JPH02174113A - Deviation detection - Google Patents

Abstract

PURPOSE:To execute a stable detection operation for many hours by a method wherein, instead of a galvanomirror, a scanning slit is used for a scanning optical system. CONSTITUTION:A mask 1 and a wafer 2 are arranged by keeping an interval of a prescribed gap S; a linear Fresnel's zone plate(LFZP) 3 whose focal distance is equal to the gap S is installed on the mask 1; a linear diffraction grating 4 is installed on the water 2. A laser beam 5 is magnified by using a lens 6; after that, it is condensed by using a condensing lens 7; the LFZP 3 is irradiated with the laser beam; the laser beam which has been reflected and diffracted by the linear diffraction grating 4 on the wafer 2 and has been passed through the LFZP 3 again is separated from an incident optical axis by using a half- mirror 8; the laser beam is passed through a rotary slit 9 and is detected by using a photosensor 10. In addition, a reference light source 11 and a photosensor 12 for reference use are installed so as to sandwich the rotary slit 9; an output (a) of the photosensor 10 is detected synchronously with an output (b) of the photosensor 12 for reference use by using a synchronous detector 13; a dislocation signal (c) is obtained. Thereby, it is possible to stably detect a derivation with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting positional misalignment, and particularly to a method for detecting misalignment between a mask and a wafer that can be applied to an X-ray exposure apparatus.

[Technological environment]

In recent years, semiconductor devices, as typified by DRAMs, have tended to become highly integrated, and even the minimum size of very large scale integrated circuits (VLSI) is about to enter the micron to submicron range.

Under these circumstances, in conventional optical semiconductor exposure equipment that uses ultraviolet g-line and i-line, the limit of resolution depending on the wavelength of light is said to be 0.5 μm.
There is a strong desire for the emergence of an exposure apparatus that can handle patterns with dimensions smaller than m.

X-ray exposure apparatuses are currently seen as promising as next-generation exposure apparatuses, and research and development are currently underway.

[Conventional technology]

As a conventional technique, for example, Journal of Vacuum Science
of Vaccum 5science Tech
no logy) 16 (6) volume, 1954-1958
Page, November/December, 1979 0ptical
Aliment System for Sub
micron X-ray Lithogra
As reported in phy, there is an alignment method using a linear Fresnel zone plate (LH2P).

Next, a conventional positional deviation detection method will be described in detail with reference to the drawings.

FIG. 4 is a cross-sectional view for explaining an example of a conventional positional deviation detection method.

In the positional deviation detection method shown in FIG. 4, a linear diffraction grating 15 is imprinted on a wafer 14, and a mask 16 is opposed to the wafer 14 with a predetermined gap therebetween.

An LFZP 17 whose focal length is equal to the gap between the mask 6 and the wafer 14 is drawn on the mask 16 .

Parallel laser beam 18 incident from above the mask 16
is condensed by the LFZPl 7 and focused on the surface of the wafer 14 to form a slit-shaped image.

When this imaged slit and the linear diffraction grating 15 on the surface of the wafer 14 are aligned, the laser beam 18 is diffracted, passes through the LFZPl7 again, becomes parallel light, and is detected as an alignment signal.

FIG. 5 is a plan view showing the structure of the LFZP of the mask mark.

LFZP has a structure in which stripes of various widths and intervals are lined up, and the stripes are represented by rll, the distance from the center of the mark. Here, f is the focal length and λ is the wavelength of the laser used for alignment. Although the central stripe of the LFZP shown in the figure is transparent, the opposite configuration is also possible.

FIG. 6 is a plan view showing details of the linear diffraction grating 15.

The linear diffraction grating has a structure in which rectangles of equal size are arranged at equal intervals, and the diffraction angle is determined by the pitch P.

FIG. 7 is a schematic diagram showing an example of the use of the positional deviation detection method shown in FIG. 4.

As shown in Japanese Patent Application Laid-open No. 55-43598, the seventh
The automatic stacking device shown in the figure consists of table 19 and table 1.
a piezoelectric transducer 20 that moves one in the X direction;
The wafer 14 is mounted on a wafer 9 and has a linear diffraction grating 15 engraved thereon, and a mask 16 faces the wafer 14 at a distance of several tens of μm and has an LFZP drawn thereon in advance.

A parallel laser beam emitted from a laser light source 21 is focused by a lens 22, and a galvanometer mirror 2 is driven by a motor 24 excited by a generator 23.
5, passes through the lens 26, and passes through the mask 16.
Irradiate the LFZPl 7 above.

Regarding the lens 26, the irradiation position on the galvanometer mirror 25 and the irradiation position on the mask 16 are conjugate positions. Furthermore, the lens 22 and the lens 26 constitute an afocal optical system.

Therefore, the angle of incidence of the laser beam on the mask 16 can be changed by the galvanometer mirror 25, and the LFZP
The laser beam focused by l 7 scans over the wafer 14 .

The diffracted light from the linear line grating 15 on the wafer 14 is spatially separated from the incident light and detected by the detector 27.

The signal from the detector 27 and the signal from the generator 23 are input to a phase detector 28, and a phase difference signal d is obtained by detecting the phase difference between the two signals.

This phase shift signal d is input to the power source 29 of the piezoelectric transducer 20, and the stage 19 is moved according to the positional shift to overlay the mask 16 and the wafer 14.

