Various kinds of plasma are used for industrial applications. Among those, low pressure gas discharge plasma has been recognized to be a most elegant and efficient means for dry processing, such as treatment and deposition of material, etching, oxidation and polymerization. For this reason, special attention is directed toward low pressure gas discharge, which is driven by direct current (d.c.) or high frequency (h.f.) electric field. The plasma thus produced is a partially ionized one with low-temperature and low-density. Therefore, the properties of the discharge as well as the plasma are governed by various collision processes. In this note, the initation and sustainment of the d.c. and h.f. discharges are considered. Also, the positive ion sheath formed around the electrode and the positive column with charge neutrality are separately discussed. Further, detailed descriptions are given to elucidate peculiar phenomena appearing in the h.f. discharge. These include the trapping of the charged particles, the sheath potential as affected by the asymmetrical electrode area and the self-bias voltage.
New diagnostic means based on laser spectroscopy are described. These include laser-induced fluorescence, Raman spectroscoy and coherent anti-Stokes Raman spectroscopy (CARS). These new techniques are required to clarify gas-phase processes involved in various CVD methods, including plasma processes. There are specific requirements for the diagnostic means to be useful. Each of the spectroscopic means has been examined to see how these requirements are satisfied, and any shortcomings are explained. CARS is described most in detail, because of a strong interest in this technique recently. The experimental setup is based on either a Nd : YAG laser or an excimer laser in combination with dye lasers. It has been applied to a diagnostic study of CO2 laser CVD of silane, where the internal excitation of material gas molecules is examined and the rise in gas temperature following light absorption is measured as a function of a distance from a substrate.
The energy of active species such as electrons, ions, excited atoms, excited molecules and ultraviolet rays generated in low-temperature plasma is comparable to the bond energy of organic compounds. In low-temperature plasma, these active species react with organic polymer to make free radicals in the suface layer and sometimes induce polymer surface etching. Consequently these radicals react with excited atoms and excited molecules in the plasma and oxygen in the air to make functional groups on the surface of the polymer, or react with each other to form crosslinking. Furthermore these radicals react with monomers to form graft co-polymerization layer on the surface of the polymer. The surface of the polymer treated with low-temperature plama has many characteristic properties such as high surface tension, good adhesiveness, decreased leakage of additives and so on. The low-temperature plasma treatment is useful and unique technique for modifying the surface of various polymers.
Oxygen under low pressure is electronically excited and dissociated to atomic oxygen which reacts with solid samples and gently decomposes organic matrices to leave inorganic ash materials. This so-called plasma ashing is therefore featured by low temperature incineration together with high recovery of inorganic constituents. It has been revealed that the initial oxidation products from the contact of atomic oxygen with the alkyl groups of the organic samples are mostly carbonyl compounds and, in the case of reaction with unsaturated groups, epoxide compounds are also obtained. A fine capillary thermometer placed on the surface of the sample measured temperatures of 120-150°C during the plasma ashing, but the actual temperature at the oxidation sites were expected to be 200-300°C, temperatures derived from a comparative study for heat polymerization of orthophosphate during the plasma ashing and a furnace heating of known temperatures. The plasma conditions relative to oxidation rates, pretreatment of samples of different types and some applications to analytical chemistry are described and discussed.
A new process for the preparation of ultrafine powders of metals and ceramics was developed by the authors from a technique of arc melting of metals in an atmosphere of hydrogen, nitrogen, or oxygen at 0.1M Pa pressure. An arc, in gases such as hydrogen, nitrogen, oxygen, is a kind of reactive thermal plasma, which plays an important role for the formation of ultrafine particles from massive molten materials. That is, an enhanced evaporation phenomenon is induced by the dissolution-evolution reaction of plasma gas on materials, and ultrafine powders are formed. This paper describes the formation mechanism, formation rate, size, crystal structure and some properties of ultrafine powders obtained by this new process, such as the metals Ag, Al, Sc, Cr, Si, Pd, Fe, Cu, Ti, Ni, V, Mo, Ta, W and the ceramics CaO, MgO, Al2O3, TiO2, ZrO2, WO3, MoO3, Nb2O5, TiN, ZrN, Al+AIN, SiC, TiC, WC,
Recent progress in materials processing by using reactive plasma or photochemical technique is reviewed. The characteristic features of both techniques are discussed in terms of chemical reactions which proceed in the plasma or under photoirradiation.
