JP3857908B2 - Alignment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alignment method performed when performing projection exposure, for example.
[0002]
[Prior art]
As a projection exposure apparatus for lithography, a DMD (digital mirror device: one of spatial light modulators) configured to include a plurality of mirrors capable of independently controlling the tilt of the reflecting surface is provided, and by electrostatic solution action by a control computer There has been considered a projection exposure apparatus that controls rotation of each micromirror, causes the DMD to carry a predetermined exposure pattern by this rotation control, and projects the predetermined pattern onto an exposure object.
[0003]
For example, when an integrated circuit pattern is formed on a semiconductor substrate using this projection exposure apparatus, it is necessary to transfer different exposure patterns to the same object many times. Alignment is required each time.
[0004]
[Problems to be solved by the invention]
However, conventionally, there has been no effective alignment method for projection exposure having a spatial light modulator. Conventionally, there has been no effective autofocus method for projection exposure having a spatial light modulator.
[0005]
The present invention has been made in view of such problems, and a main object of the present invention is to provide an effective alignment method used for projection exposure having a spatial light modulator.
[0007]
[Means for Solving the Problems]
The alignment apparatus of the present invention projects and exposes an exposure pattern carried on a spatial light modulator configured to include a plurality of mirrors that can independently control the inclination of a reflecting surface to an object, thereby forming unevenness on the object. In projecting and exposing another exposure pattern to the object after forming a pattern, the one exposure pattern carried by the spatial modulator is projected onto the uneven pattern of the object, and light of the uneven pattern is obtained. The object is aligned based on the detection result of the image.
[0008]
In this alignment method, it is preferable to use the degree of deviation of the optical image from the reference position as the “optical image detection result”. Furthermore, focusing may be performed in consideration of “the blur condition of the light image”. In addition, it is preferable that the “spatial light modulator used for alignment” is a spatial light modulator used for the previous projection exposure and used for the next projection exposure. In addition, when light is projected onto an object via a spatial modulator during alignment or focusing by the one alignment method, it is not always necessary to use the entire spatial light modulator, and a part of the spatial light modulator. May be used. Further, it is preferable that the exposure pattern of the spatial light modulator is formed by a control computer.
[0009]
According to this alignment method, when performing projection exposure, light is projected onto an object through a spatial light modulator, a light image of the previous concave / convex pattern is detected, the degree of deviation of the object is obtained, and the degree of deviation is determined. Alignment is performed.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a projection exposure apparatus used in the alignment method of the embodiment. The projection exposure apparatus 100 is configured as follows.
[0011]
In the figure, reference numeral 1 denotes a light source. The light source 1 is not particularly limited, and a metal halide lamp, a halogen lamp, a xenon lamp, or the like is used. A reflector 2 is installed near the light source 1. The reflector 2 acts to reflect the light from the light source 1 to be focused light and to direct it to a DMD (digital mirror device: spatial light modulator) 3 in the next stage. The focused light may be parallel light.
[0012]
Parallel light from the reflector 2 enters the DMD 3 from an oblique direction. The DMD has a rectangular or rectangular shape as a whole, and has a structure in which micromirrors are arranged in a matrix. The micromirrors are rotationally controlled by an electrostatic field effect by a control computer (not shown), and the DMD 3 can carry a predetermined mirror pattern (exposure pattern) by this rotational control.
[0013]
In the figure, reference numeral 4 denotes an equal magnification imaging telecentric optical system. This equal-magnification imaging telecentric optical system 4 has an optical axis parallel to the normal direction of the DMD 3. This equal-magnification imaging telecentric optical system 4 irradiates the test surface of the object 5 in parallel with the light (reflected light) reflected by the DMD 3.
[0014]
The light source 1, the reflector 2, the DMD 3, and the equal magnification imaging telecentric optical system 4 constitute a PC projector.
[0015]
The object 5 is placed on the XYθ stage 10 (FIG. 2). The stage 10 moves or rotates the object 10 in two orthogonal directions within a plane orthogonal to the optical axis of the equal magnification imaging telecentric optical system 4, and the light of the equal magnification imaging telecentric optical system 4. It is comprised so that the target object 10 can be moved to an axial direction.
[0016]
A half mirror 6 is provided between the DMD 3 and the equal magnification imaging telecentric optical system 4. The half mirror 6 transmits the light from the DMD 3 and directs it to the equal-magnification imaging telecentric optical system 4, and also reflects the light from the equal-magnification imaging telecentric optical system 4 and directs it to the detection unit 7. .
[0017]
The detection unit 7 is configured by a photodiode. By this photodiode, the reflected light on the surface to be measured is received through the equal magnification imaging telecentric optical system 4 and the half mirror 6. The detection unit 7 may be composed of a CMOS instead of a photodiode.
[0018]
Next, a control system of the projection exposure apparatus 100 of the embodiment will be described. FIG. 2 shows the configuration of the control system.
[0019]
The control system includes a control computer 21. The control computer 21 is connected to the light source 1, DMD 3, detection unit 7, stage 10, and display unit 22 via a driver or the like (not shown) to process data from them or to process a predetermined program or data. You can control them based on this.
[0020]
Here, the processing of data from the detection unit 7 will be described. The light image received by the detection unit 7 is converted into electrical data and sent to the control computer 21. In this case, the detection unit 7 receives the optical image by causing the control computer 21 to move the stage 10 so that the object 5 is orthogonal to the optical axis of the equal-magnification imaging telecentric optical system 4. This is done several times in between, moving in two directions or rotating. The alignment is performed by processing the electrical data thus obtained.
[0021]
