JPH03124016A - X-ray mask and manufacture thereof - Google Patents

Abstract

PURPOSE:To keep a high position accuracy by using a membrane which consists of a lower layer having enough tensile stress for self-supporting and a lower layer having only a negligibly small stress in comparison with that of the lower layer. CONSTITUTION:A membrane has a lower layer 1 and an upper layer 2; a tensile stress 3 is formed in the lower layer 1, which is strong enough for self-supporting and only a negligibly small stress in comparison with the tensile stress 3 of the lower layer 1 is produced in the upper layer 2. A mask pattern is formed on the membrane by a material which absorbs X-ray to manufacture an X-ray mask. In manufacture of the membrane, after a membrane 1 having enough tensile stress is manufactured, ion implantation is carried out to a surface part of the membrane 1. The upper layer 2 whereto ion implantation is carried out becomes a film having a small stress. Thereby, a high position accuracy can be kept.

Description

[Detailed Description of the Invention] [Summary] Regarding an X-ray mask used in X-ray exposure technology and its manufacturing method, it is possible to maintain high positional accuracy even if the membrane is etched to some extent and the film thickness varies locally. The purpose is to provide an X-ray mask that can transmit X-rays of a predetermined wavelength, and a mask pattern that is made of a membrane made of a material that can transmit X-rays of a predetermined wavelength and a material that absorbs the X-rays provided on the membrane. In the X-ray mask, the membrane has a lower layer that has sufficient tensile stress to support itself, and an upper layer that is formed on the lower layer and has negligible stress compared to the stress of the lower layer. It consists of:

[Industrial Field of Application] The present invention relates to X-ray exposure technology, and particularly to an X-ray mask used in X-ray exposure technology and a method for manufacturing the same.

2. Description of the Related Art Semiconductor integrated circuit devices are becoming more and more highly integrated, and each element and wiring tends to be miniaturized.

In order to realize an M4 pattern, a high resolution exposure technique is required. For light exposure using ultraviolet light as an exposure source, one with a shorter wavelength has been developed. Electron beam exposure has the advantage of high resolution and the ability to create lenses electromagnetically, but requires a vacuum. Although X-ray exposure can achieve high resolution without necessarily requiring a vacuum,
It is difficult to create a lens system, and close exposure or close exposure is the main method.

An X-ray exposure mask used for such contact exposure or close exposure is required to have a high precision of, for example, a minimum line width of 0.15 μm. Furthermore, there is no solid material that is highly transparent to electron beams and X-rays, so the mask is formed on a film-like membrane made of a material with low absorption.

"Prior Art" FIGS. 2(A) to 2(F) schematically show a method of manufacturing an X-ray mask according to a conventional technique.

First, as shown in FIG. 2(A), a SiC film 52 having a thickness of about 2 μm is deposited on a silicon wafer 51 of an appropriate size by chemical vapor deposition (CVD). The SiC film is a material that absorbs little X-rays. For example, a SiC film with a thickness of 2 μm exhibits a transmittance of about 70% for wavelengths 4 to 8 xl.

The center of the silicon wafer 51 is etched in a later step, and serves as a support frame for the SiC film 52 that will become an X-ray transparent membrane.

Next, as shown in FIG. 2(B), the silicon wafer 5
The central portion of the SiC film 52 on the back side of the silicon wafer 1 is removed by etching to form an opening 53 exposing the silicon wafer 51. This aperture defines the maximum usable area of the X-ray mask to be created later.

As shown in FIG. 2C, a film 55 of tantalum (Ha), which is a material that strongly absorbs X-rays, is formed on the SiC film 52 on the front side of the silicon wafer 51. As the X-ray absorber, in addition to Ta, W, Au, etc. can be used.

At this stage, the membrane 52, which has low absorption of X-rays, is
A structure is created in which an absorbent material film 55 is laminated on top of the absorbent material film 55.

As shown in FIG. 2(D), an X-ray mask support frame 56 is bonded to the back side of the silicon wafer 51. This support frame 56 is made of SiC ceramic, for example.

An opening 57 having substantially the same shape as the opening 53 of the SiC11g52 is formed in the center of the support frame 56.

