JP4307598B2 - Focusing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a focusing device used for a microscope, an optical measuring instrument, and the like.
[0002]
[Prior art]
Conventionally, as a focusing device, for example, as disclosed in JP-A-59-177510, measurement light is irradiated onto a subject surface through an objective lens, and focusing on the subject surface is performed based on the reflected light. What you have done is known.
[0003]
FIG. 6 shows a schematic configuration of such a focusing device, in which a laser beam emitted from a semiconductor laser 1 is reflected by a deflecting beam splitter 2, converted into a parallel beam by an imaging lens 3, and a ¼ wavelength plate. 4 is transmitted, and then condensed on the surface of the subject 6 on the stage 601 through the objective lens 5. Then, the light reflected from the surface of the subject 6 enters the deflecting beam splitter 2 again through the objective lens 5, the quarter-wave plate 4, and the imaging lens 3, and this time passes through the deflecting beam splitter 2. Then, the beam is split in two directions by the beam splitter 7, and one light beam is received by the first light receiving element 9 through the first diaphragm 8 positioned in front of the focusing point P of the imaging lens 3 by the distance L. In addition, the other light beam is received by the second light receiving element 11 through the second diaphragm 10 disposed behind the focusing point P of the imaging lens 3 by a distance L. Further, an electric signal corresponding to the amount of reflected light on the surface of the subject 6 from the first light receiving element 9 and the second light receiving element 11 is input to the signal processing system 12, and for each of the input electric signals Then, a predetermined calculation is performed, and an error signal corresponding to the displacement of the surface of the subject 6 is output.
[0004]
In this case, if the signal processing system 12 is supplied with electrical signals A and B having the characteristics shown in FIG. 7A as inputs from the first light receiving element 9 and the second light receiving element 11, As a signal for detecting the displacement of the surface of the subject 6, (A−B) / (A + B) is calculated, and an error signal that becomes 0 at the focal point F as shown in FIG. The driver 13 (13 ′) moves the objective lens 5 and the subject 6 relatively in the optical axis direction (Z direction) so that the surface of the subject 6 is located at a position where the error signal becomes 0, The focus position is obtained.
[0005]
In addition, relative movement between the objective lens 5 and the subject 6 is limited by monitoring the limit position by providing, for example, a limit detector 14 in order to prevent mechanical limitations and collision between the objective lens 5 and the subject 6. The focus search range is limited.
[0006]
Thus, for example, as shown in FIG. 8, the limiting position where the distance between the objective lens 5 and the subject 6 is the maximum is the focusing search upper limit position (upper limit U), and the distance between the objective lens 5 and the subject 6 is the minimum. Assuming that the in-focus search lower limit position (lower limit D), the in-focus position search is performed in the range between the upper limit U and the lower limit D.
In the drawing, 15 is an illumination power source for observation, and 16 is an observation optical system.
[0007]
[Problems to be solved by the invention]
By the way, when the subject 6 is a semiconductor wafer, the search position is different as shown in FIG. 8 only by the search position being different even on the same wafer due to, for example, bending when supporting the stage 601. The height of the wafer surface may differ between A and the search position B. In such a case, the in-focus search range required for the search position A is A ′, whereas the in-focus search range required for the search position B is B ′, and these required in-focus search ranges A 'And B' are different.
[0008]
For this reason, if the search position is moved to B from the state in which the search position A is focused in the focus search range A ′, the focus search range A ′ is focused on the search position B. Without being obtained, the apparatus once increases the distance between the objective lens 5 and the subject 6 to the in-focus search upper limit position (upper limit U) and reduces the distance from this position in the in-focus search lower limit position (lower limit D) direction. There is a problem in that the focus search is performed for the entire focus search range, the focus operation time is significantly increased, and the work efficiency of subject observation and the like is significantly reduced.
