Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-07-21
2001-08-28
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S055000, C355S077000, C430S022000
Reexamination Certificate
active
06281965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method for exposure of mask pattern on a photosensitive substrate in fabricating semiconductor devices etc., and an exposure system using the exposure method. Particularly, the invention is suitably applicable to the photolithography process wherein sequential exposures are effected in a layer as called as a middle layer not requiring a so high resolution, which is for example an ion-implanted layer used in fabricating semiconductor memories etc., and in a layer as called as a critical layer requiring a high resolution.
2. Related Background Art
The reduction projection exposure apparatus (steppers etc.) have been heretofore used in the photolithography process for fabricating the semiconductor devices such as VLSI, or liquid crystal displays etc. Generally, the semiconductor devices such as VLSI are formed by superimposing many patterns in layers on a wafer, and among those layers a layer requiring the highest resolution is called as a critical layer. In contrast with it, a layer not requiring a so high resolution, for example the ion-implanted layer used in fabricating semiconductor memories etc., is called as a middle layer. In other words, line widths of pattern in exposure in the middle layer are wider than those in exposure in the critical layer.
For example, recent VLSI fabrication plants often use separate exposure units for different layers each in its proper exposure in a fabrication process of a type of VLSI in order to enhance the throughput of fabrication steps. For example in the cases of fabricating VLSI having both the critical layer and the middle layer, a projection exposure apparatus with high resolution for critical layer was used also in exposure in the middle layer, or for exposure in the middle layer an exposure apparatus of the aligner type was used to effect full exposure on a single wafer. In the case of the former, an array (shot map) of shot areas in the middle layer was the same as that in the critical layer, whereby obviating the necessity to produce a new shot map for middle layer. Further, the latter also obviated the necessity to produce the shot map.
In the conventional technology as described above, the projection exposure apparatus for critical layer is ready for high resolutions. Therefore, when the exposure in the middle layer was effected by the projection exposure apparatus for critical layer, a reduction ratio of a projection optical system was too high, which narrows the field size, causing a problem of incapability to increase the throughput. Namely, the number of shot areas to be exposed on a wafer became too large with the narrow field size, requiring a longer exposure time in proportion to the number of shot areas. There was another problem that because the projection optical system with high resolution was expensive, the whole of the plural exposure units, used in fabricating a type of VLSI etc., became expensive.
When the exposure in the middle layer was conducted by the exposure apparatus of the aligner type, there was a problem that a sufficient resolution was not assured for large-scale wafers.
Also, high registration accuracy needs to be maintained in overlap exposures in different layers on VLSI. In order to enhance the registration accuracy as required, alignment marks (wafer marks) are formed in a predetermined array on a wafer, and alignment of wafer is carried out based on positions of these wafer marks. Accordingly, the time necessary for alignment also needs to be shortened in order to enhance the throughput of exposure steps.
SUMMARY OF THE INVENTION
In view of the above points, an object of the present invention is to provide an exposure method by which, in fabricating a substrate with a critical layer and a middle layer mixed therein by the photolithography process, exposures can be effected in respective layers each in its necessary resolution even for large-scale substrates and by which the exposures can be made with a high throughput using inexpensive exposure units. In addition, another object of the present invention is to provide an exposure system which can carry out the exposure method. A further object of the present invention is to provide an exposure method which can further enhance the throughput while decreasing the alignment time.
The exposure method according to the present invention is an exposure method for effecting overlap exposures of different mask patterns in an exposure area on a photosensitive substrate, using, for example as shown in FIG.
1
and
FIGS. 2A-2C
, a first exposure apparatus having a first exposure field and a second exposure apparatus having a second exposure field larger than the first exposure field, wherein in an exposure of a first mask pattern in the exposure area on the photosensitive substrate using the first exposure apparatus, the exposure is effected according to a first shot map formed by dividing the exposure area on the photosensitive substrate in units of first shot areas each corresponding to the first exposure field and wherein in an exposure of a second mask pattern in the exposure area on the photosensitive substrate using the second exposure apparatus, the exposure is effected according to a second shot map (
FIG. 2C
) having a shot number being minimum when a region containing the first shot map is divided in units of second shot areas each corresponding to the second exposure field.
In this case, an example of the second shot areas forming the second shot map is such an arrangement that the second shot areas each are constructed in units of first shot areas in those forming the first shot map.
In another case, for example as shown in
FIGS. 5A-5C
, where an exposure of a plurality of same partial patterns is effected in each of the first shot areas forming the first shot map, the second shot areas forming the second shot map each are preferably separated in units of exposure regions of the partial patterns in the first shot areas forming the first shot map.
Another preferable arrangement is, for example as shown in
FIGS. 6A-6C
, such that alignment marks are formed in a predetermined array in the first shot map on the photosensitive substrate, exposures are effected according to the first shot map on the photosensitive substrate with the first exposure apparatus, and thereafter for exposures according to the second shot map with the second exposure apparatus, alignment is made between the second exposure field and each shot area in the second shot map, using an alignment mark closest to a measurement position of the second exposure apparatus out of the alignment marks in the first shot map.
Further, the exposure system according to the present invention is an exposure system, for example as shown in
FIG. 1
, having a first exposure apparatus with a first exposure field and a second exposure apparatus with a second exposure field larger than the first exposure field, and effecting exposures in an exposure area on a photosensitive substrate with superposition of different mask patterns using the first exposure apparatus and second exposure apparatus in order, said exposure system comprising first shot map forming means, provided in the first exposure apparatus, for forming a first shot map by dividing the exposure area on the photosensitive substrate in units of first shot areas each corresponding to the first exposure field, control means for transferring information on the first shot map to the second exposure apparatus, and second shot map forming means for forming a second shot map, based on the information on the first shot map, so that a number of shots therein becomes minimum when the region containing the first shot map on the photosensitive substrate is divided in units of second shot areas each corresponding to the second exposure field, wherein an exposure is effected according to the first shot map with the first exposure apparatus whereas an exposure is effected according to the second shot map with the second exposure apparatus.
In such exposure
Adams Russell
Fuller Roy
Miles & Stockbridge P.C.
Nikon Corporation
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