Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2000-06-21
2002-01-01
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C356S399000, C355S053000
Reexamination Certificate
active
06335537
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a projection exposure apparatus and exposure method which employ a photolithography process in which a pattern formed in a reticle which is a mask is exposed onto a substrate to which a photosensitive agent has been applied, when manufacturing microdevices such as semiconductor elements, liquid crystal display elements, image picking up devices (CCD), and thin film magnetic heads and the like. In particular, the present invention relates to the correction of the baseline amount, which is one of the operational amounts necessary when conducting the relative positioning of the pattern of the reticle and the substrate.
The present application is based on Japanese Patent Application No. HEI 9-361485, and the contents thereof are incorporated by reference.
BACKGROUND ART
In photolithography processes for manufacturing semiconductor elements or liquid crystal display elements or the like, a projection exposure apparatus is employed which obtains the semiconductor elements or liquid crystal display elements by applying a photosensitive agent onto the surface of a substrate (a semiconductor wafer surface or a liquid crystal glass substrate surface), and exposing, onto the substrate surface, via a projection optical system, the image of a reticle having formed therein a desired element circuit pattern.
As shown in
FIG. 11
, this projection optical apparatus
1
generally comprises a light source (not depicted in the figures) which emits illumination light for exposure which is irradiated onto a pattern formed in reticle R, a projection optical system P for reduction-projecting the pattern onto the surface of a substrate W, and a stage S for moving the substrate W below the projection optical system P, and the like.
In the photolithography process, during the above-described exposure operation, some sort of stratagem is necessary to align a plurality of shot regions on substrate W with various reticle patterns. In order to respond to this need, alignment marks (marks) A which are associated with each shot region are normally provided on substrate W, and the alignment of the reticle pattern with the regions on the substrate W, that is to say, the positioning thereof, is conducted by detecting these marks using a position detecting optical system Q which is provided separately from the projection optical system P.
As shown in
FIG. 11
, this position detecting optical system Q is an off-axis optical system having an optical axis QX which is parallel to the optical axis PX of the projection optical system P described above, and comprises an illumination optical part Q
1
which irradiates a broadband light (having a wavelength within a range of approximately 550 to 750 nm) onto the alignment mark A, an imaging optical part Q
2
into which is inputted the light generated by the illumination of the alignment mark A, and which forms an image of the alignment mark A on image pickup element Qc, and image processing part Q
3
which is connected to the image pickup element Qc. In imaging optical part Q
2
, an index plate Qk which is provided with index marks is provided in the optical path, and an image of the index marks of this index plate Qk is formed on the image pickup element Qc. The image processing part Q
3
detects the amount of positional displacement between the image of the index marks formed on the image pickup element Qc and the image of the alignment marks A. An alignment controller (not depicted in the figure) conducts positioning by moving the stage S based on this amount of positional displacement and the position of the stage S which is detected by a laser interferometer during the image pickup of alignment marks A.
In alignment such as that described above, an operational amount, termed a baseline amount, is generally required, and this is obtained in the manner described below. Now, the reference mark FM which is formed on the stage S is detected by the positional detection optical system Q. At this time, the amount of positional displacement with the image of the index marks on index plate Qk is detected, and the position of stage S during the detection of the reference mark FM is determined. Furthermore, based on the amount of positional displacement and the position of stage S, the position X
1
of stage S when the amount of positional displacement is 0 is determined. This position X
1
is stored in the storage region of an alignment controller, which is not depicted in the figure, of projection exposure apparatus
1
.
Next, the stage S is moved so that the reference mark FM is essentially directly beneath the projection optical system P, or in other words, so that the reference mark FM is disposed at a position conjugate with the reticle marks Rm via projection optical system P. An image of the reticle marks Rm and an image of the reference mark FM projected by the projection optical system P are formed on the image pickup element of an alignment optical system (not depicted in the figure) which is disposed above the reticle R. Additionally, the reticle marks Rm form a reference during alignment. The alignment optical system detects the amount of positional displacement of these two mark images. The alignment controller determines the position X
2
of the stage S when the amount of positional displacement is 0, based on the amount of positional displacement and the position of stage S as determined by a laser interferometer. This position X
2
which is thus determined is stored in the storage region of the alignment controller described above.
The baseline amount B is obtained using position X
1
and position X
2
, which relate to the stage and which were determined as described above; the baseline amount B is equal to X
2
−X
1
.
When the image of the reticle pattern is transferred onto a shot region on substrate W, the alignment mark A belonging to this shot region is detected by the positional detection optical system Q and the position thereof is determined, and the stage S is moved based on this determined position and the baseline amount B described above. By means of this, the image of the reticle pattern Rm is accurately aligned with the shot region.
In this way, the baseline amount B is an operational amount which is extremely important in the photolithography process, and a strictly accurate measured value thereof is required. However, here, there are a number of difficult problems which need to be solved.
For example, when semiconductor elements are manufactured, a number of types of semiconductor wafers having different reflectances and the like are employed, and the thin films or optical characteristics of the plurality of layers layered on these semiconductor wafers also differ. Furthermore, the alignment marks which are formed on these layers together with the circuit patterns themselves may change in shape in the process of etching and the like. Accordingly, it is difficult to always precisely detect the position of the alignment marks using the same positional detecting optical system irrespective of the type of semiconductor wafer or layer or the like.
In order to take account of this state of affairs, there have been proposals to increase the detection accuracy of the alignment mark image by improving the positional detection optical system Q, as disclosed in Japanese Patent Application, First publication, No. HEI 8-327318 and the corresponding U.S. Pat. No. 5,706,091. The direct problem to be solved in the above application relates to the fact that, as a result of the flattening process of the semiconductor wafers, changes in the unevenness of the alignment mark provided on the wafer become extremely small, and as a result, the detection of the mark becomes difficult.
In order to solve this problem, as shown in
FIG. 11
, the invention disclosed in the documents described above is provided, in the illumination optical part Q
1
and the imaging optical part Q
2
of the positional detection optical system Q, with an illumination light limiting member q
1
and a phase plate q
2
which may be inserted
No affiliations
Allen Stephone B.
Nikon Corporation
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