JPH04318550A - Defect inspecting device - Google Patents

Abstract

PURPOSE:To provide a defect inspecting device for a phase shift mask whose phase shift part and transparent part are easily discriminated. CONSTITUTION:A downward lighting system and a transmission lighting system are provided with light sources 11 and 21, aperture stops 12 and 22, wavelenght selection filters 13 and 23, and lens systems respectively. The wavelength of downward illumination light is selected so as to meet conditions under which the phase shift part is seen brightly by interference between reflected light beams from the top surface and reverse surface of a phase shift film and the wavelength of transmitted illumination light is selected so as to satisfy conditions under which the phase shift part is seen darkly. The transmitted light and/or reflected light from the mask passes through an objective lens 2 to form a pattern image on an image pickup element 4. The signal from the image pickup element 4 is compared by a comparing circuit with design data, etc., to discriminate whether or not there is a defect. Further, the pattern image is displayed even on a monitor 10 and a light shield part, the phase shift part, and the transparent part are seen in different colors in the presence of both downward lighting and transmission lighting.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to an apparatus for inspecting defects in a photomask (also called a reticle) used as a projection master in a lithography process for manufacturing semiconductor devices, and in particular, it relates to an apparatus for inspecting defects in a photomask (also called a reticle) used as a projection original in a lithography process for manufacturing semiconductor devices. The present invention relates to a defect inspection apparatus suitable for inspecting a phase shift mask equipped with a phase shift section (also referred to as a phase shift section; hereinafter referred to as a phase shift section) that allows the phase shift section to move.

0002

[Prior Art] A photomask used as a projection master in the lithography process of semiconductor device manufacturing generally has a structure in which a light-shielding pattern made of a metal such as chromium is formed on a glass substrate that is almost transparent to exposure light. It consisted of only a light-shielding part and a transparent part.

[0003] In such photomask defect inspection, a method is adopted in which a projected image of the photomask is detected and a comparison is made to determine whether the brightness distribution of the projected image is a predetermined brightness/darkness distribution. Specifically, the detection signal (photoelectric detection signal) of a photomask projected image is compared with pattern design data stored on a magnetic tape, or the projected images of two photomasks are compared (so-called die -to-die), defect detection is performed.

On the other hand, in recent years, in order to cope with the miniaturization of circuit patterns, various phase shift masks have been developed in which a phase shift film is added to specific parts of a photomask to change the phase of transmitted light, thereby increasing the contrast of the projected image. Proposed. For example, Japanese Patent Publication No. 62-50811 discloses a technique related to a phase shift mask using spatial wavelength modulation.

[0005]

[Problems to be Solved by the Invention] However, conventional defect inspection equipment has the following problems when inspecting a phase shift mask that has a phase shift part in addition to a transparent part and a light shielding part. Ta. This point will be explained with reference to FIGS. 2 and 3.

In FIGS. 2A and 2B, a phase shift film 32 is disposed on a substrate 30 that is substantially transparent to exposure light.
is added to form a phase shift section 101. Note that the film 31 provided on the surface of the substrate 30 is a conductive film provided when exposing using an electron beam, and this conductive film 31 is also transparent to exposure light.

When the phase shift masks shown in FIGS. 2(a) and 2(b) are transmitted through illumination, the light intensity distribution of the transmitted light is as shown in FIG. 2(c).
As shown, a transparent part 100 and a phase shift part 10
1, the light intensity is almost the same, and the light intensity drops at the boundary between the two. That is, even if the dark line along the outline of the phase shift section 101 can be recognized, it is difficult to distinguish between the phase shift section 101 and the transparent section 100.

[0008] Also, in FIGS. 3(a) and 3(b),
On the substrate 30 having a conductive film 31 on its surface, light-shielding films (light-shielding parts) 33 (three light-shielding parts are shown in the figure) are provided at predetermined intervals, and the light-shielding part 33 in the center and the paper surface A phase shift portion 201 is provided between the light shielding portions 33 on the left side so as to span both light shielding portions 33, and a transparent portion 200 without a phase shift film is provided between the light shielding portion 33 on the right side of the paper.

The light intensity distribution when the phase shift masks shown in FIGS. 3(a) and 3(b) are transmitted and illuminated is as shown in FIG. 3(c). That is, the light intensity is zero in the portion corresponding to the light shielding portion 33, and the light intensity is approximately the same in the transparent portion 200 and the phase shift portion 201. In this case, since the outline of the phase shift part 201 is on the light shielding part 33, even the dark line along the outline of the phase shift part 201 as shown in FIG. 2(c) cannot be recognized, and the transparent part 200 and the phase shift part 201 are I can't tell at all.

Therefore, with the conventional defect inspection apparatus, it is impossible to inspect the phase shift mask, including inspection of the shape of the phase shift part, the transparent part of the phase shift part, the relative position with respect to the light shielding part, etc.

