JP2002296197A - Surface inspection instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface inspection instrument for identifying, with high accuracy, the category of a defect in a light penetrating substrate having a semi transparent film on the surface thereof when the surface inspection is done. SOLUTION: In this surface inspection instrument, a first detection means 2a, 2b outputs a detective signal by finding the reflected light of a light-beam corresponding to the defect on the surface of the frontal side of the light- penetrating substrate having the semi-transparent film. A second detection means 3a, 3b outputs a detective signal by finding a transmission light of the beam corresponding to the defect on the surface of the opposite side of the above substrate. In an identifying means 8 thereof, a reference function is established to define the correlation between a level of each detective signal obtained by the first and the second means, respectively, such a level of which (each detective signal) is compared by using the reference function as a comparison standard, and, then, the identifying means identifies which of all the plurality of categories the from category to category varying defect present in the substrate's surface falls under, based upon the comparison results.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection apparatus for optically detecting a defect present on a surface of an inspection object to determine the type of the defect, and more particularly, to a light having a translucent film on the surface. The present invention relates to a surface inspection apparatus that determines a type of a defect existing on a substrate surface of a transparent substrate.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, a photomask is used as a pattern master when a circuit pattern is transferred onto a semiconductor wafer. A photomask is made by exposing a photoresist on a mask blank. The photoresist is produced by spin-coating an electron beam resist on the surface of a mask blank and patterning it by an electron beam lithography apparatus. As described above, the mask blank is a material for manufacturing a photomask, and is usually formed by coating a chromium film on a surface of a synthetic quartz substrate (glass substrate) polished with high precision by sputtering. In the mask blanks, if defects such as minute pinholes or foreign matter (particles) are present in the chromium film, the defects are transferred during the transfer of the circuit pattern and affect the quality of the semiconductor device. An inspection for the presence or absence of a defect is performed.

As an effective method for detecting these various defects, a conventional surface inspection apparatus utilizes the light-shielding property of a chromium film (light transmittance in the visible light region is 0.1% or less) to detect defects. The method of determining the type is used. That is, the laser beam and the mask blank are relatively moved in different directions (for example, the X direction and the Y direction), and the laser beam from the foreign material is detected by a rear light receiver disposed on the substrate surface side (chrome film side) of the mask blank. Scattered light (reflected light), and the rear photodetector detects the diffracted light of the laser beam from the pinhole (reflected light obtained by reflection on the glass substrate), and detects the light opposite to the substrate surface of the mask blank. The diffracted light of the laser beam from the pinhole (transmitted light obtained by passing through the pinhole) is detected by a front light receiver disposed on the side (glass substrate side). As described above, when the scattered light and the diffracted light of the foreign matter and the pinhole are respectively detected by the rear light receiver and the front light receiver, and the scattered light is detected only by the rear light receiver, the foreign matter is detected based on the detection signal of the scattered light. When a diffracted light is detected by the rear photodetector and the front photodetector, a pinhole is determined based on the detection signal of the diffracted light.

[0004]

In the photomask, a phase shift mask capable of improving the resolution of a pattern tends to become mainstream in the future, and there is a halftone phase mask as an example of the phase shift mask. This halftone phase mask has an advantage in that the surface of the glass substrate is coated with a translucent halftone film instead of the conventional chromium film, and the mask can be easily formed. The halftone film of the mask blank, which is a material for manufacturing a halftone phase mask, has a light transmittance in the visible light region of about 10 to 50%, and has a much higher light transmittance than the chrome film. Therefore, when trying to determine defects such as pinholes and foreign matter present in the halftone film using the conventional surface inspection apparatus, the scattered light of the laser beam from the foreign matter passes through the halftone film. And it is detected by the front receiver. As a result, the scattered light and the diffracted light of the laser beam are detected by the front light receiving device and the rear light receiving device irrespective of the type of defect, and there is a problem that the pinhole and the foreign matter cannot be discriminated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in consideration of the above circumstances, and has been made in consideration of the above circumstances. It is intended to provide an inspection device.

