As the size of virtually every electronic device gets smaller and smaller, the ability to etch semiconductors with very small, very dense patterns becomes increasingly important. Increasing the density of the design naturally requires decreasing the lateral dimensions of the various engraved structures. To maintain functionality at these submicron dimensions, it is often necessary to etch structures with very large aspect ratios, on the order of 10-100. Plasma dry etching is the most efficient way to etch such structures; Wet etching processes depend on the orientation of the crystals and it can be difficult if not impossible to achieve the desired aspect ratios. Etching high aspect ratio structures with plasmas offers a unique challenge; maintaining the necessarily high degree of anisotropy without succumbing to a variety of different profile defects has proven difficult. This article will offer a review of the origins of the main profile defects observed and reported in the literature so far, as well as the strategies used to minimize their severity. The most appropriate system for etching high aspect ratios into silicon is a high-density, low-pressure system. (HDLP), where the ion density is generally at least an order of magnitude greater than in early reactive ion etching systems. HDLP systems also offer the added feature of being able to control ion density and energy independently by varying the source power and bias power, respectively. This ability means that ion flow can be significantly more anisotropic than in older RIE systems. Pressures have generally been reported in the range 1-25 mTorr with ion densities on the order of 1012 cm-3. Halogen-based chemicals are used virtually... in the center of the paper... stretched, the larger flank area makes checking for defects even more difficult. Ions that may have hit the bottom at a near-normal angle when the aspect ratio is small may end up dispersing from the sidewall and contributing to microtrenching when the aspect ratio is large. Further work is needed to investigate new methods to control bowing, undercutting, and microtrenching. Additional additives may be able to help balance passivation more precisely to eliminate kinks and undercuts without producing sloping sidewalls, or they may increase the directionality of the ion velocity distribution to reduce microtrenching. As plasma etching technology is pushed to its limits by the continued pressure to miniaturize, improve performance and capacity, minimizing and eliminating defects will remain one of the most important topics in plasma machining.