JPH04131852A - Manufacturing of photomask with phase shifting layer - Google Patents

Abstract

PURPOSE:To reduce the number of processes and to contrive the reduction in cost by developing a spin-on glass (SOG) layer being coated with a solvent uniformly, washing away the spin-on glass except a portion being irradiated with electrolytic dissociation radiant rays, and subsequently sintering a substrate after washing out the SOG. CONSTITUTION:The SOG is a film changed to a silicon oxide on which an organic medium solution of an organic silicon compound is applied, dried, heated, and the SOG is spin-applied on the substrate which is soft calcined (80-120 deg.C). After soft-calcing, it is irradiated with radiant rays of electron beams, ion beams, X rays, gamma rays, SOR, etc., and energy rays of laser, etc., and is developed with a solvent of alcohol, etc., when a part of SOG being irradiated with energy rays remains with the difference of the molecular weight. The SOG has a property for which the molecular weight is increased, even though the irradiation amount of energy rays is small. Hence after the SOG coating, the exposure, the development and the sintering process only are conducted, then the decrease of the manufacturing process, the reduction in cost and the reduction in the defect generating ratio are attained.

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 LSI and VLSI), and in particular, it relates to a method for manufacturing a photomask used for manufacturing high-density integrated circuits such as LSI and VLSI, and in particular, The present invention relates to a method of manufacturing a photomask having a phase shift layer that can be formed with high precision.

Conventional technology: Semiconductor integrated circuits such as IC, LSI, and VLSI are manufactured using a so-called 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 developed and etched. (manufactured by repeating lithography steps).

Photomasks called reticles used in f-lithography are increasingly required to have higher precision as semiconductor integrated circuits become more sophisticated and highly integrated. Taking DRAM, which is an LSI, as an example, the dimensional deviation in a 5x reticle for IM bit DRAM, that is, a reticle with a size 5 times the size of the pattern to be exposed, is calculated by taking an average value of 23σ (σ is the standard deviation). 0.15 μm accuracy is required even in the case of
．． 16Mbit DRA with dimensional accuracy of 1 to 0.15μm
A 5x reticle for M 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.
, 4Mbit]) Further miniaturization is required, such as 0.8μm for RAM and 0.6μm for 16Mbit DRAM, 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 for improving the resolution and contrast of a projection projection by manipulating the phase of light passing through the reticle.

(Phase Shift) IJ Sogerafy will be briefly explained according to the 7 aspects. Figure 2 is a diagram showing the principle of the phase shift method, and Figure 3 is a diagram showing the conventional method.
) is the cross section V 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, the second section (d) and the third section (
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 3rd PK (a),
A light-shielding film 2 made of chromium or the like is deposited on a substrate 1 made of glass or the like to form a predetermined pattern of light-transmitting layers.
As shown in [:K (a>), a phase shifter 3 made of a transparent material of t is provided on one of the adjacent light transmitting/receiving portions on the reticle to invert the phase (phase difference 180'').

Therefore, in the conventional method, the amplitude of the light on the reticle is in the same phase as shown in FIG. 3(b), and the amplitude of the light on the wafer is also in the same phase as shown in FIG. 3(c).
As a result, the patterns on the wafer cannot be separated as shown in 3rd Em (d)! In contrast, in phase shift lithography, as shown in Figure 2(b), the light that has passed through the phase shifter should not be made to have opposite phases between adjacent patterns; At this point, the light intensity becomes zero, and 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 conventionally can be separated, and the resolution can be increased.

Next, an example of a conventional manufacturing process for a phase shift reticle will be explained with reference to sections. No. 47 is a cross section V showing the manufacturing process of the phase shift reticle, in which 11 is a substrate, 12
is a chromium film, 13 is a resist layer, 14 is ionizing radiation, 1
5 is a resist pattern, 16 is an etching gas plasma, 17 is a chrome 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, 2
4 indicates a phase shift pattern, and 25 indicates 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. Then, a heat drying process is performed to form a resist layer 13 having a thickness of about 0.1 to 2.0 μm. 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 FIG. 6(b), a pattern is drawn on the resist layer 13 using 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 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 FIG.

