Yoshikazu Yamaoka

Fabrication of Silicon Field Emitter Arrays Integrated with Beam Focusing Lens

A new field emitter structure capable of generating a focused electron beam (FEB) was fabricated. The present structure is basically similar to a double-gated structure, however, the two gate openings are arranged in the same way as a confocal in-plane lens structure. The inner gate acts as an extraction gate with a 0.6-µm-diameter opening and the outer one acts as an electrostatic focusing lens with a 2.4-µm-diameter opening. The field emission characteristics were evaluated and a beam current of 70 nA/tip was obtained when a bias voltage of 70 V was applied to the two gates. The beam focusing characteristics were also evaluated and the beam could be focused by decreasing the focusing lens voltage without a significant decrease in the beam current.

Surface reactions during etching of organic low-k films by plasmas of N2 and H2

Surface reactions during etching of organic low-k film by N2 and H2 plasmas were studied through observations of the surface resident species using in situ infrared spectroscopy and in vacuo electron-spin-resonance techniques. We observed surface modifications by the formation of CN and NH bonds after exposure to plasmas generated from N2 and H2. The number of carbon dangling bonds were greater in processes where H2 was present. The passivation of carbon dangling bonds leads to CH3, NH3, and CN functionalities, which are the precursors for etching products that are desorbed, which includes volatile forms such as HCN and C2N2.

Fabrication of silicon field emitter arrays with 0.1-μm-diameter gate by focused ion beam lithography

Cone-shaped silicon (Si) field-emitter arrays (FEAs) with 0.1-µ m-diameter gates were fabricated by focused ion beam (FIB) lithography. In the fabrication process, a 200 keV Be2+ FIB with a beam diameter of 0.06 µ m was irradiated to a positive-tone electron-beam resist to form an array of silicon oxide ( SiOx ) disks used as masks for cone-shape etching of a Si substrate. We have succeeded in the operation of the present FEA and obtained the emission current of 1 nA/tip at the gate voltage of 25 V.

Effects of Air Exposure on SiO2 Surfaces Irradiated with Fluorocarbon Plasma

Etching performance is strongly related to the structure of the surface reaction layer of the etched substrate. The substrate should generally be transferred under a vacuum for surface analysis, but this is not always possible due to experimental restrictions. The effects of air exposure on the surface of SiO2 irradiated with fluorocarbon plasma were studied using quasi-in situ X-ray photoelectron spectroscopy. It was found that the chemical compositions and the thickness of the fluorocarbon layer were not affected by air exposure, but the atomic concentration of fluorine contained in the surface reaction layer decreased dramatically.

Down to 0.1 µm Pattern Replication in Synchrotron Radiation Lithography

We studied sub-quarter- to sub-0.1-µ m pattern replication characteristics in synchrotron radiation (SR) lithography using a highly accurate low-contrast mask. AZ-PN100 (a chemical amplification negative-type resist) has a wide exposure latitude of more than ±10% for lines and spaces down to 0.12 µ m at a post exposure baking temperature of 110° C. Lines and spaces down to 0.1 µ m were clearly replicated in AZ-PN100. Sub-0.1-µ m lines and spaces and various types of pattern with 0.1 µ m features were successfully replicated in ZEP-520. These results indicate that SR lithography has potential for 0.1-µ m pattern replication. Insufficient mask linearity reduced the common exposure latitude. However, the mask feature bias technique can be used to expand the common exposure latitude.

Pattern replication accuracy in 1:1 synchrotron radiation lithography

Abstract The replicated pattern distortion for feature sizes down to 0.15 μm, characterized by pattern linearity, pattern density dependence, and corner rounding, is investigated in synchrotron radiation (SR) lithography. In the investigation, a highly accurate X-ray mask delineated by a focused ion beam, a chemically amplified resist, and a Fresnel diffraction model simulator are used. At a 15 μm mask-to-wafer gap, no pattern proximity effect is observed. The corner rounding radius due to Fresnel diffraction is approximately 0.04 μm.

Pattern replication accuracy in 1 : 1 SR lithography

Abstract The replicated pattern distortion for feature sizes down to 0.15 μm, characterized by pattern linearity, pattern density dependence, and corner rounding, is investigated in synchrotron radiation (SR) lithography, using a highly accurate x-ray mask delineated by a focused ion beam. At a 15 μm mask-to-wafer gap, no proximity effect is observed. The corner rounding due to Fresnel diffraction is approximately 0.04 μm.

Exposure and resist-process condition dependence of replicated-pattern accuracy in SR lithography

Replicated pattern accuracy was investigated in synchrotron radiation (SR) lithography, using a chemically amplified (CA) negative-type resist and a highly accurate x-ray mask delineated by focused ion beams (FIB). The size of the hole resist pattern which is arranged in a lattice is affected by the proximity gap and the pattern pitch, but that of the dot resist pattern is hardly dependent on these variables. The dot resist pattern, which was replicated with the 0.25- micrometers -square hole mask pattern, became circular with a proximity gap of over 20 micrometers . In order to obtain highly accurate pattern shape as well as pattern size, the proximity gap should be less than 20 micrometers . The resist pattern size and shape depend on the exposure dose. This was confirmed through the simulation of Fresnel diffraction. The resist pattern was influenced considerably by the post-exposure baking (PEB) conditions, temperature and time. The PEB condition dependence of a replicated pattern was investigated. It is effective to extend the PEB time to improve the sensitivity without deforming the pattern shape.

Fabrication of x-ray masks with 0.15-um level two-dimensional patterns by using highly accurate FIB lithography

A highly accurate focused ion beam (FIB) lithography and its application to the x-ray mask fabrication are discussed. The pattern delineation accuracy in FIB lithography was investigated by drawing various two-dimensional (2-D) test patterns. We could obtain 0.15 micrometers feature resist patterns on the heavy-metal layers of the x-ray mask substrate. FIB lithography suffers little proximity effect and thus various 2-D test patterns were obtained with small distortion. The FIB drawn patterns were precisely transferred into the W absorber layer by the time modulated etching technique. X-ray masks used for the evaluation of the pattern replication accuracy in synchrotron radiation lithography were successfully fabricated.