JP3322223B2 - Phase shift mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a phase shift mask used in photolithography, and more particularly to a phase shift mask having a function of correcting pattern deformation.

[0002]

2. Description of the Related Art Phase shift masks have been developed to extend the limits of optical lithography. A phase shift mask changes the phase of transmitted light of a transmission mask (reflected light in a reflection mask such as an X-ray) partially by 180 degrees, and is caused by the interference between light having no phase and light whose phase has been changed by 180 degrees. The light that does not contribute to the pattern is canceled out, and the intensity distribution of the light that contributes to the pattern on the image plane is sharpened. Although there are various types of phase shift masks, most of them require a special mask design, and there is still a problem in the manufacture of masks, which has not yet been put to practical use. However, a phase shift mask called a halftone (attenuation) method has almost completely solved these design and manufacturing problems, and has been gradually used in semiconductor manufacturing. The halftone type phase shift mask (hereinafter, abbreviated as a halftone mask) is to generate a small amount of transmitted light in a portion of the mask which is originally a completely light-shielded region, and to add the transmitted light to light of a peripheral transparent region. This is a phase shift mask having a phase difference of 180 degrees.

FIG. 8 shows an example of a conventional halftone mask. FIG. 8A is a plan view and FIG. 8B is a longitudinal sectional view. On a quartz transparent substrate 11, molybdenum oxynitride (MoSiON) or chromium oxynitride (CrO
By forming a translucent film such as N) and setting the film thickness to a predetermined thickness, the phase difference of the transmitted light transmitted through the translucent film is adjusted to 180 degrees. The film that is translucent and generates a phase difference of 180 degrees in transmitted light is referred to as a halftone film 12. In order to set the phase difference to 180 degrees, it is necessary to set the thickness t of the halftone film 12 to the following value. t = λ / (2 × (n−1)) Here, λ is the wavelength of the exposure light, and n is the refractive index of the halftone film 12 with respect to the exposure light. The transmittance of the halftone film 12 is 4
The value is generally about 20%, but the optimum value differs depending on the applied pattern and exposure conditions (numerical aperture NA of the exposure apparatus, coherent factor σ, etc.).

Further, a pattern for forming an exposure pattern, here a hole pattern 1 is opened in a part of the halftone film 12, and a light shielding film 13 is provided in a peripheral region surrounding the hole pattern 1. It is arranged. The light shielding film 13 needs to be able to be selectively etched with the halftone film 12. For example, when molybdenum oxynitride is used for the halftone film 12, chromium (more precisely, two layers of chromium oxide and chromium) is used as the material of the light shielding film 13. Chromium is wet-etched (ceric ammonium nitrate)
Can be removed without affecting molybdenum oxynitride silicide. The light-shielding film 13 is provided to prevent unnecessary light from leaking to an adjacent exposure area when the exposure apparatus transfers a mask pattern onto a semiconductor substrate (hereinafter, referred to as a wafer). When the light-shielding film 13 is not provided, the transmitted light of the halftone film 12 is irradiated at the boundary of the exposure region, the photosensitive resin (hereinafter, referred to as a resist) in that portion is developed, or the dimension of the resist pattern changes. Problems occur.

[0005] However, it has been reported that when a halftone mask is used, the resolution and depth of focus are improved, but the pattern to be exposed is deformed. For example, the 45th Association of Applied Physics-related Associations
o. 2, pp. 733, Lecture No. 30p-YL-2, Uchiyama et al., "Study of Contact Hole Pattern Formation by Combination of Halftone Phase Shift Method and Modified Illumination Method (1)", March 30, 1998. For this reason, when forming a hole pattern for opening a contact hole or a through hole of a semiconductor device using a halftone mask, when the hole pattern is deformed or displaced by the halftone mask as described above. ,
In addition to the increase in connection resistance due to the decrease in the contact area in the hole, the hole pattern may contact a pattern formed in another step and destroy the function of the semiconductor element.
For example, a capacitor contact hole pattern of a RAM must be formed between a bit line and a word line so as not to contact these lines, and the allowable range of superposition is required to be about 1/4 of the design rule of a semiconductor element. Have been.
That is, in a DRAM having a rule of 0.2 μm, only a misalignment of about 50 nm is allowed, which is almost the same value as the stage accuracy of the exposure apparatus. Is expected.