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. , dry etching the portion to be processed exposed from the opening of the resist pattern 15, that is, the chromium Fj 12, using the etching gas plasma 16;
A chrome pattern 17 is formed. It is clear 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 IK (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.

Subsequently, this photomask is inspected, pattern corrected if necessary, and after cleaning, a transparent film 19 made of SiO2 or the like is formed on the chrome pattern 17, as shown in FIG. Next, as shown in FIG. 3(C), an ionizing radiation resist layer 20 such as polytetramethylated polystyrene is formed on the transparent film 19 in the same manner as described above, and as shown in FIG. , align the resist layer 20 according to a conventional method, and apply ionizing radiation 21 from an electron beam exposure device or the like.
A predetermined pattern is drawn, developed, and rinsed.
As shown in the figure (''), a resist pattern 22 is formed.

Next, after performing a heat treatment and a descum treatment as necessary, the resist pattern 22 is
The portion of the transparent film 19 exposed through the opening is dry-etched using an etching gas plasma 23 to form a phase shifter pattern 24. Note that the formation of this phase shifter pattern 24 may be performed 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.

[Issues that Hathu tries to solve]

However, in the above-described conventional phase shift mask manufacturing method, transparent i! Il! In order to form a pattern on the film 19, a pattern is drawn on the resist layer 20 using ionizing radiation using an ionizing radiation exposure device, and after this is developed, a phase shifter is etched (wet or dry etching).
After forming the phase shifter pattern 24, the remaining resist must be removed. This requires a large number of manufacturing steps and increases the possibility that defects will occur in the phase shifter pattern and the like. Moreover, the cost also increases. The number of manufacturing steps can be reduced, the occurrence of the above-mentioned defects can be prevented, and costs can be reduced.

The present invention was made in response to this situation, and
The purpose is to provide a method for manufacturing a photomask having a phase shift layer that reduces the number of manufacturing steps for a phase shift photomask, reduces the incidence of defects such as phase shifter patterns, and reduces costs. That's true.

[Means to Solve the Problems] In view of the above-mentioned problems, Hu Kibatsu developed a photomask manufacturing process based on the conventional ionizing radiation phosphorography with a large vAi.
As a result of research to develop a method for stably manufacturing a high-precision phase shift reticle, we found that when forming a 5OG (spin-on-glass) pattern as a phase shifter pattern, SOG was directly irradiated with energy beams. drawing,
We discovered that it is possible to stably manufacture highly accurate phase shift reticles by using a pattern forming method.
Based on this knowledge, we have completed the Honfahu.

Before explaining the manufacturing method of Honhathu, SOG will be briefly explained. SOG (spin-on glass) refers to a film formed by coating, drying, and heating a solution of an organic silicon compound in an organic solvent to transform it into silicon oxide. As a starting material for SOG, tetraethoxysilane (S i (OC2H
5) Metal alkoxides such as 4), water, bipolar solvents such as methanol, and hydrochloric acid are used. In addition, in order to leave a methyl group (-CH,) in SOG, triethoxymethylsilane (CH3S i (OC2Hs) +), dinitoxydimethylsilane ((CH3)2S 1(○C,H,),
), trimethylethoxysilane ((CH3)-5i (
OC2HS)) is also several percent to tetraethoxysilane.
Dozens of additives are added. An example of the mixing ratio of these starting materials is S1(OCaHs)n:CH3S1(OCs
Hs)z: H2O: C,H,OH: HCfloo
:2+660+1050:6.

Hydrolysis reaction and polycondensation are initiated by such mixing of starting materials. This reaction is formally a hydrolysis of: S
i (OEt)a −H2O, :shiS i (OEt
)zOH, S i (OEt)z(OH)z, etc+
E to H (Et:C2H3) Polycondensation: =S 1-OH ○-3i=→Mi Si
OS i =+HaO (hereinafter, blank space) Total reaction; mouth S l (OEt), (OH), Oa, 5ti-
a-b) I'.

