JP3209638B2 - X-ray exposure mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray exposure mask (hereinafter referred to as "X-ray mask") used in X-ray lithography, and more particularly, to significantly reduce positional distortion of a pattern due to X-ray irradiation. It relates to an X-ray mask that has been made.

[0002]

2. Description of the Related Art Along with the high integration of LSI, miniaturization of a pattern to be mounted has been rapidly progressing. inside that,
The lithography technology for forming a fine pattern is approaching the limit in principle by the conventional method using ultraviolet light. Therefore, X-ray lithography technology using synchrotron radiation as a light source attracts attention, and research and development are being actively conducted for practical use. Of particular interest in the X-ray lithography technique is a method using the same-size proximity exposure. In this case, a pattern having the same size as the pattern to be formed must be formed on the mask. Therefore, the positional accuracy of the pattern on the X-ray mask is a particularly important problem.

The basic structure of a conventional X-ray mask is as shown in FIG. That is, the X-ray absorbing pattern 13 and the X-rays supporting the X-ray absorbing pattern 13
It comprises a line permeable film 12 and a support frame 11 (usually Si having a thickness of 1 to 2 mm) for fixing the outer periphery thereof.

The X-ray transmitting film 12 is made of a thin film having a thickness of about 1 to 2 μm, such as SiN or SiC, which easily transmits X-rays, and etches (back-etches) Si (support substrate) other than a portion serving as a frame. By usually removing the film by anisotropic wet etching), the film is processed into a self-supporting single film (membrane), and sufficient transparency necessary for X-ray transfer is obtained. Among the materials used for the X-ray transmission film 12, S
Since iC has a higher Young's modulus than SiN, the positional distortion due to the deformation of the membrane is small, but the transmittance of visible light (633 nm) required for alignment is low, and the flatness of the surface is poor. On the other hand, SiN has high visible light transmittance and good flatness, and is considered to be promising as an X-ray transmission film.

[0005]

However, the above S
Pattern distortion caused by X-ray irradiation of the iN membrane is described, for example, in T. Arakawa, H. Okuyama, K. Okada, H. Naga.
sawa, T.Syoki and Y.Yamaguchi; Jpn.J.Appl.Phys., Vol.
31 (1992) p. 4459, which is larger than that of a SiC membrane, for example, 10 MJ / cm for SiC.
The standard deviation (σ) of the amount of displacement is 25 to ^{3 with} the X-ray absorption of ^3.
In contrast to 6 nm, SiN is 33 to 97 nm for an X-ray absorption of 6.5 MJ / cm ³ .

[0006] Irradiation-induced positional distortion of an X-ray membrane is required to have a 3σ of 30 nm or less at an X-ray absorption of 100 MJ / cm ³ corresponding to 10 ⁶ shots with SiN when the minimum line width is 0.25 μm. I have. However, S
The iN membrane has a problem that a large pattern position distortion occurs due to the X-ray irradiation as described above.

That is, the SiN membrane according to the conventional structure receives a tensile stress from the Si support, so that X
When the line is illuminated, the stress is relieved by breaking the bond bonds in the SiN, which causes the Si support to pull the membrane further outward, causing the membrane to stretch. This will distort the pattern toward the outside of the membrane. In fact, a large positional distortion as described above has been observed in a conventional SiN membrane due to X-ray irradiation.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to solve the problem of X-ray irradiation induced positional distortion caused when SiN is used as an X-ray transmitting film. Another object of the present invention is to provide an X-ray mask that can maintain the pattern position accuracy for a long period of time.

[0009]

Means for Solving the Problems The present inventors have solved the above problems.
In view of the foregoing, as a result of intensive studies, the object of the present invention is to provide at least an X-ray absorbing pattern, an X-ray permeable film holding the X-ray absorbing pattern, and a support frame for fixing the outer periphery of the X-ray permeable film. in X-ray exposure mask having bets, the X-ray transparent film, on both surfaces of the main X-ray transparent film stress is alleviated by irradiating and X-ray having a tensile stress, and having a compressive stress A sub-X-ray transmitting film whose stress is relaxed by irradiating X-rays is formed, and the sub-X-ray transmitting film is
When the stress is K times the stress of the main X-ray transmitting film,
The total thickness of the X-ray transmission film is 1 / K times the thickness of the main X-ray transmission film
An X-ray exposure mask is provided.
And that it is achieved by.

The invention of claim 2 is characterized in that SiN is used as the main X-ray transmission film.

The invention according to claim 3 is characterized in that SiO ₂ is used as the sub X-ray transmission film.

