Yasuhiro Miyakawa

Mechanisms of high PSG/SiO2 selective etching in a highly polymerized fluorocarbon plasma

We have investigated high selective etching mechanisms of phosphosilicate glass (PSG) over SiO2 in a highly polymerized fluorocarbon plasma, by studying the Ar+ induced reactions between the adsorption layer and the underlying substrates with X-ray photoelectron spectroscopy. Both of SiO2 and PSG were found to react in a very near surface region, chiefly with the adsorption layer, by reflecting the reactivity in SiOxFy reaction layer below the surface. The mechanisms of the reactivity variance were explained by the difference in density of active sites for unsaturated CFx chemisorption induced by ion bombardment, and the difference of Si-O bond breakability of the underlying substrates. These effects are caused by the existence of P-O or P=O bonds in PSG.

Mechanisms of Surface Reaction in Fluorocarbon Dry Etching of Silicon Dioxide—An Effect of Thermal Excitation

Ion bombardment-induced thermal reaction between a fluorocarbon adlayer and a SiO2 surface in a reactive-ion-etching (RIE) environment which was simulated in an ultrahigh-vacuum thermal desorption mass spectroscopy (TDS) apparatus has been studied. The RIE-induced fluorocarbon chemisorbed layer, covering the SiO2 surface, was observed to be thermally stimulated to react chemically with the SiO2 in the TDS apparatus with an activation energy of approximately 1.9 eV. A terminal group, chemisorbed at the adlayer/SiO2 interface, could be an active participant in the thermal reaction. This observation indicates the possibility that chemical sputtering could occur in the actual RIE through a thermal excitation step, induced by ion bombardment. A significant difference in the RIE-induced mixing of fluorine atoms between SiO2 and Si also appeared in their TDS spectra.

Reaction Studies between Fluorocarbon Films and Si Using Temperature-Programmed X-Ray Photoelectron and Desorption Spectroscopies

Surface structure of plasma-polymerized fluorocarbon thin film on Si and gas desorption were concurrently studied as a function of temperature between 20 and 700° C using temperature-programmed X-ray photoelectron spectroscopy with a residual gas analyzer. The films, consisting of CF3, CF2, CF and C-CFx bonds, with the F/C ratio of 1.7 were found to be stable up to 200° C and to thermally decompose above 200° C. SiF4 desorption, following gradual pyrolysis with decrease in CF3, CF2 and CF bonds due to desorption of fluorocarbon gases, was observed for F/C ratios ranging from 1 to 0.1. The pyrolytic process of the film and the thermal reaction with Si substrates were further discussed based on results of additional desorption and ion-induced reaction experiments.

Roles of Ions and Radicals in Silicon Oxide Etching

Thermally stimulated desorption and X-ray photoelectron spectroscopy were used to study the adsorptive condition of reactive-ion-etched SiO2 and PSG surfaces. Its relationship to the different reactivity between SiO2 and PSG under the condition of highly polymerized fluorocarbon plasma was discussed. The reaction process of radicals under the thermally excited condition was also investigated in a microwave-excited downstream reactor. The C, F molecules which covered the oxide surfaces as etching species during RIE were found to be chemisorbed, and as residues, they were adsorbed weakly. It was also found that oxygen atoms have the effect of decreasing the activation energy of the spontaneous reaction with the oxide surfaces in the fluorocarbon plasma.

0.2 μm hole pattern generation by critical dimension biassing using resin overcoat

A method of generating very small hole patterns by introduction of transfer bias into a resist pattern after original resist pattern generation has been developed and evaluated. Introduction of transfer bias was carried out using a resin overcoating and strippig process and a novolak resist pattern was used as the original hole pattern. The overcoating resin used was polymethylmethacrylate (PMMA) and transfer bias was introduced by intermixing of novolak resin and PMMA during the PMMA baking step. From scanning electron microscope (SEM) observation, it appeared that 0.20 µ m hole pattern generation was possible by i-line lithography. The amount of undersize was controllable by PMMA bake temperature, and 0.06-0.15 µ m undersize could be achieved by using a bake temperature range of 60-120° C. From results of etching SiO2 substrate using overcoat treated hole pattern, it appeared that the mixinglayer functioned as an etching mask for oxide film.

