JPH06347335A - Phase difference measuring apparatus - Google Patents

Abstract

PURPOSE:To measure a phase value of a shifter portion of a phase shift mask directly with an exposure wavelength. CONSTITUTION:Luminous flux from a KrF laser 2 is divided in two on a clad surface 9 so that individual luminous fluxes reflected on a multiple layer film 8 of an induction body are overlapped on the clad surface 9 to produce an interference light, which is admitted onto a Si photo detector 6. A minimum space is so arranged that an optical path length varying element 3 is buried into one synthetic quartz optical path 1 and a phase shift mask 5 into the other synthetic quartz 1. Thus, a phase shift value with a phase shifter is measured accurately from changes in the intensity of light and shade of an interference portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase difference measuring device.

[0002]

2. Description of the Related Art Phase shift masks are considered promising for high integration of memories and the like as one method of super-resolution exposure. Since the amount of phase shift is calculated by the product of the refractive index and the film thickness of the thin film that becomes the shifter, it is necessary to measure both accurately. However, depending on the exposure wavelength, it is not easy to measure the film thickness and refractive index accurately, so it is desirable to directly measure the phase difference. The simplest method for measuring the phase difference is to install the interference optical system such as Mach-Zehnder and insert the sample into the optical path, and then calculate the phase difference from the amount of interference fringe deviation that occurs when the reference sample is inserted. It is a method of conversion. In this method, since the boundary between the bright line and the dark line is not always clear, an error is likely to occur in reading and the accuracy is low. The method of adjusting the optical axis strictly until there is only one fringe and measuring the intensity of dark and light at the interference part is more accurate in principle than the previous method, but it takes time to adjust and most of the exposure The measurement is difficult because it is easily affected by the air turbulence. As a method for facilitating the adjustment and measurement, the beam is split using a double image prism, and the phase difference between both is sequentially changed by an electro-optical element, and the sample to be measured and the reference portion are simultaneously irradiated with the phase difference. After that, the method of observing the interference intensity after multiplexing and matching the polarizations is described in A.
P. 199 by Ghosh
2 years (SPIE, Vol1)
673, 242 to 254). This method can obtain highly accurate measurement results when measuring at wavelengths suitable for optical parts, but it is necessary to use a large number of birefringent crystals such as calcite, and direct measurement with ultraviolet light used for exposure is difficult.

[0003]

As described above, according to the conventional method, it is difficult to directly measure the phase difference of the phase shift mask with high accuracy at the same wavelength as that used for exposure. An object of the present invention is to obtain a phase difference measuring device that solves the problems of the conventional method.

[0004]

In the phase difference measuring device of the present invention, there is a minimum space in which a sample to be measured and a fine optical path length adjusting means can be inserted in a part of an interferometer having two optical paths, and the other optical paths are ultraviolet rays. It is characterized by being filled with a solid having a high transmittance. Also, a first surface that splits the light flux from the light source into two optical paths, a second surface that superimposes the light fluxes of the two optical paths, and a reflection that guides the light flux from the first surface to the second surface. Means and a sample to be measured in one optical path, the other has an optical path length fine adjustment means for exposure, the sample to be measured, all the optical paths except the optical path length fine adjustment means are solids having high ultraviolet transmittance. The sample to be measured and the optical path difference adjusting means may be on the same optical path, or the first surface and the second surface may be on the same surface.

[0005]

In the phase difference measuring apparatus according to the present invention, as the simplest example, the right apex portion of an isosceles right triangular prism is cut off in parallel with the hypotenuse of an isosceles triangle, and a reflection film is deposited on the cut surface. It is composed of two quadrangular prisms that are bonded together by bonding their hypotenuses. This shape is equal to a prism in which the right-angled portion is cut parallel to the bonding surface. If synthetic quartz is used as the material, it is possible to measure with ultraviolet light. If a dielectric multilayer film or the like is vapor-deposited on the adhesive surface of the measurement that reflects light, and if it is adhered with a Canadian balsam that has a refractive index close to that of synthetic quartz and sufficiently transmits ultraviolet light, the reflected light amount and the transmitted light amount are almost equal. It is possible to obtain. The light incident on the adhesive surface at an angle of 45 degrees is divided into two light rays, one reflected by the inclined surface and the other traveling straight, with a substantially equal amount of light.

The split lights are reflected by the reflecting film vapor deposition surface and merge again on the slope, and the respective reflected lights and transmitted lights interfere with each other. The optical path length is controlled by cutting a groove at two points in the optical path of the quadrangular prism, inserting a wedge made of a material having a sufficiently high light transmittance into one of the grooves, and sliding the wedge. Further, the sample whose phase amount is to be measured is inserted into the other groove. The intensity of the interference light periodically changes due to the sliding of the wedge, and becomes maximum when the optical path length difference between both optical paths becomes an even multiple of a half wavelength, and becomes minimum when an odd multiple of a half wavelength. Since the optical path length is continuously variable due to the sliding of the wedge, a periodic pattern of intensity change with the sliding distance as a variable can be individually obtained for the sample. Therefore, the phase difference between different substances can be measured by measuring both the shifts of these patterns in the sliding distance direction with the maximum value or the minimum value as a guide.

