JPH0620912A - Projection aligner - Google Patents

Abstract

PURPOSE:To minimize focal difference in the orthogonal biaxial directions on a substrate generated by the state of the polarized light of illumination light projected to the projection optical system of a projection aligner, and to increase the substantial depth of a focus. CONSTITUTION:A linearly polarized light plate 40 is arranged between a light source 1 and a projection optical system PL. The linearly polarized light plate 40 is rotated, and rotation is stopped at a position, where focal difference in the orthogonal biaxial directions on a substrate in the direction of polarized light is minimized. The substantial depth of a focus is increased through exposure under the state. A circularly polarized light plate 41 is disposed between the projection optical system PL and a wafer W, thus preventing the directional properties of image formation characteristics by the direction of polarized light, then obtaining more excellent image formation characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus, and more particularly to a projection exposure apparatus for manufacturing semiconductor elements or liquid crystal substrates.

[0002]

2. Description of the Related Art In this type of apparatus, when exposure is performed with a linearly polarized light beam, the reflectance of the surface of the photosensitive material differs depending on the polarization direction (P-polarized light and S-polarized light), and the line width of the projected pattern is different. Come on. That is, when exposure is performed with a linearly polarized light beam, the imaging characteristics have a directivity. Therefore, in the conventional device, a circularly polarizing plate or a depolarizing plate is provided to make linearly polarized light circularly polarized light or non-polarized light to prevent the influence of the reflectance of the surface of the photosensitive agent. By making the polarization characteristic circularly polarized or non-polarized in this way, the influence of the reflectance on the surface of the photosensitive agent is reduced.

[0003]

According to the conventional technique as described above, the influence of the reflectance of the surface of the photosensitizer is reduced. However, as described above, in the conventional apparatus, even if the polarization state of the illumination light incident on the projection optical system is circularly polarized or non-polarized, the distortion on the projection optical system, the aberration, or the like causes the light on the photosensitive substrate to increase.
A difference occurs between the line widths of the patterns in the dimension direction.
It is considered that this is because the focal positions in the two-dimensional direction (vertical direction and horizontal direction) on the photosensitive substrate are different.

This state is shown in FIG. FIG. 10 is a diagram schematically showing that the focal position is different in the two-dimensional direction (vertical direction and horizontal direction on the photosensitive substrate) within the visual field of the projection optical system. The triangle indicating the vertical focus position fy is indicated as ΔY, the triangle indicating the horizontal focus position fx is indicated as ΔX, and the difference between these two focus positions is indicated as ΔZ. Further, here, the relationship between the two focal positions and the focal depths is shown, and the focal depths in the vertical direction and the lateral direction are Δfy and Δfx, respectively.
It shows with. The substantial depth of focus is the overlapping portion Δf (hatched portion) of these two depths of focus, which is smaller than the depth of focus of each of them.

The focus positions in the vertical and horizontal directions are considered to have a close relationship with the polarization direction of the illumination light, and a focus difference occurs due to the distortion of the projection optical system and the polarization direction.
Therefore, there is a problem that the substantial depth of focus of the projection optical system cannot be improved only by reducing the influence of the reflectance due to the photosensitive agent. Therefore, it is an object of the present invention to increase the total depth of focus by minimizing the focus difference in the two-dimensional direction on the photosensitive substrate of the projection optical system.

[0006]

In order to solve the above problems, according to the present invention, an illumination optical system for illuminating a mask (R) having a predetermined pattern (PA) formed by light emitted from a light source (1). In a projection exposure apparatus for forming an image of (6) and a pattern on a photosensitive substrate (W) via a projection optical system (PL),
A polarization state adjusting means (40) provided between the light source and the projection optical system; and a polarization state adjusting means for the optical axis (A of the projection optical system.
X) and rotate it in a plane perpendicular to the plane 2
A driving means (33) for relatively moving the respective focal positions in the axial direction and a control means (32) for controlling the driving means so as to minimize the difference between the respective focal positions are provided.

