JPH0227713A - Patterning method of tungsten film, manufacture of x-ray mask and formation of wiring pattern - Google Patents

Abstract

PURPOSE:To form the fine pattern of a W film with high accuracy so as to have a vertical sidewall by using the oxide film of Al as an etching mask material at the time of the selective etching of the W film. CONSTITUTION:An SiC film 11 is formed onto an Si substrate 10, and a W film 12 as an X-ray absorber layer is shaped onto the SiC film 11. An Al film 13 is formed onto the W film 12, and a resist pattern 14 is shaped onto the Al film 13. The Al film 13 is etched selectively through anisotropic etching treatment while employing the resist pattern 14 as a mask. The Al film is oxidized and an Al2O3 film 15 is shaped, and the W film 12 is etched selectively through anisotropic etching treatment while using the Al2O3 film 15 as a mask. Accordingly, the fine pattern of the W film can be formed with high accuracy so as to have vertical sidewalls.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for patterning a tungsten film to form a fine pattern of tungsten, and further relates to a method for manufacturing an X-mask using the same. and a method for forming a wiring pattern.

(Prior Art) In recent years, X-ray lithography, which uses X-rays with a shorter wavelength than light, has been attracting attention as a way to overcome the limitations of pattern miniaturization by light exposure. In this X-ray phosphorography, unlike an exposure method using light, there is currently no technology for reducing and transferring a predetermined pattern. Therefore, an X-ray mask that selectively transmits X-rays is placed between the X-ray source and the object to be exposed, and this mask is irradiated with a beam of X-rays to obtain a transferred pattern on the surface of the object to be exposed. A so-called 1:1 ratio transfer method is used.

Therefore, since the accuracy of the same-size mask pattern (one positional dimension) directly becomes the device accuracy, the X-ray mask pattern is required to have a positional accuracy of 10 minutes of the minimum line width.

Furthermore, since SOR light (synchrotron radiation) is considered to be the preferred X-ray source, it must have a structure that will not be damaged by the powerful x41. Furthermore, in order for the line width to start from 0.5 .mu.m and move toward 0.1 .mu.m in the future, the aspect ratio of the pattern on the X-ray mask will increase, increasing various manufacturing difficulties. In other words, in the X-ray exposure method, the structure of a practical X-ray mask and the
The development of a line mask manufacturing method is the most important key to commercialization.

An X-ray mask generally consists of a mask pattern (X-ray absorber pattern) made of a material with a high absorption rate for soft X-rays, and a supporting material made of a material with a particularly low absorption rate for soft X-rays. In addition to the thin film (membrane), this membrane is extremely thin and mechanically weak, so it requires a support frame to support it.

FIG. 4 is a cross-sectional view showing an example of a conventional X-ray mask manufacturing process (J, Vae, Sc1. Technol,
21.4 (1982), P, 1 (117), First, as shown in FIG. 4(a), a SiN film 4 with an internal stress of 5 to 15×108 dyn/cm 2 is formed on the St substrate 40 by the LPCVD method. Furthermore, a thin SiN film 42 is also formed on the back side of the St substrate 40. Here, the SiN film 41
becomes a thin film (membrane) that transmits X-rays. The membrane must be a self-supporting film that transmits X-rays, has excellent transparency to alignment light (visible and infrared light), and has tensile stress. Currently, BN.

St, SLC, Ti, etc. have been reported.

Next, as shown in FIG. 4(b), the SiN film 4 on the back side is
After opening the central part of 2, a W film 43 is formed as an X-ray absorber on the SiN@41 on the front side. The X-ray absorber thin film is required to have a large X-ray absorption coefficient at the exposure wavelength, low internal stress, and easy microfabrication.

Currently, Au, Ta, W, WN, etc. have been reported, and since a low internal stress of I x 108 dyn/am2 is essential, sputtering, plasma CV
It is deposited with stress controlled by the D method, heat/CVD method, plating method, etc.

Next, as shown in FIG. 4(c), a stress-controlled 5in2 film 44 is formed on the W film 43 by sputtering. Subsequently, a resist 45 for electron beam drawing is applied on the SLO□ film 44, and a pattern is drawn on the resist 45 by an electron beam drawing method.
5. Open the desired pattern. Here, since the X-ray absorber pattern is required to have a large aspect ratio and a vertical cross section, a two-layer or three-layer structure of resist/intermediate layer/W is used.

