JP2008216590A - Defect detection method and defect detection device for gray tone mask, defect detection method for photomask, method for manufacturing gray tone mask, and pattern transfer method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a defect detection method for a gray tone mask, the method capable of accurately judging the presence or absence of a defect in a semitransmitting part of a gray tone mask having a region where a fine pattern is formed, the fine pattern less than the resolution limit under the exposure conditions when the mask is used, and capable of improving the reliability of defect inspection. <P>SOLUTION: The defect detecting method for a gray tone mask is provided, the mask having a light shielding part, a light transmitting part and a light semitransmitting part, and including a region where a fine light-shielding pattern less than the resolution limit under the exposure conditions upon exposing the mask is formed, in the semitransmitting part. The method includes: a step of scanning the light semitransmitting part to obtain a transmittance signal; and a judging step of judging the presence or absence of a defect in the semitransmitting part by comparing the transmittance signal to the preliminarily determined transmittance allowance in the semitransmitting part. In the step of obtaining the transmittance signal, the semitransmitting part is irradiated with light from a predetermined light source; an image defocused in a predetermined amount from the just-focus position formed by the transmitted beam through the semitransmitting part is photographed by an imaging means; and the transmittance signal is obtained from the photographed image. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

 The present invention relates to a defect inspection method and a defect inspection apparatus for a photomask including a gray-tone mask and a fine pattern used for manufacturing a liquid crystal display (hereinafter referred to as LCD). Further, the present invention relates to a method for transferring a pattern formed on a mask.

  At present, in the field of LCD, a thin film transistor liquid crystal display (hereinafter referred to as TFT-LCD) is advantageous in that it is thinner and has lower power consumption than a CRT (cathode ray tube). Commercialization is progressing rapidly. A TFT-LCD includes a TFT substrate having a structure in which TFTs are arranged in pixels arranged in a matrix, and a color filter in which red, green, and blue pixel patterns are arranged corresponding to each pixel. It has a schematic structure superimposed under the intervention of. In TFT-LCD, the number of manufacturing processes is large, and the TFT substrate alone is manufactured using 5 to 6 photomasks. Under such circumstances, a method of manufacturing a TFT substrate using four photomasks has been proposed (for example, Non-Patent Document 1 below).

  In this method, the number of masks to be used is reduced by using a photomask (hereinafter referred to as a gray tone mask) having a light-shielding portion, a light-transmitting portion, and a semi-light-transmitting portion (semi-transmissive portion). Here, the semi-transparent portion means that when a pattern is transferred to a transfer object using a mask, the amount of exposure light transmitted therethrough is reduced by a predetermined amount, and the photoresist film on the transfer object after development is developed. A part that controls the amount of remaining film is referred to as a gray-tone mask.

  As a gray-tone mask used here, one having a structure in which a semi-translucent portion is formed in a fine pattern is known. For example, as shown in FIG. 4A, the light-shielding portion 1 corresponding to the source / drain, the light-transmitting portion 2, and the semi-transmissive portion 3 corresponding to the channel portion are provided. This is an area where a light-shielding pattern 3a composed of a fine pattern below the resolution limit is formed under the exposure conditions of an LCD exposure machine that uses a gray-tone mask. Reference numeral 3b denotes a fine transmission portion that is below the resolution limit under the exposure conditions of the exposure machine in the semi-transmission portion 3. Both the light-shielding portion 1 and the light-shielding pattern 3a can be formed from films of the same thickness made of the same material such as chromium or a chromium compound. Both the transmissive portion 2 and the fine transmissive portion 3b are portions of the transparent substrate where a light-shielding film or the like is not formed on the transparent substrate. In many cases, the resolution limit of an LCD exposure apparatus using a gray-tone mask is about 3 μm for a stepper type exposure apparatus and about 4 μm for a mirror projection type exposure apparatus. For this reason, for example, in FIG. 4 (1), the space width of the fine transmission portion 3b in the semi-transmission portion 3 is less than 3 μm, and the line width of the light shielding pattern 3a is less than 3 μm. It can be. Alternatively, by adjusting the resolving conditions of the exposure machine, the fine pattern can be set to a condition that does not substantially resolve.

  The above-mentioned fine pattern type semi-transparent part is a line-and-space type of fine pattern to design the semi-transparent part, specifically, to give a halftone effect intermediate between the light-shielding part and the translucent part. There is a choice of whether to use a dot (halftone dot) type or another pattern, and in the case of the line and space type, how much the line width is to be set, and the part through which light is transmitted is shielded It is possible to design in consideration of what the ratio of the part is to be handled and how much the overall transmittance is designed.

