JP2005144585A - Nanomask etching by neutral chlorine atom parallel beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize fine processing of a semiconductor substrate of a nanometer size by a highly accurate means suitable for mass production. <P>SOLUTION: A precision processing method of a microstructure includes a step (a) of arranging organic molecules 2 holding particulates 1 on the substrate, and a step (b) of etching the substrate 6 with at least the particulates 1 as an etching mask. The precision processing method of the microstructure is characterized by etching by using neutral particles as etching gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a precision processing method of a microstructure, and more particularly, to a method capable of forming a microscopic structure having a uniform size of about several tens of nanometers with high productivity on an industrial scale.

  At present, the development of semiconductor devices is remarkable in the electronics field. As these semiconductor devices are miniaturized, the higher integration of elements becomes possible, and therefore, it is aimed to produce devices of extremely small size.

  Conventionally, the fabrication of fine devices of the order of submicrometers has been realized by downsizing ordinary transistors, and the downsizing is based on lithography technology.

  That is, a resist film that is altered by light, X-rays, electron beams, or the like is coated on a substrate, a reticle (photomask) having an appropriate pattern is placed thereon, and light, X-rays, or This is a technique based on forming a resist pattern on a substrate by irradiating an electron beam or the like to alter the resist film and removing either the altered resist film or the resist film that has not been altered.

  On the other hand, in the field of semiconductors, the possibility of a quantum effect element in a semiconductor region having dimensions of several tens of nanometers has been shown, and its high functionality has attracted attention. For this reason, in the field of semiconductors, establishment of a processing technique for forming an extremely fine structure of several tens of nanometers or less is desired.

  However, in lithography technology, it is impossible to eliminate errors when aligning photomasks, and since light is used, there is a limit to miniaturization technology that makes processing finer than the wavelength of light, resist materials for light, etc. However, there is a problem in forming a microstructure having a size of several tens of nanometers due to a limitation in accuracy due to a defect in the spatial resolution of the alteration.

For this reason, a method of minimizing the lithography process by the self-alignment technique has been performed, but these methods have not yet completely solved the problem of forming a microstructure evenly ( For example, refer nonpatent literature 1).
T. Tada, two others, “Fabrication of Photonic Crystals Consisting of Si Nanopillars by Plasma Etching Using Self Formed Masks”, Japanese Journal of Applied Physics, 1999, Vol. 38, Part 1, 12B, 7253

  Therefore, in the field of ultra-small semiconductor devices of several tens of nanometers or less, there is an urgent need to develop a method that can be processed with a high precision and suitable for mass production, which has been impossible until now. In addition, for the practical use of a semiconductor device, it is also necessary that the size of the formed microstructure is uniform.

  An object of the present invention is to solve these problems and to propose a method that can be processed with high accuracy and suitable for mass production.

  An object of the present invention is to provide a method for processing a microstructure with high accuracy and suitable for mass production in the field of ultra-small size semiconductor devices of several tens of nanometers or less.

  The first fine structure processing method of the present invention includes a step (a) of placing organic molecules holding fine particles on a substrate in a holding portion capable of holding fine particles, and using at least the fine particles as an etching mask. And (b) etching the substrate. Accordingly, since the substrate can be etched using the fine particles arranged on the substrate as a mask, a microstructure having a size equivalent to that of organic molecules or fine particles can be formed. Therefore, a fine structure exceeding the limit of the lithography technique can be formed.

  In the precision processing method of the first microstructure, the organic molecule is preferably a molecule containing a protein. For example, if a spherical shell protein such as ferritin is used, fine particles having a uniform size can be arranged and fixed on a substrate, so that a uniform microstructure can be formed at a high density. In addition, the position of the micro object can be easily controlled. In the step of removing organic molecules described later, the organic molecules can be easily removed while leaving the inorganic substance on the substrate.

  Further, the precision processing method of the first microstructure further includes a step of removing the organic molecules and leaving the fine particles on the substrate after the step (a) and before the step (b). In the step (b), it is preferable to etch using the fine particles as an etching mask.

  Further, in the precision processing method of the first microstructure, the step of (a ′) holding the fine particles in the liquid molecule in the liquid before the step (a) can be reliably performed by further including the step (a ′). Since organic molecules holding fine particles of the size can be obtained, a desired pattern can be formed without any defects. It is desirable that the organic substance is a protein having a constant size. The fine particles may be held after fixing organic molecules on the substrate.

  In the precision processing method of the first microstructure, the organic molecule may be a tube protein such as TMV or bacterial flagellar fiber, and the fine particles may be a rod-like substance. Thereby, a fine rod-shaped structure can be formed in step (b).

  The fine structure processing method of the present invention includes a step (a) in which at least a part of a surface of a substrate is bonded to a protein, and a step (b) in which a protein holding an inorganic material is fixed on the substrate. And a step (c) of reactively etching the substrate using at least the fine particles as an etching mask.

