JP2019028171A - Photomask inspection method, photomask manufacturing method, and photomask inspection apparatus - Google Patents

Abstract

A phase shift amount of a phase shift portion included in a transfer pattern of a photomask can be easily and directly measured.
A photomask inspection method for measuring a phase characteristic of a phase shift portion included in a transfer pattern of a photomask, the step of setting the photomask in an inspection apparatus equipped with a projection optical system, and a set An optical image data acquisition step for acquiring optical image data by exposing a photomask and projecting an optical image of the phase shift unit onto the imaging surface, and a phase shift amount of the phase shift unit using the acquired optical image data An optical image data acquisition step, wherein at least a part of the photomask, the projection optical system, and the imaging surface is moved in the optical axis direction, and an optical image in each of a plurality of focus states In the calculation step, a CD value is obtained from the optical image data for each of a plurality of focus states, and the phase shift amount is calculated based on the CD value of the optical image. Mel.
[Selection] Figure 2

Description

  The present invention relates to inspection of a photomask for manufacturing an electronic device, and more particularly to inspection of a photomask suitable for manufacturing a display device. In particular, the present invention relates to a method and an apparatus for measuring a phase shift amount of a photomask (phase shift mask) having a transfer pattern using a phase shift effect.

  A phase shift mask is mainly used for a photomask for manufacturing a semiconductor device because it is superior in transfer performance, particularly in depth of focus and contrast, compared to a binary mask. An inspection method for inspecting the phase shift amount of the phase shift mask pattern has been proposed.

  Patent Document 1 describes a phase inspection method for measuring a phase shift caused by a translucent phase shift film formed on an exposure mask. This phase inspection method uses a first pattern group consisting of lines / spaces formed on a light-shielding film and a second pattern group consisting of lines / spaces formed on a translucent phase shift film, to perform projection exposure. Forming an optical image of each pattern group on a measurement surface via an optical system; obtaining a plurality of the optical images by changing the measurement surface in the optical axis (Z) direction; Calculating the difference between the focal position of the first pattern group and the focal position of the second pattern group from the plurality of optical images, and the phase difference caused by the translucent phase shift film from the calculated focal position difference The process of calculating.

  Patent Document 2 describes a measurement method for simultaneously measuring the phase shift amount and transmittance of a phase shifter formed on a halftone phase shift mask using a shearing interferometer. In this measurement method, an illumination beam is projected toward a monitor pattern that is configured by a light transmission part formed on a halftone film or is formed by a halftone film formed on a light transmission part, and the shearing amount of the shearing interferometer is calculated. The first and second interference images formed by the transmitted light that has been adjusted and transmitted through the monitor pattern and the transmitted light that has transmitted through the peripheral area of the monitor pattern, and the transmitted light that has transmitted through the peripheral area of the monitor pattern are formed. Forming a laterally shifted interference image including the third interference image on the two-dimensional imaging device, and performing phase modulation for one period on the laterally shifted interference image including the first to third interference images, Obtaining phase modulation data indicating the relationship between the phase modulation amount and the luminance value for the first to third interference images, respectively, and the phases of the first and second interference images Calculating a phase shift amount between the first interference image and the second interference image using the key data and outputting the phase shift amount as a phase shift amount of the phase shifter; and phase modulation data of the first interference image And calculating the square of the ratio between the amplitude of the third interference image and the amplitude of the phase modulation data of the third interference image, and outputting the result as the transmittance of the phase shifter.

Japanese Patent No. 3431411 Japanese Patent No. 5660514

  In display devices including liquid crystal display devices (Liquid Crystal Display) and organic EL (Organic Electro Luminescence) display devices, it is brighter and more power-saving, and has improved display performance such as high definition, high speed display, and wide viewing angle. Is desired.

  For example, in the case of a thin film transistor (“TFT”) used in the display device, a contact hole formed in an interlayer insulating film among the plurality of patterns constituting the TFT is surely an upper layer and a lower layer pattern. If there is no action to connect, correct operation is not guaranteed. On the other hand, for example, in order to increase the aperture ratio of a liquid crystal display device as much as possible to obtain a bright and power-saving display device, the diameter of the contact hole is required to be sufficiently small. Along with demands, it is desired to reduce the diameter of the hole pattern (for example, less than 3 μm). For example, a hole pattern having a diameter of 0.8 μm or more and 2.5 μm or less, and further a diameter of 2.0 μm or less is required. Specifically, formation of a pattern having a diameter of 0.8 to 1.8 μm is also desired. it is conceivable that.

  On the other hand, the NA (numerical aperture) of the optical system possessed by the exposure apparatus used in this field is about 0.08 to 0.15, and the exposure light source is often i-line, h-line, or g-line. By using a broad wavelength light source including these, a light amount for irradiating a large area is obtained, and there is a strong tendency to place importance on production efficiency and cost.

  By the way, as is well known, halftone phase shift masks that have been used in the manufacture of semiconductor devices shift the phase of irradiated exposure light by approximately 180 degrees and a semitransparent film (phase shift film) having a predetermined transmittance. (Also referred to as a film) and having a transfer pattern, and a photomask that improves resolution by utilizing light interference. Specifically, it is said that there is an effect of improving DOF (Depth of Focus) and contrast. Also, this type of photomask (Attenuated Phase Shift Mask) is different from other types (Alternating Phase-Shift Mask) in that it has less restrictions on pattern design and is advantageously applied to hole patterns, especially to isolated hole patterns. , Has been effective.

