The field of plasma etching is reviewed. Plasma etching, a revolutionary extension of the technique of physical sputtering, was introduced to integrated circuit manufacturing as early as the mid 1960s and more widely in the early 1970s, in an effort to reduce liquid waste disposal in manufacturing and achieve selectivities that were difficult to obtain with wet chemistry. Quickly,the ability to anisotropically etch silicon, aluminum, and silicon dioxide in plasmas became the breakthrough that allowed the features in integrated circuits to continue to shrink over the next 40 years. Some of this early history is reviewed, and a discussion of the evolution in plasma reactor design is included. Some basic principles related to plasma etching such as evaporation rates and Langmuir–Hinshelwood adsorption are introduced. Etching mechanisms of selected materials, silicon,silicon dioxide, and low dielectric-constant materials are discussed in detail. A detailed treatment is presented of applications in current silicon integrated circuit fabrication. Finally, some predictions are offered for future needs and advances in plasma etching for silicon and nonsilicon-based devices.

As new, advanced high-k dielectrics are being developed to replace SiO2 in future generations of microelectronics devices, understanding their etch characteristics becomes vital for integration into the manufacturing process. We report on the etch rates and possible mechanisms for one such dielectric, Zr1−xAlxOy (x≈0.2), in plasmas containing a mixture of Cl2 and BCl3, as a function of gas composition and ion impact energy. Higher concentrations of BCl3 enhance the etch rate as well as selectivity of Zr1−xAlxOy etching as compared to the etching of α-Si, whereas increasing ion energy increases the etching rates but decreases selectivity. In a high density helical resonator plasma, etching rates on the order of 700 Å/min and 1:1 selectivity are typical. Angle-resolved x-ray photoelectron spectroscopy was used to study the composition of the upper ∼30 Å of the film, before and at the end of the etching process. We found that the etching rate of Zr1−xAlxOy does not change with time for the range of Cl2/BCl3 ratios and ion energies investigated, whereas the α-Si etching rate in pure BCl3 plasma and at zero substrate bias decreases with time, due to the formation of a B–Si film on the surface.

We have studied the effects of source and bias powers, pressure, and feed gas composition on the shapes of SiO2-masked crystalline silicon features etched in a transformer-coupled high density plasma system. Higher etching rates were obtained at higher source and bias powers, and higher pressure. The etching rates of isolated and nested trenches, isolated lines, and holes were nearly the same, indicating a negligible pattern density dependence. We did, however, observe a very weak decrease in etch rates with increasing aspect ratio at 2 mTorr in a pure Cl2 plasma. At 10 mTorr, no aspect ratio dependence was observed, except at the highest source and bias powers. Microtrenching was observed under certain plasma conditions and could be reduced by using higher bias powers. At 10 mTorr in a pure chlorine plasma, we observed a slight taper at the bottoms of the etched features and the formation of narrow microtrenches near feature corners. At 2 mTorr, the microtrenches were broader and overlapped near the center of narrow trenches to form pyramid-shaped trench bottoms. When a HBr plasma was used instead of Cl2, the etching rate decreased by 50% but the etching profiles were more vertical and the trench bottoms were flat. Isolated lines etched in the HBr plasma, however, revealed broad but shallow microtrenches near the edges of the line, suggesting that the flat trench bottoms were a result of broad microtrenches that overlapped. Trenches of 3 μm depth and aspect ratios of 7 have been obtained using either HBr or Cl2, exhibiting similar microfeatures as observed when etching shallower trenches.