The principle of alignment of this embodiment will be described. When the uneven pattern shown in FIG. 3 (the bright portion is a concave portion) is formed on the test surface of the object 5, the bright portion also moves in the XY direction when the object 5 moves in the XY direction. Moving. This means that if the reference position in the XY direction is determined and the amount of deviation from the reference position of the bright part is obtained, the amount of displacement of the object 5 in the XY direction can be obtained. In this case, the reference position in the XY direction is uniquely determined from the previous exposure pattern (mirror pattern). In other words, when the previous exposure pattern is projected, it can be known which part is a concave part or a convex part, and that part may be used as a reference position. The amount of displacement in the XY directions can be easily obtained by a similar method.
[0022]
The principle of focusing according to the present embodiment will be described. When the position of the object 5 is moved in the optical axis (Z) direction of the equal-magnification imaging telecentric optical system 4, the light image becomes thin and clear or thick. It may be blurred. In this case, the object 5 is aligned with the portion where the optical image is thin and clear (the portion where the focus is in focus). Whether or not the image is in focus is determined by calculating the width of the optical image and comparing it.
[0023]
This alignment method will be described by taking a case where a semiconductor integrated circuit pattern is formed as an example.
[0024]
When forming an insulating film on the semiconductor substrate on which the impurity layer is formed and then forming a wiring on the insulating film in contact with the impurity layer, a photoresist (a positive resist is not limited) is applied on the insulating film. The photoresist is pre-baked and post-baked. Thereafter, the photoresist is projected and exposed (first projection exposure) with ultraviolet rays (light) having a hole pattern (exposure pattern) and developed. Thereby, a hole is formed in a predetermined portion of the insulating film. Next, the photoresist is peeled off and a wiring material is deposited on the entire surface. As a result, the wiring material contacts the impurity layer. Next, the wiring material is patterned. In this patterning, a photoresist (a positive resist is not limited) is applied again, and the photoresist is pre-baked and post-baked. Thereafter, the photoresist is subjected to projection exposure (second projection exposure) with ultraviolet rays (light) having a wiring pattern (exposure pattern) and developed. Then, the wiring material is etched using the photoresist as a mask to perform patterning.
[0025]
In this case, the alignment of the semiconductor substrate is required in the second projection exposure, but when performing the alignment, for example, the exposure pattern used in the first projection exposure is used. That is, after the semiconductor substrate is aligned to some extent, the first exposure pattern is projected onto the semiconductor substrate by the DMD 3. Then, the reflected light (light image) is detected by the detection unit 7. In this case, since the photoresist portion corresponding to the hole portion of the insulating film formed by the first exposure pattern is a concave portion following the insulating film, when light hits this concave portion, the edge portion of the concave portion Is weakened by scattering and becomes a dark part, while the light intensity at the bottom of the concave part is strong and becomes a bright part. Therefore, it can be determined how much the boundary between the dark part and the bright part is displaced from the reference position.
[0026]
In addition, it is also possible to detect a positional deviation by forming a special uneven pattern as an index without using a circuit pattern and detecting it.
[0027]
Note that focusing is preferably performed before positioning. This is because positioning is easier when the subject is in focus.
[0028]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to this embodiment, A various deformation | transformation is possible in the range which does not deviate from the summary.
[0029]
For example, although the half mirror 6 is provided between the DMD 3 and the equal-magnification imaging telecentric optical system 4 in the embodiment, it may be provided between the equal-magnification imaging telecentric optical system 4 and the object 5.
[0030]
Moreover, although the previous exposure pattern was projected on the uneven | corrugated pattern of a target object, you may make it project the light which does not have a pattern on an uneven | corrugated pattern. Since the previous exposure pattern and the concavo-convex pattern have a one-to-one correspondence, if the previous exposure pattern is known, the concavo-convex pattern when the object is at the normal position, and thus the light / dark pattern can be predicted. Therefore, the amount of deviation from the actual light and dark pattern can be obtained with reference to the predicted light and dark pattern, and alignment can be performed based on this amount of deviation.
[0031]
【The invention's effect】
The effect of the representative one of the present invention will be described. One exposure pattern carried by a spatial light modulator including a plurality of mirrors capable of independently controlling the tilt of the reflecting surface is projected and exposed on an object. In projecting and exposing another exposure pattern to the object after forming a concavo-convex pattern on the object, the one exposure pattern carried by the spatial modulator is projected onto the concavo-convex pattern of the object , Since the object is aligned based on the detection result of the light image of the uneven pattern, the alignment can be easily performed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a main part of a projection exposure apparatus used in an alignment method of a first embodiment.
FIG. 2 is a view for explaining a control system of a projection exposure apparatus used in the alignment method of the first embodiment.
FIG. 3 is a diagram for explaining an alignment method according to the first embodiment;
[Explanation of symbols]
1 Light source 2 Reflector 3 DMD
4 equal-magnification imaging telecentric optical system 5 object 6 half mirror 7 detector

Claims (3)

After one exposure pattern carried by a spatial light modulator configured to include a plurality of mirrors that can independently control the inclination of the reflecting surface is projected and exposed to an object to form an uneven pattern on the object, another In projecting and exposing the exposure pattern to the object, the one exposure pattern carried by the spatial modulator is projected onto the uneven pattern of the object, and based on the detection result of the optical image of the uneven pattern. An alignment method characterized in that the object is aligned. The alignment method according to claim 1, wherein alignment is performed by detecting a positional deviation of the uneven pattern . The alignment method according to claim 2, wherein focusing is performed by detecting a degree of blur of the light image of the uneven pattern and moving the object in a direction in which blur is eliminated .

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