JPH03154804A - Method for detecting position deviation between mask and wafer - Google Patents

Abstract

PURPOSE:To detect the position deviation between the mask and wafer with high accuracy by providing a linear Fresnel zone plate which has an opening part in the center on the mask, and irradiating the linear diffraction grating on the wafer with a laser beam through the opening part. CONSTITUTION:The mask 1 and wafer 2 are installed at the interval of a specific gap S and the linear Fresnel zone plate(LFZP) 4 which has focal length equal to the gap S and also has the opening part 3 in the center is provided on the mask 1. The linear diffraction grating 5 on the wafer 2 is irradiated with the laser light 6 through the opening part 3, the laser beam 6 which is reflected and diffracted by the linear diffraction grating 5 is collimated by the LFZP 4 to form an image through a leans 8, and the position of the image is measured through a rotary slit 9 formed in the image formation surface of the lens 8. The laser beam 6 passes through the LFZP 4 only once when projected, a decrease in the intensity of the reflected and diffracted light is small, and a signal with a high SN ratio is obtained, so that the position deviation can be detected with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for detecting misalignment between a mask and a wafer, and in particular to a method for detecting misalignment between a mask and a wafer.
The present invention relates to a method for detecting misalignment between a mask and a wafer that can be applied to a line exposure apparatus.

[Technological environment]

In recent years, semiconductors, as typified by DRAM, are becoming highly integrated, and the minimum line width of a VLSI pattern is about to move from microns to submicrons.

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 about 0.5 μm.
There is a strong desire for next-generation exposure equipment that can handle patterns of 5 μm or less. X-ray exposure devices are currently seen as promising as this next-generation exposure device, and research and development are currently underway.

[Conventional technology]

As a conventional technique, for example, B.

Fay et al. in the Journal of Vacuum Science
C u u lll5science Technology
ogy) Vol, 16(6)pp, 1954-195
8° Nov/Dec, 1979, “Optical Alignment System for Submicron X-ray Lithography”
Ent Syst e Tafor Submi
There is an alignment method that utilizes a linear Fresnel zone plate (LFZP), as reported in Cron X-ray Lithography.

Here, the principle will be explained with reference to the drawings.

FIG. 5 is a sectional view showing an alignment method using LFZP.

A linear diffraction grating 16 is engraved on the wafer 15, and a matrix 1 is placed on the wafer 15 at a predetermined gap.
7 is facing. On the mask 17, an LFZP 18 whose focal point distance is equal to the gap between the mask and the wafer is drawn.

FIG. 6 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 expressed as r=n+n, where r is 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.0 Although the stripe at the center of the LFZP shown in the figure is transparent, the opposite configuration is also possible.

Further, FIG. 7 is a plan view showing a linear diffraction grating of a wafer mark. The linear diffraction grating has a structure in which rectangles of equal size are lined up at equal intervals, and the diffraction angle is determined by the pitch P of the diffraction grating.

In FIG. 5, a parallel laser beam 19 incident from above the mask 17 is condensed by the LFZP 18 and focused on the surface of the wafer 15 to form a slit-shaped image.

This imaged slit and the linear diffraction grating 16 on the wafer surface
When the two overlap in a straight line, the laser beam is diffracted and L
The parallel light passes through the FZP 18 and is detected as an alignment signal.

FIG. 8 is a perspective view showing an automatic overlaying apparatus using the conventional LFZP alignment method disclosed in Japanese Patent Application Laid-Open No. 55-43598.

The automatic stacking apparatus shown in FIG. 8 includes a table 20, a piezoelectric transducer 21 that moves the table in the X direction, a wafer 15 mounted on the table and on which a linear diffraction grating 16 is engraved in advance, and the The mask 17 is placed opposite to the wafer 15 with an interval of several tens of μm and has an LFZP 18 drawn in advance.

The device further includes a laser light source 22, said laser light source 2
The parallel laser beam emitted from the first lens 23
The light is focused by a galvanometer mirror 26 driven by a motor 25 excited by a generator 24, passes through a second lens 27, and irradiates the LFZP 18 on the mask 17. Regarding the second lens 27, the irradiation position on the galvanometer mirror 26 and the irradiation position on the mask 17 are conjugate positions.

Furthermore, the first lens 23 and the second lens 27 constitute an afocal optical system.

Therefore, the angle of incidence of the laser beam on the mask 17 can be changed by the galvanometer mirror 26, and the beam focused by the LFZP 18 scans over the wafer 15, as shown in FIG.

