JPH04131853A - Method for correcting phase shift photomask - Google Patents

Abstract

PURPOSE:To stably correct a lack part by forming a thin film consisting of SOG(spin on glass), then irradiating a part corresponding to the defect part of a phase shifter with an energy rays, and continuously developing and heating it. CONSTITUTION:The lack part 33 of a phase shifter pattern to which the primer material of the spin on glass 34 is applied is irradiated with the energy rays 36 in accordance with the shape of the lack part. After the irradiation with the energy rays 36, a substrate 30 is developed by a solvent and the spin on glass at a part other than the part which is irradiated with the energy rays is washed away and burned. The lack part of the phase shifter is easily corrected by the extension of ordinary lithographic technique such as the formation of the SOG thin film and the exposure with the energy rays, and the phase shift photomask having the defect is used with high quality again.

Description

[Detailed description of the invention] [Field of industrial application: This invention relates to a method for manufacturing a photomask used in the manufacture of high-density integrated circuits such as LSI and VLSI, and in particular,
The present invention relates to a method of repairing a photomask having a phase shift layer when forming fine patterns with high precision.

[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 an S1 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 when the average value = 3σ (σ is the deviation of the rubbing part).
Similarly, a 5x reticle for a 4V bit DRAM is 0.
16 Mbit DRAM with dimensional accuracy of 1 to 0.15 μm
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 μm for 1M pitch) DRAM.
, 0.8μm for 4Mbit DRAM, 16Mbit D
RAMs are required to be further miniaturized to 0.6 μm, and various exposure methods are being researched to meet these demands.

However, when it comes to next-generation device patterns in the 64-Mbit DRAM class, for example, the conventional stepper exposure method using a reticle reaches the resolution limit of the resist pattern.
A reticle based on a new concept called a phase shift mask has been proposed, as disclosed in Japanese Patent Publication No. 59296/1983. Phase shift lithography using a phase shift reticle is a technique that improves the resolution and contrast of a projected image by manipulating the phase of light that passes through the reticle.

(Phase Shift) The IJ sogerafy will be briefly explained according to the drawings. Figure 2 is a diagram showing the principle of the phase shift method, and Figure 3 is a diagram showing the conventional method.
> is a cross-sectional view of the reticle, Figures 2(b) and 3(b)
is the amplitude of the light on the reticle, Figures 2(C) and 3(c)
) is the amplitude of the light on the wafer, Fig. 2(d) and Fig. 3(
d) shows the light intensity on the wafer, 1 is the substrate,
2 is a light shielding film, 3 is a phase shifter, and 4 is 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, and a light-transmitting part in a predetermined pattern is formed. 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
), and the amplitude of the light on the wafer also becomes the same phase as shown in Figure 3(c).As a result, the patterns on the wafer can be separated as shown in Figure 3(d). In contrast, in phase shift lithography, the light transmitted through the phase shifter is the 21st! (
As shown in b), since adjacent patterns are set in opposite phases to each other, the light intensity becomes zero at the pattern boundary;
Adjacent patterns can be clearly separated as shown in FIG. 2(d). In this way, in phase shift lithography, patterns that could not be separated in the past can be separated, and resolution can be improved.

Next, an example of a manufacturing process for a phase shift reticle will be described with reference to the drawings. FIG. 4 is a cross-sectional view showing the manufacturing process of a phase shift reticle, in which 11 is a substrate, X2 is a chromium film, 13 is a resist layer, 14 is an ionizing radiation, 15 is a resist pattern, 16 is an etching gas plasma, 17
18 is a chromium pattern, 18 is an oxygen plasma, 19 is a transparent film, 20 is a resist layer, 21 is an ionizing radiation, 22 is a resist pattern, 23 is an etching gas plasma, 24 is a phase shift pattern, and 25 is an oxygen plasma.

