JPS60115225A - Observation apparatus - Google Patents

Abstract

PURPOSE:To enable to scan an alignment mark in the direction at the right angle to the arranging direction thereof and observing it with natural condition by providing a 90 deg. image rotator to any one of the first and second optical systems. CONSTITUTION:The light from the laser 1 is scanned in lateral by a rotating polygonal mirror 3. The scanning lights 110 spatially divided by a prism 25 is rotated for 90 deg. in the scanning direction by 90 deg. image rotators 7, 7a. The scanning light sent from the image rotators 7, 7a passes a lens 8, a beam spliter 9, an objective lens of microscope 11 and scans in vertical an alignment mark F of reticle 12 and also scans in vertical an alignment mark of wafer 13. The light reflected from the alignment mark of wafer 13 and reticle 12 lighted by the scanning beam and light for lighting enters again the objective lens 11. Thereby, the alignment marks of reticle and wafer are read by a light detector 18.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an observation device for observing alignment marks during alignment of objects, and an aligner for manufacturing semiconductor devices using this observation device.

The well-known Toshie O and L8 constructions are manufactured by overlapping several layers of double-rudder circuit patterns. As semiconductor devices become faster and more dense, the line width of circuit patterns continues to become smaller).

Accordingly, high overlay accuracy on the order of submicrons is required. A step-and-repeat type aligner called a stepper, for example, is known as an aligner that can accommodate such high precision and miniaturization.

The stepper projects and transfers the pattern on the reticle onto the wafer at reduced or equal magnification. In this case, the exposure area is limited due to constraints on the optical system that performs projection transfer. In order to expose the entire surface of the wafer, the pattern is printed, the wafer is moved in steps, and the pattern is printed on a new area of the wafer, which is repeated. As wafers become larger and larger, the number of steps required increases and processing time increases. On the other hand, in order to sequentially print patterns with a stippler, the reticle and the area of the wafer must be aligned relative to each other prior to printing. The method by which alignment is performed is extremely important in terms of alignment accuracy and alignment time. The method of aligning the reticle with the area of the wafer is the Offer/Xis method, which first positions the reticle at a location away from the printing position, and then relies on the accuracy of the laser interferometer to carry out the printing. There is a way to go. However, although this method is high-speed, it is not possible to directly check the alignment state at the position where the printing is performed, it is not possible to deal with the non-linear physical expansion and contraction of the wafer that occurs as the process progresses, and the stage The disadvantage is that the accuracy of the movement monitor becomes a factor of error.

On the other hand, there is a TTL method in which the wafer is observed through a projection optical system at or near the position where printing is actually performed, and the reticle and wafer are aligned. When the TTL method is used, it is possible to avoid the effects of the wafer distortion and stage accuracy described above, so it is expected that the alignment accuracy between the reticle and the wafer will be improved.

Regarding the TTL method, a method using laser beam scanning is known as a conventional technique.

JP-A-54-55562, filed by the present applicant, is one example. FIG. 1 shows a simple embodiment of this method, in which the light from one laser light source 1 is divided into two left and right objective lenses 11, and the reticle 12 and wafer 13 are separated at two locations. Detect positional deviation. By detecting the amount of misalignment at two locations, two types of misalignment, parallel translation (x+y) and rotation) can be corrected by moving either the reticle or the wafer relative to the center.

In the figure, 1 is a laser, 2# is a condenser lens for focusing the t laser system, 3 is a rotating polygon mirror, 4 is a #'if-θ lens, and 5 is a beam splitter.

