JPH0577168B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention relates to a projection exposure apparatus for transferring a reticle pattern or a mask pattern onto a wafer, and particularly relates to a through-the-lens (TTL) method using a projection optical system. The present invention relates to a projection exposure apparatus that performs alignment.

[Background of the Invention] Generally, in a projection exposure apparatus for LSI or VLSI manufacturing, a reticle pattern (or mask pattern) is projected onto a wafer through a projection lens with a reduction magnification of about 1/5 or 1/10.
The same pattern is repeatedly exposed on each wafer. Therefore, before each exposure, the relative position of the reticle and wafer is measured through the projection lens.
It will be necessary to align. In order to automatically perform this operation, the reticle and wafer require marks for alignment, that is, reticle marks and wafer marks. Moreover, usually LSI,
In the VLSI manufacturing process, the alignment and exposure steps are included multiple times, so multiple alignment marks are often created in sequence at different positions from the marks used in the previous process.

In general, there are two types of projection lenses for projection exposure equipment: a double-telecentric type and a single-telecentric type.The principal ray on the wafer side of the reticle projection image is incident perpendicularly to the wafer surface in both the double-telecentric type and the single-telecentric type. The side chief ray is perpendicular to the reticle plane in the case of the double-telecenter type, whereas in the case of the single-telecenter type, it is tilted away from perpendicular to the reticle plane at image heights other than the optical axis. The slope changes depending on the image height.

Therefore, when using a single-telecentric lens as the projection lens and detecting the optical signal of the wafer mark through the lens to detect the relative position between the reticle and the wafer, when the image height of the wafer mark changes, the principal ray on the reticle side changes. Image heights other than the optical axis have an inclination that deviates from perpendicular to the reticle surface, and this inclination changes depending on the image height, so the optical axis position of the optical signal incident on the optical signal selection means of the wafer mark changes and is correct. The drawback was that optical signal detection was no longer possible.

In addition, a double telecentric lens is used as the projection lens,
Even when detecting an optical signal of a wafer mark through a lens, if the lens has a telecentricity error, if the image height of the wafer mark changes, the optical axis position of the optical signal incident on the optical signal selection means will change due to telecentricity. Since it changes by the amount of error, there is a drawback that the imaging position of the optical signal relative to the optical signal selection means is shifted, making it impossible to detect the correct optical signal, similar to when a single-telecentric type lens is used.

[Object of the Invention] The present invention eliminates the above-mentioned drawbacks of the conventional example, and provides a projection exposure apparatus that can always make a relative alignment signal between a reticle and a wafer enter an optimal position of an optical signal selection means. The purpose is to

[Means for Achieving the Object] In order to achieve the above object, the present invention includes a projection optical system for transferring a pattern on a first object onto a second object, and an optical signal selection means. In a projection exposure apparatus having an alignment optical system equipped with a photoelectric conversion means for converting an optical signal from a second object into an electrical signal via a system, for matching the deviation of the optical axis of the optical signal with respect to the optical signal selection means. The apparatus is characterized in that it includes an optical means for changing the optical axis of the optical signal before the optical signal selection means in the alignment optical system. As a specific example, the optical axis position of the optical signal and the optical signal selection means can be adjusted by tilting a parallel plane glass and moving the optical axis of the optical signal in parallel according to the fluctuation of the optical signal imaging position due to the telecentricity characteristic of the projection lens. It has a function to automatically correct the relative position, and always makes the relative positioning signal between the reticle and the wafer enter the optimum position of the optical signal selection means.

[Operations and Effects] According to the above configuration, when the optical axis of the optical signal is misaligned with respect to the optical signal selection means, the optical means disposed in front of the optical signal selection means adjusts the optical axis of the optical signal and the optical signal selection means. Since the optical axes are aligned, the first
The alignment accuracy between the object and the second object can be maintained at a high level.

[Description of Examples] Hereinafter, the present invention will be described in more detail with reference to Examples.

Figure 5 shows a state in which the optical axis of the optical signal of the wafer mark and the optical axis of the alignment optical system are aligned in a device that detects the optical signal of the wafer mark through a projection lens to detect the relative position of the reticle and the wafer. .

