Shigeru Okamura

AlN capped annealing of Si implanted semi‐insulating GaAs

AlN capped annealing can be used successfully for thin n‐layer formation to minimize the thermal conversion effects. Si ions were implanted into Cr‐doped semi‐insulating GaAs substrates with 145 keV, to a dose of 2.40×1012 cm−2. Subsequently, the samples were annealed at 850 °C, 20 min with reactive sputtered AlN cap. The carrier profiles fit very well to the theoretical one. No thermal pits, cracks, and peeling‐off were observed even on 1.2‐μm‐thick AlN cap after up to 1000 °C annealing.

Asymmetric peak line shape of infrared dielectric function spectra for thermally grown silicon dioxide films

Measured infrared dielectric function spectra ranging from 300 to 1400 cm−1 for thermally grown silicon dioxide films were studied. The dielectric function spectra were calculated by requiring the calculated spectra to fit to the actual spectra. The peak line shape of the dielectric function can be described by a Gaussian distribution, but not by a Lorentzian line shape. In detail, frequencies of half height for the imaginary part of the dielectric function of high- and low-frequency edges are not actually symmetrical. According to interpretations based on a central and noncentral force network model, the asymmetric distribution of the dielectric function arises from the symmetrical distribution of the bond angles of a random network of the SiO4 tetrahedra. For that reason, we developed a dielectric function model which can describe an asymmetrical Gaussian line shape. This asymmetric Gaussian model minimizes the number of parameters needed, which are the one center position and low- and high-Gaussian dis...

Quartz Crystal Microbalance for Silicon Surface Organic Contamination

A quartz crystal microbalance (QCM) was used to develop a real-time measurement method of airborne organic contamination on a silicon surface. At the relative humidity of 40-50%, the amount of adsorbed water on the silicon surface was determined to be several tens to 100 ng cm - 2 . Under this condition, the adsorption and desorption of diethyl phthalate can be measured at the time corresponding to the operations of the diethyl phthalate vapor supply. Its adsorption rate and desorption rate are consistent with those evaluated in a clean room. Based on the weight evaluation of various contaminations, the significant part of the change in the surface concentration obtained by the QCM method in a clean room can be assigned to airborne organic contamination.

Time-Dependent Airborne Organic Contamination on Silicon Wafer Surface Stored in a Plastic Box

The time-dependent airborne organic contamination on a silicon wafer surface in a wafer storage box is studied using a model of the multicomponent organic species adsorption-induced contamination (MOSAIC) linked with the experiment. Both the adsorption rate and the desorption rate of the organic species in the wafer storage box were found to be much lower than those in the clean room air; this result is considered to be consistent with the very small concentrations and the very small transport rates of the organic species in the gas phase in the wafer storage box. The organic contamination in the wafer storage box follows the MOSAIC model similar to that in the clean room air.

Measurement of spectral and spatial intensity distributions of synchrotron radiation in soft x‐ray region by means of helium gas scattering

We measured the spectral and spatial intensity distributions of synchrotron radiation (SR) in the soft x‐ray region using an energy‐dispersive method with a Si(Li) detector at the Photon Factory. By measuring the intensity of x rays scattered by helium gas, we could reduce the high SR intensity to the sensitivity range of a Si(Li) detector and, by selecting the scattering angle, we used this method as a polarimeter. In the soft x‐ray region above 2 keV, the measured spectral and spatial profiles of the direct beam transmitted through a Be window were almost the same as the calculated values, but absolute intensity was about 30% less than calculated. This is largely due to the geometric errors of the measuring system. We also measured the intensity distribution of the beam reflected from fused quartz mirrors. The spectrum profiles agreed with the calculated values, but absolute intensity was somewhat less than expected, and the spatial distribution had a complicated profile because of imperfections in the ...

