JP2790127B2 - Photomask and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask for a projection exposure apparatus, and more particularly to a photomask used for forming a fine pattern in a semiconductor device manufacturing process and a method of manufacturing the same.

[0002]

2. Description of the Related Art At present, in a manufacturing process of a semiconductor device, an optical lithography technique is used to form a pattern on a semiconductor substrate. In optical lithography, a photomask (an exposure original plate on which a pattern composed of a transparent area and a light-shielded area is formed by a reduction projection exposure apparatus. When the reduction ratio is not 1: 1, it is particularly called a reticle. Is transferred onto a semiconductor substrate coated with a photosensitive resin, and a predetermined pattern of the photosensitive resin can be obtained by development. The conventional optical lithography technology has responded to the development of an exposure apparatus, particularly to the miniaturization of a semiconductor device pattern by increasing the NA of a projection lens.

[0003] Here, the NA (numerical aperture) corresponds to how much light the lens can collect, and the larger the value, the more light that is spread can be collected, indicating that the performance of the lens is high. . In general, Rayleigh (Rayleig)
h), as is well known as the equation of h),
(The size of the fine pattern that can be resolved) and NA
There is a relationship of R = K1 × λ / NA (where K1 is a constant depending on the process such as the performance of the photosensitive resin), and as the NA becomes larger, the limit resolution becomes finer.

[0004] However, although the resolution is improved by increasing the NA of the exposure apparatus, the depth of focus (the range in which the deviation of the focal position can be tolerated) decreases, and it becomes difficult to further miniaturize the focal depth. Have been. Although the explanation of the actual physical meaning is omitted here, the depth of focus DO
For F and NA, DOF = K2 × λ / NA ² (where K
2 is a process-dependent constant). That is, as the NA increases, the DOF decreases, and a slight shift of the focal position cannot be tolerated.

Accordingly, various super-resolution techniques have been studied. In general, the super-resolution technique is a technique for improving the light intensity distribution on an imaging plane by controlling the transmittance and phase of light on a pupil plane of an illumination optical system, a photomask, and a projection lens system. Among various methods, improvement in resolution characteristics by optimizing an illumination system, that is, a so-called modified illumination method is highly feasible and has attracted particular attention in recent years.

Next, before describing the modified illumination method, the illumination optical system of the exposure apparatus will be described.

In the manufacture of a semiconductor device, not only miniaturization of a pattern but also improvement of its dimensional accuracy is required. In order to control the size of a pattern to be formed over the entire exposure region of the semiconductor substrate, it is necessary to illuminate the entire exposure region on the photomask with uniform intensity. However, if the photomask is illuminated by one light source, the distance from the light source to each position on the photomask is different, so that a difference in illuminance necessarily occurs. Therefore, in a normal exposure apparatus, a required illuminance uniformity is obtained by illuminating a photomask with a large number of light sources and superimposing a large number of illuminance distributions. In other words, the light emitted from the mercury lamp, which is the source of the light, is led to the fly-eye lens, which is an optical element in which single lenses of the same type are bundled in a plurality of rows, and each of the fly-eye lenses is focused. About 100 point light sources are formed. By illuminating the photomask with this point light source group, several percent
Illuminance uniformity is obtained by the deviation of.

Therefore, when the illumination system is viewed from the photomask side, only the point light source group formed by the fly-eye lens can be seen, and the original arc shape of the mercury lamp does not affect the illumination state of the photomask. . In other words, the light emission shape and light intensity distribution of the original mercury lamp have no bearing on the resolution characteristics of the exposure apparatus, but only the shape of the point light source group formed by this fly-eye lens and its light intensity distribution. Has become. Therefore, this point light source group is also called an effective light source. Generally, in an exposure apparatus, the size of this point light source group is represented by a coherent factor σ (σ = NA of illumination system / NA of projection lens system). Usually σ
= 0.5-0.7, but the optimum value may be selected in the range of σ = 0.3-0.8 depending on the mask pattern.

Furthermore, a technique for controlling the shape of the effective light source to improve the resolution characteristics has been proposed, and is generally called a modified illumination method in the sense that the shape of the effective light source is changed (as will be described below). In addition, changing the shape of the effective light source changes the incident angle of light illuminating the photomask, and is therefore sometimes called an oblique illumination method.) Then, in order to change the shape of the light source, usually, apertures or filters of various shapes are arranged immediately after the fly-eye lens. For example, as shown in FIG. 8C, there is an illumination method in which the central part of the stop is shielded from light and only the peripheral part of the fly-eye lens is used. Note that the modified illumination method is further classified according to the shape of the light source, and when a ring-type light source is used as shown in FIG.

Next, the effect of the modified illumination method will be described. In a normal illumination method, a stop 102A having a circular aperture is used as shown in FIG. At this time, as shown in FIG. 2B, there is light that is incident on the photomask 100 almost perpendicularly. In order to resolve the pattern of the photomask 100, it is necessary to collect at least 0th-order light and +1 or -1st-order light out of the diffracted light. However, when the pattern becomes finer, the diffraction angle increases. It does not enter the projection lens system 103. Therefore, in a fine pattern, vertically incident light becomes a noise component that does not contribute, and lowers the contrast of the light intensity distribution on the image plane. However, if a stop 102B having a ring-shaped opening as shown in FIG.
Light is obliquely incident on 00, and accordingly, either the +1 or −1 order diffracted light enters the projection lens 103, and most of the illuminating light serves to resolve the pattern. .

As described above, the resolution and the depth of focus can be improved by removing the vertical incident component which does not contribute to the resolution in the illumination light. However, as described herein, this modified illumination method is effective only for a periodic pattern in which diffracted light is generated, and has no effect on an isolated pattern. Therefore, Japanese Patent Laid-Open No.
As disclosed in JP-A-268714, a method has been proposed in which a fine pattern having a resolution lower than the resolution limit (hereinafter, referred to as an auxiliary pattern) is arranged around the pattern and the resolution is improved by devising an irradiation method. Was.

