Preparation method of semiconductor element

The invention discloses a preparation method of a semiconductor element. The preparation method comprises the following steps: providing a substrate; forming a word line trench in the substrate; conformally forming a first insulating layer in the word line trench, and conformally forming a first barrier layer on the first insulating layer; conformally forming a first nucleating layer on the first barrier layer; performing a post-treatment on the first nucleating layer, wherein the post-treatment comprises a diborane-containing reducing agent and a tungsten-containing precursor; forming a first bulk layer on the first nucleating layer, wherein the first nucleating layer and the first bulk layer are configured as a first conductive layer; and performing a planarization process to turn the first insulating layer, the first barrier layer and the first conductive layer into a word line insulating layer, a word line barrier layer and a word line conductive layer respectively and correspondingly, the word line insul