JP3053096B2 - Foreign object detection method and device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting foreign matter on a semiconductor LSI wafer or mask, and more particularly to a method for detecting foreign matter on a semiconductor LSI wafer or mask. The present invention relates to a foreign matter detection method and apparatus suitable for a foreign matter inspection for detecting a minute foreign matter such as small particles at high speed and with high sensitivity.

[Conventional technology]

In the first example of the conventional method and apparatus for detecting foreign matter on a wafer with a pattern, inspection of foreign matter on a wafer with a pattern in an intermediate process of LSI manufacturing is indispensable for improving the manufacturing yield and the reliability. Then, automation of this work was
55-149829, JP-A-54-101390, JP-A-55-94145
This is realized by a detection method using polarized light as described in JP-A-56-30630. The principle of this foreign matter detection method will be described with reference to FIGS. 21 (a), (b) and (c) and FIGS. 22 (a) and (b).

FIGS. 21 (a), (b) and (c) are explanatory views of the principle of foreign matter inspection showing a first example of a conventional foreign matter inspection method and apparatus. 21 (a), (b) and (c), the S-polarized laser beam 15c is irradiated horizontally on the wafer 7 as shown in FIG. 21 (a). At this time, the reflected light 12P from the pattern 2 perpendicular to the illumination light 15c on the wafer 7 does not change its polarization and proceeds to the objective lens 6 as S-polarized light. This reflected light 12P
Since the analyzer 151 is arranged so that the analysis axis is perpendicular to the polarized light, the reflected light 12P is extinguished and does not reach the detector 20. As shown in FIG. 21 (b), the reflected light 12P from the pattern 2 having an angle with respect to the illumination light 15c does not enter the objective lens 6 and is not detected. When the illuminating light (Y direction) 15c hits the foreign matter 13 on the wafer 7 as shown in FIG. 21 (c), the reflected light 12 changes its polarization to generate P-polarized light (a kind of depolarization phenomenon). ). Since this passes through the analyzer 151, the foreign matter 13 can be detected by the detector 20.

22 (a) and 22 (b) are a perspective view and a discrimination ratio graph of an optical system of a first example of a conventional foreign matter detection method and apparatus. 22 (a) and 22 (b), when the inclination angle φ of the S-polarized laser beam 15c from the laser light source 15 with respect to the wafer 7 shown in FIG. Measurement data of the discrimination ratio, which is the ratio of the foreign matter scattered light intensity 12 to the pattern scattered light intensity 12p for the 0.5 μm foreign matter and the 1 μm foreign matter shown in FIG. 22 (b) detected by the detector 20 via the photon 151. Is obtained. This inclination angle φ
A method of detecting and comparing the inclination angle φ within an appropriate range by using the output characteristics of the foreign substance 13 and the pattern 2 due to the above-mentioned method is adopted.

A second example of a conventional method and apparatus for detecting foreign matter on a wafer with a pattern includes a polarized laser illumination 15c having a large scattering effect on foreign matter 13 as disclosed in Japanese Patent Application Laid-Open No. 61-104243. Focusing on two types of illumination, a small scattering effect, and that the scattered light by the previous illumination is likely to be generated by the foreign matter and the scattered light by the subsequent illumination is likely to be generated by the pattern,
There is one in which fine foreign substances can be detected more stably and with higher sensitivity by detecting the ratio of both scattered light signals. Further, the second conventional example uses a plurality of photoelectric conversion solid-state imaging devices in which the size of each pixel of the light receiving unit is about 5 × 5 μm ² (converted on the sample surface) or less, and outputs an output signal from each device. Simultaneously, by performing the parallel comparison processing, foreign matter inspection can be performed with high sensitivity without deteriorating the high-speed performance. The principle of this foreign matter detection method will be described with reference to FIGS. 23 to 26 (a) and (b).

FIG. 23 is a perspective view of an optical system of a second example of a conventional foreign matter detection method and apparatus. In FIG. 23, the foreign matter 13 and the pattern 2 by the inclination angle φ shown in FIGS.
For example, the low-angle S-polarized illumination light 15c (wavelength λ ₁ ) by the laser light source 15L and the condenser lens 15bL and the high-angle S light by the laser light source 15H and the condenser lens 15bH are used. The same sample point on the sample 7 is illuminated with the polarized illumination light (wavelength λ ₂ ) 11, and only the P-polarized component of the scattered light 12 that has passed through the objective lens 6 and the color separation branch prism 150 and the analyzers 151L and 151H is emitted. The output signals V _L and V _H are detected by the photoelectric conversion solid-state imaging devices 20L and 20H, compared by the analog comparison / division circuit 100, and binarized by the binarization circuit 101, and then the binarized signal is output. It is taken out through the OR circuit 22.

24 (a) to (g) are explanatory diagrams of the output signals and the like in FIG. In FIGS. 24 (a) to (g), FIG.
Are foreign substances 13a and 13 different in size from the pattern (POLY-Si) 2.
The sample (Si wafer) 7 where b exists is laid on the sample from an oblique low angle.
FIG. 24 (b) shows a waveform of the output signal _VL in the case where the scattered light 12P, 12 is generated by irradiating the light 15c, and FIG. shows the waveform of the binary signal Sd by the threshold V _0. FIG. 24 (d) is a side view showing a case where laser light 11 is irradiated from an obliquely high angle onto a sample (Si wafer) 7 on which a pattern 2 and foreign substances 13a and 13b are present, and FIG. e) shows the waveform of the output signal V _H in that case. Further
FIG. 24 (f) shows the waveform of the output signal ratio _VL / _VH , and FIG. 24 (g) shows the waveform of the binarized signal Sd based on the threshold value m.

