JPH0443407B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a projection exposure method for sequentially transferring a plurality of original images onto an object to be exposed, and is particularly suitable for transferring a circuit pattern onto a semiconductor wafer. This invention relates to a projection exposure method.

[Background of the invention]

A highly integrated semiconductor is obtained by sequentially overlapping and transferring the patterns of a plurality of original images onto a semiconductor wafer (hereinafter referred to as a wafer), which is an object to be exposed. 1st
The figure schematically shows a projection exposure apparatus used for manufacturing highly integrated semiconductors.

In FIG. 1, drive motors 12 and 14 are attached to an XY stage 10 so that a wafer 16 can be fixed on the upper surface thereof. Drive motors 12 and 14 move the XY stage at a predetermined pitch in the X and Y directions shown in the figure in a so-called step-and-repeat manner. and,
The position of the XY stage 10 is
is detected by the laser length measuring device 20 via
Positioning is controlled with an accuracy of approximately 0.05μm.

A reduction lens 22 is arranged above the wafer 16, and an original mounting table 26 for fixing a pattern original (reticle) 24 is provided above the reduction lens 22. Irradiation holes 28 and 30, the details of which will be described later, are formed in the pattern original 24 at predetermined positions. Furthermore, light from an exposure illumination device 32 is projected onto the pattern original 24 via a condenser lens 34 .

A detection pattern 36 is formed on the wafer 16 described above.
is transferred, and this transferred pattern 36 can be detected by a pair of pattern detection devices 40 and 50. Each pattern detection device 40, 5
0 has pattern detectors 41 and 51, collimators 42 and 52, half mirrors 43 and 53, mirrors 44 and 54, and illumination devices 45 and 55, respectively.

The wafer 16 is made up of a plurality of chips 60, as shown in FIG. 2, and a detection pattern 36 is transferred to each chip 60.

Transfer of a pattern using the projection exposure apparatus configured as described above has conventionally been performed as follows. First, the XY stage 10 on which the wafer 16 is placed is stopped at a predetermined position, and the first pattern original 24 is fixed on the original mounting table 26. and,
Light is focused and projected from the exposure illumination device 32 onto the pattern original 24 via the condenser lens 34.
The light transmitted through the pattern original plate 24 is passed through the reduction lens 2
2 and forms an image of the pattern drawn on the pattern original 24 onto the wafer 16. When the pattern is transferred to one chip 60, the drive motors 12 and 14 are driven by a control device (not shown) to move the XY stage by one step in order to transfer the pattern to the next chip. The amount of movement of this XY stage is detected by the laser length measuring device 20,
It is controlled with a positioning accuracy of about 0.05μm.
When the pattern is transferred to all the chips 60 formed on the wafer 16 in this way, the original plate mounting table 2
The next pattern original plate 24 is fixed on top, and the patterns are transferred onto the wafer 16 in a similar manner in an overlapping manner. At this time, the pattern already transferred on the wafer 16 and the pattern drawn on the next pattern master 24 are
It is necessary to systematically match and overlap. This overlapping of patterns has conventionally been done as follows.

First, light is projected onto the half mirrors 43, 53 from the illumination devices 45, 55 of the pattern detection devices 40, 50. After the light is reflected by the half mirrors 43 and 53 and the mirrors 44 and 54, it is guided to the reduction lens 22 through the irradiation holes 28 and 30 formed in the pattern original 24, and is irradiated onto the wafer 16.
This light is further reflected by the wafer 16, and the image of the detection pattern 36 on the wafer 16 is enlarged and formed on the pattern original 24. This enlarged image of the detection pattern 36 is reflected by the mirrors 44, 54, and passes through the half mirrors 43, 53 and the collimators 42, 52 to the pattern detectors 41, 51.
guided by. Therefore, as measurement points on the wafer 16, a pair of chips 60a and 60b, which are predetermined
The detection patterns 36a and 36b within the wafer 16 are detected simultaneously or sequentially, and the arrangement state of the previous pattern transferred onto the wafer 16 is determined. Then, a relative error between the imaged position of these detection patterns 36a, 36b on the pattern original plate 24 and the position of the detection mark drawn on the pattern original plate 24 is detected, and this relative error is fed back to the control device. hand
The XY stage 10 was moved so that there was no relative error, and the next pattern was transferred. However, when using this conventional method, the detected detection pattern 3
If one or both of 6a and 36b are erroneously detected, there is no way to detect this erroneous detection, and the pattern on the wafer 16 and the pattern drawn on the pattern master 24 cannot be sufficiently matched. The pattern of the original pattern plate 24 is transferred, which is a major cause of defects in the highly integrated semiconductor manufacturing process.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a projection exposure method that can match a pattern on an object that has already been transferred to an original image to be transferred next.

