Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-09-13
2002-01-08
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S017000, C430S022000, C430S030000
Reexamination Certificate
active
06337162
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of exposure, exposure apparatus, photomask, method of production of a photomask, microdevice, and method of production of a microdevice.
DESCRIPTION OF THE RELATED ART
In the photolithographic process for production of a semiconductor integrated circuit, liquid crystal display element, thin film magnetic head, pickup element, or other microdevice, a pattern of a photomask is transferred to a semiconductor wafer or glass plate coated with a photoresist (hereinafter also called a “photosensitive substrate”). As this type of projection exposure apparatus, wide use has conventionally been made of a step-and-repeat type exposure apparatus (stepper). This step-and-repeat type exposure apparatus reduces and projects the pattern of the photomask all together on each shot area of a wafer for exposure. When finishing exposing one shot area, it moves the wafer and exposes the next shot area. This action is successively repeated.
To enlarge the scope of exposure of the mask pattern, a step-and-scan type exposure apparatus has been developed which restricts the exposure light from the illumination system to a slit shape (for example, a rectangular shape), uses this slit light to reduce and project part of the mask pattern on the wafer, and makes the mask and wafer synchronously move to be scanned by the projection optical system in that state. This step-and-scan type exposure apparatus (scanning stepper) has both the advantage of the transfer method of an aligner of transferring the pattern of the entire mask on the entire surface of the wafer by an equal magnification using a single scanning light beam and the advantage of the transfer method of the above stepper. Note that the photomask used in this step-and-repeat or step-and-scan reduction projection type exposure apparatus is also called a “reticle”.
The photomask used in this type of exposure apparatus has conventionally been produced by using an electron beam lithography system or a laser beam lithography system to draw a master pattern on a photomask substrate. That is, a mask material has been formed on the substrate, a resist coated, then an electron beam lithography system or laser beam lithography system used to draw the master pattern. Next, the resist has been developed, then etched etc. to form the master pattern by the mask material. In this case, if the reduction magnification of the reduction projection type exposure apparatus using this photomask is 1/&bgr;, the master pattern drawn on the photomask may be a &bgr;-fold enlarged pattern of the device pattern, so the drawing error of the lithography system is reduced to about 1/&bgr; on the device. Therefore, it becomes possible in practice to form the device pattern by a resolution of about 1/&bgr; the resolution of the lithography system.
In a projection exposure apparatus producing a microdevice using such a photomask (hereinafter sometimes referred to as a “device exposure apparatus”), there is distortion or coma aberration or other aberration of the projection optical system, projection magnification error, drawing error of the pattern of the photomask, rotation, shift, and other offset of the photomask with respect to the projection optical system, bending and other deformation error of the photomask accompanying holding on the stage, and other error, so there was the problem that error occurred in the position or shape of the pattern formed on the substrate for producing the device and the characteristics of the microdevice produced deteriorated.
Further, in the above way, in the past, the master pattern of the photomask had been drawn by an electron beam lithography system or laser beam lithography system. These lithographic systems draw the master pattern directly based on drawing data from a control computer. Recent LSIs and other devices, however, have become larger in area and have been increasingly improved in fineness and integration, so the master pattern required for the exposure has also become larger in area and finer. Further, as the photomask, use has been also made of reticles provided with correction patterns for preventing transfer of unnecessary patterns by double exposure, so-called phase shift reticles providing a phase shift between adjoining patterns, etc., but with such special photomasks, the amount of the drawing data tends to become greater than that of other photomasks. Due to this, the drawing data required by the lithography system for producing the photomask becomes massive.
Therefore, the drawing time required for drawing the master pattern of a single photomask by the lithography system has recently grown from 10 hours to as much as 24 hours or so. This longer drawing time has become one factor behind the rising cost of production of photomasks.
In this regard, in an electron beam lithography system, it is necessary to correct for the proximity effect due to the back scattering distinctive to electron beams. Further, it is necessary to correct for electric field unevenness at the periphery of the substrate due to the charging of the surface of the substrate. Therefore, to draw the master pattern as designed, it is necessary to measure for error in the drawing position etc. in advance under various conditions and make complicated corrections at the time of drawing with a high accuracy and stability. Making such complicated corrections during the above extremely long drawing time with a high accuracy and stability, however, is difficult. The problem of drift in the drawing position occurs during the drawing. Further, it is possible to interrupt the drawing and calibrate for error, but this has the problem of further increasing the overall drawing time.
Further, the resolution and other characteristics of resists for electron beams have not been improved that much and there will probably not been any rapid improvement in these characteristics in the future either. Therefore, if the pattern rule of semiconductor devices etc. becomes further finer in the future, the drawing time for the master pattern of one photomask will become too long, the resolution of the electron beam resist will approach its limits, and the necessary drawing accuracy may no longer be obtained. Further, the amount of the drawing data in the control computer is also becoming so massive as to be difficult for use in a single drawing process.
On the other hand, a laser beam lithography system draws a master pattern using an ultraviolet band laser beam. It has the advantages that a resist offering a higher resolution than an electron beam lithography system can be used and there is no proximity effect due to back scattering. The resolution of a laser beam lithography system, however, is inferior to that of an electron beam lithography system. Further, a laser beam lithography system is also a system which draws the master pattern directly, so the amount of the drawing data becomes massive, the processing of the data is becoming difficult, and the drawing time is becoming extremely long. Therefore, the required drawing accuracy may no longer be able to be obtained due to drift etc. of drawing position etc.
Further, a working mask is sometimes produced by a projection exposure apparatus transferring the pattern formed on the master mask to a photomask substrate (blank) (hereinafter also referred to as a “reticle exposure apparatus”), but due to analogous problems as with the above device exposure apparatus for producing a microdevice, that is, distortion and coma aberration and other aberration of the projection exposure apparatus, projection magnification error, drawing error of the pattern of the master mask (master drawing error), rotation, shift, and other offset of the master mask with respect to the projection optical system, bending and other deformation error of the master mask due to holding on the stage, and other error, error occurs in the position and shape of the pattern formed on the blank, the continuity and periodicity of the pattern become poor particularly at the stitching portions, the acc
Nikon Corporation
Oliff & Berridg,e PLC
Young Christopher G.
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