JP4392272B2 - TEM sample preparation method - Google Patents

Description

  The present invention relates to a method for cutting and creating a sample for observing a desired portion of a semiconductor wafer or the like with a transmission electron microscope (TEM) using a focused ion beam (FIB) apparatus.

  In order to observe a cross section of a semiconductor wafer with a TEM, it has been conventionally performed that a sample is cut out by locally making a hole by etching using FIB without breaking a material such as a wafer. In this method, as shown in FIG. 5 (a), a protective film is first formed by FIB-CVD on a processed portion of sample 1 (wafer), and then, as shown in FIGS. A focused ion beam is irradiated from above the surface, and both sides of the observation cross section 2 are removed by etching to form square front holes 3 and rear holes 4. The size of the hole is such that the front hole 3 tilts the sample stage and the observation cross section can be observed with a scanning ion microscope. The rear hole 4 has the same width as the front hole 3 and the depth is about 2/3. Drilled. The sample surface is tilted to scan the focused ion beam as shown by the arrow as shown in FIG. In order to prevent the positional deviation of the thinned sample at the time of processing, it is necessary to leave an unprocessed part in the peripheral part of the cutting process. Then, after the cutting process, the thin sample is moved and adhered onto an arbitrary mesh by a probe operated by a micromanipulator, the sample surface is returned to the original state, and a beam is irradiated from above the sample surface to further reduce the thickness. The TEM observation sample is completed to complete the TEM observation sample. However, since the sliced sample before transporting remains a part of the connection that has not been cut, this part is finally ready for transport. The section sample is transported after cutting by etching or by physically folding the probe by moving it. The probe holds and holds the section mainly by FIB-CVD, but when the section sample is cut or folded, the section sample rebounds or the positional relationship between the probe and the sample moves due to drift, and the probe is separated from the probe. There was a habit of losing. In addition, there is a similar possibility when section bonding by FIB-CVD is insufficient, and once lost, it is an extremely small piece that cannot be found, and a series of work will be attributed to water bubbles Become.

  Patent Document 1 proposes a processing method that can securely hold a glass probe after the thinning finish processing and stably place a sample for TEM observation by transferring and placing on a mesh. As a problem, a focused ion beam is irradiated onto the wafer-shaped sample from above the sample surface, and both sides of the observation cross section are etched, and the sample surface is tilted in a state where the thinning has progressed moderately to focus on the thinned sample. Scan the ion beam, cut at least the bottom (shown as a bottom cut in FIG. 4A), return the sample surface to the original, and irradiate the focused ion beam from above to make a thin slice. Processing. When this finishing process is completed, both sides that have not been cut are irradiated with a focused ion beam from above the sample surface to perform the cut process (shown as a side cut in FIG. 4B). Is disclosed. In this method, after finishing the sample surface, the position of beam irradiation in the direction of the thin piece is positioned near both ends of the thin piece, and the remaining both sides are cut. In this case, the section sample is completely separated from the wafer, and there is no need to fold the connection portion and pick up. Therefore, if the work is proceeding as planned, there will be no problem that the slice sample will be splashed and lost as in the conventional case, but this separation process is performed by one point irradiation of the ion beam. It is not possible to work while confirming with a scanning ion microscope (SIM) image whether the sample is completely separated from the wafer. Further, since the thinning process is performed before separation from the wafer, the thin piece portion is distorted and bent, or the thin piece may splash and be lost at the time of separation.

Therefore, the applicant separates the observation area from the wafer in the form of fine blocks or fine plate-like pieces before thinning and transfers them to the block-like sample fixing table with a micromanipulator and fixes them. A method for executing the chemical processing is presented and is filed as Japanese Patent Application No. 2003-157120. As shown in FIG. 3, a fine block is cut out from a large sample main body, and this is transferred and fixed on a sample fixing table, and then thinning is performed by FIB etching. According to this method, there is no fear that the section will be splashed and lost, and there is no fear that the sample observation surface will be damaged by the ion beam at the time of cutting after finishing. Since the cutting process is the work of performing the FIB scan in the processing frame and etching, the SIM image of the entire cutting area cannot be observed, and the FIB-CVD fixing state during transportation and the information on the cutting state by etching are not available. Can't get. Therefore, when picking up the cut-out piece, it must be performed in a place where it has not been confirmed whether or not the separation from the sample body has been completed, and there are problems in terms of work efficiency and stability.
Japanese Patent Laid-Open No. 2001-141620 “Incision Processing Method for Sample for Transmission Electron Microscope” Published on May 25, 2001 Japanese Patent Application No. 2003-157120 “Pickup sample vertical positioning method and sample with vertical mark”

  The problem to be solved by the present invention is that a TEM sample is cut out from a large sample main body such as a wafer by using an FIB apparatus, and the detachment state is not lost due to splashing at the time of separation. An object of the present invention is to present a technique that can be reliably transferred to a fixed base by a probe of a manipulator while observing and confirming with an image.

