JP2007292507A - Sample-manufacturing method of transmission electron microscope, and convergent ion beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sample-manufacturing method of a transmission electron microscope, capable of suppressing the deformation of a sample caused by the shrinkage of the low dielectric constant interlaminar insulating film of a semiconductor device, at observation due to the transmission electron microscope. <P>SOLUTION: A slice part, containing a desired observation place 2 due to the transmission electron microscope, is formed by processing the sample 1, and after a thin film is formed on the surface of the sample containing the slice part, the slice part is processed by a converged ion beam and the thin film of a part of the slice part is removed, to obtain the observation sample of the transmission electron microscope. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a specimen of a transmission electron microscope for observing a cross section of a semiconductor device in detail using a focused ion beam apparatus, and a focused ion beam apparatus for use in the sample producing method. .

  In recent years, more detailed shape observation methods are required as semiconductor devices become finer. As a detailed shape evaluation method, there is a method using a transmission electron microscope (TEM). Thin-film samples with a film thickness of about 100 nm are necessary for TEM observation, and sample production using a focused ion beam (FIB) is a method for producing thin-film samples for observing the cross-sectional structure of semiconductor devices. A method is known (see, for example, Patent Document 1).

  An example of a TEM observation thin sample preparation method using FIB processing will be described with reference to FIG. In FIG. 7, reference numeral 1 denotes an Si substrate on which a semiconductor device is formed. Reference numeral 2 denotes an observation target portion of a semiconductor device to be observed by a cross-sectional TEM, and reference numeral 3 denotes a protrusion formed by machining. FIG. 7B shows a thin piece portion 4 processed by FIB.

First, as shown in FIG. 7A, the shape of the protrusion 3 including the observation relevant portion 2 to be observed by the cross-sectional TEM is processed on the Si substrate 1 by machining. The protrusion 3 has a width (Wb) of 30 to 50 μm and a height (d) of 30 to 50 μm. Next, as shown in FIG. 7 (b), a processing of about 10 μm in depth and about 10 μm in width is performed on both sides of the observation target portion 2 by FIB processing, and a thin piece portion 4 having a thickness of about 100 nm is left in the central portion. The observation relevant part 2 in the thin piece part 4 is observed with a TEM.
JP 2002-39926 A

  However, the sample preparation method using the conventional FIB has the following problems. That is, in recent years, a low dielectric constant interlayer insulating film having a low dielectric constant has been used as an interlayer insulating film in order to solve the problem of wiring capacitance in accordance with miniaturization of semiconductor devices. The low dielectric constant film is a film containing C in order to lower the dielectric constant. Therefore, there are cases where the organic bond is broken by electron beam irradiation during TEM observation, and the low dielectric constant interlayer insulating film contracts. As a result, there arises a problem that an accurate sectional shape cannot be observed.

  An object of the present invention is to provide a sample preparation method for a transmission electron microscope capable of suppressing deformation of the sample due to shrinkage of a low dielectric constant interlayer insulating film of a semiconductor device during observation with a transmission electron microscope. To do. Moreover, it aims at providing the focused ion beam apparatus used for the sample preparation method.

  In order to solve the above-described problems, in the sample preparation method for a transmission electron microscope of the present invention, a thin piece portion including a desired observation position by a transmission electron microscope is formed by processing the sample, and the thin piece portion is formed. After forming a thin film on the surface of the sample, the thin piece portion is processed by a focused ion beam to remove a part of the thin portion of the thin piece portion to obtain an observation sample of the transmission electron microscope.

  Thereby, an observation sample is reinforced by holding a thin piece part with a thin film. Therefore, when the observation sample created in this way is observed with a transmission electron microscope, deformation of the sample due to the electron beam can be suppressed, and a desired observation location can be accurately observed and evaluated. Specifically, in the observation of semiconductor devices having a low dielectric constant interlayer insulation film, the thin film formed on the thin piece prevents deformation due to the shrinkage of the low dielectric constant interlayer insulation film. Shape evaluation is possible.

  In the sample preparation method of the transmission electron microscope of the present invention having the above-described configuration, the thin film formation and the processing with the focused ion beam can be repeated a plurality of times.

  The thin film is preferably formed using a plasma polymerization method.

  In the plasma polymerization method, methane and ethylene can be used as source gases.

  The thin film is preferably made of carbon.

