JP3047886B2 - Automatic focusing device and automatic focusing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device and an automatic focusing method, and more particularly, to a light beam adjusting means for adjusting a light beam supplied from a light source to focus on a vicinity of a test object, and a light beam adjusting means. A four-division light receiving element that receives the reflected light reflected by the specimen and detects the focal position on the specimen, and focusing means that performs focusing on the specimen based on the detected focal position. And an automatic focusing method comprising:

[0002]

2. Description of the Related Art An apparatus for inspecting masks and wafers for semiconductor manufacturing is always equipped with an automatic focusing device to prevent defocus during inspection.

[0003] As this automatic focusing device, a number of systems have been conventionally known. For example, methods using an astigmatism method, a knife edge method, a skew method, a Foucault method, and a critical angle method are known.

FIG. 7 is a schematic diagram showing the configuration of an automatic focusing apparatus to which the so-called skew method is applied. The automatic focusing apparatus 100 includes a half mirror 110 that reflects a light beam for focus detection, and an objective lens 130 that converges the reflected light beam and focuses the light near the semiconductor mask 120.
And a condenser lens 140 for converging the reflected light from the semiconductor mask 120, and a two-part light receiving element 150 for receiving the converged reflected light and detecting a focal position.

With this configuration, when the light beam for focus detection is reflected by the half mirror 110 and is incident on the objective lens 130, the objective lens 130
Focus near. The light reflected by the semiconductor mask 120 is reflected by the objective lens 130 and the half mirror 110.
Then, the light is received by the two-part light receiving element 150 via the condenser lens 140. Then, the two-piece light receiving element 150 detects the focal position as shown in FIG. In addition, (1) of FIG.
8 shows the two-divided light receiving element 150 at the time of focusing, and FIG.
(2) and (3) show the two-divided light receiving element 150 at the time of defocus.

[0006]

In the above-mentioned conventional automatic focusing apparatus, the reflected light from the semiconductor mask 120 is received by the two-divided light receiving element 150, and the defocus is detected from the difference in the amount of light.

Therefore, when there is a pattern having a different reflectance on the semiconductor mask 120, the reflected light from the semiconductor mask 120 becomes less uniform than when there is no pattern. The focus signal F is 0 even at the time of in-focus in FIG.
It does not work and malfunctions.

The present invention has been made in view of the above problems, and has an automatic focusing apparatus and an automatic focusing apparatus capable of performing focusing without depending on patterns having different reflectances formed on a test object. The purpose is to provide a method.

[0009]

In order to achieve the above object, the invention according to claim 1 comprises a light beam adjusting means for adjusting a light beam supplied from a light source so as to focus on the vicinity of an object, and a light beam adjusting means for adjusting the light beam. A four-division light receiving element that receives the reflected light reflected by the specimen and detects the focal position on the specimen, and focusing means that performs focusing on the specimen based on the detected focal position. In an automatic focusing apparatus comprising: the focusing means, sum signal output means for obtaining the sum of output signals from two elements located on the diagonal of the four-divided light receiving element, and outputting a sum signal to each, A difference signal output means for obtaining a difference between the respective sum signals and outputting a difference signal; a comparison result output means for comparing magnitudes of output signals from two elements positioned on a diagonal line and outputting a comparison result; Result of the above two elements When the larger of the output signal from the device, it is constituted comprising a sign inverting means for inverting the sign of the difference signal.

That is, when the light beam adjusting means adjusts the light beam supplied from the light source to focus on the vicinity of the test object,
When the four-divided light receiving element receives the reflected light reflected by the object with the four-divided light receiving element and detects the focal position on the same object, the sum signal output means outputs the signal on the diagonal line of the four-divided light receiving element. The sum of the output signals from the two elements located at the position is calculated, and the difference between the sum signals output respectively is obtained. The difference signal output means obtains the difference between these sum signals and outputs the difference signal.

When the comparison result output means compares the magnitudes of the output signals from the two elements located on the diagonal line and outputs the comparison result, the sign inversion means determines the sign of the same difference signal based on the comparison result. Is inverted. Then, focusing on the subject is performed based on the difference signal whose sign is inverted.

The light beam adjusting means only needs to be able to adjust the light beam supplied from the light source to focus on the vicinity of the test object, and may be a combination of a beam splitter, a relay lens, a dichroic mirror, and an objective lens. There may be.

According to a second aspect of the present invention, as an example of the configuration of the light beam adjusting means, in the automatic focusing apparatus according to the first aspect, the light beam adjusting means converts a light beam of focus detection light smaller than an aperture into a light beam. The objective lens is provided with a test object inspection objective lens which is incident while being shifted in parallel to the axis.

