JPH0468352A - Photomask with phase shift layer and manufacture thereof - Google Patents

Abstract

PURPOSE:To stably obtain a phase shift mask which has high accuracy and is easily inspected and corrected by using photomask blanks in the structure of an etching stopper layer, a transparent thin film layer, and a light shielding thin film formed on a substrate of glass, etc., in this order. CONSTITUTION:The photomask blanks in the structure of the etching stopper layer 31, transparent thin layer 32, and light shielding thin film 33 formed on the substrate 30 in this order are used as a substrate for a phase shift reticle. In this case, the substrate 30 is formed preferably of high-impurity composite quartz glass, CaF2, etc., the etching stopper layer 31 is formed of a tantalum film, a silicon nitride film, etc., and the transparent layer 32 is formed of an SiO2 thin film, a CaF2 thin film, etc. Further, the light shielding thin film 33 is preferably a chromium thin film, a molybdenum silicide thin film, etc. Consequently, the phase shift mask which has high resolution, a high contrast, and high accuracy and is easily inspected and corrected can be obtained stably and easily.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a photomask used in the production of high-density integrated circuits such as LSI and VLSI, and a method for producing the same, and in particular, to a photomask for producing fine patterns with high precision. The present invention relates to a photomask having a phase shift layer when forming the same, and a method for manufacturing the same.

[Conventional technology]

Semiconductor integrated circuits such as ICs, LSIs, and VLSIs require repeating a so-called lithography process in which a resist is applied onto a substrate to be processed such as a Si wafer, a desired pattern is exposed using a stepper, etc., and then development and etching are performed. Manufactured by.

Photomasks called reticles used in such lithography processes are used to improve the performance of semiconductor integrated circuits.
With the increase in integration, there is a tendency for higher precision to be required. For example, taking DRAM, which is a typical LSI, a 5x reticle for IM bit DRAM, that is,
The dimensional deviation of a reticle that is five times the size of the pattern to be exposed requires an accuracy of 0.15 μm even if the average value ±3σ (σ is the standard deviation) is taken.
Similarly, a 5x reticle for a 4Mbit DRAM is 0.
16M human DRAM with dimensional accuracy of 1 to 0.15μm
A 5x reticle is required to have a dimensional accuracy of 0.05 to 0.1 μm.

Furthermore, the line width of device patterns formed using these reticles is 1.2 am for IM pit DRAM.
, 4-bit DRAM is 0.8μm, 16Mbit DR
In AM, there is a demand for further miniaturization of 0.6 μm, and in order to meet this demand, various exposure methods are being researched.

However, when it comes to next-generation device patterns in the 64MDRAM class, for example, the conventional stepper exposure method using a reticle reaches the resolution limit of the resist pattern. Publication, Special Publication No. 62-59296
A reticle based on a new concept called a phase shift mask has been proposed, as shown in Japanese Patent Application No. Phase shift lithography using a phase shift reticle is
By manipulating the phase of light passing through the reticle,
This is a technology that improves the resolution and contrast of projected images.

Phase shift lithography will be briefly explained according to the drawings. Figure 2 shows the principle of the phase shift method, Figure 3 shows the conventional method, Figures 2(a) and 3(a) are cross-sectional views of the reticle, and Figure 2(b) 3(b) shows the amplitude of the light on the reticle, 2(C) and 3(C) show the amplitude of the light on the wafer, 2(d) and 3(d)
indicate the light intensity on the wafer, l indicates the substrate, 2 indicates the light shielding film, 3 indicates the phase shifter, and 4 indicates the incident light.