  In recent years, in the manufacture of display devices, the demand for pattern miniaturization is high as described above, and therefore, application of a halftone phase shift mask, which has been widely used as a technology for manufacturing semiconductor devices, has begun to be studied. Yes.

  In the manufacturing process of the photomask, various inspections are performed on the coordinates of the formed transfer pattern and the presence or absence of defects. In the phase shift mask, if the phase shift amount deviates from the design value, the transferability is deteriorated, so that an inspection process for measuring the phase shift amount is required.

  However, according to the methods of Patent Document 1 and Patent Document 2, it is necessary to form a monitor pattern having a predetermined design for phase difference measurement outside the transfer pattern region of the photomask. Therefore, the phase difference of the phase shift portion cannot be measured for a photomask that does not have a predetermined monitor pattern.

  Further, the measured result is the phase shift amount of the monitor pattern portion, not the direct measurement of the transfer pattern. Here, the transfer pattern refers to a pattern to be transferred onto the transfer target based on the design of the device to be obtained. In the case of a semiconductor manufacturing photomask having a side of about 6 inches, the phase shift amount of the monitor pattern portion is almost the same as that of the transfer pattern portion, and it is considered that there is no particular problem. On the other hand, a photomask for a display device has a large substrate size (for example, a square with a substrate main surface of 300 to 2000 mm), and in a film forming apparatus for a phase shift film, variation in the in-plane film thickness is zero. Have difficulty. Therefore, the phase shift amount of the monitor pattern portion provided near the outer edge of the substrate may deviate from the phase shift amount inside the transfer pattern, and the phase shift effect generated during pattern transfer cannot be accurately grasped. There is.

  SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a method and an apparatus for easily and directly measuring the phase shift amount of a phase shift portion included in a transfer pattern.

(First aspect)
The first aspect of the present invention is:
A photomask inspection method for measuring phase characteristics of a phase shift portion included in a photomask transfer pattern,
Setting the photomask on an inspection apparatus equipped with a projection optical system;
Exposing the set photomask, and projecting the optical image of the phase shift unit onto the imaging surface by the projection optical system, thereby obtaining optical image data; and
Using the obtained optical image data to obtain a phase shift amount of the phase shift unit, and
In the optical image data acquisition step, at least a part of the photomask, the projection optical system, and the imaging surface is moved in the optical axis direction to acquire the optical image data in each of a plurality of focus states. ,
In the calculation step, a CD value is obtained from the optical image data for each of the plurality of focus states, and the phase shift amount is obtained based on a CD value of the optical image.
This is a photomask inspection method.
(Second aspect)
The second aspect of the present invention is:
The photomask inspection method according to the first aspect, wherein, in the calculation step, the phase shift amount of the photomask is obtained based on a correlation between a focus state where the CD value is maximum and the phase shift amount. is there.
(Third aspect)
The third aspect of the present invention is:
Prior to the calculation step, for the transfer pattern, grasp the correlation between the focus state where the CD value of the optical image formed by the projection optical system is maximum and the phase shift amount of the phase shift unit. The photomask inspection method according to the first or second aspect, comprising a pre-process.
(Fourth aspect)
The fourth aspect of the present invention is:
The pre-process includes a step of grasping a correlation between a focus state of an optical image formed by the projection optical system and a CD value variation of the optical image due to the focus state with respect to the transfer pattern. 3. A method for inspecting a phosphor mask according to the third aspect.
(Fifth aspect)
According to a fifth aspect of the present invention,
The photomask inspection method according to any one of the first to fourth aspects, wherein the transfer pattern includes an isolated pattern.
(Sixth aspect)
The sixth aspect of the present invention is:
The transfer pattern is the photomask inspection method according to any one of the first to fifth aspects, wherein the transfer pattern includes a hole pattern.
(Seventh aspect)
The seventh aspect of the present invention is
The phase shift portion is formed by forming a phase shift film having an exposure light transmittance T of 2 to 10% and a phase shift amount φ of 170 to 190 degrees on a transparent substrate constituting the photomask. A photomask inspection method according to any one of the sixth to sixth aspects.
(Eighth aspect)
The eighth aspect of the present invention is
It is a photomask manufacturing method including the photomask inspection method according to any one of the first to seventh aspects.
(Ninth aspect)
The ninth aspect of the present invention provides
In the photomask inspection apparatus for measuring the phase characteristics of the phase shift unit included in the photomask transfer pattern,
A mask holding means for holding a photomask as a subject;
A light source that emits light;
An illumination optical system for guiding the light emitted from the light source and irradiating the photomask held by the mask holding means;
A projection optical system that receives the light beam transmitted through the photomask and guides it to the imaging surface;
An optical image acquisition unit comprising an imaging unit on the imaging surface;
A drive unit for moving at least a part of the photomask, the projection optical system, and the imaging surface in an optical axis direction to change a focus state on the imaging surface;
A measuring unit that measures a moving distance when at least a part of the photomask, the projection optical system, and the imaging surface is moved by the driving unit;
From the optical image data acquired by the optical image acquisition unit, the CD value of the optical image on the imaging surface is obtained, and based on the movement distance measured by the measurement unit and the CD value, the phase shift unit A calculation unit for calculating a phase shift amount;
This is a photomask inspection apparatus.
(Tenth aspect)
The tenth aspect of the present invention provides
The projection optical system includes an objective lens,
The drive means moves the objective lens in the optical axis direction.
The photomask inspection apparatus according to the ninth aspect.
(Eleventh aspect)
The eleventh aspect of the present invention is
The photomask inspection apparatus according to the ninth or tenth aspect, wherein the calculation unit includes a memory unit that stores in advance a correlation between the phase shift amount and the movement distance at which the CD value is the maximum value. .
(Twelfth aspect)
The twelfth aspect of the present invention provides
The projection optical system is the photomask inspection apparatus according to any one of the ninth to eleventh aspects, which includes an autofocus mechanism.

  According to the present invention, the phase shift amount of the phase shift portion included in the transfer pattern of the photomask can be directly and easily measured.

It is a figure which illustrates the photomask used as a test object, (a) is a figure which shows the planar view of a structural example, (b) is a figure which shows the cross section of a structural example, (c) shows the example of the optical image obtained. FIG. It is the schematic which shows the structural example of the photomask inspection apparatus which concerns on embodiment of this invention. It is a figure which shows the example of CD change of the optical image by a defocus amount about the phase shift film from which a phase shift amount differs. It is a flowchart which shows the inspection flow of the phase shift amount by the photomask inspection method implemented in embodiment of this invention. It is a figure which illustrates the planar view of the structural example of the reference mask used for calibration curve preparation. It is a figure which shows the specific example of the optical image data used for a calibration curve preparation, (a) is a figure which shows the example of the optical image data by a reference mask with a phase difference of 170 degrees, (b) is a reference with a phase difference of 175 degrees The figure which shows the example of the optical image data by a mask, (c) is the figure which shows the example of the optical image data by the reference mask of phase difference 180 degree | times, (d) is the example of the optical image data by the reference mask of phase difference 185 degree | times. FIG. 6A is a diagram showing an example of optical image data using a reference mask having a phase difference of 190 degrees. It is a figure which shows the specific example of the behavior of CD change with respect to a defocus, (a) is a figure which shows the example of CD change by the reference mask of phase difference 170 degree, (b) is CD change by the reference mask of phase difference 175 degree (C) is a diagram showing an example of CD change by a reference mask with a phase difference of 180 degrees, (d) is a diagram showing an example of CD change by a reference mask with a phase difference of 185 degrees, (a) It is a figure which shows the example of CD change by the reference mask of 190 phase differences. It is a figure which shows an example of the correlation with the phase shift amount of a photomask, and the vertex X coordinate of CD change with respect to a defocus. It is a figure which shows the specific example of the measurement of phase shift amount about the photomask used as a test object, (a) is a figure which shows the example of optical image data, (b) is a figure which shows the example of a focus-CD curve, (c) ) Is a diagram showing an example of calculating the phase shift amount from the calibration curve. It is a figure which shows the example of the correlation (calibration curve) when trying to form the hole pattern of a different size.

<Phase shift mask>
In general, in a phase shift mask manufacturing process, a phase shift film is used so that a phase shift amount of a phase shift portion is approximately 180 degrees (for example, 170 degrees to 190 degrees) with respect to a wavelength included in exposure light. The composition and film thickness are selected. However, it is desirable to measure the phase shift amount for the purpose of confirming the presence or absence of a change in the phase shift amount after the manufacturing process or after manufacture, or confirming whether the intended specific phase shift amount has been achieved. .

  FIG. 1 illustrates a photomask (also referred to as a test mask) as a test object. FIG. 1A shows a plan view, and FIG. 1B shows a cross section. The test mask 1 is a so-called halftone phase shift mask. This test mask (phase shift mask) 1 is formed with a phase shift portion 3 that surrounds a hole pattern composed of a light transmitting portion 2 and inverts the phase of exposure light. The phase shift unit 3 includes a phase shift film 5 formed on a transparent substrate 4 such as a glass substrate. The phase shift unit 3 sets the exposure light transmittance T (%) (for example, the transmittance for the i-line when i-line is used as the representative wavelength of the light included in the exposure light) to 2 ≦ T ≦ 10. be able to. This transmittance is based on the transmittance of the transparent substrate 4. This range is desirable because the influence of the side lobe in the optical image is small and the following calculation can be performed more accurately. In the present embodiment, the phase shift film 5 having a transmittance of 5.2% is used.

  When this phase shift mask 1 is exposed by an exposure apparatus, a transfer image (optical image) as shown in FIG. 1C can be formed on the transfer target. The exposure apparatus is, for example, an equal magnification projection exposure apparatus, and an optical condition having an NA of about 0.08 to 0.20 and a coherence factor σ of about 0.5 to 1.0 can be applied.

  The hole pattern CD on the photomask (Critical Dimension, used here for the meaning of the pattern width) is 4 μm or less (for example, 1.5 to 4.0 μm), and 4 μm or less (for example, 0.50) on the transfer target. Consider a case where a hole pattern having a CD of .about.3.5 .mu.m, more preferably 1.0 to 2.5 .mu.m) is formed. In such a fine hole pattern, the effect of the phase shift mask is advantageously exhibited. In this embodiment, the hole pattern CD on the mask is set to 2.5 μm, and the target CD of the hole pattern formed on the transfer body is set to 2.0 μm as an example.

  When the photomask 1 is set in an exposure apparatus and irradiated with exposure light, a transfer image can be formed on the transfer target. The exposure light may be light including any of i-line, h-line, and g-line, and may be broad wavelength light including all of i-line, h-line, and g-line. However, in the inspection method / apparatus of the present embodiment described below, the inspection is performed at a single wavelength using a representative wavelength included in the exposure light. Furthermore, it is preferable that the apparatus of this embodiment can use light of a plurality of wavelengths such as i-line, h-line, and g-line as a single wavelength.

  With the photomask 1 of FIG. 1 set in the exposure apparatus, any one of the photomask 1, the optical system of the exposure apparatus, and the transfer surface is moved relative to the optical axis direction (hereinafter also referred to as the Z direction). The focus state can be changed including the just focus state or the defocus state defocused from the position by a predetermined distance. At this time, the optical image formed on the transfer object changes.

  In the present embodiment, as will be described in detail later, a changing optical image is acquired by an imaging unit, and the phase shift characteristics of the phase shift unit 3 of the photomask 1 serving as a subject, specifically, Checks the amount of phase shift.

<Photomask inspection system>
FIG. 2 illustrates a photomask inspection apparatus (hereinafter also referred to as the present apparatus) 10 according to the present embodiment.

  This apparatus 10 is for inspecting the phase characteristics of the phase shift unit 3 included in the transfer pattern of the photomask 1, and specifically measures the phase shift amount of the phase shift unit 3 with respect to predetermined exposure light. To do.

  In order to measure the phase shift amount, the apparatus 10 is configured as follows. Note that the light source 11 and the optical systems 13 and 14 included in the apparatus 10 are preferably the same as the configuration of the exposure apparatus to be used for exposure of the photomask 1 serving as the subject.

(light source)
For example, the light source 11 provided in the present apparatus 10 can have the same wavelength as the light source of the exposure apparatus. Specifically, if the light source of the exposure apparatus includes i-line, h-line, and g-line wavelengths, it is preferable to provide one of them as the light source 11. If the exposure apparatus has a light source including a broad wavelength including all of i-line, h-line, and g-line, the light source 11 that emits the representative wavelength (for example, i-line) can be used.

(Holding means)
The apparatus 10 also has a mask holding unit (hereinafter also simply referred to as a holding unit) 12 that holds the photomask 1 that is a subject. The photomask 1 serving as a subject can be a so-called phase shift mask provided with a transfer pattern including a phase shift portion on a transparent substrate. For example, as a result of patterning the phase shift film formed on the transparent substrate and having the light transmitting portion and the phase shift portion, or forming the phase shift film and the light shielding film on the transparent substrate and patterning each, Examples thereof include a light transmitting part, a light shielding part, and a phase shift part. Furthermore, the present invention may be applied to a phase shift mask (so-called Levenson mask or chromeless mask) having a phase shift portion in which a transparent substrate surface is dug to a predetermined depth.

(Illumination optics)
Furthermore, the apparatus 10 has an illumination optical system 13. The illumination optical system 13 includes, for example, an illumination lens and an aperture, and guides the light beam emitted from the light source 11 onto the surface of the photomask 1 held by the holding unit 12.

(Projection optics)
The apparatus 10 also includes a projection optical system 14 that guides the light transmitted through the photomask 1 to the imaging surface 15. The projection optical system 14 can include an objective lens and a magnification adjustment lens. As a result, an optical image of the transfer pattern of the photomask 1 is formed on the imaging surface 15 described later at a predetermined magnification.

(Optical image acquisition unit)
The light emitted from the projection optical system 14 reaches the image pickup surface 15, and optical image data (specifically, two-dimensional optical image data) is obtained by an image pickup means (image pickup element, here, CCD) provided on the surface 15. ) Is acquired. That is, this part for acquiring optical image data is the optical image acquisition unit 16 of the apparatus 10.

(Drive part)
In the apparatus 10, at least a part of the photomask 1, the projection optical system 14, and the imaging surface 15 of the optical image acquisition unit 16 is entirely or partially (one or more) in the Z direction. It is movable (hereinafter also referred to as Z movement). Preferably, either the projection optical system 14 (particularly the objective lens) or the photomask 1 is Z-moved in terms of device design. Here, the Z direction is the optical axis direction of the projection optical system 14. Therefore, the present apparatus 10 is provided with a drive unit 17 for moving them.

  In this apparatus 10, the objective lens that is a part of the projection optical system 14 moves Z. The amount of movement is precisely controlled, and the position can be controlled in units of 5 μm, for example. The drive unit 17 that performs such precise Z movement can be configured by using, for example, a known drive source (for example, a servo motor, a piezo element, or the like).

(Measurement part)
In addition, the apparatus 10 includes a measurement unit 18 for measuring a movement amount at the time of Z movement (hereinafter also referred to as Z measurement). The measurement unit 18 grasps the position of the Z movement target by means such as a laser interferometer and measures the movement distance. Note that the measurement unit 18 may measure the movement distance by grasping the position before and after the movement, or may grasp the position of the object by measuring the movement distance. In the present embodiment, the grasping of the position and the measurement of the movement distance are both included in the measurement of the movement distance.

In the Z movement, when the transfer pattern of the photomask 1 forms an image on the imaging surface 15, the focus state can be changed to form a just focus and a plurality of different defocus states. .
For this reason, it is preferable that the drive unit 17 has an autofocus mechanism for determining the just focus position, and measurement is performed so that a predetermined amount of defocus state can be easily formed from the just focus position. A configuration in which the portion 18 and the driving portion 17 cooperate is preferable. Note that the autofocus mechanism here refers to at least a part of the photomask 1, the projection optical system 14, and the imaging surface 15 that can be moved in whole or in part in the Z direction, and the position in the Z direction is directly set. A mechanism that can measure and adjust to the just focus position.

(Calculation unit)
The apparatus 10 includes a calculation unit 19 for calculating a phase shift amount together with the drive unit 17 that controls the above-described driving. Moreover, the calculating part 19 can have a memory part which stores and memorize | stores in advance useful information used for a calculation. Such a calculation part 19 can be comprised using the computer apparatus which performs a predetermined program, for example. The details of these functions by the calculation unit 19 will be described later.

<Principle of photomask inspection method>
Hereinafter, the principle of the photomask inspection method according to the embodiment of the present invention will be described using optical simulation.

  For example, using the phase shift film 5 having a phase shift amount of 180 degrees, the photomask 1 of FIG. 1 is formed and exposed to form a transfer target surface (generally formed on the film surface to be etched). Transfer to the resist film). When the photomask shown in FIG. 1 is set on the apparatus 10 and exposed, an optical image of a transfer pattern is generated on the imaging surface 15 of the apparatus 10 corresponding to the transfer surface, and the optical image two-dimensional data is obtained by the imaging means. Can be obtained. This optical image two-dimensional data is expressed as shown in FIG. 1C, where the horizontal axis indicates the position and the vertical axis indicates the light intensity.

  Here, for example, the objective lens is moved Z to change the focus state, and the two-dimensional optical image data is acquired. When two-dimensional optical image data of a just focus position and a defocus position of ± 5 to 30 μm is acquired for every 5 μm movement, and the CD values of the obtained images are plotted, respectively, a mountain-shaped curve ( A thick solid curve) is obtained. Note that, here, the light amount at which the target CD (2.0 μm) can be obtained at the just focus position is used as a threshold value, and the CD value at this light amount is obtained and plotted in each defocus state.

Here, the optical simulation was performed assuming the following exposure conditions.
Optical conditions of exposure apparatus: projection optical system NA = 0.085, σ = 0.65, exposure light i-line resist conditions: Di700
Substrate material: SiO ₂
Pattern: Isolated hole pattern, CD on photomask = 2.5 μm, target CD of transferred image = 2.0 μm

  As a result, the CD value of the hole pattern becomes maximum at the time of just focus, and the CD value decreases when defocused to the + side or the − side (see the solid line of 180 degrees in FIG. 3). ). In addition, Resist CD in FIG. 3 means CD (micrometer) of the transfer image formed on a to-be-transferred body.

  Next, when the phase shift amount of the phase shift unit 3 of the photomask 1 is changed, the CD value in each focus state is plotted as described above. This was superimposed on the solid curve in FIG. 3 for each phase shift amount (see the lines of 170 degrees, 175 degrees,... In FIG. 3).

  As a result, if the phase shift amount is changed by 5 degrees and a curve is drawn for the phase shift amount of 170 to 190 degrees, the position of the mountain-shaped curve shifts to the left and right, and the X coordinate of the peak position moves accordingly. I understand that.

That is, it can be understood that there is a correlation between the phase shift amount of the phase shift unit 3 and the focus state (defocus amount) having the CD maximum value. Therefore, if this correlation is grasped, the phase shift amount can be accurately known by measuring the defocus amount having the CD maximum value for the photomask 1 of the subject having the unknown phase shift amount. it can.
That is, for each of a plurality of focus states, a CD value can be obtained from optical image data, and the phase shift amount of the photomask can be obtained based on the CD value of the optical image. Here, “based on the CD value of the optical image” may be obtained by obtaining the defocus amount having the CD maximum value as described above, or by obtaining the CD maximum value itself as described later. Good.

  Since this correlation is considered to be unique to an exposure apparatus having a predetermined optical system, an optical system having the same specifications as the exposure apparatus used for exposure of the photomask 1 is used, and the photomask inspection according to this embodiment is performed. It is preferable to prepare the apparatus 10.

<Specific Example of Photomask Inspection Method>
Subsequently, a photomask inspection method performed using the photomask inspection apparatus 10 of the present embodiment based on the above principle will be specifically described in detail as an example of the present invention (hereinafter also referred to as the present example). To do.

  FIG. 4 illustrates an inspection flow of the phase shift amount by the photomask inspection method of this embodiment.

  The inspection flow exemplified here includes (1) a flow for grasping the correlation (pre-process) and (2) a flow for measuring the test mask 1.

(1) Grasping the correlation In this embodiment, first, the correlation between the phase shift amount of the phase shift unit 3 and the defocus amount indicating the CD maximum value when it is exposed is grasped. Specifically, a calibration curve as a reference is obtained.

  In grasping the correlation, first, five types of phase shift masks (hereinafter also referred to as reference masks) having different phase shift amounts are prepared.

  FIG. 5 illustrates a reference mask. Each of the five types of reference masks 20 is obtained by forming a phase shift film on a 6-inch square transparent substrate and patterning the monitor pattern 21 illustrated in FIG. Here, the phase shift amount of each reference mask 20 is 170 degrees, 175 degrees, 180 degrees, 185 degrees, and 190 degrees.

  These reference masks 20 are measured using a phase difference measuring machine (for example, Lasertec MPM series) used for a semiconductor device (LSI) manufacturing photomask to accurately grasp the phase shift amount. did. The reference mask 20 shown in FIG. 5 has four light-transmitting portions arranged in a radial pattern as the monitor pattern 21, and the size of these light-transmitting portions is based on the designation of the measuring instrument (for example, W1 ≧ 20 μm, W 2 ≧ 40 μm, d ≧ 15 μm), and the center of gravity of the pattern (see the x in the figure) is the measurement location of the measuring instrument. Such a monitor pattern 21 enables accurate measurement of the phase shift amount using the measuring instrument (see step (i) in FIG. 4).

  On the other hand, a square hole pattern 22 is formed in the vicinity of the center of the reference mask 20, which is formed based on the pattern of the photomask 1 for which the phase shift amount is to be measured as a subject. It is assumed that the subject has a hole pattern having a CD of 2.5 μm as in the photomask 1 described above, and thereby a 2.0 μm hole pattern is formed on the transfer target.

  When the five types of reference masks 20 are prepared, the prepared reference masks 20 are sequentially set in the apparatus 10. Then, two-dimensional optical image data is acquired at the just focus position for the region mainly including the hole pattern 22 of each reference mask 20. Further, by moving the objective lens Z from the just focus position, the objective lens is defocused by a predetermined distance to form a plurality of defocus states, and two-dimensional optical image data in each defocus state is acquired. Here, as an example, six types of defocus states of ± 5 μm, ± 10 μm, and ± 15 μm are formed with respect to the just focus position, and the two-dimensional optical image data is acquired. Also in this case, the exposure conditions were optical system NA = 0.085, σ = 0.065, and the light source was i-line (365 nm).

  The results are shown in FIGS. 6 (a) to (e). Here, FIGS. 7A to 7E show the case where the light intensity for forming a 2 μm CD hole pattern at the time of just focus is used as a threshold, and the CD at that time is plotted against the defocus amount. .

  According to the focus-CD curves shown in FIGS. 7A to 7E, it can be seen that the behavior of the CD change with respect to the focus state is clearly different due to the difference in the phase shift amount. For example, when the phase shift amount φ is φ <180 degrees, the defocus amount (vertex X coordinate) indicating the maximum value of the CD curve is on the negative side, whereas when φ> 180 degrees, the vertex is The X coordinate is closer to the plus side (see step (ii) in FIG. 4).

  According to the examination of the inventors of the present application, the correlation between the phase shift amount and the vertex X coordinate can be approximated by a linear expression, and the correlation between the phase shift amount and the vertex Y coordinate can be approximated by a quadratic expression. . This is shown in FIG.

  That is, as described above, the correlation between the phase shift amount of the phase shift unit and the CD maximum value obtained when the phase shift unit is exposed or the defocus amount indicating the CD maximum value can be grasped. More specifically, the measurement result of the phase shift amount of each reference mask 20 (that is, the result of (i) in FIG. 4) and the variation of the CD maximum value with respect to the defocus when it is exposed (that is, (ii) in FIG. 4). 4), a calibration curve serving as a reference can be obtained by grasping the correlation between the phase shift amount and the CD maximum value or the defocus amount indicating the CD maximum value (steps in FIG. 4). (See (iii)). Here, a linear equation indicating the correlation between the phase shift amount and the defocus amount (vertex X coordinate) indicating the CD maximum value is used as a calibration curve, and the calibration curve based on the linear equation is used, so that the photomask 1 serving as the subject is detected. The amount of phase shift will be inspected.

  Note that the correlation between the phase shift amount and the vertex coordinates is preferably stored in a memory unit associated with the calculation unit 19 of the apparatus 10 as calibration curve data used for measurement of the subsequent test mask.

(2) Inspection of phase shift amount (measurement of test mask)
When the calibration curve is obtained by grasping the correlation between the phase shift amount and the vertex coordinates, the phase shift amount of the test mask 1 having an unknown phase shift amount can be measured and inspected using the grasped correlation. it can.

  In measuring the amount of phase shift, first, a photomask (test mask) 1 having a phase shift unit 3 to be tested is prepared. Here, a phase shift film 5 is formed on a transparent substrate 4 made of glass, and a halftone phase shift mask in which the pattern shown in FIG. 1A is formed on the phase shift film 5 is used. As the material of the phase shift film 5, the main component is Cr compound (oxide, nitride carbide, oxynitride, oxynitride carbonization, etc.) or metal silicide (MoSi, etc.), and the transmittance is 2 to 10% (more The film is preferably 3 to 8%), and can be formed by sputtering film formation.

  When the test mask 1 is prepared, the test mask 1 is set in the apparatus 10 and exposed under the same conditions as the actual exposure conditions. At this time, a plurality of focus states are formed by Z movement, and two-dimensional optical image data is acquired in each focus state. This is shown in FIG.

  A focus-CD curve shown in FIG. 9B is obtained by plotting the defocus amount that is the maximum CD value from the two-dimensional optical image data thus obtained. Here, the X coordinate of the vertex of the curve is shifted to the minus side from the just focus, indicating −3.332 μm (see step (iv) in FIG. 4 above).