The diffracted light from the linear diffraction grating 16 on the wafer 15 is spatially separated from the incident light and detected by the detector 28.

The signal from the detector 28 and the signal from the generator 24 are input to a lock-in amplifier 29, and a phase difference signal d is obtained by detecting the phase difference between the two signals.

This positional deviation signal d is input to the power source 30 of the piezoelectric transducer, and the table is moved according to the positional deviation, and the mask 17 is
Then, the wafers 15 are stacked.

[Problem to be solved by the invention]

The conventional mask and wafer misalignment detection method described above is
Since the laser beam passes through the LFZP twice, once when it enters and once when it exits, there was a drawback that the intensity of the reflected and diffracted light was low (the S/N ratio was poor).

Furthermore, the intensity of the reflected diffracted light decreases significantly with respect to the gap deviation between the mask and the wafer, and there is a drawback that the gap must be set with high precision before detecting the positional deviation.

[Means to solve the problem]

A method for detecting misalignment between a mask and a wafer according to the present invention includes: installing a mask and a wafer facing each other, and providing a linear Fresnel zone plate having an opening in the center on the mask;
A linear diffraction grating is provided on the wafer, and a laser beam is irradiated onto the linear diffraction grating on the wafer through the opening of the linear Fresnel zone plate. - The method includes imaging a laser beam collimated by a Fresnel zone plate with a lens, and measuring the position of the image formed by the lens.

〔Example〕

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

FIG. 1 is a block diagram showing one embodiment of the present invention.

The method for detecting misalignment between a mask and a wafer shown in FIG. A linear diffraction grating 5 is provided on the wafer 2, and the laser beam 6 is transmitted through a beam expander 7.
The beam diameter is expanded by the beam expander 7, the laser beam 6 is focused by the lens 8, and the laser beam 6 focused by the lens 8 is irradiated onto the linear diffraction grating 5 through the aperture 3. The laser beam 6 reflected and diffracted by the linear diffraction grating 5 is collimated by the LFZP4,
The laser beam 6 collimated by the LFZP 4 is passed through the lens 8 again to form an image, a rotating slit 9 is arranged on the imaging plane of the lens 8, and the laser beam 6 that has passed through the rotating slit 9 is focused by the receiver lens 10. , the photosensor 11 is arranged at the focal point of the receiver lens 10, the reference light source 12 and the reference photosensor 13 are provided across the rotation slit 9, and the output a of the reference photosensor 13 is used as a reference signal to output the photosensor 11. The output signal C is phase-detected by the lock-in amplifier 14 to obtain a positional deviation signal C.

In this embodiment, a half mirror 15 separates the incident laser beam from the reflected and diffracted laser beam.

2(a) is a plan view of the LFZP4 shown in FIG. 1, and FIG. 2(b) is a sectional view showing the action of the LFZP4 shown in FIG. 1.

The edge of each slit of LFZP4 shown in FIG. 2(a) is defined by rII=n, where the distance from the center is rl
+n λ 4 (n=1.2, 3...), r2sm-1
The portion where <r<rzm (m=1.2...) is opaque. Here, f is the focal length and λ is the wavelength of the laser beam 6.

From the above formula, focal length f = 40 μm, wavelength λ = 632
．． 8nm (He-Ne laser), Fig. 2(a)
The width of the central opening of LFZP4 shown in is 2 r 1=
It becomes 10.08 μm.

Therefore, the laser beam 6 irradiated onto the linear diffraction grating 5 on the wafer 2 must be focused to a beam diameter of about 10 μm.

Figure 3(a) shows the LFZP shown in Figures 2(a) and (b).
L F Z P with the opaque part closest to the center of 4 deleted
4b is a plan view of LFZP 4b, and FIG. 3(b) is a sectional view showing the action of the LFZP 4b shown in FIG. 3(a).

The width of the central opening of L F Z P 4 b is 2rs=
It becomes 17°53 μm, and when using LFZP4, there is no need to focus the laser beam 6 narrowly. Furthermore, the alignment accuracy of the mask 1 with respect to the laser beam 6 may be moderate.

The laser beam 6 scattered at the edge of the linear diffraction grating 5 is collimated by an LFZP 4 having a focal length equal to the gap S between the mask 1 and the wafer 2, and is further imaged by a lens 8.

That is, an enlarged image of the linear diffraction grating 5 on the wafer 2 is projected onto the focal plane of the lens 8.

FIG. 4 is a schematic diagram showing a projection optical system composed of the LFZP 4 on the mask 1 and the lens 8.

