JPH03102249A - Method and apparatus for detecting foreign matter - Google Patents

Abstract

PURPOSE:To inspect the fine foreign matter on a sample at a high speed by discriminating the same from a pattern by alternately performing the first and second illuminations in a time sharing manner and detecting the scattering beam from an objective body in a time sharing manner in synchronous relation to both illuminations by one photoelectric converter. CONSTITUTION:An oblique illumination system L performing oblique illumination is constituted of a laser beam source 15 and a condensing lens 15b. A vertical illumination system H performing linear vertical illumination (second illumination) is constituted of a laser beam source 1, a condensing lens 21, a cylindrical lens 14, a translucent prism 3, a field lens 4 and an objective lens 6. Detection systems L, H are constituted of a shield plate 18, an image forming lens 16, a unidimensional solid-state imaging device (detector) 20 and a signal processing circuit 300. The scattering beams generated by the illumination systems L, H pass through the objective lens 6, the translucent prism 3 and the shield plate 18 to be formed into an image on the detector 20. The first and second illuminations are performed in a time sharing manner to emit beams in a pulsating manner and, by synchronously detecting the outputs VL, VH of the detector 20, scattering beams due to two kinds of illumination beams can be separated and detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a foreign matter inspection method and apparatus for detecting foreign matter on semiconductor LSI chips or masks, and particularly relates to
The present invention relates to a foreign matter detection method and apparatus suitable for foreign matter inspection that detects small foreign matter on patterned wafers, etc. at high speed and with high sensitivity during intermediate manufacturing steps.

[Conventional technology]

Inspection of foreign substances on patterned wafers in the intermediate process of conventional LSI manufacturing is essential for improving product yield and reliability. This foreign object inspection method and apparatus for automatically detecting minute foreign objects on a patterned wafer are disclosed in Japanese Patent Application Laid-open No. 104243/1983, using illumination L that has a large scattering effect on foreign objects and scattering. A small effect light F! Two types of AH illumination are performed, and the ratio of the scattered light signals due to illuminations L and H is detected, noting that the scattered light caused by illumination L is likely to be generated by foreign objects, and the scattered light caused by illumination H is likely to be generated by patterns. This allows for stable and highly sensitive detection of minute foreign matter. In addition, as a scattered light detector, multiple photoelectric conversion solid-state image sensors with a light receiving area of each pixel having a size of approximately 5 x 5 μm2 (converted to the sample surface) or less are used, and the output from the light receiving area of each pixel is simultaneously detected. By performing parallel comparison processing, foreign matter inspection can be performed with high sensitivity without deteriorating high speed. Next, an example in which the above-mentioned conventional technique is further developed will be explained with reference to FIGS. 11 to 14.

FIG. 11 is a perspective view of an illumination/detection system showing a further developed example of the conventional foreign matter inspection method and apparatus. In the gu diagram, conventional illumination L and H are each equipped with oblique illumination. Wr.
An example of development using incident illumination will be shown. For example, oblique S-polarized illumination 15c (wavelength
, ) to the same sample point, and color separation prism 150 and analyzer 151 L . At 151H, only the P-polarized component of the scattered light 12 is detected by detectors 20L and 20H and compared.

FIG. 12 is an explanatory diagram of the principle of foreign object detection in FIG.
The valorization method is shown. FIG. 12a shows a foreign object 13a. 13b is present, for example, a Si wafer is irradiated with oblique S-polarized light 8A15C, and FIG. 12b shows the output signal V in that case.
12C shows its binary signal Sd. In this case, the scattered light 1 is the same as the pattern scattered light 12 p.
The minute foreign matter 13 that causes 2 is undetectable. Figure 12d
12 shows the case where the same place is irradiated with the epi-projection S-polarized illumination 11, and FIG. 12e shows the output signal v1 in that case. 12th
Figure f shows the ratio Vr,7'hr of the two output signals VL*Vi.
FIG. 12g shows its binary signal Sd. This makes it possible to detect small foreign objects 13a.

FIG. 13 is a block diagram of the signal processing circuit of FIG. 11. In FIG. 1813, the output signals Vr-+Vit of the detectors 20L and 20H are used to calculate a signal ratio Vc/Vx in an analog comparison calculation circuit 100 for each corresponding pixel, and are binarized in a binarization circuit 101. The output of the binarization circuit 101 is OR
The circuit 102 calculates the logical sum, and if there is a value of '1', it is stored in the foreign object memory.As described above, the two detectors 20
L. 20H needs to accurately detect the same point on the sample.

