Hideyuki Kazumi

Analysis of Plasma Chemical Reactions in Dry Etching of Silicon Dioxide

A computational model for chemical reactions in plasmas has been developed and applied to the gas-phase chemistry of dry etching of silicon dioxide. An ab-initio molecular orbital method is used to determine the dissociation processes and the threshold energies for gases and neutral radicals. Plasma chemistry is calculated by the plasma chemical kinetic method. The chemical compositions of the dry etching plasmas were investigated for fluorocarbon gases. Calculated ion fluxes, electron temperatures, and densities agreed with experimental results within factors of three. The differences in plasma characteristics between CHF3/CH2F2 and C4F8 were attributed to differences in the products and threshold energies of the dissociation reactions. Correlations could be found between the composition of radicals in a plasma and the etch selectivity in C4F8.

Radical and Ion Compositions of BCl3/Cl2 Plasma and Their Relation to Aluminum Etch Characteristics

Plasma compositions in BCl3/Cl2 were calculated using a molecular orbital method and a plasma kinetic method. The key factors for plasma compositions and their relations to the etch characteristics of Al-based multilayers were investigated. The etch rate of Al seemed to be correlated with the Cl density rather than the Cl2 density. The etch rates of TiN and the resist were also related to the Cl density and the ion density. Therefore the ion energy distribution (IED) impinging on the wafer was also calculated and the rf frequency dependence of the selectivity of the TiN/resist was evaluated using an etching model. Even if the rf frequency increased to 10 MHz, where the IED had a single peak, the predicted selectivity was slightly improved. A narrower IED was required.

Model prediction of radical composition in plasmas and correlation with measured etch characteristics of silicon dioxide

A computational model for plasma chemical reactions has been developed. An ab initio molecular orbital method was used to determine dissociation paths and their threshold energies. Plasma characteristics were calculated by a plasma kinetic method. The radical compositions in , with additional gases such as Ar, He and , were calculated. Radicals influencing the selective etching of over were analysed. With increased microwave power or decreased flow rate, density decreased and CF, C and F densities increased. The increase of radicals with abundant carbon relative to fluorine would result in high etch selectivity of over and a low etch rate. Increases in the concentration of F radicals are correlated with increases in etch rates. Electron temperature was high with He addition, and dropped with alone and Ar addition discharges. On the contrary, the electron density was high in the reverse order. The highest etch selectivity was obtained with He addition. A high electron temperature discharge would be one solution to obtain high etch selectivity of over .

A plasma kinetics model: analysis of wall loss reactions in dry etching of silicon dioxide

Abstract Computational models for gas-phase chemical reactions in plasmas and for sticking reactions on metallic Al walls have been developed and applied to the plasma chemistry of dry etching of silicon dioxide. Dissociation paths and threshold energies of gases are determined by using an ab initio density functional molecular orbital method, and dissociation cross sections are approximated. The electron energy distribution function is determined by using a particle-in-cell model with the Monte Carlo collision method, and dissociation reaction rates are determined. Plasma densities, electron temperatures. and radical densities are calculated by a kinetic model which consists of the fluid equations for plasmas and rate equations for radicals. The model effectiveness was confirmed by results comparison for the Ar discharge in an radio-frequency device. The chemical compositions of the dry etching plasmas have been investigated for C 4 F 8 . Calculated electron temperatures and densities agree with experimental results within factors of three. Correlations could be found between the composition of radicals in the plasma and the etch selectivities in C 4 F 8 . Adsorption potentials of fluorocarbon radicals on Al (III) surface clusters have been calculated by using molecular orbital method, and sticking coefficients are estimated. Sticking coefficient of fluorine atom is the largest and decrease in order of F, C, CF, H, CF 2 , and CF 3 . Effects of hypervalence bonding at Al surface are discussed. Phenomena [1] of no film depositions in CF 4 RF plasma and film depositions in RF plasma of CF 4 mixed with H 2 were explained by hypervalence reactions of Al.

Dependence of secondary-electron yield on aspect ratio of several trench patterns

Systematic understanding of the mechanism of secondary-electron (SE) emission is important to simulate an SEM image of a high-aspect-ratio (AR) structure. The simulation technique for a high-AR structure is useful for optimizing the observation conditions of SEM. Trench patterns with AR between 0.5 and 8 were fabricated on the same substrate, and dependence of SE yield on AR of the trench patterns was determined from SEM images for several landing energies of primary electrons. In addition, to understand the SE emission inside a trench, Monte-Carlo simulation of the signal intensity for Si was performed. The SEM observations and simulation results indicate that SEM image contrast at the bottom of a trench improves with decreasing landing energy (owing to a positive charging effect) and that reflection of SEs at the sidewall of a trench is essential for accurately estimating SE emission for the high-AR structure with AR over eight.