FIGS. 25 (a) to (h) and FIGS. 26 (a) to (d) are optical path diagrams of the polarized light in FIG. 25 (a) to 25 (h), FIG. 25 (a) shows a model of the above illumination / analysis conditions, and shows the S-polarized illumination light 15c, 11 on the sample 7 described above.
Using (L) and S (H), the color separation branch prism 150 is used.
Output signals V _L , V of P-polarized component analysis using
_{Although the} case where _H is obtained is shown, the present invention is not limited to this case, and various illumination / analysis conditions shown in FIGS. 25 (b) to (h) and FIGS. 26 (a) to (d) can be used. . Foreign matter in this
Illumination / analysis conditions L for emphasizing 13a and 13b are S-polarized illumination S (L) for P-polarized component analysis or P-polarized illumination P
In (L), one of the conditions for the analysis of the P deflection component is used. The reason has been described in the above-mentioned Japanese Patent Application Laid-Open No. 61-104243. The illumination / analysis condition H for emphasizing one pattern 2 may be any condition other than any of the above illumination / analysis conditions L. Therefore, it is not always necessary to use polarization by laser light illumination. Is also good. That is, incoherent light such as a normal halogen lamp may be used, which is indicated by S + P in FIGS. 26 (a) to (d).

The above color separation branch prism 150 is disclosed in Japanese Patent Application Laid-Open No. 55-149829.
Or a dichroic prism (or mirror) described in JP-A-56-43539 or a combination of a light splitting prism (semi-transmissive mirror) and a color filter or interference filter. You may. The laser light sources 15L and 15H are He-Ne laser (λ = 6.328 °), Ga
AlAs laser diode (λ = 7.800 to 8.300Å), InGaAs
If two different types are selected from a P laser diode (λ = 13.000 °) and an Ar laser (eg λ = 4580 °), the light is condensed on the surface of the sample 7 by the condenser lenses 15bL and 15bH. Therefore, a high illuminance can be obtained, and the detection of the scattered lights 12P and 12 becomes more stable. As described above, in the second conventional example, the foreign matter emphasis illumination / analysis condition L satisfies the condition of P polarization component analysis with S polarization illumination S (L) or P polarization component analysis with P polarization illumination P (L). ,
The essential condition is that the pattern-enhanced illumination H of the foreign matter-enhanced illumination L has different wavelengths λ ₁ and λ ₂ .

FIG. 27 is a detailed circuit diagram of a signal processing circuit including the analog comparison division circuit of FIG. In FIG. 27, the detector 20
L, the output signal V _L of 20H, V _H corresponding output signal at the analog comparator division circuit 100 for each pixel i~n that ratio V _L / V _H is calculated by the threshold value m in the binarizing circuit 101 It is binarized. The binarized signal of the binarization circuit 101 is ORed by the OR circuit 22, and when there is “1”, it is stored in the foreign substance memory 23. Then the 28th
The analog comparison method of FIG. 23 (FIG. 27) will be described in further detail with reference to FIGS. 30 (a) and (b) from FIGS. (A), (b) and (c).

28 (a), (b) and (c) are explanatory diagrams of the experimental results under the illumination / analysis conditions of FIG. 23.
(B) shows a top view and a side view of the state of the reflected light (scattered light) 12P and 12 from the circuit pattern 2 and the foreign matter 13 by the illumination light 15c and 11 on the sample 7 in FIG. FIG. 3C shows the experimental data relationship between the output signals V _L and V _H in that state. 28th
28A, 28B and 28C, in this experiment, the scattered light 12P of the pattern 2 in FIGS.
The pattern 2 is rotated while the pattern 2 is rotated by an angle .eta.
The output signal V _L of the scattered light 12P of emissions 2 measures the V _H. One of the foreign matter 13 using standard particles 0.5,0.7,1,2Myuemu (no need to rotate in this case), the output signal V _L of the scattered light 12 of the foreign matter 13 measures the V _H . In relation diagram of data, pattern - - Experimental data of the output signal V _L and the output signal V _H of this measurement Figure 28 (c) also patterns in any angle down 2 eta - down 2
Output signal ratio (white circle) V _L / V _H is the discrimination line V _L / V _H = m
(Reciprocal of the slope of the broken line in the figure)
It can be seen that the output signal ratio (black circles) V _L / V _H from the 0.7-2 μm standard particles and the actual foreign matter (large) U of one foreign matter 13 is larger than the threshold value m of the discrimination line (shaded area). Here, the reason why the angle η is rotated is that patterns 2 having various angles η exist on the surface of the sample wafer 7, and it is necessary to discriminate these and stably detect the foreign matter 13. 28th
The objective lens 6 in FIG. 2B has a lens frame 6a. Next pattern of FIG. 28 (c) - down 2 and output signal V _L of the foreign matter 13, V _H characteristic patterns by electric circuits in consideration of the - Figure 29 a discrimination method for down 2 and the foreign matter 13 (a), (B) and FIG. 30 (a),
This will be described with reference to FIG.

FIGS. 29 (a) and (b) show the output signal ratio V _L of FIG. 28 (c).
FIG. 3 is a characteristic diagram of / V _H and a circuit diagram of an analog comparison / divider circuit thereof. In FIGS. 29 (a) and (b), FIG. 29 (a)
29 (b) shows an example of a discrimination circuit for realizing the characteristics of the output signal ratio V _L / V _H of FIG. 29, wherein the output signals V _L and V _H are analog comparison divisions. The output signal ratio V _L / V _H is calculated by the circuit 100, and the threshold value m is calculated by the binarization circuit 101.
"1" when the output signal ratio V _L / V _H > m
^* Is output. Here, when the output signal _VH is small, the calculation error of the output signal ratio V _L / V _H becomes large and the calculation result becomes unstable (for example, when V _H is zero, V _L / V _H = ∞). Therefore, as a method for avoiding this, in the case of the output signal V _L / V _TH (V _TH is the value of the output signal V _L corresponding to the foreign substance 13 of about 0.5 μm) as shown in FIG. Output signal ratio only for " ^** )
The calculation result of V _L / V _H may be set to valid “1”. This is the 29th
Binarization circuit 1 based on threshold value V _TH of output signal _{VL in} FIG.
04, the output “1” ^*, and the AND circuit 103 of the output “1” ^** .

FIGS. 30 (a) and (b) show the output signal difference V _L of FIG. 28 (c).
FIG. 3 is a characteristic diagram of −V _H and a circuit diagram of an analog comparison and subtraction circuit thereof. FIGS. 30 (a) and 30 (b) show examples of a discrimination circuit using an analog comparison and subtraction circuit 105 for realizing the characteristic of the output signal difference _VL − _VH of FIG. 30 (a). Is adjusted by adjusting the intensity of the illumination light 15c, 11 of one of the illuminations L, H and the gain of the output amplifier (not shown) of one of the imaging elements 20L, 20H. Degrees). The output “1” ^* of the subtraction result _VL − _VH of the output signals _VL and _VH of the analog comparison and subtraction circuit 105 in FIG. 30 (b) is when the output of the binarization circuit 104 is “1” ^** . Valid only when (V _L > V _TH ). Instead of the analog comparison division or subtraction shown in FIG. 29 (b) or 30 (b), the output signals V _L and V _H may be A / D converted and then digitally operated.

