JP2001264262A - Surface foreign matter inspecting method and surface foreign matter inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface foreign matter inspecting method and inspecting device capable of conveniently making a total inspection for comparatively large foreign matter or a flaw or the like on a wafer or a liquid crystal substrate in a state of inspection standard is constant. SOLUTION: This device has illumination optical systems 3 and 4 illuminating substantially the whole face of an object 1 to be inspected, light receiving optical systems 5 and 7 collectively receiving scattered light from foreign matter adhered to a surface of the object for detecting the total quantity of scattered light by their pupil faces, and a spatial filter part 6 extracting light of a particular direction from the object.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for inspecting foreign matter adhering to the surface of a semiconductor circuit element or a liquid crystal display element during a manufacturing process thereof.

[0002]

2. Description of the Related Art In a manufacturing process of a semiconductor circuit element or a liquid crystal display element, if foreign matter such as dust adheres, a defect occurs in a circuit pattern and a desired performance cannot be obtained. For this reason, many high-sensitivity foreign-matter inspection apparatuses that scan laser light to detect scattered light from foreign matter have been conventionally proposed. However, these conventional foreign-matter inspection apparatuses require a long processing time because they scan laser spots, and it is practically impossible to inspect all manufactured products. Therefore, at present, the inspection by the conventional foreign matter inspection apparatus is performed by a sampling inspection. However, it is desirable to perform a 100% inspection because the attachment of foreign matter occurs accidentally.

In addition, a technique has been developed to provide a redundant circuit for a defect caused by the adhesion of a foreign substance as described above, so that circuit characteristics can be maintained even if a certain degree of defect exists. ing. Therefore, the necessity of performing the above-described high-sensitivity foreign substance inspection on all products has been reduced. Particularly, in the case of a semiconductor circuit element, it is common to manufacture a plurality of products of about 20 to 100 pieces on one substrate. For this reason, if there are several defects, if they are determined to be defective and reconstructed or discarded, the yield of the products will be reduced, and the production cost may be increased. Therefore, it is often the case that a relatively large foreign matter is attached to all the products to be manufactured by visual inspection by an inspector.

[0004]

However, the visual inspection performed by the inspector is susceptible to the skill of the inspector, and thus has the disadvantage that the inspection standard tends to fluctuate. Further, in the visual appearance inspection, since the film thickness unevenness and the pattern abnormality are simultaneously inspected, the illumination is not installed so as to be optimal for the foreign matter inspection. For this reason, foreign substances and scratches may not be found due to the effect of the printed pattern.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a surface inspection system capable of easily performing a 100% inspection of relatively large foreign objects and scratches on a wafer or a liquid crystal substrate with a fixed inspection standard. It is an object to provide a method and an inspection device.

[0006]

In order to solve the above-mentioned problems, the present invention provides a step of irradiating almost the entire surface of a test object with illumination light, and a method of scattering light from a foreign substance adhering to the surface of the test object. Receiving the light in a batch by the light receiving optical system, detecting the total amount of the scattered light substantially at the pupil plane of the light receiving optical system, and extracting light in a specific direction from the test object. A method for inspecting a surface foreign matter is provided. Here, the foreign matter includes not only dust and dirt but also flaws that generate scattered light.

In a preferred aspect, the step of rotating the test object about a predetermined axis and the minimum value of the total amount of light detected by the light receiving optical system are compared with a predetermined threshold value. And determining whether the foreign matter is good or bad.

The present invention is also directed to an illumination optical system for illuminating substantially the entire surface of a test object, and collectively receiving scattered light from a foreign substance adhering to the surface of the test object. Provided is a surface foreign matter inspection device, comprising: a light receiving optical system that detects the total amount of the scattered light on a pupil plane; and a spatial filter unit that extracts light in a specific direction from the test object.

In a preferred aspect, the rotation unit for rotating the object around a predetermined axis is compared with a minimum value of the total amount of light detected by the light receiving optical system and a predetermined threshold value. It is preferable that the apparatus further includes a comparison operation unit that performs quality judgment on the foreign matter of the object.