  When the exposure is performed with the above-mentioned large LCD exposure machine, the exposure light that has passed through the semi-transparent portion 3 has a smaller exposure amount than the translucent portion as a whole. When the type photoresist is in a condition that disappears after development, the positive type photoresist on the transferred material exposed through the semi-translucent portion 3 is left on the substrate only after the development, the film thickness is reduced. Can do. At this time, since the resist can have a difference in solubility in the developer at the portion corresponding to the normal light-shielding portion 1 and the portion corresponding to the semi-transparent portion 3 due to the difference in the exposure amount, the resist shape after development is as shown in FIG. As shown in (2), the portion 41 corresponding to the normal light-shielding portion 1 is, for example, about 1.3 μm, the portion 43 corresponding to the semi-light-transmitting portion 3 is, for example, about 0.3 μm, and the portion corresponding to the light-transmitting portion 2 Can selectively change the film thickness as in the portion 42 without resist. Then, the first etching of the substrate to be processed is performed in the portion 42 without the resist, the resist of the thin portion 43 corresponding to the semi-translucent portion 3 is removed by ashing or the like, and the second etching is performed in this portion. The process for two conventional masks can be performed with one mask, and the number of masks can be reduced.

  As an inspection method of a semi-translucent portion composed of a fine pattern in the gray tone mask as described above, an inspection method disclosed in Patent Document 1 is known. That is, Patent Document 1 discloses that a light-shielding portion, a transmission portion, and a region in which the transmission amount is adjusted, and the film thickness of the photoresist is selectively changed by reducing the transmission amount of light transmitted through this region. A gray-tone mask having a desired semi-transparent portion, wherein the semi-transparent portion is a half-tone mask comprising a region in which a light-shielding pattern equal to or lower than a resolution limit of an exposure apparatus using a gray-tone mask is formed. A method for inspecting a defect of a translucent part, the step of obtaining a transmissivity signal by scanning the semi-translucent part, and the transmissivity characteristic of the translucent part when the gray tone mask is used for the transmissivity signal A step of performing a correction process approximated to the above, and a determination that a defect has occurred in the semi-transparent part when the transmittance signal after the correction process exceeds a threshold value of a transmittance defect in the semi-transparent part provided in advance Including the step of Defect inspection method Leh tone mask is described.

JP 2003-307501 A “Monthly FP Intelligence”, May 1999, p. 31-35

In the prior art disclosed in the above-mentioned Patent Document 1, a comparative inspection that has been performed on a conventional mask including only a light-shielding portion and a transparent portion is not sufficient for the inspection of the semi-transparent portion of the gray tone mask. In view of a certain point, a method for detecting a defect by providing a threshold value of transmittance in advance has been proposed. That is, the pattern in the mask is scanned, and a defect is detected using a predetermined transmittance defect threshold for the obtained transmittance signal. Further, when inspecting a semi-transparent portion made of a fine pattern, if this portion is scanned to obtain a transmittance signal, the transmittance signal may be periodically changed, so that the signal is flattened. To perform blurring. In addition, it is possible to avoid detecting a pseudo defect by performing a defect inspection. As the blurring process in this case, the blurring function used in the conventional image processing can be used.
However, the present inventors have generated pseudo defects (those that are not defects but are determined to be pseudo defects) that cannot be eliminated by the above-described inspection method, or cannot detect defects with sufficient accuracy. It has been found that inconvenience occurs in the mask inspection accuracy.

  For example, FIG. 5 shows a mask pattern including a semi-transparent portion 3 composed of a fine pattern formed by line and space of a light shielding portion and a light transmitting portion. The line widths of the central light-shielding part (light-shielding pattern 3a) and the light-transmitting parts (fine transmissive part 3b) on both sides thereof are both 1 μm. This is scanned by the above-described prior art method to obtain a transmittance signal. In other words, a light source and illumination optical system, an optical system including an objective lens, and an imaging means (a line CCD or a CCD employing TDI (Time Delay Integration) can be selected as appropriate) are parallel to the mask main plane with respect to the mask. By scanning (or moving the mask with respect to the optical system and the image pickup means for scanning), a transmittance signal is obtained. Since the pixel size of the image pickup means (here, the line CCD) is 1 μm here, the relative relationship between each pixel of the image pickup means (here, the pixels A to F are shown) and the pattern during scanning is 1 to 10 in FIG. There are various cases as shown in the figure (indicated by circled numbers).

  In the case of a positional relationship of “1”, a comb-shaped image 61 as shown in FIG. In the case of the positional relationship of “1” in FIG. 5, the pixels C, D, and E match the positions of the light transmitting portion, the light shielding portion, and the light transmitting portion, respectively. Is 100% (here, the transmissivity of the translucent part is assumed to be 100%), D is zero, and E is 100%. Theoretically, the transmissivity indicated by a broken line in FIG. A distribution curve 61 is obtained. However, since the transmittance distribution becomes slightly broad due to the interference of light, actually, the transmittance distribution curve 62 shown by the solid line in FIG. 6 is acquired.

  Next, when the CCD pixel and the fine pattern are in a positional relationship such as “5” in FIG. 5, the one in the state of the transmittance distribution curve 63 indicated by the alternate long and short dash line in FIG. 6 is acquired. At this time, a transmittance signal of about 40% is obtained for pixel B, about 60% for C, about 40% for D, and about 60% for E.

