JP2008111904A - Method for forming electrode pattern and electrode pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming an electrode pattern by which the electrode pattern having a gap of 20 nm or less can be formed with high dimension controllability and the electric resistance of the electrode pattern itself can be controlled, and to provide the electrode pattern. <P>SOLUTION: The method for forming the electrode pattern includes steps of: forming a mask pattern on a substrate by transferring a design pattern 10 having a pair of patterns 11, 11' having corners 11a, 11a' disposed with the vertexes A, A' opposing to each other by exposure using light or a charged particle beam; and forming an electrode pattern having a gap on the substrate by transferring the mask pattern. The electrode pattern obtained by the method is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode pattern forming method and an electrode pattern, and more particularly to an electrode pattern forming method and an electrode pattern having a gap (nano gap) of 20 nm or less.

  Up to now, the semiconductor industry has been miniaturized in a top-down manner, but the end of the miniaturization has begun to be seen, and silicon-based semiconductors are provided by having each molecule function as a transistor or wiring. Attention has been focused on molecular electronics technology that uses molecular elements that can break down the barriers to miniaturization of technology (for example, see Non-Patent Document 1).

  However, molecular electronics is a bottom-up technology, and even if molecular devices that show the role of transistors and wiring are found, the issue of how to realize a substrate on which a huge number of molecular devices are mounted Has not been solved yet, and it is necessary to start by preparing an environment in which the characteristics of molecular devices can be evaluated.

  An important role in this environmental maintenance is the creation of an electrode pattern (hereinafter referred to as a nanogap electrode) having a gap (nanogap) of 20 nm or less. As a method for forming the nanogap electrode, various methods shown below have been reported.

  For example, a method of creating a nanogap electrode by etching a lower electrode layer using a metal mask processed by irradiation of a focused ion beam (see, for example, Patent Document 1 and Non-Patent Document 2) A method of forming an electrode having a nanogap of 5 nm or less by obliquely vapor-depositing a metal with respect to a previously formed pattern (see, for example, Patent Document 2) is disclosed.

  Further, after forming a pair of electrodes having a wide gap on the substrate at opposing positions, in order to narrow the gap to 20 nm or less, a method of plating the pair of electrodes (see, for example, Patent Document 3) A method for depositing metal on the pair of electrodes (for example, see Non-Patent Document 3) has also been reported.

  Further, in Patent Document 2 described above, as a conventional technique, a fine metal wire and an electrode are formed in advance using an exposure means such as an electron beam, and a current is passed through the fine wire to locally break the electric field to form a nanogap. And a resist pattern in which two fine line-shaped opening patterns are opposed to each other using electron beam exposure, and an electrode layer is formed on the substrate and the resist pattern, and then lifted off. Thus, a method for forming a nanogap electrode has also been reported.

  As described above, there is no standard method for forming the nanogap electrode, and the target gap size varies depending on the molecular device to be handled. In this situation, studies are being conducted to form the gap with good controllability.

  However, among the various methods, the method using the electron beam exposure described as the prior art in Patent Document 2 described above is an electron beam exposure apparatus or electron beam that has been used in the development of conventional silicon-based semiconductor processes. It has an excellent point that it can use existing equipment such as resist, resist coating / developing equipment, pattern inspection / length measuring equipment. In particular, although the resolution is inferior to that of a point-type electron beam or ion beam, if a variable shaping type or partial batch type electron beam exposure capable of exposing each rectangular area can be used, a significant throughput can be achieved. Improvement can be expected.

  Here, a method of forming a nanogap electrode using the above-described electron beam exposure will be described. First, FIG. 9 shows a design pattern 100 for forming a nanogap electrode. The design pattern 100 includes a pair of rectangular thin line patterns 102 and 102 ′ having a gap G and a short side between a pair of large rectangular patterns 101 and 101 ′ arranged with one side facing each other. Are arranged in a state of facing each other. By transferring the design pattern 100 onto the substrate to form an electrode pattern, the gap G between the thin line patterns 102 and 102 'becomes a gap between the electrode patterns. Further, the rectangular pattern 101, 101 'is transferred to form an electrode portion, which is used for characteristic evaluation of a molecular element formed in the nano gap.