[0010] In a preferred aspect, it is desirable that the spatial filter section is provided near a pupil plane of the light receiving optical system.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a foreign matter inspection apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a view showing a configuration of a foreign substance inspection apparatus according to a first embodiment. The wafer 1 as a test object is transferred to a predetermined position by a transfer device (not shown), and is attracted to a holder 2 that can rotate in a horizontal plane.
Illumination light from the light source 3 is reflected by the concave mirror 4 which is an illumination optical system, and illuminates the entire surface of the wafer 1 at a predetermined angle. In the illumination optical system using the concave mirror 4, since the optical path is bent by the concave mirror 4, the concave mirror 4 is inclined so that the light source 3 and the test object 1 do not interfere with each other. It is desirable that the light beam illuminating any arbitrary position on the wafer 1 has a uniform incident angle and falls within a certain range. For this reason, the light source 3 is a concave mirror 4 which is a position on the pupil plane of the illumination optical system.
It is located at a position that is approximately a focal distance from the camera.
The incident angle with respect to the wafer 1 is in the range of 60 to 90 degrees with the normal to the wafer surface being 0 degree, and the numerical aperture of a light beam illuminating an arbitrary point on the wafer is 0.1 or less. Is desirable. Further, when the incident angle is large, the width of the light beam illuminating the wafer 1 becomes narrow. Therefore, the concave mirror 4 does not necessarily have to be circular and may be formed in a band shape.

If foreign matter is attached to the wafer 1, the above-described illumination light is isotropically scattered in all directions. This scattered light is condensed by a concave mirror 5 which is a light receiving optical system provided substantially vertically above the wafer 1, and is passed through a spatial filter 6 provided near a pupil plane of the light receiving optical system to form an SPD (silicon photodiode). The signal is converted into an electric signal by a photoelectric conversion element 7 such as a photomultiplier or a photomultiplier tube and sent to a control / arithmetic processing unit 8. The control / arithmetic processing unit 8 sends a signal to a drive mechanism 9 that rotates the holder 2 about the axis A, and rotates the wafer 1. The photoelectric conversion element 7 continuously detects the amount of light received from the rotating wafer. Next, the control / arithmetic processing unit 8 obtains the minimum value of the received light amount. The control / arithmetic processing unit 8 stores a preset threshold value. Then, the control / arithmetic processing unit 8 determines the quality of the wafer 1 by comparing the minimum light amount with the threshold value. The result of the pass / fail judgment of the wafer 1 is sent to the process management system, and the wafer judged to be non-defective is advanced to the next step. On the other hand, a wafer determined to be defective is subjected to rework in which the pattern is peeled off and the same process is performed again, or recycle processing in which the pattern is polished and the process is restarted from the first process.

The amount of scattered light from the foreign material increases as the diameter of the foreign material increases. From a large foreign matter that has a fatal effect that cannot be dealt with by the above-described redundant circuit over several circuit elements, strong scattered light is generated and a large foreign matter signal is obtained. When there are many relatively small foreign matters on the wafer that can be relieved by the above-described redundant circuit, the photoelectric conversion element 7 is provided near the pupil of the light receiving optical system 5. The scattered light from the light beam is integrated to produce a large foreign matter signal. In addition to the fact that relatively small foreign matter is difficult to detect even with conventional visual inspection, the yield can be reduced if the redundant circuit can be used (remedy) as described above, or if all detected items are treated as defective. Therefore, even if a certain amount of foreign matter is present, the process proceeds to the next step. Actually, the work is performed in a clean room where dust measures have been taken,
Among the generated foreign substances, large ones are almost completely removed, and foreign matters adhering to the wafer are relatively small. For this reason, it may be basically considered that it is equal to seeing whether the total (total number) of the number of foreign substances having a small diameter exceeds a predetermined value.

The scattered light from the foreign matter has a directional characteristic depending on the size of the foreign matter, but isotropically spreads in all directions. On the other hand, when the illumination light is incident on the circuit pattern formed on the surface of the wafer 1, diffracted light is generated according to the direction and the period in which the pattern is repeated. When this diffracted light is incident on the photoelectric conversion element of the light receiving optical system, even if no foreign matter is attached, the signal strength is increased and a control signal is generated as if the foreign matter signal was generated in a pseudo manner. It will be judged by.

