JP2006080360A - Membrane mask and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane mask which has a high membrane strength, in which the stress control of the membrane is possible and which is excellent in an electron beam transmission property, and to provide a method of manufacturing the same. <P>SOLUTION: The membrane mask includes a substrate, the membrane supported by this substrate, and a mask body formed on this membrane and having a transparent hole pattern which a charged particle beam penetrates. The membrane is made of a diamond membrane containing a nitrogen of 3×10<SP>18</SP>cm<SP>-3</SP>or more. The membrane is formed by a plasma CVD method using a raw material gas containing a hydrocarbon, a hydrogen and 0.5% or more of a nitrogen source gas on the substrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a membrane mask used for charged particle beam exposure such as an electron beam or an ion beam in a manufacturing process of a semiconductor or the like, and a manufacturing method thereof.

  In recent years, miniaturization of semiconductor elements has been progressing rapidly. Various exposure techniques have been developed as manufacturing techniques for elements having such fine patterns. For example, there are an exposure method using an electron beam such as an electron beam partial exposure and an electron beam stepper exposure, an exposure method using ions, an exposure method using light in a vacuum ultraviolet region, an exposure method using light in the extreme ultraviolet region, etc. .

  Among these, as one of exposure methods using an electron beam, a method of reducing exposure using an electron beam stepper has been proposed (for example, see Non-Patent Document 1). In this method, high-speed electrons accelerated at about 20 to 100 kV are normally reduced and exposed to 1/4 using an electron beam mask and an electron lens to form a desired pattern such as a semiconductor circuit. Membrane masks and stencil masks have been proposed as electron beam masks used here.

  The membrane mask is composed of a mask layer obtained by patterning a thin film made of a heavy metal that easily scatters an electron beam on a thin film (membrane) made of a light element that easily transmits an electron beam. For example, a silicon nitride film is used as the membrane material, and a tungsten thin film is used as the scattering layer material. On the other hand, the stencil mask does not have a membrane thin film, and a through hole is provided in the exposed portion. As the scattering layer, single crystal silicon is usually used, and its thickness is usually about 2 μm.

  In the stencil mask, a through-hole through which an electron beam passes is provided in the mask itself, and exposure electrons can freely pass through the opening, so that there is no energy loss of the electron beam. Therefore, compared with the membrane mask, there is no reduction in resolution due to chromatic aberration. However, since the portion through which the electron beam passes completely penetrates, if the opening pattern is closed, the mask member inside thereof is lost. In order to avoid this, it is necessary to divide the pattern into two or more complementary masks.

  For example, in the case of a donut-shaped pattern, the pattern is divided into two semicircles, divided into respective complementary masks, arranged on the respective complementary masks, and exposed twice to complete the pattern on the wafer. Further, it is necessary to divide a pattern having a problem in mechanical strength such as a large mask member supported by a small support portion. As described above, the stencil mask has a serious problem that the throughput is sacrificed because the number of exposures is doubled by dividing the mask.

  On the other hand, since the membrane mask does not require mask division as in the case of the stencil mask described above, there is no reduction in throughput that is regarded as most important as the next-generation exposure method. However, since a membrane thin film is interposed in the electron beam exposure part, even if conventional silicon nitride is used as the membrane material and the film thickness is reduced, the ratio of non-scattered electrons is small. Further, most of the electrons whose angles are changed by elastic scattering are cut by the limiting aperture, so that the loss of the beam current is large. Furthermore, some of the electrons that pass through the limiting aperture and contribute to the exposure also lose energy due to inelastic scattering such as plasmon excitation. As a result, the energy dispersion of exposure electrons increases, that is, the resolution decreases due to chromatic aberration.

  Recently, a membrane mask using diamond-like carbon (DLC) has been proposed as a membrane mask for the purpose of reducing electron scattering at the membrane, and also for the mask matrix (see, for example, Non-Patent Document 1). ).

  DLC is a general term for amorphous carbon that generally exhibits diamond-like mechanical properties, and its structure and physical properties vary greatly depending on the production method. According to the above literature, the Young's modulus of DLC is 130 to 300 GPa, which is higher than that of silicon nitride (130 to 160 GPa) conventionally used as a membrane material. Further, since DLC is composed of carbon atoms, it has a smaller atomic number and density than silicon nitride, and can reduce electron scattering.

