JP3243784B2 - Work table positioning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work table positioning apparatus, and more particularly, to a wafer foreign matter inspection apparatus which prevents a laser optical position sensor from being misaligned due to a temperature drift when the inspection table is focused. The present invention relates to a focusing apparatus for a wafer foreign matter inspection apparatus that can perform the focusing.

[0002]

2. Description of the Related Art FIG. 5 shows a focusing system of a conventional wafer foreign matter inspection apparatus. Reference numeral 5 denotes an inspection table on which the wafer 1 is placed. The inspection table 5 traverses the laser beam from the laser light source 3 to receive a light beam 2 of a cylindrical laser beam having a thickness over the entire focusing area so as to cross the inspection area. This is received on the element 4 side. Then, the amount of light blocked by the inspection table 5 is measured by the passing amount, and when the amount of blocking corresponds to the focal position, the inspection table 5 is stopped, and the position of the wafer 1 is positioned at that height. The foreign matter detection optical system 6 is focused on the lens 1. Reference numeral 7 denotes a lens system that converts the light from the laser light source 3 into a parallel irradiation light beam. Reference numeral 8 denotes a lens system that focuses the parallel irradiation light beam on the light receiving surface of the light receiving element. For simplicity, only one convex lens is represented as a representative. Incidentally, such a positioning method of the inspection table is generally referred to as an optical displacement measurement method or a displacement position sensor method, and the focus position is initially set by a separate focus mechanism, for example, by a wafer. Focusing is performed by projecting two fringe pattern images slightly displaced from one another, and the output voltage value of the light receiving element 4 at that time is obtained in advance as a focusing voltage value.

[0003] If the focusing on the wafer 1 is determined by the focusing mechanism each time, the throughput decreases. Therefore, the focusing position of the inspection table 5 on which the wafer 1 is precisely placed by the focusing mechanism only at the beginning. (Height) is obtained in advance, and the amount of received light at that time is obtained as an output of the light receiving element 4. Thereafter, by setting the height of the inspection table 5 at the same position as the output, the foreign matter detection optical system 6 is positioned on the wafer 1 simply and at high speed, thereby focusing.

[0004]

However, in such an optical displacement measurement using a light emitting element and a light receiving element, a change in the temperature characteristic on the light receiving element side, that is, a so-called temperature drift, becomes a problem. That is, as shown in FIG.
When the output voltage value at the in-focus position Zf is Vf, and the characteristic of the output voltage value with respect to the height of the inspection table 5 is measured, and the characteristic graph at the time of focusing is G1, this characteristic is As the voltage rises, the output voltage Vf sequentially decreases. When the ambient temperature rises, the characteristic graph G
1 drifts to the right, and the characteristic changes to graph G2. When the ambient temperature decreases, the characteristic graph G1 drifts to the left, and the characteristic changes to a graph G3. As a result, even if the output voltage value Vf corresponding to the in-focus position Zf is set, the height (the position in the Z direction) of the inspection table 5 with respect to the output voltage value Vf depends on the drift characteristic due to the temperature at that time. And Δd from the original focus position Zf.
2. It is shifted by Δd3. As a result, a detection error occurs, and the accuracy of foreign matter detection decreases. Even if the temperature is compensated by a temperature compensating circuit or the like to avoid such a situation, as long as the temperature is compensated by the circuit, the circuit is also affected by the temperature, and there is a limit in eliminating the influence of the temperature. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the related art, and an object of the present invention is to provide a work table positioning device that can position a work table such as an inspection table at a predetermined position even when there is a temperature drift. To provide.

[0005]

The features of the work table positioning device of the present invention for achieving the above object are as follows.
An irradiation light source for irradiating a light beam in a range over the position detection area;
A light receiving device that receives light from the irradiation light source, a work table that traverses in a direction of sequentially blocking light beams from one side in a range of a position detection area between the light receiving device and the irradiation light source, and A shielding plate that blocks a part of the light beam from one side is provided, and the detection voltage of the light receiving device when shielded only by the shielding plate and the detection voltage of the light receiving device when the work table is positioned at a predetermined position. The difference between the detected voltage and the reference value is stored as a reference value, and the position of the work table at a predetermined position is detected by the light receiving device when the work table is shielded only by the shield plate and the light reception when the work table is moving transversely. The work table is positioned at a position where the difference value from the detection voltage of the container is obtained and the difference value substantially becomes a reference value.