  According to the precision machining method for a microstructure according to the present invention, it is possible to form a microstructure with a uniform size (that is, precision machining of the microstructure).

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
In this embodiment, ferritin containing iron oxide (the following iron oxides are all Fe ₂ O ₃ ) is arranged on the substrate, and at least the dot of iron oxide inside ferritin is used as a mask without using a resist film. This is a method of precision machining. In all embodiments of the present invention, the substrate refers to the entire substrate including a structure such as an oxide film or a gate electrode formed on the substrate. Various materials such as metals, semiconductors, and dielectrics can be used as the material of the substrate. Among these, a semiconductor substrate is particularly preferably used. As the semiconductor substrate, any of a silicon substrate and a compound semiconductor substrate such as GaAs or InP can be used. The most desirable among the semiconductor substrates is a silicon substrate. Hereinafter, an example using a silicon substrate will be described.

  As schematically shown in FIG. 1, ferritin is composed of a spherical nucleus 1 containing about 4,500 inorganic atoms such as iron, and 24 identical subunits each having a molecular weight of about 20,000. It is a metalloprotein complex composed of an outer shell 2 formed to surround the periphery. The outer diameter of ferritin is about 12 nm, and the diameter of the core 1 held inside is about 7 nm. A state in which the nucleus 1 is removed from the ferritin is called apoferritin, and includes a holding portion (lumen) for holding the nucleus.

  This embodiment is divided into a stage in which ferritin is two-dimensionally arranged and fixed on the substrate and a stage in which the substrate is processed using at least dots made of iron oxide inside ferritin as a mask.

  In this embodiment, only iron is described as a material of dots introduced into apoferritin, but it serves as an etching mask for chromium, manganese, cobalt, nickel, aluminum, tungsten, zinc, and their oxides and hydroxides. It may be a substance. A good selection ratio can be obtained by selecting an appropriate combination of dot materials depending on the substrate material and the type of etching gas.

  The apoferritin in this embodiment may be extracted from an organ such as a spleen or liver of an animal such as a horse or cow, or may be produced in a bacterial body such as Escherichia coli by a genetic engineering technique. good.

  In the following embodiments, apoferritin is used to arrange fine particles that serve as a mask for lithography or etching, but the outer shell of viruses such as adenovirus, rotavirus, HK97, CCMV, etc. Other proteins having a function of retaining fine particles, such as ferritin family proteins such as Dps protein and MrgA protein, bacterial flagellar fibers such as ferritin, and the like can also be used. TMV and bacterial flagellar fibers can form fine particles that serve as a cylindrical mask. By appropriately selecting a protein, it is possible to process to form a microstructure corresponding to the size and shape of the fine particles.

(Description of etching equipment)
Next, the etching apparatus will be described with reference to FIG. The etching apparatus has two vacuum chambers, an ICP chamber 109 and an etching chamber 111. The two chambers are separated by the lower electrode 103. The ICP chamber 109 is configured to generate ion-coupled plasma excited therein by a 13.56 MHz high-frequency electric field that is passed through an ICP antenna (coil) 105 outside the ICP chamber 109. The volume of the ICP chamber 105 is usually about several tens of liters.

  A reactive gas in an amount of several tens of sccm is introduced into the ICP chamber to generate plasma of the reactive gas. An example of the reactive gas is chlorine gas. It is also possible to introduce chlorine gas into the ICP chamber, generate chlorine plasma, extract chlorine ions from the chlorine plasma with an electric field, and etch the sample 107. For example, if a negative voltage is applied to the sample stage on which the sample 107 is placed, positive chlorine ions collide with the sample and cause a reaction to perform etching. However, in this case, it is only possible to etch several nanometers in the depth direction while maintaining the shape of a mask with a size of several nanometers, and etching with a high aspect ratio as described later is impossible. .

  The lower electrode 103 located between the ICP chamber 109 and the etching chamber 111 has a plurality of pores, desirably 10 or more, more desirably 100 or more. The lower electrode 103 is made of a conductive material such as metal or graphite, and graphite is particularly suitable. A DC bias or an RF bias can be applied to the lower electrode.

  As shown in FIG. 2, the pores of the lower electrode 103 are formed from the ICP chamber through the etching chamber, and ions and neutral particles can move through both chambers. The shape of the pore is, for example, a cylindrical shape having a diameter of 1 mm and a depth of 10 mm. The ratio of the depth and diameter (aspect ratio) of the pores is preferably at least 2/1 or more, more preferably 5/1 or more, and preferably about 10/1. If the aspect ratio is small, there is no effect of being a pore. However, if the aspect ratio is too large, it is difficult for the particles to pass through, so the aspect ratio is preferably 20/1 or less. The thickness of the lower electrode (depth of the pores) is preferably about 5 mm or more and 20 mm or less. More desirably, it is 8 mm or more and 12 mm or less.

