JP2000330261A - Laser correcting device and method for guaranteeing defect of photomask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quantitatively evaluate the exposure transfer performance of the correction part of the defect of a photomask and to accurately decide mask quality by providing a simulation means which converts image data of an area including a defective part so as to obtain light intensity distribution in the case of exposing and transferring a mask pattern onto a wafer. SOLUTION: This device is equipped with the simulation means which converts the image data on the specified area including the defective part so as to obtain the light intensity distribution in the case of exposing and transferring the mask pattern onto the wafer by using a specified exposing condition. In the device, the image data fetched by an image data fetching means 8 are converted into pattern data for light intensity simulation by an image data converting means 9. Simulation calculation is performed by using the pattern data for light intensity simulation in a light intensity simulation 10, whereby a light intensity distribution value is obtained. In such a case, the input/output of the data and simulation processing and the light are all controlled and executed by a control processor 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask defect repair apparatus and a defect assurance method, and more particularly to a laser repair apparatus and a photomask defect assurance method used in a defect repair step and steps before and after the step.

[0002]

2. Description of the Related Art Defects that occur in a manufacturing process of a photomask used for forming a fine circuit pattern such as a semiconductor LSI circuit are roughly classified into two types: a black type defect and a white type defect. FIG. 4 is a conceptual explanatory view showing a defect generated on the photomask in a plane. The former black type defect refers to a defect in which a light-shielding film, a foreign substance, a contaminant, or the like remains in a portion other than a normal pattern, as shown in defects a and b in FIG.
The white defect refers to a defect in which a part of a normal pattern is missing or missing, as shown in defects c and d in FIG. When observed with transmitted light, black-based defects appear to be blackened by being shielded from light, and white-based defects appear to be transmitted.

When such a defect on the photomask exists, it may sometimes be fatal in a semiconductor circuit, depending on the size of the defect and its relative position to the pattern. Therefore, if there is such a defect on the photomask, it must be corrected. In particular, most of current photomasks have a magnified pattern of 5 times or 4 times called a reticle, and a circuit pattern can be formed on one mask substrate only on one surface or two surfaces. May not be acceptable. That is, it is necessary to form a completely defect-free photomask pattern. However, it is extremely difficult to make a defect-free photomask from the beginning in an actual photomask manufacturing process, and the yield is significantly reduced. Is required.

Conventionally, a photomask defect repairing operation uses a dedicated repairing device. However, the repairing method differs between the black-based defect and the white-based defect, and different devices are used. In particular, for repairing black-based defects such as the defects a and b in FIG. 4, a method of removing a defect by irradiating a laser beam with a laser repairing device is used. FIG. 3 is a block diagram illustrating the configuration of a conventional laser correction device. In the figure, a laser beam generated by a laser light source 31 is first shaped by a laser beam optical system 32. Meanwhile, mask control stage 3
Photomask 3 mounted on 3 and inspected in advance for defects
In step 6, the defect information reading means 37 reads the defect position information of the mask, and moves the defect portion to be corrected on the stage under the control of the control processor 35 so that the defective portion falls within the field of view of the optical microscope 34 for pattern observation. The instruction operation to the control processor is input by input means 39 such as a keyboard. After confirming with the eyepiece of the microscope or the screen of the monitor 38 that the defect portion has entered the field of view using the pattern observation optical microscope 34, the defect portion is irradiated with the beam-shaped laser beam. Defects made of a metal film can be removed and corrected by the action of energy.

Incidentally, a pulsed YAG laser is usually used as the laser light source 31, and a laser beam optical system shapes a laser beam into a desired beam shape by passing the laser beam through a slit. The pattern observation optical microscope 34 has a structure similar to that of a normal optical microscope, and includes an eyepiece, an objective lens, and an illumination system. A television camera for monitoring and a digital camera for image processing are attached for observation. . Before repairing the photomask, the defect location is specified using a defect inspection machine, and the defect position information is recorded on an information recording medium such as a magnetic card, a floppy disk, or a magneto-optical disk, and the defect information is read by a laser correction device. Means 37
To read the information. Based on the information, the controller 35 operates the mask control stage 33 by moving the stage to move the corresponding defect portion of the mask into the observation field of view and irradiate the laser beam.