[Problems to be solved by the invention]

The first problem of the second example of the related art is that a foreign substance is overlooked. In order to discriminate the 0.5 μm foreign matter from the pattern based on the measurement result shown in FIG. 22 (b), the inclination angle φ of the illumination L is about 0 ° to 5 ° and the inclination angle φ of the illumination H is 10 °. It is desirable to compare the scattered light signals as described above. Also 0.
In order to detect a 5 μm foreign matter at a high S / N ratio, an objective lens 6 having a large aperture capable of effectively condensing scattered light is required. As a result, the lens frame 6a in FIG. When the angle φ is 10 ° or more, the illumination light 11 and the lens frame (gold frame)
6a interferes and sufficient discrimination performance cannot be obtained. As a result, the foreign matter of 0.5 μm is overlooked as shown in FIG. 28 (c).
Although the above is experimental data using a spherical particle called a standard particle as a foreign particle model, the submicron real foreign particle Q in FIG. 28 (c) is also overlooked.

A second problem of the second example of the above prior art is that the intensity of foreign matter scattered light is insufficient. Later, as shown in FIG.
When the illumination light 15c of the oblique illumination L that emphasizes
In the second conventional example, the detector 20L detects foreign matter scattered light 1
Since it is the P-polarized component 12 (P) of the two, it is significantly smaller than the S-polarized component 12 (S) in which the polarization is maintained.
Sufficient light intensity cannot be obtained from the detector 20L. From the results, the first
3Since a sufficient S / N ratio cannot be obtained for the output signal _VL (P) shown in FIG. 3 (c), a low-pass filter process is performed on the output signal _VL to reduce noise N. Takes a long time.

A third problem of the second example of the above prior art is that the sensitivity of the minute foreign matter on the mirror surface is insufficient. Inspection of foreign matter on LSI wafers and the like requires, first, inspection performance of 0.5 μm foreign matter or more on the pattern, and second, inspection performance of 0.1 μm foreign matter or more on mirror surface and mirror surface film formation. Is normal. Here, as shown in FIGS. 14 (a) and 14 (b), in the case of a submicron foreign substance 13, the foreign substance scattered light 1 generated by the tilt angle illumination 15c (11)
Since the forward scattered light 12f of 2 is strong and the side scattered light 12e incident on the objective lens 6 is weak, it is possible to increase the aperture angle α of the objective lens 6 and detect a part of the forward scattered light 12f. Although desirable, the opening angle α is limited for the reason described in the first problem. For this reason, 0.1
Output signal V _L (V _H ) shown in FIG. 13 (b) for μm foreign matter
Cannot be detected because a sufficient amount of light cannot be obtained.

An object of the present invention is to provide a foreign matter inspection method and apparatus for detecting minute foreign matter of about 0.5 μm on a sample with a pattern at high speed by distinguishing the foreign matter from the pattern.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a foreign matter inspection method is described in which a desired region of the surface of a sample having an uneven pattern on the surface is irradiated with light having a first wavelength from a direction inclined with respect to the surface of the sample. Oblique illumination, and epi-illumination of a desired area on the surface of the sample with light having a second wavelength different from the first wavelength from a direction substantially perpendicular to the surface of the sample;
Scattered light generated from a desired region by oblique illumination with light having a wavelength of 2 is separated from light scattered by light having a second wavelength and detected to obtain a first detection signal, and light having a second wavelength. The scattered light generated from a desired area by the epi-illumination is separated from the scattered light by the light having the first wavelength, and the 0th-order diffracted light is shielded and detected to obtain a second detection signal. By comparing the value of the ratio of the first detection signal with a preset value, the scattered light from the concavo-convex pattern and the scattered light from the foreign material can be distinguished from each other by 0.5 μm existing on the sample surface including on the concavo-convex pattern. A method for detecting small foreign matter was adopted.

In order to achieve the above object, according to the present invention, a foreign substance inspection apparatus is provided in which a desired region on a surface of a sample having a concavo-convex pattern on a surface is firstly inclined from a direction inclined to the surface of the sample.
Oblique illumination means for illuminating with light having a wavelength of, and a desired area on the surface of the sample with light having a second wavelength different from the first wavelength from a direction substantially perpendicular to the surface of the sample. A first scatterer that separates and detects scattered light illuminated by the epi-illumination unit and scattered light generated from a desired region by the oblique illumination unit from light having a second wavelength and outputs a first detection signal; A light detection unit and scattered light generated from a desired area illuminated by the epi-illumination unit are separated from scattered light by light having the first wavelength, and the 0th-order diffracted light is shielded and detected, and a second detection signal is output. A second scattered light detecting means, and a value of a ratio between a first detection signal output from the first scattered light detecting means and a second detection signal output from the second scattered light detecting means. By comparing the ratio value with a preset value, It was constructed and a signal processing means for detecting a smaller foreign matter than 0.5μm on the surface of the sample by distinguishing the scattered light from the turbulent light and foreign matter.

[Action]

In the above foreign matter detection method and apparatus, the high-inclination angle illumination is epi-illumination H in addition to the oblique illumination L.
15 Figure-17 foreign matter and pattern for scattered light signal ratio V _L / V _H in accordance with oblique illumination L and incident-light illumination H as shown in FIG - fine foreign matter for the discrimination threshold m for emissions can be reduced and the pattern - down The discrimination performance is improved, and since the large scattered light in which the polarization of the oblique illumination L does not change can be used as shown in FIG. 13, a larger scattered light signal _VL can be obtained, so that high-speed inspection is possible. Becomes

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 20.

