JPH06186006A - Surface accuracy measuring method for substrate surface and original plate for surface accuracy measurement - Google Patents

Abstract

PURPOSE:To simply measure the flatness of the surface of an exposure substrate such as a wafer in a state where the substrate is set inside an image-formation optical device such as a projection exposure device. CONSTITUTION:Two sets of lines and space patterns are adjacently formed on a mask original plate, and the first period pattern 21 is provided with phase shifters 11, 12, 13 to give three kinds of phase differences of 0 deg., 120 deg., 240 deg. in order to illuminating light, and the slippage caused by the slippage of a focal point of a pattern position on each projected image is measured between the first period pattern 21 and the second period pattern 22 having no phase shifter for measuring the flatness of the surface of a substrate such as a wafer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface accuracy measuring method of an image forming substrate surface in an image forming optical system typified by a projection exposure apparatus used for manufacturing semiconductor elements and the like, and more particularly, to a flat surface of the substrate surface. The present invention relates to a method for measuring the degree of rotation using the above-mentioned imaging optical system, and a surface accuracy measurement original plate used for the method.

[0002]

2. Description of the Related Art Conventionally, as a method of measuring surface accuracy such as flatness of a substrate surface, a method utilizing an interference phenomenon of light is generally used.

In this case, an interferometer is used for the measurement, and as examples of the interferometer, a Twyman-Green interferometer, a Fizeau interferometer and the like are known. These interferometers measure the difference between the reference surface that serves as a reference and the surface to be measured by utilizing the interference of light.For example, the light reflected by the reference surface that serves as the reference and the surface that is measured are reflected. The light is caused to interfere with each other, and the resulting change in interference fringes is detected to measure the difference between the reference surface and the measured surface. Since these interferometry methods have a simple principle, they are used in various fields as a method of measuring the unevenness of the surface to be measured. This method is described in, for example, Proceedings No.
3 17p-N-13 (page 798).

[0004]

However, in the above-mentioned conventional technique, it is necessary to install the measurement surface of the object to be measured at the measurement position of the interferometer, and the object to be measured remains mounted on another device. In this state, measurement involves many difficulties. For example, in a projection exposure apparatus used for manufacturing semiconductor elements and the like, it is almost impossible to perform measurement with an exposure substrate such as a wafer set on the stage of the apparatus.

On the other hand, in the above projection exposure apparatus, as a method for measuring the flatness of the substrate surface, there is a method using a focus sensor for irradiating the substrate surface with laser light and detecting reflected light with an optical position detector. However, this method is easily affected by the accuracy of the focus sensor, the mechanical accuracy of the wafer stage, the inclination of the substrate surface, etc., and the measurement accuracy is not sufficient.
Further, since the laser light is narrowed down, it is impossible to measure the entire transfer area at once, and the stage always moves.

The present invention has been made in order to solve these problems, and a surface accuracy measurement capable of setting a substrate such as a wafer in an image forming optical system and measuring the flatness of the substrate surface in that state. An object of the present invention is to provide a method and an original plate for measuring surface accuracy used for the method.

[0007]

In order to achieve this object, in the present invention, an imaging optical system such as a projection exposure apparatus is used as it is, a special mask pattern is formed on a mask original plate, and the image is formed on a wafer. A flatness of the substrate surface is measured by projecting and forming an image on the substrate surface such as, and then measuring the deviation amount of the image position caused by the deviation of the substrate surface from the positive focal plane of the imaging optical system. Is.

The special mask pattern is, for example, a periodic pattern such as line & space, and at least three kinds of different phases are equal to the phase difference value with respect to the illumination light for illuminating the mask original plate. It is provided with a phase shifter that gives a staircase at, for example, 0 degrees, 120 degrees, 24
A value obtained by dividing a natural number multiple of 360 degrees or 360 degrees by the number of phase seeds, such as 0 degree, is defined as a phase difference value. For example, 120 degrees is a value obtained by dividing 360 degrees by the phase seed 3.
This causes the image positions on the substrate to deviate according to the amount of defocus. However, a phase difference value that is a natural number multiple of 180 degrees is excluded because no image displacement occurs.