Therefore, the above-mentioned document proposes a method of correcting deformation when using a halftone mask by using illumination conditions. For example, a hole pattern that is dense in the vertical direction and coarse in the horizontal direction is deformed vertically under small σ illumination conditions, and conversely horizontally deformed under oblique incidence illumination conditions such as annular illumination and four-point illumination. . Therefore, if the illumination conditions are optimized for the pattern layout (optimization of the shape of the effective light source), the deformation of the hole pattern can be eliminated. Note that the illumination conditions of the exposure apparatus are changed by changing the shape of the effective light source formed by the fly-eye lens using a diaphragm or a filter. To increase the depth of focus of isolated patterns and phase shift masks, a small σ
An illumination condition called an illumination condition in which the effective light source is narrowed down is used. Conversely, illumination that obstructs the center of the effective light source, called oblique illumination, is used to increase the depth of focus of the periodic pattern. FIG. 9 shows an effective light source of four-point illumination, which is one of the oblique incidence illumination. In this four-point illumination, the exposure characteristic changes by changing the size (σ2) of each of the four light sources and the position (σ1) from the center of each light source.

[0007]

However, in a technique involving a change in illumination conditions, as in this conventional technique, the aberration (distortion, coma, spherical surface, astigmatism, etc.) of the projection lens is simultaneously reduced with the deformation of the pattern. Will change it.
Therefore, considering the accuracy and dimensional accuracy overlay often if certain lighting conditions in the exposure device can not be used occurs, occurs a problem that can not always be suitably exposed hole patterns as described above I have. For this reason, there has been a demand for a method of correcting the deformation of the pattern without changing the illumination conditions of the exposure apparatus (illumination conditions in which the lens characteristics are guaranteed).

It is an object of the present invention to provide a phase shift mask which has a function of correcting pattern deformation and enables exposure of a proper pattern without changing illumination conditions.

[0009]

A phase shift mask according to the present invention comprises: a transparent substrate that transmits light or a reflective substrate that reflects light;
A halftone film formed on the transparent substrate or the reflection substrate to invert the phase of light transmitted therethrough; an opening pattern formed in the halftone film; and a light-shielding film formed on the halftone film. for example, pre-Symbol phase shift mask is constructed as a phase shift mask <br/> Re that performed the exposure in oblique incidence illumination conditions, such as annular illumination or 4-point illumination, the phase shift
The opening pattern formed on the mask is
Configured as multiple aperture patterns arranged in close proximity
The light-shielding film is located on the sides of the plurality of opening patterns that are close to each other.
Is located along the side, and the side orthogonal to this side
The configuration is not provided. Alternatively, the phase shift mask phase shift Ru is performed exposing the small σ illumination conditions
A mask formed on the phase shift mask.
Opening patterns are arranged close to each other along one direction of the plane
It is configured as a plurality of opening patterns, and the light-shielding film is
Arranged along the sides of the mouth pattern that are close to each other
It is not installed on the side that is orthogonal to this side.
Configuration.

According to the present invention, the bias of the light intensity distribution in the pattern provided on the halftone film is corrected by the light shielding film provided along the pattern, and a uniform light intensity distribution in the pattern is obtained. This allows
The deformation of the exposure pattern due to the bias of the light intensity distribution is corrected, so that proper pattern exposure can be realized without changing the illumination conditions.

[0011]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the phase shift mask of the present invention.
1A shows a plan view, and FIG. 1B shows a reference example .
Is a longitudinal sectional view thereof. This embodiment is an example in which a mask for forming two 0.2 μm square holes on a wafer is provided, and a halftone film 12 is formed on a transparent substrate 11 made of quartz. The halftone film 12 has a transmittance of 6% and a phase difference of 180 °, and has a hole pattern for exposing the holes with a mask bias of 0.04 μm and a thickness of 0.24 μm. A pair of hole patterns 1 (1a, 1b) having an opening size of 1.2 μm □ are opened at relatively close intervals along one direction (the left-right direction in the drawing) corresponding to the above holes. Further, on the halftone film 12, a light shielding film 13 (13
a, 13b) are formed, and the light shielding films 13a, 1b are formed.
3b has one side of the hole pattern 1a, 1
b are formed along the left side and the right side, respectively.
The plane dimension of the light shielding film 13 is a length L = 1.2 μm.
m and width W = 1.0 μm.

A method of manufacturing the phase shift mask shown in FIG. 1 will be described with reference to FIG. FIG. 2 shows a main mask manufacturing process. First, as shown in FIG. 2A, a mask substrate in which a halftone film 12 of molybdenum oxynitride silicide and a light shielding film 13 of chrome are formed on a transparent substrate 11 of synthetic quartz. The molybdenum oxynitride silicide constituting the halftone film 12 has a refractive index n of 2.1 with respect to light used in an exposure apparatus, that is, KrF excimer laser light (wavelength λ = 248 nm) as described later. Then, the thickness t of the halftone film 12 is calculated from the above equation as t = λ / (2 × (n−1)) = 248 / (2 × (2.1)
-1)) = 113 nm. Thereby, a phase difference of 180 degrees is generated between the light transmitted through the halftone film 12 and the light not transmitted. The light-shielding film 13 has a thickness of 50 nm. At this thickness, the transmittance is 0.1% or less, and 6% of the light transmitted through the halftone film 12 can be completely shielded.

