JP3636571B2 - Alignment method and exposure apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alignment method and an exposure apparatus, and in particular, an IC formed on a reticle , which is a first object, used in a step-and-repeat or step-and-scan projection exposure apparatus for manufacturing a semiconductor element, BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment method suitable for performing relative alignment (alignment) between a pattern related to LSI, VLSI, etc. and a pattern formed on a wafer as a second object, and an exposure apparatus to which the alignment method is applied. Is.
[0002]
[Prior art]
As the density of semiconductor integrated circuits increases, projection exposure apparatuses for manufacturing semiconductor elements are required to project and expose circuit patterns on the reticle surface onto the wafer surface with an increasingly higher resolution. As a method for improving the projection resolving power of the exposure apparatus, there is a method of increasing the NA of the projection optical system by fixing the wavelength of the exposure light, or shortening the wavelength of the exposure light, for example, from g-line to i-line, i There is a method of shifting from the line to the oscillation wavelength of the excimer laser.
[0003]
On the other hand, with the miniaturization of circuit patterns, it is required to align the electronic circuit pattern formed on the reticle and the pattern on the wafer with high accuracy. The alignment between the reticle and the wafer uses exposure light that sensitizes the resist applied on the wafer surface and non-exposure light that does not sensitize the resist, for example, a wavelength of 633 nm, which is the oscillation wavelength of a He-Ne laser. There is a case. The alignment wavelength currently in practical use is mostly non-exposure light because it is less susceptible to the semiconductor process.
[0004]
The present applicant has also proposed an alignment apparatus using non-exposure light in Japanese Patent Application Laid-Open No. 63-32303, Japanese Patent Application Laid-Open No. 2-130908, etc. ing. This method is called a non-exposure TTL Offaxis method, and is a method of observing a pattern on a wafer with non-exposure light via a projection optical system that transfers and projects the pattern on the reticle onto the wafer. When observed at the wavelength of the non-exposure light, chromatic aberration occurs in the projection optical system, and the chromatic aberration is corrected by the alignment optical system. On the other hand, there is also a method called a Non-TTL Offaxis method in which a wafer is observed and aligned with a completely independent optical system (Offaxis microscope) without using a projection optical system.
[0005]
As seen in the above-mentioned application, in most of the alignment methods that are actually used at present, an optical image of an alignment mark on a wafer is formed on an image sensor such as a CCD camera, and an electric signal obtained from the image sensor is obtained. A so-called image processing method is employed in which the position of the wafer is detected by processing.
[0006]
[Problems to be solved by the invention]
The above-mentioned non-exposure TTL Offaxis method using image processing by the present applicant is used for an i-line stepper that uses i-line as exposure light, but a projection exposure apparatus that uses an excimer laser as an exposure light source, a so-called excimer stepper. Has not been adopted. This is because, in the case of an excimer stepper, aberration at a non-exposure wavelength in the projection optical system, for example, chromatic aberration at a wavelength of 633 nm is very large. If an alignment method based on image processing in the excimer stepper is to be configured with a non-exposure TTL Offaxis method with a numerical aperture (NA) of 0.2 or more, the alignment correction optical system is as large as the projection optical system. That is, there is almost no possibility in making it into a device.
[0007]
Even if the optical system can be configured with that size, the sensitivity of each optical system, which becomes a variation factor of the baseline indicating the relative relationship between the TTL Offaxis correction optical system and the projection optical system, is increased. For this reason, the non-exposure light TTL Offaxis system, which should be characterized by the baseline stability, has the same drawbacks as the Non-TTL Offaxis system. Of course, although there are advantages in terms of the driving stroke and accuracy of the stage that drives the wafer specific to the TTL Offaxis system, the Non-TTL Offaxis system is more advantageous in terms of configuration in terms of the size of the apparatus. .
[0008]
For this reason, most excimer steppers employ a non-exposure light non-TTL offset method that is not affected by the projection optical system, instead of the non-exposure light TTL offset method described above. In the non-exposure Non-TTL Offaxis system, the distance between the Offaxis microscope and the projection optical system, that is, the temporal variation of the so-called baseline is the main factor of deterioration in accuracy. For this reason, it is necessary for high accuracy to use a member that is not easily affected by heat, or to frequently perform baseline correction.