FIG. 1 is a perspective view of an illumination / detection system showing a first embodiment of a method and an apparatus for detecting foreign matter on a patterned wafer according to the present invention. In FIG. 1, an oblique illumination system L for illuminating the sample substrate 7 obliquely includes a laser light source 15,
And a condenser lens 15b. The epi-illumination system H for performing linear epi-illumination on one of the sample substrates 7 has a laser light source 1.
, Condensing lens 21, cylindrical lens 14, transflective prism 3, field lens 4, and objective lens 6.
It is composed of The detection system L based on oblique illumination is configured such that scattered light reflected by the color separation prism 150 is imaged by the imaging lens 9 and imaged by the one-dimensional solid-state imaging device (detector) 20L. On the other hand, a detection system H by epi-illumination includes a light-shielding plate 18 having a light-shielding portion 18a for shielding the 0th-order diffracted light, an imaging lens 16,
A one-dimensional solid-state imaging device (detector) 20H.
The output signals V _L and V _H detected by the detectors 20L and 20H are extracted through an analog comparison / division circuit 100, a binarization circuit 101, and an OR circuit 22. In this epi-illumination system H, a cylindrical lens 14 of an optical element for focusing one-dimensionally is installed, and the laser illumination light 11 is focused on a linear spot 11f on the sample 7, so that the sample 7 is scanned in the Y direction. No means is required.
The optical path of the epi-illumination system H will be described with reference to FIG.

2 (a), (b), (c) to (f) are a side view, a plan view and a partial cross-sectional view of the optical path of the epi-illumination system H in which the semi-transmissive prism 3 of FIG. 1 is omitted. . 2 (a) to 2 (f), in the epi-illumination system H, the laser light 11 passing through the condenser lens 21 from the laser light source 1 of FIGS. 2 (a) and 2 (b) passes through the cylindrical lens 14. When passing, the second
A linear laser spot 11c is formed as shown in FIG. Further, the laser light 11 reflected by the semi-transmissive prism 3 is
A linear spot 11d is formed in the stop 4a of the field lens 4 shown in FIG. 2D, and a linear spot 11e is formed in the stop 6a of the objective lens 6 shown in FIG. After passing through 6, a linear spot 11f shown in FIG. When there is no foreign matter 13 on the sample 7 illuminated by the epi-illumination system H, the reflected light 11 from the sample substrate 7 returns to the translucent prism 3 by returning along the completely same optical path as the illuminating light 11. The reflected light 11 that has passed through the semi-transmissive prism 3 is shielded by the linear light-shielding portion 18a of the light-shielding plate 18 provided in the optical path of the detection system H by the epi-illumination shown in FIG. Next, the optical path and image formation of the scattered light 12 from the foreign substance 13 when the foreign substance 13 on the sample 7 exists at the end of the linear spot 11f will be described with reference to FIG.

FIGS. 3 (a), (b), (c) to (g) respectively show the optical paths of the detection systems H and L in which the transmission prism for detecting the scattered light 12 from the foreign material 13 on the sample 7 in FIG. 1 is omitted. It is the side view, top view, and partial sectional view of FIG. 3 (a) to 3 (f), scattering from the end of the linear spot 11f shown in FIG. 3 (g) where the foreign matter 13 exists on the sample 7 in FIGS. 3 (a) and 3 (b). The light 12 spreads over the entire surface into the aperture 6a of the objective lens 6 shown in FIG. 3 (f) and becomes scattered into the aperture 4a of the field lens 4 shown in FIG. 3 (e) after passing through the objective lens 6. Image 12d. Then, the scattered light 12 that has passed through the semi-transmissive prism 3 by the scattered light 12 from the
After passing through the color separation prism 150 (FIG. 1), the image forming lens 16 forms an image 1 on the detector 20H shown in FIG.
2h. Here, all the scattered lights 12 pass through the transparent portion outside the linear light shielding portion 18a of the light shielding plate 18 shown in FIG. 3 (d). This is because the scattered light 12 is higher-order diffracted light than the first-order diffracted light, and its spread 12i is distributed outside the linear light-shielding portion 18a where the zero-order diffracted light (reflected light 12 from the surface of the sample 7) is distributed. is there. The scattered light 12 that has passed through the semi-transmissive prism 3 with the scattered light 12 by the other oblique illumination system L is a color separation prism.
The light is reflected by 150 and forms an image on the detector 20L by the imaging lens 9 installed in the optical path of the detection system L by oblique illumination.
Next, an embodiment of the polarization of the illumination light 11 and the scattered light 12 in FIG. 1 will be described with reference to FIGS.

FIGS. 4, 5, and 6 show the polarization 3 of the optical system of FIG.
FIG. 6 is an optical path diagram in a polarization state showing one embodiment. 4 to 6, the oblique illumination system L and the epi-illumination illumination system H are S-polarized light (linearly polarized light having a vibration component in the X direction).
The pattern 2 on the surface and the scattered light 12 from the foreign matter 13 are a mixture of P-polarized light (linearly polarized light having a vibration component in the Y direction) and S-polarized light. Further, the wavelengths of the illumination lights 15c and 11 of the illumination systems L and H are λ ₁ and λ ₂ , respectively, and the scattered light 12 by the illumination systems L and H is separated by the color separation prism 150 and reaches the detectors 20L and 20H. . The polarized light embodiment shown in FIG. 4 detects both (S + P) polarized lights of the scattered light 12 by the detection systems L and H, and is an example which enables a higher-speed inspection than the second conventional example. In the embodiment of polarized light shown in FIG. 5, a polarizing element 151 such as an analyzer
This is an example in which polarized light is detected, and the discrimination ratio between the foreign substance 13 and the pattern 2 can be improved as compared with the second conventional example. 6 is an example using a dichroic prism 150a having color separation and deflection characteristics, and a color filter 152.
By using in combination with the above, color separation is possible, and this example is also an example in which the discrimination ratio can be improved.

FIGS. 7A, 7B, and 7C are transmission characteristic graphs of the color separation prism 150, the dichroic prism 150a, and the color filter 152 of FIGS. 4, 5, and 6, respectively.
7 (a), 7 (b) and 7 (c), with respect to the wavelengths including the illumination light wavelengths λ ₁ and λ ₂ of the illumination systems L and H of the optical elements of the color separation prism 150, the dichroic prism 15a and the color filter 152. The transmittance T (%) is shown. For the color separation, various configurations such as a combination of a semi-transmissive mirror (or a semi-transmissive prism) and a color filter can be considered.

