Akihiro Usujima

Optical and Electrical Properties of CuIn5S8 and AgIn5S8 Single Crystals

The energy gaps at 300 and 96 K of CuIn5S8 and AgIn5S8 single crystals were determined from the optical absorption measurements. The peaks of the photoconductive spectra observed at 300 and 77 K were in good agreement with the energy gaps. The resistivity and the mobility for the samples with less sulphur than the stoichiometric one were determined from the electrical measurements.

Direct Measurement of Offset Spacer Effect on Carrier Profiles in Sub-50 nm p-Metal Oxide Semiconductor Field-Effect Transistors

We have directly measured the effect of the bottom shape in the offset spacer on the two-dimensional (2-D) carrier profiles of the sub-50 nm p-metal oxide semiconductor field-effect transistors (MOSFETs). It has been observed that the doping profile of the Sb pocket implanted with a high angle tilt is very sensitive to the bottom shape of the notched offset spacer. It has been confirmed that the Sb pocket deeply implanted leads to the decrease of 2 nm in the average overlap length of the extension region at a depth of 5 nm when the bottom shape is slightly upped at the notched offset spacer. The increased effective channel length is considered to enhance the dependence of the threshold voltage on the body bias voltage. Moreover, it is considered from the measured carrier profiles that the reduction in carrier concentration in the top channel region lowers the threshold voltage.

Pitch dependence of linewidth in the 0.25 μm patterns fabricated using positive chemically amplified resist

We investigated the proximity bias characteristic of 0.25 µ m patterns used with three types of positive chemically amplified resists of differing material and properties. To determine the proximity bias characteristics, we examined how the relationship between the pitch and the linewidth varies with post-exposure-bake (PEB) temperature and time. Our experiment revealed that each resist exhibits its own unique proximity bias characteristics. We also found that the proximity bias characteristics of the three resists depended to a large extent on the PEB temperature: the lower the PEB temperature, the greater the resemblance of the proximity bias characteristics to the optical characteristic. Considering this and using the pitch vs. linewidth curve with PEB time as a parameter, we concluded that the proximity bias characteristic of resists largely depends on the diffusion of acids and other thermal effects in the resists. These characteristics resemble optical characteristics as the PEB temperature decreases, the acids diffuse to a lesser extent, and the thermal effects decrease.

Resist residue generated on TiN topographic substrates in positive chemically amplified resists

When positive chemically amplified resists are used on basic stepped substrates to produce patterns, a resist residue often forms at the bottom of the step. This paper discusses the results of investigating the cause of the chemically amplified resist residue formation as it is encountered during patterning on stepped substrates.

Practical evaluation of 16M-DRAMs production with i-line phase-shift lithography

We have fabricated 16M-DRAMs with i-line phase-shift lithography using 8 inch wafers. Edge-contrast enhancement type was used as a phase-shift reticle. The effects on i-line phase- shift lithography were evaluated for the patterns which have a small focus and alignment margin. It was found that the phase-shift lithography has a large effect on enlarging focus margin of small size patterns like 0.5 micrometers . We evaluated the effect of phase-shift lithography by a trial manufacturing of 16M-DRAMs. As a result, i-line phase-shift lithography was found to have a possibility of high yield production of 16M-DRAMs. However, it was also found that there were several rejected pattern widths which were caused by variation of shifter width in the phase-shift reticle. So it is necessary to improve these rejected patterns for the application of this method to 16M-DRAMs.