[0007]

According to the present invention, the polarization state adjusting means such as a linear polarizing plate is inserted between the light source and the projection optical system, and the polarization state adjusting means is rotated in a plane perpendicular to the optical axis of the projection optical system. The focus position is relatively changed in the two orthogonal directions (vertical direction and horizontal direction). Then, the rotation of the linear polarization adjusting means is stopped at the positions where the respective focal positions are closest to each other, and the linear polarization adjusting means is fixed at this position. Since the respective focal positions are closest to each other, the overlapping portions of the respective focal depths are the largest and the substantial focal depth is expanded.

Further, by inserting a circularly polarizing plate or the like between the projection optical system and the photosensitive substrate, linearly polarized light is converted into circularly polarized light (circularly polarized light close to random polarized light) or non-polarized light, and the reflectance of the photosensitive agent It is possible to eliminate the directionality of the imaging characteristic due to the difference and further improve the imaging performance.

[0009]

1 is a schematic view of a projection exposure apparatus suitable for one embodiment of the present invention. In FIG. 1, an illumination light source 1 for exposure such as an ultra-high pressure mercury lamp, an excimer laser light source is a g-line, i
Illumination light IL having a wavelength (exposure wavelength) that sensitizes the resist layer, such as a line or ultraviolet pulse light (for example, KrF excimer laser light), is generated. The illumination light IL enters the illumination optical system 6 including an optical integrator (fly eye lens), a relay lens, a condenser lens, and the like. The mirror 22 is retracted from the optical path in the normal state (during exposure),
As will be described later, the projection optical system PL depending on the polarization state of the illumination light
It is inserted on the optical axis only when measuring the imaging characteristics of.

Illumination light IL that has been made uniform in luminous flux and reduced in speckles in illumination optical system 6 is reflected by mirror 7
After passing through the relay lenses 9a and 9b and the variable blind 10, the light is reflected vertically downward by the mirror 12 and reaches the main condenser lens 13 to illuminate the pattern area PA of the reticle R with uniform illuminance. The surface of the variable blind 10 is a surface conjugate with the reticle R, and the illumination field of the reticle R can be arbitrarily selected by opening and closing the movable blade that constitutes the variable blind 10 by the drive motor 11 to change the opening shape. it can.

The reticle R is mounted on a reticle stage RS which can be two-dimensionally moved in a plane (horizontal plane) perpendicular to the optical axis AX of the projection optical system PL, and the center point of the pattern area PA is the optical axis AX. Positioned to match. The reticle R is initially set by a reticle alignment system R that photoelectrically detects an alignment mark (not shown) around the reticle.
This is performed by finely moving the reticle stage RS based on the mark detection signal from A. The reticle R is used after being appropriately replaced by a reticle exchanger (not shown).
The illumination light IL that has passed through the pattern area PA enters the projection optical system PL that is telecentric on both sides via the linear polarization plate 40.

The linear polarizing plate 40 is arranged in the space between the reticle R and the projection optical system PL, and aligns the polarization direction of the illumination light IL passing through the reticle R in one direction. Linear polarizing plate 40
Can be rotated in a plane perpendicular to the optical axis AX by a driving device 33 such as a motor or a gear. Further, the drive device 33 is provided with a rotation angle detection means such as a rotary encoder, and can detect the rotation position of the linear polarizing plate 40. The linear polarizing plate 40 is capable of changing the respective focal positions of the wafer W in two orthogonal directions (reference X direction and reference Y direction). That is, the relative position between the focus position in the reference X-axis direction and the focus position in the reference Y direction can be changed, and ideally, the rotation is performed so that the focus positions in the X direction and the Y direction substantially match. To be done. Further, the driving device 33 can move the linear polarizing plate 40 in and out of the optical path.

