JP3210705B2 - Phase shift photomask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used for manufacturing high-density integrated circuits such as LSIs and VLSIs, and more particularly to a phase shifter having a phase shift layer for forming a fine pattern with high precision. It relates to a shift photomask.

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs apply a resist on a substrate to be processed such as a Si wafer, expose a desired pattern by a stepper or the like, and then perform development and etching. It is manufactured by repeating a lithography process.

A photomask called a reticle used in such a lithography process tends to be required to have higher and higher precision in accordance with higher performance and higher integration of a semiconductor integrated circuit. DRA which is LSI
Taking M as an example, the dimensional deviation of a 5 × reticle for a 1M bit DRAM, that is, a reticle having a size 5 times the size of a pattern to be exposed, is an average ± 3σ (σ is a standard deviation). Also, an accuracy of 0.15 μm is required. Similarly, a quintuple reticle for a 4 Mbit DRAM has a dimensional accuracy of 0.1 to 0.15 μm,
5x reticle for bit DRAM is 0.05-0.1μm
Dimensional accuracy is required.

Furthermore, the line width of a device pattern formed using these reticles is 1 Mbit DRAM.
1.2 μm, 0.8 μm for 4 Mbit DRAM, 1 μm
A 6-Mbit DRAM is required to be further miniaturized to 0.6 μm, and various exposure methods are being studied to meet such a demand.

However, in the case of the next-generation device pattern of, for example, a 64-Mbit DRAM class, the resolution of a resist pattern is limited by the conventional stepper exposure method using a reticle.
No. 44, Japanese Patent Publication No. 62-59296, and the like, a reticle based on a new concept called a phase shift mask has been 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.

[0006] Phase shift lithography will be briefly described with reference to the drawings. FIG. 3 is a diagram showing the principle of the phase shift method,
FIG. 4 is a view showing a conventional method, and FIG. 3 (a) and FIG.
(A) is a cross-sectional view of the reticle, and (b) and (b) of FIG.
3 (c) and 4 (c) show the light amplitude on the wafer, and FIGS. 3 (d) and 4 (d) show the light intensity on the wafer, respectively. A substrate 2, a light shielding film 3, a phase shifter 3, and an incident light 4 are shown.

In the conventional method, as shown in FIG. 4A, a light-shielding film 2 made of chrome or the like is formed on a substrate 1 made of quartz glass or the like, and a light transmitting portion having a predetermined pattern is formed. However, in phase shift lithography, as shown in FIG. 3A, a phase shifter 3 composed of a transmission film for inverting the phase (a phase difference of 180 °) is provided on one of the adjacent light transmission portions on the reticle. Is provided.
Accordingly, in the conventional method, the amplitude of the light on the reticle is in phase as shown in FIG. 4B, and the amplitude of the light on the wafer is also in phase as shown in FIG. 4C. While the pattern on the wafer cannot be separated as shown in FIG. 4D, in phase shift lithography, the light transmitted through the phase shifter
As shown in FIG. 3B, since the phases are made opposite to each other between the adjacent patterns, the light intensity becomes zero at the boundary of the patterns, and the adjacent patterns are clearly separated as shown in FIG. 3D. be able to. As described above, in the phase shift lithography, a pattern that cannot be separated conventionally can be separated and the resolution can be improved.

Next, one of the manufacturing steps of the phase shift reticle
An example will be described with reference to the drawings. FIG. 5 is a cross-sectional view showing a manufacturing process of the phase shift reticle, in which 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, Reference numeral 17 denotes a chromium pattern, 18 denotes an oxygen plasma, 19 denotes a transparent film, 20 denotes a resist layer, 21 denotes ionizing radiation, 22 denotes a resist pattern, 23 denotes an etching gas plasma, 24 denotes a phase shift pattern, and 25 denotes an oxygen plasma.