  Then, according to the method of Patent Document 1, the transmittance distribution curves 62 and 63 in FIG. 6 are each subjected to the blurring process used in the image processing technique, and then the transmittance after the blurring process is compared with a preset threshold value. . However, here, the transmittance distribution curves obtained from the same pattern are different between 62 (in the case of “1” positional relationship) and 63 (in the case of “5” positional relationship). . Accordingly, the transmittance distributions obtained by performing the same blurring process on them are also different as shown by curves 71 (bluring process on curve 62) and 72 (bluring process on curve 63) in FIG. Therefore, depending on how the threshold value of the semi-translucent portion is provided, the case of the positional relationship of “1” and the case of the positional relationship of “5” may be different in the conclusion of defect determination. Although this defect determination depends on the transmittance allowable range of the semi-transparent portion, for example, when 50 ± 10%, the transmittance distribution curve 72 after the blurring process obtained in the case of the positional relationship of “5”, for example. Even if the mask is determined to be non-defective based on the above, if the positional relationship is “1”, a portion where the transmittance distribution curve 71 after the blurring process exceeds the allowable transmittance range occurs, and the mask is determined to be defective. The case where it is done arises. Here, it is possible to set a threshold (that is, to increase the width ΔT of the transmittance allowable range) to such an extent that it is not determined to be defective even in the case of the positional relationship of “1”. This causes a problem that the inspection accuracy is lowered.

  If the method of Patent Document 1 is further developed, in order to accurately grasp the transmittance of the fine pattern portion that cannot be resolved, reflecting the resolution conditions of the exposure machine when using the mask, it is more fine. It is considered that it is sufficient to acquire a transparent signal and flatten it in a blurred state close to the exposure condition. For example, as shown in FIGS. 8A and 8B, it can be said that an imaging means having a relatively small pixel relative to the dimension of the pattern may be used. FIG. 8A shows a case of 1/2 pixel size, and FIG. 8B shows a case of 1/5 pixel size. However, the image pickup means having smaller pixels exceeds the specification normally used as a defect inspection apparatus for manufacturing a liquid crystal device, which increases the cost of the apparatus and greatly increases the inspection time. Naturally, the amount of data of the acquired transmittance signal is enormous, which makes data processing difficult. In the first place, it is important for the semi-transparent part using the fine pattern that the exposure light transmittance of the part satisfies the desired specification, and it is not meaningful to inspect the shape of the fine pattern one by one. As described above, it is not efficient from the viewpoint of cost and inspection time to prepare a device having a fine pixel size.

As described above, in a gray-tone mask in which a semi-transparent portion is formed by a fine pattern, when the dimension of the fine pattern and the image pickup pixel size of the inspection machine inspecting it approach each other, The output of the transmittance distribution varies depending on the positional relationship, and the determination of the presence or absence of defects is not consistent. This is because image information lost due to the pixel size of the image sensor when imaging the semi-transparent portion affects the defect determination. In recent years, the size of the semi-transmission part (for example, the channel part in the thin film transistor) tends to be further reduced, and the desire of the translucency of the semi-transmission part desired by the mask user is diversified. In addition, a fine pattern size of the semi-translucent portion is required to be small, and a situation in which antagonism with the pixel size size cannot be ignored arises.
In particular, the gray-tone mask for manufacturing liquid crystal display devices is large and has a side of 30 cm or more, and in some cases 100 cm or more. Therefore, inspection efficiency is extremely important, and the unit price is high. Heavy reliability is required.

  The present invention has been made in view of the above-described conventional problems, and a gray tone having a region in which a semi-transparent portion is formed with a fine pattern below the resolution limit under exposure conditions exposed when using a gray tone mask. It is a first object of the present invention to provide a gray-tone mask defect inspection method, a defect inspection apparatus, and the like that can accurately determine the presence or absence of a defect in a semi-transparent portion of a mask and improve the reliability of defect inspection. The second object of the present invention is to provide a method of manufacturing a gray-tone mask having a defect inspection process to which such a defect inspection method is applied. It is a third object of the present invention to provide a method for transferring a pattern formed on a gray tone mask obtained by performing the defect inspection process.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1) A light-shielding portion, a light-transmitting portion, and a region where the amount of transmission is adjusted, and the amount of light transmitted through this region is reduced to selectively change the film thickness of the photoresist on the transfer target. A gray-tone mask having a semi-transparent portion for the purpose, wherein the semi-transparent portion is formed with a fine light-shielding pattern below a resolution limit under exposure conditions exposed when using the gray-tone mask. A method for inspecting a defect of a gray-tone mask having a step of scanning the semi-transparent portion to obtain a transmittance signal, and comparing the transmittance signal with an allowable transmittance value in a semi-transparent portion provided in advance And determining the presence or absence of a defect in the semi-translucent portion, and in the step of obtaining the transmittance signal, the semi-transparent portion is irradiated with a predetermined light source and transmitted through the semi-transparent portion. Predetermined from the just focus position by transmitted light flux The defocused image captured by the imaging means, a defect inspection method of the gray-tone mask and obtaining a transmittance signal from the captured image.