FIG. 14 is an explanatory diagram of the problem in FIG. 11. In FIG. 14, two detectors 20L. If the detection point on the sample of 20H is shifted, pattern 2 or foreign matter 13a
．． 13b may be different or a time lag may occur, making it impossible to perform accurate comparison calculations and deteriorating foreign object detection sensitivity. However, two detectors 20L. Since it is extremely difficult to accurately align the 20H, it is difficult to avoid deterioration in foreign object detection sensitivity. Moreover, even if alignment is performed once, the detectors 20L and 20H
Occurrence of slight positional deviation (drift) cannot be avoided. There are also two detectors 20L. 20H sensitivity adjustment is required.

Furthermore, the detectors 20L and 20H have parallel outputs, and 2
one detector 20L. Since 20H is used, the scale of the signal amplification circuit required for each pixel becomes large.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into account the positional deviation of the two detectors, and has problems such as deterioration of foreign object detection sensitivity.

The purpose of the present invention is to eliminate deterioration in foreign object detection sensitivity caused by detector positional deviation errors and sensitivity adjustment errors, and to detect minute foreign objects in the size of a 0.5μ groove on a patterned sample using a simple circuit configuration. It is an object of the present invention to provide a method and apparatus for inspecting foreign substances that can be separately inspected at high speed.

[Means to solve the problem]

In order to achieve the above object, the foreign object detection method and apparatus according to the present invention alternately perform the first illumination and the second illumination in a time-sharing manner, and use one photoelectric conversion element to perform the first and second illumination. Foreign matter on the target object is detected by synchronously detecting scattered light from the target object in a time-division manner.

[Effect]

The foreign object detection method and device described above perform the first illumination (oblique illumination) and the second focusing illumination (epi-illumination) in a time-sharing manner in a pulsed manner, and perform the second illumination in synchronization with the first and second illumination. 1 TeruF! A(
Scattered light detection using oblique illumination and second illumination (epi-illumination)
Since the detection of scattered light and the detection of scattered light can be performed using the same photoelectric conversion element (detector), deterioration in foreign object detection sensitivity can be eliminated.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 1O.

FIG. 1 is a perspective view of an illumination/detection system showing an embodiment of the foreign object detection method and apparatus according to the present invention. In FIG. 1, the oblique illumination system L that performs oblique illumination (first illumination F!A) on the sample 7 includes a laser light source 15 and a condenser lens l5b.
It consists of Linear epi-illumination (second
The aerial illumination system H that performs the illumination) is composed of a laser light source 1, a condenser lens 21, a cylindrical lens 14, a semi-transparent prism 3, a field lens 4, and an objective lens 6. Detection system L. H is a light-shielding plate 18 having a light-shielding portion 18a that shields zero-order diffracted light, an imaging lens 16,
One-dimensional solid-state image sensor (detector) 20 and signal processing circuit 3
00.

In the above configuration, the epi-illumination system H uses the cylindrical lens 14, which is an optical element that focuses light into a linear shape, to focus the laser illumination light l1 on the linear spot t-11f on the sample 7, so that Y Directional scanning becomes unnecessary. When the laser light l1 from the laser light source l passes through the condensing lens 21j} and passes through the cylindrical lens 14, it forms a linear laser spot 11o. Further, the laser beam l1 reflected by the semi-transparent prism 3 forms a linear spot 11d within the aperture 4a of the field lens 4, and a linear spot within the aperture 6a of the objective lens 6.

After passing through the objective lens 6, a linear spot l1 appears on the sample 7.
f is focused. Lighting system L. The scattered light generated by H passes through the objective lens 6, the semi-transparent prism 3, and the light shielding plate 18, and then is focused on the detector 2o by the imaging lens 16.

This oblique illumination uA (first illumination) and epi-illumination illumination (second illumination) are emitted in pulses in a time-division manner, and the output Vt of the detector is
*By synchronously detecting Vx, it is possible to separately detect scattered light caused by two types of illumination light.

2 to 5 are optical schematic diagrams of the polarization state of the illumination/detection system showing an embodiment of the foreign object detection method and apparatus according to the present invention. In the embodiment of FIG. 2, the illumination light l1 and the scattered light l of FIG.
The second polarization state will be explained. Oblique illumination system L and epi-illumination system H
is S-polarized light (linearly polarized light with some vibration in all X directions), and J! Scattered light from objects and patterns 12
is P polarized light (linear polarized light with a vibrational component in the Y direction) and S@
It becomes a mixture of i light. In this example, the detector addition is the total scattered light (
In order to detect S-polarized light (10P-polarized light), the amount of scattered light detected is large and high S/N detection is possible, making high-speed inspection possible.

The embodiments shown in FIGS. 3 to 5 are 1
This is an example of improving the discrimination ratio between four objects and patterns. In the embodiment shown in FIG. 3, a polarization probe 151 such as an analyzer is installed in the detection system H to detect only the P-polarized component of the scattered light l1, making it possible to improve the discrimination ratio between foreign objects and patterns. . In the *m example in FIG. 4, a polarizing beam splitter 150 m is used instead of the polarizing element 151 in FIG. The amount of detected light can be increased and high S/N detection becomes possible.

