A method for manufacturing a dummy gate in a gate-last process and a dummy gate in a gate-last process are provided. The method includes: providing a semiconductor substrate; growing a gate oxide layer on the semiconductor substrate; depositing bottom-layer amorphous silicon on the gate oxide layer; depositing an ONO structured hard mask on the bottom-layer amorphous silicon; depositing top-layer amorphous silicon on the ONO structured hard mask; depositing a hard mask layer on the top-layer amorphous silicon; forming photoresist lines on the hard mask layer, and trimming the formed photoresist lines so that the trimmed photoresist lines a width less than or equal to 22 nm; and etching the hard mask layer, the top-layer amorphous silicon, the ONO structured hard mask and the bottom-layer amorphous silicon in accordance with the trimmed photoresist lines, and removing the photoresist lines, the hard mask layer and the top-layer amorphous silicon.