However, since DLC usually shows a strong compressive stress and has an amorphous structure, it is difficult to control the film quality, and it is also difficult to adjust the stress. In addition, it is also known that stress can be relieved by doping such DLC with other elements such as silicon, but for that purpose, introduction of other elements of several tens of percent or more is usually required. The physical property values (high hardness, high thermal conductivity, etc.) as much as DLC composed of Furthermore, as described above, DLC has an amorphous structure, and when doped, there is a change in structure and physical properties due to mixing of other elements, so that it is difficult to obtain sufficient electron beam irradiation resistance.
H. Yamashita et. Al., J. Vac. Sci. Technol, B18, 3237 (2000)

  The present invention has been made under such circumstances, and an object of the present invention is to provide a membrane mask having high film strength, capable of controlling the stress of the membrane, and having excellent electron beam transmission characteristics, and a method for manufacturing the same. .

In order to solve the above problems, one embodiment of the present invention includes a base, a membrane supported by the base, and a mask base that is formed on the membrane and has a transmission hole pattern through which a charged particle beam passes. The membrane comprises a diamond film containing nitrogen of 3 × 10 ¹⁸ cm ⁻³ or more.

  In the membrane mask configured as described above, a diamond film having a high hardness and a high Young's modulus is used as the membrane, so that a membrane with high mechanical strength can be configured, the area of the membrane portion without the base can be increased, and more A fine pattern can be formed, and the degree of freedom in circuit pattern design can be improved. Further, since diamond is a light element, it is possible to realize a mask having a high electron transmittance and a small loss of exposure electrons.

  In addition, when the diamond film contains more than the specified amount of nitrogen, the flatness of the film is improved, so that the degree of freedom of the process is increased, the processing accuracy of the mask base is improved, and a finer pattern is formed. Is possible.

  Furthermore, conductivity can be imparted to the diamond film, which is originally an insulator, by allowing the diamond film to contain a specified amount or more of nitrogen. Thereby, it is not necessary to attach a conductive film separately or to perform a surface treatment, and it is possible to realize a membrane mask having a simple structure with only a diamond film and having good characteristics not to be charged up.

  Furthermore, by containing more than a specified amount of nitrogen in the diamond film, it becomes possible to relieve the stress of the diamond film that originally has a strong tensile stress.

  In the membrane mask according to one embodiment of the present invention, the flatness of the surface of the diamond film can be less than 50 nm.

  Another aspect of the present invention is a step of forming a diamond film on a substrate by a plasma CVD method using a source gas containing hydrocarbon, hydrogen, and a nitrogen source gas of 0.5% or more. Forming a mask material layer; processing the substrate to form openings; forming a membrane mask substrate; forming an organic resist pattern on the mask material layer; and using the organic resist pattern as an etching mask And a step of etching the mask material layer to form a mask mother body. A method for manufacturing a membrane mask is provided.

  In such a membrane mask manufacturing method, by adding a predetermined amount of nitrogen source gas to the source gas in the plasma CVD method, CN and C2 (dimer) in the reaction system increase, and their generation density increases. As a result, a membrane made of a diamond film having a small crystal grain size and high surface smoothness can be obtained. As a result, it is possible to improve the processing accuracy of the mask base that requires ultrafine patterning on the membrane.

  Further, since the membrane surface is flat, polishing treatment after film formation is unnecessary, and the mask base material can be formed immediately after film formation. Therefore, the membrane mask can be manufactured by a simple process.

  The plasma CVD method for forming the diamond film desirably uses microwave plasma of 1 kW or more.

  According to the present invention, it is possible to provide a membrane mask that can be easily thinned, can control stress, has high workability, has high film strength, and has high pattern accuracy. Since this membrane mask has good flatness on the surface of the membrane, the degree of freedom of the process is increased, the processing accuracy of the mask base is improved, and a membrane mask with a finer pattern can be obtained. Further, this membrane mask has a good characteristic that the membrane does not charge up because the membrane has conductivity.

  Further, according to the present invention, the membrane is formed by a diamond film having a small crystal grain size and high surface smoothness obtained by a plasma CVD method using a source gas to which a predetermined amount of nitrogen source gas is added, Therefore, a mask base with a fine pattern can be formed on it with high accuracy.

  Furthermore, by including a predetermined amount or more of nitrogen in the diamond film constituting the membrane, it becomes possible to relieve the stress of the diamond film having a strong tensile stress.

  The best mode for carrying out the invention will be described below.

The membrane mask according to an embodiment of the present invention is characterized in that the membrane is made of a diamond film containing nitrogen of 3 × 10 ¹⁸ cm ⁻³ or more.

As described above, the diamond film containing nitrogen of 3 × 10 ¹⁸ cm ⁻³ or more has excellent surface flatness of less than 50 nm, and has conductivity. In membrane masks that contain such a diamond film as the mask matrix, the membrane surface has good flatness, increasing the degree of freedom of the process and improving the processing accuracy of the mask matrix formed on it. A fine pattern can be obtained. Further, since the membrane has conductivity, it is not necessary to attach a conductive film separately or to perform surface treatment, and it is possible to realize a membrane mask having good characteristics that does not charge up.

  In addition, when the diamond film contains more than a specified amount of nitrogen, the stress of the diamond film that originally has a strong tensile stress can be relaxed.

If the nitrogen content is less than 3 × 10 ¹⁸ cm ⁻³ , the surface of the diamond film is inferior in flatness and the conductivity becomes low, and a membrane mask having the above characteristics cannot be realized.

  As the substrate, a processed silicon single crystal substrate, glass substrate, quartz substrate or the like can be used.

  Hereinafter, the manufacturing method of the membrane mask which concerns on one Embodiment of this invention mentioned above is demonstrated with reference to FIG.

  First, as shown in FIG. 1A, a diamond film 2 is formed on a substrate 1 by a plasma CVD method using a source gas containing hydrocarbon, hydrogen, and a nitrogen source gas of 0.5% or more.

  A thermal CVD method or the like can be used instead of the plasma CVD method.

  As the hydrocarbon, methane, ethylene, acetylene or the like can be used, and as the nitrogen source gas, nitrogen, ammonia or the like can be used.

As described above, the formed diamond film 2 contains nitrogen of 3 × 10 ¹⁸ cm ⁻³ or more. Thus, the diamond film 2 containing nitrogen of 3 × 10 ¹⁸ cm ⁻³ or more can be obtained by using a source gas containing 0.5% or more of a nitrogen source gas together with hydrocarbons and hydrogen in the CVD method. I can do it. In particular, a diamond film containing nitrogen of 3 × 10 ¹⁸ cm ⁻³ or more can be obtained more reliably by a plasma CVD method using microwave plasma of 1 kW or more.

  Thus, by adding a predetermined amount of nitrogen source gas to the source gas in CVD, CN and C2 (dimer) in the reaction system increase, and their generation density increases, resulting in crystal grains. A diamond film having a small diameter and high surface smoothness can be obtained.

  Next, as shown in FIG. 1B, a mask material layer 3 is formed on the diamond film. Examples of the mask material include tantalum, tungsten, chromium, chromium nitride, and the like.

  Next, as shown in FIG. 1C, the back surface of the substrate 1 is processed to form a membrane mask base having an opening. The processing of the back surface of the substrate 1 can be performed using photolithography and RIE. For example, an etching mask is formed on the surface of the substrate 1 excluding a portion to be removed by photolithography, and the substrate 1 is etched by using this as a mask, for example, by RIE, thereby obtaining a membrane mask base 4 having an opening. I can do it.

  Then, after forming an organic resist layer on the mask material layer 3, patterning is performed by lithography to form an organic resist pattern 5 as shown in FIG. Subsequently, using this organic resist pattern 5 as an etching mask, the mask material layer 3 is etched to form a mask base 6. For the etching of the mask material layer 3, for example, reactive ion etching (RIE) can be used.

  Finally, the organic resist pattern 5 is removed to obtain a membrane mask as shown in FIG.

  The membrane mask obtained by the above-described method is formed by plasma CVD using a source gas containing hydrocarbon, hydrogen, and nitrogen source gas of 0.5% or more, and has good flatness and conductivity. Since the diamond film having a thickness is used as a membrane, it can be formed with a fine pattern with high accuracy and has good characteristics of not being charged up.

  Hereinafter, examples of the present invention will be shown, and the present invention will be described more specifically.

Example 1
With reference to FIG. 1 (a)-(e), the manufacturing process of the membrane mask which concerns on one Example of this invention is demonstrated.

