JP2007256854A - Method for manufacturing nano pattern and nano pattern substrate, semiconductor memory cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method by which surface roughness of a fine pattern can be controlled in a molecular level without excessively increasing complexity of manufacturing. <P>SOLUTION: The method for manufacturing a nano pattern includes steps of: forming an alignment layer containing a photoisomerization compound on a substrate; forming a liquid crystal layer containing a liquid crystal polymer having a main chain and a side chain on the alignment layer; irradiating the alignment layer with linearly polarized UV light to align the main chain of the liquid crystal polymer in the liquid crystal layer to a predetermined direction in accordance with the photoisomerization compound which is photoisomerized by the UV light; and subjecting the substrate to isotropic dry etching by using the liquid crystal layer as a mask to form a nano pattern having projected portions in a certain pitch corresponding to the length of the side chain of the liquid crystal polymer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor manufacturing technique, for example, a manufacturing method suitable for forming a fin portion of a double gate field effect transistor (FET).

  In general, it is preferable to manufacture smaller transistors in order to increase the component density on the integrated circuit. In terms of structure, a three-dimensional transistor using a three-dimensional silicon layer has been studied by various companies, and a fin type transistor is one of them. A fin-type transistor requires a structure in which a plurality of vertical fins are arranged, each fin is 10 nm or less, and the fins are periodically arranged.

It has been studied to manufacture such a fine pattern by performing so-called sidewall image transfer (for example, Patent Document 1). In this method, SiN or the like is vapor-deposited on SOG to which a resist pattern of a size that can be produced is transferred, and the substrate is processed using a SiN film remaining on the side wall of SOG as a mask through a flattening process by dry etching. At present, it is used in research and development as a method for obtaining fine patterns with the least edge roughness. However, the process is much more complicated than the photolithography process, and thus the manufacturing cost is high, which is not practical for mass production.

By the way, in the field of liquid crystal display devices, there is an attempt to control alignment of liquid crystal using a polymer alignment film as an alignment film. The photosensitive side chain polymer film is irradiated with linearly polarized ultraviolet rays to dimerize the photosensitive groups to obtain an alignment film having arbitrary alignment characteristics (for example, Patent Document 2).
JP 2005-175480 A JP-A-11-181127

  In order to solve the above problems, an object of the present invention is to provide a manufacturing method capable of controlling the surface roughness of a fine pattern at a molecular level without excessively increasing the manufacturing complexity.

  The nanopattern manufacturing method of the present invention includes a step of forming an alignment film having a photoisomerizable compound on a substrate, and a step of forming a liquid crystal layer containing a liquid crystalline polymer having a main chain and a side chain on the alignment film. Irradiating the alignment film with linearly polarized ultraviolet light, aligning the main chain of the liquid crystalline polymer in the liquid crystal layer in a predetermined direction corresponding to the photoisomerized compound photoisomerized by the ultraviolet light, and liquid crystal And a step of performing anisotropic dry etching of the substrate using the layer as a mask to form a nanopattern having convex portions with a constant pitch corresponding to the length of the side chain of the liquid crystalline polymer. . It is also possible to remove the main chain of the liquid crystalline polymer and leave the side chain during the dry etching.

  Further, an SOG film can be formed on the substrate surface before the step of forming the alignment film. The liquid crystalline polymer may be a polymer that forms a smectic liquid crystal phase.

    According to the present invention, it is possible to provide a manufacturing method capable of controlling the surface roughness of a fine pattern at a molecular level without excessively increasing the manufacturing complexity, and can be applied to substrate processing and precision parts using the substrate. can do.

  The present inventor has found that the present invention can be applied to the formation of the fine pattern by orienting and dimerizing the photosensitive side chain polymer and providing a difference in dry etching resistance for each pattern.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 is a diagram conceptually showing an overall flow showing a manufacturing process of a nanopattern according to an embodiment of the present invention. [FIG. 1] (a) is a view in which an alignment film 2 is formed on a surface of a substrate 1. The substrate 1 is made of Si used for a semiconductor or SiN or BSG film formed on the Si surface in consideration of dry etching described later. The alignment film 2 contains a photoisomerizable compound. A photoisomerizable compound is a molecule that undergoes a change in molecular axis orientation by linearly polarized light.

