JP2009025133A - Sample preparing method and sample preparing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a sample reduced in its surface unevenness in preparing a cross-sectional sample for use in observing TEM or SEM by an ion beam etching method, and to provide a sample preparing apparatus. <P>SOLUTION: In the sample preparing method and the sample preparing apparatus, the incident direction of an ion beam to the sample is changed by rotating the sample 1 or an ion gun 5 and the moving speed of the sample or ion gun in the case where an angle α is 30-90° and -30 to -90° is set to 1/3-2/3 of the moving speed in the case where the angle α is -30 to 30° to eliminate stripe-like surface unevenness produced by the ion beam etching method. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sample preparation method and a sample preparation device, and more particularly to a sample preparation method and a sample preparation device by ion beam etching.

  As a method for preparing a thin film sample used for transmission electron microscope (TEM) observation or a cross-sectional sample used for scanning electron microscope (SEM) observation, a shielding material is arranged on a part of the upper surface of the sample, and an unshielded portion is ionized. A method of removing by beam etching (hereinafter referred to as ion beam etching method) has been widely used in recent years (Patent Documents 1 to 3).

  When compared with other sample preparation methods such as the electrolytic polishing method, the ion milling method (Patent Documents 4 and 5), and the Ga focused ion beam processing method (Patent Document 6), the advantages of the ion beam etching method are as follows: When an oxide film or corrosion product does not adhere to the sample surface as in the electrolytic polishing method, and (2) When the ion beam is irradiated at an angle with respect to the sample observation surface as in the ion milling method, the sample surface layer In the above method, the ion beam is incident in parallel to the observation surface, so that damage is difficult to accumulate in the sample. (3) Since inert Ar gas is used, Ga focused ion beam processing is performed. As in the method, there is almost no ion implantation of the irradiated ion species, and (4) a simple sample preparation technique is not required as compared with other methods.

  However, it is inevitable that a sample produced by ion beam etching has streaky surface irregularities on the sample observation surface. Actually, a method of performing ion beam etching while rotating the sample so as not to form streak-like surface irregularities is used, but there is almost no effect. Such streaky surface irregularities are problematic because they greatly reduce the image quality in TEM observation and SEM observation.

Japanese Patent No. 3263920 JP-A-2005-37164 JP 2005-77359 A JP-A-4-268434 JP 61-139742 A JP-A-2-132345

  Accordingly, an object of the present invention is to provide a method and an apparatus for producing a sample with few streak-like irregularities on the sample surface when producing a cross-sectional sample used for observation of a TEM, SEM or the like by an ion beam etching method.

  The inventor changes the incident direction of the ion beam with respect to the sample by rotating the sample and / or moving the ion gun, and the incident angle of the ion beam with respect to the sample upper surface normal is a high angle (30 to 90 degrees and −30 to −30). 90 degrees), the sample rotation speed V1 is set to 1/3 to 2/3 of the sample rotation speed V2 or the ion gun movement speed V4 when the incident angle is a low angle (-30 to 30 degrees). Thus, the present inventors have found that streaky surface irregularities formed by a cross-sectional ion beam etching method can be eliminated, and the present invention has been completed.

The main points are as follows.
(1) A shielding material is arranged on a part of the upper surface of the flat sample, and an ion beam is irradiated from above the shielding material, leaving the sample portion shielded by the shielding material without ion etching, and the shielding material A sample preparation method for removing only a portion not shielded by ion etching by ion etching, wherein the sample is rotated while irradiating the ion beam, and an incident angle of the ion beam with respect to a sample upper surface normal is 30 to 90 degrees and The sample rotation speed V1 in the case of −30 to −90 degrees is set to 1/3 to 2/3 of the sample rotation speed V2 in the case where the incident angle is −30 to 30 degrees. Manufacturing method.
(2) The sample preparation method according to (1), wherein the incident angle of the ion beam with respect to the sample upper surface normal is changed by moving the position of the ion gun.
(3) A shielding material is disposed on a part of the upper surface of the flat sample, irradiated with an ion beam from above the shielding material, leaving the sample portion shielded by the shielding material without ion etching, and the shielding material A method of preparing a sample in which only a portion not shielded by ion etching is removed by ion etching, and the incident angle of the ion beam with respect to a sample upper surface normal is changed by moving the position of an ion gun, and the sample of the ion beam The ion gun moving speed V3 when the incident angle with respect to the upper surface normal is 30 to 90 degrees and −30 to −90 degrees is 1/3 of the ion gun moving speed V4 when the incident angle is −30 to 30 degrees. A method for preparing a sample, characterized in that ˜2 / 3.
(4) A shielding material is disposed on a part of the upper surface of the flat sample, irradiated with an ion beam from above the shielding material, leaving the sample portion shielded by the shielding material without ion etching, and the shielding material A sample preparation apparatus for removing only a portion not shielded by ion etching by means of ion etching, a sample rotating means for rotating the sample in a plane parallel to the ion beam, and a sample rotating speed changing means for changing the rotating speed of the sample And an angle detection means for detecting an angle formed by the ion beam incident direction and the sample upper surface normal.
(5) The sample preparation according to (4), further comprising position moving means for moving the position of the ion gun during ion beam irradiation, and moving speed changing means for changing the moving speed of the ion gun. apparatus.
(6) A shielding material is disposed on a part of the upper surface of the flat sample, irradiated with an ion beam from above the shielding material, and the sample part shielded by the shielding material is left without being ion-etched, and the shielding material A sample preparation apparatus that removes only a portion not shielded by ion etching by ion etching, a position moving means for moving the position of the ion gun during ion beam irradiation, a moving speed changing means for changing the moving speed of the ion gun, An angle detection means for detecting an angle formed by an ion beam incident direction and the sample upper surface normal line.