Conventionally, when a laser correction device having the above-described configuration is used, it is not possible for an operator to determine whether a desired correction has been accurately performed on a defect correction portion based on an image obtained by monitoring a correction portion. did not become. If it is determined that the correction is insufficient, if a black defect remains, the laser beam is irradiated again to correct it. At this time, if the pattern is cut off due to excessive irradiation of the laser, it becomes an uncorrectable defect, so that careful work is required. In some cases, laser beam irradiation traces may remain at defect repair locations. Since that part is in the transparent part on the glass substrate of the photomask, when it is exposed and transferred on the wafer using this mask,
Defective parts such as distortion of the pattern shape and remaining resist film are left out, and there is a risk of affecting all semiconductor chips.

Further, since the irradiation position accuracy of the laser beam is limited, it is extremely difficult to completely correct a defect or the like on the edge portion of the pattern, and a slight projection or a chipped portion is formed on the pattern edge. There was sometimes. If the protrusions or chips are very slight, they are judged to be non-defective as being within the defect standard.However, since the defect shapes are various, the judgment is left to the operator's own empirical judgment. Was. In addition, since the determination is based on the image reflected on the monitor, there is a problem in quality assurance if the determination is not appropriate and the observation accuracy is not good. In the actual photomask inspection and repairing process, repair work is performed after the defect inspection, but after that, the defect inspection is often performed again to guarantee. Since the defect inspection takes time, the process load is large, and performing the defect inspection twice is a serious problem.

Further, in recent years, the miniaturization of semiconductor circuits has been remarkably advanced, and the defect standards of photomasks have become very strict. Therefore, it is necessary to correct even defects near the detection limit of a defect inspection machine. Along with this, the demand for defect correction accuracy has become stricter, and the above problems have become more serious. As described above, when the accuracy of laser correction of a photomask defect is insufficient, there is a problem that when a defect of a corrected portion occurs, the transferability of the photomask is affected. In addition, since the quality judgment of the corrected portion is based on the empirical judgment of the operator, there is no guarantee that accurate judgment can always be made.
Also, it is very difficult to judge the exposure transferability of the corrected part,
Practically, it is necessary to perform the defect inspection by the defect inspection machine two or more times.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to quantitatively evaluate the exposure and transferability of a repaired portion of a photomask defect and to accurately determine the quality. It is an object to provide a laser repair device and a defect assurance method.

[0010]

Means provided by the present invention for solving the above-mentioned problems are as follows. In the first aspect, a laser repairing apparatus for removing and repairing a photomask defect includes a laser repairing device which includes a defective portion including a defective portion. Light intensity simulation means is provided for converting the image data of the area and obtaining a light intensity distribution when the mask pattern is exposed and transferred onto the wafer under predetermined exposure conditions.

[0011] In the second aspect, the laser correction device,
Image observation means for optically magnifying and observing a photomask pattern to obtain an optical image, image capturing means for capturing the optical image from the image observation means, and processing the captured image by a computer. Image data converting means for converting the mask pattern data into mask pattern data, and light intensity simulation means for obtaining a light intensity distribution when a mask pattern is exposed on a wafer using the mask pattern data and predetermined exposure conditions. It is characterized by having been provided.

According to a third aspect of the present invention, in the photomask defect assurance method, a light intensity simulation is performed using the optical images before and after the correction of the defective portion of the photomask, and the defect correction portion is determined by comparing the obtained light intensity distribution. It is characterized by performing an analysis evaluation of the correction accuracy and an exposure transferability evaluation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the laser correction device of the present invention. In FIG. 1, first, a laser beam is generated by a laser light source 1 and beam shaping is performed by a laser beam optical system 2. On the other hand, a photomask 6 for which a defect of the target sample has been inspected is mounted on the mask control stage 3, and control of the control processor 5 is performed based on positional information on the mask of the defect read by the defect information reading means 7. Moves the photomask to a stage, and adjusts the position so as to be within the observation field of view of the optical microscope 4. The instruction operation of the control processor 5 is given by input means 12 such as a keyboard, and the image of the defect is confirmed by the monitor 11.

