JP2616732B2 - Reticle inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reticle inspection method for irradiating a laser beam on a reticle having a plurality of patterns formed thereon, and scattered light of the reticle to a light receiving portion to inspect the reticle for foreign matter.

[0002]

2. Description of the Related Art A lithography process is one of the most important processes in a semiconductor device manufacturing process. In this step, an exposure apparatus for transferring a pattern such as a circuit element onto a semiconductor wafer has been used. A pattern to be transferred to a semiconductor wafer is formed on a reticle equipped with this exposure apparatus, and the pattern on this reticle is formed to be enlarged about 5 to 10 times as large as the pattern of an actual semiconductor wafer. Further, in recent years, as the integration of integrated circuits has progressed, the reticle pattern has become finer, and even a small foreign matter attached to the reticle has caused a defect in the semiconductor device.

[0003] For this reason, the reticle on which the pattern is formed has been stored by covering the reticle pattern surface with a transparent protective film at intervals so as to prevent foreign matter from adhering. Then, when used, the stored reticle is loaded into an exposure apparatus, and a resist is applied to a quartz plate coated with chromium over the entire surface, and a pattern is transferred to the quartz plate, and development etching is performed. After that, the pattern was observed with a microscope or the like, and it was checked whether or not foreign matter had adhered as compared with the previous time to determine whether or not use was possible.

However, although this method can surely inspect the presence or absence of foreign matter, it has a disadvantage that it takes a lot of time and requires a long waiting time for the exposure apparatus. Thus, Japanese Patent Application Laid-Open No. 3-84441 discloses an example of an inspection method for determining whether a reticle can be used in a shorter time.

In this reticle inspection method, first, a laser beam is scanned on a reticle including a pattern without a fatal defect, an origin mark, and a rotation reference mark, the reticle surface is scanned, and scattered light from a foreign substance enters a light receiving portion. If there is a foreign substance, the position data of the foreign substance on the reticle is obtained, and then the position data of the foreign substance is set to X using the origin mark and the rotation axis mark of the reticle as reference points for either the origin or the XY axis.
It is converted as a Y coordinate value and stored in one memory. Then, when the reticle is used for exposure, the laser beam is scanned on the reticle surface in the same manner as the previous time, and the reticle is inspected for foreign substances again, and the coordinates of the foreign substances on the reticle are stored in another memory.

If the coordinates of the foreign matter stored in the previous memory and the coordinates of the foreign matter in the other memory are the same and the position coordinates are the same, it is determined that there is no change in the state of the reticle pattern from the previous time. Was determined to be usable.

[0007]

However, in recent years,
With the miniaturization of semiconductor design rules, the pattern size on the reticle has become finer and the number of elements has also increased. For this reason, it is difficult to create the original reticle without defects, and most reticles fix defects by some means and then use them as finished products. This defect correction method is divided into two types: a black defect in which chromium, which is a light shielding portion, remains and a white defect in which chromium is missing. Generally, in the case of a black defect, a method of removing chromium by a laser beam is used, and in the case of a white defect, the defect is corrected by depositing carbon using FIB. As a result, the defect repair mark has a rougher surface than the uncorrected portion, and in the above-described reticle inspection method using the scattered light of the laser, the defect is repaired even if the sensitivity of one light receiving unit is improved. Since the light intensity of the scattered light from the trace is weak, a sufficient SN ratio cannot be obtained, and the detection becomes unstable. Also, the scattered light from this correction mark changes depending on the laser beam diameter and irradiation direction,
There is a problem in that the scattered light cannot be captured with good reproducibility by the light receiving unit, and it becomes impossible to distinguish whether it is a correction mark or a foreign matter.

Further, even if the entire reticle surface is scanned with a thin laser beam in order to more accurately catch the foreign matter, there is a disadvantage that the inspection time is longer and the determination of the use is delayed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a reticle inspection method capable of discriminating between a foreign matter and a correction mark, inspecting the presence or absence of the foreign matter in the reticle, and determining whether the reticle can be used in a short time.

