JPH11326229A - Foreign matter inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To directly, highly accurately position a wafer at an inspection stage, by obtaining coordinates of three points of an outer circumference of the wafer to a center of the inspection stage on the basis of detection signals corresponding to detection pixels of an optical sensor, and obtaining a center coordinate of the wafer. SOLUTION: An MPU 131 carries out a wafer-positioning program 136, positioning an inspection area above a linear sensor 120, rotating an XYZθ table 122 thereby obtaining an edge detection characteristic curve, calculating an eccentricity amount of the wafer 1, and positioning a center of the wafer 1. Thereafter, the MPU moves the wafer 1 along a Y axis, calculates a correction angle, rotates the table 122, and corrects an angle of the wafer based on the Y axis. The MPU then carries out a center coordinate detection program 137, obtains coordinates of three points, and calculates a center coordinate of the wafer 1 as an offset amount. At a foreign matter detection program 134, a coordinate of a foreign matter is converted with the offset amount to a coordinate of the wafer 1, displayed on a display to be a foreign matter detection data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus, and more particularly, to a foreign matter inspection apparatus capable of accurately positioning a wafer to be inspected on an inspection stage of a wafer inspection apparatus.

[0002]

2. Description of the Related Art Wafers used as materials for semiconductor ICs are inspected by an optical foreign particle inspection apparatus because the quality of the wafer deteriorates when foreign substances adhere to the surface. Inspection is carried out by automated lines.

First, a description will be given of a conventional pre-alignment technique shown in Japanese Patent Application Laid-Open No. 4-290455 filed by the applicant before being mounted on an inspection stage with reference to FIG. In FIG. 5A, reference numeral 5 denotes a pre-alignment stage having a rotation mechanism (not shown) and an edge detector 6 using a CCD for the wafer cassette and the inspection stage. The arm is attracted to the handling arm 3 (see FIG. 5C), transported to the pre-alignment stage 5, and the arm is released from the attraction, and is attracted to the stage.
The wafer 1 is pre-aligned here by the method described below, and then the handling arm 3 (see FIG. 5C)
Is transferred to the inspection stage by the
The flat (OF) is placed with its midpoint c or V notch (shown simply as V in the figure) on an axis parallel to the y-axis.

In FIG. 5A, the wafer 1 attracted to the rotating mechanism of the pre-alignment stage is rotated in the θ direction, and the first edge of the wafer shown in FIG. A curve is determined. Since the center O 'of the wafer and the center O of rotation are generally displaced, this edge curve forms a sine wave. However, portions corresponding to OF and OF 'are recessed as shown. In the case of a V notch, a narrow range is reduced. Therefore, in FIG. 5A, two straight lines perpendicular to the rotation center O of the rotation mechanism are drawn, and the intersections with the circumference of the wafer are defined as p, q, r, and s. However,
Each point is taken to avoid the position of OF, OF 'or V.

Here, it is assumed that an XY coordinate system is set for the pre-alignment stage so that the center of rotation O is the origin O (0,0), and a straight line pr is a u-axis.
Consider a uv coordinate system with the straight line qs as the v axis. Note that the coordinates of the center O ′ of the wafer with respect to the uv coordinate system are the center values of both straight lines, and the coordinates (u ₀ , v ₀ ) of the center O ′ of the wafer in the uv coordinate system are expressed by the following equation. . u ₀ = (pr) / 2 (1) v ₀ = (qs) / 2 (2) where p, q, r, and s are the first edge curves Is the value of each point.

Here, assuming that the angle between the uv coordinate system and the XY coordinate system is Θ, since Θ is known, the coordinates (u ₀ , v ₀ ) can be expressed by the following equation to obtain the coordinates (X ₀ , Y ₀ ) of the XY coordinate system. ). X ₀ = u ₀ cos Θ−v ₀ sin… (3) Y ₀ = u ₀ sin Θ + v ₀ cos Θ (4) Further, the angle between the straight line OO ′ and the Y axis from the coordinates (X ₀ , Y ₀ ). φ can be calculated by the following equation. φ = arctan (X ₀ / Y ₀ ) (5) Now, when the wafer is rotated by an angle (−φ), the center O ′ comes on the Y axis, and the state shown by the dotted line in FIG. Next, when the wafer is moved (-Y ₀ ) by the handling arm 3, the wafer is brought into the state shown by the dashed line in FIG.
And are aligned. Although there are two stages,
Focusing on the linear movement function of the handling arm, accurate positioning can be performed with a simple operation.

