JP3913319B2 - Method for manufacturing halftone phase shift mask - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photomask used when transferring a fine pattern such as an LSI using a projection exposure apparatus, and more particularly to a method of manufacturing a halftone phase shift mask that improves the resolution by giving a phase difference between exposure light.
[0002]
[Prior art]
In manufacturing a semiconductor LSI, a phase shift mask is used as one of photomasks as a fine pattern transfer mask. This phase shift mask can improve the resolution of a transfer pattern by providing a phase difference between exposure light passing through the mask. As one of the phase shift masks, a phase shift mask described in JP-A-4-136854 is known as a mask particularly suitable for transferring isolated hole or space patterns.
[0003]
This phase shift mask forms, on a transparent substrate, a semi-transparent film that transmits light of intensity that does not substantially contribute to exposure, and at the same time, shifts the phase of the light passing therethrough. A mask pattern having a translucent portion that transmits light having an intensity that contributes substantially to exposure and a semi-transparent portion that transmits light having an intensity that does not substantially contribute to exposure by selectively removing the portion Is formed. This phase shift mask shifts the phase of light passing through the semi-translucent portion, so that the phase of light passing through the semi-transparent portion is substantially inverted with respect to the phase of light passing through the translucent portion. By satisfying the relationship, the light that has passed through the vicinity of the boundary between the translucent part and the semi-translucent part and wraps around by the diffraction cancels each other, so that the contrast of the boundary part can be maintained well. This is what is called a halftone phase shift mask.
[0004]
In this phase shift mask, when the wavelength of the exposure light is λ and the refractive index of the semi-transparent film with respect to the exposure light is n, the thickness t of the semi-transparent film is generally t = λ / {2 ( n-1)}
In general, the transmissivity of the semi-transparent film at the wavelength of the exposure light is set to about 1 to 50%.
[0005]
The above-described semi-transparent film has a two-layer structure, in which the phase difference is adjusted mainly by an SOG (coating glass: spin-on glass) film, and the transmittance is determined by a thin chromium film. However, the above-described structure has some problems in manufacturing the mask pattern. The film formation method and the pattern processing method are different between the SOG film and the chromium film, so that defects are likely to occur during the process, and since the refractive index of SOG is small, the required film thickness for phase inversion with exposure light is small. It is thicker than a normal light-shielding film and difficult to process. Further, SOG has low mechanical strength and poor adhesion to a chromium film, so that film peeling is likely to occur.
[0006]
Therefore, in order to solve these problems, single layer films capable of simultaneously controlling the phase difference and the transmittance with one film have been developed. As the composition of the single layer film, a chromium system and a molybdenum silicide system are generally used, and the chromium system is known as a chromium oxide film, a chromium oxynitride film, etc., and the molybdenum silicide system includes oxidized molybdenum and silicon. (MoSiO), nitrided molybdenum and silicon (MoSiN), oxynitrided molybdenum and silicon (MoSiON), oxidized carbonized molybdenum and silicon (MoSiOC), oxycarbonitized molybdenum and silicon (MoSiOCN), etc. It has been. More specifically, MoSiN is made of metal-bonded MoSi and a nitride of Mo or Si. These single-layer films are formed by reactive sputtering using a chromium or molybdenum silicide target. For the mask pattern formation, wet etching or dry etching is used for chrome, and dry etching is used for molybdenum silicide.
[0007]
In order to maximize the characteristics of the phase shift mask, it is ideal that the amount of phase shift is 180 °, but it is desirable that the phase shift is practically within a range of ± 3 °. Since the half-tone phase shift mask using the single layer film controls the phase difference and the transmittance simultaneously with one film, the production of the half-tone phase shift mask blank requires high-precision control of film quality and film thickness. . Further, the mask line width (CD: Critical Dimension) is also required to have higher accuracy than a normal mask.
[0008]
Usually, the mask production using the chromium-based photomask blank is performed by a process as shown in FIG. First, as shown in FIG. 7A, a chromium film 12 is formed on a transparent substrate 11 by sputtering or the like, and a resist 13 is applied thereon to obtain a photomask blank. Next, as shown in FIG. 7B, the resist 13 is exposed and developed to obtain a resist pattern 13a. Thereafter, using the resist pattern 13a as a mask, the chromium film 12 is etched as shown in FIG. 7C to form the chromium film pattern 12a, and finally the resist pattern 13a is peeled off as shown in FIG. 7D. By doing so, a photomask is completed. Such a process is the same when using a molybdenum silicide photomask blank.
