JPS62160723A - Alignment apparatus - Google Patents

Abstract

PURPOSE:To make an ideal off-axis alignment free from offset possible, by performing the fine alignment of a reticle and a wafer applying an alignment optical system fixed with respect to a base. CONSTITUTION:A mounting stand on which a photo-sensitive substrate is mounted is capable of two-dimensional movement, and marks for alignment formed on the back surface of the photo-sensitive substrate can be observed by an alignment optical system. On the other part of the mounting stand than the mounting part of the photo-sensitive substrate, an optical pass-length calibration means is provided. The focal position of the alignment optical system is calibrated by an amount nearly corresponding with the thickness of photo-sensitive substrate, and a transferred image on the surface of photo-sensitive substrate on the mounting stand can be observed by the alignment optical system. According to such a means, the alignment optical system is capable of observing both of the transferred image formed on the surface of photo-sensitive substrate and the marks formed on the back surface of photo-sensitive substrate. Alignment accuracy can be increased, and matching between alignment systems can be easily attained, thereby.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an exposure apparatus that prints a necessary pattern on, for example, a resist layer on a semiconductor wafer, and particularly relates to an improvement of an alignment apparatus thereof. It is.

[Background of the invention]

In a conventional exposure apparatus, alignment marks are generally formed on the surface of a semiconductor wafer to be exposed, that is, the surface on which a resist (registration) IN is formed and irradiated with light. Then, using this mark and an alignment mark formed on the reticle or mask, the semiconductor wafer and the reticle (or mask) are aligned.

However, in such an alignment method, the alignment marks are observed through a resist layer coated on the wafer surface, making it difficult to observe them clearly, resulting in an increase in alignment errors. Particularly in recent years, as the degree of integration of integrated circuits has improved, patterns have tended to become increasingly finer, and there has been a desire to reduce such alignment errors.

Further, when performing die-by-die alignment as such alignment, it is necessary to provide a device such as an alignment optical system on the reticle, or it is necessary to set marks for die-by-die at fixed positions.

On the other hand, if such alignment devices are separated, it becomes necessary to perform matching between each alignment system.

[Purpose of the invention]

The present invention has been made in view of the above, and an object of the present invention is to provide an alignment device that improves alignment precision, allows easy matching between alignment systems, and provides a high degree of freedom in selecting mark positions. Its purpose is to

[Summary of the invention]

According to the present invention, the mounting table on which the photosensitive substrate is placed is two-dimensionally movable and is configured such that the back surface of the photosensitive substrate can be observed using an alignment optical system. The formed alignment mark is observed by an alignment optical system.

Optical path length correction means is provided in a portion of the mounting table other than the portion on which the photosensitive substrate is mounted. This optical path length correction means corrects the point position of the alignment optical system by an amount corresponding to the thickness of the photosensitive substrate, thereby observing the transferred image on the surface of the photosensitive substrate on the mounting table using the alignment optical system. It is now possible to do so. By this means, the alignment optical system can observe both the transferred image (pattern or mark) formed on the front side of the photosensitive substrate and the mark etc. formed on the back side of the photosensitive substrate.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the overall configuration of an embodiment of the present invention. In this figure, a reticle R on which a pattern to be exposed is formed is held in a reticle holder 1; The reticle R is supported at an appropriate position by a column 2. The reticle R is provided with alignment marks sx, sy, and sθ, and the reticle holder 1 is configured to be movable relative to the column 2 by a drive unit 3. has been done.

Next, a projection lens 4 is arranged below the column 2, and the wafer W is arranged at an optical position that is conjugate with the reticle R of the projection lens 4.

This wafer W is placed on a glass plate 5, and the glass plate 5 is further supported by a θ table 6. The θ table 6 is configured to be slightly rotatable about a rotation center 6a, and is driven by a θ table drive section 7, and the rotation angle is read by a θ angle reading encoder 8. The glass plate 5 described above is provided with a glass block 5A as an optical path length correcting means at an appropriate position, and a basic mark FM is formed on the surface of the glass block 5A.

This part will be explained in detail later.

Next, the θ table 6 is placed on two tables 9 that can be moved slightly in two directions, that is, in the up and down directions.

The movement of the two tables 9 is carried out by a two-table driving section 11 under the guidance of two-direction movement guide rollers 10.

Next, the two tables 9 described above are placed on the X stage 12 via two-direction movement guide rollers 10. This Y stage 12 is capable of rectilinear movement in a direction perpendicular to the plane of the drawing, and is driven by a Y stage drive section 16.