(Structure 2) In the case of the said imaging, according to the pattern shape or dimension of the said semi-translucent part, or according to the capability of an inspection machine, or according to the exposure conditions at the time of mask use, or the process process after mask exposure 2. The gray-tone mask defect inspection method according to Configuration 1, wherein the defocus amount is determined according to conditions.
(Configuration 3) The determination of the defocus amount is such that when the normal fine light-shielding pattern forming region in the semi-translucent part is imaged, the light intensity difference between adjacent pixels among the pixels of the imaging unit arranged is 5 The gray-tone mask defect inspection method according to Configuration 1 or 2, wherein the condition is such that the ratio is equal to or less than%.

(Configuration 4) The configuration 1 is characterized in that the ratio between the pixel size of the image pickup means and the line width of the light-shielding pattern or light-transmitting pattern in the fine light-shielding pattern forming region is in a range of 1 / 2-2. 4. The gray-tone mask defect inspection method according to any one of items 1 to 3.
(Configuration 5) The transmissivity allowable value of the semi-transparent part is obtained by imaging the fine light-shielding pattern forming region of the semi-transparent part in the gray tone mask without defocusing with the imaging unit, and signal flattening the captured image. Range in which the determination result when using a transmittance signal obtained by performing image processing for conversion is different from the determination result when using a transmittance signal obtained by performing imaging with defocusing The gray-tone mask defect inspection method according to any one of Configurations 1 to 4, wherein the defect inspection method is configured as follows.

(Configuration 6) A defect inspection method for a fine pattern portion in a photomask having a fine pattern portion, the step of obtaining a transmittance signal by scanning the fine pattern portion, and a fine signal provided in advance A determination step of determining the presence or absence of a defect in the fine pattern portion in comparison with an allowable transmittance value in the pattern portion, and in the step of obtaining the transmittance signal, the fine pattern portion is irradiated with a predetermined light source, A defect inspection method for a photomask, wherein an image defocused by a predetermined amount from a just focus position by a transmitted light beam transmitted through a fine pattern portion is picked up by an image pickup means, and a transmittance signal is obtained from the picked-up image. .

(Configuration 7) A light-shielding portion, a transmission portion, and a region in which the amount of transmission is adjusted, and the amount of light transmitted through this region is reduced to selectively change the thickness of the photoresist on the transfer target pair. A gray-tone mask defect inspection apparatus having a semi-transparent portion for the purpose of scanning a pattern formed in the mask with a parallel light source and a light receiving lens and receiving a transmitted light beam; An imaging means for imaging the transmitted light, and a transmittance signal obtained from an image captured by the imaging means, and compared with a transmittance permissible value in a semi-transmission part provided in advance, and a defect in the semi-transmission part Determination means for determining presence / absence, and the optical system and / or the imaging unit is configured so that an image obtained by defocusing a predetermined amount from the just focus position is captured by the imaging unit. Def It is a defect inspection apparatus of the gray-tone mask, characterized in that a carcass means.

(Configuration 8) For input of defocus amount determinant data relating to the pattern shape or size of the semi-translucent portion, the capability of the inspection machine, the exposure condition when using the mask, or the processing process condition after the mask exposure Accordingly, the gray-tone mask defect inspection apparatus according to Configuration 7, further comprising a control unit that drives and maintains the optical system or the imaging unit at a position that satisfies the defocus amount.
(Structure 9) The determination means stores in advance a transmittance allowable value range in the semi-translucent portion, a transmittance allowable range in the light transmissive portion, and a transmittance allowable range in the light shielding portion, and the transmittance 9. The gray-tone mask defect inspection apparatus according to Configuration 7 or 8, wherein a comparison with a signal is performed.

(Structure 10) A gray tone mask manufacturing method comprising a defect inspection step of performing a defect inspection using the defect inspection method according to any one of Structures 1 to 5.
(Structure 11) A pattern transfer method characterized by irradiating a gray-tone mask obtained by the manufacturing method according to Structure 10 with exposure light and transferring a pattern formed on the gray-tone mask to a transfer target. .

  According to the defect inspection method for a gray-tone mask of the present invention, the transmittance is obtained by scanning a semi-transparent portion having a region where a fine light-shielding pattern below the resolution limit under an exposure condition that is exposed when the gray-tone mask is used. A step of obtaining a signal, and a step of comparing the transmittance signal with an allowable transmittance value in a semi-transparent portion provided in advance to determine the presence or absence of a defect in the semi-transparent portion, and In the step of obtaining a signal, the semi-transparent portion is irradiated with a predetermined light source, and an image defocused by a predetermined amount from the just focus position by the transmitted light beam transmitted through the semi-transparent portion is captured by an imaging unit, A transmittance signal is obtained from the captured image, and the determination step is performed using the transmittance signal thus obtained. As a result, even if the pattern to be inspected is the same, it is possible to avoid the problem that the defect inspection judgment varies depending on the relative position between the pixel of the image pickup means and the pattern, and the semi-transparent portion is exposed when the gray tone mask is used. Since it is possible to accurately determine the presence or absence of a defect in the semi-transparent portion in a gray tone mask having a region where a fine pattern less than the resolution limit under exposure conditions is formed, it is possible to improve the reliability of defect inspection. Such a defect inspection method is not limited to a so-called gray tone mask, and can be preferably applied to defect inspection of a fine pattern portion in a photomask including a fine pattern.