  Next, a method for forming the electrode pattern by transferring the design pattern 100 will be described. First, a positive resist is applied on the substrate to form a resist film, and then the design pattern 100 is transferred to the resist film by variable-shaped electron beam exposure. Specifically, the rectangular pattern 101 is transferred, and the fine line pattern 102 is transferred so that one short side of the fine line pattern 102 overlaps the central portion of one side of the rectangular pattern 101. Next, the fine line pattern 102 ′ is transferred with the other short side facing the other short side of the fine line pattern 102 with an interval of several nm to several tens of nm. Thereafter, the rectangular pattern 101 ′ is transferred in a state where the other short side of the thin line pattern 102 ′ and the central portion of one side of the rectangular pattern 101 ′ overlap. Thereafter, development is performed to form a resist pattern in which the design pattern 100 is provided as an opening pattern.

  Next, an electrode layer made of gold (Au) or platinum (Pt) is formed on the substrate and the resist pattern by vapor deposition, and the electrode layer on the resist pattern is removed together with the resist pattern by a lift-off method. As a result, an electrode pattern is formed in the opening pattern. As described above, nanogap electrodes are formed, and molecular elements are formed in the nanogap between the electrode patterns.

Japanese Patent Laid-Open No. 2004-247203 JP-A-2005-079335 Japanese Patent Laid-Open No. 2004-100009 Science Graphics Limited, “Molecular Electronics”, [online], [October 24, 2006 search], Internet <URL: http://www.nanoelectronics.jp/kaitai/moletronics/index.htm> Maskless fabrication of nanoelectrode structures with nanogaps by using Ga focused ion beams, “Microelectronic Engineering”, (USA) 2005, 78-79, p.253-259 Controlled fabrication of metallic electrodes with atomic separation "APPLIED PHYSICS LETTERS" (USA) April 1999, vol. 74, Number 14 5

  However, in the method of transferring the design pattern 100 shown in FIG. 9, if the width S of the rectangular thin line patterns 102 and 102 ′ facing each other is large, the influence of electron scattering (proximity effect) when transferred to the resist film. Therefore, the opening patterns communicate with each other and a gap is not formed. Therefore, it is necessary to reduce the width S of the thin line patterns 102 and 102 ′. However, when the width S of the thin line patterns 102 and 102 'is reduced, the exposure amount changes greatly even if the dimension of the width S is slightly changed, and the gap between the thin line patterns 102 and 102' serving as the non-exposed portions. Since the exposure distribution in the region where G is transferred changes, it is difficult to form an electrode pattern having a desired gap without variation in gap width.

  Furthermore, when the width S of the fine line patterns 102 and 102 'is reduced, the width of the electrode pattern obtained by transferring the fine line patterns 102 and 102' is also reduced, and the electrical resistance is increased. In addition, in order to increase the distance D between the rectangular patterns 101 and 101 ′ in order to avoid the proximity effect to the gap G due to the exposure of the rectangular patterns 101 and 101 ′, the length of the thin line patterns 102 and 102 ′ is increased. This increases the electrical resistance. Therefore, there is a problem that it is difficult to evaluate the electrical characteristics of the molecular element formed between the electrode patterns due to the influence of the electrical resistance. Furthermore, since the gap G is narrow, it is difficult to form a mask, so that there is a problem that partial batch electron beam exposure is difficult.

  Accordingly, an object of the present invention is to provide an electrode pattern forming method and an electrode pattern that can form an electrode pattern having a gap of 20 nm or less with good dimension controllability and can suppress the electric resistance of the electrode pattern itself. Yes.

  In order to achieve the above-described object, the electrode pattern forming method of the present invention is characterized by sequentially performing the following steps. First, in the first step, a mask pattern is formed on a substrate by transferring a design pattern including a pair of patterns having corners arranged with apexes facing each other by exposure using light or a charged particle beam. Form. Next, in the second step, an electrode pattern having a gap is formed on the substrate by transferring the mask pattern.

