JPS5989417A - Method for setting of mask in printing device - Google Patents

Abstract

PURPOSE:To reduce the searching period for the titled printing device by a method wherein the stage supporting a mask is fixed when the alignment marks located on the mask are detected. CONSTITUTION:A detecting device moves on the mask and detects the alignment marks 54 and 54' provided on the mask, the mask 1 is shifted by driving the shifting means based on the detected signal and, at the same time, the reference mark and the alignment mark on the wafer are brought in the range of detection of the detecting means by moving the detecting means. Then, an automatic alignment of the reference mark and the alignment mark is performed. As a result, the searching period is cut down, and the alignment mark and the reference mark can be brought to closer to the position before a fine alignment is performed, thereby enabling to perform the alignment operation in a short period.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for aligning two objects, and more particularly to an apparatus for aligning a mask or a wafer before printing a semiconductor integrated circuit pattern on a mask or reticle onto a wafer. suitable for

The semiconductor manufacturing process includes a step of sequentially transferring several patterns onto a wafer to form a semiconductor integrated circuit. In this case, in order to accurately position another pattern on the wafer onto which the previous pattern has already been transferred, it is necessary to align the pattern, the etymask, and the wafer with high precision. And this alignment is
Normally, alignment marks written on the mask and wafer are photoelectrically detected and automatically achieved using the detected signals.

On the other hand, recently there are masks that store masks, and masks that automatically attach masks in carriers to the mask set position.
Devices equipped with a change if are known. This mechanism requires a preliminary positioning function (referred to as mask alignment) to accurately set the mask at a predetermined position on the printing stage.

An object of the present invention is to provide an apparatus that achieves accurate mask alignment in a short time.

/7/ / /' , /' / /' / /' The present invention will be described in detail below with reference to the drawings, and FIG. 1 shows the external appearance. 1 is a mask provided with an integrated circuit pattern, and is provided with other mask alignment marks and mask/wafer alignment marks. Reference numeral 2 denotes a mask stage that holds the mask 1 and moves the mask 1 in a plane and in a rotational direction. 3 is a reduction projection lens, 4
shall be a wafer having a photosensitive layer, and shall have a mask-wafer alignment mark and a wafer-alignment mark. 5 is a wafer 1 stage. wafer 1
The stage 5 holds the wafer 4 and moves it in a plane and in the rotational direction, and also moves between the wafer printing position (inside the projection needle) and the television/wafer alignment position. 6 is an objective lens of a detection device for television wafer alignment, 7 is an image pickup tube or a solid-state image sensor, and 8 is a television receiver for video observation. 9 is a binocular unit, which is useful for observing the surface of Ueno-4 through the projection lens 3. Reference numeral 10 denotes an upper unit that houses an illumination optical system for converging the mask illumination light emitted from the light source 10& and a detection device for mask/wafer alignment. The wafer stage 5 holds the wafer transported by a wafer transport means (not shown) in a predetermined position, and first moves to a position where the alignment mark on the wafer is within the field of view of the television wafer alignment objective lens 6. . The positional accuracy at this time is due to mechanical alignment accuracy, and the field of view of the objective lens 6 is approximately 1 mm to 2 mm in diameter. The alignment mark within this field of view is detected by the image pickup tube 7, and the alignment mark is detected by the image pickup tube 7.
Using a TV/wafer alignment reference mark (described later) provided in the alignment optical system as a reference, the coordinate position of the alignment mark is detected. On the other hand, since the detection position for auto alignment of the projection optical system and the position of the reference mark for TV/wafer alignment mentioned above are set in advance, the auto alignment position can be determined from the coordinate position of these two points and the TV/wafer alignment mark. The feeding amount of the wafer stage 5 is determined.

Position detection accuracy for TV/wafer alignment is ±5μ
Even if we take into account the error caused by the movement of the wafer stage from the TV/Uni I alignment position to the mask wafer alignment position, it is ±10μ.
That's about it.

Therefore, alignment only needs to be performed within a range of approximately ±10μ,
This is a field of view that is less than 1/100 of the field of view of the conventional alignment, and alignment can be performed at a higher speed than the conventional alignment.The TV/wafer alignment will be explained in detail later.

