JP2000010260A - Black defect repair method for mask repair device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce transmittance due to Ga stain to both a glass substrate exposed by an ion beam and a glass portion underlying a black defect in a mask defect repair apparatus applying a focused ion beam. The phase shift of transmitted light due to the shaving of the glass surface is reduced. SOLUTION: Scanning is performed at a scanning speed such that the effect of suppressing the Ga stain of the assist gas and the irradiation density at which the abrasion of the Ga stain and the glass surface does not cause a problem is obtained, and an image of the correction position and its surroundings is once captured. A region where a black defect is present is identified from the captured image by image processing, and the black defect is corrected by using selective scanning of only the black defect region at a scanning speed at which the gas-assisted etching effect is maximized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting a black defect of a photomask and a reticle defect correction apparatus in the manufacture of an integrated circuit.

[0002]

2. Description of the Related Art The miniaturization of Si semiconductor integrated circuits is remarkable, and the pattern size on a photomask or a reticle used for transfer is also becoming finer. In addition to the miniaturization of pattern dimensions, super-resolution techniques such as phase shift masks are being put into practical use to improve the resolution limit of optical lithography. Defects on the photomask or reticle are transferred to the wafer and cause a reduction in yield, so before transferring the mask pattern to the wafer, the presence or absence of defects on the photomask or reticle by the defect inspection device Location is checked,
If there is a defect, a defect correction process is performed by a defect correction device before transfer to the wafer. Due to the technical trends described above, a device having a small processing size or a phase shift mask is also required for defect correction of a photomask or a reticle. Focused ion beam devices using liquid metal Ga ion sources have become the mainstream of mask repair devices instead of defect repair devices using lasers due to their fine processing dimensions. In the defect repair apparatus using the above-described ion beam, when correcting a white defect, the source gas adsorbed on the surface is decomposed only at a location where the ion beam squeezes finely to form a thin film, and when a black defect is corrected, the focused ion beam is repaired. High processing accuracy is realized by utilizing the sputtering effect of the above or the effect of etching only where the ion beam narrowed down in the presence of the assist gas is applied.

[0003] Conventionally used photomasks are obtained by depositing a metal film such as Cr on a glass such as quartz glass by sputtering to form a light shielding film, and converting the mask pattern into a difference in light transmittance. The structure of the phase shift mask consists of glass such as quartz glass and a light-shielding film made of metal such as Cr and MoSi, similar to the conventional one.However, a phase shifter is provided to actively use the phase information of transmitted light. The resolution is being improved. At the time of the black defect repair using the above focused ion beam device, the glass portion irradiated with the Ga ⁺ ion beam may have a decrease in transmittance due to Ga ion implantation (Ga stain) or the glass surface due to the Ga ⁺ ion beam. However, there is a problem that the phase of the transmitted light changes due to the scraping.

As a method of reducing damage to a glass substrate, for example, an image as shown in Japanese Patent Publication No. Sho 62-60699 is taken, an irradiation area of an ion beam is determined, and only a processing area is selectively scanned to perform sputtering. There is a method of correcting a black defect with an effect. In the above method, the exposed glass substrate is irradiated with the ion beam only when capturing an image, and is not irradiated during processing, so that damage to the Ga stain and the glass surface is greatly reduced. But,
Since the processing area (black defect part) is shaved by the sputter effect, when reaching the underlying glass substrate, even if the shaving of the underlying substrate is reduced by the end point detection, the processing area may be removed to the underlying glass substrate. A decrease in transmittance due to Ga ion implantation is inevitable. In addition, Ga stain and glass surface shaving due to the ion beam may occur during image capturing.

On the other hand, with respect to Ga stain, when gas assisted etching is performed using an assist gas at the time of the above-described black defect repair, the etching speed becomes faster than when repairing by sputtering, and at the same time, the ion beam irradiation area is reduced. It has been reported that since the implanted Ga is removed by the reaction with the etching gas, the Ga stain is suppressed and the transmittance of the repair region is improved (LR Harriot, J. Vac.
i. Technol. B11 , 2200 (1993), etc.). However, when the processing time is prolonged, the time for irradiating the exposed glass substrate with the Ga ⁺ ion beam is prolonged, so that the transmittance also decreases due to the Ga stain. Of course, at this time, the surface of the exposed glass substrate is shaved by the Ga ⁺ ion beam, so that a phase shift of transmitted light also occurs.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a glass substrate which is exposed by an ion beam generated at the time of repairing a defect of a photomask or a reticle and a glass part of a base of a black defect. It is an object of the present invention to reduce the transmittance due to Ga stain to both of them and to reduce the phase shift of the transmitted light due to the shaving of the glass surface.

[0007]

When confirming the shape and position of a defect, the irradiation density of Ga ions to the exposed portion of the glass substrate does not cause Ga stain or surface shaving.
(For example, 4 × 10 ¹⁴ ions / cm ² or less), and a secondary ion image at the correction position and its surroundings is once captured. A region where a light-shielding film or a black defect exists is identified from the captured secondary ion image by image processing. Defect fixes are
With the assist gas flowing, only the black defect portion identified by the image processing is selectively scanned at a scanning speed at which the effect of the gas assisted etching is maximized to correct the black defect.

