Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-07-21
2003-10-07
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S282000, C430S030000, C430S942000, C313S389000
Reexamination Certificate
active
06630681
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to microlithography, which is a key technology used in the manufacture of semiconductor integrated circuits, displays, and the like. More specifically, the invention pertains to microlithography performed using a charged particle beam (e.g., electron beam or ion beam) as an energy beam.
BACKGROUND OF THE INVENTION
Conventional apparatus for performing charged-particle-beam (CPB) microlithography are represented by various electron-beam microlithography systems such as Gaussian spot-beam systems, variable-shaped beam systems, cell projection-exposure systems, and shaped-beam exposure systems. In many of these systems, the maximum field size that can be exposed is relatively small, on the order of 10 &mgr;m square (on the substrate) per exposure. More recent divided-reticle electron-beam microlithography systems have been developed that can expose a pattern divided into square sections (“subfields”) as large as 250 &mgr;m square on the substrate, wherein the various subfields are exposed individually in a sequential manner. Current research also is directed to the development of ion-beam microlithography systems that can expose even larger regions per “shot.”
One technical challenge to exposing larger regions per shot is adequate control of the Coulomb effect. The Coulomb effect is manifest as image blur due to Coulomb interactions (repulsion) between individual charged particles in the charged particle beam that causes the particles to scatter. Adequately controlling the Coulomb effect allows higher resolution exposures to be made with minimal blurring, even when using a higher illumination-beam current than in prior systems.
Unfortunately, exposing a larger region typically is accompanied by a more prominent space-charge effect (in which the charge distribution created by the charged particle beam produces its own lens action). The space-charge effect is especially important when using CPB microlithography to fabricate semiconductor devices having a minimum linewidth of 0.1 &mgr;m or less. In such applications, a failure to correct aberrations due to the space-charge effect can seriously degrade the performance of the semiconductor devices produced.
Changing the beam current can change image magnification and focus due to the space-charge effect. The degree of image defocus (referred to as “Coulomb defocus”) varies with certain parameters such as pattern-element density. Coulomb defocus of a particular image can be corrected by repositioning the focal point of the beam. However, in divided-reticle microlithographic exposure, a large number of subfields are exposed to transfer an entire pattern. Each subfield typically has a different distribution of pattern elements. Consequently, the need to perform focus and magnification alignment for each respective subfield constitutes a major problem. For CPB microlithography systems, the ability to predict and correct, accurately and rapidly, changes in the image due to the space-charge effect is a critical requirement for a practical high-resolution CPB microlithography system.
One system proposed as a solution to this problem is disclosed in U.S. Pat. No. 6,087,669. This system corrects changes in image magnification, rotation, astigmatism, and distortion due to the space-charge effect as caused by changes in beam current and by differences in the distribution of pattern elements from subfield to subfield. However, this device falls short of achieving more accurate exposures due to its inability to make more accurate corrections of aberrations arising from the space-charge effect.
Conventionally, little consideration is given to converting integrated-circuit design data into exposure-correction data useful for correcting aberrations due to the space-charge effect. There also is a marked lack of contemporary knowledge of how to go about computing data for making accurate corrections of the space-charge effect in microlithography systems such as divided-reticle systems in which the distribution of pattern elements differs from one subfield to the next.
SUMMARY OF THE INVENTION
In view of the shortcomings of the prior art as summarized above, an object of the invention is to provide charged-particle-beam (CPB) microlithography apparatus, methods, data-conversion methods, reticles, and semiconductor-device manufacturing methods in which high-resolution exposures are obtained, especially exposures in which aberrations caused by space-charge effects are reduced substantially.
To such ends, and according to a first aspect of the invention, CPB microlithography apparatus are provided for transferring a pattern, defined on a reticle segmented into multiple exposure regions, onto a sensitive substrate. An embodiment of such an apparatus comprises an illumination-optical system, a projection-optical system, a beam-correction-optical system, and a control computer. The illumination-optical system is situated and configured to direct a charged-particle illumination beam from a source to a selected exposure region on the reticle. The projection-optical system is situated and configured to direct a charged-particle patterned beam, formed by passage of a portion of the illumination beam through the exposure region, from the exposure region onto the sensitive substrate, so as to form a transfer image of the exposure region on a selected corresponding region of the substrate. The beam-correction-optical system is situated and configured to correct the transfer image based on correction data for correcting a space-charge-effect (SCE)-based aberration. The beam-correction-optical system also can correct conventional aberrations, e.g., image-field-curvature, and astigmatism, based on conventional methods. The control computer is connected to the beam-correction-optical system and is configured to control the beam-correction-optical system from the following types of input data: (a) the distribution of pattern elements in the exposure region, (b) the illumination-beam current, (c) the spread-angle distribution of the illumination beam, (d) the beam-accelerating voltage to which the illumination beam is subjected, (e) the axial distance between the reticle and the sensitive substrate, and (f) optical characteristics of the projection-optical system. A processor (or multiple respective processors) normally is used to calculate correction data from the input data. The processor(s) can be integrated into the CPB microlithography apparatus or, alternatively, provided separately from the CPB microlithography apparatus, wherein only the calculated correction data (from the processors) are input into the CPB microlithography apparatus. I.e., the processors(s) or software controlling them can be provided separately as separate products from the CPB microlithography apparatus itself.
The exposure regions on the reticle can be in the form of subfields each defining a respective portion of the pattern, wherein each exposure region is substantially coextensive with a respective subfield. In such a configuration, the control computer is configured to cause the illumination beam to illuminate the subfields sequentially and to cause the patterned beam to transfer images of the respective pattern portions defined within the subfields to the sensitive substrate in sequence.
Alternatively, the exposure regions on the reticle can be in the form of deflection fields each defining a respective portion of the pattern. In such a configuration, the control computer is configured to cause the illumination beam to scan the deflection fields sequentially and to cause the patterned beam to transfer images of the respective pattern portions defined within the deflection fields to the sensitive substrate in sequence.
The beam-correction-optical system desirably is configured to correct at least one of rotation, magnification, focal point, astigmatism, anisotropic magnification, orthogonality, and position of the transfer image. Further desirably, the beam-correction-optical system corrects more than one of these characteristics. To s
Gill Erin-Michael
Klarquist & Sparkman, LLP
Lee John R.
Nikon Corporation
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