JP2001210575A - Lithography method, masking material and resist material thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithography method for forming a new pattern of submicron order, a masking material and a resist material thereof. SOLUTION: A method includes the steps of 1) forming a material as a masking film 1, of which the threshold level of field emission varies, as a result of a property variation while receiving irradiation of an electron beam or injection of a tunneling current, 2) drawing a prescribed pattern on the masking film formed by an electron beam, so that the threshold level of field emission varies, 3) forming a material of which the property varies by field emission as a resist film 3 on a semiconductor substrate, 4) putting the masking film on the resist film, 5) transcribing the variation in properties corresponding to the pattern of the masking film to the resist film by making a field emission partially generated by putting voltage between the masking film 1 and the resist film 3, and 6) partially removing the resist film, depending on a variation of these properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a lithography method for forming a pattern on the order of submicrons, a mask material therefor, and a resist material.

[0002]

2. Description of the Related Art As a method for manufacturing an integrated circuit,
Lithography is known. Lithography is a process of uniformly covering a semiconductor substrate such as silicon with a resist or a film sensitive to light or electrons, and irradiating a predetermined surface portion with an exposure source (light, X-ray or electron beam) through a specific pattern original plate. Prepare. By lithography, various circuits can be realized by forming fine patterns on a semiconductor substrate.

[0003]

When conventional lithography is used, the resolution is limited to about 0.15 μm. If you try to form a finer pattern than that,
Another lithography technique must be used. As a lithography technique for forming such a submicron pattern, there is a technique utilizing DUV (Deep Ultraviolet Light). According to this method, a pattern of about 0.08 μm can be formed, but there is a problem that there is no appropriate lens for DUV.

[0004] Further, if EUV (extreme ultraviolet light = soft X-ray) is used, it is possible to form a finer pattern. However, there is no easy-to-use powerful radiation source.
Large equipment is required, such as synchrotron radiation (electromagnetic radiation that occurs when charged particles (usually electrons), which have relatively high energy, bend in a magnetic field). In addition, there is a method of directly exposing using a narrowly focused electron beam, but this method requires drawing a pattern with a single stroke, and requires drawing a pattern for each substrate, which is time-consuming, There is a problem that is not suitable for.

Although a parallel exposure method using an electron beam has been proposed, it takes a long time because the irradiation intensity per unit area is not sufficient, and an electron beam having a large energy to increase the resolution of an electromagnetic lens. Since it is necessary to use the substrate, there is a problem that the substrate is heated to a high temperature. Further, there is an imprinting method in which a mold having a fine uneven pattern prepared in advance is pressed against the resist, but there is a problem that positioning is difficult.

As described above, at present, there is no best lithography method for forming a pattern on the order of 10 nanometers. An object of the present invention is to provide a lithography method for forming a completely new pattern on the order of 10 nanometers, and a mask material and a resist material therefor.

[0007]

In order to solve the above problems, a lithography method according to the present invention uses a material whose physical properties are changed by irradiation with an electron beam and whose threshold voltage for field emission or tunneling is changed. A step of forming a mask film, a step of drawing a predetermined pattern with an electron beam or a tunnel current on the formed mask film so that a threshold voltage of field emission or tunneling is changed, and a step of forming physical properties by field emission or tunneling. Forming a changing material as a resist film on a semiconductor substrate; superposing the mask film on the resist film; and applying a voltage between the mask film and the resist film to partially perform field emission or tunneling. Cause the Comprising a transfer step of causing a change in the physical properties corresponding to the pattern of the click film on the resist film, a step of the resist film partially removed in accordance with a change in the physical properties.

The electron beam used for patterning the mask is realized by, for example, low-energy electron irradiation using a scanning tunneling microscope (STM). Alternatively, the electron beam used for patterning the mask can be generated using, for example, a known electron beam drawing apparatus.
Although there is a possibility that the resolution is slightly deteriorated as compared with the case where the STM is used, a resolution comparable to ordinary electron lithography can be obtained. The tunnel current used for patterning the mask is, for example, a scanning tunneling microscope (ST
M). Tunneling current includes both electrons and holes. The hole injection can be performed by using the tunneling of the STM, and the resolution may be higher than in the case of the electron injection.

Preferably, the pattern of the mask film is an electron emission source or a hole emission source.

