JPH0468351A - Manufacture of phase shift photomask - Google Patents

Abstract

PURPOSE:To draw a pattern with high accuracy without any alignment mark detection error by detecting an alignment mark which is exposed previously and performing pattern exposure when a shifter pattern is formed. CONSTITUTION:When a shifter is formed, the alignment mark AM on a reticle is exposed and the alignment mark AM which is exposed is detected with the electron beam of an electron beam exposure device to accurately align the shifter pattern 28, thereby drawing the pattern. Thus, the alignment mark AM which is exposed previously is detected to perform the pattern exposure, so the pattern can be drawn with high accuracy without any alignment mark detection error. Consequently, a high-accuracy phase shift reticle can stably be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a photomask used for manufacturing high-density integrated circuits such as LSIs and VLSIs, and in particular, it relates to a method for manufacturing a photomask used for manufacturing high-density integrated circuits such as LSIs and VLSIs, and in particular, it relates to a method for manufacturing a photomask used for manufacturing high-density integrated circuits such as LSIs and VLSIs. The present invention relates to a method of manufacturing a photomask having a phase shift layer during formation.

[Conventional technology]

Semiconductor integrated circuits such as ICs, LSIs, and VLSIs are manufactured by coating a resist on a substrate to be processed such as a silicon wafer, exposing a desired pattern using a stepper, etc., and then repeating so-called lithography processes such as development and etching. Manufactured.

Photomasks called reticles used in such lithography processes are used to improve the performance of semiconductor integrated circuits.
With higher 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 has a dimensional accuracy of 1t0.
15 μm (3σ), 5x reticle for 4 Mbit DRAM has dimensional accuracy of 0.1 to 0.15 μm (3 cr), 16
The 5x reticle for M-bit DRAM has a dimensional accuracy of 0.05
A value of ~0.1 μm is required.

Furthermore, the device patterns formed using these reticles are 12 μm for IM bit DRAM and 0.8 μm for 4 M bit DRAM. czmS 16Mbit DRA
0 in M. With the demand for further miniaturization of 6 μm, various exposure methods are being actively researched.

However, when it comes to device patterns of the next generation, for example, 64 Mbit DRAM class, the conventional stepper exposure method using a reticle has reached the resolution limit of the resist pattern, and new reticle concepts such as phase shift masks have begun to be proposed. (Unexamined Japanese Patent Publication No. 58-17
No. 3744, Special Publication No. 62-59296). Phase shift lithography using a phase shift reticle according to this proposal is a technology that improves the resolution and contrast of a projected image by manipulating the phase of light that passes through the reticle.

The above phase shift lithography will be briefly explained with reference to the drawings. Figure 2 shows the principle of the phase shift method in comparison with the conventional method, where (a) and (a') are cross-sectional views of the reticle, and (b) and (b') are the amplitudes of the light on the reticle. , (C
), (a') are the amplitudes of the light on the wafer, (d), (a'
) indicates the light intensity on the wafer, 11 indicates the glass substrate, 1
2 is a light shielding film made of chromium or the like, 13 is a phase shifter, and 14 is incident light. In phase shift lithography, the phase is inverted (phase difference 1
Transparent membrane (shifter) for 80°! 3 (Fig. 2(a')). The light transmitted through the light transmitting part has opposite phases between adjacent patterns (Fig. 2 (b')).
), the light intensity becomes zero at the boundary of the pattern, and the pattern separates (Cd' in Figure 2)). In this way, phase shift lithography can separate patterns that could not be separated using conventional methods, resulting in improved resolution.

Next, a known manufacturing process for a phase shift reticle as described above will be explained with reference to the drawings. FIG. 3 is a cross-sectional view showing the process of manufacturing a phase shift reticle, in which 1 is a substrate, 2 is a chromium film, 3 is a resist layer, 4 is an ionizing radiation, and 5
6 shows an exposed portion, 6 shows an etching gas plasma, 7 shows an oxygen plasma, 8 shows a transparent film (shifter), and 9 shows an etching gas plasma for the transparent film.

