JPH05129396A - Foreign matter tester - Google Patents

Abstract

PURPOSE:To make it possible to discriminate a foreign matter effectively from a fine circuit pattern irrespective of the layout position of a light receiving device. CONSTITUTION:Light from a light source 6 enters a board 1 equipped with a fine circuit pattern at a specified incident angle and aperture angle by way of a lens 5, a mirror 4 and an f-theta lens 3. An incident luminous flux I and the board 1 are designed to move in the directions of X and Y in a relative manner, and the whole surface of the board 1 can be illuminated with the incident luminous flux I. The light receiving device 2 has a light receiving surfaces 2A and 2B respectively which share a longitudinal direction and a shorter direction. The distance between the light receiving surfaces 2A and 2B is determined in such a fashion that the distance between orthogonal projections C1 and C2 may be virtually identical to the orthogonal projection width i1 of the incident luminous flux I. A discrete diffraction light is generated from the incident point O. When a foreign matter exists, continuous scattered light is generated. A logical product of each photo-electric signal transmitted from the two planes is determined by a control system 8, which makes it possible to discriminate the foreign matter from the circuit pattern from the result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection device,
In particular, the present invention relates to a foreign matter inspection apparatus suitable for detecting foreign matter attached to a substrate such as a reticle or a photomask on which a circuit pattern used in a semiconductor manufacturing apparatus is formed.

[0002]

2. Description of the Related Art Generally, in an IC manufacturing process, an exposure circuit pattern formed on a substrate such as a reticle or a photomask is transferred onto a wafer surface coated with a resist by a semiconductor printing apparatus (stepper or aligner). Is being done. At this time, if foreign matter such as dust is present on the substrate surface, the foreign matter is transferred together with the circuit pattern, and the IC
This causes a decrease in manufacturing yield.

Therefore, it is indispensable to detect the presence of foreign matter on the substrate in the IC manufacturing process, and various inspection methods have been proposed conventionally. FIG. 18 is a perspective view showing an example of a conventional foreign matter inspection device. In the figure,
The beam emitted from the laser 161 is a beam expander.
After being magnified in parallel by 162 or the like, it is incident on the surface of the substrate 165 via the scanning mirror 163 and the scanning lens 164. The scanning mirror 163 is configured to be rotatable or vibrable, and the scanning mirror 163 scans the light flux incident on the surface of the substrate 165 on the substrate 165. Then, a plurality of light receiving means are provided at positions apart from the optical paths of the regular reflection light and the regular transmission light from the substrate.
166, 167, 168 are provided, and these plurality of light receiving means 166, 1
The presence of foreign matter on the substrate 165 is detected based on the output signals from 67 and 168. The presence of foreign matter is detected by, for example, taking the logical product of the output signals from the light receiving means 166 1, 167, 168. That is, since the diffracted light from the circuit pattern has a strong directivity, the output values of the photodetectors are different from each other, but the scattered light from the foreign matter has almost no directivity, and therefore the output signals of the photodetectors are equal. Therefore, it is possible to discriminate between the foreign matter and the circuit pattern by taking the logical product of the output values of the photodetectors each having an appropriate threshold or more.

Next, referring to FIGS. 16 and 17, the range H
It is considered that the above light is received by the light receiver and the foreign matter and the pattern are discriminated. 16 and 17 show examples in which light receivers each having an optical axis forming an angle of 90 degrees or more with respect to the direction of the specularly reflected light flux are arranged, the vertical axis represents the intensity of diffracted light, and the horizontal axis represents the diffraction. It is assumed that the distribution position of light on the orthographic diagram on the substrate is represented. 16 and 17, O ₁ represents the position of specularly reflected light, I ₀ represents the intensity of specularly reflected light, and v ₀ represents the interval of diffracted light. FIG. 16 shows the case of a pattern having a low degree of fineness, and the intensity of diffracted light from the pattern is smaller than the intensity of scattered light from foreign matter shown by the dotted line. In FIG. 16, the intensity: D of the scattered light of the foreign matter is represented by the range H.
Consider receiving light at. The intensity of the foreign substance scattered light is shown by a dotted line. In this case, the light amount Sd incident on the light receiver is expressed by the following equation.

Sd = N × H (1) Therefore, by setting a threshold value below the received light amount Sd,
Foreign matter can be detected. On the other hand, when the diffracted light is generated, the light amount of the pattern diffracted light received is equal to the sum of the integrated value of the diffracted light 16-1 and the integrated value of 16-2 indicated by the diagonal lines in the figure. Become. In the case shown in FIG. 16, the light amount of the pattern diffracted light is smaller than the foreign substance scattered light amount Sd, and therefore it is possible to discriminate by the threshold value.

