WO2007125726A1

WO2007125726A1 - Method and apparatus for ionization by cluster ion impact which can realize imaging, and etching method and apparatus

Info

Publication number: WO2007125726A1
Application number: PCT/JP2007/057328
Authority: WO
Inventors: Kenzo Hiraoka
Original assignee: University Of Yamanashi
Priority date: 2006-04-28
Filing date: 2007-03-26
Publication date: 2007-11-08
Also published as: JP4639341B2; JPWO2007125726A1

Abstract

A beam of a population of charged drops on micron order is produced within a charged drop generation chamber (31), for example, by various electrosprays (for example, nanoelectrosprays) (32) including cold electrosprays and is accelerated by a high voltage electric field of about 10 kV within a vacuum acceleration chamber (41) to impact the beam against a biological sample thin film coated onto a cooled sample substrate to achieve ionization of a biopolymer. A mask (50) is disposed in front of the sample substrate to restrict the spreading of beam-shaped charged drops, and only charged drops passed through a micropore (50a) in a mask (50) are allowed to collide against the sample. The position of collision of charged drops can be varied by changing the position of the mask (50) to obtain two-dimensional information (imaging). Charged drops of an etching solution (including an aqueous solution) are produced and are led to a vacuum acceleration chamber (41, 41B). The charged drops are accelerated toward the position of an object Su by an electric field formed within the acceleration chamber and are allowed to collide against the surface of the object, whereby the surface of the object is etched in a layer-by-layer state or in a state closed to the layer-by-layer state.

Description

Due to cluster ion impact that can be imaged

Etching method and device

Technical field

The present invention provides an ion book by cluster ion bombardment capable of imaging.

In particular, the mass spectrometry of environmental science-related and life science-related samples (including biopolymer samples) such as drugs, plasticizers, pigments, fullerenes, amino acids, peptides, protein molecules, and DNA molecules. The present invention relates to an ionization method opto-apparatus that is suitable for this purpose and can acquire (imaging) molecular level spatial information (particularly two-dimensional distribution information) of a sample. Furthermore, the present invention relates to a fine etching method and apparatus for material surfaces (including metals and semiconductor materials) by cluster ion bombardment.

Background art

Matrix-assisted laser desorption / ionization (MALDI) and ion bombardment (FABZSIMS) are mainly used for conventional biological imaging. Tato ^ is "Imaging mass spectrometry: a new tool to investigate the spatial organization of peptides and proteins in mammalian tissue sections" Current Opinion in Chemical Biology 2002, 6, 676-681, "Direct molecular imaging of Lymnaea s tagnal is nervous tissue at subcellular spatial resolution by mass spectrometry "See Anal. Chera. 2005, 77, 735-741.

MA LDI irradiates a sample with a laser and uses the energy from this. The sample is desorbed and ionized by the ablation of the matrix and analyzed. For this reason, it is necessary to apply a matrix (for example, sinapinic acid) that absorbs laser light (generally a wavelength of 337 nra) to the sample. Since a matrix agent is applied to the sample surface, there is a problem in that chemical noise occurs when imaging a biological sample. Another problem is that the sample is damaged by laser irradiation, which causes damage to the sample. In addition, there is a limit to laser beam focusing (spot size) (Bragg diffraction conditions), and the irradiated area is sputtered severely, making it difficult to obtain high-resolution imaging images. Since many matrices and biological samples themselves are scattered by a single laser irradiation, they are not suitable for depth analysis and have low detection sensitivity.

Since F A B Z S I M S uses fast atoms and ions, there is a problem in that the primary impact particles penetrate deeply into the sample and destroy it violently chemically.

The inventor has already described “ionization method by cluster ion bombardment” (. Electrosprayed droplet impact ionization) (E D I) ¾: proposal 7 (WO 2 0 0 5/0 8 3 4 1 5 A 1). This EDI method enables extremely soft desorption and ionization without destroying biological samples or drugs. This is because the energy per unit mass of the multiply-charged ion cluster used in EDI is less than 1 eV / u, and only the surface layer molecules are desorbed and ionized only by shock wave heating.

On the other hand, the miniaturization of silicon-based semiconductors has progressed to a thickness of several hundred angstroms. Such thin films are manufactured using plasma CVD or MBE (raole molecular beam epitaxy). The technology for depositing films is making great progress, but—and the resulting films are reproducible at the atomic level. The technology for etching and removing at this time has been delayed. In plasma etching, spattering by ion bombardment is the main process, and damage to the ultrathin film is inevitable. There is also a technology (SIMS) that uses an argon atom (or ion) beam, but only a few atomic layers on the surface of the thin film cannot be etched, and the internal structure of the thin film is damaged, resulting in extremely fine semiconductor technology. Application to is difficult. In order to overcome this industrial deadlock, it is essential to develop breakthrough technology that etches only a few atomic (molecular) layers without damaging the internal structure at all. Disclosure of the invention

The present invention provides a method and apparatus in which the above ionization method and apparatus using cluster ion bombardment are improved so that imaging can be performed.