Preferably, in the step of forming the mask film, the material of the mask film is taC (tetrahedral amorphous carbon).

Preferably, in the step of forming the resist film, the material of the resist film is a carbon material containing C60.

Preferably, in the transfer step, a positive voltage is applied to the resist film side and a negative voltage is applied to the mask film side to inject electrons from the pattern of the mask film into the resist film.

Preferably, in the transfer step, holes are injected from the pattern of the mask film into the resist film by applying a negative voltage to the resist film side and a positive voltage to the mask film side.

The mask material for lithography according to the present invention is characterized in that physical properties are changed by irradiation with an electron beam or injection of a tunnel current, and a threshold voltage for field emission or tunneling is changed.

[0015] The resist material for lithography according to the present invention is characterized in that its physical properties change due to field emission or tunneling and become insoluble or soluble in a solvent.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 of the Invention A preferred embodiment of the present invention will be described with reference to the drawings. FIG.
Shows a step of manufacturing a mask in the lithography method according to the embodiment of the present invention. FIG. 2 shows a step of forming a resist on a semiconductor substrate into a predetermined pattern using the mask in the lithography method according to the embodiment of the present invention. FIG. 3 is an explanatory diagram (FIGS. 3A and 3B) of a mask manufacturing process according to an embodiment of the present invention and an explanatory diagram of a process of forming a resist on a semiconductor substrate into a predetermined pattern using a mask (FIG. FIG.

First, a process of manufacturing a mask will be described with reference to FIG. Prepare the mask material (S
1). The mask material is deposited on the substrate 2 by a physical or chemical method to form a mask film 2. The physical property that the material of the mask should have is that the physical property changes due to the irradiation of the electron beam or the injection of the tunnel current, and the threshold voltage of the field emission or the tunneling changes. Desirably, in addition to this, the current density in field emission or tunneling is high, the voltage-current characteristics are very nonlinear, a flat film is obtained, the electrical insulation is high, and the chemical That it is abrasion resistant, mechanically stable, and withstands many times of contact exposure.

As a material of such a mask, for example,
taC (tetrahedral amorph)
ous Carbon). Specifically, carbon ions generated by arc discharge or the like are accelerated and irradiated and deposited on a substrate. When deposited by a chemical method, the mask film contains hydrogen and is likely to cause a change with time. Therefore, it is desirable to use a physical method.

A predetermined pattern is drawn on the mask with an electron beam (S2). As shown in FIG. 3A, electrons accelerated at a predetermined energy are irradiated on a mask 1 of a taC film formed on a substrate 2. For example, an electron beam of about 10 keV is applied while lowering the current density so as to increase the resolution. Then, as shown in FIG. 3B, the structure of the portion 1a irradiated with electrons changes, and the physical properties change accordingly. Specifically, the sp ³ / sp ² orbital hybrid ratio of the portion 1a irradiated with electrons changes,
Field emission or tunneling threshold voltage changes. In the case of taC, the threshold voltage increases. This will be described in more detail.

FIG. 4 shows the sp ³ orbital hybrid ratio (sp) of the taC film.
⁴ is a graph showing a relationship between a threshold voltage that generates a field emission current of ¹ μA / cm ² and an amount representing a relation between carbon atoms having tetrahedral bonding based on ^three- orbit hybridization.
As can be seen from this graph, the higher the sp ³ orbital hybridization rate, the lower the field emission threshold voltage.

FIG. 5 is a graph showing the relationship between the field emission current density and the electric field intensity on the taC film surface. s
p ³ it can be seen that the threshold voltage of the field emission when orbital hybridization rate is high is reduced.

As can be seen from FIG. 5, the relationship between current density and electric field intensity is very nonlinear. Therefore, when a voltage is applied in the appropriate field strength to the membrane, in correspondence with the difference in the sp ³ orbital hybridization rate, it is possible to give a large difference in current density.

It is also known that when a current is injected into the taC film from the tip of a scanning tunneling microscope (STM) into the taC film, the sp ³ -like structure can be locally changed to the sp ² -like structure (TWMercer et al.). ., Appl. Phys. Lett. 72, 2
244 (1998)).

A similar modification from the sp ³ -like coupling structure to the sp ² -like coupling structure is performed by an electron beam of a usual electron beam lithography apparatus, and the threshold voltage of the field emission of the modified portion is locally increased. The threshold voltage of the mask may be reduced by the electron beam irradiation. This means
It may depend on the starting state of the mask film. Either case is included in the present invention.

