JPH08272074A - Halftone phase shift photomask and blank for halftone phase shift photomask - Google Patents

Abstract

PURPOSE: To provide a halftone phase shift photomask which has sufficient transmittance to short wavelength light, is usable for high-resolution lithography and is preducible without etching stop layers by including layers mainly composed of compds. of chromium and aluminum as halftone phase shift layers. CONSTITUTION: The halftone phase shift mask including at least one layers mainly composed of the compds. of the chromium and aluminum as the halftone phase shift layers and blank for the halftone phase shift are provided. The films 302, 304 mainly composed of the compds. of the chromium and aluminum are changed in their film properties by the ratios of the chromium and the aluminum. The transmittance is lowered but the chemical resistance is good if the chromium is contained therein at a higher ratio. On the other hand, the transmittance is good and the chemical resistance is poor if the aluminum is included at a higher ratio. Since the transmittance of the short wavelength region is excellent, the transmittance to allow the sufficient use of the films as the halftone phase shift films is obtd. even if the films are formed by as much as the film thickness to invert the phase of a krypton fluoride excimer laser beam on the transparent substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used for manufacturing high-density integrated circuits such as LSI and VLSI, and a photomask blank for manufacturing the photomask, and more particularly to a projected image of a fine dimension. And a blank for a halftone phase shift photomask for producing this phase shift photomask.

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs and VLSIs are manufactured by repeating a so-called lithography process using a photomask. The use of a phase shift photomask as shown in Japanese Patent No. 173744, Japanese Patent Publication No. 62-59296, etc. has been studied. Various types of phase shift photomasks have been proposed. Among them, for example, Japanese Patent Laid-Open No. 4-136
So-called halftone phase shift photomasks such as those disclosed in U.S. Pat. No. 854, U.S. Pat. No. 4,890,309 and the like have attracted attention from the viewpoint of early commercialization.
Several proposals have been made regarding structures and materials capable of improving the yield by reducing the number of manufacturing steps and reducing the cost, as in Japanese Patent No. 2259 and Japanese Patent Laid-Open No. 5-127361.

Here, a halftone phase shift photomask will be briefly described with reference to the drawings. FIG. 3 is a diagram showing the principle of the halftone phase shift method, and FIG. 4 is a diagram showing the conventional method. 3A and 4A are cross-sectional views of the photomask, FIGS. 3B and 4B are amplitudes of light on the photomask, and FIGS. 3C and 4C are Amplitude of light on the wafer, FIGS. 3D and 4D show light intensity on the wafer, respectively, 101 and 201 are substrates, 202
Is a 100% light-shielding film, and 102 is a phase of incident light substantially 1
Halftone phase shift films, which are shifted by 80 degrees and have a transmittance of 1 to 50%, 103 and 203 are incident light. In the conventional method, as shown in FIG. 4A, 10 made of chromium or the like is formed on a substrate 201 made of quartz glass or the like.
Only the 0% light-shielding film 202 is formed, and the light-transmitting portion having a desired pattern is formed. The light intensity distribution on the wafer is widened at the bottom as shown in FIG. I will end up. On the other hand, in the halftone phase shift shift method, since the phase of the light transmitted through the halftone phase shift film 102 and the light transmitted through the opening thereof are substantially inverted, as shown in FIG. Above, the light intensity at the pattern boundary becomes 0, and the spread of the skirt can be suppressed, so that the resolution can be improved.

Here, it should be noted that in the type of phase shift lithography other than the halftone, the light shielding film and the phase shifter film are made of different materials and patterns.
Half-tone phase shift lithography requires half a phase, whereas halftone phase shift lithography requires only one pattern because half-tone phase shift lithography requires one pattern. Has become a big advantage.

