JPS61123139A - Alignment apparatus - Google Patents

Abstract

PURPOSE:To prevent overlapping of alignment mark between exposure shots at the time of step and repeat exposure by forming asymmetrically the right and left optical systems and arranging the observation positions with level difference on the reticle. CONSTITUTION:The light emitted from a laser 1 scans the surface of reticle 12 through a couple of objective lenses 11 in accordance with rotation of a rotary polygonal mirror 3. Here, the right and left optical systems are formed asymmetrically and the observation positions are provided on the reticle 12 with level difference. Namely, the observation positions 27, 28 in such structure are located on the reticle. In addition, the region scanned by the laser beam is indicated as the hatched region in the figure and the alignmark mark can be housed within the shaded region. In other words, this device has a long span of observation position and can suppress an error of rotating component. Thereby, a problem of ununiformity in alignment accuracy which may be considered to be generated in accordance with the alignment mark position can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a 7-alignment device for aligning a plurality of objects, particularly when exposing a pattern on a reticle onto a wafer in a step-and-repeat manner in a semiconductor manufacturing process. The present invention relates to an alignment device used to sequentially overlap a pattern on a reticle with a plurality of patterns on a wafer.

(Prior Art) A typical example of a device that automatically aligns a plurality of objects is an aligner, which is a manufacturing device for semiconductor devices such as ICs and LSIs. I.C.

LSIs are manufactured by stacking multiple circuit patterns in many layers. As semiconductor devices become faster and more dense, the line width of a single circuit pattern continues to become smaller.
As a result, a high degree of alignment accuracy on the submicron order is required.

An example of an aligner that is compatible with such high precision and miniaturization is a steno knob 7-tribeat type device called a stepper.

In STETSUNO Z-, the pattern on the reticle is projected and transferred onto the wafer at reduced or equal magnification. At this time, 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 operation of baking, moving the wafer in steps, and then baking again is repeated.

As wafers become larger, the number of steps required increases and processing time increases.

On the other hand, in order for the stepper to perform sequential printing, the reticle and wafer must be aligned relative to each other, so the method of alignment is a very important parameter.

One method of positioning is the off-axis method, in which the position is determined in advance at a location away from the location where the printing will be performed, and then the printing is performed by relying on the accuracy of laser interference. However, although this method is fast, it is not possible to directly check the alignment state at the position where printing is performed, it is not possible to deal with nonlinear distortion that occurs as the sea urchin/\\ progresses through the upper stage, and it is difficult to monitor the movement of the stage. There is a drawback that accuracy 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 seven alignments are performed with the reticle.

When using the TTL method, the aforementioned wafer distortion occurs.

Since it is possible to avoid the influence of stage accuracy, improvement in alignment accuracy can be expected.

For the TTL method, a method using laser beam scanning is known as a conventional technique. Japanese Patent Laid-Open No. 54-53562, to which the present applicant belongs, is one example. In FIG. 1, which is a simple embodiment of this system, light from one laser light source 1 is divided into two objective lenses 11 on the left and right, and the positional deviation between the reticle 12 and the wafer 13 is detected at two locations. By detecting the amount of deviation at two locations, the two degrees of freedom, parallel movement and rotation, can be completely suppressed.

In this figure, ■ is a racer, 2 is a condensing lens that focuses the laser system, 3 is a rotating polygon mirror, and 4 is f-θ
Lens 5 is a beam splitter.The light emitted from the laser 1 is scanned according to the rotation of the rotating polygon mirror 3, and enters the optical system below the beam splitter 5. 6 is a field lens, 25 is a field dividing prism.

7 is a polarizing beam splitter, 18 is a relay lens, and 9 is a beam splitter.The light reflected or passed through these elements enters the objective lens 11, forms an image on the object plane, and performs scanning. The system from the pupil imaging lens 14 to the detector 18 is a photoelectric detection system. 15 is a color filter, and 16 is a spatial frequency filter, which serves to cut specularly reflected light and extract scattered light. 17 is a condenser lens.

Light source 19, condenser lens 20, color filter 21
is an illumination optical system, and the erector 22 and eyepiece 23 are an observation optical system. The operation of this optical system is detailed in the above-mentioned Japanese Patent Application Laid-Open No. 54-53562, so a description thereof will be omitted here.

In this example, in order to effectively use the amount of light, the scanning laser beam is
It is divided into left and right by a field dividing prism 25 placed on the common plane of the reticle 12 and wafer 13. The scanning line is orthogonal to the ridgeline of the field dividing prism 25.

Another important function of the microscope system for performing alignment, that is, the alignment scope, other than photoelectric detection is the observation function. In particular, observation functions such as monitoring the matching state of the reticle 12 and the wafer 13 or checking the initial settings of the reticle 12 can be said to be an indispensable element for the alignment scope. 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.

