JP5097521B2 - Photomask inspection apparatus, photomask inspection method, photomask manufacturing method for liquid crystal device manufacturing, and pattern transfer method - Google Patents

Description

  The present invention relates to a photomask inspection apparatus and a photomask inspection method for inspecting the performance of an exposure photomask, and in particular, a large-sized photomask inspection apparatus for manufacturing a flat panel display (FPD) device. And an inspection method. The present invention also relates to a method for manufacturing a photomask for manufacturing a liquid crystal device and a pattern transfer method.

  Conventionally, for inspection of the performance of a photomask, Patent Document 1 describes an apparatus for inspecting a defect by detecting an intensity distribution of transmitted illumination light of a photomask to be inspected by an imaging device (CCD). Yes. In this apparatus, the inspection light is condensed and irradiated onto a photomask having a fine pattern with a pitch of about 0.3 μm, and the inspection light transmitted through the photomask is enlarged to irradiate the CCD with a resolution of about 7 μm. I am trying to pick up images.

  That is, in this inspection apparatus, a photomask is placed horizontally on a stage, and inspection light from a light source is irradiated onto the photomask via an illumination optical system. The stage can be moved in the in-plane direction of the photomask. In this inspection apparatus, inspection light that has passed through a photomask is enlarged and irradiated onto an image sensor to form an image, thereby obtaining a photomask image.

  Patent Document 2 describes an inspection apparatus that can detect defects and foreign matter of a photomask that is actually transferred to a wafer by an exposure apparatus. In addition to defects and foreign matter that could be detected by conventional inspection equipment, this equipment also inspects phase shift masks and reticle shifter defects, and exposure wavelength-dependent mask substrate defects. It is possible.

JP-A-5-249646 JP-A-4-328548

  Patent Document 1 does not mention a technique for imaging a predetermined portion in the photomask plane, but the stage can be moved in the in-plane direction of the photomask, and the photomask has 5 sides. Since it is a square substrate of about 6 inches to 6 inches, it is considered that this inspection apparatus can inspect the entire surface of the photomask without any inconvenience.

  Further, in Patent Document 1, in order to evaluate the influence of a focus shift due to a resist thickness in an exposure process using a photomask and a defect of a phase shift mask having a fine concavo-convex pattern, the image sensor is taken from the focus position of the inspection light. It is described that an image obtained by shifting an image is compared with an image signal based on a designed mask pattern and an image signal captured using an imaging element as a focal position.

  In other words, in an actual IC manufacturing process, thin film stacking is repeated many times, and in an exposure process using a photomask, there is a case where the focus is shifted by the resist thickness and reduced irradiation is performed. Considering the fine pattern pitch of the mask, the influence of defocusing cannot be overlooked, and it is considered important to evaluate the influence of defocusing when using a phase shift mask capable of increasing the depth of focus.

  Therefore, in this inspection apparatus, in order to evaluate the influence of defocus due to a step on the surface to be transferred when using a phase shift mask, the imaging device can be displaced in the optical axis direction of the inspection light. Position displacement means is provided, and an image sensor corresponding to a transfer surface in an exposure process using a photomask is shifted from the focal position in the optical axis direction to inspect the influence.

  By the way, a photomask used for manufacturing a display device called a flat panel display (hereinafter referred to as “FPD”) such as a so-called liquid crystal display panel has a large size whose one side exceeds 1 m. . For manufacturing a display device, for example, a photomask having a main plane size of 1220 mm × 1400 mm and a thickness of 13 mm is used. Such a photomask increases in weight as the size increases, and for example, a photomask having a weight of about 50 kg is used. The pattern pitch is usually about several μm to several hundred μm.

  The following problems exist in the inspection for performing defect inspection and performance evaluation of such a large photomask.

  That is, when such a large photomask is placed horizontally on a stage as described in Patent Document 1, the installation area of the inspection apparatus becomes large. Furthermore, since a large photomask cannot inspect the entire surface with a single field of view, it is necessary to inspect the inspection area by dividing it into a plurality of areas. If it is moved in a horizontal plane, there is a problem that the installation area of the inspection apparatus is further increased.

  Further, when the photomask is held horizontally, there is a problem that the probability that particles (dust) falling in the air due to gravity adhere to the photomask increases.

  The inspection apparatus described in Patent Document 2 can cope with a reticle having a relatively small size, but the above-described problem occurs when a large photomask is inspected.

  The warpage due to its own weight when the photomask is held horizontally is considered to occur in an exposure apparatus that performs exposure using this photomask. In the exposure apparatus, focus adjustment is performed according to the warpage of the photomask. Exposure is performed while Therefore, in the conventional inspection apparatus in which only the image sensor is moved in the optical axis direction to perform the focus adjustment, the focusing operation of the exposure apparatus, the exposure pattern obtained in the exposure apparatus cannot be correctly reproduced, The performance evaluation and defect inspection of a large photomask cannot be performed satisfactorily.

  In other words, in an inspection apparatus in which only the image sensor is moved in the optical axis direction to adjust the focus, the image by the photomask in the exposure apparatus that performs exposure while the photomask is warped by its own weight is actually It is reproduced on the inspection machine before the exposure, so that the focus margin at the time of exposure cannot be evaluated precisely. Specifically, in order to verify the focusing margin allowed for the exposure of the photomask, a quantitative simulation is performed on how to position the objective lens and the object to be exposed (transfer object) in the exposure apparatus. Can not do it.

  Further, in such an inspection apparatus, it is not possible to quantitatively simulate the amount of movement of the objective lens system and the object to be exposed when defocusing is performed by an exposure machine that uses a large photomask. As a result, the conventional inspection apparatus cannot be applied to the evaluation of the focus margin in exposure or the inspection of a gray tone mask having a fine pattern that may be intentionally defocused. Here, the gray tone mask is intended to selectively reduce the amount of exposure light transmitted through the mask and selectively adjust the remaining film thickness after development of the photoresist on the transfer target. A photomask.

  Large photomasks for manufacturing liquid crystal display devices are usually exposed with exposure light in the wavelength band of i-line to g-line. In order to predict and evaluate the resist pattern obtained on the transfer object or the film pattern produced using it by forming a state approximating the photomask transmitted light that the resist film on the transfer object receives during exposure It is necessary to most realistically reproduce the actual exposure state.

  Therefore, a preferred embodiment of the present invention is proposed in view of the above situation, and the performance evaluation and defect inspection of a large photomask are performed while suppressing an increase in the installation area of the apparatus. Provided is a photomask inspection apparatus and a photomask inspection method that can be performed well with high accuracy under conditions that match the use conditions, and that ensure safety and handling properties for large photomasks, and Another object of the present invention is to provide a photomask manufacturing method and a pattern transfer method for manufacturing a liquid crystal device using the photomask inspection apparatus and the photomask inspection method.

  In order to solve the above-described problems and achieve the above object, a photomask inspection apparatus according to the present invention has any one of the following configurations.

[Configuration 1]
A photomask inspection device used to inspect flat panel display apparatus for manufacturing a photomask, a photomask is subject to hold as the main plane of the photomask is substantially vertical, the mask holding means A light source that emits a light beam having a predetermined wavelength, an illumination optical system that guides the light beam from the light source and irradiates the photomask held by the mask holding means, and a light beam that is irradiated to the photomask and passes through the photomask. An objective lens system, an imaging unit that receives a light beam that has passed through the objective lens system and captures an image of a photomask, a support unit that supports the illumination optical system, the objective lens system, and the imaging unit, and a respective support unit. A moving operation means for moving and a control means for controlling the moving operation means are provided, and the control means controls the moving operation means to control illumination. The optical system, the objective lens system, and the imaging unit are moved and operated in a plane parallel to the main plane of the photomask held by the mask holding unit, the optical axes thereof are aligned, and the optical system is positioned at a predetermined position, and objective lens system and the imaging means is characterized in that the optical axis is adjustable in position.

[Configuration 2]
In the photomask inspection apparatus having configuration 1, the numerical apertures of the objective lens system and the illumination optical system are variable, and the control means determines the numerical aperture of the objective lens system or the numerical aperture of the illumination optical system. By setting it to a predetermined value, the ratio of the numerical aperture of the illumination optical system to the numerical aperture of the objective lens system is controlled to a predetermined value.

