KR100249726B1 - Phase shift photo mask - Google Patents

Abstract

The present invention is a phase shift photomask using a film made of a material which is excellent in etching selectivity and capable of automatically stopping etching as an etching stopper layer, wherein at least the silicon oxide provided on the substrate and its surface through a light shielding pattern or directly In a phase shift photomask having a phase shifter pattern made of a material, MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , _{BaF 2-2x} O _y , La ₂ on the substrate surface When the phase shifter pattern is formed by etching by providing an etching stopper layer of F _6-2x O _y or Ce ₂ F _6-2x O _y , the transparent film for phase shifter can be etched accurately and accurately by the etching stopper action of this layer. Can be.

Description

Phase shift photo mask

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to photomasks used in the manufacture of high density integrated circuits such as LSIs and ultra-LSIs, and more particularly to a phase shift photomask having a phase shift layer when forming a fine pattern with high precision.

Semiconductor integrated circuits such as ICs, LSIs and ultra-LSIs are manufactured by repeating a so-called lithography process in which a resist is applied on a substrate to be processed, such as a Si wafer, a desired pattern is exposed with a stepper, and then developed and etched. It is becoming.

Photomasks, which are called reticles used in such lithography processes, tend to be increasingly demanded for high performance and high integration of semiconductor integrated circuits. The deviation difference in dimensions in a 5 times reticle, i.e., a reticle having a size 5 times larger than the pattern to be exposed, requires an accuracy of 0.15 占 퐉 even when the average value ± 3σ (σ is the standard difference). The 5-fold reticle for bit DRAMs requires a dimensional accuracy of 0.1 to 0.15 mu m.

In addition, the line width of the device pattern formed using these reticles is increasingly required to be 1.2 μm in 1M bit DRAM, 0.8 μm in 4M bit DRAM and 0.6 μm in 16M bit DRAM. Exposure methods have been studied.

By the way, for example, when it becomes the next-generation device pattern of 64Mbit DRAM class, the resolution limit of a resist pattern will become the resolution of the stepper exposure system using the reticle so far.

Therefore, for example, a reticle of a new method called a phase shift mask as shown in JP-A-58-173744 and JP-A-62-59296 is proposed. Phase shift lithography using this phase shift reticle is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light passing through the reticle.

Phase shift lithography is briefly described with reference to the drawings. 3 is a view showing the principle of the phase shift method, Figure 4 shows a conventional method, Figures 3 (a) and 4 (a) is a cross-sectional view of the reticle, Figures 3 (b) and 4 (b) are reticles 3 (c) and 4 (c) show the amplitude of the light on the wafer, and Figs. 3 (d) and 4 (d) show the light intensity on the wafer, respectively, reference numeral 1 denotes the substrate and 2 the light shielding film. 3 denotes a phase shifter and 4 denotes incident light.

In the conventional method, as shown in Fig. 4A, a light shielding film 2 made of chromium or the like is formed on a substrate 1 made of quartz glass or the like to form a light transmitting portion having a predetermined pattern. In Fig. 3 (a), a phase shifter 3 made of a transmissive film for inverting the phase (phase difference 180 °) is provided on one of the adjacent light transmitting portions on the reticle. Therefore, in the conventional method, the amplitude of the light on the reticle is in the same phase as shown in Fig. 4 (b), and the amplitude of the light on the wafer is in the same phase as shown in Fig. 4 (c). While the patterns on the wafer cannot be separated as described above, in the phase shift lithography, the light transmitted through the phase shifter is formed in opposite phases between adjacent patterns as shown in FIG. As the intensity becomes 0, adjacent patterns can be clearly separated as shown in Fig. 3 (d). In this manner, in phase shift lithography, a pattern that has not been conventionally separated can be separated, thereby improving the resolution.

Next, an example of the manufacturing process of a phase shift reticle is demonstrated, referring drawings.