Therefore, the wafer 1 is rotated about the axis A to change the direction in which the diffracted light is generated, and the amount of scattered light from the foreign material is measured in a state where the influence of the diffracted light from the pattern is minimal. Avoid detecting the foreign object signal. FIG. 2 is a diagram showing an example of a change in the amount of light received by the light receiving optical system when the holder 2 is rotated once with a wafer having a repetitive pattern as a test object. Here, the horizontal axis represents the rotation angle (degree), and the vertical axis represents the amount of received light. The repetition direction of the pattern becomes parallel to the incident direction of the illumination light, and the amount of received light increases when the diffracted light from the pattern enters a range where the light receiving optical system receives light. In addition, the pattern formed on the actual semiconductor wafer is not limited to the one in which the vertical and horizontal directions, that is, the directions of the repeated patterns are orthogonal. Therefore, as a condition under which the diffracted light from the pattern does not enter the light receiving optical system, the amount of received light at a position where the amount of received light is minimized by rotating the wafer 1 is used to determine the quality of the wafer. Furthermore, since the actual repetition period of the pattern of the semiconductor wafer is not constant, it is desirable to provide the spatial filter 6 and to prevent unnecessary diffracted light from the pattern from entering the photoelectric conversion element 7.

FIG. 2B is a diagram showing the configuration of the spatial filter 6. A light-shielding band SD is provided so that light traveling on a plane PP including the optical axis of the illumination optical system 4 and the optical axis of the light-receiving optical system 5 does not enter. The light from the wafer 1 passes through the opening AP.
Pass through. It is desirable that the width of the light-shielding band SD is slightly larger than the size L of the light source image formed on the spatial filter 6 by the light source 3 via the illumination optical system 4, the wafer 1, and the light receiving optical system 5. Further, the light receiving region of the photoelectric conversion element may have the same shape as the opening of the spatial filter 6 as shown in FIG.

(Second Embodiment) FIG. 6 is a view showing a configuration of a surface inspection apparatus according to a second embodiment of the present invention. This surface inspection apparatus uses a refractive optical system as an optical system. Similarly to the first embodiment, the light beam from the light source 13 is applied to the wafer 11 mounted on the rotatable holder 12 through the illumination optical system 14 at a large incident angle similarly to the first embodiment. . The light scattered by the foreign matter adhering to the wafer 11 is collected near the pupil plane of the light receiving optical system by the light receiving lens 15 provided substantially vertically above the wafer 11. The light passing through the stop or the spatial filter 16 provided near the pupil plane is photoelectrically converted by the photoelectric conversion element 17 and sent to the control / arithmetic processing unit 18 as a light receiving signal. The control / arithmetic processing unit 18 sends a signal to the drive mechanism of the holder 12 as in the first embodiment, and rotates the holder 12 about the axis A to obtain the minimum value of the amount of received light. Thereafter, the quality of the wafer 11 is determined in the same manner as in the first embodiment. The spatial filter 16 has a shape as shown in FIG. 2B so that diffracted light from a pattern formed on the wafer 11 does not enter the photoelectric conversion element 17 as in the first embodiment. Is desirable.

Next, the sectional shape of the illumination light beam will be described. At a large incident angle, the illuminating light flux in a plane including the direction in which the illuminating light is incident and the normal line of the wafer 11 is about the size of the wafer multiplied by the cosine of the incident angle. For this reason, if the light beam is greatly expanded, an area larger than the size of the wafer 11 will be illuminated, and the illumination efficiency will be reduced. On the other hand, in the direction in which the illumination light is incident and the direction perpendicular to the plane including the normal line of the wafer 11, an illumination light flux of at least the size of the wafer is required regardless of the incident angle. In order to improve the illumination efficiency, the illumination optical system 14 of the present embodiment is configured as shown in FIG.
It is composed of two cylindrical lenses 14a and 14b. The cylindrical lens 14a has a refractive power in a direction including the direction in which the illumination light is incident and the normal line of the wafer 11, that is, a direction including the paper surface in FIG. 4, and the cylindrical lens 14b has a refractive power in a direction perpendicular to the paper surface in FIG. Are arranged. Each cylindrical lens 14
a and 14b are light sources 13 each of which is a cylindrical lens 14;
Arrangements are made so as to be in the vicinity of the focal positions of a and 14b, and the center of a light beam applied to an arbitrary point on the wafer 11 is substantially parallel.

