JPS6174338A - Optical alignment device - Google Patents

Abstract

PURPOSE:To easily perform a highly accurate position-detection and alignment by a method wherein a position-detection in a wide range on the surface of the material to be observed is performed using a plurality of slit images, and an average position is detected. CONSTITUTION:A trial printing is performed by vertically moving a wafer 2 microscopically. The position of the wafer 2 at the most excellent condition of resolution is memorized in a memory storage as the data of the position x1, x2, x3, ... xn of the slit image 5'b on a sensor 12. Then, a slit image 5b is projected and image-formed on the newly set wafer 2. Based on the above- mentioned image, a focusing is performed by vertically moving a wafer stage 16 in such a manner that the slit image 5'b to be image-formed on the sensor 12 will be brought to the position indicated by the positional data x1, x2, x3, ...xn in the memory storage. As a result, a position detection and an alignment can be performed easily in a highly accurate manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical alignment device, and in particular to a reduction lens of a reduction projection exposure device used for printing circuit patterns such as LSI on semiconductor wafers. The present invention relates to an optical alignment device suitable for focus detection and focusing on a wafer.

[Background of the invention]

Conventionally, in a method of detecting and aligning the surface of an object to be observed, such as an LSI pattern on a semiconductor wafer, by detecting a positional shift with respect to the focal point, a cross section of about 3 mm x O, 1+u+ is formed on the surface of the object to be observed. A single elongated light beam is irradiated obliquely, and the reflected light from the surface of the object to be observed is photoelectrically converted to detect the optical axis position of the reflected light. However, when detecting the surface of an object to be observed using a light beam with such a small cross-sectional shape, it is possible to detect irregularities in the surface shape of the object, or the reflectance of the surface may vary within a minute area. This has the disadvantage that accurate position detection and alignment become difficult due to the influence of the surface condition.

Japanese Unexamined Patent Publication No. 56-42205 discloses one solution to this problem, in which the elongated direction of the beam cross section on the surface of the object to be observed is
Although methods have been disclosed for irradiating a light beam in a direction that is not affected by the surface shape of the surface of the object to be observed, the reality is that this is not yet a sufficient solution. It is difficult to detect warps, undulations, tilts, etc. on the surface of the object to be observed, and if the object is translucent, there is a difference between the light beam reflected from the surface and the light beam that enters the interior and is reflected at the boundary with the layer below. There is also a light beam that comes out again, but if these are mixed, the detection light will not be uniform, and the problem of deterioration of detection accuracy remains unsolved.

[Purpose of the invention]

The object of the present invention is to solve the problems of the prior art mentioned above and solve the problems of the prior art. An object of the present invention is to provide an optical alignment device capable of highly accurate position detection and alignment regardless of the surface shape of a ritual object.

[Summary of the invention]

The optical alignment device of the present invention for achieving the above-mentioned object includes: an irradiation optical system that lines up and irradiates a plurality of light beams with a predetermined cross-sectional shape onto a limited surface area spread over the surface of an object; A photoelectric conversion means for receiving the reflected light of each irradiated light on the surface area, a position detection means for detecting the position of the optical axis of each reflected light received by the photoelectric conversion means, and a position detection means for detecting the position of the optical axis of each reflected light received by the photoelectric conversion means; and a displacement means for moving the object to be observed according to the position of the optical axis of each reflected light.

By position detection using multiple slit images! Even if the surface shape of the object to be inspected has, for example, unevenness or warpage, the average position can be detected.

[Embodiments of the invention]

An embodiment in which the present invention is applied to a focusing device of a reduction projection exposure apparatus will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram showing an embodiment of a focusing device, and shows an optical/mechanical system for aligning a wafer 2 to the focal position of a reduction lens 1. As shown in FIG.

In FIG. 1, a laser beam from a laser light source 3 is expanded by a beam expander 4 in the direction of the plane of the drawing to form a flat beam, and the beam is made incident on a slit 5. The light having an elongated cross section that has passed through the slit 5 is incident on the first reflecting mirror 7 via the second lens 9, and the optical path is bent by the mirror 7 in a direction perpendicular to the elongated direction of the cross section of the light beam, and the light beam is directed onto the wafer 2. An image 5' of the slit 5 is projected and formed onto the wafer 2 by irradiating the light obliquely from above. The optical path of this slit image 5' is bent by a second reflecting mirror 8, and an image is formed in front of the objective lens 10 by a second lens 9. The slit image at this position has the same shape as the image at the slit 5 position. The objective lens 10 is for further enlarging this slit image, but since the field of view of the objective lens 10 is limited, the first cylindrical lens 11 is arranged in this example to compress the slit image in the longitudinal direction. It is. The slit image magnified by the objective lens 10 is projected onto a linear image sensor I2 such as a CCD, but in this case as well, since the light receiving part of the sensor 12 is a narrow window, a second cylindrical lens 13 is arranged, All of the slit images are compressed and projected onto the light-receiving pixel array of the sensor 12.

