Plasma etching of DLC films for microfluidic channels

doi:10.1016/S0026-2692(03)00077-6

Microelectronics Journal

Volume 34, Issues 5–8, May–August 2003, Pages 635-638

https://doi.org/10.1016/S0026-2692(03)00077-6 Get rights and content

Abstract

The goal of this work is to study the effect of plasma etching process on the surface properties of diamond-like carbon thin films having in mind the applicability of this material for construction of microfluidic channels. The films were deposited by dc magnetron sputtering onto p-type (100) 3 in. silicon wafers, at a deposition rate of 8 nm/min. The etch processes have been carried out in a RIE reactor with the discharge produced in an atmosphere of oxygen diluted in argon. Oxygen contents varied from 0 to 100% and different values of the power discharge (from 20 up to 150 W) have been applied. The surface roughness and wall profiles were examined by atomic force microscopy and scanning electron microscopy in order to verify the quality of the final surface obtained after etching.

Introduction

The development of nano- and micro-technologies has made important impacts in many areas, such as in the electronic, medical, automotive, avionic and aerospace industries promoting significant improvements of the microelectronic systems and on the products for civil use. Certainly these processes are related to the new materials and techniques that have been intensively studied in this period.

Diamond-like carbon (DLC) films are classified among these materials, because of their attractive mechanical, optical, electrical and chemical properties. They are widely used as protection films of magnetic recording disk due to its hardness, chemical inertness and low friction coefficient [1], [2]. One more advantage associated with DLC is that its properties can be easily tailored by the ratio of the tetrahedral bonding population to the trigonal bonding population (sp³/sp² ratio).

When these films are conveniently lithographed and plasma etched, it could be possible to produce microfluid channels to be used in the so-called lab-on-a-chip technology. Silicon and glasses are the usual materials for these channels. To evaluate the applicability of DLC for this technology it is necessary to study the effects of plasma etching on the morphology of this film. In this article etching rate and surface roughness are the main parameters that we measured considering various operational conditions for RIE of DLC.

Section snippets

Experimental

DLC films were deposited by a 150 W dc magnetron sputtering of a graphite target with the discharge produced in a gas mixture of 10% CH₄ and 90% argon. The films exhibit high hardness of the order of 10 GPa, and friction coefficient as slow as 0.15. Fig. 1 shows a typical DLC Raman spectrum containing a mixed structure of microcrystalline diamond and graphite as well as a disordered structure.

The spectrum has a well-pronounced single peak centered on 1565 cm⁻¹ with shoulder at around 1400 cm⁻¹.

Results and discussions

Fig. 2 shows the behavior of the etching rate and the rms roughness as a function of the rf power. These etches were performed at a pressure of 6.6 Pa and using pure oxygen, at a flow rate kept at 5 sccm. In this figure, an increase in the etching rate up to 220 nm/min was observed when the rf power is increased. Roughness increases gradually from 0.3 up to 0.8 nm with the power. The roughness of the films etched at power higher than 80 W could not be determined by AFM because their values were

Conclusions

RIE etching of DLC films has been carried out and the qualities of the processed surfaces were investigated by AFM. The etching rate and surface roughness were measured as function of the rf power supplied to the discharge and with respect to the oxygen content in the oxygen/argon gas mixture. The main conclusions of this work are:

•
Increasing the rf power an increase in the etching rate and in the rms roughness was observed. Working at power higher than 80 W high values of etching rate, about 200

Acknowledgements

The authors would like to acknowledge the ‘Laboratrio de Filmes Finos do IFUSP’, Brazil, for the SPM facility and to technician Alexandre Marques Camponutti for the technical support in SEM analyses. The financial support of FAPESP, CAPES, CNPq and FINEP is also acknowledged.

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There are more references available in the full text version of this article.

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