Further, in order to facilitate the measurement of the deviation amount of the image position of these first mask patterns, a phase difference is added to the illumination light in the same mask original plate so as to be adjacent to the first mask patterns. A second mask pattern that is not given, that is, serves as a reference that does not deviate the image position, is arranged in parallel. The second mask pattern may be a single opening pattern or may be a pattern in which lines and spaces are periodically arranged. Especially in the latter case, a vernier pattern is formed by slightly changing the period between the first pattern and the second pattern, and the measurement is facilitated.

Further, by arranging these measurement patterns over the entire surface of the pattern transfer area in the mask original plate, the flatness of the entire transfer area can be measured by one exposure.

[0011]

For example, in a reduction projection exposure apparatus, when a pattern formed on a mask original plate is imaged and exposed on a substrate surface such as a wafer, it is important that the substrate surface is correctly aligned with the imaging surface. . Particularly, as semiconductor devices have become highly integrated and pattern sizes have become low sub-μm, as in recent years, the depth of focus of the imaging system also falls below μm, and the problem becomes extremely severe. Therefore, the unevenness of the surface of the substrate such as a wafer, that is, the flatness is, in terms of pattern resolution,
It is a very important factor. Therefore, the present invention is such that the flatness of the substrate surface can be measured in the actual imaging optical system using the phase shift method.

By the way, the phase shift method was devised as a method for improving the resolution in the reduced projection exposure method, and a transparent thin film called a phase shifter was superposed on a predetermined pattern on a mask to give a phase difference to the exposure light. It was introduced. For example, in the case of the line & space pattern, a phase shifter is provided for every other transmission pattern so that the phase difference of the light passing through the transmission patterns adjacent to each other on the mask becomes 180 degrees. As a result, in the light-shielded area between the transmission patterns, the light transmitted through the transmission patterns on both sides interferes with each other and cancels each other out, weakening the light intensity and improving the contrast, thus improving the resolution. About this, for example, IEE, Transaction on Electron Devices, and ED2.
9, No. 12 (1982), pages 1828-1836
Page (IEEE, Trans. Electron Devices, ED29, No.12 (198
2), pp1828-1836).

The above-mentioned document describes the case where the phase difference is 180 degrees, but on the other hand, 0 degrees, 120 degrees, and 24 degrees are used.
There is also a method of using three types of phase difference of 0 degree. This method
If the phase difference is only 180 degrees, it is introduced because the phase difference between adjacent patterns does not always become 180 degrees depending on the shape and arrangement of the pattern. This is described in, for example, Proceedings of the 53rd Japan Society of Applied Physics Academic Conference, No. 2, 16p-L-4 (475 pages)
Are described in.

By the way, next, in the line & space mask pattern as shown in FIG. 9, the phase difference of the transmitted light changes to 0 degree (11), 120 degree (12) and 240 degree (13) in order. Consider the case of imaging on the substrate surface.

First, when the image is in focus, an image is formed on the surface of the substrate at a position corresponding to the mask pattern. However, when the focal point is deviated, the image on the substrate surface is formed at a position deviated from the position corresponding to the mask pattern. With a mask pattern that does not give a phase difference, such an image position shift does not occur.Therefore, at a defocused position, there is a difference in image position between the mask pattern that gives a phase difference and the mask pattern that does not give a phase difference. Occurs.

Such a phenomenon occurs in a periodic pattern having a phase difference value obtained by dividing 360 degrees by a natural number of 3 or more. For example, the phase difference with respect to the illumination light is 0 degrees, 9 degrees.
The same occurs in the periodic patterns of 0 degree, 180 degrees, and 270 degrees. A value obtained by dividing a natural number times 360 degrees by a natural number of 3 or more may be used as the phase difference value. However, when the phase difference value is 180 degrees or a natural multiple thereof, the image position shift phenomenon does not occur, so it must be excluded. For example, in a periodic mask pattern such as a line & space pattern, in the case of a conventional mask, 0th-order diffracted light is generated in the optical axis direction which is a direction perpendicular to the mask, and + 1st-order diffracted light and -1st-order diffracted light are symmetrically generated. Folding light, + 2nd-order diffracted light and -2nd-order diffracted light,
And diffracted light is generated in that order. These diffracted lights are projected and imaged on the substrate by the imaging system to form an optical image. Here, since the diffracted light is generated symmetrically with respect to the optical axis, the optical image is blurred due to defocus, but the position on the substrate where the optical image is formed does not deviate.