[Summary of the invention]

The present invention detects three detection marks on the exposed object onto which the patterns of multiple original images are sequentially superimposed and transferred, determines the relative position between each of these detection marks, compares it with a design value, and calculates the relative position. If there is a mark that does not match the design value, increase the number of detection marks sequentially, confirm that at least 2 or more detection marks are detected correctly, and check whether these 2 or more detection marks are detected correctly. The above object is achieved by matching the previous pattern that has already been transferred onto the object to be exposed based on the mark with the pattern of the subsequent original image that is to be transferred next.

[Embodiments of the invention]

A preferred embodiment of the projection exposure method according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 shows the positions of detection marks to be detected in an embodiment of the projection exposure method according to the present invention, and FIG. 4 shows the details of the positional relationship. In FIGS. 3 and 4, the same pattern is transferred onto each of a large number of chips 60 formed on the wafer 16, and detection marks are formed at the same positions. The detection mark to be detected is the chip 60a,
Detection marks T ₁ , T ₂ in 60b, 60c, 60d,
T ₃ and T ₄ . The coordinates of each of these detection marks are
T ₁ (x ₁ , y ₁ ), T ₂ (x ₂ , y ₂ ), T ₃ (x ₃ , y ₃ ), T ₄ (x ₄ ,
_y4 ). And the chips 60a and 60b are
Each of the n chips is located at both ends of a line, with the chip 60c being located at the center between the chips 60a and 60b, and the chip 60d being located at the center between the chips 60a and 60c. The size of each chip is assumed to be X×Y.

Under such conditions, the chips 60a, 60b
The center-to-center distance between them corresponds to the distance between the detection patterns T ₁ and T ₂ , and if the exposure point is positioned by the XY stage and the error is 0, then _{1 2} = |y ₁ −y ₂ |=L=( n-1) Y holds true. In the detection patterns T ₁ to _{T 3} , if the positioning error of the XY stage is 0 and the correct detection pattern is detected, the following equations hold true for the x-direction and y-direction coordinates, respectively.

||y ₁ −y ₂ |/L=|y ₁ −y ₃ |/L/2|=0 …(1) ||x ₁ −x ₂ |/L=|x ₁ −x ₃ |/L/ 2|=0 …(2) However, in reality, the stage positioning error is approximately
Since it is about 0.05 μm, the three detection marks T ₁ ~
The conditions for positive detection of both T ₃ are as follows.

||y ₁ −y ₂ |/L=|y ₁ −y ₃ |/L/2|≦C …(3) ||x ₁ −x ₂ |/L=|x ₁ −x ₃ |/L/ 2|≦C (4) Here, C has a value of about 0.1 μm, taking into account the above-mentioned detection error and expansion and contraction of the wafer 16.

Next, a method for determining whether or not a correct detection mark is detected will be explained in detail with reference to FIG.

The control device of the exposure machine (not shown) is in step 101.
Detection marks T ₁ , T ₂ , and T ₃ of the three chips 60a, 60b, and 60c are detected. and,
In step 102, equation (3) is calculated, and if equation (3) is satisfied, the process proceeds to step 103. Then, the y-coordinate of the exposure point for overlapping each chip is calculated based on the data of the detection marks T ₁ and T ₂ ,
Proceeding to step 104, it is determined whether equation (4) holds. If formula (4) is satisfied, step 105
Then, the x-coordinate is calculated in the same way as the y-coordinate, and the exposure machine moves to an exposure operation for overlaying.

When the control device discovers that equation (3) does not hold in step 102, it proceeds to step 106,
The detection pattern _T4 in the fourth chip 60d is detected, and the process proceeds to step 107, where the following equations (5) to (10) are calculated.

｜｜y ₁ −y ₂ ｜/L−｜y ₁ −y ₄ ｜/(L/2)−2Y｜≦
C…(5) ||y ₁ −y ₂ |/L−|y ₄ −y ₂ |/(L/2)+2Y|≦
C…(6) ||y ₁ −y ₃ |/L/2−|y ₁ −y ₄ |/(L/2)−2Y
|≦C…(7) ||y ₁ −y ₃ |/L/2−|y ₄ −y ₃ |/2Y|≦C…(8) | |y ₃ −y ₂ |/L/2−| y ₄ −y ₂ |/(L/2)−2Y
|≦C...(9) |||y ₃ −y ₂ |/L/2−|y ₄ −y ₃ |/2Y|≦C…(10) Then, among the four detection patterns T ₁ to T ₄ , 3
The condition for this to be correct is that there must be two or more that satisfy equations (5) to (10) above. Therefore, the control device determines in step 108 whether or not there are two or more equations that satisfy equations (5) to (10) based on the calculation results in step 107.
If there are more than 3 correct answers in step 109.
The coordinates of each exposure point are automatically calculated based on the y-coordinates of the two detection marks, and the exposure machine moves on to the exposure operation for overlaying. If (5) in step 108
If it is found that there are no two or more items that satisfy equations (10), the process proceeds to step 110, where the exposure machine stops the automatic detection operation and shifts to visual detection by the operator.

