Polymers etching

Kinetics of Polymer Etching in an Oxygen Glow Discharge... 

Fig. 1. The organic polymer etching rate is a linear function of the bombardment energy flux as determined by Visser and de Vries [29] (triangles) and by Jurgensen and Rammelsberg [34] (squares).

Figure 6. Polymer etching rates in CF4 reactive ion etching 0.21 W/cm2 R.F. power density, 4 x 10-4 Torr, -500 V bias potential. The thickness loss is shown in the unit of 1.6 x 10-6 m.

Many attempts have been made to find correlations between etch resistance of a polymer and its chemical nature. The thumb rule advices to use aromatic groups incorporated into a polymer to enhance etch resistance. However, about 20 years ago it was found that aromatic rings were not strictly needed to improve polymer etch resistance. It was the carbon-to-hydrogen atoms ratio for a polymer that was related to its resistance in oxygen plasma. An increase in the ratio tends to produce a decreased rate of the RIE in O2. 

Anisotropy/sidewall angle Mask selectivity Substrate selectivity Etched surface quality Throughput A rough order of magnitude estimate of etch rates is as follows 1(X) nm/min for simple research reactors, 1 pm/min for production tools, and 10-50 pm/min for silicon DRIE reactors. Exact values depend on particular reactor design, RF power source, and other hardware factors. Silicon etch rate is much faster than oxide or polymer etch rate in the same reactor. More extensive passivation translates to reduced etch rate but also reduced undercut and more vertical sidewalls. 

Polymers can be etched by oxygen plasmas using silicon, metal, and oxide masks. Etch rates of a few pm/min have been demonstrated with 20 1 aspect ratios. A Bosch process for polymer etching involves an O2 etch step followed by a C4Fg passivation step. 

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