5 is a cross-sectional view showing the manufacturing process of the phase shift reticle, wherein reference numeral 11 is a quartz substrate, 12 is a chromium film, 13 is a resist layer, 14 is ionizing radiation, 15 is a resist pattern, 16 is an etching gas plasma, 17 Silver chromium pattern, 18 is oxygen plasma, 19 is transparent film, 20 is resist layer, 21 is ionizing radiation, 22 is resist pattern, 23 is etching gas plasma, 24 is phase shift pattern, and 25 is oxygen plasma.

First, as shown in Fig. 5 (a), a chromium film 12 is formed on the optically polished quartz substrate 11, and then ionizing radiation resists such as chloromethylated polystyrene are uniformly prepared by a conventional method such as spin coating. After coating, heat-drying is performed to form a resist layer 13 having a thickness of about 0.1 to 2.0 mu m. The heat drying treatment here is different depending on the type of resist to be used, but is usually performed at ± 80 to 150 ° C for about 20 to 60 minutes.

Next, as shown in Fig. 5B, the resist layer 13 is patterned with ionizing radiation 14 by an exposure apparatus such as an electron beam drawing apparatus in accordance with a conventional method. After developing with a developer mainly composed of an organic solvent of, the substrate is rinsed with alcohol to form a resist pattern 15 as shown in Fig. 5C.

Thereafter, if necessary, heat treatment and descum treatment are performed to remove the pieces of resist or hair-like resist remaining on the edge portion of the resist pattern 15, and then, as shown in Fig. 5 (d). A chrome pattern 17 is formed by dry etching the portion to be exposed through the opening of 15, that is, the chromium layer 12 with the etching gas plasma 16. It is also known to those skilled in the art that the formation of the chromium pattern 17 may be wet etching instead of dry etching by the etching gas plasma 16.

After etching in this manner, as shown in Fig. 5E, the resist pattern 15, i.e., the remaining resist is incinerated and removed by oxygen plasma 18, as shown in Fig. 5F. Complete the photomask. It is also possible to perform this treatment by solvent peeling instead of the ashing treatment by the oxygen plasma 18.

Subsequently, the photomask is inspected and, if necessary, the pattern is corrected and washed, and as shown in FIG. 5 (g), a transparent film 19 made of SiO ₂ or the like is formed on the chromium pattern 17. Next, as shown in Fig. 5 (h), an ionizing radiation resist layer 20 such as chloromethylated polystyrene is formed on the transparent film 19 in the same manner as above, and as shown in Fig. 5 (i), The resist layer 20 is aligned in accordance with a conventional method, and a predetermined pattern is drawn, developed, and rinsed with ionizing radiation 21 such as an electron beam exposure apparatus, as shown in Fig. 5 (j). The resist pattern 22 is formed.

Next, after the heat treatment and the discompression process are necessary, as shown in FIG. 5 (k), the portion of the transparent film 19 exposed through the opening of the resist pattern 22 is dried by the etching gas plasma 23. By etching, the phase shifter pattern 24 is formed.

The phase shifter pattern 24 may be formed by wet etching instead of dry etching by the etching gas plasma 23.

The remaining resist is then incinerated with an oxygen plasma 25 as shown in Fig. 5 (l). By the above process, the phase shift mask which has the phase shifter 24 as shown to FIG. 5 (m) is completed.

By the way, in the conventional method of manufacturing a phase shift reticle as described above, etching control in the depth direction of the transparent film 19 forming the phase shifter must be precise. In particular, since the substrate 11 and the transparent film 19 are made of the same SiO ₂ material, if the etching is continued after the etching of the transparent film 19 is completed, the substrate 11 is also etched so that the phase shift amount of the phase shifter is 180. It becomes larger than °, making it difficult to transfer the correct pattern.

Therefore, the present applicant provides an etching stopper layer between the transparent film forming the phase shifter and the substrate, and automatically stops the etching by this layer. Japanese Patent Application Laid-Open Nos. Hei 2-29801 and Hei 2-181795 As suggested. Materials for etching stopper layers proposed in these applications include tantalum, molybdenum, tungsten, silicon nitride, SnO _2, and the like. Among them, as the etching stopper in the present state is used it is SnO _2. SnO ₂ is widely known as a transparent conductive film. However, SnO ₂ is absorbable in the ultraviolet region and the transmittance is lowered. In order to secure 85% or more of i-ray transmittance, the film thickness needs to be 15 nm or less. In addition, the selectivity with the phase shifter layer is also insufficient to 10 or less.