[0006]

A surface inspection apparatus according to the present invention comprises: an irradiating means for irradiating a light beam to a substrate surface of a translucent substrate having a translucent film on the surface; First detecting means for detecting reflected light of the light beam corresponding to the defect on the substrate surface and outputting a detection signal; and detecting the reflected light of the light beam corresponding to the defect on the substrate surface on the side opposite to the substrate surface. A second detection means for detecting the transmitted light and outputting a detection signal, and a reference function defining the correlation between the levels of the detection signals of the first and second detection means are set. As a comparison standard, the levels of the respective detection signals of the first and second detection means are compared, and based on the comparison result, it is determined whether the defect existing on the substrate surface corresponds to one of a plurality of different types of defects. Discriminating means for discriminating. . According to this, the levels of the respective detection signals of the first and second detection means are compared using the reference function defining the correlation between the levels of the respective detection signals of the first and second detection means as a comparison reference. By doing so, it is determined whether the defect existing on the substrate surface corresponds to any of a plurality of different types of defects, so that the defect type existing on the substrate surface can be determined with high accuracy.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a surface inspection apparatus according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view showing a schematic configuration of a surface inspection apparatus, and FIG. 2 is a block diagram showing a hardware configuration of the apparatus. In FIG. 1, a surface inspection apparatus A includes a halftone film (a light transmittance in a visible light region of about 1) which is a translucent film on a surface of a light transmitting glass substrate M1.
(0-50%) This is applied to the surface inspection of a mask blank M coated with M2. The mask blank M to be inspected has a substrate surface side (halftone film M
The laser beam is emitted from the light projecting device 1 from the second side). The light projecting device 1 includes, for example, an argon laser oscillator 1a as a light source. The laser beam L emitted from the argon laser oscillator 1a is introduced into a beam expander 1c by a mirror 1b, expanded to an appropriate beam diameter by the beam expander 1c, and then expanded into a polygon mirror 1d, a scan lens 1e, a mirror 1f, and the like. Is irradiated onto the surface of the substrate of the mask blank M via the light source and converged in a spot shape, and is scanned in the X direction by the rotation of the polygon mirror 1d. The mask blank M is held on both sides corresponding to the scanning direction of the laser beam L by a pair of arms (not shown) (not shown), and is step-moved in the Y direction by the pair of arms in synchronization with the scanning of the laser beam L. Is done.

On the substrate surface side of the mask blank M, a pair of rear light receivers 2a for receiving the reflected light of the laser beam L reflected from the mask blank M on the rear side (irradiation side of the laser beam L) of the mask blank M And 2b. The rear light receivers 2a and 2b are arranged at an angle of 20 ° to 70 ° with respect to the laser beam L as shown in FIG. On a side opposite to the substrate surface of the mask blank M, a pair of light receiving the transmitted light of the laser beam L passing through the mask blank M on the front side of the mask blank M (the side opposite to the irradiation side of the laser beam L). Front light receivers 3a and 3b are provided. The front light receivers 3a and 3b are arranged at an angle of 20 ° to 70 ° with respect to the irradiation direction of the laser beam L, as shown in FIG. As shown in FIG. 4A, during the scanning of the laser beam L, when the laser beam L irradiates the pinhole H existing in the halftone film M2 of the mask blank M, the irradiation beam is mostly pinned. The diffracted light passes through the hole H and spreads from the opening exposed surface M11 of the glass substrate M1 to the periphery, and transmits through the glass substrate M1.
Part of the irradiation beam is applied to the opening exposed surface M11 of the glass substrate M1.
And diffracted light L2 that spreads from the opening of the pinhole H to the periphery. Therefore, when the pinhole H exists in the halftone film M2, the amount of diffraction light of the diffracted light L2 on the substrate surface side of the mask blank M is equal to the diffracted light L on the opposite side to the substrate surface.
1, the intensity of the diffracted light L2 on the substrate surface side of the mask blank M increases, and the intensity of the diffracted light L1 on the side opposite to the substrate surface of the mask blank M decreases. Thereby, as shown in FIG.
The rear photodetectors 2a and 2b on the substrate surface side of the mask blank M receive the diffracted light L2 with low intensity, and the front photodetectors 3a and 3b on the opposite side of the mask blank M from the substrate surface.
Receive the diffracted light L1 having a large intensity. On the other hand, FIG.
As shown in (b), when the foreign matter P existing in the halftone film M2 of the mask blank M is irradiated with the laser beam L, the irradiated beam is omnidirectional without being emphasized in a specific direction. It becomes scattered light scattered in random directions. Of the scattered light, the scattered light L1 scattered to the side opposite to the substrate surface of the mask blank M passes through the halftone film M2, so that the amount of scattered light is reduced and the intensity is reduced. Since the scattered light L2 scattered to the front side does not pass through the halftone film M2, the amount of scattered light does not decrease, and therefore, the intensity is larger than the intensity of the scattered light L1. Therefore, when the foreign matter P exists in the halftone film M2, as shown in FIG.
And 2b receive the scattered light L3 having a large intensity, and the front light receivers 3a and 3b on the opposite side of the substrate surface of the mask blank M receive the scattered light L4 having a small intensity.