In the embodiment shown in FIG. 5, the oblique illumination system L and epi-illumination system H have different wavelengths λ1, λ! This is an example in which a dichroic mirror 150 m having color separation and polarization characteristics is used, and by combining it with a color filter 152, the illumination system L#H (7J) scattered light can be separated.

In this embodiment, since the light shielding plate 18 is installed only on the side where the scattered light (λ,) detected by the epi-illumination system H is detected, the amount of scattered light detected by the oblique illumination system L can be obtained. The scattered light branched by the dichroic mirror 150a passes through mirrors 154, 155 and a semi-transparent prism 153 and enters the detector 2o.

In this embodiment as well, the discrimination ratio between foreign matter and patterns can be improved.

FIGS. 6(a) to 6(C) are explanatory views of the emission timing of the laser light sources shown in FIGS. 1 to 5. FIGS. Figure 6(a)-(d)
In the embodiments shown in FIGS. 1 to 5, oblique illumination and epi-illumination are emitted in a pulsed manner in a time-division manner, and the output Vz . By synchronously detecting Vx, both scattered lights are detected separately, and FIG. 6 (&) shows the pixel size 2.
0.5μ inside the detector 4 of 5μmo (converted to the sample surface)
Fig. 6(b) shows the change in the light intensity of the scattered light signal Vz * Vz at that time, and i@6(e) shows the oblique illumination L and epi-illumination, respectively. It shows the timing for time-divisionally illuminating the L. The H lights are shifted and emitted alternately so as not to overlap. Since this interval Δt is short, a semiconductor laser that can be driven at high speed is suitable for the laser light source 15.1.

FIG. 7 is an explanatory diagram of the timing of light emission and detection in FIGS. 1 to 5. In Fig. 7, Fig. 7 a to e show cases where two illuminations are performed consecutively, and Fig. 7 a shows pattern 2.
and foreign matter 13a. For example, the case where the oblique illumination laser beam 15a is irradiated onto the St wafer where the wafer 13b is present is shown.
FIG. 7b shows the output signal VL at that time. FIG. 7C shows the case where epi-illumination laser light 11 is irradiated to the same location,
FIG. 7d shows the output signal v1 at that time. Figure 7 ● is 2
The ratio vL/vH of two output signals is shown.

Figures 7f to 0 show the case where the two illuminations of the present invention are performed in a time-sharing manner in a pulsed manner, Figure 7f shows the light emission timing of the oblique illumination 15C, and Figure 7g shows the continuous illumination. FIG. 7h shows the output signal VL' when illumination is performed at the light emission timing. Figure 7i shows the light emission timing of the epi-illumination 11, Figure 7j shows the output signal Vl when continuous illumination is performed, and Figure 7k shows the output signal Vl' when illumination is performed at the same light emission timing. show.

Figure 7 t shows the illumination L. Indicates the output signal VL' + VH' of detector 4 when H is illuminated at that emission timing,
@7 Figure m shows a signal obtained by sampling and holding the output signal VL/+V,/. Figure 7n shows the sample.
The signal ratio vL'/vH' obtained using the hold signal is shown, and FIG. 70 shows the foreign object signal Sd obtained by binarizing this signal ratio Vz'/VH'.

FIG. 8 is an explanatory diagram of the duty of the timing of light emission and detection in FIGS. 1 to 5. In FIG. 8, since electrical delays generally occur in the detector 20 and the signal processing circuit 300, two lights L. In order to accurately detect the light scattered by H and obtain the output signal VL*Vx, the duty of the light emission timing Tz*Tz must be set to 50 degrees or less. Using the sample pulses SL and SI synchronized with this light emission timing TLmTy, the output signal Vz +
By sampling and holding Vg, the output signal V
L' s Vx' can be obtained.

FIG. 9 is a block diagram of a drive circuit and a signal processing circuit 30 showing an embodiment of the foreign object detection method and apparatus according to the present invention. In FIG. 9, the timing generation circuit 20
0 is a laser starting timing pulse TL*Tx given to the laser drive circuits 15a, lm, and the laser light sources 15,1
emit light in a time-divided manner. Timing pulse Tg #T
x is simultaneously given to the signal separation circuit 201, separated into the output signal Vz * Vz of the detector, and sent to the hold circuit 202L.
The scattered light signal vL' at the oblique illumination timing TL is held, and the hold circuit 202H outputs the epi-illumination timing T.
The scattered light signal VI' of z is held. Scattered light signal vz
The signal ratio vL'/vI' is calculated from '+Vx' by the analog comparison calculation circuit 100, and the signal ratio vL'/vI' is converted to 2{It by the threshold value m by the binarization circuit 101, whereby a signal indicating the detection of the foreign object 13 is obtained. In this case, for the image gL-H of the detector 20, the analog comparison calculation circuit 100 and the binarization circuit 101
By using multiple units and processing them simultaneously in parallel, high-speed and highly sensitive foreign object detection is possible. The OR circuit 22 is the detector 2
A foreign object signal detected by any of pixels i to n of 0 is output and stored in a foreign object memory.