In the above description, an increase in the threshold voltage of the field emission causes an increase in the threshold voltage of the tunneling in the tunneling. Therefore, even when the resist exposure described later is performed in the tunneling mode,
The method is applicable.

Next, a process of forming a resist on a semiconductor substrate in a predetermined pattern will be described with reference to FIG. A resist film 3 is formed on a semiconductor substrate (S3). As the resist film 3, a C60-based resist material can be used.
The physical properties that the resist film 3 should have are that it is injected with electrons or holes to be insolubilized in a solvent (hereinafter referred to as solidification for simplicity), and that the injection energy for that is as low as possible.

The mask 1 is overlaid on the resist 3 (S4).
It is desirable that the mask 1 be as close as possible to the resist 3. A voltage is applied between the mask 1 and the resist 3 so that the mask 1
Is transferred (S5). In the example of FIG.
A positive voltage is applied to the substrate 4 on the resist 3 side, and a negative voltage is applied to the substrate 2 on the mask side. In this case, the pattern 1 of the mask 1
From a, electrons are injected into the resist 3. As a property of the resist, it is desirable to polymerize at a voltage as low as possible. C60 (a large molecule consisting only of carbon; a hollow cluster having a surface network structure in which 60 carbon atoms are connected in a hexagonal and pentagonal form) contained in the resist material,
For example, when the distance between the mask and the resist film is 1 nm, and a voltage of about 6 V is applied thereto, 1 nA
A small amount of current can flow in a region of 1 nm ² . The current density at this time reaches 10 ⁸ mA / cm ² . Also, even in the case of field emission, as can be seen from FIG. 5, the current density can reach 0.1 mA / cm ² . C60
Since the sensitivity of the system resist is 1 mC / cm ² (however, if the sensitivity is higher than this, the statistical fluctuation of polymerization becomes large, and the uniformity of solidification is impaired). Further, from the viewpoint of the aspect ratio of the pattern formed on the resist, it is desirable that the resist film is as thin as possible. In addition, contrary to the application of the voltage shown in FIG.
A positive voltage may be applied to the mask 1 side. In this case, holes are injected into the resist, but the resist solidifies as in the case of electrons.

Develop (S6). Specifically, the resist film that has not been solidified is removed with a solvent.

According to the above procedure, a pattern on the order of 10 nm can be formed on the resist film 3 on the semiconductor substrate 4.

According to the method / apparatus of the embodiment of the present invention, a desired pattern can be formed with a very high resolution of 10 nm. In addition, there is an advantage in that mass productivity is high and it can be realized with simple equipment as compared with a method of forming patterns one by one using an electron beam narrowed down on an etching resist.

According to the embodiment of the present invention, since a low-energy electron beam is used, there is no secondary effect such as generation of secondary electrons. it can. Also, the current density is 1 mA / c
In the case of about m ² , the calorific value is 1 mA / cm ² × 10 V = 1
Since it is 0 mW / cm ² , a rise in temperature can be avoided.

Further, according to the embodiment of the present invention, by utilizing the tunneling, the spread of the electron beam can be avoided, and the hole can be injected.

Further, according to the embodiment of the present invention, since the contact exposure method is employed, the spread of the electron beam can be avoided, and the displacement of the pattern due to thermal drift or the like can be avoided. .

Further, according to the embodiment of the present invention,
Since a taC film is used as a mask, the field electron emission capability is high.
(With appropriate surface treatment, 1 mA /
cm ²), And a flat film can be obtained. Moreover, the insulation is high
Since the mask and resist can be in close contact,
Is easy. And chemically without hydrogen
It is stable. Moreover, it is wear-resistant and mechanically stable,
It can withstand a large number of contact exposures.

According to the embodiment of the present invention, since a C60-based material is used as a resist, a pattern having a small size of about 1 nmφ can be formed, and low-energy electron beam exposure can be performed. . C60
Since the system resist (C60 derivative obtained by adding a modifying molecule to C60) has a small molecular size of 0.7 nm, high-resolution drawing can be performed. Further, from the viewpoint of etching resistance, it is desirable that the remaining portion after development is a carbon film, and in that sense, C60 is preferable.

