JP4696365B2 - Levenson type phase shift mask - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Levenson-type phase shift mask used for LSI manufacturing, and more specifically, can be used in a projection exposure apparatus like a conventional photomask, and is caused by unnecessary light reflected on the photomask surface. The present invention relates to a Levenson-type phase shift mask that can prevent deterioration of transfer accuracy and improve the resolution of a transfer pattern.
[0002]
[Prior art]
FIG. 5A is a cross-sectional view showing an example of the structure of a conventional photomask. As shown in FIG. 5A, the conventional photomask has a light-shielding film pattern (12) having a light-shielding property against projection light and a thickness of about 100 nm formed on one surface of a transparent substrate (11). It is. Here, the light-shielding film pattern (12) may have a multilayer structure in order to reduce the reflection of the surface.
[0003]
As the integration of LSI advances, the design rule includes a fine line width near the wavelength of the light source to be exposed, and the projection light that has passed through the opening pattern (16) of the photomask is projected on the wafer. By diffracting and interfering with each other, there is a problem that the light intensity at the pattern boundary part is strengthened, the resist on the wafer is exposed, and the transferred pattern is not separated and resolved.
[0004]
Therefore, IBM's Levenson et al. Proposed a phase shift technique for improving the resolution of a fine pattern by giving a phase difference of 180 degrees to the phase of projection light transmitted through adjacent opening patterns of a photomask. (In Japanese Patent Laid-Open No. 58-173744, the principle is described in Japanese Patent Publication No. 62-50811)
In other words, by providing a phase shift portion in one of the adjacent opening patterns, when the transmitted light is diffracted and interferes with each other, both phases are reversed, and as a result, the light intensity at the boundary portion is weakened and transferred. The pattern will be separated and resolved.
Since this relationship is established before and after the focal point, even if the focal point is slightly deviated, the resolution is improved as compared with the conventional exposure method, and the focal depth is improved.
[0005]
A photomask that provides a phase shift portion in one of adjacent opening patterns and inverts the phase of transmitted light as described above is generally called a Levenson-type phase shift mask or an alternative type phase shift mask.
(For example, Reference 1; Mulberry principle “Frontier of lithography technology (1) Mask technology”, O plus E, No. 182, January 1995, p. 92)
There are two methods for providing a phase shift portion in one of the opening patterns: a substrate digging type for forming a digging portion in a transparent substrate and a shifter type for forming a transparent thin film pattern called a shifter layer. . Furthermore, the shifter mold is formed by forming a transparent film on the transparent substrate prior to the light shielding film and forming a shifter pattern after forming the light shielding film pattern in the same manner as the digging mold. After the light shielding film pattern is formed on the substrate, a transparent film is formed, and then there are two types of upper shifter type in which a shifter pattern is formed.
[0006]
5B, 5C, and 5D are respectively a Levenson type phase shift mask (digging type), a Levenson type phase shift mask (lower shifter type), and a Levenson type phase shift mask ( This is the basic structure of the upper shifter type.
(13) is a digging type phase shifter section, (14) is a lower shifter type phase shifter section, and (15) is an upper shifter type phase shifter section.
Note that the light shielding film pattern (12) as these constituent elements may have a multilayer structure in order to reduce the surface reflection.
[0007]
[Problems to be solved by the invention]
One of the problems when performing projection exposure on a wafer using a photomask is a problem of deterioration in transfer accuracy due to unnecessary light reflected on the wafer surface and the photomask surface. In particular, when the base of the resist on the wafer side is a metal layer such as Al, since the reflectance is high, it is necessary to provide an antireflection film on the metal layer, and selection of an optimal antireflection film has been attempted. .
(For example, reference 3; ULSI lithography technology innovation (Science Forum), 1994, p. 60)
[0008]
However, the above-mentioned anti-reflection coating for the light reflected on the photo mask surface is not sufficiently studied, and anti-reflection that can cope with photo masks of unusual forms such as future pattern line width miniaturization and phase shift masks. Technology is needed.
In this case, since a new antireflection film may increase the film defects or the manufacturing process may be complicated, a new antireflection film may increase photomask defects, It is necessary to select structures and materials that do not complicate the manufacturing process.
