JPH08213303A - Reflective x-ray mask and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a reflective X-ray mask and manufacturing method thereof not to deteriorate the X-ray reflectance of multilayer films. CONSTITUTION: A reflective X ray mask having an X ray reflection film 2 and intermediate layers 3 and X ray absorber layers 4 formed in a pattern shape is constituted with the etching selection ratio between the intermediate layers 3 and the X ray absorber layers 4 exceeding 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type X-ray mask for X-ray exposure (hereinafter referred to as a reflection mask) and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, semiconductor devices are required to have higher integration. Therefore, the line width of the circuit pattern is required to be smaller and smaller. The circuit pattern is formed by the photolithographic etching method.
There is a step of projecting and exposing a mask called a reticle on the photoresist. Since the wavelength of the light at the time of exposure determines the minimum line width, the wavelength of the light source is required to be short. However, 1G or more memory IC (0.15
In order to produce a resolution of less than μmL & S),
The current UV rays cannot be used. Therefore, an X-ray projection exposure method, which exposes soft X-rays having a shorter wavelength, is drawing attention.

So far, a transmission type mask has been proposed as a mask for X-ray exposure. The structure of the transmissive mask is
An X-ray absorber layer in which a desired circuit pattern is formed of a material having a large X-ray absorption coefficient, a free-standing film having a large transmission coefficient with respect to the X-ray wavelength used, and a circuit pattern portion are removed to hold the free-standing film. It consists of a substrate. That is, the X-ray absorber is formed on a self-supporting film having a thickness of several microns. Therefore, the transmissive mask has drawbacks such as low mechanical strength and thermal deformation during exposure. A reflective mask has been proposed as a method for solving the drawbacks of the transmissive mask.

The reflection mask includes (1) a pattern-formed X-ray reflection layer and (2) a pattern-formed X-ray absorber layer placed on the X-ray reflection layer. is there. The X-ray reflection layer is also called a multi-layered film mirror, and has a structure in which two kinds of substances having different refractive indexes are alternately laminated on the order of several nm. Thus, the multilayer film having a periodic structure reflects X-rays when incident X-rays of a certain wavelength satisfy the Bragg condition.

As the X-ray absorber, a substance having a high X-ray absorption coefficient at the wavelength of X-rays used at the time of exposure is used, and the substance varies depending on the etching method used when forming the pattern. In case of reactive ion etching, W, T
a, Ge or the like is used, and Au is used in the case of ion beam etching. The reflective mask is manufactured by the following steps. (1) Step of forming an X-ray reflection film on the substrate; (2) Step of forming an X-ray absorber layer on the X-ray reflection film; (3) Step of applying a photoresist on the X-ray absorber layer. (4) A step of forming a resist pattern on the photoresist by an electron beam drawing method; (5) A step of patterning the X-ray absorber layer by dry etching or the like (pattern transfer); (6) Remaining Step of removing the resist; The reflection mask is susceptible to damage due to etching in the X-ray reflection layer in the etching step (5) of the X-ray absorber layer,
As a result, the X-ray reflectance of the reflection mask is reduced.
Reactive ion etching has been often used for such an etching process. However, with the further miniaturization of circuits in the future, high energy conditions with excellent anisotropic control, or ion beam etching will be used, and it is necessary to support such high energy etching. A reflective mask is required.

[0006]

In the case of the conventional example in which the X-ray absorber layer is simply arranged on the multilayer film to form the pattern, X
The etching of the multilayer film starts at the same time as the etching of the line absorber, and the surface roughness of the uppermost layer of the multilayer film increases, or several or tens of layers are etched from the uppermost layer of the multilayer film, reducing the number of layers. As a result, the X-ray reflection efficiency is greatly reduced. Also,
When there is an intermediate layer on the multilayer film, the thickness decreases in proportion to the thickness of the intermediate layer. When such a reflection mask is used for X-ray reduction projection exposure, the optimum exposure time becomes long and the throughput decreases. In the reflection mask and its manufacturing method, how to form a fine and highly precise pattern without giving etching damage to the multilayer film is a major problem.