Furthermore, the present invention provides an etching method and an optical apparatus utilizing the above-described ionization method and apparatus by cluster ion bombardment. In the ionization method by cluster ion bombardment according to the present invention, charged droplets of a volatile liquid are generated by an electrospray method under atmospheric pressure, and the generated charged droplets are guided to a vacuum chamber and formed in the vacuum chamber. The charged droplet is accelerated by the electric field toward the sample position, and the spread of the beam (beam diameter) of the charged droplet that collides with the sample is limited by the fine holes in the mask placed in front of the sample position. is there. The ionization method according to the present invention can be used for mass spectrometry, in which case the generated ions are guided to a mass spectrometer. A large number of charged droplets of volatile liquid are continuously generated as a group and accelerated to form a beam that travels toward the sample. The spread (beam diameter) of the charged droplet beam is limited by the mask placed in front of the sample, and some of the charged droplets that have passed through the fine holes in the mask Collide with sample. In this way, the position and range of the charged droplets that collide with the sample can be controlled. If the collision position of the charged droplet is fixed, information on the depth direction of the sample can be obtained, and if the collision position is scanned two-dimensionally with respect to the sample surface, the molecules of the sample surface layer Two-dimensional distribution information can be obtained.

In particular, the present invention increases its utility value by determining the position where the charged droplet should collide with the sample by the position of the micropore.

In order to obtain two-dimensional distribution information, at least one of the fine holes in the mask and the sample should be scanned relatively two-dimensionally. In this case, the mask microhole and the sample do not necessarily have to be displaced in parallel, but may be inclined. In a special form, the fine holes in the mask are scanned two-dimensionally with respect to the sample. In addition, charged droplets may be scanned by electric or magnetic fields.

The fine hole may be a single fine hole formed in a mask or may be formed by two intersecting fine slits formed in two mask members.

A mass spectrometry method can also be realized using the ionization method described above. In this case, ions of the sample that have been desorbed and ionized by the collision of charged droplets are introduced into the mass spectrometer.

The volatile liquid is preferably water, but methanol or ethanol is also acceptable. Water includes water with the addition of weakly acidic solutions and weakly alkaline solutions. In order to facilitate the generation of charged droplets, it is recommended that an electrolyte be dissolved in water to form an aqueous solution, which is used as the charged droplet liquid.

The ionization apparatus according to the present invention is provided outside the ion inlet of the mass spectrometer, communicates with the inside of the mass spectrometer through the ion inlet, and has a vacuum acceleration chamber in which an acceleration electrode, a mask, and a sample stage are arranged. Acceleration with A charged droplet generation chamber that communicates with the vacuum acceleration chamber through a droplet inlet of the vacuum acceleration chamber, and a charged liquid that generates charged droplets of a volatile liquid in the charged droplet generation chamber. The mask has micropores and is placed in front of the sample stage. The sample stage and the micropores in the mask are related to the direction of the surface of the sample stage. Means that the fine holes of the mask and the surface of the sample stage are not necessarily displaced in parallel, but may be displaced in an oblique direction. The charged droplets generated by the droplet generator are guided from the charged droplet generation chamber to the vacuum acceleration chamber through the droplet inlet and accelerated by the acceleration electrode to which a high voltage is applied. The spread is limited by the fine holes in the mask. The charged droplets that have passed through the fine holes collide with the sample on the sample stage, and as a result, desorbed and ionized ions from the specimen are introduced into the mass spectrometer through the ion inlet. It is designed to be

The vacuum accelerating chamber and the droplet generating chamber do not need to be separated from each other, and may be simply divided into regions (spaces) (may be partially overlapped).

The ionization method according to the present invention can be realized by using the above ionizer.

The electrospray method is preferably used to generate charged droplets. When cold nitrogen (N ₂ ) gas with controlled temperature is used in combination, cooling, generation of charged droplets (spraying), and transfer to the vacuum chamber (vacuum acceleration chamber) can be performed efficiently. The generation of charged droplets can be performed under atmospheric pressure (including reduced pressure). When generating charged droplets under atmospheric pressure, nitrogen gas (which may be cooled) is used as the nebulizer gas for the purpose of efficiently generating charged droplets by the electrospray method. Good. Under atmospheric pressure 2007/057328

It is desirable that the charged droplet generation chamber (ion source) in Fig. 6 is a space (closed space) isolated from the atmospheric air. This is because atmospheric air (laboratory air) can contaminate the ion source gas, including the electrospray device. By using a clean nitrogen nebulizer gas, atmospheric pressure gas in the ion source is not contaminated.

According to the present invention (especially according to the above-mentioned electrospray method), it is possible to generate a beam by a charged droplet group of a micro-order. The charged droplet beam is sampled in the vacuum chamber (vacuum acceleration chamber) while maintaining the micron-order droplet size (beam spread or beam diameter). In addition, the beam diameter is limited by the mask before colliding with the sample, and the charged droplet beam diameter is on the order of submicron by passing through the microhole.

