Edge flaw detection device

An edge flaw detection device includes an elliptical mirror having a mirror surface on the inside thereof and having a cutout that allows an object to be inserted therethrough formed at the apex thereof, a light-emitting unit that radiates coherent light toward an edge of the object arranged in the vicinity of a first focal position of the elliptical mirror, a photo detector that is arranged in a second focal position of the elliptical mirror, and a light-shielding member that shields low-order diffracted light that is reflected regularly. The light-emitting unit is moved in the thickness direction of the object by a moving member so that the light-emitting unit can radiate the coherent light in a different radiation range in the thickness direction at the edge of the object.

This application is the U.S. national phase of International Application No. PCT/JP2005/014664, filed 10 Aug. 2005.

TECHNICAL FIELD

The present invention relates to an edge flaw detection device that optically detects a flaw at an edge of an object.

BACKGROUND ART

A detection device using an elliptical mirror is suggested as an edge flaw detection device that detects flaws such as narrow and long edge cracks, deficits, or polishing marks that are formed in edges, for example, the peripheral edges of silicon wafers. For example, a device is suggested in which a light-absorbing member is arranged on the mirror surface of an elliptical mirror, the light-absorbing member is made to absorb the low-order diffracted light that is regular reflection light, and only high-order diffracted light that is reflected irregularly by a flaw of an edge is detected by a photo detector provided in a second focal position (for example, refer to Patent Document 1). Further, a device is suggested in which, apart from a first photo detector provided in the second focal position, a second photo detector provided in the vicinity of an object set in a first focal position, enabling detection for vertical flaws and horizontal flaws by means of two light-receiving units (for example, refer to Patent Document 2).

However, although these edge flaw detection devices can detect the whole periphery of the edge of an object by rotating it, the specific position and size of the flaw in the thickness direction orthogonal to a circumferential direction remain unknown. Further, although it is possible to estimate the type of a flaw to some degree from the intensity of the light detected by a light-receiving unit, there was a limitation in discriminating from one parameter of luminous intensity for details.

DISCLOSURE OF INVENTION

The invention has been made in view of the aforementioned situations, and proposes an edge flaw detection device capable of detecting the specific position of a flaw at an edge of an object in the thickness direction, the size of the flaw, and the type of the flaw.

The invention provides an edge flaw detection device including an elliptical mirror having a mirror surface on an inside thereof, a light-emitting unit that radiates coherent light toward an edge of an object, the edge of the object being arranged in a vicinity of a first focal position of the elliptical mirror, a photo detector that is arranged in a second focal position of the elliptical mirror and is capable of detecting the diffracted light resulting when the radiated coherent light is reflected by the edge of the object and by the elliptical mirror so as to arrive at the second focal position, and a light-shielding member that shields low-order diffracted light which is regularly reflected among the diffracted light, a position of the light-emitting unit being freely set in a thickness direction of the object by a moving member so that the light-emitting unit can radiate the coherent light in a different radiation range in the thickness direction at the edge of the object.

According to the edge flaw detection device of this invention, it is possible to irradiate coherent light in a different radiation range in the thickness direction of the edge of the object by means of the moving member. Thus, by detecting the intensity of the diffracted light corresponding to an individual radiation range using the photo detector, the specific position of a flaw in the thickness direction and the size of the flaw can be detected.

Further, the invention provides an edge flaw detection device including an elliptical mirror having a mirror surface on an inside thereof, a plurality of light-emitting units that radiate coherent light toward an edge of an object, the object being arranged in a vicinity of a first focal position of the elliptical mirror, a photo detector that is arranged in a second focal position of the elliptical mirror and is capable of detecting the diffracted light resulting when the radiated coherent light is reflected by the edge of the object and by the elliptical mirror so as to arrive at the second focal position, and a light-shielding member that shields low-order diffracted light which is regularly reflected among the diffracted light, a plurality of the light-emitting units being provided in different positions in a thickness direction of the object, and each of a plurality of the light-emitting units being able to radiate the coherent light from a different direction, in a different radiation range in the thickness direction at the edge of the object.

According to the edge flaw detection device of this invention, it is possible to irradiate coherent light in a different radiation range in the thickness direction at the edge of the object by means of the plurality of the light-emitting units. Thus, by detecting the intensity of the diffracted light corresponding to an individual light-emitting unit, the specific position of a flaw in the thickness direction and the size of the flaw can be detected.

Moreover, in the edge flaw detection device of the above invention, the light-emitting unit may be constituted to include a light source that radiates the coherent light, and a condensing member that optically acts on the coherent light radiated from the light source so that the coherent light is radiated while the radiation range is reduced in the thickness direction at the edge of the object.

