JPS635521A - Projection optical apparatus - Google Patents

Abstract

PURPOSE:To simplify the constitution of a photodetector system while improving the precision thereof by a method wherein a reticle is irradiated with a light emitting mark provided on a stage through the intermedialy of an optical projector to focus any transmitting or reflecting light ray from the reticle. CONSTITUTION:An alignment system 20 is composed of a mirror 5, an optical detector 4 including objective lenses and a photodetector 3. The mirror 5 is obliquely provided above a mark 6a to focus the image of mark 6a on the photodetector surface of detector 3. The alignment can be made by means of irradiating a reference mark 8 mounted on a freely movable stage 9 with light ray further to irradiate a reticle 6 formed of the mark 6a with the beans emitted from the reference mark 8 focussing the transmitting or reflecting light ray so that an overlapped point of the reference mark 8 and the reticle mark 6a may be detected to make the alignment. Through these procedures, the constitution of alignment system can be simplified to improve the accuracy in alignment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a position detection device used in an exposure apparatus or the like that projects a reticle image onto a wafer.

[Background of the invention]

Conventionally, as a position detection (referred to as breath alignment) device for the above-mentioned exposure device, a mark formed on the reticle is illuminated from the top of the reticle, a 7-dimensional image thereof is projected by a projection optical system, and a reference mark is placed. An apparatus is known that aligns a reticle by moving a stage so that a reference mark on the stand overlaps the reticle mark. The above marks are usually formed individually around the circuit pattern of the reticle for X, Y, and θ alignment, and when irradiating these marks, the entire surface is irradiated to simultaneously illuminate the three marks. Two irradiation methods are used: irradiation and independent irradiation in which each of the three marks is irradiated independently. In either case, the irradiation light passes through the reticle and projection optical system and is irradiated onto the stage, and the amount of light reflected from the reference mark on the stage is detected again via the projection optical system and reticle, so that both marks overlap. The alignment of the reticle with respect to the device is performed based on changes in the amount of light during the process.

By the way, in the above irradiation, in the case of full-surface irradiation, the projection lens absorbs more light energy, causing magnification and focus fluctuations in the projection lens system, which reduces alignment accuracy.However, in the case of independent irradiation, Since it is necessary to provide three illumination systems, the disadvantage is that the structure of the alignment system becomes complicated.

[Purpose of the invention]

The present invention aims to eliminate the drawbacks of the conventional devices described above and to provide an alignment device with high precision and a simple structure of the light receiving system.

[Summary of the Invention] The present invention provides a reticle with a structure in which a luminescent mark is provided on a stage, the luminescent mark illuminates the reticle through a projection optical system, and light transmitted or reflected from the reticle mark is collected. The technical point is that an alignment device is provided to impede high alignment accuracy.

〔Example〕

FIG. 1 is a block diagram of an alignment device 1 showing an embodiment of the present invention. In FIG. 1, (1) is a control device that centrally controls the entire device. A reticle (6) having a circuit pattern and alignment marks (6a') is held in a reticle holder RH.

The reticle holder RH is moved by a motor M1 driven by a command from a control device (1).

The alignment system I system of the present invention includes a mirror (5), a detection optical system (4) including an objective lens, and a photodetector (3).
). The mirror (5) is installed obliquely above the mark (6a), and the image of the mark (6&) is placed on the detector (3).
) is imaged on the light receiving surface. The photoelectric signal (ff) from the detector (3) is amplified by the amplifier (2a) and then input to the analog-to-digital converter (hereinafter referred to as ADO) (2),
The signal level is converted to a digital value. ADC
The output signal of (2) is used as an alignment signal by the control device (
1) Enter.

Now, the pattern image of the reticle (6) is projected by the projection lens (7).
The image is formed on a predetermined image plane via the . Photoregis) -
The coated wafer side is placed on the stage (9) so that it coincides with the image plane. The stage (9) can be moved two-dimensionally by a motor M driven by a command from the control device (1), and the coordinate position of the stage (9) is measured by an interferometer (101) using a laser beam. The control device (1) also has a function of servo-controlling the motor M2 while reading position information from the interferometer 00).

