JPH01101630A - Position detection device in x-ray aligner - Google Patents

Abstract

PURPOSE:To clearly detect sharp alignment marks or the like without causing magnification error or the like by detecting the alignment marks formed on a wafer and a mask with use of a reflecting prism and a chromatic aberration objective lens both disposed outside a X-ray exposure region. CONSTITUTION:A detecting optical system of a position detector device employs a chromatic aberration objective lens 1 and a reflecting prism 3 in a combination thereof. The reflecting prism 3 is disposed at a position in the very close vicinity of a X-ray exposure region and in the very close vicinity of a mask 2 in its height. A light beam reflected obliquely upwardly on the reflecting surface of the reflecting prism 3 is allowed to enter the chromatic aberration objective lens 1. Accordingly, any alignment is possible even during the exposure of X-rays, thereby enabling simultaneous and vertical detection of an alignment mark P formed on the mask and the wafer 2. Hereby, any alignment mark and the like can clearly be detected over a wide range without causing any blurred image and magnification error, assuring accurate positioning.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a position in an X-ray exposure apparatus used in the manufacture of semiconductors that detects an alignment pattern without interfering with exposure X-rays. The present invention relates to an n-detection device.

[Prior Art] In the X IJi M optical system, improvement of throughput and alignment accuracy are cited as challenges, but an alignment method that satisfies these issues is one that allows exposure while detecting the alignment pattern within the exposure field. detection is most desirable.

The currently published alignment methods can be broadly classified into the following two types. That is, (1)! Alignment marks can be detected even in light, making servo control possible even during exposure.

(2) It is impossible to detect alignment marks during exposure;
The objective lens of the detection system is moved back from the exposure area using the cartridge method or during exposure.

The advantages of method (1) above over method (2) will be explained in terms of throughput and alignment accuracy.

In the case of (2) above, during X-ray exposure, the detection device of the cartridge or objective lens must be evacuated from the wafer exposure area, and a time lag is necessarily required due to the movement time, which naturally causes a reduction in throughput. .

In the case of (2) above, the fact that the alignment mark cannot be detected during exposure means that the positional relationship between the mask and wafer is not compensated for during the retraction time of the detection device and the exposure time. In proportion to the length, the mask and wafer positions will fluctuate from the positions originally compensated for by alignment due to vibrations and changes in environmental conditions.

Currently, the exposure time for X-rays is approximately 10 seconds even when the most powerful synchrotron radiation (SOR) is used, which is considerably longer than for optical exposure. During this time, it is extremely difficult to maintain a constant positional relationship between the mask and the wafer, both mechanically and in terms of control. In addition, the drive device of the detection device becomes a source of vibration, which further reduces accuracy.

In this way, detecting alignment marks even during exposure is becoming an indispensable condition for X-ray exposure apparatuses in terms of improving throughput and alignment accuracy.

In addition, in the method (1) above, (1) diffraction grating method (linear Fresnel, circular Fresnel, diffraction grating) and (2) pattern measurement method (bifocal optical WJ microscope).

Oblique detection) can be mentioned.

Since the present invention relates to the pattern measurement method (2) above, this detection method will be explained in detail below.

a. Oblique detection method (for example, Japanese Patent Application Laid-Open No. 61-193448
(Refer to the publication) This is a system in which the objective lens of the detection system is placed outside the exposure area of the wafer with its optical axis obliquely to the wafer surface.This is an excellent method that solves the following two problems. It is something. That is, (1) it is possible to overcome the gap between the mask and the wafer, and (2) it is possible to detect the alignment mark even during exposure without interfering with the exposure XM.

b. Detection method using a bifocal optical microscope (precision machinery V
ol, 51. No. 5 (1985) PP.

156-162) This is a method of simultaneously detecting the positions of the mask and the wafer by bringing an objective lens having a bifocal point using birefringence close to the exposure area of the wafer.

[Problems to be Solved by the Invention] By the way, in the detection system using the above-mentioned bifocal optical microscope, the position of the alignment mark is quite far from the exposure area, and unnecessary redundant areas are placed in the exposure area of the wafer. Space will be required. The width ζ of the space is basically expressed by the following equation.