[0009]
At present, detection using an alignment mark formed by a wafer process is performed. In this case, since the shape of the alignment mark varies depending on the process, there may be a step structure in which image processing is difficult. For example, in a flattening process such as a CMP process, the alignment signal is lowered, and deterioration of detection accuracy and detection rate are problematic.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the alignment method and the exposure apparatus of the present invention form a plurality of notch marks in advance on the periphery of the wafer, use the notch marks as reference marks, and determine the positions of the notch marks as a projection optical system. And a high-precision detection system such as a TTL + TTR exposure light scope that detects through a reticle. Specifically, an exposure apparatus according to the present invention is an exposure apparatus that performs exposure transfer by aligning a pattern on a first object with a pattern on a second object, and a plurality of notch marks formed in advance on the second object. A measurement system that measures the position of
Storage means for storing information on the positions of the plurality of notch marks obtained based on the measurement result by the measurement system in the first exposure process; and the second exposure process after the first exposure process. And determining means for determining the position of the pattern on the second object in the second exposure step based on the measurement result of the measurement system and the information stored in the storage means. The alignment method of the present invention is an alignment method used in an exposure apparatus that aligns a pattern on a first object with a pattern on a second object and performs exposure transfer. The positions of a plurality of notch marks formed in advance on the second object are measured, information on the positions of the plurality of notch marks obtained based on the measurement results is stored, and a second after the first exposure step is stored. In the second exposure step, the positions of a plurality of notch marks formed in advance on the second object are measured, and the second object in the second exposure step is based on the measurement result and the stored information. It is characterized by determining the position of the upper pattern.
[0011]
In general, a wafer is formed with marks such as an orientation flat 1a shown in FIG. 8A and a notch 1b shown in FIG. 8B in order to detect the outer shape. The center of the outline was sought. FIG. 9 shows an example of the mark detection. In this figure, the wafer 1 is rotated by the rotary stage RS, and the line sensor LS receives the light L1 from the light emitting diodes LED arranged in the peripheral portion of the wafer. is there. The position of the orientation flat or notch is detected by monitoring the output fluctuation from the line sensor LS. The position detection accuracy in the configuration shown in FIG. 9 is on the order of several tens of microns. In the configuration of FIG. 9, it is difficult to desire submicron order detection.
[0012]
In the present invention, in order to perform two-dimensional position detection, a plurality of notch marks are arranged around the wafer, and a dedicated detection system is provided for the plurality of notch marks arranged, thereby reducing the problem of detection rate and detection accuracy. It is characterized by solving. Since the plurality of notch marks are marks uniquely arranged on the wafer, if the position of the notch is accurately detected on the exposure apparatus side, the pattern on the wafer is automatically determined according to the notch mark. This method is stable for most processes, and enables highly accurate alignment.
[0013]
Furthermore, it has been found in rare cases that the shape of the notch itself is deformed by the influence of the process during the examination process of the present invention, and an offset of the shift component occurs during detection. Another object of the present invention is to provide an alignment method and an alignment apparatus that enable notch measurement that is not affected by the process. The inventors have found that the notch mark is deformed only at the upper part and the lower part is not easily deformed. Therefore, the present invention is characterized in that only the lower part of the notch mark is detected by a detection system having a detection condition that is not affected by the upper surface.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the detection system for detecting the notch mark with high accuracy includes (1) TTL + TTR detection system, (2) Non-TTL Offset detection system, and (3) TTL Offset detection system. The TTL + Offaxis detection system of configuration (3) is through a projection optical system (this is defined as “TTL”), but if the reticle is defined as “TTR” hereinafter, the reticle is not through (not TTR). It is.
[0015]
FIG. 1 shows a state in which a plurality of notch marks 2, 3, 4 are formed in advance on a wafer 1 to be used for position detection used in the present invention, and FIG. It is a principal part schematic diagram. The alignment apparatus functions as one component of an exposure apparatus for manufacturing semiconductor elements. A plurality of notch marks serve as reference marks, and a plurality of notch marks are arranged for two-dimensional alignment.
[0016]
FIG. 2 shows a so-called TTL + TTR detection system that detects a plurality of notch marks 2, 3, and 4 on a wafer through a projection optical system (TTL) and through a reticle R (TTR). In a detection system that transmits through a reticle (TTR) and detects with exposure light via a projection optical system (TTL), for example, in the case of an i-line stepper, i-line (365 nm) using an ultrahigh-pressure Hg lamp as a light source, Excimer laser oscillation wavelength (248 nm or 193 nm) is used.