However, as the pattern fineness increases,
As shown in FIG. 17, the intensity distribution of the diffracted light becomes isotropic.
When the light receiver is arranged as in the case of FIG. 16, the light amount of the pattern diffracted light is the integrated value of the shaded portion 17-1 in FIG. 17, and the light amount of the diffracted light exceeds the light amount Sd of the foreign substance scattered light. Discrimination becomes impossible. As mentioned above,
Along with the miniaturization of IC circuit patterns, the circuit patterns on the substrate such as a reticle or a photomask are also miniaturized, the spatial discreteness of diffracted light distribution is increased, and the intensity distribution of diffracted light that appears discretely is isotropic. It has become a target. For this reason, it has become difficult to distinguish scattered light from foreign matter and diffracted light from a circuit pattern.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to inspect foreign matters on a substrate having a fine circuit pattern with a high separation detection rate. An object is to provide an inspection device.

[0008]

A light source (6) for irradiating an inspected object having a circuit pattern formed on its surface with a coherent light beam, and a light beam emitted from the light source on the inspected object (1) at a predetermined opening. A light collecting means (3) for collecting light at an inspection point (O) at an angle (γ), and a moving means (4) for relatively moving the incident light beam condensed at a predetermined opening angle and the inspection object. A detection means (2) for receiving a scattered light flux generated when the condensed light flux is incident on the inspection object, and detects a foreign matter on the inspection object based on an output signal from the detection means. In the foreign matter inspection apparatus, the detection means is provided with at least two light receiving surfaces (2A, 2B) having a longitudinal direction and a lateral direction, and the two light receiving surfaces have an arbitrary radius centered on the inspection point and having the substrate as an equatorial plane. In the orthographic projection diagram of the curved section by the virtual sphere (S) onto the substrate Particle inspection apparatus characterized by spacing orthogonal projection with respect to the light plane is provided so as to be substantially equal to the orthogonal projection of the width of the light beam incident on the substrate.

[0009]

According to the present invention, the orthographic projection of the curved cross section of the phantom sphere having an arbitrary radius centered on the condensing point of the incident light beam and having the substrate as the equatorial plane and the orthographic projection of the curved cross section of the diffracted light are substantially equal. Focusing on that, the light receiving surface is configured to have a longitudinal direction and a lateral direction, and the interval in the lateral direction of the orthogonal projection of the light beam incident on the light receiving surface on the substrate of the curved cross section by the sphere is set to the above-mentioned incidence. Since the distance between the light flux and the orthogonal projection of the light flux on the substrate is made substantially equal, the circuit pattern and the foreign matter can be discriminated with high resolution and high SN ratio.

[0010]

1 is a perspective view showing the structure of a first embodiment of the present invention. The light beam emitted from the laser light source 6 in FIG. 1 is passed through the beam expander 5 and the substrate 1 via the f-θ lens 3 which constitutes a part of the moving means for relatively moving the substrate 1 (reticle, wafer, etc.). Focus on. The condensed incident light flux I is optically scanned on the substrate 1 by the vibrating mirror 4 along the X direction. The f-θ lens 4 is a lens system having a large focal length, and the incident direction of the incident light flux I on the substrate 1 is substantially the same as the Y direction. The substrate 1 is placed on a stage (not shown) that can move in the Y direction, and the vibration mirror 4 and the stage enable the entire surface of the substrate 1 to be inspected. A fine circuit pattern is provided on the substrate 1, and when the incident light flux I is irradiated, discrete diffracted light is generated from the circuit pattern. The light receiver 2 is
It has light-receiving surfaces 2A and 2B for outputting respective independent photoelectric signals, and each light-receiving surface has a longitudinal direction and a lateral direction.

Now, let us consider a sphere S having an arbitrary radius which is schematically drawn with the incident point O of the incident light beam I as the center. Light receiving surface 2
The curved cross section on the sphere S by A, 2B (hatched portion) becomes the curved cross section 2A1, 2B1 (hatched portion) in the figure, and the curved cross section 2A
Orthogonal projections C ₁ and C ₂ of ₁ and 2B1 onto the substrate inspection surface (XY plane) on the substrate 1 have longitudinal directions parallel to the X direction, respectively, and the space between the orthogonal projections C ₁ and C _{2 in} the lateral direction. Mv are separated by v ₀ . Here, v ₀ is the curved section i due to the incident light beam I
Is the length in the V direction of the orthogonal projection diagram i ₁ of the curved section 2A1,
2B1 is a region where the diffracted light penetrates the sphere S, assuming that the light receiving surfaces 2A and 2B receive the diffracted light. Similarly, the curved cross section i refers to a region where the incident light flux I penetrates the sphere S.

The lengths of the light receiving surfaces 2A and 2B in the lateral direction are set so that the lengths D ₁ and D ₂ of the orthogonal projections C ₁ and C _{2 in} the Y direction are v ₁ and v ₂ , respectively. .. Light receiving surface 2A,
It is preferable that the width of 2B in the lateral direction is shorter in consideration of the ability to discriminate the pattern from the foreign matter. As a result, the decreasing areas of the light receiving surfaces 2A and 2B can be compensated by lengthening the longitudinal direction, the amount of received light can be compensated, and the electrical SN ratio can be prevented from lowering. It should be noted that in FIG.
Although it is provided on the −θ lens 3 side, it is not limited to this. The light receiving surfaces 2A and 2B are provided on a sphere S ₁ having an arbitrary radius, and the distance between the light receiving surfaces 2A and 2B is
Details of the shape, the arrangement direction, and the like will be described later.