[Configuration 3]
The photomask inspection apparatus having configuration 1 or configuration 2 includes a calculation unit that performs calculation using light intensity distribution data of transmitted light in a predetermined region of the photomask based on an image obtained by the imaging unit. It is characterized by this.

[Configuration 4 ]
In the photomask inspection apparatus having the configuration 1 or the configuration 2, the mask holding means is configured to tilt the main surface of the photomask from an angle that is inclined from the vertical and within 10 degrees from the vertical. It is characterized by holding.

[Configuration 5 ]
In the photomask inspection apparatus having any one of Configurations 1 to 4 , the light beam emitted from the light source and passed through the illumination optical system includes at least one of g-line, h-line, or i-line, or Among these, a light beam that is a mixture of any two or more is included.

[Configuration 6 ]
In the photomask inspection apparatus having any one of Configurations 1 to 5 , the illumination optical system is characterized in that a range in which the photomask is irradiated with the light beam is wider than the imaging field of view of the imaging means.

[Configuration 7 ]
In the photomask inspection apparatus having any one of Configurations 1 to 6 , the illumination optical system includes a field stop. The field stop irradiates the photomask with a light flux, and the light amount distribution is on the photomask. The diameter of the portion within 5% is 30% or more larger than the diameter of the imaging field of the imaging means.

[Configuration 8 ]
A photomask inspection apparatus having any one of Configurations 1 to 7 , further comprising an angle adjustment mechanism that performs fine adjustment of an optical axis of at least one of an illumination optical system or an objective lens system and an imaging unit. To do.

[Configuration 9 ]
In the photomask inspection apparatus having any one of Configurations 1 to 8 , the objective lens system and the illumination optical system include an aperture mechanism that can change the numerical aperture.

  The photomask inspection method according to the present invention has any one of the following configurations.

[Configuration 10 ]
A method for inspecting a photomask used for inspecting a photomask for manufacturing a flat panel display device, wherein a photomask in which a film having a predetermined pattern is formed on a transparent substrate has a main plane of the photomask approximately A photomask is irradiated with a light beam from a light source that is held vertically and emits a light beam of a predetermined wavelength through an illumination optical system, and the light beam that has passed through the photomask is received by an imaging unit through an objective lens system. A photomask inspection method for inspecting a photomask by picking up an image of an illumination optical system, an objective lens system and an image pickup means in a plane parallel to a main plane of the photomask held by the mask holding means in moving operation, is located at a predetermined position in these conditions the optical axes are coincident, further, the objective lens system and the imaging means, in the direction of the optical axis Located adjusted to a constant relative position, and is characterized in that captures an image of the photomask by the imaging means.

[Configuration 11 ]
In the photomask inspection method having the configuration 10 , the photomask image is picked up by the image pickup means by grasping in advance the exposure conditions to be applied when using the photomask, and the spectral characteristics and objectives determined based on the exposure conditions. This is performed using the ratio of the numerical aperture of the lens system and the numerical aperture of the illumination optical system to the numerical aperture of the objective lens system.

[Configuration 12 ]
In the photomask inspection method having the configuration 10 or the configuration 11 , the photomask is held with the main plane of the photomask at an angle within 10 degrees from the vertical.

[Configuration 13 ]
In the photomask inspection method having any one of Configurations 10 to 12 , the light beam applied to the photomask includes at least one of g-line, h-line, and i-line, or any of these These are characterized by using a light beam in which two or more of the above are mixed.

[Configuration 14 ]
In the inspection method for a photomask having any one of Configurations 10 to 13 , the wavelength distribution of illumination light used in an exposure apparatus that performs exposure using the photomask is grasped in advance as a light beam irradiated to the photomask. Based on the wavelength distribution, a light flux having a wavelength distribution determined based on the wavelength distribution is used.

[Configuration 15 ]
A photomask inspection method having any one of Structures 10 to 14 , further comprising a step of finely adjusting the optical axis of at least one of the illumination optical system or the objective lens system and the imaging means. It is.

[Configuration 16 ]
In the photomask inspection method having any one of Configurations 10 to 15 , the photomask is formed by forming a pattern including a light-shielding portion and a light-transmitting portion on a transparent substrate, and the photomask is obtained from the obtained captured image. The intensity distribution data of the transmitted light in the predetermined area is acquired.

[Configuration 17 ]
In the photomask inspection method having the configuration 16 , the photomask has a white defect or a black defect in the light shielding portion or the light transmitting portion, and the captured image of the defective portion or the transmission of the defective portion is included. Light intensity distribution data of light is obtained, and whether or not the photomask needs to be corrected is determined based on the data.

  The method for manufacturing a photomask for manufacturing a liquid crystal device according to the present invention has the following configuration.

[Configuration 18 ]
It has an inspection process by a photomask inspection method having any one of Configurations 10 to 17 .

  Furthermore, the pattern transfer method according to the present invention has the following configuration.

[Configuration 19 ]
Using the photomask for manufacturing a liquid crystal device manufactured by the method for manufacturing a photomask for manufacturing a liquid crystal device having the structure 18 , the exposure apparatus exposes light of a predetermined wavelength, and transfers the pattern to the transfer target. To do.

  In the photomask inspection apparatus according to the present invention having the structure 1, the control means controls the moving operation means for moving the supporting means for supporting the illumination optical system, the objective lens system, and the imaging means, respectively. The optical system, the objective lens system, and the imaging unit are moved and operated in a plane parallel to the main plane of the photomask held by the mask holding unit, the optical axes thereof are aligned, and the optical system is positioned at a predetermined position, and Since the position of at least one of the objective lens system and the image pickup means can be adjusted in the optical axis direction, the focusing operation of the exposure apparatus used when using the mask, and the exposure pattern image obtained in the exposure apparatus are realistic. Can be reproduced under conditions.

  That is, in this inspection apparatus, it is possible to evaluate a focus margin in an exposure apparatus that performs exposure in a state where the photomask is warped by its own weight. Specifically, in order to verify the focusing margin allowed for the exposure of the photomask, a quantitative simulation is performed on how to position the objective lens and the object to be exposed (transfer object) in the exposure apparatus. can do.

  Alternatively, by adjusting the relative position between the objective lens and the object to be exposed, it is possible to evaluate the transmitted light distribution of the photomask when the optical system of the exposure machine when using the photomask is taken into consideration. Further, in this inspection apparatus, the amount of movement of the objective lens system and the object to be exposed when defocused can be quantitatively simulated. Thus, this inspection apparatus can also be applied to inspection of a gray tone mask that may be intentionally defocused (focus offset) in exposure.

  In the photomask inspection apparatus according to the present invention having configuration 2, the control means controls the ratio of the numerical aperture of the objective lens system and the numerical aperture of the illumination optical system to the numerical aperture of the objective lens system to a predetermined value. The exposure pattern in the exposure apparatus can be simulated well.

  The photomask inspection apparatus according to the present invention having the configuration 3 includes calculation means for performing calculation using light intensity distribution data of transmitted light in a predetermined region of the photomask based on an image obtained by the imaging means. The transfer pattern obtained from the photomask can be predicted and evaluated by a desired calculation method, and the quality of the photomask can be determined to determine the possibility and necessity of defect correction.

  In the photomask inspection apparatus according to the present invention having the configuration 4, the mask holding means fixes and holds the photomask with the main plane of the photomask being substantially vertical, thereby suppressing an increase in the installation area of the apparatus. On the other hand, safety and handling properties for a large photomask can be ensured.

  In the photomask inspection apparatus according to the present invention having the configuration 5, the photomask is held at an angle inclined from the vertical to the main plane of the photomask and within 10 degrees from the vertical. It is possible to ensure the safety and handling properties of a large photomask while suppressing an increase in the installation area.

  In the photomask inspection apparatus according to the present invention having the configuration 6, the light beam emitted from the light source and having passed through the illumination optical system includes at least one of g-line, h-line, and i-line, or these Since it includes a light beam in which two or more of them are mixed, it is possible to correctly reproduce an exposure pattern obtained in an exposure apparatus that performs exposure using a large photomask.