FIG. 2 shows an embodiment for achieving mask alignment and mask-wafer alignment. In the figure, a mask 1, a reduction projection lens 3, a wafer 4, and a wafer stage 5 are the same as in FIG. The projection lens 3 is schematically depicted for convenience. Reference numerals 11 and 11' are mask alignment marks, which are carved in immovable locations such as the lens barrel or a part of the device.

On the other hand, the third
45 for scan line 60, as shown by numbering 75.76 in the figure.
``Alignment marks in the form of lines or slits arranged at an angle are provided.
1. The positions indicated by zf are numbered 71, 72, 73 for the third time.
, 74, which are arranged at an angle of 45' with respect to the scanning line 60, are provided with seven alignment marks in the form of lines or slits. Normally, positioning is performed using signals from both the left and right observation systems.

Note that the 7 alignment marks on the mask 1 and the alignment marks on the wafer are aligned so that the dimensions of both alignment marks do not change even if projection or back projection is performed when a system other than the same-magnification projection system is used. Here, the size of the alignment mark of the mask is set so that the size of the alignment mark of the mask is divided by the size of the alignment mark of the mask to obtain the reduction magnification.

Returning to FIG. 2, 22 is a laser light source, and 23 is an optical deflector such as an acousto-optic device. The optical deflector 23 switches the light emission direction upward, horizontally, and downward in response to a switching signal from the outside. 24 and 25 are convergent cylindrical lenses, which are arranged so that their generating lines are perpendicular to each other, and have the function of converting the cross-sectional shape of the laser beam into a linear shape.

26 and 27 are trapezoidal prisms, which have the function of refracting the light deflected upward and downward by the optical deflector 23 in opposite directions. 2
8 is a rotating polygon mirror (polygon) that rotates around a rotation axis 29 .

Depending on the state of the optical deflector 23, the laser beam 30 emitted from the laser light source 22 is divided into a slit-shaped beam 30a passing through the cylindrical lens 24 and the prism 26, a slit-shaped beam 30b1 passing through the cylindrical lens 25 and the prism 27, or Spot-like ray 30c traveling straight
In either case, the rotating polygon mirror 2
8 converges to a single point 31. 32, 33, and 34 are intermediate lenses, 35 is an optical path splitting mirror, and 36 is a visual observation system 3.
7. Forms 38/-F mirror, 37 is lens,
Reference numeral 38 denotes an eyepiece lens system t: which forms an image of the X-'' plane.039 forms an illumination system 40.41 for visual observation light.
40 is a condenser lens, and 41 is a lamp. 42 is a half mirror forming photoelectric detection systems 43, 44, 45, and 46; 43 is a mirror; 44 is a lens; 45 is a spatial filter; 46 is a condenser lens; and 47 is a photodetector. 48.49° 50.51 is a total reflection mirror, 52 is a prism, and 53 is an f-θ objective lens. 54 is the position of an alignment pattern provided on the mask 1 for mask alignment.

As shown in Figure 2, the signal detection system consists of completely symmetrical left and right systems.If the operator 9111 is on the front side of the paper, the system shown with a dash is the signal detection system on the right, and the system without a dash is the signal detection system on the left. I will call it.

The intermediate lenses 32, 33, and 34 form the origin of the deflection from the rotating polygon mirror 28 at @56 in the aperture position 55 of the objective lens 53. Therefore, the laser beam is scanned over the mask and wafer by the rotation of the rotating polygon mirror 28.

In addition, in the objective lens system, an objective lens 53, an aperture 55
, the mirror 51 and the prism 52 are movable in the XY directions by a moving means (not shown).
-4 observation and measurement positions can be changed arbitrarily.

For example, when the mirror 51 moves in the direction indicated by arrow A in the X direction, the objective lens 53 and the aperture 55 simultaneously move in the A direction, and in order to keep the optical path length constant, the prism 52 also moves in the A direction. The mirror 51 moves by 1/2 of the amount it moves.

On the other hand, when moving in the Y direction, the entire optical system for observation and position detection moves in the Y direction (direction perpendicular to the plane of the paper).