In the case of a phase shift mask in which a phase shifter that gives a phase difference of 180 degrees is repeatedly arranged for every other periodic transmission pattern, 1 is provided between illumination lights passing through adjacent openings.
Since a phase difference of 80 degrees is given, the 0th-order diffracted light in the optical axis direction disappears, and ± 1 / 2-order diffracted light, ± 3 /
Diffracted light is sequentially generated such as second-order diffracted light. In this case as well, since diffracted light is generated symmetrically with respect to the optical axis, similarly, deviation of the optical image due to defocus is not generated.

On the other hand, in the case of a phase shift mask in which the phase is arranged stepwise with respect to the periodic pattern with a phase difference value other than 180 ° or a value that is a natural number multiple of 180 °, both sides of a certain transmission pattern are adjacent. Since the phase values differ between the transmission patterns of, the phases are asymmetrically arranged and a bias occurs.

For example, in the case of a phase shift mask in which phase differences are periodically arranged in three types of 0 degree, 120 degrees, and 240 degrees, the same phase difference is arranged for every three openings. Therefore, the phase differences on both sides of the transmission pattern having a phase difference of 0 degrees are 120 degrees and 240 degrees, respectively, and the phase differences are asymmetrically arranged, so that a phase deviation occurs. As a result, the diffracted light generated by the illumination light that has passed through the mask becomes asymmetric with respect to the optical axis, so that the optical image is deviated in the plane of the substrate due to defocus.

Here, an example in which a phase shift mask in which the above three types of phase differences are periodically arranged in a periodic transmission pattern is used, the light intensity distribution I (x) on the substrate in perfect coherent illumination is shown. ) Is theoretically calculated, the following equation is obtained.

[0021]

[Equation 1]

Where x is the position in the periodic direction on the substrate, λ
Is the wavelength of the illumination light, L is the arrangement pattern of the transmission pattern, and z is the defocus amount. The width of the transmission pattern was L / 2. As expressed by (Equation 1), it can be seen that the position on the substrate surface where the optical image is formed is linearly displaced with respect to the defocus amount z.

FIG. 1 shows the numerical aperture (N) of the lens of the imaging optical system.
A) is 0.52, the coherence factor (σ) value indicating the degree of interference of illumination light is 0.3 and 0.5, and the exposure wavelength λ is 365 nm. The result of the calculation is shown. Here, the pattern shown in FIG. 5 is assumed as the mask pattern. That is, the opening pattern width is 0.4 μm, the arrangement pitch of the openings is 0.8 μm, and the phase difference given to the illumination light that has passed through the transmission pattern in the periodic pattern 21 is 0 degrees (in order of positive position). 11), 120 degrees (12), 240
(13). The horizontal axis in FIG. 1 represents the amount of defocus,
The vertical axis represents the amount of positional deviation of the projected image formed on the substrate. Here, the smaller the σ value is, the larger the positional deviation amount is because the smaller the σ value is, the higher the coherence of the illumination light is and the larger the interference effect is. Note that FIG. 14 schematically shows the light intensity distributions of the images corresponding to the masks AA ′ (21) and BB ′ (24) when the mask of FIG. 5 is out of focus. As shown in FIG. 14, a positional shift occurs between the image of the periodic pattern 21 to which the phase difference is given and the image of the periodic pattern 24 to which the phase difference is not given.

FIG. 8 shows that the phase difference is 240 degrees (1
3), 120 degrees (12), and 0 degrees (11) in that order, conversely in FIG. 9, 0 degrees (11), 120 degrees (12), 240 degrees (1
3 shows an example in which they are arranged in the order of 3). 8 and 9
In and, the magnitude of the positional deviation is the same, but the direction of the positional deviation is opposite. The positional deviation amount varies depending on the optical constant of the apparatus used, the mask pattern size, the phase difference value to be given, and the like, but the deviation amount and the deviation direction are uniquely determined under certain fixed conditions. Therefore, it becomes possible to measure the amount of defocus of the substrate surface, that is, the flatness of the substrate surface by measuring the amount of positional deviation and the direction thereof.

By the way, in general, there is a method of using a vernier pattern as a method of measuring the amount of deviation and the dimension with high accuracy and easily. In the vernier pattern, two sets of periodic patterns having slightly different periods are arranged, one of the periodic patterns is used as a reference pattern, and the other is used as a measurement pattern. For example, if two sets of periodic patterns having a period of 0.80 μm and 0.81 μm are used as vernier patterns,
The amount of deviation can be measured with a resolution of 0.01 μm. This method is used when measuring the overlay accuracy of the projection exposure apparatus, and the same principle is used for the calipers scale.