When adopting the embodiment shown in FIG. 1, the relationship between the observed image fields is shown in FIG.
5, a scanning line 32 of the laser beam, 33 a field of view corresponding to the objective lens 11 on the right side, and 34 a field of view corresponding to the objective lens 11 on the left side. In fact, the scanning line scans the object plane in the horizontal direction, and alignment marks for the reticle 12 and wafer 13 are placed at corresponding positions. Alignment marks are useful in the process of manufacturing semiconductor devices, but they do not perform actual circuit functions as actual semiconductor devices.

At the end of wafer processing, the alignment mark becomes a dead space. Therefore, it is desirable that the area occupied by the 7 alignment marks be as small as possible in order to increase the yield of actual devices. In a reticle (mask) as shown in FIG. 3, this problem can be solved by housing the alignment marks within the scribe lines between each chip. In this case, since the alignment scope scans in the horizontal direction,
The alignment mark may be housed within the horizontal scribe line.

However, especially in the case of a miniature stepper, there are cases where the entire reticle corresponds to one chip and scribe lines exist only at the periphery. FIG. 4 shows an example where only one chip exists on the reticle L. The hatched portion in FIG. 8 is the alignment mark.

When scanning in the lateral direction, the alignment mark must be placed at a position far away from the center. As a result, the accuracy of alignment is worse near the sides without alignment marks than in the vicinity of the sides with marks. That is, since it is deviated from the center of the chip, the alignment accuracy differs between the side with the alignment mark and the side without the 7-alignment pook, which is not preferable.

(Object of the Invention) The present invention was made in view of the above circumstances, and its purpose is to provide an alignment device that can eliminate non-uniformity in alignment accuracy caused by problems in the position of alignment marks during step-and-repeat exposure. It is about providing.

A further object of the present invention is to provide an alignment device that can adequately handle scribe lines whose width tends to become narrower year by year.

(Explanation of Examples) Hereinafter, the present invention will be explained with specific examples.

FIG. 5 shows one of the preferred embodiments of the 7-alignment device of the present invention. The system in FIG. 5 is a modification of the system in FIG. 1, and the numbers 1 correspond to each other. That is, there is no change in the fact that the light emitted from the laser l scans the reticle surface (mask surface) 12 through the two objective lenses 11 as the rotating polygon mirror 3 rotates. The arrangement in Figure 5 is different from Figure 1 because
If we follow the order in which the light is emitted from the laser l, it starts after the optical system is divided into left and right sides through the field-of-view dividing prism 25. That is, the left and right optical systems are configured asymmetrically, and the observation positions on the reticle 12 are at different levels. That is, the fifth
The observed positions in the system of the figure are the positions 27 and 28 in FIG. Further, the area scanned by the laser beam is shaded in the figure. The alignment mark is stored in the shaded area. That is, the mark can be placed within the scribe line. This method is characterized in that it can best suppress errors in rotational components because the span of the observation point is long.

The stepped structure of the optical system shown in FIG. 5 shows that such an effect can be easily achieved by slightly modifying the conventional optical system. The dashes in the figure are used to show the effect caused by the asymmetry of the left and right optical paths, and the functions of the parts are exactly the same as those without the dashes.

FIGS. 7 and 8 show examples in which alignment marks are arranged on scribe lines on the wafer. In both FIGS. 7 and 8, the reticle is composed of one chip, which is printed using a step-and-repeat method. Although the alignment marks are located within the scribe lines that are the boundaries of the individual actual elements, the arrangement method is different between FIG. 7 and FIG. 8. As is clear from the example shown in FIG. 6, alignment marks placed on the right and left sides are used in the unexamined example. In FIG. 7, adjacent chips share a scribe line. i.e. 3OA, 30B around the chip 30
.

When focusing on the four marks 30C and 30D, the marks used for the chip 30 are 30B and 30C. 3
0A is a mark for the upper chip 29, and 30D is a mark for the lower chip 31.

On the other hand, FIG. 8 shows an embodiment in which the inside of the scribe line is further divided into two, and the alignment marks are placed adjacent to each chip. In this case, compared to the case shown in FIG. 7, there is an advantage that the number of stored marks is doubled. However, it is also true that the method shown in FIG. 7 has the advantage that the width of the scribe line can be narrower. In recent years, the width of scribe lines has tended to become narrower and narrower, and in this case, the method shown in FIG. 7 can be said to be more advantageous.

Now, although the case where the alignment mark extends in the horizontal direction has been shown, the non-axisymmetric arrangement of the mark, that is, the arrangement at different levels, is also effective when the mark exists in the vertical direction. An example is shown in Fig. 9. Fig. 9(a) shows the case where a reticle on which four chips A, B, C, and D are formed as shown in Fig. 9(b) is printed by step-and-repeat. As shown, alignment marks P and Q are formed on the reticle, and P and Q are at different levels.

As explained in FIG. 6, the alignment marks of the reticle may be provided at the lower left y and the first right portion Q' of the reticle, but the case where they are provided at positions P and Q will be described here.

Figure 9 (L
) as shown. Further, FIG. 9(L) shows the position of the alignment mark on the wafer. That is,
In shot 40, chips 4OA, 40B, 40C.

