JP4926383B2 - Photomask defect correction method - Google Patents

Description

  The present invention relates to a method for correcting black defects in a semiconductor photomask (also referred to as a reticle) and an LCD mask.

In recent years, with higher integration of semiconductor integrated circuits, further miniaturization has been demanded for photomasks used for circuit fabrication. In addition to miniaturization of pattern dimensions, high resolution techniques such as phase shift masks have been put into practical use in order to improve the resolution limit of photolithography. In photolithography, if a defect exists on the photomask, the defect is transferred onto the wafer and causes a decrease in yield. Therefore, before transferring the mask pattern onto the wafer, the defect inspection apparatus can check whether there is a defect in the photomask. The existence location is checked, and if there is a defect, a defect correction process is performed by a defect correction device and the defect-free mask is supplied.
With the miniaturization of the pattern dimensions, the size of the defective portion that has to be corrected in the photomask is becoming smaller and the accuracy in the correction is also getting smaller. There is also a need for a mask that uses a high-resolution technique such as a phase shift mask.
There are two types of defects in the photomask: when an originally required pattern is missing or missing (referred to as a white defect) and when an unnecessary surplus pattern exists (referred to as a black defect). In the case of a black defect, a normal pattern can be obtained by removing excess portions.

Currently, the correction method using a laser beam and the correction method using a focused ion beam (FIB) are the mainstream methods for correcting a black defect in a photomask, and both are methods for directly correcting a defect film.
FIG. 2 is a conceptual diagram collectively showing the steps of a conventional correction method using a laser beam and a correction method using a focused ion beam. FIG. 2A shows a state where a light-shielding film pattern 22 is formed of a metal film such as chromium on the surface of a glass substrate 21 such as a quartz substrate, and a black defect portion 23 exists. FIG. 2B is a process diagram in which the black defect portion 23 is irradiated with the laser beam or the ion beam 24, and FIG. 2C shows the state of the photomask from which the black defect portion 23 has been removed.

Conventionally, a black defect portion is corrected by a method of evaporating and removing the defect portion using pulsed laser light such as Nd: YAG. In this laser beam irradiation correction method, a laser beam spread over a certain range is made to have a predetermined shape (usually rectangular), size, and intensity distribution with an aperture, and is usually further reduced and condensed after passing through the aperture. Irradiate the part to be corrected, but due to poor alignment of the aperture, poor focus adjustment, poor optical axis adjustment, etc., because the intensity of the irradiated beam end is not uniform, The corrected end is not linear, and fine irregularities are likely to appear on the edge.
In addition, when removing the black defect portion by evaporating with the laser beam, as shown in FIG. 2C, the quartz glass or the like is cleaved and scattered, and the glass substrate under the defect is caused by unevenness of about 5 nm to 10 nm. Substrate damage 26 occurs, the surface corresponding to the correction portion becomes rough, and the transmittance of the glass substrate decreases. Although the i-line stepper does not have much influence, the exposure light source becomes an excimer laser, and KrF excimer laser (248 nm) and ArF excimer laser (193 nm) become shorter in wavelength, and the light transmittance due to roughening of the correction portion The decline is becoming a problem.

On the other hand, instead of correcting with a laser beam, a black defect correcting method using a focused ion beam is also used as one that can cope with miniaturization. However, since the defect itself is indefinite, it is difficult to correct only the defect site, damage to the glass substrate around the defect occurs, and gallium is usually used as the ion beam. 2 is implanted into the underlying glass substrate, and as shown in FIG. 2 (c), glass substrate damage 26 occurs due to the phenomenon of so-called gallium stain, and there is a problem in that the light transmittance of the corrected portion is lowered. Even if the acceleration voltage of gallium ions is lowered, the gallium stain phenomenon is implanted into the glass substrate, and the decrease in transmittance due to the gallium stain phenomenon becomes a more serious problem as the exposure wavelength becomes shorter. For example, the transmittance of the ArF excimer laser at the location corrected by the ion beam is about 90%.
Further, at the time of correcting the black defect portion by the ion beam, as shown in FIG. 2C, a glass digging phenomenon called a river bed 25 due to overetching of the glass substrate occurred around the defect (for example, (See Patent Document 2).
Since the river bed disturbs the phase of the transmitted light, it adversely affects the transfer result, and is a factor that degrades the processing quality of the corrected portion of the black defect portion. With the recent shortening of the wavelength of the light source of a reduction projection exposure apparatus, even a riverbed with a depth that is not a problem in the past has come to affect the transfer result, and there is a strong demand for defect correction technology that does not cause a riverbed. It has been.