Therefore, in the present invention, a mask pattern that does not give a phase difference is used as one periodic pattern of the vernier pattern, and a mask pattern that gives a phase difference is used as the other periodic pattern. FIG. 2 is a diagram schematically showing an example of such a vernier pattern. Here, the second periodic pattern 22 is used as the reference pattern, and the first periodic pattern 22 is used as the measurement pattern.
Corresponds to the periodic pattern 21. Second cycle pattern 2
2 is a normal transmission pattern, and the period of the opening 11 'is 0.81.
μm, the opening width is 0.4 μm, and the first periodic pattern 21 has an opening cycle of 0.80 μm and an opening width of 0.4.
.mu.m, and the phase differences of 0 degree (11), 120 degrees (12), and 240 degrees (13) are given in order from the left.

By the way, the relationship between the amount of defocus and the amount of pattern misregistration is almost linear as shown in FIG.

[0028]

[Equation 2]

It can be represented by Here, the pattern position shift amount is δd, the focus shift amount is δz, and N of the imaging optical system is set.
A = 0.52, σ = 0.3, and λ = 365 nm were assumed. The proportionality coefficient 0.09 is a constant that depends on the conditions of the imaging system, the pattern size, the period, and the like. Then, the vernier pattern of FIG. 2 is transferred to the resist on the substrate by the imaging optical system, and the positional deviation amount δz of the resist pattern between the periodic pattern 21 and the periodic pattern 22 is measured. The amount of defocus δz can be obtained. It should be noted that by utilizing the fact that the direction of the positional deviation of the patterns is reversed depending on the arrangement order of the phase differences, for example, one cycle pattern of the vernier pattern is 0 degree, 120 degrees, and 240 degrees in the order of the other cycle pattern. Is a mask pattern in which a phase difference is given in the order of 0 degree, 240 degrees, and 120 degrees, the relative displacement amount is about 2
Since it is doubled, the measurement becomes easy and the measurement accuracy can be improved.

By providing these measurement patterns on the entire surface of the pattern transfer area of the mask original plate, the amount of defocus, that is, the unevenness and flatness of the surface of the substrate can be obtained for the entire surface of the pattern transfer area on the substrate surface. FIG. 4 shows an example thereof, in which the measurement pattern 31 is set in the pattern transfer area 30.
This is an example of individual arrangement. Further, if the periodic patterns shown in FIGS. 8 and 9 are uniformly provided on the entire surface of the pattern transfer area 30, the defocus amount at a specific position, that is, the absolute value of the unevenness of the substrate surface cannot be obtained. Although it is difficult, a position shift occurs in a place where the unevenness changes, and a distortion occurs in the periodic pattern, so that the place where the unevenness exists can be easily found.

In an actual projection exposure apparatus, the image plane is not always a perfect plane due to the characteristics of the image forming optical system.
It may be slightly curved. Therefore, since the influence of this field curvature is included in the above-mentioned measurement result of the flatness, it is necessary to consider the influence of this field curvature in advance. However, conversely, from this measurement result, it is also possible to correct the unevenness of the substrate stage on which the exposure substrate is installed, and to make the substrate surface correctly coincide with the image plane, and if a perfectly flat substrate is used, It is also possible to measure the curvature of field of the imaging optical system.

As described above, according to the present invention, it is possible to measure the flatness of a substrate such as a wafer mounted in an imaging optical system such as a projection exposure apparatus.

[0033]

【Example】

[Embodiment 1] In this embodiment, first, an original plate for measuring surface accuracy for an i-line (exposure wavelength λ = 365 nm) reduction projection exposure apparatus (numerical aperture NA = 0.52) (hereinafter, The mask manufacturing method will be described.

FIG. 2 shows a schematic view of the measurement pattern used in this example. The pattern shown in FIG. 2 is used as a vernier pattern, and one of the transmission patterns 11 near the center is arranged so as to be continuous without displacement. The period of the opening of the first periodic pattern 21 is 0.80 μm, the width of the transmission patterns 11, 12 and 13 is 0.4 μm, and the period of the second periodic pattern 22 that does not give a phase difference is 0.81 μm. The width of the pattern 11 'was 0.4 μm. Further, the length of the periodic patterns 21 and 22 is set to 10 μm, and the length is set to 15 μm for every five lines, but this is because the convenience at the time of measurement is taken into consideration, and these shapes and dimensions are not limited to those described above. Absent.