  The film thickness of the thin film is preferably 50 nm to 500 nm.

  Moreover, it is preferable that the said observation sample has the said thin film piece with a film thickness of 500 nm or less.

  The focused ion beam apparatus of the present invention includes an ion source that generates ions, an extraction electrode that applies a voltage to the ions generated from the ion source to form an ion beam, a lens that narrows the ion beam, and the ion A lens for scanning the beam; a sample stage on which the sample is placed; a sample chamber for processing the sample with the ion beam; and the sample chamber connected to the sample through a valve; And a plasma polymerization chamber for forming a thin film.

  With such a configuration, FIB processing and deposition of the plasma polymerized film can be performed without taking the sample out of the vacuum, and the TEM sample can be easily manufactured by the sample preparation method of the present invention.

  In the focused ion beam apparatus of the present invention having the above-described configuration, the plasma polymerization chamber holds the sample stage and serves as a cathode, a sample stage holding part, an anode provided to face the sample stage holding part, It is preferable to include a power source for applying a voltage between the sample stage holding unit and the anode, and a gas inlet for introducing a raw material gas for plasma polymerization into the plasma polymerization chamber.

  The sample stage is provided with an electrode plate having an opening in which the sample is placed, and after forming the thin film, the electrode plate and the sample placed on the sample stage It is preferably movable so as to shield between the anode. When cleaning the surface of the sample table, which is a cathode electrode, the sample held on the sample table is covered with a negative electrode plate, thereby preventing contamination of the sample when the cathode electrode is etched with an ion beam. It becomes possible to perform cleaning in the apparatus.

  Further, it is preferable that a cooling plate cooled with liquid nitrogen is disposed between the sample chamber and the plasma polymerization chamber. Thereby, the residual gas in the plasma polymerization apparatus does not flow into the FIB sample chamber, and the plasma polymerization film can be further easily formed in the FIB apparatus.

  In the sample preparation method and focused ion beam apparatus of the transmission electron microscope of the present invention, the thin piece portion including the observation portion is covered with a thin film, so that the shape of the semiconductor device can be accurately evaluated by observation with the transmission electron microscope.

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

(First embodiment)
A TEM sample preparation method according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing the sample preparation method of the present embodiment. It should be noted that the same elements as those in the conventional example shown in FIG. 6 are denoted by the same reference numerals to simplify the repeated description.

  In FIG. 1, the Si substrate 1, the observation target portion 2 to be observed by cross-sectional TEM, and the thin piece portion 4 a produced by machining and FIB processing are the same as in the conventional example. This embodiment is different from the conventional example in that a plasma-polymerized carbon film 5 deposited for the first time and a plasma-polymerized carbon film 6 deposited for the second time are provided.

  First, as shown in FIG. 1 (a), a thin piece portion 4a having a width (Wa) of about 1 μm including an observation target portion 2 to be observed by a cross-sectional TEM observation is formed on the Si substrate 1 by machining and roughing with an FIB apparatus. To do. Next, as shown in FIG. 1B, a carbon film 5 having a film thickness of about 50 nm is deposited by plasma polymerization using methane and ethylene as source gases.

  The film thickness of the carbon film is preferably about 50 to 500 nm.

  Next, as shown in FIG. 1 (c), by FIB finishing, cross-section processing is performed to the vicinity where TEM observation is desired (processing from the left side in the drawing of FIG. 1 (c)) to form a thin flake portion 4b. Thereafter, as shown in FIG. 1D, a carbon film 6 is deposited again by about 50 nm by plasma polymerization. Subsequently, as shown in FIG. 1 (e), by FIB processing from the opposite side to the case of FIG. 1 (c), it is processed to the vicinity of the observation target portion 2 where the cross-section TEM observation is desired, and the thin piece further thinned. Part 4c is formed. When the sample film thickness of the thin piece portion 4c is thick, the above carbon film deposition and FIB processing are repeated as necessary.

  Here, the film thickness of the thin piece portion after the carbon film deposition and FIB processing is finished is preferably about 500 nm or less.

  The finished sample is arranged as shown in FIG. 2 schematically, and TEM observation is performed with the electron beam 7. In this way, the TEM observation is performed with the carbon film 6 attached to the sample. However, since the carbon film is a film mainly composed of C and H having a small atomic number, the film thickness of the present embodiment is not suitable for TEM observation. It does not affect.