First, as shown in FIG. 4(a), a chromium film 12 is formed on an optically polished substrate 11, and then an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a conventional method such as spin coating. A resist layer 13 having a thickness of about 0.1 to 2.0 μm is formed by applying heat and drying treatment. The heat drying treatment is usually carried out at a temperature of 80 to 150° C. for about 20 to 60 minutes, although it depends on the type of resist used.

Next, as shown in E(b), a pattern is drawn on the resist layer 13 using ionizing radiation 14 using an exposure device such as an electron beam lithography device according to a conventional method, and an a-containing solvent such as ethyl cellosolve or ester is used as the main component. After development with a developer solution, the resist pattern 15 is rinsed with alcohol to form a resist pattern 15 as shown in section (C).

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 15, whiskers, etc., and then as shown in FIG. Then, the portion to be processed exposed through the opening of the resist pattern 15, that is, the chromium layer 12, is dry etched using an 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 using the etching gas plasma 16.

After etching in this way, as shown in EZ (e), the resist pattern 15, that is, the remaining resist, is removed by ashing with oxygen plasma 18,
Complete a photomask as shown in f). Note that this treatment is performed in place of the ashing treatment using oxygen plasma 18.
It is also possible to carry out by solvent stripping.

After inspecting this photomask, making pattern corrections if necessary, and cleaning, a transparent film 19 made of 5i02 or the like is formed on the chrome pattern 17 as shown in the same figure ((a)). Next, as shown in the same figure,
An ionizing radiation resist layer 20 made of polytetramethylated polystyrene or the like is formed on the transparent film 19 in the same manner as described above, and as shown in FIG. Ionizing radiation from electron beam exposure equipment, etc. 2
1, a predetermined pattern is drawn, developed and rinsed, and as shown in FIG.
to be accomplished.

Next, after performing a heat treatment and a descum treatment as necessary, the portion of the transparent film 19 exposed through the opening of the resist pattern 22 is dried with an etching gas plasma 23, as shown in FIG. Etching is performed to form a phase shifter pattern 24. Note that the phase shifter pattern 24 may be formed by wet etching instead of dry etching using the etching gas plasma 23.

Next, the remaining resist is removed as shown in (1) of the same figure.
Ashing is removed by oxygen plasma 25. Through the above steps, a phase shift mask having a phase shifter 24 as shown in FIG. 3(E) is completed.

[Problems to be Solved by the Invention] By the way, in the conventional manufacturing method of a phase shift reticle as described above, even if a defect occurs in the normal reticle before forming a phase shifter, a method for repairing it has already been established. As a result, a defect-free reticle could be manufactured. That is,
Black defects, such as chromium residue, are sublimated and blown away with a laser beam, and white defects, where chromium is missing, are removed using the lift-off method.
Alternatively, a method has been established in which defects are repaired by depositing a carbon film on white defect areas using an ion beam while emitting carbon-rich gas.

However, regarding the phase shifter of the phase shift reticle -
However, no correction method has been developed at all, and even if a phase shift reticle can be made to some extent, if a defect occurs, it cannot be put to practical use at all.

The present invention was made in view of this situation, and
The purpose is to provide a more practical method of correcting defects in the phase shifter of a phase shift reticle, and in particular a method of correcting its omission.

In view of the above-mentioned problems, the present invention was developed as a result of research to develop a practical and highly accurate method for modifying the phase shifter of a phase shift reticle. After forming a thin film of spin-on glass, the part corresponding to the missing part of the phase shifter is irradiated with an energy beam, followed by development and heating. It was discovered that the missing portion could be stably corrected, and the present invention was completed based on this knowledge.

That is, the present invention uniformly applies a starting material for spin-on glass to a photomask that has a phase shift layer formed from a substrate, a light-shielding film pattern, and a phase shifter pattern, and has a missing portion in a part of the phase shifter pattern. a step of heat-treating a photomask coated with a starting material for spin-on glass; and a step of irradiating the missing portion of the phase shifter pattern coated with the starting material of spin-on glass with energy rays according to the shape of the missing portion. ,
A method for repairing a phase shift photomask, comprising the steps of: developing the substrate after energy ray irradiation with a solvent to wash away spin-on glass other than the area irradiated with the energy ray; and baking the developed substrate. It is.