FIG. 8 is an optical path diagram of an illumination / detection system showing a second embodiment of the method and the apparatus for detecting foreign matter on a patterned wafer according to the present invention. 8, the light shielding plate 18 of the embodiment of FIGS. 1 to 6 is installed below the color separation prism 150, whereas the light shielding plate 18 of the embodiment of FIG. An example in which it is installed above a prism 150 is shown. Thereby, the scattered light 12 from the foreign matter 13 by the oblique illumination system L can be effectively detected by the detection system L without being affected by the light shielding plate 18.

9 (a), 9 (b) and 9 (c) show patterns according to the present invention.
FIG. 9 is a block diagram of an apparatus configuration shown in FIGS. 1 to 8 showing an embodiment of a method for detecting foreign matter on a wafer with attached wafers and an apparatus therefor, and an explanatory view of a method of feeding a sample. FIG. 9 (a),
(B) and (c), the solid-state imaging device of FIG. 9 (a)
20L, 20H output signal ratio V _L / V _H is compared with analog comparison division circuit 100
(Shown in FIG. 17i) and binarizing with the threshold value m by the binarizing circuit 101 (shown in FIG. 17j), the detection sensitivity can be improved as compared with the second conventional example. . In this case, it is necessary to perform analog comparison division in parallel using a plurality of analog comparison division circuits 100 and binarization circuits 101 for the pixels i to n of the solid-state imaging devices (detectors) 20L and 20H. (See Fig. 27). The OR circuit 22 outputs a foreign matter signal (“1” in FIG. 17j) generated in any of the pixels i to n of the detectors 20L and 20H to the foreign matter display circuit 33. Image position 12h of linear laser spot 11f
Are provided with one-dimensional solid-state imaging devices (detectors) 20L and 20H, synchronous scanning of these devices is performed, and scanning is performed in the Y direction by a common drive circuit 202. Further, in combination with the feed in the X direction of the feed stage 220 on which the sample 7 is mounted, the sample 7 can be two-dimensionally scanned. If the sample 7a in FIG. 9B is rectangular, the sample 7a is zigzag-fed in the XY direction. When the sample 7b in FIG. 9 (c) is circular, the longitudinal direction of the linear laser spot 11f is made to coincide with the radial direction of the sample 7b, and the sample 7b is fed linearly in the θ direction. .

FIG. 10 is a block diagram of a signal processing circuit connected to the optical system of FIGS. 1 to 8 showing a third embodiment of the method and the apparatus for detecting foreign matter on a mirror surface according to the present invention. In FIG. 10, the reflected light 11 from the sample 7 having the optical system configuration shown in FIGS.
Reaches detectors 20L and 20H. So calculates the signal V _L + V _H to enter the detector 20L, the output signal V _L of 20H, the V _H to the adder circuit 700,
The binarization circuit 101 binarizes the signal with the threshold value _VTH to obtain a foreign substance signal. As described above, in the present embodiment, the oblique illumination L can effectively detect the scattered light 12 from the foreign matter 13 due to the epi-illumination H, and can completely block the reflected light from the sample surface. It is greatly improved as compared with the second conventional example.

FIG. 11 is a perspective view of an illumination / detection system showing a fourth embodiment of a method and an apparatus for detecting foreign matter on a mirror surface according to the present invention. FIG. 12 is an optical path diagram of the polarization state of FIG. In FIGS. 11 and 12, there is shown an example for further increasing the intensity of the foreign matter scattered light by the epi-illumination H compared to the embodiment of FIG. The elements different from those of the optical system shown in FIGS. 1 to 8 are a polarizing beam splitter 3a and a glass block for correcting an optical path length.
150b. These optical elements are inserted and installed by a switching mechanism (indicated by arrows in and out in the figure). In this case, it is not used for the oblique illumination L.

With the above configuration, the laser light 11 output from the laser light source 1
Is S-polarized light, which passes through the polarizing prism 3a and becomes a laser beam spot 11d in the stop 4a of the field lens 4. The laser beam 11 that has passed through the field lens 4 is a quarter-wave plate 300
And a laser beam spot 11f is formed on the sample 7 by the objective lens 6. When there is no foreign matter 13 on the sample 7, the laser reflected light (zero-order diffracted light) 11 from the sample display passes through the objective lens 6, the quarter-wave plate 300 and the field lens 4 again, and the polarization prism 3a After 100% transmission with
The light is shielded by the eight light shielding portions 18a. Here, the field lens 4
Is the spread 11e of the laser light at the stop 6a of the objective lens 6.
Is image-formed and projected on the light shielding portion 18a. The light shielding plate 18 is formed, for example, on a transparent glass with an opaque film formed at the center to obtain a light shielding portion 18a. Here, the laser illumination light 11 passes through the quarter-wave plate 300,
Further, when the laser reflected light 11 passes, the S
Since the polarization of the reflected light 11 changes to P-polarized light, the reflected light 11 transmits 100% through the polarizing prism 3a.

Further, when there is a foreign substance 13 on the sample 7, when the illumination light 11 irradiates the foreign substance 13, scattered light (higher-order diffracted light) 12 is generated from the foreign substance 13, and the scattered light 12 is spread over the entire surface inside the aperture 6a of the objective lens 6. And returns on the same optical path as the above-mentioned reflected light 11. The surface of the foreign substance 13 has a shape of minute irregularities, and the polarization of the scattered light 12 is eliminated and both the polarizations S and P are present.
The P-polarized light after transmission through the quarter-wave plate 300 is strong, which is transmitted through the polarizing prism 3a, passes through the transmission part outside the light-shielding part 18a of the light-shielding plate 18, is collected by the imaging lens 16, and is detected. Container 20
Leads to H. According to the present embodiment, by replacing the transflective prism 3 with the polarizing beam splitter 3a, the intensity of foreign matter scattered light is more than four times as large as that of the embodiment of FIG.

The color separation prism 15 with the configuration of the optical system shown in FIG. 11 (FIG. 12)
By using 0, in the fifth embodiment using the signal processing circuit of FIG. 10, both effects of the embodiment of FIG. 10 and the embodiment of FIG. 11 can be obtained. In this case, the scattered light 12 of the foreign matter 13 due to the oblique illumination L passes through the quarter-wave plate 300 and then is partially reflected and lost when passing through the polarizing beam splitter 3a. The scattered light 12 of the foreign matter 13 due to H is the same as that of the embodiment of FIG. 11 (FIG. 12), and the scattered light intensity of the foreign matter 13 is further increased as compared with the embodiment of FIG.