Next, the Y stage 12 is provided above the X stage 14. This X stage 14 is driven by an X stage drive unit 15 in the left and right directions in the figure, that is, in directions perpendicular to the z and y directions.
It is configured to be movable. This X stage 14 is arranged on a surface plate or a column plate 16.

Next, an objective optical system 17 is fixedly provided at approximately the center of the upper surface of this column space 16 between it and the glass plate 5 and facing toward the projection lens 4 . This objective optical system 17 is for detecting marks formed on the back surface of the wafer W. Furthermore, this objective optical system 17 detects the mark Sθ on the reticle R when the wafer W is not on the glass plate 5.

The projection lens 4 is installed so that the projected images of sx and sy can also be observed.
It is arranged coaxially with the optical axis AX of.

A light source 18 such as a laser is provided laterally inside the column base 16, and the light is configured to enter the objective optical system 17 through a half mirror 19. Further, on the bottom side of the column base 16, an alignment sensor section 20θ is provided corresponding to the objective optical system 17 and the half mirror 19.

20X and 20Y are provided respectively. These alignment sensor sections 20θ, 20X, and 20Y photoelectrically detect the marks formed on the back surface of the wafer W or the projected images of the marks Sθ, sx, and sy on the reticle R, and align these marks with a predetermined detection center. This is to detect the deviation of the Since these alignment optical systems are all fixed to a surface plate, that is, the column base 16, they are hardly affected by vibrations of the stage or the like. Therefore, alignment can be performed with high precision.

Next, a movable mirror 30 is provided on the side above the two stages 9 mentioned above, and a fixed mirror 31 is fixed to the lower part of the lens barrel of the projection lens 4. The movable mirror 60 includes a mirror 32
The light from the interferometer 64 is incident on the fixed mirror 31 via the beam splitter 33, and the light from the interferometer 64 is incident on the fixed mirror 31 via the beam splitter 33. 34 lights are incident on the movable mirror 30 and the fixed mirror 31, respectively, and the coordinate values of the wafer W by the Y and X stages 12 and 14 are measured by using the interference of each reflected light. .

Next, the alignment sensor section 20θ/20X described above,
20Y are each connected to the alignment processing section 40. The alignment processing unit 40 determines the amount of position correction of the wafer W in the θ, X, and Y directions based on alignment signals from the alignment sensor units 20θ, 20X, and 20Y.

Next, the drive unit 3, the θ table drive unit 7, the angle reading encoder 8, the table drive unit 11, the Y stage drive unit 13, the X stage drive unit 15, the interferometer 64, and the alignment processing unit 40 are is also connected to the main controller 50. This main controller 50 (controls the drive unit 6 during alignment of the al reticle R), controls the θ table drive unit 7, angle reading encoder 8, Y stage drive unit 16, and X during global alignment of the wafer W. Stage drive unit 15, control by interferometer 64, (C) 2-table drive unit 1 during alignment for each exposure shot (so-called die-pie-die alignment)
1. It controls the control by the Y stage drive section 13, the X stage drive section 15, the interferometer 64, the alignment processing section 40, etc.

FIG. 2 shows an example of a projected image of marks sx, sy, and sθ on the reticle R on the wafer W. In this figure, the inner frame represents a small shot size SS, and the outer frame represents a large shot size LS. Note that the shot size is the size of one pattern to be exposed. In both cases, the shot center or reticle center SC is shown together.

The mark images sxs, sys, sθS are shot size S
Marks sx, sy of reticle R at S.

This is a projected image of Sθ, and mark images 3XL and SYL.

SOL is a projected image of marks sx, sy, sθ of reticle R at shot size L8. The x-y coordinates in this figure are two-digit running coordinates on the wafer stage.

Next, with reference to FIG. 3, the glass block 5A of the glass plate 5 shown in FIG. 1 and the fiducial mark FM (Videocular Mark) will be explained.

The glass block 5A is provided on the glass plate 5 at a position other than the wafer mounting surface, and the surface height of the glass block 5A is higher than the surface of the wafer W placed on the glass plate 5 or the exposure surface. almost corresponds to the height of The fiducial mark FM is formed of paulownia material such as chrome on the glass block 5A.

In FIG. 3, the glass block 5A has a circular plane, and two sets of fiducial marks FMX, FMy are formed corresponding to the same coordinates as the running coordinates x, y of the wafer W shown in FIG.
are formed respectively. The fiducial mark FMx consists of two parallel lines extending in the y direction.
y consists of two parallel lines extending in the X direction.