That is, when the light beam of the focus detection light smaller than the aperture is incident while being shifted in parallel to the optical axis, the object lens for inspection of the object focuses on the vicinity of the object.

The four-divided light receiving element only needs to be able to receive the reflected light reflected by the test object and to detect the focal position on the test object, and the amount of the reflected light received by each light receiving element The focus position may be detected based on

The focusing means only needs to be able to perform focusing on the test object based on the detected focal position. At the time of focusing, the focusing means converts reflected light received by the four-division light receiving element into each light. It may be moved in parallel or perpendicular to the joint of the light receiving elements, or may be moved in a direction connecting two diagonally located elements.

As an example of the configuration of the focusing means in the latter case, the invention according to claim 3 is an automatic focusing device according to claim 1 or 2, wherein the focusing means is provided with the sign inversion. When focusing on the test object based on the difference signal whose sign is inverted by the means, the direction connecting the centers of the two elements positioned on the diagonal line with the reflected light received by the four-division light receiving element. It is configured to be moved to.

That is, when the sign inverting means inverts the sign of the difference signal, the focusing means performs focusing on the test object based on the difference signal. Then
The reflected light received by the four-division light receiving element is moved in a direction connecting the centers of the two elements located on the diagonal line.

The invention according to claim 4 is an example of the test object on which the focusing means performs focusing.
In the automatic focusing apparatus according to any one of the first to third aspects, the focusing means is configured to perform focusing on a semiconductor manufacturing mask.

That is, the focusing means performs focusing on the semiconductor manufacturing mask based on the difference signal whose sign has been inverted by the sign inverting means.

According to another aspect of the present invention, there is provided an automatic focusing apparatus according to any one of the first to third aspects, wherein the focusing means is a semiconductor. It is configured to perform focusing on a manufacturing wafer.

That is, the focusing means performs focusing on the semiconductor manufacturing wafer based on the difference signal having the sign inverted by the sign inverting means.

As described above, the method of performing focusing on the test object is not necessarily limited to the above-described apparatus, and as an example, the invention according to claim 6 is as follows.
When adjusting the luminous flux supplied from the light source to focus on the vicinity of the test object, the reflected light reflected by this test object is received by the quadrant light receiving element to detect the focal position in the test object. Then, the sum of output signals from two elements located on the diagonal line of the same four-divided light receiving element is obtained, and further, a difference signal is output by obtaining a difference between the respective sum signals output respectively.
The sign of the same difference signal is inverted based on the comparison result output by comparing the magnitudes of the output signals from the two elements located on the diagonal line, and the specimen is tested based on the inverted difference signal. In which focusing is performed.

That is, the present invention is not necessarily limited to the form of the apparatus, but is also effective as a method.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of a focus detection system in a semiconductor mask pattern inspection apparatus according to an embodiment of the present invention.

The focus detection system 10 includes a light beam supply unit 20 for adjusting and outputting a light beam supplied from a light source, a semiconductor mask 30 for reflecting the output light beam and supplying the same to the same light beam supply unit 20. A light receiving element unit 40 that outputs a signal in accordance with a focal position where a light beam from the semiconductor mask 30 incident through the light beam supply unit 20 is connected; an arithmetic circuit 50 that outputs a focus signal based on the output signal; , The semiconductor mask 30 based on the output focus signal.
And an objective lens driving unit 60 for performing focusing in the above.

With such a configuration, the light beam supply unit 20
When the semiconductor mask 30 adjusts and outputs the light beam supplied from the light source, the semiconductor mask 30 reflects the output light beam and supplies it to the light beam supply unit 20. Then, the light receiving element unit 40 outputs a signal according to the focal position where the light beam from the semiconductor mask 30 incident via the light beam supply unit 20 is connected. Then, when the arithmetic circuit 50 outputs a focus signal based on the output signal, the objective lens driving unit 60 performs focusing on the semiconductor mask 30 based on the focus signal.

The light beam supply unit 20 is provided with a beam splitter 21 arranged to receive a light beam from a light source, a relay lens 22 for converting the light beam incident from the beam splitter 21, and a light beam incident from the relay lens 22. Dichroic mirror 23 that selectively transmits light of a predetermined wavelength
And an objective lens 24 for focusing a light beam incident from the dichroic mirror 23.