  Moreover, the electrode pattern of this invention is an electrode pattern formed by the said formation method.

  According to such an electrode pattern forming method and the electrode pattern obtained thereby, a mask is formed on a substrate by transferring a design pattern including a pair of patterns having corners arranged with apexes facing each other. Since the pattern is formed, as described with reference to FIG. 9 in the background art, the gap between the pair of patterns is transferred as compared with the case of transferring the design pattern arranged with the sides facing each other. Proximity effect due to electron scattering to the region is suppressed. For this reason, a larger pattern can be disposed as the pair of patterns, and a portion to which the pattern is transferred can be functioned as an electrode portion, and electric resistance can be reduced. In addition, since it becomes possible to arrange a larger pattern as a pair of patterns, variation in exposure amount in a region where the gap between the pair of patterns is transferred is reduced. The width variation is reduced.

  As described above, according to the electrode pattern forming method and the electrode pattern of the present invention, it is possible to reduce the variation in the width of the gap between the electrode patterns, so that the yield of the electrode pattern having a gap of 20 nm or less is increased. Can be improved. Further, since the electrical resistance of the electrode pattern is reduced, it can be suitably used for characteristic evaluation when a molecular element is formed in the gap between the electrode patterns.

  Hereinafter, an example of an embodiment according to an electrode pattern forming method of the present invention will be described in detail with reference to the drawings.

<Design pattern>
First, FIG. 1 shows a design pattern of an electrode pattern used when forming the electrode pattern of this embodiment.

  As shown in this figure, the design pattern 10 includes a pair of rectangular patterns 11 and 11 ′, for example. As a characteristic configuration of the present invention, the pair of patterns 11 and 11 'are arranged in a state where the vertices A and A' of one corner 11a and 11a 'face each other with a gap therebetween.

  Here, the pair of patterns 11 and 11 ′ are divided into vertices A and A ′ so that the corners 11a and 11a ′ are half-divided by straight lines L passing through the vertices A and A ′ of the respective corners 11a and 11a ′. Are spaced apart from each other by ΔX and ΔY in the XY direction from the position where they are aligned. Here, the dimensions W and H of the pair of patterns 11 and 11 ′ are each about several hundred nm, and ΔX and ΔY are provided in a range of about 20 nm to 60 nm. These are defined according to the resolution of the exposure apparatus. Here, for example, ΔX = ΔY = 30 nm, and the pair of patterns 11, 11 ′ are arranged so that the corners 11 a, 11 a ′ are divided in half by the straight line L.

  As described above, by arranging the pair of patterns 11 and 11 ′, compared to the case of transferring the design pattern arranged with the short sides facing each other as described with reference to FIG. 9 in the background art. The proximity effect due to electron scattering to the region where the gap 11G between the pair of patterns 11 and 11 ′ is transferred is suppressed. Therefore, a larger pattern can be arranged as the pair of patterns 11 and 11 ′, and the region where the patterns 11 and 11 ′ are transferred functions as an electrode portion, so that the electric resistance is reduced. And since the fluctuation | variation of the exposure amount of the area | region where the said gap 11G is transcribe | transferred becomes small, the dispersion | variation in the gap width between the electrode patterns formed is reduced.

  Here, the pair of patterns 11 and 11 ′ may be arranged in any direction as long as the positional relationship between the opposing vertices A and A ′ is satisfied and the sides are not opposed to each other. . However, as described above, the pair of patterns 11 and 11 ′ are arranged so that the corners 11a and 11a ′ are divided in half by the straight line L passing through the vertices A and A ′. Since the width of the gap between the electrode patterns to be formed can be aligned in the length direction, it is preferable.