In the conventional method, as shown in FIG. 3(a), a light-shielding film 2 made of chromium or the like is formed on a substrate 1 made of glass or the like to form a light-transmitting part in a predetermined pattern. However, in phase shift lithography, Fig. 2 (a
), a phase shifter 3 made of a transmission film for inverting the phase (phase difference of 180°) is provided on one of the adjacent light transmission parts on the reticle. therefore,
In the conventional method, the amplitude of the light on the reticle is as shown in Figure 3 (b
), the amplitude of the light on the wafer also becomes the same phase as shown in Figure 3(C), and as a result, the patterns on the wafer are separated as shown in Figure 3(d). In contrast, in phase shift lithography, the light transmitted through the phase shifter is shown in Figure 2(b).
As shown in Figure 2, since adjacent patterns are made in opposite phases to each other, the light intensity becomes zero at the pattern boundary, and the second
Adjacent patterns can be clearly separated as shown in Figure (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.

To explain a specific pattern example of a fetomask (reticle) having this phase shift layer, as shown in the plan view of the reticle pattern in FIG.
In the case of a pattern in which are arranged alternately (Figure (a)),
A shifter layer 3 is provided in every other space S part so as to completely cover the space part S. In addition, an isolated hole pattern h such as a contact hole (Figure (b)) is
An unresolved slit-shaped space S' called an auxiliary pattern must be additionally created around the periphery, and the shifter layer 3 must be provided to cover the auxiliary pattern.

However, although this phase shift method satisfactorily achieves its purpose in the case of a simple pattern as shown in Figure 4, it becomes difficult to design the shifter pattern in the case of a complex pattern such as a normal device pattern. In some cases, it may not be possible to design a shifter depending on the pattern arrangement.

Therefore, recently, a self-alignment type phase shift mask has been devised (rNIKKEI
MICRODEVICES J January 1990 issue p
p, 78-79). This self-aligned phase shift mask, as shown in cross section in FIG. Based on the same principle as the conventional method, this method aims to improve resolution by emphasizing contrast at pattern edge portions.

Next, the manufacturing process of such a self-aligned phase shift reticle will be explained with reference to the drawings. FIG. 5 is a cross-sectional view showing the manufacturing process of a self-aligned phase shift reticle, in which 11 is a substrate, 12 is a chromium film, and 13 is a PMM.
14 shows a resist film such as A, 14 shows light for back exposure, and 15 shows a phase shift pattern.

First, a chromium film pattern I is placed on the optically polished substrate]1.
On the reticle (Fig. 5(a)) formed with
An ionizing radiation resist such as A (polymethyl methacrylate) is uniformly applied by a conventional method such as spin coating, and then heated and dried to form a resist layer 13 with a thickness of 406 nm (FIG. 6(b)). The heat drying process depends on the type of resist used, but usually 80 to 200
It is carried out at ℃ for about 20 to 60 minutes. .

Next, back exposure is performed from the back surface of this substrate 11 using deep ultraviolet light or the like I4. After exposure, the film was developed with a developer containing a growing solvent such as ester, and rinsed with alcohol, as shown in the same figure (C).
Resist pattern 1 is placed on top of the ROM pattern as shown in
A pattern of 5 overlapping shapes is formed.

Next, a chromium pattern is side-etched on this substrate using a chromium etching solution containing ceric ammonium nitrate as a main component, and a shifter 15 made of a resist layer is formed into a canopy shape as shown in FIG. A self-aligned phase shift reticle formed to protrude is completed.

[Invention or problem to be solved]

However, in the conventional self-aligning phase shift reticle described above, the shifter is formed to protrude like a canopy, so a highly accurate mask cannot be created, and the shifter is easily damaged. Furthermore, it was difficult to inspect for defects and almost impossible to correct, making it impractical for research purposes but not for practical use.

The present invention was made in view of this situation,
The purpose is to provide a phase shift photomask constructed using a photomask blank arranged such that it is located under a relatively convergent or wide phase shift pattern or a reticle pattern, and a method for manufacturing the same. That's true.

[Means to solve the problem]

In view of the above problems, the present invention was developed as a result of research to develop a method for stably manufacturing a highly practical and highly accurate phase shift reticle.As a substrate for a phase soft reticle, an etching stopper layer and a transparent etching layer are formed on the substrate as a substrate for a phase soft reticle. The inventors discovered that a highly accurate phase soft reticle can be stably manufactured by using a photomask blank having a structure in which a film layer and a light-shielding thin film are formed in this order, and based on this knowledge, the present invention was completed. .

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a photomask and a method for manufacturing the same according to the present invention will be described below with reference to the drawings. 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 30 is a substrate, 31 is an etching stopper layer, 32 is a transparent film layer, and 33 is a light shielding layer. 34 is a resist layer, 35 is a resist pattern, and 36 is an ionizing radiation.

First, as shown in FIG. 1(a), on an optically polished substrate 30, a uniform etching stopper layer 31 with a thickness of Il-100 nm, a transparent film layer 32 with a thickness of 100 to 11,000 nm, and a light shielding layer with a thickness of 50 to 200 nm are formed. 33 are sequentially formed to constitute a photomask blank.

Next, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied onto the photomask blank by a conventional method such as spin coating, and a heat drying process is performed to form a resist layer 34 with a thickness of about 0.1 to 20 μm. Form.

Here, the substrate 30 may be a phase shift mask of the present invention, or considering that it is normally used for short wavelengths such as i-line or excimer laser, quartz, high-purity quartz, MgFz, C
It is preferable to use aFz or the like. However, for wavelengths longer than that, it is difficult to use low expansion glass, white plate glass, blue plate glass, etc. Further, the etching stopper layer 31 is preferably a thin film of tantalum, molybdenum, tungsten, silicon nitride, or the like. Further, the transparent film layer 32 is preferably a high-purity S s 02 film, or a silicon nitride film, MgF2, CaF2, etc. can also be used. Coating methods for these films include sputtering, CVD, and spin-on glass coating (for example,
Spin coating siloxane and heating 5102
(forms a film) or is adopted. Further, the light shielding layer 33 can be formed by forming a single layer or a multilayer thin film of chromium, chromium nitride, chromium oxide, tungsten, molybdenum, molybdenum silicide, or the like.

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

Next, as shown in FIG. 1(b), on the resist layer 34,
A predetermined pattern is drawn using an exposure device using ionizing radiation 36 such as an electron beam drawing device in accordance with a conventional method, and after development with a developer whose main component is a growth solvent such as ethyl cellosolve or ester, the same figure is obtained by rinsing with alcohol. A resist pattern 35 as shown in (C) is formed.

Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as the resist layer remaining on the edge portions of the resist pattern 35, whiskers, etc.
), the portion to be processed exposed through the opening of the resist pattern 35, ie, the light-transmitting layer 33, is dry-etched with an etching gas plasma 37 to form a light-shielding pattern 38 (FIG. 3(d)). It is clear to those skilled in the art that the light shielding pattern 38 may be formed by wet etching instead of dry etching using the etching gas plasma 37.

After etching in this manner, the remaining resist 35 is ashed and removed by oxygen plasma 39, as shown in FIG. 3D, and an etching stopper is placed on the substrate 30, as shown in FIG. A layer 31 is formed, a shifter layer 32 is formed thereon, and a photomask having a predetermined light shielding pattern 38 formed thereon is created.

Note that the remaining resist 35 can be removed by solvent stripping instead of the ashing process using the oxygen plasma 39.

Next, this photomask is inspected, the pattern is corrected if necessary, and after cleaning, a photoresist such as 0FPR-800 is applied by spin coating on the light shielding pattern 38, as shown in FIG. A resist layer 40 having a thickness of about 1 to 2 μm is formed by applying the resist layer uniformly by a conventional method and performing a heat drying process.

Subsequently, the resist layer 40 is back-exposed 41 from the glass substrate 30 side, developed with an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, and rinsed with pure water to form a resist pattern on the light-shielding pattern 38. Form a riding pattern.

Next, as shown in FIG. 1(g), the portion to be processed exposed through the opening of this resist pattern, that is, the shifter layer 32, is dry-etched using an etching gas plasma 42 to form a shifter pattern 43. Figure h)).

