Method for forming semiconductor device

A method, comprising:

• forming a dielectric layer over a substrate;
• forming a patterned amorphous silicon layer over the dielectric layer;
• depositing a first spacer layer over the patterned amorphous silicon layer;
• depositing a second spacer layer over the first spacer layer to form a bilayer spacer film including the first spacer layer and the second spacer layer;
• forming a hard mask covering a first horizontal portion of the bilayer spacer film, wherein a top surface of the hard mask is lower than a topmost position of the bilayer spacer film;
• performing an etching process to remove a second horizontal portion of the bilayer spacer film not covered by the hard mask, wherein the first horizontal portion of the bilayer spacer film and a vertical portion of the bilayer spacer film along a sidewall of the patterned amorphous silicon layer remain after the etching process is complete;
• and
• etching the dielectric layer by using the remaining first horizontal portion and vertical portion of the bilayer spacer film and the hard mask as an etch mask.

A method, comprising:

• forming a dielectric layer over a substrate;
• forming a patterned amorphous silicon layer over the dielectric layer;
• depositing a first spacer layer over the patterned amorphous silicon layer;
• depositing a second spacer layer over the first spacer layer, wherein the first spacer layer and the second spacer layer are made of titanium oxide;
• forming a hard mask layer over a first portion of the second spacer layer, while leaving a second portion of the second spacer layer uncovered by the hard mask layer;
• and
• performing an etching process to etch the dielectric layer by using the patterned amorphous silicon layer, the first spacer layer, the second spacer layer, and the hard mask layer as an etch mask.