[0017]
FIG. 2 shows an example of an excimer stepper. Oscillation light (pulse light) 6 from an excimer laser 5 as exposure light is guided by a fiber 7 and incident on an illumination system 8 of an alignment scope AS as an alignment microscope. The lens 10 and the objective lens 11 are transmitted, and the reticle 12 is illuminated. The light transmitted through the reticle 12 passes through the projection optical system 13 and illuminates the notch mark 2 on the wafer 1.
[0018]
The illuminated image 14 of the notch mark 2 passes through the projection optical system 13, reticle 12, objective lens 11 and relay lens 10, opposite to that at the time of illumination, and becomes an erect image by the erector 15. Image on top. The image 14 is photoelectrically converted by the CCD camera 16 and is captured and processed by a computer 51 including a high-speed image processing electronic circuit to detect the position of the notch mark 2. In this embodiment, the alignment scope AS and the computer 51 constitute a measurement system that measures the notch mark 2.
[0019]
When the position of the notch mark 2 is detected, the XY stage 18 controlled by the laser interferometer 26 moves the wafer 1 to a position where the notch mark 3 can be detected. When the detection of the notch mark 3 is completed, the XY stage 18 moves the wafer 1 to a position where the notch mark 4 can be detected. In this way, the positions of a plurality of notch marks are detected.
[0020]
A reticle mark 19 shown in FIG. 3 is arranged on the reticle 12, and a relative position between the notch marks 2, 3, 4 and the reticle mark 19 is detected. FIG. 4 shows an image when the notch mark 2 is detected, and FIGS. 5 and 6 show images when the notch marks 3 and 4 are detected, respectively.
[0021]
In FIG. 2, reference numeral 20 denotes an illumination system, which illuminates the reticle 12 on which a circuit pattern is formed with exposure light. The projection optical system 13 has a function of reducing and projecting a circuit pattern on the surface of the reticle 12 onto the surface of the wafer 1 by 1/5 times, for example.
[0022]
The wafer 1 is placed on the wafer chuck 21. The wafer chuck 21 is disposed on a θ-Z stage 22 that is a driving means, and adsorbs the wafer 1 to the chuck surface so that the position of the wafer 1 does not shift due to various vibrations. The θ-Z stage 22 is configured on the tilt stage 23 and has a role of moving the wafer 1 up and down in the optical axis direction of the projection optical system that is the focus direction.
[0023]
The tilt stage 23 is configured on the XY stage 18 controlled by the laser interferometer 26 and corrects the warpage of the wafer 1 so as to be minimized with respect to the image plane of the projection optical system 13. Further, the tilt stage 23 can be driven in the focus direction by itself. The bar mirror 25 configured on the tilt stage 23 monitors the driving amount of the XY stage 18 by a laser interferometer 26. The laser interferometer 26 transmits a measurement value relating to the driving amount to the computer 51 through a line.
[0024]
The focus measurement light projecting system 29 and detection system 30 shown in FIG. 2 detect not only the focus but also the tilt of the wafer surface, and the tilt stage 23 corrects the amount using the detection result. The focus measurement value of the surface of the wafer 1 is transferred from the detection system 30 to the computer 51 through a line.
[0025]
The sequence of notch mark detection is first performed at the beginning of the semiconductor element manufacturing process, so-called first mask. The vertical / horizontal magnification of each wafer measured at this time is stored in the storage means in the computer 51 as a unique value for each wafer. In the subsequent second and subsequent steps, the above-described notch mark detection sequence is performed. Since the value at the time of notch detection is stored as a value unique to each wafer, the deformation of each wafer can be traced for each process. The shift component at this time uses an average value of the notch marks 2, 3 and 4. Also, the vertical / horizontal magnification is corrected by reflecting the difference from the vertical / horizontal magnification measured at the time of the above-mentioned first mask as a change in magnification between processes and reflecting it in the driving amount of the XY stage 18 or reticle stage at the time of wafer exposure and the reduction magnification of the projection optical system 13. Then, sequential exposure is performed.
