A method of manufacturing an integrated circuit with MOS transistors having high breakdown voltages, and with precision resistors

The method described provides for the formation of an implantation mask of polycrystalline silicon comprising strips (14) for constituting the gate electrodes of the MOS transistors and portions (16) defining openings (17) for the formation of resistors, low-dose ionic implantation (18) through the implantation mask to form pairs of regions (19, 20) at the sides of the gate strips (14) and resistive regions (21) through the openings, the formation of an insulating layer (30) on the entire structure thus produced, and anisotropic etching of the insulating layer (30) so as to uncover the areas of the substrate not covered by the polycrystalline silicon mask but leaving a residue (22) of insulating material along the edges of the gate strips (14). To compensate for the removal of a surface layer from the resistive regions due to the anisotropic etching, a second low-dose implantation is carried out without masking of the substrate, with a dose and an energy such as to produce a predetermined resistivity for the resistive regions (21) without altering the resistivities of the source and drain regions of the MOS transistors.