JP3463406B2 - X-ray reflection type 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 reflection type mask suitable for use in an X-ray optical system.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of semiconductor integrated circuit elements, reduction projection lithography technology using X-rays has been developed in order to improve the resolution of an optical system limited by the diffraction limit of light. That is, since the X-ray has a shorter wavelength than the ultraviolet ray used conventionally, it is possible to project a finer circuit pattern.

In order to project a circuit pattern, a mask on which the circuit pattern is drawn is required. As such a mask, two types are known, a transmission type mask and a reflection type mask. The transmissive mask has a desired pattern formed by using a thin film made of a substance that easily absorbs X-rays on a self-supporting film (membrane) having a thickness of 1 μm or less made of a substance that easily transmits X-rays. is there.

However, this transmissive mask has a very weak membrane strength, which makes it difficult to manufacture a mask having a large area. The membrane is likely to be deformed due to heat generated by X-ray absorption during X-ray irradiation. , Etc. Therefore, in order to solve such a problem, a reflective mask has been developed. The reflection type mask is formed by using an X-ray reflection multilayer film and forming a pattern by its reflectance distribution. Specifically, a pattern processing of the X-ray reflection multilayer film mirror or a pattern processing of the absorption layer (absorber) formed on the X-ray reflection multilayer film 2 provided on the substrate 1 (FIG. 2). It has been known.

In such a reflective mask, the thick substrate 1
Since the pattern is formed on the upper surface, the above problems do not occur. The X-ray reflective multilayer film (hereinafter, may be simply referred to as a multilayer film) 2 formed on the surface of the mask substrate has two types of material layers having different refractive indexes and having a thickness of several nm on the substrate 1. They are alternately laminated (alternate multilayer film).

Generally, the two types of material layers are a layer composed of a material containing a heavy element as a main component (heavy atomic layer) and a layer composed of a material containing a light element as a main component (light atomic layer). The multilayer film 2 utilizes the interference effect of light reflected at a number of interfaces, and the length of one cycle (cycle length) of the multilayer film is d,
When the incident angle of X-rays is θ and the wavelength of X-rays is λ, the multilayer film exhibits high reflectance when the Bragg condition (2d · sin θ = nλ, where n is a positive integer) is satisfied.

There are two methods for producing a reflective mask by patterning an absorbing layer (absorber) formed on an X-ray reflecting multilayer film (mirror). One is a method in which after forming an absorption layer on the multilayer film 2, a resist pattern is formed and the pattern is transferred to the absorption layer by dry etching or the like. In this method, since the multilayer film 2 is damaged when the pattern is transferred to the absorption layer, there arises a problem that the reflectance of the multilayer film is lowered.

The other is a method of forming a resist pattern on the multilayer film 2 and using the pattern as a stencil mask to add an absorption layer by a lift-off method or a plating method. In this method, since the multilayer film 2 is not damaged, a good reflective mask can be obtained. The present applicant also paid attention to this method and proposed a method for manufacturing a reflective mask (Japanese Patent Application No. 6-168566).

In the case of the plating method, when the electrolytic plating method is used, a conductive substance is placed on the surface and used as an electrode for depositing the absorber. When the electroless plating method is used, a catalytically active substance is placed on the surface and used as a reaction initiator for the reduction reaction. The manufacturing process (one example) of the method of adding the patterned absorption layer 3 is shown in FIG. First, the multilayer film 2 is formed on the substrate 1 (FIG. 3A). At this time, the multilayer film 2
The multi-layered film 2 is formed so that the uppermost layer is a substance having conductivity and catalytic activity. In general, since the heavy atom layer often exhibits electroconductivity and catalytic activity, the heavy atom layer is the uppermost layer.

When the substance forming the multilayer film does not have these properties, an extremely thin conductive film or catalytically active film may be formed to the extent that the reflectance of the multilayer film 2 is not affected. Next, a resist 5 is applied on the multilayer film 2 (FIG. 3B), and pattern exposure and development are performed to form a resist pattern 5 ′ (FIG. 3C). After using this resist pattern 5'as a mold, the absorbing layer 3 is selectively grown only on the portion where the resist is removed by a plating method (see FIG. 3).
(D)) When the resist pattern 5'is removed, a reflective mask is obtained (FIG. 3 (e)).

