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.

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Plasma etching: Yesterday, today, and tomorrow

An apparatus for dissociating gases includes a plasma chamber that may be formed from a metallic material and a transformer having a magnetic core surrounding a portion of the plasma chamber and having a primary winding. The apparatus also includes one or more switching semiconductor devices that are directly coupled to a voltage supply and that have an output coupled to the primary winding of the transformer. The one or more switching semiconductor devices drive current in the primary winding that induces a potential inside the chamber that forms a plasma which completes a secondary circuit of the transformer.

Toroidal low-field reactive gas source

Macromolecular plasma-chemistry: an emerging field of polymer science

Global (volume-averaged) models of high-density, low-pressure electropositive and electronegative discharges are described both for continuous wave (CW) and for pulsed-power excitation. Argon and chlorine discharges are treated. The particle and energy balance equations are applied to determine the charged particle and neutral dynamics. For argon just after the power has been turned on, the analysis shows an initial very sharp rise in electron temperature , followed by a decay of and an increase in the electron density to steady state values during the pulse-on time. Just after the power has been turned off, decays rapidly and decays more slowly. The time-average can be considerably higher than that for CW discharges for the same time-average power. For chlorine, a CW discharge is highly dissociated and the negative ion density is lower than . For a pulsed discharge, the initial rise and subsequent decay of just after the power has been turned off are determined analytically. A pulsed discharge can have the same neutral radical (Cl) flux to the walls for a reduced average power. The analytical models are compared to more complete global model simulations and to experimental observations. We find that global models can provide considerable insight into the discharge dynamics.

https://iopscience.iop.org/article/10.1088/0963-0252/5/2/006/pdf

Global models of pulse-power-modulated high-density, low-pressure discharges

There is disclosed a plasma reactor for processing a semiconductor workpiece such as a wafer, including a chamber having an overhead ceiling with a three-dimensional shape such as a hemisphere or dome. The reactor further includes an inductive antenna over the ceiling which may be conformal or nonconformal in shape with the ceiling. The ceiling may be a semiconductor material so that it can function as both a window for the inductive field of the antenna as well as an electrode which can be grounded, or to which RF power may be applied or which may be allowed to float electrically. The reactor includes various features which allow the radial distribution of the plasma ion density across the wafer surface to be adjusted to an optimum distribution for processing uniformity across the wafer surface.

Parallel plate electrode plasma reactor having an inductive antenna and adjustable radial distribution of plasma ion density

Comprehensive measurements of charged particles and neutral radicals in an inductively coupled plasma (ICP) are performed to understand and control the etching process using a CF4/H2 gas. The electron density in the ICP reactor decreases exponentially in a downstream region while the most abundant ionic species CF+ increases in proportion to the rf power with the CF+3 density almost constant. The neutral radical diagnostics by appearance mass spectrometry indicate 10 times more F atoms and somewhat fewer CFx radicals (x=1–3) in ICP, compared with a high‐pressure capacitively coupled plasma diode. Such a small ratio of the CFx density to the F density is possibly a cause of the low etch selectivity of SiO2 to Si in ICP etching. Two innovative methods to achieve the high selectivity in ICPs are demonstrated. One is wall heating (100–200 °C), which leads to a drastic increase in CFx densities with the F density almost constant. The other is a pulse modulation of rf power at 30–50 μs durations where the time‐...

Y. Hikosaka

Papers

Diagnostics and control of radicals in an inductively coupled etching reactor