According to the edge flaw detection device of this invention, by reducing the radiation range of the coherent light that is radiated onto the edge of an object in the thickness direction, an intensity difference in the diffracted light detected by the photo detector depending on the position of a flaw in the thickness direction and the size of the flaw can be clarified when coherent light is irradiated by the light-emitting unit from a different position in the thickness direction.

Moreover, in the edge detection device of the above invention, the light-emitting unit may be able to radiate coherent light at various wavelengths.

According to the edge flaw detection device of this invention, by detecting the intensity of the diffracted light by coherent light at different various wavelengths by means of the photo detector, a fine flaw can be detected, or a flaw that could not be detected since coherent light having a long wavelength is largely absorbed, or a flaw that irregularly reflects only coherent light having a specific wavelength can be detected.

According to the invention, since the radiation range of the coherent light that is radiated from a light-emitting unit can be changed in the thickness direction of an object, the specific position of a flaw in the thickness direction of the object, and the size of the flaw can be specified. Moreover, by using coherent light at different various wavelengths, a fine flaw can be detected, or a flaw that could not be detected since coherent light having a long wavelength is largely absorbed, or a flaw that irregularly reflects only the coherent light having a specific wavelength can be detected. As a result, fine edge flaw detection can be realized.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

FIGS. 1 to 10illustrate a first embodiment according to the invention.FIG. 1illustrates a longitudinal sectional view of an edge flaw detection device taken along its vertical plane, andFIG. 2illustrates a longitudinal sectional view of the edge flaw detection device taken along its horizontal plane.FIG. 3illustrates an explanatory view of the edge of an object irradiated by a light-emitting unit. Further,FIGS. 4 and 6illustrate the enlarged sectional views of the edge of the object, andFIGS. 5 and 7illustrate their enlarged front views. Moreover,FIG. 8illustrates a graph showing an example of a detection result by a photo detector when a radiation range is changed in the thickness direction,FIG. 9illustrates a graph showing an example of a detection result by the photo detector when the wavelength of the coherent light to be irradiated is changed, andFIG. 10illustrates a graph showing an example of a detection result by the photo detector when the radiation range is changed in the thickness direction using coherent light at a plurality of wavelengths.

As shown inFIGS. 1 and 2, the edge flaw detection device1includes an elliptical mirror2that has a mirror surface2bat its inside2aand has a notch2dat an apex2cthat allows an object3to be inserted therethrough, a light-emitting unit4that irradiates coherent light C toward an edge3aof the object3arranged in the vicinity of a first focal position A of the elliptical mirror2, and a photo detector5that is arranged in a second focal position B of the elliptical mirror2. Further, the edge flaw detection device1includes a holding portion6that rotatably holds the object3, a moving member7that makes the light-emitting unit4rotatable about the first focal position A of the elliptical mirror2in the thickness direction of the object3, and a light-shielding member8provided in the elliptical mirror2. The object3is, for example, a plate-like silicon wafer, a semiconductor wafer, etc.

As shown inFIG. 3, the light-emitting unit4includes a light source9that emits coherent light C, and a condensing member10that optically acts on the emitted coherent light C. The light source9is, for example, a laser beam, and its wavelength is freely adjustable. More specifically, He—Ne lasers or semiconductor lasers are used; by enabling switching between a plurality of lasers with different wavelengths, the wavelength can be freely adjusted. Alternatively, a wavelength-variable laser may be used. Further, the condensing member10is a lens that reduces a radiation range11in the thickness direction of the edge3aof the object3, when the coherent light C emitted from the light source9is irradiated toward the edge3aof the object3. Above-mentioned light-emitting unit4can be freely set into position in the thickness direction of the object3by the moving member7, and can radiate the coherent light C in different radiation ranges in the thickness direction of the edge3aof the object3. Further, as shown inFIGS. 1 and 2, the photo detector5detects the diffracted light D that is obtained when the diffracted light D, which is radiated from the light-emitting unit4and is reflected by the edge3aof the object3, is reflected by the elliptical mirror2, and is condensed on the second focal position B, and the photo detector is a photodiode, for example.

As shown inFIGS. 1 and 2, the holding portion6can position the edge3aof the object3in the vicinity of the first focal position A of the elliptical mirror2, and can move the edge3aof the object3in a circumferential direction on the first focal position A by rotating its rotary shaft6a. Further, the light-shielding member8is a masking tape that is adhered with a predetermined width on an intersection line where a plane that is parallel to the thickness direction of the object3including the first focal position A and the second focal position B, and the elliptical mirror2intersect with each other. The diffracted light D that has reached the light-shielding member8will be absorbed by the light-shielding member8, without being reflected and reaching the photo detector5. Further, a light-shielding plate12is provided on the side of the first focal position A of the photo detector5. This is provided to prevent coherent light C, radiated from the light-emitting unit4, from being reflected by the edge3aof the object3and becoming diffracted light D, but then directly reaching the photo detector5without being reflected by the elliptical mirror2.

