JPH0429214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reticle and a projection exposure method using the same, and particularly to a method for printing a pattern formed on a reticle onto each shot while aligning a wafer for manufacturing semiconductor devices for each shot. This relates to an alignment method.

A typical example of an alignment device used to automatically align a plurality of objects is an aligner, which is a manufacturing device for semiconductor devices such as ICs and LSIs. ICs and LSIs are manufactured by layering complex circuit patterns. As semiconductor devices become faster and more dense, the line width of circuit patterns continues to become smaller, and as a result, high overlay accuracy on the order of submicrons is required.

An example of an aligner that can accommodate such high precision and miniaturization is a step-and-repeat aligner called a stepper.
The stepper projects and transfers the pattern on the reticle 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 process is repeated by printing the pattern, moving the wafer in steps, and printing the pattern in new areas on the wafer. As wafers become larger, the number of steps required increases and processing time increases. On the other hand, in order to sequentially print patterns using a stepper, the reticle and a predetermined section on the wafer must be aligned relative to each other prior to printing. Therefore, the method by which positioning is performed is a very important parameter.

The formula for aligning the reticle with a predetermined section of the wafer is the off-axis method, in which the positioning is done in advance at a location away from the printing position, and then the printing is done by relying on the accuracy of the laser interferometer. There is a way to go about it.
However, although this method is fast, it is difficult to directly check the alignment state at the position where the printing is performed, and it is difficult to deal with nonlinear physical distortion that occurs on the wafer as it progresses through the process, that is, local expansion and contraction. The disadvantages are that the precision of the stage movement monitor becomes a source 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 alignment between the reticle and the wafer is performed. If the TTL method is used, it is possible to avoid the effects of wafer distortion and stage accuracy mentioned 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.
Japanese Unexamined Patent Publication No. 54-53562 filed by the present applicant is one example. The first example briefly shows an example of this method.
In the figure, light from one laser light source 1 is divided into two left and right objective lenses 11, and the positional deviation between the reticle 12 and the wafer 13 is detected at two locations. 2
Parallel movement (x,
Two types of misalignment, y) and rotational (θ), can be corrected by moving one of the reticle or wafer relative to the other. 1 in the diagram
2 is a laser, 2 is a condensing lens for focusing the laser system, 3 is a rotating polygon mirror, 4 is an f-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 enters the optical system below the beam splitter 5. 6 is a field lens, 25 is a field dividing prism, and the prism 25 divides the scanning laser beam into two optical paths. In this respect, prism 25 can be referred to as a field and space dividing prism. 7 is a polarizing beam splitter, 8 is a relay lens, and 9 is a beam splitter. 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 block specularly reflected light and extract scattered light for photoelectric detection. 17 is a condenser lens. The light source 19, condenser lens 20, and color filter 21 constitute an illumination optical system, and the erector 22 and eyepiece 23 constitute an observation optical system. The operation of this optical system is detailed in Japanese Unexamined Patent Publication No. 53562/1983, so a detailed description thereof will be omitted here.

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

Another important function of a microscope system for performing alignment, that is, an alignment scope, other than photoelectric detection is an observation function. In particular, the observation function is an indispensable element for an alignment scope, for monitoring the matching state of the reticle and wafer or for 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.

When the embodiment of FIG. 1 is adopted, the eyepiece 2
The relationship between the image fields observed in 3 is shown in FIG. Visual field dividing prism 2 where 31 in the figure is the dividing line of the visual field
5 ridgeline, 32 is the scanning line of the laser beam, 33
34 is a field of view corresponding to the right objective lens, and 34 is a field of view corresponding to the left objective lens. In fact, the scanning laser beam scans the object plane in the lateral direction at the positions where the alignment marks of the reticle and wafer are placed.

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 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.
This problem is solved by storing the alignment mark inside the alignment mark itself, which eliminates the dead space caused by the alignment mark itself. In this case, since the scanning by the alignment scope is horizontal, the alignment mark is a horizontal scribe line 103 close to the center line of the reticle.
It would be better if it could be stored inside.

However, especially in the case of a reduction type stepper, the entire reticle corresponds to one chip, and the scribe line may exist only at the periphery. FIG. 4 shows an example where only one chip 101 exists on the reticle 12. The alignment mark 102 is indicated by diagonal lines in the figure. As can be easily understood from FIG. 4, the paired alignment marks 102 are aligned in the same line at a large distance from the center line of the reticle 12, so that areas of the reticle and wafer far away from the alignment marks 102 are not aligned. The alignment accuracy becomes worse compared to the area near where the mark is placed.