[0010]

A feature of the present invention is that an alignment mark and a reticle on which a plurality of patterns are formed based on the alignment mark are irradiated with a laser beam, and scattered light enters a light receiving portion and is applied to the reticle. In a reticle inspection method for determining the presence or absence of foreign matter, a relative position coordinate between a position coordinate of a correction mark and a position coordinate of the alignment mark is determined in advance as a reticle defect position coordinate for a defective portion of a pattern. Calibrate the origin and scanning movement amount of the laser to irradiate the reticle with the alignment, and then scan over the entire area of the reticle with a laser beam with a relatively large spot diameter to allow the scattered light to enter the light receiving unit. The position coordinates of the reticle defect portion determined in advance are stored in a memory, and the position coordinates of the reticle defect portion are determined in advance. And the position coordinates of the detected foreign matter are compared. If the position coordinates match, the reticle is scanned with the laser beam having a smaller spot diameter of the laser beam to detect the foreign matter and detect the foreign matter. This is a reticle inspection method that determines that there is no foreign substance when the position coordinates match the reticle defect coordinates.

[0011]

Next, the present invention will be described with reference to the drawings.

FIGS. 1A and 1B are a flow chart and a schematic diagram of an inspection apparatus for explaining an embodiment of a reticle inspection method according to the present invention. The method of inspecting the reticle will be described later in detail, but when correcting the defective portion 9a of the pattern 9 of the reticle 10, the relative position coordinates between the position coordinates of the defective portion 9a and the position coordinates of the alignment mark 10a are determined. Fig. 1
(B) is stored in the storage unit. Further, when the correction has not been made, it is not necessary to store it. Next, in step A of FIG. 1A, the reticle 10 on the stage 8 is aligned, as will be described in detail later. Then, step B in FIG.
As will be described in detail later, the origin of the laser and the scanning movement amount (scanning width) of the laser are set using the detector 7, and the preparation is completed. Next, in step C of FIG. 1A, the laser beam spot is set to, for example, about 0.1 to 5 mm, and the stage 8 is moved in the direction perpendicular to the paper surface while scanning the reticle 10 so as to have the same diameter as the laser spot diameter. A step feed is performed according to the size, and the entire area of the reticle 10 is scanned to check whether or not foreign matter is present by checking whether or not scattered light enters the two photomultipliers 5. At this time, the moving position of the stage 8 and the laser spot position at the time of laser scanning are sequentially recorded, and when scattered light enters the photomultiplier 5, the laser spot position coordinates are obtained from the sequentially recorded position coordinates. The coordinate values are stored in the storage unit.

Next, in step D, if no foreign matter is found on the reticle 10 without pattern correction, the process proceeds to step E without foreign matter and is made usable. If it is determined in step D that there is a foreign substance, in step F, the comparison determination section determines whether the position coordinates of the reticle defect correction mark stored in advance in the storage section match the position coordinates of the detected foreign substance. If they do not match, in step G, there is a foreign substance, and it cannot be used.

If the result of the determination in step F is YES,
A laser spot is narrowed down to about 1 to 10 μm by a method described later, and the stage 8 is finely stepped in accordance with the spot diameter, and the surface of the reticle 10 is scanned with a laser beam to check for the presence of foreign matter. Next, in Step I, if the position coordinates of the reticle defect correction mark are again compared with the position coordinates of the detected foreign matter, if the foreign matter is determined to be a reticle defect correction mark, the foreign matter is not counted as a foreign matter. Also,
If NO, the foreign matter cannot be used in the exposure apparatus.

First, a method for obtaining the position coordinates of a reticle defect correction mark, which is a pattern correction mark, will be described. FIG. 2 is a view schematically showing a defect inspection apparatus, and FIG. 3 is a flowchart for explaining a method for obtaining position coordinates of a defective portion. The coordinates of the reticle position correction mark are measured as the position coordinates of the reticle defect portion at the time of reticle defect correction.

