Method of measuring numerical aperture of exposure machine, control wafer, photomask, and method of monitoring numerical aperture of exposure machine
A method of measuring a numerical aperture of an exposure machine is described. A control wafer having vernier marks thereon and an aberration mask having pinholes therein are provided, wherein each pinhole corresponds to a vernier mark in position. A lithography process using the exposure machine and the aberration mask is performed to the control wafer, so as to form over each vernier mark a photoresist pattern having the same shape of the illumination pattern of the light source of the exposure machine. The numerical aperture of the exposure machine is then derived from a graduation of the vernier mark corresponding to an outer edge of the photoresist pattern.
1. A method of measuring a numerical aperture (NA) of an exposure machine, wherein a light source of the exposure machine has an illumination pattern, the method comprising:
providing a control wafer having a plurality of vernier marks thereon;
providing an aberration mask having a plurality of pinholes therein, wherein each pinhole corresponds to a vernier mark in position;
performing a lithography process using the exposure machine and the aberration mask to the control wafer, so as to form a photoresist pattern having the same shape of the illumination pattern over each vernier mark; and
deriving the NA of the exposure machine from a graduation of the vernier mark corresponding to an outer edge of the photoresist pattern.
2. The method of claim 1 , wherein the photoresist pattern comprises at least one opening formed in a positive photoresist layer on the control wafer.
3. The method of claim 1 , wherein each of the vernier marks comprises at least one graduated linear pattern.
4. The method of claim 3 , wherein each of the vernier marks comprises an X-directional graduated linear pattern, a Y-directional graduated linear pattern, a 45° graduated linear pattern and a −45° graduated linear pattern, wherein respective centers of the four graduated linear patterns coincide with each other.
5. The method of claim 1 , wherein the light source is an on-axis light source.
6. The method of claim 1 , wherein the light source is an off-axis light source.
7. The method of claim 6 , wherein the illumination pattern of the off-axis light source is a ring-shaped illumination pattern, an X-dipolar illumination pattern, a Y-dipolar illumination pattern or a quadrupolar illumination pattern.
8. A method of monitoring a numerical aperture (NA) of an exposure machine, wherein a light source of the exposure machine has an illumination pattern, the method comprising:
providing a control wafer having a plurality of vernier marks thereon;
providing an aberration mask having a plurality of pinholes therein, wherein each pinhole corresponds to a vernier mark in position;
setting the exposure machine according to a required NA;
performing a lithography process using the exposure machine and the aberration mask to the control wafer, so as to form a photoresist pattern having the same shape of the illumination pattern over each vernier mark;
deriving a real NA of the exposure machine from a graduation of the vernier mark corresponding to an outer edge of the photoresist pattern;
comparing the real NA with the required NA and adjusting the exposure machine according to a result of the comparison; and
establishing an NA database of exposure machine.
9. The method of claim 8 , wherein the NA database includes parameter settings corresponding to the required NA, the real NA, the result of the comparison and a result of the adjustment of the exposure machine.