JPH06194820A - Production of phase shift mask - Google Patents

Abstract

PURPOSE:To enhance the adhesiveness between a resist layer and a phase shift layer, to suppress the generation of pattern defects and to form phase shift patterns with high accuracy by forming a metallic thin-film layer on a phase shift layer and forming the resist layer thereon. CONSTITUTION:Light shielding patterns are formed by providing a light shielding layer 2 on a transparent substrate 1. An etching stopper layer 3, the phase shift layer 4 and the metallic thin-film layer 5 are provided in this order. In succession, the electron beam resist layer 6 is formed by application and is subjected to overlap plotting 7 with electron beams. The metallic thin-film layer 5 is then patterned by executing prescribed developing and etching. The phase shift layer 4 is thereafter etched with the resist patterns and the metallic thin-film patterns as a mask. The remaining resists and metallic thin-film patterns are removed, by which the phase shift mask is obtd. The material constituting the metallic thin-film layer 5 consists preferably of molybdenum, tantalum, tungsten, aluminum or nickel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called phase used as an original plate for photofabrication when forming an extremely fine pattern as represented by the manufacture of semiconductor integrated circuits such as LSI and VLSI. The present invention relates to a shift mask manufacturing method.

[0002]

2. Description of the Related Art In a conventional photomask, when projection exposure of a fine pattern is performed, light passing through a light transmitting portion of the mask is diffracted and interferes with each other in adjacent patterns.
There has been a problem that the patterns transferred onto the wafer are not separated and resolved by intensifying the light intensities at the pattern boundaries and exposing them to each other. This phenomenon has a stronger tendency for finer patterns closer to the exposure wavelength, and in principle it has been impossible to resolve fine patterns below the wavelength of light with a conventional photomask and a conventional exposure optical system.

Therefore, a photomask using a so-called phase shift technique (generally, a phase shift mask and a phase shift mask) is used in which the resolution of a fine pattern is improved by setting the phase shifts of projection lights passing through adjacent patterns to 180 ° with respect to each other. Was called) was developed.

That is, by providing a phase shift portion made of a transparent material on one side of the adjacent openings, when the transmitted lights are diffracted and interfere with each other, the light intensities at the boundaries are reversed because the phases are inverted. They weaken each other and the intensity becomes zero. As a result, the transfer pattern is separated and resolved. Since this relationship holds before and after the focus, the resolution is improved and the focus margin is improved even if the focus is slightly deviated.

Such a phase shift technique is based on IBM's Le
Proposed by Venson et al., JP-A-58-173
No. 744, and in principle, Japanese Patent Publication No. 62-
It is described in Japanese Patent No. 50811.

In order to maximize the effect of the phase shift technique, it is desirable that the phase shifts are 180 ° with respect to each other. For this purpose, a phase shift layer having a film thickness d may be formed so that the following expression, that is, d = λ / {2 (n-1)} (i) is established. Here, d is the film thickness of the phase shift portion,
λ is the exposure wavelength, and n is the refractive index.

2A to 2D show a method of manufacturing a phase shift mask according to the prior art. First, in FIG. 2A, the light shielding layer 12 is formed on the transparent substrate 11.
Is provided, and the light-shielding pattern is formed by a predetermined lithography process. Then, as shown in FIG. 2B, an etching stopper layer 13 and a phase shift layer 14 are provided in this order, and HMDS (hexamethyldisilazane) treatment is further performed on the etching stopper layer 13 and the phase shift layer 14, and then an electron beam resist is applied. The layer 15 and the conductive polymer layer 16 are provided in this order,
Overlay drawing 17 using an electron beam is performed under a predetermined exposure condition.

In this overlay drawing, overlaying is performed on the light-shielding pattern in the lower layer, and the drawing device reads the alignment mark formed in the light-shielding pattern and corrects the positional coordinate deviation based on this. Then, the phase shift pattern is drawn.

