Semiconductor device and manufacturing method thereof

A manufacturing method of a semiconductor device, comprising:

• providing a word line structure and a hard mask stack on the word line structure, wherein the word line structure comprises active areas, word lines, isolation structures and a protection layer, each of the active areas is sandwiched by the word lines, a first portion of each of the active areas is covered by the word lines, each of the isolation structures is sandwiched by the word lines, and the protection layer covers the active areas, the word lines, and the isolation structures;
• performing a first photolithography process to etch the hard mask stack by using a first photomask, wherein the first photomask is along a first direction;
• performing a second photolithography process to etch the hard mask stack by using a second photomask, wherein the second photomask is along a second direction, and the second direction is different from the first direction;
• and
• forming protection pillars covering the word lines and the isolation structures by etching the protection layer by using the hard mask stack as a mask, wherein the protection pillars cover the first portion of each of the active areas, and a second portion of each of the active areas is exposed, wherein the first photolithography process defines a first sidewall and a second sidewall of each of the protection pillars, the second photolithography process defines a third sidewall and a fourth sidewall of each of the protection pillars, the first sidewall is opposite to the second sidewall, the third sidewall is opposite to the fourth sidewall, and the third sidewall is adjacent to the first sidewall.