  According to the method and apparatus of the present invention, when a shielding material is arranged on a part of the upper surface of the sample and an unshielded part is removed by ion beam etching, a sample with less streaky surface irregularities on the sample observation surface can be produced. Thus, the image quality in the TEM or SEM is remarkably improved, and detailed observation / analysis of the sample is facilitated.

The present invention will be described below with reference to the accompanying drawings.
FIG. 1 is an overview of the apparatus. A flat sample 1 is placed in a vacuum sample chamber 2 and a shielding material 3 is placed on the upper surface of the sample. The shielding material 3 is disposed so as not to cover the entire upper surface of the sample but to have a part that is not partially shielded. Usually, it is desirable to expose the sample about 10 to 20 μm from the end of the shielding material (exposure width X shown in FIG. 2). The width W of the sample (FIG. 2) is not particularly limited, but since the ion beam irradiation region is about several hundreds μm to 1 mm, the region to be etched does not change even if it is larger than that. Further, as will be described later, in order to enhance the effect of removing the streaky irregularities due to the sample rotation, it is desirable that the area is smaller than the ion beam irradiation region.

  An inert gas 4 such as Ar is sent into the ion gun 5 to generate an ion beam, and the ion beam is irradiated from above the sample 1 and the shielding material 3. By removing an unshielded portion of the sample by etching by ion beam irradiation, a cross-sectional sample can be manufactured. Here, if the width of the shielding material is reduced, a thin film sample is obtained (FIG. 3).

  Although there is no restriction | limiting in particular in the magnitude | size of a shielding material, In order to observe as large an area | region as possible, it is desirable that it is wider than an ion beam irradiation area | region. The height Y (FIG. 2) of the shielding material is desirably about 0.5 mm to 5 mm. Since the shielding material is etched simultaneously with the sample, if the height of the shielding material is too low, the shielding material disappears before the removal of the sample by etching is completed. When adjusting the sample exposure width, the position is usually adjusted while looking at the optical microscope. However, if the height of the shielding material is too high, the difference between the focal position of the sample and the shielding material in the optical microscope observation is too large. , Position adjustment is difficult. That is, it is desirable that the height of the shielding material is as low as possible so that it does not disappear by etching. Therefore, the optimum height depends on the material of the shielding material and the etching time. The material is preferably as hard as possible, and Mo, Ta, W, etc. are suitable.

  When the irradiation angle of the ion beam with respect to the sample is constant, streaky irregularities parallel to the incident direction of the ion beam are formed on the observation surface 6. In order to reduce the streaky surface irregularities, the sample is usually subjected to in-plane rotation in a plane parallel to the observation surface 6 while irradiating an ion beam. The sample may be rotated continuously, or may be reciprocated in a certain angle range (for example, the angle α is in the range of 45 degrees to −45 degrees). However, when the sample rotation speed is constant, the degree of streaky surface unevenness is hardly reduced (FIG. 4).

  FIG. 4 is an SEM observation of a cross-sectional sample produced by Ar ion etching with a constant sample rotation speed (0.9 rpm). The ion gun was not moved, the sample was rotated in the range of −45 ° to 45 °, the acceleration voltage of the Ar ion beam was 5 kV, and the beam current was 150 μA. The shielding material is made of Mo and has a height of 1 mm. The sample is steel having the composition shown in Table 1. The time required for etching is 3 hours. In FIG. 4, the vertical streaks are the contrast due to surface irregularities. The horizontal stripe pattern represents the structure of the sample. It can be seen that the tissue is difficult to see due to the contrast caused by the surface irregularities.