An object of the present invention is to provide a reflection mask which does not reduce the X-ray reflectance of a multilayer film and a method for manufacturing the same.

[0008]

As a result of earnest research, an X-ray absorber layer is formed by arranging an intermediate layer made of a substance having specific characteristics on a multilayer film and forming an X-ray absorber layer thereon. It has been found that it is possible to prevent etching damage to the multilayer film when the pattern is transferred to the linear absorber layer. If there is an intermediate layer on the multilayer film,
Since the X-ray reflection efficiency decreases in proportion to the thickness of the intermediate layer,
The combination of the material used for the intermediate layer and its removal method was found.

The reflection mask of the present invention comprises an X-ray reflection film, an intermediate layer and an X-ray absorber layer formed in a pattern, and the etching selection ratio between the intermediate layer and the X-ray absorber layer is It is characterized by being 5 or more. Further, the intermediate layer is a reflection mask containing chromium or titanium as a main component.

Further, the reflection mask of the present invention comprises an X-ray reflection film, an intermediate layer and an X-ray absorber layer which are formed in a pattern, and the intermediate layer is located on the X-ray absorber layer side. And a second intermediate layer located on the side of the reflective film.
An intermediate layer, wherein the first intermediate layer is chromium, titanium,
Consists of a material whose main component is nickel, gold or platinum,
The second intermediate layer is made of a carbon-based material.

The method of manufacturing a reflection mask of the present invention comprises an X-ray reflection film, a patterned intermediate layer and an X-ray absorber layer, and (1) forms a pattern on the X-ray absorber layer. Etching step; (2) an etching step of removing an intermediate layer formed in a portion used as an X-ray reflection portion after the pattern formation is completed, wherein the etching steps (1) and (2) are different from each other. It is characterized in that it is manufactured.

[0012]

The basic manufacturing method of the reflection mask for X-ray exposure according to the present invention is shown in FIG. (1) Step of forming an X-ray reflection film on the substrate (2) Step of forming an intermediate layer on the multilayer film (3) Step of forming an X-ray absorber layer on the intermediate layer (4) Step of applying a resist (etching mask) on the X-ray absorber layer and forming a pattern by photolithography, dry etching, etc. (5) Etching step for removing the residual resist and the intermediate layer other than the X-ray absorption region For the etching, an ion beam etching method using an inert gas or a reactive ion etching method using a reactive gas such as CF4, CHF3 or O2 may be used alone or in combination. At the time of etching, it is necessary that the difference between the etching rates of the material to be etched and the material that should not be etched be sufficiently large. This etching rate ratio is called an etching selection ratio. That is, it is necessary that the X-ray absorber layer that is the material to be etched and the multilayer film that should not be etched have a high etching selection ratio.

In the examples, the overetching rate is
In the layer to be etched / base substrate, the ratio of the etching time until the layer to be etched is exposed to expose the base substrate and the time to etch the base substrate. The present invention regarding the material and structure of the intermediate layer is made in consideration of the two etching steps of the pattern transfer step and the intermediate layer removing step of the manufacturing process in order to suppress the decrease in the X-ray reflectance of the multilayer film of the reflection mask. It is a thing.

Each claim will be described with reference to FIG. In claim 1 and claim 2, the X-ray absorber layer 4
On the other hand, a material having a large etching selection ratio (a large etching rate ratio) is used for the intermediate layer 3. By adopting such a method, even when the X-ray absorber layer 4 is over-etched during the pattern transfer process, the underlying multilayer film 2 is not damaged by etching.

For the intermediate layer, a material having a high selection ratio with respect to the X-ray absorber layer is selected. For example, a case will be described where Au is used to transfer a pattern to an X-ray absorber by an ion beam etching method. The intermediate layer has a selection ratio of 15 to 20.
Ti and C having a selection ratio of 6 to 10 in addition to Cr having
NiCr, which is a compound containing r as a main component, is effective. In particular, the Cr film is a substance that is very difficult to etch,
In physical etching, the etching rate is very slow. Therefore, it is a material very suitable for use as an etching stopper.

Further, in the case of the pattern transfer process by the reactive ion etching method using W, Ta or the like for the X-ray absorber layer, a carbon-based material is used for the intermediate layer. In the case of an intermediate layer having a two-layer structure, it is effective to use Au or Pt for the first layer and a carbon-based material for the second layer. Next, the intermediate layer removing step will be described.

Further, after transferring the pattern of the X-ray absorber layer, the intermediate layer must be peeled off as a reflection mask in order to secure the X-ray reflection amount. In the peeling by reactive ion etching or ion etching in which ions have a large acceleration energy, the underlying multilayer film is damaged and the X-ray reflection efficiency is significantly reduced. It is necessary that the method does not cause etching damage to the film. In the case of peeling using a wet etchant, if an etching-free etchant is used for the underlying multilayer film, the interlayer can be peeled off without significantly damaging the multilayer film by etching. For example, a method of removing Cr will be described.

The pattern of the X-ray absorber layer 4 is transferred to the multilayer film 2 having Si as the uppermost layer. After that, when the intermediate layer 3 is removed by using a Cr etchant (composition: cerium nitrate second ammonium, perchloric acid, water), etching damage is not given to the multilayer film 2 and a decrease in X-ray reflectance can be suppressed. it can. According to claim 3, the intermediate layer has a double structure, and the intermediate layer shown in claims 1 and 2 is formed on the upper layer (the first intermediate layer 3).
a)). The lower layer is a substance that can be removed by a method that does not damage the multilayer film 2 by etching, such as oxygen ashing. As an example, a carbon-based film (second intermediate layer 3
Place b). Such a configuration is very effective when it is necessary to use a reactive etching method that causes etching damage to the underlying multilayer film when the intermediate layer is peeled off. It is also effective in the ion beam etching method.

A material is selected for the first intermediate layer 3a by an etching method for forming a pattern on the X-ray absorber layer.
The material of the first intermediate layer may have a selection ratio of 5 or more with respect to the X-ray absorber layer. For example, in the case of reactive ion etching, Au or Pt is used. In the case of ion beam etching, Cr, Ti or the like is used. As the carbon-based film, an amorphous carbon film is used in this embodiment, but the present invention is not limited to this.

The etching step of the method for manufacturing the reflection mask of the present invention includes (1) an etching step of forming a pattern on the X-ray absorber layer; (2) an etching step of forming an X-ray reflecting portion after the pattern formation is completed. The etching step for removing the intermediate layer is performed in two steps, and the etching steps (1) and (2) use different etching methods (or etching conditions).

In the etching step (1), an etching method using high ion energy, for example, ion beam etching is performed, and the intermediate layer having a high etching selection ratio prevents damage to the surface of the multilayer film to be the X-ray reflecting portion. In the etching step (2), a mild etching method is used. For example, when a material containing chromium as a main component is selected for the intermediate layer, by performing ion beam etching in the etching step (1) and wet etching using a chromium etchant in the etching step (2),
It is possible to prevent damage to the surface of the multilayer film that becomes the X-ray reflection portion.

In the etching step having the first and second intermediate layers as in claim 3, in the etching step (1), a reactive ion etching method using a fluorine-based gas or a chlorine-based gas, an etching step ( When the reactive ion etching method using an oxygen-based gas is applied to 2), X
It is possible to prevent damage to the surface of the multilayer film that becomes the line reflection portion. Thus, the reflection mask manufactured without damaging the multilayer film by etching can be used as a reflection mask having a very high X-ray reflectance.

As an example, Mo / corresponding to a wavelength of 13 nm
Considering the Si multilayer film, the Mo / Si multilayer film achieves a reflectance of 60% or more with respect to direct incident light, but several pairs on the surface of the multilayer film are damaged or ions are implanted into the multilayer film. When the material constituting the multilayer film is deteriorated, the reflection efficiency of the multilayer film is drastically reduced. However, by using the intermediate layer according to the present invention, the pattern transfer of the X-ray absorber layer can be performed without lowering the X-ray reflection efficiency of the multilayer film.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0025]

First, a first embodiment of the present invention will be described. FIG. 1 is a structural sectional view of a first embodiment of an X-ray absorber layer-added type reflection mask according to claims 1 and 2. FIG. 3 is an explanatory diagram of the manufacturing process of the reflection mask.

On the substrate 1 made of Si wafer, Mo / S
The i multilayer film 2 was formed by the ion beam sputtering method (see step 1 in FIG. 3). The number of layers of the Mo / Si multilayer film 2 is N =
50, the cycle length d = 6.7 nm, and the film thickness ratio Γ = 0.5,
As the intermediate layer 3, for example, Cr was deposited thereon by a magnetron sputtering method to a thickness of about 10 to 20 nm. Further, the X-ray absorber layer 4 (for example, Au) was formed on the intermediate layer 3 with an appropriate thickness.

An etching mask 5 is formed on the X-ray absorber layer in order to transfer the pattern of the X-ray absorber layer 4 into a desired pattern (see step 2 in FIG. 3). Assuming that the etching mask 5 is made of a resist, first, a positive resist for i-line PFi-15 (manufactured by Sumitomo Chemical Co., Ltd.) is about 1 μm
Was formed by a spin coating method, and then prebaked on a hot plate at 90 ° C. for 1 minute. The exposure was performed using a reduction projection exposure apparatus: NSR1505i6A (manufactured by Nikon Corporation) with an exposure dose amount of about 160 mJ / cm 2. After exposure, it was baked on a 110 ° C. hot plate for another 1 minute. After developing for 1 minute with HMD-3 developer (Tokyo Oka), it was washed with water (step 3 exposure in FIG.
See development).

Using this etching mask 5, pattern transfer to the X-ray absorber layer 4 was performed by an ion beam etching (milling) method. Multipurpose ion shower device EIS-200ER using argon gas as the ion source
(Manufactured by Elionix) was used. This apparatus was equipped with an ECR plasma source, and the plasma generation conditions were an argon gas pressure of about 5 × 10 −3 Pa, a microwave output of 60 W, and an electromagnetic field output scale of 8.0. The ion beam extraction conditions were an acceleration voltage of 700 V and no neutralizer was used. As a result of etching under such conditions, the time required for etching Au was about 13 minutes and 20 seconds. The etching rate is about 15 nm / min.

However, it is considered that there is a portion that is partially underetched, and in order to completely transfer the pattern, etching was further performed for 20 minutes over 16 minutes. At that time, the etching rate of the Cr layer 3 disposed as the lower layer as the intermediate layer was about 0.8 nm / min, which was about 1/19 of the etching rate of Au. 20%
It was found that the etching amount was only about 0.13 nm under the over-etching condition. From this result, it was found that Cr is effective as the material of the intermediate layer as the etching stopper. (Step 4 of FIG. 3
(See transfer) The next step is an intermediate layer removing step.

In order to maximize the X-ray reflection efficiency as a reflection mask, the Cr film (intermediate layer 3) must be removed in the portion where the X-ray absorber layer 4 is absent.
Cr was removed with a chromium etchant (composition: cerium nitrate second ammonium, perchloric acid, water). Since this etching method is isotropic etching, the pattern is peeled off if it is left in the etchant for a long time. Therefore, the etching time is set to 1 minute at room temperature. Further, since the etchant causes etching damage to Mo,
The Mo / Si multilayer film 2 is formed as the uppermost layer Si so as to prevent etching damage.

As described above, when the X-ray absorber layer pattern is transferred, the etching selection ratio with respect to the X-ray absorber layer is large, and a substance that can be peeled off without damaging the multilayer film 2 by etching is used as the intermediate layer 3. When used as
Without reducing the X-ray reflection efficiency of the Si multilayer film 2.
The pattern transfer of the X-ray absorber layer 4 can be performed.
(Refer to the removal of the intermediate layer in step 5 of FIG. 3) When the above results are examined by the X-ray reflectance of the multilayer film,
The reflectance of the Mo / Si multilayer film corresponding to the wavelength of m was 60%, and the reflectance before the mask was manufactured was maintained even after the mask was manufactured. By using the intermediate layer according to the present invention, the pattern transfer of the X-ray absorber layer and the removal of the intermediate layer after the pattern transfer can be performed without lowering the X-ray reflectance of the multilayer film.

Next, a second embodiment will be described. Figure 2
[FIG. 8] is a structural cross-sectional view of a second embodiment of the X-ray absorber addition type reflection mask. FIG. 3 is an explanatory diagram of the manufacturing process of the reflection mask. Mo / Si on Si wafer 1
The multilayer film 2 is formed under the same conditions as in Example 1 (see step 1 in FIG. 3). A carbon film to be the second intermediate layer 3b was formed thereon by an ion beam sputtering method with a thickness of about 5 nm.
Further, a Cr film to be the second intermediate layer 3a is formed with a thickness of about 10 nm. Further, an X-ray absorber layer 4 (W, as an example) was formed thereon with a proper thickness by a magnetron sputtering method. After that, an etching mask 5 was formed on the X-ray absorber layer in order to transfer the pattern of the X-ray absorber layer 4 into a desired pattern (see step 2 in FIG. 3). next,
0.5 positive electron beam positive resist (OEBR-1000)
After application to a thickness of 5 μm, prebaking was performed at 170 ° C. for 20 minutes, and patterning was performed using an electron beam drawing apparatus. At that time, the acceleration voltage was set to 30 KV. After stirring with a dedicated developer for 3 minutes at room temperature, rinse with pure water was performed (see exposure or drawing / development in step 3 of FIG. 3). Using this pattern as an etching mask 5, the pattern was transferred to the X-ray absorber layer 4.

As an example, the material of the X-ray absorber layer was W (tungsten), and the film thickness was about 0.1 μm. The pattern transfer was performed by a reactive ion etching method using a fluorine-based gas (CF4, CHF3, etc.). The etching end point was set to 20% over so that the X-ray absorber layer 4 could be completely etched. The multilayer film 2 is very susceptible to etching damage to fluorine-based gas. However, in this embodiment, since the first intermediate layer 3a and the second intermediate layer 3b, which are two intermediate layers, are provided as the etching stopper between the multilayer film 2 and the multilayer film 2, the multilayer film is not damaged even if over-etching. It does not enter (see step 3 transfer in FIG. 3).

In order to secure the X-ray reflection amount, after transferring the pattern of the X-ray absorber layer, the Cr film of the first intermediate layer 3a in the portion contributing to the X-ray reflection was removed. The removal method was a reactive ion etching method using a mixed gas of carbon tetrachloride and oxygen as a material gas. The etching conditions are a gas pressure of 40 Pa, a mixing ratio of 1: 1.74, and an Rf output of 100 W. Then, the second intermediate layer 3b was removed by oxygen ashing. The ashing condition is oxygen gas pressure 1
0 Pa, Rf output 50 W, self bias 100 V
Below. In oxygen ashing, by controlling the self-bias to 100 V or less, it is possible to prevent etching damage to the Mo / Si multilayer film 2 under the second intermediate layer. (Refer to Step 5 Intermediate layer removal in FIG. 3) As described above, in the reactive ion etching method using CF4 gas, when W is used for the X-ray absorber layer, the first intermediate layer, the second intermediate layer, and the second intermediate layer Excessive etching was prevented by the stepped etching stopper. At that time, the first intermediate layer 3a
As the material, a substance having an etching selection ratio with respect to the X-ray absorber layer W of 5 or more is selected. In this embodiment, Cr is used. In the etching step of removing the first intermediate layer 3a, the etching selection ratio using C for the second intermediate layer 3b with respect to the X-ray absorber layer W is about 20.

