JP3004076B2 - Sample surface position measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample surface position measuring device for optically measuring the position of a sample surface, and particularly to measuring the height position of a sample surface such as a wafer or a mask in a semiconductor manufacturing apparatus or an inspection apparatus. The present invention relates to a sample surface position measuring device suitable for performing the measurement.

[0002]

2. Description of the Related Art In a device having a projection imaging optical system such as an LSI inspection device, for example, a mask / reticle defect inspection device, when a pattern on a sample surface such as a mask substrate is projected and imaged, the sample is warped and other factors. Changes the position of the sample surface (distance to the optical system). For this reason, the imaging characteristic is deteriorated beyond the depth of focus of the projection optical system, and so-called out-of-focus occurs. Therefore, conventionally, a method of measuring the amount of change in the position of the sample surface and correcting the amount in accordance with the amount of change has been adopted.

FIG. 6 shows a conventional sample surface position measuring device.
(Japanese Patent Application Laid-Open No. 56-2632). In this device, the laser light source L
And focusing the light emitted by the lens L ₁ on the spot irradiated onto the sample surface from and forms on the detector D of the reflected light by the lens L _2. Then, the height position of the sample surface is measured by calculating the detection output of the detector D. E in FIG. 6 is an electron optical column,
P _{1 to} P ₄ indicate reflection mirrors.

However, this type of measuring apparatus has the following problems. That is, in order to increase the resolution of the projection optical system with the recent miniaturization of LSI patterns,
As shown in FIG. 7, there is a strong tendency to increase the NA (numerical aperture) of the objective lens 50. Further, in order to prevent dust from adhering on the sample surface, especially on the mask surface, there is an increasing demand for the inspection of a sample in which a transparent pellicle film 52 is mounted on the surface of the mask 51. For this reason, the margin of the space between the projection optical system and the sample surface is reduced, and it is difficult to configure a conventional measuring device.

[0005]

As described above, conventionally, the NA of the projection optical system is increased, and the margin of space between the projection optical system and the sample surface is reduced in the inspection of the sample surface with the pellicle film. This makes it difficult to configure a conventional measuring device.

The present invention has been made in consideration of the above circumstances, and has as its object to reduce the height position of the sample surface even when the space margin between the projection optical system and the sample surface is reduced. An object of the present invention is to provide a sample surface position measuring device capable of measuring.

[0007]

The gist of the present invention is to irradiate a measuring light onto a surface of a sample to be measured through an objective lens of a projection optical system and detect reflected light to measure a height position of the sample surface. Is to do.

That is, according to the present invention, there is provided a sample surface position measuring apparatus for irradiating light to a measured sample surface and detecting reflected light thereof to measure the height position of the sample surface. A projection optical system that has an optical axis and is used for projection imaging using a first light of a predetermined wavelength, and a second light having a different wavelength from the first light on the sample surface through an objective lens of the projection optical system. Is irradiated as focused light , and the second light is irradiated to the objective lens.
Through only a part of the sample surface that is offset from the center of the
A measuring light irradiating unit for causing the light to enter from an oblique direction and a wavelength selecting element (for example,
A dichroic mirror that transmits the first light and reflects the second light) and a photoelectric detector that detects the position of the reflected light that is reflected on the sample surface by the irradiation of the second light and obtained through the wavelength selection element. (For example, a semiconductor position detector) and means for measuring the height position of the sample surface based on the detection output of the photoelectric detector. Preferred embodiments of the present invention include the following. (1) The wavelength of the first light and the wavelength of the second light are 40 nm or more
Remote, the objective lens couples to both the first and second light.
Aberration correction. (2) The light source of the measurement light irradiating unit is a semiconductor laser.
When. (3) The oscillation mode of the semiconductor laser is single mode.
That.

[0009]

According to the present invention, since the second light for measurement passes through the objective lens, the second light does not matter regardless of the magnitude of the NA of the optical lens and the magnitude of the space between the sample surface and the objective lens.
Can be irradiated on the sample surface, and the reflected light can be guided to the photoelectric detector. Therefore, no matter how large the NA of the objective lens of the projection optical system or the sample surface with the pellicle film, the height position can be measured. Further, since the coaxial optical system is employed, the focus shift between the objective lens and the detection optical system which occurs in the conventional method (FIG. 6) does not occur.

Further, if the objective lens is also corrected for the aberration of the second light for measurement, the image forming characteristic on the sample surface is good, and
Highly accurate position measurement is possible. In addition, a second
40 nm from the wavelength of the first light of the projection imaging system
With the above separation, the dichroic mirror etc.
It is possible to easily separate the two lights.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a sample surface position measuring apparatus according to one embodiment of the present invention. The apparatus of this embodiment is provided in an inspection apparatus for inspecting a pattern of a mask reticle, and measures a position of a sample surface.