Subsequently, as shown in FIG. 2C, the conductive polymer layer 16 is removed, development is performed to form a resist pattern, and the resist pattern is used as a masking pattern for etching. The shift layer 14 is etched to form a phase shift pattern. Finally, as shown in FIG. 2D, the resist layer is removed to obtain a phase shift mask.

In this step, the material of the light shielding layer 12 is made of metal such as chromium or chromium oxide (or metal oxide or metal nitride), and the material of the phase shift layer 14 is made of SiO ₂ . The conductive polymer layer 16 is provided in order to perform drawing with an electron beam with high accuracy, and its function is to provide a transparent substrate when irradiating the electron beam resist with an electron beam.
The conductivity of the conductive polymer layer 16 prevents the occurrence of a charging phenomenon that occurs because both the phase shift layer and the electron beam resist have insulating properties. The conductive polymer layer 16 can generally be removed by immersion treatment in a solvent or water, and some can be removed with a resist developer.

Further, the HMDS is a kind of so-called silane coupling agent and has an effect as a surfactant for making the hydrophilic surface hydrophobic by coating it. In this case HMDS is caused hydrophilic -OH groups and the coupling reactions on the surface of a material consisting of SiO _2, to make a hydrophobic group on the surface, serves as an intermediate layer of SiO ₂ and the resist And improve adhesion. Since HMDS itself is volatile at room temperature and volatilizes except for the molecular layer that was involved in the surface modification, it does not affect the subsequent lithographic processing steps.
No HMDS removal process is required.

As the etching method of the phase shift layer, either wet etching or dry etching can be used. As the material of the etching stopper layer, a material having high resistance is used according to these etching methods. . Further, the mask referred to in the present invention means an exposure original plate which is used by being loaded in a projection exposure apparatus or a reduction projection exposure apparatus (generally called a stepper) which is one of the main manufacturing apparatuses of semiconductor integrated circuits. As is expected, it may be generally expressed as a photomask or a reticle.

However, according to the above method, in the step of applying a resist to the phase shift layer material SiO ₂ , a hydrophobic resist is applied to the hydrophilic SiO ₂ surface to form an adhesive layer. However, the resist pattern was peeled off during development.
What is used there is the HMDS. However, H
The MDS coating treatment is intended to prevent the peeling of the resist pattern. Even by this method, a large number of H ₂ O molecules are adsorbed on the SiO ₂ surface before the treatment, or moisture is absorbed with time. For this reason, the adhesive strength at the interface is likely to be lowered, and it was not a solution that would give us peace of mind even if the HMDS coating treatment was applied.

Further, in the case of forming a fine semiconductor integrated circuit pattern having a line width of about 1 μm, foreign matter contained in the HMDS itself or dust which may be adhered during the coating process causes a pattern defect. It becomes a problem as a cause of. Alternatively, even if the adhesive force is only slightly deteriorated, since the object is such a fine semiconductor integrated circuit pattern, the pattern edge portion is not formed well with satisfactory accuracy, and, for example, the pattern is jagged. Defects such as sticking and deformation were likely to occur.

Further, when the phase shift layer is dry-etched using the resist pattern as a masking pattern, the resist pattern is also removed at the same time as the etching of the phase shift layer, which is an advantage of dry etching. The anisotropic etching becomes worse. That is, at this time, there was a serious drawback in that the cross section of the edge portion of the phase shift pattern was not vertical but an inclined surface was formed, and as a result, the pattern dimension width also changed and it became difficult to obtain a predetermined dimension value. .

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to enhance the adhesiveness between a resist layer and a phase shift layer to prevent the occurrence of pattern defects. It is an object to suppress and enable highly accurate formation of a phase shift pattern.

[0017]

Means provided by the present invention for solving the above-mentioned problems are, namely, a method of manufacturing a phase shift mask having a light-shielding portion, a light-transmitting portion and a phase shift portion on a transparent substrate. 2. In the method of manufacturing a phase shift mask, at least, a metal thin film layer is formed on a layer of a material forming the phase shift portion, and then a resist layer is formed.