[Problem to be solved by the invention]

The above-described conventional positional deviation detection method has a disadvantage in that the reproducibility of positional deviation detection is poor because the positioning reproducibility of the galvanometer mirror is poor.

[Means to solve the problem]

In the positional deviation detection method of the present invention, a mask and a wafer are placed facing each other, a linear Fresnel zone plate is provided on the mask, a linear diffraction grating is provided on the wafer, and a laser beam is applied to the position on the mask. irradiating a linear Fresnel zone plate, detecting diffracted reflected light from the linear diffraction grating on the wafer with a photosensor through a scanning slit, and synchronously detecting the output of the photosensor. .

〔Example〕

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

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

The positional misalignment detection method shown in FIG.
A LFZP 3 with a focal length equal to the gap S is provided on the mask 1, a linear diffraction grating 4 is provided on the wafer 2, and the laser beam 5 is expanded by a lens 6 and then focused. Focus the light with optical lens 7 and LFZP3
The laser beam is reflected and diffracted by the linear diffraction grating 4 on the wafer 2 and passes through the LFZP again.
A reference light source 11 and a reference photosensor 12 are provided across the rotating slit 9, and the output a of the photosensor 10 is detected by a photosensor 10 through a rotating slit 9. The output of the sensor 12 is synchronously detected by a synchronous detector 13 to obtain a positional deviation signal C.

2 is a plan view showing the LFZP 3 and the linear diffraction grating 4 seen from the direction A shown in FIG. 1, and FIG. 3 is a plan view showing the LFZP 3, the linear diffraction grating 4, and the laser beam 5 shown in FIG.
FIG.

Laser beam 5 is focused by condensing lens 7 and becomes LF
When the ZP3 is irradiated, it is irradiated with beams having various incident angles, so the spot focused by the LFZP3 is not a thin line but has a certain width.

This spot width defines the maximum tilt angle of the incident beam as θ. Then, it is expressed as S·θ0. However, S is the gap between the mask 1 and the wafer 2.

If the linear diffraction grating 4 is located within this spot of width S·θ0, the laser beam 5 will be reflected and diffracted.

If θ is the angle between the optical axis of the irradiated laser beam 5 and the reflected diffracted light when projected onto a plane perpendicular to the LFZP 3, the angle θ changes depending on the position of the linear diffraction grating 4.

The amount of relative positional deviation between LFZP3 and linear diffraction grating 4 is Δ
When expressed as X, the angle θ is expressed as θ=Δx/S.

Therefore, by detecting the position where the reflected diffraction light from the linear diffraction grating 4 is again focused by the condenser lens 7, the relative positional shift between the mask 1 and the wafer 2 can be detected.

The spot position of the reflected diffracted light focused by the condenser lens 7 can be detected with high precision by providing a scanning slit on the imaging plane and synchronously detecting the intensity of the light passing through the slit.

In this example, in order to increase the stability of the slit movement,
A reference signal is obtained by using a disk-shaped rotating slit 9 and separately providing a reference light source 11 and a reference sensor 12. As long as the positions of the reference light source 11 and the reference sensor 12 are fixed, uneven rotation of the rotating slit 9 will not affect the positional deviation accuracy, and stable and highly accurate positional deviation detection is possible.

In this embodiment, a rotating slit is used as the scanning slit, but a vibrating slit using a solenoid may also be used. At this time, the reference signal can be a signal obtained from a reference light source and a reference sensor as in the case of the rotating slit, but a signal obtained by measuring the displacement of the vibrating slit with a linear sensor can be used. You can also do that.

〔Effect of the invention〕

The positional deviation detection method of the present invention uses a scanning slit with high positional accuracy instead of a galvanometer mirror in the scanning optical system, so stable detection can be performed over a long period of time. This has the effect that positional deviations can be detected.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing one embodiment of the present invention, and Fig. 2 is a schematic diagram showing an embodiment of the present invention.
LFZP3 and linear diffraction grating 4 viewed from direction A shown in the figure
Figure 3 is a plan view showing the LF shown in Figure 1.
A sectional view showing details of the ZP 3, the linear diffraction grating 4, and the laser beam 5, FIG. 4 is a sectional view illustrating an example of a conventional positional deviation detection method, and FIG. 5 is a LFZP of a mask mark. 6 is a plan view showing the details of the linear diffraction grating, and FIG. 7 is a schematic diagram showing an example of the use of the positional deviation detection method shown in FIG. 4. 1.16...Mask, 2,14...Wafer, 3.17...LFZP, 4,15...
... Linear diffraction grating, 5, 18 ... Laser beam, 6 ... Lens, 7 ... Condensing lens, 8 ... Half mirror 9 ...Rotating slit, 10...Photo sensor, 13,28...
... Phase detector, 19 ... Stage, 21
...Laser light source, 23...Generator, 25...Galvanometer.

Claims (1)

[Claims] A mask and a wafer are placed facing each other, a linear Fresnel zone plate is provided on the mask, a linear diffraction grating is provided on the wafer, and a laser beam is irradiated to the linear Fresnel zone plate on the mask, A positional deviation detection method comprising: detecting diffracted reflected light from the linear diffraction grating on the wafer with a photosensor through a scanning slit, and synchronously detecting the output of the photosensor.