  Here, since the exposure is performed by the electron beam exposure of the variable shaping method in the subsequent process, the patterns 11 and 11 ′ constituting the design pattern 10 are each rectangular, and therefore the corner portions 11a and 11a ′. However, the exposure method of the present invention is not limited to variable-shaped electron beam exposure. By arranging the pair of patterns 11 and 11 ′ as described above, the fluctuation of the exposure amount in the region to which the gap 11G is transferred can be suppressed, so that the width of the gap 11G can be made larger than before. It is also possible to adopt a partial batch exposure method in which exposure is performed through a mask provided with the design pattern 10. In this case, the shape of the patterns 11 and 11 ′ is not limited to the rectangular shape, and the pattern 11 and 11 ′ may have a pair of patterns having corner portions 11a and 11a ′ arranged with the vertices A and A ′ facing each other. Good. In this case, the angle of the opposing corners is preferably 60 degrees or more and 90 degrees or less.

  Furthermore, the present invention is not limited to electron beam exposure, and may be light exposure or charged particle beam exposure other than the electron beam exposure described above. However, since electron beam exposure has higher resolution than light exposure and is highly versatile in charged particle beam exposure, it is preferable to use electron beam exposure.

<Method for forming electrode pattern>
Next, a method for forming an electrode pattern using the design pattern 10 as described above will be described. Here, a method of forming a molecular switch will be described based on the flowchart of FIG. 2 and the process diagram of FIG.

  First, as shown in FIG. 3A, a positive resist (for example, an electron beam exposure chemistry manufactured by Tokyo Ohka Kogyo Co., Ltd.) is formed on a substrate 21 made of, for example, a silicon substrate provided with an insulating film made of an oxide film on the surface side. Amplified positive resist (OEBR-CAP138 PM) is applied to form a resist film (not shown).

  Next, the design pattern 10 (see FIG. 1) is transferred to the resist film by, for example, exposure using a variable shaping type electron beam exposure machine. Specifically, for example, after the pattern 11 is transferred, the vertex A ′ of the corner 11a ′ is located at a position away from the vertex A of the corner 11a of the pattern 11 by ΔX, ΔY (here, ΔX = ΔY = 30 nm). The pattern 11 ′ is transferred so as to be arranged. Thereafter, development is performed to form a resist pattern 22 having the design pattern 10 transferred as an opening pattern 22a (S1). This suppresses the proximity effect due to electron scattering to the region where the gap 11G between the pair of patterns 11 and 11 ′ is transferred, as compared to the case of transferring the design pattern arranged with the sides facing each other. Therefore, it is possible to form the resist portion 22b between the opening patterns 22a, which becomes a gap between electrode patterns formed in a later process, with a fine width.

  Next, as shown in FIG. 3B, an electrode layer 23 ′ in which, for example, chromium (Cr) 5 nm and Au 20 nm are sequentially stacked is formed on the substrate 21 and the resist pattern 22 by, for example, vapor deposition ( S2).

  Subsequently, as shown in FIG. 3C, the resist layer 22 and the electrode layer 23 ′ on the resist pattern 22 (see FIG. 3B) are removed together with the resist pattern 22 by a lift-off method. Since the electrode layer 23 'is also removed, the electrode pattern 23 having a gap 23G of 20 nm or less is formed in the opening pattern 22a (S3).

  After that, as shown in FIG. 3D, the substrate 21 provided with the electrode pattern 23 is immersed in a liquid containing a molecular material that forms a molecular switch. Thereby, the molecular element 24 is self-grown in the gap 23G between the electrode patterns 23. Thereafter, the molecular switch is formed by taking it out into the atmosphere (S4).

  According to such a method of forming the electrode pattern 23 and the electrode pattern 23 obtained thereby, the pair of patterns 11 and 11 ′ having the corner portions 11a and 11a ′ arranged with the vertices A and A ′ facing each other are obtained. By transferring the design pattern 10 provided, variation in the width of the gap 23G between the electrode patterns 23 can be reduced, so that the yield of the electrode patterns 23 having a gap 23G of 20 nm or less can be improved. Moreover, since it becomes possible to arrange a larger pattern as the pair of patterns 11 and 11 ′, the electrical resistance of the electrode pattern 23 itself is reduced. Therefore, it can be suitably used for characteristic evaluation when molecular elements are formed in the gap 23G between the electrode patterns 23.