[0012] In addition to the modified illumination method, a phase shift mask, which is a super-resolution method by improving the photomask side, has been actively studied.

As a phase shift mask, a method called a Shibuya-Levenson method, which is suitable for a periodic pattern in which the phase of light passing through a transparent region is alternately changed by 180 degrees, was first proposed. However, this was severely limited by the patterns that could be applied,
Other schemes, such as auxiliary patterns, rims, have been proposed. In particular, a large depth of focus has conventionally been required for the formation of a contact hole, but it is difficult to achieve this. Therefore, there is a strong demand for improvement using a phase shift mask, and an auxiliary pattern method, a rim method, and a halftone method ( For example, Japanese Patent Application Laid-Open No. 4-136854) has been studied. Above all, the halftone type phase shift mask is
Attention has been paid to masks because they are easier to fabricate than other methods.

Next, the halftone type phase shift mask will be described with reference to the drawings as compared with a normal photomask. 9 and 10 used in this description, (a) is a plan view, (b) is a cross-sectional view taken along the line AA in (a), and (c) is a view immediately after the mask. (D) shows the light intensity distribution on the imaging plane. Each of the patterns on the mask was a single isolated line pattern.

First, FIG. 9 shows a general ordinary mask. In a normal mask, as shown in FIG. 1B, a chrome (C) having a thickness of 70 to 100 nm is formed on a transparent substrate 1 such as quartz.
r) and a light-shielding film 3 of chromium oxide (CrO) are formed, and by selectively removing the light-shielding film 3, a pattern including a transparent region and a light-shielding region is formed. And
The amplitude of the light passing through the mask is constant at the transparent part and zero at the light shielding part. Generally, an image formed through an optical system is described by Fourier transform.However, a mask pattern illuminated by transmitted illumination and subjected to Fourier transform is subjected to Fourier inverse transform by a projection lens system, and the original mask pattern is again formed on the image plane. It is formed. However, at this time, since the projection lens system operates as a low-pass filter, higher-order components of the Fourier transform are eliminated. Therefore, the amplitude of the light having a rectangular shape immediately after transmission through the mask and the distribution of the light intensity given by the square of the amplitude, which does not lose the rectangularity on the image forming surface, are as shown in FIG. Becomes

FIG. 10 shows a halftone type phase shift mask. This type of mask has a transparent region 1 and a translucent region formed by a translucent film 2 of a predetermined thickness such as chromium oxynitride on a transparent substrate 1. The transmittance of this translucent film is generally about 3 to 15%, and the phase of light transmitted through the transparent region and the phase of light transmitted through the translucent region is 180%.
The degree is reversed. Since light has a wavelength of 1 / n (n is the refractive index of the substance) in a substance to be transmitted, the light is transmitted through the translucent film 2 and is not transmitted due to a difference in the optical path length in the translucent film. A phase difference can be created. The phase difference θ caused by the translucent film 2 is θ = 360 × t
× (n−1) / λ, where λ is the wavelength of the exposure light, n is the refractive index of the translucent film material, and t is the thickness of the transparent film.
Therefore, in order to obtain a phase difference of 180 degrees, the thickness t of the translucent film is set to t = λ / 2 (n−1). By controlling the phase in this manner, lights having different phases cancel each other at the edge portion of the translucent film 2, and the light intensity distribution of the main pattern can be improved. However, since light leaks over the entire surface of the mask of the halftone system, when light is exposed on a semiconductor substrate using this photomask, the light leaks a plurality of times at the boundary between adjacent exposure regions. It has been pointed out that a problem of pattern abnormality (film loss of photosensitive resin) due to overlapping light is caused. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 6-28063, there has been proposed a method of forming a light-shielding region frame (hereinafter, referred to as a light-shielding band) with a light-shielding film on a semi-transparent region around an exposure region. This prevents film loss at the boundary between adjacent exposure regions.

Further, a combination of the above-described modified illumination method and this halftone mask has been studied. this is. In the conventional illumination method, the pattern is resolved by the 0th order light and ± 1st order light, whereas in the modified illumination, the pattern is resolved by the 0th order light and one of the +1 or −1 order light. This is because the contrast of the pattern is reduced as compared with the related art (however, the contrast reduction when the focal position is changed is smaller in the deformed illumination and the focal depth is wider). Therefore, using a halftone mask, the 0th-order light is reduced (the 0th-order light has an average intensity, so it decreases when light of the opposite phase is leaked). In this way, by appropriately adjusting the intensities of the 0th-order and 1st-order diffracted light, the contrast of the image can be improved (a photomask having a periodic pattern of a halftone phase shift method), and a wider focal depth can be obtained.

Although not related to the halftone mask, there is a method described in JP-A-62-291660. This is because, as the pattern size approaches the resolution limit of the exposure apparatus, the ratio of the light intensity on the semiconductor substrate corresponding to the transmitting portion and the light shielding portion of the mask decreases, so that the optimal exposure amount increases as the pattern size decreases. Become. Since various patterns are mixed on the semiconductor substrate, the optimum exposure amount differs for each pattern, and it becomes impossible to precisely control the dimensions and shapes of all the patterns. In order to solve this problem, when there are a plurality of line and space patterns, a translucent transmittance control film is provided to reduce the transmittance of the light transmitting portion of the large line and space pattern.