In the present embodiment, information about the polarization direction of the linear polarizing plate 40 (rotation angle etc.) is input by an input means 42 such as a console.
Is input to the control means 32. And the control means 32
Rotates the linear polarizing plate 40 based on this information and stops the rotation at the position where the polarization direction is optimum. Then, the driving means 33 is controlled so as to maintain the polarization direction. The illumination light IL whose focal position in the X direction and the Y direction is adjusted by the linear polarization plate 40 reaches the circular polarization plate 41 such as a λ / 4 plate via the projection optical system PL. The illumination light IL is polarized by the circularly polarizing plate 41 and reaches the wafer W as circularly polarized light or non-polarized light having a shape close to random polarization. The projection optical system PL is a reticle R
An image of the circuit pattern is formed on a surface of which a resist layer is formed, and is projected (imaged) so as to be superposed on one shot area on the wafer W held so as to be substantially coincident with the image plane. The wafer W is moved by the drive motor 17 in the optical axis AX direction (Z
Mounted on a Z stage 14 that can be moved in the direction). The Z stage 14 is mounted on the XY stage 15 which can be two-dimensionally moved by the drive motor 18, and the XY stage 1
5 is a reticle R for one shot area of the wafer W
When the transfer of is completed, the next area on the wafer is moved until it coincides with the exposure area of the projection optical system PL. The two-dimensional position of the XY stage 15 is constantly detected by the interferometer 19 with a resolution of, for example, about 0.01 μm. Therefore, a movable mirror 14m that reflects the laser light from the interferometer 19 is provided at the end of the Z stage 14. Interferometer 1
9 and the movable mirror 14m are provided in pairs for position detection in the X and Y directions.

On the Z stage 14, a projection optical system P is also provided.
A reference member 20 used when measuring the imaging characteristics of L is provided. As shown in FIG. 3, the reference member 20 has an exposure area (image field IF) of the projection optical system PL.
At the position corresponding to 1 place in the center and 4 places in the periphery,
Five opening patterns 21a to 21e provided with the lattice pattern shown in FIG. 2 are provided. In FIG. 3, a circular area IF having a radius r indicates the maximum exposure area of the projection optical system PL, and a square inscribed in this circle indicates the maximum chip area where the wafer can be actually exposed. In FIG. 2, the black background is the light shielding portion and the white background is the light transmitting portion. In FIG. 3, each lattice pattern has an inclination of 45 degrees with respect to the X axis. In this embodiment, the opening patterns 21a to 21e are collectively called the opening 21. The opening 21 is illuminated from below by the measurement illumination system LL.

The measurement illumination system LL includes a mirror 22, a half mirror 23, a lens 24, an optical fiber 25 and a lens 26 which are inserted into the optical path of the illumination light IL by a driving device (not shown).
And the mirror 27, and guides the illumination light IL into the wafer stage 15. The illumination light IL emitted from the opening 21 reaches the reticle R via the projection optical system PL, is reflected by the back surface of the reticle R, and is again opened via the projection optical system PL.
Return to. This reflected light passes through the opening 21 and then the mirror 2
The light enters the photoelectric detector 28 including a photomultiplier, SPD, etc. through the lens 7, the lens 26, the fiber 25, the lens 24, and the half mirror 23, is photoelectrically converted by the photoelectric detector 28, and is output as an electric signal. Here, although not shown, the five openings 21a to 21e are individually illuminated and the reflected light is individually received.

In FIG. 1, reference numeral 29 is an oblique incidence type detection optical system (focus detection system), for example, Japanese Patent Publication No. 2-1036.
It is disclosed in Japanese Patent Publication No. The focus detection system 29 detects the position of the wafer surface in the vertical direction (Z direction) with respect to the best image plane of the projection optical system PL. The focus detection system 29 includes a light source 29a that emits illumination light that is incident on the wafer surface from an oblique direction with respect to the optical axis AX, and a light receiving optical system 29b that receives light reflected by the wafer surface. In this embodiment, the angle of the parallel flat glass (plane parallel) (not shown) provided in advance inside the light receiving optical system 29b is adjusted so that the best designed image plane becomes the zero point reference. That is,
The focus detection system 29 is calibrated. Then, using the reference member 20, the best focus position of the projection optical system PL is obtained. Reticle R is Reticle Stage R
The XY stage 15 is moved by the interferometer 19 while being mounted on the S.
Of the opening 21 on the reference member 20 while monitoring the position of
XY so that the center of is on the optical axis AX of the projection optical system PL.
The stage 15 is moved by the motor 18. At this time, the motor 17 is simultaneously driven to move the Z stage 14 to the projection optical system P.
Several times the depth of focus (± DOF) from the position (design value) that is considered to be the best focus position of L (for example, 2 · DO)
F) Lower (or raise) about. At the same time, the mirror 22 is moved into the optical path to guide the illumination light IL to the opening 21, and the back surface (pattern surface) of the reticle R is illuminated via the specific pattern of the opening 21 and the projection optical system PL. The illumination light reflected from the reticle R is again projected onto the projection optical system PL and the aperture 2
After passing through 1, mirror 27, lens 26, optical fiber 2
5, incident on the photoelectric detector 28 via the lens 24 and the half mirror 23. Then, in this state, Z stage 14
The motor 17 scans upwards (or downwards) about twice the moving amount (2 · DOF) of the Z stage. At this time, the output of the photoelectric detector 28 (that is, the photoelectric signal corresponding to the intensity of the reflected light that has passed through the opening 21) and the Z stage 14
The outputs of the focus detection system 29 corresponding to the positions of are simultaneously sampled to obtain information as shown in FIG. The output of the photoelectric detector 28 has a mountain-shaped waveform shape as shown in FIG. 4, and the output value of the focus detection system 29 at the apex is f. The sampling may be performed, for example, for each unit movement amount (for example, 0.02 μm) of the Z stage 14 or for each unit time.