  The change in molecular axis orientation here is a phenomenon in which the direction of the molecular axis changes after absorbing light energy of linearly polarized light. As a photoisomerization compound for this purpose, a molecule containing at least one double bond selected from C = C, C = N, N = N, and the double bond being non-aromatic is effectively used. Is done. The wavelength of light absorbed by the photoisomerized compound is not limited to the visible light region, but includes those in the ultraviolet and infrared regions that are not observed with the naked eye. When the layer of this photoisomerized compound is irradiated with linearly polarized light including the wavelength range absorbed by the compound, the molecular axis orientation easily changes. This phenomenon of molecular axis orientation change due to irradiation with linearly polarized light is interpreted as follows. That is, in the ground state of ethylene, which is the simplest molecule having a non-aromatic double bond, two carbon atoms and four hydrogen atoms are in the same plane, whereas in the photoexcited state, two sets of It is well known that the planes formed by the H—C—H atomic groups have a twisted structure orthogonal to each other. Similarly, it is estimated that the photoisomerized compound loses the planarity of the double bond in the photoexcited state and undergoes a change in molecular axis orientation in the process of returning to the ground state via the twisted structure that accompanies it. .

  Specific examples of photoisomerization compounds include aromatic azo compounds such as azobenzene, azonaphthalene, bisazo compounds, and formazan, which are non-aromatic N = N-bonded compounds, and azoxybenzene as a basic skeleton. Things. In addition, aromatic Schiff bases and aromatic hydrazones that are non-aromatic compounds having a C═N bond can also be exemplified.

  The film thickness of the alignment film 2 containing the photoisomerizable compound is desirably 5 μm or less, and preferably 1 nm to 0.1 μm. The alignment film 2 can be formed by a general method, and can be formed by surface treatment using hydrolysis, LB film method, spin coating method, wet surface treatment, or dry surface treatment. It is. In the case of spin coating, the spin coater preferably has a rotation speed of 500 to 5000 rpm. Further, the rotation speed of the spin coater is more preferably 500 to 2000 rpm. Drying after spin coating can be performed by a hot plate that is generally widely used. In addition, 30 to 130 degreeC is suitable for the hotplate temperature used for leveling. Moreover, as for the hotplate temperature used for leveling, 30 to 80 degreeC is more desirable.

  [FIG. 1] (b) is a diagram in which a liquid crystal layer 3 is formed on the alignment film 2 produced in (a). The liquid crystalline polymer used in the liquid crystal layer 3 is not a so-called nematic liquid crystal material used in a liquid crystal display device, but a liquid crystal material that has a smectic phase. Liquid crystalline polymer is a polymer having a main chain structure such as hydrocarbon, acrylate, methacrylate, siloxane, etc. with substituents such as biphenyl, terphenyl, phenylbenzoate, and azobenzene, which are frequently used as mesogenic components in the side chain. It is. Moreover, it is good also as a structure which introduce | transduced photosensitive groups, such as a cinnamic acid group (or its derivative group), into the mesogenic component of a side chain as needed. These liquid crystalline polymers are applied in the form of a solution (spin coating) and dried to form the liquid crystal layer 3.

  The reason why the liquid crystalline polymer is in the smectic phase is to arrange the liquid crystalline polymer in a layered manner. The liquid crystalline polymer exhibits a phase transition for each temperature through a liquid, a nematic phase, a cholesteric phase, a smectic phase, a solid and a temperature lowering process, and forms the liquid crystal layer 3 at a phase transition temperature corresponding to the liquid crystal material. In addition, you may perform a baking process, after apply | coating a liquid crystalline polymer. The firing condition is preferably higher than the phase transition temperature, and the alignment of the alignment film 2 easily acts on the liquid crystal layer 3. Once alignment is obtained in the liquid crystal layer 3, the alignment state is maintained even after the temperature is lowered to room temperature. In general, the phase transition temperature of a liquid crystalline polymer having a rigid side chain is often room temperature or higher, and after cooling, it often becomes a solid while maintaining the alignment state.

  Further, for example, a tricyclic compound or a bicyclic compound may be added within a range that does not break the smectic phase, in order to increase the thermal stability of the liquid crystal. Furthermore, the liquid crystal phase 3 can be made into a uniform smectic phase by adding a photopolymerizable nematic phase monomer liquid crystal to the liquid crystal polymer and making the monomer photopolymerize / polymer.

Further, the smectic phase may take a form called SmA, SmB, or SmC depending on the orientation state, but SmB having excellent ordering in the liquid crystal layer 3 is preferable.