Subsequently, this substrate is treated with an etching solution containing ceric ammonium nitrate as a main component to side-etch the light shielding film 38 sandwiched between the shifter 43 and the resist 40. The amount of side etching depends on the type and size of the pattern, but is usually about 0.1 to 0.5 μm.

After etching in this manner, the remaining resist 40 is ashed and removed by oxygen plasma 44, as shown in FIG. do.

Note that the photomask having a phase shift layer and the method for manufacturing the same are not necessarily limited to those described above, and various modifications can be made.

That is, the photomask having a phase shift layer of the present invention uses a photomask blank having a structure in which an etching stopper layer, a transparent film layer, and a light-shielding thin film are formed in this order on a substrate as a substrate to be processed for the photomask. It is characterized by being configured as follows.

In this case, the substrate may include high-purity synthetic quartz glass,
Low expansion glass, white plate glass, blue plate glass, M g F
The etching stopper layer is preferably a tantalum film, a molybdenum film, a tungsten film, or a silicon nitride film, and the transparent film layer is a SiO2 thin film,
It is preferable that the light-shielding thin film is a silicon nitride thin film, a M g F 2 thin film, a CaF 2 thin film, etc.; It is desirable that the material be a multilayer film, etc.

The specific structure of this photomask includes a phase shift layer obtained by patterning a transparent film layer having a predetermined thickness formed on an etching stopper layer on a substrate, and a phase shift layer formed on the transparent film layer. The pattern of the phase shift layer is aligned with the reticle and protrudes outward by a predetermined width from each edge of the reticle. A shift mask is preferable from the viewpoint of photomask resolution and contrast, and is also preferable from the viewpoint of defect inspection and correction.

In addition, in the method for manufacturing a photomask having a phase shift layer as described above, ionizing radiation is applied to a substrate having a structure in which an etching stopper layer, a transparent film layer, and a light-shielding thin film are formed in this order on the substrate. a step of forming a resist thin film;
A process of irradiating this ionizing radiation resist thin film with a pattern of ionizing radiation and developing it to form a pattern, a process of etching the exposed light-shielding thin film using this ionizing radiation resist pattern as a mask, and a process of etching the remaining ionizing radiation resist thin film. a step of removing the photoresist, and a step of forming a photoresist thin film on the buttered light-shielding thin film.
A process of back-exposing and developing this photoresist thin film from the glass substrate side to form a pattern, a process of side etching the light-shielding thin film layer sandwiched between the photoresist thin film layer and the transparent film layer, and an etching process. This method is characterized by the step of removing the photoresist after the photoresist is finished.

In this case, the substrate may include high-purity synthetic quartz glass,
Low expansion glass, white plate glass, blue plate glass, M g F
The etching stopper layer is preferably a tantalum film, a molybdenum film, a tungsten film, or a silicon nitride film, and the transparent film layer is preferably a 5iOz thin film, A silicon nitride thin film, a MgF thin film, a CaF2 thin film, etc. are preferable, and the light-shielding thin film is preferably a chromium thin film, a chromium nitride thin film, a chromium oxide thin film, a tungsten thin film, a molybdenum thin film, a molybdenum silicide thin film, or a multilayer thereof. Preferably, it is a membrane or the like.

[Effect]

Theoretically, phase shift masks can provide high-resolution patterns and are said to be very useful for the high integration of LSI and VLSI in the future. When trying to manufacture products, there are problems with high-precision patterning, inspection, and correction.

In the present invention, by using a photomask blank having a structure in which an etching stopper layer, a transparent film layer, and a light-shielding thin film are formed in this order on a substrate such as glass as a substrate to be processed, high resolution, high contrast, A phase shift mask that is highly accurate and easy to inspect and modify can be manufactured stably and easily.

〔Example〕

Examples of the present invention will be described below.

