JP2008298932A - Method for inspecting photomask, method for manufacturing photomask, method for manufacturing electronic component, and test mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To successfuly carry out condition matching with an exposure device for actual exposure in an inspection method for a photomask in which a photomask as an inspection object is irradiated with a beam at a predetermined wavelength and the beam passing through the photomask is picked up by an imaging means to obtain intensity data of the light. <P>SOLUTION: A test mask is used for exposure and development to obtain a test resist pattern, which is measured to obtain a real exposure test pattern data. The test mask is irradiated with light under predetermined optical conditions to obtain a light transmission pattern by an imaging means, and a light transmission test pattern data is obtained based on the light transmission pattern. The real exposure test pattern data is compared with the light transmission test pattern data. Optical conditions are set based on the comparison results; a photomask as an inspection object is irradiated with light to obtain a light transmission pattern; and the photomask is inspected based on the obtained pattern. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photomask inspection method for inspecting the performance of a photomask used for manufacturing an electronic component, a photomask manufacturing method including an inspection step by this inspection method, and a photomask obtained by this manufacturing method The present invention relates to a method for manufacturing an electronic component using a photomask and a test mask that can be used for the method for inspecting the photomask.

  In particular, as an electronic component, a photomask for manufacturing a display device represented by a flat panel display (FPD) device, in particular, for manufacturing a liquid crystal display device, for example, for manufacturing a thin film transistor (TFT), a color filter (CF) The present invention relates to an inspection method used for manufacturing a photomask useful for manufacturing.

  Conventionally, for inspection of the performance of a photomask, Patent Document 1 discloses an apparatus for inspecting a defect of a photomask by detecting an intensity distribution of transmitted illumination light of an exposure photomask to be inspected by an image sensor (CCD). Is described. 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. This inspection apparatus includes a control unit that causes an image pickup element to shift an image from a focal position. This inspection apparatus is said to have an effect that the photomask can be inspected and evaluated including the influence of defocus during actual exposure.

  Further, 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

  By the way, when inspecting a photomask using the inspection apparatus as described above, if the conditions at the time of imaging in the inspection apparatus to be used are not consistent with the conditions at the time of actual exposure using the photomask, It is difficult to correctly evaluate the test results.

  Further, for example, when a reduction projection type exposure apparatus used for IC manufacturing is used, the light source used in the exposure apparatus is a single wavelength light source. Therefore, the spectral characteristics of the light source and the spectral sensitivity characteristics of the resist film are used. In addition, factors such as the spectral sensitivity characteristics of the imaging means do not matter. However, in the manufacturing process of various electronic components, since exposure conditions influenced by the spectral characteristics of the light source, the resist film, or the spectral sensitivity characteristics of the developing means are applied, depending on the conventional inspection apparatus, Accurate inspection cannot be performed.

  By the way, the inventors of the present invention first irradiate a photomask to be inspected with a light beam having a predetermined wavelength, and image the light beam that has passed through the photomask with an imaging means to obtain light intensity data. In this case, a light beam that includes at least one of g-line, h-line, and i-line, or a light beam that is a mixture of any two or more of these is used, and this light beam is wavelength-selected. It has been proposed to irradiate a photomask through a filter and to inspect an inspection apparatus used therefor.

  In this inspection method, a photomask can be inspected using a light source having spectral characteristics similar to those of an exposure apparatus that actually performs exposure using a photomask, and the light transmission amount and resolution at the time of actual exposure are limited to some extent. It can be reproduced or approximated correctly.

  Therefore, in this inspection method, the quality of the resist pattern formed by actual exposure using a photomask or the pattern of the processed layer obtained by etching the processed layer using this resist pattern as a mask is determined. Predictions can be made without exposure and development. In addition, this inspection method can not only determine the quality of the photomask but also know to some extent knowledge such as whether the photomask needs to be corrected, whether it can be corrected, and how to correct it.

  However, in this inspection method, it may be difficult to completely reflect the exposure conditions of the exposure apparatus used for actual exposure, that is, the spectral characteristics and resolution of the light source. In addition, factors that are caused by other than the exposure device, such as the spectral sensitivity of the resist material forming the resist film and the spectral sensitivity characteristics of the imaging means (CCD, etc.) used to acquire transmitted light data, are more difficult to match. is there.

  In view of this, the present invention provides a photomask inspection method for irradiating a photomask to be inspected with a light beam having a predetermined wavelength and imaging the light beam that has passed through the photomask with an imaging means to obtain light intensity data. Provides a photomask inspection method that can be well matched with the exposure apparatus that performs the inspection, or can quantitatively grasp the correlation with the actual exposure conditions and other conditions. Provided is a photomask manufacturing method including an inspection step by the method, an electronic component manufacturing method using the photomask obtained by the manufacturing method, and a test mask used for the photomask inspection method are provided. For the purpose.

  In order to solve the above-mentioned problems and achieve the above-mentioned object, the present inventors, as a result of intensive studies, have found that between an inspection apparatus (simulator) used in execution of the above-described inspection method and an exposure apparatus that performs actual exposure. It has been found that it is useful to use a test mask to provide knowledge that enables the inspection apparatus to set conditions suitable for inspection.

  That is, the photomask inspection method according to the present invention has any one of the following configurations.

[Configuration 1]
Exposure of exposure light using a photomask to the resist film formed on the layer to be etched is performed with a predetermined pattern to make this resist film a resist pattern that serves as a mask in the etching process. A method of inspecting a photomask used for performing a test resist pattern, wherein a test resist film on which a predetermined test pattern is formed is exposed to a test resist film to obtain a developed test resist pattern, and a test resist Measuring a test layer pattern obtained by etching a pattern or a test layer using the test resist pattern as a mask to obtain actual exposure test pattern data; The light transmission pattern of the test mask can be obtained by the imaging means by performing light irradiation under conditions A step of obtaining light transmission test pattern data based on the transmitted light transmission pattern, a step of comparing actual exposure test pattern data and light transmission test pattern data, and a predetermined optical condition for a photomask to be inspected And a step of obtaining a light transmission pattern of the photomask to be inspected by an imaging means by irradiating light under the same or different conditions, and a photomask to be inspected based on a comparison result obtained in the comparison step It is characterized by performing evaluation.

  Here, the layer to be processed is a layer having a desired functionality of the transfer target, and may be a single layer or a stacked layer. This layer to be processed is designed according to the intended use of the transfer target.

[Configuration 2]
In the photomask inspection method having Configuration 1, the optical condition applied to the acquisition of the light transmission pattern of the photomask to be inspected is set based on the comparison result obtained in the comparison step It is.

[Configuration 3]
In the photomask inspection method having Configuration 1 or Configuration 2, the test resist pattern has a portion where the thickness of the resist changes stepwise or continuously. .

[Configuration 4]
In the photomask inspection method having any one of Configurations 1 to 3, when acquiring the light transmission pattern of the test mask by the imaging unit, a plurality of conditions are set as predetermined optical conditions, and a plurality of times are obtained. It is characterized by acquiring.

[Configuration 5]
In the photomask inspection method having any one of Configurations 2 to 4, after setting the optical conditions based on the comparison result, the test mask is again irradiated with light by this setting, and the light transmission pattern is obtained by the imaging unit. The method includes the step of obtaining the light transmission test pattern data to obtain the comparison result, and again comparing with the actual exposure test pattern data to obtain a comparison result.

[Configuration 6]
In the photomask inspection method having any one of Configurations 1 to 5, the optical conditions are an objective lens system having a numerical aperture of an objective lens system used for acquiring a light transmission pattern and a numerical aperture of an illumination optical system. It includes at least one of a ratio to the numerical aperture, a spectral characteristic of irradiation light, and a focus amount.

[Configuration 7]
In the photomask inspection method having any one of Configurations 1 to 5, the resist material forming the test resist pattern is the same material as the resist material forming the resist film exposed using the photomask to be inspected It is characterized by being.

