Relation of polymer structure to plasma etching behavior: Role of atomic fluorine

Abstract

Plasma etching of organic polymers typically involves the use of feed gas mixtures of oxygen with a fluorocarbon. The reactive etchants are generally accepted to be atomic fluorine and atomic oxygen. The roles of these etchants are discussed with special attention being given to the part played by atomic fluorine. Mechanisms are inferred theoretically from a molecular orbital study, and experimentally from the surface composition of plasma treated samples. Hydrogen abstraction by fluorine leads to enhanced etching of saturated polymer structures while addition of fluorine is the dominant mechanism for unsaturated moieties. Etch rate behavior for polyimide, polyisoprene, and polyethylene as a function of gas composition is discussed in terms of the affinity that fluorine has for the surface of the saturated and unsaturated polymers.

Plasma Etching of Organic Polymers

“…The approach of Cain et al [50] employs the use of molecular orbital calculations at the Extended Huckel level. Oxygen atom attack of polymers can be viewed in terms of changes in the molecular orbitals of the polymer.…”

“…Cain et aL [50] have calculated relative bond strengths (actually overlap populations which infer a degree of bonding between two atoms in a compound) for various model compounds. A comparison of the carboncarbon relative bond strengths in ethane, ethylene, and various oxygenated and fluorinated derivatives of these compounds is shown in Table 3.…”

“…In another series of investigations Egitto and coworkers [18,50,100] examined the etching rates of three polymers in 0 2 / C F 4 plasmas and examined their surfaces using XPS techniques. One test would be to study aromatic polymers which have no hydrogens on the aromatic ring or which are completely deuterated.…”

Optimization of the Microwave Induced Plasma system for failure analysis in integrated circuit packaging

“…Plasma etching systems are commonly used to etch photoresists during IC fabrication. Such system usually uses radiofrequency (13.56 MHz) oxygen plasma, and the etch rate of epoxy materials is around 1 to 5 um/min [3][4][5]. In the mold compound, epoxy only accounts for 20~30% mass percentage while silica filler accounts for 60~80%.…”

Microfabrication Techniques for Plastic Microelectromechanical Systems (MEMS)

“…Figure 16 shows etching rate behavior for three polymer films in various CF 4 -O 2 gas compositions [55]. The etch rate for polyethylene is of importance in this research.…”