Now, in this embodiment, a reference mark plate (8) having a slit-like minute transparent part (aperture) is provided on the stage (9). This reference mark plate (8) is illuminated from inside the stage (9) by light from the optical fiber 〇υ reflected by the mirror (5). A light source (2) is arranged at the other end of the fiber 〇〇, and light having the same wavelength as the exposure light is guided through the shutter αB. The shutter α opening is opened and closed by a solenoid fin driven by the control device (1). The light source side may also be used as a light source for exposure, or may be a laser light source having a spectrum of approximately the same wavelength as the exposure light. The light emitted from the optical fiber αD and illuminating the reference mark plate (8) illuminates the slit-shaped transparent portion almost uniformly. Therefore, project
When the reference mark plate (8) is viewed from the side of the lens (7), it becomes a slit-shaped mark that itself emits light. Note that the illumination light of the reference mark plate (8) may have a wavelength corrected for the chromatic aberration of the projection lens (7), and does not necessarily have to match the wavelength of the exposure light.

When the mark on the reference mark plate (8) emits light, the emitted mark image is formed on the lower surface of the reticle (6) through the projection lens (7).
8) is positioned at the projection point of the mark (6a), the luminescent mark image enters the detector (3) via the reticle (6LE mirror (5)) and the detection optical system (4).

Next, the operation will be explained. FIG. 2 is a diagram showing an example of the planar arrangement of marks used for alignment and mark scanning. Figure 2 (,) shows the y-axis marks (8) perpendicular to each other.
Fig. 2(b) shows a light-emitting reference plate (8) consisting of an X-axis mark (8a) and an X-axis mark (8a). The arrangement of the light-shielding cross-shaped marks (6a) and (6b) provided is shown, and FIG. 2(C) shows the mark (6a) on the reticle (6).

It(6a') by the projection lens (7) of (6b),
(6b') is shown when it is scanned by the reference mark plate (8). As shown in FIG. 2(e), the image (61'>(6b') is scanned by the reference mark plate (8) in the order of points P., P□# P Np P 31, and the detector (3) at this time Based on the signals from the interferometer 01 and the reticle 01, two-dimensional alignment of the reticle (6) can be performed.As shown in FIG. Move the reference mark from point P to P8 in the direction of
) of stage (9) so that it overlaps with the Y axis of *(61').
scan. When the marks overlap, that portion is blocked and the amount of light received by the detector (3) decreases. When the stage (9) is moved further, the X-axis mark (8a) of the reference mark is moved to the reticle (k7-ri) as shown in Fig. 3(C).
It overlaps with the X axis of @(fEa') in 6a), and the detector (
3) The amount of light received decreases. Thereafter, the reference mark plate (8) is moved to point P, as shown in FIG. 3(b).

move towards. Figure 4 is a diagram showing changes in the amount of light received by the detector (3) as a function of time t.
At each time of b) and (e), the reference mark (8
b) and the reticle mark (6a) overlap at position Yr, and the reference mark (8&) and mark (6a) overlap at position Xr, indicating that the amount of light is significantly reduced. The sight value of this detector (3) and each movement of the stage (9) in the X-axis and Y-axis directions measured by the interferometer 00)! li! I.J.
1 to the control device (1), the control device (1) uses the previously measured distance between the reference mark (8) and the sea urchin 8 αJ to determine not only the alignment of the reticle (6) with respect to the device itself, but also the alignment of the reticle (6) with respect to the wafer side. Alignment 1- with the reticle (6) can be performed. In addition, in Fig. 4, the button 1-
The left side of the waveform is detected by the interferometer in the Y-axis direction, and the right side is detected by the interferometer in the X-axis direction.

As shown in Fig. 2(b) (C), reticle marks (eaL (6b)) are formed at two locations on the reticle, and reference marks (8) are overlapped with each of these two marks. If we detect the two-dimensional position of the stage scream at the time, we can determine its value, especially the positional interval in the X direction between mark images (6a') and (6b'), and the mark (6a) on the reticle.
.

From the design distance in (6b), the amount of change in projection magnification can be determined. There are also two marks (6a), (
The rotation amount of the reticle (6) can also be detected from the amount of positional deviation in the Y-axis direction of the mark images (6a') and (6b') when the reference mark (8) and the reference mark (6b) are overlapped. can.