  [FIG. 1] (c) is a view in which ultraviolet rays are irradiated from the upper part of the substrate. 4 is a polarizing plate and 5 is a mask. In-plane structural anisotropy is induced by irradiating the alignment film 2 formed in (a) with linearly polarized light. That is, when a photo-isomerized compound is irradiated with linearly polarized light, it undergoes a trans-cis-trans isomerization cycle and is finally rearranged so that its transition moment is orthogonal to the polarization direction. In order to align the direction of photoisomerization, it is necessary to irradiate linearly polarized light, and it is important to irradiate polarized light having a uniform electric field vector through a polarizing plate. As ultraviolet rays to be irradiated, g-line having a wavelength of 436 nm and i-line having a wavelength of 356 nm used as a light source of a projection exposure apparatus (stepper) are preferable. The alignment of the liquid crystalline polymer in the liquid crystal layer 3 appears as a joint phenomenon of the photoisomerization of the photoisomerizable compound in the alignment film 2. This is the same as a known liquid crystal photo-alignment technique, and it is possible to align the smectic liquid crystal alignment pattern in a desired direction. The alignment method of the liquid crystalline polymer, that is, the interfacial molecular alignment mechanism is a complex cause of various causes, and the inventors have determined that the alignment film 2 used as one embodiment of the present invention is uniaxially aligned with a photoisomerized compound and is anisotropic. In addition, it is considered that the charge generated by the stress effectively acts on the liquid crystal molecules, and therefore gives the alignment of the liquid crystalline polymer.

  [FIG. 1] (d) is a diagram in which liquid crystalline polymers are aligned corresponding to the portions irradiated with linearly polarized ultraviolet rays. The main chain of the liquid crystalline polymer is oriented in the front and back direction of the paper, and the ellipse in the figure represents a side chain bonded to the main chain of the liquid crystalline polymer. In order to increase the regularity of the alignment of the liquid crystal, the thickness of the liquid crystal layer 3 is desirably 50 nm to 200 nm. If the thickness exceeds 200 nm, the irradiated polarized ultraviolet rays are attenuated, and it is not preferable because there is a possibility that sufficient energy does not reach the photoisomerized compound. Further, the regularity of the liquid crystal material in the direction perpendicular to the substrate is disturbed. On the other hand, if it is smaller than 50 nm, the selectivity at the time of anisotropic dry etching cannot be sufficiently obtained, which is not preferable. The same effect can be expected by forming a liquid crystal layer after aligning the photoisomerized compound of the alignment film 2 on the substrate with linearly polarized light.

  [FIG. 1] (e) is a diagram in which anisotropic dry etching is performed to transfer a pattern to the substrate 1. The term “transfer” as used herein refers to a process in which an upper layer is used as a mask and a pattern such as width and pitch is transferred to a lower layer with an equivalent pattern or an inverted pattern. The liquid crystalline polymer corresponding to the portion irradiated with the linearly polarized light of the alignment film 2 is aligned at a pitch twice as long as the mesogen molecular length. While the polymer side chain is a rigid molecule containing an aromatic ring, the polymer main chain is a single bond between carbons, so there is a difference in dry etching resistance between the side chain and the main chain, resulting in an etching selectivity to the substrate. Occurs. That is, in this step, the liquid crystal layer 3 can be used as a mask for the substrate 1 by adjusting the length of the mesogen molecules as side chains in accordance with the desired width and pitch (line and space) of the convex portions.

Note that the selection ratio of anisotropic dry etching is small, and the etching depth may be insufficient depending on the type of the substrate 1 and the conditions of the dry etching apparatus. In that case, a photosensitive coated glass material can be formed between the substrate 1 and the alignment film 2. For example, a photosensitive coated glass material having etching resistance such as SOG may be formed, and the pattern of the liquid crystal layer 3 may be transferred to the SOG once. After transfer to SOG, it can be transferred again to the substrate by dry etching using SOG as a mask. The SOG layer is about 30 nm to 100 nm, and with the method of the present invention, a line pattern having a pitch twice the mesogen molecular length can be obtained periodically. Note that CF ₄ , SF ₆ , Cl _2, or the like is used as a gas for anisotropic dry etching. The width of the convex portion of the substrate 1 or SOG after the anisotropic dry etching process is almost twice as long as the side chain (mesogen molecule) of the liquid crystalline polymer, and the pitch can be adjusted as appropriate by the mask.

