Manufacturing method of memory device

A method of manufacturing a memory device, comprising:

• forming an active region, a word line, and an initial bit line contact structure in a substrate;
• and
• forming a bit line on the substrate, and removing a portion of the initial bit line contact structure not overlapped with the bit line to form a bit line contact structure,
• wherein the word line extends along a first direction, the bit line extends along a second direction intersected with the first direction, the active region is intersected with the word line and the bit line and extends along a third direction different from the first direction and the second direction, and the bit line contact structure is disposed between the active region and the bit line, and
• wherein a lithography process for forming the initial bit line contact structure comprises using a free-form lens array to allow a light pass through the free-form lens array before the light is incident on a photomask, the free-form lens array comprises a plurality of lenses arranged along a parallelogram-like contour having a long axis, an angle between an extending direction of the long axis and the third direction is less than an angle between the extending direction of the long axis and the first direction and is less than an angle between the extending direction of the long axis and the second direction.