[0026]
In the measurement of the notch mark, not only the X and Y shift components but also the magnification, orthogonality, rotation, shot-related magnification, and rotation of the entire wafer are determined based on the notch mark reference by the determining means in the computer 51 . At this time, if the parameters such as the process magnification for each wafer are stable and constant values, the parameters are determined with the first few sheets without having to remember the measurement values at the time of the first mask for each wafer, The remaining wafer can be exposed by reflecting the determined value at the time of exposure.
[0027]
In TTL + TTR exposure light detection, the reticle and notch mark can be directly measured to detect the relative position between the reticle and the wafer, so that it is not necessary to take into account fluctuations in the baseline between the projection optical system and the microscope in the detection using the Offaxis microscope. The advantages of the exposure light detection system can be utilized. TTL + TTR exposure light detection does not require the use of materials that are not easily affected by heat, as in the case of using an Offaxis microscope, and it is not necessary to frequently perform baseline correction, so that reduction in apparatus cost and improvement in throughput can be achieved. It becomes. Further, since the notch mark is detected, it is not affected by a semiconductor process such as CMP, so that complicated optimization is unnecessary and COO can be improved.
A similar configuration is possible for the Non-TTL Offaxis detection system having the configuration (2) and the TTL + Offaxis detection system having the configuration (3).
[0028]
However, as described above, it has been found that the shape of the notch itself is also deformed due to the influence of the process, and there is a rare case where an offset of the shift component occurs during detection. In order to enable notch measurement that is not affected by the process, the fact that the inventor found that the notch mark is deformed only at the upper part of the mark and the lower part is not easily deformed is used. Therefore, the present invention is characterized in that only the lower portion of the notch mark is detected so as not to be affected by the upper surface. Further, the notch mark carved on the wafer is carved so that the area on the upper side, that is, the front side is smaller than the area on the lower side, that is, the back side.
[0029]
FIG. 7 is an explanatory diagram showing the principle of alignment according to the present invention. The cross section of the wafer 1 has a tapered shape in which the relationship between the upper part (front surface) 62 and the lower part (back surface) 63 is small and the area of the lower part is large. Therefore, the end face 64 of the wafer 1 is not perpendicular to the wafer chuck 21 but is inclined, and the lower surface is always observable when observed from above.
[0030]
A detection system 65 detects the lower part of the notch mark and has an optical depth such that the upper surface 62 and the lower surface 63 cannot be observed simultaneously. Specifically, there are a method of setting the value of 4λFe∧2 representing the optical depth range to a value that is 1/10 or less of the wafer thickness d, and a method of configuring with a confocal microscope. .
[0031]
Hereinafter, for convenience, a method of separating and detecting the lower surface 63 of the wafer 1 from the upper surface 62 will be referred to as separation detection, and a detection system for performing the detection will be referred to as a separation detection system.
[0032]
As described above, since only the upper surface 62 of the notch mark is deformed by the influence of the process, if only the lower surface of the notch mark can be detected separately from the upper surface, it is independent of the influence of the process, that is, a semiconductor such as CMP is formed. A detection system that is not affected by the process can be constructed. In addition, a constant mark called a notch mark can always be observed in this system, which eliminates the need for complex optimization, improves COO, and enables stable and highly accurate alignment. Become.
[0033]
There are (4) TTL + TTR separation detection system (5) Non-TTL Offaxis separation detection system (6) TTL + Offaxis separation detection system and the like for the configuration of the detection system for separating and detecting notch marks with high accuracy. The TTL + Offaxis separation detection system having the configuration (6) is a detection system that passes through the projection optical system (TTL) but does not pass through the reticle (not TTR).
[0034]
The configuration in which the TTL + TTR separation detection system of configuration (4) is applied to the alignment apparatus is basically the same as the configuration of FIG. In the wafer position detection, the positions of a plurality of notch marks formed in the peripheral portion of the wafer are detected by a TTL + TTR exposure light scope. Although the operation of the optical system of FIG. 2 has already been described, the condition of the configuration (4) is that the wavelength λ of the wafer detection system and the NA of the detection system are set to values that can be separated and detected as described above. Another configuration may be a confocal detection system.
[0035]
In this embodiment, since the reticle and the relative position of the reticle and wafer can be detected directly under the three or more notch marks, the fluctuation of the baseline between the projection optical system and the microscope in the detection using the Offaxis microscope is considered. It is possible to take advantage of the TTL + TTR exposure light detection system that is not required.
