JP2004191358A - Sample preparation method and device by composite charge particle beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To present a processing method which prevents the problem of damages on a sample surface caused by Ga used as an ion source in the processing of a sample using a converging beam having good processing efficiency, and to provide a device for executing the method. <P>SOLUTION: In the sample processing method of the present invention, in the operations of making a sample into thin or small pieces and exposing a surface thereof to be observed, in order to remove damages on the sample surface due to an ion beam (FIB), rough processing is executed by etching by use of an initial converging ion beam, and finish processing is then executed by gas assist etching by use of an electron beam (EB). As the device, an electron beam body tube which can perform processing is installed, in addition to a FIB body tube, in one sample room. A gas introduction device is further provided which injects a starting material gas for CVD and/or an assist gas for etching to a beam irradiation position. In this way, the processings selectively using both the charge particle beams to execute the processing of the TEM sample can be sequentially performed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a sample processing method for performing a combination of processing using a focused ion beam and processing using an electron beam, and an apparatus for performing the processing.

  When observing a cross section or a surface of a sample using a TEM or SPM, it is well known to perform thinning or fragmentation using a focused ion beam apparatus as one method of preparing a sample for observation. In addition, when a physical property such as an electrical or magnetic property of a sample observation surface is measured using the SPM, the sample is cut into small pieces by a focused ion beam apparatus. For example, as a method of preparing a sample for TEM observation, there are known a method of mechanically cutting out a small piece from a wafer-like sample and processing the same, and a method of extracting a thinned sample by etching the wafer as it is. Have been. As described in Patent Document 1, the former method of manufacturing a TEM sample (1) cuts a portion including a cross-sectional portion to be observed from a wafer into a block shape, and cuts the block into a convex shape as shown in FIG. Into small pieces. (2) This small piece is placed on the sample stage of the FIB apparatus, and as shown in FIG. 4B, a focused ion beam (FIB) is first irradiated onto the surface portion of the observation section while the source gas is injected by the gas introducing device 8. Then, a deposition film for protection is formed, and then (3) as shown in FIG. 4C, a focused ion beam is irradiated from above the surface of the sample, and the rear side of the observation section is subjected to sputter etching or gas assist etching. Drilling is performed, and then the front side of the observation section is dug by etching in the same manner. That is, both sides of the observation cross section are thinned by a focused ion beam apparatus so that the electron beam can pass therethrough. In order to enhance the processing efficiency at this time, the ion beam to be irradiated is etched by a high energy beam having a high acceleration voltage and a large beam current. The observation surface is damaged by this high-energy etching process, and it is in a rough-cut state. (4) After roughing is completed, finish using a low-energy beam with a low acceleration voltage and a low beam current. Processing is performed to complete the TEM sample. This finishing is for polishing the surface of the sample which has been roughly cut. The TEM sample thus finished is placed on a sample stage of a TEM device, and irradiated with an electron beam (EB) so as to transmit through an observation section as shown in FIG. To obtain an observation image.

  The latter TEM sample manufacturing method is, for example, as shown in Patent Document 2. First, as shown in FIG. 3A, a protective deposit film is formed on the wafer surface in the observation section by a gas gun. As shown in FIGS. 3 (b) and 3 (c), a focused ion beam is irradiated from above the surface of the sample, and both sides of the observation cross section are scraped off by etching. ， Drill a rear hole. The size of the hole is such that the front hole is tilted on the sample stage and the observation cross section can be observed with a scanning ion microscope, and the rear hole is the same width as the front hole and about 2/3 in depth. You. The sample surface is tilted, and as shown in FIG. 3D, an incision is made in the bottom of the sliced sample as an observation cross section. At this time, the cutting of the bottom is performed by scanning the focused ion beam as shown by an arrow in FIG. FIG. 5 is an image diagram of a microscope observation image obtained by observing a portion formed by drilling from obliquely above. At this time, the sample surface is damaged by the notch processing, so the sample section must be polished again. In the method of Patent Document 2, in order to prevent the displacement of the sliced sample during the finishing process, the above-mentioned cutting process is performed only on the bottom portion of the sample 2 as shown in A, and the sliced sample is firmly fixed on both sides. In this state, finishing is performed with a low-energy ion beam from above, and the cuts on both sides are focused ion beams from above that do not damage the observation cross section after finishing as shown in FIG. 5B. It is something to do. In this manner, the focused ion beam is irradiated to perform the cutting process, and the manipulator (glass probe) is operated as shown in FIGS. 6A and 6B to separate the section sample from the sample main body, and as shown in FIG. 6C. Move and place on a collodion membrane-attached mesh (150 mesh) or the like. As shown in FIG. 6D, the section sample cut out on the mesh surface adheres, and the sample for TEM observation is completed.