Such cluster ions are accelerated by an electric field in the vacuum chamber (vacuum acceleration chamber), which gives kinetic energy and impinges on the sample (for example, a biological sample thin film). A shock wave is generated at the collision interface, and the sample is desorbed and ionized in picosecond order.

Since the sample is bombarded with cluster ions, the target molecules are excited by electrons and vibration at the same time, and the kinetic energy of the molecules in the sample film is also efficiently excited. In this way, the sample is impacted by the soft ion due to the cluster ions, so even molecules with molecular weights exceeding tens of thousands are ionized without being damaged.

In addition, since the sample is vaporized and ionized within a short period of picoseconds shorter than the recombination lifetime between the positive and negative ions, recombination between the positive and negative ions is suppressed, and the generated ions are efficiently massed. It can be led to an analysis device.

As a biological sample to be used, use a frozen sample to prevent its drying. T / JP2007 / 057328

However, it goes without saying that this invention can also be applied to dried samples.

The present invention also provides an etching method using charged droplets. In the etching method according to the present invention, charged droplets of the etching solution are generated and guided to the vacuum chamber, and the charged droplets are accelerated toward the position of the object by the electric field formed in the vacuum chamber and collide with the surface of the object. Thus, the surface of the object is etched.

The etching device according to the present invention includes a charged droplet generator that generates a droplet of an etching solution under atmospheric pressure, and an accelerating electrode and a holding table for holding an object, and the charged droplet. It has a vacuum accelerating chamber in which fine charged holes for charged droplets generated by the generator are formed, and the charged liquid droplets generated by the charged droplet generator and introduced through the fine introduced holes are subjected to high voltage. An acceleration device is provided that accelerates the applied acceleration electrode to collide with the surface of the object held on the holding table and etches the surface of the object.

Charged droplets can be generated by electrospray at atmospheric pressure. Hydrofluoric acid, dilute nitric acid, acetic acid, etc. can be used as the solution for generating the electrospray (etching solution, mainly aqueous solution). Atomic level etching of silicon or silicon oxide can be performed by impact of charged droplets of hydrofluoric acid. Atomic level etching of metal thin films can be performed by impact of charged droplets of dilute nitric acid. Atom and molecular level etching of organic thin film materials and inorganic materials (metals, semiconductors, insulators, etc.) can also be performed by electromagnetic wave impact of acetic acid aqueous solution.

The etching solution need not cause a chemical reaction with the object. The etching solution may be an aqueous solution, an organic solvent (for example, methanol), or an organic solvent in an aqueous solution. Need In other words, the etching solution only needs to be multivalently charged. For example, water (pure water) can be used as the etching solution. However, charged droplets are more likely to be generated by the electrospray method when an electrolyte such as acetic acid or ammonia is dissolved in water to form an aqueous solution. The charged droplets are desirably multivalent charged droplets having a charge of several tens or hundreds.

It is preferable to pass the generated charged droplets through the ion guide, select only the droplets with a relatively large charged charge, guide them to the accelerator, and accelerate. Since charged droplets are charged with multiple charges as described above, they can be accelerated by an electric field at a very high speed (for example, about 10 times the speed of sound).

The present invention accelerates charged droplets of a multivalent number (for example, a mass of 10 million (u), a valence of 100, or a larger size and a higher valence) at high speed. ) Based on the technology of collision with the surface. When charged droplets with multivalent (for example, 100) charges collide with a solid surface at high speed, a shock wave is generated at the interface. The interface gas generated by this shock wave is a supercritical fluid gas that far exceeds the critical limit of water supercritical fluid (water). Since collisions at the interface are coherent (all colliding water molecules collide with the substrate in the same direction), the reproducibility of the phenomenon is extremely high. In addition, this supercritical state is relaxed (cooled) in about picoseconds by the fast energy dissipation process, so the inside of the film is not damaged. In addition, the film thickness that desorbs from the surface is limited to a few atoms (molecules), making it an optimal ultra-fine processing technology. By selecting the type of etching solution to be electrosprayed, various semiconductors (Si, Ge, etc.), silicon oxides (semiconductor oxides), insulators, organic material thin films, etc. Even metals (stainless steel, nickel, iron, copper, tin, gold, silver, etc.) can be layered at atomic level, with a layer of layer-by-layer. Moreover, it becomes possible to perform etching in a state close to this. Since the ion source (electrostatic droplet source) is an atmospheric pressure electrical spray, it can be easily installed in semiconductor manufacturing equipment, and the principle is simple, so no skilled technology is required. It is a simple, highly efficient and inexpensive technology.

Since charged droplets are charged fine particles, the beam can be swept in two orthogonal directions (X and Y directions) by a deflection electrode. Large-area machining technology can be realized by sweeping or scanning the charged droplet beam or target (its holding base) in a wide range (two-dimensionally) in the X and Y directions. Precision processing of large-area high-definition semiconductor materials, metals, organic thin films, and insulator films is possible. To form a fine pattern, it is only necessary to etch only the necessary part using a mask.