[0006]

As described above, by providing the shield plate for blocking a part of the light beam from one side along the shield of the work table, the light receiver can move the work table until the work table is exceeded. Regardless, it receives a certain amount of light. As a result, characteristics are obtained as shown in FIG. That is, the output voltage characteristic is such that the output voltage value at the in-focus position is Vf,
For example, when a characteristic of an output voltage value with respect to a height Z of an inspection table is measured as a work table, FIG.
Assuming that the characteristic at the time of focusing performed separately by the focusing mechanism is Ga, this is the position Z at which the shielding plate shields.
The voltage is constant until S, and thereafter, the output voltage Vf gradually decreases as the inspection table rises. When the ambient temperature increases, the characteristic graph Ga drifts to the right, and the characteristic changes to Gb. When the ambient temperature decreases, the characteristic graph Ga drifts to the left and the characteristic changes to Gc. Even in this temperature drift state, the position of the position ZS at which the previous shielding plate shields hardly changes. At this time, the height (position in the Z direction) of the inspection table with respect to the output voltage value Vf changes to Zb and Zc according to the respective characteristics, and Δd respectively from the original in-focus position.
b, Δdc.

However, at this time, the voltage values Va, Vb, Vc shielded by the shield plate are also represented by the characteristic graphs Ga, Gb, Gc.
Drift with. In the case of temperature drift, the characteristic graphs Ga, Gb, and Gc have a relationship of substantially parallel movement, so that the drift amounts of the voltage values Va, Vb, and Vc and the drift amounts of the output voltages Vf, Vfb, and Vfc at the in-focus position. Are approximately equal. Therefore, the difference values in the characteristic graphs Gb and Gc,
That is, Vb-Vfb and Vc-Vfc are constant values Vr (= Va
-Vf, the reference value for focusing). Therefore, regarding the setting of the focus position of the inspection table, the detection voltage value Vs of the light receiving element 4 when the light beam is shielded only by the light shielding plate and the light receiving element 4 when the inspection table further shields the light beam beyond the above light shielding position. If the difference value V = Vs−Vd from the detected voltage value Vd is detected and the difference value is set to Vr, the focus position can always be set regardless of the temperature drift. That is, in the present invention, a light-shielding plate is provided for a light beam for performing position detection, and a part of the light-shielding plate is shielded. Positioning such as focusing is performed based on a difference between detection values when light is shielded beyond the light shielding position. By doing so, since these two detected values both fluctuate almost in the same manner due to the temperature drift, the difference value eliminates the influence of the temperature drift, and the reference value at the position where the difference value is first positioned. By adjusting to the difference value, it is possible to easily and quickly position the work table, and to eliminate a positioning error due to a temperature drift.

[0008]

1 is a block diagram mainly showing a detection optical system of an embodiment of a foreign substance inspection apparatus to which a work table positioning apparatus according to the present invention is applied, and FIG. 2 is a flowchart of a focusing position setting process. 3 is an explanatory diagram of position detection of the inspection table in the present invention, and FIG. 4 is an explanatory diagram of output voltage characteristics of the light receiving element. 1 shown in FIG.
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
D) 17, an X moving mechanism 18, a control circuit 19, an interface 20, and a positioning unit (described later) for an inspection table as in FIG. 5, and the inspection table 12 has a wafer 1 mounted thereon. Further, the control circuit 19 generates a drive control signal to 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 substance inspection optical system 11 includes a detection optical system 15 and a projection optical system 16 as shown in the drawing.
The light projecting optical system 16 irradiates the inspection area 30 on the wafer 1 having a width in the sub-scanning direction with a laser beam. Then, the upward scattered light is received and detected by a detection optical system 15 provided at an upper portion in the vertical direction of the inspection table 12. The foreign matter inspection optical system 11 is fixed to the X direction moving mechanism 18 and shifts in the X direction. The length of the inspection area 30 in the X direction is the width of one line in the main scanning direction. Therefore, the scanning pitch in the sub-scanning direction (X direction) corresponds to this width. The light projecting optical system 16 includes a semiconductor laser light source 161, condensing lens systems 162, 163, 164, and a reflecting mirror 165. The light projecting optical system 16 focuses the laser beam into an oblong shape corresponding to the inspection area 30. Irradiation is performed at an elevation angle of 30 ° from the wafer 1.