The scanning beam 61 of the optical path 30a passing through the cylindrical lens 24 forms an angle θ=45° with respect to the scanning axis 60,
It is parallel to the mark 71, 72, 75. When scanning is performed in this state, the photodetector 47,4τ has a voltage Sl as shown in FIG. 3 (tB).

S? O st t s where a signal of lI+ s is obtained.
, , and sn are signals corresponding to the alignment marks 71, 75, and 72, respectively. Further, even if there is minute dust on the scanning surface, unlike the case of a spot beam, it is averaged and is not practically detected as an output.

On the other hand, the optical path 30b passing through the cylindrical lens 25
The scanning beam 62 is inclined θ=-45'' with respect to the scanning axis 60 and is parallel to the marks 73, 74, and 76, so the detection signal becomes S?3+S?, S hinge in FIG. .Therefore, the detection signal S□r Syg + b* *S'lS
l sya t S? By measuring the interval 4, the amount of deviation between the mask and the wafer can be detected, and when they match, the intervals between the detection signals become equal.

The present applicant has proposed auto-alignment in Japanese Patent Laid-Open Nos. 53-90872 and 1987-91754.

As described above, using FIGS. 2 and 3, the alignment mark 20 on the mask 1 and the alignment mark 2 on the wafer surface are
1 alignment, that is, mask-wafer alignment, the present invention is particularly concerned with the alignment mark 54 on the mask 1 surface and the lens barrel 3 using the optical system and the alignment mark of the same shape as described above. The point is that the positioning of the mask reference mark 11 that is supported by non-uniform means, that is, the mask alignment can be performed. In this case, as described above, the objective lens 53, pupil 55, mirror 51, and prism 52 are aligned with the mask reference mark 11 in the direction A in FIG.
Move to the position and perform alignment.

The pattern for mask alignment is the pattern shown at 71, 72° 73.74 in Figure 3 for the mask reference mark 11, and the alignment mark shown at 75° 76 in Figure 3 for the mask area alignment mark 54. is provided.

Therefore, in mask alignment, the mask and mask reference mark are aligned in exactly the same way as in mask-wafer alignment, and the mask is set at a predetermined position relative to the lens 3. Since the reduction projection lens 3 is not used, the 7 alignment marks 54 and the mask reference marks 11 on the mask surface may be patterns with the same magnification.

By the way, since a reduction projection optical system is used in the stepper-type printing apparatus, the mask stage that holds the mask is usually moved for positioning during wafer alignment (Fig. 1, 2). It is. On the other hand, also in mask alignment, the mask stage moves to perform positioning. Therefore, in any case, two-line patterns 75 and 76 are provided on the moving mask side, but this is only one embodiment of the present invention, and four-line patterns 71 and 72 are provided on the mask side. , 73, 74 may be provided, and the number of patterns on the mask may be different between mask alignment and wafer alignment, and there is no limitation on pattern selection.

Next, the method of mask alignment will be explained in detail.

In mask alignment, the mask is transported from the mask change mechanism to the mask stage by means not shown,
However, since the positioning at this time is performed mechanically, the accuracy is low, and an error of several hundred μm occurs.

Therefore, when the field of view of the objective lens is narrowed, the mask alignment mark is not necessarily located within the field of view, that is, within the scanning range of the laser beam. Due to an error when setting the mask, the alignment mark on the mask may be out of view. In that case, ;S3 figure t131
No. 4j sys t S□, S□, S, 4th S was detected in S03. S. Since the signal of is not detected,
Auto alignment is not achieved.

In such a case, a process of searching for the mark on the mask is required, but in the conventional example, the stage holding the wafer or mask moves and searches for the mark while repeating what is called a groping drive. It's here.

In order to make the following explanation more understandable, a conventional groping drive example will be explained for the fourth position.