Next, the wafer is rotated to obtain a second edge curve shown in FIG. In this curve, the sine wave disappears and becomes a straight line, but the portion of OF, OF 'or V is concave, and the concave of OF is larger than OF', so that the θ angle of the midpoint c of OF can be obtained. . The same applies to the θ angle of V. Here, the wafer is further rotated, and the midpoint c of the OF is
Alternatively, the pre-alignment ends when the V and Y axes stop at a position where the angle is ε. The angle ε is the amount of deviation of the rotation angle when the wafers of the inspection stage and the pre-alignment stage are set at their respective center positions.

[0008]

As described above, conventionally, a method has been adopted in which the wafer is loaded into the inspection stage after high-precision positioning is once performed by the pre-alignment stage.
However, when the pre-alignment stage is provided, the size of the apparatus is increased, and when the positioning processing is performed with high precision as described above, the load of the data processing of the processor in the pre-alignment increases. Further, when more accurate positioning is required, even if the wafer is carried into the foreign matter inspection stage at the set angle ε, there is a slight shift when the wafer is carried into the inspection stage, and the wafer is not a perfect circle. Therefore, there is a problem that even if the above-described positioning is performed, the center position coordinates of the wafer on the inspection stage of the foreign matter inspection system cannot be matched.

If the coordinate deviation of the center position of the wafer on the inspection stage is large, the coordinate accuracy of the foreign matter in the foreign matter detection decreases. As a result, when the foreign substance is inspected again, the position of the foreign substance may be erroneously recognized, or when the object is observed with a microscope, a scanning electron microscope (SEM), or the like, the target foreign substance cannot be found or an incorrect foreign substance is observed. Will be done. For this purpose, it is necessary to calculate the center of the wafer to obtain it.However, if the outer periphery of the wafer is obtained by a foreign substance inspection or the like, and the processing for obtaining the center of the wafer is performed again from the inspection result, the processing load is reduced. Inspection efficiency decreases. In addition, in the case of a V-notched wafer or the like, the wafer is damaged or chipped at the time of positioning by the notch, so that the positioning accuracy is reduced. The present invention has been made in view of the above, and it is an object of the present invention to provide a foreign substance inspection apparatus capable of directly performing high-precision positioning on an inspection stage instead of a pre-alignment stage.

[0010]

A feature of the wafer positioning method of the present invention for achieving the above object is that the X-axis of the inspection stage or the X-axis of the inspection stage is used to detect the edge of the wafer placed on the inspection stage. Provide an optical sensor in which a large number of detection elements are arranged corresponding to pixels along any of the Y axes,
A center positioning means for rotating the inspection stage to determine the amount of eccentricity of the wafer with respect to the inspection stage and for centering the wafer with respect to the inspection stage in accordance with the amount of eccentricity; and a detection signal corresponding to a detection pixel of the optical sensor. Center coordinate calculating means for calculating the coordinates of the three points on the outer periphery of the wafer with respect to the center with respect to the inspection stage based on the above, and calculating the center coordinates of the wafer. Things.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, an edge detection sensor having a pixel-corresponding array is provided, an eccentric amount of a wafer with respect to an inspection stage is obtained from the light receiving pixel position, and the center is aligned by a center aligning means. Since the coordinates of the three points on the outer periphery of the wafer with respect to the center with respect to the inspection stage are obtained by the center coordinate calculating means based on the detection signal corresponding to the pixel of the sensor and the center coordinates of the wafer are calculated, the wafer on the inspection stage is calculated. Can be determined more accurately and in a simple process. As a result, there is no need to calculate the center of the wafer by finding the outer periphery of the wafer by foreign substance inspection or the like, and the processing load of the processor can be reduced.

[0012]

FIG. 1 is a block diagram mainly showing a detection optical system of a foreign matter inspection apparatus according to an embodiment of the present invention. FIG. 2 is an explanatory view showing a relationship between a linear sensor, a wafer and irradiation light, and FIG. Is a flowchart of wafer positioning and center coordinate detection processing,
FIG. 4 is an explanatory diagram of the processing. As shown in FIG.
Denotes a foreign matter inspection apparatus, which includes a foreign matter inspection optical system 11, an inspection table 12, a data processing / control device 13, a table driving circuit 14, an A / D conversion circuit (A
/ D) 17, an X moving mechanism 18, a control circuit 19, and an interface 20, and the inspection table 12 has the wafer 1 mounted thereon. In addition, the control circuit 19 generates various control signals for driving the X moving mechanism 18 and the CCD control / signal readout circuit 155 in accordance with a signal from the data processing / control device 13 via the interface 20.