  In the photomask inspection apparatus according to the present invention having the configuration 7, the illumination optical system has a wider range for irradiating the photomask with the light beam than the imaging field of the imaging means. Therefore, the objective lens system and the imaging means for the illumination optical system The allowable range of the optical axis deviation can be widened.

  In the photomask inspection apparatus according to the present invention having the configuration 8, the diameter of the portion where the light quantity distribution of the light beam irradiated onto the photomask is within 5% by the field stop of the illumination optical system is the image pick-up by the image pickup means. Since it is larger by 30% or more than the diameter of the field of view, it is possible to widen the allowable range of the optical axis shift of the objective lens system and the imaging means with respect to the illumination optical system.

  The photomask inspection apparatus according to the present invention having the structure 9 includes an illumination optical system or an angle adjustment mechanism for finely adjusting the optical axis of at least one of the objective lens system and the imaging unit. The optical axis shift of the objective lens system and the imaging means can be suppressed.

  In the photomask inspection apparatus according to the present invention having the structure 10, since the objective lens system and the illumination optical system have a diaphragm mechanism that makes the numerical aperture variable, the numerical aperture can be easily controlled by the control means. be able to.

  In the photomask inspection method according to the present invention having the structure 11, at least one of the objective lens system and the image pickup means is adjusted to a predetermined relative position in the optical axis direction, and the photomask is used by the image pickup means. Therefore, the focusing operation of the exposure apparatus and the exposure pattern obtained by the exposure apparatus can be correctly reproduced.

  In the photomask inspection method according to the present invention having the configuration 12, the exposure conditions to be applied when using the photomask are grasped in advance, the spectral characteristics determined based on the exposure conditions, the numerical aperture of the objective lens system, and Since the image of the photomask is picked up by the image pickup means using the ratio of the numerical aperture of the illumination optical system to the numerical aperture of the objective lens system, the exposure pattern in the exposure apparatus can be simulated well.

  In the photomask inspection method according to the present invention having the structure 13, since the photomask is fixed and held with the main plane of the photomask being substantially vertical, a large-sized photomask is suppressed while suppressing an increase in the installation area of the apparatus. Safety and handling properties for the mask can be ensured.

  In the photomask inspection method according to the present invention having the structure 14, the photomask is held at an angle of 10 degrees or less from the vertical to the main plane of the photomask. Safety and handling properties for the photomask can be ensured.

  In the photomask inspection method according to the present invention having the configuration 15, since the photomask is held at an angle inclined from the main plane of the photomask at an angle within 10 degrees from the vertical, the apparatus It is possible to ensure the safety and handling properties of a large photomask while suppressing an increase in the installation area.

  In the photomask inspection method according to the present invention having the configuration 16, at least one of g-line, h-line, and i-line is included as the light beam applied to the photomask, or any two of them. Since the light flux mixed above is used, an exposure pattern obtained in an exposure apparatus that performs exposure using a large photomask can be correctly reproduced.

  In the photomask inspection method according to the present invention having the structure 17, the wavelength distribution of the illumination light used in an exposure apparatus that performs exposure using the photomask is grasped in advance as a light beam irradiated to the photomask, Since a light flux having a wavelength distribution determined based on the wavelength distribution is used, an exposure pattern obtained in an exposure apparatus that performs exposure using a large photomask can be correctly reproduced.

  In the photomask inspection method according to the present invention having the configuration 18, since the light beam from the light source is irradiated over a range wider than the imaging field of the imaging unit, the objective lens system for the illumination optical system and the light of the imaging unit The allowable range of axis deviation can be widened.

  In the photomask inspection method according to the present invention having the structure 19, the diameter of the portion where the light quantity distribution is within 5% in the light beam irradiated to the photomask is 30% of the diameter of the imaging field of the imaging means. Since it is larger as described above, it is possible to widen the allowable range of the optical axis shift of the objective lens system and the imaging means with respect to the illumination optical system.

  The photomask inspection method according to the present invention having the configuration 20 includes the step of finely adjusting the optical axis of at least one of the illumination optical system or the objective lens system and the imaging means. The optical axis shift of the system and the imaging means can be suppressed.

  In the photomask inspection method according to the present invention having the structure 21, the photomask is formed by forming a pattern including a light-shielding portion and a light-transmitting portion on a transparent substrate. Since the intensity distribution data of the transmitted light of the area is acquired, the exposure pattern in the exposure apparatus can be simulated well.

  In the photomask inspection method according to the present invention having the configuration 22, the photomask has a white defect or a black defect in the light shielding portion or the light transmitting portion, and the captured image of the defective portion, or Since the light intensity distribution data of the transmitted light of the defective portion is obtained and the necessity of correction of the photomask is determined based on the data, the presence / absence of a white defect or a black defect, whether the defect is corrected or not is determined. Can be judged.

  In the photomask inspection method according to the present invention having configuration 23, an area that is greater than or equal to a predetermined threshold and / or less than or equal to a predetermined threshold is inspected by intensity distribution data acquired from a captured image. The exposure pattern can be simulated well.

  In the method for manufacturing a photomask for manufacturing a liquid crystal device according to the present invention having the structure 24, the photomask inspection method according to the present invention includes an inspection process. A mask can be manufactured.

  In the pattern transfer method according to the present invention having the structure 25, light of a predetermined wavelength is exposed by an exposure apparatus using the photomask for manufacturing a liquid crystal device manufactured by the method for manufacturing a photomask for manufacturing a liquid crystal device according to the present invention. In addition, since the pattern is transferred to the transfer target, good pattern transfer can be performed.

  That is, the present invention can satisfactorily perform performance evaluation and defect inspection of a large photomask while suppressing an increase in the installation area of the apparatus, and secures safety and handling properties for a large photomask. Provided are a photomask inspection apparatus and a photomask inspection method, and further provide a photomask manufacturing method and a pattern transfer method for manufacturing a liquid crystal device using the photomask inspection apparatus and the photomask inspection method. It can be done.

  The best mode for carrying out the present invention will be described below.

[Outline of Photomask Inspection Apparatus According to the Present Invention]
The photomask inspection apparatus according to the present invention creates an exposure condition equivalent to that in an exposure apparatus that performs exposure using a photomask made of a transparent substrate, or an exposure condition obtained based on the exposure condition of the exposure apparatus, It is an apparatus that simulates an image transferred to a transfer target (such as a glass substrate coated with a resist) by exposure in an exposure apparatus, can be captured by an imaging means, and can be obtained as light intensity distribution data. Note that the exposure apparatus is an apparatus that transfers a pattern formed on a photomask onto a transfer target under certain exposure conditions.

  And in this photomask inspection apparatus, based on the light intensity distribution of the photomask transmitted light that can be grasped from the image data obtained by the imaging means, the shape of the resist pattern formed on the resist film on the transfer object, Various analyzes and evaluations can be performed, including variations in pattern dimensions and transmittance. Note that the photomask to be inspected by this inspection apparatus includes not only the photomask that is the final product but also an intermediate during the production of the photomask.

  The inspection apparatus and the inspection method of the present invention are designed to transmit light under conditions approximating exposure conditions for the purpose of simulating a transferred image when a pattern formed on a photomask by exposure is transferred onto a transfer target. The imaging is performed under such a condition that the exposure condition can be approximated by calculation. In particular, it can be suitably applied to simulation of a large photomask for manufacturing a liquid crystal display device. Unlike a general defect inspection device, which scans a pattern using a line sensor and compares the obtained data with other patterns and data, a predetermined area of the mask is scanned using an area sensor. Captured as a captured image. Therefore, it is preferable that an arbitrary position on the surface of the photomask that is an object to be inspected can be imaged, but it is not particularly necessary to scan the entire surface at high speed. This is because the transfer state of the entire surface can be grasped if the pattern transfer state of a partial region in the surface can be simulated.

  The apparatus of the present invention preferably includes an arithmetic unit. Thus, if appropriate parameters are introduced, the characteristics of the exposure machine, the effect on individual transfer due to individual differences of the exposure machine, and the development and etching of the transfer target after exposure, circuit patterns are formed. The state to be performed can also be simulated by calculation.

