JPS6222434A - Positioning method for mask in projection exposure device - Google Patents

Abstract

PURPOSE:To calibrate an origin in a wafer-position detecting means easily by imaging a reference-positioning mark for a second mask section to a wafer or a section corresponding to the wafer by non-exposure beams while an image formed in projected optically to a photoelectric detecting element and determining the origin of the wafer on the basis of a detecting value on the projection. CONSTITUTION:A mask positioning mark on a mask 3 is irradiated by non- exposure beams Ln, the positioning mark is read by an image sensor 27, a signal from the image sensor 27 is inputted to a control section 15, and the mask is set at a predetermined reference position. Reflected beams from a positioning mark 6a on a wafer 6 are read by an image sensor 25 through a half mirror 23, and a detecting signal from the image sensor 25 is inputted to the control section 15. A detecting value by the image sensor 25 and a reference position are compared by the control section 15, and a stage driving mechanism 13 is operated only by a section corresponding to a difference value between these detecting value and reference position and the wafer 6 is set at a prescribed reference position, thus completing positioning.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for aligning a mask in a projection exposure apparatus, and in particular, to a method for easily and accurately aligning the origin of an alignment mechanism used for aligning a wafer. The present invention relates to a mask alignment method that can be performed.

[Conventional technology]

Alignment devices in conventional projection exposure apparatuses, especially those in reduction projection exposure apparatuses, require finer patterns due to higher integration of circuit patterns and repeat pattern printing many times, making it difficult to achieve precise alignment. required. Therefore, it is necessary to detect the position of the wafer from the alignment mark on the wafer and move the mounting table on which the wafer is placed relative to the mask side to align the projected image of the mask with the alignment mark on the wafer. Note that this alignment can also be achieved by moving the mask side. In this case, the movement of the mask is reduced to a reduction rate of, for example, 1/10, making it easy to make precise adjustments.

Here, mark position detection includes methods that use a reduction projection lens and methods that use a separate lens.
The detection position is performed in at least two directions, the X direction and the Y direction.

As an alignment device for this type of conventional projection exposure equipment,
For example, there is one disclosed in Japanese Unexamined Patent Publication No. 59-74652.

This device includes a stage capable of two-dimensional movement on which an object to be exposed is placed; illumination means for illuminating a mask on which marks are drawn with light of a predetermined exposure wavelength; and an image of the illuminated mask to be exposed. In an exposure apparatus having a projection optical system for projecting onto an object, light having a wavelength substantially equal to the exposure wavelength is transmitted through the projection optical system in order to correlate the relative positions of the stage and the mask. A photoelectric detector is provided on the stage to detect the mark image of the mask projected by the projection optical system, and with this configuration, the image of the alignment mark on the wafer and the mask projected back by the projection optical system can be detected. This has the advantage that the stage on which the wafer is placed and the mask can be matched with high precision without the need to superimpose and observe the upper alignment mark at the same time.

[Problem that the invention seeks to solve]

However, in the alignment device of the conventional projection exposure apparatus described above, the stage on which the wafer is placed has a high precision (
In addition, it requires a separate light source that is substantially equal to the exposure wavelength, making the configuration complex, large, and expensive. There was a problem in that it depended on the accuracy of the measuring instrument and caused deterioration of accuracy.

Therefore, the present invention has been made by focusing on the problems of the conventional example, and provides a position in a projection exposure apparatus that allows the origin of the wafer position detection means to be easily calibrated without making any improvements to the conventional apparatus. The purpose is to provide a matching method.

[Means for solving problems]

In order to achieve the above object, the present invention provides a projection exposure apparatus that projects and exposes a mask pattern onto a wafer.
A first mask portion having an alignment mark formed at the mask position for aligning the mask, and a reference alignment that serves as a reference for relative alignment between the mask and the wafer using a non-exposure light beam that is difficult to expose the resist of the wafer. An origin calibration mask is arranged in parallel with the second mask part on which the mark is formed, separated by the amount of chromatic aberration between the two, and at least the mask positioning mark of the first mask part is detected by the mask position detection means. Then, the origin calibration mask is positioned, and the reference alignment mark of the second mask portion is imaged on the wafer or a corresponding portion thereof by the non-exposure light beam output from the light source device. The method is characterized in that the image is optically projected onto a photoelectric detection element and the wafer origin is determined based on the detected value.