(Example 1) As shown in FIG. 1(a), 100 people coated a tantalum thin film as an etching stopper layer 31 and a 3i0* transparent film 32 for a shifter on an optically polished high-purity synthetic quartz glass 30. A resist solution made of chloromethylated polystyrene is applied by spin coating on a 120 nm chromium film with a thickness of 406 nm and a low reflection film on the surface as a light-shielding thin film 33, or on a fetomask blank formed in this order. Prebaking was performed at 120° C. for 30 minutes to obtain a uniform resist film 34 with a thickness of 0.5 μm.

Next, as shown in FIG. 1(b), a pattern is drawn on the resist film 34 at 2 μC/aIr using an electron beam drawing device, developed for 60 seconds with a mixed solution of ethyl cellosolve and isoamyl acetate, and developed with isopropyl alcohol. A resist pattern 35 was formed by rinsing for 30 seconds.

Subsequently, the light shielding film 33 exposed through the opening of the resist pattern 35 is etched with an aqueous solution containing ceric ammonium nitrate as a main component, and then the remaining resist 35 is etched as shown in FIG. 1(d). , 2 Torr, 400
Ashing and removal was performed using a W oxygen plasma 39 to obtain a photomask pattern 38 as shown in FIG. 3(e).

The quality of the light-shielding film pattern 38 of the photomask manufactured in this manner is inspected using a normal mask inspection device (for example, 7MD manufactured by Nippon Lasertic Co., Ltd. or the one manufactured by KAL), and the light-shielding film pattern 38 may be modified as necessary. After that, a fetresist solution of 0FPR-800 was applied on this mask substrate by spin coating method, and it was heated at 90°C for 3
Pre-baked for 0 minutes, and the thickness was 1 as shown in Figure 1(f).
A resist film 40 having a uniform thickness of μm was obtained. Next, this substrate was developed using a G-line aligner from the glass surface opposite to the resist surface by back exposure (41), with an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, and rinsed with pure water. As a result, a pattern consisting of two layers of a light-shielding film 38 and a resist 40 as shown in FIG. 3(g) was obtained.

Next, as shown in FIG. 1(g), using this resist pattern as a mask, the exposed 5iO7 layer 32 for the shifter was etched using an RIE dry etching device with an output of 250 W and a CF film.
, and 02 for 15 minutes to obtain a shifter pattern 43 as shown in FIG. At this time, dry etching is
Etching was stopped at the tantalum thin film layer 31, which is an etching stopper layer, and uniform etching could be performed.

After the shifter layer etching, the substrate is sprayed with an aqueous solution containing ceric ammonium nitrate as a main component, and the chromium film layer 38 sandwiched between the resist layer 4o and the SiO2 shifter layer 43 is side-etched by 0°3 μm. The sample was then washed with pure water (Fig. 1(i)).

Finally, as shown in FIG. 1(1), the remaining resist 4o is removed by ashing with a 2 Torr, 400W oxygen plasma 44, and a self-aligned phase shift mask (see FIG.
j)) was obtained.

The phase shift mask manufactured in this way was highly accurate and practical, and easy to inspect and correct defects.

〔Effect of the invention〕

In the photomask having a phase shift layer and the manufacturing method thereof of the present invention, a photomask having a structure in which an etching stopper layer, a transparent film layer, and a light-shielding thin film are formed in this order on a substrate such as glass as a substrate to be processed. By using blanks, it is possible to stably and easily manufacture a phase shift mask that has high resolution, high contrast, high precision, and is easy to inspect and modify.