With this configuration, when a light beam for focus detection smaller than the aperture of the objective lens 24 enters the beam splitter 21 while deviating from the optical axis, it is converted into a light beam of an appropriate size via the relay lens 22. Is done. The converted light beam is applied to a dichroic mirror 2 set at 45 degrees.
3 through the semiconductor mask 30 through the objective lens 24.
Focus near the. This light flux is reflected by the semiconductor mask 30, passes through the objective lens 24, the dichroic mirror 23, and the relay lens 22, and then passes through the beam splitter 2.
The light reflected at 1 is supplied to the light receiving element unit 40.

The relay lens 22 also performs light beam conversion, but is provided mainly for adjusting the focus detection optical system.

Since the inspection of the semiconductor mask 30 is performed by a light beam having a predetermined wavelength from the reflection direction of the beam splitter 21, the dichroic mirror 23 separates a light beam for focus detection and a light beam for mask inspection having different wavelengths from each other. I do.

The semiconductor mask 30 has a mask surface on which the light beam supplied from the light beam supply unit 20 is focused. The semiconductor lens 30 is focused on the mask surface by the objective lens 24, and reflects the incident light beam to reflect the light beam. Supply to the supply unit 20.

The light receiving element section 40 includes a condenser lens 41 for converging a light beam from the semiconductor mask 30 incident through the light beam supply section 20, a four-division light receiving element 42 for focusing the converged light beam, and And outputs a signal indicating the focal position detected based on the amount of light received by each element constituting the four-division light receiving element 42.

FIG. 2 shows the four-divided light receiving element 42 and the arithmetic circuit 5
0 is shown by a block diagram. Note that output signals when the four elements A, B, C, and D constituting the four-division light receiving element 42 are irradiated with light are a, b, c, and d, respectively.

The arithmetic circuit 50 calculates the sum of the output signals a and c from the two elements A and C and outputs a sum signal a + c, and the output signals b and D from the two elements B and D. d
, And a sum signal calculation circuit 52 that outputs a sum signal b + d, and a difference between each of the sum signals a + c and b + d output from the sum signal calculation circuits 51 and 52 to calculate a difference signal Q = (a +
c) a difference signal calculation circuit 53 that outputs-(b + d), a BD determination circuit 54 that determines the magnitude of the output signals b and d from the two elements B and D and outputs a determination signal, and a determination signal based on the determination signal. And a sign inverting circuit 55 for inverting the sign of the difference signal.

With such a configuration, the four-divided light receiving element 4
When the output signals a, b, c, and d are output from the elements A, B, C, and D constituting the sum signal calculation circuit 5, respectively,
1 calculates the sum of the output signals a and c and outputs a sum signal a + c, and the sum signal calculation circuit 52 calculates the sum of the output signals b and d and outputs the sum signal b + d. Then, the difference signal calculation circuit 5
3 calculates the difference between the sum signals a + c and b + d to calculate the difference signal Q
= (A + c)-(b + d).

On the other hand, the BD determination circuit 54 outputs the output signal b,
It determines the magnitude of d and outputs a determination signal. For example, b>
When d, a positive (+) determination signal is output, and when b <d, a negative (-) determination signal is output.

Then, the sign inverting circuit 55 outputs the focus signal F by inverting the sign of the difference signal Q based on the determination signal. Therefore, the focus signal F is b
> D, F = Q, and b <d, F = -Q. When b = d, F = 0.

Accordingly, a sum signal calculation circuit 51 for calculating the sum of the output signals a and c and outputting the sum signal a + c, and a sum signal calculation circuit for calculating the sum of the output signals b and d and outputting the sum signal b + d Reference numeral 52 in this meaning constitutes a sum signal output means according to the present invention.

The difference signal calculating circuit 53 which calculates the difference between the sum signals a + c and b + d and outputs the difference signal Q = (a + c)-(b + d) is a difference signal output means according to the present invention. Is composed.

Further, the BD determination circuit 54 which determines the magnitude of the output signals b and d and outputs a determination signal is provided in this sense.
The sign inverting circuit 55 that constitutes the comparison result output means according to the present invention and inverts the sign of the difference signal Q based on the determination signal and outputs the focus signal F is, in this sense, the sign inverting means according to the present invention. Is composed.

The objective lens driving section 60 includes a piezo element (not shown) that can move the minute displacement at high speed to drive the objective lens 24, and focuses on the semiconductor mask 30 based on the focus signal F output from the arithmetic circuit 50. Perform alignment.

At this time, when the focal plane of the objective lens 24 moves, the return light from the parfocal plane reflected on the four-division light receiving element 42 is, as shown in FIG.
It moves to the element D side along the arrow 70 connecting the center of the element and the element D, and becomes as shown in FIG.

