JP3322476B2 - Thin film patterning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for patterning a thin film. In particular, the present invention relates to a method for forming an absorber of an X-ray exposure mask used in X-ray exposure. In the present invention, the amount of side etching of the X-ray exposure mask is reduced, and an X-ray exposure mask having a high pattern transfer rate can be formed.

[0002]

2. Description of the Related Art Ultra-fine processing is required in thin-film forming technology for semiconductor devices, and X-ray exposure techniques suitable for this ultra-fine processing are being developed. For the X-ray exposure, an X-ray exposure mask including an absorber that absorbs X-rays and blocks transmission of the X-rays to a non-processed object is used. Generally, W (tungsten), Ti-W is used as an absorber of an X-ray exposure mask.
A high melting point metal (or transition metal) thin film such as (tungsten titanium) or Ta (tantalum) is used.

A method for forming the X-ray exposure mask, particularly an absorber for the X-ray exposure mask, will be described with reference to FIGS.

First, as shown in FIG. 13, as a first step, a thin film 12, which is an absorber of an X-ray exposure mask, is formed on the surface of a substrate 10, and an etching mask 13 is formed on a predetermined region on the surface of the thin film 12. To form As the thin film 12, a W thin film is used, and this W thin film is deposited by a sputtering apparatus. Generally, a Cr (chromium) thin film having a pattern formed by a lift-off technique is used as the etching mask 13. The base 10 is a substrate on which an absorber for an X-ray exposure mask is formed.

Next, as shown in FIG. 14, the thin film 12 is patterned as a second step. An etching mask 13 is used for patterning, and the thin film 12 exposed from the etching mask 13 is removed by etching. The etching is performed by anisotropic etching using SF ₆ as an etching gas. Thereafter, if necessary, the etching mask 13 is removed, and the absorber of the mask for X-ray exposure is completed with the etched thin film 12.

In the anisotropic etching, etching proceeds with both ions and F radicals accelerated by an electric field.
If an electric field is generated in a direction perpendicular to the surface of the substrate 10, ions are accelerated in the same direction, and patterning is performed with the etched side wall of the W thin film being substantially vertical.
That is, in anisotropic etching, the vertical direction (vertical direction)
High anisotropy is obtained.

On the other hand, since F radicals are not affected by an electric field, isotropic etching proceeds in the vertical and horizontal directions. Therefore, as shown in FIG. 14, an undercut whose size is smaller than the size of the etching mask 13 occurs in the thin film 12 by lateral etching (side etching).

In the method of forming an absorber for an X-ray exposure mask, an undercut occurs in the thin film 12, and the pattern size difference transferred from the etching mask 13 to the thin film 12 is large. That is, the pattern transfer rate is poor, and is not suitable for ultrafine processing.

Therefore, as shown in FIG. 15, a protective film is generally formed on the etched side wall of the thin film 12 during anisotropic etching, and the progress of side etching is suppressed. The protective film is formed by a gas for forming a sidewall protective film mixed in the etching gas. For example, CHF ₃ is used as a sidewall protective film forming gas, and a protective film made of a thin film presumed to be an organic polymer compound is formed on the etched side wall of the W thin film.

In the anisotropic etching, the substrate 10
And an etching method for reducing the undercut of the thin film 12 is adopted. The base 10 is cooled to, for example, −50 degrees.

[0011]

However, in the above-described method of forming an absorber for an X-ray exposure mask, the following points are not taken into consideration.

First, when forming a protective film on the side wall of the thin film 12 during anisotropic etching, a special gas for forming a side wall protective film is used for the anisotropic etching. Since CHF ₃ is used as the gas for forming the side wall protective film, the safety during the forming process, during gas handling, and the like is reduced. Moreover, the cost of CHF ₃ is high.

Second, when the substrate 10 is cooled during anisotropic etching, a cooling system is required in the etching apparatus. For this reason, the etching apparatus becomes complicated and large, and the cost of the etching equipment increases. As a result, the production cost of the mask for X-ray exposure increases.

The present invention has been made to solve such problems, and the objects of the present invention are as follows.

(1) To provide a thin film patterning method capable of performing patterning with high anisotropy without employing a protective film forming process and a cooling system and simplifying the thin film forming process.

(2) An X-ray exposure mask which can perform patterning with high anisotropy without using a protective film forming process and a cooling system, can simplify the thin film forming process, and has an excellent X-ray absorptivity. A method of forming is provided.

[0017]

The present invention has been made based on the following facts obtained as a result of research conducted by the present inventors. That, F radicals when actively mixing nitrogen into W thin film to be used as an absorber of the X-ray exposure mask, to form a WN _X of amorphous structure was patterned with this WN _X in SF ₆ Side etching can be reduced.

Therefore, the thin film patterning method of claim 1
The method comprises the following steps (1) and (2):
Make a summary. (1) Naturally in a system for forming a thin film on W or a mixture of W
More than mixed and can be etched in step (2)
Within 10 atomic percent of either nitrogen or oxygen
In the range of 30 to 30 atomic percent
Forming a thin film having a crystalline structure on the substrate surface. (2) Part of the thin film in a system for patterning the thin film
In both ions and radicals accelerated to the region
Etching and patterning the thin film
About.

According to a second aspect of the present invention, there is provided a thin film patterning method comprising:
The invention according to claim 1, wherein the W is nitrogen.
Mix within the range of atomic percent to 20 atomic percent
That a thin film having an inserted amorphous structure is formed.
Summary of

According to a third aspect of the present invention, there is provided a thin film patterning method comprising:
In the invention described in claim 2, the patterning is performed.
That the thin film is used as a mask for X-ray exposure
Make it the gist

According to a fourth aspect of the present invention, there is provided a thin film patterning method comprising:
The invention according to any one of claims 1 to 3
The thin film is formed under the following conditions (1) to (3).
The gist is that it is done. (1) The thin film is deposited by high frequency magnetron sputtering
It is. (2) Ar in the high frequency magnetron sputtering
A sputter gas mixed with either N ₂ or O ₂ is used.
Nitrogen and oxygen during the deposition of W or a mixture of W
You. (3) The substrate temperature is set to room temperature.

According to a fifth aspect of the present invention, there is provided a thin film patterning method comprising:
The invention according to any one of claims 1 to 4
The thin film is patterned under the following conditions (1) to (3).
It is the gist that it is learned. (1) The thin film is etched by ECR etching
You. (2) In the ECR etching, SF ₆ is used as a main component.
An etching gas is used.

[0023]

[0024]

According to the present invention, firstly, more nitrogen and oxygen are positively mixed into the W or the mixture of W before the patterning is naturally performed, and the WN _x having an amorphous structure is first obtained. , nitride of W mixture, a thin film made of an oxide of WO _y or W mixture is formed. Nitrogen or oxygen mixed into the thin film in an appropriate amount suppresses the progress of etching by radicals generated during patterning. That is, since etching with accelerated ions becomes dominant in the patterning of the thin film, the undercut generated on the side wall of the patterned thin film is reduced, and high anisotropy is obtained in the patterning. That is, high anisotropy is obtained in patterning of the thin film, so that it is not necessary to form a protective film on the side wall of the thin film. Further, since high anisotropy is obtained at room temperature, a cooling system can be eliminated. on the other hand,
When the amount of nitrogen and oxygen mixed in the thin film increases, the thin film becomes in a ceramic state and cannot be etched by accelerated ions. Therefore, the amount of nitrogen and oxygen mixed in the thin film is suppressed to a range that can be etched. In the present invention, either W or a mixture of W is mixed with nitrogen or oxygen in a range of 10 atomic percent or more and 30 atomic percent or less.

Furthermore, in the present invention, secondly, a thin film having an amorphous structure in which nitrogen is mixed in the W in a range of 10 atomic percent to 20 atomic percent is formed. The WN _x thin film containing nitrogen in this range has an excellent X-ray absorption rate and can be used as an absorber of an X-ray exposure mask. That is, it is possible to form an X-ray exposure mask that is formed with high anisotropy, has a high pattern transfer rate, and has an excellent X-ray absorption rate.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

A method for forming an X-ray exposure mask according to the present invention will be described with reference to FIGS.

First, as shown in FIG. 1, a thin film 2 is formed on the surface of a substrate 1 as a first step. This thin film 2 is used as an absorber of an X-ray exposure mask. A radio frequency (RF) magnetron sputtering device is used for forming the thin film 2.
The thin film 2 is formed under the following conditions.

(1) As a target, a W target optimal for an absorber of an X-ray exposure mask is used.

(2) As the sputtering gas, a mixed gas obtained by mixing N ₂ with Ar is used. For the purpose of the N2 is to be mixed aggressively in W film deposited, of the N ₂ Ar
Is set in the range of more than 0% by volume and 50% by volume or less.

(3) High frequency power density is 3-4 W / cm ²
(Around 300 W).

(4) The temperature of the base 1 (substrate temperature) is set to room temperature.

(5) The film forming pressure is set to 1.33 to 4.0 Pa.

The thin film 2 made of WN _X thin film of amorphous structure which nitrogen is mixed in the above conditions (amorphous structure) is formed. WN _X film is formed to a thickness of about appropriate 400~800nm as an absorber of the X-ray exposure mask. Chamber of the high-frequency magnetron sputtering apparatus in WN _X film, i.e. several times to be compared to the amount of nitrogen contained in the gas and air except the sputtering gas in the vacuum system during film formation is mixed naturally in W films More than several tens of times
Nitrogen is mixed in. The WN _X film in this Example 1
0 atomic percent or more of nitrogen is incorporated.

On the other hand, when the mixed amount of nitrogen in the WN _X film is excessively increased WN _X film becomes a ceramic state, it can not be etched with accelerated ions of the anisotropic etching. Therefore, nitrogen is mixed into the WN _x thin film in a range where etching can be performed. In this embodiment, WN _X
The thin film contains 30 atomic percent or less of nitrogen .

Furthermore, the value at the wavelength of X-rays used in a film thickness and X-ray exposure of the WN _X film is changed, the WN _X thin film when the film thickness of the WN _X thin film is formed under the above conditions If the amount of nitrogen exceeds 20 atomic percent, the X-ray absorption exceeds the allowable range. In other words, since it becomes inappropriate as an absorber material for an X-ray exposure mask, the amount of nitrogen mixed into the WN _x thin film is set to 20 atomic percent or less.

Next, as shown in FIG. 2, an etching mask 3 is formed in a part of the surface of the thin film 2 as a second step. As the etching mask 3, for example, a Cr thin film formed by a lift-off technique is used. In the lift-off technique, a resist coated and masked is used for selective formation of a Cr thin film (formation of a Cr thin film pattern). As the resist, for example, CEBR-1010 (trade name, manufactured by Tokyo Ohkasha Co., Ltd.) is used. The FIB (Focus Ion Beem) method is used for drawing the mask pattern. The minimum processing size width of the etching mask 3 is, for example, 0.1 μm.

Next, as shown in FIG. 3, as a third step, the thin film 2 is subjected to anisotropic etching, and the thin film 2 is patterned. ECR for patterning thin film 2
(Electron Cyclotron Resonance) An etching apparatus is used, and the thin film 2 is patterned under the following conditions.

(1) The microwave power is set to 300W.

(2) The radio frequency (RF) bias is set to 80W.

(3) SF ₆ or SF is used as the etching gas
An etching gas containing ₆ as a main component is used.

(4) The gas flow rate is set to 0.5 sccm.

(5) The gas pressure is set to 2 × 10 ⁻³ Pa.

(6) The temperature of the base 1 (substrate temperature) is set to room temperature.

Under the above conditions, plasma ions are generated from the etching gas in the chamber of the ECR etching apparatus, that is, in the vacuum system at the time of thin film patterning. The ions in the plasma state are accelerated by the electric field, and the thin film 2 is etched in the vertical direction (thickness direction) with the accelerated ions. At the same time, F radicals for performing isotropic etching, particularly lateral etching, are generated from the etching gas, and the thin film 2 is etched by both the accelerated ions and F radicals.

In this embodiment, the W thin film is positively
The thin film 2 is formed of a WN _x thin film having an amorphous structure mixed with nitrogen , and the thin film 2 is etched by both accelerated ions and F radicals. As shown in FIG. 3, almost no undercut occurs on the side wall of the thin film 2 patterned as described above, and the side wall of the thin film 2 is formed substantially perpendicular to the surface of the base 1.

Next, as a fourth step, the etching mask 3 is removed, and an absorber for an X-ray exposure mask is completed. In this embodiment, only the absorber of the mask for X-ray exposure is described, but since the absorber itself cannot secure the mechanical strength, a frame (support) is actually formed around the absorber. You. When the frame is formed, an X-ray exposure mask is completed.

[0048] Here, the relationship between nitrogen amount and WNx film patterning sidewall shape is mixed in WN _X film, commentary sectional view depicting a scanning electron microscope (SEM) photograph and the photograph It is explained using. WN
Each of the _X thin films is formed with a thickness of 550 nm, and the pattern dimensions of the etching mask 3 are all formed with 100 nm.

Patterning of Pure W Thin Film FIG. 4 is a scanning electron micrograph of the patterned pure W thin film, and FIG. 5 shows a cross section for explanation. As shown in FIGS. 4 and 5, in the pure W thin film, the amount of etching in the lateral direction due to F radicals is large, and an undercut occurs on the side wall of the pure W thin film. Since the undercut is large, a bent pure W thin film exists.

The patterning FIG. 1 of WNx film 6 is a scanning electron micrograph of WNx thin film is patterned, a glossary for cross-section in FIG. Photograph shown in FIG. 6 Ar is a ratio N ₂ of about 2.9 vol%: WNx the sputtering gas flow ratio is adjusted in N ₂ is used formed
3 shows a cross-sectional shape of a thin film. As shown in FIG. 6 and FIG.
In the Nx thin film, the lateral etching due to F radicals is in a non-negligible range, and although the undercut is slightly improved, it is not appropriate as the cross-sectional shape of the WNx thin film. In addition, there is a variation in the cross-sectional shape of the WNx thin film due to the undercut.

The patterning FIG. 2 of WNx film 8 is a scanning electron micrograph of WNx thin film is patterned, a glossary for section in FIG. Photograph shown in FIG. 8 Ar is a ratio N ₂ of about 3.8 vol%: WNx the sputtering gas flow ratio is adjusted in N ₂ was used to form
3 shows a cross-sectional shape of a thin film. As shown in FIG. 8 and FIG.
In the Nx thin film, lateral etching due to F radicals is suppressed, and there is almost no undercut on the side wall. In other words, the side walls of the WNx thin film are formed substantially perpendicular to the surface of the base 1, and there is no variation in the cross-sectional shape of the WNx thin film. It is optimal as the cross-sectional shape of the WNx thin film.

FIG. 12 shows the relationship between the film density of the WN _x thin film and the concentration of N ₂ mixed with the sputtering gas. FIG.
WN _X film is the film formation pressure shown in 2 2.66 Pa, RF power density is 3.82W / cm ^2, the substrate temperature is room temperature, the film deposition rate is formed under the conditions of each of 20min. When N2 concentration to be mixed in the sputtering gas in the formation of WN _X film is more than 3.8% by volume film density 16.
Since it is reduced to 2 g / cm ³ or less and the X-ray absorptivity is reduced, it becomes unsuitable as an absorber material for an X-ray exposure mask.
Therefore, in this embodiment, the WN _x thin film as the absorber of the X-ray exposure mask has an N ₂ concentration of the sputtering gas of 3.0 to 3.0.
It is preferable to set in the range of 3.8% by volume. WNx
The concentration of nitrogen mixed in the thin film corresponds to 20 atomic percent or less.

[0053] patterning 3 10 of WN _X film is a scanning electron micrograph of WNx thin film is patterned, a glossary for cross-section in FIG. 11. FIG.
Photograph shown in the N ₂ is Ar at a rate of about 5.7 vol%: shows the N ₂ of sputtering gas flow ratio is adjusted is used formed WNx film cross-sectional shape. As shown in FIGS. 10 and 11, in the WN _x thin film, lateral etching due to F radicals is almost completely suppressed, and the lateral etching rate becomes considerably slower (the etching rate becomes slower as the amount of mixed nitrogen increases). Therefore, there is no undercut of the side wall. That is, the side wall of the WN _x thin film is formed perpendicular to the surface of the substrate 1, and there is no variation in the cross-sectional shape of the WN _x thin film. Is optimal as a cross-sectional shape of the WN _X film is, X-rays absorption rate is inappropriate as an absorber material for X-ray exposure mask so reduced.

In the above description, a WN _x thin film is used as an absorber of an X-ray exposure mask, but the present invention relates to a mixture of W having the same characteristics as an absorber, specifically, T
Nitrogen may be mixed into the i-W thin film. Also, it is conceivable that nitrogen is similarly mixed into a Ta thin film used as an absorber of an X-ray exposure mask.

Further, in the present invention, oxygen can be used in place of nitrogen mixed in the W thin film or the like. That is, in the present invention, for example, pre-WO _y thin film is formed, the WO _y
Etching is performed with both ions and radicals accelerated to the thin film.

As described above, the present embodiment has the following advantages.

First, before patterning, W or W
Many nitrogen than is mixed naturally mixtures, oxygen is mixed aggressively, WN _X having an amorphous structure, a nitride of W mixture, a thin film 2 comprising an oxide of WO _y or W mixture It is formed. Nitrogen or oxygen mixed into the thin film 2 in an appropriate amount suppresses progress of etching by radicals generated during patterning. That is, since etching with accelerated ions becomes dominant in the patterning of the thin film 2, the undercut generated on the side wall of the patterned thin film 2 is reduced, and high anisotropy is obtained in the patterning. . That is, high anisotropy is obtained in the patterning of the thin film 2, so that it is not necessary to form a protective film on the side wall of the thin film 2, and further, since high anisotropy is obtained at room temperature, a cooling system can be eliminated. When it becomes unnecessary to form a protective film on the side wall of the thin film 2, CHF
_3. The use of nitrogen or oxygen, which is safer in the forming process, can be used. Moreover, nitrogen or oxygen is inexpensive. On the other hand, the nitrogen to be mixed in the thin film 2, the amount of oxygen is increased becomes the ceramic state, can not be etched with accelerated ions, nitrogen mixed in the thin film 2
The amounts of element and oxygen can be suppressed to the extent that they can be etched.

Secondly, a thin film 2 having an amorphous structure in which nitrogen is mixed in the range of 10 atomic percent to 20 atomic percent in W is formed. The WN _x thin film containing nitrogen in this range has an excellent X-ray absorption rate and can be used as an absorber of an X-ray exposure mask. That is, it is possible to form an X-ray exposure mask that is formed with high anisotropy, has a high pattern transfer rate, and has an excellent X-ray absorption rate.

The present invention is not limited to the above embodiment, but can be variously modified without departing from the scope of the invention.

For example, in the present invention, the thin film 2 is coated with nitrogen and acid.
Both hydrogen may be mixed. Further, the present invention can be applied to a stencil mask used in a photoexcitation process other than the X-ray exposure mask, and more specifically, to an absorber of the stencil mask. In the stencil mask, a protective film such as Au is formed on the surface of the absorber for the purpose of preventing corrosion of the absorber.
A thin film is coated. Further, the present invention can be applied not only to an etching mask but also to an impurity introduction mask. Further, the present invention relates to a mask used for a semiconductor device other than a mask such as an X-ray exposure mask.
It can be applied to patterning of thin films and Ti-W thin films. These thin films are used for wiring, barrier layers, and the like.

[0061]

As described above, according to the present invention,
The following effects can be obtained.

(1) It is possible to provide a thin film patterning method capable of performing patterning with high anisotropy without employing a protective film forming process and a cooling system and simplifying the thin film forming process.

(2) An X-ray exposure mask which can perform patterning with high anisotropy without using a protective film forming process and a cooling system, can simplify the thin film forming process, and has an excellent X-ray absorptivity. A forming method can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an X-ray exposure mask in a first step for explaining a method of forming an X-ray exposure mask according to the present invention.

FIG. 2 is a sectional view of an X-ray exposure mask in a second step.

FIG. 3 is a sectional view of an X-ray exposure mask in a third step.

FIG. 4 is a diagram showing a scanning electron micrograph of a thin film.

FIG. 5 is a sectional view for explaining the scanning electron micrograph shown in FIG. 4;

FIG. 6 is a diagram showing a scanning electron micrograph of a thin film.

FIG. 7 is a sectional view for explanation of the scanning electron microscope photograph shown in FIG. 6;

FIG. 8 is a diagram showing a scanning electron micrograph of a thin film.

FIG. 9 is a sectional view for explanation of the scanning electron micrograph shown in FIG. 8;

FIG. 10 is a diagram showing a scanning electron micrograph of a thin film.

FIG. 11 is a sectional view for explanation of the scanning electron micrograph shown in FIG. 10;

FIG. 12 is a diagram showing a relationship between a film density of a thin film and a gas concentration mixed with a sputtering gas.

FIG. 13 is a cross-sectional view of an X-ray exposure mask in a first step for explaining a conventional method for forming an X-ray exposure mask.

FIG. 14 is a sectional view of an X-ray exposure mask in a second step.

FIG. 15 is a cross-sectional view of an X-ray exposure mask in a predetermined step illustrating another method for forming a conventional X-ray exposure mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Thin film 3 Etching mask

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-22391 (JP, A) JP-A-4-105320 (JP, A) JP-A-7-135157 (JP, A) JP-A-5-135 234961 (JP, A) JP-A-5-136103 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23F 1/00-4/04 G03F 1/16 H01L 21/027

Claims (5)

(57) [Claims] 1. A thin film patterning method comprising the following steps (1) and (2). (1) Nitrogen or oxygen in a range of more than 10 atomic percent and not more than 30 atomic percent within a range that is more than naturally mixed in a system for forming a thin film on W or a mixture of W and that can be etched in step (2) Forming a thin film having an amorphous structure mixed on the surface of the substrate. (2) A step of patterning the thin film by performing anisotropic etching with both accelerated ions and radicals on a partial region of the thin film in a system for patterning the thin film. 2. The thin film patterning method according to claim 1, wherein a thin film having an amorphous structure in which nitrogen is mixed in the W in a range of 10 atomic percent to 20 atomic percent is formed. Characterized thin film patterning method. 3. The thin film patterning method according to claim 2, wherein the patterned thin film is used as an X-ray exposure mask. 4. The thin film patterning method according to claim 1, wherein the thin film is formed under the following conditions (1) to (3). Patterning method. (1) The thin film is deposited by high frequency magnetron sputtering. (2) In the high-frequency magnetron sputtering, a sputtering gas in which Ar is mixed with N ₂ or O ₂ is used, and nitrogen or oxygen is mixed during deposition of W or a mixture of W. (3) The substrate temperature is set to room temperature. 5. The thin film patterning method according to claim 1, wherein the thin film is patterned under the following conditions (1) to (3). Patterning method. (1) The thin film is etched by ECR etching. (2) In the ECR etching, an etching gas containing SF ₆ as a main component is used. (3) The substrate temperature is set to room temperature.