JPH045657A - Method for measuring and inspecting thickness of phase shift film of phase shift mask, production of phase shift mask and method for inspecting defect of phase shift mask - Google Patents

Abstract

PURPOSE:To nondestructively measure film thicknesses by providing 2nd pattern forming parts without having phase shift films further to the phase shift mask having 1st pattern forming parts and determining and comparing the best focus positions of both. CONSTITUTION:Light transparent parts 12 which allow the transmission of exposing light without phase shifting are provided in correspondence to the patterns to be formed and the phase shift parts 11, 11a to shift the phase of the exposing light are formed in proximity to the transparent parts 12. The focus is changed by using this mask and the resist on the substrate to be exposed is thereby exposed, by which the patterns are transferred to the resist. The best focus position of both patterns of the case of the presence of the phase shift films and the case of the absence thereof and the difference between both are determined by measuring the transferred patterns. The deviation quantity of the focuses can be theoretically determined by simulation from the shapes, materials, etc., of the patterns and the phase shift films and, therefore, the film thicknesses are determined from the actually measured deviation quantity.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

Industrial application field Overview of the invention Conventional technology Problems to be solved by the invention Purpose of the invention Means and effects for solving the problems Examples Example-1 Example-2 Example-3 Effects of the invention [ Industrial Application Field] Each invention of the present application relates to a phase shift mask, and includes a method for measuring and inspecting a phase shift film thickness of a phase shift mask, a method for manufacturing a phase shift mask, and a defect inspection for a phase shift mask. It is about the method. Phase shift masks can be used in various pattern forming techniques, and can be used, for example, as masks for forming resist patterns in semiconductor device manufacturing processes. This can be used in fields where phase shift masks are applied.

[Summary of the Invention] The invention of claim 1.2 of the present application includes a light shielding portion on a substrate,
A phase shift mask having a first pattern forming section including a light transmitting section and a phase shift film is further provided with a second pattern forming section having no phase shift film, and a pattern formed by both pattern forming sections is formed. By finding and comparing the best focus position of both, the film thickness of the phase shift film can be determined, or whether the film thickness is appropriate can be inspected, or the film thickness of the phase shift film can be adjusted to the optimal film thickness. By forming the phase shift film, the thickness of the phase shift film can be easily measured non-destructively, or it can be inspected whether the film thickness is optimal or not, and the film can be formed with the optimal film thickness.

The invention of claim 2 of the present application provides a substrate and a phase shift film,
By inspecting a phase shift mask made of a material that has a different transmittance for light of a specific wavelength and using light of the specific wavelength, defects in phase shift masks that were previously considered impossible can be detected. This made inspection possible.

[Conventional technology]

The processing dimensions of semiconductor devices and the like tend to become smaller year by year. For this reason, in order to further improve the resolution of photolithography technology for producing miniaturized semiconductor devices, so-called phase shift technology, which imparts a phase difference to the light passing through a mask and thereby improves the light intensity profile, is gaining attention. Bathing.

Regarding the phase shift method, see Japanese Patent Application Laid-open No. 173744, MARCD, LEVENSON et al.
oving Re5solutionin Photol
ithography 1with a Phase-
Shifting Mask”IEEE TRANSA
CTIONS ON ELECTRON DEVICE
S, VOL.

ED-29No, 12. DECEMBER1982,
P1828-1836, also MARCD, LEVEN
SON et al.”The Phase-Shifting M
askI[:ImagingSimulations
and Submicrometer Re5istE
xposures" same magazine Vol', ED-31, No.
,6. It is described in JUNE 1984, pp. 753-763.

The conventionally known phase shift method will be explained using FIG. 7 as follows.