Next, as shown in FIG.
4 is applied, and a mask pattern is drawn using an electron beam drawing apparatus. Here, a pattern of a portion to be a transparent region such as a hole pattern is drawn. Then, FIG.
As shown in FIG. 5, after opening a window in the hole pattern region of the resist 14, the light shielding film 13 and the halftone film 12 are selectively removed by dry etching using the resist 14 as a mask. A gas containing chlorine (such as Cl ₂ ) is used for etching the light shielding film 13, and a gas containing fluorine (such as CF ₃ ) is used for etching the halftone film 12. Thus, hole patterns 1a and 1b are opened in the light shielding film 13 and the halftone film 12, respectively.

Next, as shown in FIG. 2D, the resist 14 is peeled off, a resist 15 is applied again, and a pattern of a light-shielded area is drawn using an electron beam drawing apparatus in the same manner as described above. Then, as shown in FIG.
After patterning the resist 15, the resist 15
Is used as a mask to selectively remove the light shielding film 13 by wet etching (aqueous cerium ammonium nitrate solution). Thereafter, as shown in FIG. 2F, when the resist 15 is peeled off, the phase shift mask shown in FIG. 1 is manufactured.

The exposure of the hole pattern is performed on the wafer by using the phase shift mask having the above configuration. In this embodiment, the exposure apparatus at this time uses a reduction ratio of 1/5, N
A = 0.55, 4-point annular illumination (σ in the direction of 45 degrees from the center)
A KrF excimer laser exposure apparatus having four effective light sources having a size of σ2 = 0.2) is used at a position of 1 = 0.6.
Therefore, a 0.2 μm square hole pattern is exposed on the wafer. Then, the relative light intensity of the exposure on the wafer with the hole pattern 1a along the line AA in FIG.
FIG. 3 shows the light intensity distribution when the width W of No. 3 is changed. In the figure, the x-axis is a position on the image plane, and the center of the hole pattern 1a is located at x = 0 nm. Therefore, the edge of the hole pattern to be formed on the wafer is X
= ± 100 nm (± 0.1 μm). The y-axis is called a relative light intensity, and is a value obtained by standardizing the light intensity of a sufficiently wide area where no pattern exists as 1 as one.

As can be seen from FIG. 3, without the light shielding film 13 (W = 0 μm), the light intensity on the left side is lower than that on the right side of the hole pattern 1a, and the pattern is shifted to the right as a whole. Then, as the width W of the light shielding film 13 increases, the light intensity on the left side of the pattern gradually increases, and W = 0.
At 15 μm or more, the left and right edge portions of the pattern (X = −10
(0 nm and +100 nm). As a method of predicting a resist pattern from this light intensity distribution,
Generally, there is a simple resist development model called an exposure threshold model. This is a model assuming that a portion having a certain intensity or higher in a light intensity distribution is removed by development, and a portion below that intensity is not melted even if developed. FIG. 4 shows the relationship between the shift amount of the resist pattern (the shift of the center position of the hole pattern) and the width W of the light-shielding film 13 obtained from the light intensity distribution of FIG. 3 using the exposure threshold model. Light shielding film 13
When the width W = 0 μm, a displacement of 10 nm in the X direction occurs, but when the width W is 0.15 μm or more, the displacement is suppressed to about 1 nm. Note that the hole pattern 1b has characteristics in which the left and right directions are opposite to those of the hole pattern 1a.

Accordingly, by disposing a light-shielding film having a certain width along one side of the hole pattern, the relative light intensity on the side where the light-shielding film exists is increased with respect to the relative light intensity on the opposite side. Is possible, and the light intensities on the sides of the hole pattern facing each other can be equalized. Therefore, if exposure is performed with an appropriate exposure amount,
Exposure states on opposing sides of the hole pattern can be equalized, and pattern deformation due to the exposure apparatus illumination conditions as described above can be corrected. Incidentally, in the case of this example, since the hole pattern is dense in the horizontal direction and coarse in the vertical direction, the horizontal dimension may be short and deformed under oblique incidence illumination conditions of the four-point illumination of the exposure apparatus. The presence of the light-shielding film 13 allows the lateral dimension to be corrected in the long direction, and allows exposure of a hole pattern without deformation. This allows
Exposure equipment illumination conditions (illumination conditions with guaranteed lens characteristics)
Can be realized without changing the pattern.