As shown in FIG. 2(E), the silicon wafer 51 with the supporting frame 56 attached thereto is etched from the opening 5753 on the back side with a mixed solution of, for example, hydrofluoric acid (HF) and nitric acid (HNO3). The central portion of the SiC film 52 is removed to expose the SiC film 52. In this way, the X! ! A mask membrane 52 and an absorber film 55 thereon are formed. Here, in order for the absorber membrane 55, which serves as an X-ray mask, to maintain its position accurately, the membrane 52 must have sufficient strength and provide supporting force. Its manufacturing process gives tensile stress.

Parameters for the process are selected.

Thereafter, as shown in FIG. 2(F), a photoresist layer 58 is applied on the absorber film 55 made of Ta, a pattern is developed, and the underlying absorber film 55 is patterned by etching. In this way, the absorber pattern 55 is formed on the membrane 52.

If the absorber vA55 has stress inside, and as a result of buttering the absorber, some parts of the absorber film 55 remain on the membrane 52 and some parts do not. A local stress distribution is formed due to the stress, and as a result, the membrane 52 expands and contracts depending on where the absorber film 55 is present and where it is not, reducing positional accuracy. 55 controls to a low stress state.

Membrane material is 5x10~4xlO9dyn/al
Moreover, the absorber film was controlled to have a low stress of about 1 x 108 dyn/cl or less.

Even if the X-ray absorber film is created in a stress-free state with low stress so that the pattern is not distorted by patterning, there is another problem.

For example, buttering of an X-ray absorber film such as Ta is performed by reactive ion etching (RIE) using a mixed residue of CQ2 and CCQ4. However, in such RIE, it is difficult to maintain a high etching rate selectivity for Ta, which is an X-ray absorber, and SiC, which is a membrane material. It is difficult to stop suddenly,
There is a problem of over-etching which also etch the membrane 52.

As shown in FIG. 3(A), when the membrane 52 is partially etched, the thickness of the membrane 52 will be distributed locally, and tensile stress is formed inside the membrane 52. Therefore, if the thickness is distributed, the tensile stress will also be distributed locally, which causes local expansion and contraction of the membrane 52, causing local movement of the pattern and pattern distortion.

It is not impossible to increase the etching selectivity between the X-ray absorber and the membrane, but if the parameters are selected in this way, an etching mask as shown in FIG. Lower undercuts are more likely to occur. That is, even if there is no distribution in the thickness of the membrane 52, the dimensional accuracy of the X-ray absorber film 55 is reduced.

[Problems to be Solved by the Invention] As explained above, according to the conventional technology, even if the stress of the X-ray absorber film is carefully controlled to a very low value,
There has been a problem in that positional accuracy deteriorates due to overetching and the like.

An object of the present invention is to provide an X-ray mask that can maintain high positional accuracy even if the membrane is etched to some extent and its film thickness varies locally.

Another object of the present invention is to provide a manufacturing method for manufacturing such an X-ray mask.

[Means to solve the problem] FIGS. 1A to 1D are diagrams explaining the principle of the present invention.

FIG. 1(A) is a sectional view schematically showing the structure of a membrane for an X-ray mask. The membrane has a lower layer 1 and an upper layer 2, and the lower layer 1 has a tensile stress 3 strong enough to self-support the membrane, and the upper layer 2 has a tensile stress 3 that is negligible compared to the tensile stress 3 of the lower layer 1. Minor stress 4
only occurs. In other words, the upper layer is a film that can be regarded as a stress-reflecting film. A mask pattern is formed on the membrane using a material that absorbs X-rays to create an X-ray mask.

A membrane consisting of such 21 structures is shown in Figure 1 (B
), (C). The method shown in Figure 1 (B) involves first creating a membrane 1 with sufficient tensile stress, and then implanting ions into the surface of the membrane l. As a result, the tensile stress acting on the membrane is alleviated. In this way, the ion-implanted upper layer 2 becomes a film with low stress.

FIG. 1(C) is an example in which the lower layer and the upper layer are created in separate processes. After forming the lower layer 1 by a process that generates sufficient tensile stress, such as pyrolytic CVD, plasma C
The upper layer 2 is created with less stress by VD. That is, a plasma CVD film 2 with low stress is deposited on the lower layer 1 while using plasma 5. By appropriately selecting plasma CVD parameters, the stress acting inside the plasma CVD film 2 can be reduced.