Each of the photoelectric signals output from the light receiver 2 is input to the control unit 8. Now, the signal processing system will be described with reference to FIG. The photoelectric signals from the light receiving surfaces 2A and 2B are input to the amplifiers 101 and 102, respectively. Then, the amplified signals e1 and e2 are input to the comparators 105 and 106, respectively. The slice voltage Vs from the slice level generator 111 is applied to the other input of the comparator. The comparators 105 and 106 compare the voltage values of the signals e1 and e2 with the slice voltage Vs.
When the voltage values of the signals e1 and e2 are larger than the slice voltage Vs, the signals e3 and e4 are output to the AND circuit 109, respectively. When the voltage values of the signals e1 and e2 are smaller than the slice voltage Vs, the signals are not output from the comparators 105 and 106 to the AND circuit 109. By adjusting the slice voltage Vs by the slice level generator 111, the size of the foreign matter to be detected can be set.
By ANDing the signals e3 and e4 with the AND circuit 109, the circuit pattern and the foreign matter can be discriminated. By arranging the light receiving surfaces 2A and 2B under a predetermined condition (details will be described later), the light receiving surfaces 2A and 2B do not simultaneously receive the spatially discrete diffracted light from the circuit pattern, and the calculation result becomes 0. On the other hand, spatially continuous scattered light from a foreign substance is simultaneously input to each light receiving surface, and the calculation result is 1. As described above, the circuit pattern and the foreign matter can be easily discriminated. The above circuits are provided in the control unit 8 which controls the apparatus as a whole.

The circuit pattern of a memory IC such as a DRAM, which is formed on the substrate 1 by patterning with a relatively high degree of fineness, includes many two-dimensional periodic patterns. X with a cycle in the direction
Alternatively, most of the patterns have a line symmetrical period in the Y direction. Here, it is assumed that the X direction and the Y direction of the substrate coincide with the X direction and the Y direction in FIG. 1, and are simply referred to as “X direction and Y direction” below. In this embodiment, the fine two-dimensional periodic pattern provided on the substrate 1 is an element isolation pattern, a capacitor, a contact hole or the like.

The diffracted light generated by this two-dimensional periodic pattern will be described below. FIG. 3 is a diagram schematically showing a part of FIG. 1 in order to show a state of diffracted light generated from a two-dimensional periodic pattern. In FIG. 3, the incident light flux I is a conical light flux having a predetermined aperture angle (angle determined by the numerical aperture of the f-θ lens 3) γ centered on the point O, and is a sphere S.
I am accustomed to a part of the curved surface. This common portion is shown as a curved section i in the figure. Further, the orthogonal projection of the curved cross section i on the XY plane is shown as the orthogonal projection i ₁ . Similarly, for the regular reflection light flux Ir, the penetrating portion of the sphere S is shown as a curved cross section r, and the orthogonal projection of the curved cross section r on the XY plane is shown as the orthogonal projection r ₁ . Since the point O coincides with the focus point of the incident light flux I, the orthographic projection r ₁ has a congruent shape with the orthographic projection i ₁ .

The shapes of the orthographic projection i ₁ and the orthographic projection r ₁ are determined by the aperture angle γ and the incident angle θ of the incident light beam I. Now, the radius of the sphere S is 1 / λ (λ = wavelength of the incident light beam I),
The length v ₀ in the V direction and the length u ₀ in the U direction of the orthographic projection i ₁ (or the orthographic projection r ₁ ) are expressed by equations (2) and (3). v ₀ = 2 / λ · sinγ · cos θ (2) u ₀ = 2 / λ · sinγ (3) Here, since the irradiation area of the incident beam I is smaller than the circuit pattern, a plurality of circuit patterns do not enter the irradiation area. In this case, the generation of diffracted light was simple, and a conventional foreign matter inspection apparatus as shown in FIG. 18 could be used. However, if the pattern is miniaturized and a plurality of circuit patterns exist in the irradiation region Is as shown in FIG. 4, diffracted light is generated discretely and has a macroscopically isotropic diffracted light distribution.
Therefore, as described above, it is difficult to distinguish the foreign matter from the circuit pattern. FIG. 4 shows a two-dimensional pattern arranged at a pitch 2P in both X and Y directions. In this embodiment, since the incident light flux I is incident on the circuit pattern at the incident angle θ, the irradiation area Is has an elliptical shape. Therefore, even if the diffracted light is from the patterns arranged at the same pitch in the X and Y directions, the shape of the orthogonal projection has the lateral direction in the Y direction, and the interval between the diffracted lights in the Y direction is widened.