For example, when forming a line-and-space pattern, a normal conventional mask uses a light-shielding material such as Cr (chromium) on a transparent substrate l such as a quartz substrate, as shown in Figure 7(a). A light shielding part 10 is formed using a material, and a repeating pattern of lines and spaces is formed thereby to serve as an exposure mask. Ideally, the intensity distribution of the light transmitted through this exposure mask is zero at the light shielding part 10, and at other parts (transmissive parts 12a, 12b), as shown by the symbol A1 in FIG. 7(a). Let's pass through. Considering one transmitting part 12a, the transmitted light given to the exposed material has a light intensity distribution with hill-like peaks at both sides, as shown by A2 in FIG. 7(a), due to light diffraction, etc. become. The transmitted light toward the transmitting portion 12b is indicated by a dashed-dotted line. Combining the light from each transmission part 12a and 12b, A3
As shown in the figure, the light intensity distribution loses its sharpness and the image becomes blurred due to light diffraction, making it impossible to achieve sharp exposure. On the other hand, the light transmitting portion 12a of the repeating pattern.

If phase shift parts 11a are provided on every other part 12b as shown in FIG. and focus latitude is improved. That is, Fig. 7 (
As shown in b), one of the transmission parts 12a is provided with a phase shift part 1.
When 1a is formed, if it provides a phase shift of, for example, 180°, the light passing through the phase shift portion 11a is inverted as indicated by the symbol B1. Since the light from the adjacent transmission section 12b does not pass through the phase shift section 11a, such inversion does not occur. The light applied to the exposed material is inverted and cancels each other out at the bottom of the light intensity distribution at the position shown at 82 in the figure, and the distribution of light applied to the exposed material is as shown in Figure 7(b). As shown in 83, it has a sharp ideal shape.

In the above case, in order to most ensure this effect, it is most advantageous to invert the phase by 180 degrees.The phase shift part 11a is formed with a film thickness such that the refractive index of the phase shift part, λ is the exposure wavelength) is provided. .

When forming a pattern by exposure, the one that performs reduced projection is sometimes called a reticle, and the one that projects one-to-one is called a mask, or the one that corresponds to the original is called a reticle, and the one that reproduces it is called a mask. However, in the present invention, masks and reticles in various meanings are collectively referred to as a mask.

[Problems to be Solved by the Invention] There are still many problems to be solved in the field of phase shift masks.

The first problem is that it is extremely difficult to measure the thickness of the phase shift film. As mentioned above, in the phase shift technique, the effect is maximum when the phase difference is 180°. The phase difference is controlled by the thickness of the phase shift film, and the optimum film thickness is determined by D-λ/2(n-1), where n is the refractive index of the material of the phase shift film and λ is the exposure wavelength. There is.

However, in general, the area where the phase shift film is formed is very small, and the underlying layer transmits light, so it is impossible to measure the film thickness using conventional methods such as optical means, and film thickness measurement is difficult in practice. It was difficult.

For this reason, it has been difficult to know whether the thickness of the phase shift film is optimal or not. Furthermore, various materials and formation methods can be considered for the phase shift film, but the problem becomes even more difficult to solve when it comes to finding a method for measuring film thickness that can be used universally, or a means for knowing whether the film thickness is optimal. .

At the experimental level, it is possible to determine the thickness of the phase shift film by breaking the phase shift mask and observing it with an SEM, but this method does not allow for non-destructive measurement, and at the mass production stage, this method cannot be used. I can not use it.

Furthermore, in relation to the first problem, in the prior art, there is a problem in that it is not necessarily easy to obtain a phase shift mask by forming a phase shift film with an appropriate thickness.

This is the second problem. That is, as described above, since it is difficult to measure the thickness of a phase shift film, even if an attempt is made to form a film with an appropriate thickness, it is not possible to form a film while measuring the film thickness. In this case, regarding the first problem, it is also impossible to utilize SEM observation, which was possible at the experimental level. Therefore, even if the appropriate film thickness was known, it was extremely difficult to form the phase shift film while controlling the film thickness so that the film thickness could be obtained. Furthermore, when a new material is used for a phase shift film and the refractive index is unknown, the optimum film thickness cannot be immediately determined. Alternatively, there may be other cases in which the appropriate film thickness is not known. In such a case, it would be desirable to be able to form a film with an optimal film thickness even if the appropriate film thickness cannot be calculated numerically, but this has not been possible in the past.