In addition, it is not necessarily easy to stop the etching accurately so that the etching stopper layer made of such a material is sufficiently satisfied.

This invention is made | formed in view of such a situation, The objective is to provide the phase shift photomask which used the film | membrane of the material which is excellent in etching selectivity and can stop an etching automatically reliably as an etching stopper layer.

1 is a cross-sectional view showing a step of the method of manufacturing a phase shift photomask according to the present invention;

2 is a cross-sectional view showing a manufacturing process of another phase shift photomask according to the present invention;

3 shows the principle of the phase shift method;

3 shows a conventional method;

4 is a view showing a manufacturing process of a conventional phase shift photomask.

In view of the above problems, the present invention has been conducted to develop a phase shifter of a practical and highly accurate phase shift reticle. As a result, a metal fluoride is formed by mixing oxygen with an inert gas as a sputter gas and sputtering therein. The oxide film was found to have almost the same etching selectivity as the metal fluoride, so that the transparency was good and the hardness was high in the ultraviolet region, thereby completing the present invention.

That is, the phase shift photomask of the present invention in at least the substrate and its surface the phase shifter pattern is a phase shift photomasks with silicon oxide through the light-shielding pattern, or directly installed from a material containing as a main component to, MgF the surface of the substrate _{2 Consisting of a film of -2x} O _y , CaF _2-2x O _y , LiF _2-2x O _y , _{BaF 2-2x} O _y , La ₂ F _6-2x O _y , or Ce ₂ F _6-2x O _y It is characterized by.

The phase shift photomask of the present invention is an etching stopper layer between a substrate and a protective film for phase shifter, MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , _{BaF 2-2x} O _y , La ₂ F _6-2x O _y or Ce ₂ F _6-2x O _y is provided. Metal fluorides such as MgF ₂ are known as materials having good transmittance at short wavelengths. Even with a substrate having a thickness of about 1 mm, i-line transmittance is 93% or more and KrF laser light transmittance is 92% or more. When MgF ₂ is normally used as an etching stopper layer, a sputter using an inert gas such as Ar is used with a metal fluoride such as MgF ₂ as a target. At this time, the film formed on the substrate becomes a film containing many metal components, and the film thickness is reduced to about 62% of i-line transmittance and 50% of KrF laser transmittance at a thickness of 100 nm. In order to prevent this, it is conceivable to form a reactive sputter in which fluorine gas is mixed with an inert gas. However, since fluorine gas is a corrosive gas, practical use is not possible due to the problem of device corrosion.

The present invention provides a practical etching stopper in which MgF _2-2x O _y is produced by incorporating and sputtering oxygen into an inert gas as a sputter gas, and selectivity with a phase shifter such as MgF ₂ , i-ray transmittance, and KrF laser light transmittance are obtained. It is also characterized by the possibility of producing the layer.

Hereinafter, an embodiment of the phase shift photomask of the present invention will be described with reference to a manufacturing method of the phase shift photomask.

1 is a cross-sectional view showing a step of a method for manufacturing a photomask (phase shift photomask) having a phase shift layer of the present invention, the drawing reference numeral 30 represents a substrate, 31 is _2-2x O _y MgF, CaF _2-2x An etch stopper layer of O _y , LiF _2-2x O _y , _{BaF 2-2x} O _y , La ₂ F _6-2x O _y , or Ce ₂ F _6-2x O _y , 32 is a light shielding layer, 33 is a resist layer , 34 is ionizing radiation, 35 is resist pattern, 36 is etching gas plasma, 37 is shading pattern, 38 is oxygen plasma, 39 is transparent film, 40 is resist layer, 41 is ionizing radiation, 42 is resist pattern, 43 is reactive 44 denotes a phase shift pattern, and 45 denotes an oxygen plasma.

