Abstract

The sp2-rich hydrogenated amorphous carbon (a-C:H) is widely adopted as hard masks in semiconductor-device fabrication processes. The ion-enhanced etch characteristics of sp2-rich a-C:H films on ion density and ion energy were investigated in CF4 plasmas and O2 plasmas in this work. The etch rate of sp2-rich a-C:H films in O2 plasmas increased linearly with ion density when no bias power was applied, while the fluorocarbon deposition was observed in CF4 plasmas instead of etching without bias power. The etch rate was found to be dependent on the half-order curve of ion energy in both CF4 plasmas and O2 plasmas when bias power was applied. An ion-enhanced etching model was suggested to fit the etch rates of a-C:H in CF4 plasmas and O2 plasmas. Then, the etch yield and the threshold energy for etching were determined based on this model from experimental etch rates in CF4 plasma and O2 plasma. The etch yield of 3.45 was observed in CF4 plasmas, while 12.3 was obtained in O2 plasmas, owing to the high reactivity of O radicals with carbon atoms. The threshold energy of 12 eV for a-C:H etching was obtained in O2 plasmas, while the high threshold energy of 156 eV was observed in CF4 plasmas. This high threshold energy is attributed to the formation of a fluorocarbon layer that protects the a-C:H films from ion-enhanced etching.

Highlights

  • Etch characteristics of sp2-rich amorphous carbon (a-C):H films were investigated with different ion density and ion energy in CF4 plasmas and O2 plasmas

  • The etch rate of sp2-rich a-C:H films increases linearly with ion density in O2 plasmas, while no etch was observed in CF4 plasmas when no bias power was applied

  • Etch characteristics of sp2 -rich a-C:H films were investigated with different ion density and ion energy in CF4 plasmas and O2 plasmas

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Summary

Introduction

Hydrogenated amorphous carbon (a-C:H) layers are widely used as a hard mask in semiconductor-device fabrication processes. The a-C:H layers are replacing conventional organic photoresists in high-aspect-ratio etching processes because they can provide a higher etch resistance and etch selectivity than photoresists to various harsh etching chemicals, such as fluorocarbon plasmas [9,10,11]. A-C:H films are attractive because they are easy to be removed with oxygen plasmas when they are compared with other non-carbon inorganic mask materials. A-C:H films with high sp2 /sp ratio, or sp2 -rich a-C:H films are preferred over sp3 -rich a-C:H for hard mask applications in semiconductor processes [9,18]

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