Nobuhiro Miki

Principles of wet chemical processing in ULSI microfabrication

Fine patterning technology for integrated device manufacturing requires properties such as surface cleanliness, surface smoothness, complete uniformity, and complete etching linearity in wet chemical processing. An improved chemical composition for buffered hydrogen fluoride (BHF:NH/sub 4/F+HF+H/sub 2/O) is determined based on fundamental research into the chemical reaction mechanism of BHF and SiO/sub 2/. Advanced wet chemical processing based on investigation of chemical reaction mechanisms and properties of liquid chemicals, concentrating on the SiO/sub 2/ patterning process by BHF, is described. The principles of wet chemical processing in silicon technology are based on the following: the determination of the dominant reaction (etching) species, the influence of the solubility of the etching products in BHF on etching uniformity and linearity, stability of chemical composition without solid-phase segregation, and an improvement of the wettability of liquid chemicals on the wafer surface by the addition of a surfactant. >

Gas-phase selective etching of native oxide

Gas-phase selective etching of native oxide film formed on a silicon surface is an essential requirement for ULSI process technologies. Ultraclear anhydrous hydrogen fluoride (AHF) gas and a corrosion-free system were developed for this etching process. The reaction mechanism of silicon oxide film with moistureless HF was investigated, and selective etching conditions were developed. The gas-phase selective etching of native oxide in an environment of strictly controlled AHF concentration in N/sub 2/ is described. >

Surface active buffered hydrogen fluoride having excellent wettability for ULSI processing

By incorporating selected hydrocarbon surfactants, a surface-active BHF (buffered hydrogen fluoride) has been tailored to achieve the following requirements: (1) the same etch rate as that of conventional BHF; (2) low contact angle; (3) nonsegregation; (4) nonfoaming; (5) low particulate count; (6) few impurities (possibility of purification); (7) low particulate adhesion on the wafer surface; (8) no surface residues; (9) excellent surface smoothness; and (10) high SiO/sub 2//Si etching selectivity. In order to satisfy these requirements, surfactants must satisfy the following characteristics: (1) good solubility in BHF; (2) hydrophilic property at the wafer surface, (3) nondecomposition in BHF; (4) nonreaction with BHF; and (5) sufficient lowering of contact angle at the critical micelle concentration (CMC). Aliphatic amines satisfy these requirements but have foaming problems. The requirements have been achieved using a binary surfactant system consisting of a combination of aliphatic amine and aliphatic alcohol or aliphatic acid. >

Fluorine passivation of metal surface for self-cleaning semiconductor equipment

Fluorine passivation of metal surfaces for ULSI process equipment is investigated and passivated film quality is evaluated. Well-polished and pretreated bare surfaces of stainless steel and nickel are passivated with oxygen-free, high-purity fluorine (O/sub 2/ and HF less than 1 p.p.m.), and a uniform and stable passivated surface is obtained by introducing two-step fluoridation, i.e. direct fluoridation and the succeeding thermal modification (heat treatment in nitrogen). The fundamental mechanism of the surface fluoridation is investigated by differential thermal analysis. The chemical structure of the passivated films is examined by X-ray diffraction and X-ray photoelectron spectroscopy. Passivated films of stainless steel exhibit a double-layer structure, such as FeF/sub 2/ covered by CrF/sub 2/, which has a lower vapor pressure than divalent metal fluorides such as FeF/sub 2/, NiF/sub 2/, and MnF/sub 2/. It has been confirmed that the first fluoridation step produces a nonstoichiometric fluoride which is converted to the stoichiometric structure by the heat treatment in nitrogen. Good passivation performance is achieved as a result of this thermal modification. >

Optimization of fluorine passivation of stainless steel surfaces

The optimum conditions for the fluorine passivation of 316L stainless steel are described. The direct fluoridation products formed at temperatures of 320 degrees C or lower are composed solely of FeF/sub 2/, while those which were formed at the temperatures of 330 degrees C or higher have a compound-phase composition of FeF/sub 2/ and FeF/sub 3/. At a critical temperature (400 degrees C for 316L stainless steel) of the thermal modification process, FeF/sub 3/ is converted to FeF/sub 2/ and disappears completely as the temperature rises. Meanwhile, CrF/sub 3/ is formed at a certain temperature (440 degrees C for 316L stainless steel). The two-phase composition gets further crystallized as the thermal modification temperature rises. As the crystal growth induces the cracks on the fluoridated film, it is very difficult to form a satisfactory passivation film from the two-phase composition by thermal modification. It is confirmed that excellent passivation film has been obtained from the single-phase composition by the optimum fluoridation following the optimum thermal modification. >

Low outgassing and anticorrosive metal surface treatment for ultrahigh vacuum equipment

We report on a stainless steel passivation technology useful for the future We report on a stainless steel passivation technology useful for the future submicron ultralarge‐scale integration (ULSI) manufacturing. In the near future, low pressure processing will become more important. With presently available equipment, outgassing from the inner surface of metal chambers is one of the factors that can hinder ultrahigh vacuum processing. Therefore, absorbed molecular contaminations must be eliminated. We report the development of low outgassing metal surface that is derived from an O2 or F2 passivation process. This process requires an initial metal surface to have mirror finish without Beilby layer. Specifically, by using a 316L stainless surface, under clean conditions, outgas volume of moisture are shown to be reduced by a factor of 102, compared with conventional finished steel surfaces. In addition O2/F2 passivation, though inherently different, give stainless steel surfaces that show excellent corrosi...

Progressive Technology of Fluoride Chemicals for ULSI Manufacturing

Atomically clean and native oxide-free silicon surface is obtained by hydrogen fluoride gas treatment in fluorine passivated metallic system. Selective etching of natj-ve oxide from several silicon oxide films is achieved in extremely anhydrous environment. The terminated fluorine on silicon surface can be removed by the Xe or IR irradiation and the single crystalline of epitaxial silicon is performed on the bare silicon surface. The clean-up effect of surface impurities by hydrogen fluoride gas is recognized.

Outgas-Free, Corrosion-Free Metal Surfaces for ULSI Manufacturing

Realization of an ultra-clean process environment, in which contamination f rom mol-ecules adsorbed by the waf er surf ace i s fully controlled, is extremely important for the production of future submicron ULSI devices. The key to the achievement of such an ultra-clean process environment is the proper treatment of the surface of the stainless steel. That is extensively used in the ultra-hiSh pur ity gas supply Iine and the process chamber . Of central importance is control-ling the process ambienee for minimized both outgas and corrosion-rel-ated contamination.