First, as shown in FIG. 3(a), an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied on a mask substrate l which has been optically polished and has a chromium film 2 on its surface by a conventional method such as spin coating. A thin resist film 3 having a thickness of about 0.1 to 2.0 μm is formed by coating the resist film on the substrate and subjecting it to a heat drying process. The heat drying process is usually performed at 80 to 200° C. for about 20 to 60 minutes, although it depends on the type of resist.

Next, as shown in FIG. 4B, a pattern is drawn on the ionizing radiation resist layer 3 using an exposure device using ionizing radiation 4 such as an electron beam drawing device according to a conventional method, and as shown in FIG. After development with a developer containing an organic solvent such as ethyl cellosolve or ester as a main component, the resist pattern is formed by rinsing with alcohol.

Furthermore, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as resist scraps and whiskers remaining at the edges of the resist pattern, and then as shown in the figure (
As shown in d), the portion to be processed exposed through the opening of the resist pattern is wet etched or dry etched using etching gas plasma 6 to form a pattern.

After etching in this way, the remaining resist 5 is stripped off with a solvent or removed by ashing with oxygen plasma 7, as shown in Figure (e), and a photomask as shown in Figure (F) is completed. let

Subsequently, this photomask is inspected, pattern corrections are made if necessary, and after cleaning, SiO2 and Si*N4 are deposited on the chrome pattern as shown in FIG.
, PMMA or the like is formed to transmit at least ultraviolet rays. Next, as shown in FIG. 6(h), an ionizing radiation resist layer 3 made of chloromethylated polystyrene or the like is provided on the transparent film 8 in the same manner as described above, and as shown in FIG. The resist layer 3 is aligned in accordance with a conventional method, a pattern is drawn using ionizing radiation 4 from an electron beam exposure device, etc., and a resist pattern is formed by developing and rinsing (FIG. 6(j)).

Furthermore, after performing a heat treatment and a descum treatment as necessary, as shown in FIG. 9 to form a pattern.

The remaining resist film is removed by solvent stripping or ashing with oxygen plasma 7, as shown in the figure (1).
A phase shift mask as shown in m) is completed.

[Problem to be solved by the invention]

However, in order to pattern a transparent film used as a phase shifter on a reticle, when a pattern is drawn at a predetermined position using ionizing radiation such as an electron beam exposure device on an ionizing radiation resist layer coated on the transparent film, The alignment mark must be detected through a two-layer film of a transparent film and an ionizing radiation resist formed thereon. In order to detect alignment marks through such a two-layer film, the electron beam exposure apparatus requires an accelerating voltage of several tens of kilovolts. Therefore, before exposing the phase shifter pattern using an electron beam exposure system with an acceleration voltage of 10 to 20 KV, which is the most practical in terms of accuracy, reliability, throughput, etc. for photomask manufacturing, it is necessary to There is a problem in that the line exposure device cannot detect the reticle alignment mark. That is, FIG. 4(a) shows a cross section of the alignment mark AM portion in step (h) of FIG. 8. The ionizing radiation resist layer 3 is laminated, and even if an attempt is made to detect the alignment mark AM with an electron beam accelerated at 10 to 20 KV through these two layers, the transmitted output is shown in Fig. 4 (b). The alignment mark AM cannot be detected. The alignment mark AM in this state is shown in Fig. 4 (C).
In order to detect accurately with such an output, as described above, the acceleration voltage of the electron beam exposure apparatus needs to be several 1 OKV. Therefore, in order to accurately detect the alignment mark AM and create a phase shift mask, it is necessary to improve the accelerating voltage of the conventional photomask drawing device to 30 to 50 KV, or to create a new one that satisfies this requirement. It was necessary to purchase equipment, etc.