[Configuration of Photomask Inspection Apparatus According to the Present Invention]
In an example of this photomask inspection apparatus, as shown in FIG. 1, a photomask 3 as a subject is held by a mask holding means 3a. The mask holding means 3a supports the lower end portion and the vicinity of the side edge portion of the photomask 3 in a state where the main plane of the photomask 3 is substantially vertical, and holds the photomask 3 tilted and fixed. It has become. This mask holding means 3a is a large-sized photomask 3 (for example, one whose main plane has a side of 300 mm or more. Specifically, the main plane has a size of 1220 mm × 1400 mm and a thickness of 13 mm, etc.) A photomask 3 having a size can be held. That is, since the mask holding means 3a mainly supports the lower end portion of the photomask 3 in a state where the main plane is substantially vertical, even if the size of the photomask 3 is different, the photomask 3 is different by the same support member. 3 lower end portions can be supported.

  In this inspection apparatus, since the photomask 3 is supported in a state where the main plane of the photomask 3 is substantially vertical, there is an advantage that an analysis can be performed while eliminating the influence of deflection due to the weight of the photomask. Furthermore, it can be mounted on a limited installation area, and the risk of particle falling onto the photomask 3 can be reduced.

  Here, “substantially vertical” means a vertical or slightly inclined state, and preferably refers to a state in which the angle from the vertical indicated by θ in FIG. 1 is within about 10 degrees, more preferably. Further, it means a state in which the angle is 2 degrees to 10 degrees from the vertical, and more preferably 4 degrees to 10 degrees from the vertical. In this range, when the photomask 3 is placed on the apparatus of the present invention, the photomask can be held most stably, and the photomask can be inspected as it is.

  That is, by using the mask holding means 3a that supports the photomask 3 at an angle, the photomask 3 is prevented from being overturned in the process of holding the photomask 3, and the photomask 3 is stably held. Can be fixed. In order to stably hold the photomask in the apparatus, it is preferable to support the photomask in a slightly inclined state by a frame (not shown) that hinders the vicinity of the periphery of the photomask. This not only prevents the total weight of the photomask from concentrating on the lower end face of the photomask, but also prevents damage caused by the weight of the photomask. is there. In addition, it is preferable to fix the photomask by using a mask holding means 3a that supports the photomask 3 after placing it by tilting. However, when adopting such an inclined arrangement of the photomask, it is necessary to consider the arrangement of the optical system, which will be described later.

  The photomask inspection apparatus has a light source 1 that emits a light beam having a predetermined wavelength (or wavelength range). As the light source 1, for example, a halogen lamp, a metal halide lamp, a UHP lamp (ultra-high pressure mercury lamp) or the like can be used.

  As the light source 1, a light source that emits inspection light having a wavelength distribution that approximates exposure light in an exposure apparatus that performs exposure using a photomask 3 that has undergone inspection or has at least a part of its wavelength component is used. Is preferred. Specifically, this inspection light includes at least one of g-line (436 nm), h-line (405 nm), or i-line (365 nm), and further includes all these wavelength components. It is also possible to apply mixed light including any two or more of the wavelength components. In order to adjust the mixing ratio of these wavelength components, a wavelength selection filter 6 such as an optical filter can be used.

  Usually, when exposing a large mask for manufacturing an FPD, light having a wavelength range including these wavelengths, that is, mixed light is often used. Therefore, even in this inspection apparatus, a desired light intensity ratio is obtained. When mixed light is applied, the desired light intensity ratio is preferably determined based on the characteristics of the light source of the exposure apparatus that is actually used.

  In this inspection apparatus, the inspection light reflecting the actual exposure conditions can be performed when the wavelength distribution of the inspection light emitted from the light source 1 is the same as or substantially equal to the wavelength distribution of the exposure light in the exposure apparatus. That is, depending on the exposure light, what is regarded as a defect under white light can be treated as a normal pattern in the exposure apparatus, and conversely, what is not regarded as a defect under white light is regarded as a normal pattern in the exposure apparatus. This is because it may not be handled.

  Alternatively, as another preferred embodiment, the light source 1 of the present inspection apparatus can irradiate exposure light with a single wavelength, and can analyze photomask transmitted light with a single wavelength, or when mixed light with a plurality of wavelengths is applied. It is possible to simulate the mixed light exposure by guiding the transmitted light by calculation.

  The inspection apparatus includes an illumination optical system 2 that guides the inspection light from the light source 1 and irradiates the photomask 3 held by the mask holding unit 3a with the inspection light. The illumination optical system 2 includes a diaphragm mechanism in order to make the numerical aperture (NA) variable. Furthermore, the illumination optical system 2 preferably includes a field stop for adjusting the irradiation range of the inspection light on the photomask 3. The inspection light that has passed through the illumination optical system 2 is irradiated onto the photomask 3 held by the mask holding means 3a.

  The inspection light applied to the photomask 3 passes through the photomask 3 and enters the objective lens system 4. The objective lens system 4 includes a diaphragm mechanism, so that the numerical aperture (NA) is variable. The objective lens system 4 includes, for example, a first group (simulator lens) 4a in which inspection light that has passed through the photomask 3 is incident and this light beam is corrected to infinity to obtain parallel light, and a light beam that has passed through the first group. And a second group (imaging lens) 4b for forming an image.

  In this inspection apparatus, since the numerical aperture of the illumination optical system 2 and the numerical aperture of the objective lens system 4 are variable, the ratio of the numerical aperture of the illumination optical system 2 to the numerical aperture of the objective lens system 4, that is, The sigma value (σ: coherence) can be varied.

  The light beam that has passed through the objective lens system 4 is received by the imaging means 5. The imaging unit 5 captures an image of the photomask 3. As this imaging means 5, for example, an imaging element such as a CCD can be used.

  In the inspection apparatus, a calculation unit 11 and a display unit 12 are provided that perform image processing, calculation, comparison with a predetermined threshold value, display, and the like for the captured image obtained by the imaging unit 5.

  Further, in this inspection apparatus, a predetermined calculation (wavelength synthesis calculation) is performed by the calculation means 11 on the captured image obtained using the predetermined exposure light or the light intensity distribution data obtained based on the captured image. To obtain a captured image or light intensity distribution data under conditions using other exposure light. For example, in this inspection apparatus, when the light intensity distribution is obtained under exposure conditions with the same intensity ratio of g-line, h-line and i-line, the intensity of g-line, h-line and i-line is 1: 2: 1. It is possible to obtain the light intensity distribution when the exposure is performed under the ratio exposure conditions. As a result, in this inspection apparatus, it is possible to perform an evaluation that reproduces or approximates the exposure conditions in the exposure apparatus that is actually used, including individual differences of exposure apparatuses that expose the photomask and wavelength fluctuations due to changes over time. In addition, regarding the resist pattern formed when the pattern is transferred onto the transfer object using the photomask, it is determined whether or not this can be achieved when a desired photoresist remaining film amount is assumed. Alternatively, it is possible to easily obtain optimum exposure conditions that can be achieved.

  As shown in FIG. 2, the illumination optical system 2 and the objective lens system 4 supported by the support means and the movement operation means receive gravity due to their own weights in a direction substantially orthogonal to the optical axis. Therefore, there is a possibility that the optical axis shift is likely to occur between the illumination optical system 2 and the objective lens system 4. Further, if the photomask is held in a slightly inclined state, the illumination optical system 2 and the objective lens system 4 face each other with the optical axis orthogonal to the inclined surface. In this case, the illumination optical system 2 and the objective lens system are likely to be misaligned by rotating around the center of gravity due to their own weights. As a result, if either or both are misaligned, both optical axes Are not consistent. At this time, the position at which the illumination optical system irradiates the light beam on the photomask and the position at which the objective lens system captures the light on the photomask as a light beam are shifted.