In FIG. 1, reference numeral 1 denotes a mask or reticle which is an object to be inspected (a sample to be measured), 2 denotes an objective lens of an inspection optical system (projection optical system), 3 denotes a dichroic mirror, and 4 denotes measurement light (second light). Semiconductor laser (light irradiating part for measurement)
5 is a condenser lens, 6 is an aperture, 7 is a relay lens, 8 is a reflection mirror, 9 is a relay lens, 10 is a photoelectric detector, 11
Is an adder, 12 is a subtractor, 13 is a divider, 14 is a position measuring circuit, 15 is light for inspection (first light), and 16 is a relay lens of an inspection optical system.

The semiconductor laser 4 has, for example, an oscillation wavelength of 67.
It emits visible light of about 0 nm. As this semiconductor laser 4, one having a structure using InGaAIP as shown in FIG. 2 is commercially available, and an output of 5 mW or more can be obtained. In particular, in the case of the refractive index guided type, as shown in FIG. 3, extremely good monochromaticity is obtained by single mode oscillation. The photoelectric detector 10 is, for example, a semiconductor position detector (P) using a known lateral light effect.
SD).

The light used for inspection is 400 to 600 nm.
Of the wavelength of As this light source, for example, a g-line, an e-line, an α-line of a mercury lamp can be considered as a light source having a high intensity. The dichroic mirror 3 has a characteristic of transmitting the inspection use light (λ = 400 to 600 nm) and reflecting the semiconductor laser light (λ = 670 nm). Here, when the laser beam is separated from the inspection light by 40 nm or more as described later, a dichroic mirror can be easily realized by depositing a multilayer film.

The objective lens 2 of the inspection optical system is usually designed to correct the aberration only for the wavelength of the light used for inspection, but here, the aberration is also corrected for the wavelength of the semiconductor laser light. In particular, in the present embodiment, the measurement light uses only a part of the objective lens 2 instead of the full aperture.
This aberration is an advantageous optical system.

In this embodiment, the laser beam emitted from the semiconductor laser 4 forms a point image near the stop 6 by the condenser lens 5 once. Thereafter, the light is reflected by the dichroic mirror 3 through the relay lens 7, enters the objective lens 2, and forms a spot image on the surface of the sample 1 via the objective lens 2. The light reflected on the sample surface passes through the objective lens 2 again, is reflected by the dichroic mirror 3, passes through the reflection mirror 8 and the relay lens 9, and forms a spot image on the PSD 10 again.

The above is a case where the spot image at the position of the sample surface is under the optimum imaging condition. If the position of the sample surface is shifted by Δz as shown in FIG. The position of the light also shifts. The PSD 10 is a device in which a resistive thin film is formed on a semiconductor substrate and output terminals are provided at both ends of the thin film, and the semiconductor substrate is grounded. An unbalanced signal is output from a pair of output terminals due to displacement of a light spot irradiation position of the resistive thin film. Is output. Therefore, if this output signal is processed by a signal processing circuit including an adder 11, a subtractor 12, a divider 13, and the like, and further processed by a position measuring circuit 14, the position of the sample surface can be determined from the above-mentioned optimum imaging condition. You can find out how far it is off. P
When the relationship between the positional deviation amounts Δx and Δz on the SD 10 is obtained, Δx = 2 · β · sin θ ₀ · Δz ‥‥‥ (1) Here, θ ₀ is the incident angle, and β is the optical magnification (determined by the objective lens and the relay lens). For example, θ ₀ = 3
Assuming 0 ° and β = 60 times, Δx = 60 · Δz

If Δz = 1 μm on the sample surface, PS
Δx = 60 μm on D. This proportionality constant 2 · β · s
inθ ₀ can be freely changed by changing the θ ₀ and β.

The signal processing in the signal processing circuit includes the output signal (subtraction value) of the subtractor 12 and the adder 1
By inputting the output signal of 1 (addition value) to the divider 13 and dividing the subtraction value by the addition value, a normalized signal can be obtained.

The point to be noted in the above embodiment is that the objective lens 2 is first corrected for aberrations with respect to the light for measurement. A spot image can be formed. In the present embodiment, a monochromatic semiconductor laser is further used as a light source for measurement, and since the optical system passes through only a part of the objective lens 2, the optical system is advantageous in terms of aberration. This is very important because the smaller the image on the sample surface, the smaller the measurement error due to the effect of the pattern on the sample surface.

In the dichroic mirror 3, since the inspection light and the measurement light (semiconductor laser light) can be easily separated, they do not influence each other. This is due to the effect of separating the wavelengths of the two lights by 40 nm or more. Although there is a dichroic mirror that separates light having a wavelength difference of about 20 nm, FIG. 5 shows an example of its spectral transmission characteristics (see FIG. 5), considering conditions used in the device, such as ease of optical design and aging of the multilayer film. Even if designed with a separation width of 20 nm as shown in FIG. As a result of our intensive studies, we found that this wavelength difference was 4
It has been found that the condition of 0 nm or more is the best for practical use. In other words, the condition is that the separation of light by the dichroic mirror 3 can be performed stably, and the aberration correction of the objective lens 2 is also convenient.