First, in FIG. 1A, a light shielding layer 32 having a thickness of 10 to 200 nm is sequentially formed on an optically polished substrate 30, and an ionizing radiation resist such as chloromethylated polystyrene is spin-coated. It is uniformly applied by the method and heat-dried to form a resist layer 33 having a thickness of about 0.1 to 2.0 mu m. Here, the substrate 30 is preferably quartz or high-purity synthetic quartz, considering that the phase shift mask is for short wavelengths such as i-rays or excimer lasers, but in addition, low expansion glass, white plate, blue plate (SL), MgF ₂ , CaF ₂ Etc. can be used. The etching stopper layer 31 may include MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , _{BaF 2-2x} O _y , La ₂ F _6-2x O _y , or Ce ₂ F ₆ Can be formed using _-2x O _y . Herein, _x is in a range of 0.01 to 0.5, and _y is preferably in a range of _y ≦ _x . When argon is used as the sputter gas, _x and _y in this range are obtained by mixing 50% or less of oxygen. The i-line transmittance at this time was 92%, the KrF laser light transmittance at 90%, and the etching selectivity with SOG was 120.

In addition, the light shielding layer 32 may be formed by forming a chromium thin film in a single layer or a multilayer, but may be formed using chromium nitride, chromium oxide, tungsten, molybdenum, molybdenum silicide, or the like. In addition, although the heat-drying process of a resist changes with kinds of resist, it is usually performed for about 5 to 60 minutes at 80-200 degreeC.

Next, as shown in Fig. 1 (b), a predetermined pattern is drawn on the resist layer 33 by an exposure apparatus by ionizing radiation 34 such as an electron beam drawing apparatus in accordance with a conventional method, and ethyl cellosol After developing with a developer mainly composed of organic solvents such as bromine or ester, and rinsing with alcohol, a resist pattern 35 as shown in Fig. 1C is formed.

Thereafter, if necessary, heat treatment and decompression are performed to remove the pieces of the resist remaining in the edge portions of the resist pattern 35 and the unnecessary resist in the form of hairs. Then, as shown in Fig. 1 (d), the resist pattern ( The light-shielding pattern 37 is formed by dry etching the part to be exposed from the opening of the opening 35, that is, the light shielding layer 32 with the etching gas plasma 36. The light shielding pattern 37 may be formed by wet etching instead of dry etching by the etching gas plasma 36.

After etching in this manner, as shown in FIG. 1 (e), the remaining resist 35 is removed by incineration with an oxygen plasma 38 to etch the stopper on the substrate 30 as shown in FIG. 1 (f). The photomask in which the layer 31 is formed and the predetermined light shielding pattern 37 was formed on it is created. This treatment can also be performed by solvent peeling instead of the incineration treatment by the oxygen plasma 38.

Subsequently, the photomask is inspected and, if necessary, the pattern is corrected and washed, and as shown in FIG. 1 (g), a transparent film containing SiO ₂ as a main component by vapor deposition on the light shielding pattern 37 and SOG is shown. Form 39. The film thickness d of the transparent film 39 is a value given by d = λ / 2 (n-1) when the refractive index of the material forming the transparent film 39 is n and the exposure wavelength is λ. If n = 1.45 and? = 365 nm, the value of d is about 406 nm.

Next, as shown in Fig. 1B, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied on the transparent film 39 to form a resist layer 40, and Fig. 1 As shown in (i), the resist layer 40 is aligned in accordance with a conventional method, and a predetermined pattern is drawn at a position where the phase should be shifted by ionizing radiation 41 such as an electron beam exposure apparatus. The resist pattern 42 is formed by developing and rinsing as shown in Fig. 1 (j).

Subsequently, after the heat treatment and the discompression process are necessary, as shown in Fig. 1 (k), portions of the transparent film 39 exposed through the openings of the resist pattern 42 are CF ₄ , C ₂ F ₆ , The phase shift pattern 44 is formed by dry etching by reactive ion etching with CHF ₃ + O ₂ and reactive ions 43 using these mixed gases.

