Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Patent
1996-09-17
1998-09-01
Nguyen, Kiet T.
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
250398, H01J 3730
Patent
active
058013881
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a particle beam imaging system, and in particular, an ionic optic imaging system.
BACKGROUND INFORMATION
The lithographic step is especially important amongst the different steps which must be carried out to produce semiconductor elements. Each lithographic step commences with the application of a thin sheet of light-sensitive (or particle beam sensitive) material, the so-called photo-resist or for short "resist" onto a wafer made in particular from silicium. A lithographic device then projects the structure present on a mask in the form of one or several transparent spots onto the wafer provided with the resist. Where appropriate, optical elements are located between the mask and the wafer. The expansion of the projected structure of the mask on the wafer is mostly much smaller than the wafer. After the projection process, the wafer is displaced and the same structure of the mask is projected to a different spot on the wafer. This process of projection and displacement is repeated again and again until the entire wafer surface has been covered. By virtue of the subsequent development of the resist, the desired sample for example in the form of resist-free spots is obtained on the wafer. The wafer can then be subjected in further steps to any of the known treatment procedures, such as etching, ion implantation or application and diffusion of doping material. The wafer is checked after these further steps, coated again with resist and the entire aforementioned step sequence repeated approximately 10-20 times, until finally a chess board-type arrangement of identical microcircuits is produced on the wafer.
Most of the conventional projection lithographic methods employ light to irradiate the resist but the requirement for smaller structures and higher densities of the components of the microcircuits has lead to an intensive search for other irradiation methods which in their resolution are not limited as is the case when employing light owing to its relatively long wave length. Great efforts have been undertaken to use X-ray beams in lithographic devices, whereas other methods such as for example the particle beam, in particular ion beam lithography have in fact been awarded some but considerably less consideration.
For a particle beam, and in particular ionic optic imaging systems, preferably for lithographic purposes, comprising a particle source, in particular an ion source, for the purpose of imaging onto the wafer a structure located on a mask in the form of one or a plurality of holes by way of at least two collecting lenses located between the mask and a wafer, it has already been proposed in European Patent Application No. 93 890 058.6 to design at least one of the collecting lenses as a so-called three electrode grating lens which consists of two tube electrodes. Between the electrodes is located a third electrode which is designed as a plate comprising a plurality of holes, preferably as a grating, wherein the plate, more specifically the grating, is arranged perpendicular to the optical axis, so that by virtue of the plate, i.e. the grating, the lens is divided into two regions, wherein it is preferable to provide different voltages at the three electrodes. One of the lens regions of the three electrode grating lens having a grating as the middle electrode can have a positive refractive power, the second lens region however can have a negative refractive power, wherein the absolute value of the refractive power of the lens region having the negative refractive power (the dispersing region) is lower that the refractive power of the lens region having the positive refractive power (collecting region). In the case of an imaging system of this type, it is possible despite the different absolute amounts of the refractive powers for the image distortion coefficients to be compensated to a great extent if the dispersing region comprising corresponding greater image distortions of the 3rd order than the collecting region.
The use of a three-elect
REFERENCES:
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patent: 5378917 (1995-01-01), Chalupka et al.
patent: 5436460 (1995-07-01), Stengl et al.
patent: 5637879 (1997-06-01), Schueler
Chalupka et al. "Novel electrostatic column for ion projection lithography" Journal of Vacuum Science & Technology B, Aug. 12, 1994, pp. 3513-3517.
Weidenhausen et al., Stochastic Ray Deflections In Focused Charged Particle Beams, Optik 69, No. 3 (1985) 126-134.
Chalupka Alfred
Stengl Gerhard
Vonach Herbert
IMS-Ionen Mikropfabrikations Systeme GmbH
Nguyen Kiet T.
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