[Function] By creating the lower layer as a layer with sufficient tensile stress and creating the upper layer as a layer with negligible small stress compared to the lower layer, an X-ray absorber film is provided on the upper layer, and the butter Even if overetching occurs during etching, the non-uniformity in film thickness distribution can be kept within the upper layer. Even if the thickness of the upper layer varies, as shown in FIG. 1(D), only a small stress exists in the upper layer 2, so the stress distribution remains substantially uniform. Therefore, expansion and contraction of the membrane can be prevented and high positional accuracy can be achieved.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 4A, 4B, and 4C show an X-ray mask according to an embodiment of the present invention.

FIG. 4(A) shows a cross-sectional configuration of 5iCIl!, in which tensile stress is generated on the surface of an annular silicon substrate 10 having an opening 20 cut out in the center! 11 is stretched and SiC
It is attached to a support frame 18 made of ceramic.

On the surface of the SiC film 11, which has tensile stress, there is a stress-free 5iCJ1 film that suppresses the tensile stress to a low level.
912 is formed.

SiC has low absorption of X″m and forms a membrane for holding the mask.A Ta layer 6 made of Ta, which has a strong ability to absorb X-rays, is laminated thereon. is SiC film 11.12
and Ta layer 6 are stretched in the form of a film. The Ta layer 6 is selectively etched to form a pattern for X-ray exposure.

Figure 4 (B) shows an enlarged view of the Ta pattern formed on the membrane. A SiC film 12 is formed, and 1116 (1) a on top of it is patterned into a predetermined shape.

The lower layer SiC with strong tensile stress [11 has a thickness of 2 μm, for example.
For example, the stress-free upper layer 5iC1lj12 has a thickness of ~0.2 μm, and the TaJ pattern 16 has a thickness of, for example, about 0.8 μm.

Over-etching that is likely to occur during patterning of the Ta layer 6, which is an X-ray absorber, will be explained with reference to FIG. 4(C). On top of the Ta layer weight 6, for example, a thickness of about 0.
A 5 μm novolak resin photoresist layer is applied and developed to form a resist pattern 19, and the underlying Ta layer 6 is selectively etched. For example, CR2 and C
By reactive ion etching using Cl14, Ta1li is etched in a shape that is faithful to the shape of the resist pattern 19.
Etch 16. In this etching, the ratio of the etching speed between the plate and the underlying SiC is not so high.

Therefore, when TayAl 6 is completely etched,
There is a high possibility that some exposed portions of the underlying SiC film 12 will be etched.

FIG. 4(C) shows a state in which the surface portion of the 5iCrA 12 is thus over-etched and a recess 21 is formed. Conventionally, when overetching occurs, the internal stress of SiCrIA changes, causing a change in the stress distribution within the SiC film, resulting in distortion of the mask pattern.

In this example, the SiC film 11 with strong tensile stress is controlled to have a tensile stress of 2 x 109 to 4 x 109 dyn/C12, and the SiC film 12 with small tensile stress thereon is controlled to have a tensile stress of about 8 x 108 dyn/cra2 or less. The stress is controlled.

For example, the SiC film 11 has a thickness of about 2 μm and a stress of 4
109dyn/C12, and the SiC film 1 thereon
2 has a thickness of 0.1 μm and a stress of 5×108 dyn, for example.
If the following is true, even if the total thickness of the upper layer Si011g12 is overetched by 0.1 μm, mechanically the overetched portion only corresponds to the lower layer SCCl2O thickness of 0.0125 μm. Therefore, local changes in stress caused by overetching remain extremely small. For example, if over-etching conventionally caused a stress change equivalent to a stress of approximately 5×10 dyn/an2 in an absorber with a thickness of 0.8 μm, in this example, the stress change in the absorber is almost 1
It will be an order of magnitude lower.

The X-ray mask configured in this manner exhibits a transmittance of approximately 70% for X-rays with wavelengths of 4 to 8 in the SiC membrane portion where the Ta layer 6 does not exist, and in the portion where the Tal layer 16 exists. , shows a contrast of 10.

FIGS. 5A to 5E show the manufacturing process of the X-ray mask as described above.