Adsorption and Desorption of Dibutyl Phthalate on Si Surface Measured in Controlled Atmosphere using Quartz Crystal Microbalance Method

The adsorption of dibutyl phthalate (DBP) molecules on the surface of Si was studied using a highly sensitive quartz crystal microbalance (QCM) and new sliding chamber system, and using the accurate decomposition analysis of the decay curve method. It has been understood that the DBP molecules are adsorbed on the Si surface at three different kinds of adsorption sites that require different desorption energies; two of the three are in equilibrium with the DBP molecular density in the vapor phase, one being a site that has a 400 s desorption time constant at 23°C which seems to be the isolated admolecules, and the other site has a 1900 s desorption time constant which seems to be the cohesion of the admolecules. The third site is a site that has an 18000 s desorption time constant that seems to be restricted by something on the surface, such as an atomic terrace edge or crystal defect.

Simultaneous Observation of Molecular Contamination Behavior in Semiconductor Clean room Using Quartz Crystal Microbalance

To search the cause and mechanism of the molecular contamination trouble that sometimes occurs in the semiconductor manufacturing, we developed a quartz crystal microbalance (QCM) molecular contamination monitoring system that is able to carry out two-dimensional simultaneous observation with a high sensitivity. As the result of long-term simultaneous observation of different QCM sensor surface materials in an operating semiconductor clean room, it has been understood that QCM can monitor the changes in the molecular contamination environment very sensitively. We observed for the first time the emission phenomenon of molecular contamination that is discharged from equipments synchronizing with the process sequence by observation of the QCM system. Moreover, the phenomena of NOx in a clean room air of less than 100 ppb promoting the adsorption of the molecular contaminants were observed. The multipoint continuous monitoring of the clean room atmosphere by the QCM system was shown to be very effective in the clarification of the cause of molecular contamination trouble.

Observation of adsorption phenomena of dibutyl phthalate molecules on Si surface using quartz crystal microbalance method

The adsorption phenomena of dibutyl phthalate (DBP) molecules on the Si surface were observed in detail using a highly sensitive quartz crystal microbalance (QCM) and a new method involving a sliding chamber system. As a result of the precise observation of the adsorption phenomena and an accurate decomposition analysis, the typical Langmuir adsorption phenomenon with a time constant of 350 s was observed following the rapid adsorption phenomenon that occurs within the first 10 s and the next adsorption phenomenon of increasing linearly. After almost reaching the adsorption equilibrium amount, another Langmuir adsorption phenomena for a time constant of 3000 s was also observed; the Langmuir adsorption phenomenon for a time constant of 350 s seems to be that of an isolated admolecule whereas that for 3000 s seems to be one where admolecule cohere by mutual migration on a surface.

Synchrotron radiation beamline for x‐ray lithography

We designed a synchrotron radiation (SR) beamline for x‐ray lithography and optimized the beamline based on ray‐tracing calculations. For a beamline with a single toroidal mirror, the intensity uniformity in the horizontal direction can be improved by making the meridian radius different from that of the general focal condition. We used this method to determine beamline parameters. Converging the SR beam gave an intensity gain of about 4, and we reduced the nonuniformity of intensity distribution to less than 3%. We also estimated the overlay error due to incorrect mirror parameters to be a maximum of 14 nm with a gap of 20 μm. We calculated an exposure‐gap diagram using simulation codes; the calculation accounted for absorbed energy distribution due to Fresnel diffraction, penumbral blur, electron ranges of the secondary electrons in the resist, and development properties. We found that there is a dose margin of at least ±5% to achieve ±10% linewidth control for 0.15 μm feature size for gaps below 20 μm. We made preliminary measurements of spectra and intensity distributions for the constructed beamline, and showed that the performance is as predicted by our calculations.

X-ray lithography beam line BL-17C at the photon factory

Abstract We constructed a beam line, BL-17C, for X-ray lithography at the Photon Factory. In this beam line, two parallel mirrors are used to cutoff high-energy photons and to keep the light path of the reflected beam unchanged when the glancing angle of the mirrors changes. We studied the reflective characteristics of mirrors using He gas scattering to measure reflected and incident light spectra. The obtained reflectivity for a fused quartz mirror with a roughness of 0.3 nm nearly equaled the theoretical value.