JPS623257A - Formation of mask pattern and mask base used for it - Google Patents

Abstract

PURPOSE:To form a mask pattern for forming a high-precision mask by laminating a thin film on a light-shading layer formed on a mask base material, forming a resist pattern on the thin film layer, executing wet etching, and further, dry etching to form a light-shading layer pattern. CONSTITUTION:A polymethyl methacrylate film 14 is formed on the light-shading Cr film 13 formed on the mask base, and the resist pattern 14 is formed by depicting a desired pattern with electron beams, and developing it with isoamyl acetate. Then, the thin Cr film 13 is selectively removed with an etching solution of ceric ammonium nitrate and perchloric acid to form an opening W1 faithful to the resist pattern opening WR. A molybdenum silicide film 12 is selectively removed by using a gas mixture of tetrafluoromethane and oxygen and the reactive ion etching method, thus permitting the obtained film pattern to be regulated to <=0.05mum in dimensional change between the initial resist pattern 14 and this pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for forming a mask pattern, and in particular to a method for forming a mask pattern, particularly a reticle or The present invention relates to a method for forming a mask pattern necessary for creating a master mask.

[Technical background of the invention and its problems] With the progress of semiconductor technology, the integration of semiconductor devices including ultra-LSIs has been increasing, and a highly accurate fine pattern forming technology is required.

To use such a forming technique on a mass production line, high speed is required, and progress in pattern transfer techniques such as steppers is essential. Therefore, submicron pattern transfer technologies such as steppers using i-rays, electron beam transfer, and X-ray transfer are being researched and developed. It's getting more and more difficult.

Therefore, it is naturally expected that reticles and master masks, which serve as the original drawings for pattern transfer, will have higher precision, and as well as miniaturization of the minimum size that can be formed, higher dimensional accuracy is also required, such as 0.1 μm (3σ). It has come to the point where the following dimensional accuracy is required.

Conventionally, a chrome mask substrate widely used for reticles and master masks, as shown in FIG. A light shielding layer 22 made of a ROM layer which is opaque to the light, and a low reflection film 23 made of a chromium oxide layer for suppressing reflected light during exposure are sequentially laminated.

By selectively etching and removing the light shielding layer 22 and the low reflection film on this chrome mask substrate using the resist pattern as a mask, a desired mask pattern is formed, and this is used as a reticle or master mask. In this case, the problem is how faithfully chrome etching can be performed to the resist pattern. Wet methods and dry methods are known as chrome etching methods.

First, in forming a mask pattern using a wet method, as shown in FIG. 7(a), a resist pattern 24 is formed on the chromium mask substrate, and using this resist pattern 24 as a mask, ceric ammonium nitrate is This is done by immersing the etching solution in an etching solution consisting of perchloric acid or by spraying the etching solution onto the set to remove unnecessary portions of the chromium layer 22 and the chromium oxide layer 23. When etched by the wet method as shown in Fig. 7(b)
As shown in FIG. 2, the etching progresses to the lower side of the resist pattern 24, and a large difference in pattern conversion occurs between the resist pattern 24 and the patterns of the chromium layer 22 and chromium oxide layer 23 (hereinafter referred to as chrome pattern). And the rank ranges from 0.1 to 0.2σm, so Fig. 7 (
C).

As shown in (d), the resist pattern 24 has the same size Ω.
. If there is a punched pattern and a left pattern, the dimensions of the chrome pattern after etching are Ω1. Ω2 (half width of optical density), and the difference Ω1-92 is 0.2 to 0.
．． In addition to reaching a diameter of 4 μm or more, the cross-sectional shape of the chrome pattern also had problems such as undercutting, and there was a limit to high precision.

On the other hand, to form a mask pattern using the dry method, as shown in FIG. 8(a), a resist pattern 25 is formed on a chrome mask substrate, and this resist pattern is used as a mask. This is done by etching away the unnecessary portions of the chromium layer 22 and chromium oxide layer 23 using mixed gas plasma of a chlorine-based gas such as carbon tetrachloride (CCΩ4) and oxygen (O2) gas. By the way, in recent years, electron beam sensitive resists used in the resist pattern formation method using the electron beam writing method, which has been widely used, have high sensitivity and high resolution, but have low resistance to plasma, and the chromium layer 22 and oxidation In the plasma etching process for selectively removing the chromium layer 23, the resist 25 is significantly thinned and the resist recedes, resulting in dimensional changes, and the chromium pattern after etching has a cross-sectional shape as shown in FIG. 8(b). This creates a sloping pattern. For this reason, FIG. 8(C).

As shown in (d), the resist pattern 25 has the same size Ω.
. When there is a punched pattern and a left pattern, the dimensions of the chrome pattern after etching are Ω1' and Ω', respectively.
Then, the difference Ω ′-92′ is still 0.2 to 0.3 μ
m, and there remained a problem in forming a highly accurate mask pattern.

In recent years, molybdenum silicide mask substrates in which a molybdenum silicide (MOSi2) thin film is formed on a mask base material have attracted attention as mask substrates for dry etching, but these also have more or less the same problems.

To create a high-precision reticle or master mask, (1) a high-viscosity resist pattern formation technology, (2) a high-viscosity etching technology that faithfully forms a light-shielding pattern from the resist pattern without pattern conversion, and A suitable mask substrate was required.

[Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to form a mask pattern for creating a high-precision mask that is the key to pattern transfer technology for mass production.

[Summary of the Invention] In order to achieve the above object, according to the present invention, as a mask substrate, on a light shielding layer formed on a mask base material, further:
A stack of thin film layers that are resistant to the etching conditions in the patterning process of the light shielding layer is used, a resist pattern is formed on the thin film layer, and then the thin film layer is wet etched using this resist pattern as a mask. Then, using the pattern of the thin film layer as a mask, the light shielding layer is dry etched to form a light shielding layer pattern.

In addition, the mask substrate of the present invention uses a metal film or a metal silicide film as a light shielding layer against electromagnetic waves in a predetermined wavelength range used for pattern transfer, and etching conditions are applied to the upper layer in the patterning process of the light shielding layer. It is formed by forming a thin film layer that is resistant to.

That is, the thin film layer is further formed on the light-shielding layer including the light-shielding film made of metal or metal silicide formed on the mask base material to enhance the masking effect during etching for patterning the light-shielding layer. The purpose is to form a light shielding layer pattern with good dimensional accuracy.

[Effects of the Invention] According to the present invention, the thin film layer is etched by a wet etching method, which simplifies the process and eliminates the difference in pattern conversion between the resist pattern and the light-shielding pattern, which was considered to be at the limit in conventional methods. It has become possible to dramatically reduce this.

Further, since the thin film layer has resistance even when a resist having relatively low dry etching resistance is used, it is possible to form a light-shielding layer pattern that is faithful to the resist pattern and has good dimensional accuracy and cross-sectional profile.

Furthermore, even if various correction measures (pattern size correction, dose amount correction, high acceleration voltage, multilayer resist method, etc.) are implemented for the proximity effect in conventional electron beam lithography, the difference in pattern size conversion is large, resulting in high Although it has been impossible to faithfully reproduce precision patterns, the method of the present invention makes it possible to reduce the difference in pattern dimension conversion, making it possible to reproduce a light-shielding pattern that is faithful to the resist pattern.

In addition, highly accurate mask patterns can now be easily realized, and pattern transfer technology for highly integrated devices in the submicron region has become reliable.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a cross-sectional view of a mask substrate according to an embodiment of the present invention. This mask substrate is made of molybdenum silicide (MoS 12 ) film 12 and a chromium thin film 13 with a thickness of 30OA as a thin film for forming fine patterns
are sequentially laminated. Note that the chromium thin film 1
3 is more than 3 times the selected gas for the mixed gas of fluorine-based gas of tetrafluoromethane (CF4) and 'M gas or hydrogen gas used in the dry etching process for buttering the molybdenum silicide film 12. It has a relative resistance.

In addition, in forming this mask substrate, on the mask base material 11,
This is done by sequentially laminating a molybdenum silicide film and a chromium thin film using sputter deposition.

Next, a method for forming a high-precision mask using this mask substrate will be described.

First, polymethyl methacrylate (
After forming the PMMA) film 14, electron beam irradiation is performed at an acceleration voltage of 50 KV and a dose of 50 μC/cd to draw a desired pattern, followed by development using isoamyl acetate ([AA)] to form the resist pattern 14. do.

(FIG. 2(a)) Next, using the resist pattern 14 as a mask, the chromium thin film 13 is selectively removed as shown in FIG. 2(b) using an etching solution consisting of ceric ammonium nitrate and perchloric acid. do. At this time, spray etching was used for 10 seconds at room temperature. The opening WI thus formed was formed faithfully to the opening WR of the resist pattern, and no dimensional change due to film thinning of the resist pattern was observed. The thin chrome film has good adhesion to the resistor, and unlike the thick chrome film described as a light-shielding film in the prior art described above, a thin chrome film of up to about 400A is faithful to the resist pattern and has a nearly vertical profile. A frontage can be obtained.

Subsequently, the molybdenum silicide film 12 is selectively removed by reactive ion etching using a mixed gas of tetrafluoromethane (CF4) and 02 at 200 W and 10.06 Torr for 5 minutes. In this step, the resist pattern 14 is gradually removed, but since the chromium thin film has sufficient resistance, there is little film loss and it effectively acts as a mask for the underlying molybdenum silicide film 12.

Therefore, as shown in FIG. 2(C), the pattern of the formed molybdenum silicide film is the same as that of the original resist pattern 14.
It was possible to suppress the dimensional change to within 0.05 μm. Also, at this time, the resist pattern 14
was gradually removed by thinning of the film by reactive ion etching, and no special resist stripping process was required.

Note that the thin film using this example itself has good light-shielding properties, so Cr as shown in FIG. 2(C)
Although the MOS i 2 composite pattern can be used as a high-precision mask, if necessary, it can be used as a high-precision mask.
), the RI01m film may be removed.

It goes without saying that other materials such as polymethyl methacrylate, polyglycidyl methacrylate (PGMA), etc. may be used as the resist. When polyglycidyl methacrylate is used as a resist, 2
By performing electron beam writing at 0 KV and 1 μC/d and then developing with a mixed solution of methyl ethyl ketone and ethanol, a mask pattern with good dimensional accuracy is formed as in the embodiment. It goes without saying that the method for forming the resist pattern is not limited to electron beam writing, and that any known pattern forming method such as light exposure may be used.

Furthermore, the present invention relates to Cr-M shown in Examples.

The light shielding layer is not limited to the Si2 composite mask substrate, but may include a light shielding film 12 and a low reflection film 1 as shown in FIGS. 3 to 5.
4, a light-shielding film 12 and a conductive film 15 made of indium or tin oxide, etc., a light-shielding film 112. Conductive film 15. It is also applicable to cases where the light shielding layer is of a laminated type, such as one consisting of a three-layer structure of the low reflection film 14. M o as the light shielding film 12
In addition to S i 2, there are also Taxi, 'TiSi,
By forming the fine pattern forming thin film 13 which is applicable to WSi2, Ta, etc. and has etching resistance, it becomes possible to form a mask with good dimensional accuracy.

Furthermore, the thin film 13 for forming a fine pattern is not limited to a chromium thin film, and exhibits relatively strong etch resistance under conditions where the light shielding layer is easily etched; Any material that can be easily etched away with an etching solution that exhibits etching resistance may be used. However, chromium has good adhesion to the resist and is an effective film for improving pattern accuracy. Further, for example, chromium oxide can also be used as a material for the thin film 13, and at the same time, it can also be used as a low reflection film.

The film thickness can also be selected as appropriate, taking into account the pinhole characteristics, the film thickness of the light-shielding layer, and the dry etch resistance of the resist used for the resist pattern. For 40~40
Approximately 0A is desirable.

In addition, the mask base material is not limited to low expansion glass or quartz, and can be selected as appropriate depending on the pattern transfer technology to be applied. When used as an X-ray mask, silicon, silicon nitride, Polyimide etc. can also be used.

Also, when forming a mask pattern for charged beam projection exposure method using a charged beam having a predetermined energy or a channeling mask pattern, the present invention can be applied by appropriately selecting the base material and the light shielding material. Needless to say, it can be applied.

Furthermore, the etching gas for the light shielding layer is not limited to tetrafluoromethane (CF4), but also sulfur hexafluoride (SF6), octafluoropropane (03F8), etc.
It is also effective to use other fluorine-based gases such as any of these or a mixed gas of hydrogen gas (H2) or oxygen gas (0□).

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a mask substrate according to an embodiment of the present invention, FIGS. 2(a) to (C) are diagrams showing a process of forming a mask pattern using the same mask substrate, and FIG. 2(d) is a diagram showing a mask pattern forming process using the same mask substrate. , FIG. 3 to FIG. 5 are diagrams showing other embodiments of the present invention, FIG. 6 is a diagram showing an example of a conventional mask substrate, and FIG. FIG. 8 and FIG. 8 are diagrams showing how a mask pattern is formed when a conventional mask substrate is used. DESCRIPTION OF SYMBOLS 11... Mask base material, 12... MoSi2 film (light-shielding layer), 13... Bachrome thin film (coating layer), 14... Resist pattern, 21... Base material, 22... Light-shielding layer,
23...Low reflection film, 24...Resist pattern. Figure 2 (0) Figure 1 Figure 2 (b) Figure 2 (C) Figure 2 (d) Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 (0) Figure 7 (b) )

Claims (24)

[Claims] (1) In a method of forming a mask pattern on a mask substrate, which is provided with a light shielding layer against electromagnetic waves in a predetermined wavelength range or a charged beam with a predetermined energy on a mask base material, the mask substrate further includes a light shielding layer on the light shielding layer. A step of forming a resist pattern on the thin film layer using a laminated thin film layer that is resistant to the etching conditions in the patterning process, and then wet etching the thin film layer using the resist pattern as a mask. a first etching step for selectively removing the light shielding layer; and a second etching step for selectively removing the light shielding layer by dry etching using the pattern of the thin film layer as a mask. A method for forming a mask pattern characterized by: (2) The method for forming a mask pattern according to claim (1), wherein the etching conditions in the wet etching step are such that the light shielding layer has resistance. (3) The method for forming a mask pattern according to claim (1), wherein the second etching step is a dry etching step using a fluorine-based gas. (4) Claims (1) to (3) characterized in that the first etching step is a wet etching step using a solution consisting of ceric ammonium nitrate and perchloric acid. The method for forming a mask pattern according to any one of the above. (5) The fluorine-based gas is tetrafluoromethane (CF
_4), octafluoropropane (C_3F_8), boron chloride (BCl_3), or a mixed gas of these and oxygen gas or hydrogen gas. How to form a pattern. (6) The method for forming a mask pattern according to claim (1), wherein a mask substrate is used in which the light-shielding layer includes a light-shielding film made of metal silicide. (7) The metal silicide is MOSi_2, TaSi
_2, TiSi_2, or WSi_2. The method for forming a mask pattern according to claim (6). (8) The method for forming a mask pattern according to claim (1), wherein a mask substrate is used in which the light-shielding layer includes a light-shielding film made of a metal such as Mo, Ta, Ti, or W. (9) As the light-shielding layer, in addition to the light-shielding film, a mask substrate laminated with a low-reflection film and/or a conductive film for electromagnetic waves in the predetermined wavelength range is used. The method for forming the mask pattern described above. (10) The method for forming a mask pattern according to claim (9), wherein the low reflection film uses a mask substrate made of a chromium oxide film. (11) The method for forming a mask pattern according to claim (9), wherein a mask substrate is used in which the conductive film is made of indium oxide or tin oxide. (12) The thin film layer uses a mask substrate made of chromium, chromium oxide, or a stack of these.
) to (11). (13) The mask pattern according to any one of claims (3) to (12), wherein the step of dry etching the light shielding layer is a step using anisotropic etching. How to form. (14) a mask base material, a light shielding layer formed on the mask base material and containing a metal film or metal silicide thin film that has shielding properties against electromagnetic waves in a predetermined wavelength range or charged beams with a predetermined energy; and the light shielding layer. 1. A mask substrate comprising a thin film layer that is resistant to etching conditions. (15) The thin film layer is made of a material that makes the light shielding layer resistant to wet etching conditions for patterning the thin film layer. mask board. (16) The mask substrate according to claim (14), wherein the light shielding layer is made of a material that is patterned by a dry etching method using a fluorine-based gas. (17) The thin film layer is made of a material patterned by a wet etching method using an etching solution containing ceric ammonium nitrate and/or perchloric acid. mask substrate. (18) The fluorine-based gas is tetrafluoromethane (C
F_4), octafluoropropane (C_3F_8),
The mask substrate according to claim 16, characterized in that the gas is sulfur hexafluoride (SF_6) or a mixed gas of these and oxygen or hydrogen gas. (19) The metal silicide thin film includes molybdenum silicide (MoSi_2), tantalum silicide (TaSi_2),
_2), titanium silicide (TiSi_2), and tungsten silicide (WSi_2). (20) In addition to the light shielding film, the light shielding layer is made of a laminated layer of a low reflection film for electromagnetic waves in the predetermined wavelength range and/or a conductive film.
The mask substrate according to any one of items 4) to 19). (21) The mask substrate according to claim (20), wherein the low reflection film is made of a chromium oxide film. (22) Claim (20) characterized in that the conductive film is made of indium oxide or tin oxide.
Mask substrate described in section. (23) The mask substrate according to claim (14), wherein the thin film layer is made of chromium, chromium oxide, or a stack of these. (24) The mask substrate according to claim (14), wherein the thin film layer has a thickness of 40 to 400 Å.