After passing through a lens 2, the alignment light emitted from the laser 1 is irradiated onto a reticle 6 via a polygon mirror 3, a mirror 4, and an objective lens 5. The reticle 6 is provided with marks for alignment with the wafer 8 , and the alignment light that has passed through the reticle 6 is irradiated via the projection lens 7 onto the wafer mark provided in the scribe area of the wafer 8 . Note that the wafer 8 is placed on a sample stage 9. The reflected light from the wafer mark, that is, the optical signal from the wafer mark, passes through the projection lens 7 and reaches the mirror 4 through the same path as the incident light. The light then enters an optical signal selection means 11 for detecting the relative position of the reticle 6 and the wafer 8, and a photoelectric conversion means 12 for converting the selected light into an electrical signal.
By electrically processing the output of this photoelectric conversion means, the relative position of the reticle 6 and the wafer 8 is detected.

FIG. 2 shows the positional relationship between the optical signal and the optical signal selection means, and S1 to S4 are optical signals whose directionality is determined according to the shape of the wafer mark. W1~W4
is an optical signal selection window, which is arranged according to the imaging position and directionality of the optical signal.

FIG. 3 is a plan view showing the arrangement of the photoelectric conversion means, in which each photoelectric conversion element D1 to D4 is positioned at the optical signal selection window W1 to W4 in order to independently convert the optical signal S1 to S4 into an electric signal. are arranged accordingly.

FIG. 4 shows the output voltage waveforms and voltage values of each of the photoelectric conversion elements D1 to D4, and shows the waveforms V1 to D4.
V4 and voltage values v1 to v4 are photoelectric conversion element D1
-D4 respectively.

As shown in FIG. 5, when the optical axis of the optical signal and the optical axis of the alignment optical system match, the output voltages v1 to v4 become v1=v2=v3=v4.
This is the case when the relative position between the optical signal selection means and the optical signal axis is optimal.

FIG. 1 shows a schematic block configuration of a projection exposure apparatus according to an embodiment of the present invention. The apparatus shown in the figure changes the optical axis position of the optical signal incident on the optical signal selection means 11 according to the telecentricity characteristic of the projection lens 7 when changing the optical axis of the alignment optical system with respect to the optical axis of the projection optical system. It has a function that automatically corrects to the optimal position. Note that numerals 1 to 12 are the same as in FIG. 5.

The apparatus shown in FIG. 1 will be explained in detail below.

The image height of the wafer mark was changed from image height a, where the optical axis of the optical signal of the wafer mark and the optical axis of the alignment optical system coincide with each other, as explained in FIG. 5, to image height b, as shown in FIG. In this case, the optical axis position of the optical signal of the wafer mark incident on the optical signal selection means 11 changes as shown by the broken line due to the telecentricity characteristic of the projection lens 7. Therefore, the optical signal imaging position with respect to the optical signal selection means 11 is shifted by ΔY,
If this continues, correct optical signal detection will not be possible.

FIG. 6 shows a state in which the optical signal imaging position is shifted with respect to the optical signal selection means.

FIG. 7 shows the output voltage waveform from the photoelectric conversion means in the state shown in FIG. V1' to V4' are the photoelectric conversion output waveforms of the optical signals passing through the optical signal selection windows W1 to W4, and v1' to v4' are the output voltage values thereof.

Therefore, in this embodiment, the output voltage v1' from the photoelectric conversion means 12 as shown in FIG. ~v
4', the optical signals S1' to S are generated as shown in FIG.
4' and the optical signal selection means 11 is detected, and based on the detection signal from the detection means 13, the controller 14 adjusts the output voltages v1' to v4' to be equal. That is, the tilt adjustment mechanism 15 is driven to tilt the parallel plane glass 16 so that the light quantities of the four optical signals are balanced, thereby correcting the optical signal imaging position (that is, the optical signal optical axis position) to the optimum position.

Next, the operation of automatically aligning the optical axis of the optical signal to the optical signal selection means 11 in the exposure apparatus of FIG. 1 will be described with reference to the flowchart of FIG. 8. This operation is controlled by the detection means 13 and controller 14 shown in FIG. 1, which are comprised of a microprocessor (not shown) or the like.

After the auto-alignment starts, the detection means 13 monitors the output signals of each photoelectric conversion element D1 to D4, and when a wafer mark signal is detected,
First, output voltages v1 and v2 are compared. here,
If the direction perpendicular to the paper in Fig. 1 is the X axis, the vertical direction is the Y axis, and the horizontal direction is the Z axis, then if v1 and v
If the magnitudes of 2 are different, the optical signal selection means 1
Since the optical axis position of the optical signal is shifted in the Y-axis direction with respect to 1, a magnitude determination signal is output by determining the magnitude of v1 and v2. The controller 14 drives the tilt adjustment means 15 in accordance with this magnitude discrimination signal. This drive operates the tilt adjusting means 15 so that, for example, if v1<v2, the parallel plane glass 16 rotates clockwise about the X axis, and if v1>v2, rotates counterclockwise.