By the way, the halftone phase shift film 102 of the halftone phase shift photomask is required to have two functions of phase inversion and transmittance adjustment. Of these, for the phase inversion function, it is sufficient that the phase is substantially inverted between the exposure light passing through the halftone phase shift film 102 and the exposure light passing through the opening. Here, the halftone phase shift film 102
, For example M. Born, E .; Wolf "Prin
When treated as an absorbing film shown in “Chips of Optics” on pages 628 to 632, multiple interference can be ignored, and thus the phase change φ of the vertically transmitted light is When φ is included in the range of nπ ± π / 3 (n is an odd number), the above-mentioned phase shift effect is obtained. In the formula (1), φ is a phase change that light vertically transmitted through a photomask in which a multilayer film of (m-2) layers is formed on a substrate, and χ ^{k, k 1} is the k-th Layers and (k + 1)
The phase change occurring at the interface with the th layer, u _k and d _k are the refractive index and film thickness of the material forming the k th layer, and λ is the wavelength of the exposure light. However, the layer where k = 1 is the substrate and k = m
The layer is air.

On the other hand, the exposure light transmittance of the halftone phase shift film 102 for obtaining the halftone phase shift effect is determined by the size, area, arrangement, shape, etc. of the transfer pattern, and differs depending on the pattern. In effect,
In order to obtain the above-mentioned effect, the exposure light transmittance of the halftone phase shift film must be included within the range of optimum transmittance ± several% centering on the optimum transmittance determined by the pattern. Usually, this optimum transmittance is 1 depending on the transfer pattern when the opening is 100%.
It fluctuates widely within a wide range of 50% to 50%. That is, halftone phase shift photomasks having various transmittances are required in order to deal with all patterns.

In practice, the phase inversion function and the transmittance adjusting function are the complex refractive index (refractive index and extinction) of the material forming the halftone phase shift film (in the case of multiple layers, each material forming each layer). Coefficient) and film thickness. That is,
A material in which the thickness of the halftone phase shift film is adjusted so that the phase difference φ obtained by the formula (1) is within the range of nπ ± π / 3 (n is an odd number) is a material of the halftone phase shift photomask. It can be used as a halftone phase shift layer. As such a material, for example, Japanese Patent Laid-Open No. 5-1
A film containing a chromium compound as a main component, which is disclosed in Japanese Patent No. 27361, is known.

[0008]

By the way, the above-mentioned film containing a chromium compound as a main component is formed of chromium oxide, nitride,
These films are oxynitride, oxycarbide, and oxycarbonitride, and the transmittance of these films for exposure light largely changes depending on the wavelength of exposure light. For example, FIG. 5 shows a spectral transmittance curve of a chromium oxide film formed on a synthetic quartz substrate by a reactive sputtering method of a chromium target in an oxygen atmosphere.
Here, the thickness of the chromium oxide film is about 50 nanometers. As is clear from FIG. 5, the transmittance of the chromium oxide film drops sharply in the short wavelength region. Therefore, the halftone phase shift photomask using chromium oxide as a semi-transparent film can be used for g-line (436 nm) and i-line (365 nm) exposure of a high pressure mercury lamp, but has a higher resolution. Deep Fluoride Krypton Excimer Laser (248 nm)
In UV (far ultraviolet) exposure, there is a problem that the transmittance is too low to be used. Further, the chromium nitride film, the chromium oxynitride film, the chromium oxycarbide film, and the chromium oxycarbonitride film also have a problem that they cannot be used for high resolution lithography because they cannot be used for the krypton fluoride excimer laser exposure.

Therefore, as a means for solving the above problems,
One using a chromium-silicon compound film as disclosed in Japanese Patent Application Laid-Open No. 5-2259, or N.K. Yoshio
kaet al. , Proc. 1993 IEEE I
nt. Electron Devices Meetin
g, Washington D .; As shown in C, a molybdenum-silicon compound film or the like can be considered. However, even though good transmittance can be obtained in deep UV regions such as krypton fluoride excimer laser with these films, the film quality of the base material, especially the etching characteristics, is different from that of the conventional photomask light-shielding film. An additional etching process must be added. Further, since the etching selection ratio with respect to the underlying quartz substrate is small, it is necessary to provide an etching stop layer, and there is a problem that the number of steps is newly provided, the number of steps is increased, and the yield is reduced.

The present invention has been made in view of such a situation, and an object thereof is to have a sufficient transmittance for short wavelength light and to be used for high resolution lithography such as krypton fluoride excimer laser exposure. It is possible to provide a halftone phase shift photomask and a blank for a halftone phase shift photomask which can be manufactured by one-time plate making and without providing an etching stop layer.