Next, a first embodiment of the present invention will be described with reference to the drawings. Here, KrF of NA = 0.6
The halftone mask used in the excimer laser exposure apparatus will be described, and two different illumination conditions are shown.
There are two illumination conditions: four-point illumination (σ1 = 0.6, σ2 = 0.2) and small σ illumination (σ = 0.3). FIG. 5A shows a conventional halftone mask shown for comparison. In order to make the description easy to understand, it is assumed that the exposure magnification of the exposure apparatus is 1 and a mask for forming a 0.2 μm square hole on a wafer is used. ) Has a periodicity of 0.4 μm pitch,
It is isolated in the horizontal direction (left-right direction in the figure) (sufficiently separated from the left and right patterns). Further, since a mask bias of 0.04 μm is applied, the dimension of the hole pattern is 0.24 μm square. Then, FIG.
Fig. 5 (c) shows a phase shift mask for preventing deformation of a hole pattern under four-point illumination conditions, and Fig. 5 (c) shows a phase shift mask for preventing deformation of a hole pattern under small σ illumination conditions. In the phase shift mask of FIG. 5B, the light shielding film 13 is formed along the vertical side where the hole patterns 1 are continuous. The vertical width of the light shielding film 13 is 0.2 μm and the horizontal length is 0.24 μm. In the phase shift mask of FIG. 5C, the light-shielding film 13 is formed along a horizontal side orthogonal to the vertical direction in which the hole patterns 1 are continuous. The width of the light-shielding film in the vertical direction is 0.2 μm.

First, the case where the exposure apparatus uses four-point illumination will be described. FIG. 6A shows a light intensity distribution when the conventional phase shift mask of FIG. 5A is used for this exposure apparatus. The X / Y axes in FIG. 6A are the horizontal / vertical directions in the figure,
The center of hole pattern 1 is located at (X, Y) = (0, 0). In addition, the contour lines in this figure are shown in increments of 0.1 of the relative light intensity, and in actual exposure, a hole pattern having the same shape as the contour line having a relative light intensity of about 0.2 to 0.3 depends on the exposure amount. can get. As shown in the figure, in the case of four-point illumination, the hole pattern is deformed so as to shrink in a periodic direction and extend in a non-periodic direction. On the other hand, as shown in FIG. 5B, in the four-point illumination exposure apparatus, a light-shielding film 13 is formed in the Y direction in which the pattern shrinks, FIG. 6B shows the intensity distribution. As can be seen from FIG.
An almost perfect circular hole pattern is obtained by the phase shift mask of FIG. 5B, and the deformation of the hole pattern is corrected. That is, in the conventional phase shift mask, the vertical and horizontal dimensional difference is about 0.015 μm,
In the phase shift mask of FIG. 5B according to the present invention, the vertical and horizontal dimensional differences are almost zero.

The case where the exposure apparatus is a small σ illumination apparatus will be described. FIG. 7A shows a light intensity distribution when the conventional phase shift mask of FIG. 5A is used for this exposure apparatus. Under this illumination condition, the hole pattern extends in the vertical direction with periodicity and contracts in the horizontal direction, which is an isolated state. On the other hand, FIG. 7B shows a light intensity distribution when a phase shift mask in which a light shielding film 13 is formed in the lateral direction in which the pattern shrinks as shown in FIG. . As can be seen from FIG. 7B, the light intensity in the horizontal direction of the hole pattern is increased, and a hole pattern close to a circle is obtained. Under this small σ illumination condition, the pattern is significantly deformed, and the conventional phase shift mask is about 0.04 μm.
Although a difference in m vertical and horizontal dimensions occurs, in the phase shift mask of the present invention, the difference in vertical and horizontal dimensions has been improved to about 0.01 μm.

In each of the above embodiments, the light shielding film 1
3 does not necessarily have one side in contact with one side of the hole pattern, and can correct the shape of the pattern even if it is separated by a minute dimension, for example, about 0.1 μm. In the above, the description has been given of the transmission type mask used in the photolithography. However, the present invention can be similarly applied to a projection exposure mask using other wavelengths such as X-rays, and can also be applied to a reflection type mask.