During the scanning of the laser beam L, the rear light receivers 2a and 2b convert the diffracted light L2 from the pinhole H or the scattered light L3 from the foreign matter P (hereinafter, the diffracted light L2 and the scattered light L3 into the reflected light L2, L3), the reflected light L2, L3 is output to the photomultiplier 5 via the optical fibers 4a and 4b shown in FIG. In the photomultiplier 5, the reflected light L
2 and L3 are photoelectrically converted, and a detection signal (current value according to the luminance level) iF corresponding to the light receiving level (luminance level) of the reflected lights L2 and L3 is output to the data processing circuit 8. The front light receivers 3a and 3b transmit the diffracted light L1 from the pinhole H or the scattered light L4 from the foreign matter P (hereinafter, the diffracted light L1 and the scattered light L4 are referred to as transmitted light L1 and L4 during the scanning of the laser beam L. 2), the transmitted light L1 and L4 are transmitted to the optical fibers 6a and 6a shown in FIG.
The signal is output to the photomultiplier 7 via b. The photomultiplier 7 photoelectrically converts the transmitted lights L1 and L4, and generates a detection signal (current value corresponding to the luminance level) i according to the light receiving level (luminance level) of the transmitted light L1 and L4.
B is output to the data processing circuit 8.

Referring to FIG. 5, a process of discriminating a pinhole from a foreign substance in data processing circuit 8 will be described. The data processing circuit 8 includes an interface 8a, an MPU 8b, and a memory 8c (not shown). In the data processing circuit 8, the MPU 8b executes a program stored in the memory 8c, and
Are processed by the interface 8a, and the detection signals iF and iB obtained from
After conversion into predetermined detection data (voltage data) vF and vB according to the detection level of B, the detection data vF and vB are fetched (step S1), and the next step S
Proceed to 2.

In step S2, the MPU 8b performs a discriminating process for discriminating between pinholes and foreign matters using the defect determination table T shown in FIG. As described above, the detection level of the transmitted light of the pinhole by the front light reception is larger than the detection level of the reflected light of the pinhole by the rear light reception,
Further, the detection level of the reflected light of the foreign substance by the rear light reception is smaller than the detection level of the transmitted light of the foreign substance by the front light reception. However, when comparing the detection level of the reflected light of the foreign matter by the rear light reception and the detection level of the reflected light of the pinhole by the rear light reception, the detection level of the reflected light of the foreign matter is larger than the detection level of the reflected light of the pinhole. Tend to be. Further, when the detection level of the transmitted light of the foreign substance by the front light reception is compared with the detection level of the transmitted light of the pinhole by the front light reception, the detection level of the transmitted light of the pinhole is larger than the detection level of the transmitted light of the foreign substance. Tend to be. Therefore, pinholes and foreign matter can be determined to some extent from the ratio (ratio) of the detection data vF of the front light reception to the detection data vB of the rear light reception. MPU8b
Then, the pinhole and the foreign matter are determined using the defect determination table T in which a reference function defining the correlation between the detection level of the transmitted light and the detection level of the reflected light is set. In the defect determination table T, the horizontal axis (X-axis) corresponds to the detection level of the front light reception, and the vertical axis (Y-axis) corresponds to the detection level of the rear light reception. S is set. The discrimination line S is represented by the general formula y = ax. Here, “a” is a slope. This inclination a
Is determined using the following method. That is, a plurality of types of standard particles having different sizes are adhered to the halftone film of the mask blank for foreign substance evaluation, and detection data of transmitted light of front light reception and detection data of reflected light of rear light reception are obtained for the standard particles. It is obtained from the ratio (ratio) of the detection data of the front light reception to the detection data of the rear light reception. Although the inclination a is smaller than the inclination (= 1) of the broken line shown in the figure, as the size of the foreign matter increases, the ratio of the transmitted light by the front light reception becomes larger than the reflection light by the rear light reception. That's why. M
The PU 8b compares the respective detection levels of the detection data vB of the rear light reception and the detection data vF of the front light reception with the discrimination line S as a comparison standard, and when each of the detection data vB and vF is in an area below the discrimination line S It is determined as a pinhole (step S3), and when the respective detection data vF and vB fall in the area above the discrimination line S, it is determined as a foreign substance (step S3).
4).