The foreign matter inspection optical system 11 comprises a detection optical system 15 and a projection optical system 16 as shown in the drawing.
The light projecting optical system 16 irradiates a laser beam to the inspection area 3 (foreign matter detection area) on the wafer 1 having a predetermined width in the sub-scanning direction. Then, the upward scattered light is received and detected by the detection optical system 15 provided above the inspection table 12 in the vertical direction. The foreign substance inspection optical system 11 includes an X-direction moving mechanism 18.
, And shifts in the X direction. The length of the inspection area 3 in the X direction is the width of one line in the main scanning direction. Therefore, the movement pitch in the sub-scanning direction (X direction) corresponds to this width. The projection optical system 16 includes a semiconductor laser light source 161 and condenser lens systems 162, 163, 16
4, and a reflection mirror 165. The laser beam is focused into an oval shape corresponding to the inspection area 3 and is irradiated onto the inspection area 3 of the wafer 1 at an elevation angle of about 30 ° as viewed from the wafer 1.

The detection optical system 15 is connected to the inspection area 3 of the wafer 1.
, A spatial filter 152 disposed behind the objective lens 151, a condenser lens system 153 disposed behind the objective lens 151, and a CCD sensor 154 that receives the entire image of the inspection area 3 formed by the condenser lens system 153. And CC
It comprises a CCD control / signal readout circuit 155 for reading out a detection signal from the D sensor 154. The CCD control / signal readout circuit 155 is controlled by the data processing / controller 13 via the interface 20 and the control circuit 19, serially reads out a detection signal detected in accordance with the received light intensity, and sends it out to the A / D 17. The data processing and control device 1 converts the data into a digital value through the interface 20.
3 as a detection signal (digital value).

Here, the detection optical system 15 is arranged so that the inspection area 3 corresponds to a position in the Y direction corresponding to the leading portion of the movement start position of the wafer 1 in the main scanning direction (Y direction). . In the inspection area 3, since the wafer 1 has a circular shape and a part of the inspection area 3 deviates from the outer shape of the wafer 1, for convenience of illustration and explanation, the inspection area 3 is slightly inward in the X direction in the drawing. The inspection area 3 is drawn at a position slightly inside the head position. The data processing / control device 13 is usually
1 and a memory 132 and the like.
Is received via the interface 20 and the bus 133 and stored in the memory 132. Then, the memory 132
Stores various programs including a foreign substance detection program 134, a wafer scanning program 135, a wafer positioning program 136, a center coordinate detection program 137, and the like.

The table drive circuit 14 is a drive circuit that reciprocates the inspection table 12 in the Y direction in accordance with the execution of the wafer scanning program 135 by the MPU 131. Further, in the Y direction, an amount corresponding to the diameter D + α of the wafer 1 (α is
When the movement of (scan margin) is completed, the XYZθ table 122 is rotated by 180 °, and the drive for performing the return movement of the diameter D + α in the Y direction is performed. This means that in scanning the wafer 1, reciprocating scanning and rotation in the Y direction are performed, and
This is a drive circuit that rotates by 80 °. Further, in the center positioning of the wafer 1, it is also a drive circuit that performs a minute movement for positioning the wafer 1 in the XY directions.
The XYZθ table 122 is a table that can be slightly moved in the X and Y directions and that rotates. When the center of the wafer 1 is positioned, the wafer 1 is thereby rotated.

The inspection table 12 includes a Y table 121, an XYZθ table 122, and an XYZθ table
2 is provided with a center positioning mechanism 123 provided in the center 2. The center positioning mechanism 123 is a diaphragm mechanism including a plurality of rollers 124, 124,... As the rollers 124, 124,... Rotate from the outside to the inside in a similar manner to the so-called shutter diaphragm, the center of the wafer 1 placed on the inspection table 12 is positioned at the center of the inspection table 12. Here, this is an operation corresponding to pre-alignment. This inspection table 1
Below the two wafers 1, a linear sensor (one-dimensional CCD sensor) 120 is provided parallel to the X-axis of the inspection table 12 and supported by a table 127 (see FIG. 2). The linear sensor 120 corresponds to the edge detector 6 in FIG. 5, and receives the laser beam corresponding to the inspection area 3 when the inspection area 3 is disposed above the inspection area 3.

The linear sensor 120 is converted into a digital value by an A / D conversion circuit (A / D) 17a and is taken into the data processing device 13 via the interface 20. FIG. 2 shows the relationship between the linear sensor 120, the wafer 1, and the laser beam. Note that, instead of the inspection region 3 formed by the detection optical system 15, a laser light source that generates parallel light may be provided in parallel corresponding to the pixel detected by the linear sensor 120. The Y table 121 is a moving table for scanning the wafer 1, and includes a base plate 125 and a table 127 that slides on rails 126, 126 provided in the base plate 125 in the Y direction. XYZθ table 122 is a table placed on table 127, and its movement in the X and Y directions is for centering wafer 1.
The movement in the Z direction is performed by an elevating mechanism provided inside and fixed on the table 127. The elevating mechanism mainly moves the wafer 1 in the up-down direction for focusing, and sets the position of the wafer in the up-down direction.

