JPH08226900A - Surface condition inspection method - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To obtain a surface state inspection method capable of highly accurately detecting foreign matter such as dust adhering to the surface of a reticle or a pellicle. A substrate is provided by illuminating the surface of a substrate having a plurality of patterns extending in mutually different directions with illumination light and detecting light generated in the detection direction among diffracted light and scattered light generated from the substrate surface by the illumination. In the method for inspecting the surface state of the substrate, a plurality of inspection states are set for the inspection positions on the substrate surface, and when there is light generated in the detection direction in each of the plurality of inspection states, there is a foreign substance at the inspection position. To judge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface state inspection method, and more particularly to a substrate such as a reticle or a photomask on which a circuit pattern used in a semiconductor manufacturing apparatus is formed, and foreign matter other than the circuit pattern on the substrate, For example, the present invention relates to a surface state inspection method suitable for detecting impermeable dust and the like.

[0002]

2. Description of the Related Art Generally, in an IC manufacturing process, an exposure circuit pattern formed on a substrate such as a reticle or a photomask is formed on a wafer surface coated with a resist by a semiconductor printing apparatus (stepper or mask aligner). It is transcribed and manufactured. At this time, if foreign matter such as dust is present on the surface of the substrate, the foreign matter is also simultaneously transferred at the time of transfer, which causes a decrease in yield of IC manufacturing.

In particular, when a reticle is used and a circuit pattern is repeatedly printed on the wafer surface by the step-and-repeat method, one foreign substance on the reticle surface is printed on the entire surface of the wafer, greatly reducing the yield of IC manufacturing. It becomes a cause. Therefore, in recent years, the presence of foreign matter such as dust on the substrate has become a big problem. Therefore, various methods have been proposed for detecting a defect in a circuit pattern such as a reticle or a photomask and a foreign substance on the circuit pattern.

One of those methods is a method of comparing with design data. This is to store the design data that is the ideal pattern of the reticle or photomask in advance so that it can be processed by a computer, irradiate the reticle with a beam of a laser or the like, and compare the pattern from the transmitted light with the design data. This is a method for detecting a defect in a circuit pattern such as a reticle or a foreign substance, and it is also possible to detect a common defect of each chip on a photomask due to a malfunction of a pattern generator or the like.

However, since the method handles a huge amount of design data, the inspection time is long and high positioning accuracy is required for the positioning of the test object.

Another method is to compare adjacent chips. Since this detects defects by comparing the chip patterns on the photomask, it is unnecessary to compare anything other than the test object such as design data,
Inspection time is also short. However, in this method, in the case of a stepper reticle or the like, one chip in one reticle cannot be in principle inspected.

Therefore, neither of the above two methods is suitable for a reticle inspection method for steppers, especially for an automated foreign matter inspection apparatus that requires high-speed inspection. Therefore,
As a method of compensating for the above-mentioned defects, there is a method utilizing the characteristic that a foreign substance scatters light isotropically. For example, FIG. 4 shows an embodiment using this method.

In the figure, the scanning mirror 22 and the lens 2
The optical path of the light flux from the laser 23 via the mirror 20
By selectively inserting into two, two mirrors 15,
The light is made incident on the front surface and the back surface of the substrate 5 in sequence by 19 and the scanning mirror 22 is rotated or vibrated to scan the substrate 5. A plurality of light receiving portions 16, 17, 1 are provided at positions apart from the optical paths of the reflected light and the transmitted light directly from the substrate 5.
8 is provided, and the presence of foreign matter on the substrate 5 is detected using the output signals from the plurality of light receiving units 16, 17, and 18.

That is, since the diffracted light from the circuit pattern has a strong directivity, the output values from the respective light receiving parts are different, but the diffracted light from the foreign matter is isotropically scattered, so that the output from each light receiving part is different. The values are equal. Therefore, the presence of foreign matter is detected by comparing the output values of the respective light receiving units at this time.