Next, the operation of the edge flaw detection device1will be described. As shown inFIG. 1, a case where the existence or nonexistence of any flaw is detected in an arbitrary circumferential position at the edge3aof the object3is described. First, the light-emitting unit4is located in a central position O to irradiate the edge3aof the object3.FIG. 4illustrates an enlarged front view of the edge3aof the object3when being irradiated in the central position O, andFIG. 5illustrates an enlarged sectional view. As shown inFIG. 4andFIG. 5, when a flaw3bis located at upper part of the edge3aof the object3, the flaw3bis not included in the radiation range11owhen being irradiated from the central position O. For this reason, the radiated coherent light C is regularly reflected to be low-order diffracted light D1. The low-order diffracted light D1heads for the second focal position B via the vicinity of the axis L in plan view as a path as shown inFIG. 2and the light has a certain degree of spread in the thickness direction according to the shape of the edge3aof the object3in side view as shown inFIGS. 1 and 5. For this reason, the low-order diffracted light D1is absorbed by the light-shielding member8or the light-shielding plate12, and much of the light does not reach the photo detector5.

In addition, if located in the central position O to irradiate the edge3aof the object3with the coherent light C as described above, the coherent light C will be radiated through the axis L of the elliptical mirror2. Instead of this, the optical axis of the light source9may be arranged so as to deviate slightly (about 4 degrees) with respect to the axis L of the elliptical mirror2so that the light source9and the second focal point B may not overlap with each other. Thereby, the low-order diffracted light D1resulting when radiated coherent light C is regularly reflected by the edge3aof the object3, also deviates from the axis L of the elliptical mirror2. Thus, it is possible to omit the light-shielding plate12.

In this case, although the optical axis of the light source9may be tilted in the horizontal direction with respect to the axis L of the elliptical mirror2, it is preferably tilted in the vertical direction. This is because, when the coherent light C is radiated onto the edge face3aof the horizontally supported object3, from the direction tilted in the horizontal direction with respect to the axis L of the elliptical mirror2, there is a disadvantage in that the scattered and reflected light in the lateral direction, including many kinds of information required for flaw detection, may be biased to the lateral direction, and effective information may be damaged. On the other hand, when the optical axis of the light source is tilted in the vertical direction, the scattered and reflected light in the vertical direction seldom includes information required for flaw detection. Thus, the above-described problem does not tend to occur. In addition, even when tilted in the horizontal direction, the scattered and reflected light in the lateral direction may be condensed on a photo detector by the contrivance of forming the elliptical mirror2into a laterally asymmetrical shape, or the like.

Next, as shown inFIG. 1, suppose that sequential irradiation is performed while the light-emitting unit4is moved upward and reaches an upper position P.FIG. 6illustrates an enlarged front view of the edge3aof the object3when being irradiated in the upper position O, andFIG. 7illustrates an enlarged sectional view. As shown inFIG. 6andFIG. 7, since the radiation range11poverlaps a flaw3b, the coherent light C is irregularly reflected by the flaw3b, and becomes high-order diffracted light D2. For this reason, as shown inFIGS. 1,2, and7, the diffracted light D2is not absorbed by the light-shielding member8, but much of the light is reflected to the elliptical mirror2, and is detected by the photo detector5in the second focal position B.FIG. 8shows the relationship between the irradiation angle φ and the intensity R of the light detected by the photo detector5when the irradiation angle φ in the central position O is defined as zero degrees. As shown inFIG. 8, if located in the central position O or lower than the central position where the irradiation angle φ is a negative value, the low-order diffracted light D1of regular reflection is obtained, and most of the light does not reach the photo detector5. Thus, the intensity R of the light remains at a lower level. Moving upward from the central position O and the irradiation angle φ indicating a positive value, the flaw3bis included in the radiation range11. Thus, the high-order diffracted light D2is generated as a result of the irregular reflection and the intensity R of the light increases gradually, and reaches a maximum value in the upper position P. As described above, by irradiating while the radiation range in the thickness direction of the object3is changed in an arbitrary edge3aof the object3, the information showing the position of a flaw in the thickness direction or the state (size, shape, etc.) of the flaw can be obtained. Also, if the rotary shaft6aof the holding portion6is rotated and the edge3ais moved in the circumferential direction, the existence or nonexistence of any flaw at the edge3aof the object3, and the position and size of the flaw can be investigated in detail in the circumferential direction and the thickness direction.