  Next, the present invention will be described in detail using examples.

  FIG. 4 shows a design pattern 30 for measuring four electrodes having a pattern of the measurement pad 31 so that the characteristics of the molecular element can be evaluated. FIG. 4 is a full view, and FIG. 5 is an enlarged view of a main part of a region Y in FIG.

  As shown in FIG. 5, a pair of 500 nm □ rectangular patterns 11 and 11 ′ are arranged so that the vertices A and A ′ face each other in the −45 degree direction, and ΔX and ΔY described with reference to FIG. Each is set to 30 nm. In addition, a pair of patterns 12 and 12 ′ that define the length of the gap G in the 45-degree direction of the pair of patterns 11 and 11 ′ are formed. The electrode portions formed by transferring the patterns 12 and 12 'are not severely limited as compared to the distance between the electrode patterns formed by transferring the pair of patterns 11 and 11'.

  FIG. 6 shows an SEM image of the electrode pattern 23 formed by transferring the design pattern. Here, it was confirmed that a gap 23 having a width of 11.8 nm was formed.

  Further, FIG. 7 shows a distribution diagram of the result of measuring the width of the gap 23 obtained by exposing the design pattern 30 (see FIG. 4) on the entire surface of the 200 mm wafer. As shown in this distribution chart, it was confirmed that a sufficient number of electrode patterns were obtained for molecular device evaluation with a peak at around 20 nm. In the obtained gap 23G, the ratio of the width of 20 nm or less was about 30%. Although illustration is omitted here, when the electrode pattern is formed by transferring the design pattern of FIG. 9, an electrode having a gap of 20 nm or less only with a probability of about one tenth of this data. It was confirmed that no pattern was obtained.

  FIG. 8 is a graph showing the insulation characteristics of the obtained electrode pattern 23, and it was confirmed that good insulation characteristics were obtained.

  From the above, by using the method for forming an electrode pattern of the present invention, an electrode pattern 23 having a gap 23G of 20 nm or less can be formed with a high yield, and the obtained electrode pattern 23 is used for measuring the performance of molecular elements. As a result, it was confirmed that it was suitably used.

It is a design pattern used for embodiment which concerns on the formation method of the electrode pattern of this invention. It is a flowchart of embodiment which concerns on the formation method of the electrode pattern of this invention. It is process drawing of embodiment which concerns on the formation method of the electrode pattern of this invention. It is a design pattern for 4 electrode measurement of the Example of this invention. It is a principal part enlarged view of the area | region Y of FIG. It is a SEM photograph of the electrode pattern in an example. It is a distribution map of the gap width between electrode patterns. It is a graph which shows the insulation characteristic between electrode patterns. It is a design pattern for demonstrating the formation method of the conventional electrode pattern.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Design pattern 11, 11 '... Pattern, 11a, 11a' ... Corner, A, A '... Vertex, 21 ... Substrate, 22 ... Resist pattern (mask pattern), 23 ... Electrode pattern, 23' ... Electrode layer , 23G ... Gap

Claims (4)

A first step of forming a mask pattern on a substrate by transferring a design pattern including a pair of patterns having corners arranged with their apexes facing each other by exposure using light or a charged particle beam; and ,
A method of forming an electrode pattern, comprising: a second step of forming an electrode pattern having a gap on the substrate by transferring the mask pattern. In the formation method of the electrode pattern according to claim 1,
In the first step, the mask pattern in which the pair of patterns is provided as an opening pattern is formed,
In the second step, after the electrode layer is formed on the mask pattern and the substrate, the electrode pattern is formed by removing the electrode layer on the mask pattern together with the mask pattern by a lift-off method. A method for forming an electrode pattern. In the formation method of the electrode pattern according to claim 1,
In the first step, the design pattern having a pair of rectangular patterns is transferred by variable shaping electron beam exposure. An electrode pattern having a gap provided on a substrate,
An electrode pattern formed by transferring onto a substrate a design pattern having a pair of corners with corners arranged with their vertices facing each other by exposure using light or a charged particle beam .