The light emitted from the laser 1 scans according to the rotation of the rotating polygon mirror 3, and the beam splitter' -5 or less +7) Optical system 4
I'm going in. 6 field lenses, 25 is a field-of-view dividing prism. J's A25 divides the scanning laser beam into two optical paths 1. At this point prism 25
It can be said to be a field-of-field and space-dividing prism. 7
is the polarizing beam sinter 18 is the relay lens, ? Fi
The light reflected or passed through these members by the beam splitter enters the objective lens 11, forms an image on the object surface, and performs scanning. The system from the pupil imaging lens 14 to the detector 18 is a photoelectric detection system. Reference numeral 15 denotes a color filter and a 16Fi spatial frequency filter, which serves to rapidly cut off specularly reflected light and output scattered light for photoelectric detection. 17 is a condenser lens. A light source 19 and a condenser lens 20% color filter 21 constitute an illumination-optical system, and an erector 22
, the eyepiece lens 23 constitutes an observation optical system. The operation of this optical system is described in detail in Japanese Patent Application Laid-Open No. 54-55562, so it will not be described here. In this embodiment, the rounding and scanning laser beam, which uses the amount of light effectively, is divided in its deflection width to the left and right by a field dividing prism 25 placed at the conjugate plane of the reticle and the wafer.

The scanning line is orthogonal to the ridgeline of the field dividing prism. Each of the scanning beams spatially divided by the prism 25 enters the objective lens 11 and scans the alignment mark y on the reticle 12 in the direction of the arrow.

The other important function of the microscope system for alignment, that is, the alignment scope, other than the detection of mushroom electricity is the observation function. In particular, the observation function can be said to be an indispensable element for an alignment scope, such as monitoring the matching state of the reticle and wafer or checking the initial settings of the reticle. What is desirable about an alignment scope as an observation optical system is that the observable image can be seen in a natural and easy-to-see form.

FIG. 2 shows the relationship between the image fields observed through the eyepiece lens 23 when the embodiment shown in FIG. 1 is employed. In the figure, numeral 31 is the ridge line of the field dividing prism 25, which is a dividing line of the field of view, 52 is the scanning line of the laser beam, 53 is the field of view corresponding to the right objective lens, and 34 is the field of view corresponding to the left objective lens. 100 is an alignment mark simply indicated by the letter r. As shown in the second figure, in the microscope field of view, the left mark of the reticle is observed in the right field of view, the right mark in the left field of view, and each mark is observed as an erect image. Alignment marks are useful in the process of manufacturing semiconductor devices, but they do not perform any actual circuit function as actual semiconductor elements, so the alignment marks become dead space when wafer processing is finished. Therefore, it is desirable that the area occupied by the alignment mark be as small as possible in order to increase the yield of actual devices. When there is a reticle 12 (or mask) as shown in FIG. 3, if the alignment mark is accommodated in the scribe line between each chip 1010, there will be no dead space due to the alignment mark itself, and this problem will be solved. . In this case, since the scanning by the laser beam is in the direction that connects the seven alignment marks (hereinafter defined as the lateral direction in this specification), the alignment marks are accommodated in the lateral scribe line close to the center line of the reticle. Just do what you want. The purpose of bringing the alignment mark as close as possible to the center line of the reticle is to improve the alignment accuracy between the reticle and the wafer.

However, especially in the case of a reduction shop's stepper, there are cases where the entire reticle corresponds to one chip and the scribe line exists only at the periphery. 4 shows an example where only one chip exists on the reticle. The shaded lines in the figure are 72 imment marks 102, 10.
This is part 3. That is, when the laser scan is in the horizontal direction, the alignment mark is a diagonal line 102 or 103.
It is conceivable to form it in the part. However, 10
When the 7 alignment marks are located in the portion 3, the portion where the alignment marks protrude becomes large because the laser scanning light is in the horizontal direction. This means, for example, that the width of the scribe line increases, which has a significant impact on the chip yield. If the alignment mark is set at 1020 parts, the laser scanning width and position can be controlled more roughly than in the case described above, but compared to the alignment mark located at the center, the alignment mark is located at the upper part. Therefore, the above-mentioned problem can be solved by positioning the lower misaligned portion 104 in the center, making the alignment mark portion vertically long, and scanning the laser beam in the vertical direction. Two scanning beams were obtained by rotating systems 1 and 2.3 containing In the example, the scanning line of the laser beam is divided into two along the scanning direction, so the scanning beam light intensity is halved, and after 31, it is only 9
It is possible to convert a horizontal scan to a vertical scan by inserting a 0° rotated image low cheater.

