JPH04324653A - Dust particle inspection equipment - Google Patents

Abstract

PURPOSE:To detect dust particles adhered on the surface of an object to be tested independently of grain diameters, by performing inspection using laser rays having a plurality of mutually different wavelengths. CONSTITUTION:A wafer 1 is irradiated with laser rays having at least two kinds of wavelengths from laser oscillators 2a, 2b. Scattered rays of the respective wavelengths are detected by detectors 3a, 3b and detectors 4a, 4b, and subjected to photoelectric conversion. Each of the outputs are compared by comparators 5a, 5b, 5c, 5d using previously set threshold values. Logical add of the respective outputs of comparison results for every wavelengths is obtained by an OR circuit 6, thereby attaining final detection results.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting minute foreign matter, and more particularly to a technique that is effective when used to detect foreign matter by irradiating the surface of a wafer or the like with a laser beam.

0002

2. Description of the Related Art For example, there is a method that uses a scattering phenomenon of laser light as a means for detecting minute foreign particles in the form of particles adhering to the surface of a wafer. This method scans a predetermined part of a wafer rotating within a predetermined plane while irradiating a laser beam of one type of wavelength to detect scattered light from foreign objects on the wafer surface. A foreign object is detected when the detected value exceeds the threshold value.

Regarding this type of device, for example, “
Hitachi Review vol. 65, No. 7 (1983)” P39
~P42 "Detection of fine particles by surface inspection device".

0004

[Problems to be Solved by the Invention] According to the studies of the present inventors, when irradiating laser light with one type of wavelength, detection characteristics for foreign particles having a particle size approximately equal to the wavelength of the irradiated laser light are detected. The inventors have discovered that the sensitivity decreases and there is a risk of missing foreign objects. In particular, there was a tendency for the phenomenon to appear more prominently in spherical particles such as standard particles.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a technique that can detect foreign substances adhering to the surface of an object to be inspected, regardless of particle size.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0007]

[Means for Solving the Problems] Among the inventions disclosed in this application, a brief overview of typical inventions will be as follows.
It is as follows.

That is, at least 2
a laser beam generating means for irradiating laser beams with different wavelengths;
a detection means for detecting scattered light at each wavelength and photo-electrical conversion; a comparison means for comparing the output at each wavelength of the detection means using a preset threshold value and outputting a comparison result for each wavelength; A logic means for calculating the logical sum of the outputs of the respective comparison means is provided.

[0009]

[Operation] According to the above-mentioned means, by irradiating the object to be inspected with a plurality of laser beams of different wavelengths and taking the logical sum of the detection results for each of them, a plurality of sensitivities with different drop regions of sensitivity characteristics are obtained. Properties can be synthesized. Therefore, it is possible to compensate for the sensitivity reduction region specific to each wavelength and make the apparent sensitivity characteristic into a direct proportional curve, making it possible to detect all foreign substances that were previously overlooked by inspection using a single wavelength. Become.

0010

Embodiment 1 FIG. 1 is a block diagram showing a foreign matter inspection apparatus according to the present invention.

Two laser generators 2a and 2b (laser light generating means) having different wavelengths are disposed above the wafer 1, which is an object to be inspected, and the laser generator 2a irradiates the wafer 1 obliquely above the wafer 1. Detector 3a detects scattered light for
, 3b (detection means) are arranged at the target position, and similarly, detectors 4a and 4b (detection means) which are adjacent to the detectors 3a and 3b and detect the scattered light in response to the irradiation of the laser generator 2b are arranged at the target position. It is arranged. Detectors 3a, 3b, 4a,
Comparators 5a, 5b, 5c, and 5d (comparison means) are connected to each of 4b, and each output has an OR (
An OR) circuit 6 (logic means) is connected. In addition, each of the comparators 5a, 5b, 5c, and 5d has threshold values Vr1, Vr2, Vr3, and Vr for comparison with the input.
Each of r4 is input. This threshold value is set to a voltage value corresponding to the minimum value of the particle size to be detected. When setting the threshold value, the sensitivity characteristics of the detector (the relationship between the detection signal intensity and the particle size) are determined in advance. Sensitivity characteristics can be determined by applying polystyrene latex of various particle sizes to a wafer and determining the detection power at that time.

In this embodiment, a He--Ne laser with a wavelength of 0.633 μm is used as the laser generator 2a.
An Ar laser with a wavelength of 0.488 μm is used as the laser generator 2b.

Next, the operation of the embodiment having the above configuration will be explained.

Laser beams sequentially emitted from the laser generators 2a and 2b are irradiated vertically onto the surface of the rotating wafer 1, and scattered light generated by the irradiation is detected by the detector 3a.
, 3b and detectors 4a, 4b, and are converted into electrical signals. Detectors 3a and 3b have detection characteristics shown in FIG. 2, and detectors 4a and 4b have detection characteristics shown in FIG. 3. As shown in each figure, the detection signal intensity with respect to the particle size (μmφ) of the object to be detected is nonlinear, and there is a region where it decreases midway. This is due to the fact that scattering becomes less likely to occur depending on the particle size, but if a threshold is set at the area where the detection characteristics decrease, there is a risk that foreign objects may not be detected at the area where the detection characteristics decrease below this threshold. There is.

However, as is clear from FIGS. 2 and 3, this region of reduced detection intensity varies depending on the wavelength. Therefore, in the present invention, by utilizing this characteristic, the wavelengths of the laser beams of the laser generators 2a, 2b and the detectors 3a, 3b are made to be different, so as to compensate for the region in which the detection characteristics deteriorate, and as shown in FIG. By preventing a drop in the particle diameter value, the detection signal intensity is made to be proportional to the particle size value.

