JPH04134254A - Foreign matter inspection device - Google Patents

Abstract

PURPOSE:To prevent erroneous sensing pattern due to rear face reflexion and inspecting eventual existence of foreign matter and its size by allowing the incident beam onto the surface to be projected at an incident angle of 50-90 deg., and specifying the setting of a photo-sensor. CONSTITUTION:The incident angle of a beam projected onto a surface shall range 50-90 deg., and a photo-sensor is located so as to meet the condition W<2XTXtan{sin<-1>sin(90-alpha)/n}xsin(90-beta), where W is width of slit image in the direction of the incident beam, T is thickness of base board to be inspected, (n) is refraction coefficient of the base board, alpha is elevation angle in receiving the beam, and beta is beam receipt angle on horizontal plane. Thereby erroneous sensing of pattern resulting from rear face reflexion is precluded to permit precise inspection of foreign matter.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to reticles and masks used for printing patterns on semiconductor wafers in LSI manufacturing processes, or product wafers on which patterns are formed.
The present invention relates to a foreign matter inspection device for inspecting whether or not foreign matter such as particles is attached to the surface of a substrate to be inspected, and furthermore, the size of the foreign matter if any foreign matter is attached.

(Prior Art) As a conventional example of this type of foreign matter inspection device, there is one having a configuration as shown in FIG.

That is, a stage (
(not shown) is linearly moved and scanned in the X direction on a horizontal plane, and a laser beam (for example, linearly polarized S-polarized light, which is a type of incident light 4
The intensity of the reflected scattered light 5 from the surface 1 is set diagonally above the side of the substrate 3 to be inspected in the X direction. A polarizing plate 6 that transmits only polarized light components having a specific polarization angle, and a photomultiplier tube (hereinafter referred to as
The sensor is configured to perform measurement using a detection optical system 9 consisting of a photomultiplier 7 and a preamplifier 8.

According to the above configuration, if there is a pattern or part of a pattern corner that forms an angle of 45° with respect to the incident light 4 on the surface 1 of the reticle 3, reflected scattered light is reflected toward the detection optical system 9 at that part. 5, most of it is polarized light with a specific polarization angle (in this example, P-polarized light with a polarization angle of 90°), so the analysis axis of the polarizing plate 6 should be set and arranged perpendicular to this. For example, the reflected and scattered light 5 is all cut off and does not reach the photomultiplier 7, so in this case, the photomultiplier 7
Since no light is detected, it is determined that there is no foreign substance on the surface 1.

On the other hand, when a foreign object is present on the surface 1 of the reticle 3, the reflected and scattered light 5 reflected toward the detection optical system 9 by the foreign object contains a mixture of S-polarized light component and P-polarized light component. Therefore, although the P-polarized component is canted in the polarizing plate 6, the S-polarized component passes through the polarizing plate 6 and reaches the photomultiplier 7. Therefore, in this case, the photomultiplier 7 detects the light. The signal is extracted via the preamplifier 8, and it is determined that a foreign object is present.

[Problem to be solved by the invention]

By the way, in recent semiconductors, the degree of integration has progressed significantly, and the pattern 2 has become even finer. Along with this, there is a need to detect even finer foreign particles, which can lead to errors. It is important to avoid detection.

Therefore, the inventor investigated the relationship between the incident light and the photodetector, that is,
When we examined the optical arrangement I, we found the following 15 points.

■ When a laser beam with a certain polarization angle is made incident as incident light 4 on a substrate to be inspected, such as a transparent substrate with pattern 2 drawn in chrome, such as reticle 3,
As shown in FIG. 14, the surface reflected light 10 is generated by reflection from the pattern 2, and this surface reflected light 10 passes through the polarizing plate 6 and enters the photomultiplier 7.

On the other hand, there is light that is reflected by the pattern 2 and travels into the reticle 3. Most of this light passes through the reticle 3 as transmitted light 12, but the remaining part is reflected on the back surface 11 of the reticle 3 and proceeds to the front surface 1 side, passes through the polarizing plate 6 as back reflected light 13, and passes through the photomultiplier 7. incident on . Note that 14 is a slit image, and 15 is direct light.