[0009]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a focusing apparatus that can set a focus search range required for each subject and can significantly reduce the time required for the focus search operation. And
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, the subject surface is irradiated with the measurement light through the objective lens, and the subject and the objective lens are moved relative to each other in the optical axis direction based on the reflected light. in focusing device to find the focus to the surface, the performs a focusing operation Te into a plurality of measurement points along the measurement lines set on the subject, said subject or an objective lens in each of these measurement points Position detecting means for detecting the position in the optical axis direction, and adding a predetermined value to the maximum value and the minimum value of the position in the optical axis direction of the subject or objective lens detected by the position detecting means ; and a focusing search range setting means for setting a focus search range by, performing a focusing operation for the subject surface on the basis of the focus search range set by the focus search range setting means That It is a feature.
[0011]
According to a second aspect of the present invention, in the first aspect of the present invention, the measurement line set on the subject includes at least a straight line or a curved line passing through the center of the subject.
[0012]
The invention according to claim 3 is the invention according to claim 1, further comprising a confocal correction table storing a confocal correction value for each objective lens, and the confocality of the confocal correction table corresponding to the objective lens. The focus search range set by the focus search range setting means is corrected based on the correction value.
[0013]
As a result, according to the first aspect of the present invention, it is possible to narrow down the focus search range necessary for the subject in order to search for the focus position, thereby greatly reducing the time required for the focus search operation. it can.
[0014]
According to the second aspect of the present invention, since the focus search range can be set based on the measurement values at the measurement points over a wide range including the central portion of the subject, a highly accurate focus search range can be set.
According to the third aspect of the present invention, even when a confocal correction amount exists between the objective lenses, it is possible to set an appropriate in-focus search range according to the subject in consideration of the confocal correction amount.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows a schematic configuration of a focusing apparatus to which the present invention is applied, and the same parts as those in FIG. 6 are denoted by the same reference numerals.
[0016]
In this case, it is assumed that the semiconductor wafer 6 ′ is placed on the stage 601 as a subject. The central portion of the semiconductor wafer 6 ′ is sucked and held by an air chuck 601 a on the stage 601.
[0017]
A counter 17 is connected to the driver 13. The counter 17 detects the distance between the objective lens 5 and the semiconductor wafer 6 ′. Here, information on the optical axis direction (Z direction) between the objective lens 5 and the semiconductor wafer 6 ′ is obtained from the driver 13. It receives and detects the coordinate position of the objective lens 5 in the Z direction.
[0018]
Focus counter range setting means 18 is connected to the counter 17. The focus search range setting means 18 includes a memory 181 and a comparator 182. Here, the memory 181 stores the contents of the counter 17. In this case, there are two data stored in the memory 181, one is the upper limit data (MAX value) of the focus search range, and the other is the lower limit data (MIN value) of the focus search range. . The comparator 182 compares the contents of the counter 17 and the memory 181 and updates the MAX value and the MIN value in the memory 181 based on the comparison result.
[0019]
A focus controller 19, an XY driver 20 and an offset unit 21 are connected to the focus search range setting means 18. The focus controller 19 is inserted in front of the driver 13 and controls the focus search range based on outputs from the memory 181 and the comparator 182. The XY driver 20 is for driving the stage 601 in the XY direction so as to move the semiconductor wafer 6 ′ in a direction orthogonal to the optical axis direction (Z direction). The offset unit 21 is for correcting the focus search range set by the focus search range setting means 18.
[0020]
Next, the operation of the embodiment configured as described above will be described.
First, a semiconductor wafer 6 ′ arbitrarily extracted as a basic sample first is set on the stage 601, and a focus search range is set.
[0021]
Also in this case, the central portion of the semiconductor wafer 6 ′ is sucked and held by the air chuck 601 a on the stage 601. Further, the objective lens 5 having the lowest magnification is used. This is because the lower magnification provides better followability of focusing, and is not necessarily limited to this.
[0022]
Next, as shown in FIG. 2, a measurement line SP for setting a focus search range is determined on the semiconductor wafer 6 ′. In this case, the measurement line SP designates the peripheral edge on the semiconductor wafer 6 ′ as the measurement start point S, and extends straight from the measurement start point S to the diagonal peripheral edge through the center of the semiconductor wafer 6 ′. It consists of lines.
