Motosuke Miyoshi

Electron beam inspection system based on the projection imaging electron microscope

An electron beam inspection system based on the projection imaging electron microscope was developed and the proof-of-concept system has been constructed and evaluated. The secondary electrons are projected through the projection imaging optics and imaged onto the image detection system. The projected secondary electron image is amplified by the microchannel plate and converted to an optical image by the fluorescent screen and detected by the 2048 element, eight-tap time delay and integration (TDI) image sensor. The stage is linearly moved in synchronism with the TDI signal output data rate, and then, the secondary electron image is continuously captured. The spatial resolution of around 0.1 μm has been obtained in this experiment. Several images obtained by the TDI imaging mode are also demonstrated.

Beam induced deposition of an ultraviolet transparent silicon oxide film by focused gallium ion beam

We have deposited a silicon oxide (SiOx) film with a high optical transmittance in the DUV region by a focused ion beam induced deposition technique using a gallium ion beam and a mixture of oxygen and TMCTS(1,3,5,7‐tetramethylcyclotetrasiloxane) as a source gas. The optical transmittance of a 0.3 μm thick film is higher than 90% at the wavelength of 250 nm. The transmittance of the deposited SiOx film depends on both the source gas and ion beam irradiation conditions. A scaling to explain the transmittance along with the ion beam conditions is proposed.

Negative charging-up contrast formation of multilayered structures with a nonpenetrating electron beam in scanning-electron microscope

In this article, we explain the contrast-formation mechanisms of the scanning-electron microscope for insulating samples under a nonpenetrating irradiation condition. Our fundamental point is that the detected secondary-electron signal current is only modified by the surface potential distribution. We propose a semiempirical model to explain the image contrast caused by excess negative-charge buildup on the surface of the insulating samples. The model treats the redistribution of secondary electrons and the contribution of tertiary electrons. The image-contrast formation mechanism of two typical examples is explained.

Alignment system using voltage contrast images for low-energy electron-beam lithography

We have proposed an alignment system for low-energy electron-beam lithography. The proposed alignment system is based on the following unique concepts: (1) an alignment mark is detected using voltage contrast images caused by charging, and (2) to improve the alignment accuracy of global alignment, the alignment accuracy can be inspected before the pattern exposure without any loss of time. In order to verify these concepts, we performed a series of experiments. Using an electron beam of a few keV, we detected a mark buried by thick insulator films; even if direct access to the marks by the primary beam is prevented, the mark detection is possible. Also, we confirmed that the simultaneous observation of exposure patterns and alignment mark is possible using the voltage contrast images caused by charging: the inspection is possible for the exposure status without resist development.

Development of a projection imaging electron microscope with electrostatic lenses

In the semiconductor industry, the inspection technique using an electron beam is expected to play an important role because of its high spatial resolution. In comparison with conventional scanning techniques, direct imaging produced by projection optics offers both faster mapping rates due to parallel detection and higher resolution. An electron microscope based on the projection imaging optics has been designed and constructed. Secondary electrons emitted by the area exposure are projected through the projection optics consisting of fully electrostatic lenses, and then imaged onto the image detection system. A computational analysis indicates resolution of 0.27 μm which can satisfy both adequate resolution and image grab time. An image of a 0.2 μm design rule device is demonstrated.

Edge Roughness Study of Chemically Amplified Resist in Low-Energy Electron-Beam Lithography Using Computer Simulation

We investigated the line edge roughness (LER) of chemically amplified resist (CAR) in the high-sensitivity resist process in low-energy electron beam lithography (LEEBL). We have confirmed that a sub-100 nm pattern having a small line edge roughness could be obtained at the exposure dose below sub-1 µC/cm2 for LEEBL. In order to explain the experimental results, we have proposed a resist exposure model, considering the generation yield and diffusion of secondary electrons (SEs). Based on the proposed model, we analyzed the LER for LEEBL using a simulation. When the beam blur and the acceptable LER were 30 nm (σ) and 2 nm (σ), the acceptable exposure doses for 2–5 keV and 50 keV were 0.3 µC/cm2 and 2.5 µC/cm2, respectively. This means that a high-sensitivity CAR process at the exposure dose below 0.5 µC/cm2 can be achieved in LEEBL.

Accuracy of Overlay Metrology with Nonp-enetrating and Negative-Charging Electron Beam of the Scanning Electron Microscope

The overlay metrology, which detects a difference in structures below insulator films, is realized by using the non-penetrating and negative-charging electron beam of the scanning electron microscope (SEM). Although high accuracy is obtained in a stable state of image contrast, it takes a long time to attain such state. It is shown experimentally that the speed of attaining the stable state depends on the linear charge density and that a high beam current is desirable for reducing measuring time.

New registration technique using voltage-contrast images for low-energy electron-beam lithography

We have developed a new registration technique for low energy electron beam lithography. A notable feature of this technique is the use of voltage contrast images caused by charging at the resist surface. Using the electron beam of incident energy range of 1keV to 4.5keV, we detected the mark buried by thick insulator films; even if direct access tot he marks by the primary beam is prevented, the mark detection is possible. The detection time is a few milliseconds, and it is sufficiently fast. We confirmed that this technique is available for various layers of DRAM. Also the possible mechanism that may explain the voltage contrast image caused by negative charging is discussed.

An electron beam test system linked with a CAD database

In this paper, the advantages of shorter setup time and ease of operation achieved by linking a CAD system to an electron beam test system are presented. More specifically, by referring to mask pattern data in a CAD database, automatic positioning can be achieved within an accuracy of 0.25 @mm to match any designated target position specified on the terminal screen. In addition, automatic generation of a circuit test vector can be realized with a significant decrease in the required setup time.

Effect of the Electron-Irradiation-Induced-Contamination of the Etching Process of a Photoresist

Electron-irradiation-induced-contamination interferes with the progress of etching and results in an etch residue. Hydrocarbon molecules from an irradiated photoresist mainly contribute to the growth of a contamination layer. There is a threshold dosage below which no etch residue exists.