Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2001-07-16
2003-12-02
Tran, Huan (Department: 2861)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
Reexamination Certificate
active
06657211
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to the combination of two different methods that are used in electron beam lithography, namely electron beam writing and electron beam projection lithography.
2. Background Art
In electron beam writing, the substrate is sequentially exposed by means of a focused electron beam, wherein the beam either scans in the form of lines over the whole specimen and the desired structure is written on the object by corresponding stopping-out of the beam, or, as in the vector scan method, the focused electron beam is guided only over the regions to be exposed. Electron beam writing is distinguished by high flexibility, since the circuit geometries are stored in the computer and can be optionally varied. Furthermore, very high resolutions can be attained by electron beam writing, since electron foci with diameters smaller than 100 nm can already be attained with simple electron-optical imaging systems. However, it is disadvantageous that the process is very time-consuming, due to the sequential, pointwise writing. Electron beam writing is therefore at present mainly used for the production of the masks required in projection lithography.
Electron beam writers are based, as regards equipment technology, on scanning electron microscopes, which are as a rule considerably simpler than transmission electron microscopes. In addition to the usual components for a scanning electron microscope, all that is further required is a so-called beam-blanker, by means of which the electron beam can be deflected onto a diaphragm in order to switch the electron beam “off” at the places which are not to be exposed.
In electron beam projection lithography, analogously to optical lithography, a larger portion of a mask is illuminated simultaneously and is imaged on a reduced scale on a wafer by means of a projection optics. Since a whole field is imaged simultaneously in electron beam projection lithography, the attainable throughputs can be markedly higher in comparison with electron beam writers. However, due to the lens aberrations of uncorrected electron-optical systems, only subfields of the mask, of size about 1 mm×1 mm, can be simultaneously imaged on a reduced scale on the wafer. For the exposure of a whole circuit, these subfields have to be placed against each other by an electron-optical or mechanical displacement, or by a combination of the two displacement methods.
A corresponding electron beam projection lithography system is known, for example, from U.S. Pat. No. 3,876,883. It is already described there that for adjusting the mask and wafer relative to each other, the excitation of the condenser ahead of the mask can be varied such that the electron beam is focused on the mask. The subsequent projection system then images onto the wafer the electron focus arising in the mask plane.
Further similar electron beam projection lithography systems are described, for example, in U.S. Pat. No. 4,140,913 and in European Patent Document 0 367 496.
A disadvantage of electron beam projection lithography systems is that a corresponding mask is necessary for each structure to be exposed. The preparation of customer-specific circuits in small numbers is not economic, because of the high costs associated with mask production.
A known intermediate form between electron beam writing and electron beam projection lithography is writing with a shaped electron beam. Instead of a focused electron beam, the profile of the electron beam is shaped using a diaphragm, and the diaphragm is projected onto the substrate to be exposed. The diaphragm apertures have standard geometric shapes, the overall pattern to be produced on the substrate then being combined from these geometric standard shapes. This variant thus manages without specific masks, but is only slightly faster than writing with a focused electron beam, and is markedly slower than electron beam projection lithography.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and an electron beam projection lithography system with which customer-specific circuits can be produced very economically, even in small numbers.
This object is attained by an electron beam projection lithography system comprising an electron source providing an electron beam, a condenser system, a mask plane behind the condenser system as seen in the direction of the electron beam, a substrate plane, a projective system that follows the mask plane as seen in the direction of the electron beam and is excitable such that the mask plane is imaged on a reduced scale in the substrate plane, a control system, and a projector deflection system in or before the projective system as seen in the direction of the electron beam, wherein the control system is arranged to change over condenser excitation or deflection elements such that a small focused or shaped beam profile is produced is the mask plane and wherein the projector system is driven such that a focused or shaped electron beam with a small beam profile is movable in the substrate plane along stored or computed paths. The object is attained by a method of electron beam lithography comprising in a first step electron-optically imaging a mask by a projective system on a substrate to be exposed arranged in a substrate plane, and in a second step guiding a focused electron beam or an electron beam with a shaped profile over the substrate by focusing the electron beam in a plane of the mask or shaping a beam profile of the electron beam before the plane of the mask and deflecting the focused electron beam or the electron beam with a shaped profile by a deflection system.
The present invention is based on a combination of electron beam projection lithography with electron beam writing in a single apparatus. In the method according to the invention, firstly a mask is electron-optically imaged in a first step onto the substrate to be exposed by means of a projective system. For this purpose, the mask has the coarser structures to be produced and/or universally necessary structures. In a second step, by focusing the electron beam in the mask plane or by forming the electron beam ahead of the mask plane by means of a diaphragm, further imaging onto the substrate to be exposed of the focus arising in the mask plane, or of the image of the beam shaping diaphragm arranged ahead of the mask plane, and targeted deflection of the electron focus or of the shaped electron beam in the substrate plane by a deflecting system, the fine structure not present in the mask but nevertheless necessary, and/or the conductor paths and other structures not present in the mask but nevertheless corresponding to the customer's requirements, are written onto the substrate.
Electron beam writing takes place, according to a first embodiment of the invention, by means of an electron beam that is focused in the substrate plane. In a second embodiment, the electron beam writing takes place with an electron beam shaped by a diaphragm, the diaphragm then having regions that have standard shapes and are transmissive for electrons.
Both steps of the combination according to the invention can of course be carried out one after another with multiple iterations, for the exposure of larger fields on the substrate. Since both steps are carried out in multiple succession with the same apparatus, no readjustment of the substrate relative to the optical axis of the apparatus is required between the two steps.
An electron beam projection lithography system according to the invention has an electron source, a preferably multi-stage condenser, a mask plane provided following the condenser, and a projective system following the mask plane. The projective system can be excited such that the mask is imaged on the substrate on a reduced scale. By means of a control system, the condenser excitation can be changed
LandOfFree
Process for electron beam lithography, and electron-optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for electron beam lithography, and electron-optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for electron beam lithography, and electron-optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3117982