JP2609538B2 - Reflective mask - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask used in a manufacturing process of a semiconductor device, and more particularly to a reflective mask for pattern transfer in soft X-ray exposure or vacuum ultraviolet exposure. .

[Conventional technology]

An X-ray exposure method using an X-ray mask is superior to electron beam exposure or the like in terms of fineness and productivity. Conventionally, in this method, a transmission-type X-ray mask formed by processing a pattern for absorbing X-rays formed on a film transparent to X-rays is used. This X-ray mask is set at a minute interval of several tens of μm with respect to the wafer coated with the resist,
A line is illuminated. Thereby, the X-ray transmitted through the X-ray mask
When the resist is exposed by the line and the resist is developed, a resist pattern is obtained. By the way, in the conventional method, since the same-size transfer is performed, transfer accuracy higher than the pattern accuracy of the electron beam exposure apparatus used for pattern drawing of the X-ray mask cannot be obtained. The transmission film supporting the X-ray absorbing pattern of the X-ray mask has a thickness of 2 μm to secure the X-ray transmittance.
Since an extremely thin film having a thickness of about m is used, it is often difficult to manufacture a large-area X-ray mask. In order to solve such a problem, an X-ray reduction projection exposure method using synchrotron radiation (Kinoshita et al .: Proceedings of the 47th JSAP, p322, 28p-ZF-15) is emitted. ing. According to this method, an image of an X-ray mask is reduced and projected by a reflection optical system onto a resist-coated wafer to perform exposure. Two types of X-ray masks, a transmission type mask and a reflection type mask, are considered. Since the transmission type X-ray mask requires an extremely thin X-ray transmission film as in the case of the same magnification transfer, it is difficult to increase the diameter. On the other hand, a reflective X-ray mask is advantageous in manufacturing because a pattern can be formed on a sufficiently thick substrate. Therefore, it is considered preferable to use a reflective mask for the X-ray reduction projection exposure. By the way, a reflective mask or a reflective optical system used in the X-ray reduction projection exposure has a surface coated with a multilayer film that reflects X-rays of a specific wavelength in order to increase the reflectance. As the multilayer film, a pair of heavy atoms and light atoms such as tungsten (W) / carbon (C) or molybdenum (Mo) / silicon (Si) is used. The multilayer film formation interval is determined by the Bragg diffraction condition from the X-ray wavelength and the incident angle.

Conventionally, a processing method as shown in the cross-sectional view shown in FIG. 4 (K. Hoh and H. Tanino: Bulletion of El
ectrotechnical Laboratory, Vol.49 No.12 (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 is processed in the following procedure. First, a multilayer film is formed on the silicon substrate 43.
42 (for example, tungsten / carbon) is deposited, and a resist 41 is applied on the multilayer film 42. Next, resist 41
Is exposed using a light mask or an electron beam to form a predetermined pattern (FIG. 1A). Then, using the resist 41 as a mask, the multilayer film 42 is removed by dry etching (FIG. 9B). After that, the resist 41 is peeled off using oxygen plasma to form a conventional reflective mask (FIG. 3C).

As another conventional example, a processing method as shown in a sectional view of FIG. 5 has been proposed. In the figure, the same parts as those in FIG. 4 are denoted by the same reference numerals. 52 is an absorber for absorbing X-rays. The processing method of the mask is the same as that of FIG.
A multilayer film 42 (for example, tungsten / carbon) is formed thereon, and an absorber 52 having a low reflectance by absorbing X-rays is formed thereon. After that, apply the resist 41 on the absorber 52,
Exposure is performed using a light mask or an electron beam to form a predetermined pattern (FIG. 1A). Next, the absorber 52 is removed by dry etching using the resist 41 as a mask. After that, the resist 41 is peeled off using oxygen plasma to form a conventional reflective mask. (FIG. 2B).