Now, the previous wafer positioning program 13
6, the MPU 131 executes this to position the inspection area 3 above the linear sensor 120, and
Table 122 is rotated to obtain an eccentric amount as shown in FIG. 4A from the edge detection characteristic curve E, and the center of rotation of the XYZ θ table 122 and the center of the wafer 1 are determined according to the eccentric amount. Align with. In FIG. 4A, the horizontal axis is the rotation angle θ of the wafer, and the vertical axis is the light receiving pixel position of the linear sensor 120. Nc
Is a center pixel position in a light receiving pixel viewed from a light receiving characteristic when the wafer is rotated. Further, FIG.
The OF position is obtained from the edge detection characteristic curve E of FIG.
The position of F is set to be perpendicular to the linear sensor 120, the wafer 1 is moved by a predetermined amount in the Y direction, and light receiving pixel position data as shown in FIG. Then, the angle with the Y axis is calculated to perform the angle correction. In FIG. 4B, the horizontal axis is Y
This is the amount of movement in the axial direction, and the vertical axis is the light receiving pixel position of the linear sensor 120. Here, the shift angle is twice the amount of increase in the number of light receiving elements / the amount of movement in the Y-axis direction. This is because the central angle of the wafer 1 is twice as large as the increased pixel amount of the light receiving element / the shift angle of the movement amount in the Y-axis direction corresponds to the circumferential angle. Incidentally, the above-described sampling of the eccentric amount and the center positioning of the wafer by this are known as a technique of pre-alignment. For example, Japanese Patent Application Laid-Open No. Hei 2-205049 by the applicant and Japanese Patent Application Laid-Open No.
No. 57636, etc., and details thereof are omitted. Further, in the case of a V-notched wafer, the above-described angle correction is not performed.

The center coordinate detection program 137 calculates the center of the wafer from the outer periphery of the wafer 1 and calculates the deviation between the actual center of the wafer and the center of the inspection table 12 with higher accuracy. When the MPU 131 executes this, as shown in FIG. 4C, any three points A, B, and C (where O
(Except on F), the midpoint of each chord is calculated in the geometric calculation, and the center coordinate as viewed from the circumference of the wafer 1 is obtained as the intersection of the center lines passing through the midpoint of each chord. . The coordinates of this intersection point are the center of the wafer 1 and represent the amount of deviation from the center of the XYZθ table 122.
This is calculated as the offset amount. This offset amount is used as a coordinate conversion value for the detected foreign matter,
It is converted into coordinates on the wafer 1. Any three points A,
For the coordinates of B and C, the center of the XYZθ table 122 is determined by the angle α when the XYZθ table 122 is rotated by an arbitrary angle α and the last light receiving pixel position in the detection signal of the linear sensor 120 when the angle α is rotated. Is XY
The coordinates of the detection point as coordinates are obtained, and the coordinates when the rotation angle α is returned to the original position can be obtained in relation to the rotation angle α. Since the linear sensor 120 is mounted along the X axis, the X, Y coordinates from the current center of the XYZθ table 122 can be detected based on the relationship between the mounting position and the last light receiving pixel position. In this way, the coordinates of each of the three points are obtained by rotating by an arbitrary angle.

FIG. 3 shows a wafer positioning program 13.
6 is a flowchart of wafer positioning and center coordinate calculation processing performed by the MPU 131 executing the center coordinate detection program 137. First, MPU
131 executes the wafer positioning program 136,
The inspection area is positioned above the linear sensor 120 (step 101), and the XYZθ table 122 is rotated to obtain an edge detection characteristic curve E to calculate the amount of eccentricity of the wafer 1 (step 102). (Step 103). Next, an OF angle (position) on the wafer is obtained from the edge detection characteristic curve E (step 10).
4) The OF position is set so as to be perpendicular to the linear sensor 120 (step 105), and the correction angle is calculated by moving the wafer along the Y axis (step 106). X
Table 122 is rotated to correct the angle of the wafer with respect to the Y axis (step 107).

Next, the MPU 131 executes the center coordinate detection program 137 to obtain the coordinates of the three points A, B, and C (step 108), and calculates the center coordinates of the wafer 1 as an offset amount (step 109). ), The calculated offset amount is stored in the memory 132 (step 110).
When the foreign substance detection program 134 is executed, the coordinates of the collected foreign substance are converted into coordinates on the wafer 1 based on the offset amount, displayed on a display, and used as foreign substance detection data. You. In addition,
In the case of a V notch wafer, there is no step from step 104 to step 107.