[0011] The present invention has been made in view of the above points, and provides a defect inspection device that can easily distinguish between transparent parts and phase shift parts, and can easily and accurately inspect phase shift masks. The purpose is to provide the following.

0012

[Means for Solving the Problems] The defect inspection device of the present invention inspects a photomask having a phase shifter portion that changes the phase of transmitted light. comprising a transmitted illumination means for illuminating the photomask, an epi-illumination means for epi-illuminating the photomask, and an imaging means for receiving transmitted light and/or reflected light from the photomask and detecting an image of the photomask, and , the wavelength range of the transmitted illumination light and the wavelength range of the epi-illumination light can be set separately.

[0013]

[Operation] The operation of the present invention will be explained with reference to FIG. 2(b) mentioned above. Phase shift section 101 of phase shift mask
is composed of a transparent thin film having a specific thickness in order to provide a predetermined phase difference to the exposure light. For example, the condition for the phase shift unit 101 to give a phase difference π to the exposure wavelength λ is λ/2 if the phase difference π is converted into an optical path difference, so |n1 −n0 |・d=λ/ 2...Given by (1). However, the refractive index and thickness of the phase shift film 32 are n1 and d, respectively, and the refractive index of the atmosphere (usually air) where the phase shift mask is placed is n0.

Next, the light reflected on the surface of the phase shift film 32 (the interface between the atmosphere and the phase shift film 32) and the light reflected on the back surface of the phase shift film 32 (the interface between the phase shift film 32 and the conductive film 31) are separated. The wavelength of the illumination light when the phase shift section 101 appears bright and the wavelength of the illumination light when it appears dark due to interference are determined. When the refractive index of the phase shift film 32 is n1 and the refractive index of the conductive film 31 is n3, if the relationship between n1 and n3 is n1 > n3, then if the phase change upon reflection is taken into account (n1 > n3 If so, the phase changes by π upon reflection on the back surface of the phase shift film 32), 2n1 d=(2m+1)λ/2 (bright)...(2
)2n1 d=2m・λ/2 (dark)
...The conditional expression (3) holds true. However, m is an integer.

On the other hand, if n1 < n3, no phase change occurs upon reflection on the back surface of the phase shift film 32.
2n1 d=2m・λ/2 (bright)
...(4)2n1 d=(2m+1)λ/2 (dark)
...(5).

For example, in a phase shift mask for exposure wavelength λ=365 nm, when the phase shift section 101 gives a phase difference of π to transmitted light, the thickness d of the phase shift film 32 is n1 = 1.5. , n0 =1, d=365 nm from equation (1). When epi-illuminating this phase shift mask and detecting reflected light, if n1 > n3, the wavelength of the illumination light that makes the phase shift section 101 appear bright is λ=730 nm, 438 nm according to equation (2).
,... becomes. Conversely, the wavelengths at which the phase shift section 101 appears dark are λ=547.5 nm, 365 nm, . . . .

Therefore, if n1 > n3, for example, if g-line (436 nm) is used as the wavelength for epi-illumination, the g-line will be reflected by the light shielding part 33 and the phase shift part 101 (the reflection intensity will be different from the light shielding part). 33), only a small amount is reflected by the transparent portion 100. Further, if e-line (546 nm) is used as the wavelength for transmitted illumination, the e-line is transmitted through the phase shift section 101 and the transparent section 100, and the e-line is not transmitted through the light shielding section 33.

That is, when observing the above-mentioned phase shift mask under g-line epi-illumination and e-line transmitted illumination, the light-shielding portion 33 is colored only by the g-line (blue), and the transparent portion 100 is mainly colored by the e-line (yellow). green), the phase shift section 101 appears as a mixture of g-line and e-line (blue+yellow-green), making it possible to distinguish the colors of the light shielding section 33, the transparent section 100, and the phase shift section 101. Of course, even with epi-illumination alone, there is a difference in the intensity of reflected light (light shielding part 3
Three types can be distinguished by 3>phase shift section 101>transparent section 100). At this time, by adjusting the intensity of the transmitted illumination light and the epi-illumination light (for example, by weakening the epi-illumination light so that the reflection of the g-line at the transparent part 100 becomes almost zero), the phase shift between the transparent part 100 and the epi-illumination light can be adjusted. The difference in color of the portion 101 becomes clearer.

Note that although the phase shift mask shown in FIGS. 2 and 3 is provided with a conductive film 31 on the substrate 30, this conductive film 31 is not necessarily required. When there is no conductive film 31, the refractive index of the substrate 30 is n2, and n1>
The conditions for n2 are equations (2) and (3), and the conditions for n1 < n2 are equations (4) and (5).
It goes without saying that this will happen.