Here, since a slit indicating a position where the laser beam is irradiated on the mask is displayed in the field of view of the optical microscope 4, accurate positioning of the laser beam irradiation can be performed. Then, after the defect of the photomask 6 enters the observation field of view and the laser beam irradiation position is accurately aligned, the laser beam is irradiated to remove and correct the black-based defect. Further, the defect information reading means 7 uses an information recording / reading device such as a disk drive for reading information from a magnetic recording medium such as a floppy disk containing defect information.

Next, a predetermined pattern area including a photomask defect, which is observed by the optical microscope 4 as an image observation means, is captured as image data by the image capturing means 8. The image capturing means may be any one that can record, save, and output a mask pattern observed by some means as image data. For example, it can be realized by adding a television monitor and a camera or a video device to the optical microscope, and capturing the observation screen into the camera or the video through the monitor. Further, a camera may be directly provided on the optical microscope. The image data is stored in an information recording unit 13 using a large-capacity information recording medium such as a hard disk.
Saved by. Here, the image data only needs to be able to determine the shape of a mask pattern or a defective portion, and may be an analog photographic image, a digital image by a digital camera, or a video scanning screen.

Next, the image data captured by the image data capturing means 8 is converted by the image data converting means 9 into light intensity simulation pattern data. Here, the light intensity simulation pattern data is obtained by shaping the entire image data including the mask pattern into a rectangle, dividing the image data into grids of a predetermined size, and transmitting the gradation values of each grid under predetermined conditions. This is the data converted to rate values. That is, the mask pattern is represented as transmittance distribution data, and is numerically arranged in a matrix array of numerical values. The transmittance value is a value of the intensity ratio of the transmitted light when the light-shielding portion of the mask pattern is set to 0 and the light-transmitting portion is set to 1. Since a normal mask pattern includes only the light-shielding portion and the transmitting portion, It takes only 0 or 1 value. However, for example, when there is a translucent film residue or stain, the transmittance may take an intermediate value.
Further, an intermediate gradation may be obtained due to processing of background noise or reflected light of an analog signal caused by the apparatus when the image data is taken in by the image data taking means. In such a case, after image data matching the actual mask pattern is obtained using generally known image processing techniques such as binarization processing, edge detection, and smoothing processing, light intensity simulation is performed. What is necessary is just to convert it into data for use.

Using the light intensity simulation data converted and generated by the image data converting means, a simulation calculation is performed in the light intensity simulation 10 to obtain a light intensity distribution value. In this procedure, the control processor 5 controls and executes all data input / output and simulation processing. Here, the light intensity simulation is to obtain an exposure distribution on a wafer when a photomask is mounted on an exposure apparatus and is exposed and transferred onto the wafer, in other words, a light intensity distribution is obtained by a simulation calculation. The light intensity simulation is calculated from predetermined exposure conditions represented by parameters of the optical system of the exposure apparatus and the light intensity simulation pattern data. Note that the theory underlying the light intensity simulation is described in, for example, H.H. There is an imaging optics theory by Hopkins et al. (For example, Born and Wolf, "Principles of Optics" (1975)).

The data input when executing the light intensity simulation is an image of the mask pattern including the defect correction portion as described above, and the simulation result based on this is the exposure intensity distribution when the mask pattern is exposed and transferred. Is equivalent to Therefore, the exposure transfer evaluation of the mask pattern including the defect correction portion can be performed from the result obtained by the simulation. The light intensity simulation result is numerical data indicating the light intensity distribution, and is subjected to graphic processing using visualization software or the like, so that a contour map or a color-coded diagram is displayed on the screen of the monitor 11, so that defect correction can be performed. It can be confirmed that the light intensity distribution equivalent to the normal pattern transfer result is obtained when the device performs well, and the light intensity distribution different from the normal pattern transfer result is obtained when the defect correction is defective. Understand. Further, since the light intensity distribution value can be output as a numerical distribution, it is also possible to numerically analyze the degree of difference.

FIG. 2 is a flowchart illustrating a procedure of a photomask defect assurance method using a laser repair apparatus according to an embodiment of the present invention. In FIG. 2, first, a photomask of a target sample is prepared in a photomask preparation 21 and is inspected by a defect inspection 22 to detect a defect. At that time, the presence or absence of a defect is determined in the defect determination 23,
If it is determined that there is a defect, the next image capture / data conversion 2
Perform 4. At this time, if there is no defect, the photomask is non-defective and the process ends.