[0009]
Here, for the chromium-based etching, for example, wet etching using ceric ammonium nitrate or dry etching using Cl ₂ , CCl ₄ , or the like is used. In the molybdenum silicide system, a dry etching technique using CF ₄ or the like is used. In these processes, in the case of a molybdenum silicide system, a problem with a halftone phase shift mask is not a problem with a normal mask.
[0010]
In the case of chromium-based etching, the above chemicals and gases are both resistant to the substrate glass and hardly etched, that is, the etching selectivity between chromium and glass is several tens to several hundreds, whereas the molybdenum silicide-based etching is In this case, the glass is also slightly etched (selectivity is about several to several tens). Even if the substrate glass is slightly dug in a normal mask, there is no influence on the actual mask use. However, the halftone phase shift mask has a phase difference of 180 ° between the glass exposed portion and the film. Therefore, when the glass is etched, the phase amount calculated from the refractive index of the glass and the etched depth changes.
[0011]
However, this problem can be avoided by designing a halftone film in which the amount by which glass is etched (that is, the amount of phase difference) is calculated in advance. Japanese Patent Application Laid-Open No. 7-56317 discloses that this fact is used to correct the deviation from the target phase difference and to obtain a highly accurate phase shift mask.
[0012]
[Problems to be solved by the invention]
However, in the case of chrome-based etching, etching is performed in the lateral direction by adding an etching time, and finishes beyond the designed dimensions of the patterned resist. In other words, the CD can be controlled while the substrate glass. However, in the case of molybdenum silicide system, the substrate glass is similarly finished and the substrate glass is also etched.
[0013]
FIG. 8 and FIG. 9 are diagrams showing such a state. FIG. 8 is a case of a chromium system, and FIG. 9 is a case of a molybdenum silicide system. When the chrome film pattern 22 or the molybdenum silicide film pattern 23 is additionally etched using the resist pattern 21 as a mask, the chrome film pattern 22 is over-etched by side etching as shown in FIG. However, in the case of a molybdenum silicide system, the molybdenum silicide film pattern 23 is overfinished and the glass substrate 24 is etched at the same time as shown in FIG. 9B. End up. In other words, in the halftone phase shift mask, the phase difference between CD and phase can be controlled independently in the chromium system, but not in the molybdenum silicide system, and a high-accuracy mask having a value satisfying both the CD and the phase difference is obtained. There was a problem that it was not possible.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention (first present invention) forms a semi-transparent film having a predetermined phase shift amount and transmittance on a transparent substrate, and this semi-transparent film is formed with a resist pattern. A process of forming a semi-transparent film pattern by dry etching on the mask, and when the phase difference or line width obtained as a result of this process exceeds the allowable range, only the requirements exceeding the allowable range are adjusted and within the allowable range. The method of manufacturing a halftone phase shift mask includes the step of adding dry etching by changing the etching conditions to satisfy the following conditions.
[0015]
In the second aspect of the present invention, a semi-transparent film having a predetermined phase shift amount and transmittance is formed on a transparent substrate, and this semi-transparent film is dry-etched using a resist pattern as a mask to perform the semi-transparent film. When the pattern formation process and the phase difference and line width obtained as a result of this process exceed the allowable range, both are adjusted so that both are within the allowable range. And a method of manufacturing a halftone phase shift mask.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a method of manufacturing a halftone phase shift mask according to the present invention will be described in detail with reference to the accompanying drawings, but before that, an outline of the present invention will be described.
[0017]
According to the first aspect of the present invention, there is provided a method for obtaining a high-accuracy mask having a value satisfying both of CD and phase difference in a metal silicide halftone phase shift mask such as molybdenum silicide, which can control the CD and phase difference as much as possible. .
[0018]
In general, control parameters for dry etching mainly include gas type, pressure, and RF power, and various conditions can be set by combinations thereof, and there are optimum conditions according to the purpose.
[0019]
As for the reaction mechanism in which radicals are the main reaction, the progress of etching is isotropic as shown in FIG. 2 as in the case of wet etching.