[Configuration 8]
In the photomask inspection method having any one of Configurations 1 to 7, the correlation between the actual exposure test pattern data and the light transmission test pattern is grasped based on the comparison result obtained in the comparison step. The photomask to be inspected is evaluated based on this correlation.

[Configuration 9]
In the photomask inspection method having any one of Configurations 1 to 8, the photomask to be inspected includes a transmission portion that transmits exposure light, a light-shielding portion that blocks exposure light, and a part of the exposure light. And a gray tone portion that is reduced and transmitted.

[Configuration 10]
In the photomask inspection method according to any one of Configurations 1 to 9, a test pattern including a portion in which a plurality of unit patterns are arranged is formed on the test mask. The pattern shape is sequentially changed based on a rule.

[Configuration 11]
In the photomask inspection method according to any one of Configurations 1 to 9, a test pattern including a portion in which a plurality of unit patterns are arranged is formed on the test mask. It has a portion whose pattern shape is sequentially changed based on a rule.

[Configuration 12]
In the photomask inspection method having the configuration 10 or the configuration 11, the sequential change of the pattern shape based on a certain rule is a change of the line width.

[Configuration 13]
In the photomask inspection method having the configuration 10 or the configuration 11, the sequential change in the pattern shape based on a certain rule is a change in the effective transmittance with respect to the exposure light.

  The photomask manufacturing method according to the present invention has the following configuration.

[Configuration 14]
An inspection process for performing a photomask inspection method having any one of Configurations 1 to 13 is provided.

  An electronic component manufacturing method according to the present invention has the following configuration.

[Configuration 15]
Using the photomask manufactured by the photomask manufacturing method having the structure 14, the method includes exposing the resist film formed on the processing layer for manufacturing the electronic component. .

  The test mask according to the present invention has the following configuration.

[Configuration 16]
A resist film formed on a layer to be etched is exposed using a photomask, and a predetermined pattern is exposed to make this resist film a resist pattern that serves as a mask in the etching process. A test mask used for inspecting a photomask used in the test, comprising a transmission part that transmits exposure light, a light shielding part that blocks exposure light, and a gray tone part that reduces and transmits part of the exposure light In the test mask in which the pattern is formed, the test pattern includes a portion in which a plurality of unit patterns whose pattern shapes are sequentially changed based on a certain rule are arranged, and the area of the gray tone portion in each unit pattern is constant. It is characterized by being different based on the rules.

  Such a test mask is useful for approximating and evaluating the shape of a resist pattern to be formed with respect to the difference in the width of a channel portion in a gray-tone mask for manufacturing a thin film transistor.

[Configuration 17]
A resist film formed on a layer to be etched is exposed using a photomask, and a predetermined pattern is exposed to make this resist film a resist pattern that serves as a mask in the etching process. A test mask used for inspecting a photomask used in the test, comprising a transmission part that transmits exposure light, a light shielding part that blocks exposure light, and a gray tone part that reduces and transmits part of the exposure light In the test mask in which the pattern is formed, the test pattern includes a portion in which a plurality of unit patterns whose pattern shapes are sequentially changed based on a certain rule are arranged, and a predetermined exposure condition of the gray tone portion in each unit pattern The effective transmittance in each is different based on certain rules. .

  Here, the effective transmittance is a gray tone having a transmittance (for example, 40 to 60%) reduced by a predetermined amount when the exposure amount transmittance of a light-transmitting portion having a sufficiently large area is defined as 100%. In a gray-tone mask having a portion, when the gray-tone mask is exposed by an exposure device, the effective exposure light transmittance of the gray-tone portion varies depending on the pattern area, the resolution of the optical system used in the exposure device, and the like. It is derived from and defined. That is, under the exposure conditions of the gray tone mask, when the transmittance of the light transmitting portion with respect to the exposure light is 100% and the transmittance of the light shielding portion is 0%, the transmittance of the transmitted light that is actually transmitted through the gray tone portion is Say. For example, a photomask having a gray tone portion in which a translucent film having a transmitted light amount smaller than 100% (for example, 20 to 80%) is formed in the gray tone portion (hereinafter referred to as “semi-transparent film type gray tone mask”). )), The light transmittance of the semi-transparent film portion adjacent to the portion where the light-shielding film is formed is blurred without being completely resolved at the resolution of the exposure apparatus ( Therefore, it is a transmittance including that it is lower than a semi-transparent film portion having an infinite width where the same film is formed.

  That is, when actually using a semi-transparent film type gray tone mask, the shape of the resist pattern formed as the gray tone portion is determined not by the transmissivity as the semi-transparent film but under the exposure conditions. This is the transmittance in a blurred state, and this is called effective transmittance. The effective transmittance is a transmittance resulting from the influence of the resolution of the exposure apparatus and the shape of the pattern in addition to the transmittance of the film itself as described above. The effective transmittance decreases as the semi-transparent film forming portion becomes minute and the influence of the adjacent light shielding film increases.

  Similarly, a photomask having a gray tone portion that reduces the amount of transmitted light by having a light-shielding or semi-transparent fine pattern below the resolution limit under exposure conditions (hereinafter referred to as “fine pattern type gray”). Also in “tone mask”, the transmittance under actual exposure conditions reflecting the resolution of the exposure apparatus and the pattern shape can be treated as the effective transmittance.

[Configuration 18]
In the test mask having the configuration 16 or the configuration 17, the test pattern has a gray tone portion adjacent to two or more light shielding portions and sandwiched between the light shielding portions.

[Configuration 19]
In the test mask having the configuration 19, a plurality of light shielding portions are characterized in that the interval between the two light shielding portions changes stepwise because the line widths differ stepwise. .

  Such a test mask is useful for approximating and evaluating the shape of a resist pattern to be formed with respect to a change in the width of a channel portion in a gray-tone mask for manufacturing a thin film transistor.

[Configuration 20]
In the test mask having any one of Configurations 16 to 19, the test pattern has a gray tone portion having a pattern with a line width less than or equal to a resolution limit under a predetermined optical condition at the time of exposure. Is.

  The evaluation of such a gray-tone pattern is very important in evaluating the resist pattern shape for producing a channel part adjacent to and sandwiched between a source and a drain part in a photomask for manufacturing a thin film transistor. Useful.

[Configuration 21]
In the test mask having any one of Configurations 16 to 19, the unit pattern has a gray tone portion in which a semi-transparent film that transmits the exposure light with a predetermined amount reduced is formed. It is.

  In the photomask inspection method according to the present invention having Configuration 1, using a test mask on which a predetermined test pattern is formed, exposing the test resist film to obtain a developed test resist pattern; A test resist pattern, or a step of measuring a test target layer pattern obtained by etching a target layer using the test resist pattern as a mask to obtain actual exposure test pattern data; A step of obtaining light transmission test pattern data based on the light transmission pattern obtained by irradiating light under the optical conditions of the above and obtaining the light transmission pattern of the test mask by the imaging means, and actual exposure test pattern data and light transmission test A process for comparing pattern data and a predetermined optical for the photomask to be inspected A step of obtaining light transmission patterns of the photomask to be inspected by the imaging means by irradiating light under the same or different conditions, and a photo to be inspected based on the comparison result obtained in the comparison Since the mask is evaluated, it is possible to satisfactorily match the conditions with the exposure apparatus that performs actual exposure.

  The present invention is particularly effective when the photomask to be inspected is a display device manufacturing photomask. The photomask for manufacturing a display device is a photomask for manufacturing a display device typified by a flat panel display device among the photomasks for manufacturing an electronic component. For example, a liquid crystal display, a plasma display panel, an electroluminescence manufacturing photomask There is no limitation on the application. In particular, the present invention has a remarkable effect for a photomask for manufacturing a liquid crystal display device, for example, a thin film transistor (TFT) or a color filter (CF).

  In the photomask inspection method according to the present invention having the configuration 2, the optical condition applied to the acquisition of the light transmission pattern of the photomask to be inspected is set based on the comparison result obtained in the comparison step. Thus, it is possible to satisfactorily match the conditions with the exposure apparatus that performs the actual exposure.