When 400 is printed, the alignment marks on the wafer corresponding to the 7 alignment marks P,Q on the reticle are 40P, 40Q, and the alignment marks on the wafer corresponding to the 7 alignment marks P,Q on the reticle in the next shot 41 are 40P, 40Q.
The alignment marks are 41F and 41Q. Here, since alignment marks 40Q and 4LP on the wafer are not in the same position, there is a situation where the 7 alignment marks on the wafer overlap with the alignment mark image on the reticle in one shot and cannot function as alignment marks in the next shot. It can be avoided. Note that the same numbers in FIG. 9 indicate that the images were printed using the same shot.

FIG. 1O shows an embodiment of an optical system that scans a laser beam in the vertical direction. Here, a combination of mirrors 9 and 9a is used to scan the laser in the vertical direction. Of course, the left and right objective lenses 11 are provided at different levels corresponding to the positions of the 7 alignment marks in FIG. In the step-and-repeat method, the operation of printing each shot and stepping to the next shot is repeated, so the connection between each shot becomes a major problem. In particular, since the scribe line is located in the boundary area, the problem is how to properly insert information into the scribe line. As mentioned above, the reason why P and Q are at different levels in Figure 9 is that when you step to the next shot,
The P and Q prints show a wheel whose image does not overlap with the 7 alignment marks on the wafer in the next shot, making it possible to efficiently place alignment marks within the scribe line. On the other hand, to place marks efficiently, wIJ
Considering the situation as shown in FIG. 9(a), it is necessary to determine the mutual positional relationship in advance for printing P and Q so that the images do not overlap the 7 alignment marks of the wafer in the next shot.

Now, as the above-mentioned 7 alignment mark, for example, a conventionally known mark, ie, an example as shown in FIG.
is a mark on the wafer, and as is clear from Figure 1,
Each mark 51, 52 is configured as a mark group in which a plurality of line-shaped marks are gathered in a predetermined relationship. Also,
In the figure, 53 is a scanning line. Since it is a TTL method, the mark on the reticle and the mark on the wafer are simultaneously detected through the reticle, and based on the signal, a drive system (not shown)
I'm doing a alignment. By the way, when the marks are arranged as shown in FIG. 9, if P and Q are the same mark, there is a possibility that P and Q may be confused when a deviation occurs due to a rotation error. In that case, confusion can be avoided by marking P and Q in opposite directions, for example. FIG. 12 shows a case where such a method is applied to a reticle, in which the directions of marks P and Q are reversed. Seven alignment marks on the scribe line on the wafer corresponding to this are constructed as shown in FIG. In other words, since the directions of P and Q are different, it is impossible to confuse the two.

(Effect of the invention) Below 1. As described above, according to the present invention, it is possible to arrange seven alignment marks at different levels within the scribe area on both sides of a pattern on a wafer, which causes problems especially in step-and-repeat type exposure equipment. The overlapping of seven alignment marks between each exposure shot can be eliminated. Therefore, it is possible to arrange the alignment marks in a manner that can eliminate the problem of non-uniform alignment accuracy that may occur depending on the position of the alignment marks.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a conventional 7-line optical system, Figure 2 is a diagram showing the relationship between the scanning beam and the field of view, Figure 3 is a diagram showing a mask or reticle, and Figure 4 is an illustration of a conventional 1-chip reticle. FIG. 5 is a diagram showing the arrangement of alignment marks, and FIG. 5 is an optical system arrangement diagram of an embodiment of the 7 alignment apparatus of the present invention. Figure 6 shows the position of the alignment marks in the system shown in Figure 5, Figures 7 and 8 show the 7 alignment marks on the wafer when using the reticle in Figure 6, and Figure 9. Figure 9 (a) shows the wafer, Figure (b) shows the reticle, and Figure 10 shows the alignment of the 9th alignment. FIG. 11 is an optical system layout diagram of an embodiment of the 7-alignment apparatus of the present invention using marks, and FIG.
Fig. 12 is an example of 7 alignment marks on a reticle, and Fig. 13 is an example of alignment marks on a wafer scribe line. f-theta lens, 6 is a field lens, 7 is a polarizing beam splitter, 8 is a relay lens, 11 is an objective lens, 12 is a reticle, 13 is a wafer, 14 is a pupil imaging lens, 16 is a stopper, 17 is a condenser lens, 18 is a photodetector, 19 is a light source, 2
2 is an erecta-123 is an eyepiece. 25 is a field dividing prism, and 26 is a projection optical system.

Claims (1)

[Claims] When exposing a reticle pattern on a reticle while sequentially overlapping multiple wafer patterns on a wafer using step-and-repeat, each alignment mark, which is composed of a group of predetermined marks arranged for each wafer pattern, is In an alignment device that superimposes a reticle pattern on a wafer pattern by observing with an objective lens, one of the objective lenses observes an alignment mark placed in one of the scribe areas on both sides of the wafer pattern, and the other observes the scribe area. An alignment device characterized in that it is configured to observe an alignment mark placed on the other side of the region at a different level from the alignment mark.