  The TEM sample preparation method of the present invention includes a step of forming a plate-like cut piece and a support portion supporting the cut piece in a large sample body by FIB etching, and a vertical pillar by FIB-CVD on the shoulder of the cut piece. Cutting the section from the sample body by FIB etching, operating the micromanipulator while observing the SIM image, and applying the load by bringing the tip of the probe into contact with the tip of the pillar and applying the load. A step of confirming separation from the sample body, a step of fixing the tip of the contacted probe and the tip of the pillar by FIB-CVD, and a section cut by operating the micromanipulator while observing a SIM image And a step of transferring to a fixed base.

  In the TEM sample preparation method of the present invention, since the plate-shaped cut section is formed in a form supported by the support portion, the cut section can be completely separated from the sample main body by FIB etching. In addition, the sample will not splash and be lost or fallen over, making it difficult to handle.

  In the TEM sample preparation method of the present invention, after the cut section is cut from the sample body by FIB etching, the micromanipulator is operated while observing the SIM image to bring the tip of the probe into contact with the tip of the pillar. Can be observed with a SIM image, so that it can be confirmed that the sample is completely separated, contact information with the probe, and the like. Further, when the tip of the probe and the tip of the pillar are brought into contact with each other, the completely separated sample moves, so that damage to the probe tip can be reduced. Even if the tip of the probe and the tip of the pillar are fixed, an excessive load is not applied when the sample drifts, and the tip of the probe and the sample are not damaged or splashed off.

  In general, the above-described effects can be stably handled by the TEM sample preparation method of the present invention, so that the burden on the operator can be reduced and operational errors can be reduced.

  In the TEM sample preparation method of the present invention, first, a region to be observed in a cross section in a large sample body such as a semiconductor wafer is specified, and a thin film portion that becomes a plate-shaped cut section including the region and its end are formed. A film thickness portion serving as a support structure for supporting the cut section is formed by FIB etching. The length of the thin film portion to be a plate-shaped cut piece is about 30 μm × height 10 μm × width 5 μm. The thickness of the width is a thickness necessary for mounting on the sample fixing base and is too thick for a TEM sample. The support structure that supports the cut-out piece is configured to sandwich the plate-like cut-out piece in the longitudinal direction with a gap.

  1A to 1F show a method for processing a cut section according to the present invention.

  As shown in FIG. 1A, a region A is formed as a rear hole 4 by FIB etching in a rear portion of a portion (hereinafter referred to as a cross-sectional observation region) 2 serving as a cross-sectional observation region. The hole surface at this time is processed at a distance of about 7 to 8 μm from the cross-sectional observation region 2 in order to form a support structure which is a film thickness portion. Subsequently, a region of about 10 μm is left from one longitudinal side surface of the rear hole 4, and another region is further drilled as a rear hole 4 to a distance of about 3 to 4 μm from the cross-sectional observation region 2 by FIB etching. This processed surface becomes the back side surface of the plate-shaped cut section. Next, the front side machining is performed, which is almost the same as the rear side machining. That is, a region C is formed as a front hole 3 in the front portion of the cross-sectional observation region 2 by FIB etching. However, the depth of the front hole 3 needs to be dimensioned so that beam irradiation is possible (about 30 μm) when the sample stage is tilted and bottom cut is performed as described later. This etching process is performed at a distance of about 7 to 8 μm from the cross-sectional observation region 2 to form a support portion. Subsequently, about 10 μm is left from the same longitudinal side surface as the rear side, and the other region is further drilled as a front hole 3 to a distance of about 3 to 4 μm from the cross-sectional observation region 2 by FIB etching. This processed surface becomes the front side surface of the plate-shaped cut piece.

  In the above-described etching operation, the procedure of i → b → c → d was explained. However, the present invention is not limited to this, and those skilled in the art will be able to perform processing by an appropriate procedure such as c → d → b → b. Easy to understand. Moreover, the dimension value shown here is one standard, and it is only necessary to construct a support structure that supports the cut section, and there is no special numerical limitation.

