JPH03166744A - Microprocessing method for cross section - Google Patents

Abstract

PURPOSE:To prevent the influence of an uneven part on the surface of a sample from exhibiting as a vertical stripe on a section and to obtain an accurate sectional image by inclining the sample when the section is formed. CONSTITUTION:After a film 3 is adhered, a sample stage is so rotated that the direction of the part to be formed with a section becomes 90 deg. with respect to an oblique axis, the stage is then inclined at a suitable angle (e.g. 45 deg.), and a hole 4 of a square shape is opened with a sectional position 2 to be desirably observed in an etching function as one side. Since an FIB is obliquely emitted to a sample at the time of processing the section, no vertical stripe due to an abrupt uneven part of the surface is formed. Thus, an accurate sectional shape is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for processing a cross section of a specific position of a semiconductor device for failure analysis or the like. [Prior art] With the increasing integration and miniaturization of LSIs (large-scale integrated circuits), a technology has been proposed that uses focused ion beam equipment to perform cross-sectional processing and cross-sectional observation of LSIs during the development and manufacturing processes. There is.

This involves locating the cross-sectional area using the scanning ion microscope function, then drilling a rectangular hole in the cross-sectional area using the maskless etching function to expose the desired cut-off area, and then tilting the sample. This is a technique in which the cross-section is oriented in the direction of ion beam irradiation and the cross-section processed portion is observed again using the scanning ion microscope function.

[Problem to be solved by the invention]

This method has the drawback that the unevenness of the sample surface affects the cut cross section, causing vertical streaks to occur, making it difficult to obtain accurate cross-sectional images.

One way to solve this problem is to flatten the surface of the sample by processing it using FIBCVD (focused ion beam chemical vapor deposition) before cutting the cross section. As a result, the wiring pattern may be difficult to see on a scanning ion microscope image, making it difficult to identify the processing location.

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

[Means to solve the problem]

The outline of the invention disclosed in this application is as follows. ■Using the scanning ion microscope function to scan a certain section of the sample,
Perform positioning.

(2) Depending on the situation, a maskless etching function is then used to locally apply a film to a region including the cross-sectional processing position.

■Next, use the maskless etching function to drill a rectangular hole so that one of the side walls of the hole is at the observed cross-sectional position. (2) Next, tilt the sample about 1 and process the cross section so that the desired observation cross section appears.

(2) Rotate and tilt the sample in a direction in which the desired cross section can be observed, and use the scanning ion microscope function to observe the cross section of the machined hole (including measurement and analysis).

In addition, as for the processing order, rotate and tilt the sample as described in the above ■ after the above ■ (if the above ■ is not performed, after the above ■), then drill a square hole. A method of solving the problem can also be achieved by changing the processing order so that one of the cross-sections is located at the desired cross-sectional position.

[Effect]

When processing a cross section at an arbitrary position on a sample, tilt the sample and form a cross section perpendicular to the plane that includes the tilt axis to prevent the effects of surface irregularities from appearing as vertical streaks on the cross section. This allows you to obtain accurate cross sections. [Example] Fig. 1 shows an example of the present invention, in which L by an ion beam is
This is a diagram for explaining the SI micro-section processing method, and the first
Figure (a) is a diagram showing the cross-sectional position 2 of the LSI to be observed with a dashed-dotted line; Figure tel is a diagram showing the sample in Figure 1 fbl after it has been rotated 90' clockwise by the rotation mechanism of the sample stage, Figure 1 fdl is a diagram with the sample stage tilted (amplifier on the right side), Figure 1 (e) is a diagram in which a rectangular hole is made using the etching function, with the observation position as one side;
fl is a diagram after rotating the sample stage 90 degrees counterclockwise with the sample stage tilted, and Figure 1 1gl is a diagram showing the sample stage further tilted (to 60', for example), and the cross section is observed in the ion beam irradiation direction. It is a view facing the possible position.

FIG. 2 fa+ is a diagram showing an example of a cross section formed by a conventional processing method, and FIG. 2 bl is a diagram showing an example of a cross section formed by implementing the present invention.

Figure 3 is a diagram of the focused ion beam device and image processing circuit used in the present invention. Here, 1 is L51.2 is the cross-sectional processing position, 3 is the film attachment part by FIBCVD, 4 is the hole punching part, 5 is the cross section, 6 is the insulating film, 7 is the upper layer wiring, 8 is the lower layer wiring, 9 is the Si substrate, 10 is a vertical stripe, 11 is a slight diagonal stripe, 21 is an ion column, 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, and 27 is a vacuum chamber. , 28 is an ion beam, 31 is a scanning control section, 32 is an image capture/reconstruction control section, 33 is an image memory section, 34 is an amplifier, and 35 is a display section.