Next, focusing on the periodicity of the fine two-dimensional periodic pattern, the distribution state of the diffracted light will be described. First, FIG.
Consider the distribution state of diffracted light from a fine two-dimensional periodic pattern along the X and Y orthogonal coordinates as shown in (a). Figure 5
In the DRAM, the two-dimensional periodic pattern as shown in FIG.
It is often used for capacitors and contact holes. FIG. 5B is a diagram showing the orthogonal projection of the curved cross section in which the diffracted light from the circuit pattern penetrates the sphere S in the same drawing procedure as the orthogonal projection r ₁ (i ₁ ) of FIG. The pitch is Px,
The pitch in the Y direction is Py. In FIG. 5B, the coordinate axis U,
V is a new coordinate axis with the center of the orthographic projection r ₁ of the regular reflection light Ir as the origin O ₁ , and the XY coordinate indicates the real plane and the unit is the length, whereas the UV coordinate is the direction of the diffracted light. It is a Fourier plane for displaying the cosine, and its unit is the spatial frequency. Diffracted light from a fine circuit pattern is spatially generated with a discrete degree, and the orthogonal projection of the diffracted light is also discrete as shown in FIG. 5B. Further, the orthogonal projection of each of the discrete diffracted lights has a shape congruent with the orthogonal projection r ₁ of the specular reflection light. Further, the pitch of the orthogonal projection of the diffracted light is inversely proportional to the pattern rule, and the pitch in the U direction is 1 / Px and the pitch in the V direction is 1 / Py.

FIG. 3 shows one of the orthographic projections of these diffracted lights.
An orthographic projection E₁And its curved section E are shown. Where the orthographic projection
E₁O at the intersection of the X-axis and a straight line passing through the center of
₂, And the intersection O₂A straight line parallel to the Z axis including₁Indicated by
And the intersection O with the center of the curved section E ₂A straight line including and₂Indicated by
You Straight line n₁And straight line n₂Angle formed by and (parallel to V direction
Let β be the spatial angle formed by the curve F on the sphere S. Well
Also, as shown in FIG. 9, the V direction with the incident point O of the curved cross section E as the center
Let the spatial angle with respect to the direction be 2ε.

FIG. 6A shows a periodic pattern arranged at the pitch Pb in the a-axis and b-axis directions. a axis and b
The axis has a line-symmetrical relationship with the X-axis and the Y-axis, and each is inclined by θ _{1 with} respect to the X-axis. Figure 6 (a)
The pattern shown in (1) is often used as an element isolation body in DRAM. FIG. 6B shows the orthogonal projection of the diffracted light from the circuit pattern of FIG. 6A, and the relationship with FIG. 6A is the relationship between FIG. 5A and FIG. It is the same. Figure 6
The periodic direction a ₁ in (b) is the periodic direction a in FIG. 6 (a).
6A, the periodic direction b ₁ of the orthogonal projection of the diffracted light in FIG. 6A is orthogonal to the periodic direction b in FIG. 6B. The pitch in the periodic direction a ₁ or b ₁ of the orthogonal projection of the diffracted light is 1 / Pb, which is inversely proportional to the pattern pitch Pb.

FIG. 7A shows c which is symmetrical with respect to the X axis and the Y axis.
It is a figure which shows the example which the general pattern which has a periodic direction in an axis and a d-axis is arranged by the pitch Pd in each periodic direction. The c-axis and the d-axis are each inclined by θ _{2 with} respect to the X-axis. Since the coordinates on the V-axis where the diffracted light is distributed do not depend on the shape of each pattern, only the existing positions are indicated by circles. FIG. 7B shows the orthogonal projection of the diffracted light from the circuit pattern of FIG. 7A, and the relationship with FIG.
The relationship between (a) and FIG. 5 (b) is the same. Figure 7 (b)
The orthographic projection of the diffracted light of is distributed on the c _a axis and the d ₁ axis. Figure 6
As in the case of, c-axis and c _a-axis, and the d-axis and the d ₁ axes are orthogonal and a pitch 1 / Pd orthogonal projection of the period direction of the diffraction light is inversely proportional to the pitch Pd of the pattern.

Next, the discrimination between the circuit pattern and the foreign matter according to this embodiment will be described. FIG. 8 is a diagram showing the principle of discrimination by the discreteness when there are two light receiving surfaces, the vertical axis shows the intensity of diffracted light and the intensity of light scattered from foreign matter, and the horizontal axis is on the V axis. Shows the position of the orthographic projection of. here,
Assuming a two-dimensional periodic pattern as shown in FIGS. 5A, 6A, and 7A, FIG. 5B and FIG.
Of the diffracted light distributions shown in (b) and FIG. 7 (b), consider the intensity distribution of the diffracted light in a line in which the orthogonal projection is parallel to the V axis. As described above, the diffracted light from the fine pattern is distributed discretely. Further, as described above, the orthographic projection of each diffracted light and the orthographic projection r ₁ of the regular reflection light beam Ir are almost congruent with each other, and the orthographic projection r ₁ of the regular reflection light beam Ir and the incident light beam I shown in FIG. The shape is almost congruent with the projection i ₁ . Therefore, the orthographic projection i ₁
And the orthographic projection of each diffracted light have almost the same shape. Paying attention to the discreteness and the shape of the orthogonal projection of each diffracted light, the description will be made with reference to FIG. Orthogonal projection C of the two light receiving surfaces 2A and 2B of the light receiver 2
The distance Mv between ₁ and C ₂ is set to be not less than the width v ₀ of the orthogonal projection i of the incident light beam I in the V direction. [2]. Diffracted light sum of orthogonal projection C ₁ between the width D ₁ of the V direction and the width D ₂ of the positive projection C ₂ in the V direction the light-receiving surface 2B and two orthogonal projection interval Mv of the light receiving surface 2A are adjacent in the V direction It should be less than the interval.