However, in such a case as -7f, the reflected light from the reticle also passes through this 90@rotating image low cheater and enters the eyepiece image 23, so the alignment mark y itself -4190
'It is rotated and is no longer in its natural state of observation.

The present invention has been developed in consideration of the above points.

Therefore, an object of the present invention is to provide a first embodiment in which alignment marks are scanned in a direction perpendicular to the arrangement direction of the alignment marks and the alignment marks are made in a natural state.

The light from the laser 1 is scanned in the lateral direction by a rotating polygon mirror 3. Reference numeral 25 denotes a prism arranged so that its ridgeline 31 crosses at right angles to the scanning direction. A reflective film is formed on the roof surface of this prism. The light from the laser 1 is transmitted through the lens 2.4 on or near this roof surface.
Imaged by GIC. Each of the spatially divided scanning beams 110 has a 90° image lochie turf, 7a.
The scanning direction is rotated by 90°. The 90° image rotor cheater is composed of a prism having a reflective slope and a glass block having a polarizing beam sinter that rotates by 90° with respect to the reflective slope. Note that other types of image low cheaters may be used.The scanning light from the image low cheaters passes through a lens 8, a beam splitter 9, and a microscope objective lens 11 to a reticle (not shown). The alignment mark F of the reticle 12 held in the holder is scanned in the vertical direction.The reticle A/12 and the prism 25 are in a conjugate relationship.Similarly to FIG.
In the downward direction tC, the projection lens 29 and Ueno-13 are arranged.

Therefore, the light that scans the 72-dimensional mark F on the reticle 12 also scans the alignment mark on the wafer 13 in the vertical direction. 19, 20, and 21 are illumination systems that illuminate the alignment mark portion through the objective lens 11. Light from the alignment marks on the wafer 13 and reticle 12 illuminated by the scanning beam and illumination light enters the objective lens 11 again. The light from this alignment mark passes through member 9.8 and enters the glass pop-up 7.

However, the ψ placed inside the lens 29 of the returned light
By passing through plate 111 twice, it has been rotated 90° relative to the scanning beam. Therefore, it passes through the polarizing beam splitter 7. Note that the placement position of the λ/4 plate is not limited to the projection lens, but may also be placed within the polarizing beam splitter.
Anywhere between 7 and 13 is fine.

Since the light from the alignment mark passes through the polarizing beam splitter, these lights travel along an optical path different from the optical path of the scanning beam. That is, these lights do not pass through the 90' image low cheetah. The light that has passed through the polarizing beam sinter 7 is directed by a mirror 43 to a roof prism 41 having a ridgeline 51. This roof prism 41 integrates the light from the two objective lenses 11. The surface of this roof prism is reticle 12.
is a conjugate plane. The direction of the laser scanning line formed on this surface is parallel to the ridgeline of the roof prism 41. This is because the light that forms this image does not pass through the 90@image low cheetah. Therefore, the effect on the image lochie turf 7aIfiFij 7 is the same as if two roof prisms 25, 41 were arranged so that their ridgelines were orthogonal. This inverted image is then observed as an upright image by the microscope eyepiece system 42, 22.25. Also, the light passing through the semi-transparent mirror 45 is transmitted through the lens 14.
, 16, 17 and is directed to a photodetector 18 through a spatial filter 15 that passes only the scattered light. Therefore, the alignment mark on the reticle and wafer scanned by the light beam is read by the photodetector 018. As in Fig. 1, this read signal is used to detect the amount of positional deviation by the arithmetic processing circuit, and move the Ueno 1-chuck 13' in the X, Y, and Q directions using a motor, etc. to correct this amount of deviation. and align the reticle and wafer in the desired positional relationship.