Next, detection of the defective portion of the phase shift portion will be explained with reference to FIG. 4. In figure (a),
Phase shift section 201 provided between two light shielding sections 33
There is a circular cutout 201a (a transparent portion without a phase shift film) approximately in the center. When such a defective part is observed with transmitted illumination, the intensity distribution of the transmitted light is as shown in Fig. 4(b), and the part corresponding to the outline of the defective part (the boundary between the phase shift part 201 and the defective part 201a) The transmitted light intensity drops at , and the outline of the defective portion 201a is detected.

Further, the reflected light intensity when observed with epi-illumination is shown in FIG. 4(c). That is, the reflected light intensity is
3, the reflected light intensity is lower in the phase shift portion 201 than in the light shielding portion 33, and the reflected light intensity in the defective portion 201a is even lower than that in the phase shift portion 201.

Therefore, even with epi-illumination alone, the phase shift section 2
Although it is possible to identify the missing part 201a of 01,
During actual inspection, first use epi-illumination to distinguish between light-blocking areas, phase-shifted areas, and transparent areas, and then use transmitted illumination to detect defective areas to more accurately inspect defects. can.

The wavelengths of the transmitted illumination light and the epi-illumination light in the present invention are determined by the conditions under which the phase shift portion appears dark (Equation (3) or Equation (5)) and the conditions under which the phase shift portion appears bright (Equation (2)). ) or formula (4) ) need not be strictly satisfied. If the wavelength is selected to satisfy the above-mentioned conditions, the contrast of the image of the phase shift mask will be the highest, which is preferable for inspection. If the wavelength is set such that a wavelength of 100% is produced, and if light of a wavelength other than the epi-illumination light is selected as the transmitted illumination light, it is possible to distinguish the light-shielding part, the phase shift part, and the transparent part by color separation.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a defect inspection apparatus according to an embodiment of the present invention. To make the description concrete, it is assumed that the phase shift mask 1 to be inspected in this example has the structure shown in FIGS. 2 and 3 described above, and is used at an exposure wavelength of 365 nm. Further, n1 (refractive index of phase shift film)>n3 (refractive index of conductive film).

In the figure, a light beam from an epi-illumination light source 21 passes through an aperture diaphragm 22 for varying spatial coherence, and enters a wavelength selection filter 23, where it is filtered at a predetermined wavelength that satisfies equation (2) above. area light (e.g. g-line)
only are selected. The epi-illumination light that has passed through the wavelength selection filter 23 passes through a condenser lens 24 and becomes a parallel beam of light, which is then arranged to correspond to the inspection area of the phase shift mask by a field stop 25 arranged in a conjugate relationship with the pattern forming surface of the mask 1. narrowed down to size. Subsequently, the epi-illumination light reaches the semi-transmissive mirror 27 via the relay lens 26, where it is reflected downward. After the epi-illumination light forms a light source image at the entrance pupil position of the objective lens 2, it is irradiated via the objective lens 2 onto the mask 1 held horizontally. The epi-illumination described above has a Kohler illumination configuration, and uniform epi-illumination is applied to the phase shift mask.

On the other hand, the light beam from the light source 11 for transmitted illumination passes through the aperture diaphragm 12 for variable spatial coherence, and enters the wavelength selection filter 13, where it is filtered as described above (
3) Only light in a predetermined wavelength range (for example, e-ray) that satisfies the formula is selected. The transmitted illumination light that has passed through the wavelength selection filter 13 passes through a condenser lens 14 and becomes a parallel beam of light, which is then arranged to correspond to the inspection area of the phase shift mask by a field stop 15 arranged in a conjugate relationship with the pattern forming surface of the mask 1. narrowed down to size. Subsequently, the transmitted illumination light reaches the reflecting mirror 17 via the relay lens 16, where it is reflected upward. The transmitted illumination light forms a light source image at the entrance pupil position of the lens 18, and then is irradiated onto the mask 1 through the lens 18. The above-described transmitted illumination system has a Koehler illumination configuration similar to the epi-illumination system, and provides uniform transmitted illumination to the phase shift mask.

Next, the reflected light and/or transmitted light from the mask 1 is condensed by the objective lens 2, transmitted through the semi-transparent mirror 27, and transmitted through the relay lens 3 to, for example, color C.
An image of a mask pattern is formed on an image sensor 4 made of a CD or the like.

The photoelectric conversion signal from the image sensor 4 is sent to the monitor 10 and is also sent to the magnetic tape (M
T) 7, a buffer memory 8, a comparator 6, and a determination circuit 9. The comparison/judgment circuit 20 obtains an image of a predetermined area of the mask 1 based on the data of the MT 7 and temporarily stores it in the buffer memory 8 . The comparator 6 compares the contents of the buffer memory 8 with the contents of the image memory 5, and the determination circuit 9 determines whether there is a defect.