FIG. 10 is a block diagram of an apparatus configuration showing an embodiment of the foreign object detection method and apparatus according to the present invention. In FIG. 10, the sample 7 is fixed to a feed stage 220 and can be moved in the X and Y directions by motors 47 and 50. Further, the feed stage 220 is held via a plate spring 49, and is movable in the vertical direction (Δ2) by the motor 6. The height of the sample surface is measured using an automatic focus sensor, and a motor drive circuit 31 drives a motor mallet to control Δ2 so that the sample surface comes to the focal position of the objective lens 6. The microcomputer 32 controls the motor 47. 50 to drive the feed stage 220 in order to inspect the entire surface of the sample.

Further, the microcomputer 32 outputs the output signal of the OR circuit n of the signal processing circuit blade to the foreign object display circuit O.

In the above embodiment, the analog comparison calculation circuit 202 is used, but the outputs of the detector circuits 2t to n are A/D converted,
Holding, comparison, and binarization can also be performed digitally.

According to the above embodiment, since the number of detection circuits can be reduced to one, it is possible to eliminate the deterioration in the foreign object detection sensitivity caused by the positioning error l. Also, by integrating the detection circuit into one,
It becomes possible to reduce the scale of circuits such as analog amplifiers.

〔Effect of the invention〕

According to the present invention, it is possible to stably and highly sensitively detect minute foreign objects present on a target object while maintaining the high speed of detecting foreign objects such as patterned wafers.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an illumination/detection system showing an embodiment of the present invention, FIGS. 2 to 5 are light M diagrams of polarization states of the illumination/detection system of an embodiment of the present invention, and FIG. Figure 6 (&) to (c) are the first
Figures ~, 11! Explanatory diagram of the emission timing of the laser light source in Figure 5, Figure 7. FIG. 8 is an explanatory diagram of the timing of light emission and detection in FIGS. 1 to 5, FIG. 9 is a block diagram of a circuit showing an embodiment of the present invention, and FIG. 10 is a diagram showing an embodiment of the present invention. A block diagram of the device configuration, FIG. 11 is a perspective view of the illumination/detection system showing a conventional development example, FIG. 12 is an explanatory diagram of the detection principle of FIG. 1l, and FIG. 13 is a block diagram of the circuit of FIG. 11. , 1st
FIG. 4 is an explanatory diagram of the problem in FIG. 11. l...Laser light source 2...Pattern 3...
Semi-transparent prism 4...Field lens 6...
Objective lens 7...Sample l1...Illumination light
12...Scattered light 13. 13 a. 1
3 b - Foreign matter 15 - Laser light source 15 b.
...Condensing lens 15 C... Teruo Hikari l6...
Imaging lens 18... Light shielding plate processing... Detector
21... Condensing lens 22... OR circuit
Power...Signal processing circuit 100...Analog comparison calculation circuit 101...Binarization circuit i50a...Dichroic mirror 151...Polarizing element (analyzer) 152...Color filter 153... Semi-transparent prisms 154, 155...Mirror 200...Timing generation circuit 202...Hold circuit 300...Signal processing circuit II-4t Ka 10 figure Y 6 figure 1 Box 3 figure 30 Figure 11 Clan 12 figure L Eye 1 figure running eating method q (X) Male 1 j figure m

Claims (1)

[Claims] 1. A foreign substance on the target object is emphasized by the first illumination and detected by the photoelectric conversion element, a background on the target object is emphasized by the second illumination and detected by the photoelectric conversion element, In a foreign object detection method in which a foreign object on a target object is revealed and detected using a detection signal obtained by a first illumination and a detection signal obtained by a second illumination, the first illumination and the second illumination are alternated in a time-sharing manner. A method for detecting a foreign object, characterized in that detection using the first illumination and the second illumination is performed in a time-sharing manner using one photoelectric conversion element in synchronization with the first illumination and the second illumination. 2. The foreign matter on the target object is emphasized by the first illumination means and detected by the photoelectric conversion element, the background on the target object is emphasized by the second illumination means and detected by the photoelectric conversion element, and the first illumination In a foreign object detection device, the foreign object detection device has a means for detecting a foreign object on a target object by making it visible based on a detection signal obtained by the first illumination means and a detection signal obtained by the second illumination means. means for driving alternately in divisions;
Foreign matter characterized by having means for time-sharing detection by the first illumination means and the second illumination means in synchronization with the driving of the first illumination means and the second illumination means using two photoelectric conversion elements. Inspection equipment.