In the etching method according to the present invention, ions desorbed and ionized from the surface of the object by collision of charged droplets can be introduced into the mass spectrometer. That is, the etching apparatus and the mass spectrometer according to the present invention can realize a complex etching surface analyzer, a complex mass spectrometer, or various complex apparatuses (scanning tunnel microscope, photoelectron spectrometer, etc.). Brief Description of Drawings

Fig. 1 shows the configuration of the ionizer.

Fig. 2 is a perspective view showing the mask and its drive unit.

Fig. 3 is a perspective view showing a modification of the mask and its driving device.

Fig. 4 is a block diagram showing an embodiment of the etching apparatus.

Figures 5A to 5C show the phenomenon that the surface of the object is etched.

FIG. 6 is a block diagram showing another embodiment of the etching apparatus. T / JP2007 / 057328

Fig. 7 shows the configuration of the etching equipment used in the experiment.

Fig. 8 and Fig. 9 show the mass analysis results of ions produced by etching. BEST MODE FOR CARRYING OUT THE INVENTION

First, an embodiment of an ionization method and apparatus will be described.

In Fig. 1, the ionizer 20 is installed in the part of the mass spectrometer 10 that includes the ion inlet.

A mass spectrometer (for example, a time-of-flight mass spectrometer) 10 is provided with a gap 11 having a hole 11a at the ion inlet. Ions with the same direction are introduced to the inside of the mass spectrometer through the hole 11a (ion inlet). The inside of the mass spectrometer 10 is kept at a high vacuum by an exhaust device (not shown).

The ionization device 20 includes a charged droplet generator 30 (an ion source chamber, a chamber equipped with a general electrospray, nanoelectrospray, or corona red electrospray) 31, The charging droplet generating chamber 31 and an accelerating device 40 having a vacuum accelerating chamber 41 connected in a straight line are configured.

The charged droplet generator 30 includes the above-described electrospray device 32. The electrospray device 32 has a metal (conductive) capillary tube (capillary) 33 to which a high voltage is applied and a space around it. And a surrounding go pipe 34. The tips of the metal thin tube 33 and the surrounding tube 34 protrude into the charged droplet generation chamber 31. The metal thin tube 33 is supplied with a cooled or room temperature volatile liquid (solution) as charged droplets. A cooling medium such as nitrogen (N ₂ ) gas is supplied as a nebulizer gas in the space between the metal thin tube 33 and the surrounding tube 34 (atmospheric pressure or pressure in the vicinity thereof: atmospheric pressure including these) ) Nitrogen gas is supplied from a nitrogen production machine or a nitrogen cylinder, or is generated from liquid nitrogen, and is introduced into the surrounding pipe 34 under temperature control. Cooling with nitrogen gas makes it possible to generate larger-sized charged droplets (cluster ions). Also, without cooling with nitrogen gas, the tip of the capillary 33 is sufficiently close to the small hole 34a of the charged droplet sampling orifice 34 described later to prevent the charged droplets from drying out. Large charged droplets can be taken into the vacuum. The temperature of the droplets taken into the vacuum decreases rapidly due to the vaporization of the solvent. As a result, the vapor pressure drops, so there is little reduction in the size of the droplets under vacuum. Fly in a vacuum while maintaining almost the same volume.

From the tip of the metal tube 33 to which a high voltage is applied, a highly charged droplet group D is sprayed into the charged droplet generation chamber 31 in the form of a beam (a few millimeters in diameter). Also, nitrogen gas is sprayed into the charged droplet generation chamber 31 from the tip of the surrounding tube 34 around the tip of the metal thin tube 33. Nitrogen gas assists fogging of the charged droplets and cools the charged droplets. In addition, the charged droplet beam D is transferred toward the vacuum acceleration chamber 41 in the cooled state. Nitrogen gas is discharged to the outside from the charged droplet generation chamber 31 through the exhaust port. Depending on the experimental conditions, it is not necessary to cool the charged droplets, but it is preferable to cool them.

A charged droplet is a volatile liquid. When charged droplets vaporize (dry), the droplet size decreases. In order to suppress the vaporization of the charged droplets, nitrogen gas cools the charged droplets during the generation of the charged droplets and until the charged droplets reach the vacuum acceleration chamber 41. The cooling temperature is preferably about immediately before the charged droplets solidify. However, it may not always be necessary to cool charged droplets. If the distance between the tip of the thin metal tube 33 and the small hole 34a of the charged droplet sampling orifice 34 is shortened (closed), the drying (vaporization) of the charged droplets can be prevented. . The volatile liquid that forms charged droplets is typically an aqueous solution containing an electrolyte (for example, water with a weakly acidic or weakly alkaline solution such as acetic acid or ammonia) or water. Etc. You can mix methanol or acetonitrile with water, or just methanol.