Furthermore, in the case of using the above alignment device, the curve showing the change in the scene (see Fig. 4) is a change in the cumulative amount of light, so it is not a Gaussian curve but a rising and falling slope SLP as shown in Fig. 5. is a straight curve with a nearly constant slope. In the case of a Gaussian curve, the position is detected by filtering at a steep slope position, so accuracy deteriorates depending on the shape of the edge of the mark, etc. However, in the case of a curve like the one shown in Figure 5, the cumulative Since the waveform is caused by changes in the scene, even if the waveform becomes noisy, it is possible to prevent extreme deterioration in accuracy by averaging the slopes of each W (multiple points on the slope SLI').

In addition, as in the above embodiment, mark detection is performed by changing the amount of light, so the reference mark (8) is not exactly conjugate with the marks (6&) and (6b) of the optical tickle (6). Similar mark detection is also possible without deteriorating accuracy. This means that the fiducial mark (8
) and the imaging plane of the projection lens (7) (defocus).

Furthermore, in the above embodiment, each mark (8) of the reference mark (8)
&l, (8b) width in alignment 1-direction is mark image (6a'), (6b') of reticle (6)
Although the width is approximately the same as that of the mark image (6a'), it is not necessary to do so.

Reference mark (8a) for the width of (6b'),
The width of (8b) may be made smaller. Also reticle (6)
The upper marks (6a) and (6b) may be cross-shaped transmission patterns formed within the light-shielding portion. Although the above embodiments used the transmitted light of the reticle, the reflected light of the reticle may also be used. FIG. 4 is a block diagram of a device that receives light through a detector (3). In this case, if the mark (6a) is a reflective cross shape, the mark (6a) and the reference mark (8a) ),
(8b) A photoelectric output having a peak waveform can be obtained at the time when the waveform (8b) overlaps with the waveform.

Furthermore, as shown in Fig. 1, in a device equipped with an alignment system that detects the mark on the α country on the sea urchin through the projection lens (7) without using the reticle (6), this alignment The distance (so-called baseline) between the detection center point of the wafer mark and the projection point of the mark (6 angles) can also be measured by running a reference mark (8). In this case, a mark pattern (8a) with a shape that can be detected by the alignment system (2) is placed on the surface of the reference mark plate (8).

It is preferable to provide it in a predetermined positional relationship with (8b).

〔Effect of the invention〕

The present invention provides an exposure apparatus in which a reference mark placed on a movable stage is irradiated with light, and a beam emitted from the reference mark is irradiated onto a reticle on which the mark is formed.
The structure is configured to collect the transmitted light or reflected light, detect the overlapping point between the reference mark and the reticle mark from the change in the light intensity, and perform alignment, thereby achieving excellent effects as described below. I was able to do that.

■The structure of the alignment device is simple.

■Improves alignment accuracy.

■vr rate i conversion and reticle rotary cyan amount can be detected.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an alignment device showing an embodiment of the present invention, Fig. 2 (@) shows a reference mark, (b) shows a reticle mark, and (C) shows a reticle with two marks. 3 is an explanatory diagram of the relative position of the reference mark and reticle mark, FIG. 4 is a diagram showing changes in the amount of light received by the detector, FIG. 5 is a diagram showing changes in the amount of light, and FIG. is a configuration diagram of another embodiment. [Explanation of symbols of main parts] (3) is a detector, (4) is an objective lens, (6) is a reticle, (6a) is a mark, (7) is a projection lens, (8) is a
) is the reference mark, (9) is the stage, α[ is the interferometer, (
13) is a wafer.

Claims (1)

[Claims] An original pattern formed on a mask is formed on a predetermined image plane through a projection optical system, and is held on a stage that moves two-dimensionally in a plane substantially parallel to the image plane. An apparatus for forming a projected image of the original pattern on a substrate, comprising: a light emitting reference member provided on the stage and having a light emitting surface of a predetermined shape; a position measuring means for measuring the position of the stage; the mask and the projection image. an optical system for observing an object located on the predetermined imaging plane via an optical system; when the light emitting surface of the light emitting reference member is moved within the field of view of the optical system, light information incident on the optical system; a photoelectric detector for detecting; and mask position detecting means for detecting the position of the mask with respect to the device based on the detection symbol from the photoelectric detector and the position information from the position measuring means. Characteristic projection optical device.