The figure depicts the locus of the objective lens when searching for an alignment mark on a mask or wafer surface. However, in reality, instead of moving the objective lens in the X and Y directions, it is preferable to move the stage holding the mask or the mask, but for the sake of explanation here, the objective lens is moved. Assume that the mask has been transported to position A (FIG. 4), which is approximately below the objective lens 53, by a well-known transport means (position A is referred to as the initial setting position). However, there is an error in the mask setting, and The length L and width T of the beam scanning range (
(See Figure 3) If - is not large enough to include the setting error, the mark M is not detected at position A, so the objective lens moves to the boundary of the groping drive range and starts groping drive from point B. Then, search for the mark while moving B-)C-)D-+E... In this example, mark M is detected during the third round trip to J-.

The following difficulties can be pointed out in the conventional example described above.

(1) Even though the probability of a mark existing is high near point A, it moves to the boundary area point B, where the probability of its existence is low, and starts the search from point B, so it takes a long time to detect the mark. .

(2) Since the stage is generally driven at low speed and with high precision, when searching for an alignment mark for alignment of a mask, etc., it takes time to move the stage and the detection time becomes long.

Since the embodiment described later adopts the following configuration, the detection time can be shortened.

(1) Search from the periphery of the initially set position of the objective lens toward the boundary area.

(2) More preferably, the stage is fixed during groping drive, and the objective lens, aperture, and optical
The prism 52 constituting the trombone is moved, and the entire scanning optical system 22 to 55 is moved in the Y direction. Generally, the stage is required to have the most precise positioning, so the transport mechanism must have a structure that meets this requirement. Therefore, it is not suitable for moving the stage at high speed.

FIG. 4(B) shows the locus of the groping drive according to the embodiment of the present invention. Here, the objective lens system searches for the mark while moving spirally from the initial setting position [A on the mask as A→P→Q→R→S→..., in this example, on the path from U to V. Mark M is detected. Since the probability that a mark exists is generally high near point A, there is an advantage that the time required for detection is short. It is assumed that the objective lens system is always set at the same position at the starting point of operation.

FIG. 5 shows a flow diagram showing movement of the objective lens system. When the groping drive starts at 501, the X direction movement force/Y direction movement counter is first cleared at 502. These two counters are counters that determine the amount of movement of the objective lens in the X and Y directions (the X and Y directions are shown in FIG. 4 fB+). Next, in step 503, a limit is determined to determine whether or not the boundary in the X direction of the groping drive has been reached.
A check is performed, and if it is within the limit, the content N of the X-direction movement counter is incremented at 504.

If the limit is reached after going through this loop several times as described later, jump 504 and go from 503 to 505.
Move to. At 505, movement is performed in the positive direction of X, and the amount of movement at this time is, for example, TXN. (T is the laser scan l as shown in Fig. 3) Here, in the first loop, A → shown in Fig. 4 (B)
P is moved.

Once the predetermined scene has been moved in the X direction, a limit check is performed in the (-) Y direction at 506, and if it is within the limit, the content M of the Y direction movement counter is checked at 507, as in the X direction. Increment, 5 if the limit is reached
The process in step 07 is jumped to and step 508 is performed. 508 is (-
) in the Y direction by an amount of LXM (L is the laser scan length shown in FIG. 3).

Similarly, 509.510.511 is processed in the (-)X direction, and then 512% 513.514 is processed in the Y direction. Next, check at 515 whether or not the limit of the groping drive has been reached in both the KX direction and the Y direction, and if so, check at 515.
It ends at 6, and if there is still some drive area left, it returns to 503.
Jump to and repeat the loop described above until you reach the limit.

Here, if we explain the amount of movement in the X direction and Y direction using the symbols in Figure 4 tBl, Tsukuda is twice that amount, Koma is three times that amount...
・Ashi, again, candy is twice as expensive as bad, W is three times as expensive as PQ, etc. Therefore, the number increases by one time and one time each time in the X direction and the Y direction, and this amount is counted by the X direction movement counter and the Y direction movement counter. Also M
The quantities 4 and 4 are equal to the laser scan width T and the laser scan length Ltd, respectively.

The situation in which one of the directions in fBl in FIG. This corresponds to passing the process 70- of 506→507.

Note that the example explained here is a method of searching in which two alignment patterns 75 and 76 on the mask are always detected. For example, after first detecting one of the above-mentioned patterns, Depending on the method of book detection, the pitch of the groping drive may be rough. In other words, day and day are T and L respectively.
It may be longer, so the amount of travel of the groping drive is not specifically limited to the trays described above.

