JPH06204117A - Position alignment method - Google Patents

Abstract

PURPOSE:To save prealignment using observation optical system, by increasing position deviation which can be detected by the images of alignment marks of a wafer and a mask. CONSTITUTION:The right and the left (x) alignment marks Max, Mbx, arranged in a pair of minute regions of a mask M consist of a pair of (x) line patterns Ma1, Ma2, Mb1, Mb2 putting the centers of the minute regions between them. The right and the left (x) alignment marks Wax, Wbx, arranged in a pair of minute regions of a wafer W consist of an (x) line pattern Wa1 and an (x) line pattern Wb1 which are deviated in the opposite directions from the centers of the minute regions. The position alignment of the wafer W and the mask M in the (x) direction is performed as follows; while each of the (x) line patterns of the wafer W and the mask M are observed on the TV screen of an observation optical system E1 the wafer W and the mask M are relatively moved, and the centers of the respective minute regions are made to coincide with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment method for aligning a wafer to be exposed with a mask in a semiconductor exposure process.

[0002]

2. Description of the Related Art In a semiconductor exposure process, it is required to align a wafer to be exposed with a mask with high accuracy, but it is necessary to observe an alignment mark provided on the wafer and the mask with an image recognition device. Final alignment (hereinafter referred to as "final alignment")
First, rough alignment (hereinafter referred to as "pre-alignment") is required before performing.

As a pre-alignment method, a mechanical alignment method in which a positioning pin or the like is pressed against the outer peripheral portion of the wafer, or a pre-alignment mark is added on the wafer and the pre-alignment mark is observed by the image recognizing device or the like and predetermined. There is a method for detecting the amount of positional deviation with respect to the reference position. In the latter case, it is necessary to provide a lens exchange device for changing the observation magnification for pre-alignment in the observation optical system for obtaining the image of the alignment mark for the final alignment.

FIG. 11 shows a conventional exposure apparatus of the type in which a pre-alignment mark is added to a wafer and the wafer is observed by an image recognition apparatus to perform pre-alignment. In FIG. 11, 13 is an air bearing, 18
While the mask 15 and the wafer 17 are kept parallel to the projection optical system 11 by the connecting plate, they can be moved forward or backward (Y direction) in the direction perpendicular to the paper surface of FIG. Further, 14 is a mask moving stage and 16 is a wafer moving stage, which moves in the X, Y and θ directions.
Here, the X direction refers to the left-right direction of the paper (perpendicular to the Y direction), and the θ direction refers to the rotation direction of the mask or wafer.

Reference numerals 12a and 12b denote left and right objective lenses, and 19
Is a relay lens, 20 is a mirror, and 21 is a roof prism, and the observation optical system E ₀ forms images of the left and right objective lenses 12a and 12b on the surface of the roof prism 21. These images are input to the TV camera 24 through the erector lens 13a and the reflection mirror 23, or
It can be visually observed through the eyepiece lens 25. The observation objects of the left and right objective lenses 12a and 12b can observe a predetermined range of the mask 15 and the wafer 17 by moving the connecting plate 18 by the air bearing 13. The observation magnification can be changed by switching the erector lenses 13a and 13b.

The image captured by the TV camera 24 is analyzed by the image recognition device 26, and the interface 2
It inputs to CPU28 via 7. The CPU 28 outputs the movement amount of the wafer moving stage based on this image data via the interface 29, and the wafer moving stage 1
Drive 6 As a result, the wafer is positioned or the mask and the wafer are aligned.

FIG. 12 is a diagram for explaining pre-alignment and final alignment in the exposure apparatus of FIG.
First, the mask 15 and the wafer 17 are integrally moved in the Y direction by a carriage (not shown), so that the left and right objective lenses 12a and 12b pass through the windows 15a and 15b of the mask 15 and the left and right pre-alignment marks P of the wafer 17. _a , P
It is moved to the position where the image of _b is obtained. Here, the observation magnification is 1
The double erector lens 13a is inserted into the observation optical path to obtain a wide field of view and pre-alignment is performed. After that, the above-mentioned carriage is driven so that the left and right objective lenses 12a and 12b are aligned with the alignment marks M _c and M _{d of the} mask 15 and the wafer 1.
The mask 15 and the wafer 17 are integrally moved by the carriage so as to reach the positions where the images of the alignment marks W _c and W _d of 7 are obtained. At the same time, an erector lens 13b with an observation magnification of 5 times is inserted in the observation optical path to observe the relative positions of the left and right alignment marks M _c and M _{d of the} mask 15 and the left and right alignment marks W _c and W _d of the wafer 17 with high precision and high accuracy. Then, the positional displacement between the mask 15 and the wafer 17 is calculated by image processing in the image recognition device 26, and the wafer moving stage 16 is driven based on this to perform the final alignment.

