JPH04356050A - Production of photomask having phase shift layer - Google Patents

Abstract

PURPOSE:To produce a phase shift reticule having high accuracy by eliminating the degradation in resolution and fluctuation in sizes by the conductive films provided in order to prevent charge-up. CONSTITUTION:This process for producing the photomask having the phase shifter layers consists in forming a resist thin film 35 on a substrate 31 formed with a phase shifter layer 34 on the photomask, plotting patterns on this resist thin film 35 by ionization radiations 37, developing the resist thin film 35 after patter plotting to form resist patterns, and etching the exposed phase shifter layer 34 with such resist patterns as a mask, then removing the remaining resist. The conductive thin film 36 is formed in order to prevent charge-up by a Langmuir-Blodgett's technique on or below the resist thin film 35 and thereafter, the patterns are plotted by the ionization radiation 37.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a photomask used in the manufacture of high-density integrated circuits such as LSIs and VLSIs, and a method of manufacturing the same, and particularly relates to a phase shift when forming fine patterns with high precision. The present invention relates to a method of manufacturing a photomask having layers.

0002

[Prior Art] Semiconductor integrated circuits such as ICs, LSIs, and VLSIs are manufactured by coating a resist on a substrate to be processed such as a Si wafer, exposing a desired pattern using a stepper, etc., and then developing and etching it. It is manufactured by repeating the lithography process.

Photomasks called reticles used in such lithography processes tend to be required to have higher precision as semiconductor integrated circuits become more sophisticated and highly integrated. DRA which is LSI
Taking M as an example, the dimensional deviation of a 5x reticle for a 1M bit DRAM, that is, a reticle with a size 5 times the size of the pattern to be exposed, is the average value ± 3σ (σ is the standard deviation). Similarly, a 5x reticle for 4 Mbit DRAM requires a dimensional accuracy of 0.1 to 0.15 μm, and a 5x reticle for 16 Mbit DRAM requires a dimensional accuracy of 0.05 to 0.1 μm. dimensional accuracy is required.

Furthermore, the line width of device patterns formed using these reticles is 1 Mbit DRAM.
1.2μm for 4M bit DRAM, 0.8μm for 1
In 6 Mbit DRAM, there is a demand for further miniaturization of 0.6 μm, and in order to meet such demands, various exposure methods are being researched.

However, when it comes to next-generation device patterns, such as those in the 64M DRAM class, the conventional stepper exposure method using a reticle reaches the resolution limit of the resist pattern, and in order to overcome this limit,
For example, JP-A-58-173744, JP-A-62
A reticle based on a new concept called a phase shift mask has been proposed, as shown in Japanese Patent No. 59296 and the like. Phase shift lithography using a phase shift reticle is a technique that improves the resolution and contrast of a projected image by manipulating the phase of light transmitted through the reticle.

Phase shift lithography will be briefly explained with reference to the drawings. FIG. 5 is a diagram showing the principle of the phase shift method,
FIG. 6 is a diagram showing the conventional method, and FIGS. 5(a) and 6(a)
) is a cross-sectional view of the reticle, FIGS. 5(b) and 6(b) are the amplitudes of light on the reticle, FIGS. 5(c) and 6(c) are the amplitudes of light on the wafer, and FIG. 5(d) And FIG. 6(d) shows the light intensity on the wafer, where 1 is the substrate, 2 is the light shielding film,
3 indicates a phase shifter, and 4 indicates incident light.

In the conventional method, as shown in FIG. 5(a), a light-shielding film 2 made of chromium or the like is formed on a substrate 1 made of glass or the like, and a light-transmitting part in a predetermined pattern is formed. However, in phase shift lithography,
As shown in FIG. 5A, a phase shifter 3 made of a transmission film for inverting the phase (180° phase difference) is provided on one of the adjacent light transmission parts on the reticle. Therefore, in the conventional method, the amplitudes of the lights on the reticle are in phase as shown in FIG. 6(b), and the amplitudes of the lights on the wafer are also in phase as shown in FIG. 6(c). While it is not possible to separate the patterns on the wafer as shown in Fig. 6(d), in phase shift lithography, the light transmitted through the phase shifter is separated as shown in Fig. 5(b).
As shown in Fig. 5, since the adjacent patterns are made in opposite phases to each other, the light intensity becomes zero at the pattern boundary, and as shown in Fig.
Adjacent patterns can be clearly separated as shown in (d). In this way, in phase shift lithography, patterns that could not be separated in the past can be separated, and resolution can be improved.