However, the polarization direction of the back surface reflected light 13 is different from that of the front surface reflected light 10, as shown by the arrow in the figure, and as a result, the reflected scattered light 5 from the pattern 2
Since the polarization ratio of the pattern 2 decreases, the reflected and scattered light 5 becomes stronger, and the ability to discriminate between the pattern 2 and foreign matter decreases. Figure 15 shows the influence of the presence or absence of back reflection on pattern detection errors. In this figure, the solid line A is the characteristic curve when there is back reflection, and the imaginary line B is the characteristic curve when there is no back reflection. The characteristic curves are shown, and the horizontal axis shows the polarization angle by the polarizing plate 6.

In order to avoid erroneous pattern detection due to this backside reflection, consider the thickness of the reticle 3, the width of the slit image 14 in the direction of incidence of the incident light 4, the receiving elevation angle and the receiving horizontal angle of the photomultiplier 7 (all of which will be described later), etc. Then, the position of the photomaru 7 can be set.

■ Figure 16 shows the influence of the directly reflected light 16, and this influence is due to the fact that the position of the photomul 7 is 90° with respect to the incident light 4.
This occurs not only at the time of , but also at other angles, and by eliminating this, erroneous detection of pattern 2 can be reduced.

In order to avoid pattern detection errors due to direct reflection, the angle of incidence of the incident light 4 at the center of the reticle 3, the inclination angle of the pattern 2, the deflection angle of the incident light 4, the normal line at any point of the pattern edge, and the Angle (both will be explained later)
The position of the photomaru 7 may be set by taking these factors into consideration.

(2) If a foreign object is present on the back surface 11 of the reticle 3, it may be erroneously detected as a foreign object on the front surface depending on its location. That is, as shown in FIG. 17, the foreign object 17 forms a projection image (
There is no problem at all when the foreign object is located outside the hunting part 14A in Fig. 17, but this foreign object 1
7 is within the range of the projected image 144, an erroneous detection of a foreign object on the back surface occurs.

In order to avoid this false detection of foreign objects on the back surface, the light receiving elevation angle α of the photomul 7 (the angle formed by the line 18 connecting the center of the light receiving surface of the photomul 7 and the inspection area on the surface 11 of the reticle 3 and the surface 11 to be inspected) and the light receiving horizontal angle β (the angle formed by the line 19 when the line 1 is projected directly below onto the surface 11 and the direction of incidence (X-axis) of the incident light 4) may be set as appropriate.

(2) When performing measurements using the pellicle 20, it is preferable to avoid any influence due to its installation. As shown in FIG. 18, this pellicle 20 includes a pellicle membrane 22 made of, for example, nitrocellulose, stretched over one end of a ring-shaped pellicle frame 21 made of, for example, aluminum.
This is to prevent foreign matter from adhering to the reticle 3, but depending on the installation position of the photomul 7, there may be areas where it cannot be detected (
Hunting portion) 23 in FIG. 18 may occur.

In order to avoid being affected by this pellicle frame 21,
The photomultiplier 7 may be provided at a predetermined position.

As can be understood from the above explanation, in order to inspect foreign objects with higher accuracy and to avoid false detection, it is especially important to consider the factor ① among the factors ② to ② above, that is, the pattern due to back surface reflection. It is sufficient to prevent false detection.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a foreign matter inspection device that can accurately inspect the presence or absence of foreign matter and its size while preventing erroneous pattern detection due to backside reflection.

[Means to solve the problem]

In order to achieve the above-mentioned object, the following two means are adopted in this application.