[0036]
TTL + TTR exposure light detection does not require the use of materials that are not easily affected by heat, as in the case of using an Offaxis microscope, and it is not necessary to frequently perform baseline correction, so that reduction in apparatus cost and improvement in throughput can be achieved. It becomes. In addition, since the notch mark is detected, it is not affected by a semiconductor process such as CMP, so that complicated optimization is unnecessary and COO can be improved.
[0037]
In the non-TTL off-axis separation detection system having the configuration (5), the wavelength of the detection system λ and the detection NA can be separated as described above as in the configuration (4), and the process can be performed by performing confocal detection. An unaffected detection system is achieved.
[0038]
As an application of the configuration (5), in order to obtain the stability of the baseline, it is necessary to have a configuration that is not subject to baseline fluctuations in each wafer. For this reason, two types, a non-TTL Offaxis detection system that performs separation detection and a detection system that has the same optical conditions as the TTL + TTR detection system, are configured. The TTL + TTR detection system is not necessarily a separate detection system. The same notch mark is measured with these two types of detection systems, and the difference between the measured values at this time is taken as an offset. The variation of the offset value corresponds to the variation of the baseline. Next, a notch mark is measured by a TTL + TTR detection system, and exposure is performed in consideration of the offset.
[0039]
Here, the same optical conditions include not only design values such as the detection wavelength, NA, and illumination σ but also the identity of the adjustment state. By setting the same optical condition, the offset value generated in the Non-TTL Offset detection system and the offset value generated in the TTL + TTR detection system when the notch mark is deformed due to the process can be made the same value. .
[0040]
The concept of TIS (Tool Induced Shift) may be used to quantitatively grasp the manufacturing and adjustment state. In the TIS adjustment, an offset (Wafer Induced Shift) generated due to a wafer pattern factor to be measured is separated from an offset TIS generated due to a detection system factor. Measurement is performed in a reference state where the arrangement of patterns to be measured for separation is 0 degrees and two states where the pattern is rotated 180 degrees, that is, the wafer is rotated 180 degrees. The TIS value is determined from the measurement result, and the detection system can be adjusted so as to reduce the TIS value. A proposal using an adjustment method based on TIS was proposed by the present applicant in Japanese Patent Application No. 8-112059 and put into practical use. In order to make the two detection systems compatible, it is essential to adjust the TIS value to a certain small value or less.
[0041]
The TTL Offaxis separation detection system of configuration (6) has the advantages of the above two systems that the baseline is more stable and the alignment wavelength need not be exposure light than the non-TTL Offaxis detection system of configuration (5). It is. However, because of the TTL for detecting non-exposure light, it is necessary to correct the aberration of non-exposure light generated in the projection optical system, and it is difficult to achieve a higher NA than the above two systems. Is effective.
[0042]
The above three detection systems from (4) to (6) have their respective characteristics, but all of them can detect the lower part of the notch mark separately and enable stable high-precision alignment that is not affected by the process. .
[0043]
The configuration of the notch mark is not limited to the three marks 2, 3, and 4 as shown in FIG. 1, but it can be expected to improve accuracy by increasing the number. However, for example, when the number of notches is four, the orientation of the wafer in the rotational direction may not be uniquely determined. In that case, a detection system different from that shown in this embodiment may be provided to detect the orientation in the rotational direction.
[0044]
【The invention's effect】
As described above, according to the alignment method and the exposure apparatus of the present invention can be carried out was cheap boss, a highly accurate positioning.