The measurement of the position coordinates of the defective portion of the reticle is as follows.
First, in steps A and B, the circuit pattern area of the reticle 10 is
The image is taken into the computer using. Next, in step C, the reticle design data on the database and the CCV
By comparing the data obtained by the camera 11 or, when the same plurality of circuit patterns are arranged on one reticle, by comparing the images at the same place in other circuit patterns, If there is, there is a possibility of a reticle defect, so a location different from the design data in the database is extracted, and the portion is observed with a microscope, and it is determined that the defect is not a foreign substance but a reticle defect. The position coordinates of the defective portion of the reticle are calculated from the position, and the position coordinates and the type of the defect (whether chromium remains or is missing) are stored in the porcelain disk of the disk device. Next, the defective portion at the location stored in the porcelain disk is corrected by a laser repair device or a FIB device, and the position coordinates of the defective portion are stored in the storage unit in FIG.

Next, a case where the laser spot diameter is changed will be described. The laser oscillator 1 shown in FIG.
A laser, an Ar laser, a He-Cd laser, or the like is properly used depending on the required foreign substance detection sensitivity. Roughly, if the sensitivity is 0.8 μm or more, a He—Ne laser may be used.
When the thickness is 5 to 0.8 μm, an Ar laser is preferable. When the thickness is 0.5 μm or less, a He—Cd laser is required. The spot size of the laser is switched by inserting the zoom lens 3 into the path of the laser light reflected by the mirror 2, and the beam is scanned over the entire surface of the reticle 10 by the scan mirror 4.

FIG. 4 is a diagram showing the upper surface of the stage of FIG. 1,
FIG. 5 is an enlarged view of the detector of FIG. Next, a method of calibrating the origin and the amount of laser scanning will be described. As shown in FIG. 4, the detectors 7 are arranged on all sides of the reticle 10, the beam is scanned to the position of the detector 7, and the position of the scan mirror 4 when the laser is incident on the detector 7 is stored in advance. Scan mirror 4 compared to the position of mirror 4
By adjusting the rotation angle of the scan mirror 4, the origin position and the movement amount of the scan mirror 4 are calibrated. The configuration of the detector 7 includes a photomultiplier 13 and a pinhole 12, as shown in FIG.

FIG. 6 is a view showing an optical system for aligning the reticle, FIG. 7 is a view showing the position of a reference mark when aligning the reticle, and FIGS. 8 (a) and 8 (b) are taken in. FIG. 3 is a diagram illustrating an image of a reference mark and an image signal waveform. Next, an alignment method of the reticle 6 will be described.

The optical system for alignment is similar to the optical system of a metal microscope, as shown in FIG. 6, and the reticle 10, the index 14, and the observation surface are optically conjugate. In the alignment of the reticle, it is necessary to correct the fluctuation of the alignment optical system with respect to the reference point in order to reduce the measurement error. In this method, as shown in FIG. 7, a reference mark 16 is set in a reticle stage immediately below an alignment optical system. FIG. 8 shows the structure of the fiducial mark.
Since the reference mark 16 is located below the reticle surface, a focus correction lens 15 for correcting the focus position of the microscope is provided. The reference mark 16 may be the same as the alignment mark 10a in FIG. 1B used for the stepper on the reticle 10.

Next, a method of measuring a position error of the reticle 10 will be described. FIG. 8 shows an example of an image obtained by the reticle alignment optical system in FIG. FIG. 8 (a)
Is a case where the reference mark is made up of a plurality of strips. Since the index 14 in the optical system is illuminated from the back side and a shadow is observed, the reflected light from the reference mark becomes dark, and both of them are brightened. Can be distinguished. And CCD camera 1
FIG. 8A shows a waveform obtained by extracting the signal intensity at the measurement position from the image obtained in step 1. From this signal, the positional relationship between the mark on the reticle and the index 14 is obtained, and the reticle 10
Is corrected. FIG. 8B shows an example in which the alignment mark is a cross. In this case as well, the signal intensity at the measurement position is as shown in FIG. 8B as in the case described above, and the positions of the mark and the index 14 can be obtained. From the result, the reticle displacement is calculated.

