Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2001-12-10
2004-10-19
Mathews, Alan (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
Reexamination Certificate
active
06806941
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a pattern forming technique using a charged particle beam or an electromagnetic wave beam, and more particularly to a pattern forming method and a pattern forming apparatus for positioning a beam of any voluntary shape and repeating shot exposure and butt-joining shots to form a desired pattern.
With the advance of high integration techniques relating to VLSIs and pattern dimension refining techniques, it has been difficult to secure accurate pattern dimensions. In particular, it is considered necessary to keep the dimensions of gate patterns within ±10% of the target dimension, in order to restrain variations in the characteristics of a transistor within an allowable range. Further, it is considered necessary to keep a dimension error due to lithography within ±7% of the above target dimension. For example, where the gate pattern dimension is 0.15 &mgr;m, the allowable dimension error in the lithography process is less than ±0.0105 &mgr;m.
Consider the case of forming a device pattern by first forming a master mask (a photomask, an X-ray mask, an electron beam mask, an ion beam mask, etc.) for the device pattern using a mask writing tool (which writes a pattern with an electron beam or a laser beam), then radiating the master mask with electromagnetic waves such as light, an X-ray, etc., or with charged particles such as an electron beam, an ion beam, etc. to thereby project an image of the mask on a wafer. In this case, the writing accuracy of the mask writing tool may be a main cause of the dimension error.
In the shot-by-shot exposure processing represented by the electron beam exposure technique, there are known a raster scan system for scanning a constant beam, and a vector scan system for positioning a beam at an individual coordinate to perform exposure thereat. The raster scan system performs beam scanning in an analog manner. In this case, to increase the speed of processing, the speed of beam scanning is increased. If the beam size is reduced in order to enhance the resolution, the speed of processing will inevitably decrease. As a method for realizing higher processing, the vector scan system is proposed, which employs a variable shaped beam and can increase the beam size. In this system, setting of the beam size and positioning of the beam are controlled by digital processing. Accordingly, the throughput and the pattern accuracy depend upon the setting speed of a DAC (digital-to-analog converter) employed therein.
A master mask such as a photomask, etc. requires high accuracy in pattern position and dimension. For example, a photomask for a semiconductor element requires that variations in pattern dimension should fall within a range of about 1/30 or less of a minimum line width, and variations in position should fall within a range of 5% or less of the minimum line width. In addition, further enhancement of accuracy is now required since the size of a semiconductor element has been reduced to 70% in every three years.
BRIEF SUMMARY OF THE INVENTION
It is the object of the invention to provide a pattern forming method and a pattern forming apparatus, which use position information concerning an area requiring high dimension accuracy in order to realize high writing accuracy.
According to a first aspect of the invention, there is provided a method of forming a pattern for a semiconductor device, comprising:
the step of forming a photosensitive film on a substrate; and
the step of radiating the photosensitive film on the substrate with a beam of a predetermined shape obtained from one of a charged particle beam and an electromagnetic beam, thereby forming an exposed region of a desired shape, the step including the step of exposing each of unit regions by a single shot of the beam of the predetermined shape for a predetermined period of time, repeating the exposure a plurality of times, and butt-joining the exposed unit regions to thereby form the exposed region of the desired shape;
wherein, in the step of forming the exposed region of the desired shape, butting portions of the unit regions are situated in a first area of a layer to be formed other than a second area of the layer in which predetermined characteristics of a function of the semiconductor device are determined by a pattern width of the exposed region in association with another pattern formed in another layer.
Preferably, the first area in which the butting portions of the unit regions are situated corresponds to an isolation region employed in the semiconductor device.
More preferably, the second area in which the predetermined characteristics of the predetermined function are determined by the pattern width of the exposed region corresponds to an active region incorporated in a transistor in the semiconductor device.
Also preferably, the region in which the predetermined characteristics of the predetermined function are determined by the pattern width of the exposed region corresponds to an electrode region to which an interlayer contact in the semiconductor device is connected.
The step of forming the photosensitive film on the substrate may use a positive-type photosensitive material or a negative-type photosensitive material.
According to a second aspect of the invention, there is provided a method of forming a pattern comprising:
the step of forming a photosensitive film on a substrate; and
the step of radiating the photosensitive film on the substrate with a beam of a predetermined shape obtained from one of a charged particle beam and an electromagnetic beam and emitted from a writing tool, thereby forming an exposed region of a desired shape, the step including the step of exposing each of unit regions by a single shot of the beam of the predetermined shape for a predetermined period of time, repeating the exposure a plurality of times, and butt-joining the exposed unit regions to thereby form the exposed region of the desired shape;
wherein the step of forming the exposed region of the desired shape includes the step of subjecting predetermined ones of the unit regions to single shot exposure, and subjecting the other ones of the unit regions to multiple shot exposure.
Preferably, in the step of forming the exposed region of the desired shape, the multiple shot exposure is performed by repeating the same shot exposure in the same position.
Alternatively, in the step of forming the exposed region of the desired shape, the multiple shot exposure is performed by changing the butting position of the unit regions in units of a single shot exposure treatment.
Alternatively, the step of forming the exposed region of the desired shape selectively uses multiple shot exposure in which the same shot exposure is repeated in the same position, and multiple shot exposure in which the butting position of the unit regions is changed in units of a single shot exposure treatment.
The step of forming the photosensitive film on the substrate may use a positive-type photosensitive material or a negative-type photosensitive material.
Preferably, the step of forming the photosensitive film on the substrate includes the step of using a combination of manners of optical overlap of first and second apertures employed in the writing tool to form the beam of the predetermined shape, and the same combination of the manners of optical overlap of the first and second apertures is used at the time of subjecting to single shot exposure those of the unit regions which have the same shape.
According to a third aspect of the invention, there is provided an apparatus for forming a pattern for a semiconductor device, comprising:
beam shaping means for shaping, to a predetermined shape, one of a charged particle beam and an electromagnetic beam;
positioning means for positioning the position of the beam of the predetermined shape in a single unit region of a substrate with a photosensitive film formed thereon; and
shot exposure means for radiating the single unit region with the beam for a predetermined period of time;
wherein the shot exposure means repe
Hara Shigehiro
Higashikawa Iwao
Inoue Soichi
Ogawa Yoji
Yamamoto Kazuko
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