[0010] The detection optical system 15 is connected to the inspection area 3 of the wafer 1.
0, an objective lens 151, a spatial filter 152 disposed behind the objective lens 151, a condenser lens system 153 disposed behind the objective lens 151, and a CCD that receives the entire image of the inspection area 30 formed by the condenser lens system 153. Sensor 154,
Then, the detection signal from the CCD sensor 154 is read out.
And a CCD control / signal readout circuit 155. The CCD control / signal readout circuit 155 includes the data processing / control device 13
Is controlled via a control circuit 19 and an interface 20 and serially reads out a detection signal detected in accordance with the received light intensity, converts it into a digital value via an A / D 17 and an interface 20, and sends it to the data processing / control device 13. Send out. Here, the detection optical system 15 is in the main scanning direction (Y direction).
In FIG. 3, the wafer 1 is arranged corresponding to the inspection area 30 so as to correspond to the leading portion of the movement start position.

The data processing / control device 13 usually has an
U131 and a memory 132, etc.
The signal from D17 is received via the interface 20 and the bus 133 and stored in the memory 132. The memory 132 stores various programs including a foreign substance detection program 134, a wafer scanning program 135, a focusing program 136, and the like. further,
The parameter storage area 137 stores the difference value Vr (Vr = Va−Vf) in FIG. 4 described above.

The difference value Vr is equal to the detection voltage value Vf of the light receiving element 4 with the light shielding plate 9 described later when the wafer 1 is actually placed on the inspection table 12 by the focusing means and focused. When the inspection table 12 does not block the light beam 2 without raising the inspection table 12,
However, the voltage value when the light is shielded by the light shielding plate 9 is measured as Va, and the difference value (Va−Vf) is calculated and stored as Vr. Table drive circuit 1
4 is a wafer scanning program 135 by the MPU 131
The inspection table 12 is moved in the Y direction according to the execution of
In the Y direction, the diameter D + α of the wafer 1 (α is a scanning margin)
At the end of the movement of the Zθ table 142,
A rotation is made to make a return movement by a diameter D + α in the Y direction. That is, reciprocal scanning and rotational scanning in the Y direction are performed.

The inspection table 12 includes a Y table 121, a Zθ table 122, and a center positioning mechanism 123 provided on the Zθ table 122. The center positioning mechanism 123 is a diaphragm mechanism including a plurality of rollers 124, 124,... The rollers 124 and 1 are similar to a so-called shutter aperture.
Are rotated from the outside to the inside to position the center of the wafer 1 at the center of the inspection table 12. The Y table 121 includes a base plate 125 and a table 127 that slides on rails 126 and 126 provided in the base plate 125 in the Y direction. The Zθ table 122 is
A table placed on the table 127, and its Z
The movement in the direction is performed by an elevating mechanism provided inside and fixed on a table 127, and mainly sets the vertical position of the wafer 1 by a focusing process described later.

Here, an apparatus for setting the inspection table 12 at the in-focus height is provided in the same manner as in FIG. this is,
FIG. 1 and FIG. 3 illustrating the position detection of the inspection table.
As shown in FIG. 5, except that a light shielding plate 9 is provided, the configuration is similar to that of FIG. That is, here, the light shielding plate 9 is provided on the front surface of the lens system 8 before the light receiving element 4. Then, as shown in FIG. 1, the detection signal of the light receiving element 4 is supplied to the A / D 17 via the amplifier circuit 41.
To the MPU 131 via the interface 20
And is subjected to predetermined processing. In addition, the laser light source 3
Are driven via the control circuit 19 and the drive circuit 31.
As shown in FIG. 3, one side (lower side) of the light shielding plate 9 for sequentially shielding the light beam 2 when the inspection table 12 is raised and the height is sequentially increased from the lower side in the Z direction, as shown in FIG. Is arranged so as to cover a part of the light beam 2 from its end. As a result, as described above, the light receiving element 4
Output voltage characteristics become characteristics like the characteristic graphs Ga, Gb, and Gc in FIG. 4 as the inspection table 12 rises.

FIG. 2 is a flowchart of the focusing by the focusing program 136, which is executed prior to the foreign matter detection processing. First, the inspection table 12 is set to an initial position (Step 101). This position is a lower reference position where the light beam 2 is not blocked. Then, the current output voltage of the light receiving element 4 is detected, and the detected output voltage is stored in the memory 132 as the detected voltage value Vs (step 10).
2). Next, the Z table is driven by a predetermined amount and the inspection table 1 is driven.
2 is raised (step 103). And the light receiving element 4
Is detected, and the detected voltage value is stored in the memory 132 as Vd (step 104). Further, a difference value V = Vs-Vd is calculated (step 105). Further, it is determined whether or not Vr−δ ≦ V ≦ Vr + δ is satisfied (step 106). Here, δ is an allowable error of the focusing position.