The relationship as shown in FIG. 4 is obtained by the opening 2
If 1 is at a position conjugate with the reticle R, the illumination light emitted from the aperture 21 forms a clear image on the reticle R. Therefore, when the reflected light enters the opening 21, a clear image of the lattice pattern is formed. When the reflected light passes through the opening 21, almost no reflected light is blocked by the light blocking portion,
The amount of light received by the photoelectric detector 28 increases as compared with the case of defocusing. Therefore, in FIG. 4, the photoelectric detector 28
The output value f obtained by the focus detector 29 at the peak output of becomes the optimum focus position (best focus position) of the projection optical system PL. The main control system 32 obtains the peak value from the output of the photoelectric detector 28, and obtains the focus position from the output value of the focus detection system 29 at that time. In this embodiment, the opening 21 is composed of five openings, and the average value of the five focus positions is the best focus position. Since the reflected light from each opening can be individually received, the Z stage 1
4 moves only once. If the best focus position is found, compare it with the best focus position in the design above,
The difference is added to the focus detection system 29 as an offset. This offset may drive the above-mentioned parallel plate glass, or may only add the offset electrically. Also,
An irradiation amount monitor 43 having a light receiving surface on a surface substantially equal to the surface of the photosensitizer applied on the wafer W is provided on the Z stage 14. The irradiation amount monitor 43 can detect the illuminance of the illumination light reaching the wafer W.

Information about the optimum polarization directions (rotation angles) of the projection optical system PL and the linear polarizing plate 40 can be obtained by performing a test print using a test reticle as shown in FIG. The test reticle is provided with test patterns having the same line width in the X and Y directions. FIG. 6 is a view showing a resist image when trial baking is performed using the X and Y patterns of FIG. 5 while rotating the linear polarizing plate 40 at every predetermined angle (for example, every 10 degrees). FIG. 6A shows the case where the focus position in the X direction is the best focus, and FIG. 6B shows the case where the focus positions in both the X and Y directions are substantially the same (the line width of the pattern in the X direction and the Y direction). Direction line width of the pattern becomes almost equal), and FIG. 6C shows a case where the best focus is obtained in the Y direction. Therefore, as shown in FIG. 6B, the rotation angle of the linear polarizing plate 40 when the focal positions in both the X and Y directions are substantially the same may be input by the input means 42.

Here, by changing the polarization direction of the light beam incident on the projection optical system, two orthogonal light beams are formed on the photosensitive substrate.
The fact that the focal positions in the axial directions (XY directions) are different will be conceptually described with reference to FIG. In FIG. 7, it is assumed that reference coordinate axes (Y axis, X axis) are predetermined on the photosensitive substrate. FIG. 7 shows the focal position (fx, fy), the focal difference (ΔZ), the focal depth (Δfx, Δfy), and the substantial focal depth (Δfx) in the XY directions on the photosensitive substrate in a predetermined polarization direction.
y) is shown. The reference numerals used in FIG. 7 are the same as those in FIG. 10, and the same reference numerals are given.

