JP3908526B2 - Photomask defect correction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photomask defect correcting method.
[0002]
[Prior art]
The miniaturization of Si semiconductor integrated circuits is remarkable, and along with this, the pattern dimensions of masks used for transfer are also becoming finer. Reduced projection exposure apparatuses have responded to this demand with higher NA and shorter wavelengths. At the present time when advancement of miniaturization is required, a phase shift mask, which is a kind of super-resolution technique, has been used in order to improve resolution and depth of focus while maintaining a reduced projection exposure apparatus. If there is a defect in the mask, it will be transferred to the wafer and reduce the yield.Therefore, before transferring the mask pattern to the wafer, the defect inspection device will check the presence or absence of the mask defect and the defect location. If it exists, a defect correction process is performed by a defect correction device before transfer to the wafer. Due to the technical trend as described above, it is required to deal with small defects in mask defect correction. Conventional mask defect correction has been performed with a correction device using a laser or ion beam, but scanning probe microscopes are used to correct defects in masks because of the demand for miniaturization and high accuracy. It is starting to be tried.
[0003]
For black defect correction using a scanning probe microscope, it is removed by a method of physically scraping with a probe harder than the workpiece (e.g. SPIE Proceedings 4186, 670 (2001)) or laser ablation with a near-field light microscope. Methods (eg SPIE Proceedings 2793, 481 (1996)) have been reported. Although there has been no report using a scanning probe microscope for correcting white defects, it has been reported that a fine metal film with a diameter of several tens of nanometers can be generated by using a scanning tunneling microscope to decompose a metal organic gas by an electric field between the probe and the substrate. (For example, Proc. IEEE 85,589 (1997), Appl. Phys. Lett. 68, 2210 (1997)), white defects can be corrected by using this metal film as a shielding film. In addition to electric fields, it has been reported that a metal film with a diameter of several tens of nanometers can be formed by decomposing organometallic gas using near-field light using a near-field light microscope (Appl. Phys. Lett. 76, 2173 (2000 )).
[0004]
In any processing using the above scanning probe microscope, if there is a thermal gradient, the processing position will shift due to drift over time, so it is necessary to correct the drift or wait until the drift subsides before starting processing. Processing cannot be performed. Usually, when the sample is introduced, the temperature difference between the sample and the sample holding mechanism is different, so that processing is started after the thermal drift is subsided. In particular, in the case of a photomask, since thermal conductivity is not good, it takes time to reach thermal equilibrium, and thermal drift occurs for a long time. In this case, as a matter of course, the throughput decreases due to the waiting time. In addition, even if processing is started, the etching rate or film deposition rate is slow, so the processing time is long, and even if processing is started after sufficient waiting, the processing position will change due to drift due to changes in room temperature, etc. Can not do. If the machining is interrupted periodically, the image is observed, the drift amount is calculated from the comparison with the previous image, and the machining is resumed by applying feedback to the scanning position. Although it is possible, there is a problem that increasing the number of times of imaging improves the accuracy but decreases the throughput.
[0005]
If a mirror is provided on the side of the sample holding mechanism and the drift is corrected by feeding back the scanning range of the scanning probe microscope probe from the distance measurement by the laser interferometer, the drift can be corrected without reducing the throughput. There is a problem that correction cannot be made for thermal drift such as when the temperature differs between the sample and the sample holding mechanism or due to local thermal expansion of the sample when there is a heat source near the sample.
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a method for correcting fine black defects or white defects on a photomask with high throughput and high accuracy in a photomask correcting method using a scanning probe microscope .
[0007]
[Means for Solving the Problems]
Recently, studies on surface electrical conduction using a scanning probe microscope that can independently drive two or more probes have been reported (for example, Applied Physics 67, 1361 (1998), Applied Physics 70, 1165 (2001)). . The present invention is a modification of this apparatus and applied to defect correction of a photomask. In the defect correction method of a photomask using a scanning probe microscope having two independently operable probes, one probe is provided. Thus, black defects and white defects are corrected, the drift amount is detected by the other probe, and drift correction is performed in parallel with the processing. As shown in FIG. 1, while one or more processing probes 1 are selectively scanned and corrected only for black defects or white defect areas 6 that are distinguished from the glass substrate 3 and the normal pattern 4, they are in parallel. Using the probe 2 that can be driven independently of the processing probe 1 as an atomic force microscope probe in non-contact mode, the drift correction pattern 5 is continuously imaged and drifted compared to the previous image. The amount is calculated, and the drift is corrected by appropriately feeding back the scanning range of the processing probe 1.
