JPH0629687B2 - Reduction projection exposure system - Google Patents

Description

The present invention relates to a reduction projection exposure apparatus used for manufacturing semiconductor devices and the like, and more particularly to a positioning mark detecting mechanism.

[Conventional technology]

Positioning of a wafer in a conventional reduction projection exposure apparatus has been performed as follows. That is, while moving the semiconductor wafer, the semiconductor wafer is irradiated with laser light, and the reflected light is received by the photodetector. When this photodetector is installed at a position where the first-order diffracted light from the diffraction grating of the positioning mark formed on the semiconductor wafer should be formed, and the intensity of the light received by the photodetector becomes maximum. Then, the position is determined by recognizing this as the position of the wafer positioning mark.

[Problems to be solved by the invention]

In the above-described conventional wafer positioning method, when the output signal intensity of the photodetector installed at a specific position is higher than the set threshold value, the mechanism is recognized as a positioning mark. There is a drawback in that even when strong scattered light from an internal pattern having a high surface is received, the internal pattern is erroneously recognized as a positioning mark.

It is an object of the present invention to provide a reduction projection exposure apparatus having a function of discriminating between diffracted light from a positioning mark and scattered light from an internal pattern outside the inspection target.

[Differences from the Prior Art of the Invention]

In contrast to the conventional wafer positioning method described above, according to the present invention, a plurality of photodetectors are arranged and positioning is performed only after confirming that the distribution of the signal intensity at each position has a predetermined relationship. The difference is that it is recognized as a mark.

[Means for solving problems]

In order to achieve the above-mentioned object, a reduction projection exposure apparatus according to the present invention is a reduction projection exposure apparatus having an optical system, a wafer positioning mark, and a pair of photodetectors, wherein the optical system is a laser light source. The semiconductor wafer is irradiated with the light flux of, and the wafer positioning mark is provided on the semiconductor wafer and reflects the diffracted light by the irradiation of the laser light. The light intensity of the peak value and the bottom value of the nth-order diffracted light is detected.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is an optical path diagram showing an optical system of laser light of a reduction projection exposure apparatus of the present invention. In the figure, the laser light emitted from the laser light source 1 passes through the half mirror 6, passes through the objective lens 2, and is irradiated onto the semiconductor wafer 3. The laser light emitted onto the wafer 3 is reflected, scattered, or diffracted by the pattern on the wafer, and a part of the light passes through the objective lens 2 again, the optical path is changed by the half mirror 6, and a photodetector is installed. Form an image at position 7.

Diffraction grating-shaped wafer positioning marks 4 shown in FIG. 2 are formed on the wafer 3. l is a luminous flux of laser irradiation light. Move the semiconductor wafer 3 on a plane,
When the light beam 1 of the laser irradiation light is applied to the wafer positioning mark 4, the laser light is diffracted in a specific direction by the diffraction grating of the wafer positioning mark 4, and the diffracted light is incident on the photodetector installation position 7 as shown in FIG. As shown, it forms an image at a specific position as light having a specific intensity distribution. The pattern of the distribution is stored and displayed on the display unit 5.

In FIG. 3, the peaks of the light intensity of a, b, c (a ', b', c ') are the 0th order and the 1st order due to the wafer positioning mark 4, respectively.
It is the second and second order diffracted light. In FIG. 1, two photodetectors 8 and 9 are installed at the photodetector installation position 7. In relation to FIG. 3, for example, the photodetectors 8 and 9 are fixed at the peak position b and the bottom position d of the first-order diffracted light shown in FIG. The detection output of 9 is displayed on the display 5, and the light intensity received by the photodetector 8 is equal to or higher than a certain set value, and the light intensity received by the photodetector 9 is the light received by the photodetector 8. Only when the intensity is weaker than the intensity, it is determined that the diffracted light is diffracted by the wafer positioning mark, the wafer 3 is moved in that state, and when the light intensity received by the photodetector 8 becomes the strongest, the wafer positioning mark position Recognize that

On the other hand, strong scattered light from the internal pattern having a highly reflective surface on the wafer is imaged as light having a light intensity distribution as shown in FIG. 4 at the photodetector installation position. In this case, even if the light intensity received by the photodetector 8 shows a value equal to or larger than the set value, the light intensity received by the photodetector 9 becomes stronger than the light intensity received by the photodetector 8. The internal pattern that is not the inspection target is not erroneously recognized as a wafer positioning mark.

Second Embodiment Next, a second embodiment of the present invention will be described. 4 in this example
The two photodetectors 8, 9, 10, 11 are installed at the photodetector installation position 7 in FIG. In this embodiment, with respect to the diffracted light by the wafer positioning mark 4 shown in FIG. 3, the photodetectors 8 and 10 are respectively located at the peak positions b and b'of the first-order diffracted light on both sides of the 0th-order diffracted light. The photodetectors 9 and 11 are fixed at the positions of the bottom positions d and d '. In this embodiment, the light intensities received by the photodetectors 8 and 10 simultaneously show a value equal to or higher than a certain set level, and the light intensities received by the photodetectors 9 and 11 coincide with those of the photodetectors 8 and 10. Only when it is weaker than either of the light intensities, the diffracted light is judged to be the diffracted light by the wafer positioning mark, and the wafer 3 is moved even in that state, and the average value of the light intensity received by the photodetectors 8 and 10 is the strongest When it becomes, it is recognized that it is at the wafer positioning mark position.

In the second embodiment, as compared with the first embodiment, since the wafer positioning mark position is recognized by the peak position and the bottom position of the first-order diffracted light on both sides, the probability of misrecognition is further reduced.

〔The invention's effect〕

As described above, according to the present invention, a plurality of photodetectors that receive the reflected light from the semiconductor wafer at a plurality of positions,
By detecting the wafer positioning mark that determines that the distribution of signal intensity at each position has a predetermined relationship, irregular scattered light due to the pattern on the wafer is erroneously recognized as a wafer positioning mark. It has an effect that can be eliminated.

[Brief description of drawings]

FIG. 1 is an optical path diagram of a laser beam of a reduction projection exposure apparatus of the present invention, FIG. 2 is a diagram showing a positioning mark shape on a wafer, FIG. 3 is a diagram showing diffracted light from a wafer positioning mark, and FIG. FIG. 6 is a diagram showing scattered light from an internal pattern on a wafer. 1 ... Laser light source, 2 ... Objective lens 3 ... Semiconductor wafer, 4 ... Wafer positioning mark 5 ... Indicator, 6 ... Half mirror 7 ... Photodetector installation position, 8, 9, 10, 11 ... Photodetector

Claims (1)

[Claims] 1. A reduction projection exposure apparatus having an optical system, a wafer positioning mark, and a pair of photodetectors, wherein the optical system irradiates a light beam from a laser light source onto a semiconductor wafer. The wafer positioning mark is provided on the semiconductor wafer and reflects the diffracted light by the irradiation of the laser beam. The photodetector set is the n-th order diffracted light peak value and the bottom value light from the wafer positioning mark. A reduced projection exposure apparatus characterized by detecting intensity.