FIGS. 13 (a), (b) and (c) are explanatory diagrams of the polarization characteristics of the scattered light 12 from the foreign material 13 due to the oblique illumination L in the embodiment of FIGS. 1 to 12. 13 (a), (b) and (c), FIG. 13 (a) shows scattered light 12 from the foreign material 13 when the oblique illumination light 15c for emphasizing the foreign material 13 on the sample 7 is S-polarized light.
(S), 12 (P), and FIGS. 13 (b), (c),
(D) shows the output signals V _L (S) and V of the detector 20L, respectively.
_L (P) and _VL (P + S). The scattered light 12 generated from the foreign material 13 by the oblique illumination light (S-polarized light) 15c in FIG. 13A includes an S-polarized scattered light 12 (S) and a P-polarized scattered light 12 (P).
When the size of the foreign matter 13 is about 1 μm or less, the scattered light 12 (S) whose polarization does not change is about 10 to 100 times larger than the scattered light 12 (P) whose polarization changes. Figure 13 is a result, the second example of the conventional as an output signal V _L of the detector 20L scattered light 12 of (c)
While the output signal V _L (P) due to (P) is detected, the scattered light shown in FIGS.
Output signal V _L (S), V _L (P by 12 (S), 12 (P + S)
Since + S) can be detected either, the signal intensity of the output signal V _L as compared with the conventional second example becomes larger can increase the S / N ratio of the output signal V _L, enabling high-speed inspection Become.

14 (a), (b), (c) and (d) show FIGS. 1 to
FIG. 12 is an explanatory diagram of directions of scattered light 12 from a foreign substance 13 due to oblique illumination L and epi-illumination H in the embodiment of FIG. FIG. 14 (a) shows forward scattered light 12f and side scattered light 12e from the foreign matter 13 due to the oblique illumination light 15c (11), and FIG. 14 (b) shows the output signal V _L.
(V _H ), and FIG. 14 (c) shows the foreign matter caused by the incident illumination light 11.
Scattered light 12 from 13 shows the (12f + 12e), FIG. 14 (d) are indicative of the output signal V _H. 14 (a) and (b), when the foreign matter 13 in FIG. 14 (a) is a submicron foreign matter of about 0.1 μm, the foreign matter scattered light 12 generated by the oblique illumination light 15c (11) Since the forward scattered light 12f is strong and the side scattered light 12e incident on the objective lens 6 is weak, it is desirable to increase the opening angle α of the objective lens 6 to detect a part of the forward scattered light 12f. The opening angle is limited. The output signal V _L (V _H ) of the detector 20L (20H) for the 0.1 μm foreign matter 13 on the mirror sample in this case in FIG. 14 (b) is small and cannot be detected because a sufficient amount of light cannot be obtained. 14th
Sub-micron foreign matter 13 of FIG.
In the case of the scattered light 12 (12f
+ 12e) can be effectively collected by the objective lens 6 and detected.
Output signal V _H of detectors 20L in this case in FIG. 14 (d) are increased. In the embodiment of the present invention, since the epi-illumination H is used, high sensitivity detection of the minute foreign matter 13 on the mirror surface and detection of the minute foreign matter 13 on the pattern 2 can be performed by the same optical system.

FIGS. 15 (a), (b) and (c) are explanatory diagrams of the experimental results under the illumination / detection conditions of the embodiment of FIGS. 1 to 12, and FIG.
15A and 15B are a top view and a side view showing a state of the circuit pattern 2 and the scattered lights 12P and 12 from the foreign matter 13 by the illuminating lights 15c and 11 on the sample 7, respectively. ) _Shows the experimental data relation diagram of the output signals _VL and VH in that state. In FIGS. 15 (a), (b) and (c), FIG.
(B) is the same as the second example of the related art, but different in that the high tilt angle illumination H is the epi-illumination illumination H. In this case, the output signals _VL and _VH of the pattern 2 of the experimental data of FIG. 15 (c) for the reasons described later with reference to FIGS. 16 (a) to (e) and FIG. The measured values (open circles) are different from those in FIG. 28 (c).
From this experimental result, the slope of the discrimination line m is large (threshold m
Can be detected), so that the measured values (black circles) of the 0.5 μm standard particle foreign material 13 and the submicron real foreign material Q can be detected. The reason will be described with reference to FIGS. 16 (a) to (e) and FIG.

FIGS. 16 (a) to 16 (e) show the magnitude of the intensity of the scattered light from the circuit pattern 2 and the foreign matter 13 on the sample wafer with respect to the irradiation laser beams 15c and 11 of the embodiment shown in FIGS. It is explanatory drawing of a relationship. FIG. 16 (a) shows the intensity ratio of the scattered light (P-polarized light) 12P, 12 caused by the depolarization of the pattern 2 and the foreign substances 13a, 13b, 13c to the oblique illumination light (S-polarized light) 15c. FIGS. 16 (b) and (c) show the intensity ratio between the pattern 2 and the scattered lights 12P and 12 of the foreign substances 13a, 13b and 13c due to the inclination angle φ, and FIG. 16 (c) shows the incident illumination light. (Φ = 90 °) Pattern 2 for 11
This is the case of the intensity ratio between the scattered lights 12P and 12 of the foreign substances 13a, 13b and 13c. FIG. 16 (d) shows the scattered light 12P from pattern 2 here.
And scattered light 12 from a minute foreign substance 13 of about 0.5 μm, and 1 μm
The scattered light intensity of a scattered light 12 from a foreign material 13b having a height of not less than m and the scattered light 12 of a foreign material 13c having a flat and minute unevenness are shown. In FIG. 26 (d), the inclination angle φ is φ
= 0 ° to 5 ° (L), φ = 10 ° to 30 ° (H of the second conventional example), and φ = 90 ° (H of the present invention). Furthermore, φ = 0 ° ～ 5 ° and φ = 10 ° ～
In the case of 30 mm, it is assumed that the scattered light is generated as shown in FIG.
(B) is shown separately. FIG. 16 (e) shows the use conditions of the second conventional example and the embodiment of the present invention. FIGS. 17 (b), (d) and (h) qualitatively show the totals shown in the table separately in FIG. 16 (d).