In this case, it is also preferable that the modified portion of the phase shift photomask is shaped by a laser beam or an ion beam after the modification step is completed.

Hereinafter, the correction method of the present invention will be explained with reference to FIG. FIG. 1 shows a phase shift photomask (
3 is a cross-sectional view showing the steps of a method for repairing a phase shift layer of a reticle, in which 30 is a substrate, 31 is a light shielding layer, 32 is a phase shifter, 33 is a missing portion of the phase shifter, and 34 is an SO
35 is an exposed portion, 36 is an energy beam, and 37 is a laser beam.

Before explaining FIG. 1, the SOG will be briefly explained.

SOC (spin-on glass) refers to a film formed by coating, drying, and heating a solution of an organic silicon compound in an organic solvent and converting it into silicon oxide. As starting materials for SOG, metal alkoxides such as tetraethoxysilane (Sl(○C2H6)-), water, bipolar solvents such as methanol, and hydrochloric acid are used. In addition, triethoxymethylsilane (CH=S i (OC2HS) 3) or jetoxydimethylsilane ((CH3)2S i (OC2H3)
) 2) is also added in an amount of several percent to several tens of percent based on tetraethoxysilane. An example of the mixing ratio of these starting materials is S i (OCiH-)-: CH3S i (QC-
H8) 3H20: C, H50H: HC1 = 100:2:660:1050:6.

Hydrolysis reaction and polycondensation are initiated by such mixing of starting materials. This reaction is formally a hydrolysis of: S
1(OEt)* +H20#S i (OEt)30
H, S i (OEt:h(OH)z, etc+
E tOH (Et:CzHs) Polycondensation: Mi S i -OH+HO-5i =→=S i
−〇−3i”卆H,0 Total reaction: ;=[S i (OEt), (OH)−〇o, S (
s-a-1,1, + (4-a) EtOH Through such hydrolytic condensation, 5i-
0 polymer (polysilicate) is obtained.

In the case of SOG containing a methyl group, S i (
A mixture of OC, Hs), CH, Si (OCR=)3 is used. This reaction formula is formally expressed as follows.

+H20=S 1(OEt)sOH+ CH3S i (OEt)2(OH)+s i (OE
t)-(OH)+CH3S i (OEt)(OH)a
, etc, +EtOH condensation polymerization: =S i -OH
+HO-5i Mi→Mi5i-0-3i Mi+H20 Total reaction [(CH3)U, aS i (OE t)-(OH)b
o o, s ++-4-. Ko.

+ (4-a) EtOH Spin-coding this low molecular weight SOG onto a substrate and soft baking (80° to 120″) slightly increases the molecular weight of the SOG.

Heating [(CHs)-7a S i (OEt)-(OH)b
Oc′l−=[(CH3)−/□5i(OEt),
ゆ(OE()b,oC,],.

a” <a, b” <bSc” >cSn” >n When this substrate is further heated at 400°C to 500°C, dehydration,
As the dealcoholization reaction progresses, the molecular weight increases rapidly,
It becomes a dense SOC film.

[(CHa)a*zas i (OE t)-*(OH
)be○c*]as→ 口(CHa)-・/-S i
(OH)-0xko,・n゛→■,X→0. y→2
approach.

In SOG containing methyl groups, the methyl groups remain in the film even after heating to 400°C to 500°C. An example of the structure of SOG after heating at 400°C to 500°C is shown in FIG.

After the above soft bake, electron beam, ion beam,
rays, T-rays, synchrotron radiation such as SOR, and light such as lasers (hereinafter referred to as
It's called an energy line. ), polymerization occurs in the irradiated area and the molecular weight increases.

When this SOG is developed with a solvent such as alcohol after being irradiated with energy rays, the portion of SOG irradiated with energy rays remains due to the difference in molecular weight.

