JPH023217A - Reflection mask - Google Patents

Abstract

PURPOSE:To make a contrast of a reflectance at a ditch portion and a flat pattern infinitely great for unnecessitating an aftertreatment after formation of a reflection film and for keeping the reflection surface in a good condition by forming a ditch having on its bottom recessed and projected portions on a surface of a substrate and by forming a reflection film on the surface of the substrate including the ditch portion. CONSTITUTION:The resist 11 is applied on a silicon substrate 12 and is exposed using a photomask or the electron beams to form a specified pattern. Using this resist as a mask, reactive ion etching is conducted on the silicon substrate 12 in an atmosphere including chlorine gas to form a ditch 13 having on its bottom needle-shaped protrusions of some 100 to 10000Angstrom . Then, the resist 11 is exfoliated by an oxygen plasma. A multi-layer film 14 is deposited on the whole surface of the substrate to form a reflection mask. Since the thickness of the multi-layer film 14 is some 1000Angstrom or about, the bottom 13a of the ditch 13 keeps unevenness even after the film 14 is deposited on it. The surface of the substrate 12 is polished like a mirror, and so the portion except for the ditch 13 is a mirror-like surface.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a mask used in the manufacturing process of semiconductor devices, and particularly to a reflective mask for batten transfer in soft X-ray exposure or vacuum ultraviolet exposure. .

[Conventional technology]

The X-ray exposure method using one X-ray screen is superior to electron beam exposure and the like in terms of fineness and productivity.

Conventionally, in this method, a batten that absorbs X-rays was formed on a film that was transparent to X-rays. A transmission type X-ray mask is used. This X-ray mask is placed at a minute interval of several tens of micrometers from a wafer coated with resist, and uniformly irradiates the wafer with X-rays. As a result, the resist is exposed to the X-rays transmitted through the X-ray mask, and when the resist is developed, a resist baton is obtained. By the way, since this conventional method uses same-size transfer, it is not possible to obtain a transfer precision higher than that of an electron beam exposure device used for drawing a stamp on an X-ray mask. In addition, in order to ensure X-ray transmittance, the transparent membrane that supports the X-ray absorbing button of an X-ray mask is extremely thin, about 2 μm, so it is difficult to manufacture large-area X-ray masks. is very difficult. Therefore, in order to solve this problem, an X-ray reduction projection exposure method using synchrotron radiation (Kinoshita et al.:
Proceedings of the 47th Japan Society of Applied Physics, p322.28p
-ZF-15) is being considered. In this method, exposure is performed by reducing and projecting an image of an X-ray mask onto a wafer coated with resist using a reflective optical system. Two types of X-ray masks are considered: transmission masks and reflection masks. Transmission-type X-ray masks require a very thin X-ray transparent film, similar to those used in equal-magnification transfer, so it is difficult to increase the diameter. - On the other hand, a reflective X-ray mask is advantageous in terms of manufacturing because a pattern can be formed on a sufficiently thick substrate. Therefore, it is considered desirable to use a reflective mask for X-ray reduction projection exposure. By the way, in order to increase the reflectance, a reflective mask and a reflective optical system used in X-ray reduction projection exposure are coated with a multilayer film that reflects xH at a specific wavelength. The multilayer film uses a pair of heavy atoms, such as tungsten (W)/carbon (C) or molybdenum (Mo)/silicon (S+). The formation interval of the multilayer film is determined by the Bragg diffraction conditions based on the X-ray wavelength and incident angle.

Conventionally, the processing method (K, Hoh and H, Tan1n
.

: Bull*ton of Electro
technical laboratory, Vo
1, 49Nn12 (1985) p47 54) has been proposed. In the figure, 41 is a resist, 42 is a multilayer film, and 43 is a silicon substrate. The mask processing method is performed in the following steps. First, a multilayer film 42 (for example, tungsten/carbon) is deposited on a silicon substrate 43, and a resist 41 is applied onto the multilayer film 42. Next, the resist 41 is exposed using a light mask or an electron beam to form a predetermined pattern (FIG. 4(a)). Then, using the resist 41 as a mask, the multilayer film 42 is removed by dry etching (FIG. 4(b)).

After that, the resist 41 is removed using oxygen plasma,
A conventional reflective mask is formed ((C) in the same figure).

Further, as another conventional example, a processing method as shown in the sectional view shown in FIG. 5 has been proposed. In the figure, the same parts as in FIG. 4 are given the same reference numerals. 52 is an absorber that absorbs X-rays. The mask processing method is similar to that shown in Fig. 4.
A multilayer NM42C (for example, tungsten/carbon) is formed on the upper layer 3 to form an absorber 52 that absorbs KX-rays and has a low reflectance. After that, the resist 41 is placed on the absorber 52.
is coated and exposed using a photomask or an electron beam to form a predetermined pattern (FIG. 4(a)).

Next, the absorber 52 is removed by dry etching using the resist 41 as a mask. Thereafter, the resist 41 is removed using oxygen plasma to form a conventional reflective mask. (Figure (b)).

[Problem to be solved by the invention]

However, since the conventional reflective mask is configured as described above, it has the following drawbacks. First, the fourth
In the reflective mask shown in the figure, a multilayer film 42 is etched using a resist 41 as a mask, and then the resist 41 is peeled off using oxygen plasma. For this reason, for example, the multilayer film 42
If the upper layer is carbon, there is a drawback that the carbon is etched by the oxygen plasma in the same way as the resist 41, resulting in a reduction in reflection contrast. Here, it has been proposed to remove the resist 41 using an organic solution without using oxygen plasma, but since the surface of the resist 41 is altered (due to dry etching) during the etching process of the multilayer film 42, the resist 41 is completely removed. It was difficult to peel it off. Further, when the surface of the multilayer film 42 is made of tungsten or molybdenum, an oxide film is formed on the surface by oxygen plasma, which causes a decrease in X-ray reflectance. Furthermore, when the multilayer film 42 is made of tungsten/carbon, the carbon is etched by oxygen plasma as described above, so undercutting progresses from the pattern sidewall of the multilayer film 42 to the carbon layer while the resist 41 is peeled off. This resulted in a deterioration in pattern accuracy.

Next, in the reflective mask shown in FIG. 5, dry etching is used to obtain the pattern of the absorber 52. Therefore, when the etching of the absorber 52 is completed, the multilayer film 42
becomes K when exposed to plasma. Generally, it is difficult to obtain a fairly high etching selectivity with dry etching, and the multilayer film 42 is also etched due to overetching. Since the multilayer film 42 is made of an extremely thin film of several 1 OA, the multilayer film 42 may be damaged by over-etching.
The impact of the destruction is extremely large. Furthermore, the multilayer i surface, which requires a surface roughness of several angstroms or less, becomes rough due to the impact of plasma ions, causing a decrease in X-ray reflectance. Furthermore, etching residues such as reaction products may adhere to the reflective surface. In order to avoid these effects, it is possible to process the absorber 52 by wet etching, but since this results in isotropic etching, it is not possible to obtain a highly accurate batten.

Furthermore, as a drawback during exposure, when a light source with continuous wavelengths such as synchrotron radiation light is used for mask exposure, in the reflective mask shown in FIG. However, it can reflect ultraviolet light and expose the resist on the wafer. In this case, the contrast of the battens is reduced, which is a major drawback particularly in terms of forming fine battens.

Furthermore, when overlapping exposure is performed, marks are provided on the mask and aligned with the marks on the wafer. However, with conventional reflective masks, it is not possible to achieve a large contrast between the multilayer film and the underlying surface in visible light, which reduces the S/N ratio of the mark detection signal and affects the accuracy of the button position. There were drawbacks.

[Means to solve the problem]

The reflective mask according to the present invention includes a groove formed on the surface of a substrate and having an uneven bottom, and a reflective film formed on the substrate having the groove.

The device also includes a groove portion formed on the surface of the high melting point metal film on the substrate and having an uneven bottom portion, and a reflective film formed on the high melting point metal film having the groove portion.

[Effect]

A groove portion having an uneven bottom portion formed on the substrate surface lowers the reflectance.

Further, the groove portion having an uneven bottom portion formed on the surface of the high melting point metal film lowers the reflectance.

〔Example〕

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

FIG. 1 is a sectional view of a method of processing a reflective mask according to a first embodiment of the present invention. In the figure, 1) is a resist, 12 is a silicon substrate, 13 is a groove, 13a is a groove bottom, and 14 is a multilayer film serving as a reflective film. The mask processing method is performed in the following steps. First, silicon substrate 1
A resist 1) is applied onto the resist 2 and exposed using a light mask or an electron beam to form a predetermined pattern (FIG. 2(a)).

Next, using this resist 1) as a mask, the underlying silicon substrate 12 is dry etched to form a groove 13. At this time, the dry etching uses reactive ion etching (RIE) using chlorine (C2z) gas as an atmosphere. As etching conditions, for example, in the case of a cathode couple type etching apparatus, the chlorine (C10) gas pressure is 7 Pa and the RF power is 100 W. Further, the etching depth is approximately several μm.

Etching under these conditions makes it possible to form groove bottom elevations (irregularities) (FIG. 4(b)).

These needle-like protrusions appear black when observed under visible light;
It can be seen that the reflectance is extremely reduced.

Next, the Lujist 1) is peeled off using 8-element plasma (see figure (C)
)). In addition, sulfuric acid (H2SO4) is used to remove resist 1).
A decahydrogen peroxide solution (H2(h) solution may also be used. After that, a multilayer film 14 is deposited on the entire surface of the silicon substrate to form a reflective mask (FIG. 1(d)).Here, the multilayer film is For example, assuming the wavelength of X-rays is 100A, tungsten (W)/
A combination of carbon (C) is used. For direct incidence, the tungsten film thickness is 2OA.

The carbon film thickness is set to 3OA, and several tens of carbon films are stacked on top of each other to increase the X-ray reflectance. The thickness of the multilayer film 14 formed in this way is about several thousand amps, and even if the groove bottom 13aK is deposited, the needle-like protrusions will not be flattened, and the multilayer film 14 at that part will not be flattened. The surface becomes uneven. On the other hand, since the surface of the silicon substrate 120 is mirror-polished, the multilayer film 14 deposited on the surface of the silicon substrate 12 that is not etched except for the groove 13 has a mirror-like surface like the underlying layer.

Next, the reflection characteristics of this reflection type mask will be explained.

The reflectance R of the multilayer film 14 decreases depending on the surface roughness, and the ideal value Ro also decreases. And this reflectance R is R=RO@XPC-2(2πσcosθ/λ)! ] is given. However, it is assumed that the rma value of the surface roughness is σ, the wavelength of the X-ray is λ, and the incident angle is θ. Also, Figure 2 shows the incident angle θ of X-rays.
FIG. 3 is a characteristic diagram showing the relationship between reflectance and surface roughness at =0. In the figure, characteristic A.

The characteristic curve when . For example, at a wavelength of 100 mm, if the surface roughness of the multilayer film is 5 A (rms), a reflectance of 92% of the ideal value can be obtained. Surface roughness is 10J (rm
s) is 45% of the ideal value, so if you want to obtain a high reflectance, the surface roughness of the underlying silicon substrate should be 5A (rm
s) It is desirable to use the following: Next, in order to function as a reflective mask, the Ur
In the top view, it is necessary that the groove portion 130 portion does not reflect X-rays. For example, considering the wavelength Zoo A, if the surface roughness exceeds 2OA (rms), the reflectance will be less than 5% of the ideal value, and the contrast with respect to the ideal reflective surface will become large.

If the surface roughness is 100100A (r), infinite contrast can be obtained.As explained in the processing method above,
Since the groove bottom 13m has irregularities of several hundred OA, the reflectance of X-rays can be considered to be zero. Also, wavelengths of 1000A and 20A
Since reflection of 00A light and 500A (rma) light can be ignored if there is surface roughness, these lights can also be cut in the same way as X-rays. Furthermore, the fact that the surface of the groove bottom 13m appears black indicates that even visible light is cut. Therefore, in the reflective mask of the present invention, it is only necessary to consider the reflection from the multilayer film surface formed on the flat silicon surface other than the grooves, which makes it an ideal reflective mask with almost infinite contrast. I know what will happen.

In this way, the reflective mask in this embodiment has a groove portion 1 on the surface of a flat silicon substrate 12 with uneven protrusions on the bottom surface.
3 is formed, and the multilayer film 14 for X-ray reflection is formed thereon, so that the contrast in reflectance between the flat part other than the groove part 13 and the multilayer film 14 formed on the uneven surface of the groove bottom part 13 & is almost the same. It can be infinite. Furthermore, since there is no need to perform any treatment such as plasma etching after the multilayer film 14 is formed, a good reflective surface can be maintained.

In the above embodiment, the resist 1) was used as a mask, but an insulating film (Si02) may be used as a mask. In this case, the etched surface tends to become more rough. The reason for this is thought to be that an insulating film (SiOz) is formed on the silicon surface, which acts as an etching mask.

Furthermore, although chlorine (Ctz) gas was used as the dry etching atmosphere in the above embodiments, a fluorocarbon-based gas or an oxygen-added gas system such as SF6+02 may be used.

In addition, in the above embodiment, the groove 1 is formed in the silicon/substrate 12.
3 was processed, but an insulating film (S I
Alternatively, the silicon may be etched by forming an insulating film (Si02) using a resist mask and processing the insulating film (Si02) in the trench 13 until the silicon surface is exposed. After that, if the resist is peeled off and the multilayer film 14 is formed, it is insulated! (Si02
) is the underlying layer, and a reflective mask is obtained in which the multilayer film portion serves as a reflective surface.

Further, in the above embodiment, a silicon substrate 1 is used as the substrate.
2 was used, but any material that can form unevenness on the groove bottom 13 may be used. For example, a gallium arsenide (GaAs) substrate may be used, and in this case, chlorine (CI-2) gas may be used for the dry etching atmosphere as in the case of the silicon substrate 12.

FIG. 3 is a sectional view of a processing method for a reflective mask showing a second embodiment of the present invention. In the figures, the same or equivalent parts as in FIG. 1 are given the same reference numerals. 15 is a molybdenum film corresponding to a high melting point metal film, and 16 is an insulating film (Si02).

The mask processing method is performed in the following steps. First, a dimolybdenum film 1 is deposited on a silicon substrate 12 by electron beam evaporation.
5 is formed with a thickness of about 1 μm, and an insulating film (Sto
w) 16 is formed to a thickness of about 1000 Å. Furthermore, a resist 1) is applied on this insulating film 16 and exposed using a photomask or an electron beam to form a predetermined pattern (
Figure (a)). Next, using the resist 1) pattern as a mask, the underlying insulation M16 is etched using CF4+H2 gas until the molybdenum film 15 is exposed.
Dry etching by RIE). Thereafter, molybdenum film 15 is similarly dry etched using CF4+02 gas to form grooves 13. By the way, the molybdenum film 15 is a thin film with a columnar structure and has columnar grain boundaries. Therefore, when the molybdenum film 15 is dry-etched, the etching proceeds from the crystal grain boundaries, and in the middle of the etching, needle-like protrusions (irregularities) in units of crystal grains are formed over the entire surface. The size of the crystal grains depends on the film formation conditions, but it is several tens of thousands.
When the etching is continued from 0A to 1000A, it is possible to form a groove 13 in which the etched surface becomes black and has concavities and convexities that scatter visible light as in the previous embodiment (FIG. 2(b)). Next, resist 1) is peeled off and the same figure (c) is obtained.
We obtain the structure shown in At this time, the surface of the insulating film 16 is not etched, so that it maintains a flat surface. and,
As shown in FIG. 3(d)K, a multilayer film 14 is formed on the entire surface to form a reflective mask.

The mask with this structure functions as a reflective mask because
Since it is the same as the previous embodiment, it will be omitted here.

Although the molybdenum film 15 was used as the refractory metal film in the above embodiment, a tungsten film or the like may also be used.

〔Effect of the invention〕

As explained above, the present invention has the following effects.

(,) Flat substrate or flat high melting point gold I! Since a groove with an uneven bottom surface is formed on the surface of the A film, and a reflective film is formed on top of the groove, the contrast between the reflectance between this groove and the flat area other than the groove can be made almost infinite. can.

(b) Since the present invention does not require post-treatment after forming the reflective film, a good reflective surface can be maintained.

(c) The uneven surface can prevent the reflection of not only X-rays but also vacuum ultraviolet rays and ultraviolet rays, so it is possible to remove excess reflected light that degrades the exposure baton quality from surfaces other than the flat reflective surface that corresponds to the mask baton. can.

(d) According to the present invention, a reflective mark for mask alignment can be detected with good contrast using visible light, and the accuracy of the button position can be improved.

(.) The present invention can be used not only for X-ray exposure but also as a high-contrast reflective mask for light.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the processing method showing the first embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between reflectance and surface roughness, and Fig. 3 is a cross-sectional view of the processing method showing the first embodiment of the present invention. 4 and 5 are cross-sectional views of a conventional processing method. 1)...Resist, 12...Silicon substrate, 1
3...Groove portion, 13&...Groove bottom, 14...Multilayer film, 15...Molybdenum film, 16...Insulating film (S102). Fig. 1 Held patent applicant: Nippon Telegraph and Telephone Corporation agent Masaki Yamakawa (TL or one person) Fig. Tomokaiza (A) Fig.

Claims (2)

[Claims] (1) A reflective mask characterized in that a groove portion having an uneven bottom is formed on the surface of a substrate, and a reflective film is formed on the upper layer of the substrate including the groove portion. (2) A reflective mask characterized in that a groove having an uneven bottom is formed on the surface of a high melting point metal film on a substrate, and a reflective film is formed on the high melting point metal film including the groove.