Thick benzocyclobutene etching using high density $SF6/O2$ plasmas

Etching of thick nonphotosensitive benzocyclobutene (BCB) was investigated using a high density $SF6/O2$ plasma with an inductively coupled plasma (ICP) etcher. The effects of $SF6$ concentration on etching characteristics, including etching rate, anisotropy, and residue, are fully discussed in this article. Moreover, experiments were designed and carried out to study the causes of BCB etching residue. A grasslike etching residue was observed for low $SF6$ concentration at the bottom of BCB patterns with a $SiO2/SixN$ layer and the BCB patterns cured on a $N2$-purged hotplate, while residue-free etching is obtained for the BCB patterns cured in a $N2$-purged vacuum chamber. A high $SF6$ concentration and exclusion of $O2$ during hard curing are important to prevent the grasslike etching residue. A highly anisotropic and residue-free etching of thick $(∼13μm)$ BCB is achieved for BCB cured in a $N2$-purged vacuum chamber at $250°C$ for 1 h and with a pure $SF6$ plasma under etching conditions of 700 W ICP power, 100 W reactive ion etching power, 15 mTorr chamber pressure, and 50 SCCM (SCCM denotes cubic centimeter per minute at STP) gas flow. Mechanisms for the dependence of the etching characteristics on $SF6$ concentration are discussed.