As described above, the first intermediate layer 3a prevents etching damage to the multilayer film 2 during pattern transfer of the X-ray absorber layer 4, and the second intermediate layer 3b prevents removal of the first intermediate layer 3a. Etching damage to the film 2 can be prevented.
By using the intermediate layer having the two-layer structure of the present invention,
The pattern transfer of the X-ray absorber layer and the removal of the intermediate layer after the pattern transfer can be performed without lowering the X-ray reflectance of the multilayer film. In particular, this two-layer structure of the intermediate layer is effective in the step of removing the intermediate layer using reactive ion etching.

Looking at the above results in terms of the X-ray reflectivity of the multilayer film, the Mo / Si multilayer film corresponding to the wavelength of 13 nm has a reflectivity of 60%, and the reflectivity before manufacturing is maintained even after the mask is manufactured. Was there.

[0037]

When X-ray reduction projection exposure is performed by using the reflection mask according to the present invention, the number of layers in the multilayer film below the X-ray absorber layer is reduced by etching or ion implantation into the multilayer film is performed. Since there is no alteration, the X-rays can be reflected with high efficiency, the exposure time can be greatly shortened, and the throughput can be improved. As a result, taking semiconductor device manufacturing as an example, the device manufacturing time can be shortened, and it is possible to provide a cheap semiconductor device on the market or a product equipped with the same.

[Brief description of drawings]

FIG. 1 is a sectional view of a reflective mask that is a first embodiment of the present invention.

FIG. 2 is a sectional view of a reflection mask that is a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a manufacturing process of a reflective mask that is an embodiment of the present invention.

[Explanation of symbols for main parts]

 1 ... Substrate, 2 ... Multilayer film 3 ... Intermediate layer 3a ... First intermediate layer 3b ... Second intermediate layer 4 ... X-ray absorber layer (W, Ta, Au, etc.) 5 ... Etching mask

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/3065 21/306 H01L 21/306 S

Claims (5)

[Claims] 1. A reflection type X comprising an X-ray reflection film, a patterned intermediate layer and an X-ray absorber layer.
A reflection type X-ray mask, wherein an etching selection ratio between the intermediate layer and the X-ray absorber layer is 5 or more. 2. The reflective X-ray mask according to claim 1, wherein the intermediate layer is made of a material containing chromium or titanium as a main component. 3. A reflection type X composed of an X-ray reflection film, a patterned intermediate layer and an X-ray absorber layer.
In the line mask, the intermediate layer includes a first intermediate layer located on the X-ray absorber layer side and a second intermediate layer located on the reflection film side, and the first intermediate layer is chromium, titanium or nickel. The reflective X-ray mask according to claim 1 or 2, wherein the second intermediate layer is made of a material containing gold or platinum as a main component, and the second intermediate layer is made of a carbon-based material. 4. A reflection-type X comprising an X-ray reflection film, a patterned intermediate layer and an X-ray absorber layer.
In the method of manufacturing a line mask, (1) an etching step of forming a pattern on the X-ray absorber layer; (2) an etching step of removing an intermediate layer formed in a portion used as an X-ray reflecting portion after the pattern formation is completed;
A method of manufacturing a reflection type X-ray mask, characterized in that the etching steps (1) and (2) are performed by different etching methods. 5. The reflection type according to claim 4, wherein an ion beam etching method is used in the pattern forming step of the etching step (1), and a wet etching method is used in the intermediate layer removing step of the etching step (2). X-ray mask manufacturing method.