The difference signal Q when the return light is on the element B side and the difference signal Q when the return light is on the element D side have the same sign, and if the difference signal Q is positive, the return light The difference signal Q fluctuates as shown in FIG.

At this time, when the return light of the focus signal F moves to the element D side, the sign of the difference signal Q is inverted, and an S-shaped curve is obtained as shown in FIG.

That is, when the focus signal F is positive, it indicates that the mask surface is shifted to the front side, and when the focus signal F is negative, it indicates that the mask surface is shifted to the rear side. When the focus signal F is 0,
Means focus.

Since the semiconductor mask 30 has a pattern drawn on a glass substrate with chromium, the reflectance differs at the position where the pattern is formed.

In particular, as shown in FIG. 6, when an edge portion of a pattern is to be detected, information on a difference in reflectance on a mask surface is included in return light.
In some cases, a malfunction occurred.

FIG. 5 is a schematic diagram showing an inspection state of an edge portion of a pattern at a focal point. In the figure, the pattern of the semiconductor mask 30 is drawn in the vertical direction and the horizontal direction, and (1) to (3) show the case where there is a vertical edge on the right side, and (4) to (6) ) Indicates a case where there is a horizontal edge on the upper side. (7) to (9) show the case where there is a vertical edge on the left side, and (10) to (12)
Indicates a case where there is a horizontal edge on the lower side.

As described above, when the joints of the elements A, B, C, and D are arranged so as to be parallel or perpendicular to the edge direction of the pattern, the difference signal Q is always 0.

When there is a pattern on the mask surface when not in focus as shown in FIG. 3, a desired focus signal F as shown in FIG. 5 cannot be obtained due to the shape of this pattern,
A malfunction may occur. However, if the inspection is started after focusing is first performed without a pattern, there is no concern about such a malfunction as long as the focus does not suddenly shift significantly.

A malfunction may similarly occur when there is an oblique pattern at the time of focusing. However, the pattern formed on the semiconductor mask 30 has a small number of oblique patterns, and the probability of an erroneous operation is extremely small from experience.

Note that the arithmetic circuit 50 is provided with a sum signal calculating circuit 5 for normalizing the difference in reflectance on the mask surface.
The difference signal Q can also be obtained by the processing of the difference signal calculation circuit 53 and the difference signal Q.

In the present embodiment, a semiconductor mask is used as a test object. However, a semiconductor mask may be used as long as a focus is required, and a wafer on which a resist is patterned may be used.

Next, the operation of the focus detection system 10 in the semiconductor mask pattern inspection apparatus according to the present embodiment will be described.

The luminous flux for focus detection is applied to the beam splitter 21.
When the light is incident on the dichroic mirror 23, the light is converted into a light beam of an appropriate size by the relay lens 22.
As a result, only light having a predetermined wavelength is selectively transmitted.

When the transmitted light flux enters the objective lens 24, it is focused near the semiconductor mask 30. This light flux is reflected by the mask surface, passes through the objective lens 24, the dichroic mirror 23, and the relay lens 22, is reflected by the beam splitter 21, and is incident on the condenser lens 41. Focus is on.

Then, output signals a, b, c, and d are output according to the amounts of light detected by the elements A, B, C, and D constituting the four-division light receiving element 42.

The sum signal calculation circuit 51 calculates the sum of the output signals a and c and outputs a sum signal a + c.
Calculates the sum of the output signals b and d and outputs the sum signal b + d, the difference signal calculation circuit 53 calculates the sum signals a + c and b + d
And outputs a difference signal Q.

On the other hand, the BD determination circuit 54 outputs the output signals b and d
The sign inverting circuit 55 outputs a focus signal F by inverting the sign of the difference signal Q based on the judgment signal.

The objective lens driving section 60 drives the objective lens 24 based on the focus signal F to perform focusing on the semiconductor mask 30.

In this way, the output signals a, B, C, D from the respective elements A, B, C, D constituting the four-division light receiving element 42 are respectively given.
When b, c, and d are output, the difference signal calculation circuit 53 outputs the difference signal Q based on the sum signal a + c output from the sum signal calculation circuit 51 and the sum signal b + d output from the sum signal calculation circuit 52. = (A + c)-(b + d), and the sign inversion circuit 55 judges the magnitude of the output signals b and d, and inverts the sign of the difference signal Q based on the judgment signal output from the BD judgment circuit 54. Since the focus signal F is output in this way, focusing can be performed without depending on patterns having different reflectances formed on the test object.