FIG. 8 shows an observed image of the system in FIG. 6. The pattern to be observed is the pattern 1. Because the ridge lines of the field dividing prism 41 and the space dividing prism 25 are optically perpendicular to each other as shown in FIG. can.

However, since the ridgeline of the roof prism 25.41 is located on the optical axis, as can be seen from FIG. 8, the left and right field of view is the ridge #j of the roof prism 41! 51, and the entire right and left visual fields cannot be observed in the horizontal direction.

To solve this drawback, remove the roof prism 25.41 from the optical axis, that is, make it an eccentric system.
resolved.

A diagram showing the action of the eccentric optical system is shown in FIG.

FIG. 10(a) ti A field dividing prism 41 that combines the fields of view of the left optical system 55a and the right optical system 55b in a normal coaxial system, that is, a system for observation as shown in FIG.
It is synthesized with Here, in order to enlarge the field of view on the left and right sides of the image as shown in figure f:g9, the axes of the optical systems 55a and 55b should not intersect at the edge 1flI51 of the prism 41 as shown in figure 10 (b).
), just shift it by Δ. The slanting direction in this case is a direction perpendicular to the ridgeline 51 of the field dividing prism 410.

In the case of an optical system with polarization as shown in Figure 10, the left or right optical system 5
5a and 551) and the erector 22, deterioration of the alignment image may occur.

To prevent this, it is desirable that the light beam at the position where the left and right visual fields are combined be telecentric. The situation during this time will be explained using FIG. Figure 11 (SL
) indicates the case where the light beam exiting the optical system 55 is not telecentric. Due to the performance of the optical system, the chief ray of the light beam above the optical axis of the erector 22 should be incident parallel to the optical axis of the erector 22, but it is incident obliquely. 1st
Figure 1 (1)) shows a case where the light beam exiting the optical system 55 is telecentric, and in this case, the chief ray of any light beam is telecentric.
It enters parallel to the optical axis of 22.

Therefore, there is no particular problem in combining the optical system 55 and the erector 22. When the light flux emitted from the optical system 55 is telecentric, the chief ray may be made telecentric by inserting a field lens 56 after the optical system 55 as shown in FIG.

The shift amount Δ when combining the fields of view is realized as shown in Fig. 10, but in order to prevent the vignetting caused by the roof prism 25 and to realize the observation of the upper and lower fields, as shown in Fig. 12 (a). The optical system 55 and the erector 22 are adjusted by a predetermined amount d-
For example, move the entire eyepiece system 42, 22, 25 along the ridge line 5 in the same direction as the dividing line of the field dividing prism 41.
1# and shift it upward along the line. Reference numeral 61 in the figure is the image capturing gR element, but as shown in Figure @12, the optical system 55 and the erector 22 are coaxial in the direction orthogonal to the ridge line 51, and the observation position on the image plane to be detected is The same thing can be achieved by shifting by βd.

In the embodiment of FIG. 6, two roof prisms 25.degree. 41 are used, but the present invention can be realized even with one roof prism.

An example is shown in FIG.

A prism type beam splitter that is different from the system shown in Figure 6.
Roof prism 25 shared in the optical path after reflecting 43
A prism 130 is inserted between the two. A change in the optical path length due to the insertion of the prism is corrected by the lens 131. The amount of shift of the optical path by the prism 130 is determined in advance depending on how much eccentricity is to be given.

In the embodiments shown in Figures 5jI6 and 12i, the 90@image low cheater is placed in the optical path for directing the scanning light toward the alignment mark; It is obvious that it may be placed in the optical path that receives the light from.

Furthermore, in the present invention, observation can be performed using only a laser light source. As a laser light source, for example, He-0dL/
- If a laser (441, snm) is used, the projection optical system will be
This is convenient because it eliminates the problem of chromatic aberration of the lens, such as when using a linear (455,8 nm) correction lens.

