Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2002-07-16
2004-01-13
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S022000, C430S030000, C430S396000, C430S394000
Reexamination Certificate
active
06677088
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for producing a photomask which is used as an original pattern at the time of fabricating micro devices, such as semiconductor integrated circuits, image pickup devices (CCDs or the like), liquid crystal display devices or thin-film magnetic heads, by using lithographic technology. This invention also relates to a method of manufacturing a device which uses such a photomask producing method.
BACKGROUND ART
At the time of manufacturing devices, such as semiconductor integrated circuits, a transfer system is employed which uses a photomask on which an original pattern that is a to-be-formed circuit pattern enlarged by, for example, about 4 to 5 times, and performs reduction projection of the original pattern of this photomask on a substrate to be exposed, such as a wafer or a glass plate, via a reduction projection optical system. An exposure system is used at the time of transferring the pattern of such a photomask and a photomask which is used by a reduction projection exposure apparatus of a step and repeat type is also called a “reticle”.
Conventionally, such photomasks have been produced by writing an original pattern on a predetermined substrate (blank) by using an electron beam lithography system or a laser beam lithography system. That is, after a mask material (light-shielding film) is formed on the substrate and a resist is coated thereon, the original pattern is written by using an electron beam lithography system or a laser beam lithography system. Thereafter, the resist is developed and etching or the like is performed to form the original pattern of that mask material. In this case, given that the reduction magnification of a reduction projection exposure apparatus which uses the photomask is 1/&bgr;, the original pattern that is written on the photomask can be a pattern which is the pattern of the device enlarged by &bgr;, so that a writing error by the lithography system is reduced to nearly 1/&bgr; on the device. Therefore, it is possible to substantially form the pattern of a device with a resolution that is approximately 1/&bgr; times the resolution of the lithography system.
As described above, conventionally, the original pattern of a photomask has been written by an electron beam lithography system or a laser beam lithography system. Those lithography systems write the original pattern directly based on write data from a control computer. Because the areas of devices, such as recent LSIs, are getting larger, and the miniaturization scale and integration are constantly being improved, however, the original patterns of photomasks which are needed for exposure are becoming larger in area and becoming more miniaturized. While a reticle, used in double exposure, provided with a correction pattern for preventing an unnecessary pattern from being transferred, and a so-called phase shift reticle having a phase shifter provided between adjoining patterns, etc. are used as photomasks, those special photomasks tend to have a larger amount of write data than other photomasks. Because of these reticles, the amount of write data that is needed by a lithography system for producing a photomask becomes enormously large.
Therefore, the writing time required for the lithography system to write the original pattern of a single photomask recently has become 10 to 24 hours. Such increased writing times are factor in raising the manufacturing cost for photomasks.
With regard to the above, an electron beam lithography system needs to correct the proximity effect caused by the influence of scattering specific to an electron beam, and also needs to correct an uneven electric field around the substrate which is caused by charging on the surface of the substrate. To write an original pattern as designed, therefore, it is necessary to measure in advance the error of the writing position or the like under various conditions and keep performing complex correction with high precision and stability at the time of writing. It is, however, difficult to keep performing complex correction with high precision and stability, and there has been a problem of drifting of the writing position during writing. Writing may be interrupted to carry out calibration, which inconveniently makes the overall writing time longer.
When the miniaturization of pattern rules for semiconductor devices or the like advances further, therefore, the writing time for the original pattern of a single photomask will becomes too long, resulting in a variation in precision, so that the required writing precision may not be achieved. Further, the amount of write data in a control computer is becoming so large that it is difficult to use the data in single writing.
A laser beam lithography system writes an original pattern using a laser beam in the ultraviolet range and has the advantages of being able to use a resist having a higher resolution as compared with the electron beam lithography system and is free of the scatter-originated proximity effect. But, the resolution of the laser beam lithography system is lower than that of the electron beam lithography system. As the laser beam lithography system also directly writes an original pattern, the amount of write data is becoming so large as to make data processing difficult and the writing time becomes considerably long so that the required writing precision may not be achieved due to drifting of the writing position or the like.
Although a predetermined pattern may be transferred on a substrate for a photomask by using an optical projection exposure apparatus at the time of producing the original pattern of that photomask, the accuracy of the original pattern gets lower if there is a distortion in the projection optical system which is used in the execution of that transfer, a variation in the evenness of the width of the transfer line, or the like.
When a photomask is actually mounted on a projection exposure apparatus and as original pattern of that photomask is projected on a substrate, such as a wafer, via a projection optical system, there occurs the problem of exposing a deformed image on the substrate, causing an overlap error or the like, if a distortion or the like remains in the projection optical system. Because the image forming characteristics, such as any distortion of the projection optical system, slightly differs from one projection exposure apparatus to another, it is desirable to be able to correct a projection image for each projection exposure apparatus if possible.
By the way, the recent trend in the market of semiconductor integrated circuits is change towards multi-type, small quantity production type devices, called ASICs (Application Specific ICs) or system LSIs, and the demanded delivery period from the acceptance of an order for the production of such devices to the delivery is becoming very short. In manufacturing such types of devices, therefore, it is necessary to first produce a photomask (working reticle) on which the original pattern for manufacturing the devices is formed in a short period of time and then produce the devices in a short period of time by using this photomask.
State-of-the-art devices are completed through, for example, more than 20 exposure steps, and the production of even one type of devices require about the same number of photomasks as the number of exposure steps. Further, the processing performance of the aforementioned laser beam lithography system or electron beam lithography system per unit time is low, so that writing a single photomask takes more than a day in some cases. Conventionally, the original patterns of all the photomasks to be used to produce one type of devices have been written, therefore, the overall time required was considerably long and it has been difficult to shorten the production time for one type of device.
Further, because the overall writing time has been very long, the production cost for photomasks to be used in manufacturing one type of device are very high, resulting in a high production cost for the devices.
Fu
Magome Nobutaka
Shiraishi Naomasa
Huff Mark F.
Mohamedulla Saleha
Nikon Corporation
Oliff & Berridg,e PLC
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