Firstly, as shown in FIG.
An iC film 11 is grown. For example, using 5iHCQ3, C3Ha, and H2 gases at a temperature of 1000°C and a pressure of 3
CVD is performed at Torr to grow an SC film to a thickness of about 2 μm. Note that the thickness of 2 μm is the thickness at the surface portion of the silicon substrate 10. After growth, the stress within each SiC film is approximately 4. It is set to about X109dyn/C112. This SiC film grown by low pressure chemical vapor deposition (LPGVD) is used as the lower layer of the membrane.

Next, as shown in FIG. 5(B), plasma C is placed on the surface.
A SiC film with low stress due to VD is grown.

For example, at a temperature of 300-500℃, 5n14, C3H
B, H2 gas is used to generate plasma at a pressure of I Torr, and a thickness of approximately 0.2 t is formed by plasma CVD.
, tm SiC1gA12 is grown. III after growth
For example, the stress within is 5 x 108dyn/crg
Control to 2 or less. After forming a two-layer membrane in this way, the X
Growing line mask.

That is, as shown in FIG. 5(C), the silicon substrate 1
The SiC film is etched to form an opening 24 exposing the surface of the substrate on the back side of the substrate.

As shown in FIG. 5 (D>), a Ta layer 6 serving as an X-ray absorber is deposited to a thickness of about 0.8 μm on the surface side of the silicon substrate 10 by sputtering. It is also possible to use metals with a large diameter such as W and 〇.

As shown in FIG. 5(E), a support frame 18 made of SiC ceramic or the like is placed on the lower surface side of the silicon substrate 10. Note that the support frame 18 has an opening 22 corresponding to the opening 24 of the SiC film. The silicon substrate 10 is back-etched from the opening side to form an opening 20, leaving a membrane portion. After that, a novolac resist film is formed on the Ta layer layer 6, a pattern is developed and the pattern is used as an etching mask, and the Ta layer is etched. The layer 6 is patterned to form an X-ray mask.

6(A) to 6(E) show a manufacturing process of an X-ray mask according to another embodiment of the present invention.

As shown in FIG. 6 (A>), a SiC film 11 with strong tensile stress is formed on the surface of a silicon substrate 10 by pyrolytic CVD.
Deposit a. For example, S+)IcQ3, C3H8,
Pyrolytic CVD was performed using H2 at a pressure of 3 Torr and about 1000''C to grow a film with a thickness of about 2 μm.

After that, as shown in FIG. 6(B), one silicon plate 10
An opening 24 is formed by removing the central portion of the SICIlgla on the back side of the substrate by etching.

As shown in FIG. 6C, silicon ions, for example, are implanted from within the SiC film 1 on the surface side of the silicon substrate 10. As shown in FIG. The implanted ions penetrate between the atoms of the film and create a force that tries to expand the film. Therefore, if the film has a lot of tensile stress, the implanted ions will act as a surface that reduces this tensile stress. It shows the situation.

FIG. 7 is a graph schematically showing the dose of ion implantation and the state of stress in the ion-implanted film. When a film has tensile stress in its initial state, when atoms are injected into the film by ion implantation, the insertion of atoms creates a force that tends to expand the film, reducing the tensile stress. If the film is in a stress-free state, new compressive stress will be generated within the film.

If the initial state is a tensile stress state, as the ion implantation dose increases, the tensile stress gradually decreases as shown in the figure, eventually reaches 0, and then becomes compressive stress. Although ρ1 is shown for the case where silicon ions are used as ions to be ion-implanted, it is not limited to silicon ions, but it is preferable to select ions that do not exhibit strong absorption of incident X-rays.

In this way, an ion implantation region 12 having a depth of approximately 0.2 μm is formed. This ion implantation region 12 constitutes a region where the stress is low or can be ignored compared to the stress within the underlying SiC film 1.

As shown in FIG. 6(D), the X
TaJI916, which is a line absorber, is grown by sputtering.

Next, as shown in FIG. 6(E), the opening 2 of the SiC film is opened.
A support frame 18 made of SiC ceramic or the like having an opening 22 substantially corresponding to 4 is placed on the back side of the silicon substrate 1o, and the silicon substrate 1o is etched back from the opening. In this way, an opening 20 through which the membrane is exposed is formed.