Here, the intensity distribution of the pattern image formed on the image sensor 4 is such that, as described above, in the case of epi-illumination only, the intensity of the reflected light is such that the light shielding part 33 > the phase shift part 101
, 201>transparent part 100, 200, and in the case of only transmitted illumination, transparent part 100, 200≧phase shift part 101,
201>shading part 33 (=zero), therefore, only epi-illumination or epi-illumination and transmitted illumination are performed at the same time to distinguish between the three and measure the positions of the phase shift parts 101 and 201. The phase shift unit 101,
It is preferable to detect defective portions in the transparent portions 201 and the transparent portions 100 and 200 (including unnecessary remaining portions of the light shielding film 33). At this time, it is preferable to adjust the numerical aperture of each illumination system using the aperture stops 12 and 22 so that the contrast of the pattern image is maximized.

Furthermore, if an image of the mask pattern obtained by simultaneous epi-illumination and transmitted illumination is displayed on a monitor, the light-shielding portion 3
3. Phase shift section 101, 201 transparent section 100, 200
Each color appears to be different, allowing workers to visually distinguish between the three.

In the embodiment shown in FIG. 1, the light source 21 for epi-illumination and the light source 11 for transmitted illumination are provided separately, but a diroquick mirror (which reflects light in a specific wavelength range, It is also possible to adopt a configuration in which the light beam is split by using a light beam (by transmitting the remaining light), etc., and guided to each illumination system (epi-illumination system, transmitted illumination system) by a light guide fiber.

In addition, although the transmitted light and reflected light from the mask 1 are received by the same image sensor 4 in FIG. 1, a dichroic The light blocking portion 33, the phase shift portions 101 and 201, and the transparent portions 100 and 200 may be determined by inserting a mirror to perform color separation and performing image processing using two or more image sensors.

In addition, the transmitted illumination light and the epi-illumination light are linearly polarized with different vibration directions, and a polarization selection means is arranged in the observation system to separate the polarization of the transmitted light and/or reflected light from the mask. By detecting the intensity, the light shielding section 33, phase shift section 101, 201, transparent section 100
, 200 is possible.

[0034]

As described above, the defect inspection apparatus of the present invention includes a transmitted illumination means and an epi-illumination means whose wavelengths can be set separately, and detects a pattern image by transmitted light and/or reflected light from a mask. Therefore, by setting the wavelengths of epi-illumination light and transmitted illumination light to meet specific conditions,
The light shielding part, phase shift part, and transparent part can be easily distinguished by light intensity discrimination or color discrimination. Therefore, by using the defect inspection apparatus of the present invention, it is possible to easily and accurately inspect a phase shift mask including defects and arrangement positions of phase shift portions, which has been impossible with conventional mask inspection apparatuses.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a defect inspection apparatus according to an embodiment of the present invention.

[Fig. 2] Fig. 2(a) is a partial plan view of the phase shift mask, Fig. 2(b) is a partial sectional view of the phase shift mask corresponding to Fig. 2(a), and Fig. 2(c) is a partial plan view of the phase shift mask. ), (b
) is a light intensity distribution diagram when the phase shift mask shown in FIG.

3(a) is a partial plan view of the phase shift mask, FIG. 3(b) is a partial sectional view of the phase shift mask corresponding to FIG. 3(a), and FIG. 3(c) is a partial plan view of the phase shift mask. ), (b
) is a light intensity distribution diagram when the phase shift mask shown in FIG.

FIG. 4 is a plan view of a defective part of the phase shift mask, FIG. 4(b) is a light intensity distribution diagram when the phase shift mask shown in FIG. 4(a) is illuminated through transmission, and FIG. 4(c) ) is a light intensity distribution diagram when the phase shift mask shown in FIG. 4(a) is epi-illuminated.

[Explanation of symbols]

1 Phase shift mask 2 Objective lens 4 Imaging device 5 Image memory 6 Comparator 7 MT 8 Buffer memory 9 Judgment circuit 10 Monitor 11 Light source for transmitted illumination 21 Light source for epi-illumination 20 Comparison judgment circuit 12, 22 Aperture diaphragm 13, 23 Wavelength selection filter 17 Reflector 27 Semi-transparent mirror 30 Board 31 Conductive film 32 Phase shift film 100,200 Transparent part 101, 201 Phase shift section

Claims (2)

[Claims] 1. A defect inspection apparatus that inspects a photomask having a phase shifter section that changes the phase of transmitted light, comprising a transmitted illumination means for transmitting illumination of the photomask, and an epi-illumination unit for epi-illuminating the photomask. and an imaging means for receiving transmitted light and/or reflected light from the photomask and detecting an image of the photomask, and a wavelength range of the transmitted illumination light and a wavelength range of the epi-illumination light. A defect inspection device characterized in that can be set separately. 2. The defect inspection apparatus according to claim 1, wherein the light intensity of at least one of the transmitted illumination means and the epi-illumination means can be changed.