The foreign matter inspection device according to the first invention scans and irradiates a surface of a substrate to be inspected on which a pattern is drawn with a laser beam having a certain polarization angle as incident light, and measures the intensity of reflected and scattered light from the surface. In a foreign object inspection device that detects a foreign object with a photodetector and determines the presence or absence of a foreign object on the surface and its size based on the detection result, the incident angle of the incident light with respect to the surface is set at 50° to 90°.
and the photodetector is 5in(90-α)W<2XTXtan 1sinri)X
sin(90-β) (however, the width of the W Nislit image in the incident light direction, T: thickness of the substrate to be inspected, n: refractive index of the substrate to be inspected, α: light receiving elevation angle, β: light receiving horizontal angle) is satisfied. It is distinctive in that it is positioned so that

Further, the foreign matter inspection device according to the second invention scans and irradiates the surface of the substrate to be inspected on which the pattern is drawn with a laser beam having a certain polarization angle as incident light, and removes reflected and scattered light from the surface. In a foreign matter inspection device that detects the intensity with a photodetector and determines the presence or absence of foreign matter on the surface and its size based on the detection result, the incident angle of the incident light with respect to the surface is set to 50'' to 75@ , the photodetector is defined as 5in(90-α) W <2X'rX tan (sinXsin(9
0-β) (However, the width of the W nislint image in the incident light direction, T: Thickness of the substrate to be inspected, n: Refractive index of the substrate to be inspected, α: Receiving elevation angle, β: Receiving horizontal angle) and, α≧ 15'' and β≦90°.

[Operation] According to the first invention, it is possible to avoid false detection due to back surface reflection.

Further, according to the second invention, it is possible to avoid erroneous detection due to backside reflection, and even when a pellicle is used, the influence of the pellicle frame can be eliminated.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

Note that in the following description, the same reference numerals as those shown in FIGS. 13 to 18 above indicate the same components, and therefore the explanation thereof will be omitted.

FIG. 8 is a diagram for considering where the photomultiplier 7 should be placed in order to avoid the factor (2) above, that is, erroneous pattern detection due to backside reflection. In order to avoid the influence of the light reflected by the back surface 11 of the back surface 11, that is, the back surface reflected light 13, the photomultiplier 7 should be installed at a position (angle) such that this back surface reflected light 13 does not enter the slit image 14 again. good.

This installation position can be determined as follows.

That is, let the thickness and refractive index of the reticle 3 be T and n, respectively. Also, let W be the width of the slit image 14 in the X-axis direction, and the length from the position where the incident light 4 is incident on the front surface 1 of the reticle 3 until it is reflected at the back surface 11 of the reticle 3 and exits from the front surface l again. 1, then 1 is expressed as 5in(90-α) 1-2XTXtan(sin) using also the light-receiving elevation angle α and the light-receiving horizontal angle β.

Then, since it is sufficient to make the relationship W< l
1Xsin(90-β)
...(1) is obtained.

Therefore, if the photomultiplier 7 is installed so that the above equation (1) holds true, false detection due to backside reflection can be avoided.

Figures 9 and 10 show a pattern model and an optical model, respectively, for considering where the photomultiplier 7 should be installed in order to avoid the factor (2) above, that is, erroneous pattern detection due to direct reflection. In the figure shown, the ninth
In the figure, 24 is a pattern edge portion, 25 is an incident light 4
is the reflected light on the surface of the pattern edge portion 24, 26 is the XY plane, 27 is the normal plane, and in FIG. 10, 28 is the light receiving surface, and 29 is a plane parallel to the XZ plane including the light receiving surface be.

Then, the incident angle of the incident light 4 at the center of the reticle 3 is G (0°≦G≦90°), and the inclination angle of the pattern 2 is B (
0°≦G≦180''), and the deflection angle of incident light 4 is ψ(0
°≦ψ≦10°), and the angle between the normal line at an arbitrary point of the pattern edge portion 24 and the XY plane 26 is T (0°≦γ≦9
0°), set the size as shown in FIG. 10, find U and W at an arbitrary angle T using the following equation, and plot this.

sinθ × cosψ cosB (tanB - tanψ) tan S = tan G - tanδtanψMt
an(A-θ) COSδ U=TcosSW=Tsin S+Mtanδ Note that countermeasures for this factor (①) have been conventionally taken by methods other than the above.

