Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Reexamination Certificate
2000-08-09
2003-03-25
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
C356S636000, C250S548000, C430S030000
Reexamination Certificate
active
06538740
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an adjusting method for a position detecting apparatus which detects the position or the like of a to-be-detected mark by receiving a flux of light from the to-be-detected mark, and is suitable for use in adjusting an alignment sensor provided in an exposure system that is used in a lithography process for forming a fine pattern of, for example, a semiconductor integrated circuit, an image pickup device (CCD or the like), a liquid crystal display or a thin film magnetic head or the like, or an overlay error measuring apparatus or the like for measuring an error in overlaying a plurality of layers on a substrate. This application is a continuation application based on PCT/JP99/00551 designating U.S.A.
BACKGROUND ART
In manufacturing semiconductor integrated circuits, use is made of a projection aligner (stepper or the like) which transfers the image of a pattern of a reticle used as a mask onto the shot areas on a wafer (or a glass plate or the like) on which a photoresist has been applied. For example, a semiconductor integrated circuit is formed by overlaying several tens of layers of circuit patterns on a wafer in a predetermined positional relationship. When, for example, the circuit patterns of the second and subsequent layers are projection-transferred onto the wafer, therefore, it is necessary to maintain, with high precision the alignment between the circuit patterns (existing patterns) that have been formed in the individual shot areas on the wafer in the preceding processes with the image of a pattern of the reticle to be exposed next. The projection aligner is therefore equipped with an alignment sensor which detects the position of alignment marks (wafer marks) provided in each shot area on the wafer together with the circuit pattern.
While there are various types of alignment sensors, an image-forming type (image processing type) which is unlikely to be affected by asymmetry of the wafer marks has become widespread recently. This type has an optical system with a similar structure to that of a microscope, picks up the image of a wafer mark magnified by an objective lens using an image pickup device and detects the position of that wafer mark from the image signal.
Further, an overlaying error measuring apparatus (registration measuring apparatus) is used to check the precision of overlaying of a pattern which has undergone overlaying exposure by the projection aligner on the existing patterns. While a position detecting apparatus provided in the overlaying error measuring apparatus is also an optical system similar to the image-forming type alignment sensor equipped in the exposure system, the target for measurement is the amount of misregistration between the relative positions of an underlying mark (existing mark) and an overlaying mark (new mark), not the position of a single wafer mark (absolute position).
If there remains an error in the optical characteristics of the optical system of the alignment sensor or the position detecting apparatus in the overlaying error measuring apparatus, i.e., an aberration (coma or the like) of the detecting optical system of an image-forming system or the like, or an adjustment error of the illumination system (misregistration of the aperture stop of the illumination system), the error in the optical characteristics produces an error in the detected position. This error is generally called TIS (Tool Induced Shift) because it originates from a tool.
With regard to this, there has recently been proposed a method of adjusting the optical system of a position detecting apparatus to reduce the TIS based on the measured value of the distance between two types of recessed and protruding marks (step marks) having different amounts of steps (hereinafter, this method will be called “different step mark method”). This different step mark method is disclosed in, for example, T. Kanda, K. Mishima, E. Murakami and H. Ina: Proc. SPIE, Vol. 3051, pp. 846-855 (1997). Specifically, the method measures a distance D
1
between two recessed and protruding marks having different amounts of steps on a wafer, turns the wafer 180° and then measures a distance D
2
between those two recessed and protruding marks again. In this case, the TIS is half the difference between the measured value at a rotational angle of 0° and the measured value at a rotational angle of 180°, i.e., (D
1
−D
2
)/2, and the optical system is adjusted in such a way that this TIS falls within an allowable range.
The overlaying error measuring apparatus often has a box-in-box mark, which comprises a mark on the outer frame and a mark on the inner frame, as measuring targets. Given that the amount of two-dimensional misregistration of the center of the inner frame mark which is measured with respect to the center of the outer frame mark on a substrate for evaluation is (&Dgr;X
1
, &Dgr;Y
1
) and the amount of two-dimensional misregistration of the centers of both marks which is acquired through remeasurement after the wafer is turned 180° is (&Dgr;X
2
, &Dgr;Y
2
), (Ta, Tb), the TIS of the overlaying error measuring apparatus becomes ((&Dgr;X
1
+&Dgr;X
2
)/2, (&Dgr;Y
1
+&Dgr;Y
2
)/2). In this case, the optical system is also adjusted in such a way that (Ta, Tb) as the TIS falls within an allowable range.
Conventionally, as described above, the different step mark method has been proposed to correct TIS which is a tool-induced error of the position detecting apparatus. However, the different step mark method has the disadvantage that it is difficult to accurately form two types of recessed and protruding marks, set to have predetermined steps, close to each other while the amounts of their steps are different from each other.
Even if it is possible to accurately form recessed and protruding marks with different steps, the different step mark method may be unable to adjust for the aberration of the detecting optical system with high precision even though it is effective in adjusting the position of the aperture stop of the illumination system.
Further, to correct the TIS, conventionally, after the distance or the relative misregistration between a pair of marks for evaluation on a predetermined substrate is measured, the substrate is turned 180° and the distance or the relative misregistration between the pair of marks is measured again to acquire the TIS. This disadvantageously increases the time required for the measuring operation. Normally, after the TIS is acquired in this manner and a predetermined optical member is adjusted, it is necessary to perform an operation of turning the substrate 180° and taking a measurement, and an operation of adjusting the predetermined optical member until the TIS actually falls within the allowable range. This brings about such disadvantages that the time needed for the measurement and adjustment becomes extremely long and when the rotational angle of the substrate cannot be set exactly to 180°, a measuring error remains.
Further, provision of a rotary stage which can turn the substrate 180° on a stage where the substrate is to be placed complicates and enlarges the structure of the stage, and is therefore not practical. If the substrate is temporarily removed from the stage after measuring the distance or the like between a pair of marks on the substrate on the stage and then the substrate is turned 180° and placed again on the stage, foreign matter may adhere to the substrate and the work of placing and removing the substrate is troublesome.
Further, conventionally, after the distance between two marks with different steps is detected, those marks are turned 180°, the distance is measured again and the difference between the two detected distances is taken as the TIS. This means that the average value of the results of the two detections of the distances is considered as a reference value (true value) of the distance between the two marks with different steps. When such two marks with different steps are turned 180°, however, the shapes of the marks as a whole are changed so tha
Magome Nobutaka
Shiraishi Naomasa
Font Frank G.
Lauchman Layla
Nikon Corporation
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