[0008]
[Action]
Since it is processed by a scanning probe microscope, it can cope with the correction of minute defects in the most advanced mask. The drift amount is calculated from the continuous high-resolution image of the atomic force microscope in the non-contact mode, and the drift is corrected by applying appropriate feedback to the scanning range of the processing probe. Is possible. Since the drift correction scan is performed independently of the processing scan, the throughput is not reduced due to image acquisition even if the number of drift corrections is increased. If drift correction is frequently performed only at the initial stage of machining, even if there is a slight thermal drift, the machining is not greatly affected. Therefore, the time for waiting for the thermal drift at the time of introducing the mask to be settled can be shortened. Since drift correction is performed based on the image obtained near the processing area on the mask, drift can be corrected with high accuracy even when the temperature differs between the mask and the mask holding mechanism or when there is a heat source near the mask. it can.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention in which black defects are removed as shown in FIG. 2 by physically removing a probe harder than the material to be processed will be described.
A photomask containing a black defect is introduced into a vacuum chamber containing a scanning probe microscope capable of independently driving two probes, and the stage is moved to a position having a black defect based on the coordinate information of the defect inspection apparatus. First, black defects are observed using the processing probe 10 as an atomic force microscope probe, and the black defect region 7 is extracted from the glass substrate 3 and the normal pattern 4. Drift correction in the non-contact mode using the probe 2 that can be driven independently of the processing probe 10 at the same timing as the atomic force microscope probe so that the relative position of the defect position and the correction pattern does not shift Get the image of pattern 5 used for. Processing is performed according to the following procedure.
(1) The black defect correction is performed by fixing the height of the processing probe 10 harder than the material to be processed, and selectively scanning only the black defect area 7 and physically removing it. When one scan is completed, the position of the processing probe 10 is slightly lowered, and only the black defect region 7 is selectively scanned and physically removed. In parallel with processing, high-resolution observation of drift correction pattern 5 is performed with an atomic force microscope in a non-contact mode.
(2) The drift amount is calculated by comparing the acquired image with the image of the previous drift correction pattern.
(3) When the drift amount is obtained, the machining is temporarily suspended, the scanning range of the machining probe 10 is changed in consideration of the drift amount, and the machining is resumed.
(4) Repeat steps (1) to (3) until black defect removal is completed.
Since the scanning probe microscope has high resolution and high controllability, it can cope with the correction of minute defects in the most advanced photomask. Because drift correction is performed by comparing high resolution atomic force microscope images, highly accurate drift correction is possible. In addition, since the drift correction scan is performed independently of the processing scan, the throughput is not reduced due to the image acquisition even if the number of drift corrections is increased. Furthermore, if the drift correction is frequently performed only at the initial stage of processing, even if there is a slight thermal drift, the processing is not greatly affected. Therefore, it is possible to shorten the time for waiting for the thermal drift when the photomask is introduced to stop. Because drift correction is performed based on the image near the processing area on the photomask, drift can be corrected with high precision even when the temperature differs between the photomask and the photomask holding mechanism or when there is a heat source near the photomask. be able to. As described above, since highly accurate drift correction can be performed, highly accurate black defect correction can be performed.
[0010]
Next, an example in which the white defect correction as shown in FIG. 3 is performed by decomposing the shielding film source gas by the electric field of the conductive probe will be described.
As above, a photomask containing white defects is introduced into the vacuum chamber, and the conductive probe 11 is used in the atomic force microscope mode to observe the area containing white defects and recognize the white defect area 8. To do. The processing is performed by flowing a shielding film source gas such as an organic metal gas through the gas gun 13 and using the fact that the shielding film material gas is decomposed and deposits the shielding film 9 only under the probe, the recognized white defect region The shielding film 9 is deposited by selectively scanning the conductive processing probe 11 whose height is fixed at 8 while applying a pulse voltage with the pulse power supply 14. When one scan is completed, the height of the processing probe 11 is slightly raised, and selective scanning of the white defect region 8 is repeatedly performed while applying a pulse voltage, and a shielding film is further deposited on the shielding film 9 that has been deposited repeatedly. . This procedure is repeated until a desired film thickness is obtained to correct white defects. As described above, the drift correction pattern 5 is continuously observed with the atomic force microscope in the non-contact mode in parallel with the processing to correct the drift. Defect correction can be realized.
[0011]
Next, an embodiment in which black defect removal as shown in FIG. 4 is performed by laser ablation using near-field light from a near-field light microscope will be described.
As in the case of removing black defects by physically removing a probe that is harder than the material to be processed, a photomask containing black defects is introduced into the vacuum chamber, and black defects are first included in the shear force image of a near-field light microscope. The area is observed and the black defect area 7 is recognized. Black defect removal is performed by selectively scanning only the black defect region 7 with the probe 12 having a fixed height, utilizing the fact that laser ablation by near-field light occurs only directly under the probe 12 of the near-field light microscope. . The same height control and selective scanning of the probe as in the case of removing the black defect by physically removing the probe harder than the material to be processed is repeated until the black defect can be removed by laser ablation. In parallel with processing, the drift 5 is corrected by continuously observing the drift correction pattern 5 with an atomic force microscope in a non-contact mode, so black defects are removed by physically removing the probe that is harder than the workpiece material. In the same way as in the embodiment for removing, black defect correction with high throughput and high accuracy can be realized.