When the image is deviated from the optimum image forming condition shown in FIG.
In SD10, since the position of the center of gravity of the light is obtained, there is no problem in obtaining the position of the light, and the above expression (1) is satisfied.

As described above, according to the present embodiment, the dichroic mirror 3 is arranged in a part of the inspection optical system to separate the light for inspection and the light for measurement. Irradiation onto the sample surface through the objective lens 2 of the optical system and formation of a spot image on the sample surface with high accuracy are possible. Further, light reflected from the sample surface can be guided onto the PSD 10 via the dichroic mirror 3. Therefore, the position of the sample surface can be measured with high accuracy regardless of the size of the NA of the objective lens 2 and the size of the space between the sample surface and the objective lens 2.

Therefore, since the NA of the objective lens 2 can be increased, high resolution can be expected, and the position of the sample surface can be measured even when a protective film for preventing the adhesion of dust on the sample surface is provided. There is. Further, in the present embodiment, a semiconductor laser of visible light is used as a light source for measurement, so that optical adjustment is easy, and high-speed modulation is easier than other laser light, so that the measurement system can be speeded up. There are additional effects such as.

The present invention is not limited to the embodiment described above. In the embodiment, the inspection apparatus is targeted, but may be applied to an exposure apparatus or a microscope. The object to be inspected is not limited to a mask or a reticle, but may be a wafer. Although a PSD is used as the photoelectric detector, a separate optical position detector or other optical position detecting means may be used. The wavelength of the light used for inspection is 400 to 600 nm, but it is a matter of course that the wavelength may be smaller than that. Further, as long as the first light and the second light can be separated, not only the dichroic mirror but also another wavelength selection element can be used. In addition, various modifications can be made without departing from the scope of the present invention.

[0027]

As described above in detail, according to the present invention, the light for measurement is irradiated on the surface of the sample to be measured through the objective lens of the projection optical system, the reflected light is detected, and the height position of the sample surface is detected. Is measured, regardless of the size of the NA of the optical lens,
Further, even if the space margin between the projection optical system and the sample surface is reduced, it is possible to realize a sample surface position measuring device capable of measuring the height position of the sample surface.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a sample surface position measuring apparatus according to one embodiment of the present invention;

FIG. 2 is a sectional view showing an element structure of a semiconductor laser used in the apparatus of FIG. 1;

FIG. 3 is a characteristic diagram showing an example of an output spectrum of the semiconductor laser of FIG. 2;

FIG. 4 is a schematic diagram showing a positional shift of reflected light when a sample surface position is shifted;

FIG. 5 is a characteristic diagram showing a relationship between wavelength and transmittance in a dichroic mirror;

FIG. 6 is a schematic configuration diagram showing a conventional sample surface position measuring device;

FIG. 7 is a schematic diagram for explaining a problem of the conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inspection object (sample to be measured), 2 ... Objective lens, 3 ... Dichroic mirror (wavelength selection element), 4 ... Semiconductor laser (measurement light irradiation part), 8 ... Reflection mirror, 10 ... PSD (photoelectric converter) ), 11: adder, 12: subtractor, 13: divider, 14: position measuring circuit.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshikazu Yoshino 75-1, Hasunumacho, Itabashi-ku, Tokyo Within Topcon Corporation (72) Inventor Takuji Sato 75-1, Hasunumacho, Itabashi-ku, Tokyo Within Topcon Corporation (56) reference Patent flat 1-239407 (JP, a) JP flat 1-123102 (JP, a) JP flat 3-31714 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ G01B 11/00-11/30

Claims (2)

(57) [Claims] A projection optical system having an optical axis in a direction perpendicular to the surface of a sample to be measured and used for projection imaging using first light of a predetermined wavelength, and an objective lens of the projection optical system And irradiates the sample surface with second light having a wavelength different from the first light as convergent light through the center of the objective lens.
Oblique to the sample surface
A measurement light irradiating unit that is incident from a direction, a wavelength selection element that is disposed on a side opposite to the sample surface with respect to the objective lens of the projection optical system, and that separates first light and second light; A photodetector that detects the position of reflected light reflected on the sample surface by the light irradiation and obtained through the wavelength selection element, and a height position of the sample surface based on a detection output of the photoelectric detector. A sample surface position measuring device, comprising: 2. A projection optical system having an optical axis in a direction perpendicular to the surface of a sample to be measured and used for projection imaging using first light having a predetermined wavelength, and an objective lens of the projection optical system. And irradiates the sample surface with second light having a wavelength different from the first light as convergent light through the center of the objective lens.
Oblique to the sample surface
A measuring light irradiating unit that is incident from a direction, a dichroic mirror that is arranged on the side opposite to the sample surface with respect to the objective lens of the projection optical system, and that transmits the first light and reflects the second light; And a photoelectric detector for detecting the position of the reflected light reflected by the sample surface and reflected by the dichroic mirror due to the irradiation of light, and measuring the height position of the sample surface based on the detection output of the photoelectric detector. Means for measuring a sample surface position.