  In the photomask inspection method according to the present invention having Configuration 3, the test resist pattern has a portion in which the resist thickness changes stepwise or continuously. And a gray tone portion that reduces the amount of exposure light used when using a photomask by a predetermined amount, and the film thickness is stepwise or continuous on the transfer target. In addition, it is possible to satisfactorily inspect a photomask for forming different resist patterns.

  However, the photomask to be inspected in the present invention may be a binary mask or a gray tone mask. In particular, the effect of the present invention is remarkable, having a light-shielding portion, a light-transmitting portion, and a gray tone portion that reduces the amount of exposure light transmitted by a predetermined amount, and the film thickness is stepwise on the transfer object, or This is effective for inspecting a gray-tone mask for forming different resist patterns continuously. Further, it may be a multi-tone mask having a plurality of gray-tone portions with exposure light transmittance and forming a plurality of steps in the resist pattern.

  The gray tone mask is a transparent part in which a transparent substrate is exposed, a light shielding part in which a light shielding film for shielding exposure light is formed on the transparent substrate, a light shielding film or a semi-transparent film on the transparent substrate. And a gray tone portion that transmits a predetermined amount of light by reducing the amount of transmitted light when the light transmittance is 100%. As such a gray tone mask, the present invention can be applied to either a fine pattern type gray tone mask or a semi-transparent film type gray tone.

  In the photomask inspection method according to the present invention having configuration 4, when the light transmission pattern of the test mask is acquired by the imaging means, a plurality of conditions are set as predetermined optical conditions, and acquired multiple times. Therefore, more accurate condition setting can be performed.

  In the photomask inspection method according to the present invention having the configuration 5, after setting the optical conditions based on the comparison result, the test mask is again irradiated with light by this setting, and the light transmission pattern is obtained by the imaging means. Thus, a process of obtaining light transmission test pattern data and comparing it with actual exposure test pattern data again to obtain a comparison result is included, so that more accurate condition setting can be performed.

  In the photomask inspection method according to the present invention having the configuration 6, the optical conditions are an objective lens having a numerical aperture (NA) of an objective lens system used for acquiring a light transmission pattern, and a numerical aperture of an illumination optical system. Since it includes at least one of the ratio to the numerical aperture of the system (sigma value (σ: coherence)), the spectral characteristics of the irradiation light, and the defocus amount, the condition matching with the exposure apparatus that performs the actual exposure should be performed well. Can do.

  In the photomask inspection method according to the present invention having configuration 7, the resist material forming the test resist pattern is the same material as the resist material forming the resist film exposed using the photomask to be inspected. Therefore, it is possible to satisfactorily match the conditions with the exposure apparatus that performs actual exposure.

  In the photomask inspection method according to the present invention having configuration 8, based on the comparison result obtained in the comparison step, the correlation between the actual exposure test pattern data and the light transmission test pattern is grasped, and this Since the photomask to be inspected is evaluated based on the correlation, good evaluation can be performed based on the correlation between the exposure apparatus that performs actual exposure and the inspection apparatus. Further, the influence on the pattern formation by the resist pattern formation condition and the processing layer formation condition other than the conditions by the exposure apparatus can be grasped as a correlation with the light transmission test pattern.

  In the photomask inspection method according to the present invention having the configuration 9, the photomask to be inspected reduces a transmission part that transmits exposure light, a light shielding part that blocks exposure light, and a part of the exposure light. Therefore, the optical condition of the gray tone mask can be set satisfactorily.

  In the photomask inspection method according to the present invention having configuration 10, a test pattern including a portion in which a plurality of unit patterns are arranged is formed on the test mask, and the plurality of unit patterns conform to a certain rule. Since the pattern shape is sequentially changed based on this, the optical conditions can be set satisfactorily.

  In the photomask inspection method according to the present invention having the structure 11, a test pattern including a portion in which a plurality of unit patterns are arranged is formed on the test mask, and the plurality of unit patterns conform to a certain rule. Since the pattern shape is sequentially changed based on this, the optical conditions can be set satisfactorily.

  In the photomask inspection method according to the present invention having the structure 12, since the sequential change of the pattern shape based on a certain rule is a change of the line width, the optical condition is set according to the change of the line width of the pattern. It can be performed.

  In the photomask inspection method according to the present invention having the configuration 13, since the sequential change of the pattern shape based on a certain rule is a change of the effective transmittance with respect to the exposure light, the optical condition according to the change of the transmittance Can be set.

    Since the photomask manufacturing method according to the present invention having the configuration 14 includes an inspection process for performing the photomask inspection method having any one of the configurations 1 to 13, the conditions for the exposure apparatus that performs the actual exposure are provided. A good photomask that has undergone a matching inspection process can be manufactured.

  In the manufacturing method of the electronic component according to the present invention having the configuration 15, the resist film formed on the processing layer for manufacturing the electronic component using the photomask manufactured by the photomask manufacturing method having the configuration 14. Therefore, a good electronic component can be manufactured using a good photomask.

  In the photomask according to the present invention having the configuration 16, the test pattern includes a transmissive portion that transmits the exposure light, a light shielding portion that blocks the exposure light, and a gray tone portion that transmits the exposure light while reducing a part of the exposure light. In the test mask formed, the test pattern includes a portion in which a plurality of unit patterns whose pattern shapes are sequentially changed based on a certain rule are arranged, and the area of the gray tone portion in each unit pattern is a certain rule Therefore, in the inspection method according to the present invention, the optical conditions can be set satisfactorily.

  Such a test mask is useful for approximating and evaluating the shape of a resist pattern to be formed with respect to the difference in the width of a channel portion in a gray-tone mask for manufacturing a thin film transistor.

  In the photomask according to the present invention having the structure 17, the test pattern includes a transmission part that transmits the exposure light, a light-shielding part that blocks the exposure light, and a gray tone part that reduces a part of the exposure light and transmits the light. In the test mask formed, the test pattern includes a portion in which a plurality of unit patterns whose pattern shapes are sequentially changed based on a certain rule are arranged, and the gray tone portion in each unit pattern is subjected to a predetermined exposure condition. Since the effective transmittance is different based on a certain rule, the optical conditions can be set satisfactorily in the inspection method according to the present invention.

  In the photomask according to the present invention having the structure 18, since the test pattern has a gray tone portion adjacent to two or more light-shielding portions and sandwiched between these light-shielding portions, in the inspection method according to the present invention, the optical condition Can be set satisfactorily.

  In the photomask according to the present invention having the structure 19, since the interval between the two light shielding portions changes stepwise because the line widths of the plurality of light shielding portions change stepwise, the book In the inspection method according to the invention, the optical conditions can be set satisfactorily.

  Such a test mask is useful for approximating and evaluating the shape of a resist pattern to be formed with respect to a change in the width of a channel portion in a gray-tone mask for manufacturing a thin film transistor.

  In the photomask according to the present invention having the structure 20, since the test pattern has a gray tone portion having a line width pattern equal to or lower than the resolution limit under a predetermined optical condition at the time of exposure, for the gray tone mask, The optical conditions can be set satisfactorily.

  The evaluation of such a gray-tone pattern is very important in evaluating the resist pattern shape for producing a channel part adjacent to and sandwiched between a source and a drain part in a photomask for manufacturing a thin film transistor. Useful.

  In the photomask according to the present invention having the structure 21, since the unit pattern has a gray tone portion in which a semi-transparent film that transmits the exposure light with a predetermined amount reduced is formed, the inspection method according to the present invention The optical conditions can be satisfactorily set for the gray tone mask.