2(4-a) EtOH Through such hydrolytic condensation, 51-
0 polymer (borin ricade) is obtained.

In the case of SOG containing a methyl group, S'+ is added to the starting material.
By using a mixture of (OCzHs), CH3S1(OCHs)-, methyl groups remain in the polymer.

This reaction is expressed in the following way.

Hydrolysis: S i (OEt)4=CH3S i (
OEt)+H゛-)i 20 #31(OEt), ○H-CH=S i
(OEt)=(OH)-5i (OEt)2(OH)
−=C)(3S + (OEt)(OH)2.etc,
'-EtO! (Condensation polymerization: =Si-OH?H○-5i= → MiSi -0-Si +=-820 total reaction c (cHffi), /2s i (OEt), (C
H)bo o,s (4-a-blko, -4-(4-
a) EtOH Spin-code this low molecular weight SOG onto a substrate and soft bake (80゛-120'): (CHs)n
*zas i (OEt), *(OH)be○e*:,
, *a” <a, b” <bS c” >c, n”
>n When this substrate is further heated at 400° C. to 500° C., dehydration and dealcoholization reactions proceed, the molecular weight rapidly increases, and a dense SOG film is formed.

[(CH3),,-/2S t (OE t)-(OH
)b−○el−,,*−:(CH3),・/2 S +
(OH), OyL.

Approaching n-4■, X→○, y→2.

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 500C is shown in section 5.

After soft baking, electron beam, ion beam,
When irradiated with synchrotron radiation such as X-rays, T-rays, SOR, etc., or light such as laser (hereinafter referred to as energy rays), 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.

By the way, acid generators such as triphenylsulfonium triflate, halogen acids such as tetrabromobisphenol A11.1-bisparachlorophenyl-2,2,2-trichloroethane, and onium salts are added to SOG, and after soft baking, When irradiated with energy rays, acid is generated from the acid generator, and this acid acts on the hydroxyl groups (-〇H) and ethoxy groups (-〇C2H3) remaining in SOG,
The dehydration or dealcoholization reaction progresses, increasing the molecular weight. Compared to the case where the t1 acid generator is not included, the SOG containing the acid generator has the property of increasing the molecular weight (higher sensitivity) even if the amount of energy ray irradiation is small.

Below, the manufacturing method of the present invention will be explained using drawings! ! Get used to it. FIG. 1 is a cross-sectional view showing the steps of the method for manufacturing a photomask having a phase shift layer according to the present invention, in which 30 is a substrate, 31 is a conductive layer, 32 is a light shielding layer, and 33 is a resist layer. , 34 is ionizing radiation, 35 is resist pattern, 3rd is etching gas plasma, 37 is light shielding pattern, 38
39 is an oxygen plasma, 39 is a transparent film, 40 is a ninety-degree line, and 41 is a phase shift pattern.

First, as shown in FIG.
A light shielding layer 32 with a thickness of ~200 nm is sequentially formed, and an ionizing radiation resist such as polytetramethylated polystyrene is further applied.
It is applied uniformly by conventional methods such as spin coating, and then heated and dried to achieve a smoothness of 0. A resist N33 having a thickness of about 1 to 2.0 μm is formed. Here, as the substrate 30, quartz or high-purity synthetic quartz is preferable, considering that the phase shift mask is used for short wavelengths such as one-line or excimer laser. , blue plate (SL), MgFa, CaF2, etc. can be used. Further, the light shielding layer 32 can be formed by forming a single layer or multilayer of a chromium thin film, but it can also be formed by using chromium nitride, chromium oxide, tungsten, molybdenum, molybdenum silicide, etc. I can do it. Further, the heat drying treatment is usually performed at 80 to 150° C. for about 20 to 60 minutes, although it depends on the type of resist.