Moreover, according to the defect inspection apparatus of this invention, the defect inspection method of this invention can be implemented suitably.
In addition, according to the method for manufacturing a gray-tone mask of the present invention, a gray-tone mask subjected to highly reliable defect inspection is obtained by including a defect inspection process to which the defect inspection method of the present invention is applied. be able to.

  Furthermore, according to the pattern transfer method of irradiating the gray-tone mask obtained by carrying out the defect inspection process with exposure light and transferring the pattern formed on the mask onto the transfer target, a highly reliable defect inspection Since the gray tone mask in which the above has been implemented is used, it is possible to particularly prevent transfer defects in the semi-translucent portion.

The best mode for carrying out the present invention will be described below with reference to the drawings.
The present invention provides a light-shielding portion, a light-transmitting portion, and a region in which the amount of transmission is adjusted, and selectively changes the film thickness of the photoresist on the transfer target by reducing the amount of light transmitted through this region. A gray-tone mask having a semi-transparent portion for the purpose, wherein the semi-transparent portion is formed with a fine light-shielding pattern below a resolution limit under exposure conditions exposed when using the gray-tone mask. A method for inspecting a defect of a gray-tone mask having a step of scanning the semi-transparent portion to obtain a transmittance signal, and comparing the transmittance signal with an allowable transmittance value in a semi-transparent portion provided in advance And a determination step of determining the presence or absence of a defect in the semi-translucent portion. In the step of obtaining the transmittance signal, the semi-transparent portion is irradiated with a predetermined light source, and an image defocused by a predetermined amount from the just focus position by the transmitted light beam transmitted through the semi-transparent portion is imaged. Then, a transmittance signal is obtained from the captured image. The determination step is performed using the transmittance signal thus obtained.

  In the present invention, when the fine pattern constituting the semi-transparent portion of the gray tone mask is scanned and inspected as described above, defocusing conditions applied at the time of imaging, specifically, defocusing is performed from the just focus position. It is necessary to determine a predetermined amount, that is, a defocus amount. Specifically, this defocus amount is determined according to, for example, the pattern shape or size of the semi-translucent portion, according to the capability of the inspection apparatus, according to the exposure condition when using the mask, or mask exposure. It can be determined according to the subsequent processing step conditions. Here, the capability of the inspection apparatus includes, for example, the operation accuracy in the optical axis direction of the optical system or imaging means (for example, CCD) of the inspection apparatus. Further, the exposure conditions when using the mask include the resolution of the exposure machine. Furthermore, the mask processing process conditions after exposure include a resist film thickness tolerance range, a film thickness variation tolerance range, or a resist residual film shape desired by the mask user. Preferably, at least one of these is used for determining the defocus amount. In particular, the pattern shape or pattern size of the semi-translucent portion is an important determinant.

  In addition, when the defocused captured image captures the normal fine light-shielding pattern forming region of the semi-translucent portion, the light intensity captured due to the substantially flat transmittance of the portion In the determination of the defocus amount, for example, when imaging the inside of the semi-translucent portion, the difference in light intensity between adjacent pixels in the pixels of the imaging means to be arranged is determined. Conditions such as a predetermined amount or less (for example, 5% or less) can be selected, but of course not limited thereto.

Further, the present invention is not limited to the pattern dimension of the semi-translucent portion as the inspection object, and can be applied to, for example, a fine light-shielding pattern having a line width of about 0.5 to 2.5 μm. Similarly, the line width of the translucent pattern in the fine light-shielding pattern can be effectively applied when the width is about 0.5 to 2.5 μm. Furthermore, the present invention is not particularly limited to the fine pattern shape, but can be usefully applied to, for example, a line and space of about 1 to 2 μm line width or a shape in which rectangular patterns having the above line width are arranged.
Further, the pixel size of the imaging means such as a CCD is not particularly limited, but the present invention is effectively applied when the pixel size is 0.2 μm or more, for example.

  In the present invention, there is no particular restriction on the correlation between the line width of the fine pattern of the semi-transparent portion to be inspected and the pixel size of the image pickup means, but for example, the line width of the fine pattern is When the pixel size of the imaging means is excessively large, the pattern to be inspected can be sufficiently imaged by the imaging means, so that inspection similar to general shape defect inspection (for example, die-to-die or die -to-data comparison check) can be applied. On the other hand, in the case opposite to the above, it is difficult to obtain a sufficient effect even if the optical blurring by the defocusing of the present invention is used. Therefore, when the ratio between the pixel size of the image pickup means and the line width of the fine light-shielding pattern forming region is in the range of 1/2 to 2, the effect of the present invention is remarkably obtained. The line width referred to here includes any case of the line width of the light shielding pattern or the light transmitting pattern formed in the semi-translucent portion.