  For this reason, in this inspection apparatus, FIGS. 3 and 4 are arranged so as not to hinder the inspection even when the optical axis of one or both of the illumination optical system 2 and the objective lens system 4 is deviated from the other. As shown in FIG. 2, the range in which the inspection optical beam is irradiated onto the photomask by the illumination optical system 2 includes the field of view of the objective lens system 4 and is wider than the field of view of the objective lens system 4. . The diameter of the illumination range is preferably 30% or more larger than the diameter of the objective lens field, and more preferably 30% or more and 300% or less. The range in which the inspection light is irradiated can be adjusted by the position of the light source 1 and the field stop of the illumination optical system 2.

  Furthermore, it is preferable that the light amount distribution in the light beam of the inspection light irradiated onto the photomask 3 by the illumination optical system 2 is small as shown in FIG. 5, and the diameter of the illumination range that satisfies the illuminance distribution within 5% is the objective. It is preferably 30% or more larger than the diameter of the field of view of the lens system 4. More preferably, it is desired to be large in the range of 30% to 100%. More preferably, the illuminance distribution of the illumination with the diameter is within 2%. When the light amount distribution in the light beam of the inspection light is large, especially when the optical axis of the objective lens system 4 is deviated, even if the light intensity distribution of the transmitted light of the photomask 3 is obtained, the state of the photomask is This is because there is a possibility that the inspection cannot be performed accurately.

  In this inspection apparatus, the relative optical axes of the illumination optical system 2 and the objective lens system 4 can be corrected so that the optical axes of the illumination optical system 2 and the objective lens system 4 can be corrected when they deviate beyond a certain level. It is preferable to provide an angle adjustment mechanism that finely adjusts the angle. By providing such an angle adjusting mechanism, the optical axes of the illumination optical system 2 and the objective lens system 4 can always be matched by an easy operation.

  In this inspection apparatus, at least one of the objective lens system 4 and the imaging means 5 supported by the support means 13 can be moved in the optical axis direction by the control means 14 and the movement operation means 15. The relative distance with respect to each photomask 3 can be changed. The illumination optical system 2, the objective lens system 4, and the imaging unit 5 can be moved by a control unit 14 and a moving operation unit 15. The moving operation unit 15 can move the illumination optical system 2, the objective lens system 4, and the imaging unit 5 in parallel to the main plane of the photomask 3 while matching the optical axes thereof. In this inspection apparatus, such a moving operation means 15 is provided, so that even when a large photomask is inspected, the photomask 3 is not moved in a direction parallel to the main plane. Inspection over the entire main plane of the photomask 3 is possible, and a desired inspection on the main plane can be selectively performed.

  Preferably, in this inspection apparatus, the objective lens system 4 and the imaging means 5 are independently movable in the optical axis direction, so that imaging is performed in a state that approximates an exposure apparatus that performs exposure using the photomask 3. Can do. In addition, the position of the objective lens system 4 or the position of the image pickup means 5 is intentionally offset to approximate the deflection of the mask in the exposure apparatus, or the image ( It is also possible to take a (defocused image). By evaluating the blurred image, it is possible to determine the performance of the gray-tone mask and the presence or absence of defects, as will be described later.

  The control means 14 of the inspection apparatus can control the field stop and stop mechanism of the illumination optical system 2 and the stop mechanism of the objective lens system 4. In the photomask inspection method using this inspection apparatus, the control means 14 moves the illumination optical system 2, the objective lens system 4, and the imaging means 5 in parallel to the main plane of the photomask 3 held by the mask holding means. After moving in the direction and reaching a desired position on the mask, the objective lens system 4 and the imaging means 5 can be moved independently of each other in the optical axis direction. At this time, the numerical aperture and sigma value of the objective lens system 4 (coherence, the ratio of the numerical aperture of the illumination optical system 2 to the numerical aperture of the objective lens system 4) is maintained at a predetermined value and moved to the mask main plane. Alternatively, the sigma value may be adjusted after translation to a desired position on the mask. Further, it is preferable that the illumination optical system 2, the objective lens system 4 and the image pickup means 5 are moved in parallel with the main plane of the mask while the optical axes of the illumination optical system 2, the objective lens system 4 and the image pickup means 5 are coincident. You may perform control in which.

  Thus, in this inspection apparatus, the exposure conditions, that is, the numerical aperture and sigma value of the objective lens system 4 can be freely adjusted, and the position of the objective lens system 4 or the image sensor 5 is offset. Thus, it is also possible to image a desired position on the mask in a defocused state, and to inspect line width variation due to the focus offset, a transfer image of the multitone mask, and the like. Also, as shown in FIG. 6, the light intensity distribution obtained by the imaging means 5 can be obtained by quantification, and the shape that will be transferred in the exposure apparatus by comparing this light intensity with a predetermined threshold value. (Resist transfer pattern shape formed on the resist film on the transfer object) can be obtained. Further, by comparing the light intensity obtained by the image pickup means 5 with a predetermined threshold value, the dimension of the desired resist remaining film value portion in the transfer pattern can be obtained as a numerical value.

[Inspection Method for Photomask According to the Present Invention]
FIG. 7 is a flowchart showing a procedure of a photomask inspection method performed using the above-described photomask inspection apparatus.

  In the photomask inspection method according to the present invention performed using this inspection apparatus, as shown in FIG. 7, in step st1, the photomask 3 is placed and held with the main plane being substantially vertical. As described above, the photomask is preferably slightly inclined. Next, in step st2, optical conditions such as the wavelength of the light source (λ), the numerical aperture (NA) of the objective lens system 4, and the sigma value (σ) are set.

  Next, in step st3, it is determined whether or not wavelength synthesis calculation is necessary. When the wavelength synthesis calculation is not necessary, the process proceeds to step st4, and when the wavelength synthesis calculation is necessary, the process proceeds to step st8.

  In step st4, the illumination optical system 2, the objective lens system 4 and the image pickup means 5 are respectively arranged at positions facing each other with the photomask 3 held with the main plane of the photomask held substantially vertical. The optical axis is moved to the observation position with the optical axes being matched. In step st5, the optical direction is adjusted (focus adjustment). Next, in step st6, the inspection light is irradiated and received to perform imaging, and the process proceeds to step st7.

  On the other hand, in step st8, the illumination optical system 2, the objective lens system 4 and the image pickup means 5 are respectively arranged at positions facing each other across the photomask 3 held with the main plane of the photomask being substantially vertical. Then, the optical axis is moved to the observation position in a state where both optical axes are matched. In step st9, the optical direction is adjusted (focus adjustment). Next, in step st10, the inspection light is irradiated and received, imaging is performed, and the process proceeds to step st11.

  In step st11, it is determined whether or not all images necessary for wavelength synthesis calculation have been captured. If all necessary images have not been captured, the process proceeds to step st12, the wavelength condition is changed, and the process returns to step st10. If all necessary images have been captured, the process proceeds to step st13 to perform wavelength synthesis calculation, and then proceeds to step st7.

  In step st7, the obtained data is analyzed to obtain intensity distribution data. Next, proceeding to step st14, the transmittance is calculated.

[Usage Mode of Photomask Inspection Apparatus According to the Present Invention]
As described above, the photomask serving as the subject in the photomask inspection apparatus according to the present invention includes not only a photomask completed as a product, but also an intermediate in the course of manufacturing the photomask. There are no particular restrictions on the type and application of the photomask.

  That is, in this inspection apparatus, a light shielding film mainly composed of Cr or the like is formed on the main surface of the transparent substrate, and a predetermined pattern is formed on the light shielding film by photolithography to form a pattern having a light shielding part and a light transmitting part. In addition to the formed binary mask, it is possible to inspect a gray-tone mask having a light-shielding portion, a light-transmitting portion, and a semi-light-transmitting portion that transmits part of exposure light on the main surface of the transparent substrate.

  In this inspection apparatus, a particularly remarkable effect is obtained when such a gray-tone mask is inspected. Further, the present invention can be applied to an inspection for determining whether or not a binary mask or a gray tone mask having a defect on a pattern can be used. Here, the defect includes a white defect and a black defect. Here, the white defect is a defect having a transmission amount of exposure light larger than a predetermined amount, and a black defect is a defect having a transmission amount of exposure light smaller than a predetermined amount. Say. In this inspection apparatus, it is possible to obtain a captured image of a defective portion or light intensity distribution data of transmitted light of the defective portion, and determine whether or not the photomask needs to be corrected based on this data.