First, as shown in FIG. 5A, a chromium film 12 is formed on a quartz substrate 11 which has been optically polished.
An ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a conventional method such as spin coating,
A heat drying process is performed to form a resist layer 13 having a thickness of about 0.1 to 2.0 μm. The heating and drying treatment is usually performed at ± 80 to 150 ° C., depending on the type of resist used.
Perform for about 20 to 60 minutes.

Next, as shown in FIG. 1B, a pattern is drawn on the resist layer 13 with an ionizing radiation 14 using an exposure device such as an electron beam drawing device according to a conventional method, and an organic solvent such as ethyl cellosolve or ester is drawn. After development with a developer as a main component, rinsing with alcohol is performed to form a resist pattern 15 as shown in FIG.

Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as resist dust and whiskers remaining on the edge portion of the resist pattern 15, and the like, as shown in FIG. As shown, the resist pattern 1
The chromium layer 12 is dry-etched with the etching gas plasma 16 to form a chromium pattern 17. It is obvious to those skilled in the art that the chromium pattern 17 may be formed by wet etching instead of dry etching by the etching gas plasma 16.

After etching as described above, the resist pattern 15, ie, the remaining resist is ashed and removed by oxygen plasma 18 as shown in FIG. Complete the mask. This process can be performed by solvent stripping instead of the ashing process using the oxygen plasma 18.

Subsequently, the photomask is inspected, a pattern is corrected if necessary, and the photomask is washed. Then, as shown in FIG.
_A transparent film 19 made of ₂ or the like is formed. Next, FIG.
As shown in FIG. 2, an ionizing radiation resist layer 2 such as chloromethylated polystyrene is formed on the transparent film 19 in the same manner as described above.
0 is formed, and as shown in FIG.
Then, an alignment is performed according to a conventional method, a predetermined pattern is drawn by ionizing radiation 21 such as an electron beam exposure apparatus, developed and rinsed to form a resist pattern 22 as shown in FIG.

Next, if necessary, a heating process and a descum process are performed, and as shown in FIG. 1K, the transparent film 19 exposed from the opening of the resist pattern 22 is etched with an etching gas plasma. Dry etching is performed by using 23 to form a phase shifter pattern 24. Note that the phase shifter pattern 24 may be formed by wet etching instead of dry etching by the etching gas plasma 23.

Next, the remaining resist is ashed and removed by oxygen plasma 25 as shown in FIG. Through the above steps, a phase shift mask having the phase shifter 24 as shown in FIG.

In the above-described conventional method for manufacturing a phase shift reticle, the etching control in the depth direction of the transparent film 19 forming the phase shifter must be performed accurately. In particular, since the substrate 11 and the transparent film 19 are made of the same SiO ₂ -based material, if the etching is continued even after the etching of the transparent film 19 is completed,
Is also etched, and the phase shift amount of the phase shifter becomes larger than 180 °, making it difficult to transfer an accurate pattern.

The present applicant has proposed that an etching stopper layer is provided between a transparent film forming a phase shifter and a substrate, and that the etching is automatically stopped by this layer. No. 181795. The materials for the etching stopper layer proposed in these applications were tantalum, molybdenum, tungsten, silicon nitride, and the like.

[0018]

However, with an etching stopper layer made of such a material, it is not always easy to stop the etching accurately and sufficiently. In particular, when dry etching is performed by reactive ion etching in which the transparent film for the phase shifter is etched using CF ₄ , C ₂ F ₆ , CHF ₃ + O _{2 or} a mixed gas thereof, this tendency is strong.

The present invention has been made in view of such a situation, and an object of the present invention is to provide an etching stopper layer having excellent etching selectivity, capable of automatically stopping etching automatically, and having excellent moisture resistance. To provide a phase shift photomask using a film made of such a material.