In addition, when the glass block 5A is equipped with a focusing device (not shown), the glass plate 5 can be moved up and down, so that it can be aligned accurately with the imaging plane of the projection lens 4.

Next, while referring to FIG.
The configurations of 0X, 20Y, and 20θ will be explained in detail.

Since both have the same configuration, the alignment sensing section 20Y will be explained as a representative.

As shown in FIG. 1, the imaging plane FP of the objective optical system 17 coincides with the back surface of the wafer W, and the object or aerial image P,, P, on this imaging plane FPo is the objective optical system. 17, images Qt and Qt are formed.

The aerial image P,,P, is a mark formed on the back surface of the wafer W or a mark SYL shown in FIG.

sys, sθL, and SO3 correspond to each other. These statues Q
, ·Q, are formed by the light from the light sources 55A and 55B.

The light from the light source 55A passes through the lens 53 through the shutter 54A.
incident on A. Furthermore, after passing through the half mirror 52A and the first objective lens 51A, the optical axis is bent in the direction of the objective optical system 17 by the 50 mirrors. The bent light passes through the objective optical system 17, is reflected by an object or an aerial image P on the imaging plane FP, passes through the objective optical system 17 again, and then enters the mirror 50A.

The optical axis is bent by the mirror 5DA, passes through the first objective lens 51A, and is reflected by the half mirror 52A. The reflected light passes through the window APY through the aperture plate 57A and the imaging lens 58A, and enters the television camera 59AK. Of these, the mirror 50A and the first objective lens 51A are movable as a whole in the direction of the arrow PAY except during alignment. This is an operation that should be performed in conjunction with changing the shot size LS, 88 shown in FIG. Light source 55A corresponds to light source 18 in FIG. In addition, the window APY of the aperture plate 57A
defines the detection center of the alignment centimeter section 20Y. The position of this window APY, the position of the object P, and the position of the image are all conjugate, and
The positions of the window APY and the light-receiving surface of the television camera 59A are also conjugate.The above-mentioned parts constitute the alignment sensor section 20Y. Alignment sensor section 20X.

The same applies to 20θ, and in FIG. 4, among the components of the alignment sensor section 20θ, a mirror 50B and a first objective lens 51B, which move together in the direction of the arrow ○, are shown.
, a shutter 54B, a light source 55B, an aperture plate 57B having a window APθ, and a television camera 59B.

Next, referring to FIG. 5, an example of the arrangement of marks on the imaging plane FP explained in FIG. 4 will be described.

This figure shows the shot size LS marks SX, SY, on the reticle R after removing the wafer W from the glass plate 5.
It is a projection of Sθ.

In FIG. 5, the center of the xy coordinate system corresponding to the running coordinates of the wafer stage coincides with the optical axis AX of the objective optical system 17. That is, the xy coordinate system is fixed to the objective optical system 17, and even if the glass plate 5 or the wafer W moves, the origin does not move with it.

In the image field IF, which is the field of view of the objective optical system 17, as explained in FIG.
If there is θL and the alignment is good, these images SXL.

SYL, SθL are alignment sensor parts 20X, 20
Y.

Draw a black mark at the center of the 20θ detection windows APX, APY, and APθ.

Then, when the stages 12, 14, etc. are moved, the reference mark F corresponding to the shot size LS among the base marks is
MxL and FMyL are each images SXL.

They can be arranged with SYL in the center.

Note that the reference marks FMxS and FMyS correspond to the shot size SS1.Next, the overall operation of the above embodiment will be explained with reference to Figures 6 to 9 in addition to the above-mentioned drawings. .

Note that in this embodiment, the marks sx on the reticle R,
The shapes of sy and sθ are shown in Figure 6 (like Al, and
Assume that the marks for die-by-die alignment formed on the back surface of the wafer W are as shown in the same figure (BS), and that the fiducial mark FM is shaped as shown in the same figure (C1). The senna output when the sensor means scans in the direction of the arrow from FIG. 6 to fcl is
The CDI (as shown in El, IF+ in Figure 6) is the result when the reticle R is illuminated with illumination light from above and the projected images of marks sx, sy, sθ are photoelectrically detected by the alignment sensor. It is a waveform. Figure 6 (F'l is also the waveform when the reference mark FM is illuminated with light passing through the projection lens. In either case, the mark part is light-shielding, so the sensor output is at a low level. Therefore, the alignment sensor side The mark S on the reticle R is illuminated by the illumination light from
When illuminating X, SY, Sθ or the reference mark 11'M, the reflected light from the mark portion returns to the alignment sensor, so the low level and high level of the waveform of fFl shown in Fig. 6 are reversed. . On the other hand, since only the illumination light from the alignment sensor side is used to detect marks on the back side of Ueno 1, the light is scattered at both edges of the mark, and the specularly reflected light is returned at other parts, as shown in Fig. 6 fEl. The waveform will bottom out at the edge. Also, Figure 6 (Dl
Even with a waveform like , if differential processing is performed, a waveform like that shown in FIG. 6 (ε) can be obtained, so the electrical processing circuit can be simplified.