  The cause of the occurrence of such streaky surface irregularities is unknown. However, it is certain that the direction of the ion beam with respect to the sample is related. For example, when etching is performed without rotating both the sample and the ion gun, streak unevenness parallel to the ion beam direction occurs remarkably. This is presumably because the hardness of the sample is not uniform and the ease of etching varies from place to place. Even when the sample or ion gun is rotated to change the incident direction of the ion beam to the sample, the direction of the streak in that case is parallel to the initial incident direction of the ion beam, that is, the incident direction when the rotation angle is 0 degree. . When the ion beam is first incident on the upper surface of the sample, irregularities are generated in a portion that is easily cut and a portion that is difficult to cut (FIG. 5). I don't know the reason, but it seems that the first surface irregularities are not a subsequent etching but become streaks.

  The inventor rotated the sample with streaky irregularities shown in FIG. 4 by 90 degrees and performed ion beam etching again. As a result, the first streaky irregularities disappeared, and the streaks parallel to the second ion beam direction disappeared. It was found that a concavo-convex shape was formed (FIG. 6). The conditions for the second ion etching are the same as the above conditions. The etching time was set to 3 hours as in the first etching.

  Furthermore, as a result of experimenting by changing the rotation angle and the etching time, when the rotation angle is less than 30 degrees, the first streaky unevenness disappears at least within the experimental time range (up to 5 hours). I found that there was no. However, in this experiment, since the streaky irregularities due to the second etching remain, the resulting sample is not suitable for tissue observation.

  Next, the experiment was repeated while changing the sample rotation speed. As a result, a condition was found for the streak to disappear. When the angle formed by the ion beam incident direction and the sample upper surface perpendicular is α, the range where α is 30 to −30 degrees is the low angle incidence, and the case where α is in the other angle range is the high angle incidence. When the sample rotation speed at high angle incidence is V1, and the sample rotation speed at low angle incidence is V2, the sample rotation speed is changed so that V1 is 1/3 to 2/3 of V2. As a result, the streaky surface irregularities on the observation surface, which are seen when the sample rotation speed is constant, can be greatly reduced. When V1 is less than 1/3 of V2, streaky irregularities in the direction of 45 ° obliquely with respect to the sample upper surface normal line were generated. When V1 is more than 2/3 of V2, streaky irregularities in the direction parallel to the sample upper surface normal line were generated.

  Changing the angle α can also be achieved by moving the ion gun without rotating the sample. What is important is the angle α indicating the positional relationship between the sample and the ion beam, and the same effect can be obtained by rotating the sample or moving the ion gun. FIG. 7 shows an apparatus configuration for rotating the ion gun. Whether the sample is rotated (FIG. 1) or the ion gun is rotated (FIG. 7), the rotation angle α must be controlled. As a method for controlling the rotation angle α, for example, it is possible to control the motor rotation speed. In the example of the apparatus shown in FIG. 1, the sample rotation can be realized by fixing the sample 1 to the sample table 7 with wax or the like and rotating the sample table. In the example of FIG. 7, the ion gun 5 can be moved by attaching the ion gun 5 to the support rod 12 and rotating the support rod 12. In any case, the rotation angle of the sample stage or the support bar is determined by the gear ratio of the gear 10 and the motor rotation speed. It is desirable to control the motor speed as closely as possible. For example, it is desirable to use a motor with a Hall IC type rotation detection function.

  In addition, it is desirable that the ion beam can always irradiate the same portion of the sample regardless of whether the sample is rotated or the ion gun is rotated. For this purpose, it is desirable to adjust the sample position so that the rotation axis 11 of the sample stage 7 and the ion gun support rod 12 is directly behind the etching region 6.

  The rotation speed of the sample or ion gun can be controlled by adjusting the voltage applied to the motor. There is an appropriate range for the rotational speed. If the rotation speed is too high, the vibration of the sample or ion gun becomes large, and the ion beam irradiation region may be shifted. If the rotation speed is too slow, the degree of streak unevenness increases, and the streak unevenness removal effect by controlling the rotation speed may be weakened. Therefore, about 0.1 rpm to 3 rpm is desirable at the sample rotation speed V2 at the low angle.