Next, an example of a conventional manufacturing process for a phase shift reticle will be explained with reference to FIG. 7. FIG. 7 is a cross-sectional view showing a manufacturing process for a phase shift reticle, as shown in FIG. First, a completed chrome reticle with a chrome pattern 6 provided on a substrate 5 is prepared, and then, as shown in FIG. do. Next, as shown in the figure (c), an ionizing radiation resist layer 8 such as chloromethylated polystyrene is formed on the transparent film 7, and as shown in the figure (d), the resist layer 8 is coated in a conventional manner. After alignment, a predetermined pattern is drawn using ionizing radiation 9 from an electron beam exposure device, developed, and rinsed to form a resist pattern 10 as shown in FIG.

Next, after performing heat treatment and descum treatment as necessary, the portion of the transparent film 7 exposed from the opening of the resist pattern 10 is dried with an etching gas plasma 11, as shown in FIG. Etching is performed to form a phase shifter pattern 12. Note that this phase shifter pattern 12 is formed using etching gas plasma 1.
Instead of the dry etching according to No. 1, wet etching may be used.

Next, the remaining resist is removed by ashing with oxygen plasma 13, as shown in FIG. 2(g). Through the above steps, a phase shift photomask having a phase shifter 12 as shown in FIG. 3(h) is completed.

[0011]

However, in the conventional method of manufacturing a phase shift mask as shown in FIG. In order to
When drawing a pattern on the resist layer 8 using ionizing radiation 9 from an electron beam exposure device, the pattern is drawn on the ionizing radiation resist layer 8, which is also a non-conductive material, on the base material 5 made of a non-conductive material such as glass. Therefore, there is a problem in that charge-up development due to the ionizing radiation 9 occurs and pattern accuracy decreases.

[0012]Currently, therefore, a method is used in which a conductive resin is applied on the resist layer by spin coating to prevent charge-up. In the manufacturing method, the thickness of the conductive film is 100 to 300
The film thickness becomes as thick as 5 nm, and the film thickness uniformity (±5 nm)
) is also poor, resulting in problems such as poor resolution of the resist layer and large in-plane dimensional variations. Furthermore, regarding coating technology, for example, when applying an organic solvent-based conductive polymer onto a water-soluble resist using a spin coating method, it is necessary to use a water-soluble intermediate layer such as polyvinyl alcohol. This requires additional steps and increases the film thickness, which also poses problems such as poor resolution of the resist layer.

By the way, apart from this, there is a Langmuir-Blodgett (hereinafter referred to as LB) method, which is a thin film forming method that has attracted attention in recent years. The characteristics of this method are (1
) It is possible to obtain ultra-thin organic films on the molecular order.

(2) It is possible to control molecular orientation and molecular arrangement.

(3) It is possible to easily form a heterolayer membrane in which different molecules are arranged alternately.

(4) The film can be formed at normal temperature and pressure.

[0017] etc. Since unique molecular arrangement control is possible in this way, excellent ultra-thin films with high functionality are produced by using LB films.

The present invention has been made in view of the above circumstances, and an object thereof is to effectively prevent the charge-up phenomenon when forming a phase shifter of a phase shift reticle by using a specific conductive film. A photomask with a phase shift layer that eliminates pattern distortion caused by the phenomenon, and also eliminates the reduction in resolution and dimensional variation caused by the conductive film to eliminate the charge-up phenomenon, making it possible to manufacture a high-precision phase shift reticle. An object of the present invention is to provide a manufacturing method.

