NOVELTY - Etching apparatus includes an etching chamber which includes a gas confinement apparatus and/or gas flow modifier to focus a plasma gas into the substrate to be etched and provide uniform etch rates, modulation of sidewall profile shapes or surface morphology during processing.    USE - For anisotropically etching semiconductor materials, particularly gallium arsenide and indium phosphide substrates.    ADVANTAGE - The invention effectively confines and guides gas flows in the etching chamber to provide improved uniformity in a selective etching processes without degrading the uniformity in a non-selective etching. It also achieves over 5 microns/min of gallium arsenide etch rate, an improvement of more than 30 % of the rate obtained without using the apparatus.    DETAILED DESCRIPTION - Etching apparatus comprises an etching chamber (18) having a gas input for inputting plasma etching gas, a plasma generator, a support for supporting a substrate (22) in the chamber, a gas confinement apparatus (40), and a gas flow modifier (30).    The gas confinement apparatus has a predetermined thickness and a central opening (46) for plasma to pass through. The gas flow modifier has an outer wall and inner wall which defines a hollow aperture for plasma gas (26) to flow through. The gas flow modifier is located above the support, and the gas confinement element is located above the gas flow modifier and below the gas input.    An INDEPENDENT CLAIM is also included for a method of etching a substrate in a plasma etching chamber comprising placing a substrate in the etching chamber, introducing plasma gas in the etching chamber and maintaining the plasma gas at process conditions suitable for etching the substrate, and focusing the plasma gas into the substrate by first passing the plasma gas over the gas confinement apparatus and subsequently passing the plasma gas over the gas flow modifier.    DESCRIPTION OF DRAWING(S) - The drawing shows an exemplary cross-sectional view of an etching apparatus.    etching chamber (18)    substrate (22)    plasma gas (26)    gas flow modifier (30)    gas confinement apparatus (40)    opening (46)