We have developed an innovated fabrication technology of Si, GaAs, and Ge nano-structures, i.e., we called defect-free neutral beam etching. The technology has been successfully applied to prototype the quantum nano-disks and nano-wires with ferritin based bio-templates. SEM observation verifies that the designed structures are prototyped. Photoluminescence measurements demonstrates high optical quality of nano-structures based on the technology.
A neutral beam etching process has been developed that achieves damage- free (chemically and physically) etching. Recently, it was found that transition metals could be etched using neutral beam etching through metallic complex reactions. In this process, a neutral beam is extracted from a plasma generation region into a reaction chamber. Complex reactant gases are injected into a reaction chamber which is screened from the plasma during neutral beam etching. In this paper, etching of Pt and CoFeB, candidate materials for MRAM structures by a neutral beam system is described. It was found that etch rate enhancement of Pt/CoFeB surfaces resulted from their exposure to a neutral beam from Ar/O2 plasma with simultaneous injection of EtOH /acetic acid into the reaction chamber. Etching damage was also evaluated and no magnetic hysteresis degradation has been observed. Neutral beam etching technology has the capability to make breakthrough for fabricating MRAM device.
Pores in ultra-low-k carbon-doped silicon oxide (SiOCH) film have been a serious problem because they produce fragile film strength, with the film incurring damage from integration and diffusion of Cu atoms in thermal annealing. To address this problem, we developed a practical large-radius neutral beam enhanced CVD process to precisely control the film structure so as to eliminate any pores in the film. We used the process with dimethoxy-tetramethyl-disiloxane (DMOTMDS) as a precursor to form a SiOCH film on an 8-inch Si wafer and obtained a non-porous film having an ultra-low k-value of 2.2 with sufficient modulus (>10 GPa). Analyzing the film structure by experimental and theoretical techniques showed that symmetric polymethylsilaxane (PMS) chains were grown and cross-linked to each other in the film. This particular film did not incur any damage from acid or alkali solution or oxygen plasma. Furthermore, the dense film almost completely resisted Cu diffusion into it during thermal annealing.
The serious problem associated with 193-nm lithography using an ArF photoresist is roughness formation of photoresist polymer during plasma processes. We have previously investigated the mechanism of roughness formation caused by plasma. The main deciding factor for roughness formation is a chemical reaction between photoresist polymer and reactive species from plasma. The lactone group in photoresist polymer is highly chemically reactive, and shrinking the lactone structure enhances the roughness formation. In this paper, on the basis of the mechanism of roughness formation, we propose a novel ArF photoresist polymer. The roughness formation was much more suppressed in the novel photoresist polymer during plasma etching process than in the previous type. In the novel photoresist polymer, chemical reactions were spread evenly on the photoresist film surface by adding the polar structure. As a result, decreases in the lactone group were inhibited, leading to suppressing ArF photoresist roughness.
For the past 30 years, plasma etching technology has led in the efforts to shrink the pattern size of ultralarge-scale
integrated (ULSI) devices. However, inherent problems in the plasma processes, such as charge buildup and UV photon
radiation, limit the etching performance for nanoscale devices. To overcome these problems and fabricate sub-10-nm
devices in practice, neutral-beam etching has been proposed. In this paper, we introduce the ultimate etching processes
using neutral-beam sources and discuss the fusion of top-down and bottom-up processing for future nanoscale devices.
Neutral beams can perform atomically damage-free etching and surface modification of inorganic and organic materials.
This technique is a promising candidate for the practical fabrication technology for future nano-devices.
This paper discusses microwave absorption around the electron cyclotron resonance (ECR) region in relation to the magnetic field profiles and microwave conditions, and shows how to achieve stable, uniform, and efficient microwave absorption in an ECR plasma to prevent the instability. A high-performance multi-coil system and a new microwave introduction method developed for stable plasma generation are described. Experimental results show that sufficiently precise patterning suitable for practical use is achieved.
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