[0019]

As described above,
Photomask having conventional auxiliary pattern
268714) has a problem that it is difficult to prepare a mask because a fine pattern having a resolution lower than the resolution limit is required. For example, a KrF excimer laser stepper (NA = 0.5, coherent factor σ =
(0.7, magnification = 1/5), the limit resolution is about 0.2 μm, so a pattern of about 0.1 μm, which is half of the auxiliary pattern, is required. This results in a 0.5 μm pattern on the photomask, which is below the limit at which a pattern can be stably formed with the current mask drawing apparatus. Normally, an electron beam lithography apparatus is used for mask pattern drawing, and its limit resolution is about 0.3 μm. However, in this electron beam lithography apparatus, an appropriate exposure dose differs greatly depending on the pattern size. For this reason, if the exposure amount is adjusted to the main pattern, the auxiliary pattern is insufficient in exposure amount, and the dimensions are greatly reduced. When the size of the auxiliary pattern is reduced, a sufficient depth of focus effect cannot be obtained.
Further, when the exposure amount is adjusted to the auxiliary pattern, overexposure occurs in the main pattern portion, and the mask dimensional accuracy is deteriorated. Furthermore, even if the mask pattern could be patterned somehow, a problem occurred in the next inspection step. That is, in the mask inspection apparatus, all of the auxiliary patterns have been detected as pseudo defects. Therefore, in practice, the detection sensitivity of the inspection apparatus must be lowered to perform inspection without detecting the auxiliary pattern portion, and the reliability of the mask has been extremely reduced.
With the current standard mask inspection apparatus KLA331, the fine pattern that can be inspected is less than 1 μm, and 0.5 is considered to be difficult to inspect with an optical inspection apparatus in the future.

Such a problem has been tentatively solved by using a halftone phase shift type photomask.

However, the halftone phase shift type photomask has a problem that the depth of focus cannot be sufficiently improved for an isolated pattern.
Halftone phase shift type photomasks have been developed especially for opening contact hole patterns. That is, by using the illumination system of the exposure apparatus with a low σ, it is possible to obtain a depth of focus twice or more as compared with a normal mask. That is, when forming a contact hole pattern among the isolated patterns, since there is no other type of pattern on the same mask, the illumination system can be optimized only for the contact hole pattern (the σ value of the illumination system can be reduced). Can be squeezed). However, in a general case where other patterns such as a periodic pattern as well as an isolated pattern exist on the same mask, the illumination system cannot be changed, and in this case, no effect was obtained. . Therefore,
Even when a modified illumination method such as annular illumination is used for a periodic pattern, a method of increasing the depth of focus of an isolated pattern on the same photomask has been required.

Further, in a normal photomask which is not a halftone method, in a photomask in which an isolated pattern and a periodic pattern are mixed, there is a problem that the transfer dimension of the isolated pattern is large and the transfer dimension of the periodic pattern is small. . The reason is that the relative light intensity at the light-shielding region end (the portion in contact with the light-transmitting region) in the photoresist film becomes larger in the periodic pattern due to the proximity effect. It is due to the phenomenon of shortage.

Furthermore, in addition to these structural problems of the photomask, there is a problem as a manufacturing method. It is disclosed in JP-A-6-282063 and JP-A-62-2916.
Each of the photomasks described in Japanese Patent Application Publication No. 60-260 has a light-shielding film and a translucent film, but has a problem derived from the fact that they cannot be selectively removed from each other.

First, as described in Japanese Patent Application Laid-Open No. 6-282063, this is a halftone type photomask in which a light shielding film is provided on a semitransparent film as described above. Since the light-shielding film formed on the film is selectively removed to form a light-shielding band around the exposed area, it is difficult to remove the light-shielding film without affecting the translucent film. There was also a problem. That is, when chromium oxynitride is used as a translucent film, it is impossible to selectively leave a light-shielding film on the semi-transparent film by any of dry etching and wet etching with conventional materials. Therefore, a method has been proposed in which molybdenum oxynitride is used as the translucent film and chromium is used as the light-shielding film. This is a method in which a predetermined photosensitive resin pattern is formed in a first lithography process using a mask substrate in which a translucent film of molybdenum oxynitride and a light shielding film of chromium are sequentially formed on a quartz transparent substrate.
The light-shielding film is processed by dry etching using chlorine gas, and the translucent film is processed by dry etching using fluorine gas. Once the photosensitive resin is peeled off, the lithography process is used again to leave only the light-shielding film as a light-shielding band. A photosensitive resin pattern was formed, and only the light shielding area was processed by wet etching. However, this molybdenum oxynitride silicide has a problem in that ordinary mask cleaning (for chromium-based materials) cannot be used because of its poor resistance to alkali. In addition, in the conventional mask making using a chromium-based material, when a problem occurred in the mask making, it was possible to peel off the light-shielding film and reuse the transparent substrate, but this molybdenum silicide-based material is There was no means for selectively etching the transparent substrate (quartz), and it was impossible to reuse the transparent substrate.

Next, in the device described in Japanese Patent Application Laid-Open No. 62-291660, a transmittance control film made of a translucent film is partially formed outside the light-shielding film. Since the transmittance control film is formed and processed after forming the light-shielding pattern, there is a problem that it is difficult to inspect the transmittance control film for defects and to measure the transmittance. In other words, on a transparent substrate without any pattern, it is possible to inspect the pinholes and foreign substances of the translucent transmittance control film to some extent. Inspection of defects that occur sometimes cannot be performed.

Further, there is a problem in manufacturing a mask. That is, in a normal mask, chromium and chromium oxide are used for the light-shielding film. However, forming a chromium transmittance control film partially on the mask by sputtering or CVD requires accurate position and transmittance accuracy. Was impossible in terms of face. Therefore, in consideration of actual mask production, it is necessary to use different materials for the light-shielding film and the transmittance control film so that they can have a selective etching ratio. For example, if molybdenum silicide is used for the light-shielding film and chromium is used for the transmittance control film, a wat mask in which the transmittance is partially changed as shown in JP-A-62-291660 can be manufactured. However, even when these materials are used, the above-described problems of mask cleaning and damage to the transparent substrate occur. In particular, etching damage to the transparent substrate causes a decrease in transmittance due to surface roughness, and thus poses a serious problem in a photomask having this transmittance control film.