FIG. 2 shows the shape of the slit at each imaging position in the example of FIG. (′
It is projected and imaged as a slit image 5a expanded in the width direction as shown by D, and in front of the objective lens 10 is formed as a slit image 5'a compressed in the longitudinal direction by the cylindrical lens 11 as shown by ■. Also, on the linear image sensor 12, as shown in (2), the slit image 5'a expanded by the objective lens 10 is compressed in the cylindrical lens 13 in the slit image 5'a, which is projected and imaged. .

One slit image 5a formed on the wafer 2 in FIG.
This shows the difference in the detection position due to the difference in the irradiation position. For example, if the surface of the wafer 2 has an uneven shape as shown in FIG. 3, the photoresist 14 applied thereon will also have a surface shape that follows the uneven shape. When detecting the surface of the resist 14, if the slit image 5a is small, if the concave part is detected with the light beam shown by the solid line and aligned with the focal position of the reduction lens 1, and thereby exposure is performed,
Since the surface part (convex part) is shifted from the focal position, there is a risk that the resolution may be poor in some parts, and conversely, if the convex part is detected with the light beam shown by the dashed-dotted line, the concave part will be detected. This will cause a shift in focus. Further, if the wafer 2 is tilted with respect to the optical axis of the reduction lens 1, exposure can be performed with high resolution at the focus detection position, but there is a risk that other locations may be out of focus and may even be unable to be resolved.

According to the present invention, as shown in FIG. 4, a plurality of slit images 5a are simultaneously projected and formed on the surface of the wafer 2, and the average position of each slit image is set as the in-focus position, thereby eliminating the above-mentioned defocus. It will be resolved.

FIG. 5 shows the configuration of essential parts when the present invention is applied to a plurality of slits 5 in the apparatus shown in FIG. A multiple slit 1 in which a plurality of slits 5 are arranged in parallel in this way
5, a parallel slit image 5b in which the width direction of the slit 5 is enlarged is projected onto the wafer 2 by the second lens 9.

This parallel slit image 5b is formed by the second lens 9 in front of the objective lens as an image 5'b reduced in the slit longitudinal direction. The slit image 5'b, which has been enlarged by the objective lens 10 and compressed in the slit length direction by the second cylindrical lens 13 in the same way as described above, becomes a parallel slit image 5 on the linear image sensor 12, as shown in the upper part of FIG. 'b is projected and imaged as a column, and the output of the sensor 12 at that time is as shown in the lower part of FIG.

Generally, when focusing in a reduction projection exposure apparatus, a trial printing is performed to determine the in-focus position.

This is done by positioning the wafer 2 using this as a reference position. That is, the wafer 2 is placed at a very small distance (0.5 μm
The position of the wafer 2 when the resolution is the best is determined based on the data of the position Xi, X2. Then, the slit image 5b is projected onto the newly set wafer 2, and the slit image 5b is thereby formed on the sensor 12.
"b is position data XI in the storage device, X2.X
3. ...The wafer stage 16 is moved up and down so that it comes to the position represented by Xn, and focusing is performed. The position of the slit image 5''b is determined by setting a threshold value Th for the output of the sensor 12, finding the pixel 20 of the sensor 12 corresponding to the threshold value, as shown in an enlarged view in FIG. The value may be set to the position of the slit image 5"b.1゜In the example in Figure 5, multiple slits 5 are lined up only in the X direction, but in Figure 8, multiple slits 5 are lined up in the two directions of XY. An example using multiple slits 17 in which slits 5 are lined up is shown.

In this case, the area image sensor 1 is used as the photoelectric converter.
8 is used. in this way.

By providing the slits 5 in the XY directions, even the inclination of the wafer 2 can be detected and aligned. In this case as well, the in-focus position is determined in advance by trial printing as described above, and the position of the slit image 5'b on the area image sensor 18 at that time is stored in the memory. , as shown in FIGS. 9(a) and 9(b), the position of the slit image 5b projected and imaged on the wafer 2 (this is equivalent to the position of the slit image 5'b projected and imaged on the sensor 18). ), it is also possible to detect the inclination, or posture, of the wafer 2. In FIG. 9, (a) is the in-focus position, and (b) is the vertical inclination in the X direction.

When the focus is in the Y direction, (C) is in focus in the X direction, and when there is a vertical tilt in the Y direction,
(d) shows a case where there is vertical inclination in both the X and Y directions.

In addition to the detection system described above, if the wafer is placed on a stage with a holder whose tilt can be adjusted, extremely high precision focus detection and focusing can be achieved.

Next, the incident angle and polarization direction of the light beam irradiated onto the wafer 2 will be explained with reference to FIGS. 10 and 11.