In the optical path of this measuring system, the groove portion is only a very small gap between the sample insertion portion and the wedge insertion portion.
There is almost no risk that atmospheric pressure fluctuations, temperature fluctuations, etc. will change the refractive index of air and change the optical path length. A solid having a high transmittance of ultraviolet rays has a small absorption with respect to the wavelength used for exposure.
Therefore, it is possible to use it for a long period of time by minimizing the damage by lowering the strength sufficiently so that the interference strength can be measured.

Although the simplest example has been described, the shape is not necessarily limited to this, and a reflection film is provided in a direction in which interference light can be taken out, and a groove for inserting a sample and a groove for inserting a wedge are cut. Any shape may be used as long as it is.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the apparatus according to the present invention is applied to the phase shift amount measurement of a phase shift mask for KrF exposure will be described in detail below with reference to the drawings.

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

The phase shift mask 5 is inserted into the phase shift mask insertion portion 7 of the synthetic quartz optical path 1, and the emitted light of the KrF laser 2 is made incident on the left side surface of the synthetic quartz optical path 1 from an appropriate position. The light beam is branched into two at the bonding surface 9, one of which is reflected by the dielectric multilayer film 8 and advances to the optical path in which the phase shift mask is inserted, and one to the optical path in which the variable optical path length element 3 is inserted. By sliding the optical path length variable element 3 in the direction of the arrow using the drive circuit 4, the optical path length of the optical path in which the optical path length variable element 3 is inserted continuously changes. The two light rays merge again at the bonding surface 9 and enter the Si photodetector 6. The output of the Si photodetector 6 proportional to the interference intensity is input to the Y terminal of the XY recorder 7. To the X terminal of the XY recorder 7, the voltage output from the drive circuit 4 and proportional to the moving amount of the optical path length variable element 3 is input. 2 for XY recorder 7
An interference intensity pattern having a maximum value when the optical path length difference between two optical paths is an even multiple of a half wavelength and a minimum value when an optical path length difference is an odd multiple of a half wavelength is drawn. FIGS. 2A and 2B are interference intensity patterns obtained when the shifted portion of the phase shift mask 5 and the substrate portion without the shift are measured, respectively. The pattern shift amount corresponds to the phase shift amount, and the phase difference could be measured from this measurement. Since a dielectric multilayer film was deposited on the reflection surface of the bonding surface 9 and adhered with Canadian balsam, the reflected light and the transmitted light were obtained almost equally, and the light-dark contrast of interference was sufficiently high. Since the present invention requires almost no complicated optical axis alignment, measurement preparation can be completed in an extremely short time. Since this device has a short optical path due to air, it is less susceptible to air disturbances,
Highly accurate measurement is possible. In this example, since synthetic quartz having a high transmittance of ultraviolet rays was used, the transmitted light intensity could be measured very easily and no material deterioration was observed.

The device is not necessarily only valid for KrF. An ArF laser can be used as well.

The present invention need not necessarily have the same shape as the device described in FIG. The shape shown in FIG. 3 can also be used for the purpose of the present invention. Further, it is not necessary that the surface for splitting the light and the surface to be overlapped are on the same surface as in FIGS. 1 and 3, and similar effects can be obtained even if they are not on the same surface. Further, the phase shift mask insertion portion and the variable optical path length element do not necessarily have to be in separate optical paths, and may be in the same optical path.

[0014]

As described above, according to the apparatus of the present invention, the phase difference of the phase shift mask at the wavelength used for exposure is
It can be directly measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment to which the present invention is applied.

FIG. 2 is a schematic diagram showing measurement of phase difference.

FIG. 3 is a schematic view showing another embodiment to which the present invention is applied.

[Explanation of symbols]

 1 Synthetic Quartz Optical Path 2 KrF Laser 3 Optical Path Length Variable Element 4 Driving Circuit 5 Phase Shift Mask 6 Si Photodetector 7 Phase Shift Mask Insertion Section 8 Dielectric Multilayer 9 Bonding Surface

Claims (4)

[Claims] 1. An interferometer with two optical paths has a minimum space into which a sample to be measured and an optical path length fine-adjusting means can be inserted, and the other optical paths are filled with a solid having a high ultraviolet transmittance. A phase difference measuring device characterized by. 2. A first surface for splitting a light beam from a light source into two optical paths, a second surface for superposing the light beams of the two optical paths, and a second surface for the light beam from the first surface. To the sample to be measured in one optical path, and the optical path length fine adjustment means in the other optical path, and all the optical paths other than the sample to be measured and the optical path length fine adjustment means have an ultraviolet transmittance of A phase difference measuring device comprising a high solid. 3. The phase difference measuring device according to claim 2, wherein the sample to be measured and the optical path difference adjusting means are on the same optical path. 4. The phase difference measuring device according to claim 2, wherein the first surface and the second surface are on the same surface.