Now, returning to FIG. 1, first, as shown in FIG. 1(c), on the phase shift reticle having the missing portion 33 of the phase shift (li) 132 as shown in FIG. SOG is applied by a conventional method and heat-dried to form 800 layers 34.

Here, the 5OGlt 134 is usually coated to a thickness of about 0.3 to 0.6 μm after polymerization, although it depends on the wavelength of the photomask used, the refractive index of the 800 layer 34, and the like. The heat drying treatment is usually performed at 100 to 180° C. for about 30 minutes, although it depends on the type of SOG. In addition, above 3
Regarding the thickness of the 00 layer 34, as is clear from the effect of the phase shift layer 32, the thickness of the phase shift layer 32 after modification is
It is necessary to select a thickness such that the amount of phase shift including the modified portion becomes a predetermined amount of phase shift <180').

After the SOG coating and drying, as shown in FIG. 3(b), the missing portion 33 of the phase shifter 32 is irradiated with energy rays 36 according to its size to increase the molecular weight of the exposed portion 35, and then developed. The portion 35 is left behind.

Note that the energy rays 36 irradiated in this way include:
Any of electron beams, laser ion beams, xi, gamma rays, radiation rays such as SOR, and other light may be used.

Next, this substrate was immersed in alcohol for 5 minutes and developed.
As shown in FIG. 1(C), a phase shift F reticle is obtained in which the missing portion 33 of the phase shifter 32 is repaired by the 5OG 35.

Subsequently, this substrate was heated at 250°C for 30 minutes, then at 450°C.
Heat treatment is performed at ℃ for 60 minutes to bake 5OG35.

With the above steps, the correction of the missing portion 33 of the phase shifter 32 is basically completed, but in order to obtain a phase shifter with better shaping conditions or one with improved surface quality, it is necessary to repair the missing portion 33 of the phase shifter 32 as shown in FIG. 1(d). Then, by irradiating the repaired portion 35 with a laser beam, ion beam, etc. 37 and shaping it, the first
A highly accurate phase shift reticle as shown in Figure (e) can be created.

Note that, as mentioned above, the phase shift layer 32 whose missing portion 33 is corrected by changing the SOG to 5iOi may be made of any material and its formation method may be any material, but the SOG on the missing portion and the SOG on the corrected portion may be used. If there is a large difference in refractive index between the phase shift layer 32 adjacent to the phase shift layer 32, reflection will occur at the interface, which is undesirable. SiO
It can be said that it is particularly suitable for a phase shift reticle consisting of.

[Effect]

In the repair method of the present invention, a starting material for spin-on glass is uniformly applied to a photomask having a missing part in a part of the phase shifter pattern, and the coated photomask is heat-treated to fill in the missing part of the phase shifter pattern. Normal lithography involves irradiating energy rays according to the shape of the missing parts, developing the substrate after irradiation with energy rays with a solvent, washing away the spin-on glass other than the areas irradiated with energy rays, and baking the developed substrate. By extending the technology, it is possible to correct the missing part of the phase shifter, making it easier to put phase shift photomasks into practical use, and once again eliminating phase shift photomasks that were previously treated as defective products due to defects. It can be used in high quality condition.

〔Example〕

Examples of the present invention will be described below.

Example 1 SOG was applied by spin coating onto a phase shift reticle having a defective part where a part of the phase shifter was missing, and prebaked at 150°C for 30 minutes to a thickness of 450 nm.
A SOG film of m was obtained.

Next, the missing portion of the phase shifter was exposed in the form of a missing pattern using an ion beam with an accelerating voltage of 150 kV. After exposure, this substrate was developed with ethanol for 5 minutes, and
SOG other than the exposed areas was washed away by rinsing with isopropyl alcohol for 2 minutes.

Subsequently, this substrate was heated at 250°C for 30 minutes and at 450°C for 6 minutes.
The SOG was fired by heat treatment for 0 minutes.

In the manner described above, the defective portion of the phase shifter was completely repaired.

When the thus modified phase shift reticle was used for exposure with an i-line stepper, the modified portion could be used without any problem.