[0011]

However, in the reflection type mask manufactured by the conventional manufacturing method as described above,
In order to form the X-ray absorbing layer by a plating method, a material layer (heavy atom layer) having a conductive or catalytically active property must be arranged on the uppermost layer of the multilayer film. Generally, combinations of constituent materials of an X-ray multilayer film used in X-ray reduction projection exposure include, for example, Mo / Si, Ru / Si, Pa.
/ Si, W / Si, Mo / B ₄ C, Ru / B ₄ C, W /
C, NiCr / C, etc. are mentioned.

In order to manufacture an X-ray reflection type mask by the conventional method using these multilayer films and the plating method,
A conductive heavy atom layer such as Mo, Ru, W, and NiCr, or a heavy atom layer having a catalytically active property such as Pa is arranged on the uppermost layer of the multilayer film. By the way, when a heavy atom layer is arranged on the uppermost layer of the multilayer film, there is a problem that the X-ray reflectance of the multilayer film is gradually decreased as compared with immediately after the film formation due to a change with time (for example, J. H.Underwo
od, E.I. M. Gullikson, and Khanh
Nguyen: APPLIED OPTICS 1. December 199
3. Vol.32, No.34 P. 6985 ~ 6990).

For example, when the multilayer film is stored in the atmosphere, the uppermost layer is gradually oxidized (change with time). Mo / S
In the case of the i multilayer film, molybdenum oxide or silicon oxide is formed on the outermost surface of the uppermost layer of the multilayer film. Such oxidation changes the optical constant of the uppermost layer. Since oxygen has an optical constant close to that of light atoms in the light atomic layer, when the uppermost layer is a heavy atomic layer, oxidation results in a drastic change in the optical constants as compared with the case of a light atomic layer, and X It reduces the line reflectance.

When the multilayer film is used for an X-ray reflection type mask of an X-ray projection exposure apparatus, if the X-ray reflectance of the multilayer film decreases, the X-ray irradiation time required to obtain a desired exposure amount becomes long. Therefore, there arises a problem that the throughput is reduced. Furthermore, since the X-ray irradiation amount to the mask also increases,
There is also a problem of durability of the mask. In order to prevent such a problem, a substance which has conductivity or catalytic activity and is chemically stable or has a small change in optical constant due to aging may be selected as the uppermost layer of the multilayer film. good.

However, such substances are very limited, and there is a problem that it is often very difficult to obtain the reflectance required for X-ray projection exposure even if a multilayer film is produced. The present invention has been made in view of the above problems, and an object of the present invention is to provide an X-ray reflection type mask that prevents a decrease in reflectance of a multilayer film due to a change with time.

[0016]

Therefore, the first aspect of the present invention is to provide "at least an X-ray reflection multilayer film provided on a substrate and an X-ray absorption layer provided on the multilayer film in a predetermined pattern. In the X-ray reflection type mask, the X-ray reflection mask is characterized in that a coating layer of a chemically stable substance or a substance having a small change in optical constant with time is formed on the multilayer film and the absorption layer. A mold mask (claim 1) ".

The second aspect of the present invention is to provide an X-ray reflection type mask comprising at least a substrate and an X-ray reflection multilayer film having a predetermined reflectance distribution provided on the substrate. There is provided an X-ray reflection type mask (claim 2), characterized in that a coating layer of a chemically stable substance or a substance having a small change in optical constant with time is formed thereon.

The third aspect of the present invention is that the coating layer is formed so that the X-ray reflectance of the mask is maximum or substantially maximum.
A line-reflective mask (claim 3) ". In a fourth aspect of the present invention, the X-ray reflection according to claim 1, wherein the coating layer is formed of a substance or a compound thereof forming a layer immediately below the uppermost layer of the multilayer film. A mold mask (claim 4) ".