Another example of a charged droplet generator is an ultrasonic vibration device. The charged droplet generation chamber 31 is at atmospheric pressure, but may be kept at a reduced pressure. The charged liquid droplet generation chamber 31 may be opened to the atmosphere (for example, the peripheral wall is omitted). An orifice 34 is provided at the boundary between the charged droplet generation chamber 31 and the vacuum acceleration chamber 41, and a small hole 34a is formed in the orifice 34. These small holes 34a are charged droplet introduction ports. The charged droplet generation chamber 31 and the vacuum charged droplet acceleration chamber 41 communicate with each other through the charged droplet introduction port 34a.

The charged droplet group D sprayed from the tip of the thin metal tube 33 and formed into a beam shape moves in the charged droplet generation chamber 31 in the direction of the vacuum accelerating chamber 41 together with the cooling and transporting nitrogen gas. It is introduced into the vacuum acceleration chamber 41 through the small hole 34a.

In the vacuum acceleration chamber 41, an acceleration electrode 42, a sample stage 43, and a mask 50 are provided. The acceleration electrode 42 is applied with a positive or negative high voltage (opposite to the polarity of the charged droplet) (for example, 10 KV). The charged droplet D introduced into the vacuum acceleration chamber 41 is accelerated and converged (focused) by the accelerating electrode 42, and obliquely collides with the sample S provided on the sample stage 43, and the ionized molecules are released from the sample. Release. The inside of the mass spectrometer 10 and the vacuum acceleration chamber 41 communicate with each other through the ion inlet 1 1a opened in the skimmer 11. The sample S (sample stage 43) is generated by the collision of charged droplets. Ion molecules (or atoms) that have jumped out from the surface are introduced into the mass spectrometer 10 through the ion introduction port 1 1 a. Charged droplet beam generated by the charged droplet generator 30 as described above The diameter (spread) of the (charged droplet group) is in the millimeter order. The diameter of a charged droplet (cluster single ion) ranges from a few microns to a few nanometers. This is a giant cluster ion. This giant clusterion beam is introduced from the charged droplet generation chamber 31 to the vacuum acceleration chamber 41 while maintaining a spread on the millimeter order, and is accelerated by the electric field of the acceleration electrode 42. For example, a kinetic energy of about 1 million eV (10 6 eV) is given to a single large cluster ion.

The specimen stage 43 holds, for example, a frozen biological specimen thin film S to prevent drying. The accelerated cluster single ion strikes this biological sample thin film S (for example, a biological tissue sample placed on a substrate attached to a low-temperature refrigerator).

(

Shoot. As a result, the thin film sample is vaporized within a short time of picoseconds. Equal amounts of positive and negative ions are present in the desorbed ions, but ions are generated in a time period shorter than their recombination lifetime, preventing recombination (neutralization) of the generated ions. Many ions are supplied into the mass spectrometer 10 from the vacuum acceleration chamber 41 through the ion inlet 11a. This enables highly sensitive mass spectrometry.

In addition, when a sample is bombarded by cluster ions, a shock wave is generated at the collision interface. Due to the action of this shock wave, even molecules with a molecular weight exceeding tens of thousands, such as proteins, are desorbed and ionized without being damaged. In other words, mass spectrometry (for example, orthogonal (orthogonal) time-of-flight mass spectrometry) of biomolecules including proteins becomes possible.

The mask 50 is on the flight path of the beam D by the charged droplet group accelerated in the vacuum acceleration chamber 41 and slightly before the sample stage 41, and its surface is the flight direction of the charged droplet beam (Z direction). It is arranged so that it is in the vertical direction (in line with the XY direction). The mask 50 is driven by the driving device 60 so as to be slightly displaced two-dimensionally in the direction along the surface. Specifically, as shown in Fig. 2, the mask 50 is a thin plate (preferably an insulating plate) 50 in which fine holes 50a are formed. , It is supported on a stage (not shown) that can move in the Y direction. The displacement of the mask 50 in the X direction is driven by the piezo element 61, and the displacement in the Y direction is driven by the piezo element 62. The driving device 60 includes piezo elements 61 and 62. For driving in the X and Y directions, mechanical devices other than piezo elements may be used. In conjunction with the driving of the mask 50, the cluster ion beam can be deflected by an electric field to adjust the ion beam with the maximum intensity. The surface of the mask 50 is perpendicular to the flight path of the charged droplet group. The spread of the charged droplet group D in the order of millimeters is mostly limited by the mask 50 and does not reach the sample S. A part of the charged droplets passes through the fine hole 50a of the mask 50 and collides with the sample as described above to ionize the sample. For example, with a spread of diameters 3 mm (beam diameter) charged droplets beam diameter of several _mu [pi! It collides with sample S, limited to a beam with a size of ~ 0.1 μm.

In this way, the position of the sample where the charged droplet collides is limited to a small range. By moving the mask 50 in the X and Y directions, the position of the specimen where the charged droplet collides can be changed. Therefore, two-dimensional molecular level information can be obtained by two-dimensionally scanning the impact position of the charged droplet on the surface of the sample.