If the result of the determination in step 106 is NO and V ≦ Vr−δ, the inspection table 12 is further raised in the Z direction (step 107), and
Return to 04. If the determination result is NO and V ≧ V
In the case of r + δ, the inspection table 12 is further lowered in the Z direction (Step 108), and the process returns to Step 104. In this repetitive loop, when the determination in step 105 becomes YES, the raising of the inspection table 12 is stopped (step 109). Difference value V at this time
Coincides with the reference value Vr (= Vs−Vf) at the time of focusing when the focusing is accurately performed first by the focusing mechanism, so that the inspection table 12 is positioned at the focusing position. . This positioning position is shown in FIG.
According to the characteristic graphs Ga, Gb, and Gc, they substantially coincide with the measurement position at the time of the first focusing measurement without being affected by the temperature drift. Thus, the positioning of the inspection table 12 at the focal position is completed, and the process proceeds to the foreign substance detection processing (step 110).

As described above, the light shielding amount of the light shielding plate 9 is determined by the characteristic graph G in the temperature drift characteristic of FIG.
What is necessary is just to set to the place where these linearity is good including the fluctuation range of a, Gb, and Gc. Further, the measurement of the difference value Vr at the actual focus position is performed by not only a stripe pattern but also a predetermined mark pattern on the wafer 1 by a CCD.
The point at which the level of the detection signal is detected by the sensor 154 and reaches the maximum value may be determined as the focusing position. Here, various other focusing methods can be used. In the embodiment, laser light is used, but the light beam may be white light or light emitted by an LED. Further, the light flux may have a predetermined width including the focus position in the moving direction of the detection table. Further, in the embodiments, focusing has been mainly described, but the present invention is not limited to focusing, and it is needless to say that the present invention can be applied to positioning of a work table in general.

[0018]

As described above, in the work table positioning apparatus according to the present invention, a light shielding plate is provided for a light beam for performing position detection, and a part thereof is shielded from light. Positioning such as focusing is performed based on a difference between a detection value in a state where the plate is shielded from light and a detection value when the work table shields the light beam beyond the light shielding position of the light shielding plate. By doing so, since these two detected values both fluctuate almost in the same manner due to the temperature drift, the difference value eliminates the influence of the temperature drift, and the reference value at the position where the difference value is first positioned. By adjusting to the difference value, it is possible to easily and quickly position the work table, and to eliminate a positioning error due to a temperature drift.

[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 to which a work table positioning apparatus according to the present invention is applied.

FIG. 2 is a flowchart of a focusing position setting process.

FIG. 3 is an explanatory diagram of position detection of an inspection table according to the present invention.

FIG. 4 is an explanatory diagram of output voltage characteristics of the light receiving element.

FIG. 5 is an explanatory diagram of a conventional position detection method of an inspection table that performs optical positioning.

FIG. 6 is an explanatory diagram of a temperature drift of an output voltage characteristic of a conventional light receiving element.

[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
... Detection optical system, 16 ... Projection optical system, 17: A / D conversion circuit (A / D), 18: X-direction moving mechanism, 131: MPU,
132 memory, 133 bus, 134 foreign matter detection program, 135 wafer scanning program, 136 focusing program, 137 parameter area, 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, 16
3 ... Condensing lens system, 164 ... Reflection mirror.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP 5-23063 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/68 G01N 21/88 H01L 21 / 66

Claims (1)

(57) [Claims] 1. An irradiation light source for irradiating a light beam in a range over a position detection area, a light receiver for receiving light from the irradiation light source, and a range of the position detection area between the light receiver and the irradiation light source. A work table that traverses in a direction to sequentially block the light beam from one side, and a shielding plate that blocks a part of the light beam from the one side in front of the light receiver, when the light beam is shielded only by the shielding plate The difference between the detected voltage of the light receiver and the detected voltage of the light receiver when the work table is positioned at a predetermined position is obtained and stored as a reference value, and the predetermined value of the work table is determined. The difference between the detection voltage of the light receiver when the positioning to the light is shielded only by the shield plate and the detection voltage of the light receiver when the work table is traversing is obtained. Positioning device for a work table for positioning the work table in a position to be substantially the reference value.