  However, regardless of which method the TEM sample processing is performed, Ga, which is a liquid metal, is generally used as the ion material of the focused ion beam, and the Ga surface irradiated with the slicing processing as described above applies the Ga ion to the sample surface. There is a problem of causing damage. In the roughing stage, machining is performed by increasing the acceleration voltage.However, in the finishing stage of the damaged sample surface, a procedure such as lowering the acceleration voltage and performing a careful finishing process to polish the damaged sample surface is performed. In need of. However, even if the acceleration voltage is lowered and careful processing is performed, damage due to Ga ion irradiation cannot be completely removed. When the TEM sample is observed with a TEM device, the remaining Ga affects the transmission of electrons differently from the original sample, which becomes a noise in detecting the transmitted electron beam. That is, there is a problem that the damage layer caused by the Ga ion irradiation makes the TEM observation image of the processed sample unclear.

  In addition, when a sample for evaluating physical properties such as electrical characteristics is manufactured using a focused ion beam using SPM, if gallium is implanted into the sample, the injected Ga may have an effect depending on the physical property to be evaluated. I will give it.

  Conventionally, as a processing method that does not cause such a problem, a method of manufacturing a TEM sample that does not perform processing using a focused ion beam but performs all processes from rough processing to finish processing by gas assisted etching using an electron beam is proposed. (For example, see Patent Document 3). However, in general, gas assisted etching using an electron beam is much slower than etching using a focused ion beam, and thus this prior art leaves a problem in terms of processing efficiency.

Further, a method using a low-energy gas ion beam, for example, an Ar ion beam has been proposed in order to remove the damage layer caused by the Ga ion irradiation (for example, see Patent Document 4). However, sputtering using a gas ion beam physically removes the damaged layer, so that a larger amount of the damaged layer is left as compared with gas assisted etching using an electron beam.
JP 2000-32390A FIG. JP, 2001-141620, A FIGS. 1, 2, and 4 SUMMARY OF THE INVENTION FIG. JP-A-6-26012, paragraph No. 0004, FIG.

  An object of the present invention is to provide a processing method that solves the above-mentioned problem, that is, a processing method for solving a problem of damage to a sample surface due to gallium used as an ion source in processing of a sample using a focused ion beam having excellent processing efficiency. It is to provide a device to execute.

  In the sample processing method of the present invention, in the work of thinning and shredding a sample and exposing an observation surface, etching using an initially focused ion beam is performed to remove damage in the sample due to an ion beam on the sample surface. Roughing is performed by processing, and then finishing is performed by gas-assisted etching using an electron beam.

  As an apparatus, in addition to the FIB column, an electron beam column capable of performing processing is provided in the same sample chamber, and gas introduction for injecting a source gas for CVD and / or an assist gas for etching to a beam irradiation position. An apparatus is provided, so that the processing using the selected charged particle beams can be sequentially performed in order to execute the processing of the sample.

  In the sample processing method of the present invention, in the work of thinning the sample into small pieces and exposing the observation surface, rough processing is first performed by etching using a focused ion beam, and thereafter, gas assist using an electron beam is performed. Since the finishing process is performed by etching to remove the damage of the sample surface due to the ion beam, even if the sample is processed using a focused ion beam having excellent processing efficiency, the sample surface using Ga used as an ion source can be used. Can be effectively prevented. Therefore, a high-quality sample can be provided.

  In the composite charged particle beam apparatus according to the present invention, two columns, a focused ion beam column and an electron beam column that can be processed, are attached to the sample chamber, and a source gas for CVD and / or an assist gas for etching are supplied. Since the apparatus is provided with the gas introducing device for injecting the beam at the beam irradiation position, etching or deposition using a focused ion beam or an electron beam can be selectively performed according to desired conditions. In addition, since the observation image of both the scanning ion microscope image and the scanning electron microscope image can be obtained, select the electron microscope image when you do not want to be damaged. A wide range of uses such as taking a microscopic image or comparing both microscopic images is possible. When the sample stage is provided with a tilt function, the incident beam is removed by etching the upper part of the observation surface with a focused ion beam in the preparation of the sample for observing the observation surface inside the sample by SPM. By making the light obliquely incident on the surface, it is possible to reduce the incidence of ions and damage to the observation surface.

  Further, when the SPM observation sample has different types of materials in the probe scanning plane direction, in the etching process of irradiating an electron beam while blowing an etching gas, a material which is easily etched by selecting an appropriate etching gas is etched. Materials that are difficult to etch are not etched. By observing the shape by SPM, the contrast of the material can be observed.

  Further, by using gas-assisted etching using an electron beam to remove the damaged layer, the number of damaged layers can be reduced as compared with the case where removal is performed using a gas ion beam such as an Ar ion beam. The SPM observation including the TEM observation and the physical property observation can be performed more clearly on the semiconductor sample that has been obtained.