[0063]

As described above, the present invention can provide an automatic focusing device capable of performing focusing without depending on patterns having different reflectances formed on the test object. According to the second aspect of the present invention, when focusing is performed, the reflected light received by the four-division light receiving element can be moved in a direction connecting the centers of the two elements located diagonally. Further, according to the third aspect of the present invention, it is possible to focus by making the focus detection light incident on the object lens for inspecting the test object.

Further, according to the invention of claim 4,
Focusing in a semiconductor manufacturing mask can be performed. Further, according to the fifth aspect of the invention, it is possible to perform focusing on a semiconductor manufacturing wafer.
Further, according to the invention according to claim 6, it is possible to provide an automatic focusing method capable of performing focusing without depending on patterns having different reflectances formed on the test object.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a focus detection system in a semiconductor mask pattern inspection apparatus according to an embodiment.

FIG. 2 is a block diagram illustrating a configuration of a four-division light receiving element and an arithmetic circuit.

FIG. 3 is a schematic diagram illustrating a situation when return light moves in a four-division light receiving element.

FIG. 4 is a graph showing a correlation between a focus position and a difference signal Q.

FIG. 5 is a graph showing a correlation between a focus position and a focus signal F;

FIG. 6 is a schematic diagram showing an inspection state of an edge portion of a pattern at a focal point.

FIG. 7 is a block diagram showing a configuration of a focus detection system in a conventional semiconductor mask pattern inspection apparatus.

FIG. 8 is a schematic diagram showing a situation when return light moves in a two-piece light receiving element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Focus detection system 20 Light beam supply part 21 Beam splitter 22 Relay lens 23 Dichroic mirror 24 Objective lens 30 Semiconductor mask 40 Light receiving element part 41 Condensing lens 42 Quadrant light receiving element 50 Arithmetic circuit 51 Sum signal calculation circuit 52 Sum signal calculation circuit 53 Difference signal calculation circuit 54 BD determination circuit 55 Sign inversion circuit 60 Objective lens drive unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ identification code FI H01L 21/66 G02B 7/11 M N (58) Field surveyed (Int.Cl. ⁷ , DB name) G01B 11/00-11 / 30 102 G01C 3/06 G02B 7/11 G03F 1/00-1/16 G03F 7/20-7/24 G03F 9/00-9/02 H01L 21/64-21/66

Claims (6)

(57) [Claims] 1. A light beam adjusting means for adjusting a light beam supplied from a light source to focus on the vicinity of a test object, and receiving a reflected light reflected by the test object to focus on the test object. An automatic focusing device comprising: a four-divided light receiving element for detecting a position; and focusing means for performing focusing on an object based on the detected focus position. Sum signal output means for obtaining a sum of output signals from two elements located on diagonal lines of the elements and outputting a sum signal to each of them; difference signal output means for obtaining a difference between the respective sum signals and outputting a difference signal; A comparison result output means for comparing the magnitudes of output signals from two elements located on a diagonal line and outputting a comparison result; and, as a result of the comparison, an output signal from a predetermined element is larger than the two elements. Sometimes, the sign of the difference signal is Automatic focus device, characterized by comprising a sign inverting means for. 2. The automatic focusing apparatus according to claim 1, wherein the light flux adjusting means is used for inspecting a test object which is incident while shifting the light flux of focus detection light smaller than the aperture in parallel to the optical axis. An automatic focusing device comprising an objective lens. 3. The automatic focusing apparatus according to claim 1, wherein the focusing unit is configured to detect an object based on a difference signal whose sign is inverted by the sign inverting unit. An automatic focusing device for moving the reflected light received by the four-division light receiving element in a direction connecting the centers of the two elements located on the diagonal line when performing focusing in the step (a). 4. The automatic focusing apparatus according to claim 1, wherein said focusing means performs focusing on a mask for manufacturing a semiconductor. 5. The automatic focusing apparatus according to claim 1, wherein said focusing means performs focusing on a semiconductor manufacturing wafer. 6. When the light beam supplied from the light source is adjusted to focus on the vicinity of the test object, the reflected light reflected by the test object is received by a four-division light receiving element and the test object is received. When the focal position is detected, the sum of the output signals from the two elements located on the diagonal line of the same four-divided light receiving element is obtained, and further, the difference signal is obtained by obtaining the difference between the respective sum signals output respectively. The sign of the difference signal is inverted based on the comparison result output by comparing the magnitudes of the output signals from the two elements located on the diagonal lines, and the same test is performed based on the difference signal whose sign is inverted. An automatic focusing method, wherein focusing is performed on an object.