Accordingly, a first object of the present invention is to provide a photomask in which an isolated pattern and a periodic pattern are mixed and which can be transferred with high accuracy. More specifically, the present invention provides a halftone phase shift type photomask (first photomask) in which the depth of focus of an isolated pattern is increased, and a normal photomask (second photomask) capable of transferring an isolated pattern and a periodic pattern without dimensional difference. Photomask).

A second object of the present invention is to provide a method for manufacturing a photomask having a light-shielding film and a translucent film, in particular, the first and second photomasks can be formed with good reproduction.

[0029]

According to a first aspect of the present invention, there is provided a photomask, comprising: an isolated pattern portion including a first opening provided in a semi-transparent film covering a transparent substrate; A photomask for transferring a fine pattern, the photomask having a periodic pattern portion including a plurality of second openings periodically arranged at a predetermined pitch in the translucent film in a distant region; The thickness is set to λ / 2 (n−1), where n is the refractive index, and λ is the wavelength of the exposure light at the time of transfer, and the transfer is performed by utilizing the mutual interference of the diffracted light at the periodic pattern portion. In a halftone phase shift type photomask, a predetermined dimension L
An auxiliary pattern made of a light-shielding film having a separated width W is provided, and the L and W are more than 0.2λ / NA and less than 1.3λ / NA (NA is the numerical aperture of the exposure apparatus, respectively).

Further, L and W may be equal to the width of the first opening.

The first method of manufacturing a photomask according to the present invention comprises the steps of sequentially applying a chromium (or ruthenium) translucent film and a ruthenium-based light-shielding film on a transparent substrate, The light-shielding film is selectively removed by reactive ion etching using a gas containing (chlorine) as a main component, and the first light-shielding film is periodically formed at a predetermined pitch in a first opening and an area at least a fixed distance from the first opening. A first lithography step of providing a plurality of second openings arranged in a matrix, and removing the translucent film by reactive ion etching using a gas containing chlorine (or oxygen) as a main component using the light shielding film as a mask And selectively removing the light-shielding film again by reactive ion etching using a gas containing oxygen (or chlorine) as a main component and separating the light-shielding film having a width W from the first opening by L. To Is that having a to the second lithography process.

The second photomask of the present invention comprises a first light shielding member selectively provided on a transparent substrate and a region periodically separated from the first light shielding member by at least a predetermined dimension at a predetermined pitch. A plurality of second light shields arranged and two adjacent light shields
A translucent transmittance control film that covers the transparent substrate surface between the two light-shielding bodies, and a thickness of the transmittance control film,
Assuming that the refractive index is n and the wavelength of the exposure light is λ, λ / 4 (n−
1) It is less than.

According to the first method of manufacturing a second photomask of the present invention, a translucent ruthenium (or chromium) film and a chromium (or ruthenium) light-shielding film are sequentially deposited on a transparent substrate. And selectively removing the light-shielding film by reactive ion etching using a gas containing oxygen (or chlorine) as a main component to form a first light-shielding body and a region at least a certain distance away from the first light-shielding body. A first lithography step of forming a plurality of second light shields periodically arranged at a pitch; and covering the first light shield outside an area where the second light shield is provided. A second lithography step of selectively removing the translucent film in a region where there is no gas by reactive ion etching using a gas containing chlorine (or oxygen) as a main component. , Its refractive index n, exposure As the wavelength of λ, λ / 4 (n-
1) It is less than.

According to a second method of manufacturing a photomask of the present invention, a chromium-based (or ruthenium-based) light-shielding film is deposited on a transparent substrate, and a gas containing oxygen (or chlorine) as a main component. A first light-shielding body by selectively removing the light-shielding film by reactive ion etching using a plurality of second light-shielding bodies periodically arranged at a predetermined pitch in a region at least a predetermined distance from the first light-shielding body; A first lithography step, a step of forming a ruthenium-based (or chromium-based) translucent film on the entire surface, and a step of forming the translucent film outside the region where the second light-shielding member is provided with chlorine ( Or a second lithography step of removing the semi-transparent film by a reactive ion etching using a gas containing as a main component a gas having a refractive index of n and a wavelength of exposure light of λ. As
less than λ / 4 (n-1).

In each of the above manufacturing methods, the translucent film and the light-shielding film can be formed by sputtering chromium and ruthenium in a gas atmosphere containing oxygen and / or nitrogen, respectively.

Since the first photomask has the auxiliary pattern provided near the first opening, the depth of focus is improved by utilizing the mutual interference of diffracted light in accordance with the periodic pattern having the second opening. be able to.

In the second photomask, the light intensity distribution on the image plane when the normal mask is used is different between the isolated pattern and the periodic pattern, and the line width of the transfer pattern of the positive photoresist film is relatively equal to that of the isolated pattern. The thickening proximity effect is corrected by the transmittance control film.

When manufacturing the first photomask and the second photomask, one of the light-shielding film and the translucent film is formed of a ruthenium-based material, and the other is formed of a chromium-based material. Reactive ion etching using a gas containing oxygen as a main component and the latter using a gas containing chlorine as a main component can be removed with a large selectivity.

[0039]

Next, an embodiment of the present invention will be described.

FIG. 1A is a plan view of a photomask according to the first embodiment of the present invention, and FIG.
FIG. 1C is a graph showing the amplitude distribution of the transmitted light of the photomask, and FIG. 1D is a graph showing the light intensity distribution on the imaging plane.

In this case, an i-line with a reduction ratio of 5 (magnification: 1/5) (mask pattern size: pattern size on the image plane = 5: 1), NA = 0.6 and σ = 0.6 is used as the exposure apparatus. A photomask pattern for transferring an isolated pattern having a width of 0.35 μm (on the image plane) and a line and space pattern (width = space = 0.35 μm) to a negative photoresist film, using a reduction projection exposure apparatus is shown. Shall be. The illumination method is a 50% annular illumination method.