First, as shown in FIG.
(See Figure 5).

Next, the reticle R is illuminated with illumination light LB or illumination light (55A, 55B) that illuminates the back surface, and its pattern, particularly marks sx, sy, sθ, are projected through a projection lens. At this time, the reticle R is moved by the drive unit 6 or the stage 12.14 is moved so that the marks sx, sy of the reticle R are aligned with the reference mark SX, as shown in FIG.

3Y is placed within the reference marks p'Mx and FMy.

As described above, the focal position of the projection lens 4, that is, the conjugate position is the upper surface position of the wafer W placed on the glass plate 5. Therefore, the marks sx, sy are imaged on the surface of the glass block 5A.

On the other hand, the conjugate position of the objective optical system 17 is the back surface position of the glass block 5, but since the thickness of the portion to the glass block 5 is different, the conjugate position is the surface thereof. Since this position almost coincides with the surface position of the wafer W, the images SXI of the marks sx, sy.

SYL and the reference marks F'Mx and FMy can be observed simultaneously in the objective optical system.

Here, taking the mark SY as an example, an image SYL is formed between the reference marks F'My by the exposure illumination system. Therefore, the alignment sensor part 20
When the detection window APY is scanned by Y, a signal as shown in FIG. 9(A) is obtained.

The bottoms at both ends of this figure are those of the fiducial mark FMy, and the bottom in the middle is that of the image SYL. From this signal, the deviation Δa between the center of the reference mark FMY and the center of the image SYL can be determined. This deviation Δa corresponds to the amount of deviation of the reference mark FMY and the mark SY of 1,000 km. Further, in the same figure, the shift lid Δb is the shift amount between the mark SY on the reticle R and the alignment sensor section 20Y.

Next, the shutter 54A (
4) is opened and illuminated from below by the light source 55A, the signal from the alignment sensor section 20Y becomes Wj9.
The result is as shown in Figure (B). In this case, since it is reflected light, the peaks at both ends of the figure are those of the reference mark FMY, and the intermediate peak is that of the mark SY. Since this signal was also obtained using the same detection window APY, the peak of either the left or right reference mark FMY is shown in Figure @9 (Al
By comparing this with the above, it is possible to determine the amount of deviation ΔC due to the error in telecentricity of the illumination system.

Based on the values of the deviation amounts or offset amounts Δa, Δb, and ΔC determined as described above, the accurate position of the reticle R with respect to the objective optical system 17, that is, the objective optical system 17
It becomes possible to know the position of the reticle R within the coordinates x and y centered on .

These data are sent from the alignment processing section 40 to the main control device 50.

Next, the wafer W is first coated with a resist on its back side, and a plurality of marks sx, sy, sθ of the reticle R are sequentially printed for each shot to form uneven marks using a well-known method. After the marks are formed on the back side, the wafer W is placed on the glass plate 5 so that the front side thereof faces the projection lens 4.

Then, as shown in FIG. 8, the light source 18 (or 55A,
55B, etc.), alignment is performed, and the pattern of the reticle R is printed. In alignment at this time, there is a difference Δd between the center of the detection window APY of the alignment sensing section 20Y and the center of the alignment mark SY of the target shot.
is obtained as shown in FIG. 9(O), and similarly transferred from the alignment processing section 40 to the main controller 50.

Using these offset amounts Δa, Δb, and ΔC1Δd, the alignment before the pattern printing is performed, and the alignment position is finally determined.Next, referring to FIGS. 10 and 11, , a specific example of calculating the alignment position will be explained. Note that this example shows a case where a reference mark corresponding to the mark Sθ of the reticle R is also provided on the glass block 5A.

In FIG. 10, signal waveforms corresponding to IAI in FIG. 9, which occur when the reticle R is illuminated from above, are shown for marks sx, sy, and sθ of the reticle R, respectively. Detection windows for each alignment sensor section 20X, 20Y, 20θ,
The distances from one end of APX, APY, and APθ (see Figure 5) to the center of the reference mark are DMX, DMY, and D, respectively.
Mθ and mark SX.

Let the distances to the centers of the images SXL, SYL, and SθL of sy and sθ be RX, RY, and I'tθ, respectively. Also, distance DM
With respect to
, SDMY, and SDMθ.

Next, as shown in FIG.
Marks sx, sy from one end of APθ.

Let the distances to the mark center on the back surface of the wafer W corresponding to Sθ be DX, DY, and Dθ, respectively.

In the above case, the offset tXoff, Yoff・Doff in mark detection for each x, y, θ is Xo
ff=DX-RX-(SDMX-DMX)...
...(1)Y o f f =DY-RY-(S
DMY-DMY) ......(2) θoff=
Dθ−Rθ−(SDMθ−DMθ)−YOFFSET・
...(3) It is expressed as follows.

In the above example, the alignment sensor section 20X.

Although the offset amount is determined using the detection windows of 20Y and 20θ as a reference, the offset amount may be determined with respect to the reference mark FM, for example.

In this way, by using the glass block 5A, the objective optical system 17 can observe both the mark formed on the back surface of the wafer W and the mark of the reticle R projected on the front surface. The offset amount described above can be found by By correcting the amount of offset during step-and-repeat alignment, it is possible to successfully project and transfer the pattern to the corresponding position on the front surface of the wafer W, following the alignment made by the marks on the back surface of the wafer W. .

It should be noted that the present invention is not limited to the above-described embodiments; for example, the shape of the mark on the reticle, the shape of the reference mark, etc. may be changed as desired.

Furthermore, it is more convenient to incorporate an automatic focusing mechanism for moving lens elements and the like in the optical axis direction into the alignment optical system shown in FIG. 4.

〔Effect of the invention〕

As explained above, according to the alignment device according to the present invention, the alignment optical system is fixed to a predetermined base, and there is no offset that occurs when using this alignment, and ideal off-axis alignment can be performed. Such alignment becomes more perfect due to the telecentricity between the illumination system of the reticle or mask and the self-illumination system of the alignment device, and the offset correction function that removes the offset caused by the difference in light amount between the two.

Furthermore, since the alignment result for the reticle is directly taken into consideration as an offset value for alignment to the query, it is necessary to observe the offsets in the x, y, and θ directions simultaneously.
(Then, the time required for reticle alignment is only the sampling time and computation time in the illumination system and self-illumination system of 1,000 KR, so it is possible to improve throughput.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the overall configuration of an embodiment of the present invention, Figure 2 is an explanatory diagram showing examples of marks on a reticle, Figure 3 is an explanatory diagram showing examples of reference marks, and Figure 4 is an illustration of alignment. Figure 5 is an explanatory diagram showing an example of mark arrangement in the image field of the objective optical system; Figure 6 is an illustration showing the operation of the alignment sensor unit and an example of the output signal waveform. 7 is an explanatory diagram showing the operation during fine alignment, FIG. 8 is an explanatory diagram showing the operation during guide alignment, FIG. 9 is an explanatory diagram showing the operation to obtain the offset amount, and FIG. FIGS. 10 and 11 are explanatory diagrams showing specific examples of offset amounts. Explanation of symbols of main parts, 4... Projection lens, 5... Glass plate, 5A.
...Glass block, 6...θ table, 12...
Y stage, 14...X stage, 16...column pace, 18...light source, 20X, 20Y, 20θ...
・Alignment sensor section, 40... Alignment processing section, 50... Main f%II m'Set, R・
...Reticle, W...Wafer, FM,...Mark the base. Agent Patent Attorney Masatoshi Sato (A) CB) CD) (E) 6 Shiku C no CF)

Claims (1)

[Scope of Claims] When transferring a pattern on a mask to a photosensitive layer of a photosensitive substrate, an alignment mark formed in advance on the back surface of the photosensitive substrate is detected using an alignment optical system, thereby aligning the mask with the photosensitive layer. In an alignment device that aligns the relative positional relationship with a substrate, the mounting table includes a mounting table on which the photosensitive substrate is placed so as to be movable two-dimensionally, and a back surface of the photosensitive substrate can be observed by the alignment optical system. and, the alignment optical system is provided in a part of the mounting table other than the part on which the photosensitive substrate is placed, and corrects the focal position of the alignment optical system by an amount corresponding to the thickness of the photosensitive substrate. 1. An alignment apparatus comprising: an optical path length correcting means for making it possible to observe a transferred image at a surface position of a photosensitive substrate on a mounting table.