On the other hand, the present applicant has proposed the surface condition inspection device shown in Japanese Patent Application Nos. 61-303631 and 61-30362 in order to increase the accuracy of separating foreign matters from the circuit pattern. .

In FIG. 1, a laser beam is made incident obliquely from above in the directions B1 and B2 forming an angle β with respect to the lateral directions c1 and c2 of the substrate 5 such as a reticle.
0, see FIG. 5B). And FIG. 5 (B)
As shown in FIG. 7, only the scattered light having the reflection angle α1 with respect to the substrate 5 is received among the scattered light from the foreign matter returning to the incident side on the incident surface.

FIG. 5A shows the principle of this system and is an explanatory view of the substrate 5 viewed from directly above. In the figure, the circuit pattern on the substrate 5 is shown in the vertical and horizontal directions (V1, V2 directions,
Since most of them are in the L1 and L2 directions), when a laser beam is incident on these patterns, the pattern diffracted light proceeds in the L1 and L2 directions or the V1 and V2 directions which are the orthogonal directions. Therefore, the scanning direction of the laser beam with respect to the substrate 5 is set to a direction that forms an angle β with the vertical and horizontal directions of the substrate 5. As a result, the diffracted light from the circuit pattern is dominated in the vertical and horizontal directions of the substrate 5, so that only a small amount of diffracted light from the circuit pattern is received, but the diffracted light from a foreign substance having isotropic scattering is relatively large. It will receive light. Therefore, the presence of the foreign matter is detected by determining the magnitude of the output signal from the light receiving unit 9.

However, according to the above-mentioned conventional method, when there is a circuit pattern forming an angle β with respect to the vertical and horizontal directions of the substrate 5, the same diffracted light as in the case of a foreign substance is received from this pattern. Therefore, the circuit pattern may be erroneously detected as a foreign matter.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface state inspection method capable of accurately separating a circuit pattern and a foreign substance and accurately determining the presence or absence of the foreign substance.

[0015]

According to the surface condition inspection method of the present invention, (1-1) the surface of a substrate having a plurality of patterns extending in mutually different directions is illuminated with illumination light, and the illumination is generated from the substrate surface. In the method of inspecting the surface state of the substrate by detecting the light generated in the detection direction among the diffracted light and the scattered light, a plurality of inspection states are set for the inspection position of the substrate surface, and the inspection state of the plurality of inspection states is set. It is characterized in that when there is light generated in each of the detection directions, it is determined that there is a foreign substance at the inspection position, and that the substrate is a substrate on which a circuit pattern is formed.

[0016]

1 is a schematic view of an optical system according to an embodiment of the present invention. In the figure, 1 is a laser light source, 2
Is a polygon mirror, and 4 is a light projecting section having an f-θ lens. A substrate 5 is an object to be measured such as a reticle, and a circuit pattern is formed on the surface of the substrate 5. A light condensing unit 6 condenses the scattered light flux from the foreign matter on the substrate 5. 7 is a reflecting member such as a mirror, 8 is a light guiding lens, 9 is a light receiving section, and 150
Is a rotary XY stage. The polygon mirror 2 and the light projecting section 4 form a part of the light projecting means. Further, the light collecting section 6, the reflecting member 7 and the light guiding lens constitute a part of the light receiving means.

The light beam from the laser light source 1 is reflected in one direction by the polygon mirror 2 and is condensed at a point O on the substrate 5 by the light projecting section 4. Then, the polygon mirror is rotated to scan the substrate 5 in the direction from point B1 to point B2, and
The entire surface of the substrate 5 is scanned by moving the substrate 5 in the direction of arrow S1 or arrow S2. The laser light source 1, the polygon mirror 2, and the light projecting unit 4 constitute one element of the scanning optical system. Then, the light is condensed at a point P2 via the condensing unit 6 above the substrate 5 and the reflecting member 7, and then guided to the light receiving unit (photoelectric converter) 9 by the light guiding lens 8.