Example 2 In the same manner as in Example 1, SOG was applied by spin coating onto a phase shift reticle having a defect in which a phase shifter was missing, and prebaked at 150°C for 30 minutes to form an SOG film with a thickness of 450 r and m. Obtained.

Next, the missing portion of the phase shifter was exposed to an ion beam with an accelerating voltage of 150 kV, making it slightly thicker than the missing pattern. After exposure, this substrate was developed with ethanol for 5 minutes and with isopropyl alcohol for 2 minutes to form an SOR pattern.

Subsequently, this substrate was heated at 250°C for 30 minutes and at 450°C for 6 minutes.
The SOR pattern was fired by heat treatment for 0 minutes.

Through the above process, the missing portion of the phase shifter could be repaired, but since the pattern was exposed to a thicker layer to repair it, something like a patch was formed at the edge of the repaired portion.

Therefore, the redundant repaired area was removed using laser repair for repairing black defects on photomasks, and the repaired area was reshaped.

In this way, the defect in the phase shifter was completely repaired.

It should be noted that after correcting the missing part, it was possible to reshape the corrected part using laser repair, etc. to achieve more accurate correction.

[Effects of rift]

Photomasks used in the manufacture of semiconductor integrated circuits are currently
A patterned chromium film or other light-shielding film is used on a quartz or other glass substrate, but with the recent high integration of VLSIs, the conventional exposure technology using photomasks is approaching its limits. , there is a trend toward using phase-shift photomasks. As described above, the present invention allows the missing portion of the phase shifter to be easily corrected by extending the normal lithography technology of forming a SOG thin film and exposing it to energy beams, thereby facilitating the practical use of phase shift photomasks. At the same time, phase shift photomasks that have conventionally been treated as defective products due to defects can be used again in a high-quality state.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the steps of an embodiment of the method for correcting a phase shift photomass according to the present invention, FIG. 2 is a diagram showing the principle of the phase shift method, and FIG. 3 is a diagram showing the conventional method. FIG. 4 is a cross-sectional view showing the manufacturing process of the phase shift photomask, and FIG. 5 is a view showing an example of the structure of the SOG after being heated and formed. 30... Substrate, 31... Light shielding layer, 32... Phase shifter 33... Phase shifter missing portion, 34... S
OG thin film, 35...Exposed part, 36...Energy ray, 37...Laser beam Applicant: Dai Nippon Printing Co., Ltd. Agent Patent attorney: Hiroshi Nirasawa (7 others) Figure 4 Section ■)

Claims (8)

[Claims] (1) A step of uniformly applying a starting material for spin-on glass onto a photomask having a phase shift layer consisting of a substrate, a light-shielding film pattern, and a phase shifter pattern, and having a missing part in the phase shifter pattern; A step of heat-treating a photomask coated with a starting material for glass, a step of irradiating the missing portion of the phase shifter pattern coated with the starting material of spin-on glass with energy rays according to the shape of the missing portion, and irradiation with energy rays. A method for repairing a phase shift photomask, comprising the steps of: developing the subsequent substrate with a solvent to wash away spin-on glass other than the portion irradiated with energy rays; and baking the developed substrate. (2) The method for repairing a phase shift photomask according to claim 1, wherein the phase shift layer is made of silicon oxide. (3) The method for repairing a phase shift photomask according to claim 1 or 2, wherein the energy beam is an electron beam. (4) The method for correcting a phase shift photomask according to claim 1 or 2, wherein the energy beam is an ion beam. (5) The method for correcting a phase shift photomask according to claim 1 or 2, wherein the energy ray is a radiation such as an X-ray, a γ-ray, or an SOR. (6) The method for correcting a phase shift photomask according to claim 1 or 2, wherein the energy beam is light. (7) The method for correcting a phase shift photomask according to any one of claims 1 to 6, wherein the solvent used for development is alcohol. (8) The phase shift photomask according to any one of claims 1 to 7, wherein the modified portion of the phase shift photomask is shaped by a laser beam or an ion beam after the modification step is completed. How to fix.