Next, as shown in FIG. 4(d), the 5in2 film 44 is selectively etched using the resist 45 as a mask. After that, as shown in FIG. 4(e), resist 45 and 5in2
The W film 43 is selectively etched using the film 44 as a mask.

That is, the W pattern is formed by dry etching using four masks in the SiO□ film 44. At this time, the etching method must have an appropriate etching selection ratio with the mask material, the difference in pattern conversion (difference in line width between the etched material and the mask material) must be small and the cross-sectional shape must be vertically etched, and the etching must be etched vertically. The conditions are that no particles or residues are generated, and that the etching stability and reproducibility are good.

Finally, as shown in FIG. 4(f'), the X-ray mask is completed by etching the Si substrate 40 from the back side using a wet etching method such as KOH using the SiN film 42 as a mask.

The most difficult step in the manufacturing process of the X-ray mask, which is formed using the complicated steps described above, is the microfabrication of the W film 43 as the X-ray absorber. Currently, as an example of etching fine patterns of heavy metals for X-ray masks, an example has been reported in which a 0.2 μm pattern was etched on W formed by sputtering (for example, J, Vac
, Sc1. TechnOl.

21.4 (1982), P4O10 or J, Vac,
Sci, Technol, B(5) (1987),
P2S5). In this reported example, Ni is used as the etching mask material for W, and W is etched with CBrF gas.

However, to form fine patterns of W with vertical sidewalls, reactive ion etching (RIE) technology must be used, which increases vertical ion incidence at low pressures. At low pressure, the etching rate of W is very low, and it is difficult to obtain a high etching selectivity with respect to a mask that can serve as an etching mask for W. In fact, in the reported example (example using SiO2 or Ni as a W etching mask), the W etching shape is not vertical, and the central wall of the pattern is side-etched, and the W pattern has a large taper. . This kind of shape is
This greatly affects the transferred pattern when transferred by X-ray exposure, making highly accurate pattern transfer impossible.

Note that side etching and taper of the W pattern occur due to the etching mask material SiO□ or Ni.
This is because it is weak against ion bombardment and is easily sputter-etched by high-energy F ions. Therefore, the etching mask material itself tapers and the pattern deteriorates. Since the W film is etched using this as a mask, a good fine pattern shape cannot be obtained for the W film at the same time. In addition, SiO2 film not only has poor sputter etching resistance, but also has poor sputter etching resistance.
Etching progresses due to F ions generated from N, which is one of the reasons why it is difficult to obtain a large selectivity.

On the other hand, a method has been proposed in which metal is embedded in a fine pattern previously formed on a membrane by a plating method without dry etching the heavy metal. However, this method produces a large amount of waste.

Defects occur, and the number of pattern formation steps increases.
Not practical.

(Problems to be Solved by the Invention) Conventionally, when patterning a W film, the etching selectivity between W and its mask material is small, and the mask material has poor ion sputtering resistance. It was difficult to pattern the W film with vertical sidewalls with high accuracy.

Therefore, when manufacturing an X-ray mask using a W film as an X-ray absorber layer, it is difficult to form an X-ray absorber pattern with high precision, and it is difficult to fully utilize the high resolution characteristics of X-ray lithography. could not. Further, when a W film is used as a wiring material, it is difficult to form a wiring pattern with high precision for the above reasons.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a method for patterning a tungsten film that can microfabricate a W film with vertical sidewalls with high precision. be.

Another object of the present invention is to be able to form an X-ray absorber pattern made of a W film in an X-ray mask with high precision, thereby contributing to the realization of microfabrication of next-generation VLSI devices using X-ray lithography. An object of the present invention is to provide a method for manufacturing an X-ray mask.

Furthermore, another object of the present invention is to provide a method for forming a wiring pattern that can realize a wiring pattern using a W film with high precision.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to use an At oxide film as an etching mask material when selectively etching a W film.

The present inventors conducted reactive ion etching using fluorine-based gas and chlorine-based gas on W and various mask materials by selecting various conditions such as pressure and power to improve the etching and etching characteristics. Upon investigation, we found the following facts:

That is, the W film is etched by fluorine gas, but l
It has been found that microfabrication at the /4 μm level can be achieved in a region where the pressure is low and the power is high (ie, reactive ion etching).

In such areas, etching proceeds by physical rather than chemical etching mechanisms. Furthermore, when the Al film was etched, the Al film was etched by chlorine-based gas, but not at all by fluorine-based gas. However, under the conditions of low pressure and high power where the above-mentioned reactive ion etching occurs, the Al film is sputtered and etched by fluorine-based gas, resulting in taber in the pattern of the Al film. this is,
This is because although the Al film is difficult to form fluorine compounds and is not easily removed, it has low resistance to physical impact such as sputtering.

On the other hand, when etching was performed using fluorine-based gas on an AI 203 film made by oxidizing an Al film, no deterioration of the fine pattern occurred even under the aforementioned low pressure and high power reactive ion etching conditions. . This is because the Al oxide has a large Young's modulus and changes into a strong and stable film, so it exhibits great resistance to sputtering effects. Furthermore, A l 203 is All! Similar to i,
This is because it is difficult to form a fluorine compound and is not easily removed. Further, when the etching characteristics of the W oxide film under the above-mentioned reactive scorching and splattering conditions using a fluorine-based gas were investigated, it was found that the etching rate was higher than that of the W film, and the etching rate was more likely to be etched.

Note that although the At oxide film is effective as an etching mask for the W film as described above, it is difficult to pattern the A I 2 film 3 itself. That is, Al 203 is an extremely stable member and has an extremely low etching selectivity with respect to the resist, so even if selective etching is performed using the resist as a mask, a highly accurate turn cannot be obtained. On the other hand,
AI has a sufficiently high etching selectivity with respect to the resist, and by selectively etching the resist using the resist as a mask, one pattern can be obtained with high accuracy.

The present invention focuses on these points and provides a method for patterning a tungsten film, a method for manufacturing an X-ray mask using a tungsten film as an X-ray absorber, a method for manufacturing a wiring pattern using a tungsten film as a wiring material, etc. After forming an aluminum film on the tungsten film, a resist pattern is formed on the aluminum film using resist/A.
A three-layer structure of 1/W is formed), and then anisotropic etching/soching treatment is performed using this resist turn as a mask (e.g., reactive ion etching/soching using chlorine-based gas).
The aluminum film is selectively etched by etching, and then the aluminum film is oxidized to form an aluminum oxide film. Then, using this aluminum oxide film as a mask, an anisotropic etching process (for example, a reactive etching process using a fluorine-based gas) is performed. In this method, the tungsten film is selectively etched and soched by ion etching and soching.

(Function) According to the present invention, by using the resist as a mask during selective etching of A1, AI can be patterned with high precision, and during selective etching of W, Al can be patterned with high precision.
By using 2O3 as a mask, W can be patterned with high precision. Moreover, the Al2O3 mask can be easily formed by oxidizing AI without causing any dimensional changes. This enables highly accurate microfabrication of the W film.

Further, when the present invention is applied to manufacturing an X-ray mask, the following effects can be obtained. Conventionally, when using 5in2 as a W etching mask, reactive ion etching using fluorine gas has a small selectivity ratio for SiO2 etching.
required a film thickness comparable to that of W. but,
The oxide film of AI has a large etching selectivity with respect to W, and even with only about 500 people, it is possible to etch W (film thickness 0.5 μm).
can be easily etched. By optimizing the conditions for forming At, it is possible to form a stress in the etching mask film that is as low as that of the W film. Stress changes in the oxide film do not affect the W pattern accuracy.

Furthermore, when the Al oxide film is irradiated with X-rays by X-ray exposure, it acts as an electron absorber layer that absorbs electrons such as Auger electrons and photoelectrons that are emitted to the outside from the W film that has absorbed the X-rays. Therefore, the X-ray mask in this case can exhibit significantly high mask contrast.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a sectional view showing the manufacturing process of an X-ray mask according to an embodiment of the present invention. First, as shown in FIG.
A SiC film 11 as an X-ray transparent thin film (membrane) was grown using the CVD method. For growth, an induction heating type low pressure CVD apparatus was used. Trichlorosilane (SiHCli) is used as a Si raw material, propane (C3H8) is used as a C raw material,
Hydrogen (H2) gas was used as the carrier gas. The flow rate of each gas was controlled by a mass flow controller. Also,
A format was used in which S i HCl 3 was bubbled with H2 and a portion of it was introduced into the reactor through a mass flow controller.

First, the Si substrate 10 was placed on a susceptor made of graphite coated with SiC using an LPGVD device using a high-frequency heating method. The temperature of the Si substrate 10 was raised to 1050° C. under reduced pressure, and the Si substrate 10 was vapor phase etched for 5 minutes using 1.5% HCI gas diluted with H2. As a result, the native oxide film and hydrocarbon contaminants existing on the substrate surface were removed, and the Si surface was cleaned. Thereafter, the SiC film 11 was deposited while changing the deposition pressure depending on the flow rate of the carrier gas H2.

The stress of the SiC film 11 is due to the reaction gas 5iHC1° and C3H.
It changes depending on the mixing ratio of s and the deposition pressure.

In this experiment, C, H, 200cc/1n, S i
HCl.

31/sin, H27N/mln, growth pressure 20
2 x 109 at a substrate temperature of 1100℃ under 0Pa
It was possible to deposit a SiC film 11 exhibiting a tensile stress of dyn/am 2 .

Further, when the crystallinity of the SiC film 11 at this time was evaluated, it was found that single crystal β-5iC had grown.

Next, W is sputtered on the SiC film 1 using a C sputtering device to form W as an X-ray absorber layer.
Film 12 was deposited to a thickness of 0.5 μm. The stress of the W film 12 is A'
It changed greatly depending on the pressure.

At an applied power of 3 KW and an Ar gas pressure of 50 to 1005 Torr, the stress of the W film 12 is 1×108 tensile stress.
It was dyn/cm2. Subsequently, the Al film 1 was sputtered using the same DC sputtering equipment used to sputter W.
3 was deposited on the W film 12. The thickness of the At film 13 is 5
There are 00 people. The stress of the At film 13 is also an applied force of 3KW,
The tensile stress could be controlled to 1 x 108 dyn/cm2 or less within the Ar gas pressure range of 20 to 50 mTorr. Thereafter, a resist (CMS: chloromethylated polystyrene) 14 was applied to a thickness of 0.5 μm on the AI film 13.

Next, electron beam lithography using a variable shaped beam with an accelerating voltage of 20 KeV was performed to obtain a dose ffi of 150μ.
The resist 14 was exposed to light using clc1112, and as shown in FIG.
), a desired opening (o, 2 to 0.) is formed in the resist 14.
A line and space of 5 μm) was formed.

Next, as shown in FIG. 1C, the AI film 13 was selectively etched by reactive ion etching using the resist 14 as an etching mask. At this time, a mixed gas of BCl2+CI2 was used as an etching gas, and etching was performed at a microwave power of 450 W in microwave plasma etching.

Next, after removing the resist 14, the A1 film 13 was oxidized to form an At203 film 15, as shown in FIG. 1(d). This oxidation was performed by heat treatment at 300° C. in an 02 atmosphere. At this time, the exposed W surface of the base was slightly oxidized.

On the other hand, Al@13 is sufficiently oxidized, and Al2
It was modified into an O3 film 15.

Next, as shown in FIG. 1(e), the W film 12 was selectively etched using a reactive ion etching apparatus using SFb gas using the Al2O3 film 15 as a mask. Etching pressure 5 II Torr, high frequency power 200
Anisotropic etching of the W film 12 was possible using W. At this time, the Al2O] film 1 used as an etching mask
5 was hardly touched. Further, there was no noticeable taper in the pattern shape, and it was clear that it acted as a good etching mask. This results in
Line width 0.2-0.5μ with Al2O3 film/W film structure
A fine pattern of lines and spaces of m was formed.

Finally, as shown in FIG. 1(f'), the central portion of the Si wafer 10 was back-etched. As a result, the SiC film 11 becomes a membrane, the W film 12 becomes an X-ray absorber layer, and the A
An X-ray mask using I 203 MA 15 as an electron absorber layer is completed.

In the X-ray mask thus created, the fine pattern of the W film 12, which becomes the X-ray absorber layer, is formed in a vertical shape.
Highly accurate pattern transfer is possible. Further, an oxide film 15 of A1 is formed on the W film 12, and this oxide film 15
Since it acts as an absorber layer for secondary electrons or Auger electrons generated during X-ray irradiation, it is also possible to transfer fine patterns with high contrast. Further, according to experiments conducted by the present inventors, it was confirmed that lines and spaces of 0.2 to 0.5 μm were formed on the resist as a result of SOR transfer through the above-mentioned X-ray mask.

FIG. 2 is a sectional view for explaining another embodiment of the present invention. The same parts as in Fig. 1 are given the same reference numerals.
A detailed explanation thereof will be omitted.

This example differs from the previously described example in the method of oxidizing AI. That is, in this embodiment, the above-mentioned FIG. 1(d)
In the process, 0+ ions were implanted over the entire surface. For the ion implantation, 10"c+n-3 of O+ was implanted at 1OKeV. Therefore, oxygen atoms were injected over the entire 500-layer thickness of the Al film 13. At the same time, oxygen atoms were injected into the vicinity of the surface of the W film 12. Oxygen ions are also implanted in the same manner.

As a result of this process, the A1 film 13 has oxygen atoms distributed throughout the film, so that the A1 film 13 becomes an oxide of AI, that is, the A1□03 film 15, which exhibits resistance as shown in FIG. At this time, in order to further ensure the resistance to ion etching using SF6 or the like, 0□7 annealing at about 300° C. may be performed after the ion implantation, as in FIG. 1(d).

As a result, an oxide of AI is formed over the entire area of the negative layer AI film. If only the 02 annealing shown in FIG. However, the 0 introduced by ion implantation is present throughout the entire film, making it possible to form A 120 s over the entire film. It is. At this time, O ions were also flowed into the W film 12, but there was no significant change in the etching rate for SF6.

From this point on, Al2O is used as in the previous example.

Selective etching of the W film 12 is performed using the film 15 as a mask to form a fine pattern of 0.2 to 0.5 μm line and space. Thereafter, the back surface of the St wafer 10 is etched back in the same manner as in the previous embodiment, thereby completing the X-ray mask.

Even in the X-ray mask thus formed, a fine W film 12 that acts as an X-ray absorber layer is formed, and an oxide film 15 of A1 that acts as an electron absorber layer is also formed, so that the above Effects similar to those of the embodiment can be obtained.

FIG. 3 is a sectional view showing the process of forming a wiring pattern according to another embodiment of the present invention. In this embodiment, as shown in FIG. 3(a), a W film 32 is formed on a Si substrate 30 on which predetermined elements are formed, via an insulating film 31 such as 5i02, and an AI film 33 and an AI film 33 are formed on the W film 32. A resist 34 is formed. In the figure, numeral 36 indicates an impurity diffusion layer, and numeral 37 indicates a contact hole.

Next, as shown in FIG. 3(b), the resist 34 is exposed and developed into a desired pattern to form a resist pattern.
Using this resist 34 as a mask, the Al film 33 is selectively etched. For this etching, reactive ion etching using chlorine gas was used as in the previous embodiment.

Next, after removing the resist 34, the At film 33 is oxidized to form Al2O as shown in FIG. 3(c).

A film 35 was formed. Next, as shown in Figure 3(d)-
Using the Al2O3 film 35 as a mask, the W film 32 was selectively etched. For this etching, reactive ion etching using fluorine gas was used as in the previous embodiment.

The wiring pattern of the W film 32 thus formed had vertical etched side walls, no difference in pattern dimensions, and was a highly accurate pattern as designed. Therefore, a fine wiring pattern using W as a high melting point metal can be realized with high precision, and it can be applied to the manufacture of various semiconductor devices.

Note that the present invention is not limited to the embodiments described above. For example, the method of oxidizing AI is not limited to annealing in an 02 atmosphere and ion implantation, but may also include plasma oxidation and anodic oxidation.

Any method that replaces the AI film with an oxide, such as photo-oxidation, can be used. Furthermore, activated oxygen is
It is also possible to use a method of reacting with (CDE type). The etching gas used for selectively etching A1 was BCl.