  Here, if the focus state indicating the maximum CD value is 0 (that is, just focus), the phase shift amount of the phase shift unit 3 in the test mask 1 is found to be 180 degrees. On the other hand, when the focus state showing the maximum CD value is the defocus state on the plus side or the minus side, the phase shift amount of the phase shift unit 3 in the test mask 1 may be shifted from 180 degrees. It can be grasped and the amount of deviation can be known.

  Therefore, the phase shift amount is calculated by applying the defocus amount to the linear expression of the calibration curve obtained in FIG. 8 (in this case, for example, the y value of y = 0.4746198962x−85.43219155555 -3.323 is substituted to obtain the phase shift amount x). As a result, as shown in FIG. 9C, it was revealed that the phase difference was 173 degrees (see step (v) in FIG. 4).

<Effects of this embodiment>
According to the photomask inspection apparatus 10 and the photomask inspection method using the same, even when the test mask 1 does not have a monitor pattern having a predetermined measurement area, the transfer of the test mask 1 is performed. The phase shift amount can be measured for the phase shift unit 3 included in the pattern for use. That is, the phase shift amount of the phase shift portion 3 included in the transfer pattern of the test mask 1 can be measured directly and simply. This is particularly advantageous when applied to inspection of a photomask for a display device.

  Further, according to the photomask inspection apparatus 10 and the photomask inspection method using the same, the coordinates indicating the CD maximum value in a plurality of focus states (that is, the maximum value of the CD value of the optical image) and the phase shift amount After grasping the correlation, the phase shift amount of the test mask 1 is measured based on the calibration curve indicating the correlation. Therefore, the measurement result of the phase shift amount is very accurate and highly reliable by grasping the correlation using an optical system having the same specifications as the exposure apparatus used for exposure of the test mask 1. . In addition, if the correlation is grasped in advance, when the phase shift amount is measured, it is only necessary to set the test mask 1, so that the measurement can be performed easily.

  The correlation described in (1) above assumes that a photomask having a hole pattern having a 2.5 μm CD is used, and thereby a 2.0 μm hole pattern is formed on the transfer target. did. On the other hand, the inspection method of the present invention is not limited to this pattern. It can also be applied to patterns with different designs.

For example, FIG. 10 shows a case where hole patterns having different sizes are to be formed. That is, in the case where a CD hole pattern larger than the above case or a small CD hole pattern is formed on the transfer target, the phase shift amount and the defocus amount indicating the CD maximum value when it is exposed. This is a verification of the correlation. When the photomask having a hole pattern with a CD on the mask of 2.3 μm is used for the dot-dash line graph and a 1.8 μm hole pattern is formed on the transfer target, the dotted line graph is for the CD on the mask. A case where a 2.2 μm hole pattern is formed on a transfer object using a photomask having a hole pattern having a CD of 2.7 μm is shown. R ² is the coefficient of determination.

  It can be seen that even in these cases, approximation by a linear expression is possible as described above. Further, it is preferable to grasp the correlation and prepare various calibration curves according to the design of the target pattern to be obtained. The prepared various calibration curves are preferably stored in the memory unit of the apparatus 10 as reference data.

  The use of the photomask applied to the photomask inspection apparatus 10 and the photomask inspection method using the same is not particularly limited. If it has a phase shift part, the effect mentioned above can be acquired.

  The photomask inspection apparatus 10 and the photomask inspection method using the same are particularly advantageous when applied to inspection of a photomask for a display device as described above, but are applied to a photomask for manufacturing a semiconductor device. May be. In the above description, the hole pattern is described as an example of the transfer pattern. However, the present invention is not limited to this, and another pattern (for example, a line and space pattern) may be used.

  By the way, with regard to the pattern for transfer, a dense pattern in which a large number of patterns are arranged with a certain regularity and these optically affect each other, and a pattern of such a regular arrangement exists around it. An isolated (Iso) pattern may be distinguished and called.

The photomask 1 serving as a subject may be any one of a case where a dense pattern is formed on a transfer target and a case where an isolated pattern is formed.
However, the exposure apparatus for manufacturing a semiconductor device (for LSI) has an NA exceeding 0.20, whereas the exposure apparatus for manufacturing a display device (for FPD) is about 0.085 to 0.20. That is, when a photomask for manufacturing a display device is used as a subject, a relatively low NA is applied. When an isolated line pattern is used, a change in CD due to a change in focus state is relatively small. Therefore, in order to accurately grasp the above correlation, it is necessary to form a wide range of defocus states.
Therefore, in the inspection efficiency, when a hole pattern (dense or isolated) or a line and space pattern (particularly, a fine line and space pattern with a pitch of 2.5 μm or less) is targeted, The effect of the invention becomes remarkable.

  That is, the photomask inspection apparatus 10 and the photomask inspection method using the photomask inspection apparatus 10 can be applied not only when a dense pattern is formed, but also when an isolated pattern is formed. This is advantageous when the isolated pattern is a hole pattern (that is, an isolated hole pattern).

<Modification>
The photomask inspection method and the photomask inspection apparatus according to the present invention are not limited to the aspects disclosed in the above embodiments as long as the above-described effects are not lost.