The third problem is that there is no defect inspection method for phase shift films. Normal mask defect inspection is performed using transmitted light. In other words, a normal exposure mask has a structure in which a light-shielding film such as a Cr film that blocks almost 100% of the exposure light is attached to a substrate made of quartz or the like that is transparent to light over a wide wavelength range. Therefore, if there is a defect in the light-shielding film, it can be detected by capturing the transmitted light and comparing it with a normal pattern. For example, as shown in Figure 4, although a square light transmitting part should originally be formed, the light transmitting part is missing as shown in bl and becomes a light shielding part, or conversely, as shown in b2, a light shielding part is formed. If the light-transmitting portion is missing where it should be, the defect in the light-shielding portion a can be easily detected by inspecting the transmitted light. However, as shown in FIGS. 5(a) and 5(b), the phase shift mask, on the other hand, has a phase shift film C (for example, a SiO□ film or a resist film) attached to a part of the light transmitting part to shift the phase. This phase shift film is made of the same material as the substrate, or is made of a different material but still highly transparent, so even if a defect occurs in this film, the transmitted light will only change in phase. , it is not completely blocked like a Cr film. Therefore, even when compared with a normal transmitted light pattern,
There is no difference recognized as a defect. Therefore, for this reason, it is considered impossible to inspect defects in the phase shift film. Although the above description has been given of a structure in which a phase shift film is attached on a substrate, the same situation applies to structures having other structures, such as a case where a step is formed by etching a substrate to form a phase shift portion.

As mentioned above, there are still many problems regarding the practical aspects of using phase shift masks, and for this reason, although phase shift masks are an excellent technology in principle,
The reality is that its practical application has not progressed.

[Purpose of the invention]

Each invention of the present application is intended to solve the above-mentioned problems.

The invention of claim 1 of the present application is capable of measuring the thickness of a phase shift film non-destructively and with a highly versatile method, or determining whether the thickness of the phase shift film is appropriate. The purpose of the present invention is to provide a method for measuring and inspecting the thickness of a phase shift film.

The invention of claim 2 of the present application provides a phase shift mask that can form a phase shift film while controlling the film thickness to an appropriate thickness, and that can form a film appropriately even when the appropriate film thickness is not known. The purpose is to provide a manufacturing method.

An object of the invention of claim 3 of the present application is to provide a phase shift mask defect inspection method that can easily detect defects in a phase shift film.

[Means and effects for solving the problem 3 The invention of claim 1 of the present application includes a first pattern forming section comprising a light shielding section, a light transmitting section, and a phase shift I-MW on a substrate. A second phase shift mask having no phase shift film is further added to the phase shift mask having no phase shift film.
The present invention has a configuration in which the film thickness of the phase shift film is determined or whether or not the film thickness is appropriate is determined by determining the best focus position of both patterns from the patterns formed by both pattern forming units and comparing them. This is a method for measuring and inspecting the phase shift film thickness of a phase shift mask. According to this invention, the thickness of the phase shift film can be determined non-destructively based on the correlation between the shift in the best focus position and the film thickness. In addition, it is possible to know whether the film thickness is appropriate depending on whether the best focus positions match. This can be used for general purposes regardless of the material or shape of the phase shift section. This invention has such a configuration,
This solves the first problem.

The invention of claim 2 of the present application is a method for manufacturing a phase shift mask having a first pattern forming section on a substrate that includes a light shielding section, a light transmitting section, and a phase shift film, the method comprising: A second pattern forming section not having is provided,
By determining and comparing the hemost focus positions of the patterns formed by the second pattern forming section and the first pattern forming section during manufacture, the film of the phase shift film of the first pattern forming section is determined. This is a method for manufacturing a phase shift mask in which the thickness is adjusted to an optimum film thickness.

According to this invention, a phase shift film can be formed while optimally controlling the film thickness by detecting the best focus position. Moreover, this method is also highly versatile. This invention solves the second problem by having such a configuration.

