JP2005337728A - Inspection device for foreign matter on surface of mask and inspection method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection device for the foreign matter on the surface of a mask capable of easily inspecting only the foreign matter bonded to the surface of the mask for electron beam exposure. <P>SOLUTION: The inspection device for the foreign matter on the surface of the mask is constituted of a mask stage 10 for placing the mask 11 to move and rotate the same, a laser irradiation unit 20 for irradiating the surface of the mask 11 with a laser beam, a detection part 30 for detecting the scattered beam from the foreign matter and a judging/control unit 40 for taking in the signal from the detection part 30 not only to perform the judgment as the foreign matter but also to detect the coordinate position of the foreign matter and governing the control of the whole of the inspection device. The presence of the foreign matter on the surface of the mask 11 and the coordinate position of the foreign matter can be easily detected by irradiating the surface of the mask 11 with the laser beam. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a foreign matter inspection apparatus and a foreign matter inspection method for a mask surface for electron beam exposure used in semiconductor manufacturing.

  On the mask for the electron beam exposure apparatus, a large number of various fine patterns of several tens to several hundreds of nanometers or holes are formed so that the electron beam can pass and the electron beam can be drawn. Using a mask for an exposure apparatus, the wafer is exposed at the same magnification or reduced projection on the wafer. In the manufacturing process of the electron beam exposure mask having such a minute pattern, it is necessary to finally bring the adhesion of foreign matters close to zero by sequentially performing and managing the surface inspection.

  In conventional semiconductor masks, minute foreign matter adhered during manufacture is a cause of transfer failure such as pattern chipping during electron beam exposure, and even foreign matter that does not cause transfer failure adheres to the mask. Then, since it becomes a fallen object in the exposure machine or on the wafer, strict management is performed in the manufacturing process so that no foreign matter adheres.

  Among semiconductor masks, a light-transmitting mask called a photomask is designed to prevent foreign matter from entering the pellicle by covering the mask surface with a thin film called a pellicle after cleaning at the final stage of the manufacturing process. Has been. According to this method, even if foreign matter adheres to the pellicle, the exposure pattern is hardly affected because it is not on the direct surface of the mask.

  However, in a mask for electron beam exposure, a thin film such as a pellicle blocks the passage of the electron beam and cannot be used. Therefore, there is always a possibility that foreign matter adheres to the mask surface. Therefore, a foreign matter inspection apparatus is used to manage the attached foreign matter in each process and grasp the situation. Even in the manufacturing process of a mask for an electron beam exposure apparatus, if a foreign matter inspection is performed before pattern formation, the inspection is performed using a bare wafer foreign matter inspection device.

As a conventional foreign matter inspection method, a method of detecting foreign matter scattered light using a laser has been proposed (see, for example, Patent Document 1). However, the electron beam exposure mask has a problem that it is difficult to distinguish the foreign material from the pattern because the pattern is fine.
In this case, the foreign matter detection principle is such that the reflected light from the pattern is cut using the polarization principle and only the foreign matter scattered light is detected. It is difficult to detect only foreign objects.
JP 05-2262 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a foreign matter inspection apparatus and inspection method for a mask surface that can easily inspect only foreign matters attached to the surface of an electron beam exposure mask.

In order to achieve the above object in the present invention, first, in claim 1, a mask stage 10 on which at least a mask is mounted, which can be moved and rotated, and a laser irradiation unit 20 that irradiates the mask surface with laser light; The detection unit 30 detects scattered light from a foreign object, and includes a determination / control unit 40 that takes in a signal from the detector, detects a foreign object and detects the coordinate position of the foreign object, and controls the entire inspection apparatus. This is a mask surface foreign matter inspection apparatus characterized by the above.

  According to a second aspect of the present invention, the laser beam is irradiated in parallel to the mask surface placed on the mask stage 10 to detect the scattered light from the foreign matter on the mask surface, thereby determining the presence or absence of the foreign matter and the coordinate position of the foreign matter. This is a method for inspecting a foreign substance on a mask surface characterized by detecting.

  By performing the foreign matter inspection on the mask surface for electron beam exposure using the foreign matter inspection apparatus and inspection method of the mask surface of the present invention, it becomes possible to inspect the foreign matter with a pattern of the EB mask, which has been difficult in the past, and Inspection accuracy of foreign matter inspection is greatly improved, which can contribute to improvement of the quality of the EB mask.

Hereinafter, embodiments of the present invention will be described.
As shown in FIG. 1, the apparatus for inspecting foreign matter on a mask surface according to a first aspect of the present invention mounts a mask 11, moves and rotates the mask, and irradiates the surface of the mask 11 with laser light. A laser irradiation unit 20 that performs detection, a detection unit 30 that detects scattered light from a foreign object, and a signal from the detection unit, and determines the determination as a foreign object and the coordinate position of the foreign object. The control unit 40 is configured to irradiate the surface of the mask 11 with laser light substantially in parallel so that the presence or absence of foreign matter on the surface of the mask 11 and the coordinate position of the foreign matter can be easily detected.