  The composite charged particle beam apparatus of the present invention has a tilt adjustment function on the sample stage so that the focused ion beam and the electron beam can be incident on the sample surface at a desired angle. Therefore, desired measures can be taken both in terms of processing efficiency and damage prevention.

  According to the present invention, two columns, a focused ion beam column and an electron beam column that can be processed, are attached to a sample chamber, and a source gas for CVD using an ion beam or an electron beam and / or an ion beam or an electron beam are supplied. Etching or deposition using a focused ion beam or an electron beam is selectively performed using an apparatus including a gas gun for injecting an assist gas for gas assisted etching to a beam irradiation position. FIG. 1 shows a basic configuration of such a composite charged particle beam apparatus, wherein 1 is a focused ion beam column, 2 is an electron beam column, 3 is a sample chamber, 4 is a sample stage, and 5 is a sample stage. A sample, 6 is a vacuum pump, 7 is a secondary charged particle detector, and 8 is a gas introduction device. Since the sample stage 4 performs three-dimensional processing, it needs to be provided with a five-axis drive mechanism of X, Y, Z, rotation, and tilt. However, since the electron beam column 2 used in the present invention is also used for processing, unlike a scanning microscope installed for observation in a conventional apparatus, the beam current is about several pA to several nA (for example, (1 pA to 20 nA). For observation, the beam current is about several pA to several tens pA.

A TEM sample processing method will be described as one embodiment of the present invention performed using the above-described apparatus. First, a processing method for cutting a block from a wafer and then preparing a block for TEM observation will be described. (1) A portion including a cross section to be observed is cut out from the wafer in a block shape, and the block is cut into a small block having a convex cross section as shown in FIG. (2) This small block is placed on the sample stage of the FIB apparatus, and a source gas such as W (CO) ₆ is first injected by a gas gun onto the surface of the observation section as shown in FIG. 2 (b). While irradiating with a focused ion beam, a deposit film for protection is formed. (3) As shown in FIG. 2 (c), a focused ion beam is irradiated from above the surface of the sample, and the back side of the observation section is dug by sputter etching or gas-assisted etching. Is dug by etching. That is, both sides of the observation cross section are thinned using a FIB apparatus so that the electron beam can pass through. In order to enhance the processing efficiency at this time, the ion beam to be irradiated is subjected to etching with a high energy beam having a high acceleration voltage and a large beam current. The observation surface is damaged by the high-energy etching process, is in a roughened state, and Ga used for the ion beam source is implanted into the sample processing surface as shown in FIG. Since the Ga-impregnated layer has a thickness of about 30 nm, (4) both sides of the thin section are finished by gas-assisted etching using an electron beam as shown in FIG. To complete. However, a low acceleration voltage of several hundred V to about 5 kV is used as an electron beam acceleration voltage in order to suppress heat damage to the sample. This finishing is to polish the surface of the sample which has been roughly cut and to remove the remaining layer after the implantation of Ga. The TEM sample thus finished is placed on a sample stage of a TEM device, and irradiated with an electron beam so as to transmit through an observation section as shown in FIG. To obtain an observation image.

  In addition, a processing method for extracting a sliced sample by etching the wafer as it is will be described. As shown in FIG. 3A, a CVD source gas is sprayed onto a defect area on a sample surface including a desired observation cross section, and a focused ion beam (in this case, an electron beam may be applied) is irradiated onto the defect area. A protective deposition film is formed. Subsequently, as shown in FIG. 3 (b), a focused ion beam is irradiated from above toward the rear portion of the desired observation cross-section, by sputtering etching or gas-assisted etching performed by injecting an assist gas from the gas introducing device 8. Drill a rear hole. Similarly, a front hole is formed by irradiating a focused ion beam from above toward a front portion of the observation cross-sectional portion by sputter etching or gas assist etching performed by injecting an assist gas from a gas introduction device 8. The front hole may be ahead of the machining of the rear hole. It is necessary to process the sample piece into a size that allows the observation section to be irradiated with an electron beam from obliquely forward for observing the cross section of the sample and a focused ion beam from obliquely above for cutting. When thinning by drilling on both sides so that the electron beam can penetrate the observation cross section, the ion beam to be irradiated is etched with a high energy beam with a high acceleration voltage and a large beam current to increase the processing efficiency. . For this reason, the observation surface is damaged and rough-cut, and the gallium used for the ion beam source is injected into the sample processing surface as shown in FIG. In the present invention, at this stage, the sample stage 4 is tilted, and a focused ion beam is cut from the obliquely upper part of the sliced bottom as shown in FIG. This FIB irradiation is performed before the finishing processing because it damages the observation section. Since the gallium-impregnated layer is about 30 nm in this case also in the observation cross section, after this incision processing, the rear surface of the thin section is subjected to gas-assisted etching using an electron beam as shown in FIG. In addition to polishing the surface of the sample which has been roughly cut, a layer remaining after the implantation of Ga is scraped off. Also, as shown in FIG. 3 (f), the front surface of the thin section is similarly finished. Subsequently, both sides of the thin section are irradiated with a focused ion beam from above to perform cutting. At this time, the focused ion beam is irradiated from directly above the flake sample, so that the observation section is not damaged. After the above processing steps, the section sample is separated from the sample body by operating the manipulator (glass probe) in the same manner as in the prior art shown in FIG. 6, and a collodion film-attached mesh (150 mesh) as shown in FIG. 6C. And place it on top of it. As shown in FIG. 6D, the section sample cut out on the mesh surface adheres, and the sample for TEM observation is completed. The TEM sample thus finished is placed on a sample stage of a TEM device, is irradiated and scanned with an electron beam so as to transmit through an observation section, detects transmitted electrons, and obtains an observation image.