FIG. 7 shows the left and right alignment marks M _c and M _{d of the} mask 15 and the left and right alignment marks W _c of the wafer 17 obtained on the screen of the TV camera 24 when the final alignment is completed in this way. An image of W _d is shown. The alignment mark M _{c on} the left side of the mask 15 includes a pair of x straight line patterns M _c1 and M _c2 extending in the Y direction provided in a predetermined minute region of the mask 15 and an X direction provided in a minute region adjacent to the x straight line pattern M _c1 . It is composed of a pair of y straight line patterns M _c3 and M _c4 extending in the same manner. Similarly, the right alignment mark M _{d of the} mask 15 is also a pair of x straight line patterns M _d1 and M provided in a predetermined minute area of the mask 15. It is composed of _d2 and a pair of y straight line patterns M _d3 and M _d4 provided in a minute area adjacent thereto.

The left alignment mark W _c of the wafer 17 is defined by a single x straight line pattern W _c1 extending in the Y direction provided at the center of a predetermined minute area of the wafer 17 and the center of the minute area adjacent to the x linear pattern W _c1. Y extending in the X direction
The straight line pattern W _{c2 is formed} , and similarly, the right alignment mark W _d on the wafer 17 is also formed by one x line pattern W _d1 and one y line pattern W _d2 . On the TV screen when the final alignment is completed, the x-line pattern W _c1 and the y-line pattern W _c2 of the left alignment mark W _c of the wafer 17 are respectively the x-line pattern M _c1 of the left alignment mark M _c of the mask 15. , M
_It is located at the center between _c2 and the center between y straight line patterns M _c3 and M _c4 . The same applies to the right alignment mark M _d of the wafer 17 and the right alignment mark M _d of the mask 15. In the above TV screen, the separation distance P ₀ between the left and right x linear patterns W _c1 and W _d1 of the wafer 17 is equal to the separation distance between the left and right alignment marks M _c and M _d of the mask 15 in the X direction. .

FIGS. 8 to 10 show alignment marks M _c , M _d of the mask 15 and alignment marks W _c , W _c of the mask 15 on the TV screen when the positional deviation between the mask 15 and the wafer 17 is detected. Indicates W _d . That is, FIGS. 9 and 10 show the wafer 1 on the TV screen.
The position shift amounts of the alignment marks W _c and W _{d of} No. 7 and the alignment marks M _c and M _d of the mask 15 are directed toward the lower right side and the upper left side in the figure, respectively.
6 shows the state of reaching the limit of the observable range according to 6,
FIG. 8 shows an intermediate state between the two.

The range of the amount of misregistration that can be observed by the image recognizing device 26 is between the x straight line patterns M _c1 and M _c2 of the left and right alignment marks M _c and M _d of the mask 15 on the TV screen and the x straight line pattern M. The separation distance A ₀ between _d1 and M _d2 and the y straight line pattern between M _c3 and M _c4 and y
The separation distance B ₀ between the linear patterns M _d3 and M _d4 and the wafer 1
X alignment patterns W _c1 , W _d1 and y alignment patterns W _c2 of the left and right alignment marks W _c , W _d of 7, respectively.
Each line width C ₀ of W _d2 and each x straight line pattern M _c1 , M of the left and right alignment marks M _c , M _d of the mask 15.
_c2 , M _d1 , M _d2 and each y straight line pattern M _c3 , M _c4 , M
The line width D ₀ of each of _d3 and M _d4 , the minimum value ΔX _{0 in} the X direction of the separation distance between the alignment mark of the mask 15 and the alignment mark of the wafer 17 necessary for observation by the image recognition device 26, and the minimum value in the Y direction. It is represented by the value ΔY ₀ as

Sx ₀ = ± 1/2 {A ₀ − (C ₀ + D ₀ + 2ΔX ₀ )} (1) Sy ₀ = ± 1/2 {B ₀ − (C ₀ + D ₀ + 2ΔY ₀ )} (2) where Sx ₀ : range of misregistration amount in the X direction that can be detected by the image recognition device 26 Sy ₀ : range of misregistration amount in the Y direction

[0013]

However, according to the above-mentioned conventional technique, the amount of positional deviation between the wafer and the mask in the X direction and the Y direction is expressed by the equations (1) and (2) on the TV screen, respectively, in the final alignment. If it is within the range, it can be detected by the image recognition device, but if it exceeds this range, it cannot be detected. Therefore, pre-alignment using an erector lens with an observation magnification of 1 is required as described above. In addition, if the amount of positional deviation between the wafer and the mask exceeds the above range during the final alignment process,
It is necessary to replace the erector lens with an observation magnification of 5 times with an erector lens with an observation magnification of 1 time and perform pre-alignment again.