[0009]
The present invention has been made in view of the above-described problems, and has been manufactured without complicating the manufacturing process and without increasing the factor of increasing defects when manufacturing a Levenson type phase shift mask. It is an object of the Levenson-type phase shift mask to provide a Levenson-type phase shift mask that can prevent deterioration in transfer accuracy due to unnecessary light reflected on the photomask surface and improve the resolution of the transfer pattern. To do.
[0010]
[Means for Solving the Problems]
The present invention provides an upper shifter-type Levenson in which a light-shielding film pattern and an opening pattern are repeatedly formed on a transparent substrate, and a transparent film that reverses the phase of transmitted light passing through every other opening pattern is patterned. In the type phase shift mask, the refractive index na of the light shielding film pattern and the refractive index n of the antireflection layer are such that na> n, and the transparent film is formed on the light shielding film pattern. A Levenson-type phase shift mask characterized by being the same as the material .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below based on one embodiment.
FIG. 1 is a sectional view showing an embodiment of a Levenson type phase shift mask according to the present invention. As shown in FIG. 1, the Levenson-type phase shift mask according to the present invention has a light shielding film pattern (2a) and an opening pattern (4a) repeatedly on a transparent substrate (1), and every other opening pattern. In (4a), a transparent film for inverting the phase of transmitted light passing therethrough is provided as a phase shifter portion (3a), and an antireflection layer (3b) is provided on the light shielding film pattern (2a). It is what was done.
[0013]
The present invention provides an upper shifter in which a light-shielding film pattern (2a) and an opening pattern are repeatedly present on a transparent substrate, and a transparent film that reverses the phase of transmitted light passing through every other opening pattern is patterned. In the Levenson type phase shift mask of the type, the refractive index na of the light shielding film pattern and the refractive index n of the antireflection layer satisfy the condition of na> n, and the transparent film is formed on the light shielding film pattern. It is the same as the material of the prevention layer . By making the material of the antireflection layer the same as the material of the transparent film, the number of film formation can be reduced, so that the manufacturing process can be simplified and the cause of film defects during film formation can be reduced. it can.
[0014]
Hereinafter, the refractive index, the film thickness, and the relationship of the thin film formed in the Levenson type phase shift mask according to the present invention will be described.
In general, the transmittance and reflectance of light with respect to a thin film formed on a transparent substrate are the optical constant (refractive index, extinction coefficient) and film thickness of the film, and the substrate and exposure atmosphere (usually air). It depends on the refractive index and is determined as a result of multiple interference in the film.
[0015]
The conditions for reducing the reflectance of the light-shielding two-layer film formed of the light-shielding film and the anti-reflection layer on the transparent substrate to 0, that is, the anti-reflection conditions, for example, assuming normal incidence, If the refractive indexes of the antireflection layer, the light shielding film, the transparent substrate and the air are n, na, ns and n0, respectively,
na / n = √ (ns / n0) (1)
And, if the film thicknesses of the antireflection layer and the light shielding film are d and da, respectively, d = (2m + 1) λ / 8n (m = 0, 1, 2,...)
da = (2m + 1) λ / 8na (m = 0, 1, 2,...)
(2)
λ: exposure wavelength.
[0016]
If the above mathematical expressions (1) and (2) are satisfied, the reflectance is zero. Similarly, in the case where the light shielding film is a metallic film, if the film is formed so as to satisfy n0 <na / n <ns even if the mathematical expressions (1) and (2) are not completely satisfied, An antireflection effect can be obtained.
[0017]
Thus, if the mathematical formulas (1) and (2) are satisfied, the reflectance can be kept low. However, when synthetic quartz is used as the transparent substrate as in the present invention, the refractive index is the exposure wavelength. Since ns ≈ 1.5,
na / n = √ns = 1.22
Therefore, it is necessary that na> n.
[0018]
【Example】
Hereinafter, the present invention will be described in detail by way of examples.
[0019]
<Example 1>
In the first embodiment, a case where the Levenson type phase shift mask of FIG. 1 is manufactured will be described with reference to FIGS.