The mask 50 (its fine hole 50 a) determines the position where the charged droplets collide on the sample surface. If the collision position of charged droplets is fixed, distribution information in the depth direction at the molecular level can be obtained. As described above, one-dimensional or two-dimensional information on the molecular level of the sample surface layer can be obtained by displacing the collision position of the charged droplets one-dimensionally or two-dimensionally. Instead of displacing (scanning) the mask 50, even if the sample stage 43 is displaced (scanning) Also good. If possible, charged droplets can be deflected by an electric or magnetic field and scanned.

As shown in FIG. 3, the mask 50 is formed by superposing two mask plates 51, 52 on which fine slits 51a, 52a intersecting each other are formed, so that the fine slits 51a, 52 are overlapped. The crossing position of a may be a fine hole. The mask plate 51 is supported so as to be displaceable in the X direction, and is driven in the X direction by the piezo element 61. The mask plate 52 is supported so as to be displaceable in the Y direction, and is driven in the Y direction by the piezo element 62.

Next, examples of the etching method and apparatus will be described.

FIG. 4 shows an etching apparatus 20 A combined with a mass spectrometer. In this figure, the same components as those shown in Fig. 1 are denoted by the same reference numerals, and redundant explanation is avoided.

The difference from the ionizer shown in Fig. 1 is that, first of all, an etching solution (including an aqueous solution) is used as a solution for the charged droplets generated by electrospray. .

In the etching system, the charged droplets of the etching solution generated by electrospray at atmospheric pressure are guided into the vacuum, and this is accelerated with a potential difference of about 10 kV, and the target Su is impacted. To do. Hydrofluoric acid, dilute nitric acid, acetic acid, etc. can be used as the etching solution for generating electrospray. Atomic level etching of silicon or silicon oxide can be performed by impact of charged droplets of hydrofluoric acid. Atomic level etching of metal thin films can be performed by impact of charged droplets of dilute nitric acid. Atomic and molecular level etching of organic thin film materials can be performed by charged droplet impact of acetic acid. The etching solution may be just water or an organic solvent.

The etching solution needs to have a chemical reaction with the object. Absent. The etching solution may be an aqueous solution, an organic solvent (for example, methanol), or an organic solvent in an aqueous solution. In short, the etching solution only needs to be multivalently charged. For example, water (pure water) can be used as the etching solution. However, charged droplets are more likely to be generated by the electric-orifice spray method when an electrolyte such as acetic acid or ammonia is dissolved in water to form an aqueous solution. The charged droplets are desirably multivalent charged droplets having a charge of several tens or hundreds. Etching with water is possible because various reactive species are generated in the region of the shock wave generated at the collision interface between the charged droplet and the sample, which etches metals, semiconductors, insulators, etc. It is. Such an etching action is a reactive individual etching, which enables layer-by-layer etching at the atomic level. In etching using such cluster ions, craters are not generated on the surface, so that only the surface can be etched without damage inside the sample.

The second difference from the method shown in Fig. 1 is that a holding base 43A is provided in the vacuum acceleration chamber 41 in place of the sample base. The object to be etched Su is fixedly held on the holding table 43A.

Nitrogen gas is not necessarily used. It is not always necessary to cool charged droplets. By introducing or filling the charged droplet generation chamber 31 with high-purity nitrogen gas at a temperature close to room temperature, contamination of impurities can be suppressed. It is not always necessary to provide the mask 50. Charged droplets are multivalent

Because it is charged to several tens or hundreds of valences, it can be accelerated by an electric field at high speed (for example, about 10 times the speed of sound). In addition, the charged droplet beam can be swept in two orthogonal directions (X and Y directions) by the deflection electrode. Sweep charged droplet beam or holder 43 A

(2D scanning) 'Large area etching becomes possible. In this etching method, for example, charged droplets having a mass of 10 million (u) and a valence of 100 are collided with the surface of the object Su at high speed. As shown in Fig. 5A, when a charged droplet with a 100-valent charge collides with a solid surface at a speed about 10 times the speed of sound, an impulse wave is generated at the interface as shown in Fig. 5B. The interface gas generated by this shock wave is a supercritical fluid gas that far exceeds the critical limit of water supercritical fluid (water). Since collisions at the interface are coherent (all colliding water molecules collide with the substrate in the same direction), the reproducibility of the phenomenon is extremely high. However, this supercritical state relaxes (cools) in about picoseconds, so the inside of the film is not damaged. Furthermore, as shown in Fig. 5C, the thickness of the film that desorbs from the surface is limited to a few atoms (molecules), so there are ultra-fine processing techniques and layer-by-layer surface analysis techniques. This is the optimal etching method.