FIG. 17 shows the conventional second example and the first example based on the results of FIG.
FIG. 12 is an explanatory view showing the difference between the pattern 2 and the foreign matter 13 in the embodiment of the present invention shown in FIGS. In FIG. 17, L (φ
= 0 ゜ -5 ゜), H (φ = 10 ゜ -30 ゜), H (φ = 90)
17) In the case of each illumination light, the scattered light 12P from the pattern 2 shown in FIGS. 17a, 17c, and 17g is small, medium, and large. _L , _VH , _VH (1 pixel) are small, medium, and large. Therefore, the signal ratio V _L / V used in the second conventional example of FIG.
_Since the value of the output signal ratio _VL / VH used in the embodiment of the present invention in FIG. 17i is smaller than the value of _H , the threshold value m for discrimination can be set smaller. As a result the 17th
Since the output signal ratio V _L / V _H of the foreign matter 13a is smaller than the threshold value m in the first example of the prior art in FIG. E, the binarized signal in FIG. 17 In the embodiment of the present invention shown in FIG. I, since the output signal ratio V _L / V _H of the foreign matter 13a is larger than the threshold value m,
The binarized signal in FIG. 17j becomes detectable.

In the case of the foreign matter 13b shown in FIGS. 17a, c and g, FIG. 16 (b)
Since the illumination light 15c hits a large area in the side view of the foreign matter 13b caused by the inclination angle illumination as described above, the scattered light intensity is particularly large in FIGS. 17a and 17c, and therefore the output signals of FIGS. V
_L and _VH increase. Also, in the case of the foreign matter 13c shown in FIGS. 17a, c, and g, due to minute irregularities as shown in FIG.
Scattered light intensity due to polarization increases, and
The output signals V _L and V _{H of} FIGS. From this result the 17th
The output signal ratio V _L / V _H in the case of foreign substances 13b and 13c in FIGS. E and i is larger in the embodiment of the present invention in FIG. 17i than in the second conventional example in FIG. Therefore, there is a margin for discrimination from the pattern 2. As described above, in the embodiment of the present invention, since the high-inclination illumination H of the second conventional example is the epi-illumination H, the threshold value m for discrimination can be set small, so that there is a margin for discriminating the pattern 2 and the foreign matter 13. If the detection of foreign matter of 1 μm or more is sufficient, the depolarization phenomenon does not have to be used for the illumination / detection (analysis) of the low-inclination angle illumination L. The reason and effect are explained first in Chapter 13.
It was explained in the figure.

FIG. 18 is an explanatory diagram of a polarization state usable in the illumination / detection system of the other embodiments of FIGS. In FIG. 18, the polarization conditions of the illumination and detection system of the present invention are oblique illumination L (wavelength λ ₁ ) and epi-illumination H (wavelength λ ₂ ), and cases I, II, and I
Illumination and polarization S, P, S + P of illumination L, H of the detection system are shown in the table for each of (a), (b), (c),. The polarization conditions within the broken line in the figure indicate the range of use under the same polarization conditions as the second conventional example shown in FIGS. 25 and 26. However, in the embodiment of the present invention, the range of various polarization conditions is different. Can be spread. 18th
FIGS. 19 and 20 show optical path diagrams of the polarization state within the broken line in the figure.

FIGS. 19 and 20 are optical path diagrams in the same range of polarization as FIGS. 25 and 26 which can be used in the illumination / detection systems of the other embodiments of FIGS. 19 and 20, the difference from FIGS. 25 and 26 is that the S, P, S + P polarized light S (H), P (H), S + P (H) of the high tilt angle illumination H.
Are S, P, S + P polarized light S (H), P (H), S + P of epi-illumination H
(H). 19 showing the inside of the broken line in FIG.
If the polarization conditions in the range of FIG. 20 and FIG.
Foreign matter of 5 μm or less can be detected.

In the above embodiment, the case where the target object is a semiconductor wafer has been described. However, the present invention is not limited to the wafer and can be applied to inspection of other products such as a photomask and a reticle.

In the above embodiment, when the 0.5 μm foreign matter is discriminated from the pattern, the size of the light receiving portion of each pixel is 5 × 5 μm ²
Performs high-sensitivity inspection without degrading high-speed performance by using a plurality of photoelectric conversion solid-state imaging devices of about (converted on the sample) or less and simultaneously performing parallel comparison processing of output signals from each device. It is effective in that it can be done.

Also, the pixel size limit is 1.5 x 10 μm ²
It has been confirmed by experiments that the detection of a foreign substance of μm to 2 μm is practically practical.

Further, the one-dimensional solid-state imaging devices 20L and 20H have been described as the parallel type devices, but a serial output type device such as a CCD (Charged Coupled Device) may be used.

〔The invention's effect〕

Advantageous Effects of Invention According to the present invention, there is an effect that detection of a minute foreign substance existing on a target object can be performed with high sensitivity and stability while maintaining high speed of foreign substance detection.

[Brief description of the drawings]