[Brief description of the drawings]
FIG. 1 is a wafer to which a notch mark according to the present invention is applied. FIG. 2 is a schematic view of the main part of an exposure apparatus equipped with the alignment apparatus of the present invention. FIG. 3 is an explanatory diagram of a reticle mark. [FIG. 5] Detection image of the notch mark 3 [FIG. 6] Detection image of the notch mark 4 [FIG. 7] Explanatory drawing for detecting the lower part of the notch mark of the wafer separately from the upper part [FIG. Mark [Fig. 9] Conventional detection system that detects the position by rotating the notch mark,
[Explanation of symbols]
1 wafer,
2, 3, 4 notch marks,
5 Exposure light source such as excimer laser,
7 Fiber,
8 alignment illumination optical system,
9 Beam splitter,
10 Relay lens,
11 Objective lens,
12 reticles,
13 Reduction projection optical system,
14 Mirror,
15 Electa,
16 CCD camera,
17 Notch mark image formed on CCD camera,
18 XY stage,
19 Reticle mark,
20 Illumination optics,
21 Wafer chuck,
22 θ-Z stage,
23 tilt stage,
25 bar mirror,
26 Laser interferometer,
29 Focus measurement system (projection system),
30 Focus measurement system (detection system),
51 computers,
62 Above the notch mark on the wafer,
63 Below the notch mark on the wafer,
64 wafer end face,
65 Separation detection system

Claims (17)

Oite a pattern of a first object in an exposure apparatus that exposes transferred in register to the pattern on the second object,
A measuring system for measuring the position of a plurality of notches marks previously formed on the second object,
Storage means for storing information on the positions of the plurality of notch marks obtained based on the measurement result by the measurement system in the first exposure step;
Based on the measurement result by the measurement system in the second exposure step after the first exposure step and the information stored in the storage means, the pattern on the second object in the second exposure step A determining means for determining the position;
An exposure apparatus comprising: The notch mark The exposure apparatus according to claim 1, characterized in that formed on the outer peripheral portion of the second object. It said storage means, an exposure apparatus according to claim 1 or 2, characterized in that storing the aspect ratio of the second object in the first exposure step. Said determining means, said second magnification for the entire pattern on the object, orthogonality, rotation, shift component, and for each pattern magnification and at least one of rotating the request of claims 1 to 3, characterized in Rukoto The exposure apparatus according to any one of the above. Information stored in said storage means according to claim 1, wherein said first is obtained based on the measurement result by the measurement system for a plurality of the second object in the exposure step The exposure apparatus according to any one of the above . The measurement system is an exposure apparatus according to claim 1, characterized in that it comprises a detection system for selectively detecting the lower shape of said Bruno Tchimaku. Before Symbol detection system exposure apparatus according to claim 6 optical depth, wherein the smaller again than the thickness of the second object. An apparatus according to claim 6 before Symbol detection system characterized in that it is a confocal detection system. The measurement system includes a detection system that detects the notch mark via a projection optical system for projecting a pattern on the first object onto a pattern on the second object . 8. The exposure apparatus according to any one of items 7 . The measurement system includes a projection optical system for projecting a pattern on the first object onto a pattern on the second object, and a detection system for detecting the notch mark through the first object. The exposure apparatus according to any one of claims 1 to 7 . The measurement system is detected to detect the notch mark through the optical system different from that of the projection optical system without passing through the projection optical system for projecting a pattern on the first object to the pattern on the second object an apparatus according to claim 1, characterized in that it comprises a system. The measurement system includes: a projection optical system for projecting a pattern on the first object onto a pattern on the second object; a first detection system for detecting a mark via the first object; and the projection optics And a second detection system that detects the notch mark via an optical system different from the projection optical system without using a system, and obtaining an offset between detection values of the first and second detection systems. An exposure apparatus according to claim 1, wherein: In an alignment method used in an exposure apparatus that aligns a pattern on a first object with a pattern on a second object and performs exposure transfer,
In the first exposure step, the positions of a plurality of notches marks previously formed on the second object is measured, and stores information about the positions of the plurality of notches marks obtained based on the measurement result,
In a second exposure step after the first exposure step, the positions of a plurality of notch marks formed in advance on the second object are measured, and based on the measurement result and the stored information, A positioning method, wherein a position of a pattern on the second object in a second exposure step is determined . The alignment method according to claim 13, wherein in the first exposure step, the aspect ratio of the second object is stored. In the second exposure step, the magnification for the entire pattern on the second object, orthogonality, rotation, shift component, and from the claims and at least one look characterized Rukoto of magnification and rotation of each pattern 13 Or the alignment method according to 14 . 16. The information on the positions of the plurality of notch marks obtained based on the measurement results on the plurality of second objects in the first exposure step is stored. The alignment method according to item . Measurement of the position of the notch mark before the first and second exposure step, any one of claims 13 to 16 characterized in that by selectively detecting the lower portion of the shape of the notch mark The alignment method according to item .