  By determining the defocus condition (defocus amount), using a transmittance signal based on the captured image obtained under the condition, and comparing with a preset transmittance allowable value in the semi-transparent portion In the defect determination step, for example, when the transmittance of the light-transmitting portion is 100%, the median value of the transmittance of the semi-light-transmitting portion is 50%, and the transmittance distribution of 50 ± 10% is an allowable value. be able to. The permissible transmittance value can be appropriately determined by the mask user's exposure device or by conditions such as the mask user's resist process. Furthermore, although the median value of the transmissivity of the semi-translucent portion is 50% in the above example, it can be appropriately selected within a range of 20 to 60% depending on the process conditions of the mask user.

  Note that the transmittance permissible value in the semi-transparent portion is obtained by capturing the fine light-shielding pattern of the semi-transparent portion in the gray tone mask without defocusing with the imaging unit as in the above-described conventional technique, and adding the captured image to the captured image. Determination result when using a transmittance signal obtained by performing image processing for signal flattening, and determination when using a transmittance signal obtained by performing imaging with defocusing as in the present invention In the case where the result is set to be different, according to the present invention, it is possible to avoid the problem that the above-described conventional defect determination results are mixed, and to perform highly reliable defect inspection. The effect by is remarkable. In particular, according to the inspection method of the present invention, it is possible to effectively detect a defect due to a line width (CD) error of a fine pattern of the semi-translucent portion.

  According to the present invention, there is provided an optical system that scans a pattern formed in a mask with a parallel light source and a light receiving lens and receives a transmitted light beam, and a light receiving device. An imaging means for imaging the transmitted light, and a transmittance signal obtained from an image captured by the imaging means, and compared with a transmittance permissible value in a semi-transmission part provided in advance, and a defect in the semi-transmission part Determination means for determining presence / absence, and the optical system and / or the imaging unit is configured so that an image obtained by defocusing a predetermined amount from the just focus position is captured by the imaging unit. It has defocusing means.

The defect inspection apparatus will be specifically described with reference to FIG. FIG. 1 is a perspective view showing the main components of the defect inspection apparatus according to the present invention.
As shown in FIG. 1, the defect inspection apparatus 20 includes a light source 21, an illumination optical system 22 for emitting parallel light, an objective lens 23 for receiving transmitted light, and an imaging means 24 for detecting a transmittance signal. Prepare. Here, the light source 21, the illumination optical system 22, the objective lens 23, and the imaging means (for example, CCD) 24 are arranged between the illumination optical system 22 and the objective lens 23 in a state where the respective optical axes coincide with each other. It is possible to move relative to the main plane of the gray-tone mask 10 to be inspected. Or, conversely, when the optical system is at a fixed position and the mask 10 moves in the main plane direction, the mask and the optical system move as a result, and an arbitrary point on the mask main plane is imaged. It is good also as performing.

  As described above, the defect inspection apparatus 20 includes the imaging unit 24 that relatively scans the pattern formed in the mask 10 with the light source 21, the illumination optical system 22, and the objective lens 23, and detects the transmittance signal. More specifically, it has means (usually a mask stage moving means) for moving the mask 10 and the optical system relative to each other and scanning the entire area of the main surface of the mask 10. Is transmitted by an objective lens 23, and a transmittance signal is detected by an imaging means 24 having a light receiving element such as a CCD. Further, the defect inspection apparatus 20 has a defocusing unit so that an image can be taken in a defocused state moved by a predetermined amount from the just focus position. Therefore, in the embodiment illustrated in FIG. Control means for moving the imaging means 24 relative to the main surface of the mask 10 in the optical axis direction (arrow 25 in FIG. 1) is provided. This control means is a data processing device according to the pattern shape or size of the semi-translucent portion, according to the capability of the inspection apparatus, according to the exposure condition when using the mask, or with respect to the processing process condition after the mask exposure. When a focus amount determination element is input and the defocus amount is determined based on these determination elements, the optical system (here, the objective lens 23) and / or the imaging unit 24 is set so as to satisfy the defocus amount. It is driven to a defocus position deviated by a predetermined amount from the just focus, and this state is maintained during the inspection.

  Although not shown in FIG. 1, the defect inspection apparatus 20 includes a control mechanism for the entire apparatus, movement of the optical system, arithmetic processing (signalization) of a captured image, and a threshold value (transmittance) in a determination unit. Processing means (such as a CPU) that enables comparison with a permissible value, defect determination, and the like are provided. Further, the determination means stores in advance a transmittance allowable value range in the semi-translucent portion, a transmittance allowable range in the light transmissive portion, and a transmittance allowable range in the light shielding portion, and the transmittance signal A comparison is made.

Next, a specific example in which defect inspection is performed by applying the defect inspection method of the present invention will be described.
The following is an example in which a defect inspection of a gray tone mask having a semi-transparent portion (here, transmittance of 50%) having a fine pattern region as shown in FIG. The defect inspection apparatus used here has the structure shown in FIG. A line CCD is used as the imaging means, and its pixel size is 1 μm. As in FIG. 5, the gray-tone mask pattern to be inspected is a semi-transparent portion fine pattern in which a light-shielding portion by line and space is sandwiched between the light-transmitting portions. The line width of the optical part was 1 μm.