  Therefore, this inspection apparatus has a remarkable effect when inspecting a photomask for manufacturing an FPD, and among the photomasks for manufacturing a liquid crystal device, a thin film transistor (hereinafter referred to as “TFT”). Most suitable for manufacturing. This is because, in these fields, the gray-tone mask is frequently used due to manufacturing efficiency and cost advantages, and the size of the semi-translucent portion needs to be extremely fine and precise. It is.

  Note that the semi-transparent portion includes a semi-transparent portion formed with a semi-transparent film (referred to as “semi-transparent film type”) and a semi-transparent portion by a fine pattern below the resolution limit under exposure conditions. (Referred to as “fine pattern type”).

[About gray tone mask]
Here, a gray tone mask which is an object to be inspected in the photomask inspection apparatus according to the present invention will be described.

  Liquid crystal display devices with TFTs (Liquid Crystal Display: hereinafter referred to as “LCD”) are now widely used due to the advantages of being thin and easy to consume compared to cathode ray tubes (CRT). . The TFT in the LCD is a TFT substrate having a structure in which a TFT is arranged in each pixel arranged on a matrix, and pixel patterns of red (R), green (G) and blue (B) are arranged corresponding to each pixel. The color filter thus formed is superposed via a liquid crystal phase. Such an LCD has a large number of manufacturing processes, and even a 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. This method reduces the number of masks to be used by using a photomask having a light-shielding portion, a light-transmitting portion, and a semi-light-transmitting portion (gray tone portion) (hereinafter referred to as “gray tone mask”). is there. 8 and 9 show an example of a manufacturing process of a TFT substrate using a gray tone mask.

  First, as shown in FIG. 8A, a metal film for a gate electrode is formed on a glass substrate 201, and a gate electrode 202 is formed by a photolithography process using a photomask. Thereafter, a gate insulating film 203, a first semiconductor film (a-Si) 204, a second semiconductor film (N + a-Si) 205, a source / drain metal film 206, and a positive photoresist film 207 are formed.

  Next, as shown in FIG. 8B, using a gray tone mask 100 having a light shielding portion 101, a light transmitting portion 102, and a semi-light transmitting portion (gray tone portion) 103, a positive photoresist film 207 is formed. Are exposed and developed to form a first resist pattern 207A. The first resist pattern 207A covers the TFT channel portion, the source / drain formation region, and the data line formation region, and the TFT channel portion formation region is thinner than the source / drain formation region.

  Next, as shown in FIG. 8C, the source / drain metal film 206 and the second and first semiconductor films 205 and 204 are etched using the first resist pattern 207A as a mask. Next, as shown in FIG. 9A, the resist film 207 is entirely reduced by ashing with oxygen to remove the thin resist film in the channel portion formation region, thereby forming a second resist pattern 207B. . Thereafter, as shown in FIG. 9B, using the second resist pattern 207B as a mask, the source / drain metal film 206 is etched to form source / drains 206A and 206B, and then the second semiconductor film 205 is formed. Etch. Finally, as shown in FIG. 9C, the remaining second resist pattern 207B is peeled off.

  As shown in FIG. 10, the gray tone mask 100 used here includes light shielding portions 101A and 101B corresponding to the source / drain, a light transmitting portion 102, and a gray tone portion 103 corresponding to the TFT channel portion. The gray tone portion 103 is an area where a light shielding pattern 103A composed of a fine pattern below the resolution limit of a large LCD exposure machine using the gray tone mask 100 is formed. The light shielding portions 101A and 101B and the light shielding pattern 103A are usually formed from films of the same thickness made of the same material such as chromium or a chromium compound. The resolution limit of a large LCD exposure machine using such a gray-tone mask is about 3 μm for a stepper type exposure machine and about 4 μm for a mirror projection type exposure machine. Therefore, in the gray tone portion 103, the space width of the transmissive portion 103B and the line width of the light shielding pattern 103A are set to be less than the resolution limit of the exposure machine, for example, less than 3 μm.

  In the design of such a fine pattern type gray tone portion 103, a fine pattern for providing an intermediate semi-transmission (gray tone) effect between the light shielding portions 101A and 101B and the light transmitting portion 102 is formed by a line- There is a choice between an and space type, a dot (halftone dot) type, or another pattern. In the case of the line-and-space type, consider how much the line width should be, what the ratio of the light transmitting and shielding parts should be, and how much the overall transmittance should be designed. Although designed, there has been no method for grasping how such a fine pattern is transferred onto a transfer medium when the mask is actually used. Also, in the production of gray-tone masks, extremely difficult production technologies such as the management of the center value of line widths and the management of line width variations within masks were required. There was no simple means of grasping the balance between production management and yield, such as whether variations were allowed.

  On the other hand, it has been proposed to form the gray tone portion by a semi-transparent film. By using a semi-transparent film in the gray tone portion, it is possible to reduce the exposure amount by the gray tone portion and perform half tone exposure. In addition, by using a semi-transparent film in the gray tone part, it is only necessary to consider how much the entire transmittance is necessary in the design. In the production of the gray tone mask, the film type of the semi-transparent film ( A gray tone mask can be produced simply by selecting a film material) and a film thickness. Therefore, in the manufacture of such a semi-transparent film type gray-tone mask, it is only necessary to control the thickness of the semi-transparent film, and it is relatively easy to manage. In addition, when the TFT channel portion is formed by the gray tone portion of the gray tone mask, if the semi-transparent film can be easily patterned by a photolithography process, the shape of the TFT channel portion is also complicated. It becomes possible to do.

  The semi-transparent film type gray tone mask can be manufactured, for example, as follows. Here, as an example, a pattern of a TFT substrate will be described. As described above, this pattern is formed around the light shielding portion 101 made of a pattern corresponding to the source and drain of the TFT substrate, the semi-transparent portion 103 made of a pattern corresponding to the channel portion of the TFT substrate, and the periphery of these patterns. The translucent part 102 is configured.

  First, a mask blank in which a semi-transparent film and a light-shielding film are sequentially formed on a transparent substrate is prepared, and a resist film is formed on the mask blank. Next, a pattern is drawn and developed to form a resist pattern in regions corresponding to the light shielding part and the semi-transparent part of the pattern. Next, by etching with an appropriate method, the light shielding film in the region corresponding to the light-transmitting portion where the resist pattern is not formed and the semi-light-transmitting film below it are removed to form a pattern.

  In this way, the translucent part 102 is formed, and at the same time, the light shielding pattern of the area corresponding to the light shielding part 101 and the semi-transparent part 103 of the pattern is formed. Then, after removing the remaining resist pattern, a resist film is formed again on the substrate, pattern drawing is performed, and development is performed, thereby forming a resist pattern in a region corresponding to the light shielding portion 101 of the pattern. Next, only the light shielding film in the region of the semi-translucent portion 103 where the resist pattern is not formed is removed by appropriate etching. Thereby, the semi-transparent portion 103 is formed by the pattern of the semi-transparent film, and at the same time, the pattern of the light shielding portion 101 is formed.

  Even in a gray tone mask using such a semi-transparent film, there is a problem in production management. For example, the light transmittance of the semi-transparent film and the resolution conditions of the exposure tool change depending on the wavelength of the exposure light, and the wavelength characteristics of the exposure light vary from exposure machine to exposure machine. This is because there are various mask performance factors that are difficult to perform.

[About inspection of gray tone mask]
In order to inspect defects and performance in the gray tone mask as described above, it is desirable to perform a simulation reflecting actual exposure conditions and evaluate the presence or absence of defects and the superiority or inferiority of performance.

  In a gray-tone mask, the pattern shape formed on the mask affects the resist pattern film thickness and the resist pattern shape on the transfer object formed by exposure using the mask. For example, it is necessary to evaluate whether the light transmittance of the semi-translucent part is within an appropriate range, or how the rising (sharpness or blurring) of the boundary between the semi-translucent part and the light-shielding part is required. .