[0020]

Means for Solving the Problems The present invention has been made in view of the above problems, the results of the practical and research to develop a phase shifter of accurate phase shift reticle, Al ₂ O ₃ and Mg
The inventors have found that a mixture of O, ZrO, Ta ₂ O ₃ , HfO and the like is excellent in etching selectivity and moisture resistance, and have completed the present invention based on such findings.

That is, the phase shift photomask of the present invention is an etching method in which a film made of a mixture of Al ₂ O ₃ and ZrO, Ta ₂ O ₃ or HfO is formed on a substrate mainly made of silicon oxide. A phase shifter pattern made of a material containing silicon oxide as a main component is formed so as to include a stopper layer, provide a light shielding pattern thereon, and further over at least one of the light transmitting portions adjacent to the light shielding pattern. It is characterized by having. Another phase shift photomask of the present invention is an etching method in which a film made of a mixture of Al ₂ O ₃ and MgO, ZrO, Ta ₂ O ₃ or HfO is formed on a substrate mainly made of silicon oxide. It has a stopper layer, a phase shifter pattern made of a material containing silicon oxide as a main component, and a light-shielding pattern made of a pattern side-etched on the stopper layer so as to have a dimension smaller than that of the phase shifter pattern. The pattern is formed in alignment with the phase shifter pattern.

[0022]

In the phase shift photomask of the present invention,
Al ₂ O ₃ and ZrO, Ta ₂ O ₃ or HfO on the substrate surface
When a phase shifter pattern is formed by etching, Al ₂ O ₃
And a mixture of ZrO, Ta ₂ O ₃ or HfO acts as an etching stopper layer, and can reliably etch the transparent film for the phase shifter, and can automatically stop the etching. It becomes a phase shift photomask. In addition, since the above-mentioned film has excellent moisture resistance, the phase shift photomask produced in this way has little deterioration due to the environment and has a long life.

[0023]

EXAMPLES phase shift photomask of the present invention, as an etching Sutopa layer between the transparent film substrate and the phase shifter, Al ₂ O ₃ and _{MgO, ZrO, Ta 2 O 3} , Hf
A film made of a mixture such as O is provided. Hereinafter, embodiments of the phase shift photomask of the present invention will be described while describing a method of manufacturing the phase shift photomask.

FIG. 1 is a cross-sectional view showing the steps of a method for manufacturing a photomask having a phase shift layer (phase shift photomask) according to the present invention.
etching stopper layer made of a mixture of l ₂ O ₃ and MgO, ZrO, Ta ₂ O ₃ or HfO;
Is a resist layer, 34 is ionizing radiation, 35 is a resist pattern, 36 is an etching gas plasma, 37 is a light shielding pattern, 38 is an oxygen plasma, 39 is a transparent film, 40 is a resist layer, 41 is ionizing radiation, 42 is a resist pattern,
43 is a reactive ion, 44 is a phase shift pattern, 45
Indicates oxygen plasma.

First, as shown in FIG. 1A, a uniform etching stopper layer 31 having a thickness of 10 to 500 nm and a light shielding layer 3 having a thickness of 10 to 200 nm are formed on an optically polished substrate 30.
2 is sequentially formed, and further, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a conventional method such as spin coating, and is heated and dried to a thickness of 0.1.
A resist layer 33 having a thickness of about 2.0 μm is formed. Here, considering that the phase shift mask is for a short wavelength such as an i-line or an excimer laser, quartz or high-purity synthetic quartz is desirable as the substrate 30, but other than that, low expansion glass, white plate, Blue plate (SL), MgF ₂ , Ca
It can be used F ₂ and the like. The etching stopper layer 31 is made of Al ₂ O ₃ , MgO, ZrO, Ta ₂ O.
₃ , can be formed using HfO or the like. further,
The light shielding layer 32 can be formed by forming a chromium thin film into a single layer or a multilayer, but can also be formed using chromium nitride, chromium oxide, tungsten, molybdenum, molybdenum silicide, or the like. . The heating and drying treatment is usually performed at ± 80 to 150 ° C. for about 20 to 60 minutes, depending on the type of the resist.