The light receiver 2 is arranged so as to satisfy the two conditions. By arranging the light receivers in this way, the spatially discrete diffracted light from the fine circuit pattern does not enter all of the two light-receiving surfaces 2A and 2B, while the light from the foreign matter is spatially separated. The continuous scattered light enters both of the two light receiving surfaces 2A and 2B. Therefore, as described above, the foreign matter and the circuit pattern can be discriminated by taking the logical product of the signals from the respective light receiving surfaces. This is called "discrimination by discreteness" below. The resolution Res at this time is obtained by the equation (4). Res = D ₁ + Mv + D ₂ (4). In FIG. 8, the distribution of the orthogonal projection of FIG.
6B shows the distribution of the orthogonal projections, and FIG. 7B shows the distribution of the orthogonal projections of FIG. 7B. Therefore, δ ₀ is 1 / Py, δ ₁
Is 1 / Pb · sin θ ₁ and δ ₃ is 1 / Pd · sin θ ₂
Becomes In each of the cases, the width of the orthogonal projection of each diffracted light is v ₀ , and Mv = v ₀ . And ~
In each case, the sizes of the light-receiving surfaces 2A and 2B (sizes of D ₁ and D ₂ ) are determined so that δ ≧ D ₁ + v ₀ + D ₂ . From equation (4), (D ₁ , D ₂ ) and Mv
It can be seen that the smaller the
It is advantageous in terms of resolution to make ₀ substantially equal.

In the case where the same photodetector 2 discriminates by discreteness in all cases of (D), (D ₁ + v ₀ +
The sizes of the light receiving surfaces 2A and 2B may be determined so that D ₂ ) is equal to or smaller than the smallest value of δ ₀ , δ ₁ and δ ₂ .
Similarly in the U direction, Mv ≧ u ₀ and the light receivers may be arranged so as to satisfy the above conditions [1] and [2].

Next, the relationship between the orthographic projection and the actual position of the light receiving system will be described with reference to FIGS. FIG. 9 shows Q in FIG.
The top view seen from the direction is shown. Assuming that the width of the curved section in the tangential direction on the sphere S in FIG. 9 is W, W is expressed by the following equation. W = v ₀ / cos β (5) Further, considering ε in FIG. 3, 2 / λ sin ε = W, sin ε = λ · W / 2 (6), and equations (2), (5), and (6) are obtained. the _{sinε = λ · v 0/2} · cosβ = sinγ · cosθ / cosβ (7) from.

Therefore, if the incident angle θ, the aperture angle γ, and β corresponding to the desired position of the light receiver are determined in advance, the distance between the light receiving surfaces on the curved cross section can be obtained from the equation (7), and the orthogonal projection diagram is obtained. The intervals and widths of the light receiving surfaces may be determined so as to satisfy the above conditions [1] and [2]. Here, the reason for determining the intervals and widths of the light receiving surfaces on the curved cross section using the conditions on the orthogonal projection diagram will be described. Curved section i (curved section r) of FIG.
The shape of the curved cross section is almost constant in the vicinity, and when the light receiver is arranged here, the distance between the light receiving surfaces can be obtained from the opening angle γ. However, the curved cross-section shape is slightly different from the curved cross-section i except near the curved cross-section i (other than near the curved cross-section r), and the gap or width of the light-receiving surface cannot be accurately determined only by the opening angle γ, and thus it is accurate. It is necessary to perform actual measurement, etc., in order to obtain the interval and width. On the other hand, as described above, even if the light receiver is arranged at an arbitrary position by obtaining the distance and width of the light receiving surface from the conditions of [1], [2] and (7),
The light receiving surface can be arranged according to the curved cross-sectional shape of the diffracted light. This also applies to the U direction.

In FIG. 10, the light receiving surface of the light receiver 2 is divided into three parts.
It is a figure showing the principle of discrimination by the discreteness when the resolution is increased.
The vertical axis indicates the intensity of diffracted light and the intensity of light scattered from foreign matter.
And the horizontal axis shows the position of the orthographic projection on the V axis.
It Here, in FIG. 5 (a), FIG. 6 (a), and FIG. 7 (a)
When the fineness of the two-dimensional periodic pattern as shown
In the diffracted light distribution, the orthogonal projection is in the direction parallel to the V axis.
Consider the intensity distribution of a line of diffracted light. ~ Is each ~
Orthogonality when the fineness of the circuit pattern becomes low
Assuming the distribution of shadows, ~ of each orthographic projection
Interval δ₃, Δ_Four, Δ_FiveIs the interval of each orthographic projection
It is getting smaller. In the present embodiment, [3]. The three light-receiving surfaces 2A, 2B, 2C of the light receiver 2 are positive.
Projection C₁And C₂And C₃Of the orthographic projection C₁And C₃With
The interval v is the width v of the orthographic projection i of the incident light flux I in the V direction. ₀that's all
And [4]. Orthogonal projection C of the light receiving surfaces 2A, 2B, 2C₁, C₂,
C₃The width in the V direction of D₀And the orthographic projection C₁And C₂,
And orthographic projection C₂And C₃And Mv₁And adjacent
The sum of the widths of the two orthographic projections₀Two orthos adjacent to
Shadow interval Mv₁Is between the diffracted lights that are adjacent in the V direction.
It should be less than a threshold.