[0023]
From this state, first, the stage 601 is driven by the XY driver 20, the optical axis of the objective lens 5 is made to coincide with the measurement start point S, the focusing operation is performed, and the objective lens 5 and the semiconductor wafer 6 'are taken by the counter 17. The coordinate position in the Z direction of the objective lens 5 is detected from the information in the optical axis direction (Z direction) between the two. The in-focus coordinate position of the measurement start point S is written in the MAX value and the MIN value in the memory 181 as initial values.
[0024]
Next, the stage 601 is moved by the XY driver 20, the optical axis of the objective lens 5 is moved along the measurement line SP, and the focusing operation is performed, and the counter 17 in the Z direction of the objective lens 5 at this time is moved. Detect the coordinate position. Thereafter, in the same manner, the focusing operation is performed for each measurement point while moving the optical axis of the objective lens 5 along the measurement line SP, and the coordinate position of the objective lens 5 in the Z direction is detected.
[0025]
In this case, the coordinate position in the Z direction of the objective lens 5 is curved in the direction in which the central portion of the semiconductor wafer 6 'is supported on the stage 601 and the central portion is expanded as described above. It is obtained as a locus as shown in FIG.
[0026]
Each objective coordinate position in this case is compared with the value written in the memory 181 by the comparator 182. If the comparison shows that the coordinate position is larger than the value written in the MAX value, The MAX value is updated with the value. If the value is smaller than the value written in the MIN value, the MIN value is updated with the value. Thereby, as the MAX value and the MIN value of the memory 181 at the time when the focusing operation along the measurement line SP is completed, the maximum value of the coordinate position in the Z direction of the objective lens 5 at the time of focusing on the measurement line SP. AF_U ′ and minimum value AF_D ′ are written respectively.
[0027]
In this case, if the in-focus search range thus measured is set as the in-focus search range for the subsequent in-focus operation, the in-focus search range is set when the in-focus operation is performed outside the measurement line SP. Beyond that, as described in the conventional example, the objective lens 5 is lifted to the focus search upper limit position, and the focus search is performed for the entire focus search range while reducing the distance from this position toward the focus search lower limit position. There is.
[0028]
Therefore, here, after the measurement is completed, the in-focus search range obtained as shown in FIG. 3 is revised as follows.
In this case, the offset amount F is added to the MAX value of the memory 181 and subtracted from the MIN value by the offset unit 21, and the focus search upper limit position AF_U and the focus search lower limit position AF_D of these new values are set to MAX. Value and MIN value are written in the memory 181 and the range from the MAX value to the MIN value is set as the focus search range. Here, the offset amount F of the offset unit 21 is, for example, as shown in FIG. 3, R is the distance from the maximum value AF_U ′ of the focus search range to the focus search upper limit position (upper limit U), and the minimum value AF_D ′. When the distance from the focus search lower limit position (lower limit D) is R ′, (R + R ′) / 4 is set as the maximum value and is determined from this range, and a new value is determined by the determined offset amount F. The focus search upper limit position AF_U and the focus search lower limit position AF_D are set.
[0029]
Thereafter, a focusing operation at an arbitrary observation point on the semiconductor wafer 6 ′ is performed based on the focus search range set in this way. The focusing operation in this case is performed by moving the objective lens 5 within the range of the focus search upper limit position AF_U written in the MAX value of the memory 181 and the focus search lower limit position AF_D written in the MIN value. A focus search is performed. In other words, in order to perform the focus position search operation, the focus controller 19 moves the objective lens 5 to the position indicated by the focus search upper limit position AF_U, and then the focus search lower limit position AF_D. The focus search is performed while moving the objective lens 5 toward the position.
[0030]
Therefore, according to such a configuration, in order to search for the in-focus position, conventionally, the objective lens 5 is once extended to the in-focus search upper limit position (upper limit U), and the in-focus search lower limit position from this position. A focus search lower limit from the focus search range necessary for the semiconductor wafer 6 ′, that is, the focus search upper limit position AF_U, is obtained by performing the focus search for all the focus search ranges while reducing the distance in the (lower limit D) direction. Since it is possible to narrow down the position between the positions AF_D, the time required for the focus search operation can be greatly shortened, and in particular, many defect inspections of the same type of semiconductor wafer 6 ′ can be performed. In such a case, the time loss associated with the focus search operation can be minimized, and the work efficiency can be dramatically increased.