[0022]

As described above, the phase shift mask according to the present invention inverts the phase of light transmitted through a transparent substrate or a reflective substrate formed on the transparent substrate or the reflective substrate. a halftone film, the opening pattern opened in the half-tone film, wherein comprises a light shielding film formed on the halftone film, annular illumination or 4
When exposure is performed under oblique incidence illumination conditions such as point illumination
Is the side of the light-shielding film that is close to each other in the plurality of aperture patterns.
Is located along the side, and the side orthogonal to this side
A configuration that is not provided, or, if the Ru is performed exposing the small σ illumination conditions, light-shielding film of a plurality of opening patterns
Arranged along the sides that are close to each other
Instead, it is arranged on the side orthogonal to this side.
Therefore, the bias of the light intensity distribution in the opening pattern provided in the halftone film is corrected by the light shielding film provided along the opening pattern, and a uniform light intensity distribution in the opening pattern is obtained. Thereby, the deformation of the exposure pattern due to the bias of the light intensity distribution is corrected, and the exposure of the appropriate pattern can be realized without changing the illumination conditions.

[Brief description of the drawings]

FIG. 1 is a plan view and a longitudinal sectional view of a phase shift mask according to a reference example of the present invention.

FIG. 2 is a sectional view illustrating a method of manufacturing the phase shift mask of FIG. 1 in the order of steps.

FIG. 3 is a diagram showing relative light intensity characteristics of a hole pattern when the width of a light shielding film in the phase shift mask of FIG. 1 is changed.

FIG. 4 is a diagram showing a correlation between the width of a light-shielding film and a pattern displacement.

FIG. 5 is a plan view of a conventional phase shift mask and a phase shift mask of the present invention in the first embodiment of the present invention.

FIG. 6 is a diagram showing a comparison between exposure pattern characteristics using a conventional phase shift mask and each phase shift mask of the present invention when a four-point illumination device is used.

FIG. 7 is a diagram showing a comparison between the exposure pattern characteristics of the conventional phase shift mask and the phase shift mask of the present invention when a small σ illumination device is used.

FIG. 8 is a plan view and a cross-sectional view of an example of a conventional phase shift mask.

FIG. 9 is a diagram for explaining small σ illumination.

[Explanation of symbols]

 1 (1a, 1b) Hole pattern 11 Transparent substrate 12 Halftone film 13 Light shielding film

Claims (6)

(57) [Claims] 1. A transparent substrate transmitting light, a halftone film formed on the transparent substrate for inverting the phase of transmitted light, an opening pattern formed in the halftone film, and the halftone film. And a light-shielding film formed thereon, and exposed under oblique incidence illumination conditions such as annular illumination or four-point illumination.
Is performed as a phase shift mask,
The opening pattern formed on the shift mask is one side of a plane.
A plurality of opening patterns arranged close to each other along the direction
And the light-shielding film is formed of the plurality of opening patterns.
Placed along the side that is closest to
A phase shift mask, wherein the mask is not provided on a side on the side of intersection . 2. A transparent substrate which transmits light, and said transparent substrate.
Comprising a half-tone film for inverting the phase of light transmitted is formed on an opening pattern opened in the halftone film, a light shielding film formed on the halftone film, a small σ illumination conditions Phase shift mask exposed by
Before being formed on the phase shift mask
The opening pattern is a plurality of patterns arranged close to one another in one plane.
A plurality of aperture patterns, wherein the light-shielding film is
At the positions along the sides that are close to each other
Is not provided, and is provided on the side orthogonal to the side.
A phase shift mask, which is characterized in that: 3. A reflecting substrate for reflecting light, and said reflecting substrate.
The phase of light reflected on the reflective substrate formed on
A halftone film to be rotated, and an opening in the halftone film.
Opening pattern formed on the halftone film.
Oblique incidence such as annular illumination or four-point illumination
Structured as a phase shift mask that is exposed under illumination conditions
The aperture pattern formed in the phase shift mask.
A plurality of turns are arranged close to each other along one direction of the plane.
The light shielding film is configured as an opening pattern.
Arranged along the sides of the opening pattern that are close to each other
And a phase shift mask which is not disposed on a side orthogonal to the side . 4. A reflective substrate for reflecting light, and said reflective substrate
The phase of light reflected on the reflective substrate formed on
A halftone film to be rotated, and an opening in the halftone film.
Opening pattern formed on the halftone film.
Is provided with a light shielding film, exposure is performed with a small σ illumination conditions
The phase shift mask is configured as a phase shift mask.
The opening pattern formed in the
It is configured as a plurality of aperture patterns arranged close to each other,
The light shielding film is close to the plurality of opening patterns.
It is not located at a position along the side and is orthogonal to the side.
A phase shift mask disposed on the side of the phase shift mask. 5. The phase shift mask according to claim 1, wherein the light-shielding film is formed such that a side facing the opening pattern overlaps a side of the opening pattern. 6. The phase shift mask according to claim 5, wherein the opening pattern is a rectangular hole pattern.