[0012]

Hereinafter, the configuration of the present invention will be described in detail.

FIG. 1 is a sectional view showing an example of the configuration of the X-ray mask of the present invention. According to this, a main X-ray permeable film 22 having a tensile stress and reducing the stress by irradiating X-rays, a compressive stress and an X-ray are formed on a support frame 21 made of Si. The sub-X-ray transmitting film 23 and the X-ray absorbing pattern 24 whose stress is relaxed by irradiation are sequentially formed, and the central region of the support frame 21 is removed to form a membrane. Furthermore, the main X
A sub X-ray transmission film 25 is also formed on the back surface of the membrane portion of the radiation transmission film 22. In addition, 26 of the back surface of the support frame 21
Is a back etching protection film, and the sub X-ray transmission film 25 is also formed on the surface of the protection film 26. These are formed at the time of manufacturing the mask and may be removed after the manufacturing.

As described above, it is preferable to use SiN as the main X-ray transmission film 22.

The sub X-ray transmitting films 23 and 25 are preferably made of, for example, SiO ₂ , but are not limited thereto.

These X-ray permeable films are formed by chemical vapor deposition (C
(VD method) and the like.

As an absorber for forming the X-ray absorbing pattern 24, for example, tantalum, tungsten or the like is generally used, and the pattern 24 is formed by a usual electron beam lithography method and a subsequent dry lithography method. It can be formed by etching.

As described above, the X-ray mask of the present invention
As a X-ray transmission film, a sub X-ray transmission film which receives compressive stress from the main X-ray transmission film is formed on both surfaces of a main X-ray transmission film made of, for example, SiN.

In one embodiment of the present invention, the main X
When the line transmitting film is made of SiN and the sub-X-ray transmitting film is made of SiO ₂ , the X-ray transmitting film having such a structure receives a compressive stress on SiO _{2 with} respect to a tensile stress of SiN. At this time, the stress σ applied to the entire SiO ₂ / SiN / SiO ₂ film
Is (Σ _SiN ; stress applied to SiN, σ _SiO2 ; stress applied to SiO ₂ , t _SiN ; film thickness of SiN, t _SiO2 ; total thickness of SiO ₂ ) When X-rays are irradiated, σ _SiN and σ _SiO2 are relaxed. Here, assuming that the changes are △ σ _SiN and △ σ _SiO2 respectively, the total stress change △ σ is The signs of pulling and compression are opposite to each other.

Here, in an embodiment of the present invention described later,
t _SiO2 = t _SiN / 10, and σ _SiO2 ≒ 10σ
Be considered that △ σ _SiO2 ≒ 10 △ σ _SiN from _SiN, a △ σ ≒ 0. That is, the stress of the sub X-ray transmission film is equal to the main X
When the stress is K times the stress of the X-ray transmission film, the total thickness of the sub-X-ray transmission film is preferably set to be 1 / K times the thickness of the main X-ray transmission film, so that the entire X-ray transmission film is reduced. There will be almost no change in stress. Therefore, according to the configuration of the X-ray mask of the present invention, pattern distortion due to X-ray irradiation hardly occurs.

[0022]

As described above, the X-ray mask of the present invention has a compressive stress on both surfaces of the main X-ray transmitting film which has a tensile stress and whose stress is relaxed by irradiating X-rays. And forming a sub-X-ray permeable film whose stress is relaxed by irradiating X-rays, wherein the stress of the sub-X-ray permeable film is
When the stress is K times the stress of the main X-ray transmission film, the sub-X-ray transmission
The total thickness of the film should be 1 / K times the thickness of the main X-ray transmission film.
Changes in stress caused by X-ray irradiation of the entire X-ray permeable film
This almost eliminates the
Pattern distortion due to
The position accuracy of the pattern is significantly improved and stable for a long time.
Position accuracy can be maintained.

[0023]

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

FIG. 2 is a cross-sectional view showing the manufacturing process of the X-ray mask of the present invention in the order of steps, which will be described with reference to FIG.

First, a substrate serving as the support frame 21 (the substrate in the drawing is also indicated by reference numeral 21) is Si
(3 inches, 2 mm thickness), the main X-ray transmission film 2 is formed at a film forming temperature of, for example, 850 ° C. using SiH ₂ Cl ₂ and NH ₃ as source gases by a reduced pressure chemical vapor deposition method.
2 was formed to a thickness of 2 μm. Note that a SiN film was similarly formed as the back etching protection film 26 on the back surface of the Si wafer. Further, as a sub X-ray transmitting film 23 on the SiN film on the Si wafer,
_Two films were formed to a thickness of 100 nm by electron beam evaporation. Next, a Ta film was formed by sputtering to a thickness of 0.7 μm on the SiO ₂ film as an absorber 24 ′ for forming an X-ray absorbing pattern (see FIG. 3A).