[0031]
In the first embodiment described above, the center portion of the semiconductor wafer 6 ′ as a basic sample is sucked and held by the air chuck 601a on the stage 601, but the peripheral portion of the semiconductor wafer 6 ′ is sucked. It can also be applied to what is held. In this case, the in-focus search range is set in a state where the central portion of the semiconductor wafer 6 ′ is curved in the concave direction.
[0032]
Further, although the counter 17 detects the coordinate position of the objective lens 5 in the Z direction, the counter 17 may detect the coordinate position of the stage 601 in the Z direction.
Further, the determination of the measurement line SP on the semiconductor wafer 6 ′, which is a basic sample when setting the focus search range, takes into account the maximum and minimum values of the Z-axis coordinates of the objective lens 5 during the subsequent focus. Various applications are possible. For example, if a plurality of measurement lines SP that intersect at the center of the semiconductor wafer 6 ′ are employed, the focus search range can be set with higher accuracy, and a spiral that covers the sample surface to some extent. Various settings can be made in combination with the offset amount. Further, the measurement line SP is effective not only in the horizontal direction but also in combination with the rotational movement of the semiconductor wafer 6 ′, or in consideration of the inclination and the deflection.
[0033]
Furthermore, the offset amount set by the offset unit 21 is not necessarily constant, and may be variable based on, for example, the magnification and the depth of focus of the objective lens 5, and the characteristics of the objective lens 5 due to temperature are taken into consideration. It may be a value.
[0034]
In addition, the focus search range setting operation is performed by setting the semiconductor wafer 6 ′ on the stage 601, exchanging the objective lens 5, taking in the maximum and minimum values of the objective position on the measurement line SP, and matching from the acquired value. A series of steps such as setting a focus search range may be automatically performed in combination with an electric stage, an electric revo, etc. In this way, further time efficiency can be obtained. Of course, some operations such as stage movement can be replaced with manual operation.
(Second Embodiment)
FIG. 4 shows a schematic configuration of the second embodiment of the present invention, and the same parts as those in FIG.
[0035]
In this case, reference numeral 5 ′ denotes another objective lens that replaces the objective lens 5. Further, the focus search range setting means 18 further includes a focus correction table 183 and an adder 184. The in-focus correction table 183 stores in-focus correction values for the respective objective lenses 5 and 5 ′. Here, based on the object information, the current object position with respect to the reference object in the Z-axis direction is stored. The correction amount is output. Thereby, when the objective lens 5 is changed to the objective lens 5 ′, the correction amount indicated by the in-focus correction table 183 is added to the value from the memory 181 via the adder 184 with respect to the changed objective lens 5 ′. Then, by moving the position of the objective lens 5 ′ in the Z direction, the in-focus correction at the time of objective replacement is performed.
[0036]
Next, the operation of the embodiment configured as described above will be described.
In this case, it is assumed that the objective lens 5 is changed to another objective lens 5 ′. In this case as well, the in-focus search range is set. However, during the in-focus search range setting, the correction amount is not output from the in-focus correction table 183. For this reason, the adder 184 outputs the value from the memory 181 as it is, and the same setting operation as described in the first embodiment is performed.
[0037]
Here, it is assumed that the upper limit AF_U and the lower limit AF_D are respectively set as the focus search range a as shown in FIG. 5 by the operation of setting the focus search range.
When the focusing operation is executed from this state, the in-focus correction table 183 outputs the correction amount in the Z-axis direction from the objective information of the objective lens 5 ′ after the change. Assuming that the in-focus correction amount of the objective lens 5 ′ after the change is a brass value Z_OFF_1, the upper limit AF_U and the lower limit AF_D of the focus search range a shown in FIG.