Next, as shown in FIG. 1B, a predetermined pattern is drawn on the resist layer 33 by an exposure device using ionizing radiation 34 such as an electron beam drawing device according to a conventional method, and ethylcellosolve, ester or the like is drawn. After developing with a developing solution containing an organic solvent as a main component, rinsing with an alcohol forms a resist pattern 35 as shown in FIG.

Next, if necessary, a heating process and a descum process are performed to remove unnecessary resist such as resist scraps and whiskers remaining at the edge portion of the resist pattern 35, as shown in FIG. Then, the processed portion exposed from the opening of the resist pattern 35, that is, the light-shielding layer 32 is dry-etched by the etching gas plasma 36 to form the light-shielding pattern 37. Note that this light-shielding pattern 3
It is obvious to those skilled in the art that the formation of 7 may be performed by wet etching instead of dry etching by the etching gas plasma 36.

After etching as described above, the remaining resist 35 is ashed and removed by oxygen plasma 38 as shown in FIG.
A photomask in which a conductive layer 31 is formed on a substrate 30 and a predetermined light shielding pattern 37 is formed thereon is formed. Note that this process can be performed by solvent stripping instead of the incineration process using the oxygen plasma 38.

Subsequently, the photomask is inspected, and if necessary, the pattern is modified and washed, and then, as shown in FIG. 9G, vapor deposition is performed on the light-shielding pattern 37 by spin-on-glass (SOG). A transparent film 39 mainly composed of SiO ₂ is formed. The thickness d of the transparent film 39 is a value given by d = λ / 2 (n−1), where n is the refractive index of the material forming the transparent film 39 and λ is the exposure wavelength.
When SiO ₂ is used, the value of d is about 406 nm.

Next, as shown in FIG.
9, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied to form a resist layer 40 in the same manner as described above, and as shown in FIG. Alignment is performed, a predetermined pattern is drawn at a position where the phase is to be shifted by ionizing radiation 41 of an electron beam exposure device or the like, developed and rinsed with a predetermined developing solution, and the resist is exposed as shown in FIG. The pattern 42 is formed.

Subsequently, after performing a heat treatment and a descum treatment as necessary, the transparent film 39 exposed from the opening of the resist pattern 42 is exposed to CF as shown in FIG.
₄ , dry etching is performed by reactive ion etching using reactive ions 43 using C ₂ F ₆ , CHF ₃ + O ₂ and a mixed gas thereof to form a phase shift pattern 44. The phase shift pattern 44 may be formed by wet etching using a hydrofluoric acid-based solution instead of reactive ion etching.

At this time, in the conventional method, the etching reaches the substrate 30 and it is difficult to determine the end point of the etching, or the substrate 30 is also etched, and the phase shift amount of the phase shifter is larger than 180 °. However, in the present invention, Al ₂ O, which has high etching resistance and excellent moisture resistance to the fluorine-based reactive ions, is used in the present invention. ₃ , MgO, ZrO, Ta ₂ O ₃ ,
Since a mixture such as HfO is used as the etching stopper layer 31, the transparent film 39 can be surely etched, and the etching can be automatically stopped, thereby producing a higher quality phase shift photomask. be able to.

Next, as shown in FIG. 1 (l), the remaining resist is ashed and removed by oxygen plasma 45. As a result, a highly accurate phase shift photomask as shown in FIG. This process can be performed by solvent stripping instead of the ashing process using the oxygen plasma 45.

Now, such an etching stopper layer can be applied not only to the phase shift photomask as shown in FIG. 3 but also to a phase shift photomask of another structure.
As an example, a case in which this etching stopper layer is applied to a self-alignment type phase shift photomask proposed by the present applicant in Japanese Patent Application No. 2-181795 will be briefly described below.