  As described above, according to the present embodiment, since the carbon film holds the thin piece portion formed by FIB processing, the shape change due to the shrinkage of the low dielectric constant film included in the sample during TEM observation is suppressed. The cross-sectional shape can be observed in detail.

(Second embodiment)
A focused ion beam (FIB) apparatus according to a second embodiment of the present invention will be described with reference to FIG. This FIB apparatus is an apparatus that can carry out the sample preparation method of the first embodiment. FIG. 3 is a sectional view showing a schematic structure of the FIB apparatus. In this apparatus, in addition to the FIB sample chamber 17 and the sample exchange chamber 26, a plasma polymerization chamber 19 is provided.

  In the FIB sample chamber 17, the liquid ion source 8, the extraction electrode 9, the focusing lens 11, the objective aperture 12, the scanning electrode 16, the objective lens 13, and the sample stage 14 are arranged. A sample 15 to be subjected to FIB processing is attached to a sample table 14. Reference numeral 10 denotes an ion beam extracted by the high voltage applied from the liquid ion source 8 to the extraction electrode 9. The ion beam 10 is scanned by the scanning electrode 16.

  The FIB sample chamber 17 and the sample exchange chamber 26 are connected via a gate valve 34. In order to evacuate the FIB sample chamber 17 and the sample exchange chamber 26, vacuum pumps 27 and 28 are connected via valves 29 and 30, respectively.

  The ion beam 10 extracted from the liquid ion source 8 to the extraction electrode 9 is narrowed down by the focusing lens 11, the objective aperture 12, and the objective lens 13 and focused on the sample 15 mounted on the sample stage 14. The sample 15 is processed by scanning this beam at an arbitrary x, y with the scanning electrode 16. The above is the configuration of a general FIB apparatus. In this embodiment, a function for forming a film by a plasma polymerization method is added to the FIB apparatus.

  Next, the plasma polymerization function added according to this embodiment will be described. In order to add a function of forming a film by a plasma polymerization method to a general FIB apparatus, a plasma polymerization chamber 19 is provided separated from an FIB sample chamber 17 in which an FIB sample or the like is set by a gate valve 18. The plasma polymerization chamber 19 is provided with a cathode electrode 20 constituting a sample table holding unit for setting the sample table 14, an anode 21 facing the cathode electrode 20, a gas introduction valve 22, and a gas introduction port 23. .

  Further, a power source 24 for applying a high voltage to the cathode electrode 20 and the anode 21 and a gas cylinder 25 for supplying a raw material gas for film formation through a gas introduction valve 22 are prepared. In the plasma polymerization, since the raw material gas for film formation is flowed, the vacuum pumps 27 and 28 for evacuating the FIB sample chamber 17 and the sample exchange chamber 26 and the valves 29 and 30 are separate systems, ie, It has.

  Next, a procedure for forming a film by the plasma polymerization method will be described. The sample stage 14 installed in the FIB sample chamber 17 can be moved to the plasma polymerization chamber 19 using a sample exchange rod 33 used during sample exchange. For this purpose, the gate valve 34 between the sample exchange chamber 26 and the FIB sample chamber 17 and the gate valve 18 between the FIB sample chamber 17 and the plasma polymerization chamber 19 are opened, and the sample stage 14 is attached to the FIB sample by the sample exchange rod 33. The chamber 17 is moved onto the cathode electrode 20 of the plasma polymerization chamber 19. After the sample stage 14 is moved, the two gate valves 18 and 34 are closed after the sample exchange rod 33 is pulled out to the sample exchange chamber 26. Next, the gas introduction valve 22 is opened to introduce the gas in the gas cylinder 25 into the plasma polymerization chamber 19 from the gas introduction port 23, and a high voltage is applied between the cathode electrode 20 and the anode 21 by the high voltage power source 24. Plasma is generated between the anodes 21 to deposit a plasma polymerization film on the sample stage 14 on the cathode electrode 20.

  As described above, if the FIB apparatus according to the second embodiment of the present invention is used, FIB processing and deposition of a plasma polymerization film can be performed without taking out the sample outside the vacuum. Therefore, the TEM sample can be easily manufactured by the sample manufacturing method of the first embodiment, and the shape of the semiconductor device can be accurately evaluated without contraction of the low dielectric constant insulating film included in the sample. .

(Third embodiment)
Next, an FIB apparatus according to a third embodiment will be described with reference to FIGS. However, the description of the same part as the second embodiment is omitted.

