JPH04153651A - Photomask having phase shift layer - Google Patents

Abstract

PURPOSE:To enhance resistances to chemicals, abrasion, and scratching by forming a protective layer on the almost all the surface on which the phase shift layer are formed. CONSTITUTION:A substrate 30 is coated with an organic solvent solution of an organosilicon compound as a phase shifter, dried, and heated to form an SOG (spin on glass) pattern converted into silicon oxide, and the protective layer 45 made of SiO2, TiO2, ThO2, ZnO, Al2O3, or the like, is formed by sputtering, vapor deposition, or chemical vapor deposition process on almost all the surface on which the phase shifters are formed. The SOG is weak in resistances to chemicals, abrasion, and scratching, but these resistances can be enhanced by forming this protective layer 45.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a photomask used in the manufacture of high-density integrated circuits such as LSIs and VLSIs, and particularly relates to photomasks used to form fine patterns with high precision. The present invention relates to a photomask having a phase shift layer.

[Conventional technology]

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

The photomask called a photomask used in such lithography process is 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 standard deviation) is taken.
Similarly, a 5x reticle for a 4Mbit DRAM is 0.
16M bit DRAM with dimensional accuracy of 1-0.15μm
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 μm for 1M bit DRAM.
, 0. for 4M bit DRAM. There is a demand for further miniaturization of 8 μm and 0.6 μm for 16 Mbit 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 that improves the resolution and contrast of a projected image by manipulating the phase of light that passes through the reticle.

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) is the amplitude of the light on the reticle, 2nd Eilffl(c) and 3(C) are the amplitude of the light on the wafer, and 2(d) and 3(d) are the amplitude of the light on the wafer. The above light intensity is shown respectively, 1
2 is a 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 to form a light-transmitting part in a predetermined pattern. However, in IJ Sogerafy, the second
As shown in Figure (a), a phase shifter 3 made of a transparent film is provided on one of the adjacent light transmitting parts on the reticle to invert the phase (increase the phase difference by 180°. Therefore, in the conventional method, is the amplitude of the light on the reticle is the third
The light beams on the wafer are in phase as shown in Figure 3(b), and the amplitudes of the lights on the wafer are also in phase as shown in Figure 3(C). In contrast, in phase shift lithography, the light transmitted through the phase shifter is made to have opposite phases between adjacent patterns, as shown in FIG. 2(b). The light intensity becomes zero at the pattern boundary, 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 in the past can be separated, and resolution can be improved.

Next, an example of a conventional 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, 12
1 is a chrome film, 13 is a resist layer, 14 is a 111M radiation, 15 is a resist pattern, 1G is an etching gas plasma, 17 is a chrome pattern, 18 is an oxygen plasma, 1
9 is a transparent film, 20 is a resist layer, 21 is ionizing radiation, 2
2 is a resist pattern, 23 is a wet etching, 2
4 indicates a phase shift pattern, and 25 indicates an oxygen plasma.

First, as shown in FIG. 4(a), a chromium film thickness 2 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 coating and heating and drying. The heat drying process is usually carried out at ±80 to 150°C for about 20 to 60 minutes, depending on the type of resist used, and then the resist layer 13 is coated with
A pattern is drawn with ionizing radiation 14 using an exposure device such as an electron beam lithography device according to a conventional method, and after development with a developer containing an organic solvent such as ethyl cellosolve or ester as a main component, rinsed with alcohol, A resist pattern X5 as shown in 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 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 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 manner, the resist pattern 15, that is, the remaining resist is removed by ashing with oxygen plasma 18, as shown in FIG.
Complete a photomask as shown in . Note that this treatment can also be performed by solvent stripping instead of the ashing treatment using the oxygen plasma 18.

Subsequently, this photomask is inspected, pattern corrected if necessary, and after cleaning, a transparent film 19 made of 5i02 or the like is formed on the chrome pattern 17, as shown in FIG. As a 5IO2 film, (CH3)
251 (OC, H5)2 etc. was dissolved in alcohol and spin coated on the substrate at 400°C to 5°C.
By firing at 00°C, S10. SO forming a film
G (spin-on glass) is commonly used.

This SOG membrane contains H, groups in the SOG peritoneum to reduce membrane stress, and is not completely 5iOz.

Next, as shown in FIG. 3(i), an ionizing radiation resist layer 20 made of chloromethylated polystyrene or the like 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,
A predetermined pattern is drawn using ionizing radiation 21 such as an electron beam exposure device, developed, and rinsed to form a resist pattern 22 as shown in FIG.

Next, after performing heat treatment and descum treatment as necessary, as shown in FIG. A shifter pattern 24 is formed. When the transparent film 19 is made of SOG, the selection ratio with respect to the quartz substrate is large, and a stopper layer is not required between the SOG layer and the quartz substrate.

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.

Incidentally, the phase shift photomask formed as described above requires cleaning after completion.

Methods for cleaning masks include acid cleaning, alkaline cleaning, scrub cleaning, and the like.

SOG as a phase shifter for phase shift photomasks
When using (spin-on glass), this cleaning becomes a problem. When SOG is fired at 500° C. or lower, the film contains -CH, groups, and -CH groups, and it does not become a complete SiO2 film). Therefore, acid resistance and alkali resistance are weak. Also, the surface is softer than normal 5+Oz film)
. For this reason, scrubbing will result in scratches.

If the SOG film is fired at a temperature of 700°C or higher, it will be perfect.
Regarding the IO2 film, in this case, a large stress is generated in the SOG film, causing the film to peel or crack.

For this reason, baking the SOG film at a temperature of 700°C or higher is
This is not possible with photomasks.

This introduction was made in view of this situation,
The purpose of this is to improve chemical resistance such as acid resistance and alkali resistance, abrasion resistance, and scratch resistance of the phase shift layer made of SOG etc. during the manufacturing process in photomasks having a phase shift layer. The purpose is to provide photomasks.

[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 and cleanable phase shift photomask, and found that after forming an SOG pattern as a phase shifter, the phase shifter It was discovered that a phase shift photomask can be cleaned by depositing SiO2 or the like on the entire surface of the formed enclosure by sputtering or the like, and the present invention was completed based on this knowledge.

Hereinafter, before explaining the manufacturing process of the photomask of the present invention, SOG will be briefly explained. 5OG (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 change it into silicon oxide. Tetraethoxysilane (
Metal alkoxides such as S i (OC=H5)-), water, bipolar solvents such as methanol, and hydrochloric acid are used. In addition, in order to leave a methyl group (-CH,) in SOG, triethoxymethylsilane (CHaS i (OCzHs)
), jetoxydimethylsilane ((CH.

)2S i (○C1HsL) and )limethylethoxysilane ((CHs)-31(○C,H1)) are also added in an amount of several percent to several tens of percent based on tetraethoxysilane.

To give an example of the mixing ratio of these starting materials, S i
(OC-Hs)-: CH3S 1(OC2H1L:
H,O: C2)f,OH: HCl100:2:66
It is 0:1050:6.

Hydrolysis reaction and polycondensation are initiated by such mixing of starting materials. This reaction is formally a hydrolysis of: S
I(OE tL↑H20#5i(OEt)sOH,S
i (OEt)a(OH)z, etc+Eto
H (Et:CzHs) Polycondensation: =S i -OH+HO-s i=→=Si
-0-3i Mi+HzO (Hereafter, blank space) Total reaction: ;" [S i (OE t), (OH)-0゜, S
+4-a-11J n+ (4-a) EtOH Through such hydrolytic condensation, 5i-
0 polymer (polysilicate) is obtained.

In the case of SOG containing a methyl group, s r (
OC2H5)4 , CH3S I(OCH5)3 (D
Because a mixture is used, methyl groups remain in the polymer.

This reaction is formally expressed as follows.

=HzO=S i (OEt)sOH-CH3S 1(
OEt), (OH)+S 1(OEt)2(OHLa=
CHsS i (OEt) (OH)2. etc, -LE
tOH condensation polymerization: =S i -OH + HO-5i MiMi 5i-0-SiMi + H10 Total reaction: +0.5 (4asb) ) Lao; C(CHs)-zss i (OEt) 1(OH)bo
o, 5(4-a-b,"I n+ (4-a)EtO
H Spin-coding this low molecular weight SOG onto a substrate and soft baking (80° to 120°) C(CH3)-
7z S i (OEt)-(OH)b OcE ,
, =ECHs)-*z2S + (OE t)aj○H
) b * OC * 1 n * a” <a%b” <
b, c” >c%n” >n Furthermore, this substrate was heated to 400°C.
When heated at ~500°C, dehydration and dealcoholization reactions proceed, the molecular weight increases rapidly, and becomes dense 5O (Jlj).

2 (CH3) ,, *z2S l (OE t) as
(OH) boo co2 0.

-Ic) (3), ・ZaS+(○H8, 2, ・n
-(3), approaches x-0, 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 500°C is shown in FIG.

Hereinafter, the manufacturing process of a photomask having a phase shift layer according to the present invention will be explained with reference to the drawings. FIG. 1 is a cross-sectional view showing the manufacturing process of 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, 33 is a resist layer, 34 is ionizing radiation,
35 is a resist pattern, 36 is an etching gas plasma, 37 is a light shielding pattern, 38 is an oxygen plasma, 39 is a 500 layer, 40 is a resist layer, 41 is an ionizing radiation, 42
is a resist pattern, 44 is a phase shift pattern, 45
indicates a phase shifter protective layer.

First, as shown in FIG. 1(a), a uniform conductive layer 31.50~ with a thickness of 1~30 nm is placed on an optically polished substrate 30.
A light-shielding layer 32 with a thickness of 200 nm is sequentially formed, and then an ionizing radiation resist such as polytetramethylated polystyrene is uniformly applied by a conventional method such as spin coating, and heat-dried to a thickness of 0.0 nm. 1-2. A resist layer 33 of approximately DIJm 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), MgF2, CaFz, etc. can be used. Further, the conductive layer 31 can be formed using tantalum, molybdenum, tungsten, TO mesa, or the like. 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. In addition, heat drying treatment is usually performed at 80 to 150°C for 20 to 60°C, although it depends on the type of resist.
Do this for about a minute.

Next, the same v! J et al.), in the resist layer 33,
A predetermined pattern is drawn using an exposure device using ionizing radiation 34 such as an electron beam drawing device in accordance with a conventional method, and after development with a developer containing an organic solvent such as ethyl cellosolve or ester as a main component, and rinsing with alcohol, the same figure ( 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 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 removed by ashing with oxygen plasma 38, as shown in FIG. 3(e), and as shown in FIG. A photomask is prepared in which a predetermined light shielding pattern 37 is formed on the photomask. In addition,
This treatment can also be performed by solvent stripping instead of the ashing treatment using the oxygen plasma 38.

Next, this photomask is inspected, the pattern is modified if necessary, and it is cleaned. After that, as shown by mark c in the same figure, SoG was spin-coated on the light-shielding pattern 37, the solvent was dried at 200°C, and the solvent was dried at 450°C.
The phase shifter layer 39 is formed by firing in a nitrogen atmosphere.

The III+ thickness of this phase shifter layer 39 is d=λ/2(
n-1), and using SOG, the value of d is 445 layers m due to n=1.41.

Next, as shown in FIG. 9, on the phase shifter layer 39,
In the same manner as described above, a resist layer 40 is formed by uniformly applying an ionizing radiation resist such as chloromethylated polystyrene.
As shown in 11 (il), a resist layer 40 is formed.
Alignment is carried out according to a conventional method), a predetermined pattern is drawn at the position where the phase is to be shifted by ionizing radiation 41 from an electronic IiN optical device, etc., developed with a predetermined developer, rinsed, and the same figure is obtained. As shown in (J), a resist pattern 42 is formed.

Subsequently, after performing heat treatment and descuming as necessary, the same! ! As shown in I (g), 500 layers exposed from the opening of the resist pattern 42 are wet-etched to form a phase shift pattern 44. A buffered hydrofluoric acid solution (hydrofluoric acid + ammonium fluoride) is used as the wet etching solution. SOG etching is
Substrate 30 is hardly etched because a much lower concentration solution than the normal SiO□ etching solution is used.

Next, as shown in FIG. 1 (1), the remaining resist is removed using a resist stripping solution.

After this, as shown in the same figure, the SOG pattern 44
Then, a protective layer 45 is formed on the chrome pattern 37. This protective layer 45 can be formed by sputtering method, vapor deposition method, CV
D (chemical vapor deposit)
i.

n) A SiO□ film formed by the method is used. This 8102
The thickness of the film is arbitrarily selected between 20 and 200 nm.

This S+Oz! Since the film is formed over the entire surface of the SiC film, including the part where the phase shifter 44 is not present, the phase difference caused by the phase shifter 44 does not change before and after the SiC film is formed.

As described above, in the photomask having the phase shift layer of the present invention, S0G is used as the phase shifter, and in order to ensure its chemical resistance, abrasion resistance, and scratch resistance, the protective layer 45 is formed by sputtering, Vapor deposition method or CVD
Although a 5iO7 film formed by the method is used, the material for the protective layer 45 is not limited to this.
, T h○=, ZnO1A1203 can be used.

Furthermore, when using fluorite (CaFs), which has poor chemical resistance, abrasion resistance, and scratch resistance, like SOG, as the phase shifter, it is desirable to use a similar protective layer 45.

[Effect]

As the phase shifter of the phase shift photomask, Si
O2 membranes are commonly used. Possible methods for forming the SiO2 film include sputtering, vapor deposition, CVD, and SOG spin code; however, considering the problems of productivity, film adhesion, and dust generation, sputtering and SOG spin code are the most suitable methods for forming SiO2 for phase shifters. Excellent as a film forming method. Considering step coverage and ease of film formation,
The SOG spin code method is superior to the sputtering method. The problem with the 5iO= sputtering method is that the film formation rate is slow. The biggest problem with SOG is that the film has poor chemical resistance, abrasion resistance, and scratch resistance, but in the photomask of the present invention, the surface is coated with sputtering, vapor deposition, or CVD. SioasTi02%T
By forming ha2, ZnO1, or AlzOz film as a protective film, chemical resistance, abrasion resistance, and scratch resistance are improved.

Furthermore, compared to the case where all the SIOx of the phase shifter is deposited by sputtering, the step coverage is excellent and the deposition rate is faster. Therefore, the photomask having the phase shift layer of the present invention has high precision and excellent chemical resistance and abrasion resistance.In particular, the photomask after completion can be cleaned by acid cleaning, alkali cleaning, scrub cleaning, etc. Even if the phase shift layer is cleaned, the phase shift layer will not be damaged, so accuracy and productivity will be improved.

Note that a similar effect can be obtained when using fluorite as a phase shifter.

[Example Examples of the present invention will be described below.

A two-layer structure consisting of a 200 nm thick Ta thin film as a conductive layer, an 800 nm thick chromium thin film and a 400 nm thick low reflection chromium thin film as a light shielding layer is formed on an optically polished 5 inch square high purity synthetic silica glass substrate. A resist solution of chloromethylated polystyrene was applied onto the formed mask substrate by spin coating 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 c+d to draw a pattern. After exposure, the second substrate was developed for 60 seconds with a developer made from a mixture of isoamyl acetate and ethyl cellosolve, and then rinsed with isopropyl alcohol for 30 seconds to obtain a resist pattern. Subsequently, this was post-baked 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 4 QOW to obtain a photomask before phase shifter formation. After checking the quality of the photomask manufactured in this way, 0CD-type 7 (S manufactured by Tokyo Ohka Kogyo ■) was placed on the photomask.
OG solution) was coated to a thickness of 445 m by a spin-coating method. Next, this board is 150
After drying at 450° C., firing was performed in a nitrogen atmosphere.

A resist solution of chloromethylated polystyrene was applied to this substrate by spin coating in the same manner as above, and a uniform resist film of 0.6 μm W was obtained by heating and drying. Next, pattern exposure was carried out at predetermined positions while detecting alignment marks on the photomask using an electron beam lithography system with an acceleration voltage of 20 kV. After exposure,
This substrate was developed and rinsed with the same solvent as above to obtain a resist pattern.

Subsequently, after heat treatment and descum treatment were performed, the exposed SOG film was treated with hydrofluoric acid (58 wt%) and ammonium fluoride solution (20 wt%) using the resist pattern as a mask.
) mixture (hydrofluoric acid: ammonium fluoride solution M=1:
10) Wet etching with l:. The resist used as a mask was removed with a stripping solution.

Next, S10. A film of 5 Qnm was deposited to obtain a phase shift photomask having a protective layer of 10 □ for an SOG phase shifter.

The thus completed phase shift photomask was scrub-cleaned, but no damage occurred to the SOG phase shift layer, and there were no problems as a photomask.

〔Effect of the invention〕

As a phase shifter for a phase shift photomask, S]
02 membrane is commonly used. Possible methods for forming SiO2 films include sputtering, vapor deposition, CVD, and SOG spin code, but considering the problems of productivity, film adhesion, and dust generation, sputtering and SOG spin code are the most suitable methods for phase shifters: This method is excellent as a 5i02 film forming method. In terms of step coverage and ease of film formation, the SOG spin code method is superior to the sputtering method. The problem with the SiO2 sputtering method is that the film formation rate is slow. The biggest problem with SOG is that the film has poor chemical resistance, abrasion resistance, and scratch resistance. Or S +02, Ti0a by CVD method
, ThC)a , ZnO1, or AlzO* film as a protective film, chemical resistance, abrasion resistance, and scratch resistance are improved.

Also, the phase shifter S10. Compared to the case where the film is entirely formed by sputtering, the step coverage is excellent and the film formation speed is faster. Therefore, the photomask having the phase shift layer of the present invention has high precision and excellent chemical resistance and abrasion resistance.In particular, the photomask after completion can be cleaned by acid cleaning, alkali cleaning, scrub cleaning, etc. Even if washed with
Since the phase shift layer is not scratched, accuracy and productivity are improved.

Note that a similar effect can be obtained when using fluorite as a phase shifter.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the manufacturing process of a photomask having a phase soft 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. FIG. 4 is a cross-sectional view showing the manufacturing process of a conventional phase shift reticle, and FIG. 5 is a view showing an example of the structure of an 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... 800 layers, 40... Resist layer, 4
1... Ionizing radiation, 42... Resist pattern, 4
4...Phase shift pattern, 45...Phase shifter protective layer 1 Figure M4 (S) - 11 Figure 4 O

Claims (5)

[Claims] (1) In a photomask having a phase shifter and a light shielding pattern that are separated by a light shielding region and providing a phase difference between mutually adjacent transparent regions, a protective layer of the phase shifter is provided on substantially the entire surface where the phase shifter is formed. A photomask having a phase shift layer formed therein. (2) The phase shifter is SOG (spin-on-glass)
2. The photomask having a phase shift layer according to claim 1, wherein the photomask is made of a film. (3) A photomask having a phase shift layer according to claim 1, wherein the phase shifter is made of a fluorite film. (4) The phase shift layer according to any one of claims 1 to 3, wherein the protective layer of the phase shifter is made of a SiO_2 film formed by a vapor deposition method, a sputtering method, or a CVD method. Photomask with. (5) The protective layer of the phase shifter is TiO_2, T formed by vapor deposition, sputtering, or CVD.
4. The photomask having a phase shift layer according to claim 1, wherein the photomask is made of hO_3, ZnO, or Al_2O_3 film.