The present invention was made in view of this situation, and
The purpose is to use conventional electron beam exposure equipment as is,
An object of the present invention is to provide a method for manufacturing a highly accurate phase shift mask.

[Means to solve the problem]

In view of the above problems, the present inventor conducted research to develop a method for stably manufacturing a highly accurate phase shift reticle using a conventional electron beam exposure apparatus, and as a result, when forming a shifter,
By exposing the alignment mark on the reticle, detecting the exposed alignment mark with the electron beam of the electron beam exposure device, and drawing the shifter pattern in accurate alignment, the highly accurate phase shift reticle is stabilized. The present invention was completed based on this knowledge.

Hereinafter, a method for manufacturing a phase shift photomask according to the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view showing the process of manufacturing the phase shift reticle of the present invention, in which 21 is a substrate, 22 is a chromium film, 23 is a resist layer, 24 is light or ionizing radiation,
Reference numeral 29 indicates an etching gas plasma for the transparent film 25, and reference numeral 30 indicates an oxygen plasma.

First, as shown in FIG.
A photoresist such as FPR-800 is applied uniformly by a conventional method such as spin coating, and then heated and dried.
A resist film 23 having a thickness of about 0.1 to 2.0 μm is provided. The heat drying process usually takes 80 minutes, although it depends on the type of resist.
It is carried out at 0 to 150°C for about 20 to 60 minutes.

Next, as shown in FIG. 2B, the resist 23 is pattern-exposed using an exposure device such as an aligner according to a conventional method, developed with a developer containing tetramethylammonium hydroxide as a main component, and rinsed with pure water. Then, a pattern is formed in which the alignment mark AM is covered with a resist 23 (FIG. 1(C)).

Next, as shown in FIG. 1(d), a transparent film 25 that transmits at least visible light and ultraviolet rays is formed on this substrate by sputtering, CVD, coating with spin-on glass, or the like. Subsequently, a solvent (e.g., acetone) that dissolves the patterned resist
The transparent film 25 thereon is lifted off to expose the alignment mark AM (first [N (e)
).

Next, a positive ionizing radiation resist 26 is uniformly coated on the substrate on which the transparent film 25 is formed by a conventional method such as spin coating, and then heated and dried to a thickness of 0.1 to
A resist film 26 of about 2.0 μm is provided. The heat drying process usually takes place at 80 to 150 degrees, depending on the type of resist.
C for about 20 to 60 minutes.

Next, as shown in FIG. 5F, the alignment mark AM portion of the resist layer 26 is exposed using an exposure device such as an electron beam exposure device in a conventional manner, and developed with a predetermined developer to form the alignment mark AM. Expose ((g) in the same figure). Here, since the alignment mark AM is exposed, the alignment mark AM can be detected by an exposure electron beam with a relatively low acceleration voltage such as an electron beam exposure device, and accurately aligned drawing can be easily performed.

In order to form a shifter pattern, the alignment mark AM is detected by an electron beam exposure device or the like, and pattern exposure is performed at a predetermined position (FIG. 1(g)). After pattern exposure,
A resist pattern 27 is formed by developing with a predetermined developer and rinsing with a rinse solution.

Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as the resist layer remaining at the edge portions of the resist pattern 27, whiskers, etc., as shown in FIG. Then, the portion to be processed exposed through the opening of the resist pattern 27, that is, the transparent film layer 25, is dry etched using an etching gas plasma 29 to form a shifter pattern 28. It is clear to those skilled in the art that the shifter pattern 28 may be formed by wet etching instead of the tri-etching using the etching gas plasma 29.

After etching in this manner, the remaining resist 27 is ashed and removed by oxygen plasma 30, as shown in FIG. The phase soft mask with the pattern 28 formed thereon is completed.

That is, in the present invention, in order to ensure alignment when performing pattern exposure on a resist for forming a shifter pattern, the alignment pattern is exposed and then alignment drawing is performed on the resist for forming a shifter pattern. This is a method of manufacturing a phase shift photomask characterized by the following.