As shown in FIGS. 1A and 1B, an opening 61a having a width of S = 1.75 μm is formed in the translucent film on the transparent substrate 1, and the opening 61a is formed on the translucent film 2. To L
= Light-shielding film 13 having a width of W = 1.75 μm at intervals of 1.5 μm
An auxiliary pattern a is formed. S = 1.75 μm at a distance L ₂ from such an isolated pattern portion
A plurality of openings 62a having a width are provided in parallel at an interval L ₁ = 1.75 μm to form a line and space pattern. Dimension L ₂ is at least 2S, preferably with more dimensions 3S. An isolated pattern is usually used to mean an isolated pattern where the distance between adjacent patterns is more than a certain level and the mutual influence can be ignored from the viewpoint of photolithography. It is said that the distance should be at least twice, preferably three times or more the size of the isolated pattern.

Although not shown, a light-shielding film formed simultaneously with the light-shielding film 13a is formed as a light-shielding band having a width equal to or larger than the dimension at the outer peripheral portion of the exposure area on the photomask. It is disclosed in Japanese Patent Application Laid-Open No. 6-2820 to prevent light leakage at the outer peripheral portion of the exposure area during exposure.
This is the same as the conventional example described in JP-A-63-63. Since the amplitude distribution of the light transmitted through the photomask is “0” at the light shielding film 13a, the light intensity distribution on the translucent substrate (imaging plane) also approaches the line-and-space pattern,
As a result, the depth of focus can be increased. That is,
In addition to the original edge enhancement effect of the halftone phase shift mask, by providing the light shielding film 13a (auxiliary pattern) to provide periodicity, the mutual interference of diffracted light is used. Can be given.

As described above, in the present photomask, the isolated space pattern is provided with periodicity to improve its exposure characteristics. Therefore, the arrangement of the pattern of the light shielding film 13a has an appropriate value. Usually, as shown here, it is optimal that the size W of the light shielding pattern and the distance L between the opening and the light shielding pattern are the same as the size of the opening. In other words, if the distance L between the opening and the light-shielding pattern is small, the lens cannot be resolved and the edge enhancement effect of the halftone phase shift method is lost, and if the width W of the light-shielding pattern is too narrow, periodicity is lost. Would. Here, it is appropriate that these dimensions are 0.1 μm or more on the imaging surface. On the other hand, if these dimensions L and W are too large, the effect of imparting periodicity to the isolated aperture pattern and expanding the depth of focus is reduced, and 0.8 μm or less is appropriate. Generally, when these dimensions L and W are normalized by λ / NA, they can be expressed in a manner independent of exposure conditions. Therefore, in order to improve the exposure characteristics of the isolated aperture, these dimensions L, W
Is 0.2 × λ / NA <L, W <1.3 × λ.
/ N.

FIG. 2 shows a comparison between the present photomask and a conventional halftone phase shift type photomask.
The simulation result of a 35-micrometer isolated pattern is shown.
In the figure, the horizontal axis is the focus position, and the vertical axis is the log slope at the edge of the pattern: δlnI (x) / δx.
(Where ln is the natural logarithm, I (x) is the relative light intensity, x
Denotes a position on the semiconductor substrate (imaging plane). This log slope (image log-slo)
Since pe) is related to the concentration distribution of the photosensitizing agent in the photosensitive resin after exposure, it is possible to estimate the depth of focus by assuming that the pattern is resolved at a certain log threshold or above a certain threshold value. In a normal i-line resist, the pattern is resolved with a log lobe of 7 or more.
It can be seen that the depth of focus of m (this is a value on one side of the focal position +/- and thus 1.4 μm in the range) expands to 0.8 μm (1.6 μm in the range) in the present photomask.

Next, a method of manufacturing a photomask according to the present invention will be described with reference to the drawings. FIG. 3 shows main manufacturing steps of the photomask. This is the portion shown on FIG. 1 on the photomask.

First, as shown in FIG. 3A, a translucent film 2 of chromium oxynitride is formed on a transparent substrate 1. here,
Although the optical constant of chromium oxynitride varies depending on the film forming conditions, for a halftone phase shift mask, n = 2.6 k
= 0.7 is set. The thickness t of the translucent film 2 is set to 114 nm, the phase difference is set to 180 degrees, and the transmittance is set to 5% from the equation of t = λ / 2 (n−1). This chromium oxynitride film is obtained by sputtering chromium in an atmosphere of a pressure of 10 Pa in which an argon gas, an oxygen gas and a nitrogen gas are mixed at a ratio of 2: 1: 2. After inspecting the translucent film 2 for defects such as pinholes, ruthenium is sputtered in an atmosphere in which an argon gas and an oxygen gas at a pressure of Pa are mixed at a ratio of 1: 1 to form a ruthenium oxide film thereon. Is formed as a light shielding film 13 with a thickness of 50 nm.

Next, a photosensitive resin film 5 for electron beam exposure
Is formed by a coating method, and a mask pattern is drawn (electron beam exposure). Next, after developing to form openings 61 and 62 in the photosensitive resin film 5 as shown in FIG.
The light shielding film 13 is formed by dry etching using oxygen gas.
To process. Then, as shown in FIG. 3C, the translucent film 2 is processed by dry etching (reactive ion etching) using chlorine gas using the processed light shielding film 13 as an etching mask. Then, as shown in FIG. 3D, the photosensitive resin film 5 is once peeled off, a photosensitive resin film 7 for electron beam exposure is formed, and then a pattern of a light shielding film is drawn. Here, an auxiliary pattern is drawn in the exposure area, and a light-shielding band pattern is drawn on the outer periphery of the exposure area (not shown). Next, after developing, FIG.
As shown in (e), the light shielding film 13 is processed by dry etching (reactive ion etching) using oxygen gas again using the photosensitive resin film 7a as a mask.
An auxiliary pattern by 3a and a light-shielding band around the exposure area are formed. Finally, the photosensitive resin film 7a is peeled off, and FIG.
A photomask as shown in (a) and (b) is obtained. It is considered that ruthenium oxide that is stable at room temperature is further oxidized by reactive ion etching to become volatile RnO ₄ or the like and is etched.