The present invention has been made in view of the above-mentioned conventional technique, and provides a positioning method capable of increasing the amount of positional deviation that can be detected by the image recognition device and omitting pre-alignment by the observation optical system. That is the purpose.

[0015]

In order to achieve the above object, a method of the present invention is an alignment mark in which a pair of predetermined minute areas of a wafer and a pair of predetermined minute areas of a mask are provided in each minute area. A method of aligning the wafer and the mask by performing relative positioning based on a pair of patterns in which the alignment marks of each minute region of the mask sandwich the center of the minute region. The alignment mark of one of the minute areas of the wafer consists of one pattern spaced from the center of the minute area in one direction, and the alignment mark of the other minute area of the wafer is the center of the minute area. From one pattern in the opposite direction to the above.

The alignment mark of each micro area of the wafer may be composed of a pair of patterns sandwiching the center of the micro area.

[0017]

According to the apparatus of the present invention, the alignment mark on one of the wafer and the mask is irradiated with illumination light, and while the observation mark is observed by the observation optical system, the wafer and the mask are moved relatively to each other. Pattern on the mask at a position that is offset from the center of both patterns on one side of the mask by a predetermined distance in one direction, and the pattern of the other alignment mark on the wafer from the center of both patterns on the other alignment mark of the mask. By overlapping at a position displaced by a predetermined distance in the opposite direction, the two minute regions of the wafer are positioned relative to the two minute regions of the mask, respectively, and the wafer and the mask are aligned. Compared with the case where the pattern of each alignment mark on the wafer is arranged at the center of the minute area, the amount of positional deviation that can be detected by the observation optical system increases by the amount that each pattern deviates from the center of the minute area. .

[0018]

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

FIG. 1 is an explanatory view for explaining an embodiment, and an exposure apparatus S ₁ is a well-known projection lens system 1
And the left and right objective lenses 2a and 2b, an erector lens 3 having an observation magnification of 5 times, and an observation optical system E ₁ having an image recognition device (not shown). To do. A wafer W is held on a wafer moving stage (not shown), and a mask M is held on a mask moving stage (not shown). The mask M has a pair of x-alignment marks M, which are a pair of alignment marks, in the minute regions adjacent to both side edges thereof.
_ax and M _bx , and y alignment marks M _ay and M _by which are a pair of alignment marks respectively in the minute areas adjacent to them, and the wafer W is also in the minute areas adjacent to both side edges thereof. Each has a pair of x alignment marks W _ax and W _bx ,
Also, a pair of alignment marks, y alignment marks W _ay and W _by , are respectively provided in the minute areas adjacent to this.

The x alignment mark M _{ax on} the left side of the mask M
Consists of a pair of x linear patterns M _a1 and M _a2 which are separated from each other in the X direction from the center of the minute region, and the y alignment mark M _ay is a pair separated from each other in the Y direction from the center of the minute region. Pattern of y linear patterns M _b3 and M _b4 , and similarly, the x alignment mark M _{bx on} the right side of the mask M is a pair of patterns linearly spaced from each other in the X direction from the center of the minute region. M _b1 ,
The y alignment mark M _by is composed of M _b2 and is a pair of patterns spaced from each other in the Y direction from the center of the minute region.
It consists of straight line patterns M _a3 and M _a4 .

The left x-alignment mark W _ax of the wafer W is a pattern extending in the Y direction at a position displaced to the left by a predetermined distance from the center of the minute area x.
It consists of a straight line pattern W _a1 and y alignment mark W _ay
Is a pair of y straight line patterns W _a2 and W _a3 which are spaced apart from each other in the Y direction from the center of the micro area, and similarly, the x alignment mark W _{bx on} the right side of the wafer W is also a predetermined distance from the center of the micro area. The y alignment mark W _by is composed of one pattern x straight line pattern W _b1 located at a position shifted to the right side, and the y alignment mark W _by is a pair of patterns y line linear patterns W _b2 , W spaced apart from each other in the Y direction from the center of the minute region. _It consists of _b3 .