  Next, the sample stage of the FIB apparatus is tilted to form a support portion, and the portion shown in FIG. 1B, which is the lower portion of the region left with a thickness of about 15 μm and a size of about 10 μm from one side surface. The region is a region where the bottom is shaved by a bottom cut performed when the bottom side of the plate-shaped cut piece is separated from the sample body in a later step. A similar process is also created on the rear side during bottom cut. That is, it is scraped off from the cross-sectional observation region 2 to a distance of about 3 to 4 μm by FIB etching at the time of bottom cut as in the other regions. FIG. 1C shows a plan view of this processing region viewed from above. The left side of the portion processed into a plate shape is formed thicker, and the lower portion thereof is separated into regions E and F as indicated by broken lines. However, at this point, the portion that becomes the plate-shaped cut piece and the portion that becomes the support structure remain in an integrated structure with the sample body. At this stage, the bottoms of the regions (e) and (b) may be cut in advance by about 3 to 4 μm by FIB etching.

  In the next step, the sample stage is returned to the horizontal position, and the FIB is irradiated from above to separate the plate-shaped cut section and the support section. As shown in FIG. 1D as a region G, the portion left by the thickness of about 15 μm with a dimension of about 10 μm from one longitudinal side surface for forming the support section is shown in the cross section direction on both sides of the cut section. A U-shaped cut formed by a side perpendicular thereto is processed by FIB etching and penetrated to a depth at which regions e and f are formed. By this processing, a plate-shaped cut piece and the support portion 6 are separated. In the figure, the portion that is the sample body 1 is a support portion, and the portion that is sandwiched with a gap in the support portion is a plate-shaped cut piece. Subsequently, a groove process is performed to separate the side portion on the other side of the plate-shaped cut piece from the sample body 1 as shown in FIG. At this point, the plate-shaped cut piece still maintains an integral structure with the sample body at the bottom.

  At this point in time when the cut-out section still maintains an integral structure with the sample body, a pillar (see E in FIG. 1) extending in the vertical direction is preferably formed by FIB-CVD on the shoulder of the cut-out section. Since this pillar has a height, not only is the probe easy to approach when the sample falls slightly due to a bottom cut, but also the surface of the observation cross section 2 as a contact arm that does not damage the sample or in a cut section separated from the sample body 1 It functions effectively as an indicator of direction. As the next step, the sample stage is tilted, and the bottom side of the cut section is scanned by irradiating FIB from the direction of the front hole 3 to perform bottom cut by FIB etching. At this time, a bottom cut is also made. In the present invention, since a support part is provided for holding both side surfaces in the longitudinal direction of the plate-like cut-out section, the cut-out section does not fall down even if it is completely separated from the sample body 1 and is held in a standing state. Is done. Therefore, it is not necessary to leave a connection part with the sample body partially. This is the most important feature of the present invention. In the following operations, various advantages are produced, and handling during pickup can be performed stably, reducing the burden on the operator and making TEM sample preparation work. Can reduce mistakes.

  At this point in time when the cut-out section to be picked up is completely separated from the sample body 1, all FIB processing for the cut-out section necessary until the pickup is completed. Therefore, the FIB apparatus can be simply operated in the SIM mode, and the pickup operation can be performed while observing with a microscope. The micromanipulator is operated to bring the tip of the probe into contact with the tip of the pillar formed on the shoulder of the sample (or the shoulder when the pillar is not raised). At this time, it is confirmed by observing that the cut section moves. If the cut section does not move, it means that the previous bottom cut is insufficient and the sample body 1 has not been completely separated, so the operation is repeated. When the separation is confirmed, the SIM mode is interrupted once, and the tip of the probe and the tip of the pillar of the sample (shoulder when no pillar is raised) are fixed by FIB-CVD. In the case of a section that has undergone slicing processing, it can be held by electrostatic force even if it is not fixed, but in the case of a plate-shaped cut section before slicing processing, it can be securely held by the probe tip, It is good because the sample direction is fixed and stable. When this operation is completed, the SIM mode is restored, the micromanipulator is operated, the cut slice is picked up from the sample body 1, transferred to the sample fixing table, and placed and fixed on the sample fixing table. The following operations are performed by the method disclosed in Patent Document 2 as shown in FIG. That is, if a pillar is formed, check the angle of the sample observation cross section using it as an index, fix it to the sample fixing base so that the observation cross section direction is vertical, cut the pillar by FIB etching, and remove the probe and sample. The TEM sample is completed by cutting off without damaging and performing thinning by FIB etching.