The invention according to claim 3 of the present application is a defect inspection method for a phase shift mask having a pattern forming section on a substrate, the substrate and the phase shift film. is a defect inspection method for a phase shift mask, which is formed from a material that has a difference in transmittance to light of a specific wavelength, and is configured to inspect the phase shift mask using light of the specific wavelength. . According to this invention, since the transmittance of light of the specific wavelength is different between the substrate and the phase shift mask, it is possible to inspect the quality of the mask pattern. This invention solves the third problem with this configuration.

〔Example〕

Examples of each invention of the present application will be described below.

However, it goes without saying that each invention is not limited to each embodiment described below.

Example 1 This example embodies the invention of claim 1 of the present application, and is particularly applied to phase shift mask technology used in manufacturing miniaturized and integrated semiconductor devices. It is.

The theoretical background of this embodiment embodying the invention of claim 1 is as follows.

When exposing using phase shift technology, the phase difference is 180
It is known that when the position of best focus shifts from °, the position of best focus also shifts. Figure 1(a) shows the light intensity curve (1) for the pattern without the phase shift film.
The light intensity curves (2) and (3) for the pattern of the phase shift mask are shown in FIG. This is the case. Therefore, the peak intensities of curve (1) for the case without a phase shift film and curves (2) and (3) for the phase shift mask with a phase shift film match, and therefore the best focus position matches. . Each figure in FIG. 1 shows the case where KrF excimer laser light is used as exposure light. In addition, as shown in the upper right of each figure, the width W is 0.2 μm (Fig. 1 (
Curves (2) and (3) were obtained using a phase shift mask pattern having a phase shift film formed by forming four rectangular phase shift patterns (0.16 μm only in case d).
This is what I was looking for. As shown in the figure, the case where the distance d from the center of the square pattern and the rectangular pattern was 0.4 μm was defined as a curve (2), and the case where the distance d was 0.5 μm was defined as a curve (3).

Figures 1(b) and 1(c) show the results of calculating that the best focus position shifts when the phase shifts from 180° for these phase shift masks.
d). Figure 1(b) shows when the phase difference is 195°,
Figure 1 (C) is the same. In the case of 210', Figure 1 (d)
are the same <210" and the distance d is 0.16μ
This is the case of m. In each figure, curves (2) and (3) show the light intensity when using each phase shift mask. It is also shown that the best focus position when using a pattern that does not use a phase shift film is the same as when the phase difference is 180', as shown by curve (1) in each figure. In each figure, the focus shift on the horizontal axis indicated by defocus is set in the direction in which the wafer, which is the material to be exposed, approaches the lens.

The invention of claim 1 takes note of the fact that the optimum focus position changes as the phase difference changes in this way, and utilizes this property.

This example will be explained in detail below.

In this example, the pattern shown in FIG. 6 was used as a shift mask pattern for forming contact holes. This means that four rectangular phase shift patterns 11. are formed around the four sides of a square light transmitting section 12 as shown in the upper right corner of FIG. 1(a). This is the same shape as Ila. The reason why a mask pattern having such a shape is used to form a contact hole is that, as mentioned above, the phase shift technology creates a phase difference between the light beams used to expose adjacent patterns, thereby creating an effect in which the intensities of both lights cancel each other out. This is because, since there is no close-in light when forming isolated lines or contact holes, the phase shift technology cannot be realized as it is.

Therefore, as shown in FIG. 6, a light transmitting section 12 (phase shift amount 0
) are provided corresponding to the pattern to be formed, and a phase shift unit 11.° for shifting the phase of the exposure light. ll
a (phase shift amount of 180°) is formed close to the light transmitting portion 12 (This technology is described in the report by Terasawa et al., Autumn 1988, Proceedings of the 49th Academic Conference of the Japan Society of Applied Physics). 2, page 497, 4a-7).

In this example, a pattern using no phase shift film is formed in a portion of the phase shift mask. This may be formed, for example, in a portion (such as an end portion) where there is no practical problem. Using this mask, the resist on the substrate to be exposed is exposed while changing the focus. In this case, the entire area, including the parts with and without the phase shift film, is exposed with the focus changed little by little. For example, 0
．． Exposure is performed by changing the lens position at a pitch of 3 μm.

