JPH09186210A - Observing method of section of integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an effect of an indented part of a surface from appearing in a section as a longitudinal stripe and thereby to enable attainment of an exact section, by tilting a sample at the time of processing the section at an arbitrary position of the sample and by forming the section in the direction vertical to a plane containing the axis of the tilt. SOLUTION: The position of contact of a sample LSI 1 to be observed is determined on the basis of a scanning ion microscope image and then a region 3 containing the contact is filmed by, an FIBCVD method. After filming, a sample stage is rotated so that the direction on the surface of the sample of a part of which the section is to be formed be at an angle of 90 deg. to the axis of the tilt, and then a square-shape hole is made 4 by an etching function, with the position 2 of the section to be observed made one side, by tilting the sample stage at an appropriate angle. Since FIB is cast obliquely on the sample 1 at the time of this processing of the section, a longitudinal stripe of the plane of the section due to steep indentation of the surface does not appear, and even when the effect thereof is produced, it is so small that only a few slant stripes are left, and thus an exact shape of the section is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing a specific position of a semiconductor device by cross-sectioning and observing it for defect analysis and the like.

[0002]

2. Description of the Related Art LSI (Large Scale Integrated Circuit) LSIs in the development process and manufacturing process are becoming more integrated and miniaturized.
A technique for performing the cross-section processing and cross-section observation of the above with a focused ion beam device is shown.

This is because the cross-section processed portion is positioned by the scanning ion microscope function, and the cross-section processed portion is made one surface by the maskless etching function to form a square hole to expose the desired cross-sectional portion, and then the sample is tilted. Then, the cross section is directed toward the ion beam irradiation direction, and the cross section processing section is observed again by the scanning ion microscope function.

[0004]

However, this method has a drawback in that the irregularities on the surface of the sample affect the cut cross-section, causing a phenomenon that vertical stripes run, making it difficult to obtain an accurate cross-sectional image. As one of the means for solving this problem, before the cross section cutting, the surface of the sample is FI in advance.
This can be solved by processing by BCVD (Focused Ion Beam Chemical Vapor Deposition) method and flattening, but in this case, since the sample surface is flattened, the wiring pattern is difficult to see on the scanning ion microscope image, and the processing place is It may be difficult to understand.

An object of the present invention is to provide a cross-section processing method which solves the above-mentioned drawbacks.

[0006]

The outline of the invention disclosed in the present application is as follows. Using the scanning ion microscope function, the section forming part of the sample,
Perform positioning. In some cases, next, a film is locally applied to a region including a cross-section processing position by a maskless etching function.

Next, the maskless etching function is used to form a square hole, so that one of the side walls of the hole is at the observed cross-sectional position. Next, the sample is rotated as needed and then tilted to perform cross-section processing so that a desired observation cross-section appears.

The sample is rotated and tilted in a direction in which the desired cross section can be observed, and the cross section of the machined hole is observed (including measurement and analysis) using the scanning ion microscope function. In addition, the rotation and tilt of the sample described above as the processing order is performed after the above (or after the above if the above is not executed), and then the square hole is drilled. At that time, one of the drilled holes is observed. The order of processing to obtain the desired cross-section position is also a solution.

With this structure, when the cross section of the sample is processed at an arbitrary position, the sample is tilted and the cross section is formed in the direction perpendicular to the plane including the tilt axis. Since it can be prevented from appearing, an accurate cross section can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining a method for processing a micro cross section of an LSI by an ion beam according to an embodiment of the present invention. FIG. FIG. 1 (b) is a diagram showing by hatching a region including the observation cross-section position 2 formed by the FIBCVD method, and FIG. 1 (c) is a diagram showing the sample stage of FIG. 1 (b). Fig. 1 (d) shows the sample stage tilted (right side up), and Fig. 1 (e) shows the observation position on one side due to the etching function. Figure with a square hole
(F) is a diagram showing a state in which the sample stage is rotated 90 ° counterclockwise with the sample stage tilted, and FIG. 1 (g) further tilts the sample stage (for example, to 60 °) to show the cross section in the ion beam irradiation direction. It is a figure which turned to the position which can be observed.

FIG. 2 (a) is a diagram showing an example of forming a cross section by a conventional processing method, and FIG. 2 (b) is a diagram showing an example of forming a cross section by implementing the present invention. FIG. 3 is a diagram of a focused ion beam apparatus and an image processing circuit used in the present invention. Here, 1 is LSI, 2 is cross-section processing position, 3 is FI
BCVD film deposition part, 4 hole forming part, 5 cross section,
6 is an insulating film, 7 is an upper layer wiring, 8 is a lower layer wiring, 9 is a Si substrate, 10 is a vertical stripe, 11 is a slight diagonal stripe, 21 is an ion barrel,
22 is a sample stage, 23 is a sample holder, 24 is a sample, 25 is a secondary charged particle detector, 26 is a gas gun, 27 is a vacuum chamber, 28 is a focused ion beam, 31 is a scanning control unit, 32 is an image acquisition / A reconstruction control unit, 33 is an image memory unit, 34 is an amplifier, and 35 is a display unit.

