Nobuo Ozawa

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.

Role of Oxygen in Poly-Si Etching by Cl2/O2 Plasmas.

The increase in poly-Si etch rate at low O2 concentration (1-5%) in Cl2/O2 plasmas was investigated using optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS). The OES spectrum indicates that the Cl (837.5 nm) intensities increase at low O2 concentration during the poly-Si etching but the dissociation of Cl2 is not promoted by the addition of O2 to Cl2. SiCl (287 nm) intensities decrease in the range of O2 concentration where poly-Si etch rate increases. The result of XPS shows that by increasing O2 concentration from 0% to 3%, the amount of Cl and O adsorbed onto poly-Si surface decreases and increases, respectively. In Cl2/O2 plasmas, a cause of the poly-Si etch rate increase may be that oxygen atoms adsorb more easily on the poly-Si surface than chlorine atoms, and this weakens the Si-Si back bonds.

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.

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.

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.

The Formation of Rugged Surface Polycrystalline Silicon Using Cl 2 /O 2 Plasmas: The Role of Oxygen

The formation of rugged surface polycrystalline silicon (poly-Si) using Cl 2 /O 2 plasmas in which O 2 concentration is 0-10 % has been investigated. Phosphorus doped poly-Si (n + poly-Si) surface is rugged by the plasma etching under the condition that O 2 concentration are 1-5 % at 10 Pa, but is not rugged at 1.3 Pa. On the other hand, undoped poly-Si surface is not rugged in Cl 2 /0-10 %O2 plasmas at 10 Pa. Oxygen and phosphorus play an important role in the ruggedness of n + poly-Si. The ruggedness mechanism has been investigated using scanning electron microscope, optical emission spectroscopy and mass spectrometry. The ruggedness mechanism is suggested that in Cl 2 plasmas added a small amount of oxygen, n + poly-Si is etched selectively at the grain boundaries which contain more phosphorus than in grains. The Cl emission intensity and n + poly-Si etch rate reach maximum in Cl 2 /3 %O2 plasma at 1.3 Pa. Oxygen has a possibility of promoting SiCIx dissociation and increasing Cl radicals.