It is a figure showing the basic composition of the device which performs the sample processing method by the compound charged particle beam of the present invention. FIG. 4 is a diagram illustrating a method of the present invention for processing a TEM sample based on a small block cut out from a wafer. FIG. 3 is a diagram illustrating a method of the present invention for thinning a TEM sample directly from a wafer. FIG. 4 is a diagram illustrating a conventional method for processing a TEM sample based on a small block cut out from a wafer. FIG. 4 is a diagram illustrating a conventional method for thinning a TEM sample directly from a wafer. FIG. 6 is a diagram illustrating a method of thinning a TEM sample directly from a wafer, in which a sample section is moved and fixed on a mesh to obtain a TEM sample.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Focusing ion beam column 6 Vacuum pump 2 Electron beam column 7 Secondary charged particle detector 3 Sample chamber 8 Gas introduction device 4 Sample stage 5 Sample

Claims (9)

  The sample is etched with a focused ion beam to expose the observation surface, and the exposed observation surface is blown with an etching gas and irradiated with an electron beam to etch the damaged layer formed on the exposed observation surface by the focused ion beam. A sample preparation method characterized by removing.   In a method for producing a slice sample for TEM observation of a cross section at a desired portion of the sample, a focused ion beam is scanned and irradiated from above the sample surface, and both sides of a region to be the slice are etched to include the cross section. The first step of producing a thin section, while simultaneously irradiating both cross sections of the thin section produced in the first step with an electron beam, simultaneously blowing the gas for etching the sample to the electron beam scanning irradiation area, A second step of etching and removing a damaged layer formed in the first step remaining on both cross sections of the thin section.   In a method of preparing a small sample for SPM observation of a cross section of a desired portion of a sample, a focused ion beam is scanned and irradiated from above the sample surface, both sides of a region to be the small piece are etched, and a small piece including the cross section is etched. A first step of producing, and simultaneously scanning and irradiating the observation cross section of the small piece produced by the electron beam in the first step, simultaneously spraying a gas for etching the sample to the electron beam scanning irradiation area, 2. A method for producing an SPM sample, comprising: a second step of etching and removing a damaged layer formed in the first step remaining in the observation section.   In a method of producing an observation sample by removing an upper portion covering the observation surface in order to observe a desired observation surface inside the sample by SPM, a focused ion beam is scanned and irradiated from above an area including the observation surface. A first step of removing the upper portion covering the observation surface by etching to expose the sample observation surface, and simultaneously scanning and irradiating the sample observation surface exposed in the first step with the electron beam; A second step of spraying a gas for etching a sample onto the electron beam scanning irradiation area, and etching and removing a damaged layer formed in the first step remaining on the sample observation surface. Method.   The method according to claim 1, wherein an acceleration voltage of the electron beam is several hundred V to 5 kV, and a beam current is several pA to several nA.   When performing the first step of etching by the focused ion beam and the second step of etching by spraying and irradiating an electron beam at the same time as spraying an etching gas to a desired location, a desired area is irradiated to a beam irradiation area. 6. The method according to claim 1, wherein the tilt of the sample stage is adjusted so that the beam can be irradiated at an incident angle.   5. The sample preparation method according to claim 1, wherein an incident beam when scanning and irradiating the focused ion beam from above a region including the observation surface is obliquely incident on the observation surface. 6. .   A gas introduction device is provided for mounting two columns, a focused ion beam column and an electron beam column that can be processed, to the sample chamber and injecting a source gas for CVD and / or an assist gas for etching to a beam irradiation position. A composite charged particle beam apparatus capable of selectively performing etching or deposition using a focused ion beam or an electron beam.   9. The composite charged particle beam apparatus according to claim 8, wherein a tilt adjustment function is provided on the sample stage so that the focused ion beam and the electron beam can be incident on the sample surface at a desired angle.

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