The fifth aspect of the present invention is that the multilayer film is Mo.
/ Si alternating multilayer film, and the coating layer is formed of Si or a Si compound. An X-ray reflection type mask (claim 5) according to any one of claims 1 to 4, is provided. .

[0020]

The conventional X having no coating layer according to the present invention
In the line reflection type mask, the uppermost layer of the multilayer film, which is one of the reflection portions, changes with time (chemical change such as oxidation), and its optical constant changes. In particular, when a heavy atom layer is arranged as the uppermost layer of a multilayer film, in many cases, the amount of change in this optical constant becomes large, which affects the reflection characteristics of the entire multilayer film, and as a result,
The reflectance of the entire multilayer film is greatly reduced.

However, according to the present invention, the coating layer 4 made of a chemically stable substance which is hard to undergo a chemical change such as oxidation or a substance which is hard to change the optical constant is provided with an X-ray reflection type mask (hereinafter, referred to as a mask). (Abbreviated as reflective mask)
By forming it on the surface of, the time-dependent change of the uppermost layer of the multilayer film 2 can be suppressed (see FIG. 1). Therefore, according to the present invention, it is possible to prevent the reflectance of the reflective mask from being lowered regardless of the material of the uppermost layer of the multilayer film 2 (claims 1 and 2).

As the substance forming the coating layer 4, a chemically stable substance which is hard to undergo chemical changes such as oxidation or a substance which is hard to change optical constants is selected. For example, chemically stable substances include Au, Pt, and S
Examples include iO ₂ and SiC. Further, as the substance in which the optical constant does not easily change, for example, Si at a wavelength of 13 nm may be mentioned, although it depends on the wavelength of the X-ray used.

Further, it is preferable that the coating layer 4 is formed in such a thickness as to be a continuous film so that the uppermost layer of the multilayer film 2 does not come into contact with the surrounding environment of the reflective mask. It is preferable to form the film so that the reflectance of the film does not decrease. Furthermore, it is preferable that the coating layer 4 is formed so that the reflectance of the reflective mask (or the multilayer film) becomes maximum or substantially maximum (for example, it is formed by selecting the material and the film thickness). ).

If the material and the film thickness of the coating layer 4 are selected, the coating layer 4 can be used as a reflection increasing film. Further, if the material of the coating layer 4 which is not the uppermost layer of the multilayer film constituent substances, that is, the layer immediately below the uppermost layer (in many cases, it is a light atom layer) is used, this material can form the multilayer film 2. Since it is a constituent substance, even if it is used as the material of the coating layer 4, the problem of the decrease in reflectance does not occur (claim 4).

Moreover, since the coating layer 4 can also be formed by the device in which the multilayer film 2 is formed, it is not necessary to newly introduce another device for forming the coating layer 4, and the cost performance is improved (claim 4). ). In the soft X-ray region, a wavelength of 13 nm, which is particularly promising for X-ray projection exposure
Then, if a Mo / Si multilayer film is used as the multilayer film 2 and Si or a Si compound is used as the coating layer 4, it has a high reflectance,
Moreover, X that prevents the reflectance of the multilayer film from decreasing due to aging
It is preferable because a line reflection type mask can be provided (Claim 5).

An example of the manufacturing process of the reflective mask according to the present invention is shown in FIG. First, the multilayer film 2 is formed on the substrate 1 (FIG. 4A). At this time, the multilayer film 2 is formed such that the uppermost layer of the multilayer film 2 is a substance having a conductive or catalytically active property. In general, since the heavy atom layer often exhibits conductive or catalytically active properties, the heavy atom layer is the uppermost layer.

Next, a resist 5 is applied on the multilayer film 2 (FIG. 4B), and pattern exposure and development are performed to form a resist pattern 5 '(FIG. 4C). Then, after using this resist pattern 5'as a mold, the absorber 3 is selectively grown only on the portion where the resist is removed by a plating method (electrolytic or electroless plating method) (FIG. 4).
(D)), the resist pattern 5'is removed (FIG. 4).
(E)). Further, when the coating layer 4 is formed, a reflective mask is obtained (FIG. 4 (f)).