X alignment marks M _ax , M of the mask M
The relative positions of the _bx and y alignment marks M _ay and M _by and the x alignment marks W _ax and W _{by of the} wafer W and the y alignment marks W _ay and W _by are such that the wafer moving stage is moved and the TV camera of the image recognition apparatus is operated. when aligned overlap the center of each minute area of the wafer and the mask is completed in the screen, as shown in Figure 2, each y alignment mark W _ay of the wafer W, W _by the y alignment mark M _ay mask M , M _by , and at the same time, the left x straight line pattern W _a1 of the wafer W is adjacent to the left x straight line pattern M _a1 of the left x alignment mark M _ax of the mask M,
The right x straight line pattern W _{b1 on} the wafer W is the right x pattern on the mask M.
It is set so as to be adjacent to the right x straight line pattern M _b2 of the alignment mark M _bx .

At this time, the separation distance P ₁ between the x linear patterns W _a1 and W _b1 of the left and right x alignment marks W _ax and W _bx of the wafer W and each x alignment mark M of the mask M.
_The distance P ₂ between the centers of _ax and M _{bx and} the distance x ₁ between the x alignment patterns M _a1 and M _a2 of the left x alignment mark M _ax of the mask M (the distance between the right x alignment mark M _{bx and} the straight line pattern M 1) _b1 and M _b2 ) and the y straight line pattern M _a3 of the left y alignment mark M _ay of the mask M,
The separation distance B _{1 of} M _b4 (equal to the separation distance of the y straight line patterns M _b3 and M _b4 of the right y alignment mark W _by ) and the y straight line pattern W _a2 and W of the left y alignment mark W _ay of the wafer W. The separation distance B _{2 of a3} (equal to the separation distance of the y straight line patterns W _b2 and W _b3 of the right y alignment mark M _by ) and the x straight line patterns W _a1 and W _{b1 of} the wafer W and the y straight line patterns W _a2. , W _a3, W _b2, and the line widths C ₁ of the W _b3, each x linear pattern M _{a 1} in the mask M,
M _a2 , M _b1 , M _b2 and each y straight line pattern M _a3 , M _a4 ,
The line width D ₁ of each of M _b3 and M _b4 , the minimum value ΔX _{1 in} the X direction of the separation distance of each pattern required for observation by the image recognition device, and the minimum value ΔY _{1 in} the Y direction are as follows. The relationship is established.

P ₁ = P ₂ + ΔP or P ₂ −ΔP (3) B ₁ = B ₂ + ΔB (4) Here, ΔP = A ₁ − (D ₁ + C ₁ + 2ΔX ₁ ) ...
・ (5) ΔB = D ₁ + C ₁ +2 ΔY ₁ ... (6)

That is, the left x straight line pattern W _a1 of the wafer W overlaps with a position displaced from the center between the left x straight line patterns M _a1 and M _{a2 of the} mask M by ΔP / 2 to the left or right in the drawing, and X straight line pattern W on the right side of wafer W
_a2 is overlapped at a position displaced by ΔP / 2 to the right or left in the figure from the center between the right x-line patterns M _b1 and M _b2 of the mask M, and the left y-line pattern W _a2 of the wafer W,
W _a3 is the left y straight line pattern M _a3 , M of the mask M, respectively.
The y-line patterns W _b2 , W on the right side of the wafer W are overlapped with each other at positions shifted by ΔB from the center between _{a4 in} opposite directions.
_b3 is the right y straight line patterns M _b3 and M _{b4 of the} mask M, respectively.
When the wafer W and the mask M are relatively positioned so as to overlap with each other at positions displaced from each other by ΔB in the opposite directions from each other, the alignment between them is completed.

FIG. 3 shows an example of a TV image obtained before performing the alignment. In this case, x on the left side of the wafer W
Since the x straight line pattern W _a1 of the alignment W _ax is between the x straight line patterns M _a1 and M _a2 of the left x alignment M _ax of the mask M, the image processing of these x straight line patterns M _a1 and M _a2 causes the X direction. Of the mask M, and based on this, the wafer moving stage is driven in the X direction to perform the alignment in the X direction, and then the wafer moving stage is driven in the Y direction or the θ direction to move the mask M to the left and right. the y linear pattern M _a3, M _a4 and M _b3, M _b4 of y linear pattern M _a3 of the wafer W in between each, and M _b2 in the left of the mask M, respectively y alignment mark M _ay of y linear pattern M _a3 or M _a4 and the right y alignment mark M _by adjacent to the y straight line pattern M _b3 or M _b4 ,
The TV screen of FIG. 2 or any of FIGS. 4 to 6 is obtained.

