PURPOSE: To form a through hole provided with a stable form in an InP substrate with good reproducibility by a method wherein in the case where the through hole, which reaches from the rear of the substrate to a source electrode or a drain electrode on the surface of the substrate, is formed in the substrate of a field-effect transistor by etching with a solution, the surface to be etched of the substrate is physically roughened.
CONSTITUTION: A field-effect transistor consisting of source, drain and gate electrodes is formed on the surface of an InP substrate 1 and thereafter, the substrate 1 is fixed on an Si substrate 2 using a wax and a lapping is performed on the rear 3 of the InP substrate 1 to shave the thickness of the substrate 1. After this, a mask pattern consisting of a photoresist film 4 is formed using a normal photoetching method. The size of an aperture 5, which is used for forming a through hole, in the film 4 is set in 40μm×40μm, for example. After this, an etching is performed using a K2Cr2O7/HBr/CH3COOH mixed solution, for example. During this etching, the etching is interrupted and an ultrasonic treatment is performed in water containing Al powder of a specified coarseness. Successively, the is performed with an H3PO4/H2O2/H2O mixed solution to form the through hole 6.
SASAKI KAZUMI
ODA YUJI