Preferably, the material for forming the metal thin film layer is molybdenum, tantalum, tungsten, aluminum, or nickel, in particular.

The present invention will be described in more detail below with reference to the accompanying drawings. (FIG. 1) (a) to (e) show the structure of a phase shift mask according to the present invention.

First, as shown in FIG. 1A, a light shielding layer 2 is provided on a transparent substrate 1 and a light shielding pattern is formed by a predetermined lithography process. Then (Fig. 1)
As shown in (b), the etching stopper layer 3 (film thickness 20 to 300 nm), the phase shift layer 4,
The metal thin film layer 5 is provided in this order. Subsequently, an electron beam resist layer 6 is formed by coating, and electron beam overlay drawing 7 is performed under predetermined exposure conditions.

As the material of the etching stopper layer 3, the phase shift layer 4, and the metal thin film layer 5, known thin film forming methods may be used, for example, a sputtering method,
There are vapor deposition method, CVD method, and the like, but the method is not particularly limited thereto.

The optimum value of the film thickness of the phase shift layer 4 is calculated from the above equation (a). For example, the refractive index n is 1.4
7 (SiO ₂ ) and the exposure wavelength λ is 365 nm, the film thickness d of the phase shift layer 4 is about 390 nm. However, since the above effect can be sufficiently obtained even within the range of ± 10 ° with respect to the phase inversion amount of 180 °, the film thickness d is 370 to 4
It is desirable to be in the range of 10 nm. By the way, the film thickness of the metal thin film layer 5 is not particularly limited, but is 5 to 100 n.
It is desirable to be within the range of m.

Next, predetermined development and etching are performed (FIG. 1) to pattern the metal thin film layer 5 as shown in (c). After that (FIG. 1) (d), the phase shift layer 4 is etched using the resist pattern and the metal thin film pattern as a mask. The etching method at this time may be either dry etching or wet etching, but the material of the lower etching stopper layer 3 should withstand it. Further, as shown in FIG. 1E, the remaining resist and the metal thin film pattern are removed to obtain a phase shift mask.

For the metal thin film layer 5, most metal materials can be used only for the purpose of improving the resist adhesiveness.
It must be finally removed in the mask process, and it must be able to be selectively removed with respect to the substrate, the phase shift layer, and the etching stopper layer. Molybdenum, tungsten, tantalum, aluminum, nickel, chromium, molybdenum silicide, or the like can be used.

The transparent substrate 1 is made of an optically transparent material such as synthetic quartz glass generally used for photomasks, and its thickness is not particularly limited, but usually 1.
Those having a thickness of about 5 to 7 mm are used.

The material of the etching stopper layer 3 is properly selected according to the etching method. For example, ceramic materials such as alumina, spinel, zirconia, or sialon can be used for dry etching, while silicon nitride, tin oxide, tantalum oxide, or sialon can be used for wet etching. it can. All of them are materials having high transparency with respect to the exposure wavelength, but are not particularly limited thereto. Further, the etching stopper layer 3 is
Especially for dry etching, a sufficient thickness is required, and a film thickness of about 50 to 300 nm is usually used.

The material of the phase shift layer 4 is required to be optically transparent, and SiO ₂ , SOG (spin on glass), MgF ₂ , fluorine resin, etc. can be used.
If the characteristics required in the mask process are added to the conditions, SiO ₂ is the most suitable material with high transparency, high corrosion resistance, and sufficient cleaning resistance.
O ₂ is used.

The light-shielding layer 2 is usually made of a light-shielding material such as chromium or chromium oxide used in conventional photomasks, but it has a light-shielding property when used in photofabrication for manufacturing semiconductor integrated circuits. Therefore, the optical density is usually set to about 2.0 to 4.0 because it requires an appropriate optical density. Regarding the film thickness, it is usually 20 to 300 nm in accordance with the requirements for the optical density and considering the quality of the film and the burden in the film forming process.
The degree.