For example, if the diameter of the objective lens barrel is 30 mm, the extra space will be as large as 15 mm. On the other hand, the maximum exposure area of a wafer is currently 25
Since it is 3 mm square, it can be seen how excessive the extra space is. In semiconductor production, this extra space is the biggest obstacle to reducing throughput.

Next, whether the oblique detection method a is superior in that it can detect alignment marks without interfering with exposure X-rays, or whether it is technically extremely difficult in terms of alignment accuracy. I'm holding it. That is, since it is an oblique imaging method in principle, the problem of image blurring always occurs. As shown in FIG. 2, in an exposure apparatus that irradiates X-rays perpendicularly to the exposure surface 20 of a wafer, the objective lens Ob detects from an oblique direction at an angle θ, and the depth of focus of the objective lens is agm, the imaging range is 2asinO on the mark surface on the wafer, which is very narrow, and it is extremely difficult to obtain sufficient image information for alignment. In particular, when detecting process-formed marks, it is necessary to obtain as much information as possible in order to obtain a high S/N ratio, but detection accuracy equivalent to that obtained with resist-formed marks is insufficient. It is assumed that there is.

By the way, if the aperture ratio of the objective lens is N, A = 0.32, the depth of focus is approximately ±3 pm according to Rayleigh's equation, and if the oblique angle θ is 25 degrees, the imaging range is 2 x 3 lumens. mX
s i n25'' = 2.5 m, which is an extremely narrow range.

Next, as shown in FIG.
Since the imaging plane A"B= is inclined with respect to B, A-+A
If the magnification of ' is βA, and the magnification of B→B' is 3 days, then 1βA
The relationship 1<1βn1 always exists, and it is complicated to create a pattern on a wafer or mask by fully considering this relationship.

Then, the detection objective lens must be placed at a diagonal position outside the X-ray exposure area on the wafer, which inevitably increases the focal length of the objective lens, resulting in a numerical aperture of N.
Since A tends to decrease, it becomes difficult to detect a pattern on a wafer or mask surface with sufficient precision.

Furthermore, due to the design of the detection objective lens, the gap between the mask and the wafer is limited.

As described above, the very simple idea of arranging a normal objective lens obliquely has disadvantages that cannot be overcome to improve alignment accuracy.

[Means for Solving the Problems] This invention uses a combination of a chromatic aberration objective lens and a reflection prism as a detection optical system of a one-position detection device, and the reflection prism is located very close to the boundary of the X* exposure area. It is arranged at a high position and very close to the mask, and allows the light beam reflected obliquely upward on the reflective surface of the reflective prism to enter the L color aberration objective lens.

[Function] Therefore, alignment is possible even during exposure of the wafer to X-rays, and alignment marks on the mask and the wafer can be vertically detected simultaneously by the chromatic aberration objective lens.

[Example] First, a position detection device in an X-ray exposure apparatus of the present invention will be described. The objective lens has chromatic aberration for light rays of different wavelengths, and has different focal lengths for two types of light rays, for example, g-line (input = 435 nm) and e-line (input = 546 nm). Therefore, the image point generated when a mark on the same object point is imaged using gm is different from the image point generated when e-line is used. For example, the focal length of an objective lens with numerical aperture NA±0.49 and magnification n=10 times is Fe==12.5 mm for e-line and 9g-line, respectively.

Fg=12.741mm, and the object distance S is 13.7
The image point distance S″ that occurs when the distance is 5 mm is S″
gm137.5mm, S”e=173.615mm
becomes. Using such an objective lens, the minute distance Sf
The object points, such as the mask and the wafer, are respectively M as shown in FIG.

M', the focal lengths of g-line and e-line are Fg, Fe
Since these are different, the image of the mark on the mask by the two light beams will be formed at point B, and the images of the mark on the wafer will be formed at points B and C, respectively. In other words, due to the 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 the g-line, and the mark on the wafer is an image formed by the e-line.

