JP2887407B2 - Sample observation method using focused ion beam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the evaluation of a semiconductor manufacturing process while the density of an integrated circuit of a semiconductor device (hereinafter referred to as an IC) is rapidly becoming smaller and smaller. The present invention relates to a sample observation method for performing a failure analysis.

[Summary of the Invention]

The present invention particularly relates to a method for observing a cross section of an IC. First, a focused ion beam is irradiated onto a predetermined portion of a semiconductor device while repeatedly scanning to form a groove. The IC is tilted so that the focused ion beam irradiates the side surface of the groove, and while irradiating the focused ion beam, an etching gas for etching a specific material of the IC is blown, and the side surface of the groove is etched by the material. A step is formed. Therefore, since the intensity of the secondary charged particles generated by the focused ion beam irradiation also depends on the pattern, an image of the side surface of the groove is displayed on the image display device based on the intensity of the secondary charged particles, so that the cross section of the IC can be further improved. Observe clearly.

[Conventional technology]

Conventionally, the focused ion beam has been extremely effective in the observation and evaluation of ICs and the circuit modification of prototype ICs.

FIG. 2 is a sectional view schematically showing a conventional ion beam processing apparatus. The metal ion beam 1 is generated from an ion source 11 including an extraction electrode (not shown).
Beam monitor installed around the optical axis of
12 detects the emission current. The current of the ion beam is controlled based on this current value.

A sample 2, which is an IC, is held by a sample holder 3, and the sample holder 3 is mounted on a sample stage 4 for moving the sample three-dimensionally.

The ion beam 1 has a condenser lens 13 and an objective lens 18
Thereby, the spot diameter is focused on the surface of the sample 2 to submicron. The current of the focused ion beam 1 irradiating the surface of the sample can be changed even by the movable diaphragm 16. The irradiation area of the focused ion beam 1 on the sample is as follows.
Stage 3 that can be driven, rotated and tilted in any direction
Can be arbitrarily set by controlling the XY deflector 19 and the blanker 14. The focused ion beam scans once or repeatedly in the focused ion beam 1 irradiation area. The positioning of the target processing location is performed by scanning the focused ion beam 1 over a wide range to some extent, and using the secondary charged particles 7 (secondary electrons or secondary ions) generated from the sample surface to the secondary charged particle detector 6 (secondary charged particle detector 6). Primary electron detector or secondary ion detector), and the secondary charged particle image
An image is displayed on T29. From this image observation, the XY deflector 1
Scanning of the focused ion beam 1 is controlled by 9 and the blanker 14 to determine an area. A method of forming a groove by removing the surface of the IC sample 2 is to irradiate the focused ion beam 1 while repeatedly scanning a predetermined scanning region, and remove the surface by sputtering (etching) to form a groove. next,
The sample 2 is tilted on the sample stage to observe the cross section of the formed groove. The focused ion beam 1 is irradiated while scanning the side surface of the groove for the focused ion beam 1 due to the inclination of the sample 2. Secondary charged particles (secondary electrons or secondary ions) generated by this irradiation are detected by a secondary charged particle detector 6 and the secondary charged particle image is used for image observation.
Display images on CRT29. Focused ion beam 1 at this time
Is set by the above-described method.

[Problems to be solved by the invention]

The groove side surface of the IC by sputtering (etching) processing using a focused ion beam is relatively flat, and when a cross section (groove side surface) is observed with a secondary charged particle image, materials and similar secondary charged particle generation efficiencies are used. However, when the layer is very thin, the boundary between the layers cannot be clearly observed.

[Means for solving the problem]

The present invention has been made in order to solve the above-mentioned problem, and is activated by a focused ion beam and selected for a layer of a specific material of an IC cross section before observation of a groove side surface by a focused ion beam. There is a method of irradiating a focused ion beam while blowing an etching gas exerting an etching effect on an observation cross section (side surface of a groove).

[Action]

By simultaneously spraying the etching gas and irradiating the focused ion beam on the cross section (side surface of the groove) of the sample (IC) to be observed, the etching gas is activated by the focused ion beam, and the material forming the cross section of the sample is etched. An etching effect occurs on a part. Therefore, an etching pattern or a step is formed on the cross section. Therefore, the intensity of the secondary charged particles generated by the irradiation of the focused ion beam also depends on the pattern, and the unevenness is formed, so that the image of the groove side surface based on the secondary charged particle intensity becomes clearer.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view of a main part of the embodiment, and the other parts are the same as those shown in the prior art of FIG.