[0019]

[Means for Solving the Problems] In view of the above-mentioned problems, the present invention has been made as a result of research to obtain a phase shift mask that enables ultra-fine photolithography. The present inventors discovered that a phase shift mask with higher precision can be manufactured by using this method, and based on this knowledge, they completed the present invention.

[0020] Conventional antistatic conductive layers have been applied by spin coating, so the molecular arrangement has been random. For example, if a charge transfer complex of the conductive compound tetracyanoquinodimethane (TCNQ) is simply dispersed in a polymer, it is difficult to control the molecular arrangement and the distance between molecules, and as a result, its conductivity is low. However, in order to obtain the conductivity necessary to prevent the charge-up phenomenon during electron beam exposure, the film had to be thick (100 to 200 nm). However, if this conductive compound is incorporated into the LB film, the distance between its molecular arrangements can be controlled, and since the aromatic rings of the conductive compound exist in parallel on the same plane, a thin film (2.5 to 25 nm) can be used. High conductivity and conductive anisotropy in the in-plane direction of the film can be obtained even if the film is present. In addition, in the LB method, it is possible to arrange molecules one layer at a time, so the effect as an antistatic film can be exhibited without deteriorating the performance of the resist, such as sensitivity, resolution, resist dimensions, etc.

Furthermore, since the conductive compound used here is amphiphilic, the conductive layer can be coated with either water-soluble or lipophilic resist without any intermediate layer.

A method for manufacturing a phase shift photomask using a conductive film coated by the LB method of the present invention will be described below with reference to FIG.

FIG. 2 shows N-docosylpyridinium (TCNQ), which is an example of a conductive compound used in manufacturing the phase shift photomask of the present invention.
It is 2. Other organic conductive materials include polyacetylene, polythiophene, polypyrrole, polythiazyl, polyazulene, polyindene, polyindole, polyparaphenylene, polynaphthylene, polyanthracene, polyaniline, polyphthalocyanine, polyferrocene, and the like.

FIG. 1 is a cross-sectional view showing the process of manufacturing a photomask having a phase shift layer according to the present invention, in which 31 is a substrate, 32 is a chrome pattern, 33 is an alignment mark, and 34 is a phase shift film. , 35 is an ionizing radiation resist, 36 is a conductive layer, 37 is an ionizing radiation, 38 is an exposed portion, 39 is an etching gas plasma, and 40 is an oxygen plasma.

First, a spin-on glass (
A SiO2 film is formed as the shifter layer 34 by SOG) or sputtering (FIG. (a)). continue,
An ionizing radiation resist is uniformly applied onto this phase shifter layer 34 by a conventional method such as spin coating, and then heated and dried to form a resist layer 35 with a thickness of about 0.1 to 2.0 μm (see Fig. b)). The heat drying treatment is usually carried out at 80 to 200° C. for about 20 to 60 minutes, although it depends on the type of resist used. Next, a conductive layer 36 having a thickness of about 0.0025 to 0.4 μm is formed on this resist layer 35 by the LB method. The heat drying treatment is usually performed at 60 to 100° C. for 2 to 60 minutes, although it depends on the type of conductive layer 36.

Next, as shown in FIG. 3C, alignment is performed on the resist layer 35 according to a conventional method, and a pattern is drawn with ionizing radiation 37 using an exposure device such as an electron beam drawing device. At this time, since the conductive layer 36 formed on the resist film 35 grounds the excess charge, alignment marks can be easily detected, and there is no charge-up phenomenon, allowing highly accurate drawing. Note that the same effect can be obtained even if the conductive layer 36 is formed under the resist layer 35.

Subsequently, the conductive layer 36 is peeled off with an organic solvent such as chloroform, developed with a prescribed developer, and rinsed with a prescribed rinsing liquid to form a resist pattern 38 as shown in FIG. form (conductive layer 36 and resist layer 35
If formed under , the order is reversed. ).