  When the carbon film is deposited by the plasma polymerization method in the plasma polymerization chamber 19 of the present invention, the carbon film is deposited not only on the sample but also on the cathode electrode. If a carbon film is deposited, the problem that the discharge does not continue is expected. In a general single plasma polymerization apparatus, the cathode electrode is removed and cleaned each time a carbon film is deposited. However, in the TEM sample preparation method of the present invention, the deposition of the plasma polymerized film and the FIB processing are repeatedly performed. Therefore, if the cathode electrode is removed and cleaned and then evacuated again, the working efficiency becomes very poor. In order to solve this problem, the FIB apparatus in the third embodiment is configured as follows.

  4A and 4B show sample stage portions provided in the FIB apparatus according to the third embodiment of the present invention. FIG. 4A is a plan view and FIG. 4B is a front view. Reference numeral 14 denotes a sample stage, 15 denotes a sample, 35 denotes a negative electrode plate provided on the surface of the sample stage 14, 36 denotes an opening provided in the negative electrode plate 35, 37 denotes a rotary shaft, and 38 denotes a rotary arm.

  The sample 15 is set on the sample stage 14 so as to be positioned in the opening 36 of the negative electrode plate 35. As a result, when the sample 15 is subjected to FIB processing and plasma polymerization film formation, the processing and film formation are performed with the sample 15 exposed as shown in FIG.

  FIG. 5 shows a state in which the negative electrode plate 35 is cleaned after the FIB processing and the plasma polymerized film formation are completed. FIG. 5A is a plan view, and FIG. 5B is a front view. In order to clean the negative electrode plate 35, the surface of the negative electrode plate 35 is etched with an ion beam of FIB. In this case, as shown in FIG. As the rotary shaft 37 rotates, the rotary arm 38 rotates and the cathode plate 35 moves. In this arrangement, since the sample 15 is hidden under the negative electrode plate 35, the sample 15 is not contaminated when the negative electrode plate 35 is etched by the FIB ion beam.

  Thus, according to the third embodiment of the present invention, in addition to the FIB apparatus of the second embodiment, the cathode electrode can be cleaned without contaminating the sample in the FIB apparatus. FIB processing and deposition of a plasma polymerized film are possible, and a TEM sample can be efficiently manufactured by the sample preparation method of the first embodiment.

(Fourth embodiment)
Next, an FIB apparatus according to the fourth embodiment will be described. However, the description of the same part as the second embodiment is omitted. In the plasma polymerization chamber 19 of the present invention, when a carbon film is deposited by plasma polymerization, a gas is introduced into the plasma polymerization chamber 19 (see FIG. 3). After the film formation, the gas introduction is stopped and the evacuation is performed again. However, when the gate valve 18 is opened in order to move the sample stage 14 to the FIB sample chamber 17, the gas remaining in the plasma polymerization chamber 19 is in the FIB sample chamber 17. The problem that the degree of vacuum in the FIB sample chamber 17 decreases is expected.

  In order to solve this problem, the FIB apparatus in the fourth embodiment is configured as shown in FIG. The same components as those in the FIB apparatus in FIG. 3 are denoted by the same reference numerals, and the description thereof will not be repeated.

  In the FIB apparatus of FIG. 6, two gate valves 18 are provided between the FIB sample chamber 17 and the plasma polymerization chamber 19, and a gas adsorption chamber 41 is disposed. A cooling plate 40 cooled with liquid nitrogen 39 is disposed in the gas adsorption chamber 41.

  The cooling plate 40 can adsorb residual gas in the vacuum. When the gate valve 18 is opened to move the sample stage 14, the raw material gas remaining in the plasma polymerization chamber 19 is adsorbed by the cooling plate 40, and is thus prevented from flowing into the FIB chamber 17.

  Since the raw material gas remaining in the plasma polymerization chamber according to the fourth embodiment is adsorbed by the cooling plate provided between the gate valves, it does not flow to the FIB sample chamber, but rather than the FIB apparatus of the second embodiment. The FIB sample chamber can be kept at a high degree of vacuum.

  By using the configuration of the fourth embodiment in combination with the configuration of the third embodiment, a better sample shape evaluation can be obtained. That is, a more accurate shape evaluation can be obtained by using the FIB apparatus in which the second to fourth embodiments are combined.