In the photomask manufacturing method, since both the light shielding film 13 and the translucent film 2 are processed by dry etching, there is an advantage that the dimensional accuracy is improved as compared with the conventional method using wet etching. Further, ruthenium oxide has high chemical resistance to acids and alkalis, and does not cause any problem even in a conventional mask cleaning method. In addition, chromium can be removed by wet etching conventionally used in photomask manufacturing, and ruthenium oxide can be removed by dry etching containing oxygen as a main component, so that any can be peeled off without damaging a transparent substrate such as quartz. . Therefore, even if an abnormality is found in the inspection in the final step, the light-shielding film and the translucent film are once peeled off, and the transparent substrate can be reused.

FIG. 4 is a sectional view of a photomask according to the second embodiment of the present invention.

This embodiment is an improvement of a normal photomask in which an isolated pattern and a periodic pattern are mixed.

As in the first embodiment, the magnification is 1/5 and N
Using an i-line reduction projection exposure apparatus with A = 0.6 and σ = 0.6, a positive pattern of an isolated pattern having a width of 0.35 μm and a line and space pattern having a width and space of 0.35 μm on an image forming surface is obtained. This is a photomask to be transferred to a photoresist film. The illumination method is a 50% annular illumination method.

A light-shielding film 3a having a width of 1.75 μm is provided in the isolated pattern portion, and a plurality of light-shielding films 3b having a width of 1.75 μm are provided in the line and space portion at an interval of 1.75 μm. A transmittance control film 8a made of a translucent film is provided on the entire surface of the line and space portion.

In photolithography, it is known that the pattern size of a photosensitive resin film formed on a semiconductor substrate differs even with the same mask pattern size due to the density of the pattern (proximity effect). There are various types of proximity effects such as dimensional change due to pattern density, shrinkage of line tip, rounded corners, and dimensional difference between line and space.The most well-known is dimensional change due to pattern density. In particular, the dimensional difference between the line-and-space pattern and the isolated line pattern. FIG. 5 shows a light intensity distribution (relative light intensity: a value obtained by standardizing the light intensity at the center of a sufficiently wide transparent area as 1) on the image plane according to the second embodiment. In the figure, the position on the semiconductor substrate = 0.1
75 μm is the edge of the mask pattern (0 to 0
0.175 μm is a light-shielding portion, and 0.175 to 0.35 μm is a transparent portion). The light intensity level at which the line and space pattern is formed to size is 0.297, while the light intensity level at which the isolated pattern is formed to size is 0.19.
It is 6. Therefore, at the same exposure, the isolated pattern becomes thicker than the line and space pattern,
Assuming that the line and space pattern is 0.35 μm, the isolated line becomes 0.41 μm and 0.06 μm thicker. Therefore, in order to correct the proximity effect, a translucent film (8a) having a transmittance of 67% is formed on the line and space pattern portion, so that the dimensional difference between the line and space pattern and the isolated pattern can be eliminated ( 67% line and space transmittance
Then, the relative light intensity at the pattern edge is 0.297
× 67% = 0.196, which is the same as an isolated pattern).

Here, if a phase difference occurs due to the transmittance control film, dark portions are formed near the edges of the translucent film due to interference between lights having different phases. Therefore, the phase difference (t × 360 × (n1-
1) / λ degrees, where t is the film thickness of the transmittance control film, and n is the refractive index), the smaller the better, the more the phase difference should be at least in order not to affect the pattern near the edge of the transmittance control film. It must be 90 degrees or less, and for that purpose, the thickness t of the translucent film may be set to t <λ / 4 (n−1). In this embodiment, n = 2.0, t = 12 nm, and the phase difference is 11.
8 is assumed.

Next, a manufacturing method according to the second embodiment will be described. First, ruthenium is sputtered in an atmosphere of a mixture of argon and oxygen gas at a pressure of 10 Pa at a ratio of 2: 1 to form a film having a thickness of 12 nm as shown in FIG.
Of the ruthenium oxide film 8 is formed. This ruthenium oxide film is made of the above-described transmittance control film (having a transmittance of 67 for i-line).
%), It is preferable that the phase difference does not occur as much as possible. Therefore, the oxygen pressure is reduced to increase the k value, and the n value is reduced to 2.0. After inspecting the transmittance and defects, a chromium film (thickness: 70 nm) and a chromium oxide film (thickness: 3 nm) are formed thereon.
The light-shielding film 3 made of a laminated film having a thickness of 0 nm is formed.

Then, as shown in FIG. 6B, a photosensitive resin film 63 for electron beam exposure is formed by a coating method, and a light-shielding pattern is drawn. Then, as shown in FIG. 6C, a pattern of the photosensitive resin film 63a is formed by development, and processed into a light-shielding film pattern by dry etching using chlorine gas. Then, the photosensitive resin film 63a is once peeled off, and the light-shielding pattern is inspected and corrected.
As shown in (d), a photosensitive resin film 64 is formed again by a coating method, and a translucent pattern is drawn. Then, after developing and forming a predetermined pattern (covering the line and space pattern portion) of the photosensitive resin 64a, the transmittance control film 8a is formed by dry etching using oxygen gas. Finally, the photosensitive resin film 64a is peeled off again,
The photomask shown in FIG. 4 is obtained. The transmittance control film 8
When the phase difference generated in step (a) approaches 180 degrees, light shielding portions are formed by canceling out light beams having different phase differences at the pattern edge of the transmittance control film, and an unnecessary pattern is formed on the semiconductor substrate. However, in the present embodiment, since only a phase difference of 11.8 degrees occurs in the transmittance control film 8a, there is no adverse effect on the pattern edge.