At the time of overlay drawing with an electron beam,
A conductive layer is usually required to prevent the charging phenomenon on the substrate, but according to the present invention, the metal thin film layer 5 also functions as a conductive layer due to its inherent conductivity. It is also possible to use an ultraviolet-sensitive photoresist as the resist material here, and in that case, a so-called laser drawing device may be used for drawing.

[0030]

According to the present invention, a metal thin film layer is formed on a phase shift layer made of SiO ₂ (as a new process which has not been found in the prior art), and then a resist layer is applied to form a SiO ₂ film. The adhesiveness between the phase shift layer composed of and the resist layer is extremely good, and therefore, it is possible to prevent the defect of the pattern shape caused by the lack of the pattern or the insufficient adhesion due to the peeling of the resist in the processing steps after the development. .

In general, the metal surface is hydrophobic and has good adhesiveness to the resist. This means that the adhesion of the resist to the metal film such as chromium or molybdenum silicide in the conventional mask process is very good,
It can also be confirmed from the fact that the hydrophobic treatment such as the HMDS treatment is unnecessary.

In addition, since the metal thin film layer has much higher etching resistance than the resist in the dry etching and the wet etching in the etching of the phase shift layer, an accurate etching pattern can be obtained by using this as a mask pattern. .

[0033]

The present invention will be described in more detail below with reference to examples. Cleaned synthetic quartz glass substrate (thickness 2.3m
A low reflection light-shielding film (film thickness 100 nm) in which a metal chromium film and a chromium oxide film are laminated in this order is formed on the entire surface of m and a size of 5 inches (about 12.7 cm) square by a sputtering method. After applying a positive type electron beam resist (manufactured by Chisso, trade name: PBS) to a thickness of about 500 nm and performing a predetermined pre-baking treatment, an acceleration voltage of 10 keV and a dose amount of about 2 using a raster scan type electron beam drawing apparatus. A predetermined pattern was drawn at 0.5 μC / cm ² and then developed to obtain a resist pattern.

After the predetermined post-baking treatment, the resist pattern is used as a masking pattern for etching, and the light-shielding film is wet-etched with a diammonium cerium nitrate etching solution to form a light-shielding pattern. The resist pattern was stripped using a stripping solution to obtain a light-shielding mask having the structure shown in FIG.

Next, an alumina film (thickness: 30 nm) is formed as an etching stopper material on the entire surface of the substrate including the light shielding portion and the transmission portion by a sputtering method, and SiO ₂ (thickness: 390 nm) is formed as a phase shift layer on the alumina film. ) PV
It is formed by the D method, and a molybdenum layer (thickness 5
0 nm) was formed by a sputtering method to obtain a phase shift mask substrate (blanks).

Next, after the substrate is washed and dried by a predetermined method, a positive type electron beam resist (trade name: TTCR manufactured by Toagosei Kagaku Co., Ltd.) is applied on the substrate by a spin coating method for about 50 minutes.
After applying a thickness of 0 nm and performing a predetermined baking treatment, using a vector scan type electron beam drawing device, an accelerating voltage of 20 k
V and a dose amount of about 10 μC / cm ² are overlaid on a predetermined pattern and then drawn with methyl isobutyl ketone and n.
-Development treatment was performed under a predetermined condition using a developing solution composed of a 5: 5 mixed solution with propanol to obtain a desired resist pattern. Then, using the resist pattern as a masking pattern for etching, hydrogen peroxide solution (30
% Aqueous solution) to perform wet etching of the molybdenum layer to form a pattern of the molybdenum layer.

Next, using the resist pattern and the molybdenum layer pattern as a mask, dry etching of the phase shift layer is performed using a parallel plate type reactive ion etching apparatus (RIE apparatus) to obtain good anisotropy and linearity. A phase shift layer pattern having an etching shape and good dimensional reproducibility was obtained.