Next, a method of manufacturing the first periodic pattern 21 will be described with reference to the sectional view of FIG.

First, a chromium film having a thickness of 80 nm was laminated as a light-shielding film on the synthetic quartz substrate 1. This chrome film was processed into a predetermined pattern by a known method to form a light shielding pattern 2.

Next, in order to form the first phase shifter 3, coating glass OCD type 7 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was spin-coated and heat-treated at a temperature of 200 ° C. for 30 minutes to form a coating glass film. . Generally, the film thickness d of the phase shifter for introducing the phase difference θ degree is determined by the following equation.

[0038]

[Equation 3]

Here, d is the thickness of the phase shifter film, λ is the exposure wavelength, n1 is the refractive index of the phase shifter film at the exposure wavelength λ,
θ [degree] is a phase difference. Further, n0 is the refractive index of air at the exposure wavelength λ, and may be set to 1 in practice. In this example, λ = 365 nm, n1 = 1.45, and n0 = 1. Therefore, the film thickness of the phase shifter that gives a phase difference of 120 degrees is about 270 nm from (Equation 3). Therefore, in this embodiment, the coating type glass is formed to have a film thickness of 270 nm.

Next, a negative resist RD200 for electron beam is used.
0N (Hitachi Chemical, product) is applied, pre-baking, electron beam drawing, development, and post-baking are performed under predetermined conditions.
A resist pattern was formed. Using the formed resist pattern as a mask, the coating type glass film was wet-etched using a predetermined etching solution to remove the resist pattern and form the first phase shifter 3. Then, in order to form the second phase shifter 4, the coated glass OCD type 7
(Tokyo Ohka Kogyo, product) was spin-coated and heat-treated at a temperature of 80 ° C. for 5 minutes. In the following, the fact that the coating type glass is exposed to the irradiation of electron beams and acts as a negative type is used.

Next, using an electron beam drawing apparatus, a predetermined second
The phase shifter pattern of 3 was drawn, developed with methanol for 30 seconds, and further heat-treated at a temperature of 200 ° C. for 30 minutes to form a predetermined second phase shifter 4. Here, the film thickness of the second phase shifter 4 was set to 540 nm in order to give a phase difference of 240 degrees by the second phase shifter pattern.

In this way, the mask structure shown in FIG. 6 was formed, and this was arranged side by side with the aperture group having no phase difference, and the mask having the measurement pattern shown in FIG. 2 was produced.

In this embodiment, as shown in FIG.
The measurement patterns 31 were arranged in a grid pattern at nine positions in the transfer area 30. However, the arrangement position, the arrangement number, and the like are not limited to this, and can be arbitrarily selected as needed.

Next, using the prepared mask and the above-mentioned reduction projection exposure apparatus, a resist spin-coated on a silicon substrate was exposed and developed under predetermined conditions to form a resist pattern. Then, the amount of positional deviation of the resist pattern formed using the optical microscope is measured, and the transfer region 3 is determined from the measurement result.
The focus position distribution within 0 was obtained. It should be noted that on the second periodic pattern 22, the phase difference arrangement order of 0 °, 120 °, 240 ° in the first periodic pattern 21 is reversed by 0 °, 240 °,
If the phase differences are arranged in the order of 120 degrees, the relative positional deviation amount between the two becomes approximately twice, so that the measurement becomes easy and the measurement accuracy can be improved.

Although an embodiment using a mask for transmitted illumination has been described above, it goes without saying that the same measurement can be performed by using a mask for reflected illumination based on the same principle.

Example 2 In this example, a measurement pattern as shown in FIG. 3 was formed. The period of the transmission part of the periodic pattern 23 is 0.8 μm, and the width dimension of the transmission pattern 14 is 1 μm.
And The reason why the width dimension of the transmissive pattern 14 is increased in this way is that the ordinary transmissive pattern generally has a lower resolution than the pattern using the principle of phase shift, and therefore the transmissive pattern 14 serves as a reference for measuring the image shift amount. Therefore, the pattern was wide enough to be fully resolved. Hereinafter, a method for manufacturing the periodic pattern 23 will be described with reference to the sectional structural view of FIG. 7.