Note that the method of exposing the alignment pattern is not necessarily limited to the above method, and various modifications are possible.

Specifically, the method for manufacturing a phase shift photomask of the present invention includes at least a first step of exposing a predetermined mark of a reticle formed on a substrate to form an ultraviolet light transmitting thin film having a predetermined thickness. a second step of exposing the predetermined mark of the reticle and forming an ionizing radiation resist thin film on the substrate on which the ultraviolet light transmitting thin film has been formed; a third step of irradiating a radiation resist thin film with a pattern of ionizing radiation at predetermined positions and developing it to form a resist pattern; and a third step of etching the exposed ultraviolet light transmitting thin film using the resist pattern as a mask. and a fourth step of removing the resist thin film remaining after etching.

In this case, the first step includes forming a resist thin film on the reticle, irradiating the resist thin film with a pattern of light or ionizing radiation, and developing the resist film so as to cover the predetermined mark on the reticle. A step of forming a pattern, a step of forming an ultraviolet light transmitting thin film of a predetermined thickness on the substrate on which the resist pattern is formed, and a step of cleaning the resist with a solvent that dissolves the resist to remove ultraviolet light on the predetermined marks. It has actually been realized that the second step includes a step of lifting off the light-transmitting thin film, and the second step forms an ionizing radiation resist thin film on the substrate on which the ultraviolet light-transmitting thin film was formed in the first step. and a step of irradiating the predetermined mark portion of the ionizing radiation resist thin film with a pattern of light or ionizing radiation and developing it to expose the predetermined mark.

[Effect]

Photomasks are currently routinely manufactured by electron beam lithography using electron beam exposure equipment, but with the recent increase in the integration of LSI and VLSI, a phase shift mask has been devised. When manufacturing this phase shift mask practically, the problem is that the electron beam exposure equipment used to manufacture photomasks cannot accurately detect alignment marks from above the resist film or shifter film. ing.

In the present invention, when forming a shifter pattern, pattern exposure is performed by detecting alignment marks exposed in advance, so that pattern drawing can be performed with high precision and without alignment mark detection errors. It is possible to stably manufacture a highly accurate phase shift reticle without significantly changing the conventional photomask manufacturing process using electron beam lithography.

〔Example〕

Examples of the present invention will be described below.

(Example 1) A resist solution of 0FPR800 was applied by spin coating onto a reticle as shown in FIG. 1(a), and
Pre-bake at ℃ for 30 minutes to a thickness of 1. A uniform resist film 23 with a thickness of 0 μm was obtained.

Next, as shown in FIG. 1(b), the reticle on which the resist film 23 has been formed is exposed to an aligner using a photomask consisting of a pattern that blocks light from the alignment mark AM portion on the reticle, and after exposure, It was developed with NMD-3 and rinsed with pure water to obtain a reticle in which only the alignment mark AM portion was covered with the resist film 23 (FIG. 1(C)).

Next, as shown in FIG. 1(d), E is applied to this reticle.
5102 film 25 with a thickness of 406 nm using CR-CVD equipment
After being deposited, it is treated with acetone in an ultrasonic cleaning tank.
Lift off the 5in2 film 25 in the alignment mark AM part, and 5102 in the part other than the alignment mark AM.
A reticle with a film 25 formed thereon was obtained (FIG. 1(e)).

Next, a resist solution of electron beam resist EBR-9 was applied onto this reticle by a spin coating method.
Prebaking was performed at 0° C. for 30 minutes to obtain a uniform resist film 26 with a thickness of 0.6 μm.

Next, the alignment mark AM portion was exposed to light at a dose of 20 uC/at using an electron beam exposure device with an accelerating voltage of 20 KV (Fig. 1 (f)), and then a developer consisting of a mixture of methyl isobutyl ketone and isopropyl alcohol was applied. Develop with
Rinsing with isopropyl alcohol exposed the alignment marks on the reticle.