The dry etching conditions were C ₂ F ₆ gas and H ₂ gas, a mixing ratio of C ₂ F ₆ : H ₂ = 10: 1, a power of 300 W, and a gas pressure of 0.03 Torr. The etching time at this time was about 15 minutes, and etching was performed until the etching of SiO ₂ which was the phase shift layer reached the surface of the etching stopper layer.

After the last remaining resist pattern was removed by using a dedicated stripping solution, the molybdenum layer pattern was removed by using hydrogen peroxide solution (30% aqueous solution). Finally, cleaning and drying were performed to obtain a phase shift mask having the configuration shown in (e) of FIG.

The obtained mask had no abnormalities such as missing of the phase shift pattern, and there was no pattern shape defect which is considered to be caused by poor resist adhesiveness, and a highly accurate pattern shape was obtained. Further, due to the effect of the etching stopper, the uniformity of the etching depth of the phase shift layer in the mask surface was good, and the value within the range of 20 nm or less was obtained.

Further, when this mask was used to perform exposure transfer with a projection exposure apparatus which has been used conventionally, a fine pattern of a minimum of about 0.3 μm was obtained in a resist pattern on a transfer wafer, which was a minimum resolution of 0. A high resolution improving effect was obtained as compared with the case of 5 μm.

Although a positive type electron beam resist is used in this embodiment, it is of course possible to use a negative type electron beam resist.

Although dry etching was used as the etching method for the phase shift layer, wet etching can also be performed. In this case, the etching stopper layer material may be a material having wet etching resistance. Specifically, if the phase shift material is SiO ₂ , wet etching is performed using a buffered hydrofluoric acid solution having a predetermined concentration as an etching solution. It is desirable to use tantalum, silicon nitride, tin oxide, sialon, or the like as the etching stopper material.

[0044]

The phase shift mask obtained by the method of manufacturing a phase shift mask according to the present invention has a very good adhesiveness of the resist pattern. It became possible to have a highly accurate phase shift pattern without any missing pattern due to resist peeling or pattern edge shape defect.

Further, by etching the metal thin film layer pattern as a masking pattern, the pattern reproducibility becomes good, and the etching having good anisotropy becomes possible.

Further, the metal thin film layer acts as a protective film for the phase shift pattern, has the effect of preventing the generation of chipping defects in the phase shift pattern during etching, and also has the effect of preventing defects due to contamination such as contamination. It will be possible.

That is, the method of manufacturing a phase shift mask according to the present invention enhances the adhesiveness between the resist layer and the phase shift layer, suppresses the occurrence of pattern defects, and enables the highly accurate formation of the phase shift pattern. You can now

[Brief description of drawings]

FIG. 1 is an explanatory view showing an outline of a manufacturing process in order using a cross-sectional view of one embodiment of a method of manufacturing a phase shift mask according to the present invention. ((A) to (e))

FIG. 2 is an explanatory diagram showing an example of a method of manufacturing a phase shift mask according to a conventional technique, in order, using a cross-sectional view to schematically show the manufacturing process. ((A) to (d))

[Explanation of sign]

 DESCRIPTION OF SYMBOLS 1 ... Transparent substrate 2 ... Light-shielding layer 3 ... Etching stopper layer 4 ... Phase shift layer 5 ... Metal thin film layer 6 ... Electron beam resist layer 7 ... Electron beam overlay drawing 11 ... Transparent substrate 12 ... Shading layer 13 ... Etching stopper layer 14 ... Phase shift layer 15 ... Electron beam resist layer 16 ... Conductive polymer layer 17 ... Electron beam overlay Combined drawing

Claims (2)

[Claims] 1. A method of manufacturing a phase shift mask comprising a light-shielding portion, a light transmitting portion and a phase shift portion on a transparent substrate, wherein a metal thin film layer is formed on at least a layer of a material forming the phase shift portion. A method of manufacturing a phase shift mask, which comprises forming a resist layer afterward. 2. The method of manufacturing a phase shift mask according to claim 1, wherein the material forming the metal thin film layer is made of molybdenum, tantalum, tungsten, aluminum or nickel.