[0020]
On the other hand, when ions are the main etching reaction, since the straightness of ions is used, the mask transferability is excellent, and anisotropic etching is performed as shown in FIG. When etching a molybdenum silicide semi-transparent film, the apparatus is an RIE (reactive ion etching) apparatus using parallel plate electrodes, and both active ions and radicals contribute to the etching. Etching is performed under conditions having the following properties. Therefore, depending on the setting of conditions, it can be moved to both radical-based reactions (isotropic etching) and ion-based reactions (anisotropic etching).
[0021]
FIG. 4 shows etching of MoSiN (nitrided molybdenum and silicon) and a quartz substrate (QZ) when CF ₄ / O ₂ = 95/5 sccm is used as a gas and the pressure is changed at an RF power of 100 W. FIG. 5 shows the change in speed, and FIG. 5 shows the pressure dependence of the side etching amount. As is clear from both figures, when the pressure is high, the etching rate of MoSiN is fast and the quartz is slow, and isotropic etching is performed, and the rate of increase in the side etching amount when the etching time is extended increases. On the other hand, when the pressure is low, the relationship between the etching rates is reversed and anisotropic etching is performed. Even if the etching time is extended, the increase rate of the side etching amount is small, but the etching rate of quartz is high. Therefore, the phase difference increases corresponding to the etching amount.
[0022]
Therefore, if the above properties are applied, the CD and the phase difference can be controlled almost independently. That is, first, etching is performed by calculating the amount of excavation of the quartz substrate under some anisotropic conditions, and if the CD is thinner than the design value in this process, the amount of excavation of quartz is small and the side etching amount is large. If etching is added under the conditions of the isotropic, only the CD can be adjusted without changing the phase difference. Conversely, if the CD is as designed and the phase difference is slightly lower, the etching can be added under the same conditions. The phase difference can be adjusted by digging quartz with almost no change in the CD.
[0023]
Under the etching conditions in which the above pressure is set low and the anisotropy is increased, the etching of the resist proceeds and the selection ratio tends to decrease. As another method, the pressure may be constant and the gas type may be changed. Good. If, for example, CHF ₃ or the like having a higher deposition property than CF ₄ is used as an additive gas, the side etching amount, that is, CD can be made substantially constant due to the side wall protection effect. FIG. 6 shows the dependency of the side etching amount on the CHF ₃ addition amount.
[0024]
In relation to the above technique, in the second aspect of the present invention, when both the CD and the phase difference do not fall within the allowable range, both of them can be adjusted so that both fall within the allowable range. . That is, if the CD is thinner than the design value and the phase difference is low as a result of the first etching process, if etching is added under the condition that both of them are adjusted, both the CD and the phase difference can be obtained. Both can be adjusted to within acceptable limits.
[0025]
Next, a first embodiment of the present invention will be described with reference to FIG. In the first embodiment, first, as shown in FIG. 1A, a MoSiN film 32 of molybdenum and silicon nitrided as a semi-transparent film on a transparent substrate 31 made of quartz glass whose main surface is mirror-polished. A film having a thickness of 950 nm is formed by sputtering. Next, a positive type electron beam resist (ZEP810: manufactured by Nippon Zeon Co., Ltd.) 33 is formed thereon by spin coating to form a pattern of the MoSiN film 32 and dried. Next, electron beam drawing is selectively performed on the positive electron beam resist 33 and developed to form a resist pattern 33a for pattern formation of the MoSiN film 32 as shown in FIG.
[0026]
Next, the MoSiN film 32 is etched under the following conditions (etching condition 1) using the resist pattern 33a as a mask in a parallel plate electrode type dry etching apparatus, and the MoSiN film pattern 32a is formed as shown in FIG. Form.
Etching condition 1
Gas: CF ₄ / O ₂ = 95/5 sccm
RF power: 100W
Pressure: 0.15 Torr
Time: 60sec
[0027]
Next, the resist pattern 33a is left as it is, and the CD is temporarily measured with a transmission CD measuring machine. In this case, by examining the CD conversion difference between the state with the resist and the state where the resist is peeled in advance, the CD after peeling can be estimated before peeling the resist. At this time, it was estimated that the CD after the resist peeling was 1.90 μm with respect to the design value of 2.00 μm. Further, when a part of the resist outside the main pattern was peeled and the phase difference was measured, it was 181.0 °.
[0028]
Here, in order to finish a highly accurate mask, it is necessary to bring only the CD close to the design value while keeping the phase difference as it is. Therefore, additional etching is performed under the following conditions (etching condition 2).