Further, at the edge of the flat disk-shaped wafer, the illumination light is strongly reflected and becomes unnecessary noise light. In particular,
In the present embodiment, since the wafer 11 is illuminated at a large incident angle, noise light reflected from the edge of the wafer on the side closer to the light source 13 may enter the light receiving optical system.
Therefore, it is necessary to satisfy the condition that the edge portion of the planar disk-shaped wafer does not emit light and that the illumination light enters the effective area of the wafer surface. For this reason, in the present embodiment, the screen 20 is provided on the light source side of the wafer 11 so that light reflected from the edge of the wafer is not generated.

Next, the shape of the screen 20 will be described. The screen has, for example, a semicircular shape such that the center of curvature of the wafer 11 and the center of curvature of the screen 20 coincide with each other when viewed from above, as shown in FIG. Since the illumination light beam is parallel light, the shadow of the screen is formed parallel to the central axis of the illumination light beam. Here, the height of the partition necessary to satisfy the above condition is obtained in a direction shifted by an angle φ from the direction in which the illumination light is incident.

The illumination light is applied to the wafer surface at an incident angle θ, the radius of the wafer 11 is indicated by R (indicated by the outer periphery B in FIG. 5A), and the radius of the effective area of the wafer 11 is indicated by r (FIG. a)
, The outer periphery B ′), and the screen 2
The distance to 0 is represented by L, and the height of the screen from the wafer surface is represented by h. At this time, the illumination light needs to illuminate the effective area B ′ of the wafer 11 and not to enter the edge B of the wafer 11. In this case, it is desirable that the height h satisfies the following expression.

[0023]

(Equation 1)

Actually, the strong reflected noise light from the edge portion of the wafer 11 is a portion having a rounded corner within a range of about 2 mm around the wafer. Therefore, the wafer 11
It is more preferable to use a value obtained by subtracting a portion where the corner around the wafer is rounded as the radius R of.

FIG. 5C shows a radius R of a wafer = 100 m.
m, effective area radius r = 95 mm, incident angle is 88 degrees,
It is a figure which shows the shape of a screen on the condition of the distance L = 105 mm from a wafer to a screen. The horizontal axis of FIG. 5C indicates the azimuth φ of the screen from the central axis of the illumination light beam, and the vertical axis indicates the length h (unit: mm) of the screen from the wafer surface. The upper limit HI and the lower limit LO of the shape are shown for each azimuth angle φ. The height h of the screen must be at least between the upper limit HI and the lower limit LO. Here, since the range up to the effective area of the wafer was calculated, the azimuth angle φ was calculated in the range up to ± 64 degrees (= Arcsin (95/105)). Further, in order to avoid mixing of stray light, it is desirable that light does not enter outside the effective area.

Since the thickness of a wafer processed in an actual process varies, it is desirable to change the range of light shielding by the screen 20 according to the thickness of the wafer. Therefore, when the wafer 11 is placed on the holder 12, a thin light beam from the light source 21 is obliquely applied to the surface of the wafer 11 for measuring the height of the wafer surface. The luminous flux reflected by the wafer surface 11 is detected by a PSD (light receiving position detecting element Posio).
n Sensitive Detector 22. When the height changes due to the thickness of the wafer 11 or the like, the position of the light beam incident on the PSD 22 shifts. PSD
Reference numeral 22 detects the amount of deviation and transmits the detected amount to the control / arithmetic processing unit 18. The control / arithmetic processing unit 18 calculates the height of the surface of the wafer 11 and drives the driving device 23 so that the illumination light does not enter the edge of the wafer 11 and the illumination light is applied only to the effective area.
The position of the screen 20 is moved with. In addition, the screen 20
May be fixed without moving, and the holder 12 may be moved up and down.

