Method of manufacturing buried word line structure and semiconductor memory thereof

A method of manufacturing a buried word line structure, comprising:

• providing a semiconductor substrate;
• injecting target ions into the semiconductor substrate to form an injected region in the semiconductor substrate;
• annealing the semiconductor substrate comprising the injected region to convert the injected region into an insulation region;
• forming a word line trench in the insulation region by partially etching the insulation region, a width of the word line trench being less than a width of the insulation region, a height of the word line trench being less than a height of the injected region, and a residual part of the etched insulation region being used as a gate oxide layer of the buried word line structure;
• and
• filling the word line trench with a word line metal to form the buried word line structure.