The photodetector 2 is arranged so as to satisfy the two conditions. Furthermore, when discriminating by discreteness using n light-receiving surfaces, [5]. The interval M of the orthographic projections at both ends is set to v ₀ or more, the sum of the widths of two adjacent orthographic projections, and the width Mv between the two orthographic projections.
_The arrangement is such that the sum of ₁ and the distance is less than or equal to the distance between adjacent diffracted lights in the V direction.

By arranging the photodetectors so as to satisfy the condition (3), it is possible to improve the resolution and discriminate by the discreteness. When discriminating by the discreteness is performed by such n light-receiving surfaces, the resolution Res when the width of the orthogonal projection of the light-receiving surface is set to D ₀ and Mv and v ₀ are approximately equal is obtained by the equation (8). .. Res ≧ 2D ₀ + [v ₀ − (n−2) D ₀ ] / (n−1) (8) Similarly for the U direction, Mu ≧ u ₀ and the above [3] and [4], [5] The light receiver may be arranged so as to satisfy the condition [].

Next, FIGS. 1, 5 to 7, and 11 to 13
Optimization of the two-dimensional shape and arrangement of the light-receiving surface will be described with reference to FIG. In FIG. 5B, FIG. 6B, and FIG. 7B, the orthographic projections C ₁ and C ₂ are light receivers such that the orthographic projections are arranged side by side in the V direction so that the orthographic projections have the longitudinal direction in the U direction. 2 is arranged, and the orthogonal projections C _1a and C _2a have the orthogonal projection V
It shows that the light receivers 2 are arranged so as to be arranged in parallel in the U direction so as to have a longitudinal direction in the direction. The reason why the orthogonal projection of the light receiving surface has the longitudinal direction is to increase the light receiving area and the SN ratio. Considering the radius of the actual light receiving surface, the above conditions [1], [2],
It may be arranged so as to satisfy the expression (7).

When a conical beam as shown in FIG. 3 is obliquely incident on the substrate 1, the irradiation area is elliptical as described above, and the orthogonal projection shape of the diffracted light is u ₀ > v _0. Becomes Therefore, it is advantageous in terms of resolution to arrange the light receivers 2 so that the orthogonal projections of the light receiving surfaces are arranged in the V direction.
Further, since u ₀ > v ₀ , the region where the orthogonal projection of the diffracted light does not exist becomes longer in the V direction, and the interval between the adjacent orthogonal projections of the diffracted light becomes larger, and the width of the orthogonal projections C ₁ and C ₂ is reduced. The thickness can be increased and the SN ratio can be improved. Further, the larger the incident angle θ, the smaller the interval v ₀ of the orthogonal projection of the diffracted light in the V direction and the longer the region in which the diffracted light does not exist in the V direction, which is advantageous. By such a shape and arrangement of the light receivers, it is possible to perform discrimination based on the discreteness with a good SN ratio. If the number of light receivers is not limited, the orthogonal projections (C ₁ , C ₂ ) and the orthogonal projections (C _1a , C _2a ) may be combined.

Since the orthographic projection of the light receiver has the longitudinal direction, there is an arrangement of the light receiver that cannot be discriminated by the discreteness depending on the distribution of the orthographic projection of the diffracted light. Figure 6
In (b) and FIG. 7 (b), although the orthogonal projections of the diffracted light are distributed in the U direction, they are not aligned in the V direction, so that the two orthogonal projections C _1a and C _2a are both diffracted. It overlaps with the orthographic projection of light. This means that the two light receiving surfaces 2A,
Both of 2B mean that diffracted light from the circuit pattern is incident, and discrimination based on discreteness cannot be performed. Therefore,
Even in the case of FIG. 6B and FIG. 7B, the orthogonal projection C in the V direction
_It is preferable to arrange the light receiver 2 so that ₁ and C ₂ are arranged in parallel.
It goes without saying that there is an advantage in arranging the orthogonal projections C ₁ and C _{2 in} the V direction for the same reason as in the case of FIG. 5B. By arranging such a photodetector, it is possible to perform discrimination based on the discreteness of the SN ratio with respect to pattern noise.