[0008]

According to the above method, the glass substrate on the photomask or the reticle is exposed only to the ion beam of a low irradiation dose by the fast scanning only at the time of capturing an image. There is less concern about phase shift due to surface abrasion. The glass substrate below the black defect part that is selectively scanned at the time of defect correction,
Since Ga injected into the ion beam irradiation region is removed by a reaction with the etching gas, Ga stain is suppressed, and a decrease in transmittance is suppressed low. Also, due to the difference in the selectivity between the light-shielding film and the glass substrate in the gas assisted etching, the phase shift due to the abrasion of the glass surface in the above-mentioned correction region by the Ga ⁺ ion beam can be significantly reduced.

[0009]

An embodiment of the present invention will be described below with reference to FIG. After accelerating the ion beam 2 extracted from the Ga liquid metal ion source 1 to about 20 kV, it is focused to a beam diameter of 0.2 μm or less by the condenser lens 3a or the objective lens 3b, and scans the photomask or reticle 5 by the deflection electrode 4 . Since the photomask or reticle 5 is formed by depositing a metal film such as Cr on a glass substrate which is an insulator, the electron beam 11 of about 400 V generated by the charge nutrizer 10 is used as a photomask so that charge-up does not occur. Alternatively, charge neutralization is performed by applying the ion beam 2 to the same position on the reticle 5 as the irradiation position. Secondary ions 6 generated by irradiation of the focused ion beam 2 are:
After being collected and focused by the electric field of the transfer optical system 7, they are mass-separated by the sector magnetic field 8 and guided to the detectors 9. The secondary ion image is formed by making the signal intensity of each detector correspond to the color of one pixel on the CRT and displaying it in synchronization with the scanning of the deflection electrode 4.

[0010] A defect to be corrected is specified from the secondary ion image, and the defect is corrected by a gas gun 14 provided near the sample.
While supplying a gas for etching or deposition from the nozzle, the focused ion beam 2 is irradiated to a region including a defect. In the case of a black defect, an excess light-shielding film is removed by utilizing a gas-assisted etching effect of a halogen element-containing gas such as XeF ₂ . The end point of the etching is detected by monitoring the material constituting the light shielding film such as Cr and the secondary ion intensity of Si on the glass substrate. In the case of a white defect, correction is performed by decomposing and depositing a source gas containing a light-shielding substance such as carbon by the energy of an ion beam.

Particularly, in the present invention, the above-described black defect correction is performed in the following procedure. 1) Confirmation of the shape and position of the defect is achieved by irradiating the exposed portion of the glass substrate with Ga ions to an irradiation density (e.g., 4 × 10 ¹⁴ ions / cm ² or less) that does not cause any problems with the removal of Ga stain or the glass surface. Scanning is performed at such a scanning speed, and the secondary ion image at the correction position and its surroundings is temporarily stored in the storage device 12. 2) Based on the captured secondary ion image,
Computer or image processing unit 13
Identify with. 3) Thereafter, only the black defect portion 23 as shown by the hatched portion in FIG. 2 is selectively scanned in the presence of the assist gas at this time at a scanning speed at which the gas assisted etching effect is maximized. Gas-assisted etching is performed so as not to irradiate the exposed glass portion 22 to correct the defective portion. The glass substrate below the black defect part is a light-shielding film of gas-assisted etching that suppresses Ga stain due to the effect that Ga injected into the ion beam irradiation area is removed by the reaction with the etching gas. And the glass substrate greatly reduces the selectivity. FIG. 3 shows a flow of a series of operations for the above-described black defect correction.

In the above-described black defect and white defect repair, in order to improve the processing accuracy of the defect repair portion, at the time of the black defect repair, the focused ion beam is scanned by slightly expanding to the non-defect side of the region recognized as the defect. When correcting a white defect, the focused ion beam may be scanned by slightly narrowing the area recognized as a defect in consideration of the spread of the deposition film after deposition.

Hereinafter, another embodiment based on the above idea will be described. In the apparatus shown in FIG. 1, fast scanning is performed so that the irradiation amount of Ga ions to the exposed portion of the glass substrate is not increased, and the secondary ion images at the correction position and the surrounding area are temporarily stored in the storage device 12, and the light shielding film Even if the image processing unit 13 identifies the existing region of 21 or the black defect region 23, the surface of the photomask or the reticle 5 is covered with a thin film such as an oxide film or a carbon-containing contamination film generated by electron beam irradiation. In this case, the desired secondary ion generation efficiency is reduced, and an image with a good S / N cannot be obtained by one scan. Multiple scans are required to obtain accurate correction location information (the amount of Ga ion irradiation on the exposed portion of the glass substrate increases). Therefore, as shown by the dotted line in FIG. 4, only a region in which the region composed of the light-shielding film 21 and the black defect region 23 extracted from the image captured in the single scan described above is slightly expanded toward the glass substrate has a good S / N ratio. Scanning is repeated until an image is obtained, and the secondary ion image is taken in again, and the area where the light-shielding film 21 and the black defect area 23 exist is identified by the computer or the image processing unit 13. By limiting the scanning area at the stage of obtaining an image with a good S / N ratio, it is possible to minimize the exposure of the exposed glass substrate to an extra ion beam that causes a decrease in transmittance and a phase shift. The black defect repair process is performed at a high ion beam irradiation density in the same manner as in FIG. FIG. 5 shows a flow of a series of operations for correcting a black defect when an image having a good S / N cannot be obtained by one scan.