When the photoresist 14 is applied to the wafer 2, the traveling direction of the light is as shown in FIG. There is light that enters, light that is reflected within the resist 14, and light that enters the underlayer 19. If the light is reflected only by the surface of the resist 14, the linear image sensor 12 or the area image sensor 18 can detect the focused position on the resist surface. However, the base layer 1
If there is reflected light from 9, it may not be possible to accurately determine which position is being detected on the sensor 6
Therefore, it is necessary to make the reflectance on the surface of the resist 14 as high as possible, and for this reason, it is preferable that the angle of incidence of the light beam onto the wafer 2 be set to 70° or more, and that the incident light beam be S-polarized.

(Effects of the Invention) As described above, according to the present invention, since position detection is performed over a relatively wide range on the surface of the object to be observed, the surface shape of the object to be observed may have irregularities, warps, undulations, etc. In addition, as a method for detecting the average position over a wide range, a plurality of elongated beam slits are waved to form an image on the surface of the object to be observed, and the slit image is This method uses a method to optically guide and detect the light onto the light-receiving surface of the photoelectric conversion element, making it possible to detect the position and orientation of the object to be observed from the slit image position on the light-receiving surface. By using it for focus detection and focusing of the reduction lens of the device, it is possible to achieve highly accurate printing of a reticle image onto a wafer, thereby improving the yield of LSI products and achieving higher integration.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of an optical/mechanical system showing an embodiment in which the present invention is applied to a focus detection/focusing device of a reduction projection exposure apparatus, and Fig. 2 shows the shapes of slit images of various parts in Fig. 1. FIG. 3 is a conceptual diagram showing the deviation of the focus detection position when the detection area is minute, and FIG. 4 is a conceptual diagram showing the detection of the average focal position using a plurality of slit images according to the present invention. , FIG. 5 is a block diagram of the main parts showing the multiple slit system according to the present invention, and FIG. 6 is a distribution of outputs with respect to sensor pixel positions with attached slit images projected onto the light-receiving surface of the linear image sensor. FIG. 7 is a diagram showing the output distribution for sensor pixel positions enlarged by enlarging one slit in FIG. Figure 8 is an overall configuration diagram of a focusing device with slits provided in two directions, X and Y, and Figures 9 (a) to (
d) is a conceptual diagram showing the state of the posture of the object to be sacrificed according to the method shown in FIG. The figure is a diagram showing changes in reflectance on a resist due to differences in incident angle and polarization. DESCRIPTION OF SYMBOLS 1... Reduction lens, 2... Wafer, 3... Laser light source, 5... Slit, 6... 1st lens, 9...
Second lens, 10...Objective lens, 12...Linear image sensor, 13...Second cylindrical lens, 14...
・Photoresist, 15...Multiple slits, 16...
・Wafer stage, 17...Multiple slits, 18...
・Area image sensor. Agent Patent Attorney Tadashi Akimoto Figure 1 Figure 2 Figure 3 Figure 5 Figure 6 Figure 7 Mao Todoroki Echo Figure 8 Figure 9 (a) (b) (c)
(d) ≧ = 100% Fig. 11

Claims (1)

[Claims] 1. A light beam with a limited cross-sectional shape is irradiated onto the surface of the object to be observed, and the optical axis position of the reflected light is detected to perform relative positioning with respect to the focal point of the object to be observed. The optical alignment device includes: an irradiation optical system that irradiates a plurality of light beams side by side on a surface area spread over a surface of an object to be observed; a photoelectric conversion means that receives reflected light of each of the irradiation light beams on the surface area; a position detection means for detecting the position of the optical axis of each reflected light received by the photoelectric conversion means; and a displacement means for moving the object to be observed according to the position of the optical axis of each reflected light detected by the position detection means. An optical alignment device comprising: 2. Optical alignment according to claim 1, wherein the irradiation optical system has at least two elongated parallel slits, and images of the parallel slits are formed on the surface of the object to be observed. Device. 3. The optical alignment device according to claim 1, wherein the photoelectric conversion means has an enlarged projection lens in front of the light receiving surface for enlarging and receiving the light beam on the surface of the object to be observed. 4. Claim 1, wherein the irradiation optical system has at least two elongated parallel slits arranged in one direction, and the photoelectric conversion means has a linear image sensor that scans in one direction corresponding to the said direction. The optical alignment device described. 5. The irradiation optical system has at least two elongated parallel slits arranged in one direction and at least two other parallel slits arranged in a direction perpendicular to the said direction, and the photoelectric conversion means The optical alignment device according to claim 1, comprising an area image sensor whose light receiving surface corresponds to a plane including a direction. 6. The position detection means is provided with a storage means for storing detection results, and the relative displacement position of the position detection result is given to the displacement means using the past detection results stored in the storage means as a reference value. The optical alignment device according to item 1. 7. The light beam irradiated from the irradiation optical system is S-polarized light,
The optical alignment device according to claim 1, wherein the angle of incidence on the surface of the object to be observed is 70° or more.