In recent years, in a method of correcting black defects using a focused ion beam, in order to reduce gallium stain and the like, an etching gas is introduced and excited by gallium ions to selectively etch only the defect. GAE method) Ru been put to practical use Tsutsua.
However, the above-mentioned FIB-GAE method has a problem in that the accuracy of taking in the defect shape is poor, and the substrate is dug or left behind due to over-processing or under-processing at the defect boundary. Further, depending on the material of the light-shielding film forming the pattern, there is a problem that the end point of etching cannot be detected, and the optical transmittance is reduced due to gallium implantation into the quartz glass substrate. Furthermore, there is a problem of gallium implantation due to repeated image image capture, and even with this technique, it is impossible to completely recover the transmittance, which becomes a problem as the exposure wavelength becomes shorter. .
JP 2002-214760 A JP 2000-10260 A

The present invention has been made in view of the above problems, and an object of the present invention is to cause damage to a glass substrate, which occurs in a photomask defect correction method using a laser beam or an ion beam, and to correct a correction portion. rough glass substrate surface of the portion corresponding to the problem that would have the transmittance decreases, the problem of reducing the light transmittance of the modified portion and the glass substrate damage due gallium stains, to eliminate the occurrence of river beds problems, The present invention provides a method for correcting a black defect portion of a photomask that is not damaged by a glass substrate.

In order to solve the above problems, a photomask defect correcting method according to the invention of claim 1 is a photomask defect correcting method having a black defect portion, wherein the photomask is a black defect portion on a glass substrate. A step of applying a positive resist on the photomask to form a resist film; and a photomask substrate on which the resist film is formed is placed in an apparatus having a scanning electron microscope, and the black A step of determining a region to be corrected by taking in a secondary electron image of the defective portion, and irradiating an electron beam while blowing an assist gas to the region to be corrected, and removing a resist portion in the region to be corrected to remove a black defect portion a step of exposing and a step of removing by wet etching or dry etching the black defect portion that has issued the exposed, and a step of removing the resist film, the glass substrate It is characterized in that to correct the black defect portion without causing image.
A defect correction method for a photomask according to the invention of claim 2 is a defect correction method for a photomask having a black defect portion, wherein the photomask has a black defect portion on a glass substrate, and the photomask A step of forming a resist film by applying a positive resist thereon, and a photomask substrate on which the resist film is formed is placed in an apparatus having a scanning electron microscope and an ion beam column, A step of taking an electronic image and determining a region to be corrected; and a step of irradiating an ion beam while blowing an assist gas to the region to be corrected, removing a resist portion in the region to be corrected and exposing a black defect portion; includes a step of removing the black defect portion that has issued the exposed by wet etching or dry etching, removing the resist film, the da on the glass substrate It is characterized in that to correct the black defect portion without causing over-di.
The defect correction method for a photomask according to the invention of claim 3 is characterized in that the assist gas generates OH ions by electron beam irradiation.
A defect correcting method for a photomask according to a fourth aspect of the invention is characterized in that the assist gas generates OH ions by ion beam irradiation.
The defect correction method for a photomask according to the invention of claim 5 is characterized in that the assist gas uses water vapor.
According to a sixth aspect of the present invention, there is provided a photomask defect correcting method, wherein a conductive layer is provided on a resist film formed by applying the resist.
According to a seventh aspect of the present invention, there is provided a photomask defect correcting method, wherein the step of removing the exposed black defect portion by wet etching or dry etching is continuously performed in an apparatus having the scanning electron microscope. It is what.
In the photomask defect correcting method according to the invention of claim 8, the step of removing the exposed black defect portion by wet etching or dry etching is continuously performed in an apparatus having the scanning electron microscope and an ion beam column. It is characterized by doing.