Next, when the light receiver 2 has a plurality of light receiving surfaces,
Will be explained. FIG. 11 shows the case of FIG. 5 (b), for example.
And three orthographic projections C with the longitudinal direction in the U direction ₁, C₂,
C₃Are arranged in parallel in the V direction. Interval M
v, Mv₁, And width D₀Is the above condition [3], [4]
Meets For actual light receiving surface conditions (shape, spacing)
If it is constructed so as to satisfy the above equation (5),
Yes. In addition, these three orthographic projections may be arranged side by side in the U direction.
Yes.

FIG. 12 shows, for example, the case of FIG. 5B, in which nine orthogonal projections of the light receiving surface are arranged. The light-receiving surface in the case of FIG. 12 has resolution in both U and V directions. Here, the intervals Mv, Mv ₁ and the width D ₀
Satisfies the above condition [5]. In this case, it is assumed that the condition in the U direction is determined by the condition in the V direction.
The actual conditions (shape, spacing) of the light receiving surface may be configured so as to satisfy the above expression (7).

Further, FIG. 13 shows, for example, the case of FIG. 5B, in which 49 projection views of the light receiving surface are arranged in a grid pattern. Here, the intervals Mv, Mv ₁ and the width D ₀ satisfy the above condition [5]. in this case,
It is assumed that the U-direction condition is determined by the V-direction condition. Thus, the resolution is improved by arranging the orthogonal projections of the light receiving surface in a grid pattern. The actual conditions (shape, interval) of the light receiving surface may be configured so as to satisfy the above expression (5).

A photodetector 2 capable of obtaining an orthogonal projection as shown in FIG.
A variable slit is provided in the vicinity of the light receiving surface to define the shape and direction of the orthogonal projection. For example, (C ₁ , C ₂ ) and (C _{1a in FIG} .
C _2a ), or C _{1 to} C ₃ in FIG. 11 and C _{1 to} C _{9 in} FIG.
Alternatively, an orthographic projection such as Further, instead of the variable slit, electrical masking may be used to process the signal from only the light receiving surface corresponding to the orthogonal projection of the desired shape and direction. Next, the procedure for optimizing the light receiver will be described.

Determination of required detected foreign matter: Usually set to about 1/5 of the pattern rule. As a result, as shown in FIG.
The detection threshold value described in FIG. 17 is determined. Investigation of pattern diffracted light pitch required for discriminating by discreteness: When the threshold value of necessary foreign matter is set to D as shown in FIG. 16, pattern diffracted light of FIG. 15 does not require discrimination by discreteness, and FIG. Required for pattern diffracted light. That is, the pitch of the pattern diffracted light that starts to exceed Sd in the equation (1) must be specified. The diffracted light incident on the light receiver is a high-order diffracted light, and the high-order diffracted light is dominated by the pattern edge. Here, the pattern edge means the thickness of the chrome pattern 20 as shown in FIG.
It means a short side portion of d (≈normally 0.1 μm). The higher the amount of diffracted light, the greater the total area in the beam,
The longer the long side, the more it increases. With respect to the circuit pattern actually used, the pattern rules are studded until it becomes a pattern rule that requires discrimination of discreteness by experiments, and the pattern pitch Pd when the threshold value Sd is exceeded is obtained, and the pattern diffracted light interval corresponding to this is determined. The width and the number of light receivers for discriminating this can be determined.

FIG. 15 is a diagram schematically showing FIG. 17, and shows an example in which a photodetector having an orthogonal projection as shown in FIG. 15 is applied. Here, if the diffracted light pitch that is the integrated intensity Sd of the light receiving range H is Pm, the above equation (8) may be satisfied in order to discriminate the diffracted light interval δ with n light receivers. In FIG. 15, the integrated light receiving range H is the light receiving width h
However, for the sake of convenience, Sd may be determined by using a 3D ₀ signal as an integral value.

Now, optical scanning is performed by the vibrating mirror 4,
When the inspection point moves to the points L and R, a sphere is schematically newly drawn around the inspection point, and the photocathodes 2A and 2B and the exit pupil 7 are drawn.
The f-θ lens 3 and the light receiver 2 are compared with the optical scanning distance so that the relationship between the light flux formed by the inspection point, the curved cross section of the newly drawn sphere, and the orthogonal projection thereof does not change as much as possible. It is desirable to place it far enough so that the inspection point
The above relationship may be satisfied in the state of being closest to the light receiver.

In the above embodiment, the diffracted light and the scattered light are directly incident on the light receiver 2, but they may be incident via a lens system. The light receiving surface may be at a position image-conjugated to the substrate 1, or may be arranged at the pupil plane of the lens system or near the conjugate plane position thereof. Further, although the incident light flux I is obliquely incident on the substrate 1 at the incident angle θ, it may be vertically incident at an incident angle of zero.

It is also possible to inspect a reticle with a phase shifter that is often used for periodic patterns. Also, the throughput is higher than the data comparison. Also, when inspecting a reticle with a pellicle, scattered light from the pellicle frame is often generated by the incident light, especially when inspecting the reticle surface near the pellicle frame. The receiver must be arranged so that it has an optical axis in a direction perpendicular to the plane. According to the present invention, even if such a light receiver arrangement is adopted, it is possible to efficiently discriminate a foreign matter from a pattern.