  In the etching apparatus of this embodiment, the pores provided in the lower electrode 103 are effective for performing deeper etching while maintaining a mask shape of several nanometers. This will be described separately when using negative ions generated in the ICP chamber and when using positive ions.

  First, when positive ions are used, the pores of the lower electrode 103 are effective for generating a parallel positive ion beam having high anisotropy, and are also destructive for nanoparticles. This is effective because the sample 107 is not directly irradiated with ultraviolet rays having a wavelength of 200 nm or less. In this case, for example, if a positive voltage is applied to the upper electrode and a negative voltage is applied to the lower electrode, a positive chloride ion parallel beam can be extracted by the elongated pores. Also, most of the ultraviolet light is cut off. Etching with this beam is also possible. The effect of preventing ultraviolet rays is effective for both negative ions and neutral particles.

  A more preferred embodiment of the device is when negative ions are used.

  For example, when chlorine gas is used, the excitation state of the chlorine ion plasma is made intermittent so that the state of the chlorine plasma is not only positive chlorine ions during normal continuous excitation but also negative chlorine during the non-excitation time. Ions are generated. This negative chlorine ion is produced in a large amount several tens of microseconds after the high frequency excitation of the plasma is stopped.

  In order to extract a negative chlorine ion parallel beam, a positive potential may be applied to the lower electrode 103. Alternatively, the potential of the lower electrode may be set higher than that of the upper electrode. When the length of the lower electrode is sufficiently long, the negative chlorine ions can be easily neutralized while the negative chlorine ions pass through the pores of the lower electrode 103. In the case of the lower electrode having pores having a diameter of 1 mm and a depth of 10 mm, it is possible to neutralize almost completely.

  As described above, the ion reactive etching apparatus of FIG. 2 is an apparatus that enables etching in various types of beam states. In the present invention, in particular, the use of the last neutral beam makes use of the fact that deep etching can be performed while maintaining the shape of the nanometer-size mask.

(Description of etching process)
Next, steps for processing the silicon substrate 6 will be described with reference to FIGS. In the step shown in (a), the silicon substrate 6 is first cleaned by RCA to expose silicon atoms. (B) Immediately thereafter, UV ozone treatment is performed to form an oxide film 7 on the silicon substrate. By this treatment, the silicon substrate is covered with silicon dioxide, and a hydrophilic surface terminated with an OH group is constructed. At this time, it is also possible to perform patterning using a photolithography technique. (C) Next, the substrate is immersed in a solution of ferritin particles. Remove excess solution by centrifugation immediately after removal. At this time, in order to prevent drying by wind, it is effective to control the humidity, but it is desirable to perform the centrifugation by putting the silicon substrate in a sealed container and centrifuging. Rinse with pure water as necessary is also effective in removing excess ferritin. (D) Next, the outer shell 2 made of protein is removed by treating the surface of the silicon substrate on which ferritin is disposed at 450 ° C. in a nitrogen gas atmosphere for 1 hour. As a result, only the nucleus 1 made of iron oxide is left on the silicon substrate 6. Equivalent protein removal is possible with UV ozone treatment. Although the step of removing the outer shell 2 can be omitted, the nucleus 1 is placed on the silicon substrate 6 without disturbing the position of the nucleus 1 by removing the protein portion of ferritin. More effective patterning can be achieved by the next etching process.

  Subsequently, in the step shown in FIG. 3E, etching is performed on the silicon substrate 6 on which the ferritin 4 is arranged using chlorine gas as the reactive gas and the apparatus shown in FIG. This etching is performed in two stages.

  The first stage of etching is a stage of etching the oxide film 7. The sample shown in FIG. 3D is placed in the etching chamber 111 in the lower part of the apparatus shown in FIG. The sample is placed cooled to -20 degrees. It is desirable to cool the sample to at least 0 ° C or less, preferably -10 ° C or less. Next, 60 sccm of chlorine gas is introduced into the ICP chamber 109. The pressure is suitably from 0.1 Pa to 1 Pa. Both chambers 109 and 111 are evacuated by a vacuum pump. A 1000 W electric power is applied from the ICP antenna 105 at 13.56 MHz to generate chlorine plasma. At this time, an excitation time of 50 microseconds and a non-excitation time of 50 microseconds are alternately placed. In this state, a voltage of −100 V is applied to the upper electrode 101, and a 20 W AC power of 600 kHz is applied to the graphite electrode 103 having the lower pores. As a result, a neutral chlorine beam having an energy of about 50 eV is extracted and hits the sample. This high energy neutral particle beam treatment is for removing the oxide film 7 formed on the surface of the sample of FIG. A normal silicon oxide film has a thickness of about 2 nm, and the removal may be performed for about 20 seconds under these conditions.