Now, if we place a detection system such as a television camera at point B and observe it, we will either be able to observe the mark on the mask and the mark on the wafer at the same time, or we will be able to observe them with a blurred image due to chromatic aberration. be done. The image of this blur is filtered using a filter that cuts the g-line and transmits the e-line, and vice versa.
By using a filter that is a combination of filters that transmit the line and cut the e-line, images of the mask and alignment mark on the wafer at different positions at the same point B can be obtained by removing the blurring of each chromatic aberration. It becomes possible to observe. (Unexamined Japanese Patent Publication 1986
196174)) The objective lens used in the present invention is a chromatic aberration objective lens in which the chromatic aberration is produced in the positive polarity and the aberration is well corrected. An example of the optical system specifications is shown in Table 1 below.

(Margin below) 1st-"--!', a3-1 (objective lens.

(including field lenses and relay lenses) The present invention will be described in detail below with reference to FIG. FIG. 1 is an enlarged side view of a part of the position detection device, and the chromatic aberration objective lens l is disposed obliquely outside the X-ray exposure area 2a of the wafer 2. A prism 3 having an apex angle θ is placed close to the wafer 2 so that one ridge 3a is perpendicular to the boundary line of the X-ray exposure area 2a of the wafer 2. This prism 3 has an apex angle of 30°, for example.

The apex Q of the 60'' and 90'' rectangular prisms is spaced 0.4 mm from the surface of the wafer 2, and the slope 3b forms a reflective surface.

The chromatic aberration objective lens 1 has specifications of an aperture ratio NA=0.35, a working distance WD=13, and 9 mm, and the alignment mark P on the wafer 2 is 1-4 mm from the boundary of the 25 mm square X-ray exposure area 2a. They are arranged at one or more distant locations, for example, at four corners of four locations.

Therefore, in this example, the space on the wafer 2 required for detection is 1.5 mm outside the X-ray exposure area of the wafer 2, assuming that the size of the alignment mark P is around 0.1 mm. It is only necessary for one side of . However, the width of 1.5 mm is just an example, and it is possible to make it even shorter if necessary.

The above description has been made regarding an example of measuring the alignment mark P on the wafer 2, but the same applies to a mask placed on the wafer 2.

In this invention, the alignment marks on the wafer and mask are detected by a reflective prism and a chromatic aberration objective lens placed outside the X-ray exposure area, so the chromatic aberration objective lens placed on the reflective optical axis of the reflective prism is Unlike the oblique detection method, the alignment mark can only be observed parallel to the optical axis, so there is no image blurring as described in conventional technology, and there is no need to consider corrections that take magnification errors into account, resulting in sharp images. This makes it possible to clearly detect alignment marks and the like.

[Effects of the Invention] As explained above, according to the present invention, the scribe space provided on the mask and wafer can be made much smaller than that of the conventional one, and the mask and wafer can be inspected from outside the X-ray exposure area using the brown color aberration objective lens. It is possible to observe the upper alignment marks etc. at the same time.
Servo control can be performed even during exposure. Additionally, compared to the oblique detection method, it is possible to detect a clear and wide range without causing image blur or magnification errors.
It is possible to perform accurate positioning.

[Brief explanation of the drawing]

FIG. 1 is an enlarged side view of a part of the position detection device of the X-ray exposure apparatus according to the embodiment of the invention, FIG. 2 is an explanatory diagram of the depth of focus in the oblique detection method, and FIG. is an explanatory diagram of image blur and magnification error, and Fig. 4 is an illustration of image blur and magnification error.
FIG. 2 is an explanatory diagram of a chromatic aberration objective lens. l...Chromatic aberration objective lens 2...Mask, Yaeha-3-...Prism P...Alignment mark patent applicant Sub-agent Sumitomo Heavy Industries, Ltd.
Koyama 1) Hikari Mistake 1 Figure 2 Figure 3 Figure 4 Procedure amendment (voluntary) dated February 20, 1988

Claims (1)

[Claims] A position detection device for a mask and a wafer in an X-ray exposure apparatus, in which a combination of a chromatic aberration objective lens and a reflection prism is used as a detection optical system, and the reflection prism is located extremely close to the boundary of an X-ray exposure area. The X-rays are arranged at close positions and very close in height from the mask, and are arranged so that the light beam reflected obliquely upward on the reflective surface of the reflective prism is made to enter the chromatic aberration objective lens. Position detection device in exposure equipment.