Thereby, the pattern is transferred to the resist.

By observing and measuring the transferred pattern, the best focus position of the pattern with and without the phase shift film and the difference (shift) between the two can be easily determined.

Since the amount of this focus shift can be theoretically determined by simulation from the shape, material, exposure wavelength, etc. of the pattern and phase shift film, it is possible to determine the film thickness from the actually measured amount of shift. The relationship between the amount of deviation and the film thickness may be determined in advance.

According to this embodiment, it is possible to immediately know whether the thickness of the phase shift film is optimal or not by comparing it with the case where no phase shift film is used.

In addition, by comparing the amount of deviation obtained through actual measurement with calculations or data obtained in advance (for example, data obtained by determining the relationship between the amount of deviation and film thickness by SEM observation),
The thickness of the phase shift film can be accurately determined in a non-destructive manner.

This example can be used for general purposes when various materials are used. For example, it can be used when a quartz substrate is used as the substrate, Cr is used as the light shielding part, and SiO□ or a resist film is used as the phase shift film. , can be applied to cases where any material is used, and can also be applied to cases where the composition of the material of the phase shift film is unknown.

Example-2 Next, Example-2 will be described. This embodiment embodies the invention of claim 2. This invention also utilizes the fact that the best focus position changes due to the phase shift described above.

In this example, when a phase shift film is formed during the manufacture of a phase shift mask, the film thickness is optimally controlled by adjusting the film thickness to the optimum film thickness using the same method as in Example-1. A phase shift film is obtained.

That is, in this embodiment, the material of the phase shift film is different from the material of the substrate, and a film of the material of the phase shift film is applied in advance to a relatively thick thickness before forming the phase shift mask. Next, using the same method as in Example 1, an estimate of the film thickness is made, and the phase shift film is polished and finished according to the estimate, thereby obtaining a phase shift film with an appropriate thickness.

This embodiment can be applied, for example, to forming a phase shift film using a resist on a quartz substrate. In addition, the underlying substrate is silicon nitride SiN (or 5iO7 with an etching stopper such as SiN), and on top of this is SiO□
This method can be applied when forming a phase shift film.

In the case of forming a phase shift film using a resist (such as PMMA), which is the former, a slightly thicker film is formed using the resist, a test is performed to determine the shift in the focus position, and based on this, an appropriate etching method is applied. (For example, 0
2 plasma ashing, etc.) to form an optimal film thickness.

When forming a phase shift film using the latter Sin,
Similarly, the above test was carried out with a thick layer of SiO2 applied,
Etching was performed using a fluorine-containing gas or the like to obtain the optimum film thickness.

Example 3 This example embodies the invention of claim 3 of the present application, and is particularly used as a defect inspection method for phase shift masks used in manufacturing miniaturized and integrated semiconductor devices. This is what I used.

In the invention of claim 3, the substrate and the phase shift film are:
The phase shift mask is formed from a material that has a difference in transmittance for light of a specific wavelength, and the phase shift mask is inspected using the light of the specific wavelength. When forming the phase shift film using a material different from that of the mask substrate, the phase shift film must have the same high transparency as the mask substrate at least for the exposure wavelength, and extremely low transparency for light at a certain wavelength that is transparent to the mask substrate. was used.

The latter type of light is used for inspection.

Specifically, in this embodiment, a normal configuration is used in which quartz is used as the material of the mask substrate, Cr is used as the material of the light shielding part, and a phase shift film is formed here using SiNx (silicon nitride). This X varies depending on the manufacturing conditions of silicon nitride, but is usually 1.0<x<1.2.

Figure 2 shows transmittance curves for each wavelength of quartz, SiN, and films. II is shown. The 5iNX film used here was CV
It was formed by the D method, and χ was approximately 1.1. The optimum thickness of the SiNx film as a phase shift film naturally depends on the exposure light, but here it is assumed to be 3000 people. .