Next, as shown in b) of the same figure, a predetermined pattern is drawn on the resist layer 33 using an exposure device using ionizing radiation 34 such as an electron beam drawing device according to a conventional method, and an organic solvent such as ethyl cellosolve or ester is used as a main material. After development with a developing solution as a component, rinsing with alcohol forms a resist pattern 35 as shown in FIG.

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 35, whiskers, etc., as shown in FIG.
As shown in d), the portion to be processed exposed through the opening of the resist pattern 35, that is, the light-shielding layer 32, is dry-etched using etching gas plasma 36 to form a light-shielding pattern 37. It is clear to those skilled in the art that the light shielding pattern 37 may be formed by wet etching instead of dry etching using the etching gas plasma 36.

After etching in this manner, the remaining resist 35 is ashed and removed by oxygen plasma 38 as shown in 1m (e), and the conductive layer 31 on the substrate 30 is removed as shown in 1m (f). A photomask is prepared in which a predetermined light shielding pattern 37 is formed on the photomask. Note that this treatment can also be performed by solvent stripping instead of the ashing treatment using the oxygen plasma 38.

Subsequently, this photomask is inspected, the pattern is corrected if necessary, and after cleaning, a transparent film 3 is formed using SOG on the light-shielding pattern 37, as shown in FIG.
Spin code 9 and pre-bake (soft bake). The material for forming the transparent film 39 may be any material that is solidified by being exposed to the energy rays of the energy ray exposure device and has a high refractive index.
When a few percent of the above-mentioned acid generator is added to SOG, the sensitivity is significantly increased (several hundred times) compared to normal SOG to which no acid generator is added, making it a particularly preferred material. Here, the energy rays include electron beams, ion beams, X-rays, T-rays, synchrotron radiation such as SOR, and light such as lasers. Further, the film thickness d of the transparent film 39 (well, if the refractive index of the material forming the transparent film 39 is nSt and the light wavelength is λ, then d=λ/2(n-1) is the value given.

The substrate on which the transparent layer 39 has been formed is aligned according to a conventional method, and as shown in the same hole, a predetermined pattern is directly drawn at the position where the phase shifter is to be formed using an energy beam 40 of an electron beam exposure device, and methanol Develop with an organic solvent such as When SOG containing an acid generator is used, development is performed after post-exposure beta (post-exposure beta) 42 at 80 to 100° C., as shown in FIG. 1 (1). In this way, phase shift pattern 4
Leaving SOG 1 and removing the other SOGs, the substrate was then heat treated at 250°C for 30 minutes and then at 450°C for 60 minutes to bake 5OG41, as shown in Figure 1 (J). A highly accurate phase shift reticle can be created.

Subsequently, this photomask is inspected, the pattern is modified if necessary, and after cleaning, the phase shift photomask is completed.

[Effect]

In the present invention, SOG itself, which serves as a phase shifter, is solidified by energy ray irradiation, and uses the characteristic that SOG itself is solidified by energy ray irradiation. The process of peeling off the resist is omitted, and after SOG coating, exposure,
By only performing the development and baking process, it is possible to reduce the number of manufacturing steps, lower costs, and reduce the defect rate without significantly changing the photomask manufacturing process using conventional ionizing radiation phosphorography. .

〔Example〕

Examples of the present invention will be described below.

Example 1 A 200 nm thick Ta thin film as a conductive layer was placed on an optically polished 5 inch square high purity synthetic silica glass substrate, an 800 nm thick chromium thin film and a 400 ram low reflection chromium thin film as a light shielding layer. A resist solution of polytetramethylated polystyrene was applied by spin coating onto the layered mask substrate, and prebaked at 120° C. for 30 minutes to obtain a uniform resist film with a thickness of 0.6 μm.

