Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1998-11-20
2001-01-23
Anderson, Bruce C. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492200, C250S492300, C430S296000
Reexamination Certificate
active
06177680
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electron beam (in general, particle beam) lithography used in semiconductor manufacturing. More particularly, it relates to a technique for reducing the amount of computer time and resources used in converting from the geometric data describing the various shapes on a mask or other workpiece, e.g. a wafer, to the signals to lens coils and deflectors that will write those shapes on the photoresist.
BACKGROUND OF THE INVENTION
It is known in the art, as described e.g. in U.S. Pat. No. 5,424,548, that an e-beam system must be corrected for systematic or constant errors that arise because of various non-linearities in the system. For example,
FIG. 1
shows in highly simplified form, an e-beam system in which a wafer
30
has a pattern being written on a field (or small portion)
31
.
FIG. 2
shows the wafer in more detail as being divided up into a set of fields
31
. A field represents the deflection range of the beam. Mechanical motion of the stage is used to move from one field to another. Those skilled in the art will be aware that distortions will increase non-linearly as the distance from the system axis increases and fields
31
at the edge of the wafer will have more distortion than those close in. Within a field, distortions also increase as the beam deflection increases.
It is standard practice to make a calibration wafer by writing a stock pattern, such as that shown in
FIG. 3
, measuring the wafer after transferring the pattern to the wafer, and generating an algorithm to convert the nominal data (if the fields in the system were perfect) to corrected data. Such corrected data will be referred to as global correction data and will depend on system distortions, not on the density or other features of the pattern being written. Conventional measuring systems, such as the LMS 2000 by the Leica company are commercially available to perform the measurement. Those skilled in the art will be aware that there is another class of errors that vary from one mask to another and that depend on at least the density of lines within a field
31
.
The cited patent discloses an approach to correcting such errors by adding metrology features or marks, such as those shown in
FIG. 3
, in vacant portions of the particular mask in question. Thus, the distortions in the metrology marks located within the nth field (
31
n
) will depend on the mask pattern in that field
31
n.
A sacrificial calibration wafer is made up containing the metrology marks and is discarded after the measurements for correction have been made.
As the art has progressed, the requirements for distortion correction have become more stringent and the density of features has increased, so that the previous method is no longer sufficient.
The previous method, moreover, not only made a sacrificial mask that was discarded, it also required two computer runs to generate the e-beam control data for the two masks. The computer resources used in the “post-processing” programs used to generate the e-beam data are non trivial. For example post processing for a complex state of the art microprocessor can take tens of hours on a powerful machine such as an IBM R/S 6000 mod 595. Since mask shops make masks in only small quantities, this expense cannot be spread over a lengthy production run and has a significant effect on the shop's costs.
Thus, the field of mask making has sought an economical method for obtaining pattern-dependent corrections. The field has also sought a method of reducing turn-around time in mask fabrication by reducing post-processing time.
SUMMARY OF THE INVENTION
The invention relates to a method of generating and applying correction signals to correct for pattern-dependent errors in an e-beam system, in which the post-processing computer program that converts from geometric data (referred to as input design data) to beam control data that are used to generate control signals for the various system elements (lenses, deflectors, etc) outputs two sets of beam control data in a single pass through the geometric input design data. The first set of beam control data may optionally contain systematic (non pattern-dependent) corrections, but does not contain pattern-dependent corrections. The second set of beam control data (referred to as an intermediate set of beam control data) is used to make a calibration mask and contains data that will produce metrology marks (metrology beam control data) that have been substituted for the circuit (or pattern) beam control data that produce the correct portion of the pattern for that set of locations.
The two sets of output signals are stored. The intermediate set of beam control data is used to form a calibration wafer containing the added metrology marks in place of corresponding pattern elements. These metrology marks are measured to produce correction data that are pattern-dependent and influenced by the size, shape, etc. of the nearby pattern elements.
In the fabrication of production masks, the (uncorrected) set of beam control data is read from storage and the stored control signals in the beam control data are corrected by the correction data to generate the final beam control data that are used to write the mask.
REFERENCES:
patent: 5159201 (1992-10-01), Frei
patent: 5446649 (1995-08-01), Keum
patent: 5837423 (1998-11-01), Okamoto
Dick Gregory J.
Ganong Abigail S.
Hartley John George
Pavick John W.
Puisto Denise M.
Anderson Bruce C.
International Business Machines - Corporation
Wells Nikita
LandOfFree
Correction of pattern-dependent errors in a particle beam... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Correction of pattern-dependent errors in a particle beam..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Correction of pattern-dependent errors in a particle beam... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2462748