| 摘要 |
PURPOSE:To readily obtain constant and uniform thickness by connecting one conductivity type layer with one electrode, and applying a voltage positively biasing the other conductivity type layer to the layer. CONSTITUTION:Since an N-type layer is positive to a P-type layer when a voltage is applied in a range that a P-N junction does not break down between the N-type layer and the P-type layer of a silicon plate 3, accelerated ions flow from the N-type layer side to the P-type layer side, ion impact increases at the P-type layer side as compared with the N-type Layer side, and the etching velocity at the N-type layer becomes extremely small. Accordingly, if the thickness of the N-type layer is set to the thickness of a thin portion 23, a recess 24 which allows the thickness of the N-type layer to remain is formed. The impurity density, thickness of the P-type layer and the N-type layer are considered to form a P-N junction of the plate 3 so as not break down to a bias voltage necessary for the P-N junction. If a thin layer is necessary to be of P-type, a bias is forwardly applied to the P-N junction. Thus, a constant and uniform thin layer can be obtained.
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