Photomask and pattern forming method

A method for forming a resist pattern on a semiconductor substrate, comprising:

• using a photomask having a mask pattern including a junction at which two line patterns are connected to each other with one line pattern being orthogonal to the other line pattern so as to form a T-shape, or a proximity portion at which two line patterns are located close to each other with one line pattern being substantially orthogonal to the other line pattern so as to form a T-shape, wherein a small pattern is formed on a side edge of the line pattern in the vicinity of the junction or the proximity portion so as to form a wide portion of the line pattern, the small pattern being provided within a range between 0.79 and 1.8 λ/(NA·K) of a distance from a neighboring side edge of the other line pattern, where X is a wavelength of exposure illumination light, NA is a numerical aperture of a lens used, and K is a transfer reduction ratio;
• and
• transferring the mask pattern of the photomask onto a photoresist on the semiconductor substrate with the transfer reduction ratio K ranging from 1/5 to 1/4, wherein the photomask is irradiated with off-axis illumination light during the transfer of the mask pattern.