Abstract: An etching method includes providing a substrate on a substrate support in a chamber of a plasma processing apparatus. The etching method further includes etching the substrate with plasma generated in the chamber, thereby forming a recess in the substrate. In the etching, an electrical bias is supplied to the substrate support, to attract ions from the plasma into the substrate. In the etching, at least one of a bias frequency, which is a reciprocal of a time length of a waveform cycle of the electrical bias, and a pulse duty ratio of a pulsed electrical bias is modified to maintain an ion energy flux to the substrate.

Abstract: A learning device includes a learning sheet having for each question a set of answers, only one of which is the correct answer. The sheet is mounted on a base plate having a series of conducting bands which are tortuous or undulating so that the correct answers corresponding to the appropriate associated conducting bands will not be arranged in a straight line nor made obvious to the person using the learning device.