First, a silicon oxide film 5 as a phase shifter film giving a phase difference of 120 degrees and a chromium film 80 nm as a light-shielding film are sequentially laminated on a synthetic quartz substrate 1, and the chromium film is processed into a predetermined pattern by a known method. Thus, the light shielding pattern 2 was formed. Since the refractive index n1 of the silicon oxide film was 1.45, the film thickness of the silicon oxide film 5 giving a phase difference of 120 degrees was set to about 270 nm.

Next, an electron beam positive resist OEBR2
000 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied, and prebaking, electron beam drawing, development, and postbaking were performed under predetermined conditions to form a resist pattern. Using the formed resist pattern as a mask, the silicon oxide film 5 was wet-etched using a predetermined etching solution, and the resist pattern was removed.

Thereafter, coating type glass OCD type 7 (manufactured by Tokyo Ohka Kogyo Co., Ltd.), which is the material of the second phase shifter 3, was spin-coated and heat-treated at a temperature of 80 ° C. for 5 minutes.
Next, a predetermined second phase shifter pattern was drawn by using an electron beam drawing apparatus, developed with methanol for 30 seconds, and further heat-treated at a temperature of 200 ° C. for 30 minutes to form a predetermined phase shifter 3. Here, in order to give a phase difference of 120 degrees by the phase shifter 3, the film thickness was 270 nm. In this example, the above-mentioned measurement patterns were arranged in a grid pattern at 25 locations in the transfer area.

In this embodiment, after the resist on the silicon substrate is exposed by using the above mask to form a pattern, the position of the pattern is displaced by using an electron beam length measuring device (Hitachi, S6100 type). The amount was measured and the distribution of defocus in the transfer area, that is, the flatness was obtained.

[Embodiment 3] In this embodiment, the mask pattern shown in FIG. 9 is formed on the entire surface of the transfer region by the manufacturing method described in Embodiment 1.

A resist pattern was formed by exposing and developing a resist spin-coated on a silicon substrate under predetermined conditions by using the prepared mask and the above-mentioned reduction projection exposure apparatus. When the formed resist pattern was observed, it was 20 m
A shift of the periodic pattern was observed at a position of about 10 mm from the center of the m-square transfer region, and it was found that unevenness was generated on the surface of the silicon substrate in this region.

[Embodiment 4] In this embodiment, as described in Embodiment 3, the mask pattern shown in FIG. 8 is formed on the entire surface of the transfer region.

Using the prepared mask and the above-mentioned reduction projection exposure apparatus, a positive type resist spin-coated on a silicon substrate is exposed under a predetermined condition, and the mask is rotated 180 degrees in the pattern plane to obtain a half cycle. The resist pattern was formed by shifting the pitch and exposing it in layers and developing. Here, by rotating the mask and shifting by a half of the cycle to perform double exposure, the entire exposure region is exposed. Further, by rotating the mask by 180 degrees, the pattern position shift direction is opposite to the focus shift direction. As a result, the resist pattern in the in-focus portion disappears after development, but in the portion out of focus and the pattern position deviated, the resist pattern is partially formed without being entirely exposed. Therefore, by measuring the pattern position of the portion where the resist pattern is formed, it is possible to easily measure the position where the cycle shift occurs, that is, the portion where the surface is not flat. Although the mask is rotated 180 degrees in the above description, the silicon substrate is rotated together with the substrate holder 18 without rotating the mask.
Even if it is rotated by 0 degree, the same effect can be obtained.

[Embodiment 5] FIG. 10 shows the pattern layout of the mask used in this embodiment.

In the present embodiment, as described in the third embodiment, the mask pattern shown in FIG. 8 is applied to the entire surface of the transfer area 32 in the left half of the transfer area and to the transfer area 33 in the right half.
A mask pattern shown in FIG. 9 in which the pattern on the left half surface is horizontally reversed is formed.

Next, using this mask, the silicon substrate is moved in parallel so that the transfer region 32 and the transfer region 33 overlap each other, and double exposure is performed, and the same effect as that of the fourth embodiment is obtained. In this case, it is not necessary to rotate the entire mask by 180 degrees as in the fourth embodiment, so that the measurement can be easily performed.

[Embodiment 6] In this embodiment, a mask for surface accuracy measurement is manufactured in which the measurement mask pattern shown in FIG. 5 is arranged at a predetermined position in the transfer area.