[Problems to be solved by the invention]

However, the conventional reflective mask has the following disadvantages because it is configured as described above. First, in the reflective mask of FIG. 4, after etching the multilayer film 42 using the resist 41 as a mask, the resist 41 is peeled off using oxygen plasma. For this reason, for example, when the upper layer of the multilayer film 42 is made of carbon, there is a disadvantage that the carbon is etched by the oxygen plasma in the same manner as the resist 41, and the reflection contrast is lowered. Here, a resist 41 using an organic solution without using oxygen plasma is used.
However, since the surface of the resist 41 has been altered by dry etching in the etching step of the multilayer film 42, the resist 41 could not be completely removed. 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 reduction in X-ray reflectivity. Further, when the multilayer film 42 is made of tungsten / carbon, the carbon is etched by the oxygen plasma as described above, so that the undercut advances from the pattern side wall of the multilayer film 42 to the carbon layer during the removal of the resist 41, and the pattern accuracy is reduced. Deteriorated.

Next, in the reflection type mask shown in FIG. 5, dry etching is used to obtain a pattern of the absorber 52. Therefore, when the etching of the absorber 52 is completed, the multilayer film 42 is exposed to the plasma. Generally, it is difficult to obtain a very high etching selectivity by dry etching, and the multilayer film 42 is also etched by over-etching. Since the multilayer film 42 is formed of an extremely thin film having a thickness of several tens of degrees, the effect of destruction of the multilayer film 42 due to overetching is extremely large. In addition, the impact of plasma ions causes the surface of the multilayer film, which requires a surface roughness of several angstroms or less, to be rough, which causes a decrease in X-ray reflectivity. Furthermore, the etching residue such as a reaction product may adhere to the reflection surface. Although it is conceivable to process the absorber 52 by wet etching in order to avoid these effects, it is not possible to obtain a highly accurate pattern because it results in isotropic etching.

As a disadvantage at the time of exposure, when a light source having a continuous wavelength such as synchrotron radiation is used for exposure of the mask, the reflection type mask shown in FIG. However, there are cases where the resist on the wafer is exposed by reflecting ultraviolet rays. in this case,
Since the contrast of the pattern is reduced, this is a major drawback particularly in the formation of a fine pattern.

When performing overlay exposure, a mark is provided on the mask and aligned with the mark on the wafer. However, conventional reflective masks have the disadvantage that the contrast between the multilayer film and the underlying surface cannot be increased in visible light, so that the mark detection signal S / N ratio is reduced and the pattern position accuracy is affected. Was.

[Means for solving the problem]

The reflection type mask according to the present invention includes a groove formed on the substrate surface and having irregularities on the bottom, and a reflection film formed on the substrate having the groove.

The semiconductor device further includes a groove having a concave and convex portion formed on the surface of the refractory metal film on the substrate, and a reflective film formed on the refractory metal film having the groove.

[Action]

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

In addition, a groove formed on the surface of the refractory metal film and having a concave and convex portion on the bottom lowers the reflectance.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a processing method in a reflection type mask showing a first embodiment according to the present invention. In the figure, 11 is a resist, 12 is a silicon substrate, 13 is a groove, 13a is a groove bottom, and 14 is a multilayer film corresponding to a reflection film. The mask is processed in the following procedure. First, resist 11 on silicon substrate 12
Is applied and exposed using a light mask or an electron beam to form a predetermined pattern (FIG. 3A). Next, using the resist 11 as a mask, a groove 13 is formed in the underlying silicon substrate 12 by dry etching. At this time, reactive ion etching (RIE) is used for dry etching using chlorine (Cl ₂ ) gas as an atmosphere. The etching conditions are, for example, in the case of a cathode-coupling type etching apparatus, a chlorine (Cl ₂ ) gas pressure of 7 Pa and an RF power of 100 W. Further, the etching depth is about several μm. Etching under these conditions results in several hundred mm of groove bottom 13a.
Needle-like projections (irregularities) having a size of about 1000 mm can be formed (FIG. 2B). These needle-like projections look completely black when observed with visible light, indicating that the reflectance is extremely low. Next, the resist 11 is peeled off by oxygen plasma (FIG. 3C). Further, a sulfuric acid (H ₂ SO ₄ ) + hydrogen peroxide (H ₂ O ₂ ) solution may be used for removing the resist 11. Thereafter, a multilayer mask 14 is deposited on the entire surface of the silicon substrate to form a reflection type mask (FIG. 4D). Here, for the multilayer film, for example, a combination of tungsten (W) / carbon (C) with an X-ray wavelength of 100 ° is used. For direct incidence, the thickness of tungsten is 20 mm and the thickness of carbon is 30 mm.
Then, several tens of these are superimposed to increase the reflectivity of X-rays. The film thickness of the multilayer film 14 formed in this way is about several thousand mm, and even if it is deposited on the above-mentioned groove bottom 13a, the needle-like projections do not become flat, and the surface of the multilayer film 14 at that portion is not flattened. Is in an uneven state. On the other hand, since the surface of the silicon substrate 12 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 surface like the base.