In addition, as shown inFIG. 3, if the radiation range11ato be irradiated is set in the whole thickness direction by the switching of a lens that is the condensing member10, detection of any flaw at an edge in the circumferential direction can be performed efficiently. That is, if detection in the thickness direction is performed while the radiation range11is reduced in only the portion where the existence or nonexistence of any flaw has been confirmed after the existence or nonexistence of any flaw is confirmed in the circumferential direction in the radiation range11a, detailed detection can be performed efficiently. Here, as the condensing member10that changes the radiation range11, a method of switching use of a diffusing lens system, such as a meniscus lens or a Fresnel lens, or a collecting or diffusing lens system, such as a focusing glass system can be considered. Further, this function may be given to the light-emitting unit4.

Further, the light-emitting unit4can radiate the coherent light C of various wavelengths λ. For this reason, a flaw that could not be recognized since absorption is large in the coherent light C of a long wavelength λ, can be recognized by shortening the wavelength λ.FIG. 9shows the relationship between a wavelength λ when irradiation is performed while the wavelength λ is changed, and the intensity R of the light detected by the photo detector5, in an arbitrary position at the edge3aof the object3. As shown inFIG. 9, a flaw that could not be detected at a certain wavelength λ1can be detected at a wavelength λ2, by changing the wavelength λ.FIG. 10shows a graph in the case where the irradiation angle φ of the light-emitting unit4is changed and the wavelength λ is changed. Here, individual graphs represent the relationships at the time of wavelengths λ3, λ4, λ5, and λ6, and the wavelengths λ have the magnitude relationship λ3<λ4<λ5<λ6. As shown inFIG. 10, in this example, in the vicinity of an irradiation angle φ1, the high-order diffracted light D2resulting from a flaw can be prominently detected at a small wavelength λ, and in the vicinity of an irradiation angle φ2, the high-order diffracted light D2resulting from a flaw can be strikingly detected at a large wavelength λ.

As described above, the edge flaw detection device1can detect the edge3aof the object3in detail not only in the circumferential direction of the object but in the thickness direction thereof, and can operate detection with changing the wavelength λ of the coherent light C that is irradiated according to the characteristics of a flaw. For this reason, the position, the size, range, and type of a flaw can be detected.

Second Embodiment

FIG. 11shows a second embodiment of the invention and a longitudinal sectional view of an edge flaw detection device taken along its vertical plane. In this embodiment, members common to the members used in the aforementioned embodiment are denoted by the same reference numerals, and the description thereof is omitted.

The edge flaw detection device13in this embodiment includes a plurality of light-emitting units14,15,16,17, and18. The light-emitting units14,15,16,17, and18are arrayed at substantially equal angles in the thickness direction of the object3, and each of them has a light source9and a condensing member10, and is able to irradiate the edge3aof the object3in the first focal position A.

As such, even if a light-emitting unit is not movable in the thickness direction of the object3by a moving member, the edge3aof the object3can be similarly detected in detail in the thickness direction by arranging a plurality of the light-emitting units.

Although the embodiments of the invention have been described hitherto in detail with reference to the drawing, concrete configurations are not limited to the embodiments, and the invention also includes design changes that do not depart from the spirit of the invention.

In addition, although the example where the radiation range11is reduced in the thickness direction of the edge3aof the object3by the condensing member10of the light-emitting unit has been shown, the invention is not limited thereto. Since the intensity R of the light is relatively changed by changing the radiation range in the thickness direction even if the radiation range11is large, it is possible to identify a flaw. Further, by radiating coherent light from a different angle in the same radiation range, a difference is caused in the intensity of reflected light according to the state of a flaw that is in the radiation range. By utilizing this, it is also possible to indirectly detect the state (size, an angle, etc.) of a flaw. Further, although a masking tape adhered to the elliptical mirror2is adopted as the light-shielding member8, the invention is not limited thereto. Any members may be adopted so long as they can shield the low-order diffracted light D1that is reflected regularly. For example, a light-shielding plate consisting of a plate having a predetermined width serving as a spatial filter may be arranged between the edge3aof the object3and the light source9so as to abut on the inner face of the elliptical mirror2in a vertical direction orthogonal to the face of the object3. Although this allows the low-order diffracted light D1to be shielded by the light-shielding plate, the high-order diffracted light D2leaks out of the light-shielding plate, and is condensed by the elliptical mirror2.

INDUSTRIAL APPLICABILITY

Since the radiation range of the coherent light that is radiated from a light-emitting unit can be changed in the thickness direction of an object, the specific position of a flaw in the thickness direction of the object, and the size of the flaw can be specified.