Next, after applying an electron beam resist to the surface and patterning by an electron beam exposure method, Ta was partially removed by dry etching to form an X-ray absorbing pattern 24 (FIG. 2B). reference).

Next, after removing the back-etching protective film 26 in the 30 × 30 mm area near the center of the side where no pattern is formed (the back surface) by dry etching, the Si substrate is back-etched with an aqueous KOH solution. As a result, a 25 × 25 mm membrane portion was formed at the center (see FIG. 3C).

Further, an SiO ₂ film having the same thickness as that of the front side was formed on the rear surface as the auxiliary X-ray transmission film 25 to a thickness of 100 nm by electron beam evaporation (see FIG. 4D).

Thus, the X-ray mask of the present invention is completed.

With respect to the completed X-ray mask, pattern distortion due to X-ray irradiation was measured. FIG. 3 shows a pattern formed on the X-ray mask for position distortion measurement in the present embodiment.
10 × at a pitch of 2500 μm in a membrane area of
10 are formed. The pattern position was measured using a Nikon lightwave interference coordinate measuring machine. The measurement reproduction accuracy of the position coordinates is 30 nm (3σ).

FIG. 4 shows how the position of the pattern is distorted due to X-ray irradiation of the X-ray mask in this embodiment. In the figure,
Arrow indicates coordinates measured before X-ray irradiation and about 100 MJ / cm
³ represents the difference from the coordinates measured after X-ray absorption (corresponding to 10 ⁶ shots).

As a result, in this embodiment, σ is 10 nm
As shown below, the positional distortion is significantly reduced as compared with the conventional example, and the positional distortion of the pattern hardly occurs.

[0034]

As described in detail above, the X of the present invention
According to the X-ray mask, both surfaces of the main X-ray transmission film, which has a tensile stress and has a stress that is reduced by irradiating X-rays, have compressive stress and are irradiated with X-rays. Forming a sub-X-ray permeable film that relieves stress
Then, the stress of the sub X-ray transmission film is the stress of the main X-ray transmission film.
In the case of K times the total X-ray transmission thickness of the sub X-ray transmission film,
By making the thickness of the film 1 / K times, the total X-ray transmission film
Almost no change in stress due to X-ray irradiation of body
Therefore, this causes the positional distortion of the pattern due to X-ray irradiation.
Will hardly occur, and the position accuracy of the pattern will be remarkable.
It can improve and maintain stable position accuracy for a long time.
It has excellent effects.

[0035]

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of an embodiment of an X-ray mask of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process of the X-ray mask of the present invention in the order of steps.

FIG. 3 is a diagram showing a pattern for position distortion measurement in the embodiment of the present invention.

FIG. 4 is a diagram showing a state of positional distortion due to X-ray irradiation in an example of the present invention.

FIG. 5 is a sectional view of a conventional X-ray mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Support frame 12 X-ray transmission film 13 X-ray absorption pattern 14 Back etching protection film 21 Support frame 22 Main X-ray transmission film 23 Secondary X-ray transmission film 24 X-ray absorption pattern 25 Secondary X-ray transmission film 26 Back Etch protective film 30 X-ray absorption pattern for position distortion measurement

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-56-157031 (JP, A) JP-A-63-285932 (JP, A) JP-A-6-163368 (JP, A) JP-A-5-163368 129190 (JP, A) JP-A-63-200530 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 1/16

Claims (3)

(57) [Claims] At least an X-ray absorbing pattern and said X-ray absorbing pattern
In an X-ray exposure mask having an X-ray permeable film holding a X-ray absorbing pattern and a support frame for fixing an outer periphery of the X-ray permeable film, the X-ray permeable film has a tensile stress and X there on both sides of the main X-ray transparent film stress is alleviated by irradiating a line, to form the sub X-ray membrane stress is alleviated by irradiating and X-ray having a compressive stress
The stress of the sub X-ray transmission film is the stress of the main X-ray transmission film.
When it is K times the total X-ray transmission film thickness, the main X-ray transmission
An X-ray exposure mask characterized in that the thickness of the overcoat is 1 / K times the thickness of the overcoat . 2. The X-ray exposure mask according to claim 1, wherein SiN is used as said main X-ray transmission film. 3. A process according to claim 1 or 2 X-ray exposure mask, wherein the SiO ₂ is used as the auxiliary X-ray membrane.