A progress of total dry resist process for e-beam lithography using plasma polymerization for resist casting and plasma etching for development, mostly by our group, is reviewed. i) Use of flow type reactor, ii) copolymerization of e-beam sensitive monomer with etch-resistive monomer, iii) sensitization by high-z atom, and iv) use of hydrogen plasma for development gave rise to a great extent of e-beam sensitivity which finally reached to 5μC/cm2. A modeling study of dry development have shown a linear dependence of logalithmic film thickness change to the logalithmic scission fraction per monomer unit, λ. A 0.15 of λ is found to be necessary which figure will explain observed decrese of e-beam sensitivity by dry development from that by wet development. Several way to improve dry devlopment process and also dry devlopable X-ray resign is discussed on the basis of knowleges so far obtained.
Physical and chemical interaction mehanisms between low temperature plasma and organic polymer film was elucidated on the basis of the results of quantum-chemical calculations and experimental observations. The radiation effects on polymers are approximately reproduced in low temperature plasma, because the degradable and crosslinkable properties originate from the reactions on the lower excited state potential energy hypersurfaces. In oxygen plasma, crosslinkable polymers are converted to degradable polymers by the reaction with oxgen atom. The origin of the dry etch resistance of resist film was also clarified. The elucidated interaction mechanism was applied to the molecular design of dry etch resistant and dry developable resist, an example of which was shown in the last section.
Organic thin film deposition by plasma sputtering has almost not been investigated except for polytetrafluoroethylene. Recently, polyimide and other polymers have been sputtered by several workers. The molecular structure of the sputtered polyimide film was much different from that of the target. No imide group existed in the film. Active N2 gas added to Ar gas participated in the decomposition and polymerizing reaction during sputtering. N content in the film increased by reactive sputtering. The sputtered polyimide films showed excellent properties as ultra thin solid lubricating film and heat resistant film. The sputtered polycarbonate film and the cosputtered Ekonolmetal film are of interest for basic and technical applications such as photo-senser, electrical shielding and optical filters. History and recent studies of organic film deposition by sputtering have been reviewed.
This report reviews recent developments in the investigation of the Glow-Discharge (GD) decomposition of silane (SiH4) and the growth kinetics of resulting hydrogenated amorphous silicon (a-Si : H) films. First, several advantages of GD method for a-Si : H deposition are pointed out, through which the importance of gas-phase chemical reactions as well as chemical processes on the growing surface is emphasized. Second, novel plasma diagnostic techniques are described such as optical emission spectroscopy (OES), ion mass spectrometry (MS) and coherent anti-Stokes Raman Spectroscopy (CARS). Finally, on the basis of the experimental data on Si2H6 as well as SiH4 plasma obtained by the above diagnostic techniques, detailed reaction kinetics in both plasmas are discussed, leading us towards a better understanding of the deposition mechanism of a-Si : H films.
Recent research and development on plasma-enhanced growth of dielectric films are reviewed. The technology is classified into two kinds of main methods; one is plasma-enhaced chemical vapor deposition (plasma CVD) and the other is plasma-enhanced surface reaction. Most of plasma CVD films of SiNx, SiO2 and doped SiO2 have been studied for the purpose of use for the passivation films and insulating films between interconnects in VLSI. In this paper are discussed correlations among growth conditions, atomic composition and bond structure in films, various film properties and effects on characteristics of applied devices. The technology of surface reaction is thought to be useful to the lowering of VLSI process temperature. The future trend of these methods is discussed in a view of the application to VLSI.
The recent progress in diamondlike carbon films prepared by hydrocarbon ion or plasma gas are described. The typical systems reported are classified into three types such as plasma, ion, and neutral deposition systems and each system is discussed. Next, the physical properties and the crystal structures of these films are discussed in comparison with diamond powder. Finally, the growth process of diamond films in the case of ionized deposition is discussed based on the reported data.
The plasma deposition technique has been developed for the synthesis of inorganic compounds such as Al2O3, TiC, TiN, Si3N4 and else in the form of thin solid film. Among many processes based upon the plasma deposition technique Ion Plating has already been industrialized for the hard ceramic coating on cemented carbide or high speed steel tool with TiC or TiN. Plasma CVD is also developed to suit for such ceramic coating at moderate temperature and molybdenum parts for the first wall of the nuclear fusion testing devics, JT60, were TiC coated by the modified Plasma CVD process, named TP-CVD process. Deposition of diamond or cubic boron nitride has been attempted by means of plasma CVD or Ion Bean Deposition process. This paper discribes asid processes and the characteristics of thin solid films.
Some properties of films deposited by sputtering are discussed. (Chap. 2); The construction of the sputtering systems are explained. (Chap. 3); Sputtering yield, sputtered pacticles, mean free path, sputtering atmosphere, and sputtered film are discussed in detail on the basis of sputtering. The energy of the sputtered particles is considered to be the most essential factor. (Chap. 4); The c-axis oriented ZnO film and the amorphous PbTiO3 film were studied as examples of thin films prepared by sputtering.