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Abstract

In order to study an etching rate difference of a layer formed mainly with silicon dioxide on a wafer, a thermal oxide film (113) and layers of BSG (117), BPSG (125), and PSG (129) are laminated on a wafer and are etched in a gaseous etching atmosphere consisting essentially of hydrogen fluoride or a mixture of hydrogen fluoride and water vapor. The layers are etched with various etching rates which are higher than that of the thermal oxide film. The etching rate difference is a difference between the etching rate of each layer and an etching rate of the thermal oxide film. The layers may include impurities, such as boron and phosphorus, collectively as a part of a layer material of each layer. The etching rate difference depends on the layer material. Preferably, the gaseous etching atmosphere should have a reduced pressure. Alternatively, a water vapor partial pressure should not be greater than 2000 Pa. As a further alternative, either the layer or the gaseous etching atmosphere should be heated.

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First Claim