[Effect]

In this invention, the first mask part has an alignment mark for aligning the mask formed at the mask placement position between the light source device and the wafer, and the mask is aligned with the non-exposure light that is difficult to expose the resist of the wafer. An origin calibration mask is inserted, which is arranged in parallel with a second mask part on which a reference alignment mark, which serves as a reference for relative alignment with the wafer, is formed, with a distance equal to the chromatic aberration between the two. At this time, by inserting the origin calibration mask, for example, on the light source device side of the reduction lens, at this position calibration mask position, if the reduction ratio of the reduction lens is 1/10, the wafer portion, that is, the image forming position. The vertical displacement will be expanded approximately 100 times,
The positional accuracy of the mask in the optical axis direction is 10 when viewed from the wafer part.
This is 0 times better, which means that the positional accuracy of the mask has been sufficiently improved. First, the mask positioning mark of the first mask part is detected by at least the mask position detection means to position the origin calibration mask itself, and then the light source device outputs a non-exposure light beam that does not expose the resist of the wafer. and by this, the second
The reference alignment mark of the mask section is imaged onto the wafer, and the imaged position is detected by a photoelectric detection element serving as a wafer position detector, and this is used as the measurement origin.

Thereafter, the wafer positioning is performed by a wafer position detector, and the mask positioning is performed by a mask position detector, respectively, and the positions are aligned to match the measurement origin, thereby achieving highly accurate positioning. Can be done.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a conceptual diagram of a reduction projection exposure apparatus to which the present invention can be applied.

In the figure, 1 is a mercury lamp as a light source device, and the light beam emitted from this mercury lamp 1 is transmitted through a condenser lens 2.
, is guided through a mask 3 and a reduction lens 4 onto a wafer 6 placed on a stage 5 that is three-dimensionally driven.

Between the mercury lamp l and the condenser lens 2, a light beam is provided between the mercury lamp l and the condenser lens 2, which blocks the exposure light beam (for example, light la having a shorter wavelength than the g-line) that is sensitive to the resist among the light beams output from the mercury lamp 1. An optical filter 7a that transmits only the non-exposure light beam Ln (e.g., e-ray) having a wavelength that makes it difficult to expose the coated resist, and an optical filter 7b that transmits the exposure light beam La are arranged adjacent to the frame 7c. , these are arranged to be removably inserted into the optical path from the mercury lamp 1.

Two types of masks 3 are prepared: an origin calibration mask 3a shown in FIG. 1, and an exposure mask (not shown) on which a normal circuit pattern is drawn. Here, as shown in FIG. 2(a), the origin calibration mask 3a has a mask alignment mark 3b formed on the outer peripheral edge and a mask alignment mark 3b formed in the center in the x and y force directions for alignment. As shown in FIG. 2(b), a first mask portion 3d made of a transparent material has at least a position correction mark 3c (marks in the Y direction are omitted), and a non-exposure light beam Ln. A reference alignment mark 3e formed by a straight line toward the center is formed to serve as a reference for relative alignment between the mask 3a and the wafer 6, and a position correction mark 3c of the mask portion 3d is formed corresponding to the reference alignment mark 3e. A mask alignment mark 3g corresponding to the position correction mark 3f and the mask alignment mark 3b of the first mask portion 3d.
A second mask section 3h made of a transparent material having a mask section 3h is arranged in parallel with a chromatic aberration separation distance between the two (8.6 m in the case of this embodiment). Note that each mark on each mask portion 3d and 3h is precisely formed by a pattern generator.

To configure the origin calibration mask 3a, first,
A second mask portion 3h formed as a single unit is placed at the position of the mask portion 3d in FIG. The wafer 6 is inserted so as to focus on the upper surface, and the resist is printed. Next, the second mask section 3h is removed, and the first mask section 3d formed as a single unit is set in the same position. In this case, the first mask portion 3d is set by matching the alignment mark 3b of the first mask portion 3d with the alignment mark 3g of the second mask portion 3h printed on the wafer 6. The correction mark 3c and the previously printed position correction mark 3e on the wafer will substantially match. At this time, the position of the stage 5 and the reading position of the mask alignment mark 3b of the first mask part 3d are measured as temporary origins, and a resist is applied to the wafer 6 on which the alignment mark 3e has been printed, and the position of the mask alignment mark 3b of the first mask part 3d is measured. 3d position correction mark 3c is printed on the wafer 6. Thereafter, the deviation between both mask parts 3d and 3h is measured, and based on the measurement results, the deviation amount of the mask part 3h with respect to the mask part 3d is calculated. The origin of the image sensor 25 is calculated.