  FIG. 2 schematically shows a captured image in a state where the gray tone mask to be inspected is set in the defect inspection apparatus of FIG. 1 and optically defocused according to the present invention. Also in FIG. 2, there are various cases in which the relative positional relationship between each pixel (A to F) of the CCD and the captured image at the time of scanning is 1 to 10 (indicated by a circled number in the drawing). In the schematic diagram of FIG. 2, an actual captured image is not necessarily accurately represented, but actually, an image region 11 corresponding to the light shielding portion 1 of the mask is used for optical blurring due to defocusing. And the image region 13 corresponding to the semi-transparent portion 3 of the mask are not clear.

  FIG. 3 shows the transmittance distribution acquired from the captured image in the optically defocused state. Here, both the transmittance distribution curve 31 when the relative positional relationship between the CCD pixel and the imaging pattern is “1” and the transmittance distribution curve 32 when the relative positional relationship is “5” are half Since the transmittance of the translucent part is almost flat and there is almost no difference between the transmittance distributions of the two, when the allowable transmittance ΔT of the semi-transparent part is set to 50 ± 10%, for example, FIG. In any case, the defect inspection determination is the same in any case, and it is possible to avoid the problem that the defect inspection determination varies even with the same conventional pattern to be inspected. That is, according to the present invention, it is possible to prevent the defect inspection determination from being affected by the relative position between the pixel and the pattern of the imaging means.

  As described above, according to the defect inspection method for a gray-tone mask according to the present invention, even if the pattern to be inspected is the same, it is possible to avoid the problem that the defect inspection determination varies depending on the relative position of the pixel and pattern of the imaging means. The semi-transparent part can be accurately determined whether there is a defect in the semi-transparent part in a gray-tone mask having a region where a fine pattern less than the resolution limit under the exposure conditions exposed when the gray tone mask is used. Therefore, it is possible to improve the reliability of defect inspection.

  In a gray-tone mask for manufacturing LCD devices with a large substrate size, if the conventional defect inspection method is applied, it is often detected as a pseudo defect in the transmittance signal, and the reliability of the inspection is not so high. The inspection method is extremely effective in putting a gray tone mask for LCD production into practical use. The same applies to display devices other than the LCD manufacturing mask. Note that the LCD manufacturing mask includes all masks necessary for LCD manufacturing, for example, a mask for forming a TFT (thin film transistor), a low-temperature polysilicon TFT, a color filter, and the like. Other masks for manufacturing display devices include all masks necessary for manufacturing organic EL (electroluminescence) displays, plasma displays, and the like.

  Since the present invention is an inspection method that uses a transmittance output signal acquired from a defocused captured image and does not perform pattern recognition, there is a problem that a pseudo defect caused by a specific pattern shape occurs during a fine pattern inspection (threshold value). Problem that cannot be reduced), the threshold value can be lowered, and the required accuracy (spec) of a photomask including a gray-tone mask or a fine pattern can be satisfied.

  In addition, according to the method for manufacturing a gray-tone mask of the present invention, a gray-tone mask subjected to highly reliable defect inspection is obtained by including a defect inspection process to which the defect inspection method of the present invention is applied. be able to. Furthermore, according to the pattern transfer method of irradiating the gray-tone mask obtained by carrying out the defect inspection process with exposure light and transferring the pattern formed on the mask onto the transfer target, a highly reliable defect inspection Since the gray tone mask in which the above has been implemented is used, it is possible to particularly prevent transfer defects in the semi-translucent portion.

  Moreover, according to the defect inspection method and the defect inspection apparatus of the present invention, in addition to the gray-tone mask, the present invention is also applicable to fine and high-precision pattern defect inspection such as line and space with a line width of less than 3 μm in a photomask. It is possible to obtain a uniform transmittance signal that is optically blurred by defocusing while scanning the pattern portion, and by performing defect inspection such as shape and dimension based on this signal, fine and highly accurate defects Can be detected. As a photomask including such a fine pattern, a photomask for LCD manufacturing, a display device manufacturing photomask such as an organic EL display, a plasma display, etc., which is a fine mask for forming a TFT channel part, a contact hole part, etc. A photomask having a pattern can be given.

It is a perspective view which shows the principal part of the defect inspection apparatus which concerns on this invention. It is a top view which shows typically the picked-up image of the state optically defocused in the defect inspection method which concerns on this invention. It is a figure which shows the transmittance | permeability distribution acquired from the captured image of the state defocused optically. (A) is a top view which shows an example of a fine pattern type gray tone mask, (b) is sectional drawing of the resist pattern obtained using a gray tone mask. It is a top view which shows the relative positional relationship of the pixel of an image pick-up means, and a fine pattern at the time of scanning a fine pattern by an image pick-up means. It is a figure which shows the output transmittance | permeability signal of an imaging means in case a fine pattern is scanned by an imaging means. It is a figure which shows the transmittance | permeability distribution obtained by giving the predetermined | prescribed blurring process by image processing to the output transmittance | permeability signal of an imaging means. It is a top view which shows the relative positional relationship of the pixel of an imaging means when a fine pattern is scanned with an imaging means, and a fine pattern, (a) is 1/2 pixel size with respect to the pixel size shown in FIG. ) Indicates the case of 1/5 pixel size.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light-shielding part 2 Light transmission part 3 Semi-transmission part 3a Light-shielding pattern 3b Fine transmission part 10 Gray tone mask 20 Defect inspection apparatus 21 Light source 22 Illumination optical system 23 Objective lens 24 Imaging means