A tantalum nitride film (TaN) as a light-shielding film (2) on a transparent substrate (1) made of a quartz substrate having an optical constant of refractive index ns = 1.56 with respect to exposure wavelength λ = 193 nm and extinction coefficient ks = 0 Was formed by a reactive sputtering method using argon (Ar) gas and nitrogen (N 2) gas to produce a photomask blank (FIG. 2A).
The tantalum nitride film had a predetermined thickness. Here, the optical constant of the tantalum nitride film was previously confirmed by a preliminary experiment, and the refractive index na = 2.06 and the extinction coefficient ka = 1.55 with respect to the exposure wavelength of 193 nm.
[0020]
Next, a resist pattern is formed on the photomask blank by a normal electron beam lithography process, and the light shielding film (2) is etched with carbon tetrafluoride (CF4) and oxygen (O2) using the resist pattern as a mask. After dry etching as a gas, the resist pattern was removed to produce a photomask having a light shielding film pattern (2a) (FIG. 2B).
[0021]
Next, the silicon oxynitride (SiON) film is converted into an antireflection layer and a phase shifter portion by a reactive sputtering method in which appropriate amounts of oxygen (O2) gas and nitrogen (N2) gas are added to argon (Ar) gas. The film was formed as 3).
The optical constant of this silicon oxynitride film was previously confirmed by a preliminary experiment and had a refractive index n = 1.909 and an extinction coefficient k = 0.996. The film thickness was 106.2 nm. Next, a resist pattern (4) used for patterning of the phase shifter portion was formed on the transparent film by a normal electron beam lithography process (FIG. 2C).
[0022]
Next, this transparent film was dry-etched with carbon tetrafluoride (CF4) gas, and then the resist pattern (4) was removed. At this time, the transparent film is etched so that the film thickness remains 16.0 nm on the light shielding film pattern (2a) by time control so that the transparent film becomes an antireflection layer on the light shielding film pattern (2a). ) And a transparent film (3 ′) having an antireflection layer (3b).
Next, a resist pattern (5) for removing the transparent film portion (3c) directly formed on the transparent substrate is formed on the transparent film (3 ′) by a normal electron beam lithography process. (FIG. 2D).
[0023]
Next, the transparent film portion (3c) directly formed on the transparent substrate is dry-etched with carbon tetrafluoride (CF4) gas, and then the resist pattern (5) is removed to thereby remove the present invention. A Levenson-type phase shift mask was prepared (FIG. 1).
[0024]
In FIG. 3, the reflectance with respect to the film thickness of the antireflection layer of the Levenson type phase shift mask of the present invention obtained in Example 1 is shown.
The reflectance of the light-shielding film pattern at a wavelength of 193 nm was 23.0% in the conventional case, but extremely low at 0.33% in the present invention. In the defect inspection, there was no fatal defect. In this way, a Levenson type phase shift mask having a low reflection light shielding film pattern was obtained.
[0025]
<Example 2>
In the second embodiment, an example in which the Levenson type phase shift mask of FIG. 1 is made of a material different from that of the first embodiment will be described.
Similar to Example 1, a light shielding film (2) is formed on a transparent substrate (1) made of a quartz substrate having an optical constant of refractive index ns = 1.56 and extinction coefficient ks = 0 with respect to an exposure wavelength λ = 193 nm. A niobium nitride film (NbN) was formed by a reactive sputtering method using argon (Ar) gas and nitrogen (N 2) gas to produce a photomask blank (FIG. 2A).
The niobium nitride film had a predetermined thickness. Here, the optical constant of the niobium nitride film was previously confirmed by a preliminary experiment, and the refractive index na = 1.90 and the extinction coefficient ka = 1.73 with respect to the exposure wavelength of 193 nm.
[0026]
Next, a resist pattern is formed on the photomask blank by a normal electron beam lithography process, and the light shielding film (2) is dry-etched using carbon tetrafluoride (CF4) as an etching gas using the resist pattern as a mask. Thereafter, the resist pattern was removed to produce a photomask having a light shielding film pattern (2a) (FIG. 2B).