In the method for correcting a photomask having a black defect portion of the present invention, only the resist portion in the region to be corrected of the defect portion is directly removed by electron beam irradiation or ion beam irradiation and an assist gas, and the conventional resist development process is unnecessary. Since the region other than the region to be corrected is covered with a resist film, there is no etching gas irradiation or etching solution to other than the defective portion, and an etching gas or etching solution with high selectivity can be used for the defective portion. Therefore, the correction can be performed without damaging the glass substrate such as the quartz glass substrate.
Since the correction method of the present invention does not directly use the laser beam or the ion beam for the black defect portion, there is no damage to the glass substrate, neither the transmittance reduction nor the phase change due to the gallium stain occurs, and the river bed does not occur. . Further, since the secondary electron image is used as the mask defect image, the transmission portion damage due to the imaging as in the case where the image is captured using the ion beam does not occur.
According to the photomask correction method of the present invention, a resist film is patterned by an electron beam or an ion beam, and a black defect portion is corrected based on the resist pattern. The improvement of the correction rate increases the number of non-defective masks, improving the mask manufacturing yield and shortening the mask manufacturing period.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a process sectional view showing a mask defect correcting method of the present invention. FIG. 1 shows a case where an electron beam and an ion beam are used for pattern irradiation of a resist film as a common view.
A light-shielding film pattern 2 is formed of chromium, chromium oxide or the like on a glass substrate 1 such as quartz glass or low expansion glass, and a positive electron beam resist or photo is formed on a photomask to be corrected having a black defect portion 3 to be corrected. A resist is applied to form a resist film 4 (FIG. 1A). As the positive type electron beam resist or photoresist, a positive type resist used for forming a photomask is usually used, and an alkali development type resist is preferably used.
The resist film 4 of electron beam resist or photoresist preferably has a thickness of about 100 nm to 300 nm. If the thickness is less than 100 nm, pinholes are likely to occur during etching, and if it exceeds 300 nm, pattern recognition under the resist becomes difficult.
Further, in the present invention, if a conductive layer is formed by applying a conductive resin on the surface of the resist film 4 before the defect is corrected, a charge-up phenomenon at the time of electron beam irradiation or ion beam irradiation. Is preferable. The conductive layer is used with a thickness of about several tens of nm.

Next, the above-described photomask to be corrected is placed in an apparatus having a scanning electron microscope or in an apparatus having a scanning electron microscope and an ion beam column, and the resist portion in the region to be corrected is removed and patterned. First, a case where an electron beam is used for pattern irradiation of the resist film will be described.
Next, the photomask to be corrected on which the resist film is formed is installed in an apparatus having a nozzle for assist gas introduction and having a scanning electron microscope (SEM). Based on the coordinates, a secondary electron image of the black defect portion is taken in and a region to be corrected is determined (FIG. 1B). By using SEM, the black defect portion 3 can be clearly recognized even if it is covered with the resist film 4.

  Next, the electron beam 8 is irradiated while the assist gas 7 is blown from the nozzle 6 to the region to be corrected (FIG. 1C). The assist gas 7 is not particularly limited as long as it is a substance that has a hydroxyl group and forms OH ions by electron beam irradiation in a gasified state. However, it is preferable to use water after steaming. In addition, when water vapor is used, there is an advantage that it is not charged up at the time of electron beam irradiation. Water vapor generates activated OH ions by electron beam energy. What is necessary is just to supply about 1 to 0.5 Torr of water vapor as the assist gas, for example. The electron beam irradiated portion of the resist film 4 is directly decomposed by the activated OH ions, the resist portion in the region to be corrected is removed, and the black defect portion 3 is exposed.

Subsequently, the exposed black defect portion 3 is removed by etching with an etching gas or etching solution 9 having high selective etching properties (FIG. 1D).
Finally, the resist film 4 is removed with a dedicated resist stripping solution or oxygen plasma to complete the correction (FIG. 1 (e)).
By this method, the black defect portion can be removed without damaging the glass substrate.

Next, a case where an ion beam is used for pattern irradiation of the resist film will be described.
Coordinates of the black defect part obtained from the appearance inspection device by installing the photomask to be corrected on which a resist film is formed in an apparatus having a nozzle for assist gas introduction and having a scanning electron microscope (SEM) and an ion beam column Based on the above, the secondary electron image of the black defect portion is taken in and the region to be corrected is determined (FIG. 1B).
Next, the ion beam 8 is irradiated while the assist gas 7 is blown from the nozzle 6 to the region to be corrected (FIG. 1C). As in the case of using an electron beam, the assist gas 7 is not particularly limited as long as it is a substance that has a hydroxyl group and forms OH ions by ion beam irradiation in a gasified state. Is simple and preferred. The ion beam irradiation portion of the resist film 4 is directly decomposed by the activated OH ions, the resist portion in the region to be corrected is removed, and the black defect portion 3 is exposed.

Thereafter, as in the case of the electron beam described above, the exposed black defect portion 3 is removed by etching with an etching gas or etching solution 9 having high selective etching property, the resist film 4 is removed, and the correction is completed (see FIG. 1 (e)).
In the present invention, the ion beam is used for pattern irradiation of the resist film and does not directly remove the black defect portion. Therefore, there is no damage to the glass substrate, and the gallium stain may cause a decrease in transmittance or a phase change. In addition, there is no river bed. Further, since the secondary electron image is used as the mask defect image, the transmission portion damage due to the imaging as in the case of capturing the image using the ion beam does not occur.