  For example, the use of the photomask applied to the present invention is not particularly limited, and a semiconductor manufacturing photomask may be used as a test mask. According to the photomask inspection method of the present invention, it is possible to directly measure the phase shift amount of the transfer pattern, not the monitor pattern provided outside the transfer region. This is particularly useful in a photomask for manufacturing a display device.

  As an example of a photomask for manufacturing a display device applied to the present invention, a pattern CD having a fine pattern of 4 μm or less (for example, 1.5 to 4.0 μm) can be given. These photomasks are markedly improved in transferability due to the phase shift effect. In addition, it is preferable that the transfer is performed by an equal magnification projection exposure apparatus.

  Further, according to the present invention, the phase shift amount indicated by the test mask can be known for each of the exposure wavelengths (for example, i-line, h-line, and g-line). It is possible to grasp.

  Furthermore, the photomask applied to the present invention may include another optical film or a functional film in part of or in addition to the phase shift film or the light shielding film.

(Photomask manufacturing method)
The present invention includes a photomask manufacturing method using the photomask inspection method.
That is, the photomask manufacturing method according to the present invention includes:
A step of preparing a photomask substrate on which a phase shift film is formed on a transparent substrate and a resist film is further formed;
Drawing a desired transfer pattern on the photomask substrate by a drawing apparatus such as a laser drawing machine;
Developing the resist film to form a resist pattern;
Using the resist pattern, patterning the phase shift film,
After the patterning, the phase shift amount can be inspected by the photomask inspection method according to the present invention.
The photomask substrate may be a photomask blank or a photomask intermediate during a photomask manufacturing process.

DESCRIPTION OF SYMBOLS 1 ... Photomask, 2 ... Translucent part, 3 ... Phase shift part, 4 ... Transparent substrate, 5 ... Phase shift film, 10 ... Photomask inspection apparatus, 11 ... Light source, 12 ... Mask holding means, 13 ... Illumination optical system , 14 ... projection optical system, 15 ... imaging surface, 16 ... optical image acquisition unit, 17 ... drive unit, 18 ... measurement unit, 19 ... calculation unit

Claims (12)

A photomask inspection method for measuring phase characteristics of a phase shift portion included in a photomask transfer pattern,
Setting the photomask on an inspection apparatus equipped with a projection optical system;
Exposing the set photomask, and projecting the optical image of the phase shift unit onto the imaging surface by the projection optical system, thereby obtaining optical image data; and
Using the obtained optical image data to obtain a phase shift amount of the phase shift unit, and
In the optical image data acquisition step, at least a part of the photomask, the projection optical system, and the imaging surface is moved in the optical axis direction to acquire the optical image data in each of a plurality of focus states. ,
In the calculation step, a CD value is obtained from the optical image data for each of the plurality of focus states, and the phase shift amount is obtained based on a CD value of the optical image.
Photomask inspection method.   2. The photomask inspection method according to claim 1, wherein in the calculation step, the phase shift amount of the photomask is obtained based on a correlation between a focus state where the CD value is a maximum value and the phase shift amount.   Prior to the calculation step, for the transfer pattern, grasp the correlation between the focus state where the CD value of the optical image formed by the projection optical system is maximum and the phase shift amount of the phase shift unit. The photomask inspection method according to claim 1, further comprising a pre-process.   The pre-process includes a step of grasping a correlation between a focus state of an optical image formed by the projection optical system and a change in a CD value of the optical image due to the focus state with respect to the transfer pattern. 4. A method for inspecting a phomask according to 3.   The photomask inspection method according to claim 1, wherein the transfer pattern includes an isolated pattern.   The photomask inspection method according to claim 1, wherein the transfer pattern includes a hole pattern.   2. The phase shift portion is formed by forming a phase shift film having an exposure light transmittance T of 2 to 10% and a phase shift amount φ of 170 to 190 degrees on a transparent substrate constituting the photomask. The inspection method of the photomask of any one of -6.   A photomask manufacturing method, comprising the photomask inspection method according to claim 1. In the photomask inspection apparatus for measuring the phase characteristics of the phase shift unit included in the photomask transfer pattern,
A mask holding means for holding a photomask as a subject;
A light source that emits light;
An illumination optical system for guiding the light emitted from the light source and irradiating the photomask held by the mask holding means;
A projection optical system that receives the light beam transmitted through the photomask and guides it to the imaging surface;
An optical image acquisition unit comprising an imaging unit on the imaging surface;
A drive unit for moving at least a part of the photomask, the projection optical system, and the imaging surface in an optical axis direction to change a focus state on the imaging surface;
A measuring unit that measures a moving distance when at least a part of the photomask, the projection optical system, and the imaging surface is moved by the driving unit;
From the optical image data acquired by the optical image acquisition unit, the CD value of the optical image on the imaging surface is obtained, and based on the movement distance measured by the measurement unit and the CD value, the phase shift unit A calculation unit for calculating a phase shift amount;
A photomask inspection apparatus. The projection optical system includes an objective lens,
The drive means moves the objective lens in the optical axis direction.
The photomask inspection apparatus according to claim 9.   11. The photomask inspection apparatus according to claim 9, wherein the calculation unit includes a memory unit that stores in advance a correlation between the phase shift amount and the movement distance at which the CD value is a maximum value.   The photomask inspection apparatus according to claim 9, wherein the projection optical system includes an autofocus mechanism.