In the above case, the linear sensor 12
0 may be provided along the Y-axis direction of the XYZθ table 122, another linear sensor is separately provided along the Y-axis direction, and the OF position of the wafer 1 is arranged at a right angle to this linear sensor. The angle may be corrected along the X-axis direction. As described above, it goes without saying that the linear sensor 120 in the embodiment may be a two-dimensional CCD sensor, and a linear sensor is an optical sensor in which a large number of detection elements are arranged in a predetermined direction corresponding to pixels. Good. In the case of two dimensions, it is possible to collect the average value of the detection values in the direction perpendicular to the case of one dimension. In addition, the linear sensor 120
May be made to coincide with the Y-axis direction of the inspection table 12 instead of the X-axis.

[0024]

As described above, according to the present invention, an edge detection sensor having a pixel-corresponding array is provided, and the amount of eccentricity of the wafer with respect to the inspection stage is obtained from the position of the light-receiving pixel. After the alignment, the coordinates of the three points on the outer periphery of the wafer with respect to the center with respect to the inspection stage are obtained by the center coordinate calculating means based on the detection signal corresponding to the pixel of the optical sensor, and the center coordinates of the wafer are calculated. The center position of the wafer on the inspection stage can be obtained more accurately and in a simple process. Therefore, there is no need to calculate the center of the wafer by finding the outer periphery of the wafer by foreign substance inspection or the like, and the processing load of the processor can be reduced. As a result, when a foreign substance inspection is performed again, the risk of erroneous recognition of the position of the foreign substance or a failure to find the target foreign substance when observing with a microscope or the like is reduced, and the efficiency is improved. Foreign matter inspection becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram centering on a detection optical system of an embodiment of a foreign substance inspection apparatus according to the present invention.

FIG. 2 is an explanatory diagram of a relationship between a linear sensor, a wafer, and irradiation light.

FIG. 3 is a flowchart of wafer positioning and center coordinate detection processing.

FIG. 4 is an explanatory diagram of the processing, in which (a)
Is an explanatory diagram of an edge detection characteristic curve, (b) is an explanatory diagram of a light receiving pixel position, and (c) is an explanatory diagram of a relationship between three points taken on a wafer.

5 (a) to 5 (d) are explanatory views of conventional pre-alignment performed before mounting on an inspection stage.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wafer, 2, 11 ... Foreign matter inspection optical system, 3 ... Inspection area, 10 ... Foreign matter inspection apparatus, 12 ... Inspection table, 13 ...
Data processing / control device, 14 ... Table drive circuit, 15
Detecting optical system, 16 Projecting optical system, 17 A / D conversion circuit (A / D), 18 X-direction moving mechanism, 120 Linear sensor (one-dimensional CCD sensor), 121 Y table, 1
22 XYZθ table, 131 MPU, 132 memory, 133 bus, 134 foreign matter detection program, 1
35: wafer scanning program, 136: focusing program, 151: objective lens, 152: spatial filter,
153: condenser lens system, 154: CCD sensor, 155
... CCD control / signal readout circuit, 161, semiconductor laser light source, 162, 163, condenser lens system, 164, reflection mirror.

Claims (2)

[Claims] In a foreign matter inspection apparatus having an XYθ inspection stage, detection is performed in correspondence with pixels along either the X axis or the Y axis of the inspection stage in order to detect an edge of a wafer mounted on the inspection stage. An optical sensor in which a number of elements are arranged is provided, and the inspection stage is rotated to obtain an amount of eccentricity of the wafer with respect to the inspection stage, and the center of the wafer is aligned with the inspection stage in accordance with the amount of eccentricity. Center alignment means for calculating the center coordinates of the wafer by calculating coordinates of three points on the outer periphery of the wafer with respect to the center with respect to the inspection stage based on a detection signal corresponding to the detection pixel of the optical sensor. Means for inspecting foreign matter using the calculated center coordinates as the center of a wafer in foreign matter detection. 2. The wafer according to claim 1, wherein the wafer has an orientation flat, the optical sensor is a linear sensor, and the center position adjusting means adjusts the orientation position after the center position corresponding to the eccentricity. After positioning the flat in a direction perpendicular to the pixel array direction of the optical sensor, the wafer is moved along the perpendicular direction, and the inclination angle of the wafer with respect to the perpendicular direction is obtained. The foreign matter inspection device according to claim 1, wherein the deviation is corrected.