  As described above, according to the present invention, a resist film is directly decomposed by an electron beam or an ion beam using an assist gas to form a pattern, and a black defect portion is corrected based on the resist pattern. The defect can be corrected and the conventional resist development process becomes unnecessary, so that the process can be shortened and a high-quality photomask can be obtained by improving the correction rate.

  In the photomask defect correcting method of the present invention, the step of etching and removing the exposed black defect portion is continuously performed in an apparatus having a scanning electron microscope or an apparatus having a scanning electron microscope and an ion beam column. It is also possible to do so.

Example 1
An embodiment in which the black defect portion is corrected by the correction method shown in FIG. 1 will be described. On a 6-inch square ultra-high purity synthetic quartz glass substrate 1 optically polished, a chromium light-shielding film pattern 2 having a thickness of 100 nm is formed, and a photomask having a black defect portion 3 made of an excess chromium film is prepared. On the photomask, a chemically amplified resist (OEBR-CAP209 manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied as an electron beam resist by a spin coating method, followed by baking at 130 ° C. for 20 minutes (prebaking). Then, a uniform resist film 4 having a thickness of 0.3 μm was formed (FIG. 1A).

Next, the photomask to be corrected on which the resist film is formed is placed in an apparatus having a scanning electron microscope (SEM), and the secondary electron image of the black defect portion is captured by the defect coordinates obtained from the appearance inspection apparatus. The area to be corrected was determined (FIG. 1 (b)). At this time, the degree of vacuum of the apparatus having the SEM was 1 × 10 ⁻⁶ Torr to 1 × 10 ⁻⁷ Torr.

Next, the region 6 to be corrected was irradiated with an electron beam 8 while spraying water vapor as an assist gas 7 from the nozzle 6 (FIG. 1C). The gas pressure of water vapor was about 1 Torr, and the degree of vacuum of the apparatus having the SEM became 1 × 10 ⁻⁴ Torr to 1 × 10 ⁻⁵ Torr by introducing the assist gas. The acceleration voltage during electron beam irradiation was 20 kV, and irradiation was performed for about 3 minutes. The water vapor generates activated OH ions by electron beam energy, and the electron beam irradiated portion of the resist film 4 is directly decomposed by the activated OH ions, and the resist portion in the region to be corrected is removed. The defective part 3 was exposed.

Subsequently, the photomask to be corrected in which the black defect portion 3 is exposed from the resist film 4 is taken out from the apparatus having the SEM, and dry etching apparatus (manufactured by ULVAC CO., LTD.) With an etching gas mainly containing chlorine gas. Then, the remaining resist film was removed by ashing with oxygen plasma to obtain a photomask with a corrected black defect (FIG. 1 (e)). .
According to the correction method of the present invention, the glass substrate is not damaged, the problem such as gallium stain does not occur, the transmittance of the glass substrate is not reduced, the phase is not changed, and the black defect portion of the photomask is highly accurate. It became possible to make fine corrections, and a high-quality mask was obtained.

(Example 2)
As in Example 1, a light-shielding film pattern made of chromium oxide having a thickness of 100 nm was formed on an optically polished 6-inch square ultrahigh-purity synthetic quartz glass substrate, and a photomask having a black defect portion was prepared. On the above photomask, a chemically amplified resist (OEBR-CAP209 manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied as an electron beam resist by a spin coating method, followed by baking at 130 ° C. for 20 minutes. Then, a uniform resist film having a thickness of 0.3 μm is formed, and an antistatic resin (Espacer 100 manufactured by Showa Denko KK) is further applied thereon by a spin coating method. A uniform conductive layer having a thickness of 50 nm was formed by heating and drying for 5 minutes.

  Next, the above-mentioned photomask to be corrected was placed in an apparatus having an SEM, and a secondary electron image of a black defect portion was taken in based on defect coordinates obtained from an appearance inspection apparatus, and an area to be corrected was determined.

  Next, an electron beam was irradiated while spraying water vapor as an assist gas from the nozzle onto the region to be corrected. The acceleration voltage during electron beam irradiation was 20 kV, and irradiation was performed for about 3 minutes. Similar to Example 1, the electron beam irradiated portion of the resist film was directly decomposed by the activated OH ions, the resist portion in the region to be corrected was removed, and the black defect portion was exposed.

Subsequently, the photomask to be corrected in which the black defect portion is exposed from the resist film is taken out from the apparatus having the SEM, and the black defect portion exposed by the etching liquid mainly containing ceric ammonium nitrate is wet-etched. After washing with water, the resist film was removed with a special stripping solution to obtain a photomask in which the black defect portion was corrected.
The obtained photomask was a high quality mask with no damage to the glass substrate, no decrease in transmittance of the glass substrate and no change in phase.

(Example 3)
As in Example 1, a light-shielding film pattern made of chromium oxide having a thickness of 100 nm was formed on an optically polished 6-inch square ultrahigh-purity synthetic quartz glass substrate, and a photomask having a black defect portion was prepared. On the above photomask, a chemically amplified resist (OEBR-CAP209 manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied as an electron beam resist by a spin coating method, followed by baking at 130 ° C. for 20 minutes. Then, a uniform resist film having a thickness of 0.3 μm is formed, and an antistatic resin (Espacer 100 manufactured by Showa Denko KK) is further applied thereon by a spin coating method. A uniform conductive layer having a thickness of 50 nm was formed by heating and drying for 5 minutes.

  Next, the above-mentioned photomask to be corrected is installed in an apparatus having an SEM and an ion beam column, and based on the defect coordinate data obtained from the visual inspection apparatus, the secondary electron image of the black defect portion is captured by the SEM and corrected. The area to be decided was decided.

Next, an ion beam was irradiated while spraying water vapor as an assist gas from the nozzle onto the region to be corrected . Acceleration voltage when irradiation morphism is a 20 kV, and irradiated from 1.5 for 2 minutes. Similar to Example 1, the ion beam irradiated portion of the resist film was directly decomposed by the activated OH ions, the resist portion in the region to be corrected was removed, and the black defect portion was exposed.

Subsequently, the photomask to be corrected, in which the black defect portion is exposed from the resist film, is taken out from the apparatus having the SEM and the ion beam, and the black defect portion exposed by the etching liquid mainly containing ceric ammonium nitrate is removed. After wet etching and washing with water, the resist film was removed with a special stripping solution to obtain a photomask in which the black defect portion was corrected.
The obtained photomask was a high quality mask with no damage to the glass substrate, no decrease in transmittance of the glass substrate and no change in phase.

It is process sectional drawing which shows the mask defect correction method of this invention. It is a conceptual diagram which shows collectively the process of the correction method by the conventional laser beam, and the correction method by a focused ion beam.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Light-shielding film pattern 3 Black defect part 4 Resist film 5 Electron beam scanning 6 Nozzle 7 Assist gas 8 Electron beam or ion beam 9 Etching gas or etching liquid 21 Glass substrate 22 Light-shielding film pattern 23 Black defect part 24 Laser light or Ion beam 25 River bed 26 Glass substrate damage

Claims (8)

A method for correcting a defect of a photomask having a black defect portion,
The photomask has a black defect on a glass substrate;
Applying a positive resist on the photomask to form a resist film;
Installing the photomask substrate on which the resist film is formed in an apparatus having a scanning electron microscope, and taking a secondary electron image of the black defect portion and determining a region to be corrected;
Irradiating an electron beam while blowing an assist gas to the region to be corrected, removing a resist portion in the region to be corrected and exposing a black defect portion;
Removing the exposed black defect by wet etching or dry etching ;
And a step of removing the resist film, and correcting the black defect portion without damaging the glass substrate. A method for correcting a defect of a photomask having a black defect portion,
The photomask has a black defect on a glass substrate;
Applying a positive resist on the photomask to form a resist film;
Installing the photomask substrate on which the resist film is formed in an apparatus having a scanning electron microscope and an ion beam column, and determining a region to be corrected by taking in a secondary electron image of the black defect portion;
Irradiating an ion beam while blowing an assist gas to the region to be corrected, removing a resist portion of the region to be corrected and exposing a black defect portion;
Removing the exposed black defect by wet etching or dry etching ;
And a step of removing the resist film, and correcting the black defect portion without damaging the glass substrate.   The photomask defect correction method according to claim 1, wherein the assist gas generates OH ions by electron beam irradiation.   The photomask defect correction method according to claim 2, wherein the assist gas generates OH ions by ion beam irradiation.   5. The photomask defect correction method according to claim 1, wherein the assist gas uses water vapor.   6. The method for correcting a defect in a photomask according to claim 1, wherein a conductive layer is provided on a resist film formed by applying the resist. 7. The process of removing the exposed black defect portion by wet etching or dry etching is continuously performed in an apparatus having the scanning electron microscope. A method for correcting a defect in a photomask according to claim 1. 7. The step of removing the exposed black defect portion by wet etching or dry etching is continuously performed in an apparatus having the scanning electron microscope and an ion beam column. The defect correction method of the photomask in any one of.

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