X-Ray Photoelectron Spectroscopic Studies on Pyrolysis of Plasma-Polymerized Fluorocarbon Films on Si

Temperature-programmed X-ray photoelectron spectroscopy was used to study pyrolysis of fluorocarbon thin films polymerized on Si substrates in magnetomicrowave plasma with C4F8 gas. Variations of fluorocarbon moieties were obtained at the temperature range between 20 and 700° C. The films, consisting of CF3, CF2, CF and C-CFx bonds, were found to be stable up to approximately 200° C and to be pyrolyzed via the dissociation of the terminal bonds above this temperature.

Thermal desorption spectroscopy and X-ray photoelectron spectroscopy study of CFx layer deposited on Si and SiO2

Thermal reactions between a fluorocarbon ( CFx ) layer formed with C4F8 magnetomicrowave plasma and Si and SiO2 are studied by thermal desorption spectroscopy (TDS). Atomic compositions and core spectra of the CFx layer are measured by temperature-programmed X-ray photoelectron spectroscopy (TP-XPS) with concomitant desorption gas species analysis by quadrupole mass spectrometer. The TDS study reveals that the primary reaction products are SiF4 in Si and SiF4 and CO in SiO2, and F generated from the CFx layer is a primary reactive species contributing to the formation of the reaction products not only in Si but also in SiO2. The TP-XPS study reveals that the drastic decrease of F/C ratio agrees with the desorption of SiF4 and CO.

Fine Contact Hole Etching in Magneto-Microwave Plasma

Characteristics of fine contact hole etching have been investigated in hydro-fluorocarbon magneto-microwave plasma focusing on the z component of the gradient of magnetic field at 0.0875 T ( dB/ dz) and peak-to-peak voltage of RF bias (V pp) as parameters. Decrease of dB/ dz drastically decreases the etch rate of boro-phospho silicate glass (BPSG), critical dimension loss (defined as diameter of the top of contact hole minus diameter of the bottom of resist) and selectivity over heavily doped n-type polycrystalline silicon ( n+ poly Si) and resist in fine contact holes. The changes of etching characteristics are correlated with neither F/C ratio nor C1s spectrum of deposited film, but with deposition rate in the region of high V pp, which presumably reflects the change of incident CFm + ion species with dB/ dz.

Role of Fluorine in Reactive Ion Etching of Silicon Dioxide

Thermal desorption from 15 keV, fluorine positive ion (F+)-implanted SiO2 has been studied using thermal desorption and X-ray photoelectron spectroscopies. Primary fluorine-related outgassing species SiF3+, gaseous O2, and a great amount of water evolution representing the SiO2 network modification were observed. From comparatively well-investigated desorption spectra from NF3/Ar reactive-ion-etching (RIE)-exposed and CF4/Ar RIE-exposed SiO2, similar outgassing species and the desorption temperatures were observed. The desorption states for SiF3+ were not single as previously reported in the study of desorption states related to the thermal reaction with fluorocarbon polymer, but several desorption pathways existed. The observed similarity for SiF3+ is considered to be related to the induced microstructural changes, which possibly determine the final desorption path in RIE.

Mechanisms of silicon oxide etching in a highly polymerized fluorocarbon plasma

Reactive-ion-etching (RIE) induced surface modifications of SiO2 and phosphosilicate glass (PSG) were investigated using thermal desorption mass spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS), in order to study their reactivity variance in the highly polymerized fluorocarbon plasma. Ar+ induced reactions between the fluorocarbon adsorption layer and the underlying oxide substrates were also examined. At the C,F-film/substrate interface, the adsorption layer was found to be chemisorbed to the substrates. Both SiO2 and PSG were found to react in a very near surface region, chiefly with the adsorption layer, by reflecting the reactivity in SiOxFy reaction layer below the surface. The mechanisms of the reactivity variance were explained by the difference in density of active sites for unsaturated CFX chemisorption induced by ion bombardment, and the variance of Si-O bond breakability of the substrates. These effects are caused by the existence of P-O or P = 0 bonds in PSG. Fluorocarbon chemisorption layers were also observed to be thermally stimulated to react with the substrates in TDS apparatus with to activation energy of approximately 1.9eV. This observation indicates the possibility that chemical sputtering easily occurs in actual RIE through a thermally excited step, induced by ion bombardment.