JPH04116843A - Method and device for observing cut face of sample - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for performing cross-sectional observation using focused ion beam processing for failure analysis and process analysis of semiconductor LSIs and various thin film products.

[Conventional technology]

Traditionally, in order to perform process analysis and failure analysis of semiconductor LSI etc., cross sections are created using focused ion beam processing.
A method of observing the cross section using a SEM image or a SIM image is described in JP-A-1-181529 R-Focused Ion Beam Processing Method and Apparatus" and JP-A-2-123749 R-Cross-Section Processing and Observation Apparatus.

This involves drilling a hole in the sample using a focused ion beam.

A SEM image of the side wall of the processed hole is observed.

Alternatively, the sample is rotated in the processed ion beam apparatus so that the ion beam hits the side wall of the processed hole in the sample, and then observed using a scanning ion beam microscope (SIM).

[Problem to be solved by the invention]

In this method, the redeposition phenomenon in which particles sputtered by the ion beam adhere to the side wall of the processed hole, that is, the surface on which cross-sectional observation is desired, poses a problem in obtaining a clear observation image. 18 and 19 of Japanese Unexamined Patent Publication No. 1-181529 describes an ion beam operation method for preventing re-deposition, but even with this method, some re-deposition layer is inevitably formed. For this reason, when observing a cross section using a SIM or SEM image, there is a drawback that contrast depending on the material is difficult to obtain.

For this reason, the sample may be lightly wet etched, but focused ion beam equipment, wet etching equipment,
This method has the disadvantage that the work efficiency cannot be improved because there is a lot of sample movement between M detection devices such as SEMs.

In addition, wet etching has the disadvantage that the processing speed varies considerably depending on the temperature, concentration, etc. of the chemical solution, making it difficult to perform etching suitable for cross-sectional observation. Furthermore, it was very difficult to find the location where the focused ion beam was processed during SEMIR observation.

The purpose of the present invention is to obtain cross-sectional il
! During inspection, SEM images or SI images due to differences in materials
The object of the present invention is to provide a method and apparatus for clearly obtaining the contrast of an M image. A further object of the present invention is to provide a method and apparatus for easily obtaining SEM or SIM images with clear contrast due to different materials in cross-sectional observation using focused ion beam processing. Another object of the present invention is to provide a method for easily finding a location where focused ion beam processing has been performed.

[Means to solve the problem]

In order to achieve the above object, sputter etching or ion assisted etching is performed after focused ion beam processing. Alternatively, after performing focused ion beam processing, sputter etching or ion assisted etching is performed while viewing a SIM image or SEM image.

For this purpose, a function for performing sputter etching or ion-assisted etching is added to the SEM device.

[Effect]

By sputter etching the side wall of the hole processed by the focused ion beam, the redeposited layer is removed and the substance to be observed appears on the surface.

Furthermore, by performing etching even after the substance to be observed has been exposed, the amount of processing varies depending on the material, and the amount of processing differs depending on the material, making it easier to observe. When processing is performed using etching gas by ion-assisted etching, the difference in etching speed due to the difference in material can be made even larger, and it may be easier to observe than in simple sputter etching.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 10.

FIGS. 1(a) to 1(d) show examples of the ion beam processing/observation method. FIG. 1 shows a cross section of a semiconductor LSI, which consists of a lower layer wiring 1, a contact hole 2, an upper layer wiring 3, an interlayer insulating film 4, and a protective film 5.

For example, when looking at the state of a contact hole using a cross-sectional SEM using the AA cross section shown in the figure, as shown in FIG. , a method is used to perform finishing processing with a thin beam to minimize re-adhesion to the side walls of the processed hole. However, even with this method, some re-deposition layer 7 is formed. Therefore, as shown in FIG. 1(c), the side walls are sputter-etched using an argon ion beam. At this time, if the argon beam hits the bottom of the processed hole, the bottom will be sputter-etched, and the sputtered matter will adhere to the sidewalls, so the direction of the argon ion beam is set so that it does not hit the bottom. After sputter etching until the redeposited layer is sufficiently removed, it is scanned with an electron beam and subjected to a secondary electron microscope (SEM), as shown in Figure 1(d).
) get the image. In this way, a SEM image with clear contrast can be obtained due to the difference in secondary electron emission rate between the glabellar insulating film and the wiring material.

In addition, in FIG. 1(c), when argon ions are irradiated while supplying etching gas, the etching rate differs depending on the material, so a large step can be created on the side wall, and cross-sectional SEM observation can be performed more effectively. For example, when the wiring material is an aluminum alloy, if chlorine-based gas is supplied together with argon ions, only the aluminum alloy will be selectively etched, forming unevenness on the side wall where the wiring portion is depressed and an insulating waist portion remains. Conversely, when the insulating film is made of SiO, the insulating film is selectively etched by supplying a fluorine-based gas together with argon ions, and the insulating film is dented on the side wall, leaving a wiring section. Such unevenness is formed.

2 to 5 illustrate an apparatus for carrying out the above method. FIG. 2 shows a focused ion beam processing device. The ion beam column 11 includes an ion source 12 and optical systems such as a focusing lens, a blanker, and a deflection system that are included in a normal focused ion beam device. Below this is a detector 13 that detects secondary particles. Inside the vacuum chamber 14 is
There is a Y stage 15. The position of this XY stage 15 is accurately measured by a laser interferometer 16. Further, when the sample 19 is an insulator, an electron shower 17 is provided to prevent charge-up. A load lock chamber 18 for sample introduction is provided.