FIG. 1 is a perspective view of an optical system showing a first embodiment of the present invention,
2 (a) to 2 (f) are side views, plan views and partial cross-sectional views of the optical path of the epi-illumination system of FIG. 1, and FIGS. 3 (a) to 3 (g).
4 is a side view, a plan view, and a partial cross-sectional view of an optical path of the scattered light detection system shown in FIG. 1, and FIGS. 4, 5, and 6 are optical paths of polarized light of three embodiments of the optical system shown in FIG. Figures, FIGS. 7 (a)-(c)
Is a transmission characteristic graph of the optical element shown in FIGS. 5 and 6, FIG. 8 is an optical path diagram of an optical system showing a second embodiment of the present invention, and FIGS. 9 (a) to 9 (c) are diagrams of the present invention. FIG. 10 is a block diagram of a signal processing circuit showing a third embodiment of the present invention, and FIG. 11 is a block diagram of a signal processing circuit showing a third embodiment of the present invention. FIG. 12 is a perspective view of an optical system, FIG. 12 is an optical path diagram of polarized light in FIG. 11, and FIGS. 13 (a) to 13 (d) are FIGS.
14 (a) to 14 (d) are explanatory diagrams of directions of scattered light by oblique illumination and epi-illumination in FIGS. 1 to 12. FIG. FIGS. 15 (a) to (c) are explanatory diagrams of the experimental results under the illumination / detection conditions of FIGS. 1 to 12, and FIGS. 16 (a) to (e) are the scattered lights of FIGS. 1 to 12. Explanatory diagram of strength, FIG. 17 is an explanatory diagram of a discrimination method according to FIG. 16,
FIG. 18 is an explanatory diagram of other usable polarized light in FIGS. 1 to 12, and FIGS. 19 and 20 are optical path diagrams of other usable polarized light in FIG. 1 to FIG. 22 (a) to 22 (c) are explanatory diagrams of the detection principle of the first conventional example, FIGS. 22 (a) and 22 (b) are perspective views and a discrimination ratio graph of the optical system in FIG. 21, and FIG. Second
24 (a) to (g) are explanatory diagrams of output signals and the like in FIG. 23, FIGS. 25 (a) to (h), and FIGS. 26 (a) to (d). ) Is the optical path diagram of the polarized light in FIG. 23, and FIG.
28 (a) to (c) are circuit diagrams of the signal processing circuit shown in FIG.
FIG. 23 is an explanatory view of the experimental results of the illumination / analysis conditions, and FIGS. 29 (a) and (b) are the characteristic diagrams of the output signal ratio of FIG. FIG. 30 (a),
28B is a diagram showing the characteristic of the output signal difference in FIG. 28C and a circuit diagram of the analog comparison and subtraction circuit. DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2 ... Pattern 3 ... Semi-transmissive prism 3a ... Polarizing prism (or polarizing beam splitter) 4 ... Field lens, 6 ... Objective lens 7 ... Sample ( Substrate), 9,16 Image forming lens 11 Illumination light (or reflected light) 12,12p, 12f, 12e Scattered light 13,13a, 13b, 13c Foreign matter 14 Cylindrical lens 15 Polarized laser light source, 15b Condensing lens 18 Shield plate 20, 20L, 20H One-dimensional solid-state imaging device (detector) 21 Condensing lens 22, OR circuit 23 Foreign object memory , 30 ... Auto focus sensor 31 ... Motor drive circuit 32 ... Controller (microcomputer) 33 ... Foreign matter display circuit 43 ... Motor for Z drive 47,50 ... Feed motor 49 Leaf spring 100 Analog division circuit 101,104 Binarization circuit 103 AND circuit 105 Analog subtraction circuit 150 Color separation (color separation) prism 150a Dichroic prism (or color separation prism, polarizing beam splitter, or light splitting prism) 150b Glass block 151 Polarizing element (analyzer) 152 Color filter 202 Drive circuit 220 Feeding stage , 300 ... 1/4 wavelength plate 700 ... Adder circuit

Continuation of front page (56) References JP-A-61-104243 (JP, A) JP-A-1-217243 (JP, A) JP-A-61-228332 (JP, A)

Claims (9)

(57) [Claims] An oblique illumination of a desired region of the surface of the sample having a concavo-convex pattern on the surface with light having a first wavelength from a direction inclined with respect to the surface of the sample; The desired region is epi-illuminated with light having a second wavelength different from the first wavelength from a direction substantially perpendicular to the surface of the sample, and the oblique illumination is performed by oblique illumination with light having the first wavelength. The scattered light generated from the desired area is separated from the scattered light by the light having the second wavelength and detected and detected.
And the scattered light generated from the desired area is separated from the scattered light by the light having the first wavelength by epi-illumination with the light having the second wavelength, and the 0th-order diffracted light is shielded and detected. By obtaining a second detection signal, and comparing the value of the ratio of the first detection signal to the second detection signal with a preset value, the scattered light from the concavo-convex pattern and the scattered light from the foreign substance are reduced. A foreign matter smaller than 0.5 μm present on the surface of the sample including the uneven pattern is detected. 2. The system according to claim 1, wherein the second detection signal is obtained by blocking specularly reflected light of the scattered light generated from the desired area by the epi-illumination and detecting the scattered light.
Foreign matter inspection method described. 3. The foreign matter inspection method according to claim 1, wherein the light having the first wavelength for the oblique illumination is incident on the surface of the sample at an angle of 5 degrees or less. 4. The foreign matter inspection method according to claim 1, wherein the illumination light for oblique illumination and the illumination light for epi-illumination are polarized laser lights. 5. An oblique illumination means for illuminating a desired region of the surface of the sample having a concavo-convex pattern with light having a first wavelength from a direction inclined with respect to the surface of the sample, Epi-illumination means for illuminating the desired region of the surface with light having a second wavelength different from the first wavelength from a direction substantially perpendicular to the surface of the sample, and the oblique illumination means A first scattered light detecting unit that separates and detects a scattered light generated from the desired area from a scattered light by the light having the second wavelength and outputs a first detection signal; A second scattered light detector that separates the scattered light illuminated and generated from the desired area from the scattered light by the light having the first wavelength, shields and detects the zero-order diffracted light, and outputs a second detection signal; Means and the first scattered light detection means The value of the ratio between the applied first detection signal and the second detection signal output from the second scattered light detection means is determined, and the value of the ratio is compared with a preset value to obtain the ratio from the concavo-convex pattern. A signal processing means for distinguishing the scattered light from the scattered light from the scattered light from the foreign matter and detecting a foreign matter smaller than 0.5 μm on the sample surface. 6. The foreign matter inspection apparatus according to claim 5, wherein said first scattered light detection means includes an imaging optical system for detecting an image of said desired area. 7. The image forming apparatus according to claim 1, wherein said second scattered light detecting means includes an image forming optical system for blocking specularly reflected light from said desired area and detecting an image of said desired area. The foreign matter inspection device according to claim 5. 8. The foreign matter inspection apparatus according to claim 5, wherein said oblique illumination means and said epi-illumination means respectively irradiate polarized laser light to said sample surface. 9. The foreign matter inspection apparatus according to claim 5, wherein the oblique illumination means causes the light having the first wavelength to enter the surface of the sample at an angle of 5 degrees or less.