By selecting the type of liquid to be electrosprayed, various semiconductors (Si, Ge, etc.), silicon oxide (semiconductor oxides), insulators, organic material thin films, etc. For such metals, it is possible to carry out etching technology using a layer-by-layer. Since the ion source (charged droplet source) is an atmospheric pressure electrospray, it can be easily installed in semiconductor manufacturing equipment, and the principle is simple, so no skilled technology is required. It is a simple, highly efficient and inexpensive technology. For the formation of a fine pattern, it is only necessary to use mask 50 to etch only the necessary parts. By sweeping charged droplets or holding base 43 A in the xy direction, precision processing of large-area, high-definition semiconductor materials, metals, organic thin films, and insulator films becomes possible.

According to experiments, it was confirmed that only a few molecular layers on the surface of the organic material were detached by a single charged droplet impact, and the underlying sample was not damaged at all. This is because it is an excellent etching technology that has high desorption efficiency and the thickness of the desorbed film is limited to a few molecular layers. Ions desorbed and ionized from the surface of the target object Su by the impact of charged droplets (ie, by etching) are introduced into the mass spectrometer 10 through the introduction channel (ion inlet 11a), and mass spectrometry is performed. Is done.

FIG. 6 shows another embodiment of the etching method op- eration apparatus.

An electrospray device 32B with a metal tube 33B to which a high voltage is applied is installed outside the main body of the etching device 20B and is exposed to the atmosphere. Of course, an electrospray device 32B may be installed in the charged droplet generation chamber. The electrospray device 32B generates charged droplets of the etching solution.

The main body of the etching apparatus 20B includes a roughing chamber 71, an adjustment chamber 72, and a vacuum acceleration chamber 41B of the acceleration device 40B. These chambers 71, 72, and 41B are connected in a straight line. .

The roughing chamber 71 has a slightly low degree of vacuum exhausted by a rotary pump or the like. The adjustment chamber 72 and the vacuum acceleration chamber 41B are kept at a high vacuum. The adjustment chamber 72 is provided with a quadrupole ion guide 73. The charged droplets of the etching solution generated in the electrospray device 32 B enter the roughing chamber 71 through the fine holes 71 a of the orifice in the roughing chamber 71, and further enter the adjusting chamber 72 through the fine holes 72 a. Then, the spread is suppressed by the ion guide 73 and a confined charged droplet beam is formed. In addition, a high-frequency electric field is applied to the ion guide 73, and only charged droplets with a relatively large charge and mass are selected. The selected charged droplet beam is introduced into the vacuum accelerating chamber 41B through the fine hole 41a.

In the vacuum acceleration chamber 41B, an acceleration electrode 42B, a deflection electrode 44, and a holding table 43B are arranged in this order. An object Su to be etched is fixed on the holding table 43B.

The charged droplet beam is accelerated by the acceleration electrode 42B to which a high voltage is applied. Colliding with the object S u, the object S u is etched as described above. In this embodiment, the charged droplet beam collides perpendicularly with the surface of the object Su. When the charged droplet beam passes between the deflection electrodes 44, it is swept according to the sweep voltage applied to the deflection electrodes 44. Therefore, the charged droplet scans the surface of the object.

Instead of the deflection electrode 44, the charged droplet may be swept by a magnetic field by energizing the coil. Instead of sweeping the charged droplet beam, the holder 43B may be scanned two-dimensionally. A mask can also be provided.

FIG. 7 shows an etching apparatus 20 C used in the experiment. This etching device 20 C is a force s that is combined with the time-of-flight mass spectrometer 10, and the basic structure is the same as the etching device 20B shown in FIG. Add a sign to avoid duplication.

The roughing chamber 71 is provided with a ring lens 71b, and the adjustment chamber 72 is divided into two chambers 72A and 72B which are separately evacuated, and the high-frequency quadrupole ion guide is divided into these two chambers 72A and 72B. 73 is provided.

The ions released from the surface of the target S u are collected by the extraction electrode 19, placed in the introduction chamber 14 of the mass spectrometer 10, and passed through the high-frequency quadrupole ion guide 16 into which N ₂ gas has been introduced. It converges and slows down (collision / dubbing) and is guided into the analysis chamber 17. The vacuum acceleration chamber 41B is also provided with an entrance 18 for the object Su.

As the etchant, a 1 M acetic acid aqueous solution is used, and as shown in Fig. 5A, about 100-valent water molecules collide with the target Su at a speed of about 10 times the speed of sound (12 Km / s).

Figure 8 shows the case where a 10ML (monolayer) gramicidin layer is formed on a 100ML (monolayer) arginine (Arg) layer as the object (sample). Shows the obtained mass spectrometry results. side The axis shows time (minutes) and the vertical axis shows relative intensity. First, the upper gramicidin is etched, and then the lower arginine is gradually etched. In other words, it can be seen that etching is being performed layer-by-layer or close to this.

Figure 9 shows the experimental results obtained when using an object (S n (1 nra) on S i) with a 1 nm thick tin (S n) foil on silicon. Yes. Etching is initially tin (S n) (+ S n , H + (S n O), Η + (S η Ο) 2) dominant for gradually silicon ^{_{(Η + (S i O 2}} ) 2, It can be seen that H + (S i O ₂ ) ₃ ) is etched. Tin (Sn), one of the metals, is etched layer-by-layer or close to it.