Next, the reflection characteristics of this reflection type mask will be described. The reflectance R of the multilayer film 14 is reduced by the surface roughness and becomes smaller than the ideal value _R0 . The reflectance R is given by R = R ₀ exp [−2 (2πσ cos θ / λ) ² ]. Here, the rms value of the surface roughness is σ, the wavelength of the X-ray is λ, and the incident angle is θ. FIG. 2 shows the incident angle θ of the X-ray.
FIG. 4 is a characteristic diagram showing a relationship between reflectance and surface roughness at = 0. In the figure, the characteristics A, B, and C each have an X-ray wavelength of 100 °, 1
It shows the characteristic curve when 000Å and 2000Å. For example, at a wavelength of 100 °, a reflectance of 92% of the ideal value can be obtained if the surface roughness of the multilayer film is 5 ° (rms). Surface roughness of 10 mm (rm
s) is 45% of the ideal value. Therefore, in order to obtain a high reflectance, the surface roughness of the underlying silicon substrate is also 5 mm (rms).
It is desirable to use the following. Next, in order to function as a reflective mask, it is necessary that the groove 13 in the sectional view shown in FIG. 1 does not reflect X-rays. For example, considering a wavelength of 100 mm, the surface roughness is 20 mm (rms)
When the value exceeds, the reflectance becomes 5% or less of the ideal value, and the contrast with respect to the ideal reflecting surface increases. If the surface roughness is as high as 100 mm (rms), infinite contrast can be obtained. As described in the above-mentioned processing method, since the unevenness of the groove bottom 13a is several thousand degrees, the reflectivity of X-rays may be considered to be zero. In addition, even if light having a wavelength of 1000 ° or 2000 ° has a surface roughness of 500 ° (rms), reflection can be ignored if the surface has a roughness, so that such light can be cut in the same manner as X-rays. Also, groove bottom 13
From the fact that the surface of a looks black, it can be seen that even visible light can be cut. Therefore, in the reflection type mask of the present invention, it is only necessary to consider reflection from the multilayer film surface formed on the flat silicon surface other than the groove, and an ideal reflection type mask having almost infinite contrast is required. It turns out that it becomes.

As described above, the reflection type mask according to the present embodiment has a groove 13 in which projections and depressions are provided on the bottom surface of a flat silicon substrate 12.
And the multilayer film 14 for X-ray reflection is formed thereon, so that the contrast of the reflectance between the flat portion other than the groove 13 and the multilayer film 14 formed on the uneven surface of the groove bottom 13a is almost infinite. Can be large. Further, after the formation of the multilayer film 14, it is not necessary to perform any processing such as plasma etching, so that a good reflection surface can be maintained.

Although the resist 11 is used as a mask in the above embodiment, an insulating film (SiO ₂ ) may be used as a mask. in this case,
The roughness of the etching surface tends to increase. It is considered that this is because an insulating film (SiO ₂ ) is formed on the silicon surface and has an etching action.

Although chlorine (Cl ₂ ) gas is used as the atmosphere for dry etching in the above-described embodiment, a fluorocarbon gas or a gas system to which oxygen such as SF ₆ + O ₂ is added may be used.

In the above embodiment, the groove 13 is formed in the silicon substrate 12.
However, if an insulating film (SiO ₂ ) is formed on the silicon substrate 12 and the groove 13 is formed using a resist mask until the silicon surface is exposed, the insulating film (SiO ₂ ) is processed and the silicon is etched. Good. After that, the resist is peeled off and the multilayer film 14 is removed.
Is formed, a reflective mask is obtained in which the multilayer film portion on which the insulating film (SiO ₂ ) serves as a base serves as a reflecting surface.