Next, the interlocking and independent driving of the right objective lens system and the left objective lens system, which are other advantages of the present invention, will be described.

The explanation of the operation in Figures 3 and 4 was given for the objective lens system on one side, but in reality, as shown in Figure 2, the alignment mark groping drive is performed using the objective lens systems on both the right and left sides. conduct. In this case, there are two modes: a mode in which the objective lens systems on both sides are driven in conjunction with each other, and a mode in which they are driven independently, and the desired image mode can be selected.

In this case, the time to detect the alignment mark is slightly longer on average than in the case of independent drive, which will be described later, but since the operation of the objective lens system and its control are linked, the device itself is simple. .

By gropingly driving the other objective lens system counterclockwise as shown in Figure 4 (C), the operation is slightly more complicated than with interlocking driving, but the average time to detect the alignment mark can be reduced. Becomes shorter.

The present invention resides in that the interlocking drive mode and the independent drive mode can be selected as necessary. As an example of combining these methods, for example, there is a method in which the objective lens system is first driven in conjunction with each other in the vicinity of its initial position, and then driven independently toward the periphery.

Another example is a method in which interlocking driving is performed until one pattern of alignment marks is detected, and then independent driving is performed after detection, so that both objective lens systems detect four patterns. . This method is particularly effective when the drive pitch of the groping drive described above is rough or when there is a shift in the mask in the zero direction.

Next, we will discuss the use of beam shape selection for scanning beams. As explained in FIG. 2, the laser beam 30 does not pass through the cylindrical lenses 24 and 25, but uses the optical path 30c in which it travels straight. In this case, the beam becomes a spot-like beam and does not have a tilt characteristic like a slit-like beam, so the pattern 71.72.73.74
．． Signals can be obtained for either 75.76. In particular, this method is effective in mask alignment with sufficient light intensity and a good S/N ratio, but it can also be used in mask-wafer alignment without being limited thereto. Or, for example, in mask alignment, 04 lines on the mask or 4 lines on the mask
A method may also be used in which the spot beam is used until a total of six books and reference marks are detected, and then the beam is switched to a slit beam in the middle of scanning. This method eliminates the need for complex control and allows highly accurate alignment using sheet beams.The advantage of this method is that it provides a structure that generates both sheet beams and spot beams. The reason is that they can be selected depending on the target.

Next, the positioning of the mask after the objective lens is groped will be described using FIG. 4 (Bl).

When the mask alignment mark on the mask is detected by the groping drive as described above, the objective lens position M can be easily determined from, for example, the amount of movement of the reference mark from the position A.

Therefore, next, the objective lens system (52 to 53) is returned from position M to position A, and the mask stage 2 is also moved from M to A direction. When the movement is completed, both the mask reference mark and the mask alignment mark can be seen within the field of view of the objective lens, resulting in the state shown in the third position. In this state,
Since six alignment signals can be detected, all that is required is to measure the intervals between the six signals and perform alignment.

Next, referring to FIG. 6, a description will be given of the television/queuehar alignment detection device.

In the figure, a reduction projection lens 3, a wafer 4, an objective lens 6,
The shooting tube 7 is the same as in FIG. On the other hand, 91 is a light source for illumination, and uses a halogen lamp, for example. 92 is a condenser lens.