[0027]
Next, a zirconium oxide silicon (ZrSiO) film was formed as an antireflection layer and a transparent film (3) to be a phase shifter portion by a reactive sputtering method in which an appropriate amount of oxygen (O2) gas was added to argon (Ar) gas. . The optical constants of this zirconium oxide silicon film were confirmed in advance by preliminary experiments, and had a refractive index n = 1.781 and an extinction coefficient k = 0.0418. The film thickness was 123.6 nm. Next, a resist pattern (4) used for patterning of the phase shifter portion was formed on the transparent film by a normal electron beam lithography process (FIG. 2C).
[0028]
Next, this transparent film was dry-etched with boron trichloride (BCl3) gas, and then the resist pattern (4) was removed. At this time, the transparent film is etched so that the film thickness remains 18.5 nm on the light shielding film pattern (2a) by time control so that the transparent film becomes an antireflection layer on the light shielding film pattern (2a). ) And a transparent film (3 ′) having an antireflection layer (3b).
Next, a resist pattern (5) for removing the transparent film portion (3c) directly formed on the transparent substrate is formed on the transparent film (3 ′) by a normal electron beam lithography process. (FIG. 2D).
[0029]
Next, the transparent film portion (3c) directly formed on the transparent substrate is dry-etched with boron trichloride (BCl3) gas, and then the resist pattern (5) is removed to remove the resist pattern (5). A Levenson type phase shift mask was produced (FIG. 1).
[0030]
In FIG. 4, the reflectance with respect to the film thickness of the antireflection layer of the Levenson type phase shift mask of the present invention obtained in Example 2 is shown.
The reflectance of the light-shielding film pattern at a wavelength of 193 nm was 33.3% in the conventional case, but was extremely low at 1.61% in the present invention. In the defect inspection, there was no fatal defect. In this way, a Levenson type phase shift mask having a low reflection light shielding film pattern was obtained.
[0031]
【The invention's effect】
The present invention provides a Levenson type phase shift mask of the upper shifter type, condition der as they may refractive index na of the refractive index n and the light shielding film pattern of the antireflection layer is na> n, unnecessary reflected by the photomask surface Therefore, the Levenson type phase shift mask can prevent the deterioration of the transfer accuracy due to the light and improve the resolution of the transfer pattern. Further, the present invention provides a Levenson type phase shift mask of the previous SL on shifter type, since the transparent film is the same as the material of the light shielding film pattern on the formed antireflection layer, during its production, conventional and unchanged The manufacturing process can be performed without any complicated process, and the factor of increasing defects can be suppressed without complicating the manufacturing process.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a Levenson type phase shift mask according to the present invention.
FIGS. 2A to 2D are explanatory views of a process for manufacturing a Levenson-type phase shift mask. FIGS.
3 is an explanatory diagram of the reflectance of the Levenson type phase shift mask of the present invention obtained in Example 1. FIG.
4 is an explanatory diagram of the reflectance of the Levenson-type phase shift mask of the present invention obtained in Example 2. FIG.
FIG. 5A is a cross-sectional view showing an example of the structure of a conventional photomask.
(B) is a basic structural diagram of a Levenson type phase shift mask (digging type).
(C) is a basic structural view of a Levenson type phase shift mask (lower shifter type).
(D) is a basic structural view of a Levenson type phase shift mask (upper shifter type).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 11 ... Transparent substrate 2 ... Light-shielding film 2a, 12 ... Light-shielding film pattern 3 ... Transparent film 3 '... Transparent film 3a comprised by a phase shifter part, an antireflection layer, and a transparent film part ... Phase shifter part (Transparent film)
3b: Antireflection layer 3c: Transparent film portion 4 formed directly on transparent substrate 4, 5 ... Resist pattern 4a, 16 ... Opening pattern 13 ... Digging phase shifter 14 ... Lower shifter type phase Shifter unit 15: Upper shifter type phase shifter unit

Claims (1)

An upper shifter type Levenson-type phase shift mask on which a light-shielding film pattern and an opening pattern repeatedly exist on a transparent substrate, and a transparent film that reverses the phase of transmitted light passing through every other opening pattern is patterned. The refractive index na of the light shielding film pattern and the refractive index n of the antireflection layer are such that na> n, and the transparent film is the same as the material of the antireflection layer formed on the light shielding film pattern. A Levenson-type phase shift mask characterized by being.

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