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0029]

Embodiment 1 FIG. 1 is a schematic sectional view of a reflective mask of this embodiment. A process of manufacturing the reflective mask of this embodiment will be described with reference to FIGS. Using the Si wafer 1 as a substrate, the Mo / Si alternating multilayer film 2 was formed by the ion beam sputtering method so that the uppermost layer was the Mo layer (FIG. 4).
(A)). Here, the reason why the uppermost layer is the Mo layer is that the uppermost Mo layer is used as a plating electrode when the absorber is formed by an electrolytic plating method which will be performed later.

The Mo / Si multilayer film 2 has 50 layers, the period length (the film thickness of the Mo / Si layer 1 pair) is 6.6 nm, and the film thickness ratio (=
(Mo layer thickness / period length) 0.33. On the Mo / Si multilayer film 2, a resist 5 (Sumitomo Chemical Co., Ltd .: PFi-15) is applied in a film thickness of about 1 μm, and 90 is applied using a hot plate.
Prebaking was performed for 1 minute at 0 ° C (Fig. 4 (b)). Next, the mask pattern was exposed on the resist 5 by a reduction projection exposure method using ultraviolet rays (i-line). The resist pattern to be formed was 0.4 to 4 μmL & S. After baking at 110 ° C. for 1 minute on a hot plate, it was developed with a developing solution (HMD-3) to form a resist pattern 5 ′, which was used as a plating pattern mold (FIG. 4).
(C)).

The electrolytic plating solution was an aqueous solution containing 450 g / l of nickel sulfamate, 30 g / l of boric acid and 0.5 g / l of sodium lauryl sulfate. The conditions for electrolytic plating are
For example, current density 1 A / dm ² , pH ³ to 4, bath temperature 50
℃ was made. Under this condition, an electrolytic nickel plating 3 having a thickness of about 110 nm was grown (FIG. 4 (d)), washed with pure water and dried to remove the resist pattern 5 ′ (FIG. 4 (e)). ).

To remove the resist pattern 5 ', an acetone cleaning method or an O ₂ ashing method was used. After thoroughly cleaning the surface of the reflective mask, a Si layer 4 having a thickness of 4.4 nm was formed by the ion beam sputtering method (see FIG. 4).
(F)). The reflectance of the reflective mask of this example manufactured through the above steps was observed using soft X-rays having a wavelength of 13 nm. Immediately after the production, it was about 64%, which was almost the same as that of the similarly produced multilayer film mirror (reflection type mask in which the Si layer 4 was not formed).

When the reflectance of this reflective mask of this embodiment was left in the atmosphere for 100 days or longer and the reflectance was measured, no decrease in reflectance was observed (reflectance of about 65).
%). On the other hand, when the reflectance was measured after leaving the reflective mask on which the Si layer 4 was not formed in the atmosphere for 100 days or more, a large decrease in the reflectance was found (reflectance about 55%).

[0034]

Example 2 Using the Si wafer 1 as a substrate, the Mo / SiC alternating multilayer film 2 was formed by the ion beam sputtering method so that the uppermost layer was the Mo layer (FIG. 4A).
Here, the reason why the uppermost layer is the Mo layer is that the uppermost Mo layer is used as a plating electrode when the absorber is formed by an electrolytic plating method which will be performed later.

The Mo / SiC multilayer film 2 is composed of 50 layers,
Period length 6.7 nm, film thickness ratio (= Mo layer thickness / period length) 0.
33. On the Mo / SiC multilayer film 2, a resist 5 (Sumitomo Chemical Co., Ltd .: PFi-15) is applied to a film thickness of about 1 μm,
Prebaking was performed at 90 ° C. for 1 minute using a hot plate (FIG. 4B). Next, the mask pattern was exposed on the resist 5 by a reduction projection exposure method using ultraviolet rays (i-line). The resist pattern to be formed is 0.4-4 μm
L & S. After baking at 110 ° C. for 1 minute on a hot plate, it was developed with a developing solution (HMD-3) to form a resist pattern 5 ′, which was used as a plating pattern mold (FIG. 4 (c)).