FIG. 7A shows a focus position fxa in the X direction and Y.
A focal difference ΔZa is generated between the focal point position fya in the direction,
It shows a case where the substantial depth of focus Δfxy, which is the overlapping portion of the respective depths of focus Δfxa and Δfya, is small. FIG. 7B shows a polarization direction rotated by a predetermined angle from the polarization direction of the linear polarizing plate 40 at the focal point position shown in FIG. It shows the state of the focus position in the (direction). Also in this case, a focus difference ΔZb is generated between the focus position fxb in the X direction and the focus position fyb in the Y direction, and the substantial depth of focus Δfxy that is the overlapping portion of the respective focus depths Δfxb and Δfyb is small.

The difference in focus between the X and Y directions depending on the polarization direction is that the spectral characteristics of the projection optical system differ depending on the polarization direction due to the influence of distortion of the projection optical system. Therefore, it is considered that a difference occurs in the refractive index in the X and Y directions, and as a result, a difference occurs in the focal position. Therefore, by setting the polarization direction of the linear polarizing plate 40 between FIG. 7 (a) and FIG. 7 (b) (for example, an angle of 0 ° to less than ± 90 ° with respect to the X direction), X as shown in 7 (c),
It is considered that the focus difference in the Y direction becomes smaller. Figure 7 (c)
, The focus difference ΔZc between the X-direction focus position fxc and the Y-direction focus position fyc is small, and the respective focus depths Δf.
Substantial depth of focus Δf, which is the overlapping portion of xb and Δfyb
xy increases.

Next, the operation of setting the linear polarizing plate 40 so as to have the optimum polarization direction using the test reticle shown in FIG. 5 will be described. First, the linear polarization plate 40 is driven by the driving means 33.
To retract from the optical path. Next, the above-mentioned reference member 20
The best focus position is obtained by the best focus detection using. Next, based on the output of the focus detection system 29, the Z stage 14 is moved so that the surface of the test wafer W is at the best focus position. Then, the linear polarizing plate 40 is inserted into the optical path, and the exposure is performed every time the Z stage 14 is changed by a predetermined movement unit. The XY stage 15 is moved stepwise every time the exposure performed in a predetermined movement unit (for example, 0.2 μm) of the Z stage 14 is completed. The Z stage 14 is moved up and down around the best focus position within a range of, for example, a depth of focus (Δfx, Δfy). If the depth of focus is ± 1 μm, exposure is performed 10 times in step and repeat. Then, every time the linearly polarizing plate 40 is rotated by a predetermined angle (for example, 10 degrees) from a predetermined reference position, the exposure performed by the movement of the Z stage 14 and the step movement of the XY stage 15 is repeated. From the result of this trial baking, the angle of the linear polarizing plate 40 in which the line width difference in both the XY directions is the smallest and the depth of focus becomes large is obtained.

At the time of actual exposure, this angle information is input by the input means 42, the exposure is executed in the optimum polarization direction, and the depth of focus is expanded. Further, in this embodiment, the circularly polarizing plate 41 is provided to reduce the directionality of the image forming characteristics due to the influence of the reflectance of the photosensitizer applied to the wafer W, so that even better exposure is realized. At this time, if the amount of light passing through the circularly polarizing plate 41 is lost due to the rotation of the linear polarizing plate 40, the circularly polarizing plate 41 can be rotated in a plane perpendicular to the optical axis AX, and rotated at a position where the amount of light loss is the smallest. Should be stopped. Illuminance monitor 43
To detect.

Next, a second embodiment of the present invention will be described. In this embodiment, the linear polarizing plate 40 is not subjected to trial baking.
Is rotated, and the focus position in the X direction and the focus position in the Y direction are measured for each predetermined angle by the focus position measuring method using the photoelectric detector 28 and the focus detection system 29 described in the first embodiment. ,
The linear polarizing plate 40 is stopped and fixed at a position where the two focus differences are minimized.

In this embodiment, the reference member 20 has five sets of opening patterns 21ay, 21ax each having a pair of a grid pattern in the X direction and a grid pattern in the Y direction as shown in FIG.
21 ey and 21 ex are provided. In FIG. 8, the opening patterns 21ay to 21ey with the subscript y are for measuring the focus position of the projection optical system PL in the Y direction,
The opening patterns 21ax to 21ex with the subscript x are for measuring the focus position of the projection optical system PL in the X direction. In this embodiment, a pair of opening patterns 21ay, 21a
The x to 21 ey are collectively referred to as the opening 21. Here, although illustration is omitted, five sets of openings 21ay, 21ax to 21e are provided.
y is individually illuminated, and the reflected light from the reticle R is individually received. Therefore, the first
The Z stage 14 need only be moved once, as in the embodiment of FIG.