  In particular, in the case of a gray-tone mask having a semi-transparent portion composed of a fine pattern, when the exposure is actually performed using a photomask, the fine pattern is not resolved and is regarded as a substantially uniform transmittance. Used to the extent of non-resolution. It is necessary to inspect this state in the mask manufacturing process, in a stage before shipment, and further in a stage where defect correction is performed. In response to such a problem, the present inventors have found that the inspection method using the inspection apparatus according to the present invention has a remarkable effect.

  That is, in the inspection apparatus according to the present invention, the film thickness of the photoresist is selectively changed by reducing the amount of exposure light transmitted through the semi-translucent portion and reducing the amount of irradiation of the photoresist in this region. The inspection of the gray tone mask which is the one can be performed with high accuracy by reproducing the actual exposure condition.

  In the data acquired by this inspection apparatus, if the photomask pattern is appropriately designed and appropriately formed with respect to the optical conditions given to the apparatus (conditions approximately equal to the optical conditions of the exposure machine to be used), As shown in FIG. 11 (right end view), the fine pattern formed in the semi-translucent portion is in a non-resolved state in which the substantially single density is obtained. The density of this portion indicates the light transmission amount of this portion when this gray tone mask is used, and the reduction amount of the transmission amount with respect to the light transmission portion (or the increase degree of transmission amount with respect to the light shielding portion) of this portion, The residual film amount of the resist film formed by the semi-translucent portion when the mask is used is determined. On the other hand, if the mask design is inappropriate for the exposure optical conditions, or if the pattern is not formed in a predetermined shape and size during the manufacturing process, the concentration of the semi-translucent part and the semi-transparent part Therefore, the quality of the inspection portion can be determined by comparison with the normal state.

  Therefore, when a gray-tone mask is inspected by the inspection apparatus according to the present invention, an exposure condition in which an appropriate non-resolution part as described above appears (that is, a gray part appears) is actually applied to the photomask. If the exposure conditions to be applied substantially match, it can be said that the performance of the photomask is sufficient.

  Further, when the gray tone mask is for manufacturing a thin film transistor, when a captured image is obtained in the non-resolving state as described above, an appropriate calculation is performed as necessary to obtain a channel portion, a source, It is also possible to evaluate the sharpness of the boundary portion with the drain portion and predict the three-dimensional shape of the photoresist pattern in the portion.

  Therefore, the inspection apparatus according to the present invention can be advantageously applied to inspection of a photomask having a gray tone portion composed of a fine light-shielding pattern that is below the resolution limit under actual exposure conditions.

  In this case, a photomask 3 having a fine pattern below the resolution limit is set as an object in the inspection apparatus, and the exposure conditions of an exposure machine that uses the mask are grasped in advance. The number and the sigma value (ratio of the numerical aperture of the illumination optical system 2 to the numerical aperture of the objective lens system 4) are set to predetermined values, and the position of the objective lens system 4 is appropriately adjusted in the optical axis direction to capture an image. An image in a non-resolved state of a fine pattern is obtained on the imaging surface of the means 5. And the light intensity distribution of a mask pattern can be obtained by processing the imaged image data by the calculation means 11. From the shape of the captured image and the light intensity data at a predetermined evaluation point, the superiority or inferiority of the performance of the photomask 3 and the presence or absence of defects can be evaluated.

  Further, in this inspection apparatus, as shown in FIG. 12, the objective lens system 4 and the imaging means 5 can be moved and operated in the optical axis direction, respectively. The objective lens system 4 and the imaging means 5 are independent of each other. Since the relative distance to the photomask 3 can be changed, even if the photomask 3 is warped due to its own weight in an exposure apparatus that performs exposure using the photomask 3, the exposure apparatus is approximated. It is possible to perform imaging with That is, in this inspection apparatus, the distance L1 from the photomask 3 to the objective lens system 4 and the distance L2 from the objective lens system 4 to the imaging means 5 can be freely adjusted. It is also possible to offset the position of the objective lens system 4 or the position of the image pickup element 5 and pick up a blurred image of the photomask by the image pickup means 5. By evaluating the blurred image, it is possible to determine the performance of the gray tone mask and the presence or absence of defects.

  In the inspection apparatus according to the present invention, not only a semi-transparent portion having a fine pattern below the resolution limit but also a semi-transparent film (the exposure light shielding rate is, for example, the transmissivity of the translucent portion). In contrast, a gray-tone mask having a semi-transparent portion formed by a film of 10% to 60%, more preferably 40% to 60% can also be inspected.

  For example, as shown in FIG. 13, the peak value of the light intensity of the semi-translucent portion in the captured image data is Ig, the light intensity of the sufficiently wide light-transmitting portion is Iw, and the light intensity of the light-shielding portion is Ib. Then, the transmission ratio of the semi-translucent portion to the translucent portion can be expressed as Ig / (Iw−Ib), and this can be used as an evaluation item of the photomask. With this evaluation item, it is possible to evaluate whether or not the photomask has a transmittance in a predetermined range (that is, the resist film thickness of the resist pattern formed during actual exposure is a predetermined film thickness). .

Further, when the light intensity that gives a predetermined width dimension of the semi-translucent portion (for example, the channel portion) is Ig ′, the pattern is obtained by comparing these parameters using three of Tg as follows. Can be evaluated.
Ig / (Iw−Ib) = Tg
Ig ′ / (Iw−Ib) = Tg ′ (minimum value of transmittance of channel portion)
(Tg−Tg ′) / 2 = Tgc (median value of transmittance in the channel)
| Tg−Tg ′ | = Tgd (change in channel transmittance, range)

  That is, in the above evaluation, the transmitted light intensity of the semi-transparent part, the translucent part, and the light-shielding part is obtained from the transmitted light intensity distribution data of the gray-tone mask obtained from the captured image, and from these numerical values, The transmissivity of the translucent film part (here, transmissivity means the transmissivity of the semi-translucent part relative to the difference in the transmissivity of the light-shielding part and translucent part) or the maximum value of the translucent part The mask can be evaluated by obtaining the minimum value of the transmittance, or obtaining the median value of the transmittance of the semi-translucent portion, or obtaining the range of the transmittance of the semi-transmissive portion.

  In addition, by using information obtained from the light intensity distribution, it is possible to simulate and evaluate a resist pattern formed when exposure is actually performed in an exposure apparatus using a photomask.

  As described above, in the inspection apparatus according to the present invention, a captured image having a resolution state similar to the exposure condition by an actual exposure apparatus can be obtained. Can be appropriately evaluated under the conditions. In this case, in addition to the inspection of whether or not the predetermined range of transmittance required for the semi-translucent portion is satisfied under conditions that reflect actual exposure conditions, the captured image is the same as described above. When the image quality is obtained, the sharpness of the boundary portion between the channel portion and the source / drain portions can be evaluated to predict the three-dimensional shape of the photoresist after exposure.

  Furthermore, in the inspection apparatus according to the present invention, not only the inspection and evaluation of the manufactured photomask as described above, but also the determination of whether the defect needs to be corrected or the defect correction as shown in FIG. It can also be applied to the inspection of whether the photomask correction effect is sufficient, and is extremely useful. Even if there are black defects on the photomask 3 as shown in FIG. 14A or white defects as shown in FIG. Is sufficiently small, the influence does not appear in the exposed state due to the resolution of the exposure machine. In this inspection apparatus, when the defect is sufficiently small in the imaging data obtained by the imaging means 5, it can be determined that the intensity change hardly appears and no correction is required.

  In addition, in this inspection apparatus, when a white defect is corrected by partially depositing a fine pattern having a shape different from the fine pattern in the semi-transparent portion including the fine pattern, or the defect is removed. Whether or not the correction result is sufficient when a black defect or white defect is corrected by partially depositing a fine pattern having a shape different from the original fine pattern after part of the pattern is removed Can be suitably performed.

  When the defect is corrected by additionally forming a film on the white defect part, or when the defect is corrected by peeling a part of the black defect and re-depositing the film, the material of the re-deposition is the original film. May differ from material. In addition, with respect to black defects, defect correction may be performed by removing a part of the formed film or reducing the film thickness of the film. In any of these cases, according to the inspection apparatus according to the present invention, whether the result of defect correction has a sufficient light-shielding effect or an effect as a semi-translucent part under the exposure conditions by the actual exposure apparatus. It can be inspected.