FIG. 11 is a diagram for considering where the photomultiplier 7 should be installed in order to avoid the factor (2) above, that is, erroneous detection of foreign objects on the back surface. Back surface 11 from the irradiation position of incident light 4
Let Ld be the distance from the irradiation position of the incident light 4 on the front surface 1 to the center of the slit image 14 projected on the back surface 11, then L and Ld
is L = T X tan (sin sin (90-α) L d = T X tan (sin-'Xsin(
90-β).

In order to avoid erroneous detection of a foreign object on the back surface, cases are classified according to the size of the light reception horizontal angle β. If β≦90°, Ld>L10W/2 or Ld<LW/2, and β>
In the case of 90°, it is sufficient that Ld>W/2.

As shown in FIG. 12, when inspecting foreign matter adhering to the surface 1 of the reticle 3 with the pellicle 20, the inner diameter and height H of the pellicle frame 21 become a problem. the current,
Considering the size of the pellicle frame 21 of a generally commercially available pellicle 20, if the light receiving horizontal angle β is 90' or less, the light receiving elevation angle α can be set to 15° or more. Conversely, if the light receiving horizontal angle β is larger than 90°, the entire inner surface of the pellicle 20 may not be inspected.

Figure 7 shows where to install Photomaru 7 due to factors ■
This is a three-dimensional diagram showing which of the factors -■ which erroneous detection occurs, and the symbols -■ in the figure indicate the areas where the photomultipliers 7 corresponding to the factors -■ are installed, respectively. In this figure, a blank area V indicates an area where no problem will occur due to any of the factors (1) to (2) described above even if the photomultiplier 7 is installed.

Fig. 1 shows an example in which the photomul 7 is installed in the area (3), where the incident angle of the incident light 4 is 60' (306 from the plane of the reticle 3), and the receiving elevation angle α of the photomul 7 is 40'.
°, and the light receiving horizontal angle β is 60°. Figure 2 shows the intensity of reflected and scattered light at this time; curve A shows the intensity of reflected and scattered light from the foreign object when the particle size of the foreign object is changed; It shows the intensity of reflected and scattered light from pattern 2 with a thickness of .

The following can be seen from Figure 2. That is, for example, if the particle size is 0.
One reflected scattered light intensity (S) from a 5 μm foreign object is 80 mV
On the other hand, the reflected and scattered light intensity (N) from pattern 2 with a thickness of 5 μm is as small as 12 mV (therefore, S/
N is as large as 80/12.

On the other hand, FIG. 5 shows an example of the arrangement of the photomul 7 according to the prior art. In this case, the incident angle of the incident light 4 is 54° (30° from the plane of the reticle 3), and the receiving elevation angle α of the photomul 7 is I5°. , the horizontal light receiving angle β is 90°. FIG. 6 shows the reflected and scattered light intensity at this time. In this case, the reflected and scattered light intensity (S) from the foreign matter with a particle size of 0.5 μm is 50 mV, whereas the reflected and scattered light intensity (N) from the pattern 2 with a thickness of 5 μm is as large as 200 mV, and S/ N is as small as 50/200.

In other words, according to the present invention, the intensity of the reflected and scattered light from the foreign object is greater than that from pattern 2, and the S/N is large, so the ability to discriminate between the foreign object and pattern 2 is large, and the foreign object can be inspected with high precision. be able to.

FIG. 3 shows the installation state of the photomultiplier 7 according to another embodiment of the present invention. In this case, the incident angle of the incident light 40 is 75@ (15° from the plane of the reticle 3), and the receiving elevation angle α of the photomultiplier 7 is 45°. degree, and the receiving horizontal angle β is 68 degrees. and,
FIG. 6 shows the reflected and scattered light intensity at this time.

In this example as well, the S/N is large.