Claims (11)

The purpose is to selectively change the film thickness of the photoresist on the transfer object by reducing the amount of light transmitted through the light-shielding portion, the light-transmitting portion, and the region where the amount of transmission is adjusted. A gray-tone mask having a semi-transparent portion, and a region having a fine light-shielding pattern below a resolution limit under an exposure condition where the semi-transparent portion is exposed when the gray-tone mask is used A defect inspection method,
Scanning the semi-translucent portion to obtain a transmittance signal;
A step of comparing the transmittance signal with a transmittance allowable value in a semi-transparent portion provided in advance, and determining the presence or absence of a defect in the semi-transparent portion;
In the step of obtaining the transmittance signal, the semi-transparent portion is irradiated with a predetermined light source, and an image defocused by a predetermined amount from the just focus position by the transmitted light beam transmitted through the semi-transparent portion is captured by an imaging unit. And a gray-tone mask defect inspection method, wherein a transmittance signal is obtained from the captured image.   In the imaging, according to the pattern shape or size of the semi-translucent portion, according to the capability of the inspection machine, according to the exposure condition when using the mask, or according to the processing process condition after the mask exposure 2. The gray-tone mask defect inspection method according to claim 1, wherein the defocus amount is determined.   In determining the defocus amount, when imaging the normal fine light-shielding pattern forming region in the semi-translucent portion, the light intensity difference between adjacent pixels among the pixels of the imaging unit arranged is 5% or less. 3. The gray-tone mask defect inspection method according to claim 1, wherein the conditions are set as described above.   The ratio between the pixel size of the image pickup means and the line width of the light-shielding pattern or the light-transmitting pattern in the fine light-shielding pattern forming region is in a range of 1 / 2-2. The defect inspection method for a gray-tone mask according to any one of the above.   The transmissivity allowable value of the semi-translucent portion is obtained by imaging the fine light-shielding pattern formation region of the semi-transparent portion in the gray tone mask without defocusing with the imaging unit, and flattening the signal to the captured image. The determination result when using a transmittance signal obtained by performing image processing is different from the determination result when using a transmittance signal obtained by performing imaging with defocusing. The defect inspection method for a gray-tone mask according to any one of claims 1 to 4, wherein: A defect inspection method for a fine pattern portion in a photomask having a fine pattern portion,
Scanning the fine pattern portion to obtain a transmittance signal;
A determination step of comparing the transmittance signal with an allowable transmittance value in a fine pattern portion provided in advance and determining the presence or absence of defects in the fine pattern portion;
In the step of obtaining the transmittance signal, the fine pattern portion is irradiated with a predetermined light source, and an image defocused by a predetermined amount from the just focus position by the transmitted light beam transmitted through the fine pattern portion is captured by an imaging unit, A defect inspection method for a photomask, wherein a transmittance signal is obtained from the captured image. An object of the present invention is to selectively change the film thickness of the photoresist on the transfer target pair by reducing the amount of light transmitted through the light-shielding portion, the transmission portion, and the region where the transmission amount is adjusted. A defect inspection apparatus for a gray-tone mask having a semi-translucent portion,
An optical system that scans a pattern formed in the mask with a parallel light source and a light receiving lens and receives a transmitted light beam;
Imaging means for imaging the received transmitted light;
Using a transmittance signal obtained from an image captured by the image capturing means, and comparing with a transmittance allowable value in a semi-transparent portion provided in advance, and a determination means for determining the presence or absence of a defect in the semi-transparent portion;
The optical system and / or the imaging unit includes a defocusing unit so that an image obtained by defocusing a predetermined amount of the image by the transmitted light beam from the just focus position is captured by the imaging unit. A gray-tone mask defect inspection system.   In response to the input of defocus amount determinant data regarding the pattern shape or size of the semi-translucent portion, the capability of the inspection machine, the exposure condition when using the mask, or the processing process condition after the mask exposure, 8. The gray-tone mask defect inspection apparatus according to claim 7, further comprising control means for driving and maintaining the optical system or the imaging means at a position satisfying the defocus amount.   The determination means stores in advance a transmittance allowable value range in the semi-translucent portion, a transmittance allowable range in the light transmissive portion, and a transmittance allowable range in the light shielding portion, and compares them with the transmittance signal. 9. The gray-tone mask defect inspection apparatus according to claim 7 or 8, wherein:   A method for producing a gray-tone mask, comprising a defect inspection step of performing a defect inspection using the defect inspection method according to claim 1. A pattern transfer method comprising: irradiating a gray tone mask obtained by the manufacturing method according to claim 10 with exposure light, and transferring a pattern formed on the gray tone mask onto a transfer target.

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