[0012]
Next, an example in which the white defect correction as shown in FIG. 5 is performed by decomposing the shielding film source gas with the near-field light of the near-field light microscope will be described.
As in the case of removing black defects by physically removing a probe that is harder than the material to be processed, a photomask containing white defects is introduced into the vacuum chamber, and first, white defects are included in a near-field light microscope shear force image. The region is observed and the white defect region 8 is recognized. The white defect correction uses the fact that the shielding film source gas absorbs near-field light and decomposes and deposits the shielding film 9 only under the probe 13 to deposit a shielding film source gas such as an organometallic gas into a gas gun. While flowing through 13, only the recognized white defect region 8 is selectively scanned with the near-field high-microscope probe 12 that is incident on the short-wavelength laser 13 and has a fixed height. The same probe control and selective scanning as in the case where the white defect correction is performed by decomposing the shielding film raw material gas by the electric field of the conductive probe is repeated until a desired film thickness is obtained. In parallel with processing, the drift 5 is corrected by continuously observing the drift correction pattern 5 with an atomic force microscope in a non-contact mode, so black defects are removed by physically removing the probe that is harder than the workpiece material. In the same manner as in the embodiment in the case of removing, white defect correction with high throughput and high accuracy can be realized.
[0013]
【The invention's effect】
As described above, the present invention is a photomask defect correction method using a scanning probe microscope equipped with two independently operable probes, in which one probe corrects black defects and white defects while the other. Since the drift amount is detected by the above-described probe and drift correction is performed, machining and drift correction can be performed in parallel, unlike the conventional method in which machining is interrupted and drift correction is performed. Since there is no need to interrupt processing, the working time can be reduced and high throughput can be achieved. Further, since there is no cause a decrease in throughput by increasing the drift correction number, often can be repeated drift correction can be performed as a result, the precision of the photomask defect correction.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram that best represents the features of the present invention.
FIG. 2 is a conceptual diagram illustrating an example in which black defects are removed by physically removing a probe that is harder than the material to be processed.
FIG. 3 is a conceptual diagram for explaining an embodiment when white defect correction is performed by decomposing a shielding film source gas by an electric field of a conductive probe.
FIG. 4 is a conceptual diagram illustrating an example in which black defects are removed by laser ablation using near-field light from a near-field light microscope.
FIG. 5 is a conceptual diagram illustrating an example in which white defect correction is performed by decomposing a shielding film raw material gas using near-field light from a near-field light microscope.
[Explanation of symbols]
1 Scanning probe microscope probe for processing
2 Atomic force microscope probe
3 Glass substrate
4 Normal pattern
5 Drift correction pattern
6 Defect area
7 Black defect area
8 White defect area
9 Deposited shielding film
10 Probe harder than workpiece material
11 Conductive probe
12 Near-field optical microscope probe
13 Gas gun for shielding film material
14 Pulse power supply
15 Short wavelength laser

Claims (6)

In a photomask defect correction method using a scanning probe microscope equipped with two independently operable probes , one probe detects black defects and white defects, and the other probe detects the amount of drift. A defect correction method for a photomask , wherein drift correction is performed in parallel with processing . In defect correction method of a photomask using a scanning probe microscope equipped with a probe one can operate in two or more independent is an atomic force microscope tip, wherein one of an atomic force microscope probe of a non A defect correction method for a photomask , wherein an image is acquired in a contact mode, a drift amount is detected , black defects are removed and white defect correction processing is performed with the remaining probe while correcting the drift . Black defect removal is performed by a physical removal method with one probe harder than the workpiece material, and drift correction is performed by acquiring an atomic force microscope image in non-contact mode using the other probe. The defect correcting method for a photomask according to claim 1 . White defect correction is performed by decomposing the shielding film source gas by the electric field of one of the conductive probes, and drift correction is performed by acquiring an atomic force microscope image in the non-contact mode using the other probe. The defect correction method for a photomask according to claim 1, wherein Black defect removal is performed by laser ablation with near-field light from a near-field light microscope , which is one of the probes, and drift correction is performed by acquiring an atomic force microscope image in non-contact mode using the other probe. The defect correction method for a photomask according to claim 1, wherein White defect correction is performed by decomposing the shielding film material gas by the near-field light of the near-field light microscopy, which is one of the probe, the drift correction acquiring an atomic force microscope image of the non-contact mode using the other probe defect correcting method of a photomask according to claim 1, characterized in that to.

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