The mask stage 10 is a stage having X, Y movement and rotation mechanisms, has a controller 12 that can accurately move and rotate the movement distance and rotation angle, and is program-controlled by the determination / control unit 40.
The laser irradiation unit 20 is installed on the mounting table 21, and the controller 22 controls the vertical position and rotation of the laser irradiation unit 20.
The detection unit 30 includes a detector 31 such as a photomultiplier or a solid-state imaging device and an optical system 32, and the detection area of the mask 11 is adjusted by the optical system 32.
The determination / control unit 40 takes in a signal from the detection unit, detects the determination as a foreign object and the coordinate position of the foreign object, and controls the entire inspection apparatus.

Hereinafter, the foreign matter inspection method for a mask surface according to the second aspect of the present invention will be described.
First, the inspection mask 11 is placed on the mask stage 10, the laser irradiation unit 20 is installed on the mounting table 21, and the laser beam 23 is irradiated in parallel along the surface of the mask 11 from the laser irradiation unit 20. Thus, the mounting table 21 is moved up and down and rotated to align the optical axis of the laser beam 23 (see FIGS. 2A and 2B).
Here, the position control of the mounting table 21 is performed by the controller 22.

Next, the laser beam 23 is adjusted so as to be sufficiently collimated, and the coordinate origin of the mask 11 for reproducing the coordinate position of the mask 11 on the mask stage 10 (lower left of the end of the mask 11 in FIG. 3) is set (FIG. 3). 3).
Here, the mask stage 10 has an X and Y movement and rotation mechanism, and is a stage having a length measuring function capable of displaying a coordinate position. Furthermore, it is preferable to put an alignment mark so that the positional relationship of the mask 11 can be easily determined. Here, marks are placed on the top, bottom, left, and right so that the positional relationship of the mask can be confirmed.

Next, the mask stage 10 is moved from the lower end to the upper end of the mask 11 at a predetermined pitch, and the laser beam 23 is scanned from the lower end to the upper end of the mask 11. FIG. 4A shows a state where the movement position of the mask stage 10 has moved to the upper end of the mask 11 and stopped. FIG. 4B shows a detection waveform of the scattered light from the foreign matter a, foreign matter b, and foreign matter c when the horizontal axis represents the moving position of the laser beam 23 and the vertical axis represents the signal intensity of the detector. An example is shown. The moving pitch of the mask stage 10 is set to a value smaller than the laser beam diameter. Here, the mask stage 10 is moved and the laser beam 23 is scanned, but the laser irradiation unit 20 may be moved and the laser beam 23 may be scanned.

Here, when there are foreign matter a, foreign matter b, and foreign matter c on the surface of the mask 11, first, when the foreign matter a is irradiated with the laser beam 23, scattered light is emitted from the foreign matter a, and the signal intensity I is detected by the detection unit 30. ₁ , the coordinate position y ₁ at that time is detected by the determination / control unit 40 from the mask stage 10 and stored in the memory. Similarly, for the foreign matter b and the foreign matter c, the signal intensity I ₂ , the coordinate position y _{2, the} signal intensity I ₃ , and the coordinate position y ₃ are taken into the detection unit 30 and the determination / control unit 40 and sequentially stored in the memory. Foreign matter a, foreign matter b, and foreign matter c are determined by the determination / control unit 40 as foreign matter on the surface of the mask 11.
The determination / control unit 40 has a database function that records and stores a history of inspection data for each mask type, and can arbitrarily read past inspection results of foreign matter on the mask surface, foreign matter coordinate position data, and the like. ing. Thereby, the limit value of whether or not it is a foreign object can be set in detail for each product type.
Further, the laser beam is not reflected on the surface of the mask 11 when the laser beam 23 is scanned in a state where no foreign matter is present.

Although the foreign matter a, foreign matter b, foreign matter c on the surface of the mask 11 and the coordinate position of the y-axis have been found, a method of detecting the X-axis coordinate position of the foreign matter a, foreign matter b, and foreign matter c will be described.
First, with the mask 11 placed on the mask stage 10, the mask stage 10 is moved to the initial position, the mask stage 10 is rotated by 90 °, and the moving direction of the mask stage 10 is set to the X axis. FIG. 5 shows an arrangement state of the foreign matter a, foreign matter b, and foreign matter c on the surface of the mask 11 in a state where the mask stage 10 is rotated by 90 °.

  The coordinate origin of the mask 11 for reproducing the coordinate position of the mask 11 again on the mask stage 10 (in FIG. 5, the lower left of the end of the mask 11) is set (see FIG. 5).