In the present photomask, since the processing of the transmittance control film is performed by dry etching particularly using oxygen gas, the light shielding film 3a (chromium oxide) is not damaged at all. For example, chromium oxide is known to be etched by dry etching using a fluorine gas, although the etching rate is low, but the reactant adheres to the surface being etched and causes surface roughness. However, in this embodiment, there is no problem of such etching of chromium oxide. Further, side etching does not occur in the translucent film unlike wet etching. When the side etching occurs, the light shielding film protrudes from the translucent film, which causes problems such as attachment of foreign matter and damage of the light shielding film.

Next, a third embodiment of the present invention will be described along its manufacturing steps. Here, it is assumed that the line and space portion and the isolated pattern portion of the 0.35 μm pattern are formed on the photomask as in the second embodiment.

In the actual pattern formation on the semiconductor substrate, the pattern shape of the photosensitive resin differs from that of the simulation due to the influence of the structure of the semiconductor substrate, the level difference, the aberration of the lens of the exposure apparatus or the dimensional error of the photomask itself. It becomes dimensions. Here, the dimensional difference between the line and space and the isolated line is considered. For example, when the line and space portion is located above the step of the semiconductor substrate and the isolated line is located below the step, coating is performed by a spin coating method. Depending on the difference in the thickness of the photosensitive resin, the isolated line may be thicker than the dimensional difference described above.

Therefore, in this embodiment, first,
Exposure is performed on an actual semiconductor substrate using a photomask in which a pattern of a chromium and chromium oxide light-shielding film 3b is formed on a conventional quartz transparent substrate 1 shown in FIG. The dimensions of the photosensitive resin pattern formed thereon are measured. Then, a transmittance for correcting the dimensional difference is obtained by simulation, and as shown in FIG. 7B, a predetermined thickness of ruthenium oxide 8 is formed as a transmittance control film. Then, as shown in FIG.
A photosensitive resin film 65 is applied, and a pattern of a transmittance control film is drawn. Then, as shown in FIG. 7D, a pattern of the photosensitive resin film 65a is formed by development, and a transmittance control film 8b is formed by dry etching using oxygen gas. Finally, the photosensitive resin film 65a is peeled off, and FIG.
A photomask shown in FIG.

In the present photomask, the transmittance on the photomask is controlled in consideration of the unpredictable error in the thickness of the underlayer of the semiconductor substrate, the dimensional error of the light-shielding pattern on the photomask, and the like. Further, there is an advantage that the dimensional difference can be accurately corrected. In addition, since a photomask using a conventional chromium-based material can be similarly corrected by using the present method, there is an advantage that the photomask created so far can be effectively used.

Although a line-and-space pattern has been described as a typical example of the periodic pattern, the present invention can be applied to a pattern having an arbitrary periodic pattern.

Further, a ruthenium film or a ruthenium oxide film can be used as a light shielding film, and a chromium oxide film can be used as a translucent film. Further, the method for manufacturing a photomask can be applied to any photomask having a light-shielding film and a translucent film in addition to those described above. For example, Japanese Patent Application Laid-Open No. 6-2020
No. 63 having a light-shielding band on a semi-transparent film, and Japanese Unexamined Patent Publication No. 62-291660 having a large line-and-space pattern provided with a translucent transmittance control film. Applicable to The light-shielding film is formed of chromium (or ruthenium), the translucent film is formed of ruthenium (or chromium), and the chromium-based film is patterned by reactive ion etching using a gas containing chlorine as a main component. The ruthenium-based film may be patterned by reactive ion etching using a gas containing oxygen as a main component.

[0065]

As described above, the first photomask of the present invention is located near the first opening of the isolated pattern portion in the halftone phase shift type photomask in which the isolated pattern portion and the periodic pattern portion are mixed. By providing the light-shielding auxiliary pattern on the semi-transparent film, the depth of focus of the isolated pattern portion can be increased. Therefore, there is an effect that both the isolated pattern and the periodic pattern can be accurately transferred to the photoresist film.

In the second photomask of the present invention, the light intensity on the image forming surface is obtained by providing a translucent transmittance control film in the periodic pattern portion in a normal photomask in which the isolated pattern portion and the periodic pattern portion are mixed. The proximity effect in which the distribution differs between the isolated pattern and the periodic pattern and the line width of the transfer pattern of the positive photoresist film becomes relatively large in the isolated pattern portion can be corrected. Therefore, there is an effect that both the isolated pattern and the periodic pattern can be accurately transferred.

In manufacturing such a photomask having a light-shielding film and a translucent film, one of the light-shielding film and the translucent film is formed of a ruthenium-based material, and the other is formed of a chromium-based material. By patterning the former by reactive ion etching using a gas containing oxygen as a main component and the latter by using a gas containing chlorine as a main component, it is possible to remove them with a large selectivity.

Therefore, there is an effect that a photomask can be formed with good reproducibility without adversely affecting each other.

[Brief description of the drawings]

FIG. 1 is a plan view (FIG. 1) showing a first embodiment of the present invention;
(A)), a cross-sectional view taken along line AA of FIG.
(B)), a graph showing the amplitude distribution of transmitted light (FIG. 1)
(C)), a graph showing the light intensity distribution on the image plane (FIG. 1 (d)).

FIG. 2 is a graph for explaining the first embodiment.

3A to 3E are cross-sectional views in the order of steps, illustrating the manufacturing method according to the first embodiment;

FIG. 4 is a sectional view showing a second embodiment of the present invention.

FIG. 5 is a graph for explaining a second embodiment.