In this way, the alignment mark 102 on the same scribe line 103 is located away from the center line of the reticle 12.
The deterioration in alignment accuracy caused by the juxtaposition of the chips 101 is noticeable when the number of chips 101 on the reticle 12 is one as described above. Also, this is more likely to occur when there is an odd number than when there is an even number. This is because there is no scribe line in the center.

Furthermore, if the alignment marks are provided at the same location on opposite peripheries of a pattern area of a reticle and at the same location on opposing peripheries of a pattern area printed in one shot onto a wafer. In some cases, when performing alignment on the next shot after completing the baking and stepping, the alignment mark used on the previous shot overlaps with the alignment mark used on the current shot.
A situation may arise in which the alignment mark does not actually function as an alignment mark for the next shot.

Therefore, an object of the present invention is to provide an improved alignment mark...a thin plate-like object such as a wafer, which can eliminate non-uniformity in alignment accuracy caused by the position of the alignment mark and improve alignment accuracy. It is in.

By the way, when the pattern on the reticle is printed onto the wafer, the alignment mark on the reticle is also transferred onto the wafer. If you perform processing such as development or diffusion on a wafer that has finished printing in this state, there is a possibility that marks will remain on the wafer due to the alignment marks of the reticle transferred onto the wafer (see USP, 3844655). .
Such marks on the wafer become an obstacle when aligning the alignment marks on the wafer with the alignment marks on the reticle in order to print a new pattern on the same wafer.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a reticle that can prevent traces from being left on the wafer by alignment marks of the reticle transferred onto the wafer.

Still another object of the present invention is to provide a step-and-repeat alignment method that makes it possible to prevent traces from being left on the wafer by alignment marks of a reticle transferred onto the wafer.

Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIG. 5, there is shown a preferred embodiment of an alignment apparatus according to the present invention in which a reticle constructed according to the present invention is used. The system of FIG. 5 is a variation of the system of FIG. 1, and identical parts have been given the same reference numerals. That is, there is no change in the fact that the light emitted from the laser 1 scans the reticle surface 12 through the objective lens 11 as the rotating polygon mirror 3 rotates. The arrangement of the optical system shown in FIG. 5 is different from the arrangement of the optical system shown in FIG. 1. The reason why the arrangement of the optical system shown in FIG. This is after the division. That is, the left and right optical systems are configured asymmetrically, and the mask 1
The beam scanning position and observation position on 2 are staggered. That is, the positions observed in the system of FIG. 5 are the positions 27 and 28 in FIG. 6. The areas scanned by the laser beam are the alignment marks x and w shaded in the figure. That is, the scribe line 10
The mark can be placed within 6. This method has the advantage of being able to best suppress errors in rotational components because the span connecting the observation points is long. Thus, the staggered configuration of the optical system in the alignment device according to the invention shown in FIG. 5 can be achieved by modifying the conventional optical system shown in FIG. It shows that it can be used. The reticle constructed according to the present invention shown in FIG. 6 includes a base plate 104 and a pattern forming section 105. The reticle shown in FIG. The circuit pattern formed in the pattern forming section 105 is sequentially printed onto the wafer along columns and rows by a projection optical system. The alignment marks x and w are arranged so as to sandwich the pattern forming portion 105, and are positioned in a staggered relationship so as not to be aligned in a straight line along the aforementioned column or row direction.

Figures 7 and 8 show scribe line 1 on the wafer.
This is an example in which an alignment mark is placed at 09. In both Figures 7 and 8, the reticle 12 is 1.
It consists of chips that are printed onto a wafer 13 in a step-and-repeat manner. The alignment mark is located within the scribe line 107, which is the boundary of each actual element, but the arrangement method is
The figure and Figure 8 are different. As is clear from the example of FIG. 6, the alignment marks of the reticle used in this embodiment are a pair of alignment marks X and W arranged at the upper right and lower left. In the wafer 13 shown in FIG. 7, adjacent chips share a scribe line 107. In other words, when looking at the four marks 30A, 30B, 30C, and 30D around the chip 30, the mark used for alignment when printing the chip 30 is 30B.
(X) and 30C(W). 30A is a mark for alignment when printing upper chip 29,
This is a mark for alignment when printing the 30D lower chip 31.

On the other hand, in FIG. 8, the scribe line 107
In this embodiment, the inside of the chip is further divided into two, and the alignment marks are placed adjacent to the corresponding individual chips. It is convenient to divide the scribe line into two and use the scribe line area on one side, since the scribe line area on the opposite side can be used when performing new alignment. However, it is also true that the method shown in FIG. 7 has the advantage that the width of the scribe line 107 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, above we have shown the case where the alignment mark is placed within the horizontal scribe line, but
The staggered arrangement of marks is also effective when the marks are located within a vertical scribe line.

