The invention provides a
semiconductor device and a preparation method thereof. According to the method, an
ion implantation process is performed on a part of a first interlayer
dielectric layer covering a protruding structure so as to enhance the flowability of the part of the first interlayer
dielectric layer, and after a first
backflow process is performed, the part of the first interlayer
dielectric layer subjected to
ion implantation forms a
smooth surface so as to enhance the flowability of the part of the first interlayer
dielectric layer. The step difference between a part of the first interlayer
dielectric layer located on the protruding structure and the substrate is effectively reduced. Compared with a method of superposing a layer of
dielectric structure with a
smooth surface on the first interlayer
dielectric layer, the method of the invention directly performs smooth treatment on part of the first interlayer dielectric layer, and can obtain a better surface
smoothing effect on the basis of a smaller step difference. Moreover, the second interlayer dielectric layer formed on the first interlayer dielectric layer also has a
smooth surface after the second
backflow process, thereby facilitating the prevention of
metal residues in the subsequent
metal plug forming process, relieving the
short circuit problem of the device, and improving the performance and yield of the device.