93A and 93B are a bright field diaphragm and a dark field diaphragm that can be attached and detached interchangeably, and in the figure, the bright field diaphragm 93A is installed in the optical path. A condenser lens 92 images the light source 11 onto a bright field aperture. 94 is a relay lens for illumination, and 95 is a cemented prism. The cemented prism 95 has a function of making the optical axis of the illumination system and the optical axis of the light receiving system coaxial, and includes an inner reflective surface 95a and a semi-transparent reflective surface 95b. . Here, a light source 91, a condenser lens 92, bright or dark field diaphragms 93A and 93B1, an illumination relay lens 94, a cemented prism 95, and an objective lens 6
constitutes an illumination system, and the speed of light emitted from the objective lens 6 is a mirror that falls on Unino-6. Reference numeral 98 denotes a glass plate having a reference mark for TV/wafer alignment, and the reference mark has the function of providing the origin of coordinates, so to speak. Therefore, the wafer alignment mark is detected as an X coordinate value and a Y coordinate value. Reference numeral 99 denotes an imaging lens, which together with the above-mentioned cemented lens 95, relay lens 96, mirror 97, glass plate 98, imaging lens 99, and imaging tube 7 constitutes a light receiving system, and the optical path passing through the objective lens 6 is inside the cemented prism. The light is reflected by the reflective surface 95a, reflected by the semi-transparent surface 95b, and reflected again by the inner reflective surface 15a toward the relay lens 96. The wafer alignment mark image on the wafer 4 is formed on the glass plate 98 having the reference mark, and then is imaged on the imaging surface of the image pickup tube 7 together with the reference mark image.

Next, I will explain the effect. The light flux from the illumination light source 91 is converged by the condenser lens 12, illuminates the aperture of the bright field diaphragm 93A or the dark field diaphragm 93B, further passes through the illumination relay lens 94, and is transmitted through the semi-transparent surface 95b of the cemented prism. The light is reflected by the reflective surface 95a and passes through the objective lens 6 to illuminate the wafer 4.

The light beam reflected on the surface of the wafer 4 is subjected to an imaging action by the objective lens 6, enters the cemented prism 15, and is reflected m+i.
9 s a, then semi-transparent surface 95b2 reflecting surface 1
It is reflected by 5 a and ejected, relayed by a relay lens 96 , reflected by a mirror 97 , and imaged on a glass plate 98 , and then imaged on an imaging tube 7 by an imaging lens 99 . At that time, as described above, with the bright field diaphragm 93A inserted, the gas is imaged of the reference mark on the second plate 98, the origin of the coordinates is determined using that image, and then the wafer is switched to the dark field state. The position of the wafer alignment mark image is detected by making the alignment mark image clearly visible and capturing the image. Then, according to the position of the Uni-I alignment mark detected by electrical processing, the Uni-no-- Stage 5
The Weber 4 is located at the specified position 4' in the projection field of the projection lens 30.
Move and stop so that it occupies the area.

Alternatively, the wafer 4 may be once aligned at a standard position and then deformed so as to be moved into the projection field.

The present invention described above fixes the stage that supports the mask when detecting the first alignment on the mask, so the search time can be shortened, and the alignment mark and the base mark can be brought close to each other before fine alignment. Therefore, the alignment operation takes a short time. In particular, when this alignment is achieved using a mask and a unique alignment detection device, alignment can be achieved with extremely high precision.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an apparatus according to an embodiment of the present invention. FIG. 2 is a side view of the optical system according to the embodiment. FIG. 5 (N is a plan view of the alignment mark, (Yen is a diagram of an example of the output signal when scanning the alignment mark. FIG. 4 (A) is a plan view for explaining the operation of the conventional example. In the figure, 1 is a mask, 2 is a mask stage, 5 is a reduction projection lens, 4 is a Unino~-15 is a Unino stage, 6 is an objective lens, 7 is an image pickup tube, 8 is a television receiver, 11 is a fixed mask-alignment mark, 22 is a laser light source, 25 is a light deflector, 24, 25 & cylindrical lenses, 26
and 27 are prisms, 2B is a rotating polygon mirror, 55 is an objective lens, 52 is a prism, 71, 72-75-74 are elements that form the unino side alignment marks, and 75 and 76 are mask side alignment marks. Elements forming the mark, A is the initial setting position, 4 is the alignment mark. 11

Claims (1)

[Claims] (1) In an apparatus for printing a mask pattern on a wafer, which includes a detection means for detecting a mask surface, a movement means for moving the mask, and a reference i-type for setting the mask, one of the detection means The first part moves on the mask to detect an alignment mark provided on the mask.
and a moving means is driven based on the detected signal to move the mask and also move part or all of the detection means so that the reference mark and the alignment mark of the wafer are within the detection range of the detection means. The second process of setting the fiducial mark and