In step S5, steps S3 and S4
The size and the position of the pinhole and the foreign matter determined in the above are determined. The MPU 8b executes the defect size determination program stored in the memory 8c, and executes the detection data v
The sizes of the pinhole and the foreign matter are determined based on the detection levels of F and vB. The MPU 8b has a memory 8c
Is executed based on a synchronization signal supplied in synchronization with the scanning of the laser beam L and the movement of the mask blanks M from the synchronization signal generation circuit 9 shown in FIG. The position of the foreign matter is determined, and the process proceeds to step S6.

In step S6, display processing of the size and position of the pinhole and foreign matter determined in step S5 is performed. The MPU 8b executes a defect display program stored in the memory 8c, and outputs a display command signal for displaying the size and position of the pinhole and the foreign matter to the interface 8.
a to a display device 10 such as a liquid crystal display or a CRT shown in FIG. Thereby, the size and position of the pinhole and the foreign matter are displayed on the display device 10.

In the surface inspection apparatus shown in the present embodiment, the discrimination line S set in the defect determination table T is not limited to a linear function, and a function including a curve other than the linear function is appropriately set as a discrimination line. Good. Also, Mask Blanks M
Is not limited to this, and white light or ultraviolet irradiation light may be used instead of this laser beam. Also, the front receiver and the rear receiver are
Two or more pairs may be used.

[0015]

As described above, according to the surface inspection apparatus of the present invention, the reference function defining the correlation between the levels of the detection signals of the first and second detection means is used as a comparison reference. Since the levels of the detection signals of the first and second detection means are compared, it is possible to determine whether a defect existing on the substrate surface corresponds to one of a plurality of different types of defects. Therefore, the type of defect existing on the substrate surface can be determined with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a surface inspection apparatus according to the present invention.

FIG. 2 is a block diagram showing a hardware configuration of the device.

FIG. 3 is an explanatory diagram showing a light receiving state of transmitted light by a front light receiver and a light receiving state of reflected light by a rear light receiver.

FIG. 4 is an explanatory diagram illustrating the principle of intensity of transmitted light by a front light receiver and reflected light by a rear light receiver.

FIG. 5 is a flowchart showing a discrimination process between a pinhole and a foreign matter in the data processing circuit.

FIG. 6 is an explanatory diagram of a defect determination table of the data processing circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Projector 2a, 2b Rear light receiver 3a, 3b Front light receiver 4a, 4b, 6a, 6b Optical fiber 5, 7 Photomultiplier 8 Data processing circuit 9 Synchronous signal generator 10 Display device M Mask blanks M1 Glass substrate M2 Half Tone film L Laser beam

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichiro Kato 3-16-3 Higashi, Shibuya-ku, Tokyo F-term in Hitachi Electronics Engineering Co., Ltd. 2G051 AA56 AB04 AB07 BA10 BB11 BC06 CA02 CB03 2H095 BD04 BD13 BD15 BD27

Claims (1)

[Claims] An irradiating means for irradiating a light beam to a substrate surface of a translucent substrate having a translucent film on a surface thereof; and a reflection of the light beam according to a defect on the substrate surface on the substrate surface side. First detecting means for detecting light and outputting a detection signal; and second detecting means for detecting a transmitted light of the light beam corresponding to a defect on the substrate surface on a side opposite to the substrate surface and outputting a detection signal.
And a reference function that defines the correlation between the levels of the respective detection signals of the first and second detection means, and the reference function is used as a comparison criterion for the first and second detection means. A surface inspection apparatus comprising: a comparing unit that compares levels of respective detection signals and determines whether a defect existing on the substrate surface corresponds to one of a plurality of types of different defects based on the comparison result.