  The microscope picture of each process of the TEM sample actually produced by the above-described procedure of the present invention is shown in FIG. First, A in FIG. 2 is a microscopic observation image of a processed state at the time when the process up to the paragraph number [0008] described above is completed, and corresponds to the plan view of D in FIG. It can be confirmed that the support portion connecting the left side of the central plate-shaped cut section to the sample body 1 is sandwiched with a gap, and the right side is also separated from the sample body 1 by the groove.

  FIG. 2B is an image when the bottom cut is finished and the micromanipulator is operated to move the probe tip to contact the pillar tip. Since the operation can be executed while observing the microscope image in this way, the operator's operation is very easy. This image is a viewing angle image having an inclination with respect to the surface of the sample body 1.

  C in FIG. 2 is a microscope observation image at the time when the pickup is started after the probe tip and the pillar tip are fixed. In this microscopic image, the connecting portion between the probe tip and the pillar tip appears to be in the form of a block, which indicates that it is fixed by deposition formed by FIB-CVD. D in FIG. 2 is a microscopic image at the time when the pickup is advanced and the cut sample is also removed from the support structure. E in FIG. 2 is a microscopic image when the micromanipulator is operated and the cut section is transferred to the sample fixing table, and F in FIG. 2 observes the state at this time from above the surface of the sample main body by changing the viewing angle. This is a microscopic image. In this F image, it can be seen that the cut section is picked up and an empty hole is left in the sample body 1.

  As is apparent from the above description, according to the present invention, the conventional difficulty and complexity in picking up a TEM sample are overcome, and the present invention greatly contributes to the improvement in yield in TEM sample preparation. Obviously, the present invention is not limited to this, and can be widely applied to the processing and handling of other micro (nano) devices.

It is a figure explaining the procedure by this invention which cuts a plate-shaped sample slice from a sample main body. It is a SIM observation image when the plate-shaped sample section | slice produced by implementing this invention is picked up from the sample main body. It is a figure which shows the procedure which performs the finishing process after picking up a plate-shaped sample slice. It is a figure explaining the conventional method of implementing the thinning process before pick-up. It is a figure explaining the conventional method of cutting out and processing a sample section from a sample main part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample main body 2 Cut-out section 3 Front hole 4 Back hole 5 Probe 6 Support structure 7 Sample fixing stand

Claims (6)

Creating a plate-like cut section in a large sample body and a support portion that has a gap with respect to the side surface in the longitudinal direction of the cut section and prevents collapse of the cut section by FIB etching;
A step of disconnecting from said sample body the cutout sections in FIB etching,
Operates the micromanipulator under SIM image observation, a force applied from the probe to the cutout sections, TEM sample preparation method comprising the steps of the cutout sections to ensure that the detached from the sample body. Creation of a support portion that has a gap with respect to the side surface in the longitudinal direction of the cut-out section and prevents the cut-out section from collapsing is performed by forming a U-shaped cut across the end face and the side face of the cut-out section. The TEM sample preparation method according to claim 1, wherein the TEM sample is formed by FIB etching . Wherein the cut sections before disconnecting from the sample body with FIB etching, the TEM sample preparation method according to claim 1 or 2 in the shoulder part of the cut sections is intended to take the step of forming a vertical pillar FIB-CVD.   4. The TEM sample preparation method according to claim 3, wherein a force is applied to the cut section by applying a force from the probe to the vertical pillar. In the step of confirming that it is disconnected ,
After confirming that are disconnected, the step of fixing the tip and the pillar tip of the probe in FIB-CVD,
The TEM sample preparation method according to claim 4 , further comprising: operating a micromanipulator under SIM image observation and transferring the cut section to a fixed table. Creating a plate-like cut section in a large sample body and a support portion that has a gap with respect to the side surface in the longitudinal direction of the cut section and prevents collapse of the cut section by FIB etching;
Forming a vertical pillar on the shoulder of the cut section by FIB-CVD;
Separating the cut section from the sample body by FIB etching;
Ascertaining that operates the micromanipulator under SIM image observation, the cut section is disconnected from the sample body by applying a force to the pillar by contacting the pillar tip and the tip of the probe,
Fixing the tip of the probe brought into contact with the tip of the pillar by FIB-CVD;
Operates the micromanipulator under SIM image observation, detach sections comprising a step of transferring the fixing table a TEM sample preparation methods.