Also, when the projection optical system is composed of a mirror system with no or little chromatic aberration, ij He-No laser %Ar+
It is also possible to use a laser or the like. In this way, photoelectric detection and observation can be performed using the same light source, which plays a large role in simplifying the apparatus. Note that in the present invention, it is clear that the optical intersection angle of the ridge lines of the visual field dividing prism 41 and the space dividing prism 25 is not limited to a right angle, but can be a general angle G (a right angle to be set).

[Brief explanation of drawings]

Figure 1 is a diagram of a conventional photoelectric detection and observation optical system, Figure 2 is a diagram showing the relationship between a scanning lens and a field-of-view dividing prism, Figure 3 is a diagram showing a mask or reticle, and Figure 4 is a diagram of a conventional optical system. FIG. 5 is an explanatory diagram of alignment marks in a single chip reticle according to the present invention. FIG. 6 is a diagram of the first embodiment of the present invention. FIG. 7 is an optical diagram of two field-of-view dividing prisms. Figure 8 shows the observed image when the system in Figure 6 is configured as a coaxial system. Figure 9 shows the observed image when the system in Figure 6 is configured as an eccentric system. Figures 10(a) and 10(b) are explanatory diagrams of the coaxial system and IIi core system, respectively; Figures 11(, ), (1)), and (0) are diagrams showing the action of the telecentric system; @12 Figures (-), (1)) are explanatory diagrams of an eccentric system in a direction orthogonal to the case of Figure 10, and Figure 15 is a diagram showing a second embodiment of the present invention. 1...Laser 2...Condensing lens 5...Rotating polygon mirror 4...F-θ lens 5...Beam splitter 7, 7a...Image quadrature 25...Dividing prism Applicant Canon Co., Ltd. Figure 4 102 102 5th T

Claims (1)

[Claims] (1) An observation device configured with a TC to align an object having an alignment mark, comprising: a space-dividing beam splitter for dividing the deflection width of a scanning beam; a first optical system including an objective lens for directing each of the scanning beams to the alignment mark; a second optical system having an optical path at least partially different from the optical path of the scanning beam and receiving light from the alignment mark;
an optical system, and a 90 disposed in either the first optical system or the second optical system.
An observation device characterized by comprising: an image low cheetah. (2) The space-splitting beam splitter also functions as a field-segmenting beam splitter for combining fields of view in order to observe alignment marks. Observation device. (5) The observation device according to claim 1, further comprising a field-dividing beam splitter for combining fields of view in order to observe the alignment mark. :4) The observation device according to claim 2 or 3, wherein the scanning direction of the beam intersects with the ridgeline of the space-dividing beam splitter. (5) The observation device according to claim 3, wherein the space division beam splitter and the field division beam splitter are arranged so that their ridge lines optically intersect at a predetermined angle. (6) The observation device according to claim 5, wherein the angle is 90°. (7) The observation device according to claim 3, wherein the optical axes of the front optical system and the rear optical system of the field dividing beam splitter are eccentric by a predetermined value. (8) The observation device according to claim 7, wherein the coupling portion between the front optical system and the rear optical system is constituted by a telescopic optical system. (9) Transfer the pattern formed on the reticle onto the wafer)
An aligner for manufacturing semiconductor devices by C-baking, comprising: a reticle holder for holding the reticle having a plurality of alignment marks; and a reticle holder for holding the wafer having a plurality of 72-ment marks. a moving device for relatively moving the mask holder and at least one of the reticle holder and the mask holder by 4C; an observation device configured to observe relative positional relationships; the observation device includes: a space division beam splitter for dividing the deflection width of the scanning beam; and a space division beam splitter for dividing the deflection width of the scanning beam; a first optical system including an objective lens for directing toward the alignment mark; a second optical system having at least partially an optical path different from the optical path of the scanning beam and receiving light from the alignment mark;
an optical system, and a 90 disposed in either the first optical system or the second optical system.
° Aligner-0 characterized by being composed of image low cheater