Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-01-15
2001-09-18
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S077000, C430S030000
Reexamination Certificate
active
06292255
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to photolithography as used in the manufacture of semiconductor devices, and particularly to correction of exposure in a scanning direction of a scanning photolithographic system to control or reduce linewidth variation.
BACKGROUND OF THE INVENTION
In the manufacture of semiconductor devices, photolithographic techniques are often used. Generally, this involves projecting the image of a reticle onto a photosensitive resist covered wafer and subsequent processing to create a semiconductor device. While there are many different types of photolithographic systems used in the manufacture of semiconductor devices, one type of device or tool providing imaging of very small linewidths or featured sizes is a scanning photolithographic system. One such system is sold under the trademark MICRASCAN by SVG Lithography Systems, Inc., Wilton, Conn. In a scanning photolithographic system, a rectangular shaped illumination field or slit is scanned at a predetermined rate across a reticle being imaged onto a photosensitive substrate, such as a photosensitive resist or photoresist covered wafer. The reticle and photosensitive substrate move synchronously with each other at different rates to accommodate any magnification or reduction of the image of the reticle by the projection optics used to project the image of the reticle onto the photosensitive substrate. As the feature sizes or linewidths of the various elements or circuit patterns being reproduced onto the photosensitive substrate decrease in size, there is a need to increase system performance. While projection optics have advanced considerably and are a major influence on image quality, the illumination used to project the image of the reticle onto the photosensitive substrate is also critical to system performance and quality of the finished semiconductor device. While there have been many attempts to provide more improved illumination with various illumination sources, most of these efforts have been directed to providing a uniform illumination. A device for modifying illumination used in a photolithographic device is disclosed in U.S. Pat. No. 4,516,852 entitled “Method and Apparatus for Measuring Intensity Variations in a Light Source”, issuing to Liu et al on May 14, 1985, which is herein incorporated by reference. Therein disclosed is an arcuate slit that is adjustable with a deformable band. Another system for improving illumination used in a scanning photolithographic system is disclosed in U.S. patent application Ser. No. 09/023,407 filed Feb. 12, 1998 and entitled “Adjustable Slit and Method for Varying Linewidth”, which is herein incorporated by reference. While these prior devices are useful in adjusting the illumination properties of the illumination slit used to scan a reticle, they have generally only been beneficial in improving image quality along a single axes perpendicular to the direction of scan. Therefore, there is a need to further improve system performance and image quality in a direction along the direction of scan.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus and method for reducing linewidth variation in the direction of a scanning rectangular slit illumination field of an image reproduced from a reticle. Variations in linewidth produced along the axes or direction of scan whatever their cause may be is compensated for by adjusting the dose or exposure by a predetermined amount as a function of distance in the scanning direction, thereby obtaining a controlled or reduced linewidth variation along the scan direction. Variations of a particular photolithographic device or tool in combination with a known response function of a photosensitive resist or photoresist to dose is utilized in controlling the illumination to obtain the required corrected dose resulting in a reduced linewidth variation in the scan direction. A scanning photolithographic system having an illumination source projecting the image of a reticle onto a photosensitive substrate with projection optics has an illumination control that modifies the exposure dose of electromagnetic radiation by a predetermined amount as a function of distance in the scan direction. This compensates for known or determined variations in linewidth due to the signature of a particular scanning photolithographic system or tool resulting in reduced linewidth variation in the scan direction, therefore improving overall system performance.
Accordingly, it is an object of the present invention to control or reduce linewidth variation along a scan direction in a scanning photolithographic system.
It is an advantage of the present invention that linewidth variation may be controlled or reduced independent of the underlying cause of the original linewidth variations.
It is a further advantage of the present invention that it may be easily adapted to a particular scanning photolithographic system or tool having a unique signature.
It is yet another advantage of the present invention that the correcting dose or exposure is easily controlled, adjusted and changed as underlying system performance may vary over time.
It is a feature of the present invention that the exposure or dose is varied as a function of distance along a direction of scan.
It is another feature of the present invention that the determined linewidth change as a function of dose for a particular photoresist is utilized to adjust dose in the scan direction.
These and other objects, advantages, and features will be readily apparent in view of the following detailed description.
REFERENCES:
patent: 5656182 (1997-08-01), Marchman et al.
patent: 5896188 (1999-04-01), McCullough
patent: 6013401 (2000-01-01), McCullough et al.
Adams Russell
Fattibene Arthur T.
Fattibene Paul A.
Fattibene & Fattibene
Kim Peter B.
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