A sample L to be observed as shown in FIG.
The SI contact is positioned by a scanning ion microscope image. Next, as shown in FIG. 1B, the region 3 including the contact is film-formed by the FIBCVD method. In the FIBCVD method, the raw material gas is adsorbed on the sample surface by the gas gun 26,
This is a method of selectively forming a film only in the irradiation region by locally irradiating the ion beam 28 accelerated with the energy of 30 KeV. In this embodiment, a tungsten film is formed by using W (CO) ₆ as a source gas. doing. Of course, the present invention can be implemented by changing the gas and forming another metal film. If this film deposition is performed for a long time, the surface of the film deposition region of the sample is flattened, which makes it difficult to see the wiring pattern in the scanning ion microscope image. It will be easier. After applying this film,
As shown in (c), the sample stage is rotated so that the direction on the sample surface where the cross section is formed is 90 ° with respect to the tilt axis, and then the sample stage is rotated at an appropriate angle (for example, 45 °).
A square-shaped hole 4 is formed with the cross-sectional position 2 desired to be observed by the etching function being one side. Since the FIB is obliquely irradiated to the sample during this cross-section processing,
As shown in 10 of (a), the vertical stripes in the cut cross section due to the steep irregularities on the surface disappear, and even if there is an influence,
As shown by 11 in (b), the diagonal streaks are slightly left. Therefore, a more accurate cross-sectional shape can be obtained.

In this drilling, first, rough drilling is performed to secure a visual field, and finishing is performed in two steps, so that a quick and accurate cross-section processing is performed. Coarse drilling is done with a high current beam (eg 2n-6nA), and
The finishing process is performed by irradiating the cross-sectional position 2 to be observed with a medium current beam (for example, 2 nA to 30 nA) to form a steeply inclined side wall cross section 5.

In the above-mentioned embodiment, the sample is tilted and then the cross-section is formed, but the same end face can be obtained even if the sample is tilted and finished after rough drilling. Next, as shown in FIG. 1F, the sample stage is rotated so that the processed cross section of the sample is exposed in the ion beam irradiation direction, and the sample stage is further tilted within a range in which the field of view of the cross section can be secured. This cross section is observed by a scanning ion microscope with a relatively low current beam (for example, 2 nA to 30 nA).

Incidentally, when the abnormal portion such as a foreign matter whose cross section is to be observed is small, the cross section may be formed without filming. Even in such a case, a more accurate cross-sectional shape can be obtained by performing the above operation.

[0016]

According to the present invention, by tilting the sample at the time of forming the cross section as described above, it is possible to prevent the influence of the uneven portions on the sample surface from appearing as vertical stripes on the cross section. Therefore, a more accurate sectional image can be obtained.

[Brief description of the drawings]

FIG. 1 is a top explanatory view of an embodiment in which the method of the present invention is applied when observing a cross section of a contact portion between an upper layer wiring and a lower layer wiring of an LSI, and (a) shows one section position 2 of the LSI to be observed. The view shown by the chain line, (b) shows the hatched part of the region including the observation position 2 by FIBCVD, and (c) shows the sample rotated 90 ° clockwise by the rotating mechanism of the sample stage. FIG. 6D is a diagram showing the sample stage after being processed, FIG. 7D is a diagram in which the sample stage is tilted (right side is up), and FIG.
Shows a square hole with the observation position on one side by the etching function. (F) shows the sample stage in the counterclockwise direction.
FIG. 6G is a diagram showing the state after the rotation of ∘, and FIG. 7G is a diagram in which the sample stage is further tilted (for example, 60 °) and the cross section is directed to a position where it can be observed in the ion beam irradiation direction.

FIG. 2A is a diagram showing an example in which a cross section is formed by a conventional processing method, and FIG. 2B is a diagram showing an example in which a cross section is formed by carrying out the present invention.

FIG. 3 is a schematic diagram of a focused ion beam device and an image processing circuit used in the present invention.

[Explanation of symbols]

 1 LSI 2 Cross-section processing position 3 Film deposition part by FIBCVD 4 Drilling part 5 Cross-section 6 Insulating film 7 Upper layer wiring 8 Lower layer wiring 9 Si substrate 10 Vertical streak 11 Slight diagonal streak 21 Ion lens barrel 22 Sample stage 23 Sample holder 24 Sample 25 Secondary charged particle detector 26 Gas gun 27 Vacuum chamber 28 Focused ion beam 31 Scanning control unit 32 Image acquisition / reconstruction control unit 33 Image memory unit 34 Amplifier 35 Display unit

Claims (6)

[Claims] 1. The focused ion beam is applied to the cross section of the formed foreign matter by irradiating the cross section of the foreign matter of a sample which is an integrated circuit by irradiating the focused ion beam in a predetermined region where the cross section of the foreign matter to be observed is obtained. And observing foreign matter present in the sample, the method for observing a cross section of an integrated circuit. 2. The method for observing a cross section of an integrated circuit according to claim 1, wherein the observation of the foreign matter is an analysis of the foreign matter. 3. The cross-section of the foreign matter is performed by irradiating a focused ion beam in a predetermined region such that the foreign matter of the sample, which is an integrated circuit, has a desired cross-section, and the formed cross-section is irradiated with the focused ion beam. A method for observing a cross section of an integrated circuit, wherein the sample is tilted as described above, the cross section of the formed foreign matter is irradiated with the focused ion beam, and the foreign matter present in the sample is observed. 4. The method for observing a cross section of an integrated circuit according to claim 3, wherein the observation of the foreign matter is an analysis of the foreign matter. 5. A cross-section is processed in a predetermined region of the sample by irradiating a focused ion beam in a predetermined region such that the side wall of the surface of the sample which is an integrated circuit becomes a cross-section to be observed, and the formed cross-section is subjected to the A method of observing a cross section of an integrated circuit, which comprises irradiating a focused ion beam and analyzing and observing a cross section of the sample. 6. A cross-section is processed in a predetermined region of the sample by irradiating a focused ion beam in a predetermined region so that a side wall of the surface of the sample, which is an integrated circuit, becomes a cross-section to be observed, and the formed cross-section is focused. A method for observing a cross section of an integrated circuit, comprising inclining the sample so as to be irradiated with an ion beam, irradiating the focused ion beam on the formed cross section, and analyzing and observing the cross section of the sample.