The electrolytic plating solution was an aqueous solution containing 450 g / l of nickel sulfamate, 30 g / l of boric acid, and 0.5 g / l of sodium lauryl sulfate. The conditions for electrolytic plating are
For example, current density 1 A / dm ² , pH ³ to 4, bath temperature 50
℃ was made. Under this condition, an electrolytic nickel plating 3 having a thickness of about 110 nm was grown (FIG. 4 (d)), washed with pure water and dried to remove the resist pattern 5 ′ (FIG. 4 (e)). ).

To remove the resist pattern 5 ', an acetone cleaning method or an O ₂ ashing method was used. After thoroughly cleaning the surface of the reflective mask, an SiC layer 4 having a thickness of 4.5 nm was formed by the ion beam sputtering method (see FIG. 4).
(F)). The reflectance of the reflective mask of this example manufactured through the above steps was observed using soft X-rays having a wavelength of 13 nm. Immediately after the fabrication, it was about 48%, which was almost the same as that of the similarly fabricated multilayer mirror (a reflective mask in which the SiC layer 4 was not formed).

When the reflectance of this reflective mask of this embodiment was left in the atmosphere for 100 days or more and the reflectance was measured, no decrease in reflectance was observed (reflectance of about 47).
%). On the other hand, when the reflectance was measured after the reflective mask without the SiC layer 4 left in the atmosphere for 100 days or more, the reflectance was significantly reduced (reflectance about 40%).

[0039]

As described above, according to the X-ray reflection type mask of the present invention, it is possible to prevent a decrease in X-ray reflectance due to aging and to maintain a high reflectance. If the X-ray reflection type mask of the present invention is used in an X-ray projection exposure apparatus, the exposure time can always be made constant (or substantially constant).

As a result, the throughput of the X-ray projection exposure apparatus becomes stable. Further, not only is it unnecessary to change the exposure time according to the change in reflectance, but also the exposure failure due to the decrease in reflectance does not occur, so that the non-defective rate is improved. Further, since the irradiation amount on the mask is also reduced, it is possible to suppress the deterioration of the multilayer film forming the reflective mask.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an X-ray reflection type mask (provided with a coating layer) according to the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of a conventional X-ray reflection type mask (a coating layer is not provided).

FIG. 3 is a schematic cross-sectional view showing an example of a manufacturing process of a conventional X-ray reflective mask.

FIG. 4 is a schematic cross-sectional view showing an example of a manufacturing process of an X-ray reflective mask according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... X-ray reflective multilayer film (for example, Mo / Si alternating multilayer film, Mo / SiC alternating multilayer film) 3 ... X-ray absorbing layer (absorber) 4 ... Covering layer 5 ... Resist 5 '... more than resist pattern

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-67731 (JP, A) JP-A-63-21830 (JP, A) JP-A-3-136313 (JP, A) JP-A-4- 207016 (JP, A) Actual development Sho 63-185224 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/027

Claims (5)

(57) [Claims] 1. An X-ray reflective multilayer film provided on at least a substrate, and X provided on the multilayer film in a predetermined pattern.
An X-ray reflection type mask having a line absorption layer, characterized in that a coating layer of a chemically stable substance or a substance having a small change in optical constant with time is formed on the multilayer film and the absorption layer. X-ray reflection type mask. 2. An X including at least a substrate and an X-ray reflective multilayer film having a predetermined reflectance distribution provided on the substrate.
An X-ray reflection type mask, characterized in that a coating layer of a chemically stable substance or a substance whose optical constant is small with time is formed on the multilayer film. 3. The X-ray reflective mask according to claim 1, wherein the coating layer is formed so that the X-ray reflectance of the mask becomes maximum or substantially maximum. 4. The X-ray reflection type mask according to claim 1, wherein the coating layer is formed of a substance or a compound thereof forming a layer immediately below the uppermost layer of the multilayer film. 5. The X-ray reflection type according to claim 1, wherein the multilayer film is a Mo / Si alternating multilayer film, and the coating layer is formed of Si or a Si compound. mask.