Method for fabricating a structure comprising, in succession, a support substrate, a dielectric layer, an active layer produced in a semiconductor material, a so-called separator layer of polycrystalline silicon inserted between the support substrate and the dielectric layer, the fabrication method comprising the steps of: a) providing a donor substrate produced in said semiconductor material, b) forming an embrittlement area in the donor substrate so as to delimit a first portion and a second portion of the donor substrate on either side of the embrittlement area, the first portion being intended to form the active layer, c) providing the support substrate having a resistivity greater than a predetermined value, d) forming the separator layer on the support substrate, e) forming the dielectric layer on the first portion of the donor substrate and/or on the separator layer, f) assembling the donor substrate and the support substrate through the intermediary of the dielectric layer and the separator layer, g) fracturing the donor substrate along the embrittlement area so as to obtain the structure, h) subjecting the structure to a strengthening annealing of at least 10 minutes after the step g), the fabrication method being characterized in that the step d) comprises a step d1) of vapour phase chemical deposition of the separator layer, at atmospheric pressure, and with a deposition temperature of between 800°C and 1050°C, preferably 850°C in such a way that the polycrystalline silicon of the separator layer exhibits an entirely random grain orientation over at least a portion of the thickness of the separator layer facing the support substrate, and in that the strengthening annealing is executed during the step h)at a temperature strictly greater than 950°C and less than 1200°C, and the separator layer has a thickness, denoted e, greater than or equal to a so- called critical thickness, denoted e c below which the structure exhibits a radio-frequency power in terms of second-harmonic generation less than a predetermined value, and above which the structure exhibits a radio-frequency power in terms of second-harmonic generation greater than or equal to the predetermined value, the predetermined value being between 85 and 105 dBm as an absolute value, preferentially equal to 90 dBm as an absolute value. a) providing a donor substrate produced in said semiconductor material, b) forming an embrittlement area in the donor substrate so as to delimit a first portion and a second portion of the donor substrate on either side of the embrittlement area, the first portion being intended to form the active layer, c) providing the support substrate having a resistivity greater than a predetermined value, d) forming the separator layer on the support substrate, e) forming the dielectric layer on the first portion of the donor substrate and/or on the separator layer, f) assembling the donor substrate and the support substrate through the intermediary of the dielectric layer and the separator layer, g) fracturing the donor substrate along the embrittlement area so as to obtain the structure, h) subjecting the structure to a strengthening annealing of at least 10 minutes after the step g), the fabrication method being