[Method of manufacturing photomask for manufacturing liquid crystal device]
In manufacturing a photomask for manufacturing a liquid crystal device, defects are sufficiently and sufficiently corrected by adopting a process including an inspection process by the above-described photomask inspection method according to the present invention in a generally known manufacturing process. A good photomask for manufacturing a liquid crystal device can be manufactured quickly.

[Pattern transfer method]
By using the photomask for manufacturing a liquid crystal device manufactured by the above-described method for manufacturing a photomask for manufacturing a liquid crystal device, a predetermined pattern is satisfactorily applied to the transfer object by exposing light of a predetermined wavelength with an exposure device. Can be transferred.

It is a side view which shows the structure of the inspection apparatus of the photomask which concerns on this invention. It is a side view which shows the positional relationship of the illumination optical system and objective lens system in the inspection apparatus of the said photomask. It is a perspective view which shows the positional relationship of the illumination optical system and objective lens system in the inspection apparatus of the said photomask. It is a front view which shows the relationship between the illumination range by the illumination optical system in the said photomask inspection apparatus, and the imaging range by an objective lens system. It is a graph which shows the relationship between the light intensity distribution in the illumination range by the illumination optical system in the said photomask inspection apparatus, and the imaging range by an objective lens system. It is the graph which digitized the imaging data obtained in the inspection apparatus of the photomask. It is a flowchart which shows the procedure of the inspection method of the photomask implemented in the said inspection apparatus of a photomask. It is sectional drawing which shows the manufacturing process (first half) of the TFT substrate using a gray tone mask. It is sectional drawing which shows the manufacturing process (latter half) of the TFT substrate using a gray tone mask. It is a front view which shows the structure of a gray tone mask. It is a figure which shows the state of the semi-translucent part in the imaging data obtained in the inspection apparatus of the said photomask. It is a side view which shows the positional relationship of the photomask in an inspection apparatus of the said photomask, an objective lens system, and an imaging means. It is a graph for quantifying the imaging data obtained in the photomask inspection apparatus and explaining the transmittance of the semi-translucent portion. It is a figure which shows the relationship between the size of a defect, and a transfer image in the imaging data obtained in the inspection apparatus of the photomask.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Illumination optical system 3 Photomask 4 Objective lens system 5 Imaging means

Claims (19)

A photomask inspection apparatus used for inspection of a photomask for manufacturing a flat panel display device,
The photomask is a subject, held as the main plane of the photomask is substantially vertical, and the mask holding device,
A light source that emits a light beam of a predetermined wavelength;
An illumination optical system that guides the light flux from the light source and irradiates the photomask held by the mask holding means;
An objective lens system that is irradiated onto the photomask and is incident on the light flux that has passed through the photomask;
An imaging means for receiving a light beam that has passed through the objective lens system and capturing an image of the photomask;
Support means for supporting each of the illumination optical system, the objective lens system, and the imaging means;
Moving operation means for moving the respective supporting means;
Control means for controlling the movement operation means,
The control means controls the movement operation means to move the illumination optical system, the objective lens system, and the imaging means in a plane parallel to the main plane of the photomask held by the mask holding means. And positioned at a predetermined position with these optical axes aligned, and
The objective lens system and the imaging means, the inspection apparatus of the photomask, characterized in that the optical axis is adjustable in position.   The objective lens system and the illumination optical system each have a variable numerical aperture, and the control means sets the numerical aperture of the objective lens system or the numerical aperture of the illumination optical system to a predetermined value. 2. The photomask inspection apparatus according to claim 1, wherein a ratio of a numerical aperture of the illumination optical system to a numerical aperture of the objective lens system is controlled to a predetermined value.   3. A calculation unit that performs calculation using light intensity distribution data of transmitted light in a predetermined region of the photomask based on an image obtained by the imaging unit. The inspection apparatus of the photomask as described.   The said mask holding means hold | maintains this photomask as an angle which inclined the main plane of the said photomask from perpendicular | vertical, and within 10 degree | times from perpendicular | vertical, The Claim 1 Item 3. A photomask inspection apparatus according to Item 2. The light beam emitted from the light source and passed through the illumination optical system includes at least one of g-line, h-line, and i-line, or includes a light beam obtained by mixing any two or more of these. inspection system of the photomask according to any one of claims 1 to 4, characterized. The illumination optical system, the range for irradiating the light beam on the photomask inspection apparatus of the photomask according to any one of claims 1 to 5, characterized in that wider than the imaging visual field of the imaging means . The illumination optical system includes a field stop, and the field stop irradiates the photomask with a light beam, and the diameter of the portion where the light quantity distribution is within 5% on the photomask is the image of the imaging unit. inspection system of the photomask according to any one of claims 1 to 6, characterized in that larger than 30% relative to the diameter of the field of view. The illumination optical system, or, according to any one of claims 1 to 7, characterized in that it comprises an angle adjustment mechanism for performing at least one of fine adjustment of the optical axis of the objective lens system and said image pickup means Photomask inspection equipment. The photomask inspection apparatus according to any one of claims 1 to 8 , wherein the objective lens system and the illumination optical system include a diaphragm mechanism that makes a numerical aperture variable. A photomask inspection method used for inspection of a photomask for manufacturing a flat panel display device,
Holding a photomask in which a film having a predetermined pattern is formed on a transparent substrate so that the main plane of the photomask is substantially vertical ;
A light beam from a light source that emits a light beam having a predetermined wavelength is irradiated onto the photomask through an illumination optical system, and the light beam that has passed through the photomask is received by an imaging unit through an objective lens system, and an image of the photomask is received. A photomask inspection method for inspecting the photomask by imaging
The illumination optical system, the objective lens system, and the imaging unit are moved in a plane parallel to the main plane of the photomask held by the mask holding unit, and the optical axes coincide with each other to a predetermined position. is positioned further photo of the objective lens system and the image pickup means, and position adjustment to a predetermined relative position in the optical axis direction, characterized in that it captures an image of the photomask by the image pickup means Mask inspection method. Imaging of the image of the photomask by the imaging means grasps in advance the exposure conditions to be applied when using the photomask, the spectral characteristics determined based on the exposure conditions, the numerical aperture of the objective lens system, and the The photomask inspection method according to claim 10, wherein the inspection is performed using a ratio of a numerical aperture of an illumination optical system to a numerical aperture of the objective lens system. The photomask inspection method according to claim 10 or 11 , wherein the photomask is held at an angle of 10 degrees or less from the vertical with respect to a main plane of the photomask. As the light beam to be irradiated to the photomask, at least, g-line, h-line, or include any of i lines, or claim 10, characterized by using a light beam obtained by mixing arbitrary two or more of these The photomask inspection method according to claim 12 . As a light beam to be applied to the photomask, a wavelength distribution of illumination light used in an exposure apparatus that performs exposure using the photomask is previously grasped, and a light beam having a wavelength distribution determined based on the wavelength distribution inspection method of a photomask according to any one of claims 10 to 13, characterized in that use. The illumination optical system or the objective lens system and the photo mask according to any one of claims 10 to 14 characterized by having a step of performing at least one of fine adjustment of the optical axis of said image pickup means Inspection method. The photomask has a pattern including a light-shielding part and a light-transmitting part formed on a transparent substrate, and obtains intensity distribution data of transmitted light in a predetermined area of the photomask from the obtained captured image. inspection method of a photomask according to any one of claims 10 to 15, characterized. The photomask has a white defect or a black defect in the light-shielding part or the light-transmitting part, obtains an imaged image of the defective part, or light intensity distribution data of the transmitted light of the defective part, 17. The photomask inspection method according to claim 16, wherein whether or not the photomask needs to be corrected is determined based on the data. Method of manufacturing a liquid crystal device for manufacturing a photomask, characterized by comprising a inspection process by the inspection method of a photomask according to any one of claims 10 to 17. 19. A photomask for manufacturing a liquid crystal device manufactured by the method for manufacturing a photomask for manufacturing a liquid crystal device according to claim 18, wherein a light having a predetermined wavelength is exposed by an exposure device, and the pattern is transferred to a transfer target. Pattern transfer method.