Next, while detecting the exposed alignment mark AM, a pattern is exposed at a predetermined position on the resist film 26 made of EBR-9 at a dose of 10 μC/d using an electron beam exposure device (Fig. 1(g)). , developed with a developer consisting of a mixture of methyl isobutyl ketone and isopropyl alcohol, and rinsed with isopropyl alcohol to form a resist pattern.

Subsequently, this was post-baked at 140°C for 30 minutes, and then descummed with I Torr and 100W oxygen plasma for 1 minute. Using the resist pattern as a mask, the exposed 5
The iCL film 25 was wet etched with an aqueous solution consisting of hydrofluoric acid and ammonium fluoride. Next, the remaining resist was removed by ashing with a 2 Torr, 400 W oxygen plasma (Fig. 1 (i)) A phase shift mask in which the L shifter pattern was formed with high precision was obtained (Fig. 1 (i)). (j)).

〔Effect of the invention〕

In the method for manufacturing a phase shift photomask of the present invention, when forming a shifter pattern, pattern exposure is performed by detecting alignment marks that have been exposed in advance. , pattern drawing can be performed, and it is possible to stably manufacture a high-precision phase shift reticle without significantly changing the photomask manufacturing process using conventional electron beam lithography.

[Brief explanation of the drawing]

FIG. 1 shows a method of manufacturing a phase shift photomask according to the present invention.
2 is a diagram showing the principle of the phase shift method in comparison with a conventional method. FIG. 3 is a sectional diagram showing the conventional phase shift reticle manufacturing process. FIG. 4 is a diagram showing the conventional phase shift reticle manufacturing process. FIG. 3 is a diagram for explaining the relationship between the acceleration voltage of an electron beam and an alignment mark detection signal in a shift reticle manufacturing process. AM... Alignment mark, 21... Board, 22
...Chromium film, 23...Resist layer, 24...Light or ionizing radiation, 25...Transparent film, 26...Ionizing radiation resist film, 27...Resist pattern, 2
8...Shifter pattern, 29...Etching gas plasma, 30...Oxygen plasma Diagram 2 Applicant: Dai Nippon Printing Co., Ltd. Agent Patent attorney: Hiroshi Nirasawa (7 others) Ien 1
, Mimu Ryori Saimi Mi 7 To ] Person chart number (f) 112 deni 1

Claims (3)

[Claims] (1) At least a first step of exposing a predetermined mark of a reticle formed on a substrate to form an ultraviolet light transmitting thin film having a predetermined thickness; a second step of forming an ionizing radiation resist thin film on the substrate on which the light-transmitting thin film is formed; and irradiating a pattern of ionizing radiation at a predetermined position of the ionizing radiation resist thin film while detecting the position of the exposed mark; a third step of developing to form a resist pattern; a third step of etching the exposed ultraviolet light transmitting thin film using the resist pattern as a mask; and a fourth step of removing the resist thin film remaining after etching. A method for manufacturing a phase shift photomask, comprising: (2) The first step includes forming a resist thin film on the reticle, irradiating the resist thin film with a pattern of light or ionizing radiation, and developing the resist to cover the predetermined mark on the reticle. A step of forming a pattern, a step of forming an ultraviolet light transmitting thin film of a predetermined thickness on the substrate on which the resist pattern is formed, and a step of cleaning the resist with a solvent that dissolves the resist to remove the ultraviolet light on the predetermined marks. 2. The method of manufacturing a phase shift photomask according to claim 1, further comprising the step of lifting off the light-transmitting thin film. (3) The second step includes forming an ionizing radiation resist thin film on the substrate on which the ultraviolet light transmitting thin film was formed in the first step, and applying light to the predetermined mark portion of the ionizing radiation resist thin film. 3. The method of manufacturing a phase shift photomask according to claim 1, further comprising the steps of irradiating a pattern with ionizing radiation and developing to expose the predetermined mark.