When the TV screen shown in FIG. 2 is obtained, the alignment is completed, and when the TV screen shown in FIG. 4 is obtained, the wafer moving stage is moved in the Y direction to obtain the TV screen shown in FIG. When the alignment is completed and one of the y linear patterns W _a2 , W _a3 , W _b2 , and W _b3 on the wafer W is not on the TV screen as shown in FIG. Drive in the direction to complete the alignment as shown in FIG.

According to the present embodiment, the ranges ΔS _x1 and ΔS _y1 of the positional deviation amounts in the X direction and the Y direction which can be detected by the image recognition device are expressed as follows.

S _x1 = ± {A ₁ − (C ₁ + D ₁ + 2ΔX ₁ )} ... (7) S _y1 = ± {B ₁ − (C ₁ + D ₁ + 2ΔY ₁ )} ... (8) )

That is, it is twice as large as that of the conventional example expressed by the above-mentioned equations (1) and (2). Therefore, the conventional pre-alignment is not required, and as a result,
Omission of the pre-alignment step shortens the operation time, omission of the lens switching device simplifies the device, and since the pre-alignment mark is unnecessary, restrictions on pattern design are alleviated.

[0031]

Since the present invention is configured as described above, it has the following effects.

In the alignment method for aligning the wafer and the mask with the image recognition device, the amount of positional deviation that can be detected from the images of the alignment marks of both can be increased. As a result, the pre-alignment by the observation optical system can be omitted and the throughput of the exposure apparatus can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating an example.

FIG. 2 is a diagram showing a TV screen when alignment is completed.

FIG. 3 is a diagram showing an example of a TV screen before alignment.

FIG. 4 is a TV when alignment is performed only in the X direction.
It is a figure which shows an example of a screen.

FIG. 5: TV when alignment is performed only in the X direction
It is a figure which shows the other example of a screen.

FIG. 6 is a TV when alignment is performed only in the X direction.
It is a figure which shows another example of a screen.

FIG. 7 is a diagram showing a TV screen when final alignment is completed according to a conventional example.

FIG. 8 shows T before final alignment according to a conventional example.
It is a figure which shows an example of a V screen.

FIG. 9 is a diagram showing an example of a TV screen when the limit of the range observable by the observation optical system is reached in the final alignment of the conventional example.

FIG. 10 is a diagram showing another example of the TV screen when the limit of the range observable by the observation optical system is reached in the final alignment of the conventional example.

FIG. 11 is an explanatory diagram illustrating the entire exposure apparatus.

12 is an explanatory diagram illustrating an observation optical system of the apparatus of FIG. 11, an alignment mark of a mask, and an alignment mark of a wafer.

[Explanation of symbols]

W Wafer M Mask W _ax , W _bx Wafer x alignment mark W _ay , W _by Wafer y alignment mark M _ax , M _bx Mask x alignment mark _May , M _by Mask y alignment mark W _a1 , W _b1 Wafer X linear patterns W _a2 , W _a3 , W _b2 , W _a3 wafer y linear patterns M _a1 , M _a2 , M _b1 , M _a2 mask x linear patterns M _a3 , M _a4 , M _b3 , M _a4 mask y Linear pattern 1 Projection lens system 2a, 2b Objective lens 3 Erector lens

Claims (2)

[Claims] 1. A pair of predetermined minute areas of a wafer and a pair of predetermined minute areas of a mask are relatively positioned based on an alignment mark provided in each minute area, whereby the wafer and the mask are aligned. An alignment method for performing alignment, wherein an alignment mark of each micro area of the mask comprises a pair of patterns sandwiching a center of the micro area, and an alignment mark of one micro area of the wafer is the micro area. The pattern is composed of one pattern spaced from the center of the region in one direction, and the alignment mark of the other minute region of the wafer is spaced from the center of the minute region in the opposite direction to the above.
A registration method characterized by comprising individual patterns. 2. The alignment method according to claim 1, wherein the alignment mark of each minute region of the wafer is composed of a pair of patterns sandwiching the center of the minute region.