In the present embodiment, the periods of the transmissive portions of the periodic pattern 21 and the periodic pattern 24 are 0.45 μm, and the transmissive regions are arranged adjacent to each other. Note that, as shown in FIG. 15, even if three transmissive portions are arranged at equal pitches, the positional displacement effect is produced, but it is desirable to dispose three or more transmissive portions.

The resist pattern formed using the manufactured mask was measured by using a mask pattern dimension automatic measuring device. As a result of measuring the amount of positional deviation between the resist pattern formed by the periodic pattern 21 and the pattern formed by the periodic pattern 24, it was found that the substrate was a flat surface having irregularities with a height of 1 μm.

[Embodiment 7] In this embodiment, as described in Embodiment 1, a mask having a plurality of mask patterns shown in FIG. 16 arranged in the transfer region is manufactured.

In this embodiment, the width is 0.5 μm and the length is 15 μm.
A periodic pattern in which 10 m transparent regions were arranged at a pitch of 1 μm was arranged in the central portion of a square light shielding region 10 having a side of 20 μm. The phase difference is 0 degrees (11), 120 degrees (12),
There are three types of 240 degrees (13), and they are arranged in the order shown in FIG. The dimensions are those on the substrate onto which the mask pattern is transferred, and the pattern dimension value, the phase difference, and the arrangement of the phase differences are not limited to the above.

Using the prepared mask and an i-line reduction projection exposure apparatus with a reduction ratio of 5: 1, a positive resist spin-coated on a silicon substrate was exposed under predetermined conditions. here,
In order to form one continuous resist pattern in the transmissive region instead of the periodic resist pattern, the exposure amount was made higher than usual and overexposed. Since the pattern edge position of the resist pattern formed by the periodic pattern moves in the periodic direction according to the focal position, the position of one resist pattern formed by overexposure also moves according to the focal position. On the other hand, the position of the resist pattern formed by the normal pattern arranged around the periodic pattern does not move with respect to the focal position. Thereby, the unevenness of the transfer substrate surface can be measured by measuring the relative positional relationship between the two.

The amount of positional deviation of the formed resist pattern was measured using an overlay precision automatic measurement apparatus LAMU600 (product of Hitachi, Ltd.) to measure the amount of irregularities on the surface of the silicon substrate.

[Embodiment 8] In the present embodiment, as shown in FIG. 17, the mask pattern shown in FIG. 16 and the mask pattern obtained by rotating the mask pattern by 90 degrees are arranged next to each other.
A plurality of masks arranged in the transfer area were produced. This is provided in consideration of the possibility that the image forming characteristics may differ between the vertical pattern and the horizontal pattern.

The amount of positional deviation of the resist pattern formed as described in Example 7 was measured by using an overlay accuracy automatic measuring device LAMU600 (manufactured by Hitachi, Ltd.).

The mask structure for imparting the phase difference to the illumination light is not limited to the one described above, and for example, the one without the light shielding pattern as shown in FIG. 12 or the one shown in FIG. As described above, materials 6, 7 and 8 having different refractive indexes are arranged on a transmission pattern which gives respective phase differences.

Further, although the mask original plate used for the transmissive illumination has been mainly described above, the same principle can be applied to the mask original plate used for the reflective illumination. In the reflective mask original plate 9, the portion where the light is reflected corresponds to the opening pattern of the transmissive original plate. The phase difference is, for example, as shown in FIG.
As shown in FIG. 3, it can be provided by providing steps 15, 16, 17 on the reflecting surface. For example, when the illumination light is incident on the reflection surface almost perpendicularly, a step of λ / 6 may be provided to give a phase difference of 120 degrees.

[0069]

As described above, according to the surface accuracy measuring method of the substrate surface and the surface accuracy measuring original plate of the present invention,
Since the flatness of the substrate surface can be measured from the displacement of the transfer pattern while the exposure substrate such as the wafer is set in the imaging optical system such as the projection exposure device, extremely simple and practical surface accuracy measurement. The method was realized.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a theoretical calculation result of the principle used in the present invention.

FIG. 2 is a schematic view showing an embodiment of a mask pattern according to the present invention.

FIG. 3 is a schematic view showing another embodiment of the mask pattern according to the present invention.

FIG. 4 is a schematic view showing an embodiment of the arrangement of mask patterns according to the present invention.

