Oxygen RIE pattern transfer

Figure 3.54. High aspect ratio images obtained by oxygen RIE pattern transfer with a polysiloxane as an etch mask. Reproduced with permission from reference 185.)...

Two general types of multilayer process may be distinguished, depending on whether they use oxygen reactive ion etching (RIE) (4) or optical exposure (5-11) to transfer the pattern into the resist. Optical pattern transfer may suffer from some limitation due to substrate reflections, but has an advantage in the simplicity of the equipment compared to RIE. 

Both negative and positive acting, oxygen RIE resistnt e-beam resist systems have been prepared through the incorporation of the trimethylsilylmethyl functionality into standard resist chemistry. Resins containing >10 wt% silicon display an RIE resistance more than 10 times greater than conventional photoresists and allow submicron pattern transfer with minimum linewidth loss. 

Initial processing experiments showed however, that under typical O2 RIE conditions (power 0.1 to 0.2 W/cm self-bias — —250 to —350 V, pressure — 5 to 20 mTorr O2), these resists are not very resistant, particularly under prolonged etching. Effective pattern transfer may require etch times of 15 to 30 min (11,12). which are sufficient to cause extensive degradation of the resist. Such behavior is reminiscent of poly (olefin sulfone)s such as the well-known PBS e-beam resist, which is etched 5-7 times faster than polystyrene in an oxygen plasma (5). 

Figure 5. Scanning electron micrograph depicting 1.0- xm images obtained in a silylated novolac-diazoquinone resist formulation after conventional exposure and development followed by pattern transfer by oxygen RIE.

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