In the above embodiment, the membrane has a two-layer structure, but in the case of SiC, the tensile stress of the lower layer is 2 x 1
09~4 X 109dyn/C112 or so, the tensile stress of the upper layer is at least 1/2.5 or less8
It is preferable to set it to 108 dyn/cIl" or less.

As the membrane material, in addition to SiC, silicon, silicon nitride, etc. can also be used. In the case of these materials, the tensile stress of the lower layer is limited to about 5x108 dyn/C12. The tensile stress of the upper layer is preferably about 1/2.5 or less.

Further, the materials of the upper layer and the lower layer may be different, or the structure may have three or more layers.

Although the present invention has been described above in accordance with the examples, the present invention is not limited to these examples.
It will be obvious to those skilled in the art that improvements, combinations, etc. are possible.

[Effects of the Invention] As explained above, according to the present invention, in an X-ray mask, by making the upper layer of the membrane almost stress-free, even if over-etching occurs in the etching of the X-ray absorber film, , it is possible to maintain high positional accuracy of the resulting X-ray mask pattern.

[Brief explanation of drawings]

1(A) to 1(D) are diagrams explaining the principle of the present invention, FIG. 1(A) is a schematic sectional view of the structure, and FIG. 1(B) is a schematic sectional view of the structure.
, (C) is a schematic cross-sectional view showing the manufacturing method, Figure 1 (D) is a conceptual diagram showing the function of the upper layer of the laminated structure, and Figures 2 (A) to (F) are the manufacturing of an X-ray mask using conventional technology. 3(A) and (B) are conceptual diagrams for explaining the problems of the prior art. FIG. 4(A), (B), ( C) is a diagram for explaining the X-ray mask according to the embodiment of the present invention, FIG. 4(A) is a schematic sectional view showing the cross-sectional configuration, FIG. 4(B) is a partially enlarged view of the mask portion, FIG. 4(C) shows FI of over-etching that may occur during etching of the X-ray absorber film! FIGS. 5(A) to 5(E) are diagrams showing the manufacturing process of an X-ray mask according to an embodiment of the present invention; Figures (A) to (E) are cross-sectional views of each step to explain the manufacturing process of an X-ray mask according to another embodiment of the present invention. Figure 7 shows the dose amount of ion implantation and the inside of the ion-implanted film. It is a graph conceptually showing the relationship between stress and stress. 0 1 2 6 8 9 0 1 2 4 Plasma silicon substrate SiC film with strong tensile stress SiC film with small tensile stress Ta film Support frame Resist pattern opening recess opening opening

Claims (3)

[Claims] (1) An X-ray mask having a membrane formed of a material that can transmit X-rays of a predetermined wavelength and a mask pattern formed of a material that absorbs the X-rays provided thereon, the membrane is a tensile stress sufficient to be self-supporting (
3), and an upper layer (2) formed on the lower layer, where stress (4) is negligible compared to the stress in the lower layer. mask. (2), the upper layer (2) is SiC with a thickness of 0.2 μm or less
The X-ray mask according to claim 1, wherein the X-ray mask is formed of a film. (3) A lower layer (1) made of a material that can transmit X-rays of a predetermined wavelength and has sufficient tensile stress (3) to support itself; An X-ray mask consisting of a membrane consisting of an upper layer (2) on which only a negligible stress (4) is applied compared to the stress, and a mask pattern provided on the membrane and formed of a material that absorbs X-rays. In the manufacturing method, the membrane is produced by a step of creating a lower layer consisting of a thin film with sufficient tensile stress, and a step of implanting ions from above the created thin film to create an upper layer with reduced stress on the surface area. 1. A method of manufacturing an X-ray mask, comprising: forming an X-ray mask. 4) A lower layer (1) made of a material that can transmit X-rays of a predetermined wavelength and has sufficient tensile stress (3) to support itself; Manufacture of an X-ray mask consisting of a membrane consisting of an upper layer (2) on which only a negligible stress (4) is applied compared to the above, and a mask pattern provided on the membrane and formed of a material that absorbs X-rays In the method, the membrane includes a step of creating a lower layer with sufficient tensile stress by pyrolytic chemical vapor deposition (CVD), and a step of creating an upper layer with low stress by plasma CVD.
How to make line masks.