Mitsuhiro Omura

Highly selective etch gas chemistry design for precise DSAL dry development process

Dry development process for directed-self assembly lithography (DSAL) hole shrink process has been studied with focus on etch selectivity of poly(methyl methacrylate) (PMMA) to polystyrene (PS) and suppression of etch stop. Highly selective etch of PMMA to PS was achieved using CO gas chemistry. However, it was found that PMMA etching stopped proceeding beyond a certain depth. Scanning Transmission Electron Microscopy (STEM) and X-ray Photoelectron Spectroscopy (XPS) analysis indicated that a deposition layer formed not only on PS but also on PMMA. H2 addition to CO plasma proved effective in controlling the deposition layer thickness and suppressing etch stop. CO/H2 plasma process combined with ion energy control was applied to the dry development process for hole shrink. DSAL dry development process for hole shrink process was successfully realized by designing the etch gas chemistry and controlling ion energy.

Selective etch of poly(methyl methacrylate) in block copolymer based on control of ion energy and design of gas chemistry for directed self assembly lithography

The selective etching of poly(methyl methacrylate) (PMMA) in a block copolymer was studied with a focus on the material structures of polystyrene (PS) and PMMA. Based on our predictions, we investigated the effect of ion bombardment and designed a carbon-containing gas plasma to improve selectivity. The etching characteristics of the carbon-containing gas plasma on the polymers were examined. Highly selective etching of PMMA to PS was achieved using the carbon-containing gas plasma. The carbon species in the plasma increased with increasing carbon-containing gas ratio and suppressed the PS etch rate drastically. The CO plasma process was successfully applied to a dry development process for directed-self assembly lithography.

Ultralow k1 oxide contact hole formation and metal filling using resist contact hole pattern by double line and space formation method

It was shown previously that the double line and space formation method (DLFM) is superior to other methods for forming a dense contact hole (C/H) resist pattern by simulation, and a 0.30-k1 1:1 C/H resist pattern was formed experimentally. A through process of C/H formation from resist patterning to metal filling is presented. The oxide square C/Hs transferred from the resist pattern formed by the DLFM could be filled with metal, although the transferred C/Hs had square corners in comparison with the conventional C/H resist patterning. On the other hand, the combination of the DLFM and the “pack and cover process” makes it possible to form resist random C/Hs on grids. So, the possibility of forming random C/Hs filled with metal is shown. Moreover, the resolution limit of the DLFM is discussed. The 0.29-k1 (half pitch 65-nm) and 0.27-k1 (half pitch 56-nm) 1:1 C/H resist patterns could be formed with optimized dipole illumination. So, random C/Hs with k1 below 0.30 are expected to be formed.

Highly selective removal of poly(methyl methacrylate) from polystyrene-block-poly(methyl methacrylate) by CO/H2 plasma etching

The directed self-assembly lithography process using polystyrene (PS)-block-poly(methyl methacrylate) (PMMA) requires selective removal of PMMA, which is called the development process. The development process using plasma etching (dry development) without surface roughness of the line/space pattern was investigated. First, the authors focused on the chemical compositions of PMMA and PS. Using CO plasma, highly selective etching of PMMA was achieved (PMMA/PS etch selectivity >20). It was found that the PS surface roughness induced by plasma treatment depended on the thickness of the deposition layer formed on the PS surface. To suppress the PS surface roughness because of plasma treatment, the authors controlled the thickness of the deposition layer by adding H2 gas to the CO plasma. Using CO/H2 plasma, highly selective PMMA/PS etching without surface roughness was achieved. Consequently, the authors successfully achieved dry development of random lamella patterns by application of the CO/H2 plasma process.

Dry development for a directed self-assembly lithography hole-shrink process using CO/H2 plasma

Abstract. A dry development, directed self-assembly lithography (DSAL) hole-shrink process was studied, with a focus on the selectivity of the etching of poly(methyl methacrylate) (PMMA) over polystyrene (PS), and the suppression of etch stop. The highly selective etching of PMMA over PS was achieved using CO gas chemistry. However, it was found that the PMMA etching did not proceed beyond a certain depth. Scanning transmission electron microscopy and x-ray photoelectron spectroscopy analysis indicated that a deposition layer formed not only on the PS but also on the PMMA. The addition of H2 to the CO plasma was effective in controlling the thickness of the deposition layer and in suppressing the etch stop. The CO/H2 plasma process was combined with ion energy control to achieve a dry development for hole shrinkage. The dry development DSAL hole-shrink process was successfully realized by tailoring the etching gas chemistry and controlling the ion energy.

Highly selective etching of LaAlSiOx to Si using C4F8/Ar/H2 plasma

Selective etching of LaAlSiOx to Si has been studied in inductively coupled BCl3 plasma using a hot cathode, and in capacitively coupled C4F8/Ar and C4F8/Ar/H2 plasmas. In BCl3 high-temperature etching, the etch selectivity of LaAlSiOx to Si was 0.05 at 210 °C. It was found that increasing the bias power using capacitively coupled C4F8/Ar plasma enhanced LaAlSiOx etching. Furthermore, the etch rate of LaAlSiOx increased and that of Si decreased upon the addition of H2. As a result, a high LaAlSiOx-to-Si selectivity of 6.7 was obtained when using C4F8/Ar/H2 plasma at an H2 flow rate ratio of 13%. We confirmed that H2 played different roles on the LaAlSiOx surface and on the Si surface. H2 suppressed Si etching by forming a high-C/F-ratio polymer on the Si surface, while it enhanced LaAlSiOx etching by breaking the stable metal–oxygen bonds of LaAlSiOx.