Next, an electron beam with an accelerating voltage of 20 kV was applied to the
Exposure was performed at a dose of cut, and a pattern was drawn. After exposure, this substrate was developed for 60 seconds with a developer consisting of a mixture of isopropylene acetate and ethyl cellosolve, and then rinsed with isopropyl alcohol for 30 seconds to obtain a resist pattern. Subsequently, this was boiled at 140°C for 30 minutes and then IT.

rr, descum with 100W oxygen plasma for 2 minutes and expose the exposed substrate using the resist pattern as a mask.
Dry etching was performed for 8 minutes in a plasma consisting of carbon tetrachloride and oxygen at an output of 300 W. Next, the remaining resist was removed by ashing with oxygen plasma at 2 Torr and 4Q0W to obtain a photomask before forming a phase shifter. After checking the quality of the photomask manufactured in this way, SOG was spin-coded onto the mask so that lid (=λ/2(n-1), λ: exposure wavelength, n: refractive index of sOG). , heat and dry. Next, a pattern was directly drawn at a predetermined position while detecting the alignment mark on the photomask using an electron beam drawing device with an acceleration voltage of 30 keV. After drawing, this substrate was developed using methanol as a developer.
Developed for 0 seconds and baked at 450°C for 1 hour. In this way, a phase shift photomask having a SiO2 shifter layer made of SOG was obtained.

The positional shift of the phase shifter layer of the phase shift photomask manufactured in this way shows a value within ±0.1 μm when taking the average value 3σ (σ is the standard deviation), and a highly accurate phase shift photomask can be obtained. What happened to me was mi.

Moreover, no distortion of the pattern was observed at all in the peripheral area of the mask.

[Effects of the Invention] According to the method of manufacturing a photomask having a phase shift layer of the present invention, a method in which SOG itself, which serves as a phase shifter, is solidified by energy ray irradiation5) is used, which is different from the conventional manufacturing process. The process of SOG coating - resist coating, exposure, development, etching of SOG, and peeling off of the remaining resist is omitted, and only the SOG coating - exposure, development, and baking process is performed, and the photomask is manufactured using conventional ionizing radiation phosphorography. It has become possible to reduce the number of manufacturing steps, lower costs, and reduce the defect rate without significantly changing the manufacturing process.

[Brief explanation of drawings]

Fig. 1 is a cross section Σ showing the steps 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, and Fig. 3 is a diagram showing the conventional method. 4 are cross-sectional views showing the manufacturing process of a conventional phase shift photomask, and Section 5 is a view showing an example of the structure of the SOG after being heated and formed. 30... Substrate, 31... Conductive 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... Energy ray, 41.
...Phase shift pattern, 42...Bake after exposure
(Post-exposure bake) Applicant Dai Nippon Printing Co., Ltd. Agent Patent attorney Hiroshi Nirasawa (7 others) Figure 1 Figure 1 Figure 2 Figure 3 (d) fzuiri (d) / He ＼ M4 Figure 4 (f) 1121 [11

Claims (7)

[Claims] (1) A method for manufacturing a photomask having a phase shift layer includes at least a step of uniformly applying a starting material for spin-on glass, a step of directly drawing the applied spin-on glass layer with an energy beam, and a step of directly drawing the applied spin-on glass layer with an energy beam. Manufacture of a photomask having a phase shift layer characterized by comprising a step of developing the substrate after drawing with a solvent to wash away spin-on glass other than the portion irradiated with ionizing radiation, and a step of baking the substrate after development. Method. (2) The method for manufacturing a photomask having a phase shift layer according to claim 1, wherein the starting material for the spin-on glass contains an acid generator. (3) The method for manufacturing a photomask having a phase shift layer according to claim 1 or 2, wherein the energy beam is an electron beam. (4) The method for manufacturing a photomask having a phase shift layer according to claim 1 or 2, wherein the energy beam is an ion beam. (5) The method for manufacturing a photomask having a phase shift layer 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 manufacturing a photomask having a phase shift layer according to claim 1 or 2, wherein the energy ray is light. (7) The method for manufacturing a photomask having a phase shift layer according to any one of claims 1 to 6, wherein the solvent used for development is alcohol.