  As for the sample shape, when the sample width W is smaller than that of the ion beam irradiation region, the streaky irregularities can be more effectively removed. When the sample width W is larger than the ion irradiation region, an etching region and a region that is not etched are formed. When the sample or the ion gun is rotated, as the angle α formed by the ion beam incident direction and the sample upper surface normal becomes a high angle, the area that is behind the unetched area increases, and the etching area becomes narrower. Therefore, the sample width is suitably about the same as the diameter of the ion beam, that is, about 500 μm to 1 mm. The ion beam diameter varies depending on the acceleration voltage of the ion beam and the amount of beam current. Therefore, it is desirable to change the specimen size according to the acceleration voltage and beam current amount of the ion beam. However, even when the sample width W is larger than the ion beam irradiation region, the streaky irregularities can be removed if sufficient time is taken.

Example 1
Steel having the chemical composition shown in Table 1 was produced, and a test piece having the shape shown in FIG. 8 was produced by mechanical polishing.

  Thereafter, the sample was placed in an ion beam etching apparatus, a shielding plate was placed on the upper surface of the sample (FIG. 9), and an Ar ion beam was irradiated while rotating the sample. The acceleration voltage of the Ar ion beam was 5 kV, and the ion current amount was 110 to 120 μA. The size of the ion beam irradiation area was about 500 μm in diameter. In the sample rotation, the angle α (the angle between the sample upper surface normal and the ion beam) is reciprocated in the range of 45 to −45 degrees, the rotation speed V2 in the range of α to 30 to −30 degrees is set to 2 rpm, and α is 30. The rotational speed V1 in the range of -45 degrees and -30 to -45 degrees was set to a value in the range of 0.5 to 1.8 rpm. Irradiated with an ion beam for 3 hours to prepare a cross-sectional sample.

  FIG. 10 shows the result of SEM observation of a sample manufactured under the condition of V1 = 1 rpm. The streaky surface irregularities as seen in FIG. 4 are hardly observed. SEM observation was also performed on samples prepared with each value of V1, and it was determined whether or not streak irregularities were observed. The results are summarized in Table 2.

  When V1 is more than 2/3 of V2, the effect of reducing vertical streaks is not observed. When V1 becomes less than 1/3 of V2, it has been confirmed that diagonal streak irregularities can be seen this time.

(Example 2)
The steel used in Example 1 was formed into a test piece having the shape shown in FIG. Similar to Example 1, a sample was placed in an ion beam etching apparatus, a shielding plate was placed on the upper surface of the sample (FIG. 12), and an Ar ion beam was irradiated while rotating the sample. The ion acceleration voltage and the ion current amount are the same as those in the first embodiment. The sample was rotated reciprocally in the range of α from +90 to −90 degrees. A cross-sectional sample is prepared by changing the sample rotation speed V1 at the time of high-angle ion beam irradiation and the sample rotation speed V2 at the time of low-angle ion beam irradiation, and whether or not streak irregularities are observed in the prepared sample is SEM. Judgment was made by observation.

  The results are summarized in Table 3. As in Example 1, when V1 is 2/3 or more of V2, no effect is seen, and when V1 is less than 1/3 of V2, diagonal streaks are observed.

(Example 3)
The steel used in Example 1 was formed into a test piece having the shape shown in FIG. As in Example 2, the sample was placed in the ion beam etching apparatus, a shielding plate was placed on the upper surface of the sample (FIG. 12), and the ion gun was rotated as shown in FIG. Ion beam irradiation. The ion acceleration voltage and the amount of ion current are the same as in the first embodiment. The ion gun was rotated in a reciprocating manner within a range of α of 90 to −90 degrees. Whether a cross-sectional sample is prepared by changing the ion gun moving speed V3 at the time of high-angle ion beam irradiation and the ion gun moving speed V4 at the time of low-angle ion beam irradiation, and whether or not streak unevenness is observed in the prepared sample Was determined by SEM observation.

  The results are summarized in Table 4. As in Examples 1 and 2, when V3 was more than 2/3 of V4, no effect was observed, and when V3 was less than 1/3 of V4, streaky irregularities in an oblique direction were observed.