As shown in FIG. 1(a), the contacts of the sample LSI to be observed are located using a scanning ion microscope image. Next, as shown in FIG. 1 (bl), a film is deposited on the region 3 including the contact by the FIBCVD method.

The FIBCVD method is a method that selectively forms a film only in the irradiated area by adsorbing a source gas on the sample surface using a gas gun 26 and locally irradiating it with an ion beam 28 accelerated with an energy of 20 to 30 κeV. In this example, W(Go)i is used as the raw material gas and a tungsten 1 model is used. Of course, the present invention can also be practiced by changing the gas and forming other metal films. If this film is applied for a long time, the surface of the film-applied area of the sample will be flattened, making the wiring pattern difficult to see on a scanning ion microscope image. Therefore, it is better to finish the film application before it is flattened to prevent cross-sectional formation. It becomes easier. After this film is deposited, as shown in Figure 1 fcl, the direction of the section to be formed on the sample surface is 99 with respect to the tilt axis.
Rotate the sample stage so that the angle is
A rectangular hole 4 is made using the etching function with the cross-sectional position 2 to be observed as one side.

During this cross-section processing, the FIB is irradiated obliquely onto the sample, so vertical streaks due to steep surface irregularities will not appear on the cut cross section, as shown by 10 in fat in Figure 2, and even if they are affected, as shown in Figure 2. Only a slight diagonal streak remains as shown by 11 in fbl. Therefore, a more accurate cross-sectional shape can be obtained.

This drilling process is performed in two stages: first, rough drilling to ensure visibility, and then finishing, which allows for quick and accurate cross-sectional processing. Rough drilling is done with a high current beam (e.g. 29A to 6p^), and finishing is performed by irradiating the cross-sectional position 2 to be observed with a medium current beam (e.g. 2pA to 30ρA), and the steep side wall cross-section 5 is is a formal precept.

Although the above example is an example in which the cross-sectional shape was obtained by tilting the sample, a similar end surface can also be obtained by tilting the sample after rough drilling and performing finishing machining. Next, Figure 1(f)
As shown in Figure 2, 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 where the field of view of the cross section can be secured. This cross section is connected to a relatively low current beam (for example, 29A~
Observe with a scanning ion microscope at 30 pA). In addition, if the abnormal part such as a foreign object to be observed in cross section is small, cross-sectional observation may be performed without applying a film.
Even in such a case, a more accurate cross-sectional shape can be obtained by performing the above-described operation.

〔Effect of the invention〕

According to the present invention, as described above, by tilting the sample during the cross-sectional shape, it is possible to prevent the influence of the uneven portions on the sample surface from appearing in the form of vertical lines in the cross-section. Therefore, a more accurate cross-sectional image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory top view of an example in which the method of the present invention is applied to the case of observing a cross section of a contact portion between an upper layer wiring and a lower layer wiring of an LSI. The figure shown by the dashed line, Figure 1 (BL is a diagram showing the area including the above-mentioned observation position 2 coated with a film by the FIBCVD method, Figure 1 (Cl is the sample clock by the rotating mechanism of the sample stage). Figure I (fdl) is a diagram with the sample stage tilted (amplifier on the right side), Figure I (el is a square hole with the observation position as one side) using the etching function. Figure 1 ffl shows the sample stage after it has been rotated 90 degrees counterclockwise, Figure 1 fg) shows the sample stage further tilted (
60°), and the cross section is oriented to a position where it can be observed in the ion beam irradiation direction. Figure 2 (al is a diagram showing an example of a cross section formed by a conventional processing method, Figure 2 [bl is a diagram showing an example of a cross section formed by implementing the present invention). It is a focused ion beam device and an image processing circuit diagram used in the present invention. LSI cross-section processing position FIBCVD film attachment portion drilling section cross-section Insulating film Upper layer wiring Lower layer wiring Si substrate Slight diagonal vertical streak Ion column sample stage Two sets Photo Reder Trial 4 Secondary charged particle detector Gas gun Vacuum chamber 2B・ 31・ 32・ 33・ 34・ 35・ Ion beam scanning control section Image capture/reconstruction control section Image memory section Amplifier Display section

Claims (2)

[Claims] (1) A focused ion beam column equipped with a means for switching the ion beam current value, a sample stage having at least a tilting mechanism in addition to an XY moving mechanism, and a gas gun for spraying deposition raw material gas onto the sample surface; A focused ion beam device equipped with a secondary charged particle detector and has three functions: scanning ion microscope function, maskless etching function, and maskless deposition function is used to process cross sections for cross-sectional observation of arbitrary positions on samples. A micro cross-section processing method characterized by tilting a sample during cross-section processing. (2) The micro cross section processing method according to item 1, characterized in that a film is locally formed on the surface of the region including the micro cross section forming portion by a maskless deposition function before forming the cross section.