[0041]

As described above, according to the present invention, it is possible to efficiently discriminate a fine periodic pattern from a foreign matter regardless of the arrangement position of the light receiver. In addition, the number and shape of the light receiving surface, the direction,
Since the arrangement can be changed according to the circuit pattern or the incident angle of the light flux, the discrimination can be performed under the optimum light receiving surface condition, and the discrimination accuracy is improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of a foreign matter inspection apparatus according to an embodiment of the present invention,

FIG. 2 is a diagram showing a signal processing system for discriminating a photoelectric signal of diffracted light from a circuit pattern and a photoelectric signal of scattered light from a foreign matter according to an embodiment of the present invention;

FIG. 3 is a diagram schematically showing a part of FIG. 1;

FIG. 4 is a diagram showing a relationship between a beam irradiation area and a pattern according to an embodiment of the present invention;

[FIG. 5]

FIG.

7A is a diagram showing a circuit pattern according to an embodiment of the present invention, FIG. 7B is a diagram showing an intensity distribution of diffracted light from the pattern of FIG. 7A,

FIG. 8 is a diagram for explaining the principle of discriminating between a circuit pattern and foreign matter according to the present invention;

9 is a plan view of FIG. 3 viewed from the Q direction,

FIG. 10 is a diagram for explaining the principle of discriminating between a circuit pattern and foreign matter according to the present invention;

FIG. 11

FIG. 12

FIG. 13 is a view showing a modification of the shape of the light receiving surface according to the embodiment of the present invention,

FIG. 14 is an explanatory view of a chrome pattern according to an embodiment of the present invention,

15 is a diagram schematically showing FIG. 17,

FIG. 16 is a diagram showing an intensity distribution of diffracted light from a circuit pattern of low fineness,

FIG. 17 is a diagram showing an intensity distribution of diffracted light from a circuit pattern with high fineness;

FIG. 18 is a diagram showing a conventional foreign matter inspection device.

[Explanation of symbols]

1 ... substrate 2 ... light receiver 3 ... f-theta lens 4 ... vibrating mirror 5 ... collimator lens 6 ... light source 8 ... control system S, S ₁ ... virtual sphere I ... incident beam 2A, 2B ... receiving surface 2A1,2B1 … Curved cross section of light receiving surface C ₁ , C ₂ … Orthogonal projection of 2A1, 2B1 i… Curved cross section of incident luminous flux I i ₁ … Orthogonal projection of i v ₀ … Width of V _{1 in} the V direction D ₁ , D ₂ … C ₁ , width of C ₂ Mv ... interval of C ₁ , C ₂ O ... incident point θ ... incident angle γ ... aperture angle of incident light flux I (aperture angle of f-θ lens 3) O ₁ ... origin of UV coordinate system E ₁ ... one E ... E orthogonal projection of the diffracted light curved cross-section O ₂ ... Z-axis parallel to the straight line n ₂ include intersection n ₁ ... O ₂ of the V-axis and a straight line parallel to the X axis through the E ₁ A straight line β including O ₂ and the center Ce of the curved cross section E, and the spatial angle in the V direction formed by n ₁ and n _2.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01S 3/00 F 8934-4M

Claims (5)

[Claims] 1. A light source for irradiating an inspected object having a circuit pattern formed on its surface with a coherent light beam; a light beam emitted from the light source is converged on the inspected object at an inspection point at a predetermined opening angle. Condensing means; moving means for relatively moving the incident light beam condensed at the predetermined opening angle and the inspection object; generated when the condensed light beam is incident on the inspection object A foreign matter inspecting device, comprising: a detecting means for receiving scattered light flux; and detecting a foreign matter on the inspection object based on an output signal from the detecting means, wherein the detecting means has a longitudinal direction and a lateral direction. At least two light-receiving surfaces are provided, and the two light-receiving surfaces are an orthographic projection diagram of a curved cross section of the virtual sphere centered on the inspection point and having the substrate as an equatorial plane and having an arbitrary radius on the substrate. The orthographic projection distance to the light receiving surface is Particle inspection apparatus characterized by being arranged so as to be substantially equal to the orthogonal projection of the width of the light beam incident on the substrate. 2. The at least two light-receiving surfaces are arranged in parallel so that the longitudinal directions of the orthogonal projections thereof are parallel to or perpendicular to the reference axis of the object to be inspected. Foreign matter inspection device. 3. When the signals are output from all of the at least two light receiving surfaces, it is determined that it is a foreign substance, and when the signals are not output from all of the at least two light receiving surfaces, it is determined that it is a circuit pattern. The foreign matter inspection device according to claim 1, wherein 4. The foreign matter inspection apparatus according to claim 1, further comprising variable means capable of changing at least one of the number, direction and shape of the at least two light receiving surfaces. 5. The foreign matter inspection apparatus according to claim 1, wherein the condensing optical system is arranged so that the coherent light beam is obliquely incident on the substrate at a predetermined incident angle.