After calculating the y coordinate in step 109, the automatic control device proceeds to step 104 and calculates equation (4). If equation (4) is not satisfied, step 104 is performed.
Proceed to step 111 and after detecting the 4th chip
Proceed to step 112, and in step 112, the following (11) ~
Calculate equation (16).

｜x ₁ −x ₂ ｜/L−｜x ₁ −x ₄ ｜/(L/2)−2Y≦C…
(11) ｜x ₁ −x ₂ ｜/L−｜x ₄ −x ₂ ｜/(L/2)+2Y≦C…
(12) |x ₁ −x ₃ |/L/2−|x ₁ −x ₄ |/(L/2)−2Y≦
C…(13) |x ₁ −x ₃ |/L/2−|x ₄ −x ₃ |/2Y≦C…(14) |x ₃ −x ₂ |/L/2−|x ₄ −x ₂ |/(L/2)−2Y≦
_C ... ( _{15 ) |} It is determined whether two or more of the following are satisfied. When the control device determines in step 113 that two or more of equations (11) to (16) are satisfied, the control device proceeds to step 114,
The x-coordinate is automatically calculated in the same way as the y-coordinate,
The exposure machine shifts to exposure operation for overlay.
On the other hand, if there are no two or more items that satisfy equations (11) to (16) in step 113, step 115 is performed.
Then, the exposure machine stops automatic detection operation and shifts to visual detection by the operator.

In addition, each chip 60 detected as described above
a, 60b, 60c, and 60d are arranged on a straight line. Therefore, the conditional expression regarding the x coordinate is
Although expressed in the same way as the conditional expression for the y-coordinate, the inclination of the straight line connecting each detection pattern with respect to the reference line is actually calculated.

As described above, by detecting three or more detection marks on the wafer 16, calculating the mutual position between each detection mark, and comparing it with the design value, the patterns can be superimposed based on the detection marks in the correct position. As a result, the patterns can be matched and the occurrence of defective products can be prevented.

In the above embodiment, the case where each chip to be detected is arranged on a straight line was explained.
The chips to be detected need not be arranged in a straight line. Further, in the above embodiments, pattern transfer of highly integrated semiconductors has been described, but it is needless to say that the present invention is not limited to highly integrated semiconductors.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to match the pattern on the exposed object that has already been transferred and the pattern of the original image to be transferred onto the pattern.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a projection exposure apparatus, FIG. 2 is a diagram showing the position of a detection pattern detected for overlapping patterns formed on a conventional wafer, and FIG. 3 is a diagram according to the present invention. A diagram showing the position of the detection pattern to be detected in the projection exposure method.
FIG. 5 is a detailed diagram showing the positional relationship of detection patterns to be detected, and FIG. 5 is a flowchart for determining whether the detected detection pattern is correct. 10...XY stage, 12, 14... Drive motor, 16... Wafer, 20... Laser length measuring device,
22... Reduction lens, 24... Pattern original, 3
2...Exposure illumination device, 34...Condenser lens, 36, 36a, 36b, T1 _{to T4} ...Detection pattern, 40, 50...Pattern detection device, 4
1, 51... pattern detector, 60, 60a-6
0d... Chip.

Claims (1)

[Scope of Claims] 1. An exposed object on which the patterns of a plurality of original images are sequentially transferred and superimposed on the surface thereof is placed on a two-dimensionally movable stage, and the pattern is transferred onto the exposed object. A detection mark in the pattern at the front stage is detected, and the detection mark is moved to a reference position via the stage to overlap the pattern at the front stage on the exposed object and the pattern at the rear stage original image, and the projection device In a projection exposure method in which a pattern of an original image is transferred to the exposed object, at least three detection marks in the previous pattern transferred onto the exposed object are detected, and the relative positions between the detected detection marks are detected. is determined and compared with the design value, and it is determined whether the difference between the two is within a predetermined error range to check whether or not the detection of each detection mark is an erroneous detection. A projection exposure method characterized in that the pattern of the original image in the latter stage is superimposed and transferred onto the pattern in the former stage on an object. 2. The above-mentioned detection of at least three detection marks is performed by detecting a new detection mark when it is determined that the first three detection marks include false detections, and then detecting a new detection mark between these four points. 2. The projection exposure method according to claim 1, wherein the relative position is determined and compared with the design value.