The gas is not limited to a chlorine-based gas such as CI2, and any gas that can etch AI with a high selectivity to the resist may be used. Similarly, the etching gas for selectively etching W is not limited to fluorine-based gases such as SF6.
A1□0. Any material may be used as long as it can etch W with a high selection ratio.

In addition, the membrane (X-ray transparent thin film) is not limited to SiC, but any self-supporting film with high X-ray transmittance and tensile stress may be used. Can be used. Furthermore, instead of the W film, it is also possible to use metals such as Mo and Ti. Further, in the embodiment, an example was described in which the Si wafer is back-etched after forming a W pattern on the Si wafer, but W may be formed on the membrane on the Si ring that has been back-etched first. Furthermore, conditions such as film thickness of each part can be changed as appropriate according to specifications. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, after micropatterning of Al is performed by reactive ion etching using chlorine-based gas, etc., the A1 is oxidized to form an AI oxide. However, by using this AI oxide as an etching mask and processing W into a fine pattern by reactive ion etching using a fluorine-based gas or the like, it is possible to process the W film in a fine vertical pattern. Therefore, it is possible to form a fine pattern on a W film with high precision and with vertical sidewalls, which has been difficult in the past, and its usefulness is enormous.

[Brief explanation of the drawing]

FIG. 1 is a process cross-sectional view for explaining an example in which the present invention is applied to the manufacture of an X-ray mask, FIG. 2 is a cross-sectional view for explaining an example of AI oxidation by ion implantation, and FIG. FIG. 4 is a process sectional view for explaining an embodiment in which the invention is applied to wiring pattern formation, and FIG. 4 is a process sectional view for explaining a conventional method. 10.30...Si substrate, 11...SiC film (X-ray transparent thin film) 12.32...W film, 13°33...
・Al film, 14.34...Resist, 15°25...
- AI oxide film (A1203 film) 31...5i02 film. Applicant's agent Patent attorney Takehiko Suzue IJIJIIIJIIIIII tl&2 tL3 671

Claims (5)

[Claims] (1) After forming an aluminum film on the tungsten film, a resist pattern is formed on this aluminum film, and then the aluminum film is selectively etched by an anisotropic etching process using this resist pattern as a mask, and then the aluminum film is selectively etched by an anisotropic etching process. A method for patterning a tungsten film, comprising: oxidizing the tungsten film to form an aluminum oxide film, and then selectively etching the tungsten film by anisotropic etching using the aluminum oxide film as a mask. (2) The tungsten film according to claim 1, wherein a chlorine-based gas is used as a gas when selectively etching the aluminum film, and a fluorine-based gas is used as a gas when selectively etching the tungsten film. patterning method. (3) The step of oxidizing the aluminum film includes heating in an oxygen atmosphere, irradiating with light in an oxygen atmosphere, treating with oxygen gas plasma, reacting with activated oxygen, or implanting oxygen ions. A method for patterning a tungsten film according to claim 1, characterized in that: (4) A step of forming a tungsten film to be an X-ray absorber layer on the X-ray transparent thin film, a step of forming an aluminum film on the tungsten film, and an X-ray absorber layer to be formed on the aluminum film. a step of forming a resist pattern according to the pattern; a step of selectively etching the aluminum film by anisotropic etching using the resist pattern as a mask; and an aluminum oxide film that becomes an electron absorber layer by oxidizing the aluminum film. A method for manufacturing an X-ray mask, comprising the steps of: forming a tungsten film; and selectively etching the tungsten film by anisotropic etching using the aluminum oxide film as a mask. (5) A method for forming a wiring pattern in which a wiring pattern made of a tungsten film is formed on a predetermined substrate, including a step of depositing a tungsten film as a wiring material on the substrate, and depositing an aluminum film on the tungsten film. a step of forming a resist pattern corresponding to a wiring pattern to be formed on the aluminum film; a step of selectively etching the aluminum film by an anisotropic etching process using the resist pattern as a mask; A method for forming a wiring pattern, comprising the steps of: forming an aluminum oxide film by oxidation; and selectively etching the tungsten film by anisotropic etching using the aluminum oxide film as a mask.