In this way, the origin of the image sensor 25 of the wafer position detection mechanism 11 with respect to the non-exposure light beam Ln is corrected, and the correct origin is determined. Confirm whether this origin is correct by performing printing again, and if it is out of alignment, repeat the same confirmation and adjustment as above. Adjustment in this case may be performed on the stage side.

When the origin of the image sensor 25 is determined in this way, the mask part 3d is focused on the exposure light La, and the mask part 3g is focused on the non-exposure light Ln on the wafer 6 (on the same plane) so that both the light beams La and Ln are focused. The chromatic aberration due to the wavelength of the light is set apart in the optical axis direction by the connecting member 8, and the mask parts 3d and 3h are aligned with the origin using respective position detection mechanisms 12 and 11, which will be described later, and the alignment of both is completed. At this point, the mask portions 3d and 3h and the connecting member 8 are fixed, for example, by adhesive, to form the origin calibration mask 3a. Note that the position correction mark 3 of the first mask portion 3d
c and the position correction mark 3f of the second mask portion 3h,
This is for determining the origin for configuring the origin calibration mask 3a, and is omitted from the origin calibration mask 3a for actually calibrating the measurement origin of the projection exposure apparatus.

On the other hand, a positioning device 10 is provided on the lower surface side of the mask 3. This alignment device 1° is composed of a wafer alignment mechanism 11, a mask alignment mechanism I2, a wafer moving device 13, a mask fine movement device 14, and a control section 15.

The control unit 15 has an arithmetic processing unit and a memory,
Upon receiving the detection signal from the image sensor 25 of the wafer alignment mechanism 11 and the detection signal from the image sensor 27 of the mask alignment mechanism 12, each detection signal and the mask-compatible standard stored in the internal memory of the control unit 15 are detected. A control signal corresponding to the difference value is sent to the wafer moving device 13 and the mask fine movement device 14, respectively. The wafer moving device 13 and the mask fine movement device 14 each receive this control signal and perform control to set the wafer 6 and the mask 3 at predetermined reference positions. Here, the wafer moving device 13 is composed of a stage drive 7 circuit 13a and the stage 5, and the mask fine movement device 14 is equipped with a similar mask fine movement circuit and a mask stage, and these drive circuits are controlled. A signal is provided to move the stage in a predetermined direction.

Now, the wafer alignment mechanism 11
j Surlens 2 and reference alignment mark 3e on mask portion 3h of mask 3a, half mirror 23, reduction lens 4, alignment mark 6a on wafer 6, microscope 2
On the other hand, the mask alignment mechanism 12 includes a condenser lens 2 shared with the alignment mechanism 11, a mask alignment mark 3b on the mask portion 3d, a microscope 26, and an image sensor 27. It consists of Here, the wafer alignment mechanism 11, the control section 15, and the wafer moving device 13 constitute a positioning mechanism that determines the relative position of the mask 3 and the wafer, and the mask alignment mechanism 12 and the control section 15
and the mask moving device 14 constitute a positioning mechanism that positions the mask 3.

Therefore, the light beam from the mercury lamp 1 passes through the optical filter 7a, passes through the condenser lens 2 as a non-exposure light beam Ln, reaches the mask 3, and further passes through the half mirror 23 and the reduction lens 4, and then passes through the wafer 6. The upper alignment mark 6a is irradiated. The alignment marks of mask 3 are imaged onto wafer 6 . Then, the reflected light passes through the reduction lens 5 again and reaches the half mirror 23.
Here, the reflected light beam is magnified by a microscope 24 and C
Image sensor 2 having a one-dimensional detection surface extending perpendicularly to the projected mark such as OD, diode array, etc.
5. So, this is the image sensor 25
The detection signal is sent to the control section 15. When the control unit 15 receives this detection signal, it compares it with a preset reference position corresponding to the mask stored in its internal memory and sends a control signal to the wafer moving device 13 according to the difference value. Send. the result,
The stage 5 of the wafer 6 is moved and aligned to a predetermined position.

On the other hand, the light beam that has passed through the mask positioning mark 3b on the mask portion 3d is magnified by the microscope 26, and its image is projected onto the image sensor 27, where it forms an image. This is then scanned by the image sensor 27, and its detection signal is sent to the control section 15. Similarly to the above, the control unit 15 compares this with a preset reference position corresponding to the mask stored in its internal memory, and sends a control signal according to the difference value to the mask fine movement device 14. . As a result, the stage of the mask 3 is moved, and the mask 3 is positioned at a predetermined position.