Reflecting member 7 on extension of optical axis 81 of lens 8.
The line connecting the intersection point 71 with the intersection point O on the substrate 5 is
Of the optical axis of the polygon mirror 2 and the reflection point P1 of the polygon mirror 2
The line connecting the lines is the optical axis of the light projecting unit 4. The condensing unit 6, the reflecting member 7, and the light guide lens 8 form one element of the detection optical system.

The point P2 in this embodiment is the position where the light beam diverging from the reflection point P1 is scattered by the foreign matter on the substrate 5 as the polygon mirror 2 rotates and is condensed by the light condensing unit 6.

Reference numeral 110 denotes a comparison processing means, which determines the surface state of the substrate 5 based on a plurality of inspection results of the surface state of the substrate 5 with illumination light from the same laser light source.
Therefore, the comparison processing means 110 includes a storage circuit that temporarily stores the inspection results of a plurality of times and a processing circuit that sequentially compares the inspection results of each position of the substrate, and the comparison processing is performed in a predetermined sequence. Based on this, it is executed at high speed over the entire surface of the substrate.

Reference numeral 100 denotes a controller, which controls the surface condition inspection apparatus according to this embodiment. Therefore, the comparison processing means 110, the stage driving means 120, which will be described later, and the output device 13
0 etc. operates according to the command from the controller 100. Although not shown, the polygon mirror 2 and the laser 1 may be controlled and controlled by the controller 100, and signals from an input means such as a keyboard may be controlled by the controller.
It is processed by 100 and the command is transmitted to each means.

Reference numeral 120 denotes a stage driving means for driving the stage 150 on which the substrate 5 is placed, and the stage driving means 120 can move and rotate the stage 150 in the X, Y and θ directions.

Reference numeral 130 denotes an output device for outputting the inspection result, which includes a display such as a well-known printer or CRT. The stage driving means 120 moves the stage 150 in the X direction based on a signal from the controller 100.
At this time, the surface of the substrate 5 is scanned by the light flux, the entire surface of the substrate 5 is scanned by the movement of the stage 150 in the X direction, and the light from the predetermined position is received by the light receiving element 9.

After the entire surface scanning is completed and all the signals from the light receiving element 9 are stored in the comparison processing means 110, the stage driving means 12 is driven based on the signals from the controller 100.
0 rotates the stage 150 by a predetermined angle θ and sets the relative position of the substrate 5 to the light receiving element 9 (that is, the relative position of the circuit pattern to the light receiving element 9) to a relationship different from that in the first inspection step.

Then, similarly to the first inspection, the stage 150 is moved in the X direction while scanning the substrate 5 with the illumination light from the same laser light source to scan the entire surface of the substrate 5, and the light receiving element 9 causes the substrate 5 to move. The light from each position of is received. The signal from the light receiving element 9 is input to the comparing means 110 at any time, and the second inspection result is stored.

After completion of the second inspection, the comparison processing means 110 is generated based on the signal from the controller 100.
Then, the first and second inspection results are stored over the entire measurement area of the substrate 5, and the surface state at each position of the substrate 5 is determined.

The determination result, that is, the final inspection result of the surface condition is sent via the controller 100 or the controller 10.
Based on the signal of 0, it is directly input from the comparison processing means 110 to the output device, and the inspection result is output in the form of data or drawings.

In the present embodiment, when the surface of the substrate 5 is scanned with a light beam by the rotation of the polygon mirror 2, an intersection line 11 connecting the points B1 and B2 formed by the unidirectional scanning is formed on the substrate 5. There is. A point O is formed so that the substrate 5 is formed at an angle of β with respect to the vertical and horizontal directions of the substrate so as not to coincide with the direction of the diffracted light generated from the main pattern (the majority of the circuit patterns on the substrate 5). It is rotated as the center. Then, the condensing unit 6 is connected to the substrate 5 having the optical axis of the condensing unit 6.
The projection image on the substrate 5 is displaced by an angle β so as not to coincide with the direction of the diffracted light generated from the main pattern on the substrate 5.