Next, after performing a heat drying process and a descum process as necessary, the portion of the transparent film 34 exposed from the opening of the resist pattern 38 is etched with an etching gas plasma 39, as shown in FIG. Dry etching is performed to form a phase shifter pattern 34 (FIG. 3(e)).
. It is clear to those skilled in the art that the phase shifter pattern 34 may be formed by wet etching instead of dry etching using the etching gas plasma 39.

Next, the remaining resist is removed by ashes using oxygen plasma 40, as shown in FIG. 4(f).

Through the above steps, a phase shift mask having a phase shifter 34 as shown in FIG. 3(g) is completed.

The phase shift pattern thus formed becomes a high quality phase shift photomask free from positional deviation and precision deterioration due to charge-up phenomenon during pattern exposure.

[0032] Here, a method for forming the LB conductive film used for the conductive layer 36 will be explained. A conductive compound as shown in FIG. 2 is spread on a water surface as a chloroform solution to form a monomolecular film. A cumulative film of this monomolecular film is formed on a resist layer 35 for patterning the shifter layer 34 by a vertical dipping method as shown in FIG. 3 or a horizontal adhesion method as shown in FIG.

To explain the vertical immersion method, Fig. 3(a)
) to (c), the hydrophobic group 21 and the hydrophilic group 22
When the substrate 25 that has been hydrophobized with iron stearate or the like is immersed perpendicularly to the liquid surface while applying piston pressure 24 to the surface of the lower water 23 on which a monomolecular film has been formed, the surface of the hydrophobic group 21 is The monomolecular film is transferred toward the substrate 25 side. Also, the membrane is not transferred when it is pulled up. Such a film is called an X film. As shown in FIGS. 3(d) to 3(f), a film that is transferred both during immersion and during pulling up is referred to as a Y film. Also, FIGS. 3(g) to (i)
As shown in Figure 2, a film in which no film is attached during immersion and is removed only when pulled up is called a Z film.

Further, to explain the horizontal adhesion method,
As shown in FIGS. 4(a) to 4(d), the first partition wall 2
After applying piston pressure 24 to the monomolecular film formed on the water surface divided by 6 and horizontally contacting the monomolecular film with the substrate 25 to attach the hydrophobic groups 21 to the surface of the substrate 25 (a), The second partition wall 27 is moved to the part opposite to the part in contact with the first partition wall 26 and the substrate 25 is pulled up (b, c
)). Next, in method (d), operations (a) to (c) are repeated to form a cumulative film having a predetermined thickness. In this case, only the X film is formed.

As described above, in the method of manufacturing a photomask having a phase shift layer of the present invention, a resist thin film is formed on a substrate on which a phase shifter layer is formed on the photomask, and this resist thin film is exposed to ionizing radiation. A phase shift process in which a pattern is drawn using a lithography system, the resist thin film after pattern drawing is developed to form a resist pattern, the exposed phase shifter layer is etched using this resist pattern as a mask, and the remaining resist is removed after etching is completed. A method for producing a photomask having layers, the method is characterized in that a conductive thin film is formed on or below the resist thin film by the Langmuir-Blodgett method, and then a pattern is drawn using ionizing radiation.

In this case, the Langmuir-Blodgett conductive thin film formation may be carried out by a vertical dipping method or by a horizontal deposition method.

[0037]

[Operation] Photomasks are currently routinely manufactured by electron beam lithography using electron beam exposure equipment, but with the recent increase in the integration of LSIs and VLSIs, they are becoming more and more accurate. This is required, and even when performing electron beam drawing on chrome substrates, a slight drop in accuracy due to charge-up has become a problem.

Furthermore, if such a photomask is replaced by a phase shift mask, it is expected that the accuracy in forming a phase shifter due to charge-up will be significantly degraded.

In the present invention, a conductive layer is formed by the LB method on or under a resist film formed on a substrate to be processed, and ionizing radiation drawing when creating a phase shifter pattern can be performed with high precision without charging up the substrate. It is possible to stably manufacture a highly accurate phase shift reticle without significantly changing the conventional photomask manufacturing process using ionizing radiation beam lithography.