FIGS. 6A to 6E are cross-sectional views in the order of steps, illustrating the manufacturing method according to the second embodiment; FIGS.

FIGS. 7A to 7E are cross-sectional views in the order of steps for explaining a third embodiment of the present invention.

8 is a plan view of an aperture in a normal illumination method (FIG. 8)
(A)), a schematic diagram of the optical system (FIG. 8 (b)), a plan view of the diaphragm in the annular illumination method (FIG. 8 (c)), and a schematic diagram of the optical system (FIG. 8).
(D)).

9 is a plan view of a conventional halftone phase shift type photomask (FIG. 9A), a cross-sectional view taken along line AA of FIG. 9A (FIG. 9B), and an amplitude distribution of transmitted light. (FIG. 9C) and a graph showing the light intensity distribution on the image plane (FIG. 9D).

FIG. 10 is a plan view of a conventional ordinary photomask (FIG. 10);
(A)), a cross-sectional view taken along line AA of FIG.
(B)), a graph showing the amplitude distribution of transmitted light (FIG. 10)
(C)), a graph showing the light intensity distribution on the image plane (FIG. 10)
(D)).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Translucent film 3, 3a, 3b, 13, 13a Light shielding film 5 Photosensitive resin film 61 Opening 62, 62a Opening 7, 7a Photosensitive resin film 63, 63a Photosensitive resin film 64, 64a Photosensitive resin film 65, 65a Photosensitive resin film 8, 8a, 8b Translucent film 100 Photomask 101 Flyer lens 102A, 102B Stop 103 Projection lens 104 Semiconductor substrate (photoresist film)

Claims (8)

(57) [Claims] An isolated pattern portion including a first opening provided in a semi-transparent film covering a transparent substrate, and a predetermined pitch between the semi-transparent film in an area at least a predetermined distance from the first opening. A micropattern transfer photomask having a periodic pattern portion including a plurality of second openings periodically arranged in a semi-transparent film. Assuming that the wavelength of the exposure light is λ, λ / 2 (n
In a halftone phase shift type photomask which is set to -1) and is transferred by utilizing mutual interference of diffracted light in the periodic pattern portion, a light shielding film having a width W separated by a predetermined distance L from the first opening. Where L and W exceed 0.2λ / NA, 1.3λ /
A photomask characterized by being smaller than NA (NA is the numerical aperture of an exposure apparatus, respectively). 2. The photomask according to claim 1, wherein L and W are each equal to the width of the first opening. 3. A step of sequentially applying a chromium-based (or ruthenium-based) translucent film and a ruthenium-based (or chromium-based) light-shielding film on a transparent substrate; The light-shielding film is selectively removed by reactive ion etching using a gas to be removed, and the plurality of first openings and a plurality of the light-shielding films periodically arranged at a predetermined pitch in an area at least a fixed distance from the first openings. A first lithography step of providing a second opening, a step of removing the translucent film by reactive ion etching using a gas containing chlorine (or oxygen) as a main component using the light-shielding film as a mask, A second lithography in which the light-shielding film is selectively removed by reactive ion etching using a gas containing (or chlorine) as a main component to leave the light-shielding film having a width W separated from the first opening by L. Engineering 3. The method of manufacturing a photomask according to claim 1, further comprising the steps of: 4. A first light shield selectively provided on a transparent substrate, and a plurality of second light shields periodically arranged at a predetermined pitch in an area at least a predetermined dimension away from the first light shield. And a translucent transmittance control film that covers the surface of the transparent substrate between the two adjacent light shields. The thickness of the transmittance control film is such that the refractive index is n and the exposure is n. A photomask, wherein λ is less than λ / 4 (n−1), where λ is the wavelength of light. 5. A step of sequentially applying a ruthenium (or chromium) translucent film and a chromium (or ruthenium) light-shielding film on a transparent substrate, and comprising oxygen (or chlorine) as a main component. The light-shielding film is selectively removed using reactive ion etching using a gas to form a first light-shielding body and a plurality of second light-shielding bodies periodically arranged at a predetermined pitch in an area at least a predetermined distance from the first light-shielding body. A first lithography step of forming a light-shielding body, and applying a chlorine (or oxygen) to the translucent film in a region outside the region where the second light-shielding member is provided and not covered with the first light-shielding member. A second lithography step of selectively removing by reactive ion etching using a gas containing, as a main component, the thickness of the semi-transparent film, the refractive index thereof being n, and the wavelength of exposure light being λ. As λ / 4
(N-1). 6. A step of depositing a chromium-based (or ruthenium-based) light-shielding film on a transparent substrate and selecting the light-shielding film by reactive ion etching using a gas containing oxygen (or chlorine) as a main component. A first lithography step of forming a first light-shielding body and a plurality of second light-shielding bodies periodically arranged at a predetermined pitch in a region at least a certain distance away from the first light-shielding body; Forming a semi-transparent film based on chromium (or chromium) and reacting the semi-transparent film outside the region where the second light-shielding member is provided with a gas containing chlorine (or oxygen) as a main component. A second lithography step of removing by semi-conductive ion etching, wherein the thickness of the translucent film is less than λ / 4 (n−1), where n is the refractive index and λ is the wavelength of the exposure light. Photomask manufacturing method characterized by the following: Law. 7. A step of forming a chromium (or ruthenium) light-shielding film on a transparent substrate and reactive ion etching using a gas containing chlorine as a main component (or a gas containing oxygen as a main component). Patterning a light-shielding film, forming a ruthenium-based (or chromium-based) translucent film, and performing reactive ion etching using a gas containing oxygen as a main component (or a gas containing chlorine as a main component). Patterning a translucent film. 8. The method of manufacturing a photomask according to claim 2, wherein the translucent film and the light-shielding film are formed by sputtering chromium and ruthenium in a gas atmosphere containing oxygen and / or nitrogen, respectively. .