Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Electron beam imaging
Patent
1996-06-07
1999-03-09
Baxter, Janet
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Electron beam imaging
430942, 2504923, G03C 500, A61N 500
Patent
active
058798609
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
The invention relates to a method of writing a pattern on a substrate by means of an electron beam.
It is common practice in electron beam lithography to write patterns on wafers, masks, reticles and other substrates by fracturing the patterns, i.e. breaking down each pattern into sub-patterns and by exposing the sub-patterns in sequence to build up a composite image. The pattern is conventionally divided into a grid format of square main fields and each main field is further divided into a grid format of square sub-fields. Each subfield is written by beam deflection to scan the subfield area, usually by vectoring of the beam to individual pattern shapes within the area by the most economic sequence of travel and by boustrophedon scanning of each shape. At the conclusion of each sub-field scanning the beam is moved on to the next sub-field and the process is repeated. When the pattern features of all sub-fields have been written, the substrate itself is displaced to position a succeeding main field centrally of the beam axis, so that its sub-fields can in turn be written.
The main field sizes in such fractured patterns are typically in the order of 0.1 to 4.0 millimeters square and in excess of 1,000 sub-fields are generally present on each field. The sub-field size principally depends on the fineness of the pattern features; features with a 1.0 micron dimension may be written by, for example, a resolution represented by 0.1 micron steps in the beam deflection, resulting in a sub-field size of about 100 microns square. To minimize or avoid distortion of pattern features which cross sub-field and main field boundaries or misalignment of features interconnected at these boundaries, it is necessary to apply corrections to the beam deflection system on each transition between sub-fields and main fields. These corrections compensate for, for example, deflection distortion, magnetic effects and time-related drift effects.
The afore-described lithographic techniques are in general use in the industry and are summarised in, for example, Jones and Dix: Electron Beam Lithography in Telecommunications Device Fabrication, Part 1, British Telecom Technology Journal, Vol. 7, No. 1.
Whilst such techniques are successful in microlithography, difficulties arise if they are applied to nanolithography. Nanolithography patterns are typically characterised by extremely fine features grouped centrally and coarser features graduating out towards the edges of the pattern. Writing the pattern requires the sub-fields to be only a few microns square, which results in correspondingly small main fields and sub-fields. This in turn significantly increases scanning time for the entire pattern. In addition, alignment of features at sub-field and main field boundaries is more difficult, particularly at transitions of pattern fineness.
SUMMARY OF INVENTION
It is therefore the object of the present invention to provide a method of electron beam lithography which is suitable for writing patterns with a total size and a fineness graduation and distribution of the kind encountered in nanolithography and which allows required standards of acuity to be maintained without extending throughput time.
Other objects and advantages of the invention are apparent from the following description.
According to the invention there is provided a method of writing a pattern on a substrate by means of an electron beam, wherein the pattern has features of differing degrees of fineness and is divided into a plurality of fields which are written in succession by controlled deflection of the beam relative to a neutral axis thereof, characterised in that the pattern is divided into at least two fields of differing size arranged one inside the other with a common centre point at the neutral axis and with the finer or finest of the pattern features contained in the inner field and that the at least two fields are written in succession by maintaining the substrate in a fixed location and so changing the writing resolution of the beam on transition from
REFERENCES:
patent: 4586141 (1986-04-01), Yasuda et al.
Proceedings of SPIE, vol. 923, Bellingham (USA) pp. 246-252, M. Ohyama et al. "High speed data control circuit for nanometric electron beam lithography".
English translation of JP 218115.
Shearer et al., Development of nanometric electron beam lithography system (JBX-5D II), J. Vac. Sci. Technol.B., 4(1), Jan./Feb., 1986, pp. 64-67.
Mitchell Peter Gerald
Rosolen Grahame Craig
Ashton Rosemary
Baxter Janet
Leica Microsystems Lithography Limited
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