Etching condition 2
Gas: CF ₄ / O ₂ = 95/5 sccm
RF power: 100W
Pressure: 0.3 Torr
Time: 7 sec
[0029]
Here, it can be seen from FIGS. 4 and 5 that the side etching rate is 0.015 μm / sec and the etching rate of quartz glass is 0.58 Å / sec under the condition of pressure 0.3 Torr. By adding etching, the CD value after resist removal advances by 0.105 μm to 2.005 μm, and the phase difference advances by 0.3 ° (here, when the refractive index of quartz glass at a wavelength of 248 nm is 1.508, It was 181.30 ° (13.5 ° per 1 °), and the CD was able to approach the design value while the phase difference remained almost constant.
[0030]
Next, a second embodiment of the present invention will be described. In the second embodiment, the processes are the same as those in the first embodiment up to the etching under the etching condition 1. Next, the resist pattern 33a is left as it is, and the CD is temporarily measured with a transmission CD measuring machine. At this time, it was estimated that the CD after the resist removal was 1.99 μm with respect to the design value of 2.00 μm. Further, when a part of the resist outside the main pattern was peeled and the phase difference was measured, it was 175.0 °.
[0031]
Here, in order to finish a highly accurate mask, it is necessary to bring only the phase difference close to the design value without changing the CD. Therefore, additional etching is performed under the following conditions (etching condition 3).
Etching condition 3
Gas: CF ₄ / O ₂ = 95/5 sccm
RF power: 100W
Pressure: 0.075 Torr
Time: 21sec
[0032]
Here, it can be seen from FIGS. 4 and 5 that the side etching rate is 0.0015 μm / sec and the etching rate of quartz glass is 3.2 Å / sec under the condition of pressure 0.075 Torr. By adding etching, the CD value after resist stripping advances by 0.03 μm to 2.02 μm, and the phase difference advances by 5.0 ° (here, when the refractive index of quartz glass at a wavelength of 248 nm is 1.508, 180.0 °), the CD remained almost constant, and the phase difference could be brought close to the design value.
[0033]
Next, a third embodiment of the present invention will be described. In the third embodiment, up to the etching under the etching condition 1, the steps are the same as those in the first embodiment. Next, the resist pattern 33a is left as it is, and the CD is temporarily measured with a transmission CD measuring machine. At this time, it was estimated that the CD after the resist peeling was exactly 2.00 μm with respect to the design value of 2.00 μm. Further, when a part of the resist outside the main pattern was peeled and the phase difference was measured, it was 176.0 °.
[0034]
Here, in order to finish a highly accurate mask, it is necessary to bring only the phase difference close to the design value without changing the CD. Therefore, additional etching is performed under the condition (etching condition 4) with CHF ₃ gas added at a constant pressure as follows.
Etching condition 4
Gas: CF ₄ / CHF ₃ / O ₂ = 85/10/5 sccm
RF power: 100W
Pressure: 0.15 Torr
Time: 50 sec
[0035]
Here, it can be seen from FIG. 6 that the side etching rate is 0.0004 μm / sec and the etching rate of quartz glass is 1.1 Å / sec under the above conditions. Then, the CD value after the resist removal is advanced by 0.02 μm to 2.02 μm, and the phase difference is advanced by 4.0 ° (here, when the refractive index of quartz glass at a wavelength of 248 nm is 1.508, 13 ° per 1 °). 180.0 °, and the CD remained almost constant, and the phase difference could be brought close to the design value.
[0036]
Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, up to the etching under the etching condition 1, the steps are the same as those in the first embodiment. Next, the resist pattern 33a is left as it is, and the CD is temporarily measured with a transmission CD measuring machine. At this time, it was estimated that the CD after the resist peeling was 1.95 μm with respect to the design value of 2.00 μm. Further, when a part of the resist outside the main pattern was peeled and the phase difference was measured, it was 173.0 °.
[0037]
Here, in order to finish a highly accurate mask, it is necessary to bring both the CD and the phase difference close to the design values. Therefore, additional etching is performed under the following conditions (etching condition 5).
Etching condition 5
Gas: CF ₄ / O ₂ = 95/5 sccm
RF power: 100W
Pressure: 0.15 Torr
Time: 76 sec
[0038]
Here, it can be seen from FIGS. 4 and 5 that the side etching rate is 0.0053 μm / sec and the etching rate of quartz glass is 1.42 Å / sec under the condition of pressure 0.15 Torr. By adding etching, the CD value after resist stripping advances 0.4 μm to 1.99 μm, and the phase difference advances 8.0 ° (where the refractive index of quartz glass at a wavelength of 248 nm is 1.508, It was 181.0 ° (13.5 ° per 1 °), and both the CD and the phase difference were able to approach the design values.