AF_D + Z_OFF_1
Thus, the focus search range a is corrected to the focus search range b shifted by the correction amount Z_OFF_1.
[0038]
Similarly, even when the in-focus correction amount of the objective lens 5 ′ after the change is a negative value Z_OFF_2, the upper limit AF_U and the lower limit AF_D of the focus search range a shown in FIG.
AF_D + Z_OFF_2
Thus, the in-focus search range a is corrected to the in-focus search range c shifted by the correction amount Z_OFF_2.
[0039]
In this case, of course, which focus search range b or c gives priority to the range of the upper limit U and the lower limit D, which is the limit value range.
Therefore, according to such a configuration, even when there is an in-focus correction amount between the objective lenses 5 and 5 ′, an appropriate in-focus search according to the semiconductor wafer 6 ′ in consideration of the in-focus correction amount. Since the range can be set, a more stable focusing operation can be performed quickly.
[0040]
In the first and second embodiments described above, the case where there are two light receiving elements that perform photoelectric conversion has been described, but the number is not limited to this. In the above description, the case where the objective lens 5 is driven in the optical axis direction (Z direction) by the driver 13 has been described. However, the stage 601 is driven in the optical axis direction (Z direction) using the driver 13 ′. You may do it. Further, the focus detection means is not limited to the above-described method, and other well-known methods such as a pupil division method may be employed.
[0041]
【The invention's effect】
As described above, according to the present invention, since a focus search range required for each subject can be set, the time required for the focus search can be shortened, and focusing is performed in a minimum time. be able to.
[0042]
In addition, even if there is an in-focus correction amount between each objective lens, an appropriate in-focus search range can be set according to the subject in consideration of the in-focus correction amount, and a more stable in-focus operation can be performed quickly. Can be done.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of the first embodiment;
FIG. 3 is a diagram for explaining the operation of the first embodiment;
FIG. 4 is a diagram showing a schematic configuration of a second embodiment of the present invention.
FIG. 5 is a diagram for explaining the operation of the second embodiment;
FIG. 6 is a diagram showing a schematic configuration of a conventional focusing device.
FIG. 7 is a view for explaining a focusing operation of a conventional focusing device.
FIG. 8 is a diagram for explaining a focusing operation of a conventional focusing device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Deflection beam splitter 3 ... Imaging lens 4 ... Wavelength plate 5.5 '... Objective lens 6 ... Test object 6' ... Semiconductor wafer 601 ... Stage 601a ... Air chuck 7 ... Beam splitter 8.10 ... Diaphragm DESCRIPTION OF SYMBOLS 9 ... 1st light receiving element 11 ... 2nd light receiving element 12 ... Signal processing system 13 ... Driver 14 ... Limit detector 15 ... Illumination light source 16 ... Observation optical system 17 ... Counter 18 ... Focus search range setting means 181 ... Memory 182 ... Comparator 183 ... Focus correction table 184 ... Adder 19 ... Focus controller 20 ... XY driver 21 ... Offset unit

Claims (3)

The object surface is irradiated with the measurement light through the objective lens, and the distance between the object and the objective lens is relatively moved in the optical axis direction based on the reflected light to search for the focus on the object surface. In the focusing device,
Wherein performs a focusing operation Te into a plurality of measurement points along the measurement lines set on the object, the position detection for detecting the position along the optical axis of the object or objective lens in each of these measurement points Means,
Focus search range setting means for setting a focus search range by adding a predetermined value to the maximum value and minimum value of the position of the subject or objective lens in the optical axis direction detected by the position detection means And
Focusing apparatus characterized by performing a focusing operation for the subject surface on the basis of the focus search range set by the focus search range setting means.   The focusing apparatus according to claim 1, wherein the measurement line set on the subject includes at least a straight line or a curved line passing through the center of the subject. Furthermore, it has a focusing correction table that stores the focusing correction value for each objective lens,
2. The focusing device according to claim 1, wherein the focus search range set by the focus search range setting means is corrected based on a focus correction value of the focus correction table corresponding to the objective lens. .

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