Example 4
The steel used in Example 1 was formed into a test piece having the shape shown in FIG. Similar to the third embodiment, the sample is placed in the ion beam etching apparatus, a shielding plate is placed on the upper surface of the sample (FIG. 12), and both the sample and the ion gun are rotated as shown in FIG. Was irradiated. The ion acceleration voltage and the ion current amount are the same as those in the first embodiment. The sample and the ion gun were rotated at the same rotational speed in the range of 45 to -45 degrees in the opposite direction so that the angle α formed by the sample and the ion beam changed in the range of 90 to -90 degrees. In FIG. 13, when the angle between the sample upper surface normal Ls and the apparatus axial direction L is αs, and the angle between the ion gun axial direction Lg and the apparatus axial direction L is αg, the angle α between the sample and the ion beam is α = αs + αg. The change speed V of the angle α can be defined by the sum Vs + Vg of the rotation speed Vs of the sample and the rotation speed Vg of the ion gun. The change rate V5 of the angle α when the angle α between the sample and the ion beam is high (30 to 90 degrees and −30 to −90 degrees), and the change speed V6 when the angle α is low (−30 to 30 degrees). A cross-sectional sample was prepared by changing the above, and it was determined by SEM observation whether or not streaky irregularities were observed in the prepared sample.

  The results are summarized in Table 5. As in Examples 1 and 2, when V5 is more than 2/3 of V6, no effect is observed, and when V5 is less than 1/3 of V6, streaky irregularities in an oblique direction can be seen.

It is an external view of this invention apparatus. It is an example of the shape of the sample and shielding material used by this invention. It is an example (for thin film sample preparation) of the sample and shielding material used by this invention. This is an example of cross-sectional sample observation when the sample rotation speed is constant. It is an estimation schematic diagram of the generation mechanism of a stripe pattern. It is an external appearance schematic diagram in the case of rotating a streak pattern sample 90 degrees and performing ion etching. It is an external view of this invention apparatus. 3 is an explanatory diagram for explaining the shape of a test piece used in Example 1. FIG. It is explanatory drawing for demonstrating the shielding condition in Example 1. FIG. It is a cross-sectional sample observation example when changing the sample rotation speed. It is explanatory drawing for demonstrating the shape of the test piece used in Example 2, 3, and 4. FIG. It is explanatory drawing for demonstrating the shielding condition in Example 2, 3, 4. FIG. It is an external view of this invention apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample 2 Vacuum sample chamber 3 Shielding plate 4 Inert gas 5 Ion gun 6 Etching area 7 Sample stand 8 Motor 9 Ion beam 10 Gear 11 Rotating shaft 12 Support rod

Claims (6)

A shielding material is arranged on a part of the upper surface of the flat sample, and an ion beam is irradiated from above the shielding material, leaving the sample portion shielded by the shielding material without ion etching, and shielded by the shielding material. A sample preparation method that removes only the unexposed portion by ion etching,
Rotating the sample while irradiating the ion beam; and
The sample rotation speed V1 when the incident angle of the ion beam with respect to the sample upper surface normal is 30 to 90 degrees and −30 to −90 degrees, and the sample rotation speed V2 when the incident angle is −30 to 30 degrees. A method for preparing a sample, characterized by being 1/3 to 2/3.   The sample preparation method according to claim 1, wherein the incident angle of the ion beam with respect to the sample upper surface normal is changed by moving the position of the ion gun. A shielding material is arranged on a part of the upper surface of the flat sample, and an ion beam is irradiated from above the shielding material, leaving the sample portion shielded by the shielding material without ion etching, and shielded by the shielding material. A sample preparation method that removes only the unexposed portion by ion etching,
By changing the position of the ion gun, the incident angle of the ion beam with respect to the sample upper surface normal is changed, and
The ion gun movement speed V3 when the incident angle of the ion beam with respect to the sample normal is 30 to 90 degrees and -30 to -90 degrees, and the ion gun movement speed when the incident angle is -30 to 30 degrees. A method for preparing a sample, wherein V3 is 1/3 to 2/3. A shielding material is arranged on a part of the upper surface of the flat sample, and an ion beam is irradiated from above the shielding material, leaving the sample portion shielded by the shielding material without ion etching, and shielded by the shielding material. A sample preparation device that removes only the unexposed portion by ion etching,
Means for rotating the sample in a plane parallel to the ion beam;
Sample rotation speed changing means;
An angle detection means between the ion beam incident direction and the sample upper surface normal,
A sample preparation apparatus comprising: Means for moving the position of the ion gun during ion beam irradiation;
Means for changing the moving speed of the ion gun;
The sample preparation apparatus according to claim 4, further comprising: A shielding material is arranged on a part of the upper surface of the flat sample, and an ion beam is irradiated from above the shielding material, leaving the sample portion shielded by the shielding material without ion etching, and shielded by the shielding material. A sample preparation device that removes only the unexposed portion by ion etching,
Means for moving the position of the ion gun during ion beam irradiation;
Means for changing the moving speed of the ion gun;
An angle detection means between the ion beam incident direction and the sample upper surface normal,
A sample preparation apparatus comprising: