JPH03135009A - Alignment system with wide detection angle of field and high accuracy - Google Patents

Abstract

PURPOSE:To align a mask with a wafer in an X-ray stepper aligner with superhigh accuracy and satisfactorily by a method wherein detection devices whose required angles of field are different are used properly according to whether a fine alignment operation or a coarse alignment operation is executed. CONSTITUTION:On alignment stages 11a to 11d around a base plate 13, the following are mounted in a cross-shaped manner so as to surround an X-ray exposure beam 12: three sets of detection devices 15 to 17 of an SFZP system for fine alignment use which are used to detect X, Y and theta; and one set of detection devices 14 of a wide-angle-of-field and double-focus system. A mask which has been positioned mechanically is aligned with a wafer by using the coarse alignment devices 14. When this wide-angle-of-field alignment operation is completed, a final fine alignment operation is executed by using the devices 15 to 17; the mask is aligned with the wafer with ultrahigh accuracy and satisfactorily; an exposure operation is executed by using the exposure beam.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultra-precision position detection device, and particularly to a position detection device capable of detecting the position of a mask and a wafer in an X-ray stepper exposure device on the order of 0.01 μm.

[Technical Background] The inventor of the present invention has developed a chromatic aberration double focus device (Japanese Patent Application No. 196174/1988) and a relative position detection device using a fan-shaped Fresnel zone plate (Japanese Patent Application No. 202857/1989) as ultra-precision position detection devices. has been applied for.

The inventions of these earlier applications will be briefly explained below with reference to the drawings.

The former "chromatic aberration bifocal detection device" uses an objective lens with Hosochi chromatic aberration to detect a mask and a wafer (40 μm).
The mask and wafer are simultaneously detected with high lens resolution by epi-illuminating the mask (separated by m) and imaging the mask using G-line light and the wafer using E-line light on the same plane. This allows the positions of both to be determined with high precision.

-M, the objective lens has chromatic aberration for light rays with different wavelengths, for example, g-line (n = 435 nm), e-line (n =
It has different focal lengths for the two types of light beams (546 nm). Therefore, if the mark on the same object point is g
The image point formed using line light is different from the image point formed when e-line light is used. For example, opening number NA=0.4. The focal length of the objective lens with magnification n = 10x is Fe = 12.5 mm for e-line and 1g-line light, respectively.
Fg=12.741mm, and the image point distance S'' that occurs when the object point distance S' is 13°75mm is S
″g=137.5mm, S″e=137.615mm.

Using such an objective lens, if the object points separated by a minute distance S, for example, the mask and the wafer, are located at M and M', respectively, as shown in FIG. Since the focal lengths Fg and Fe of the lights are different, the image of the mark on the mask by the two light beams is
The images of the marks on the wafer are B,
This will occur at point C, respectively. In other words, due to the axial chromatic aberration of the objective lens system, the images of the mark on the mask and the mark on the wafer are formed at the same position at point B. However, the mark on the mask is an image formed by g-line light, and the mark on the wafer is an image formed by e-line light. Now, if we place a detection system such as a television camera at point B and observe it, we can observe the mark on the mask and the mark on the wafer at the same time, but due to chromatic aberration, each mark is observed with a blurred image. be done. A pattern barrier filter that combines a filter that cuts G-line light and transmits E-line light and a filter that transmits G-line light and cuts E-line light is used to capture this blur image. By removing the blurring caused by each chromatic aberration, it becomes possible to simultaneously observe the images of the alignment mark on the mask and the alignment mark on the wafer, which are located at different positions at the same point B. The objective lens used in the former invention is a chromatic aberration objective lens that actively generates axial chromatic aberration in this way and has well corrected various aberrations.

In the above invention, since a pattern barrier filter is required, there are problems that the detection device is expensive and adjustment is time-consuming. For this reason, the inventor of the present application has developed an improved detection system that does not require a pattern barrier filter.
It has been filed as No. 261379.

On the other hand, the latter "relative position detection device using a sector Fresnel zone plate" uses a sector-shaped Fresnel zone plate (
Hereinafter, it will be referred to as SFZP. ), and an illumination device is configured to simultaneously illuminate these SFZPs from the same direction with light of multiple wavelengths,
The SFZPs of these mask marks and wafer marks are illuminated with light of different wavelengths, each SFZP is configured so that the diffraction focal planes from these SFZs and P coincide at least in one wavelength, and an objective lens having chromatic aberration is used to illuminate the SFZPs of the mask mark and wafer mark. The diffraction focal images of each of the SFZPs mentioned above are superimposed on the same imaging plane, and the images of the mask mark and wafer mark are one-dimensionally scanned by a linear sensor to detect their relative positions. It is. Incidentally, the inventor of the present application has filed an application as Japanese Patent Application No. 1-125267 for an improved detection system that has sufficient accuracy on the order of 001 μm using a shell microscope objective lens without using such a special chromatic aberration objective lens. .

[Problems to be Solved by the Invention] By the way, the above detection device is used as a mask and wafer in an aligner proximity exposure apparatus (hereinafter referred to as an aligner) that uses SOR light (synchrotron radiation light) as a radiation source. When applying the present invention to a relative position detection device (hereinafter referred to as an alignment device), the following problems will occur if the latter position detection device based on SFZP is selected.

That is, compared to the former chromatic aberration dual focus detection device, the SFZP
Since the size of the alignment mark consisting of is large, if the detection field of view is the same, the detection field of view will be reduced to several minutes due to mutual interference of light from the mask and wafer SFZP.

This point will be explained in more detail below with reference to the drawings.

Figures 3 (A) and (B) show the chromatic aberration bifocal device and SFZ.
FIG. 3 is a plan view showing an example of the arrangement of alignment marks in a detection device using P. Both have mask mark 1
, 1a are arranged on both sides of the wafer marks 2, 2a. Then, an alignment detection signal is obtained by scanning an image of these marks enlarged by an enlarging optical system one-dimensionally from right to left using, for example, a CCD.

The detection field of view by the magnifying optical system is a rectangular area with width A and length B, and the distance between the left and right wafer marks is W and the wafer S.
When the maximum horizontal width of FZP is H and the maximum horizontal width of mask SFZP is I, the detection range of each is as follows.6 Chromatic aberration double focus method: Mask sandwiched between two wafer marks 2.2 Since mark 1 can be easily detected and distinguished from wafer mark 2, its detection range is W. Further, the interval W between the wafer marks 2, 2 can be freely widened within the range of the width A of the detection field of view.

SFZP method: It is necessary to set the interval between the wafer marks 2a, 2a in such a range that the SFZP of the mask mark 1a and the SFZPs of the wafer marks 2a, 2a on both sides do not cause mutual interference of diffracted light. In the area of interference, the spot size and intensity of the Fresnel diffraction image change, which changes the alignment signal waveform and reduces position detection accuracy. Therefore, in this case, the detection range cannot be set to the interval W between the wafer marks 2a, 2a, and the detection range is determined as follows using the width H and ■ of the SFZP of the mask mark 1a and the SFZP of the wafer mark 2a. (
1) is expressed by the following equation.

Detection range = ±(W-H-I)/2... (1) Comparing the two with reference to the inventor's experimental results, W = 103 um and SF for the chromatic aberration bifocal detection device.
In the ZP type detection device, W=±5.5 gm (width: llum).

Therefore, compared to a chromatic aberration bifocal detection device, S
It can be seen that the detection range of the FZP type detection device is reduced to 1/10 or less. This comparison shows that the SFZP type detection device has a problem in that the detection range is extremely narrow compared to the chromatic aberration bifocal device.

This has a problem that must be taken into account as a problem in selecting a detection device for the first rough position detection, so-called coarse alignment, which is performed when detecting the relative position between the mask and the wafer.

Here, we will discuss a coarse alignment device in the case where an SFZP type detection device is used for highly accurate fine alignment.

Coarse alignment is the first adjustment performed primarily after the mask and wafer are set in a predetermined position by rough positioning, for example, on the order of 400 μm, such as handling. This requires the ability to detect a wide field of view that is mechanically set in advance, and the accuracy is required to be within the detection range of the secondary precision alignment, so-called fine alignment. Ru. - As an example, the specifications required of the coarse alignment device in the chromatic aberration double focus detection method are: (1) Detection range≧400 um + (2) Detection accuracy≦26 am (103 um/4, where 4 is a safety factor). A detection device that satisfies these two specifications is
For example, a magnifying optical system with a numerical aperture of 0.1 or less and a detection magnification of around 10x can be used, and the signal processing can be done using an extremely simple Al Prism6.
Next, the specifications required for the coarse alignment device in the case of the SFZP method detection device are: ■Detection range ≧
400μm, ■Detection accuracy ≦±1.3am C5-5am
/4+ where 4 is the safety factor).

If we consider the case where a detection device that satisfies these two is, for example, a course alignment device (the above-mentioned magnifying optical system) used in a color U-difference bifocal device, detection accuracy becomes an obvious problem. Furthermore, the signal processing algorithm becomes complicated.

In other words, the coarse alignment device in the SFZP method has the same detection range as the chromatic aberration method, and
You will need something with a precision of around 0x. Furthermore, the performance of this coarse alignment has a great influence on the throughput in the aligner. The throughput here represents the number of wafers that can be processed by the aligner per unit of time.

Aligners are normally operated automatically, but if, for example, the coarse alignment fails, that is, the coarse alignment accuracy is insufficient and the mask and wafer cannot be aligned within the detection range for the next fine alignment, Automatic operation is immediately stopped and the system switches to manual operation, waiting for human intervention. This time becomes an extremely large loss time in the overall throughput.

This invention was made in view of the above points, and
It is an object of the present invention to provide an alignment system with a wide detection field of view that can detect the positions of a mask and a wafer in a line stepper exposure apparatus with high precision.

[Means for Solving the Problems] In the present invention, in an alignment device in an aligner that requires proximity exposure, a chromatic aberration double focus device and an SFZP detection device are used as a position detection device for detecting the relative position of a mask and a wafer. The above-mentioned chromatic aberration bifocal device is used for coarse alignment that requires a wide detection field of view, and the fan-shaped Fresnel zone plate (SFZP) detection device is used for subsequent fine alignment that requires high detection accuracy. This is an alignment system with a wide detection field of view and high density, which is characterized by precisely aligning the mask and wafer.

[Example] Hereinafter, the present invention will be described in detail based on the drawings. FIG. 4 is a side view of the experimental apparatus when using the SFZP method as fine alignment. The X-ray mask 4 and the wafer (well mark) 5 are arranged vertically facing each other with a gap of 51 um. x is mask 4 to 0.
The relative position when moving at a pitch of OILLm is magnified and imaged by the chromatic aberration bifocal device 6, and detected by the CCD 7.

FIG. 5 shows the detection accuracy obtained when the detection magnification of the chromatic aberration bifocal device 6 is 140 times. The resolution at this time (3
o) is 0013 μm.

FIG. 6 shows the detection accuracy obtained when the detection magnification of the chromatic aberration bifocal device 6 is 52.5 times. The resolution at this time (
3o) is 0.040 μm.

From these facts, the detection magnification becomes 1/3, which means that the resolution is 52.
It can be seen that the value has decreased by about 3 times to 0.04 am, which is 5 times as much.

Next, based on these experimental results, the detection range was increased to 400 um.
Let's find the resolution when Assuming that the detection magnification and resolution are simply linearly and inversely proportional as described above, the detection range will be as shown in Table 1 below.

Table 1 From this table, if the detection magnification is increased to 30 times, SFZP
The detection range is 560 μm x 4, which is sufficient for this type of detection device.
A detection field of view of 20 tLm is obtained. The resolution at this time was 0.01 am, which was ±1.3 μm without any problem.
It becomes possible to perform alignment with the following predetermined coarse alignment detection accuracy.

Next, a configuration in which the SOROR tear aligner is actually installed in a proximity exposure apparatus (aligner) will be described. 1 and 2 show a plan view and a side view of an aligner equipped with an SFZPIllll detection device for fine alignment and a chromatic aberration bifocal device for coarse alignment. Alignment stages lla, ll around the central base plate 13
b.

11c, the lid includes three sets of SFZP type detection devices 15, 16, and 17 for detecting the X, Y, and θ directions, and a set of bifocal devices 14 for course alignment, which are located in the central X-ray exposure light area 12. They are each attached in a cross shape surrounding the

As an alignment procedure, first, after mechanical positioning is completed, coarse alignment is performed by the chromatic aberration bifocal device 14, and the zero-order and SFZ alignment steps are performed to position the mask and wafer within a predetermined alignment accuracy.
Final fine alignment is performed using the P detection device 15° 16.17 to provide precise relative positioning of the mask and wafer.

As soon as the positioning of the mask and wafer is completed in this way, exposure with X-ray exposure light 12 starts from an X-ray source (not shown). During this exposure, in order to compensate for the relative position of the mask and wafer, the SFZ
Alignment is continuously performed by the P detection device 15°16.17, and control is performed to apply feedback.

[Effects of the Invention] As explained above, in this invention, by using a chromatic aberration bifocal device for coarse alignment and a detection device using SFZP for fine alignment, it is possible to simultaneously satisfy the detection field of view and detection accuracy. This makes it possible to reliably perform high-precision alignment, creating an extremely reliable alignment system that guarantees high throughput.

[Brief explanation of the drawing]

1 and 2 are a plan view and a side view showing a wide detection field of view and high precision alignment device according to an embodiment of the present invention, and FIGS. 3(A) and 3(B) are a chromatic aberration bifocal device and an SFZ
A line diagram for explaining the detection field of the P detection device, FIG. 4 is a side view showing an experimental device for applying a chromatic aberration bifocal device to course alignment, and FIGS. 5 and 6 are experimental results. FIG. 7 is a ray diagram in the paraxial region for explaining the chromatic aberration objective lens. Fig. 1 3 11a, llb, llc, lid... Alignment stage 12... X-ray exposure light 13... Base plate 14... Chromatic aberration double focus detection device

Claims (1)

[Claims] In an alignment device for an aligner that requires proximity exposure, a dual focus detection device and an SFZP detection device are provided as a position detection device for detecting the relative position of a mask and a wafer,
For coarse alignment, which requires a wide detection field of view, the chromatic aberration dual focus detection device is used, and for subsequent fine alignment, which requires high detection accuracy, a fan-shaped Fresnel zone plate (SFZP) detection device is used. A wide detection field of view and high-precision alignment system that is designed to accurately align the mask and wafer.