The focal length of LFZP4 is fl + the focal length of lens 8 is f
2, the magnification rate of this projection optical system is f 2 / f
It is represented by s.

For example, the focal length of LFZP4 is 40 μm.

If the focal length of lens 8 is 80 m, the magnification is 20
The magnification is 00 times, and minute positional deviations of the linear diffraction grating 5 can be easily observed.

In this embodiment, the lens 8 has the function of focusing the laser beam 6 collimated by the LFZP 4 and at the same time condensing the laser beam 6 to be irradiated onto the linear diffraction grating 5. The distance to the lens 8 is arranged so that the distance to the lens 8 is equal to the focal length of the lens 8.

However, it is also possible to use separate lenses for condensing the laser beam irradiated onto the linear diffraction grating 5 and for forming an image of the laser beam collimated by the LFZP 4.

In this embodiment, the principle of position detection is applied to detect the position of the enlarged and projected linear diffraction grating 5 image. The laser beam 6 passing through the rotating slit 9 is collected by a receiver lens 10,
It is detected by the photosensor 11.

When the output of the photosensor 11 is position-detected by the lock-in amplifier 14 using the output a of the reference photosensor 13 as a reference signal, the phase of the output of the photosensor 11 changes according to the positional shift of the image of the linear diffraction grating 5. However, the lock-in amplifier 14 outputs a positional deviation signal C.

Therefore, highly accurate positional deviation detection is possible regardless of the intensity of the reflected diffracted light by the linear diffraction grating 5.

In addition to the scanning slit method shown in this example,
It is also possible to detect the linear diffraction grating 5 image using a linear image sensor or a one-dimensional COD device.

The beam expander 7 expands the diameter of the laser beam 6,
This is for effectively condensing light using the lens 8.

The larger the expansion ratio of the beam expander 7, the more the mask 1
Since the beam diameter on the plane becomes smaller, the expansion ratio of the beam expander 7 is determined from the size of the aperture 3 of the LFZP 4.

〔Effect of the invention〕

In the method for detecting misalignment between a mask and a wafer according to the present invention, the laser beam is irradiated onto the linear diffraction grating through the opening of the LFZP, so the laser beam passes through the LFZP only during output, and the intensity of the reflected diffracted light due to the LFZP is reduced. Since a signal with little deterioration and a high S/N ratio can be obtained, there is an effect that highly accurate positional deviation detection can be performed.

Furthermore, since there is little change in the intensity of the reflected diffracted light with respect to variations in the gap between the mask and the wafer, there is no need to set the gap with high accuracy, which has the effect of reducing the cost of the apparatus.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
a) is a plan view of the LFZP shown in FIG. 1, FIG. 2(b) is a sectional view showing the action of the LFZP shown in FIG. 2(a), and FIG.
Figure (a) is Figure 2 (a). (b) is a plan view of the LFZP with the central part of the LFZP removed, FIG. 3(b) is a cross-sectional view showing the action of the LFZP shown in FIG. 3(a), and FIG. 4 is a plan view of the LFZP shown in FIG. Fig. 5 is a cross-sectional view showing the principle of the conventional positional deviation detection method, Fig. 6 is a plan view showing the structure of the LFZP, and Fig. 7 is a plan view showing the structure of the linear diffraction grating. 8 are perspective views showing an automatic overlaying apparatus using a conventional positional deviation detection method. 1.17...Mask, 2,15...Wafer, 3...
・Aperture, 4, 18... LFZP, 5, 16... Linear diffraction grating, 6.19... Laser beam, 7... Beam expander, 8... Lens, 9... Rotating pick-up/socket, 10... Receiver lens, 11... Photo sensor, 14°29... Lock-in amplifier.

Claims (3)

[Claims] (1) A mask and a wafer are placed facing each other, a linear Fresnel zone plate with an opening in the center is provided on the mask, a linear diffraction grating is provided on the wafer, and a laser beam is directed to the linear Fresnel zone plate. Laser light that is irradiated onto the linear diffraction grating on the wafer through the opening of the zone plate, reflected and diffracted by the linear diffraction grating, and collimated by the linear Fresnel zone plate is imaged by a lens. A method for detecting misalignment between a mask and a wafer, the method comprising: measuring the position of an image formed by the lens. (2) The method for detecting misalignment between a mask and a wafer according to claim (1), wherein the position of the image formed by the lens is measured using a linear image sensor. (3) The method for detecting a positional deviation between a mask and a wafer according to claim (1), wherein the laser beam imaged by a lens is detected by a photosensor through a scanning slit, and the output of the photosensor is synchronously detected.