Abstract: By cultivating a D-ribose-producing microorganism of the genus Bacillus in a medium containing nutrients necessary for its growth, wherein the concentrations of L-tryptophan and L-tyrosine in the medium are controlled at 3 .mu.g/ml or less and 10 .mu.g/ml or less, respectively. D-ribose is produced in a good yield and the by-production of gluconic acid is efficiently suppressed.

Abstract: In order to selectively reduce the etching rate of the polyimide resin layer, ion implantation is carried out thereto. Preferably, the impurity ion such as As.sup.+, P.sup.+, B.sup.+, BF.sub.2.sup.+ is implanted with dosage of 1.times.10.sup.14 cm.sup.-2 or more. As a result, the polyimide resin layer has a resistivity to etching by the etchant containing hydrazine. This method can be used for preventing generation of unwanted etching in the process of forming the via hole in case of using the polyimide resin as the interlayer insulator for multiwiring structure.