Jun Kanamori

Characteristics of Very High-Aspect-Ratio Contact Hole Etching

An ultrahigh-aspect-ratio, 0.06-µ m-diameter, 2-µ m-deep contact hole pattern of SiO2 was successfully fabricated using a poly-Si mask and a magnetically enhanced reactive-ion-etching (RIE) system in a mixture of CHF3/CO gas. In this dimensional area, processing for vertical profiles is extremely difficult, and problems in the form of bowing at the sidewalls of the holes can occur. Furthermore, it is possible that ion flux and energy are significantly reduced when ions pass through the poly-Si mask, rather than through the SiO2 hole. The bowing is associated with bending of the incident ion trajectories, where the first stage of the trajectory change occurs at the mask, and subsequent multiple scattering of ions at the sidewall of the hole can occur. Other factors include sidewall protection by redeposited Si sputtered from the poly-Si mask and/or the deposited fluorocarbon polymers, and the effects of ion energy and flux bombarding these deposited materials.

Vertical Profile Control in Ultrahigh-Aspect-Ratio Contact Hole Etching with 0.05-µm-Diameter Range

Vertical processing of 0.05-µm-class SiO2 holes with an aspect ratio around 20 was realized using a dipole-ring-type magnetron reactive-ion-etching system in a mixture of C4F8/O2/Ar gas. Secondary ion mass spectrometric study of the F and C concentration profiles of the polymer deposited inside the holes in the depth direction revealed that a very small amount of polymer deposition occurred in this system. This indicates that energetic species reached the hole bottoms with excellent verticality, even in an extremely fine feature. In contrast, the CHF3/CO process (tapered shape) resulted in an extremely thick polymer and carbonized region on the sidewalls, suggesting the presence of energetic species sticking to the sidewalls. The effects of energetic species impinging onto the sidewalls and the protection resulting from polymer deposition have been discussed in terms of the etched shape and F/C depth profile. Vertical incidence of the energetic species into the holes is concluded to be a significant factor in realizing a vertical profile.

Dry-Etching Mechanism of Sputtered Pb(Zr1-xTix)O3 Film

The Pb(Zr 1-x Ti x )O 3 (PZT) etching mechanism involving an ion-assisted etching reaction in a Cl 2 helicon wave plasma environment was studied in terms of the physical-bombardment-induced structural change of the film and chemical interaction of the damaged surface with halogen. In-situ X-ray photoelectron spectroscopic analysis of a 1 keV-Ar + -irradiated PZT surface used in combination with Rutherford backscattering spectrometry revealed that the physical bombardment preferentially breaks Pb-O bonds, releasing Pb in the crystal which is subsequently sputtered from the surface, resulting in low Pb concentration on the surface. Thermal reaction study at 600°C of Cl + -, F + - and Ar + -implanted PZT using X-ray diffraction indicated that the induced low Pb concentration initiates the subsequent reaction with existing halogen on the damaged surface, which is accompanied by a structural change in the film.

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.

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.

Effect of Ti insertion between Cu and TiN layers on electromigration reliability in Cu/(Ti)/TiN/Ti layered damascene interconnects

The effect of Ti insertion between Cu and TiN layers on electromigration in Cu/(Ti)/TiN/Ti layered damascene interconnects was investigated. Ti insertion enhanced the wetting property of Cu to underlayer TiN and increased the sheet resistance of the layered film when annealed. This resistance change was caused by diffusion of Ti into the Cu film and resulting in reduction in cross-sectional area of the Cu film. The insertion of thinner Ti with air-exposure before Cu deposition was found to be effective in obtaining a lower sheet resistance for the composite Cu film and for the line resistance of a Cu damascene structure. The air-exposure treatment did not influence the via resistance. The Cu damascene interconnects with Ti insertion have up to 100 times longer electromigration lifetime than those without Ti insertion. Microstructures of the Cu film such as grain size, its distribution and texture were almost the same in samples with and without Ti insertion. The improvement of interface quality between Cu and underlayer, which would have an impact on the diffusivity of Cu atoms at the interface, and the existence of Ti in Cu play an important role in improving electromigration resistance.

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.