At this time, in the conventional method, the etching reaches the substrate 30, which makes it difficult to determine the end point of the etching, or the substrate 30 is also etched, so that the phase shift amount of the phase shifter becomes larger than 180 °, making it difficult to transfer the correct pattern. but is, in the present invention large, the etching resistance to the reactive ion of the fluorine, the transparency, and hardness superior _2-2x O _y MgF, CaF _2-2x O _{y, y} O _2-2x LiF, BaF _2-2x O _{Since y} , La ₂ F _6-2x O _y , or Ce ₂ F _6-2x O _y is used as the etching stopper layer 31, the transparent film 39 can be reliably etched and stopped automatically by etching. It is possible to create a higher quality phase shift photomask.

Next, as shown in FIG. 1 (l), the remaining resist is incinerated with an oxygen plasma 45. This completes a highly accurate phase shift photomask as shown in Fig. 1 (m). In addition, this process can also be performed by solvent peeling instead of the ashing process by the oxygen plasma 45. FIG.

Such an etching stopper layer is not limited to the phase shift photomask of the type placed on the phase shifter as shown in FIG. 3, but can also be applied to the phase shift photomask of the type placed below the phase shifter. As an example, the case where the present applicant applies this etching stopper layer to the self-aligned phase shift photomask proposed in Japanese Patent Application No. Hei 2-181795 will be briefly described below.

2 is a cross-sectional view showing a manufacturing process of another phase shift photomask, wherein 50 is a substrate, 51 is MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , and _{BaF 2-} An etch stopper layer of _2x O _y , La ₂ F _6-2x O _y , or Ce ₂ F _6-2x O _y , 52 is a transparent film, 53 is a light-shielding thin film, 54 is a resist layer, 55 is a resist pattern, 56 Silver ionizing radiation, 57 an etching gas plasma, 58 a light shielding pattern, 59 an oxygen plasma, 60 a resist layer, 61 a back exposure, 62 a reactive ion, 63 a phase shifter pattern, and 64 an oxygen plasma.

First, as shown in Fig. 2 (a), the film thickness d = lambda / 2 (mainly composed of SiO ₂ as a main component and a uniform etching stopper layer 51 of 10 to 200 nm thickness on the optically polished substrate 50). The transparent film 52 of n-1) and the light shielding layer 53 of 50-200 nm are formed sequentially, and a photomask blank is comprised.

Subsequently, a cell radiation resist such as chloromethylated polystyrene is uniformly applied on the photomask blank by a conventional method such as spin coating, and heat-dried to form a resist layer 54 having a thickness of about 0.1 to 2.0 mu m. do.

As the substrate 50, it is preferable to use quartz, high purity quartz, MgF ₂ , CaF _2, or the like, considering that the phase shift mask of the present invention is usually for short wavelengths such as i-rays or excimer lasers. However, in the case of longer wavelength than that, low expansion glass, white glass, blue glass or the like may be used. In addition, the etching stopper layer 51 is the same as in the case of Figure 1 MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , _{BaF 2-2x} O _y , La ₂ F _6-2x O _y Or Ce ₂ F _6-2x O _y . Here, _x is 0.5 and _y is preferably in a range of _y ≦ _x . The transparent film 52 is preferably a high purity SiO ₂ film, and a coating method of the film by sputtering, CVD, or SOG (for example, spin coating and heating siloxne to form a SiO ₂ film) is adopted. . The light shielding layer 53 can be formed by forming a film of chromium, chromium nitride, chromium oxide, tungsten, molybdenum, molybdenum silicide or the like in a single layer or multiple layers.

In addition, although the heat-drying process of a resist changes with kinds of resist, it normally performs about 5 to 60 minutes at 80-200 degreeC.

Next, as shown in Fig. 2B, a predetermined pattern is drawn on the resist layer 54 by an exposure apparatus using ionizing radiation 56, such as an electron beam drawing apparatus, according to a conventional method, and ethyl cellosol After developing with a developer containing organic solvents such as bromine or ester as a main component and rinsing with alcohol, a resist pattern 55 as shown in Fig. 2C is formed.

Subsequently, heat treatment and discombing are performed as necessary to remove the pieces of the resist and the hair-like resist remaining in the edge portions of the resist pattern 55 and the like, and as shown in Fig. 2C, the resist pattern 55 The light-shielding pattern 58 is formed by dry etching the workpiece, i.e., the light shielding layer 53, exposed through the opening of the () with the etching gas plasma 57 (FIG. 2 (d)). The light shielding pattern 58 may be formed by wet etching instead of dry etching by the etching gas plasma 57.