From the above, it can be seen that etching of organic material thin films, semiconductors, insulators, metals, etc. is performed layer-by-layer (or close to this). Etching of oxide semiconductors, graph items, diamonds, etc. is also possible.

Claims

The scope of the claims

1. Generate charged droplets of volatile liquid and introduce them into the vacuum chamber,

Charged droplets are accelerated toward the sample by the electric field formed in the vacuum chamber,

The spread of the charged droplet beam that collides with the sample is limited by the fine holes in the mask placed in front of the sample position.

An ionization method using cluster ion bombardment capable of imaging.

2. The ionization method according to claim 1, wherein a position where the charged droplet should collide with the sample is determined by the position of the micropore.

3. The ionization method according to claim 1 or 2, wherein at least one of the mask and the sample is relatively two-dimensionally scanned.

4. The ionization method according to any one of claims 1 to 3, wherein the sample is scanned two-dimensionally with respect to the sample.

5. The ionization method according to any one of claims 1 to 4, wherein the micro holes are formed by two intersecting micro slits formed in two mask members. .

6. The ionization method according to any one of claims 1 to 5, wherein charged droplets are generated by an electrospray method under atmospheric pressure.

7. Introducing ions of the sample desorbed or ionized by collision of charged droplets in the ionization method according to any one of claims 1 to 6 into a mass spectrometer. Method.

8. An accelerating device that is provided outside the ion inlet of the mass spectrometer, communicates with the inside of the mass spectrometer through the ion inlet, and has a vacuum accelerating chamber in which an accelerating electrode, a mask, and a sample stage are arranged. and

Charging that communicates with the vacuum acceleration chamber through the droplet inlet of the vacuum acceleration chamber A droplet generation chamber, and a charged droplet generation device that generates charged droplets of volatile liquid in the charged droplet generation chamber.

The mask has fine holes and is placed in front of the sample table. The sample table and the mask micro-holes are positioned so that they can be adjusted relative to the direction of the sample table surface.

Charged droplets generated by the charged droplet generation device are guided from the charged droplet generation chamber to the vacuum acceleration chamber through the droplet introduction port, and are applied to the acceleration electrode to which a high voltage is applied. In addition, the spread is limited by the micropores in the mask, and the charged droplets that have passed through the micropores collide with the sample on the sample stage, and are desorbed and ionized by the ions in the sample. Is introduced into the mass spectrometer through the ion inlet,

An ionizer using cluster ion bombardment capable of imaging.

9. The ionization method according to claim 8, wherein the charged droplet generation device includes an electrospray device, and the charged droplet generation chamber is open to the atmosphere.

10. Generate charged droplets of the etching solution and introduce them into the vacuum chamber.

Charged droplets are accelerated toward the target by the electric field formed in the vacuum chamber, collide with the target surface, and the target surface is etched by this.

Etching method by cluster ion bombardment.

11. The etching method according to claim 10, wherein the etching solution is an aqueous solution.

12. The etching method according to claim 10 or 11, wherein charged droplets are generated by an electrospray method at atmospheric pressure.

13. The charged droplets are multivalent charged droplets with a charge of several tens or hundreds of valences. 13. The etching method according to any one of claims 10 to 12, wherein:

14. The etching method according to claim 10, wherein at least one of the charged droplet and the object is two-dimensionally scanned.

15. The etching method according to claim 10, wherein a mask is arranged in front of the position of the object, and the spread of the charged droplet beam colliding with the object is limited by the fine holes of the mask.

16. The etching method according to claim 15, wherein a position where the charged droplet should collide with the object is determined by the position of the micro hole.

17. The etching method according to claim 15 or 16, wherein at least one of the mask and the target is moved relatively two-dimensionally.

18. Introducing ions that are desorbed and ionized from the surface of an object by collision of charged droplets in the etching method according to any one of claims 10 to 17 into a mass spectrometer. Analysis method.

17. Charged droplet generator that generates charged droplets of etching solution under atmospheric pressure, and

An acceleration electrode and a holding table for holding an object are disposed inside, and a vacuum accelerating chamber is formed in which fine introduction holes for charged droplets generated by the charged droplet generator are formed. Charged droplets generated in the charged droplet generator and introduced through the fine introduction holes are accelerated by the acceleration electrode to which a high voltage is applied and collide with the surface of the object held on the holding table. An accelerator that etches the surface of objects,

An etching apparatus having:

20. The apparatus further comprises an ion guide for selecting a charged charge and a droplet having a relatively large mass from the charged droplets generated by the charged droplet generating device and guiding them to the accelerator. The etching apparatus according to the item 19 in the range.

21. The etching apparatus according to claim 19, further comprising an introduction path for introducing ions desorbed and ionized from the surface of the object by the collision of the charged droplets into the mass spectrometer.

22. A composite apparatus comprising the etching apparatus according to claim 21 and a mass spectrometer.