  According to the sample preparation method using the focused ion beam apparatus of the present invention, for a semiconductor device having a low dielectric constant interlayer insulation film, deformation due to the shrinkage of the low dielectric constant interlayer insulation film is suppressed by the plasma polymerized film, so that it is accurate. Therefore, it is useful for evaluating a suitable shape of a semiconductor device and producing a stable semiconductor device.

Sectional schematic diagram showing a method for preparing a sample of a transmission electron microscope in the first embodiment of the present invention Cross-sectional schematic diagram showing the state of observation of a sample prepared by the sample preparation method with a transmission electron microscope Sectional schematic diagram showing a focused ion beam apparatus according to a second embodiment of the present invention. The sample stand of the focused ion beam apparatus in 3rd embodiment of this invention is shown, (a) is a top view, (b) is a front view. The operation | movement of the sample stand of the focused ion beam apparatus in the embodiment is shown, (a) is a plan view, (b) is a front view. Sectional schematic diagram showing the structure of the focused ion beam apparatus in the fourth embodiment of the present invention Schematic cross section showing a sample preparation method using a conventional focused ion beam device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Si substrate 2 Observation applicable part 3 Protrusion part 4, 4a, 4b, 4c Thin piece part 5 Plasma polymerized carbon film 6 deposited first time Plasma polymerized carbon film deposited second time 7 Electron beam 8 Liquid ion source 9 Extraction electrode 10 Ion beam 11 Focus lens 12 Objective diaphragm 13 Objective lens 14 Sample stage 15 Sample 16 Scan electrode 17 FIB sample chamber 18 Gate valve 19 Plasma polymerization chamber 20 Cathode electrode 21 Anode 22 Gas introduction valve 23 Gas introduction port 24 Power supply 25 Gas cylinder 26 Sample exchange Chambers 27, 28, 31 Vacuum pumps 29, 30, 32 Valve 33 Sample exchange rod 34 Gate valve 35 Cathode electrode plate 36 Opening portion 37 Rotating shaft 38 Rotating arm 39 Liquid nitrogen 40 Cooling plate 41 Gas adsorption chamber

Claims (11)

By processing the sample, a thin piece part including a desired observation point by a transmission electron microscope is formed,
After forming a thin film on the sample surface including the thin piece portion,
A sample preparation method for a transmission electron microscope, wherein the thin piece portion is processed by a focused ion beam to remove a part of the thin film from the thin piece portion, and is used as an observation sample of the transmission electron microscope.   The sample preparation method for a transmission electron microscope according to claim 1, wherein the thin film formation and the processing by the focused ion beam are repeated a plurality of times.   The method of claim 1, wherein the thin film is formed using a plasma polymerization method.   The said plasma polymerization method is a sample preparation method of the transmission electron microscope of Claim 3 which uses methane and ethylene as source gas.   The method of preparing a transmission electron microscope sample according to claim 1, wherein the thin film is made of carbon.   The sample preparation method for a transmission electron microscope according to claim 1, wherein the thin film has a thickness of 50 nm to 500 nm.   The transmission electron microscope sample preparation method according to claim 1, wherein the observation sample includes the thin film piece having a thickness of 500 nm or less. An ion source that generates ions;
An extraction electrode that applies a voltage to ions generated from the ion source to form an ion beam;
A lens for focusing the ion beam;
A lens that scans the ion beam;
A sample stage on which the sample is placed;
A sample chamber for processing the sample with the ion beam;
A focused ion beam apparatus comprising a plasma polymerization chamber connected to the sample chamber via a valve and forming a thin film on the sample by a plasma polymerization method. The plasma polymerization chamber holds the sample stage, and a sample stage holding part serving as a cathode;
An anode provided to face the sample stage holding unit;
A power source for applying a voltage between the sample stage holder and the anode;
The focused ion beam apparatus according to claim 8, further comprising a gas inlet for introducing a raw material gas for plasma polymerization into the plasma polymerization chamber. The sample stage is provided with an electrode plate that opens a portion on which the sample is placed,
10. The focused ion beam according to claim 9, wherein after the thin film is formed, the electrode plate is movable so as to shield between the sample placed on the sample stage and the anode. apparatus.   The focused ion beam apparatus according to claim 9 or 10, wherein a cooling plate cooled with liquid nitrogen is disposed between the sample chamber and the plasma polymerization chamber.

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