  The patterned substrate formed by such a process can be used as a fin portion of the semiconductor layer of the FET. For example, an SOI (Silicon on Insulator) substrate in which a semiconductor substrate, a buried insulating film, and a semiconductor layer are sequentially stacked is prepared. After a convex portion is formed on the semiconductor layer by the above process, gate insulation is performed on the side surface of the convex portion by a CVD method or the like. A gate electrode is formed by depositing a film and patterning dual-doped Poly-Si. Then, a FinFET can be manufactured by sequentially forming a source region, a drain region, a contact plug, and the like.

  It is also effective to use the process of the present invention in combination with a conventional photolithography process. For example, after the liquid crystal layer 3 is formed, a positive type photoresist is applied to the upper layer, the resist is exposed only to a portion where a periodic pattern is required, the liquid crystal layer 3 is exposed, and then photoisomerization is performed. Therefore, it is possible to form a smectic phase only at a specific portion of the liquid crystal layer 3 and process the substrate 1 by irradiating the alignment film 2 which is the lower layer of the liquid crystal layer 3 with the polarized light.

<Example 1>
An SOI substrate coated with SOG was prepared. On the SOG substrate, a photoisomerized compound having azobenzene represented by [Chemical Formula 1] in the side chain was applied at a film thickness of 10 nm to form an alignment film. After the application, a liquid crystal polymer represented by [Chemical Formula 2] was applied at a film thickness of 50 nm to form a liquid crystal layer. The alignment film was irradiated with ultraviolet light using a mercury lamp as a light source on a substrate through a 365 nm band-pass filter to obtain a pattern in which the liquid crystalline polymer of the liquid crystal layer was aligned in the smectic phase. This orientation pattern was transferred to the SOG layer by dry etching, and further transferred to the SOI substrate using this SOG layer as a mask. As a result, 4 nm grooves were obtained at a pitch of 10 nm.

<Example 2>
An SOI substrate coated with SOG was prepared. An azobenzene silylating agent, which is a photoisomerization compound shown in [Chemical Formula 3], was adsorbed by a dip method to form an alignment film. A liquid crystal polymer represented by [Chemical Formula 4] was applied onto the substrate after adsorption to form a liquid crystal layer. Thereafter, a resist OEBR was applied to a thickness of 1 μm, and an area of 5 μm square was exposed and developed to obtain a pattern. The alignment film was irradiated with i-line with polarization controlled from above the exposed liquid crystal layer to form a smectic phase in a 5 μm square area of the liquid crystal layer. The alignment pattern of the liquid crystal layer only within 5 μm square was transferred to SOG by dry etching, and then 4 nm grooves were transferred to the underlying SOI substrate at a pitch of 10 nm by dry etching again using SOG as a mask.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, you may delete a some component from all the components over embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  According to the present invention, a manufacturing method capable of controlling the surface roughness of a fine pattern at a molecular level without excessively increasing the manufacturing complexity is provided, and the field of semiconductor manufacturing, particularly a double gate field effect transistor (FET) is provided. It can be used for the formation of the fin part.

A diagram conceptually showing the manufacturing process of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Alignment film 3 ... Liquid crystal layer 4 ... Polarizing plate 5 ... Mask

Claims (6)

Forming an alignment film having a photoisomerizable compound on a substrate;
Forming a liquid crystal layer containing a liquid crystalline polymer having a main chain and a side chain on the alignment film;
Irradiating the alignment film with linearly polarized ultraviolet rays, and aligning the main chain of the liquid crystalline polymer of the liquid crystal layer in a predetermined direction corresponding to the photoisomerized compound photoisomerized by the ultraviolet rays;
Performing anisotropic dry etching of the substrate using the liquid crystal layer as a mask to form a nanopattern having convex portions with a constant pitch corresponding to the length of the side chain of the liquid crystalline polymer. The manufacturing method of the nano pattern characterized by these. Performing the dry etching,
The nanopattern manufacturing method according to claim 1, wherein a main chain of the liquid crystalline polymer is removed to leave a side chain. Before the step of forming the alignment film,
The nanopattern manufacturing method according to claim 1, wherein an SOG film is formed on the surface of the substrate. The method for producing a nanopattern according to claim 1, wherein the liquid crystalline polymer is a polymer that forms a smectic liquid crystal phase.   A nanopatterned substrate manufactured using the manufacturing method according to claim 1.   A field effect transistor provided with a nano pattern produced by using the manufacturing method according to claim 1 as a fin.

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