As can be understood from Figure 2, both 5iNX and quartz substrates have high transmittance at wavelengths commonly used in optical lithography, such as g 1%, i-line, and KrF excimer laser light, and are used as phase shift masks. It is clear that it is possible.

In this example, defect inspection was performed as follows. Defect inspection of the Cr pattern, which is a light shielding part, can be performed by using light of 240 nm or more. At this wavelength, quartz, S
This is because both iNx has high transmittance and defects can be detected in the Cr pattern that does not transmit light. On the other hand, 5i
Defects in N) can be inspected using 193 nm ArF excimer laser light.As shown in Figure 2, a quartz substrate has a transmittance of about 90% at this wavelength, whereas SiNx This is because the 5iNX defect is detected using the same principle as that of a light shield because it hardly transmits the light (about a few percent).

Although the above example uses SiNx as a phase shift film, it can also be applied to other materials.

For example, it can also be used when a resist is used as a material for a phase shift film.

Figure 3 shows 5E resist manufactured by Somar.
Regarding L-N552, transmittance curve m for its wavelength
a, II[b is shown. This resist has the property that its transmittance changes with light irradiation, and ma is a curve showing the light transmittance of an unirradiated resist, and mb is a curve showing the light transmittance of a resist irradiated with light at an energy of 18°53/c+fl. According to mb, after light irradiation, the wavelength is 240n.
m, the light transmittance is about 28%, and compared to quartz, a difference in transmittance can be obtained here. The optimal film thickness for a phase shift mask for KrF is about 2000 people according to the study by the present inventors, and this film thickness is about 54%.

Even when this resist is used, defect inspection can be performed in the same manner as described above.

[Effects of the Invention] As described above, the invention of claim 1 of the present application is capable of measuring the thickness of a phase shift film non-destructively and with a highly versatile method. It is possible to know whether the film thickness is appropriate or not.

According to the invention of claim 2 of the present application, the phase shift film can be formed while controlling the film thickness to be appropriate, and even when the appropriate film thickness is not known, the film can be formed appropriately.

According to the third aspect of the present invention, defects in the phase shift film can be easily detected.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(d) are diagrams for explaining Example 1 and showing the relationship between the phase difference and the shift in the best focus position. FIG. 2 and FIGS. 3(a) and 3(b) are diagrams showing the relationship between wavelength and transmittance of materials used in Example-3. FIG. 4 and FIGS. 5(a) and 5(b) are diagrams for explaining the problem. FIG. 6 is a plan view of the hole pattern forming mask. FIG. 7 is a diagram explaining the principle of a phase shift mask. 10... Light shielding part, 11. lla... Phase shift section, 12.12b... Light transmission section.

Claims (1)

[Claims] 1. A phase shift mask having a first pattern forming section on a substrate that includes a light shielding section, a light transmitting section, and a phase shift film, and a second pattern forming section that does not have a phase shift film. A pattern forming section is provided, and the best focus position of both patterns is determined from the patterns formed by both pattern forming sections and compared, thereby determining the film thickness of the phase shift film or inspecting whether or not the film thickness is appropriate. A method for measuring and inspecting the phase shift film thickness of a phase shift mask. 2. A method for manufacturing a phase shift mask having a first pattern forming section including a light shielding section, a light transmitting section, and a phase shift film on a substrate, the second pattern having no phase shift film. A forming section is provided, and by determining and comparing the best focus position of the patterns formed by the second pattern forming section and the first pattern forming section during manufacture, the first pattern forming section A method for manufacturing a phase shift mask having a structure in which the thickness of a phase shift film is adjusted to an optimum thickness. 3. A method for inspecting defects in a phase shift mask having a pattern forming section on a substrate that includes a light shielding section, a light transmitting section, and a phase shift film, the substrate and the phase shift film being exposed to light of a specific wavelength. 1. A method for inspecting defects in a phase shift mask, the phase shift mask being formed from a material having a difference in transmittance to the phase shift mask, and inspecting the phase shift mask using light of the specific wavelength.