Raster frame beam system for electron beam lithography
A method for writing a master image on a substrate includes dividing the master image into a matrix of frames, each frame including an array of pixels defining a respective frame image in a respective frame position within the master image. An electron beam is scanned in a raster pattern over the substrate, while shaping the electron beam responsively to the respective frame image of each of the frames as the electron beam is scanned over the respective frame position, so that in each frame, the electron beam simultaneously writes a multiplicity of the pixels onto the substrate.
1. A method for writing a frame image on a substrate, comprising:
directing a beam of radiation to impinge on the substrate;
shaping the beam responsively to a known reference pattern, so as to generate a reference image;
comparing the reference image to the reference pattern so as to map a distortion of the pattern;
modifying a frame pattern so as to correct for the mapped distortion; and
shaping the beam responsively to the modified frame pattern so as to write the frame image on the substrate, thereby reducing the distortion in the frame image.
2. The method according to claim 1 , wherein mapping the distortion comprises mapping a displacement of one or more pixels in the reference image.
3. The method according to claim 1 , wherein mapping the distortion comprises computing an inverse transformation to the distortion, and wherein modifying the frame pattern comprises applying the inverse transformation to the frame pattern.
4. The method according to claim 3 , wherein the substrate comprises a semiconductor wafer, and the frame image comprises a portion of a circuit pattern, and wherein shaping the beam responsively to the modified frame pattern comprises writing the circuit pattern on the wafer.
5. The method according to claim 1 , wherein comparing the reference image to the reference pattern further comprises detecting a deviation in the image comprising at least one of an image displacement, an image rotation and an intensity deviation of one or more pixels in the reference image, and wherein modifying the frame pattern comprises correcting for the deviation.
6. The method according to claim 1 , wherein the beam of radiation comprises an electron beam.
7. Apparatus for writing a frame image on a substrate, comprising:
a radiation source, which is adapted to direct a beam of radiation to impinge on the substrate; and
a controller, which is coupled to cause the radiation source to shape the beam responsively to a known reference pattern, so as to generate a reference image, and which is adapted to compare the reference image to the reference pattern so as to map a distortion of the pattern, and which is further adapted to modify a frame pattern so as to correct for the mapped distortion, and to cause the radiation source to shape the beam responsively to the modified frame pattern so as to write the frame image on the substrate, thereby reducing the distortion in the frame image.
8. The apparatus according to claim 7 , wherein the distortion corrected for by the controller comprises a displacement of one or more pixels in the reference image.
9. The apparatus according to claim 7 , wherein the controller is adapted to compute an inverse transformation to the distortion, and to modify the frame pattern by applying the inverse transformation to the frame pattern.
10. The apparatus according to claim 7 , wherein the substrate comprises a semiconductor wafer, and the frame image comprises a portion of a circuit pattern, and wherein the controller is adapted to cause the radiation source to write the circuit pattern on the wafer responsively to the modified frame pattern.
11. The apparatus according to claim 7 , wherein the controller is further adapted to detect a deviation in the image comprising at least one of an image displacement, an image rotation and an intensity deviation of one or more pixels in the reference image, and to modify the frame pattern so as to correct for the deviation.
12. The apparatus according to claim 7 , wherein the beam of radiation comprises an electron beam.