As already discussed, when inspecting the surface 1 of the reticle 3 with the pellicle 20 for foreign matter, the angle of incidence of the incident light is set at 4°, and the angle of incidence of the incident light is set at 50° to 75°, and the receiving elevation angle α is set at 15°. or more, and the receiving horizontal angle β is 90
'' or less, the entire surface 1 of the reticle 3 can be thoroughly inspected.

[Effects of the Invention] The present application is configured as described above, and according to the first invention, it is possible to prevent erroneous pattern detection due to back surface reflection and to accurately inspect foreign objects.

Further, according to the second invention, even when a pellicle is used, foreign objects can be accurately inspected without being affected by the pellicle frame.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the arrangement of a photodetector according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the intensity of reflected and scattered light at that time. FIG. 3 is a diagram schematically showing the arrangement of a photodetector according to another embodiment of the present invention, and FIG. 4 is a characteristic diagram showing the intensity of reflected and scattered light at that time. FIG. 5 is a diagram schematically showing the arrangement of a conventional photodetector;
FIG. 6 is a characteristic diagram showing the intensity of reflected and scattered light at that time. FIG. 7 is a diagram for explaining factors depending on the optical arrangement. FIG. 8 is a study diagram for avoiding erroneous pattern detection due to backside reflection. FIG. 9 and FIG. 10 are study diagrams for avoiding erroneous pattern detection due to direct reflection, and are diagrams showing a pattern model and an optical model, respectively. FIG. 11 is a study diagram for avoiding erroneous detection of foreign objects on the back side. FIG. 12 is a study diagram for avoiding the influence of vertical frames. FIG. 13 is a diagram schematically showing the configuration of a conventional foreign matter inspection device. FIG. 14 is a diagram for explaining erroneous pattern detection due to back surface reflection, and FIG. 15 is a diagram showing the influence of the presence or absence of back surface reflection on pattern erroneous detection. FIG. 16 is a diagram for explaining the influence of the directly reflected light 16. FIG. 17 is a diagram for explaining erroneous detection of foreign matter on the back side. The 18th drawing is a diagram to explain the influence of the pellicle frame. 2... Pattern, 3... Board to be inspected (reticle), 4... Incident light, 5... Reflected scattered light, 7... Photodetector (electron multiplier), 14... Slit image, W...
- Width of the slit image in the direction of incident light -1T... Thickness of the substrate to be inspected, α... Receiving elevation angle, β... Receiving horizontal angle.

Claims (2)

[Claims] (1) Scanning and irradiating the surface of the substrate to be inspected on which a pattern is drawn with a laser beam having a certain polarization angle as incident light, and detecting the intensity of reflected and scattered light from the surface with a photodetector; In a foreign object inspection device that determines the presence or absence of a foreign object on the surface and its size based on the detection result, the incident angle of the incident light with respect to the surface is set to 50 degrees or more.
90°, and the photodetector is
0-α)/n]}×sin(90-β) (where, W: width of the slit image in the incident light direction, T: thickness of the substrate to be inspected, n: refractive index of the substrate to be inspected, α: light reception A foreign object inspection device characterized in that the position is set to satisfy the angle of elevation, β: horizontal angle of light reception). (2) Scanning and irradiating the surface of the substrate to be inspected on which the pattern is drawn with a laser beam having a certain polarization angle as incident light, and detecting the intensity of reflected and scattered light from the surface with a photodetector; In a foreign object inspection device that determines the presence or absence of a foreign object on the surface and its size based on the detection result, the incident angle of the incident light with respect to the surface is set to 50 degrees or more.
75°, and the photodetector is
0-α)/n]}×sin(90-β) (where, W: width of the slit image in the incident light direction, T: thickness of the substrate to be inspected, n: refractive index of the substrate to be inspected, α: light reception A foreign matter inspection device characterized in that the position is set so as to satisfy both of the following: elevation angle, β: horizontal angle of light reception), and α≧15° and β≦90°.