The focus positions of these openings 21 are obtained by measuring the focus positions in the same manner as in the first embodiment, as shown in FIG. In this embodiment, since the reflected light from the reticle R that has passed through a total of 10 aperture patterns is individually received,
Measurement is performed 10 times in total. As in the first embodiment, the Z stage 14 is moved by about ± focus depth for each predetermined movement amount unit, the focus position is measured at each position, and the focus position is stored in the control system 32. This operation is performed every time the linearly polarizing plate 40 is rotated by a predetermined angle (for example, 10 degrees). And
The rotation angle at which the amount of deviation between the focus position in the X direction and the focus position in the Y direction is minimized for each aperture pattern is obtained. By performing exposure while maintaining the position of the linearly polarizing plate 40 at this rotation angle, the depth of focus increases.

The present invention is not limited to the above embodiment, and the linear polarizing plate 40 may be arranged anywhere in the space between the light source 1 and the projection optical system PL. Further, the method of adjusting the polarization state is not limited to changing the direction of the linearly polarized light, and the light flux incident on the projection optical system PL is made to be other than the linearly polarized light, and the focus difference is adjusted by changing the polarization state. You may For example, when circularly polarized light is made incident, the polarization state may be changed to an elliptical shape, and the shape may be changed to adjust.

Further, the light source 1 may emit linearly polarized light or circularly polarized light, or may emit random polarized light.

[0029]

As described above, according to the present invention, the substantial depth of focus can be increased by a simple structure in which a means for adjusting the polarization state is provided. Further, it is possible to reduce the deterioration of the image forming characteristic due to the influence of the polarized light, and the directionality of the image forming characteristic is reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a projection exposure apparatus suitable for an embodiment of the present invention.

FIG. 2 is a diagram showing a grid pattern provided in an opening 21 according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a reference member 20 according to an embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between an output of a photodetector 28 and an output of a focus detection system 29 according to light passing through an opening 21 according to an embodiment of the present invention.

FIG. 5 is a diagram showing a test reticle according to an embodiment of the present invention.

FIG. 6 is a diagram showing a resist image when exposure is performed using the test reticle of FIG. 5 according to an embodiment of the present invention.

FIG. 7 is a conceptual diagram illustrating that the focal position differs in the XY directions due to the difference in the polarization direction.

FIG. 8 is a diagram showing a grid pattern provided in an opening 21 according to a second embodiment of the present invention.

9 is a diagram showing a relationship between an output of a photodetector 28 and an output of a focus detection system 29 due to light that has passed through each of the grating patterns of FIG.

FIG. 10 is a conceptual diagram explaining that the focal position differs in the XY directions by the conventional device.

[Explanation of Codes] 1 ... Light source 6 ... Illumination optical system 14 ... Z stage 15 ... XY stage 20 ... Reference member 21 ... Aperture pattern 28 ... Photoelectric detector 29 ... Focus detection system 32 ... Main control system 33 ... Driving device 40 ... Linear polarization plate 41 ... Circular polarization plate 42 ... Input means 43 ... Illuminance monitor R ... Reticle W ... Wafer PL ... Projection optical system

Claims (2)

[Claims] 1. An illumination optical system for illuminating a mask on which a predetermined pattern is formed by light emitted from a light source, and a projection exposure apparatus for forming an image of the pattern on a photosensitive substrate through a projection optical system. And a polarization state adjusting means provided between the projection optical system and the projection optical system; the polarization state adjusting means is rotated in a plane perpendicular to the optical axis of the projection optical system, and the two orthogonal directions on the photosensitive substrate. 2. A projection exposure apparatus, comprising: a driving unit that relatively moves the respective focal positions in the above item; and a control unit that controls the driving unit so as to minimize the difference between the respective focal positions. 2. The projection exposure apparatus according to claim 1, further comprising a circularly polarizing plate or a depolarizing plate provided between the projection optical system and the photosensitive substrate.