An example is shown in FIG. FIG. 9a shows the case where the eticle 12 on which four chips A, B, C, and D are formed as shown in FIG. 9b is printed onto a wafer by the step-and-repeat method. The reticle 12 is formed with a pair of alignment marks P, Q arranged in a staggered relationship on opposite sides of the tip area of the reticle.

As explained in FIG. 6, the alignment marks on the reticle 12 are located at the lower left P' and upper right
Although they may be provided at Q', here we will explain the case where they are provided at positions P' and Q' close to the center of the reticle.

The state in which the alignment marks P and Q of the reticle 12 are printed on the wafer 13 by the step-and-repeat method is as shown in FIG. 9a. Further, FIG. 9a shows the positions of alignment marks on the wafer 13. That is, when the chips 40A, 40B, 40C, and 40D are printed in the shot 40, the alignment marks on the wafer corresponding to the pair of alignment marks P and Q formed on the reticle are 40P and 40Q, and the alignment marks in the next shot 41 are The alignment marks on the wafer corresponding to the alignment marks P and Q on the reticle are 41P and 41Q. In this case, since the alignment marks 40Q and 41P on the wafer are not in the same position, there is a situation where the alignment mark on the wafer overlaps with the alignment mark image on the reticle in one shot and cannot function as an alignment mark in the next shot. can be avoided.
Note that chips with the same number in FIG. 9 indicate that they were printed with the same shot.

FIG. 10 shows an embodiment of an alignment device according to the present invention of a type 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. As in the embodiment shown in FIG. 5, the left and right scanning optical systems are constructed asymmetrically, so that the left and right objective lenses 11 are positioned alternately in accordance with the positions of the alignment marks in FIG. In the step-and-repeat method, the projection optical system is used to print each shot, and the operation of stepping to the next shot is repeated, so the connection between each shot becomes a major problem.

In the alignment apparatus shown in FIG. 10, a wafer 13 is supported by a wafer carrier 110 and is moved through an and the position is stepped in the Y direction.
In addition, reticle 1 at each step (shot)
2 and the wafer 13 is performed by an X, Y, θ drive device for moving a reticle holder 111 for holding a reticle.

As mentioned above, the fact that P and Q are staggered in Figure 9 means that when you step to the next shot, P and Q
This ensures that the printed image does not overlap the alignment mark on the next shot's wafer.

To place marks more efficiently, see Figure 9a.
Considering such a situation, it is necessary to determine the mutual positional relationship in advance so that the printed images of P and Q do not overlap the alignment mark of the wafer of the next shot.

In the case of the reticle shown in FIGS. 6 and 9b, the alignment marks are located on opposite peripheries of the pattern area on the reticle, but the number of chips is large, and the alignment marks are located either vertically or horizontally. When there are several scribe lines, they may be placed at different positions on the scribe lines.

Now, as the shape of the above-mentioned alignment mark, for example, a conventionally known mark, that is, an example as shown in FIG. 11 can be cited. In the figure, 51 is a mark on the reticle, 52 indicated by a dotted line is a mark on the wafer, and 53 is a scanning line. Since it is a TTL method, marks on the reticle and marks on the wafer are simultaneously detected through the reticle, and based on the signals, alignment of the two is performed by a drive system (not shown). By the way, when marks are arranged as shown in Figure 9, if P and Q are marks of the same shape, if a shift occurs due to an error in the rotation of the reticle or wafer, P
It is also possible that the position of Q and Q are confused. In that case, confusion can be avoided by making P and Q marks facing in opposite directions, for example. FIG. 12 shows a case where such a method is applied to a reticle, and the directions of marks P and Q are reversed. Corresponding alignment marks on the same scribe line on the wafer are constructed as shown in FIG. That is, P
Since the directions of Q and Q are different, it is impossible to confuse the two.

As described above, the alignment mark arrangement according to the present invention can reliably improve the alignment accuracy between the reticle or mask and the wafer.

Furthermore, it is also significant in that it is possible to prevent overlapping of alignment marks during alignment in each step. or,
Since the alignment device according to the present invention has an asymmetrical configuration of the scanning optical system, it can adequately cope with improved alignment mark placement.

By the way, when the pattern on the reticle is printed onto the wafer, the alignment mark on the reticle is also transferred onto the wafer at the same time. In this state, an unexposed portion corresponding to the shape of the alignment mark on the reticle remains within the area of the alignment mark on the wafer. Therefore, the wafer that has finished baking in this state is developed,
When processing such as diffusion is performed, traces are left on the wafer due to the unexposed portions corresponding to the alignment marks of the reticle transferred onto the wafer. Such marks on the wafer impair the function of the alignment mark on the wafer when printing a new pattern on the same wafer, making it impossible to align the reticle and the wafer.