Next, the mask stage 10 is moved from the lower end (here, the right mark) to the upper end (here, the left mark) of the mask 11 at a predetermined pitch, and the laser beam 23 is scanned from the lower end to the upper end of the mask 11. FIG. 6A shows a state where the movement position of the mask stage 10 has moved to the upper end (right mark) of the mask 11 and stopped. FIG. 6B shows a detection waveform of the scattered light from the foreign matter b, foreign matter a, and foreign matter c when the horizontal axis represents the moving position of the laser beam 23 and the vertical axis represents the detector signal intensity. An example is shown. The moving pitch of the mask stage 10 is set to a value smaller than the laser beam diameter.
Here, since the foreign matter inspection on the surface of the mask 11 has revealed the foreign matter a, foreign matter b, foreign matter c on the surface of the mask 11 and the coordinate position of the y axis, the foreign matter a, foreign matter b, The x-axis coordinate position of the foreign object c is detected.

First, when the foreign matter b is irradiated with the laser beam 23, the scattered light is emitted from the foreign matter b and the signal intensity I ₂ detected by the detection unit 30 is the foreign matter b inspected in advance by the determination / control unit 40. It is confirmed that the coordinate position x ₁ at that time is taken in by the determination / control unit 40 from the mask stage 10, and the coordinate position x ₁ is added and stored in the foreign object b. Here, the signal intensity I ₂ of the foreign object b and the coordinate positions y ₂ and x ₁ are determined. Similarly, for the foreign object a and the foreign object c, the coordinate position x ₂ and the coordinate position x ₃ are taken into the determination / control unit 40 and sequentially stored in the memory. Here, the signal intensity I ₁ of the foreign object a, the coordinate positions y ₁ and x ₂ , the signal intensity I ₃ of the foreign object c, and the coordinate positions y ₃ and x ₃ are determined, and the foreign object a, the foreign object b, and the foreign object c are determined. Reconfirmation of the presence or absence of x and y coordinate positions are detected.

  Further, instead of the detection unit 30, an observation microscope is set, and by aligning the optical axis of the microscope with the coordinate origin of the mask 11, the foreign matter a, foreign matter b, The confirmation operation of the foreign matter c can be automatically performed using the mask stage 10.

The inspection order for foreign matter inspection of the mask is programmed in advance in the determination / control unit 40 for each product type, and the mask position, rotation control, and laser irradiation unit position control are performed by designating the product type each time. Thus, a series of inspections can be performed.
Furthermore, by providing a mask storage cassette, a transport unit, etc., a series of steps from placing the mask 11 on the mask stage 10 from the mask storage cassette, inspection of foreign matter, detection of the coordinate position of foreign matter, confirmation work, and storage of the mask 11 are performed. Can also be automated.

It is a schematic block diagram which shows one Example of the foreign material inspection apparatus of the mask surface of this invention. (A) is a schematic top view which shows the state which has irradiated the laser beam from the laser irradiation unit to the mask mounted in the mask stage. (B) is a schematic side view which shows the state which has irradiated the laser beam from the laser irradiation unit to the mask mounted in the mask stage. It is explanatory drawing which shows the state which the position adjustment of a laser beam and the coordinate origin setting of a mask are complete | finished, and inspection can be started. (A) is explanatory drawing which shows the state which scanned the mask with the laser beam. (B) is explanatory drawing which shows an example of the detection waveform in the detection part of the scattered light from the foreign material a, the foreign material b, and the foreign material c. It is explanatory drawing which shows the state which the position adjustment of a laser beam and the coordinate origin setting of a mask are complete | finished, and inspection can be started. (A) is explanatory drawing which shows the state which scanned the mask with the laser beam. (B) is explanatory drawing which shows an example of the detection waveform in the detection part of the scattered light from the foreign material a, the foreign material b, and the foreign material c.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Mask stage 11 ... Mask 12 ... Controller 20 ... Laser irradiation unit 21 ... Mounting stage 22 ... Controller 23 ... Laser beam 30 ... Detection part 31 ... Detector 32 ... Optical system 40 ... ... Judgment / control unit 100 ... Inspection devices a, b, c ... Foreign matter I ₁ , I ₂ , I ₃ ... Signal intensity x ₁ , x ₂ , x ₃ at foreign matter detection unit x-axis of foreign matter Coordinate position y ₁ , y ₂ , y ₃ ...... Coordinate position of foreign matter on y-axis

Claims (2)

  A mask stage (10) on which at least a mask is mounted, movable and rotatable, a laser irradiation unit (20) for irradiating the mask surface with laser light, and a detection unit (30) for detecting scattered light from a foreign substance, A mask surface foreign matter inspection apparatus comprising: a determination / control unit (40) which takes in a signal from a detection unit, detects a foreign matter, detects a coordinate position of the foreign matter, and controls the entire inspection apparatus.   A laser beam is irradiated in parallel to the mask surface placed on the mask stage (10), and scattered light from foreign matter on the mask surface is detected to detect the presence or absence of foreign matter and the coordinate position of the foreign matter. A foreign matter inspection method for the mask surface.

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