After etching in this manner, as shown in FIG. 2 (d), the remaining resist 55 is quenched and removed by oxygen plasma 59 to etch stopper on the substrate 50 as shown in FIG. 2 (e). The layer 51 is formed, the phase shift layer 52 is formed thereon, and the photomask in which the predetermined light shielding pattern 58 was formed is formed on it. In addition, the removal process of the remaining resist 55 can also be performed by solvent peeling instead of the ashing process by oxygen plasma 59. FIG.

Subsequently, the photomask is inspected and, if necessary, the pattern is corrected and washed, and then, as shown in FIG. 2 (f), a photoresist such as OFPR-800 or the like is spin-coated on the light shielding pattern 58. It is uniformly applied by the method of the following and heat-drying process to form a resist layer 60 of about 1 to 2㎛ thickness.

Subsequently, on the glass substrate 50 side, the resist layer 60 is back-exposed 61, developed with an aqueous alkali solution containing tetramethyl ammonium hydroxide as a main component, and rinsed with pure water to shield the light shielding pattern 58 ) Forms a pattern on which a resist pattern is placed.

Next, as shown in Fig. 2 (g), the portion to be processed exposed from the opening of the resist pattern, that is, the phase shift layer 52, is CF ₄ , C ₂ F ₆ , CHF ₃ + O ₂ and mixed gas thereof. Dry etching is performed by reactive ion etching with reactive ions 62 using to form a phase shifter pattern 63 (Fig. 2 (h)).

Subsequently, the substrate is treated with an etchant mainly composed of second cerium ammonium acetate to side-etch the light shielding film 58 sandwiched between the phase shifter 63 and the resist 60. Although this side etching amount changes with kinds and sizes of patterns, it is about 0.1-0.5 micrometer normally.

After etching in this manner, as shown in FIG. 2 (i), the remaining resist 60 is inversely removed by oxygen plasma 64 to complete a self-aligned phase shift mask as shown in FIG. 2 (j). do.

Also in this case, as in the case of FIG. 1, MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , _{BaF 2-which} have high etching resistance, excellent transparency, and hardness to the fluorine-based reactive ions. _{Since 2x} O _y , La ₂ F _6-2x O _y , or Ce ₂ F _6-2x O _y is used as the etching stopper layer 51, the transparent film 52 can be reliably etched and automatically The etching can be stopped to produce a higher quality phase shift photomask.

Although the phase shift photomask of this invention was demonstrated based on the Example, this invention is not limited to this Example, A various deformation | transformation is possible. In addition, the type of the phase shift photomask to which the etch stopper layer of the material can be applied is not limited to the above example, but may be applied to any conventionally known type, for example, a half-tone phase shift photomask. have.

In the phase shift photomask of the present invention, MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , _{BaF 2-2x} O _y , La ₂ F _6-2x O _y , Alternatively, since a film of Ce ₂ F _6-2x O _y is provided, when forming the phase shifter pattern by etching, MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , _{BaF 2-2x} Since O _y , La ₂ F _6-2x O _y , or Ce ₂ F _6-2x O _y act as an etching stopper layer, it is possible to reliably etch the transparent film for the phase shifter, and the etching can be stopped automatically. It becomes a higher quality phase shift photomask.

In addition, since the film has good transparency in the ultraviolet region, the film is suitable for a phase shift photomask using ultraviolet rays and has a high hardness, and thus the phase shift photomask prepared in this way has a low deterioration caused by the environment and thus has a long life.

Claims (1)

A phase shift photomask comprising at least a substrate and a phase shifter pattern made of a material mainly composed of silicon oxide provided directly or through a light shielding pattern on the surface thereof, the MgF _2-2x O _y , CaF _2-2x O formed on the surface of the substrate. A phase shift photomask comprising a film of _y , LiF _2-2x O _y , _{BaF 2-2x} O _y , La ₂ F _6-2x O _y , or Ce ₂ F _6-2x O _y .