Note that the light beam in this case is both the exposure light beam La and the non-exposure light beam L.
Either n or n may be used, but if resist is coated on the wafer 6, the non-exposure light beam Ln is used.

Incidentally, the reference (origin) positions stored on the memory corresponding to the image sensors 25 and 27 are determined as described below.

That is, as shown in FIG. 1, an origin calibration mask 3a is placed below the condenser lens 2, and this origin calibration mask 3a is irradiated with exposure light La' or non-exposure light Ln from the mercury lamp 1. , the mask position is adjusted by a mask positioning mechanism 12. In this case, each mask alignment mark 3b of the mask portion 3d is adjusted to be approximately at the center position of the image sensor 27 of each corresponding mask alignment mechanism 12, and each image sensor 27 at this time is
The detected value is stored in a predetermined storage area of the memory as a mask position reference value. Next, an optical filter 7 is inserted in the optical path of the mercury lamp 1 to allow only the non-exposure light beam Ln to pass through, and the origin calibration mask 3a is irradiated with this, and at this time, the wafer 6
The image sensor 25 of the wafer alignment mechanism 11 detects the reference alignment mark 3e imaged thereon, and stores the detected value in a predetermined storage area of the memory as a reference (origin) position.

Note that the image sensor 25. ．． As for the detection signal No. 27, coordinates (for example, coordinates expressed by a -dimensional distance) may be set on the image sensor, and the detection signal may be detected as a numerical value at a predetermined position.

Next, the operation of this embodiment will be briefly explained.

First, as described above, the origin calibration mask 3a is set in the projection exposure apparatus, the optical filter 7a is set in the optical path of the mercury lamp 1, and the non-exposure light Ln is irradiated. As a result, the mask alignment mechanism 12 stores the origin in the memory using the detection value of the image sensor 27 as a reference position, and the wafer alignment mechanism 11
Similarly, the origin is stored in the memory using the detected value of the image sensor 25 as the reference position.

In this state, the origin calibration mask 3a is removed, and a mask 3 having a circuit pattern to be exposed to the wafer 6 is selected. This mask 3 is formed with a mask alignment mark corresponding to the mask alignment mark 3b of the mask portion 3d.

Then, the mask positioning mark on the mask 3 is irradiated with the non-exposure light beam Ln.

Then, the alignment mark on the mask 3 is read by the image sensor 27, a signal from the image sensor 27 is input to the control section 15, and the mask is set at a predetermined reference position.

Next, the reflected light from the alignment mark 6a on the wafer 6 is read by the image sensor 25 via the half mirror 23, and the detection signal from the image sensor 25 is sent to the controller 2.
5, the control unit 15 compares the detection value of the image sensor 25 and the reference position, and operates the stage drive mechanism 13 by the amount corresponding to the difference between them to set the wafer 6 at a predetermined reference position. The alignment will be completed. After that, the optical filter is switched to 7b, and the resist on the wafer 6 is exposed to the exposure light La to complete the printing.

Note that the order of this alignment may be either the mask side first or the wafer side first.

As described above, in this embodiment, since the origin calibration mask 3a is arranged between the reduction lens 4 and the condenser lens 2, at this position calibration mask position,
If the reduction ratio of the reduction lens is set to 1/10, the vertical displacement of the wafer part will be magnified approximately 100 times, and the precision of the mask will be 100 times better when viewed from the wafer part. This means that the accuracy of the mask has been sufficiently improved. Further, even if a drift occurs in the control unit 15, the image sensor 25, etc., the origin correction can be performed using the origin calibration mask 3a, so the calibration is extremely easy. In order to perform this origin calibration, it is necessary to install an automatic mounting mechanism that automatically attaches the origin calibration bracket 3a to the mask position when necessary. This allows the origin calibration to be performed automatically, and the projection exposure equipment can be used with high accuracy. can be maintained.

Also, in this embodiment, positioning is explained without simply limiting the direction, but positioning in the X direction and positioning in the Y direction are the same, and it is sufficient to make them correspond to the X direction or the Y direction. be. Therefore, each mask alignment mechanism 12. The positioning of the wafer alignment mechanism 13 is performed using X,
Although this is performed in the Y direction, if the image sensor detects the X and Y directions simultaneously, these can be controlled simultaneously. That is, it receives detection signals in the X direction and Y direction, and controls them independently in a time-division manner.
It is sufficient to send the signals to the respective moving devices corresponding to the directions. Further, when alignment is required in only one of the X or Y directions, it goes without saying that positioning in only one direction is sufficient.