The focused ion beam 1 is irradiated while repeatedly scanning a predetermined processing area on the surface of a sample 2 (IC) placed on a sample holder 3 on which a sample stage 4 is mounted. The difference from the conventional ion beam processing apparatus is that an oxygen gas blowing apparatus 8 for blowing oxygen gas near the sample irradiation area of the focused ion beam 1 is provided. A liquid metal ion source such as gallium is used as the ion source 11, and the ion beam 1 is accelerated and focused by the extraction electrode, the condenser lens 13, the objective lens 18, and the like.
Secondary electrons generated from the surface of the sample by the scanning of the focused ion beam 1 are detected by the secondary electron detector 6, and a secondary charged particle image is displayed on the CRT 29. By observing the surface of the sample 2 displayed on the CRT 29, an area to be processed of the sample 2 is set, the driving of the sample stage 4, the XY deflector 19 and the blanker 14 are controlled, and the focused ion beam 1 is Scanning is repeatedly performed in the processing area on the front surface.

3 to 5 are cross-sectional views of an IC which simply show processing of the IC sample 2 according to the present invention. In the IC, an interlayer insulating film 34 is formed on a substrate (Si) 35, and wiring (A
l) 33 is formed, and a protective film 32 is further formed thereon.

In FIG. 3, in order to form a groove 40 on the surface of the sample 2, a predetermined processing area of the sample 2 is irradiated while repeatedly scanning with the focused ion beam 1. Thereby, the sample 1
The surface of the predetermined region is etched away by sputtering to form a groove 40.

Next, as shown in FIG. 4, the sample 2 is tilted so that the side surface of the groove 40 is irradiated with a focused ion beam. Then, while irradiating the focused ion beam 1 to the side surface of the groove 40, the etching gas is blown by an etching gas irradiation device that blows the etching gas. Here, chlorine gas is blown to etch the wiring 33 more. As shown in FIG.
Is etched deeply.

Next, as shown in FIG. 5, in this state, the secondary charged particles generated by the irradiation of the focused ion beam 1 are detected and displayed as an image.

〔The invention's effect〕

According to the present invention, observation of a multi-layered cross section of a semiconductor device is performed by stepping by layer, a boundary between layers is clarified, and a clear secondary charged particle image can be obtained in a short time. Observation of a sample for evaluation of a manufacturing process and failure analysis is facilitated.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an apparatus for carrying out the present invention, and FIG.
FIG. 3 is a cross-sectional view of a conventional apparatus, FIG. 3 is an IC cross-sectional view showing a groove forming step of the method of the present invention, FIG. 4 is an IC cross-sectional view showing etching and observation of the groove side surface of the method of the present invention, FIG. FIG. 4 is a view showing an image obtained by observing a groove side surface of an IC. DESCRIPTION OF SYMBOLS 1 ... Focused ion beam, 2 ... Sample 3 ... Sample holder 4, ... Sample stage 6 ... Secondary charged particle detector 7 ... Secondary charged particle 8 ... Etching gas spray device 11 ... Ion source 12 ... Beam monitor 13 ... Condenser lens 14 ... Blanker, 16 ... Movable aperture 18 ... Objective lens 19 ... XY XY reflector 29 ... CRT, 32 ... Protective film 33 ... Wiring, 34 ... Interlayer insulation Membrane 35 ... substrate, 40 ... hole

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/66 H01L 21/3065 G01N 23/22

Claims (1)

(57) [Claims] 1. A method for irradiating a focused ion beam on a predetermined region of a semiconductor device while repeatedly scanning the same to form a groove at a predetermined position of the semiconductor device, and irradiating the focused ion beam to a side surface of the formed groove. While driving the sample stage on which the semiconductor device is mounted, tilting the semiconductor device, while irradiating the side surface of the groove with the focused ion beam,
An etching gas for selectively etching a specific material among the materials exposed on the side surface of the groove is sprayed on the side surface of the groove, and the surface is exposed to the difference in the material constituting the side surface of the groove. Creating a difference, detecting secondary charged particles generated by irradiating the side surface of the groove with the focused ion beam, and displaying an image of the side surface of the groove based on the secondary charged particle detection intensity. A sample observation method using a focused ion beam.