[0011]

SUMMARY OF THE INVENTION In view of the above problems, the present invention has a transmittance of halftone when formed into a film thickness that inverts the phase of short wavelength light such as krypton fluoride excimer laser light. A halftone phase shift material included in a range usable as a phase shift layer, and a halftone phase shift film of a halftone phase shift photomask used for the exposure of g-line or i-line of a high pressure mercury lamp described above, or a conventional Similar to the chrome light-shielding film for photomasks, the research was completed as a result of research to develop a halftone phase shift photomask material that can be patterned in a single plate-making process.

That is, the present invention relates to a halftone phase shift photomask including at least one layer mainly containing a compound of chromium and aluminum as a halftone phase shift layer and a blank for a halftone phase shift photomask. A film mainly composed of a compound of chromium and aluminum changes its film quality depending on the ratio of chromium and aluminum, and when the amount of chromium is large, the transmittance is lowered, but the chemical resistance is good. On the other hand, when a large amount of aluminum is contained, the transmittance is good but the chemical resistance is deteriorated. Further, compared with the conventional film mainly composed of chromium oxide, chromium nitride, chromium oxynitride, chromium oxycarbide, and chromium oxycarbonitride, since the transmittance in the short wavelength region is excellent, the krypton excimer laser fluoride on the transparent substrate is excellent. Even if the film is formed with a film thickness that inverts the phase of light, it is possible to obtain a transmittance that can be sufficiently used as a halftone phase shifter film. The chemical resistance at this time is also good.

In the halftone phase shift lithography, the refractive index and the extinction coefficient of the film forming the halftone phase shift layer with exposure light are obtained by, for example, ellipsometry, and the exposure is obtained by the above equation (1). It is required that the transmittance when the film is formed on the transparent substrate is the optimum transmittance determined by the transfer pattern or the like by a film thickness necessary for inverting the phase of light. When assuming krypton fluoride excimer laser exposure, the transmittance of the film whose phase inverts is too low for a film mainly composed of chromium oxide, chromium nitride, chromium oxynitride, chromium oxycarbide, and chromium oxycarbonitride. The compound mainly composed of chromium and aluminum of the present invention, which cannot be used as a halftone phase shift layer, has a ratio of contained chromium atom and aluminum atom, oxygen atom, nitrogen atom, carbon atom, hydrogen atom and fluorine. Depending on the proportion of atoms, sulfur atoms, etc., the refractive index,
The composition can be adjusted so that the transmittance with respect to the exposure light at the film thickness when the extinction coefficient changes and the phase is inverted becomes the required optimum transmittance. In this case, a single layer can be used as the halftone phase shift layer, but a range that does not impair the phase inversion function after forming the film so that the transmittance for exposure light is higher than the required transmittance It is also possible to stack a light shielding layer for adjusting the transmittance inside. In this case, it is possible to make the halftone phase shift photomask blank substrate conductive and to manufacture a halftone phase shift photomask blank for g-line and i-line exposure having a shifter layer of the same composition. Further, when an attempt is made to inspect with light having a wavelength longer than the exposure light, the inspection cannot be performed because the transmittance is too high only with the shifter layer, but it is possible by laminating the light shielding layer. Furthermore, when the light-shielding layer is also formed of a compound of chromium and aluminum, there is an advantage that patterning can be performed without largely changing the plate making process of the conventional photomask.

In order to form the compound of chromium and aluminum of the present invention, conventional thin film forming techniques such as sputtering, ion plating and vapor deposition can be used.

In order to obtain the compound of chromium and aluminum of the present invention by the sputtering method, a target in which metallic chromium and metallic aluminum are arranged in an appropriate area ratio in consideration of the difference in sputtering rate, or chromium and aluminum are appropriately controlled. A combination of alloy targets with composition ratios, or targets of oxidization, nitriding, carbonization, oxynitriding, oxycarbonization, fluorinated chromium, and aluminum used in advance, or oxidation, nitriding, carbonization, oxynitriding, oxycarbonization, fluorine Using targets of compounded chromium and aluminum compounds, argon, neon,
Xenon, helium, sputter gas such as nitrogen alone,
Alternatively, a sputtering film is formed by direct current or high frequency discharge in an atmosphere in which these are combined. At this time, if necessary, a gas serving as an oxygen source such as oxygen, nitrogen, carbon dioxide, or fluorine, a nitrogen source, a carbon source, or a fluorine source may be mixed. Here, by changing the film forming conditions such as composition of atmospheric gas, pressure, sputtering power, and sputtering time,
The transmittance, extinction coefficient can be adjusted by changing the composition, structure, structure, etc. of the film.

In order to obtain the compound of chromium and aluminum of the present invention by the ion plating method, a raw material in which metallic chromium and metallic aluminum are arranged in a mosaic pattern,
Alternatively, a raw material of an alloy of chromium and aluminum, or a combination of chromium, which has been previously oxidized, nitrided, carbonized, oxynitrided, oxycarbonized, or a raw material of aluminum, which has been previously oxidized, nitrided, carbonized, oxynitrided, oxycarbonized, chromium, Using the raw material of the aluminum compound, argon,
Discharge is performed in a carrier gas such as neon, xenon, helium, or nitrogen alone or in an atmosphere in which these are combined, and the target is heated, evaporated, and a film is formed. At this time, if necessary, a reaction gas serving as an oxygen source such as oxygen, nitrogen, carbon dioxide, or fluorine, a nitrogen source, a carbon source, or a fluorine source can be mixed. Here, by changing the film forming conditions such as the composition of atmospheric gas, pressure, sputtering power, and sputtering time, the composition, structure, structure, etc. of the film are changed, and the transmittance, refractive index,
The extinction coefficient can be adjusted.

To obtain the compound of chromium and aluminum of the present invention by the vapor deposition method, a resistance heating method using a tungsten basket, a tungsten-plated coil or boat, a tungsten coil, or the like, or
By so-called EB vapor deposition method by electron beam irradiation, heating of metallic chromium and metallic aluminum is controlled individually,
Evaporate and form a film. At this time, a film can be formed by mixing oxygen, nitrogen, carbon dioxide, a reaction gas serving as a nitrogen source, a carbon source, and a fluorine source such as fluorine, if necessary. Here, by changing the film forming conditions such as the composition of atmospheric gas and the pressure, the composition, structure, structure, etc. of the film can be changed to adjust the transmittance, the refractive index, and the extinction coefficient.

When the compound of chromium and aluminum of the present invention is used as a single layer to form a halftone phase shift layer, since chromium atoms and aluminum atoms are used as base materials, the etching stopper is the same as the chromium light shielding film of the conventional photomask. It does not require a layer, can be etched with a chlorine-based gas, etc., and can be patterned in a single plate-making process. Further, even in the case of a multilayer film, a compound of chromium is used as a light-shielding film,
Even when using a compound of aluminum, or a compound of chromium and aluminum having a composition different from that of the halftone phase shifter layer, an etching stopper layer is not required as in the conventional case, and etching can be performed with a chlorine-based gas or the like. Platemaking can be performed in a single patterning step. Therefore, the yield can be improved and the cost can be reduced without largely changing the conventional process.

[0019]

The halftone phase shift photomask and the blank for a halftone phase shift photomask of the present invention can obtain a transmittance higher than a predetermined level even with short wavelength exposure and can be used for krypton fluoride excimer laser exposure and the like. Resolution lithography can be realized. Further, since the mask can be formed by almost the same method as the conventional photomask, the yield can be improved and the cost can be reduced.

[0020]

EXAMPLES Examples of halftone phase shift photomasks and blanks for halftone phase shift photomasks of the present invention will be described below. [Embodiment 1] An embodiment of a blank for a halftone phase shift photomask of the present invention will be described with reference to FIG. As shown in FIG. 3A, a compound film 302 of chromium and aluminum having a thickness of about 30 n is formed on a mirror-polished silicon wafer 310 by the sputtering method under the following conditions.
A film was formed to a thickness of m to obtain a polarization analysis sample 305.