FIG. 2 is a cross-sectional view showing a process for manufacturing such a phase shift photomask.
51 is Al ₂ O ₃ and MgO, ZrO, Ta ₂ O ₃ or H
An etching stopper layer made of a mixture of fO, 52 is a transparent film, 53 is a light-shielding thin film, 54 is a resist layer, 55 is a resist pattern, 56 is ionizing radiation, 57 is an etching gas plasma, 58 is a light-shielding pattern, and 59 is an oxygen plasma. , 60 indicates a resist layer, 61 indicates back exposure, 62 indicates reactive ions, 63 indicates a phase shifter pattern, and 64 indicates oxygen plasma.

First, as shown in FIG. 2A, a uniform etching stopper layer 51 having a thickness of 10 to 500 nm and an SiO film having a film thickness d = λ / 2 (n−1) are formed on an optically polished substrate 50. Transparent film 52 mainly composed of ₂ and 50 to 200 nm
Are sequentially formed to form a photomask blank.

Next, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied on the photomask blanks by a conventional method such as spin coating, and is heated and dried to a thickness of about 0.1 to 2.0 μm. A resist layer 54 is formed.

Here, considering that the phase shift mask of the present invention is generally used for a short wavelength such as an i-line or an excimer laser, quartz, high-purity quartz,
It is preferable to use MgF ₂ , CaF ₂ or the like. However, in the case of a longer wavelength, low expansion glass, white plate glass, blue plate glass, or the like may be used. The etching stopper layer 51 is formed using Al ₂ O ₃ and MgO, ZrO, Ta ₂ O ₃ , HfO, or the like, as in the case of FIG. Further, the transparent film 52 is preferably a high-purity SiO ₂ film.
A VD method or spin-on-glass coating (for example, spin coating of siloxane and heating to form a SiO ₂ film) is employed. Further, the light-shielding layer 53 can be formed by forming a single-layer or multi-layer thin film of chromium, chromium nitride, chromium oxide, tungsten, molybdenum, molybdenum silicide, or the like.

The heating and drying treatment of the resist is usually carried out at 80 to 200 ° C. and 20 to 20 ° C., depending on the type of the resist.
Perform for about 60 minutes.

Next, as shown in FIG. 2 (b), a predetermined pattern is drawn on the resist layer 54 by an exposure device using ionizing radiation 56 such as an electron beam drawing device according to a conventional method, and an ethyl cellosolve, an ester or the like is drawn. After developing with a developing solution containing an organic solvent as a main component, rinsing with alcohol forms a resist pattern 55 as shown in FIG.

Next, a heating process and a descum process are performed as necessary to remove unnecessary resist such as resist dust and whiskers remaining on the edge portion of the resist pattern 55 and the like, as shown in FIG. The portion to be processed exposed from the opening of the resist pattern 55, that is, the light shielding layer 53
Is dry-etched with an etching gas plasma 57 to form a light-shielding pattern 58 (FIG. 4D). In addition,
It is obvious to those skilled in the art that the formation of the light shielding pattern 58 may be performed by wet etching instead of dry etching by the etching gas plasma 57.

After etching as described above, the remaining resist 55 is ashed and removed by oxygen plasma 59 as shown in FIG.
An etching stopper layer 51 is formed on a substrate 50, a phase shift layer 52 is formed thereon, and a photomask on which a predetermined light shielding pattern 58 is formed is formed. Note that the removal of the remaining resist 55 can be performed by solvent stripping instead of the incineration by the oxygen plasma 59.

Subsequently, the photomask is inspected, if necessary, the pattern is modified, and after cleaning, the OFPR is placed on the light shielding pattern 58 as shown in FIG.
A photoresist such as -800 is uniformly applied by a conventional method such as spin coating, and is subjected to a heat-drying treatment.
A resist layer 60 having a thickness of about 2 μm is formed.

Subsequently, the resist layer 60 is subjected to back exposure 61 from the glass substrate 50 side, developed with an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, rinsed with pure water, and A pattern with a resist pattern is formed.