Further, in the above embodiment, a silicon substrate is used as the substrate.
Although 12 is used, any material may be used as long as unevenness can be formed on the groove bottom 13a. For example, a gallium arsenide (GaAs) substrate may be used, and in this case, a chlorine (Cl ₂ ) gas can be used as a dry etching atmosphere similarly to the silicon substrate 12.

FIG. 3 is a sectional view of a processing method in a reflective mask showing a second embodiment according to the present invention. In the figure, the first
The same or corresponding parts as those in the drawings are denoted by the same reference numerals. Reference numeral 15 denotes a molybdenum film corresponding to a high melting point metal film, and 16 denotes an insulating film (SiO ₂ ). The mask is processed in the following procedure. First, a molybdenum film 15 having a thickness of about 1 μm is formed on a silicon substrate 12 by an electron beam evaporation method, and an insulating film (SiO ₂ ) 16 is formed thereon with a thickness of about 1000 μm. Further, a resist 11 is applied on the insulating film 16 and is exposed to light using a light mask or an electron beam to form a predetermined pattern (FIG. 7A). Next, using the pattern of the resist 11 as a mask, the underlying insulating film 16 is removed by CF until the molybdenum film 15 is exposed.
Dry etching is performed by reactive ion etching (RIE) using ₄ + H ₂ gas. After that, the molybdenum film 15 is
₄ Similarly dry-etching using + O ₂ gas
To form Incidentally, the molybdenum film 15 is a columnar structure thin film, and has columnar crystal grain boundaries. Therefore, when the molybdenum film 15 is dry-etched, the molybdenum film 15 proceeds from the crystal grain boundaries, and during the etching, needle-like projections (irregularities) in units of crystal grains are formed on the entire surface. The size of the crystal grains is about several hundreds to about 1000 degrees, depending on the film forming conditions.
When the etching is advanced until the height of the projections becomes about several thousand mm, the etching surface becomes black, and the groove 13 having irregularities that scatters to visible light can be formed as in the previous embodiment (FIG. b)). Next, the resist 11 is peeled off to obtain the structure shown in FIG. At this time, since the surface of the insulating film 16 is not etched, a flat surface is maintained.
Then, as shown in FIG. 2D, a multilayer film 14 is formed on the entire surface to form a reflective mask.

The function of the mask having this structure as a reflection type mask is the same as in the previous embodiment, and will not be described here.

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

〔The invention's effect〕

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

(A) Since a groove having irregularities formed on the bottom surface is formed on the surface of a flat substrate or a flat refractory metal film, and a reflective film is formed thereon, the reflectance in the groove and the flat portion other than the groove is formed. Can be made almost infinite.

(B) In the present invention, it is not necessary to perform a post-process after the formation of the reflective film, so that a good reflective surface can be maintained.

(C) Since the uneven surface can prevent not only the reflection of X-rays but also the reflection of vacuum ultraviolet rays and ultraviolet rays, it is possible to remove extra reflected light that degrades the exposure pattern quality from other than a flat reflective surface corresponding to the mask pattern. it can.

(D) According to the present invention, a reflective mark for mask alignment can be detected by visible light with good contrast, and the pattern position accuracy can be improved.

(E) The present invention can be used as a high-contrast reflective mask for light as well as X-ray exposure.

[Brief description of the drawings]

FIG. 1 is a sectional view of a processing method showing a first embodiment according to the present invention, FIG. 2 is a characteristic diagram showing a relationship between reflectance and surface roughness, and FIG. FIGS. 4 and 5 are cross-sectional views of a conventional processing method showing an embodiment. 11 ... resist, 12 ... silicon substrate, 13 ... groove, 13
a… groove bottom, 14… multilayer film, 15… molybdenum film, 16
.... Insulating film (SiO ₂ ).

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Nobuyuki Takeuchi 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-1-152725 (JP, A)

Claims (2)

(57) [Claims] 1. A reflection type mask, wherein a groove having irregularities on the bottom is formed on the surface of a substrate, and a reflection film is formed on an upper layer of the substrate including the groove. 2. A reflection type mask comprising: a groove having an uneven surface on a bottom portion formed on a surface of a high melting point metal film on a substrate; and a reflection film formed on an upper layer of the high melting point metal film including the groove.