When the preparation is completed in this way, as described above, the laser spot is set to about 0.1 to 5 mm and the reticle 10 is scanned to check whether there is any foreign matter on the reticle 10 or not. If a foreign substance is found, it is compared with the position coordinates of the reticle defect correction mark moved from the database to the storage unit, and if so, the laser spot is narrowed down to about 1 to 10 μm. Scan again finely and precisely measure the coordinates of the foreign matter. Here, the coordinates are compared again with the coordinates of the reticle defect correction mark, and if the coordinates match the coordinates of the defect correction mark, the foreign matter is determined to be a reticle defect correction mark and is not counted as a foreign matter.

As described above, if the spot diameter of the laser beam is made relatively large and the reticle surface is scanned at a coarse pitch, one laser scan can be performed with or without correction, and it is possible to determine whether the laser can be used in a very short time. Can be determined. Further, even a fine foreign substance that cannot be detected by the first laser beam scanning can be reliably detected by the second scanning of the laser beam having a small spot diameter to determine whether or not use is possible.

[0024]

As described above, according to the present invention, the position coordinates of the pattern defect portion of the reticle are stored in advance, and the spot diameter is such that the scattered light from the pattern defect portion can enter the light receiving portion. The laser beam is scanned on the reticle surface, and the presence of foreign matter is roughly inspected based on whether or not there is scattered light entering the light receiving unit from the position coordinates of the reticle other than the defective portion. When there is no defect other than the defect, the laser beam of a narrow spot is further scanned, and the presence or absence of foreign matter is precisely inspected based on whether or not scattered light from other than the defect enters the light receiving unit. This has the effect that the presence or absence of foreign matter in the reticle can be reliably inspected regardless of whether or not the defective portion is repaired.

Further, depending on the reticle having no pattern defect portion, the presence or absence of a foreign substance can be inspected in the first rough inspection, so that it is possible to determine the usability of the reticle more quickly.

[Brief description of the drawings]

FIG. 1 is a flow chart for explaining an embodiment of a reticle inspection method according to the present invention and a schematic view of an inspection apparatus.

FIG. 2 is a view schematically showing a defect inspection apparatus.

FIG. 3 is a flowchart illustrating a method for obtaining position coordinates of a defective portion.

FIG. 4 is a diagram illustrating an upper surface of the stage in FIG. 1;

FIG. 5 is an enlarged view of the detector of FIG. 1;

FIG. 6 is a diagram showing an optical system for aligning a reticle.

FIG. 7 is a diagram showing the position of a reference mark when aligning a reticle.

FIG. 8 is a diagram showing a captured image of a reference mark and an image signal waveform.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser oscillator 2 mirror 3 zoom lens 4 scan mirror 5, 13 photomultiplier 7 detector 8, 17 stage 9 pattern 9 a defect 10 reticle 10 a alignment mark 11 CCD camera 12 pinhole 14 index 15 focus correction lens 16 reference mark

Claims (1)

(57) [Claims] 1. A reticle inspection method for irradiating a laser beam to an alignment mark and a reticle on which a plurality of patterns are formed based on the alignment mark, and entering scattered light into a light receiving portion to determine the presence or absence of foreign matter on the reticle. The relative position coordinates between the position coordinates of the correction mark and the position coordinates of the alignment mark for the defective portion of the pattern are obtained in advance as reticle defect position coordinates. First, the reticle is aligned and the laser is irradiated onto the reticle. After that, the origin and the scanning movement amount are calibrated, and then the whole area of the reticle is scanned with a laser beam having a relatively large spot diameter, and scattered light is incident on the light-receiving portion to be detected as a foreign substance, and the position coordinates of the foreign substance are detected. Is stored in the memory, and the position coordinates of the reticle defect portion obtained in advance and the position coordinates of the detected foreign matter are stored. When these position coordinates match, the reticle is scanned with a laser beam having a smaller spot diameter of the laser beam to detect foreign matter, and the position coordinates of the foreign matter and the reticle defect coordinates are calculated. A reticle inspection method characterized by determining that there is no foreign substance when they match.