Of course, in the defect repairing procedure of the present invention shown in FIG. 4, the existence of the black defect area 23 is determined by the computer or the image processing unit 13 based on the light shielding film material of the captured image and the secondary ion intensity of Si. In addition to automatic recognition by image processing, a boundary of a black defect on a captured image can be specified by an operator using an input device such as a mouse of a computer in pixel units.

Similarly, shape comparison with a normal pattern on a photomask or reticle 5 and design data (mask pattern data) on CAD or data obtained by converting design data for an electron beam drawing apparatus or a defect inspection apparatus are performed. If the present invention is applied to a black defect region extracted from a shape comparison with an ideal pattern generated through a pattern generation circuit, the black defect can be corrected with less residual Ga and less abrasion of the glass substrate by an ion beam.

[0016]

As described above, according to the present invention, both the exposed glass substrate near the black defect and the glass substrate below the defective portion are caused by the decrease in the transmittance due to the Ga stain and the shaving of the glass. The phase shift can be prevented, and the reliability of a defect correction portion of a conventional photomask or reticle and a phase shift mask using an apparatus to which the focused ion beam technique is applied can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an area selectively scanned at the time of defect correction.

FIG. 3 is a diagram showing a flow of a series of operations for correcting a black defect.

FIG. 4 is a diagram illustrating an area selectively scanned in the second and subsequent imagings of another embodiment.

FIG. 5 is a diagram illustrating a flow of a series of operations for correcting a black defect according to another embodiment.

[Explanation of symbols]

1 Ga liquid metal ion source 2 Ga ⁺ ion beam 3a Condenser lens 3b Objective lens 4 Deflection electrode 5 Photomask or reticle 6 Secondary ion 7 Transfer optics 8 Sector magnet 9 Detector 10 Charge nutrizer 11 Electron beam 12 Storage device 13 Computer or image processing unit 14 Gas gun 21 Light shielding film 22 Glass substrate 23 Black defect area

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/30 541Z F-term (Reference) 2G001 AA05 AA09 BA06 CA05 GA01 GA06 HA07 HA13 JA02 JA03 KA03 LA11 MA05 RA04 2H095 BD32 BD35 5C034 BB09

Claims (4)

[Claims] 1. An ion source for emitting Ga ⁺ ions, an ion optical system for focusing the ions, a deflection electrode for irradiating the focused ion beam to a desired position on a sample, and a surface of the sample. A detector for detecting secondary ions emitted from the detector, an image display device for displaying a mask or a reticle based on the planar intensity distribution of the secondary ions, and selectively detecting an excess portion of the mask or reticle pattern. The focused ion beam is irradiated while being repeatedly scanned, and a means for removing an excess portion of the pattern by a chemical amplification effect of the assist gas or a means for correcting a portion lacking the pattern by a deposited film due to decomposition of a source gas is provided. In the mask repairing apparatus having the above, the effect of suppressing the residual Ga in the glass substrate when the etching is performed using the assist gas and the exposure of the glass substrate Irradiation density of Ga ions
Scanning at a scanning speed of 4 × 10 ¹⁴ ion / cm ² or less, once capture the image of the correction position and its surroundings,
The region where the black defect exists is identified from the captured image by image processing, and the defect correction is performed by using selective scanning of only the black defect region at the scanning speed that maximizes the gas-assisted etching effect. A mask repair apparatus characterized in that a black defect can be repaired with less abrasion of a glass substrate by a beam. 2. A boundary of a black defect existing area of the captured image is specified in pixel units by an input device such as a computer mouse, and the defect correction is performed at a scanning speed at which a gas assisted etching effect is maximized. 2. The mask repairing apparatus according to claim 1, wherein by selectively scanning only the area regarded as a defect, black defect repairing with less residual Ga and less abrasion of the glass substrate by the ion beam can be performed. 3. A black defect region is identified by comparing the captured image with a normal pattern shape on the mask or reticle, and the defect correction is performed at a scanning speed at which a gas assisted etching effect is maximized. 2. The mask repair apparatus according to claim 1, wherein by selectively scanning only the mask, the black defect can be repaired with less residual Ga and less abrasion of the glass substrate by the ion beam. 4. A black defect area is identified by comparing the captured image and the design data with an ideal pattern generated through a pattern generation circuit, and the defect is corrected at a scanning speed at which the gas-assisted etching effect is maximized. 2. The mask repair apparatus according to claim 1, wherein by selectively scanning only the black defect area, the black defect can be repaired with less residual Ga and less abrasion of the glass substrate by the ion beam.