FIG. 5 is a schematic view showing another embodiment of the mask pattern according to the present invention.

FIG. 6 is a schematic view showing a part of a cross section of a mask that is an embodiment of the present invention.

FIG. 7 is a schematic view showing a part of a cross section of a mask which is another embodiment of the present invention.

FIG. 8 is a schematic view showing another embodiment of the mask pattern according to the present invention.

FIG. 9 is a schematic view showing another embodiment of the mask pattern according to the present invention.

FIG. 10 is a schematic view showing another embodiment of the arrangement of mask patterns according to the present invention.

FIG. 11 is a schematic view showing a part of a cross section of a mask which is another embodiment of the present invention.

FIG. 12 is a schematic view showing a part of a cross section of a mask which is another embodiment of the present invention.

FIG. 13 is a schematic view showing a part of a cross section of a reflection type mask original plate which is another embodiment of the present invention.

FIG. 14 is a schematic diagram showing another example of the theoretical calculation result of the principle used in the present invention.

FIG. 15 is a schematic view showing another embodiment of the mask pattern according to the present invention.

FIG. 16 is a schematic view showing another embodiment of the mask pattern according to the present invention.

FIG. 17 is a schematic view showing another embodiment of the mask pattern according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Synthetic quartz substrate 2, 10 ... Light-shielding film (pattern) 3 ... Phase shifter (120 degree) 4 ... Phase shifter (24
0 degree) 5 ... Silicon oxide film 6, 7, 8 ... Phase shifter made of different material 9 ... Reflective mask original plate 11, 11 ', 14 ...
Transmission pattern 12 ... Transmission pattern with a phase difference of 120 degrees 13 ... Transmission pattern with a phase difference of 240 degrees 15,16,17 ... Reflective surfaces that give a phase difference 21, 21 ', 23 ... First periodic patterns 22, 24, 24' ... second cycle pattern 30 ... pattern transfer area 31 ... measurement pattern 32 ... left half transfer area 33 ... right half transfer area 34 ... mask

Claims (8)

[Claims] 1. A method for measuring the surface accuracy of a substrate surface in an imaging optical system for forming an image of a pattern on the mask original plate on a substrate surface and exposing the same by using light transmitted through or reflected by the original mask plate. A mask pattern is formed on the original plate in which the position of the image on the substrate surface is displaced in accordance with the deviation from the positive focal plane of the imaging optical system, and the flatness of the substrate surface is measured from the displacement amount of the image. A method for measuring surface accuracy of a substrate surface in an imaging optical system, characterized by: 2. The mask pattern is arranged such that pattern regions that give at least three or more different phases to illumination light are changed periodically and the phases are changed stepwise with equal phase difference values. The surface accuracy measuring method according to claim 1, wherein the surface accuracy measuring method is a pattern. 3. The first mask pattern in which the position of the image on the substrate surface is displaced in accordance with the deviation from the positive focal plane of the imaging optical system in the original mask plate, and the position of the image is displaced. 3. The surface accuracy measuring method according to claim 1, wherein a flatness of the substrate surface is measured by providing a second mask pattern that does not exist and comparing the image positions of the two. 4. The phase difference value is 360 degrees or 360 degrees.
4. A surface according to claim 2 or 3, which is a value obtained by dividing a natural multiple of degrees by the number of the phase seeds, but excluding a value of a natural multiple of 180 degrees. Original plate for surface accuracy measurement in accuracy measurement method. 5. The second mask pattern is a pattern composed of one transmission region that does not give a phase difference to the illumination light, or a plurality of transmission regions that do not give a phase difference are periodically provided. An original plate for measuring surface accuracy in the surface accuracy measuring method according to claim 3, which is an arrayed pattern. 6. The surface accuracy in the surface accuracy measuring method according to claim 3, wherein the first mask pattern and the second mask pattern are arranged adjacent to each other in the mask original plate. Original plate for measurement. 7. A pattern in which both the first mask pattern and the second mask pattern are periodically arranged, and the cycle of the first pattern and the cycle of the second pattern are Differently, vernier patterns are formed on each other, and the original plate for surface accuracy measurement according to claim 6. 8. The surface accuracy measurement according to claim 2, wherein at least the first mask pattern among the mask patterns is arranged over the entire surface of a pattern transfer area in the mask original plate. Original plate for surface accuracy measurement in the method.