The resist material applicable to the present invention is C6
Not limited to 0 series. It is considered that the conventional negative type (type which solidifies by exposure) resist material for electron beam exposure is also solidified by low energy electron beam irradiation. Therefore, these materials can also be applied to the present invention.

In the above description, negative type patterning is performed using a C60 type resist material. However, a positive type resist material having a predetermined sensitivity is also applicable to the present invention. If the threshold voltage of the electron beam processing area increases as in the above case when a mask pattern is written, in the case of a negative type, the resist in this portion becomes soluble, which is convenient (the resist opening is narrow. If it is desired, the electron beam processing area at the time of manufacturing the mask can be narrowed). Conversely, a positive resist material is suitable for widening the resist opening even when the threshold voltage is lowered.

In the apparatus / method according to the embodiment of the present invention, it is desirable that the mask be in uniform contact with the resist in order to accurately form a fine pattern. for that purpose,
It is necessary to keep the following points in mind.

The flatness of the resist and the substrate is ensured. For example, the problem is solved by using the Mechano Chemical Polisshing method.

It is possible to avoid a decrease in adhesion due to the warpage of the substrate. For example, the mask is brought into close contact with the resist by applying light physical pressure to the entire mask (stamp method).

It is necessary to perform resist patterning with a low aspect ratio. That is, the thickness of the resist is preferably as thin as possible, as compared with the size of the opening of the pattern.
The finer the pattern, the better the resist. For this purpose, it is desirable to use a resist film having excellent etching resistance, but a carbon-based material is considered to be promising as this kind of material.

A mechanism for accurately positioning the mask is required. Although this mechanism is commonly required in nanolithography, a mechanism that gives a minute movement using the piezo effect can be considered.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the appended claims, and these are also included in the scope of the present invention. Needless to say, this is done.

[Brief description of the drawings]

FIG. 1 shows a step of manufacturing a mask according to an embodiment of the present invention.

FIG. 2 shows a step of forming a resist on a semiconductor substrate into a predetermined pattern using a mask according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a mask manufacturing process according to the embodiment of the present invention (FIGS. 3A and 3B) and an explanatory diagram of a process of forming a resist on a semiconductor substrate into a predetermined pattern using a mask (FIG. FIG.

FIG. 4 shows sp ³ orbital hybrid ratio of taC film and 1 μA / cm.
⁴ is a graph showing a relationship between threshold electric fields giving field emission current densities of ² ;

FIG. 5 is a graph showing current density versus electric field strength in taC films having different sp ³ orbital hybridization rates.

[Explanation of symbols]

 Reference Signs List 1 mask 2 substrate 3 resist 4 semiconductor substrate

Claims (8)

[Claims] A step of forming, as a mask film, a material whose physical properties change due to irradiation of an electron beam or injection of a tunnel current and which changes a threshold voltage of field emission or tunneling; and a threshold of field emission or tunneling. A step of drawing a predetermined pattern on the mask film using an electron beam or a tunnel current so that a voltage changes, and a step of forming a material whose physical properties change by field emission or tunneling on a semiconductor substrate as a resist film, A step of superposing the mask film on the resist film; and applying a voltage between the mask film and the resist film to partially cause field emission or tunneling, thereby changing physical properties corresponding to the pattern of the mask film. The resist Lithography process and a step of removing the resist film is partially in response to changes in the transfer process and the physical properties cause the. 2. The lithography method according to claim 1, wherein the pattern of the mask film is an electron emission source or a hole emission source. 3. In the step of forming the mask film,
The lithography method according to claim 1, wherein a material of the mask film is taC (tetrahedral amorphous carbon). 4. The lithography method according to claim 1, wherein in the step of forming the resist film, a material of the resist film is a carbon material containing C60. 5. In the transferring step, a positive voltage is applied to the resist film side and a negative voltage is applied to the mask film side, thereby injecting electrons from the pattern of the mask film into the resist film. The lithography method according to claim 1. 6. In the transferring step, holes are injected from the pattern of the mask film into the resist film by applying a negative voltage to the resist film side and a positive voltage to the mask film side. The lithography method according to claim 1. 7. A mask material for lithography, wherein physical properties change upon irradiation with an electron beam, and a threshold voltage for field emission or tunneling changes. 8. A resist material for lithography, wherein the physical properties are changed by field emission, and the resist material is made insoluble or soluble in a solvent.