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

Subsequently, the substrate is treated with an etching solution containing ceric ammonium nitrate as a main component, and the light-shielding film 58 sandwiched between the phase shifter 63 and the resist 60 is side-etched. The amount of side etching depends on the type and size of the pattern, but is usually 0.1 to 0.5.
It is about μm.

After the etching as described above, the remaining resist 60 is ashed and removed by an oxygen plasma 64 as shown in FIG. 3I, and a self-aligned phase as shown in FIG. The shift mask is completed.

Also in this case, as in the case of FIG. 1, the etching resistance to the fluorine-based reactive ions is high.
Al ₂ O ₃ with excellent moisture resistance and MgO, ZrO, Ta
A mixture of ₂ O ₃ , HfO, etc. is
Therefore, the transparent film 52 can be surely etched, and the etching can be stopped automatically, so that a higher quality phase shift photomask can be produced.

[0049]

As a photomask used for manufacturing a semiconductor integrated circuit, a photomask in which a light-shielding film such as a chromium film is patterned on a glass substrate such as quartz is used at present. In, the conventional exposure technology using a photomask is approaching its limit, and is shifting to a direction using a phase shift photomask.

The phase shift photomask according to the present invention
As described above, Al ₂ O ₃ , ZrO, Ta
_{Since a} film made of a mixture of ₂ O ₃ or HfO is provided, when a phase shifter pattern is formed by etching, a mixture of Al ₂ O ₃ and ZrO, Ta ₂ O ₃ or HfO acts as an etching stopper layer, Since the transparent film for the phase shifter can be surely etched and the etching can be automatically stopped,
A higher quality phase shift photomask results. In addition, since the above-mentioned film has excellent moisture resistance, the phase shift photomask produced in this way has little deterioration due to the environment and has a long life.

[Brief description of the drawings]

FIG. 1 is a sectional view showing steps of a method for manufacturing a phase shift photomask according to the present invention.

FIG. 2 is a cross-sectional view showing a step of manufacturing another phase shift photomask according to the present invention.

FIG. 3 is a diagram illustrating the principle of the phase shift method.

FIG. 4 is a diagram showing a conventional method.

FIG. 5 is a cross-sectional view showing a manufacturing process of a conventional phase shift photomask.

[Explanation of symbols]

 REFERENCE SIGNS LIST 30 substrate 31 etching stopper layer 32 light shielding layer 33 resist layer 34 ionizing radiation 35 resist pattern 36 etching gas plasma 37 light shielding pattern 38 oxygen plasma 39 transparent film 40 resist layer 41 ionizing radiation 42 resist pattern 43 reactive ions 44 phase shift pattern 45 oxygen plasma

Continuation of the front page (56) References JP-A-59-143155 (JP, A) JP-A-4-233541 (JP, A) JP-A-4-371951 (JP, A) JP-A-5-113655 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (2)

(57) [Claims] An Al ₂ O ₃ and ZrO, Ta ₂ O ₃ or HfO are formed on a substrate made of a material containing silicon oxide as a main component.
Comprising an etching stopper layer mixture is film formed consisting of, including the light-shielding pattern formed thereon, further shielding the
On at least one of the adjacent light transmission parts of the light pattern
Ride manner, a phase shift photomask, characterized in that the phase shifter pattern composed of a material mainly containing silicon oxide is formed. 2. An etching stopper layer formed of a film made of a mixture of Al ₂ O ₃ and MgO, ZrO, Ta ₂ O ₃ or HfO on a substrate made of a material containing silicon oxide as a main component. A phase shifter pattern made of a material containing silicon oxide as a main component, and further smaller in size than the phase shifter pattern.
Putters that have been side-etched to create a new pattern
Alignment light shielding pattern made of emissions is a phase shifter pattern
A phase shift photomask characterized by being formed by: