JP3308021B2 - Phase shift photomask blank and phase shift photomask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift photomask used for manufacturing high-density integrated circuits such as LSIs and VLSIs and for manufacturing high-speed devices using compound semiconductors, and a phase shift photomask blank. More particularly, the present invention relates to a phase shift photomask blank and a phase shift photomask having an etching stopper layer for protecting a transparent substrate when etching a phase shift layer.

[0002]

2. Description of the Related Art High-density integrated circuits such as ICs, LSIs, and VLSIs are developed and etched by applying a resist on a substrate to be processed such as a Si wafer and exposing a desired pattern by a stepper or the like. It is manufactured by repeating a so-called lithography process.

A photomask called a reticle used in such a lithography process tends to be required to have higher and higher precision as semiconductor integrated circuits become more precise and highly integrated. DR which is a simple LSI
Taking an AM as an example, the dimensional deviation of a 5 × reticle for a 1M bit DRAM, that is, a reticle having a size 5 times the size of a pattern to be exposed, is an average ± 3σ (σ is a standard deviation). Also, a precision of 0.15 μm is required. Similarly, a 5 × reticle for a 4 Mbit DRAM has a dimensional accuracy of 0.1 to 0.15 μm, and a 5 × reticle for a 16 Mbit DRAM has a dimensional accuracy of 0.05 to 0.1 μm. Dimensional accuracy is required.

Furthermore, the line width of a device pattern formed using these reticles is 1 Mbit DRAM.
1.2 μm, 0.8 μm for 4 Mbit DRAM, 1 μm
In the case of a 6 Mbit DRAM, a further miniaturization of 0.6 μm is required. Various exposure methods have been actively studied to meet such demands.

However, in the case of a next-generation device pattern of, for example, a 64-Mbit DRAM class, the resolution of a resist pattern is limited by a stepper exposure method using a conventional reticle. No. 173744, Japanese Patent Publication No. 62-59296, and the like, a reticle having a new concept of a phase shift photomask has been proposed. Phase shift lithography using a phase shift reticle is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light passing through the reticle.

[0006] Phase shift lithography will be briefly described with reference to the drawings. FIG. 5 is a diagram showing the principle of the phase shift method,
FIG. 6 is a diagram showing a conventional method, and FIGS.
(A) is a cross-sectional view of the reticle, and (b) and (b) of FIG.
5 (c) and 6 (c) show the light amplitude on the wafer, and FIGS. 5 (d) and 6 (d) show the light intensity on the wafer, respectively, where 1 is the light intensity on the reticle. A substrate 2, a light shielding film 3, a phase shifter 3, and an incident light 4 are shown.

In the conventional method, as shown in FIG. 6A, a light-shielding film 2 made of chrome or the like is formed on a substrate 1 made of quartz glass or the like, and a light transmitting portion of a predetermined pattern is formed. However, in phase shift lithography, as shown in FIG. 5A, a phase shifter 3 made of a transmission film for inverting the phase (a phase difference of 180 °) is provided on one of the adjacent light transmission portions on the reticle. Is provided.
Therefore, in the conventional method, the amplitude of light on the reticle is in phase as shown in FIG. 6B, and the amplitude of light on the wafer is also in phase as shown in FIG. 6C. While the pattern on the wafer cannot be separated as shown in FIG. 6D, in phase shift lithography, the light transmitted through the phase shifter
As shown in FIG. 5B, since the phases are made opposite to each other between the adjacent patterns, the light intensity becomes zero at the boundary of the patterns, and the adjacent patterns are clearly separated as shown in FIG. 5D. be able to. As described above, in the phase shift lithography, a pattern that cannot be separated conventionally can be separated, and the resolution can be improved.

Next, one of the manufacturing steps of the phase shift reticle
An example will be described with reference to the drawings. FIG. 7 is a cross-sectional view showing a manufacturing process of a conventional phase shift reticle, in which 11 is a quartz substrate, 12 is a chromium film, 13 is a resist layer, 14 is ionizing radiation, 15 is a resist pattern, and 16 is an etching gas. Plasma, 17 is a chromium pattern, 18 is an oxygen plasma, 18 is a transparent film, 20 is a resist layer, 21 is 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. 7A, a chromium film 12 is formed on an optically polished quartz substrate 11, and further,
An ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a conventional method such as spin coating,
A heat drying process is performed to form a resist layer 13 having a thickness of about 0.1 to 2.0 μm. The heating and drying treatment is usually performed at ± 80 to 150 ° C., depending on the type of resist used.
Perform for about 20 to 60 minutes.

Next, as shown in FIG. 1B, a pattern is drawn on the resist layer 13 with an 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 drawn. After development with a developer as a main component, rinsing with alcohol is performed 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 resist dust and whiskers remaining on the edge portion of the resist pattern 15, and the like, as shown in FIG. As shown, the resist pattern 1
The chromium layer 12 is dry-etched with the 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 by the etching gas plasma 16.

After etching as described above, the resist pattern 15, ie, the remaining resist is ashed and removed by oxygen plasma 18 as shown in FIG. Complete the mask. This process can be performed by solvent stripping instead of the ashing process using the oxygen plasma 18.

Subsequently, the photomask is inspected, a pattern is corrected if necessary, and the photomask is washed. Then, as shown in FIG.
_A transparent film 19 made of ₂ or the like is formed. Next, FIG.
As shown in FIG. 2, an ionizing radiation resist layer 2 such as chloromethylated polystyrene is formed on the transparent film 19 in the same manner as described above.
0 is formed, and as shown in FIG.
Then, an alignment is performed according to a conventional method, a predetermined pattern is drawn by ionizing radiation 21 such as an electron beam exposure apparatus, developed and rinsed to form a resist pattern 22 as shown in FIG.

Next, if necessary, a heating process and a descum process are performed, and as shown in FIG. 1K, the transparent film 19 exposed from the opening of the resist pattern 22 is etched with an etching gas plasma. Dry etching is performed by using 23 to form a phase shifter pattern 24. Note that the phase shifter pattern 24 may be formed by wet etching instead of dry etching by the etching gas plasma 23.

Next, the remaining resist is ashed and removed by oxygen plasma 25 as shown in FIG. Through the above steps, a phase shift photomask having the phase shifter 24 as shown in FIG.

In the above-described conventional method of manufacturing a phase shift reticle, the etching control in the depth direction of the transparent film 19 forming the phase shifter must be performed accurately. In particular, since the substrate 11 and the transparent film 19 are made of the same SiO ₂ -based material, if the etching is continued even after the etching of the transparent film 19 is completed, the substrate 11 is also etched, and the phase shift amount of the phase shifter 24 is reduced. When the angle is larger than 180 °, it is difficult to transfer an accurate pattern.

Therefore, generally, an etching stopper layer is provided between the transparent film forming the phase shifter and the substrate,
This layer automatically stops the etching,
Japanese Patent Application Nos. 2-29801, 2-18179, and 3
No. 295610. Materials proposed for the etching stopper layer proposed in these applications include tantalum, molybdenum, tungsten, silicon nitride, alumina and manganese oxide, zirconium oxide, a mixture of tantalum oxide and hafnium oxide, and the like.

[0018]

However, with an etching stopper layer made of such a material, it is not always easy to stop the etching accurately enough to be sufficiently satisfactory. Therefore, it is necessary to introduce a special material into the film forming apparatus, which complicates the manufacturing process and takes time.

The present invention has been made in view of such a situation, and an object of the present invention is to provide an etching stopper layer that is easy to form a film, has excellent etching selectivity, and reliably stops etching automatically. It is an object of the present invention to provide a phase shift photomask blank using a material capable of forming the same and a phase shift photomask produced therefrom.

[0020]

The present invention SUMMARY OF THE INVENTION In view of the above problems, as a result of the development and research of the etching stopper layer, SOG to the TiO ₂ as a main component in the material of the etching stopper layer (Spin-On- (Glass: coatable glass), formed by spin coating and baked at 150 ° C. to 1000 ° C. in the air to have excellent dry etching resistance and a transmittance of 88% or more at i-line wavelength. The inventors have found that a film can be obtained, and have completed the present invention based on such findings.

Here, SOG containing TiO ₂ as a main component is used.
, Like the SOG of SiO ₂ system, the organic solvent solution of an organic titanium compound coating, drying, a film produced by changing the heating and titanium oxide, a chemical reaction, S the SiO ₂ system
This is a reaction in which Ti is replaced in place of Si in OG, and the following reactions proceed in the order of coating, drying, and heating.
A TiO ₂ film is created.

[0022] _{[Ti (OR) a (OH)} b O c ] _{n c = 1/2 (4} -a-b), R is an organic group → _{[Ti (OR) a '(OH} ) b' O c ' _{N ′} a ′ <a, b ′ <b, c ′> c, n ′> n → [Ti (OR) _{a ″} (OH) _{b ″} O _{c ″} ] _{n ″} a ″ <a ′, b ″ < b ′, c ″> c ′, n ″> n ′ → [Ti (OH) _x O _y ] _{n ″ ′} x → 0, y → 2, n ^{″ ′} → ∞ → TiO ₂ The SOG of this TiO ₂ also As in the case of SOG of SiO ₂ , it is characterized in that the film formation process is a simple process in which a solution is applied, dried and heated in that order, and a precise film can be easily formed. Moreover, under the conditions of SiO ₂ and SOG etching, TiO _2.
Since the etching rate of SOG is about 1/10 or less as compared with the etching rate of SiO ₂ · SOG,
It can be sufficiently used as an etching stopper material for a phase shift reticle.

As the phase shift layer, a silicon dioxide film formed by a sputtering method, a CVD method or the like, a SiO ₂ SOG film formed by a coating and firing method, or the like is preferable.

As the light-shielding thin film layer, chromium, tantalum, molybdenum silicide, or the like formed by a sputtering method or the like, or a single layer or a composite layer mainly composed of an oxide, nitride, or oxynitride thereof is preferable. It is.

That is, the phase shift photomask blank of the present invention is a phase shift photomask blank having at least an etching stopper layer and a phase shift layer on a transparent substrate in order, wherein the etching stopper layer is made of TiO ₂ -coated glass. It is characterized by consisting of.

In this case, the etching stopper layer is made of Ti
It is desirable to form by spin-coating a coatable glass solution of O _2. After spin-coating the coatable glass solution of TiO ₂ , it is baked at 150 ° C. to 1000 ° C. to form Ti.
It is desirable to form an O ₂ film.

The present invention also includes a phase shift photomask having a phase shifter pattern formed by selectively removing a part of the phase shift layer from such a phase shift photomask blank.

[0028]

In the present invention, since the etching stopper layer is made of the coating glass TiO _2, because TiO ₂ is very transparent to near-ultraviolet wavelength (i-line), which can be used in the near ultraviolet range phase A shift photomask can be formed.
Further, since the etching stopper layer is made of TiO ₂ coatable glass, the film forming process can be simplified, a layer having few defects can be formed, and a phase shift photomask having few defects can be manufactured relatively easily. .

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a phase shift photomask bra according to the present invention will be described.
Link and phase shift photomasks in some embodiments
It will be described based on the following. FIG. 1 shows the present invention using a lower shifter type phase shifter.
Lower shifter type mask when applied to shift photomask
Cross section of photomask blank (A), photo by it
Sectional view (B) of the manufacturing process of the mask and the bottom
FIG. 4C is a cross-sectional view of the shifter type phase shift photomask.
You. The lower shifter type phase shift photomask
The phase shifter pattern 38 is provided below the substrate 36 (substrate side).
And the blank is shown in FIG.
As described above, the TiO 2 according to the present invention is sequentially formed on the substrate 31. _Two
SOG etching stopper layer 32, phase shift layer
33, a light-shielding thin film layer 34 is provided.
The manufacturing method of the ink is as follows._Two・ SOG
By spin coating at a speed of about 3000 rpm.
Second, a film is formed to a thickness of about 60 nm,
Heated on top of TiO_TwoA film 32 is formed. Next, TiO
_TwoSiO serving as a phase shift layer 33 on the film 32_Two・ SOG
The material is spin-coated, then baked in an oven or the like,
SiO so that d becomes d = λ / {2 (n−1)}_Twofilm
33 (λ: exposure wavelength, n: bending of phase shifter)
Rate). Next, a chromium film that is a light shielding layer or a semi-light shielding layer
34 is formed by a sputtering method, and the lower substrate shown in FIG.
The footer blank is completed.

In the manufacturing process of the lower shifter type phase shift photomask, as shown in FIG. 3B, a normal ionizing radiation resist is applied on the blank of FIG. Then, a predetermined pattern is drawn and exposed, developed and rinsed to form a resist pattern 35 (FIGS. 1B and 1A). Next, the chromium film 34 exposed from the opening of the resist pattern 35 is dry- or wet-etched to form a chromium pattern 36, and then the resist pattern is peeled off (FIGS. 1B and 1B). Next, an ionizing radiation resist or the like is applied on the chrome pattern 36,
After alignment with the chromium pattern 36 is performed according to a conventional method, exposure and development are performed to form a resist pattern 37 (FIGS. 1B and 1C). Next, the phase shift layer 33 is subjected to dry or wet etching (FIG. 6B).
(D)) By stripping the resist, a phase shift photomask having a phase shifter pattern 38 as shown in FIG.

Next, the upper shifter type phase shift photomask will be described. The upper shifter type phase shift photomask has a phase shifter pattern located above a light-shielding pattern (opposite to the substrate). FIG. 2 is a cross-sectional view (A) of the upper shifter type photomask blank, (B) and (C) a cross-sectional view of the manufactured upper shifter type phase shift photomask.
Is shown. As shown in FIG. 2A, this blank is formed by sequentially providing a TiO ₂ .SOG etching stopper layer 42 and a light-shielding thin film layer 43 according to the present invention on a substrate 41. In the manufacturing method, as in the case of the lower shifter type, TiO ₂ .SOG 42 is formed on a quartz substrate 41 by spin coating, and then a chromium film as a light shielding layer 43 is formed by sputtering. ) Is completed.

In the manufacturing process of the upper shifter type phase shift photomask, a resist pattern 44 is formed on the blank shown in FIG. 1A by a conventional method (FIGS. 1B and 1A), and the chromium film 43 is selectively etched. After forming the chromium pattern 45, the resist is stripped (FIGS. (B) and (b)).
Similarly to the lower shifter type, SiO ₂ · SOG is formed as the phase shift layer 46 (FIGS. 7B and 7C), and a resist pattern 47 is formed thereon by a conventional method (FIGS. 9B and 9C). d)) After that, the phase shift layer 46 is subjected to dry or wet etching, and the resist is stripped off.
A phase shift photomask having a phase shifter pattern 48 as shown in FIG.

Next, a case where the present invention is applied to a halftone type phase shift photomask will be described with reference to FIG. FIG. 1A is a cross-sectional view of the photomask blank, and FIG. 2B is a cross-sectional view of a halftone type phase shift photomask formed thereby. As shown in FIG. 2B, the halftone type phase shift photomask has an aligned phase shifter pattern 5 having the same pattern shape under the halftone light shielding pattern 56 (substrate side).
5 is located, and a blank for this is formed on a substrate 51 in this order by etching an TiO ₂ .SOG etching stopper layer 52 based on the present invention, as shown in FIG.
It is provided with a phase shift layer 53 and a halftone light-shielding thin film layer 54. The manufacturing method of the photomask blank and the photomask is almost the same as that of the lower shifter type phase shift photomask of FIG. 1, and the description is omitted.

Further, a case where the present invention is applied to a transmission type phase shift photomask will be described with reference to FIG. FIG. 1A is a cross-sectional view of the photomask blank, and FIG. 1B is a cross-sectional view of a transmission-type phase shift photomask. The transmission type phase shift photomask has only a phase shifter pattern 64 on a substrate 61 as shown in FIG. 7B, and a blank for that purpose is formed on a substrate 61 as shown in FIG. In turn, Ti based on the present invention
An O ₂ · SOG etching stopper layer 62 and a phase shift layer 63 are provided. The manufacturing method of the photomask blank and the photomask is almost the same as that of the upper shifter type phase shift photomask of FIG. 2, and the description is omitted.

[0035]

As is apparent from the above description, according to the phase shift photomask blank and the phase shift photomask of the present invention, the etching stopper layer is made of TiO _2.
Since TiO ₂ is very transparent to the near ultraviolet wavelength (i-line), a phase shift photomask usable in the near ultraviolet region can be configured. Also,
Since this etching stopper layer is formed from TiO ₂ coatable glass, the film forming process can be simplified, a layer having few defects can be formed, and a phase shift photomask having few defects can be manufactured relatively easily. In the production of high-density integrated circuits such as VLSIs and high-speed devices, finer patterns can be formed with a high yield, and thus higher-performance integrated circuits and high-speed devices can be manufactured with a high yield.

[Brief description of the drawings]

FIG. 1 shows a blank and a photomask manufacturing process when the present invention is applied to a lower shifter type phase shift photomask.
FIG. 4 is a cross-sectional view of a photomask.

FIG. 2 is a view similar to FIG. 1 in the case of an upper shifter type phase shift photomask.

FIG. 3 is a cross-sectional view of a blank and a photomask when applied to a halftone type phase shift photomask.

FIG. 4 is a view similar to FIG. 3 for a transmission type phase shift photomask.

FIG. 5 is a diagram illustrating the principle of the phase shift method.

FIG. 6 is a diagram showing a conventional method.

FIG. 7A is a cross-sectional view showing the first half of the manufacturing process of a conventional phase shift reticle.

FIG. 7B is a sectional view showing the latter half of the manufacturing process of the conventional phase shift reticle.

[Explanation of symbols]

 31, 41, 51, 61 substrate 32, 42, 52, 62 etching stopper layer 33, 46, 53, 63 phase shift layer 34, 43 light-shielding thin film layer 35, 44, 47 resist pattern 36, 45 ... chrome pattern 37 ... resist pattern 38,48,55,64 ... phase shifter pattern 54 ... halftone light-shielding thin film layer 56 ... halftone light-shielding pattern

Claims (4)

(57) [Claims] 1. A phase shift photomask blank having at least an etching stopper layer and a phase shift layer in order on a transparent substrate, wherein the etching stopper layer is made of TiO ₂ coatable glass. Mask blank. 2. An etching stopper layer comprising TiO ₂
The phase shift photomask blank according to claim 1 , wherein the phase shift photomask blank is formed by spin-coating the coatable glass solution of ( 1 ). 3. After spin-coating of the TiO ₂ coating glass solution, TiO ₂ and fired at 0.99 ° C. to 1000 ° C.
3. The phase shift photomask blank according to claim 2 , wherein a film is formed. Wherein at least of the TiO ₂ in order on a transparent substrate
A phase shifter pattern, wherein a phase shifter pattern is formed by selectively removing a part of a phase shift layer of a phase shift photomask blank including an etching stopper layer and a phase shift layer made of applicable glass. Shift photomask.