According to preferred embodiments of the invention, the above-mentioned problems are advantageously solved. In the reticle according to the present invention shown in FIG. 12, light transmitting portions R and S are formed adjacent to alignment marks P and Q that are alternately arranged in the upper and lower right directions in the figure across the pattern forming portion 113. ing. This light transmitting portion R, S
According to this arrangement, as shown in FIG. The unexposed portion of the reticle transferred onto the alignment mark Q of Shot 4 is
1, they are simultaneously exposed by the light transmitted through the light transmitting portion R (see FIG. 9).

Therefore, it is possible to prevent traces from remaining on the wafer due to the unexposed portions of the reticle corresponding to the alignment marks.

In the reticle according to the present invention shown in FIG. 14, light transmitting portions Y and Z are formed at positions corresponding to the alignment mark arrangement shown in FIG. According to the arrangement of the light transmitting parts Y and Z, the shot 109
The unexposed portion of the reticle transferred onto the alignment mark 109G on the wafer by the alignment mark W is exposed by the light transmitted through the light transmitting portion Z when exposed in the shot 108.

As described above, according to the present invention, when exposing each shot, the alignment mark area used in the adjacent shot can also be exposed, so that protection of the alignment mark can be achieved without providing a separate special exposure process.

Especially in steppers where alignment accuracy is strictly required, there are many advantages such as always using the same alignment mark, which makes it difficult for errors to occur because there is only one reference, and there is no need to provide multiple pairs of alignment marks. . Furthermore, according to the present invention, even when a plurality of alignment marks are provided for each shot, it is possible to reliably protect each alignment mark for each shot.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the optical system of a conventional alignment device, Fig. 2 is a diagram showing the relationship between the scanning beam and the field of view, and Fig. 3 is a diagram showing a mask or reticle on which a plurality of chips are formed on the surface. , FIG. 4 is a diagram showing the arrangement of conventional alignment marks in the case of one chip-one reticle, FIG.
The figures are a diagram showing a reticle with alignment marks arranged according to the present invention, a diagram showing the alignment marks on a wafer when the reticle of FIGS. 7 and 8 and FIG. 6 are used, and FIG. 9. a
and b are diagrams in which alignment marks are arranged according to the vertical scribe line areas of the wafer and reticle, respectively; FIG. 10 is a diagram of the optical system layout of an alignment device using the alignment marks of FIG. 9;
Figure 11 is a diagram showing the relationship between alignment marks and scanning lines on the reticle and wafer, Figure 12 is a diagram showing the alignment marks and light transmitting parts on the reticle, and Figure 13 is a diagram showing the alignment marks on the scribe line of the wafer. FIG. 14 is a diagram showing a reticle having a light transmitting portion corresponding to the alignment mark arrangement shown in FIG. 8. Explanation of symbols, alignment marks: P, Q,
X, Y, light transmitting part; R, S.

Claims (1)

[Claims] 1. Used to sequentially print a pattern on each shot area of a wafer in which a plurality of shot side alignment marks for each shot area are arranged in the scribe area by step-and-repeat exposure. A reticle that is used in conjunction with a pattern forming section on which the pattern is formed and a shot-side alignment mark for each shot area for alignment at the exposure position of each shot area of the wafer. It has a plurality of mark forming parts each having an alignment mark formed thereon, and a plurality of light transmitting parts for guiding exposure light to each of the scribe areas on both sides of the shot area located at the exposure position, and the mark forming part are arranged on both sides of the pattern forming section so as to have different levels in a predetermined direction, and the mark forming section and the light transmitting section are arranged in the opposite order in the predetermined direction on each side of the pattern forming section. A reticle characterized by being placed in the. 2. An alignment method for sequentially printing a pattern on each shot area of a wafer by step-and-repeat exposure, in which a plurality of shot-side alignment marks for each shot area are arranged in the scribe area, the alignment method comprising: Reticle-side alignment marks are formed to be used together with shot-side alignment marks for each shot area in order to align the pattern forming portion where the pattern is formed and the exposure position of each shot area of the wafer. It has a plurality of mark forming parts and a plurality of light transmitting parts for guiding exposure light to each of the scribe areas on both sides of the shot area located at the exposure position, and the mark forming part is placed on both sides of the pattern forming part. For a reticle that is arranged at different levels in a predetermined direction, and the mark forming part and the light transmitting part are arranged in the opposite order in the predetermined direction on each side of the pattern forming part. An alignment method comprising sequentially aligning each shot area of the wafer using a reticle-side alignment mark of the reticle and a shot-side alignment mark of the wafer.