  That is, the present invention provides an actual exposure in a photomask inspection method for irradiating a photomask to be inspected with a light beam having a predetermined wavelength, imaging the light beam that has passed through the photomask with an imaging means, and obtaining light intensity data. Provides a photomask inspection method that can be satisfactorily matched with an exposure apparatus that performs the above, or that can quantitatively grasp the correlation with the actual exposure conditions. Provided is a photomask manufacturing method including an inspection process, an electronic component manufacturing method using the photomask obtained by the manufacturing method, and a test mask used for 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 Method According to the Present Invention]
The method for inspecting a photomask according to the present invention involves performing exposure on an object to be transferred (glass substrate or silicon wafer) using an exposure apparatus using a photomask having a predetermined pattern formed on a transparent substrate. This is a method for inspecting a photomask by predicting an image transferred to a transfer medium by exposure in an exposure apparatus from a light intensity distribution captured by an imaging means.

  More specifically, a method of creating an exposure condition that approximates that in an exposure apparatus, and capturing and inspecting an image that approximates an image transferred to a transfer object by exposure in the exposure apparatus, or an exposure apparatus Quantitatively grasp the correlation between the resist pattern formed under the exposure conditions in and the light intensity distribution by the imaging means, and use this correlation to estimate the resist pattern formed by exposure by the photomask to be inspected ( Emulated) and inspecting methods. 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 method, based on the light intensity distribution obtained by the imaging means, the finished pattern value of the resist pattern on the transfer object or the processed layer pattern dimension processed using the resist pattern as a mask Various analyzes and evaluations can be performed including variations in the shape of the photomask due to variations in 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.

[Configuration of the inspection apparatus used in the present invention]
In this photomask inspection method, an inspection apparatus is used as shown in FIG. In this inspection apparatus, the photomask 3 to be inspected is held by the 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. The mask holding means 3a can hold the photomask 3 having a large size (for example, a main plane of 1220 mm × 1400 mm and a thickness of 13 mm) and various sizes as the photomask 3. 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.

  Here, “substantially vertical” is preferably held so that the angle from the vertical indicated by θ in FIG. 1 is within about 10 degrees, more preferably an angle of 2 degrees to 10 degrees from the vertical, more preferably It is preferable to be in a state inclined by 4 to 10 degrees from the vertical.

  In this manner, 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 provided. Can be held and fixed. Furthermore, if the photomask 3 is held completely vertical, the total weight of the photomask 3 is concentrated on the lower end portion, and the possibility that the photomask 3 is damaged increases. By using the mask holding means 3a that supports the photomask 3 at an angle, the weight of the photomask 3 can be dispersed to a plurality of support points, and damage to the photomask 3 can be prevented.

  As described above, in this inspection apparatus, the main plane of the photomask 3 is held as described above, so that an increase in the installation area of the inspection apparatus can be suppressed, and particles fall on the photomask. Can be suppressed.

  And this inspection apparatus has the light source 1 which emits the light beam of a predetermined wavelength. 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.

  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 this inspection apparatus, there are provided control means and display means (not shown) that perform image processing, calculation, comparison with a predetermined threshold value, display, and the like for the captured image obtained by the imaging means 5.

  Further, in this inspection apparatus, the control means performs a predetermined calculation on the captured image obtained using the predetermined exposure light or the light intensity distribution obtained based on the captured image to obtain another exposure light. The captured image or the light intensity distribution under the condition using can be obtained. 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, the exposure in the exposure apparatus that is actually used, including the type of illumination light source used in the exposure apparatus, individual differences, and fluctuations in intensity for each wavelength due to temporal changes in illumination used in the exposure apparatus. It is possible to perform an evaluation that reproduces the conditions, and it is possible to easily obtain an optimum exposure condition that can achieve this when a desired residual film amount of the photoresist is assumed.

  In the photomask inspection method according to the present invention performed using this inspection apparatus, the illumination optical system 2, the objective lens 4 system, and the imaging means 5 sandwich the photomask 3 held with the main plane being substantially vertical. The test light is irradiated and received in a state where the optical axes of the two are coincident with each other. The illumination optical system 2, the objective lens 4 system, and the imaging means 5 are supported by a movement operation means (not shown) so as to be movable. This moving means can move 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 while matching the respective optical axes. In this inspection apparatus, by providing such a moving operation means, even when inspecting a large photomask, without moving this photomask 3 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.

  In this inspection apparatus, the objective lens system 4 and the imaging means 5 can be moved in the direction of the optical axis by the control means, and the objective lens system 4 and the imaging means 5 can be operated independently of each other. The relative distance to the photomask 3 can be changed. In this inspection apparatus, the objective lens system 4 and the imaging means 5 can be independently moved in the optical axis direction, so that imaging can be performed in a state close to an exposure apparatus that performs exposure using the photomask 3. it can. It is also possible to offset the focus of the objective lens system 4 and capture the blurred image of the photomask 3 by the imaging 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, as will be described later.

  The control means of this inspection apparatus controls the field stop and stop mechanism of the illumination optical system 2, the stop mechanism of the objective lens system 4, and the moving operation means. In the photomask inspection method using this inspection apparatus, this control means provides the numerical aperture (NA) and sigma value of the objective lens system 4 (ratio of the numerical aperture of the illumination optical system 2 to the numerical aperture of the objective lens system 4). The photomask held by the mask holding means with the optical axes of the illumination optical system 2, the objective lens system 4 and the imaging means 5 made to coincide with each other by the moving operation means in a state where is maintained at a predetermined value. The objective lens system 4 and the imaging means 5 are moved and operated independently of each other in the optical axis direction.

[Inspection Object of Photomask Inspection Method According to the Present Invention]
The photomask to be inspected in the photomask inspection method 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 application.

  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. It is possible to inspect not only the formed binary mask but also a gray tone mask having a light shielding portion, a light transmitting portion and a gray tone portion 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.

  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, graytone masks are frequently used due to manufacturing efficiency and cost advantages, and in addition, the graytone part needs to be extremely fine and precise. is there.

  The gray tone portion is formed by a semi-transparent portion (referred to as a “semi-transparent film type”) on which a semi-transparent film is formed and a fine pattern below a resolution limit under exposure conditions. Both of those (referred to as “fine pattern type”) are included. That is, the gray tone mask is a photomask having a gray tone portion in which a translucent film having a transmitted light amount smaller than 100% (for example, 40 to 60%) is formed in the gray tone portion (semi-transparent film type). A gray-tone mask) and a photomask with a gray-tone part that reduces the amount of transmitted light by having a light-shielding property that is less than the resolution limit under exposure conditions or a semi-transparent fine pattern (fine-pattern gray tone) And (mask).

[About gray tone mask]
Here, a gray-tone mask 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. In this method, the number of masks to be used is reduced by using a gray tone mask having a light shielding portion, a light transmitting portion, and a gray tone portion. 2 and 3 show an example of a manufacturing process of a TFT substrate using a gray tone mask.

  First, as shown in FIG. 2A, a gate electrode metal film 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. 2B, the positive photoresist film 207 is exposed and developed using a gray tone mask 100 having a light shielding portion 101, a light transmitting portion 102, and a gray tone portion 103. Thus, a first resist pattern 207A is formed. 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. 2C, 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. 3A, 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. 3B, the source / drain metal film 206 is etched using the second resist pattern 207B as a mask to form source / drains 206A and 206B, and then the second semiconductor film 205 is formed. Etch. Finally, as shown in FIG. 3C, the remaining second resist pattern 207B is peeled off.

  As shown in FIG. 4, 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 having a fine pattern below the resolution limit is formed under the exposure conditions of a large LCD exposure apparatus using the gray tone mask 100. 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 an exposure apparatus for a large LCD using such 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, 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 under the exposure conditions of the exposure apparatus, 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, the line width, how much the line width, the ratio of the part that transmits light and the part that is shielded, how much the overall transmittance is designed, etc. The design must be made in consideration of the above. Also in the production of gray tone masks, very difficult production techniques such as the management of the center value of the line width and the management of variations in the line width within the mask have been required.

  Therefore, conventionally, it has been proposed to form the gray tone portion with a semi-translucent 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 ( It was thought that gray tone masks could be produced simply by selecting the film material) and film thickness. Therefore, in the production of such a semi-transparent film type gray tone mask, it is only necessary to control the thickness of the semi-transparent film, and there is a view that it is relatively easy to manage. Further, when the TFT channel portion is formed by the gray tone portion of the gray tone mask, since the patterning can be easily performed by a photolithography process if it is a semi-transparent film, the shape of the TFT channel portion is also complicated. It becomes possible.

  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 gray tone portion 103 made of a pattern corresponding to the channel portion of the TFT substrate, and the periphery of these patterns. And the translucent part 102.

  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 gray-tone 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 gray tone 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 gray tone portion 103 where the resist pattern is not formed is removed by appropriate etching. As a result, the gray tone 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.

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

  In a gray tone mask, the pattern shape formed on the mask affects the resist film thickness and the resist film shape formed by exposure using the mask. For example, not only the evaluation of the planar pattern shape, but also the light transmittance of the gray tone part is within an appropriate range, and the rise of the boundary between the gray tone part and the light shielding part (sharpness or blurring condition) It is necessary to evaluate whether it is.

  In particular, in the case of a gray-tone mask having a gray-tone 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 in a non-resolved state. 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 the photomask inspection method according to the present invention, the film thickness of the photoresist is selectively changed by reducing the amount of exposure light transmitted through the gray tone portion and reducing the amount of irradiation of the photoresist in this region. The inspection of the gray tone mask which is a thing can be performed with high accuracy by approximating the actual exposure condition. Furthermore, even if there are factors that cannot be approximated, the pattern shape of the photoresist obtained by actual exposure can be predicted with high accuracy.

  In the data acquired by this inspection apparatus, if the pattern is appropriately designed and appropriately formed with respect to the optical conditions given to the apparatus (conditions substantially equal to the optical conditions of the exposure apparatus to be used), FIG. As shown, the fine pattern formed in the gray tone portion is in a non-resolved state that substantially has a single density, similar to the state that would occur during actual exposure. The density of this portion indicates the transmittance of this portion when this gray tone mask is used, and this determines the remaining film amount of the resist film formed by the gray tone portion. On the other hand, if the design is inappropriate for the optical conditions, or if the pattern is not formed in the predetermined shape and dimensions in the manufacturing process, the density of the semi-translucent part, the shape of the gray tone part, etc. Since this indicates a state different from the normal state, 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.

  Furthermore, when a captured image is obtained in the non-resolved state as described above, the sharpness of the boundary portion between the channel portion and the source and drain portions is evaluated through an appropriate calculation as necessary, and the three-dimensionality of the photoresist is evaluated. It is also possible to predict the shape.

  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 in the inspection apparatus as an inspection target, and for example, the numerical aperture and sigma value of the objective lens system 4 (the objective lens system 4 having the numerical aperture of the illumination optical system 2). The ratio of the numerical aperture to the numerical aperture) is set to a predetermined value, and the position of the objective lens system 4 is appropriately adjusted in the optical axis direction. An image is obtained. And the light intensity distribution of a mask pattern can be obtained by processing the imaged image data by a calculation means. 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.

[About test mask]
In the photomask inspection method according to the present invention, a test mask 11 is used as shown in FIG.

  This test mask 11 mediates in order to perform optical conditions with the exposure apparatus accurately and quickly in the inspection of the photomask using the above-described inspection apparatus. In addition to this, or in place of this, with respect to conditions including factors that cannot be matched with the exposure apparatus, such as the spectral sensitivity of the resist film and the spectral sensitivity characteristics of the imaging means, It mediates between the exposure apparatus or leads to a correlation between the inspection result and the resist pattern formation result by exposure. If the correlation can be grasped quantitatively, an offset parameter that cancels the correlation is calculated. Thereafter, if this parameter is reflected in the inspection result of the photomask to be inspected, an accurate exposure result can be estimated. Specifically, for example, by the inspection method of the present invention using a test mask, the basic characteristics of the exposure conditions in the inspection apparatus are matched with the exposure conditions of the exposure apparatus. Differences and differences in conditions caused by processes other than the exposure apparatus can be grasped as conversion coefficients by the inspection process using this test mask.

  In this test mask 11, as shown in FIG. 6A, for example, the same test pattern 12 is arranged in a matrix in each of the X-axis direction and the Y-axis direction on an 800 mm × 920 mm substrate. Has been. As shown in FIG. 6B, each test pattern 12 is formed having unit patterns 13 arranged in a line in the X-axis direction and the Y-axis direction. You may arrange | position another test pattern etc. to a surplus part suitably. For example, FIG. 6B shows an example in which a position reference mark is arranged at the peripheral portion and a general resolution pattern is arranged at the central portion.

  In the test pattern of the present invention, each unit pattern 13 may be the same pattern. For example, as shown in FIG. 7, it is preferable to arrange different patterns that are useful in the evaluation process described later. In this example, 21 unit patterns 13 (wedge patterns) are arranged in the X direction, and the shape of each unit pattern 13 is changed in 21 steps in the Y direction. That is, each unit pattern 13 changes based on a certain rule in the arrangement order in both the X direction and the Y direction.

  Each unit pattern 13 is formed of a light shielding film. This unit pattern 13 is formed by a light-shielding film on a light-transmitting portion sandwiched between a pair of light-shielding portions whose width changes stepwise in the Y-axis direction indicated by “au” in FIG. It is a line-and-space pattern with vertical lines. In each unit pattern 13, the pair of light shielding portions on both sides is the same in the X-axis direction indicated by “1 to 21” in FIG. The line width of the light-shielding line portion is narrowed at a constant pitch toward “1 to 21” in the X-axis direction.

  By arranging such unit patterns 13, it is possible to approximate a mask in which the transmittance of the gray tone portion sandwiched between the light shielding portions gradually increases as shown in FIG. For example, in a gray-tone mask for forming a channel portion in a thin film transistor, it can be approximated to a mode in which the light transmittance of the gray-tone portion is gradually changed.

  On the other hand, in each unit pattern 13, in the Y direction, the line widths of the light shielding portions on both sides gradually decrease from “au”. For example, in a gray-tone mask for forming a channel portion in a thin film transistor, this can be approximated to a mode in which the width of the channel portion gradually increases as shown in FIG. Here, it is preferable for the reason described later that the change pitch of the line width of the pair of light shielding portions in each unit pattern 13 is equal to the change pitch of the line width of the central light shielding line.

  On the other hand, the unit pattern 13 arranged in this way makes it possible to evaluate the influence of the transfer to the transfer target due to the variation of the line width (CD) of the mask by observing and evaluating in an oblique direction. For example, the arrangement of “a1, b2, c3...” Also changes the pattern shape with a constant rule. This rule is that the central light-shielding line becomes thin at a constant pitch, and the light-shielding part lines on both sides. The width gets thinner at a constant pitch. This can be approximated to a photomask CD variation (a line width is increased or decreased by a predetermined amount) due to various reasons such as factors in the photomask manufacturing process.

  Therefore, when the photomask inspection method according to the present invention using such a test mask is carried out, the light intensity distribution obtained by the inspection apparatus and the transferred image obtained by performing actual exposure using the same test mask It is possible to grasp the correlation with the resist pattern on the body in relation to the change of each pattern shape.

  Further, as shown in FIG. 6B, the unit patterns 13 are arranged on the test mask 11 with an angle of 90 ° in the X direction and the Y direction. This makes it possible to evaluate non-uniform factors in the resolution of the X-direction and Y-direction patterns that can occur during the manufacture of electronic components such as liquid crystal panels. For example, if there is a difference in resolution between the scanning direction of the exposure apparatus and the direction perpendicular thereto, the state of such a difference in resolution can be evaluated.

  Here, as the unit pattern 13, as shown in FIG. 7, a line-and-space pattern in which a light-shielding line made of a light-shielding film is arranged in a light-transmitting part sandwiched between a pair of light-shielding parts whose width changes stepwise. Although the test mask 11 having a pattern (wedge pattern) has been described, the test mask in the present invention is not limited to this. Different test patterns are illustrated in FIGS. The unit pattern 13 shown in FIG. 8 has a square frame-shaped light-transmitting portion and a square-frame-shaped light shielding portion formed in the light-transmitting portion. It can be performed. The unit pattern 13 shown in FIG. 9 has a regular octagonal frame-shaped light-transmitting part and a regular octagonal frame-shaped light-shielding part formed in the light-transmitting part. Can be evaluated.

  Further, as a different mode, a semi-transparent film (a purpose of reducing the transmittance by a predetermined amount with respect to the translucent part) between the pair of light-shielding parts whose width changes in a stepped manner in the test pattern of FIG. May be formed into a unit pattern. In this case, using this test mask, it is possible to evaluate a gray tone mask having a gray tone portion on which a semi-transparent film is formed. A gray-tone mask for TFT production in which a semi-transparent film is disposed in a portion corresponding to the channel portion can be approximated.

[Inspection Method for Photomask According to the Present Invention]
In the photomask inspection method according to the present invention, first, using the above-described test mask 11, exposure is performed by an exposure apparatus that is actually used for exposure of the photomask, and the pattern is transferred to the transfer target. A resist film is applied on the processed layer of the transfer object. The layer to be processed under the resist film is formed according to the use of the transfer target.

  After the exposure, the resist film formed on the transfer body is developed to form a resist pattern. The resist pattern is preferably digitized by measuring its shape with a three-dimensional shape measuring instrument.

  Note that the photomask according to the present invention may be inspected according to the shape of the resist pattern, or an etching process is performed using the resist pattern as a mask to form a pattern of the processing layer under the resist layer (processing layer pattern). ) May be measured and the layer pattern to be processed may be measured and evaluated. In that case, it is preferable to measure and digitize the layer pattern to be processed with a shape measuring instrument.

  In this way, “actual exposure test pattern data” in which the shape of a resist pattern formed by exposure and development using a test mask is digitized can be obtained.

  In the above-described exposure (actual exposure) process, the same conditions as the exposure conditions (exposure apparatus and optical conditions during exposure) applied to the photomask (actual mask) to be actually used for inspection are applied. It is preferable to do. Furthermore, it is preferable that the resist film material to be used and the development conditions of the resist film are the same as those in the case of processing the transfer object to which the pattern is transferred using the photomask to be inspected. By doing so, the evaluation result obtained by the inspection of the photomask according to the present invention can be applied to the manufacture of a product using the photomask to be inspected.

  On the other hand, this test mask is set as an inspection object in the above-described inspection apparatus, irradiated with predetermined exposure light, and the light transmission amount distribution is acquired by the imaging means. Specifically, the light beam that has passed through the test mask is captured by a CCD camera or the like, and the obtained image is digitized to obtain “light transmission test pattern data”.

  The exposure light irradiation condition applied here is preferably as close as possible to the exposure condition when an actual product is manufactured using a photomask to be inspected. For example, it is preferable to grasp in advance the wavelength characteristics of the light source of the exposure apparatus when performing exposure using a photomask to be inspected, and to use a light source having a wavelength characteristic approximate to this in the inspection machine. Furthermore, it is preferable to perform inspection by approximating the optical conditions in the exposure apparatus (optical design values such as the numerical aperture (NA) and sigma value (σ) of the objective optical system). By doing so, it is possible to form a resist pattern by a test mask under conditions approximate to a resist pattern (or a layer pattern to be processed) formed by exposure using a photomask to be inspected. This makes it easy to perform analysis by comparing and comparing “actual exposure test pattern data” and “light transmission test pattern data”.

  After obtaining the inspection results, using the "actual exposure test pattern data", the "light transmission test pattern data" and the comparison result, the irradiation conditions can be changed to bring the exposure conditions closer to the actual exposure. Is possible. That is, in order to optimize the optical conditions in the inspection apparatus and approximate the exposure conditions in actual exposure, two numerical data (“actual exposure test pattern data” and “light transmission test” are used using a test mask. Pattern data ") is obtained and compared. And this comparison result can be used as follows.

(1) Setting of optimum conditions for inspection apparatus Based on the difference between two digitized data ("actual exposure test pattern data" and "light transmission test pattern data"), the exposure conditions in the inspection apparatus (numerical aperture (NA in the inspection apparatus)) ) And sigma value (σ), etc.) can be changed (corrected), whereby the irradiation condition (for example, resolution) in the inspection apparatus can be brought close to the exposure condition in the actual exposure apparatus.

  Further, based on the difference between the two digitized data, the inspection device is changed (corrected) by changing (correcting) the spectral characteristic (characteristic that the g-line is strong or i-line is strong) used for exposure in the inspection device. The irradiation conditions in can be brought close to the actual exposure conditions.

(2) Grasping the correlation between the light transmission amount distribution by the inspection device and the resist pattern (or processed layer film pattern) by actual exposure Grasping the correlation between the two digitized data, and using the inspection device A resist pattern obtained by actual exposure can be estimated from data obtained by measurement.

  For example, it is possible to obtain a correction coefficient (offset parameter) when correcting spectral characteristics for data obtained by the inspection apparatus. Thereby, the resolution at the time of actual exposure and the light transmission amount at the time of actual exposure can be estimated. Note that the resolution is affected by the wavelength, and when a photomask having a semi-transparent film is used, the transmittance varies depending on the wavelength. Therefore, even if the spectral characteristics of the irradiation light of the inspection machine cannot be made completely the same as that of the exposure apparatus, the actual exposure result can be estimated from the inspection of the mask to be inspected if their correlation can be quantified.

  Appropriate irradiation condition setting of the inspection apparatus obtained in this way is performed for each exposure apparatus used for actual exposure or for each product, and is stored and stored by a control apparatus connected to the inspection apparatus. Can be done.

  In addition, when performing photomask pattern correction, correction data can be calculated by incorporating the correlation. For example, it is possible to perform correction that incorporates the correlation between the light transmittance obtained by the inspection apparatus and the remaining film thickness of the resist pattern obtained by actual exposure.

  In the inspection of a gray-tone mask with a fine pattern, it is also effective in estimating the remaining film thickness (also referred to as a remaining film value) of a resist pattern obtained by exposure to a gray-tone portion. What kind of resist pattern (or layer pattern to be processed) can be obtained with what residual film thickness if a fine pattern with a certain shape is used using an inspection device with appropriate irradiation conditions Can be estimated.

  It is also preferable to grasp not only the correlation between the irradiation conditions in the inspection apparatus and the resist pattern due to actual exposure, but also the tendency of both changes due to changes in conditions. Therefore, in addition to performing multiple irradiation tests by changing the irradiation conditions, it is also possible to increase the information that can be obtained in one irradiation test by arranging multiple unit patterns with different conditions on the test mask as described above. preferable.

  Here, in the photomask inspection method according to the present invention, it is preferable to perform irradiation a plurality of times while changing the exposure conditions to obtain a captured image of the test mask by each irradiation. By using the transmitted light intensity distribution data of the test mask under a plurality of different conditions for comparison with a resist pattern by actual exposure of the test mask, more information can be obtained. For example, irradiation is performed while changing the numerical aperture (NA) by a predetermined amount, or irradiation is performed while changing the numerical aperture (NA) or coherence (σ) by a predetermined amount.

  The light intensity distribution data of the transmitted light thus obtained can be stored as a database. With this database, it is possible to precisely set the conditions of the inspection apparatus when inspecting the photomask to be inspected, and it is possible to quickly reach the optimum conditions with less wasteful experiments. In other words, when analyzing the difference between the data obtained by the inspection device and the data obtained by actual exposure, the causal relationship of the difference is derived, the correlation between both is accurately grasped, the condition setting of the inspection device is changed, It can be used for simulation of a resist pattern when it is actually exposed using a photomask.