  As shown in FIG. 1A, a diamond film 2 was formed on a single crystal silicon substrate 11 having a thickness of 525 μm using a microwave plasma CVD apparatus.

The conditions for microwave plasma CVD are as follows.
Source gas: methane (50 sccm), hydrogen (445 sccm),
Nitrogen (5sccm)
Substrate temperature: 820 ° C
Reaction pressure: 80 Torr
MW power: 2.5kW
Film thickness: 0.5 μm.

  When the diamond film 2 produced as described above was observed with an atomic force microscope (AFM), a crystal grain size of nanometer order could be confirmed. Further, the root mean square surface roughness (rms) measured by AFM on 10 μm square was very flat at 15 nm.

The presence of sp ³ (diamond bond) could be confirmed by electron beam energy loss spectroscopy (EELS). Furthermore, as a result of measuring the electrical conductivity of the film, a resistivity of several Ω was obtained.

  Next, as shown in FIG. 1B, a tantalum thin film 3 was formed on the diamond film 2 as a mask base material by sputtering.

The sputtering conditions are as follows.
Sputtering gas: Argon (33 sccm)
Substrate temperature: <100 ° C
Sputtering pressure: 5Pa
Power: 1kW
Film thickness: 50 nm
Next, as shown in FIG. 1C, the back surface of the substrate 1 was processed by photolithography and RIE to obtain a membrane mask base 4. Here, carbon tetrafluoride was used as an etching gas.

  Thereafter, an electron beam resist (not shown) was applied on the tantalum thin film 3 to a thickness of 0.5 μm. ZEP (trade name, manufactured by Nippon Zeon Co., Ltd.) was used as the electron beam resist. The electron beam resist is drawn and exposed in a pattern using an electron beam drawing machine, and then developed using a dedicated developer ZED-N50 (trade name, manufactured by Nippon Zeon Co., Ltd.). As shown in 1 (d), a resist pattern 5 was formed.

  Next, using the resist pattern 5 as a mask, the pattern was transferred to the tantalum thin film 3 by using a reactive ion etching (RIE) apparatus to form a mask base 6 as shown in FIG. The RIE conditions are as follows.

Etching gas: CF ₄ (35 sccm)
Reaction pressure: 30 mTorr
High frequency power: 300W
Finally, the resist pattern 5 was peeled off, and a membrane mask was obtained as shown in FIG.

  In the membrane mask manufactured as described above, the membrane (diamond film) 2 and the mask base 6 are both adjusted to a very low stress, and no peeling or cracking occurs, and the membrane (diamond film) 2 and Since the mask base 6 has low resistance, it was not necessary to provide a separate metal film. Further, the obtained membrane mask had high pattern accuracy and excellent charged particle beam irradiation characteristics.

  In the above embodiments, an example in which a single crystal silicon substrate is used as the substrate and a tantalum thin film is used as the mask base has been described. However, the present invention is not limited to this, and quartz or the like can be used as the substrate. is there.

  The membrane mask and the manufacturing method thereof according to the present invention can be widely used in manufacturing processes of various semiconductor devices.

It is sectional drawing which shows the manufacturing method of the membrane mask which concerns on one Embodiment of this invention to process order.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Membrane, 3 ... Mask material layer, 4 ... Membrane mask base | substrate, 5 ... Organic resist pattern, 6 ... Mask mother body.

Claims (4)

A substrate, a membrane supported by the substrate, and a mask matrix formed on the membrane and having a transmission hole pattern through which a charged particle beam passes. The membrane has a size of 3 × 10 ¹⁸ cm ⁻³ or more. A membrane mask comprising a diamond film containing nitrogen.   The membrane mask according to claim 1, wherein the diamond film has a surface flatness of less than 50 nm. Forming a diamond film on a substrate by a plasma CVD method using a source gas containing hydrocarbon, hydrogen, and a nitrogen source gas of 0.5% or more;
Forming a mask material layer on the diamond film;
Processing the substrate to form an opening and forming a membrane mask substrate;
Forming an organic resist pattern on the mask material layer; and etching the mask material layer using the organic resist pattern as an etching mask to form a mask matrix;
A method for producing a membrane mask, comprising:   The method of manufacturing a membrane mask according to claim 3, wherein the plasma CVD method uses microwave plasma of 1 kW or more.

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