Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2000-04-26
2002-01-08
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C430S296000, C430S942000
Reexamination Certificate
active
06337164
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to microlithography in which a pattern, defined on a mask or reticle, is transferred to a suitable substrate using a charged particle beam such as an electron beam. This type of microlithography has especial utility in the fabrication of semiconductor integrated circuits and displays. More particularly, the invention pertains to achieving accurate pattern-feature linewidths in the microlithographically projected pattern image even if beam-edge resolution is relatively poor.
BACKGROUND OF THE INVENTION
In recent years, as semiconductor integrated circuits increasingly have become miniaturized, the resolution limits of optical microlithography (i.e., microlithography performed using ultraviolet light as an energy beam) increasingly have become apparent. As a result, considerable development effort currently is being expended to develop microlithography apparatus and methods that employ an alternative type of energy beam that offers prospects of better resolution than optical microlithography. One candidate microlithography technology utilizes a charged particle beam, such as an electron beam or ion beam, as an energy beam. The charged particle beam passes through a charged-particle-beam (CPB)-optical system from a source (e.g., electron gun) through a reticle to a substrate (e.g., semiconductor wafer).
In conventional electron-beam microlithography, the beam-edge resolution of the electron-optical system desirably is no more than one-half to one-third the minimum linewidth of the pattern as imaged on the substrate. “Beam-edge resolution” is defined as the lateral distance over which the intensity of the beam at the beam edge increases from 12% to 88%. The lower the number denoting beam-edge resolution, the more sharply defined the beam edges. Hence, for example, if the minimum linewidth of the elements (features) of a pattern is 100 nm, then the beam-edge resolution desirably is 50 nm to 33 nm or less. However, a large beam current (i.e., a beam current of approximately 20 &mgr;A or more) can cause the beam-edge resolution to be greater than the required value due to the influence of space-charge effects. As used herein, “beam current” refers to the total current of the electron beam reaching a sensitive substrate at any one instant. A “space-charge effect” is a phenomenon in which similarly charged particles (e.g., electrons) in the beam repel each other in response to Coulomb forces between the similarly charged particles, resulting in beam spreading and consequent blurring (loss of beam-edge resolution) of the edges of the beam.
According to conventional practice, space-charge effects can be reduced by reducing the area of the substrate illuminated by the beam at any one instant and/or by reducing the beam current. Unfortunately, these tactics reduce “throughput” (number of semiconductor wafers that can be microlithographically processed per unit time) to impractical levels.
SUMMARY OF THE INVENTION
In view of the shortcomings of the prior art as summarized above, an object of the invention is to provide microlithography (pattern-transfer) methods that achieve accurate pattern-feature linewidths even if beam-edge resolution is relatively poor.
To such end, and according to a first aspect of the invention, methods are provided for performing microlithography of a pattern, defined on a reticle and having a minimum linewidth, to a sensitive substrate using a charged particle beam. According to a representative embodiment of such a method, a region of the reticle is illuminated with a charged-particle illumination beam passing through an illumination-optical system. The illumination beam passing through the illuminated region of the reticle forms a patterned beam propagating downstream of the reticle. The patterned beam is projected and focused, with demagnification, through a projection-optical system onto a corresponding region on a sensitive substrate. A minimum linewidth of the pattern defined by the reticle is determined. The projection-optical system is controlled to provide the patterned beam with a beam-edge resolution that is 0.8 to 1.0 times the minimum linewidth of the pattern.
If the beam-edge resolution is as noted above, linewidth accuracy and precision can be maintained at a value that is sufficiently better than the target value of ±10%, especially so long as the variation in the threshold value is maintained at ±1% or better.
According to another representative embodiment of methods according to the invention, the pattern as defined on the reticle is divided into multiple subfields. The subfields are illuminated successively with a charged-particle illumination beam to form a patterned beam propagating downstream of the reticle. The patterned beam from each subfield is projected and focused, with demagnification, by passage through a projection-optical system so as to form images of the subfields on respective regions on a sensitive substrate such that the images are stitched together. A predicted beam-edge resolution of the projection-optical system is calculated, based on a beam current used to illuminate each subfield. Before exposing a subfield on the reticle, dimensions of pattern features as defined in the subfield are corrected according to a ratio of pattern-feature dimension to the beam-edge resolution, so as to project the pattern features in the subfield with correct pattern-feature dimensions on the substrate.
By correcting the dimensions of the pattern features on the reticle beforehand, accuracy and precision of pattern dimensions can be increased, even in instances in which beam-edge resolution is relatively coarse.
According to yet another representative embodiment of a method according to the invention, the pattern, as defined on the reticle, is divided into multiple subfields. The subfields are illuminated successively with a charged-particle illumination beam to form a patterned beam propagating downstream of the reticle. The patterned beam is projected and focused, with demagnification, from each subfield through a projection-optical system so as to form images of the subfields on respective regions on a sensitive substrate such that the images are stitched together. A predicted beam-edge resolution of the projection-optical system is calculated, based on a beam current used to illuminate each subfield. The calculated beam-edge resolution is calculated as a function of a position, within a field of the projection-optical system, in which an image of the subfield is to be formed on the substrate. Before exposing a subfield on the reticle, dimensions of pattern features as defined in the subfield are corrected according to a ratio of pattern-feature dimension to the beam-edge resolution, so as to project the pattern features in the subfield with correct pattern-feature dimensions on the substrate.
Another representative embodiment is directed to a method for manufacturing an electronic device that includes at least one layer having a pattern formed by charged-particle-beam microlithography. (The microlithography involves illumination of a reticle, defining the pattern, by an illumination beam to form a patterned beam, and transferring of the pattern from the reticle to a sensitive substrate by reducing, projecting, and focusing the patterned beam onto the sensitive substrate. The method includes a method for controlling beam blur. In the latter method, the patterned beam is passed through a projection-optical system as the patterned beam propagates from the reticle to the sensitive substrate. A beam-edge resolution that is achievable with the projection-optical system is determined, and the projection-optical system is controlled such that a poorest beam-edge resolution achieved by the projection-optical system is 0.8 to 1.0 times a minimum linewidth of the pattern.
In another representative embodiment of a method for manufacturing an electronic device that includes at least one layer having a pattern formed by charged-particle-beam microlithography, a reticle defining the pattern is
Klarquist & Sparkman, LLP
Nikon Corporation
Young Christopher G.
LandOfFree
Charged-particle-beam microlithography methods exhibiting... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Charged-particle-beam microlithography methods exhibiting..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Charged-particle-beam microlithography methods exhibiting... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2817348