  Furthermore, the correction coefficient for the spectral characteristic of the light source of the inspection machine can be obtained from the simulation result using the test mask.

[Spectral characteristics of inspection light (1)]
By the way, as the light source 1 in this inspection apparatus, it is preferable to use a light source that emits inspection light having the same or substantially the same wavelength distribution as exposure light in an exposure apparatus that performs exposure using the photomask 3 that has undergone inspection.

  Specifically, the inspection light includes at least one of g-line (436 nm), h-line (405 nm), or i-line (365 nm) as shown in (a) of FIG. All of these wavelength components may be included, or mixed light in which any two or more of these wavelength components are mixed may be used. Usually, when exposing a large mask for manufacturing FPD, since mixed light of these wavelengths is used as exposure light, even in this inspection apparatus, when applying mixed light at a desired light intensity ratio, Preferably, it is determined based on the characteristics of the light source of the exposure apparatus used for the above. That is, the spectral characteristics of the light source of the inspection machine can be based on the characteristics of the light source of the exposure apparatus that is actually used, based on the simulation result using the test mask described above.

  The inspection light passes through a wavelength selection filter 6 such as an optical filter and is irradiated onto the photomask 3, thereby adjusting the mixing ratio of each wavelength component on the photomask 3. As the wavelength selection filter 6, as shown in FIG. 10B, a filter having a characteristic of cutting a light beam having a predetermined wavelength or less or a predetermined wavelength or more can be 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.

  Furthermore, in this inspection apparatus, as shown in (c) of FIG. 10, as a wavelength selection filter, a first filter having a characteristic of mainly transmitting only g-line emitted from the light source 1, and a light source 1 It is possible to selectively use the second filter having the characteristic of transmitting only the emitted h-line and the third filter having the characteristic of transmitting only the i-line emitted from the light source 1 selectively.

  In this case, the light intensity data dg obtained by the imaging means 5 when the first filter is used, the light intensity data dh obtained by the imaging means 5 when the second filter is used, and the third The light intensity data di obtained by the imaging means 5 when the filter is used is obtained.

  Then, the light intensity data dg, dh, and di are each given a predetermined weight and then added to thereby add a light beam in which g-line, h-line and i-line are mixed at a predetermined intensity ratio to a photomask. The light intensity data obtained when 3 is irradiated can be calculated.

  The weighting of each light intensity data dg, dh, di is such that, for example, the intensity ratio of g-line, h-line and i-line in the light beam from the light source 1 of this inspection apparatus is [1.00: 1.20: 1.30. If the intensity ratio of g-line, h-line and i-line in the exposure light from the light source of the exposure apparatus is [1.00: 0.95: 1.15], the coefficient to be multiplied by dg fg is 1.00, coefficient fh to be multiplied by dh is 0.95 / 1.20 (= 0.79), and coefficient fi to be multiplied by di is 1.15 / 1.30 (= 0.88). It becomes.

  Data obtained by adding them, that is, [fgdg + fhdh + fidi] is data indicating the light intensity distribution obtained when the exposure light is irradiated on the photomask 3 in the exposure apparatus. Note that such calculation can be performed by the control unit using the control unit as the calculation unit.

[Spectral characteristics of inspection light (2)]
Even if the inspection light emitted from the light source 1 in this inspection apparatus has a wavelength distribution different from that of the exposure light in the exposure apparatus, the exposure state in the exposure apparatus can be simulated as follows.

  In addition, by performing the operations described below, the spectral characteristics of the light source of the inspection apparatus, the spectral characteristics of the light source of the exposure apparatus, the spectral sensitivity characteristics of the resist, etc. are matched, By comparing the `` pattern data '' with the `` light transmission test pattern data '', an offset parameter at the time of inspection of the photomask can be obtained more quickly and appropriately, and the inspection of the photomask is easy, and Can be done accurately.

  In this inspection apparatus, as described above, as the wavelength selection filter, the first filter having a characteristic of mainly transmitting only g-line emitted from the light source 1 and mainly transmitting only h-line emitted from the light source 1 are transmitted. It is possible to selectively use the second filter having the characteristic to be transmitted and the third filter having the characteristic to transmit mainly only the i-line emitted from the light source 1.

  Therefore, using the test mask 11, as shown in FIG. 11, the first reference intensity data Ig obtained by the imaging means 5 when the first filter is used, and the imaging means when the second filter is used. The second reference intensity data Ih obtained by 5 and the third reference intensity data Ii obtained by the imaging means 5 when the third filter is used are obtained. Each of these reference data Ig, Ih, and Ii is a result of multiplying the spectral distribution of the light source 1, the spectral sensitivity distribution of the imaging means 5, and the spectral transmittance of each filter. Further, in this inspection apparatus, the light source 1 This is also the result of multiplication of the spectral transmittance of each optical element through which the inspection light from is transmitted.

  The spectral distribution of the light source 1, the spectral sensitivity distribution of the imaging means 5, and the spectral transmittance of each optical element are not uniform with respect to the wavelength. For this reason, as shown in FIG. 11A, the pattern imaged for a certain defect becomes a different pattern depending on the wavelength of each inspection light (g-line, h-line, i-line) used for imaging. . As shown in FIG. 11B, these patterns are recognized as patterns having different sizes when cut at a certain threshold.

  Next, first to third coefficients α, β, γ are obtained for the reference intensity data Ig, Ih, Ii that make the first to third reference intensity data Ig, Ih, Ii equal to each other. . That is, as shown in FIG. 11, the result obtained by multiplying the first reference intensity data Ig by the first coefficient α, the result obtained by multiplying the second reference intensity data Ih by the first coefficient β, Each coefficient α, β, γ is determined so that the result obtained by multiplying the reference intensity data Ii by the first coefficient γ is at the same level. Here, “equal level” means that the peak intensities of the reference intensity data Ig, Ih, Ii are equal to each other, for example.

  In this inspection apparatus, the first to third coefficients α, β, γ that make the reference intensity data Ig, Ih, Ii equal to each other are obtained in advance, and these coefficients α, β, γ are It is understood by the user who uses the inspection apparatus.

  When a photomask to be inspected is inspected, the first light intensity data Jg is obtained by the imaging means 5 using the first filter for the photomask, and the second mask is used for imaging. The second light intensity data Jh is obtained by the means 5, and the third light intensity data Ji is obtained by the imaging means 5 using the third filter.

  Next, the first light intensity data Jg is multiplied by the first coefficient α, the second light intensity data Jh is multiplied by the second coefficient β, and the third light intensity data Ji is multiplied by the third coefficient γ. As a result, the influence of the spectral distribution of the light source 1, the spectral sensitivity distribution of the image pickup means 5, and the spectral transmittance of each optical element of the inspection apparatus is corrected, and the resist as the exposure object is exposed using the photomask. Light intensity data [αJg, βJh, γJi] corresponding to the exposure state is obtained.

  As described above, such a calculation can be performed by the control unit using the control unit as the calculation unit.

  If the spectral characteristics of the exposure apparatus, that is, the spectral distribution of the light source of the exposure apparatus and the spectral transmittance of each optical element of the exposure apparatus are known, coefficients u, v, and w are determined according to these spectral characteristics. You can keep it. As the coefficients u, v, and w, for example, the h-line intensity (for example, 0.9104) and the i-line intensity (for example, 1.0746) when the g-line intensity is 1.0 are obtained. An intensity ratio (for example, 0.335: 0.305: 0.360) in which the sum of these values is 1 can be used.

  Then, by further multiplying the coefficient according to the spectral characteristics of these exposure apparatuses in correspondence with the first to third light intensity data, the exposure apparatus exposes the resist more accurately using the photomask. The light intensity data [uαJg, vβJh, wγJi] corresponding to the exposure state at the time can be obtained.