Deposition apparatus: Planar type DC magnetron sputtering apparatus Target: Metal chromium: Metal aluminum = 4
0:60 (wt%) Gas and flow rate: Argon gas 80 sccm + Oxygen gas 20 sccm Sputter pressure: 0.3 Pascal Spatter current: 0.9 amps Next, a commercially available spectroscopic ellipsometer (ES- manufactured by Sopra) is used.
4G), the refractive index u and the extinction coefficient k of the sample 305 at the KrF excimer laser wavelength (248 nm) were measured, and u = 2.0956 and k = 0.3, respectively.
It was 653. This is described in M. Born, E. W
"Principles of Optics" by olf
Calculating the film thickness required to shift the phase of transmitted light of 248 nm by 180 degrees when formed as a film on high-purity synthetic quartz used as a substrate for a photomask by treating it as a metal film shown on pages 628-632. , 115 nm.

Therefore, as shown in FIG. 1B, the compound film 30 of chromium and aluminum is formed on the high-purity synthetic quartz substrate 303 which has been optically polished and well washed under the above-mentioned film forming conditions.
4 was deposited to a thickness of about 115 nm to obtain a halftone phase shift photomask blank 306 of the present invention having a transmittance of light having a wavelength of 248 nm of about 6%. The spectral transmittance of this blank is shown in FIG.

[Embodiment 2] An embodiment of the halftone phase shift photomask of the present invention will be described with reference to the manufacturing process chart of FIG.

As shown in FIG. 2A, a desired resist pattern 402 containing an organic material as a main component was obtained on the blanks 401 obtained in Example 1 by a conventional electron beam lithography method or a photolithography method. . Next, as shown in FIG. 4B, the semitransparent film exposed from the resist pattern was subjected to high frequency under a mixed gas of CH ₂ Cl ₂ : O ₂ = 1: 2.5 and a pressure of 0.3 Torr. The desired semi-transparent film pattern 403 was obtained by performing dry etching selectively by exposing it to plasma. Finally, the remaining resist 404 is peeled off by a conventional method, and as shown in FIG. 6C, the halftone phase shift photomask 40 in which the transmittance of 248 nm light of the halftone phase shift part is 8%.
Got 5. The halftone phase shift photomask 405 has dimensional accuracy, cross-sectional shape,
The film thickness distribution, the transmittance distribution, the film adhesion to the substrate, etc. can all be put to practical use.

[0025]

As is apparent from the above description, according to the halftone phase shift photomask and the blank for a halftone phase shift photomask of the present invention, the transmittance higher than a predetermined value can be obtained even with short wavelength exposure, Since it can also be used for krypton excimer laser exposure, etc., high resolution lithography can be realized. Also, since the base materials of the halftone phase shift layer are chromium and aluminum,
Similar to the chromium light-shielding film of the conventional photomask, it can be etched with a chlorine-based gas, and it is not necessary to provide an etching stop layer, and patterning can be performed in a single plate making.
Therefore, since the plate making process of the conventional photomask is not changed or a new photomask is not provided, the yield can be improved and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a process of obtaining a halftone phase shift photomask blank according to a first embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of a halftone phase shift photomask according to a second embodiment of the present invention.

FIG. 3 is a diagram showing the principle of halftone phase shift lithography.

FIG. 4 is a diagram showing a conventional method.

FIG. 5 is a diagram showing a spectral transmittance curve of a chromium oxide film.

FIG. 6 is a diagram showing a spectral transmittance curve of a blank for a halftone phase shift photomask of Example 1.

[Explanation of symbols]

101, 201 ... Substrate 102 ... Phase inversion semi-transparent film 103, 203 ... Incident light 202 ... Shading film 301 ... Silicon wafer 302, 304 ... Compound film of chromium and aluminum 303. ..High-purity synthetic quartz substrate 305 ... Polarization analysis sample 306 ... Halftone phase shift photomask blanks 401 ... Blank 402 ... Resist pattern 403 ... Semitransparent film pattern 404 ... Resist 405 ... Halftone phase shift photomask

Claims (12)