That is, in this embodiment, the converging portion 6 is made to intersect with the branch line l1 on the substrate 5 by the incident light beam and the intersecting line 12 for condensing.
The scattered light flux generated from the foreign matter on the substrate 5 is efficiently guided to the light receiving portion 9 such that is substantially coincident with the intersection line l1.

The converging line 12 for condensing does not have to exactly coincide with the intersecting line 11 as long as it coincides with the intersecting line 11 within a range in which the scattered light beam from the foreign matter can be condensed.

2 (A) and 2 (B) are explanatory views showing a surface state inspection state according to the present invention. This figure shows an inspection method that eliminates erroneous detection and increases the accuracy of separating foreign matter by performing an additional inspection in addition to the inspection performed in the embodiment of FIG. FIG. 1A is an explanatory diagram showing a foreign matter detection method performed in the embodiment shown in FIG. FIG. 6B is an explanatory diagram showing a method of additional inspection performed in addition to the inspection shown in FIG.

In FIGS. 3A and 3B, 5 is a substrate such as a reticle or photomask, and 10 is a circuit pattern which is inclined by an angle β with respect to the vertical and horizontal directions of the substrate 5. O1, O
2 is the incident direction of the laser beam, B1 and B2 are directions O
1, the direction perpendicular to O2.

In the circuit pattern on the substrate 5, the substrate 5
It is assumed that the circuit pattern 10 is included in a direction that forms an angle β1 with respect to the vertical and horizontal directions. In FIG. 9A, the substrate 5 is rotated clockwise by an angle β1 with respect to the laser beam incident directions O1 and O2. Then, the laser beam is incident on the circuit pattern 10 forming an angle β1 with respect to the vertical and horizontal directions of the substrate 5, and relatively strong diffracted light is generated in the O1 and O2 directions. Therefore, the pattern diffracted light returning in the incident direction of the laser beam is received, resulting in erroneous detection as a foreign matter.

Therefore, as shown in FIG. 7B, the substrate 5 is returned counterclockwise by an angle β1 with respect to the laser beam incident directions O1 and O2, and is further rotated counterclockwise by an angle β2. . That is, the angle (β
Rotate 1 + β2) and inspect again. Then, the diffracted light from the pattern 10 forming an angle β1 with respect to the vertical and horizontal directions of the substrate 5 is (β1
Light is not received because it goes out in the direction of + β2).

As described above, when the circuit pattern includes a pattern forming an angle β, for example, with respect to the vertical and horizontal directions of the substrate, when the inspection is performed by scanning in the same direction as the pattern, diffracted light is received. It is impossible to distinguish whether the pattern is a foreign matter. However, when the scanning direction is further changed and the inspection is performed again (not including the vertical and horizontal directions of the substrate), if the first inspection detects a pattern, the diffracted light is not received, and if it is a foreign substance, the diffracted light is not received. Since the light is received because of the isotropic scattering property, it is possible to clearly determine whether it is a pattern or a foreign matter.

Therefore, it is only necessary to compare the two inspection results for each coordinate point on the substrate to make a final determination.

Table 1 shows an example of determining whether a circuit pattern or a foreign substance is obtained from the results of the two inspections. In the table, for example, the state where the diffracted light is received is represented as ON, and the state where the diffracted light is not received is represented as OFF, respectively.
When the logical product of the inspection results of the second time is taken, it is a foreign matter when it is ON, and a final judgment that it is a pattern when it is OFF.

In the method shown in FIGS. 2 (A) and 2 (B),
Further, if the rotation angle of the substrate 5 is changed and the inspection is performed and the number of inspections is increased, the accuracy of separating the foreign matter from the circuit pattern can be further improved.