In the above embodiment, a filter is used to obtain a light beam of a different wavelength from the exposure light beam, but this light beam may be obtained from another light source having a different wavelength.

Alternatively, a desired circuit pattern may be formed on the mask portion 3d of the origin calibration mask 3a, and the desired circuit pattern may be exposed onto the wafer 6 using this origin calibration mask 3a.

Further, the alignment marks 3b and 3e of the mask portions 3d and 3g of the mask 3 are not limited to being formed by line drawings, but may also be formed by slits, and in short, the wafer alignment mechanism 11 uses light beams that are difficult to expose to the alignment marks 3b and 3e to re-wafer. Any device may be used as long as it can measure the origin as a reference for positioning in step 6.

Further, since the mask alignment mechanism 12 does not need to have sufficient accuracy on the wafer side, a mechanical alignment mechanism may be used without using an image sensor.

Furthermore, in the above embodiment, a case has been described in which the reference alignment mark 3e of the origin calibration mask 3a is imaged on the wafer 6, but a reflecting mirror 1 is provided in place of the wafer 6, and the mark image reflected by this is transferred to the wafer. The light may be guided to the positioning mechanism 11, and in this case, the amount of light incident on the image sensor 25 can be increased.

Further, in the above embodiment, the case where the image sensors 25 and 27 are applied as the photoelectric detection element has been described, but the present invention is not limited to this, and other photoelectric detection elements such as an image pickup tube can be applied.

Although the present invention has been mainly described as an embodiment of a reduction projection type exposure apparatus, it is not limited thereto, and can of course be applied to various types of exposure apparatuses such as close exposure, 1:1 exposure, etc.

〔Effect of the invention〕

As can be understood from the above description, the present invention provides a first mask portion having an alignment mark for aligning the mask formed at the mask position, and a non-exposure light beam that is difficult to expose the resist of the wafer to the mask and the wafer. The second mark that forms a reference alignment mark that serves as a reference for relative alignment with
A mask for origin calibration is arranged in parallel with the mask part separated by the amount of chromatic aberration between the two, and a mask positioning mark of at least the first mask part is detected by the mask position detection means, and the origin calibration is performed. positioning the second mask, and then outputting the non-exposure light beam from a light source to image the alignment mark of the second mask portion onto the wafer or a corresponding portion thereof, and optically image the image. The wafer origin is determined based on the detected value by projecting it onto the sensor, and an origin calibration mask is used to determine the origin for wafer alignment.
Normally, the alignment of the mask and wafer during pattern exposure to a new wafer can be done easily and independently of each other by aligning with independent reference positions. Moreover, since the first mask portion of the origin calibration mask on which the mask alignment mark is formed and the second mask portion on which the reference alignment mark is formed are spaced apart by the amount of chromatic aberration between the two, the reference Since the alignment mark is accurately imaged on the wafer or a corresponding portion without causing a focus shift, the origin can be set with high precision.

Furthermore, since the wafer is aligned using an image sensor, there is no mechanical drive unit and reliability is increased.

[Brief explanation of drawings]

FIG. 1 is a conceptual configuration diagram showing a schematic configuration of an embodiment of a reduction projection exposure apparatus applicable to the present invention, and FIGS. and a plan view showing the second mask portion.■...Mercury lamp, 3...Mask, 3
a...Origin calibration mask, 3b...Mask positioning mark, 3d...First mask portion, 3e...Reference positioning mark, 3h・・・
...Second mask portion, 6...Wafer, 7.
... Optical filter, 10 ... Positioning device, 11 ... Wafer positioning mechanism, 12.
...Mask positioning mechanism, 13...Wafer moving device, 14...Pa...Mask fine movement device, 15
...Control unit, 25.27...Image sensor.

Claims (1)

[Claims] In a projection exposure apparatus that projects and exposes a mask pattern onto a wafer, a first mask portion having an alignment mark for aligning the mask is formed at the mask position and a non-exposure light beam that is difficult to expose the resist of the wafer. A second mask part on which a reference alignment mark is formed as a reference for relative positioning of the mask and the wafer is arranged in parallel with a second mask part separated by the amount of chromatic aberration between the two parts, and at least the first mask part is arranged in parallel. The mask position detection means detects the mask alignment mark of the second mask part to position the origin calibration mask, and then outputs the non-exposure light beam from the light source device to determine the reference position of the second mask part. Mark position in a projection exposure apparatus, characterized in that an alignment mask is imaged on the wafer or a corresponding portion thereof, the image is optically projected onto a photoelectric detection element, and the wafer origin is determined based on the detected value. How to match.