Further, since the intensity of the scattered light from the foreign matter adhering to the wafer 11 is not so strong, the illumination optical system, the wafer holder, and the light receiving optical system should be configured so that unnecessary disturbance light does not enter when capturing the inspection image. Is desirable. For this reason, it is desirable that at least the illumination optical system, the wafer holder, and the light receiving optical system are placed in a dark box provided with a shutter that can be opened and closed at a wafer entrance.
In this dark box, a so-called HEPA (High Efficiency PEPA) is used to prevent foreign matter from adhering to the wafer as a test object.
articulate Air Filter) and ULPA (Ultra Low Penetra)
It is desirable to circulate the air from an air purifier equipped with a dust collecting filter called a lamination air filter in a laminar flow.

In the above description, an example in which a reflection optical system is used for the illumination optical system and the light receiving optical system is shown as the first embodiment, and a refractive optical system is used for the illumination optical system and the light receiving optical system as the second embodiment. Although an example in which the illumination optical system and the light receiving optical system are used is shown, the illumination optical system and the light receiving optical system may be interchanged. Also,
The light sources 3 and 13 may use a secondary light source such as an optical fiber emission end. Further, in each of the above embodiments, the light receiving optical system is disposed vertically above the object 1 to be measured. It is not limited to the configuration.

[0029]

As described above, according to the present invention,
Foreign matter and scratches on the wafer surface can be inspected by a simple signal processing system, and the quality of the inspected wafer can be determined in a short time.
Therefore, it is possible to perform a 100% inspection of all wafers (process wafers) in the manufacturing process, and it is possible to prevent a decrease in the yield of semiconductor products due to accidental generation of foreign matter. further,
By using the apparatus of the present invention, a person who is most likely to generate dust in the clean room can be kept away from the wafer, so that accidental attachment of foreign substances during inspection can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a surface inspection apparatus according to a first embodiment of the present invention.

2A is a diagram illustrating the intensity of a diffracted light, and FIG. 2B is a diagram illustrating a configuration of a spatial filter.

FIG. 3 is a diagram illustrating a configuration of a surface inspection apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of an illumination optical system of the surface inspection apparatus according to the present invention.

FIG. 5 is a view showing a shape of a screen of the surface inspection apparatus according to the present invention;

[Explanation of symbols]

 Reference Signs List 1,11 Wafer 2,12 Holder 3,13 Light source 4 Concave reflecting mirror 5 Concave reflecting mirror 6,16 Spatial filter 7,17 Photoelectric conversion element 8,18 Control / arithmetic processing unit 9,19 Driving mechanism A Rotating axis AP Opening SD light-shielding band 14 illumination optical system 15 light-receiving lens 20 screen 21 light source 22 PSD 23 driving device

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2F065 AA24 AA49 AA61 CC17 DD12 FF01 FF09 FF41 GG12 HH03 HH12 JJ16 JJ17 JJ18 LL04 LL08 LL19 LL30 MM04 QQ25 QQ28 TT03 2G051 AA51 AA07 CB07 DA03 CB07 DA02 EB01 4M106 AA01 CA41 CA43 DB13 DB14 DB19 DJ06 DJ11 DJ18 DJ20 DJ21 DJ27

Claims (5)

[Claims] A step of irradiating substantially the entire surface of the test object with illumination light; and a step of collectively receiving scattered light from a foreign substance adhering to the surface of the test object by a light receiving optical system; A surface foreign matter inspection method, comprising: detecting a total amount of the scattered light substantially on a pupil surface; and extracting light in a specific direction from the test object. 2. A step of rotating the test object around a predetermined axis; comparing a minimum value of the total amount of light detected by the light receiving optical system with a predetermined threshold value; 2. The method according to claim 1, further comprising the step of: determining whether the surface is good or bad. 3. An illumination optical system for illuminating substantially the entire surface of the test object, and collectively receiving scattered light from a foreign substance adhering to the surface of the test object. A surface foreign matter inspection device comprising: a light receiving optical system that detects a total amount of scattered light; and a spatial filter that extracts light in a specific direction from the test object. 4. A rotating unit for rotating the test object around a predetermined axis, a minimum value of the total light amount detected by the light receiving optical system and a predetermined threshold value are compared, and the rotation of the test object is 4. The surface foreign matter inspection device according to claim 3, further comprising: a comparison operation unit that performs a pass / fail determination on the foreign matter. 5. The surface foreign matter inspection apparatus according to claim 3, wherein the spatial filter is provided near a pupil plane of the light receiving optical system.