Table 2 shows that the substrate 5 is formed at three angles β1, β2 and β3 with respect to the incident direction of the laser beam.
It is an example showing the result of performing the inspection by rotating. In the table, patterns A, B, and C are patterns that form angles β1, β2, and β3 with respect to the vertical or horizontal direction of the substrate 1, respectively. Then, as in the case of Table 1, the final judgment of the foreign matter or the circuit pattern is made by taking the logical product of the inspection results at the respective rotation angles, and the foreign matter separation accuracy is higher than that shown in Table 1. I can say.

[0040]

[Table 1] 3A and 3B are explanatory views showing an example of another surface state inspection state according to the present invention. FIG. 7A is an explanatory diagram for performing the inspection without rotating the substrate, and FIG. 9B is an explanatory diagram for performing the inspection by rotating the substrate counterclockwise by an angle β.

In FIGS. 1A and 1B, 5 is a substrate such as a reticle or photomask, and 12 and 13 are light receiving portions for receiving diffracted light from a circuit pattern or foreign matter. Reference numeral 14 represents a beam spot of the incident laser beam on the substrate 5. 11 is a circuit pattern having a corner. B1, B
Reference numeral 2 indicates the lateral direction of the substrate 5 when the substrate 5 is not rotated.

This embodiment differs from the embodiment of FIG.
The circuit pattern on the substrate 5 is irradiated with a laser beam having a relatively large beam diameter. This is because an actual surface condition inspecting device takes into consideration the requirement to increase the beam diameter in order to increase the inspection speed as much as possible.

On the other hand, if the beam diameter is made smaller, the isotropic scattering property of the diffracted light of the foreign matter is strengthened, but the inspection speed is lowered. Therefore, the beam diameter is decided in consideration of both factors. Usually, the beam diameter is 30 to 60 μm.

On the other hand, the circuit pattern on the substrate is 5 μm minimum.
Since there are some around m, many circuit patterns exist within the beam diameter during inspection. For example, in this embodiment, as shown in FIG.
Isotropically scattered diffracted light from a foreign substance present inside is received by the light receiving portions 12 and 13 arranged at two different positions,
Although foreign matter is detected, if, for example, a V-shaped circuit pattern 11 having a corner in the beam diameter 14 is present, diffracted light by the linear portion of the circuit pattern 11 (shown by an arrow) Is exactly the same as the light receiving parts 12 and 13
When the light is received at, the output difference between the two light receiving units 12 and 13 disappears, resulting in erroneous detection as a foreign substance.

Therefore, as shown in FIG.
When the substrate 5 is rotated counterclockwise by, for example, the angle β by applying the method shown in FIG. 3, the diffracted light from the straight portion of the doglegged circuit pattern 11 is separated from the light receiving portions 12 and 13. Ongoing light (indicated by arrow) is no longer received.

However, if it is a foreign substance, even if the substrate 5 is rotated by the angle β for inspection, the light receiving parts 12 and 1 are detected.
In 3, the same diffracted light as in the previous inspection is received.

Table 3 is an example showing two inspection results of the embodiment of FIG. In the table, PMT1 and PMT2
Represent the light receiving portions 12 and 13, respectively, and, as in Table 1 and Table 2, the logical product of the inspection results of two times is taken, and the final determination of foreign matter if ON and pattern if OFF. .

FIG. 6 is a block diagram showing an outline of the surface condition inspection method according to the present invention. As is clear from the figure, according to the present invention, the surface state is inspected N times on the entire surface of the substrate to be measured, and the inspection results of N times are compared by the comparison processing means to obtain an accurate surface state. Have obtained the inspection results of.

The comparison processing means is present at each position by comparing the inspection results N times with respect to each position on the substrate in accordance with the sequence preprogrammed in the microcomputer as shown in the previous embodiment. Is a circuit pattern, is a foreign substance, or is not present.

