Mask rom fabrication method

A mask ROM fabrication method comprising:

• Step 1:
• forming a gate dielectric layer on a substrate and a first photoresist layer on the gate dielectric layer;
• Step 2:
• letting a light having a wavelength of 365 nm pass through a first phase shift mask to photolithographically form on the first photoresist layer a plurality of first trenches having a width of 243-365 nm and revealing a portion of the gate dielectric layer;
• Step 3:
• doping the substrate to form a plurality of embedded bit lines corresponding to the first trenches;
• Step 4:
• removing the first photoresist layer;
• Step 5:
• forming a polysilicon layer on the gate dielectric layer and a second photoresist layer on the polysilicon layer;
• Step 6:
• letting the light pass through a second phase shift mask to photolithographically form on the second photoresist layer a plurality of second trenches revealing a portion of the polysilicon layer;
• Step 7:
• using an etching process to selectively remove a plurality of sacrifice regions of the polysilicon layer, which are corresponding to the second trenches, and removing the second photoresist layer to form a plurality of polysilicon word lines on the gate dielectric layer.