FIG. 3 shows a scanning electron microscope apparatus. vacuum chamber 24
Above is an electron beam column 35, which includes an electron beam source 22 and optical systems such as a focusing lens, a blanker, and a deflection system, which are included in a typical electron beam apparatus. Inside the vacuum chamber 24 is a detector 23 that detects secondary electrons.

Inside 24 is an argon ion gun 25 for sputter etching. By providing this argon ion gun 25 in the same chamber 24, sputter etching can be performed while observing with an electron beam until a clear image is obtained. When performing sputter etching, the pressure inside the vacuum chamber 24 is increased by argon gas.

Therefore, the inside of the electron beam column 35 is evacuated by the exhaust pump 28. There is a gate valve 29 at the bottom of the electron beam column.
There is and keep it closed. The gate valve 29 may be omitted and the electron beam column 35 and the vacuum chamber 24 may be communicated with each other through a narrow orifice to perform differential pumping. The stage 26 can move in the X and Y directions and rotate around the X and Z axes. After the sample 19 is placed on the plate 27, the plate 27 can be moved to the position shown by the two-dot chain line, thereby keeping the vacuum chamber 24 vacuum-tight.

Next, using the apparatus shown in FIGS. 2 and 3, sample 19 was processed and Ij! Describe how to conduct a survey.

The sample 19 is fixed to the sample fixing piece 20, placed on the sample moving plate 21, and introduced from the load lock chamber 18 into the vacuum chamber. If the sample surface is covered with an insulating material, please use the electronic shirt as shown in Figure 1 (b).
The processing shown in is performed using a focused ion beam. At this time,
The coordinates of the processing position with reference to the two marks on the sample fixing piece 20 are measured by the laser interferometer 16.

By doing so, when observing the SEM image, the observation location can be easily found.

Thereafter, the sample 19 is placed on the stage 26 of the scanning electron microscope shown in FIG. 3 while being fixed to the sample fixing piece 20. As shown in Figure 4, the sample is first brought under the argon ion gun, and as shown in Figure 5, the sample 19 is rotated around the Sputter etch. Then, as shown in Fig. 6, sample 19
is moved directly under the electron beam, the sample 19 is tilted around the X-axis as shown in FIG. 7, and the electron beam is irradiated as shown in FIG. 1(e) to observe the SEM image. At this time, first look at the two reference marks on the sample fixing piece 20, and from here on, easily observe the sample 19 based on the measured XY coordinates of the observation location, taking into account the tilt angle. You can find location 28.

As a result of SEM observation, if the redeposited matter has not been sufficiently removed, sputter etching may be performed again as shown in FIG. 4. Etching and S in the same chamber
Since EM observation is possible, work efficiency is extremely high.

Further, in FIG. 9, a gate valve 30 is connected to the vacuum chamber 24.
A configuration with . In this apparatus, when the sample 19 is placed in the argon sputtering position, the gate valve 30 is closed, so that the vacuum in the chamber containing the electron beam is not broken. After sputter etching, the gate valve 30
In the first step, the sample is introduced under the electron beam and observed.

Figures 2 to 9 show the focused ion beam device and SE
Although the M devices were separate, FIG. 10 shows the focused ion beam column 11, electron beam column 35, and argon ion gun 25.
The vacuum chamber 14.24 has a gate valve 30a,
This is an example in which they are separated via 30b and attached to the same device. In this way, processing and SEM inspection can be done in the same chamber 14.24 without breaking the vacuum.
While looking at the cross section, you can drill into the position of the cross section little by little, further improving work efficiency.

Furthermore, in FIG. 4, if an etching gas supply device 34 (shown in FIG. 6) is provided together with the argon ion gun 25 as described above, etching (ion assist, etching).

〔Effect of the invention〕

According to the present invention, when performing SEMal, the surface to be observed can be spanter-etched or ion-assisted etched using argon sputtering in the same apparatus, so that a cross section created by focused ion beam processing can be observed with good contrast.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the method of the present invention, Fig. 2 is a schematic diagram of a focused ion beam processing apparatus according to the present invention, and Figs. Schematic diagrams, Figures 5 and 7 are right side views of the sample portion corresponding to Figures 4 and 6, Figure 8 is a plan view of the sample fixing piece, and Figure 9 is a diagram of the argon ion gun and gate valve. SEM
Schematic diagram of the apparatus. FIG. 10 is a schematic diagram of an apparatus having an argon ion gun, a SEM device, and an FIB device. 1... Lower layer wiring, 2... Contact hole, 3...
・Upper layer wiring, 4... Interlayer insulating film, 5... Protective film, 6
...Focused ion beam, 7...Reattachment layer, 11...
・Ion beam column, 12...Ion source, 13...
・Detector, 15...XY stage, 16...Laser interferometer, 17...Electronic Java, 20...
- Sample fixing piece, 21...Plate for sample movement. 22... Electron beam source, 23... Detector, 25... Argon ion gun, 26... Stage, 27... Plate, 34... Etching gas supply device, 35...
Electron beam column. 1 country

Claims (1)

[Claims] 1. A method for observing a cross section of a sample, which comprises creating a cross section of the sample by processing the sample with a focused ion beam, processing the cross section by sputter etching or ion-assisted etching, and then observing it using an SEM. 2. Focused ion beam processing and SEM observation are performed while the sample is attached to a sample fixing piece with a reference mark and the mark is used as a reference for positioning the processing/observation position. Sample cross-section observation method. 3. A sample cross-section observation device in a SEM device, characterized in that an argon ion gun is provided in the same vacuum chamber as an electron beam column. 4. A sample cross-section observation device in a SEM device, characterized in that two vacuum chambers communicated via a gate valve are each provided with an electron beam column and an argon ion gun.