Therefore, according to the present invention, even if the light receiving element for surface state inspection is theoretically single, the inspection can be accurately performed. Further, when a plurality of light receiving elements are arranged in different positions to form a light receiving system, the inspection accuracy of the surface state can be remarkably improved by applying the present invention.

In the embodiments described above, the method for inspecting the surface state of the substrate has been discussed on the assumption that the foreign matter has isotropic scattering property. However, the actual foreign matter does not necessarily have isotropic scattering property. In some cases, it does not have, but may have an anisotropic scattering property. However, since the diffracted light of the circuit pattern has a strong anisotropic scattering property (strong directionality) as compared with the anisotropic scattering property of the foreign material, the foreign material may be treated by, for example, adjusting the number of received light or the light receiving position. The accuracy of separating the circuit pattern can be improved.

The angle at which the substrate is rotated may be determined in consideration of a pattern existing in the circuit pattern on the substrate and having a direction other than the vertical and horizontal directions of the substrate.

Further, in the above-described embodiments, the example in which the substrate is rotated by a certain angle is shown, but conversely, the substrate may be fixed and the optical system may be relatively rotated. That is,
The same effect can be expected by rotating only part of the light projecting means or part of the light receiving means with respect to the substrate.

Further, the present invention is not limited to the method for inspecting the surface condition for separating the foreign matter and the circuit pattern on the substrate, but generally, the surface condition of the substrate is inspected based on the scattering condition of the laser beam applied to the substrate. It is widely applicable to various uses.

[0055]

[Table 2]

[0056]

According to the present invention, by tilting the substrate and the optical system relative to each other by a certain angle and reinspecting, the accuracy of separating the foreign matter on the substrate from the circuit pattern can be greatly improved. Since the same effect as in the case of inspecting by increasing the number can be obtained, it is possible to reduce the problem due to the difference in sensitivity and the change in sensitivity of the light receiving portion, and it is possible to achieve the surface state inspection method which leads to cost reduction.

In particular, according to the present invention, a plurality of inspection states are sequentially set at the inspection position, and when light is detected in each of the inspection states, it is determined that there is a foreign substance at the inspection position. Since a common detection system can be used to achieve low cost, and multiple detections can be performed with the same sensitivity, an excellent effect that foreign matter inspection can be performed with extremely high accuracy by being distinguished from the pattern on the substrate be able to.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory view showing a surface state inspection state according to the present invention.

FIG. 3 is an explanatory view showing a surface state inspection state according to the present invention.

FIG. 4 is a schematic diagram showing a conventional surface condition inspection apparatus.

FIG. 5 is an explanatory view showing an inspection state of the embodiment of FIG.

FIG. 6 is a block diagram of an embodiment of the present invention.

[Explanation of symbols]

1 Laser Light Source 2 Polygon Mirror 4 Projector 5 Substrate such as Reticle 6 Condenser 7 Reflector 8 Light Guide Lens 9, 12, 13 Light Receiver 10 Pattern with an Inclination of Angle β1 to Main Pattern in Circuit Pattern 11 Patterns including corners other than the main pattern in the circuit pattern 14 Beam diameter of laser beam on substrate 5 100 Controller 110 Comparison processing means 120 Stage driving means 130 Output device 150 Stage

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 21/66 H01L 21/30 502V

Claims (2)

[Claims] 1. By illuminating the surface of a substrate having a plurality of patterns extending in mutually different directions with illumination light, and detecting the light generated in the detection direction among the diffracted light and scattered light generated from the substrate surface by the illumination. In the method of inspecting the surface state of a substrate, a plurality of inspection states are sequentially set for inspection positions on the substrate surface, and when there is light generated in the detection direction in each of the plurality of inspection states, a foreign substance is present at the inspection position. A method for inspecting a surface condition, which is characterized by determining that there is 2. The surface condition inspection method according to claim 1, wherein the substrate is a substrate on which a circuit pattern is formed.