[Claims] 1. A blank for a halftone phase shift photomask, wherein the halftone phase shift layer on the transparent substrate contains at least one layer containing a compound of chromium and aluminum as a main component. 2. The compound of claim 1 wherein the compound of chromium and aluminum is a compound containing at least one atom of hydrogen, carbon, sulfur, nitrogen, oxygen and fluorine in addition to a chromium atom and an aluminum atom. Blanks for halftone phase shift photomasks. 3. The layer according to claim 1, wherein the layer containing a compound of chromium and aluminum as a main component does not change the refractive index obtained by ellipsometry with exposure light by 0.1 or more, chromium, A blanket for a halftone phase shift photomask, which contains impurity atoms other than aluminum, fluorine, oxygen, carbon, sulfur, nitrogen, and hydrogen atoms. 4. The halftone phase shift layer according to any one of claims 1 to 3, wherein the phase difference φ obtained by the following formula is nπ ± π / 3 radians (n is an odd number) on the transparent substrate.
A blank for a halftone phase shift photomask, which is formed so as to have a range of. Here, φ is a phase change that light vertically transmitted through a photomask in which a multilayer film of (m-2) layers is formed on the transparent substrate, and χ ^{k, k + 1} is a k-th layer. And (k + 1)
The phase change at the interface with the th layer, u _k and d _k are the refractive index and film thickness of the material forming the k th layer, and λ is the wavelength of the exposure light. However, the layer of k = 1 is the transparent substrate, and the layer of k = m is air. 5. The transmittance of the halftone phase shift layer with respect to exposure light according to claim 1, wherein the transmittance of the transparent substrate with respect to the exposure light is 100%. A blank for a halftone phase shift photomask, which is formed on the transparent substrate to have a film thickness of 50%. 6. The halftone phase shift layer according to claim 1, wherein the halftone phase shift layer is a layer composed of at least a compound of chromium and aluminum, and chromium, chromium oxide, chromium nitride, chromium oxynitride, and chromium oxide carbide. , Any one of chromium oxycarbonitride, aluminum, aluminum oxide, aluminum nitride, aluminum oxynitride, aluminum oxycarbide, and aluminum oxycarbonitride,
Alternatively, a blank for a halftone phase shift photomask, comprising a plurality of mixtures and a layer made of a compound. 7. A halftone phase shift photomask, wherein the halftone phase shift layer on the transparent substrate includes at least one layer containing a compound of chromium and aluminum as a main component. 8. The compound of claim 7 wherein the compound of chromium and aluminum is a compound containing at least one atom of hydrogen, carbon, sulfur, nitrogen, oxygen and fluorine in addition to a chromium atom and an aluminum atom. A halftone phase shift photomask. 9. The chromium or aluminum compound according to claim 7, wherein the layer containing a compound of chromium and aluminum as a main component does not change the refractive index obtained by ellipsometry with exposure light by 0.1 or more. A halftone phase shift photomask containing an impurity atom other than aluminum, fluorine, oxygen, carbon, sulfur, nitrogen and hydrogen atoms. 10. The method according to any one of claims 7 to 9,
A halftone phase shift layer, characterized in that the halftone phase shift layer is formed on a transparent substrate such that the phase difference φ obtained by the following formula is in the range of nπ ± π / 3 radians (n is an odd number). Photo mask. Here, φ is a phase change that light vertically transmitted through a photomask in which a multilayer film of (m-2) layers is formed on the transparent substrate, and χ ^{k, k + 1} is a k-th layer. And (k + 1)
The phase change at the interface with the th layer, u _k and d _k are the refractive index and film thickness of the material forming the k th layer, and λ is the wavelength of the exposure light. However, the layer of k = 1 is the transparent substrate, and the layer of k = m is air. 11. The transmittance of the halftone phase shift layer with respect to exposure light according to claim 7, wherein the transmittance of the opening of the halftone phase shift layer with respect to the exposure light is 100%. Sometimes 1 to 50%
Is a halftone phase shift photomask. 12. The halftone phase shift layer according to claim 7, wherein the halftone phase shift layer contains at least a layer containing a compound of chromium and aluminum as a main component, and chromium, chromium oxide, chromium nitride, chromium oxynitride, Any one of chromium oxycarbide, chromium oxycarbonitride, aluminum, aluminum oxide, aluminum nitride, aluminum oxynitride, aluminum oxycarbide, aluminum oxycarbonitride, or a mixture thereof, or a layer formed of a compound. A halftone phase shift photomask.