  Furthermore, when the spectral sensitivity characteristic (absorption spectrum) of the resist is known, the coefficients x, y, and z can be determined in accordance with the spectral sensitivity characteristic. As the coefficients x, y, z, for example, the amount of absorption of h-line (for example, 1.6571) and the amount of absorption of i-line (for example, 1.8812) when the amount of absorption of g-line is 1.0. And an absorption ratio (for example, 0.220: 0.365: 0.415) in which the sum of these values is 1 can be used.

  Then, by further multiplying the coefficient corresponding to the spectral characteristic in correspondence with the first to third light intensity data, exposure when the resist is exposed to the resist using the photomask by the exposure apparatus more accurately. Light intensity data [xαJg, yβJh, zγJi] (or [xuαJg, yvβJh, zwγJi]) corresponding to the state can be obtained. Such calculation can also be performed by the control means using the control means as the calculation means.

[Photomask manufacturing method]
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.

[Method of manufacturing electronic parts]
In the present invention, a photomask manufactured by the photomask inspection method according to the present invention, in particular, a photomask whose performance has been confirmed by the photomask inspection method according to the present invention, and an exposure apparatus, An electronic component can be manufactured by exposing the resist layer formed on the processed layer of the transfer target.

  This makes it possible to stably obtain desired performance for electronic components in a short time with a high yield.

It is a side view which shows the structure of the inspection apparatus used for the inspection method of the photomask which concerns on this invention. 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 gray tone part in the imaging data obtained in the said inspection apparatus. It is a top view which shows the structure of the test mask used for the inspection method of the photomask which concerns on this invention. It is a top view which shows the unit pattern in the said test mask. It is a top view which shows the other example of the unit pattern in the said test mask. It is a top view which shows the further another example of the unit pattern in the said test mask. (A) is a graph which shows the spectral characteristic of the light source in the inspection apparatus of the said photomask, (b) is a graph which shows the spectral characteristic of the wavelength selection filter used in the inspection apparatus of the said photomask, (c ) Is a graph showing another example of the spectral characteristics of the wavelength selection filter used in the photomask inspection apparatus. The photomask inspection device is multiplied by a spectral characteristic of the light source, a spectral sensitivity distribution of the image sensor of the photomask and reference intensity data obtained corresponding to each filter, and a coefficient corresponding to each reference intensity data. It is a graph which shows a state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Illumination optical system 3 Photomask 4 Objective lens system 5 Imaging means 6 Wavelength selection filter 11 Test mask 12 Test pattern 13 Unit pattern

Claims (21)

A predetermined pattern for exposing the resist film formed on the layer to be processed to be etched with exposure light using a photomask and forming the resist film as a resist pattern serving as a mask in the etching process A photomask inspection method used for performing the exposure of
Using a test mask on which a predetermined test pattern is formed, exposing the test resist film to obtain a developed test resist pattern;
Measuring the test resist pattern or the test target layer pattern obtained by etching the target layer using the test resist pattern as a mask to obtain actual exposure test pattern data;
Irradiating the test mask with light under predetermined optical conditions, obtaining a light transmission pattern of the test mask by an imaging means, and obtaining light transmission test pattern data based on the obtained light transmission pattern; ,
Comparing the actual exposure test pattern data with the light transmission test pattern data;
A step of irradiating the photomask to be inspected with light under the same or different condition as the predetermined optical condition and obtaining a light transmission pattern of the photomask to be inspected by the imaging means,
A photomask inspection method, wherein the photomask to be inspected is evaluated based on a comparison result obtained by the comparison step. The photomask inspection method according to claim 1, wherein an optical condition applied to acquisition of a light transmission pattern of the photomask to be inspected is set based on a comparison result obtained by the comparison step. . The photomask inspection method according to claim 1, wherein the test resist pattern has a portion in which the thickness of the resist changes stepwise or continuously. The light transmission pattern of the test mask is acquired by the imaging means by setting a plurality of conditions as the predetermined optical condition and acquiring the plurality of conditions over a plurality of times. The photomask inspection method according to any one of the above. After setting the optical conditions based on the comparison result, the test mask is again irradiated with light by this setting, and a light transmission pattern is obtained by an imaging means to obtain light transmission test pattern data, and the actual exposure is again performed. The method for inspecting a photomask according to claim 2, further comprising a step of performing comparison with test pattern data to obtain the comparison result. The optical conditions include the numerical aperture of the objective lens system used for obtaining the light transmission pattern, the ratio of the numerical aperture of the illumination optical system to the numerical aperture of the objective lens system, the spectral characteristics of the irradiation light, and the defocus amount. The photomask inspection method according to claim 1, comprising at least one of the following. 6. The resist material forming the test resist pattern is the same material as the resist material forming a resist film that is exposed using the photomask to be inspected. The photomask inspection method according to claim 1. Based on the comparison result obtained by the comparison step, the correlation between the actual exposure test pattern data and the light transmission test pattern is grasped, and based on this correlation, the photomask to be inspected is determined. The photomask inspection method according to claim 1, wherein the evaluation is performed. The photomask to be inspected includes a transmission part that transmits exposure light, a light-shielding part that blocks exposure light, and a gray tone part that reduces and transmits part of the exposure light. The photomask inspection method according to any one of claims 1 to 8. The test mask includes a test pattern including a portion in which a plurality of unit patterns are arranged,
The photomask inspection method according to claim 1, wherein the plurality of unit patterns are obtained by sequentially changing a pattern shape based on a certain rule. The test mask includes a test pattern including a portion in which a plurality of unit patterns are arranged,
The photomask inspection method according to any one of claims 1 to 9, wherein the plurality of unit patterns have a portion in which a pattern shape is sequentially changed based on a certain rule. . The photomask inspection method according to claim 10, wherein the sequential change of the pattern shape based on the predetermined rule is a change of a line width. The method for inspecting a photomask according to claim 10 or 11, wherein the sequential change of the pattern shape based on the predetermined rule is a change of an effective transmittance with respect to exposure light. A method for manufacturing a photomask, comprising: an inspection step for performing the method for inspecting a photomask according to claim 1. An electronic component comprising a step of exposing a resist film formed on a processing layer for manufacturing an electronic component using the photomask manufactured by the method for manufacturing a photomask according to claim 14. Manufacturing method. The resist film formed on the layer to be etched is exposed using a photomask, and a predetermined pattern is exposed to make this resist film a resist pattern that serves as a mask in the etching process. A test mask used for inspection of a photomask used for performing,
In a test mask formed with a test pattern having a transmission part that transmits exposure light, a light shielding part that blocks exposure light, and a gray tone part that reduces and transmits part of the exposure light,
The test pattern includes a portion in which a plurality of unit patterns whose pattern shapes are sequentially changed based on a certain rule are arranged,
An area of the gray tone portion in each unit pattern is different based on the certain rule. The resist film formed on the layer to be etched is exposed using a photomask, and a predetermined pattern is exposed to make this resist film a resist pattern that serves as a mask in the etching process. A test mask used for inspection of a photomask used for performing,
In a test mask formed with a test pattern having a transmission part that transmits exposure light, a light shielding part that blocks exposure light, and a gray tone part that reduces and transmits part of the exposure light,
The test pattern includes
Including a portion in which a plurality of unit patterns whose pattern shapes are sequentially changed based on a certain rule are arranged;
The test mask, wherein the effective transmittance of the gray tone portion in each unit pattern under a predetermined exposure condition is different based on the predetermined rule. The test mask according to claim 17, wherein the test pattern includes a gray tone portion adjacent to two or more light shielding portions and sandwiched between the light shielding portions. 19. The test mask according to claim 18, wherein the plurality of light shielding portions have stepwise different line widths, whereby an interval between the two light shielding portions changes stepwise. 20. The test pattern according to claim 16, wherein the test pattern has a gray tone portion having a line width pattern equal to or less than a resolution limit under a predetermined optical condition at the time of exposure. Test mask. 20. The test according to claim 16, wherein the unit pattern includes a gray tone portion in which a semi-transparent film that transmits the exposure light with a predetermined amount reduced is formed. mask.