  The next step is to etch the exposed silicon itself. 40 sccm of chlorine gas is introduced into the ICP chamber 109. The pressure is suitably from 0.1 Pa to 1 Pa. The sealed container is evacuated with a vacuum pump. A power of 800 W is applied from the ICP antenna 105 at 13.56 MHz to generate chlorine plasma. At this time, an excitation time of 50 microseconds and a non-excitation time of 50 microseconds are alternately placed. In this state, a voltage of −100 V is applied to the upper electrode, and the graphite electrode having the lower pore is grounded. As a result, a neutral chlorine beam having an energy of about 10 eV is extracted and hits the sample. This low energy parallel neutral chlorine beam reacts with silicon and anisotropically proceeds in the depth direction. At this time, the etching speed (selection ratio) of silicon is 59 times that of iron oxide serving as a mask.

  FIG. 4 is a photograph of a scanning electron microscope in which a substrate surface obtained by processing a silicon substrate 6 on which ferritin 4 is two-dimensionally arranged at high density by the method of the present embodiment is viewed obliquely from above in a 15 degree direction. A columnar body (hereinafter referred to as a fine column) can be observed on the silicon substrate 6 obtained by etching using the nucleus 1 disposed on the silicon substrate 6 as a mask.

  Here, since the diameter of the ferritin nucleus 1 used in the present embodiment is 7 nm, the diameter of the upper end surface of the fine column formed on the silicon substrate 6 is also 7 nm.

  The size of the fine particles held by the protein such as ferritin used in the present invention is uniform and has a diameter of several nanometers. (Precision processing of the structure) is made possible by the present invention. As a method for two-dimensionally arranging and fixing ferritin on a substrate, a ferritin two-dimensional crystal can also be used if it is performed based on the method described in JP-A-11-45990.

  In the above, the case where ferritin is used as a mask has been described. However, as described above, by using an adenovirus, rotavirus, or the like as a mask, patterning according to the size of the mask becomes possible.

  The fine structure processing method of the present invention is used for manufacturing semiconductor light-emitting elements and various semiconductor devices using the quantum effect.

Diagram showing the structure of ferritin The block diagram of the apparatus which produces the parallel neutral chlorine beam in embodiment Sectional drawing which shows the patterning process of the microstructure in embodiment Scanning electron micrograph of a fine column formed by the microstructure processing method of the present invention and a schematic diagram explaining its shape

Explanation of symbols

101 Upper electrode 103 Lower electrode 105 ICP antenna 107 Sample 109 ICP chamber 111 Etching chamber

Claims (13)

(A) disposing an inorganic material or organic molecules holding fine particles on a substrate in a holding part capable of holding fine particles, and (b) etching the substrate using at least the fine particles as an etching mask. A method for precision processing of a microstructure, comprising: the organic molecule is a protein-containing molecule, and the fine particles include an inorganic substance. 2. The fine structure processing method according to claim 1, further comprising the step of removing the organic molecules and leaving the fine particles on the substrate after the step (a) and before the step (b). In step (b), the fine structure is precisely etched using the fine particles as an etching mask. 3. The precision processing method for a microstructure according to any one of claims 1 and 2, wherein the organic molecule is in a spherical shell shape. 3. The precision processing method for a microstructure according to claim 1, wherein the organic molecule is ferritin. 2. The precision processing method for a microstructure according to claim 1, wherein the organic molecule is a tubular substance. 6. The precision machining method for a microstructure according to any one of claims 1 to 5, wherein the substrate is a semiconductor substrate. 7. The precision processing method for a microstructure according to any one of claims 1 to 6, wherein the substrate is precisely processed by reactive etching. 8. The precision processing method for a microstructure according to claim 7, wherein the precision processing of the substrate is performed using neutralized atoms having no electric charge. . 8. The precision processing method for a microstructure according to claim 7, wherein the precision processing of the substrate is performed by neutralized chlorine atoms having no electric charge in the ion reactive etching. . 10. The fine structure precision processing method according to claim 9, wherein the precise processing of the substrate is performed with chlorine atoms taken out from the intermittently excited plasma during the non-excitation time. Precision machining method. 11. The precision machining method for a microstructure according to claim 10, wherein the intermittent excitation has an excitation time of 50 microseconds or more. 11. The precision machining method for a microstructure according to claim 10, wherein the intermittent excitation has an excitation time of 30 microseconds or more and a non-excitation time of 100 microseconds or less. 13. The method for precision processing of a microstructure according to claim 8-12, wherein an electric field is applied to the plasma and a through hole is provided as a method of extracting neutralized atoms or chlorine atoms having no electric charge from the excited plasma. A precision machining method for a microstructure, which is obtained by passing charged atoms through a through-hole in a plate and removing electric charges when passing through the plate.

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