After the data conversion, a simulation is performed in a light intensity simulation 25. The simulation at this time evaluates the exposure transferability of the defect. Then, the simulation result is evaluated in the defect correction determination 26, and the next laser correction 27 is performed if the defect correction is necessary. If it is determined that the defect correction is unnecessary, the procedure ends. Further, after the laser correction, an image capturing / data conversion 28 is performed again, and then a light intensity simulation 29 is performed. The simulation at this time is to evaluate the exposure transferability of the portion where the defect has been corrected.
If the corrected part evaluation 30 determines that the result is good,
finish. If the repaired portion is determined to be defective, the process returns to the laser repair 27 and the defect repair is performed again.

As described above, by performing the light intensity simulation by taking in the image data before and after the defect portion is corrected, it is possible to analyze and evaluate the correction accuracy of the photomask defect and to evaluate the exposure transferability. in this case,
As before, it is possible to evaluate the exposure transferability by light intensity simulation based on image data before and after the defect correction, instead of just performing the visual observation judgment of the presence or absence of the defect and the defect repaired part with the optical microscope. As a result, a more accurate and reliable assurance of a defect repaired portion has become possible.

[0022]

As described above, the laser repair apparatus and the photomask defect assurance method of the present invention can evaluate the exposure transferability by taking in the image of the defective portion and the defect corrected portion and performing light intensity simulation. As a result, it was possible to repair defects more reliably in exposure and transferability than conventional laser repair devices, and as a defect assurance method, it was necessary to make empirical judgments by visually observing defect repair parts in the past. However, a laser correction apparatus and a photomask defect assurance method that can evaluate and judge exposure transferability by performing light intensity simulation can be provided.

Further, in the prior art, when it was difficult to determine the defect correction portion by visual observation, the defect inspection was performed again by the defect inspection machine. However, according to the above method, the exposure and transferability can be evaluated. A laser inspection apparatus and a photomask defect assurance method that do not require re-inspection, reduce the work load required for the defect inspection / repair process, and can improve cost and delivery time.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of a laser correction device according to the present invention.

FIG. 2 is a flowchart illustrating a procedure of a photomask defect assurance method using a laser device according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a conventional laser correction device.

FIG. 4 is a conceptual explanatory view showing a defect generated on a photomask in a plane.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Laser beam optical system 3 ... Mask control stage 4 ... Optical microscope 5 ... Control processor 6 ... Photomask 7 ... Defect information reading means 8 .... Image capturing means 9 Image data converting means 10 Light intensity simulation 11 Monitor 12 Input means 13 Information recording means 21 Photomask production 22 Defects Inspection 23: Defect judgment 24, 28: Image capture / data conversion 25, 29: Light intensity simulation 26: Defect correction judgment 27: Laser correction 30: Corrected part evaluation 31 ..Laser light source 32 ・ ・ ・ Laser beam optical system 33 ・ ・ ・ Mask control stage 34 ・ ・ ・ Optical microscope 35 ・ ・ ・ Control processor 36 ・ ・ ・ Form Mask 37 ... defect information reading unit 38 ... monitor 39 ... input means a, b ... black-defect c, d ... whitish defects

Claims (3)

[Claims] 1. A laser repairing apparatus for removing and correcting a black defect of a photomask, converting image data of a predetermined area including a defective portion, and exposing and transferring a mask pattern onto a wafer under predetermined exposure conditions. A laser intensity correction means provided with a light intensity simulation means for obtaining a light intensity distribution when the laser correction is performed. 2. An image observation means for optically enlarging and observing a photomask pattern to obtain an optical image, an image acquisition means for acquiring the optical image from the image observation means, Image data conversion means for performing image processing by a computer and converting the mask pattern data into mask pattern data; and light intensity for obtaining a light intensity distribution when a mask pattern is exposed on a wafer using the mask pattern data and predetermined exposure conditions. A laser correction device, comprising: simulation means. 3. A light intensity simulation is performed using optical images before and after correction of a defective portion of a photomask, and analysis and evaluation of correction accuracy of the defect corrected portion and exposure transferability are performed by comparing the obtained light intensity distributions. A method of assuring a photomask defect, comprising performing an evaluation.