin Si membrane and a thick Au X-ray absorber was embedded in it by electroplating. A plastic material, polymethylmethacrylate (PMMA) was used for the plate substrate. For reduction of the exposure time and high-aspect-ratio fast wet development, the fabrication condition was optimized with respect to not the exposure dose but to the PMMA mean molecular weight (M.W.) changing after deep X-ray exposure as measured by gel permeation chromatography (GPC). Decrement of the PMMA M.W. and increment of the wet developer temperature accelerated the etching rate. Under optimized fabrication conditions, a microchannel with 50 µm width through 1000 µm PMMA plate, with a high aspect ratio over 20, was fabricated. By using a high-aspect-ratio open-top microchannel plate, high fluorescent electrophoresis was performed.

Oxynitridation of silicon with nitrogen plasma for flash memory applications characterized by high frequency capacitance-voltage measurements

Abstract Si(100) wafers were oxynitrided by nitrogen plasma exposure under different conditions and thermally oxidized in dry O 2 without the use of toxic or global warming gases. The atomic concentration ratio of N/Si was 0.075 at a plasma discharge power of 0.5 kW and an exposure time of 1 min and 0.176 at a plasma power of 2.0 kW and an exposure time of 3 min, as determined from X-ray photoelectron spectroscopy measurements. A progressive reduction in the oxidation rate with increasing N concentration, corresponding to an increase in N plasma power, was observed. The uniformity of film thickness over a 4-inch wafer was improved after nitrogen plasma exposure and rapid thermal oxidation, with a thickness variation of less than 2.6% compared with 13.2% for the N 2 O thermal oxidation process. The advantages of exposing Si to N plasma for application in silicon devices was investigated by high-frequency capacitance–voltage measurements. A distortion in the capacitance–voltage curve was observed for samples that did not undergo nitridation, a distortion that was not observed in the nitrided samples. Capacitance–voltage curve distortion was found to be significantly reduced by Si nitridation under low plasma power.

Inductively coupled plasma application to the resist ashing

We present a study of a resist ashing using O 2 inductively coupled plasma (ICP) at low pressure (< 10 Pa). An ashing rate of 1.5 μm was obtained at 0.6 Pa by direct exposure to the plasma. However, a serious charge-up damage appeared owing to the radiation of a large amount of charged particles. On the contrary, a structure modification to restrict the charged particles could suppress the serious charge-up damage. The ashing rate dropped to below 20% of that directly exposed to the plasma. These ashing rates were proportional to the O * spectrum intensity directly above the substrate, which was strongly dependent on the pressure. The amount of the exited particles supplied to the substrate depended on the phenomena as a function of the pressure, such as a mean free path, a plasma distribution, etc. In this paper, the alternative magnetic field measurement in the plasma indicates the energy absorption decrease to the plasma at high pressure, which is an important factor of the ICP production for processing.

A study of the reliability of MOSFETs in two stacked thin chips for 3D system in package

RF wireless communication systems consist of many different components, analog/digital CMOS, passive components, sensors. The fabrication processes of these components are so different. System in package (SiP) can mount different chips fabricated by different processes in a package. Hence, SiP is effective, especially for wireless communication systems. On SiP, thinning of stacked chip thickness is required for better heat radiation and thinner packaging height (Ikeda, A. et al., Proc. IEEE Int. Conf. on Microelectronic Test Structures, p.161-4, 2004). For highly reliable SiP, we investigated MOSFET characteristics on a thinned wafer for two stacked chips bonded by flip chip Au-Au bump interconnection.

Film Density Dependence of Polymethylmethacrylate Ablation under Synchrotron Radiation Irradiation.

Variations in the etch depth and refractive index of polymethylmethacrylate (PMMA) films of different molecular weights after synchrotron radiation (SR) irradiation are investigated. Reduction of the PMMA film molecular weight, density and thickness are observed after SR irradiation. The amount of film thickness loss depends on not only initial molecular weight but also film density. The PMMA density difference at the start of SR exposure affects the etch depth after SR ablation.

Investigation of sample behaviors inside on-chip electrophoresis microcapillary using confocal laser scanning microscopy

We report the observation of sample behaviors using the confocal laser scanning microscopy (CLSM) in on-chip microcapillary. Sample loading by pinched valve injection is observed in a new cross injector shape, which has the structure added conventional cross injector to circle shape. In sample loading, because this structure causes a different electric field compared with that in conventional cross injector, high efficient sample plug injection was performed. It is important to investigate further the detailed sample profiles using the CLSM in sample loading for development of the on-chip microcapillary. We attempt the simulation of sample loading in the cross injector using the semiconductor device simulator MEDICI in order to investigate it in further detail. The sample movements in the channel turn along the Z-direction are observed using the CLSM. In order to miniaturize the microfluidic channel, it is necessarily needed to fold the channel, but then it is inevitable that sample dispersion occurs in the turn. We present sample flow profiles along the Z-direction in the turn using the CLSM and the influence on the electrophoretic separation. Also, we improve that fabrication of duct channel for exhaustion the vaporized xylene to outside the chip and the adhesion process

Mass-production fabrication of miniaturized plastic chip devices for biochemical applications

A very important aspect in the next stage of genomic research will be the study of genetic diversity originating from an individual, for example, a single nucleotide polymorphism (SNP),. For this, the base-pair sequence needs to be determined quickly and easily; along with effectively gathering the proteins that are produced from the cell and depend on each genetic design. To meet these demands, the use of a miniaturized experimental apparatus formed on a chip is suitable as it gives a very small and well-controlled space to undertake precise analyses. This type of chip device needs to be disposable, inexpensive and of uniform quality, therefore many chips should be fabricated at the same time from a low cost chip material such as plastic. A mass production fabrication process for such plastic chips was determined as follows. A thick coating type photoresist was spin-coated onto a 4-inch size Si wafer to 20 μm thickness and patterned by UV-lithography. Thick Au structures were embedded into the resist mold by microelectropolating. After removal of the resist, Au fine structures remained and were used as a metal mold for plastic casting. Plastic, polymethylmethacrylate (PMMA), beads were dissolved in acetone and the polymer solution was cast into the metal mold under vacuum heating environment producing many identical plastic chips at a thickness of 1 mm. The size of the chemical reaction channel, one of the device’s components, was 50 μm in width and 20 μm in depth.

Fabrication of absorber-embedded in membrane type deep X-ray exposure mask with wide exposure area made with Si substrate

In this paper we study about the fabrication of absorber-embedded in membrane type deep X-ray exposure mask with wide exposure area made with Si substrate.

Fast Separation of DNA Fragments in On-chip Electrophoresis Microcapillary

Separation of DNA fragments is performed in on-chip electrophoresis microcapillary fabricated on a photosensitive glass. Since the UV-irradiated part of the photosensitive glass has the etching rate 20 times higher than the other parts, we can obtain the channel structure with the high aspect ratio, which is valuable to the high-sensitivity detection of the signal. The confocal laser scanning microscopy (CLSM) is used to observe and detect the fluorescent sample plug in the on-chip electrophoresis microcapillary. The CLSM is a powerful tool to observe and detect the sample inside the channel since it can capture the fluorescence images and can vary the laser focal plane depth. In this study, Hydroethylcellurose (HEC) polymer solution is using in the electrophoresis as sieving matrix. Therefore the on-chip electrophoresis microcapillary with the short separation channel is able to separate DNA fragments.