On the other hand, when the output voltages v1 and v2 are equal, or when the output voltages v1 and v2 become equal as a result of repeating the above-described magnitude determination of the output voltage and rotation of the parallel plane glass 16 a necessary number of times, then the output Based on the voltages v3 and v4, the shift in the X direction is detected and the tilt adjustment means 15 is driven to correct the shift in the same manner as described above. Thereby, the optical axis of the optical signal is aligned to the optimum position with respect to the optical signal selection means 11. Thereafter, auto-alignment is performed and exposure is performed using a conventional method.

[Modified Example of Embodiment] In the above embodiment, the parallel plane glass 16 is driven after detecting the deviation of the optical axis of the optical signal with respect to the optical signal selection means 11, but the known telecentricity error is The parallel plane glass 16 is tilted in advance based on the design value to correct the optical signal optical axis position, and then the amount of deviation is detected and the parallel plane glass 16 is tilted.
It is also effective to finally adjust the tilt. In this case, it is possible to reduce the time required for tilt adjustment, that is, optical signal optical axis position correction.

Furthermore, the output voltages v1 to v4 at the optimum position of the optical signal selection means may not necessarily be v1=v2=v3=v4 depending on the mark formation state, such as when the edge of the alignment mark on the wafer is tilted to one side. There is. In such a case, for example, first adjust the inclination of the parallel plane glass 16 using a standard wafer, then align the target wafer to the same position, and adjust the detection means 13 so that the error signal at this time becomes zero. The output of each photoelectric conversion element D1 to D4 may be set using a variable resistor or the like so that the four input voltages are equal. Or, in the detection means 13, v1 to v are equivalent to the above.
After multiplying 4 by an appropriate coefficient, v1, v2, and v3
and v4 may be compared. In these cases, if there are variations in optical signal versus electrical signal characteristics among the photoelectric conversion elements D1 to D4, conditions can be set including this variation.

As explained above, according to this embodiment, even if there is a change in the optical signal imaging position of the wafer mark due to the telecentricity characteristic or telecentricity error of the projection lens, the parallel plane glass can be tilted according to the change, so that the optical signal can be illuminated. The signal imaging position can be aligned with the optical signal selection means, and the alignment accuracy between the reticle and the wafer can be maintained with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a projection exposure apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing the positional relationship between optical signals and optical signal selection means, and FIG. 3 is a diagram showing the positional relationship between optical signals and optical signal selection means. FIG. 3 converts optical signals into electrical signals. 4 is a diagram showing the output voltage waveform from the photoelectric conversion means in FIG. 3, and FIG. 5 is a diagram showing the arrangement of the photoelectric conversion means shown in FIG. 6 is a diagram illustrating a state in which the optical signal imaging position is shifted with respect to the optical signal selection means, and FIG. A diagram showing the output voltage waveform from the converting means, and FIG. 8 is a flowchart for explaining the automatic positioning operation of the optical signal selection means in the apparatus of FIG. 1. 1... Laser, 2... Lens, 3... Polygon mirror, 4... Mirror, 5... Objective lens, 6...
... Reticle, 7... Projection lens, 8... Wafer,
9... Sample stage, 10... Lens, 11... Optical signal selection means, 12... Photoelectric conversion means, 13... Means for knowing the relative position of the optical axis of the projection optical system and the optical axis of the alignment optical system (detection means) , 14...controller,
15...Tilt adjustment means, 16...Parallel plane glass, S1-S4, S1'-S4'...Optical signal, W1
~W4... Optical signal selection window, D1-D4... Photoelectric conversion element, V1-V4, V1'-V4'... Output waveform from the photoelectric conversion element.

Claims (1)

[Scope of Claims] 1. A projection optical system for transferring a pattern on a first object to a second object, and an optical signal selection means, and an optical signal from the second object is transmitted through the projection optical system. In a projection exposure apparatus having an alignment optical system equipped with a photoelectric conversion means for converting a signal into an electric signal,
A projection exposure apparatus comprising an optical means for changing the optical axis of the optical signal in front of the optical signal selection means in the alignment optical system in order to match the deviation of the optical axis of the optical signal with respect to the optical signal selection means. . 2. The projection exposure apparatus according to claim 1, wherein the optical means includes a parallel plane glass that can be tilted freely, and includes means for tilting the parallel plane glass.