That is, the signals detected by the detectors 3a and 3b are compared using threshold values Vr1 and Vr2, and input signals (output signals of the detectors 3a and 3b) exceeding the thresholds are applied to the OR circuit 6. , the signals detected by the detectors 4a and 4b are compared using thresholds Vr3 and Vr4, and input signals equal to or higher than the thresholds are applied to the OR circuit 6.

The OR circuit 6 takes the logical sum of four inputs and outputs the result.

Through such processing, the detectors 3a, 3b
The detected image 7 finally obtained based on is as shown in FIG. The detected image is a detected image 9, which is a composite of the detected image 7 and the detected image 8. As a result, it is possible to reduce the chance of missing foreign objects in the areas where the detection characteristics are degraded (hatched areas) shown in FIGS. 2 and 3.

In the above embodiment, a pair of detectors (a, b) are provided on the left and right for each wavelength.
A simple configuration with one detector each may be used. In this case, the comparators 5a to 5d can be divided into two, and the OR circuit 6 can be divided into two.
It can be the input one. Furthermore, the type of wavelength is changed to 2.
However, the number of types is not limited to this, and three or more types may be used.

Furthermore, in the above embodiment, the comparators 5a to 5d
Although an independent threshold value is set for each of the detection sensitivities, a common threshold value can be given to those having the same detection sensitivity.

[0021]

Embodiment 2 FIG. 6 is a front view showing the configuration of the main parts of a second embodiment of the present invention.

In the above embodiment, two laser generators are used.
Although the types (laser generators 2a, 2b) are provided,
It is also possible to obtain two types of wavelengths with one laser generator 10. In this case, a nonlinear optical element 11 (for example, an inorganic crystal such as KDP) is inserted into the optical path of the laser beam, and wavelength conversion can be performed by controlling the applied voltage. Since the irradiation intensity changes due to wavelength conversion, it is also necessary to provide a control means to maintain the same irradiation intensity at any wavelength. Note that 12 in the figure is a slit.

[0023]

Embodiment 3 FIG. 7 is a front view showing the configuration of the main parts showing a third embodiment of the present invention.

In the embodiment shown in FIG. 1, two types of laser generators are placed adjacent to each other, and the conveyance is not carried out until the foreign object inspection is completed directly below them, but in this embodiment, the laser generator is placed at the initial position. The first wavelength (0.633 μm) is detected by the laser generator 2a and the detectors 3a and 4a, and then the wafer 1 is transferred to the laser generator 2b and the detectors 3b and 4.
Detection using the second wavelength (0.488 μm) is performed using the signal 2.b and 2.b, and after comparison processing for each, a logical sum is performed using an OR circuit. By doing so, detection processing for two wafers can be performed in parallel, which is suitable for mass production.

[0025] Above, the invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above-mentioned examples, and can be modified in various ways without departing from the gist thereof. Needless to say.

For example, although the OR circuit is used to calculate the logical sum of a plurality of detection outputs digitally, it is also possible to calculate the logical sum in an analog manner.

Furthermore, in the above description, the invention made by the present inventor was mainly applied to the field of application of the invention, which is the foreign matter inspection of wafers. However, the present invention is not limited to this, and It can also be applied to products where adhesion is a problem.

[0028]

[Effects of the Invention] Among the inventions disclosed in this application, the effects obtained by the typical inventions are briefly explained as follows.
It is as follows.

That is, at least 2
a laser beam generating means for irradiating laser beams with different wavelengths;
a detection means for detecting scattered light at each wavelength and photo-electrical conversion; a comparison means for comparing the output at each wavelength of the detection means using a preset threshold value and outputting a comparison result for each wavelength; Since a logic means is provided for calculating the logical sum of the outputs of each comparison means, the sensitivity reduction region specific to each wavelength can be compensated for, and the apparent sensitivity characteristic can be made into a direct proportional curve. Foreign objects that were overlooked during inspection can be detected without omission, and reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a foreign matter inspection device according to the present invention.

FIG. 2 is a characteristic diagram showing the relationship between foreign particle diameter and detection signal intensity in a first detector.

FIG. 3 is a characteristic diagram showing the relationship between foreign particle diameter and detection signal intensity in a second detector.

FIG. 4 is a detection signal strength characteristic diagram obtained by combining two detector outputs.

FIG. 5 is an explanatory diagram showing the principle of the present invention.

FIG. 6 is a front view showing main parts of a second embodiment of the present invention.

FIG. 7 is a front view showing main parts of a third embodiment of the present invention.

[Explanation of symbols]

1 Wafer 2a Laser generator (laser beam generating means) 2b Laser generator (laser beam generating means) 3a Detector (detecting means) 3b Detector (detecting means) 4a Detector (detecting means) 4b Detector (detecting means) 5a Comparator 5b Comparator 5c Comparator 5d Comparator 6 OR circuit (logic means) 7 Detection image 8 Detection image 9 Detection image 10 Laser generator 11 Nonlinear optical element 12 Slit

Claims (3)

[Claims] 1. Laser light generation means for irradiating an object to be inspected with laser light of at least two different wavelengths; detection means for detecting scattered light at each wavelength and performing photo-electrical conversion;
Comparing means for comparing outputs at each wavelength of the detecting means with a preset threshold value and outputting a comparison result for each wavelength, and logical means for calculating the logical sum of the respective outputs of the comparing means. A foreign object inspection device featuring: 2. The foreign matter inspection apparatus according to claim 1, wherein each of said detection means is set to a wavelength such that a sensitivity reduction portion of a sensitivity characteristic is different from each other. 3. The foreign matter inspection apparatus according to claim 1, wherein the laser beam generating means includes a nonlinear optical element interposed in one laser beam path.