[0040]

[Examples] Examples of the present invention will be described below.

Example 1 N-docosylpyridinium (TCNQ) shown in FIG.
2 The amphiphilic compound was dissolved in chloroform to obtain a 1 mM conductive film solution. Next, this conductive film solution was spread on the water surface to form a monomolecular film at a surface pressure of 30 mN/m. Four layers (thickness: 10 nm) of this monomolecular film were accumulated on a resist layer previously applied to a chromium substrate by a vertical dipping method. The obtained film was heated on a hot plate at 80° C. for 2 minutes to form a conductive film. Next, a pattern was drawn by irradiating the resist film composed of this resist layer and the conductive film with an electron beam having a beam diameter of 0.25 μm and an energy of 10 keV. At this time, since an ultra-thin conductive layer was formed on the resist film by the LB method, it was possible to draw a pattern without positional deviation, alignment marks were easy to detect, and no charge-up phenomenon occurred.

[0042] This was immersed in chloroform for 2 minutes to remove the conductive film, and then the resist was developed with an ordinary developer and rinsed with pure water to form a resist pattern. Next, after descum processing, the phase shifter layer made of SOG is etched with an etching solution made of hydrofluoric acid and ammonium fluoride, and the remaining resist is ashed with oxygen plasma of 0.3 torr and 500 W to obtain a phase shifter pattern. Ta.

The phase shift pattern thus formed is free from positional deviation and precision deterioration due to charge-up phenomenon during pattern exposure, and is free from a decrease in resist sensitivity and a reduction in resist sensitivity compared to the case of using a conductive film formed by conventional spin coating. No reduction in size was observed.

[0044]

As explained above, according to the method of manufacturing a photomask having a phase shift layer of the present invention, a conductive layer is formed by the LB method on or under a resist film formed on a substrate to be processed, It is possible to perform ionizing radiation drawing with high accuracy when creating a phase shifter pattern without charging up the substrate, and it is possible to perform high-precision drawing without significantly changing the photomask manufacturing process using conventional ionizing radiation beam lithography. It becomes possible to stably manufacture a phase shift reticle.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing steps in a method for manufacturing a photomask having a phase shift layer according to the present invention.

FIG. 2 is a diagram showing the structure of one example of a conductive compound used in the present invention.

FIG. 3 is a diagram showing a method of accumulating an LB film by a vertical dipping method.

FIG. 4 is a diagram showing a method of accumulating an LB film by a horizontal deposition method.

FIG. 5 is a diagram showing the principle of the phase shift method.

FIG. 6 is a diagram showing a conventional method.

FIG. 7 is a cross-sectional view showing the manufacturing process of a conventional phase shift photomask.

[Explanation of symbols]

31...Substrate 32...Chrome pattern 33...Alignment mark 34...Phase shift film 35...Ionizing radiation resist 36...LB method formed conductive layer 37...Ionizing radiation 38...Exposed part 39...Etching gas plasma 40...Oxygen plasma

Claims (3)

[Claims] 1. A resist thin film is formed on a substrate on which a phase shifter layer is formed on a photomask, a pattern is drawn on this resist thin film using ionizing radiation, and the resist thin film after pattern drawing is developed to form a resist pattern. A method for manufacturing a photomask having a phase shift layer, in which the exposed phase shifter layer is etched using the resist pattern as a mask, and the remaining resist is removed after the etching is completed. - A method for manufacturing a photomask having a phase shift layer, which is characterized by forming a conductive thin film using the Blodgett method and then drawing a pattern using ionizing radiation. 2. The method of manufacturing a photomask having a phase shift layer according to claim 1, wherein the Langmuir-Blodgett conductive thin film is formed by a vertical dipping method. 3. The method of manufacturing a photomask having a phase shift layer according to claim 1, wherein the Langmuir-Blodgett conductive thin film is formed by a horizontal deposition method.