[0039]
In the above embodiment, nitrided molybdenum and silicon (MoSiN) are used as the translucent film. However, oxidized molybdenum and silicon (MoSiO), oxynitrided molybdenum and silicon (MoSiON), and the like are used. It can also be used. Further, instead of molybdenum (Mo), metal silicide using tungsten (W), chromium (Cr), tantalum (Ta), or the like, which is a transition metal similar to Mo, may be used. Further, in addition to the single layer film, for example, a two layer film such as molybdenum silicide and SOG may be used. These other films can be used in the same manner as in the above embodiment.
[0040]
Furthermore, in the third embodiment, CHF ₃ is added as a gas having a strong deposition property, but a gas such as C ₂ F ₆ , C ₄ F _8, or CH ₂ F ₂ can also be used.
[0041]
Moreover, in each above-mentioned embodiment, although quartz glass is used as a transparent substrate, other glass, such as soda-lime glass, alumino borosilicate glass, borosilicate glass, can be used for others. However, in that case, a process according to the refractive index of the material, the etching rate, etc. is required.
[0042]
Further, when forming a resist pattern, exposure by light may be used in addition to the method by electron beam drawing. In that case, of course, a resist corresponding to the exposure condition is used.
[0043]
【The invention's effect】
As described above, according to the method of manufacturing a halftone phase shift mask of the present invention, the phase difference between CD and phase can be controlled independently in the manufacture of a metal silicide-based halftone phase shift mask such as molybdenum silicide. It is possible to obtain a high-accuracy mask having values satisfying both of the phase differences. In addition, according to the present invention, even when both CD and phase difference are not within the allowable range, both CD and phase difference can be within the allowable range by additional etching, and a highly accurate mask can be obtained. Can do.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first embodiment of a method of manufacturing a halftone phase shift mask according to the present invention.
FIG. 2 is a cross-sectional view showing isotropic etching.
FIG. 3 is a cross-sectional view showing anisotropic etching.
FIG. 4 is a characteristic diagram showing the pressure dependence of the etching rate.
FIG. 5 is a characteristic diagram showing the pressure dependency of the side etching amount.
FIG. 6 is a characteristic diagram showing the dependency of side etching amount on CHF ₃ addition.
FIG. 7 is a cross-sectional view showing mask fabrication using chromium-based photomask blanks.
FIG. 8 is a cross-sectional view showing a state during chromium-based etching.
FIG. 9 is a cross-sectional view showing a state during etching of a molybdenum silicide system.
[Explanation of symbols]
31 Transparent substrate 32 MoSiN film 32a MoSiN film pattern 33a Resist pattern

Claims (6)

Forming a semi-transparent film having a predetermined phase shift amount and transmittance on a transparent substrate, and forming the semi-transparent film pattern by dry etching the semi-transparent film using a resist pattern as a mask;
When the result obtained line width of the step exceeds an allowable range, the requirements of the line width was within allowable range beyond, changed to etching conditions such as the requirements of the phase difference does not exceed the allowable range And a step of adding dry etching to the halftone phase shift mask. Forming a semi-transparent film having a predetermined phase shift amount and transmittance on a transparent substrate, and forming the semi-transparent film pattern by dry etching the semi-transparent film using a resist pattern as a mask;
When the phase difference and the line width obtained as a result of the above steps exceed the allowable range, both of them are adjusted and the etching conditions are changed so that both are within the allowable range, and dry etching is added. A method for manufacturing a halftone phase shift mask, comprising:   3. The method for manufacturing a halftone phase shift mask according to claim 1, wherein the etching conditions are changed by pressure.   3. The method of manufacturing a halftone phase shift mask according to claim 1, wherein the etching condition is changed by a gas type.   5. The method of manufacturing a halftone phase shift mask according to claim 1, wherein the translucent film includes an oxidized transition metal and silicon, a nitrided transition metal and silicon, an oxynitrided transition metal and silicon. A method for producing a halftone phase shift mask, wherein the thin film is any one of the following thin films.   6. The method of manufacturing a halftone phase shift mask according to claim 5, wherein the transition metal is molybdenum.

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