JP2009042684A - Method for correcting defect in multi-gradation photomask and multi-gradation photomask having defect corrected - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a specific method for setting an optimum transmittance in consideration of wavelength dependence of a corrected semi-transmission film. <P>SOLUTION: The film thickness of a corrected semi-transmission film is controlled in such a manner that with respect to an exposure light source including a plurality of exposure light wavelengths to be used for the multi-gradation photomask, the values of the transmittance obtained by weighting averages with a spectral intensity ratio at each wavelength in an uncorrected semi-transmission film and in the corrected semi-transmission film become equal to each other. For the deposition of the corrected semi-transmission film, a gas phase deposition method such as an optical CVD method is preferably used, in which a film can be locally deposited while controlling the film thickness. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a defect correction method for a halftone type multi-tone photomask (hereinafter simply referred to as “multi-tone photomask”) including a semi-transmissive film and a multi-tone photomask to which this method is applied. is there.

  The halftone mask for multi-tone exposure has a light-shielding film and a semi-transmissive film formed on a transparent substrate, a light-transmitting portion where the transparent substrate is exposed, a light-shielding portion where no light is transmitted by the light-shielding portion, and a semi-transmissive And a halftone portion through which an amount of light corresponding to the transmittance of the film is transmitted. When exposure is performed using such a mask, the amount of exposure can be limited by the transmittance of the semi-transmissive film, so that a plurality of patterns can be formed by one exposure, and the mask exposure process can be reduced.

  Although not intended for multi-tone exposure, as a method of correcting white defects that occur in the halftone part of a halftone phase shift mask, it uses a focused ion beam (FIB) to “substantially have the same transmittance as a semitransparent film” A method of depositing a semipermeable membrane as a correction membrane is known.

  In the present specification, the semi-transmissive film formed on the halftone mask from the beginning is referred to as “unmodified semi-permeable film”, and the semi-permeable film formed as a modified film is referred to as “modified semi-permeable film”. Similarly, a light shielding film that has been formed on the halftone mask from the beginning is referred to as an “uncorrected light shielding film”, and a light shielding film that is formed as a correction film is referred to as a “modified light shielding film”.

JP 7-295204 A JP 2003-121992 A JP 2005-189492 A JP-A-8-314119 JP 2002-107913 A

  Since the halftone phase shift mask is premised on extremely fine exposure, short-wavelength and single-wavelength laser light such as F2 laser (157 nm) and ArF laser (193 nm) is used. Thus, the phase shift amount and the like are calculated to design the arrangement and size. In other words, an exposure light source having a plurality of wavelengths is not assumed.

  On the other hand, when a pattern is transferred using a photomask for multi-tone exposure, for example, a plurality of exposures such as i-line (365 nm), h-line (405 nm), and g-line (436 nm) of a mercury lamp. It is common to use an exposure light source that includes a wavelength.

  By the way, when the modified semipermeable membrane and the unmodified semipermeable membrane are compared, the composition of the membrane is greatly different due to the difference in the film forming method, and therefore the optical properties are also greatly different. Therefore, even if the transmittance at “a specific wavelength” can be made equal by a method such as controlling the film thickness, it is not equal at other wavelengths. That is, there is a “wavelength dependency” problem that cannot be ignored depending on the exposure conditions.

  FIG. 5 is a diagram showing the results of measuring the transmittance of the unmodified semipermeable membrane and the transmittance of the conventional modified semipermeable membrane for each different wavelength. In general, when depositing a modified semi-transmissive film, it has been known that the transmittance should be the same as that of the surrounding unmodified semi-transmissive film. However, conventionally, the wavelength-dependent problem is not considered. In general, correction is made so that the transmittances are almost the same at a specific wavelength (for example, only g-line). FIG. 5 shows that the transmittance is set to be approximately equal to the surroundings at the g-line (436 nm).

  However, the transmittance of this modified semipermeable membrane is smaller than that of the unmodified semipermeable membrane at wavelengths other than the g-line, such as i-line (365 nm) and h-line (405 nm). I understand that. Conventionally, since wavelength dependence was not taken into account, it was not possible to measure the transmittance several times for each wavelength of the exposure light source, so the data as shown in FIG. 5 is almost recognized as a problem in the actual process. Was not.

