Height measurement and correction method for electron beam lithography system

A method of height measurement and correction for an electron beam lithography system having two-stage deflection ("fly's eye" lens type), employing a height measuring transducer and a two-position fiducial calibration grid system;

• said method comprising:
• (1) measuring x and y deflection voltages and deriving stitching and registration correction calibration C and D coefficient values for a selected lenslet of the electron beam optical column with the electron beam of that lenslet imaged on a first fiducial calibration grid position LFG1 located above the target surface of the electron beam optical column;
• (2) for each four diagonal neighboring lenslets of the optical column, performing height measurement iteration using stitching and registration errors measured with respect to a second fiducial calibration grid position LFG2 a known distance .delta.h.sub.l from the position of the first fiducial calibration grid position LFG1;
• (3) averaging each set of four values obtained in step (2) above and identifying the results as .DELTA.h.sub.xo and .DELTA.h.sub.yo ;
• (4) measuring x and y deflection voltages and deriving stitching and registration correction calibration C and D coefficient values therefrom with the electron beam imaged on the second fiducial calibration grid position LFG2;
• (5) for each four diagonal neighbors of the selected lenslet, performing height measurement iteration using the stitching and registration errors measured at the first fiducial calibration grid position LFG1;
• (6) averaging each set of four values obtained in step (5) above and identifying the results as .DELTA.h.sub.xo ', and .DELTA.h.sub.yo ';
• (7) calculating values .DELTA.h.sub.xo and .DELTA.h.sub.yo using the following equation ##STR2## (8) using a value of .delta.h.sub.l measured at the center of the selected lenslet, calculating ##EQU8## (9) calculating a tilt correction for .delta.h.sub.l ;
• (10) calculating a tilt correction using the four values of h.sub.x obtained in step (8) above;
• (11) calcualting a tilt-corrected value of h.sub.x for all of the lenslets at the center of every lenslet;
• (12) repeating steps (3) and (4) to obtain a tilt corrected value for h.sub.y ;
• (13) calculating a tilt correction value for .delta.h.sub.o ;
• (14) at each lenslet using the tilt-corrected value of the height of LFG1 above the target surface .delta.h.sub.c at the center of the lenslet being corrected and the value h.sub.x and h.sub.y for this lenslet obtained from step (8) above, deriving deflection voltage values .DELTA.h.sub.xo and .DELTA.h.sub.yo for the lenslet being corrected from the expressions .DELTA.h.sub.xo =.delta.h.sub.c /h.sub.x and .DELTA.h.sub.yo =.delta.h.sub.l /h.sub.y ;
• and
• (15) using the C and D values obtained in step (1) for the lenslet being corrected measured on the first fiducial calibration grid position LFG1 and the values .DELTA.h.sub.xo and .DELTA.h.sub.yo obtained from step (14) above, calculating the height corrected values G and H for the lenslet being corrected from the following expressions:
• G.sub.00 =C.sub.00 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-1
• G.sub.01 =C.sub.01 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-1
• G.sub.02 =C.sub.02 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-2 +C.sub.00 .multidot.p.sub.y .multidot..DELTA.h.sub.x.sbsb.0 .multidot.
• (.DELTA.h.sub.x.sbsb.0 +1).sup.-2 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-2
• G.sub.10 =(C.sub.10 -.DELTA.h.sub.x.sbsb.0).multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-
• G.sub.11 =C.sub.11 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-1 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-1
• G.sub.12 =C.sub.12 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-1 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-2 +
• (C.sub.10 +1).multidot.p.sub.y .multidot..DELTA.h.sub.x.sbsb.0 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-2 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-2
• G.sub.20 =C.sub.20 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-2 +C.sub.00 .multidot.p.sub.x .multidot..DELTA.h.sub.x.sbsb.0 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-4
• G.sub.21 =C.sub.21 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-2 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-1
• G.sub.03 =C.sub.03
• G.sub.30 =C.sub.30 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-3 +(C.sub.10 +1).multidot.p.sub.x .multidot..DELTA.h.sub.x.sbsb.0 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-4
• H.sub.00 =D.sub.00 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-1
• H.sub.01 =(D.sub.01 -.DELTA.h.sub.y.sbsb.0).multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-1
• H.sub.02 =D.sub.02 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-2 +D.sub.00 .multidot.q.sub.y .multidot..DELTA.h.sub.y.sbsb.0 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-4
• H.sub.10 =D.sub.10 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-1
• H.sub.11 =D.sub.11 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-1 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-1
• H.sub.12 =D.sub.12 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-1 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-2
• H.sub.20 =D.sub.20 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-2 +D.sub.00 .multidot.q.sub.x .multidot..DELTA.h.sub.y.sbsb.0 .multidot.
• (.DELTA.h.sub.x.sbsb.0 +1).sup.-2 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-2
• H.sub.21 =D.sub.21 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-2 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-1 +
• (D.sub.01 +1).multidot.q.sub.x .multidot..DELTA.h.sub.y.sbsb.0 .multidot.(.DELTA.h.sub.x.sbsb.0 +1).sup.-2 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-2
• H.sub.03 =D.sub.03 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-3 +(D.sub.01 +1).multidot.q.sub.y .multidot..DELTA.h.sub.y.sbsb.0 .multidot.(.DELTA.h.sub.y.sbsb.0 +1).sup.-4
• H.sub.30 =D.sub.30
• where .DELTA.h.sub.xo =.delta.h/h.sub.x, .DELTA.h.sub.yo =.delta.h/h.sub.y ;
• h.sub.x and h.sub.y are, respectively, the heights of the x and y centers of deflection above the surface on which the C's and D's are measured;
• .delta.n is the directed distance in height from the surface on which the C's and D's are measured to the target surface on which the pattern is to be written;
• and p.sub.x, p.sub.y, q.sub.x and q.sub.y are obtained from the geometry of the fine deflector and wherein for the double dipole deflector:
• ##EQU9## where L.sub.x represents the length of the x-deflector blades, L.sub.y the length of the y-deflector blades, S the separation between the deflector segments and T the distance from the exit of the y-deflector to LFG1.

An in-situ method of height measurement and calibration correction employing an electron-beam optical column having a height measuring transducer and a multi-level fiducial calibration grid system;

• said method comprising:
• (1) performing triangulation measurements at a multiplicity of different height levels using the multi-level fiducial calibration grid system and deriving a plurality of measured signals representative of height differences between a target surface and critical fine deflection parts of the electron-beam optical column;
• (2) deriving a series of height correction parameters .DELTA.h.sub.xo.sup.(i) and .DELTA.h.sub.yo.sup.(i) from the measured signals obtained in step (1) where (i) is an iteration series index;
• (3) combining the parameters derived in step (2) with corresponding readings c.sup.(i) obtained from the height measuring transducer;
• and
• (4) fitting two functions f.sub.x and f.sub.y to the data obtained in steps (2) and (3) using a least-squares methodology to obtain the correction factors .DELTA.h.sub.xo =f.sub.x (c) and .DELTA.h.sub.yo =f.sub.y (c).