A Novel Plasma Etching Tool with RF-Biased Faraday-Shield Technology: Chamber Surface Reaction Control in the Etching of Nonvolatile Materials

A novel electro-magnetically coupled plasma (EMCP) etching tool for nonvolatile materials has been developed. The EMCP etcher is based on inductively coupled plasma generation and has a function for controlling surface reactions by supplying RF bias to a Faraday shield which covers a ceramic discharge dome. We investigated plasma controllability and chamber surface reaction controllability of the EMCP etcher and found that the RF-biased Faraday shield effectively keeps the internal surface of the dome clean in the etching processes of nonvolatile materials. Because of this feature, the EMCP etcher can be applied to the etching processes of various nonvolatile materials such as Pt, Ru, Ir, NiFe, Au, Mo, Ta, Al2O3, HfO2, ZrO2, and indium tin oxide (ITO).

Verification and extension of the MBL technique for photo resist pattern shape measurement

In order to achieve pattern shape measurement with CD-SEM, the Model Based Library (MBL) technique is in the process of development. In this study, several libraries which consisted by double trapezoid model placed in optimum layout, were used to measure the various layout patterns. In order to verify the accuracy of the MBL photoresist pattern shape measurement, CDAFM measurements were carried out as a reference metrology. Both results were compared to each other, and we confirmed that there is a linear correlation between them. After that, to expand the application field of the MBL technique, it was applied to end-of-line (EOL) shape measurement to show the capability. Finally, we confirmed the possibility that the MBL could be applied to more local area shape measurement like hot-spot analysis.

Evaluation of roughness transfer from Litho to Etch using CD-SEM

Roughness transfer from Litho to Etch has been evaluated. The impact of Line width roughness (LWR) or Line edge roughness (LER) is getting larger with shrink of semiconductor devices. In this study, the roughness measurement by using a single frame SEM image was brought in to avoid resist shrinkage, and image enhance technique is used to compensate low S/N ratio in this one frame image. CD-AFM was used as reference, and LWR measured by CD-AFM was compared to the results of one frame enhanced image taken by CD-SEM. And roughness spectrum analysis was used for evaluation of roughness characteristics taken by CD-SEM and CD-AFM, and its transition by resist shrink or by etching process. It was enabled to observe the resist roughness profile with minimum shrink by using one frame enhanced image, then roughness transfer between Litho and Etch was evaluated by comparing in exactly the same position as pre- and post-etch. As a result, it was confirmed that transferred roughness by etching was remaining the peak and valley profile in resist observed by CD-SEM, but the roughness amplitude was reduced in higher frequency domain. This result consists with the roughness characteristics comparison from Litho to Etch. This also means roughness characteristics analysis shows the actual nanoscopic event.

Developing a flexible model of electron scattering in solid for charging analysis

We have been developing a charging simulator “CHARMs”, which is based on 3D finite element method, to predict the characteristics of signal from charged pattern on surface of semi-conductor during the SEM observation. We have constructed a new flexible model to simulate the in-solid electron scattering by the Langevin equation for “CHARMs”. Our new model can manipulate the size of the diffusion cloud of scattering electron by the parameters of it and calculate ten times faster than the conventional Monte Carlo (MC) method. In addition to that, the model has the possibility to accurately describe the scattering of low energy electron. We also confirmed that the same results of the conventional MC method can be obtained from the simulation model of metal pattern buried in the sample.

Method of improving image sharpness for annular-illumination scanning electron microscopes

Annular illumination is effective in enhancing the depth of focus for scanning electron microscopes (SEMs). However, owing to high side lobes of the point-spread function (PSF), annular illumination results in poor image sharpness. The conventional deconvolution method, which converts the PSF to a delta function, can improve image sharpness, but results in artifacts due to noise amplification. In this paper, we propose an image processing method that can reduce the deterioration of image sharpness. With this method, the PSF under annular illumination is converted to that under standard illumination. Through simulations, we verified that the image sharpness of SEM images under annular illumination with the proposed method can be improved without noise amplification.