[Brief explanation of drawings]

FIG. 1 is a process cross-sectional view of one embodiment of the method for manufacturing a photomask having a phase shift layer according to the present invention, FIG. 2 is a diagram showing the principle of the phase shift method, FIG. 3 is a diagram showing a conventional method, and FIG. FIG. 4 is a plan view of a reticle pattern, and FIG. 5 is a cross-sectional view showing the manufacturing process of a conventional self-aligned phase shift mask. 30... Substrate, 31... Etching stopper layer,
32... Transparent film layer, 33... Light-shielding thin film, 34...
・Resist layer, 35...Resist pattern, 36...
・Ionizing radiation, 37...Etching gas plasma, 3
8'--Shading pattern, 39... Oxygen plasma, 40
... Photoresist layer, 41 ... Back exposure, 42
...Etching gas plasma, 43...Shifter pattern, 44...Oxygen plasma Figure 1 (1) Applicant Dai Nippon Printing Co., Ltd. Agent Patent attorney Hiroshi Nirasawa (7 others) Figure (2) ) Figure 4 (a) (b) Figure 2 Figure 3 (d) fV in (d) /He\

Claims (11)

[Claims] (1) As a substrate to be processed for a photomask, a photomask blank having a structure in which an etching stopper layer, a transparent film layer, and a light-shielding thin film are formed in this order on the substrate is used. A photomask with a phase shift layer. (2) The substrate may be made of high purity synthetic quartz glass, low expansion glass, white glass, blue glass, MgF_2 or CaF_
2. The photomask having a phase shift layer according to claim 1, wherein the photomask has a phase shift layer of 2. (3) The photomask having a phase shift layer according to claim 1 or 2, wherein the etching stopper layer is a tantalum film, a molybdenum film, a tungsten film, a silicon nitride film, or the like. (4) The photomask having a phase shift layer according to any one of claims 1 to 3, wherein the transparent film layer is a SiO_2 thin film, a silicon nitride thin film, a MgF_2 thin film, a CaF_2 thin film, or the like. (5) The light-shielding thin film is a chromium thin film, a chromium nitride thin film, a chromium oxide thin film, a tungsten thin film, a molybdenum thin film, a molybdenum silicide thin film, or a multilayer film thereof. A photomask having the phase shift layer according to item 1. (6) Patterning a phase shift layer obtained by patterning a transparent film layer having a predetermined thickness formed on an etching stopper layer on a substrate and a light-shielding thin film formed on the transparent film layer. The pattern of the phase shift layer is aligned with the reticle,
6. A photomask having a phase shift layer according to claim 1, wherein the phase shift layer protrudes outward by a predetermined width from each edge of the reticle. (7) A process of forming an ionizing radiation resist thin film on a substrate having a structure in which an etching stopper layer, a transparent film layer, and a light-shielding thin film are formed in this order, and ionizing the ionizing radiation resist thin film. A process of irradiating a pattern with radiation and developing it to form a pattern, a process of etching the exposed light-shielding thin film using this ionizing radiation resist pattern as a mask, a process of removing the remaining ionizing radiation resist thin film, and this patterning process. a step of forming a photoresist thin film on the light-shielding thin film, a step of back-exposing the photoresist thin film from the glass substrate side and developing it to form a pattern, and a step of forming a pattern between the photoresist thin film layer and the transparent film layer. 1. A method for manufacturing a photomask having a phase shift layer, comprising the steps of side-etching a light-shielding thin film layer sandwiched between the layers, and removing the photoresist after the etching is completed. (8) The substrate may be made of high purity synthetic quartz glass, low expansion glass, white glass, blue glass, MgF_2 or CaF_
8. The method for manufacturing a photomask having a phase shift layer according to claim 7, wherein the phase shift layer is 2 or the like. (9) The method for manufacturing a photomask having a phase shift layer according to claim 7 or 8, wherein the etching stopper layer is a tantalum film, a molybdenum film, a tungsten film, a silicon nitride film, or the like. (10) Manufacturing a photomask having a phase shift layer according to any one of claims 7 to 9, wherein the transparent film layer is a SiO_2 thin film, a silicon nitride thin film, a MgF_2 thin film, a CaF_2 thin film, or the like. Method. (11) Any one of claims 7 to 10, wherein the light-shielding thin film is a chromium thin film, a chromium nitride thin film, a chromium oxide thin film, a tungsten thin film, a molybdenum thin film, a molybdenum silicide thin film, or a multilayer film thereof. A method for manufacturing a photomask having a phase shift layer according to item 1.