  As described above, when the modified semi-transmissive film is deposited without considering the wavelength dependency of the transmittance of the modified semi-transmissive film, there may be a problem that the correction cannot be performed correctly depending on the exposure light source used. In particular, this problem occurs remarkably when a mixed light having a plurality of wavelengths is used, such as a mercury lamp, instead of an exposure light source such as a single wavelength laser beam.

  The present invention has been made in view of the above, and has as its main technical problem to provide a specific method for setting the optimum transmittance in consideration of the wavelength dependency of the modified semi-transmissive film. It also includes providing a method for forming a novel correction film which is the prerequisite.

  The multi-tone photomask defect correcting method according to the present invention is a multi-tone photomask defect correcting method in which at least a light-shielding film pattern and a semi-transmissive film pattern are formed on a transparent substrate. A correction semi-permeable film is deposited by a vapor deposition method for defects included in the pattern of the semi-permeable film.

  In this case, with respect to an exposure light source including a plurality of exposure wavelengths used for the multi-tone photomask, the transmittance averaged by the weighted average of the spectral intensity ratio of each wavelength for each of the unmodified semi-transmissive film and the modified semi-transmissive film. It is preferable to control the thickness of the modified semipermeable membrane so that the values are substantially equal. “Approximately equal” is intended to encompass certain tolerances. In this case, when the exposure light source is a mercury lamp, the transmittance may be weighted and averaged using a spectral intensity ratio of three wavelengths of g-line, h-line, and i-line in the spectrum included in the mixed wavelength. preferable.

  Further, the configuration is such that the formation of the corrected light-shielding film for the defect included in the pattern of the light-shielding film and the formation of the corrected semi-transmissive film for the defect included in the pattern of the semi-transmissive film are continuously performed in the same apparatus. May be.

  According to the defect correction method of the multi-tone photomask according to the present invention, the target value of the transmittance of the corrected transflective film is weighted and averaged by the ratio of the spectral intensity in each wavelength region included in the exposure light source actually used. Since it almost coincides with the above, the influence of wavelength dependency is reduced even when exposure is performed with an exposure light source including a mixed wavelength. Further, according to the multi-tone photomask of the present invention, the utilization efficiency of the photomask that requires completeness as a whole is improved, and a photomask that has been discarded as a defective product cannot be used unless defect correction is performed. The correction results in a non-defective product, and the manufacturing cost and production yield are greatly improved.

  In view of the above, the present inventors have focused on the vapor deposition method as a novel film forming method for depositing a correction film. Vapor deposition includes physical vapor deposition (PVD) and chemical vapor deposition (CVD). In particular, it is preferable to use a vapor deposition method capable of local deposition while controlling the film thickness. In the experiment, the “photo CVD method (chemical vapor deposition method)” was particularly focused on among the chemical vapor deposition methods. The photo-CVD method is a technique for irradiating a laser beam and forming a film locally on the irradiated portion of the laser beam.

  There are various shapes and sizes of defects (in the present specification, the term “defects” includes both “white defects” and “black defects”). After removing (a part of the transparent substrate is exposed by this), film formation is performed by the above-described photo-CVD method. The characteristic of the photo-CVD method is that it can be deposited several nanometers at a time by light irradiation by setting the gas concentration and laser output, and the film thickness corresponding to the desired transmittance can be greatly increased by repeated scanning. It can be achieved with high accuracy. Furthermore, since the same gas source as that for the deposition of the light shielding film can be used, it is possible to deposit the correction film continuously only by changing the film forming conditions in the same apparatus. The removal of the periphery of the defect may be performed only when necessary.

  At that time, the spectral intensity ratio of each wavelength is estimated in advance from the spectrum of the exposure light source in consideration of the exposure wavelength when transferring the pattern, and then the surrounding semi-transmissive film (unmodified semi-transmissive film) and modified semi-transmissive film The transmittance value of the modified semi-transmissive film is determined so that the transmittance values obtained by weighted averaging with the spectral intensity ratios (estimated values) of the respective wavelengths are equal.

For example, when the exposure light source is a mixed light of three wavelengths of i-line, h-line, and g-line, the spectral intensity ratio J ₁ : J ₂ : J ₃ of each light is estimated in advance from the spectrum of the exposure light source. Next, the semi-transmissive film is actually irradiated with light of this mixed wavelength, and the transmittances α ₁ , α ₂ , and α ₃ corresponding to the respective light beams are measured. Next, a weighted average value A of the obtained measurement values is obtained.

The weighted average value A is obtained by the following calculation formula.
A = α ₁ × J ₁ / (J ₁ + J ₂ + J ₃ ) + α ₂ × J ₂ / (J ₁ + J ₂ + J ₃ ) + α ₃ × J ₃ / (J ₁ + J ₂ + J ₃ ) (1) )

On the other hand, a modified semi-transmissive film is deposited by a photo-CVD method. Then, the light of the mixed wavelength similar to the above is irradiated, and the transmittances β ₁ , β ₂ , and β ₃ corresponding to each light beam are measured. Next, a weighted average B of the obtained measurement values is obtained.

This weighted average value B is obtained by the following calculation formula.
B = β ₁ × J ₁ / (J ₁ + J ₂ + J ₃ ) + β ₂ × J ₂ / (J ₁ + J ₂ + J ₃ ) + β ₃ × J ₃ / (J ₁ + J ₂ + J ₃ ) (2 )

  When the weighted average value B of the transmittance of the modified semipermeable membrane is larger than the previously obtained weighted average value A, a modified semipermeable membrane is further formed, and the value of the weighted average value B is calculated again. By repeating this work, when the value of the weighted average value A of the transmittance of the semipermeable membrane becomes equal to the value of the weighted average value B of the transmittance of the modified semipermeable membrane, it is determined that the film thickness has been optimized. finish.

If this method is generalized by mathematical induction, the calculation formulas for the weighted average values A and B are described as follows.
A = Σα _k × J _k / ΣJ _k (1 ′)
B = Σβ _k × J _k / ΣJ _k (2 ′)

  Then, the value of A is first obtained, and then the formation of the modified semipermeable membrane and the measurement of the weighted average value B of the transmittance are repeated until the value of B substantially coincides with A.

  When the generated defect reaches not only the semi-transmissive portion but also the light shielding portion, it can be corrected by combining conventional black defect correction methods. Hereinafter, embodiments of the present invention will be specifically described.

(First embodiment)
The multi-tone photomask defect correcting method according to the present invention is roughly composed of steps S0 to S7. In step S0, which is the first step, the spectral intensity ratio of each light beam included in the exposure light source is estimated. This is a preliminary preparation, and if it is performed only once, it is unnecessary from the next time.

  Fig.1 (a) is a figure which shows the spectral distribution of an ultrahigh pressure mercury lamp. The horizontal axis indicates the wavelength, and the vertical axis indicates the spectral intensity. As shown in this figure, the mercury lamp includes a plurality of wavelengths such as i-line (365 nm), h-line (405 nm), and g-line (436 nm), but the spectral intensity of each light beam is different. I understand that. Therefore, the spectral intensity ratio of each light beam is estimated by the following method.

For example, the i-line is defined as up to 350Nm～380nm, determine the area _{J 1} of the graph of Figure 1 of the section (a). Similarly, h-line is defined as 390 nm to 420 nm, similarly obtains the area _{J 2} graphs of the section. Similarly, the g-line is defined as 420Nm～450nm, likewise obtains the area _{J 3} graphs of the section.

FIG. 1B shows the result of obtaining the spectral intensity ratio from the area ratio associated with each light beam. That is, the areas J _{1 to} J ₃ obtained in this way are none other than the spectral intensity ratio of each light ray (corresponding to i-line, h-line, and g-line). Although the spectral intensity on the vertical axis in FIG. 1A is shown in arbitrary units, an absolute value is not necessary because a relative spectral intensity ratio is obtained.

  Thus, when a mercury lamp having a spectral distribution as shown in FIG. 1A is used as the exposure light source, the spectral intensity ratio of each light beam included in the exposure light source is obtained. In the above example, the wavelength range from 350 nm to 380 nm is associated with the i-line, but the spectral intensity ratio varies depending on the wavelength width associated with the exposure wavelength.

In the next step S1, the transmissivity of the semi-transmissive portion of the halftone mask that is the object of defect correction is measured. Since this transmittance has wavelength dependency, the transmittance α _k is _obtained for each light ray (i-line, h-line, g-line).

  The exposure light source contains light beams of multiple wavelengths, and the relative intensities of the light beams are different. On the other hand, the transmittance of the semi-transmissive film of the halftone mask irradiated with the exposure light source has wavelength dependency. ing. Therefore, by obtaining the weighted average value A in consideration of the relative intensity ratio of each light beam, a transmittance having a value close to that of the unmodified semi-transmissive film on average is obtained at all light wavelengths.

In the next step S2, the weighted average value A is calculated from the spectral intensity ratios J _{1 to} J _{3 of} the respective rays and the measured transmittances α _{1 to} α _{3 of} the semi-transmissive film.

  In the next step S3, in order to deposit a corrected semipermeable membrane, first, the semipermeable membrane around the defect is removed. The removal of the periphery of the defect may be performed only when necessary. Next, in step S4, a modified semi-transmissive film is actually deposited by the photo-CVD method.

In the next step S5, the transmittance of the modified semipermeable membrane is measured. This step corresponds to step S1 and is a step for measuring the transmittance of the modified semipermeable membrane. Since the transmittance has “wavelength dependency”, it is important to obtain the transmittance β _k for each light beam (i-line, h-line, g-line).

In the next step S6, a weighted average value B is calculated from the spectral intensity ratios J _{1 to} J _{3 of} the respective rays and the measured transmittances β _{1 to} β ₃ of the modified semipermeable membrane. Before depositing the modified transflective film, the transparent portion is exposed at the defect portion in step S3, so that the transmittance is 100% at all wavelengths. Therefore, the initial value of the weighted average value B is 100%. However, as the modified semipermeable membrane is deposited in step S4, the weighted average value B decreases from 100%.

  In the next step S7, the size of the weighted average value B is compared with the value of the weighted average value A of the unmodified semipermeable membrane, and steps S4 to S6 are repeated until the sizes of both are substantially the same. When the value of B substantially coincides with A, the deposition of the modified semipermeable membrane is finished.

  FIG. 2 shows the result of measuring the transmittance of the modified transflective film obtained by executing Steps S0 to S7 for each different wavelength on the premise that the above-described mercury lamp is used as an exposure light source. FIG. In addition, the result (FIG. 5) which matched the transmittance | permeability equally only with the conventional g line | wire (436 nm) is shown with the broken line as a comparative example.

  Thus, the weighted average value is calculated for the transmittance of the unmodified semi-transmissive film from the spectral intensity ratio of each light beam corresponding to each exposure wavelength, and the film thickness corresponding to this transmittance is determined as the final film of the modified semi-transmissive film. By setting the thickness, the transmittance of the modified semi-permeable membrane is such that the transmittance of the surrounding unmodified semi-permeable membrane and the transmittance of an average value close to that of the unmodified semi-permeable membrane are obtained at all light wavelengths. An effect is obtained. This is in contrast to the conventional modified semi-transmissive film, which has substantially the same transmittance only at a specific wavelength but is greatly different in other wavelength regions.

(Second Embodiment)
Next, an example in which the above-described defect correction method is applied to an actual process will be described.
FIGS. 3A to 3C and FIGS. 4D to 4E are enlarged views of the mask pattern of the halftone mask, for explaining a specific example to which the defect correction method according to the present invention is applied. The process drawing of is shown.

  FIG. 3A shows that a white defect has occurred in a part of the mask pattern. In this mask pattern structure, a light shielding film pattern 11 is formed on the surface of the transparent substrate 10, and an unmodified semi-transmissive film pattern 12 is formed thereon. This mask pattern should originally have a symmetric shape and structure with respect to the alternate long and short dash line XX shown in the figure, but a defect in which a predetermined film does not exist in a portion where the mask should originally exist (that is, a white defect). ) P and Q exist. That is, the white defect P in FIG. 3A must originally have the light-shielding film pattern 11 formed, and the white defect Q must originally not have the unmodified semi-transmissive film pattern 12 formed. They are both missing.

  In order to correct such a white defect, the present inventors examined using a photo-CVD method, and the photo-CVD method only slightly changes the film-forming conditions and makes a semi-transparent film with a light-shielding film. We have found that it is possible to deposit both films with extremely high positional accuracy and film thickness accuracy.

  FIG. 3B shows a state in which the pattern 12 of the unmodified semi-transmissive film is once removed before applying the photo-CVD method. Although this method is not particularly limited, for example, a technique called laser zapping can be used. Laser zapping is a method of removing a metal film by using the phenomenon of evaporation caused by the heat generated when the metal irradiated with the laser beam absorbs the laser beam. There is also.

  By this step, the semipermeable membrane is locally removed, and the transparent substrate is exposed at this portion. The removal of the periphery of the defect may be performed only when necessary.

  FIG. 3C shows a state in which the modified light-shielding film 21 is formed by using the photo-CVD method at a site where the white defect P of the light-shielding pattern exists. Through this process, the light shielding film pattern 11 is restored to the designed shape. The modified light shielding film 21 is made of a light shielding material such as a chromium film. When depositing by the photo-CVD method, it is only necessary to deposit under the condition that the transmittance is 0, so that the laser output is sufficiently large and the flow rate and film thickness are controlled so that the source of the source becomes a predetermined concentration or more. . However, the control is not so difficult.

  FIG. 4D shows a state in which the modified semi-transmissive film 22 is deposited using the photo-CVD method at the site where the semi-transmissive film including the white defect Q of the semi-transmissive film pattern is removed. By this step, the semi-permeable membrane pattern 12 is restored to the designed shape. The modified semipermeable membrane 22 is made of a chromium-based material such as a chromium oxide film or chromium nitride. When depositing by the photo-CVD method, it is necessary to deposit while controlling the film thickness so that the transmittance becomes a “predetermined set value”. Therefore, the chromium source source is diluted with oxygen or nitrogen and the laser output is reduced. In addition, the laser irradiation unit 20 is repeatedly scanned to gradually increase the film thickness and gradually decrease the transmittance from 100%. The laser irradiation scan is repeated until a predetermined transmittance is obtained. In order to reach the target transmittance efficiently, the material may be initially deposited under a condition that the transmittance is greatly reduced, and fine adjustment may be performed as the target transmittance is approached.

  As described above, the deposition of the modified light-shielding film and the modified semi-transmissive film need only be performed by using different gas concentrations, different laser irradiation methods, and different laser outputs. Is possible.

  In the experiment, the modified light-shielding film was deposited by laser irradiation, whereas the modified semi-transmissive film was previously deposited by removing the semi-transmissive film in a rectangular shape by laser zapping and then scanning the laser at the removed site. Irradiated. Although not shown, depending on the pattern, the scanning end portion (initial end and end) has insufficient light intensity, and the thickness of the formed modified semi-transmissive film tends to be thin, so the film thickness at both ends is not uniform. A step of removing such a portion by laser zapping may be added.

  FIG. 4E shows a state where the deposition of the modified semipermeable membrane 22 has been completed. At this time, the thickness of the modified semipermeable membrane 22 is measured. A point R in the figure indicates a transmittance measurement site of the modified semipermeable membrane 22. When measuring the transmittance, it is measured under the same conditions as the actual exposure light source. When the exposure light source includes a plurality of wavelengths, the spectral intensity ratio of each light beam is obtained in advance, and the weighted average value A is obtained. And also in the transmittance | permeability measurement point R, the transmittance | permeability is calculated | required for every wavelength of each light ray, and the value of the weighted average value B is calculated from the value. As a method for calculating these weighted average values, the method described in the first embodiment can be applied.

  When the weighted average value B of the transmittance calculated from the actual measurement value for each wavelength at the transmittance measurement point R is larger than A, the film thickness is insufficient, so the deposition of the modified semi-transmissive film 22 is continued. To do. Then, when B substantially coincides with A, the deposition of the modified semipermeable membrane is finished.

  In the second embodiment, the correction method has been described in the case where a white defect occurs in both the light shielding film and the semi-transmissive film, but it is a matter of course that it may occur separately. Moreover, not only a white defect but a black defect may be sufficient. This is because when the black defect is on the semi-transmissive film, the semi-transmissive film is once removed by laser zapping or the like, and the black defect is removed at that time. Eventually, the “defect” can be corrected for the semi-transmissive film without distinguishing between the white defect and the black defect. On the other hand, when the white defect is on the light shielding film, it is not necessary to remove the light shielding film by laser zapping or the like, and it can be corrected directly from above the white defect by the photo-CVD method or other methods such as a focused ion beam method. Even if the black defect is on the light shielding film, no correction is required.

  Therefore, according to the defect correcting method of the present invention, all white defects and black defects formed on the light shielding film and the semi-transmissive film can be removed. The transmittance of the modified semi-transmissive film is determined in consideration of the spectral intensity ratio of each light beam included in the exposure light source, so that the average value is close to that of the unmodified semi-transmissive film at all light wavelengths. Transmittance is obtained.

  An example of taking a weighted average with the spectral intensity ratio of i-line (365 nm), h-line (405 nm), and g-line (436 nm) is shown by taking a mercury lamp as an example. The technical idea of the present invention is an exposure light source Is a plurality of exposure wavelengths, the weighted average of the transmittance of the unmodified semi-transmissive film is obtained by the spectral intensity ratio for the transmittance for each exposure wavelength, and this is the setting value of the transmittance of the modified semi-transmissive film It is in the point to. In addition, although the film configuration formed in the order of the transparent substrate, the light shielding film, and the semi-transmissive film is illustrated, other film configurations, for example, the transparent substrate, the semi-transmissive film, and the light shielding film may be deposited in this order. . Of course, the present invention can also be applied to a multi-tone photomask having four or more gradations in which two or more semi-transparent substrates are formed.

  The present invention is an effective defect correction method capable of suppressing the wavelength dependency of the transmittance in consideration of the characteristics of the exposure light source for the defect of the halftone mask, and its industrial applicability is extremely large.

Fig.1 (a) is a figure which shows the spectral distribution of a mercury lamp. FIG. 1B shows the result of obtaining the spectral intensity ratio from the area ratio associated with each light beam. FIG. 2 is a diagram showing the results of measuring the transmittance of the unmodified semipermeable membrane and the transmittance of the modified semipermeable membrane for each different wavelength. In addition, the result (FIG. 5) which matched the transmittance | permeability equally only with the conventional g line | wire (436 nm) is shown with the broken line as a comparative example. FIGS. 3A to 3C are enlarged views of the mask pattern of the halftone mask, and show process diagrams for explaining a specific example to which the defect correcting method according to the present invention is applied. 4D to 4E are enlarged views of the mask pattern of the halftone mask, and show process diagrams for explaining a specific example to which the defect correction method according to the present invention is applied. FIG. 5 is a diagram showing the results of measuring the transmittance of the unmodified semipermeable membrane and the transmittance of the conventional modified semipermeable membrane at different wavelengths.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transparent substrate 11 Uncorrected light-shielding film 12 Uncorrected semi-transmissive film 20 Laser irradiation part 21 Modified light-shielding film 22 Modified semi-transmissive film P White defect of light-shielding pattern Q White defect of semi-transmissive film

Claims (5)

A defect correction method for a multi-tone photomask in which at least a light-shielding film pattern and a semi-transmissive film pattern are formed on a transparent substrate, wherein vapor deposition is performed on the defect included in the semi-transmissive film pattern. A defect repairing method comprising depositing a repaired semipermeable membrane by a method. The defect correction method according to claim 1, wherein the spectrum of each wavelength for each of the uncorrected transflective film and the corrected transflective film with respect to an exposure light source including a plurality of exposure wavelengths used in the multi-tone photomask. A defect correction method, wherein the thickness of the corrected semipermeable membrane is controlled so that transmittance values weighted and averaged by an intensity ratio are substantially equal. The defect correction method according to claim 1, wherein the formation of the correction light-shielding film for the defect included in the pattern of the light-shielding film and the formation of the correction semi-transmission film for the defect included in the pattern of the semi-transmission film are the same. A defect correction method characterized by being performed continuously in an apparatus. 3. The defect correction method according to claim 2, wherein the exposure light source is a mercury lamp, and the transmittance is a spectral intensity of three wavelengths of g-line, h-line, and i-line out of a spectrum included in the mixed wavelength. A defect correction method characterized by weighted averaging with a ratio. 5. A multi-tone photomask, wherein a defect is corrected by the method according to claim 1.

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